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Sample records for controlled radical polymerization

  1. Mechanically controlled radical polymerization initiated by ultrasound

    NASA Astrophysics Data System (ADS)

    Mohapatra, Hemakesh; Kleiman, Maya; Esser-Kahn, Aaron Palmer

    2017-02-01

    In polymer chemistry, mechanical energy degrades polymeric chains. In contrast, in nature, mechanical energy is often used to create new polymers. This mechanically stimulated growth is a key component of the robustness of biological materials. A synthetic system in which mechanical force initiates polymerization will provide similar robustness in polymeric materials. Here we show a polymerization of acrylate monomers initiated and controlled by mechanical energy provided by ultrasonic agitation. The activator for an atom-transfer radical polymerization is generated using piezochemical reduction of a Cu(II) precursor complex, which thus converts a mechanical activation of piezoelectric particles to the synthesis of a new material. This polymerization reaction has some characteristics of controlled radical polymerization, such as narrow molecular-weight distribution and linear dependence of the polymeric chain length on the time of mechanical activation. This new method of controlled radical polymerization complements the existing methods to synthesize commercially useful well-defined polymers.

  2. Mechanically controlled radical polymerization initiated by ultrasound

    NASA Astrophysics Data System (ADS)

    Mohapatra, Hemakesh; Kleiman, Maya; Esser-Kahn, Aaron Palmer

    2016-10-01

    In polymer chemistry, mechanical energy degrades polymeric chains. In contrast, in nature, mechanical energy is often used to create new polymers. This mechanically stimulated growth is a key component of the robustness of biological materials. A synthetic system in which mechanical force initiates polymerization will provide similar robustness in polymeric materials. Here we show a polymerization of acrylate monomers initiated and controlled by mechanical energy provided by ultrasonic agitation. The activator for an atom-transfer radical polymerization is generated using piezochemical reduction of a Cu(II) precursor complex, which thus converts a mechanical activation of piezoelectric particles to the synthesis of a new material. This polymerization reaction has some characteristics of controlled radical polymerization, such as narrow molecular-weight distribution and linear dependence of the polymeric chain length on the time of mechanical activation. This new method of controlled radical polymerization complements the existing methods to synthesize commercially useful well-defined polymers.

  3. TRANSITION METAL CATALYSIS IN CONTROLLED RADICAL POLYMERIZATION: ATOM TRANSFER RADICAL POLYMERIZATION. (R826735)

    EPA Science Inventory

    Novel and diversified macromolecular structures, which include polymers with designed topologies (top), compostions (middle), and functionalities (bottom), can be prepared by atom transfer radical polymerization processes. These polymers can be synthesized from a large variety of...

  4. Synthesis of glycopolymers by controlled radical polymerization techniques and their applications.

    PubMed

    Vázquez-Dorbatt, Vimary; Lee, Juneyoung; Lin, En-Wei; Maynard, Heather D

    2012-11-26

    Natural saccharides are involved in numerous biological processes. It has been shown that these carbohydrates play a role in cell adhesion and proliferation, as well as protein stabilization, organization, and recognition. Certain carbohydrates also serve as receptors for viruses and bacteria. They are over expressed in diseases such as cancer. Hence, a lot of effort has been focused on mimicking these sugars. Polymers with pendent saccharide groups, also known as glycopolymers, are studied as oligo- and polysaccharide mimics. Controlled radical polymerization (CRP) techniques such as atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP), as well as cyanoxyl-mediated free radical polymerization have allowed chemists to synthesize well-defined glycopolymers that, in some cases, have particular end-group functionalities. This review focuses on the synthesis of glycopolymers by these methods and the applications of glycopolymers as natural saccharide mimics.

  5. Continuous controlled radical polymerization of methyl acrylate in a copper tubular reactor.

    PubMed

    Chan, Nicky; Cunningham, Michael F; Hutchinson, Robin A

    2011-04-04

    The use of copper tubing as both the reactor and as a catalyst source is demonstrated for continuous controlled radical polymerization of methyl acrylate at ambient temperature and at low solvent content of 30%. The high surface area provided by the copper walls mediates the reaction via the single electron transfer-living radical polymerization (SET-LRP) mechanism. The polymerizations proceeded quickly, reaching 67% conversion at a residence time of 16 min. Ligand concentration could also be reduced without a sharp drop in polymerization rate, demonstrating the potential for decreased raw material and post-process purification costs. Chain extension experiments conducted using synthesized polymer showed high livingness. The combination of living polymer produced at high polymerization rates at ambient temperature and low volatile organic solvent content demonstrate the potential of a copper reactor for scale up of SET-LRP. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Photo-Regeneration of Severed Gel Using Photo-Controlled Radical Polymerization

    NASA Astrophysics Data System (ADS)

    Singh, Awaneesh; Kuksenok, Olga; Johnson, Jeremiah A.; Balazs, Anna C.

    Using the framework of dissipative particle dynamics (DPD) simulation, we developed a novel computational model that enables photo-regeneration of the gel matrix when a significant portion of the material is severed. We considered photo-controlled radical polymerization (photo-CRP) within polymer networks with embedded iniferters (initiators for the photo-CRP reaction). These iniferters turn on the polymerization process in the presence of light with monomers and cross-linkers in the solution. This ''photo-growth'' allow us to effectively regenerate severed gels under the application of light. The growth process can be turned off once the polymerization is near completion, which forms a new cross-linked gel that resembles the uncut material. The polymerization rate can be modulated by altering the light intensity.

  7. Radical-Mediated Enzymatic Polymerizations

    PubMed Central

    Zavada, Scott R.; Battsengel, Tsatsral; Scott, Timothy F.

    2016-01-01

    Polymerization reactions are commonly effected by exposing monomer formulations to some initiation stimulus such as elevated temperature, light, or a chemical reactant. Increasingly, these polymerization reactions are mediated by enzymes―catalytic proteins―owing to their reaction efficiency under mild conditions as well as their environmental friendliness. The utilization of enzymes, particularly oxidases and peroxidases, for generating radicals via reduction-oxidation mechanisms is especially common for initiating radical-mediated polymerization reactions, including vinyl chain-growth polymerization, atom transfer radical polymerization, thiol–ene step-growth polymerization, and polymerization via oxidative coupling. While enzyme-mediated polymerization is useful for the production of materials intended for subsequent use, it is especially well-suited for in situ polymerizations, where the polymer is formed in the place where it will be utilized. Such polymerizations are especially useful for biomedical adhesives and for sensing applications. PMID:26848652

  8. Tailoring the Structure of Polymer Networks with Photo-Controlled Radical Polymerization

    NASA Astrophysics Data System (ADS)

    Singh, Awaneesh; Kuksenok, Olga; Johnson, Jeremiah A.; Balazs, Anna C.

    Using dissipative particle dynamics (DPD) approach, we developed a novel computational model to study the photo-controlled radical polymerization (photo-CRP) within polymer networks with embedded iniferters. The polymerization process can be turned ``on'' or ``off'' in response to light and the polymerization rate can be modulated by altering the light intensity. This ``photo-growth'' approach allows us to impart changes in the gel network pore size and composition to form photo-tunable smart materials. For example, our approach allows us to design gel composites that are comprised of two distinct layers made of two compatible components at low photo-iniferter concentrations or gel composites that are comprised of two incompatible components that are relatively well intermixed at high photo-iniferter concentration.

  9. Improvement in Liquid Chromatographic Performance of Organic Polymer Monolithic Capillary Columns with Controlled Free-Radical Polymerization.

    PubMed

    Gama, Mariana R; Aggarwal, Pankaj; Liu, Kun; Lee, Milton L; Bottoli, Carla B G

    2016-12-19

    Capillary columns containing butyl or lauryl methacrylate monoliths were prepared using two different free-radical polymerization methods: conventional free-radical polymerization and controlled/living free-radical polymerization, both initiated thermally, and these methods were compared for the first time. Both monolith morphology and chromatographic efficiency were compared for the synthesized stationary phases using scanning electronic microscopy (SEM) and capillary liquid chromatography, respectively. Columns prepared using controlled method gave better chromatographic performance for both monomers tested. The lauryl-based monolith showed 7-fold improvement in chromatographic efficiency with a plate count of 42,000 plates/m (corrected for dead volume) for a non-retained compound. Columns fabricated using controlled polymerization appeared more homogenous radially with fused small globular morphologies, evaluated by SEM, and lower column permeability. The columns were compared with respect to resolving power of a series of alkylbenzenes under isocratic and gradient elution conditions.

  10. Control of the Termination Mechanism in Radical Polymerization by Viscosity: Selective Disproportionation in Viscous Media.

    PubMed

    Nakamura, Yasuyuki; Ogihara, Tasuku; Hatano, Sayaka; Abe, Manabu; Yamago, Shigeru

    2017-01-26

    The termination mechanism of radical polymerization, that is, disproportionation (Disp) versus combination (Comb), determines the chain length and end-group structure of the resulting polymer as well as polymer properties, and yet factors governing the mechanism are still unclear. Furthermore, no attempts have been made to control the mechanism. Here, the effects of temperature and viscosity on the termination of methyl methacrylate (MMA) and styrene (St) polymerization were elucidated by using small molecular model-radicals and the corresponding polymer radicals in various solvents. The results showed that Disp was preferred over Comb if the temperature was decreased and the viscosity of the media was increased for all the radicals examined. Although the temperature effect on the Disp/Comb selectivity is counterintuitive because Disp should be favored entropically over Comb considering the decrease in the number of polymer chains in Comb, the results clearly showed that the observed inverse temperature effect was a result of the viscosity effect. Disp was favored over Comb at lower temperatures and in more viscous solvents because the transition state leading to Disp is more flexible than that for Comb. Because of the significant viscosity effect, Disp selectively occurred in highly viscous solvents; the Disp/Comb selectivity was 97/3 in both MMA and St termination. For the first time, the termination mechanism was intentionally controlled and such a high Disp selectivity was observed. In particular, the termination mechanism in St is described as Comb in textbooks, but nearly complete inversion of the selectivity from Comb to Disp is realized by simply changing the viscosity of the media.

  11. Polyelectrolyte brushes grafted from cellulose nanocrystals using Cu-mediated surface-initiated controlled radical polymerization.

    PubMed

    Majoinen, Johanna; Walther, Andreas; McKee, Jason R; Kontturi, Eero; Aseyev, Vladimir; Malho, Jani Markus; Ruokolainen, Janne; Ikkala, Olli

    2011-08-08

    Herein we report the synthesis of cellulose nanocrystals (CNCs) grafted with poly(acrylic acid) (PAA) chains of different lengths using Cu-mediated surface initiated-controlled radical polymerization (SI-CRP). First, poly(tert-butylacrylate) (PtBA) brushes were synthesized; then, subsequent acid hydrolysis was used to furnish PAA brushes tethered onto the CNC surfaces. The CNCs were chemically modified to create initiator moieties on the CNC surfaces using chemical vapor deposition (CVD) and continued in solvent phase in DMF. A density of initiator groups of 4.6 bromine ester groups/nm(2) on the CNC surface was reached, suggesting a dense functionalization and a promising starting point for the controlled/living radical polymerization. The SI-CRP of tert-butylacrylate proceeded in a well-controlled manner with the aid of added sacrificial initiator, yielding polymer brushes with polydispersity values typically well below 1.12. We calculated the polymer brush grafting density to almost 0.3 chains/nm(2), corresponding to high grafting densities and dense polymer brush formation on the nanocrystals. Successful rapid acid hydrolysis to remove the tert-butyl groups yielded pH-responsive PAA-polyelectrolyte brushes bound to the CNC surface. Individually dispersed rod-like nanoparticles with brushes of PtBA or PAA were clearly visualized by AFM and TEM imaging.

  12. Application of controlled radical polymerization (CRP) in the design of functional biomedical architectures

    NASA Astrophysics Data System (ADS)

    Siegwart, Daniel John

    In this thesis, atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization were utilized in the design of synthetic polymers to create tissue engineering scaffolds and drug delivery systems with improved control over structure and functionality. Thermo-sensitive injectable hydrogels based on poly(NIPAAm) with degradable ester units within the polymer backbone and at the cross-linking sites were prepared using ATRP and RAFT. Solvent induced morphologies of poly(methyl methacrylate-b-ethylene oxide-b-methyl methacrylate) triblock copolymers synthesized by ATRP were described. A micellar structure, composed of a hydrophobic PMMA core and a PEO shell was constructed for delivery of hydrophobic drugs. ATRP was carried out in inverse miniemulsion to prepare well defined functional nanogels that were capable of entrapping and releasing various molecules (Doxorubicin, carbohydrate-based drugs, fluorophores, and gold nanoparticles). The results demonstrated that nanogels prepared by ATRP in inverse miniemulsion could be internalized into cells via clathrin-mediated endocytosis. Nanogels functionalized with integrin-binding peptides increased cellular uptake. A process called Atom Transfer Radical Coupling (ATRC) was also described, which illustrated the power of functionality in ATRP. Finally, linear polymers and cross-linked nanogels were synthesized by ATRP and functionalized with biotin, pyrene, and peptide sequences, tying together the overall themes of structural control and functionality.

  13. Functional Interfaces Constructed by Controlled/Living Radical Polymerization for Analytical Chemistry.

    PubMed

    Wang, Huai-Song; Song, Min; Hang, Tai-Jun

    2016-02-10

    The high-value applications of functional polymers in analytical science generally require well-defined interfaces, including precisely synthesized molecular architectures and compositions. Controlled/living radical polymerization (CRP) has been developed as a versatile and powerful tool for the preparation of polymers with narrow molecular weight distributions and predetermined molecular weights. Among the CRP system, atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) are well-used to develop new materials for analytical science, such as surface-modified core-shell particles, monoliths, MIP micro- or nanospheres, fluorescent nanoparticles, and multifunctional materials. In this review, we summarize the emerging functional interfaces constructed by RAFT and ATRP for applications in analytical science. Various polymers with precisely controlled architectures including homopolymers, block copolymers, molecular imprinted copolymers, and grafted copolymers were synthesized by CRP methods for molecular separation, retention, or sensing. We expect that the CRP methods will become the most popular technique for preparing functional polymers that can be broadly applied in analytical chemistry.

  14. Controlled synthesis of photochromic polymer brushes by atom transfer radical polymerization.

    SciTech Connect

    Piech, Marcin; Bell, Nelson Simmons; Long, Timothy Michael

    2005-06-01

    This work reports on the grafting of methyl methacrylate polymer brushes containing spirobenzopyran pendant groups from flat silica surfaces and colloidal particles utilizing atom transfer radical polymerization (ATRP). The reaction conditions were optimized with respect to the kind of surface bound initiator, the type of halide and ligand used in the catalytic complex, the presence/absence of untethered initiator, and solvent type. This enabled synthesis of coatings up to 80 {+-} 3 nm thick with controlled spirobenzopyran content. While polymerization kinetics indicate the presence of chain termination reactions, the 'living' character of the process is confirmed by controlled formation of block copolymer brushes. UV/vis spectroscopy was used to characterize the UV-induced isomerization of spirobenzopyran to zwitterionic merocyanine and the thermal back-reaction. Spectral and kinetic analyses of this latter bleaching process points to the existence of free and associated merocyanines in the polymeric brush in both tetrahydrofuran and toluene. However, stabilization of merocyanine species by the polymer matrix is considerably greater in toluene with thermal back-reaction rates approaching those determined for solid dry films.

  15. Engineering live cell surfaces with functional polymers via cytocompatible controlled radical polymerization

    NASA Astrophysics Data System (ADS)

    Niu, Jia; Lunn, David J.; Pusuluri, Anusha; Yoo, Justin I.; O'Malley, Michelle A.; Mitragotri, Samir; Soh, H. Tom; Hawker, Craig J.

    2017-06-01

    The capability to graft synthetic polymers onto the surfaces of live cells offers the potential to manipulate and control their phenotype and underlying cellular processes. Conventional grafting-to strategies for conjugating preformed polymers to cell surfaces are limited by low polymer grafting efficiency. Here we report an alternative grafting-from strategy for directly engineering the surfaces of live yeast and mammalian cells through cell surface-initiated controlled radical polymerization. By developing cytocompatible PET-RAFT (photoinduced electron transfer-reversible addition-fragmentation chain-transfer polymerization), synthetic polymers with narrow polydispersity (Mw/Mn < 1.3) could be obtained at room temperature in 5 minutes. This polymerization strategy enables chain growth to be initiated directly from chain-transfer agents anchored on the surface of live cells using either covalent attachment or non-covalent insertion, while maintaining high cell viability. Compared with conventional grafting-to approaches, these methods significantly improve the efficiency of grafting polymer chains and enable the active manipulation of cellular phenotypes.

  16. Protein-Polymer Conjugates: Synthetic Approaches by Controlled Radical Polymerizations & Interesting Applications

    PubMed Central

    Grover, Gregory N.; Maynard, Heather D.

    2011-01-01

    Protein-polymer conjugates are of interest to researchers in diverse fields. Attachment of polymers to proteins results in improved pharmacokinetics, which is important in medicine. From an engineering standpoint, conjugates are exciting because they exhibit properties of both the biomolecules and synthetic polymers. This allows the activity of the protein to be altered or tuned, a key aspect in therapeutic design, anchoring conjugates to surfaces, and utilizing these materials for supramolecular self-assembly. Thus, there is broad interest in straightforward synthetic methods to make protein-polymer conjugates. Controlled radical polymerization (CRP) techniques have emerged as excellent strategies to make conjugates because the resulting polymers have narrow molecular weight distributions, targeted molecular weights, and attach to specific sites on proteins. Herein, recent advances in the synthesis and application of protein-polymer conjugates by CRP are highlighted. PMID:21071260

  17. Controlled atom transfer radical polymerization of MMA onto the surface of high-density functionalized graphene oxide.

    PubMed

    Kumar, Mukesh; Chung, Jin Suk; Hur, Seung Hyun

    2014-01-01

    We report on the grafting of poly(methyl methacrylate) (PMMA) onto the surface of high-density functionalized graphene oxides (GO) through controlled radical polymerization (CRP). To increase the density of surface grafting, GO was first diazotized (DGO), followed by esterification with 2-bromoisobutyryl bromide, which resulted in an atom transfer radical polymerization (ATRP) initiator-functionalized DGO-Br. The functionalized DGO-Br was characterized by X-ray photoelectron spectroscopy (XPS), Raman, and XRD patterns. PMMA chains were then grafted onto the DGO-Br surface through a 'grafting from' technique using ATRP. Gel permeation chromatography (GPC) results revealed that polymerization of methyl methacrylate (MMA) follows CRP. Thermal studies show that the resulting graphene-PMMA nanocomposites have higher thermal stability and glass transition temperatures (T g) than those of pristine PMMA.

  18. Controlled atom transfer radical polymerization of MMA onto the surface of high-density functionalized graphene oxide

    PubMed Central

    2014-01-01

    We report on the grafting of poly(methyl methacrylate) (PMMA) onto the surface of high-density functionalized graphene oxides (GO) through controlled radical polymerization (CRP). To increase the density of surface grafting, GO was first diazotized (DGO), followed by esterification with 2-bromoisobutyryl bromide, which resulted in an atom transfer radical polymerization (ATRP) initiator-functionalized DGO-Br. The functionalized DGO-Br was characterized by X-ray photoelectron spectroscopy (XPS), Raman, and XRD patterns. PMMA chains were then grafted onto the DGO-Br surface through a ‘grafting from’ technique using ATRP. Gel permeation chromatography (GPC) results revealed that polymerization of methyl methacrylate (MMA) follows CRP. Thermal studies show that the resulting graphene-PMMA nanocomposites have higher thermal stability and glass transition temperatures (Tg) than those of pristine PMMA. PMID:25114639

  19. Controlled atom transfer radical polymerization of MMA onto the surface of high-density functionalized graphene oxide

    NASA Astrophysics Data System (ADS)

    Kumar, Mukesh; Chung, Jin Suk; Hur, Seung Hyun

    2014-07-01

    We report on the grafting of poly(methyl methacrylate) (PMMA) onto the surface of high-density functionalized graphene oxides (GO) through controlled radical polymerization (CRP). To increase the density of surface grafting, GO was first diazotized (DGO), followed by esterification with 2-bromoisobutyryl bromide, which resulted in an atom transfer radical polymerization (ATRP) initiator-functionalized DGO-Br. The functionalized DGO-Br was characterized by X-ray photoelectron spectroscopy (XPS), Raman, and XRD patterns. PMMA chains were then grafted onto the DGO-Br surface through a `grafting from' technique using ATRP. Gel permeation chromatography (GPC) results revealed that polymerization of methyl methacrylate (MMA) follows CRP. Thermal studies show that the resulting graphene-PMMA nanocomposites have higher thermal stability and glass transition temperatures ( T g) than those of pristine PMMA.

  20. Molecularly imprinted protein recognition thin films constructed by controlled/living radical polymerization.

    PubMed

    Sasaki, Shogo; Ooya, Tooru; Kitayama, Yukiya; Takeuchi, Toshifumi

    2015-02-01

    We demonstrated the synthesis of molecularly imprinted polymers (MIPs) with binding affinity toward a target protein, ribonuclease A (RNase) by atom transfer radical polymerization (ATRP) of acrylic acid, acrylamide, and N,N'-methylenebisacrylamide in the presence of RNase. The binding activity of the MIPs was evaluated by surface plasmon resonance (SPR) of the MIP thin layers prepared on the gold-coated sensor chips. The MIPs prepared by ATRP (MIP-ATRP) had a binding affinity toward RNase with larger binding amount compared to MIPs prepared by conventional free radical polymerization methods (MIP-RP). Moreover, protein selectivity was evaluated using reference proteins (cytochrome c, myoglobin, and α-lactalbumin) and was confirmed in MIP-ATRP of optimum film thickness determined experimentally to be 15-30 nm; however, protein selectivity was not achieved in all MIP-RP. We have shown that ATRP is powerful technique for preparing protein recognition materials by molecular imprinting.

  1. Redox Active Compounds in Controlled Radical Polymerization and Dye-Sensitized Solar Cells: Mutual Solutions to Disparate Problems.

    PubMed

    Ballard, Nicholas; Mecerreyes, David; Asua, José M

    2015-12-14

    Controlled radical polymerization (CRP) and dye-sensitized solar cells (DSSCs) are two fields of research that at an initial glance appear to have little in common. However, despite their obvious differences, both in application and in scientific nature, a closer look reveals a striking similarity between many of the compounds widely used as control agents in radical polymerization and as redox couples in dye-sensitized solar cells. Herein, we review the various redox active compounds used and examine the characteristics that give them the ability to perform this dual function. In addition we explore the advances in the understanding of the structural features that enhance their activity in both CRP and DSSCs. It is hoped that such a comparison will be conducive to improving process performance in both fields.

  2. Controlled radical polymerization of an acrylamide containing L-alanine moiety via ATRP.

    PubMed

    Rafiee, Zahra

    2016-02-01

    Homopolymerization of an optically active acrylamide having an amino acid moiety in the side chain, N-acryloyl-L-alanine (AAla) was carried out via atom transfer radical polymerization (ATRP) at room temperature using 2-hydroxyethyl-2'-methyl-2'-bromopropionate (HMB) or sodium-4-(bromomethyl)benzoate (SBB) as initiator in pure water, methanol/water mixture and pure methanol solvents. The polymerization reaction resulted in the optically active biocompatible amino acid-based homopolymer in good yield with narrow molecular weight distribution. The number average molecular weight increased with conversion and polydispersity was low. The structure and molecular weight of synthesized polymer were characterized by (1)H NMR, FT-IR spectroscopic techniques and size-exclusion chromatography.

  3. Controlled fabrication of theophylline imprinted polymers on multiwalled carbon nanotubes via atom transfer radical polymerization.

    PubMed

    Xu, Jianxiong; Gao, Yong; Li, Huaming

    2011-02-01

    Theophylline imprinted polymers were synthesized on the surface of multiwalled carbon nanotubes via atom transfer radical polymerization using brominated multiwalled carbon nanotubes as an initiator. The nanotube-based initiator was prepared by directly reacting acyl chloride-modified multiwalled carbon nanotubes with 2-hydroxylethyl-2'-bromoisobutyrate. The grafting copolymerization of 2-hydroxyethyl-2-methyl-2-propenoate and ethylene glycol dimethacrylate in the presence of template theophylline led to thin molecularly imprinted polymer films coating multiwalled carbon nanotubes. The thickness of molecularly imprinted polymer films prepared in this study was about 5 nm as determined by transmission electron microscopy. Fourier-transform infrared spectroscopy was utilized to follow the introduction of initiator groups as well as polymers on the carbon nanotube surfaces. Thermogravimetric analysis indicated that the molecularly imprinted polymers were successfully grown from the carbon nanotube surfaces, with the final products having a polymer weight percentage of ca. 50 wt%. The adsorption properties, such as adsorption dynamics, special binding and selective recognition capacity, of the as-prepared molecularly imprinted polymer films were evaluated. The results demonstrated that the composite of molecularly imprinted polymers and multiwalled carbon nanotubes not only possessed a rapid dynamics but also exhibited a good selectivity toward theophylline, compared to caffeine.

  4. Logic-Controlled Radical Polymerization with Heat and Light: Multiple-Stimuli Switching of Polymer Chain Growth via a Recyclable, Thermally Responsive Gel Photoredox Catalyst.

    PubMed

    Chen, Mao; Deng, Shihong; Gu, Yuwei; Lin, Jun; MacLeod, Michelle J; Johnson, Jeremiah A

    2017-02-15

    Strategies for switching polymerizations between "ON" and "OFF" states offer new possibilities for materials design and fabrication. While switching of controlled radical polymerization has been achieve using light, applied voltage, allosteric effects, chemical reagents, pH, and mechanical force, it is still challenging to introduce multiple external switches using the same catalyst to achieve logic gating of controlled polymerization reactions. Herein, we report an easy-to-synthesize thermally responsive organo-/hydro-gel that features covalently bound 10-phenylphenothiazine (PTH). With this "Gel-PTH", we demonstrate switching of controlled radical polymerization reactions using temperature "LOW"/"HIGH", light "ON"/"OFF", and catalyst presence "IN"/"OUT". Various iniferters/initiators and a wide range of monomers including acrylates, methacrylates, acrylamides, vinyl esters, and vinyl amides were polymerized by RAFT/iniferter and ATRP methods using Gel-PTH and a readily available compact fluorescent light (CFL) source. In all cases, polymer molar masses increased linearly with conversion, and narrow molar mass distributions were obtained. To further highlight the utility of Gel-PTH, we achieved "AND" gating of controlled radical polymerization wherein various combinations of three stimuli were required to induce polymer chain growth. Finally, block copolymer synthesis and catalyst recycling were demonstrated. Logic-controlled polymerization with Gel-PTH offers a straightforward approach to achieve multiplexed external switching of polymer chain growth using a single catalyst without the need for addition of exogenous reagents.

  5. Nonspherical nanoparticles with controlled morphologies via seeded surface-initiated single electron transfer radical polymerization in soap-free emulsion.

    PubMed

    Yuan, Jinfeng; Wang, Lixia; Zhu, Lei; Pan, Mingwang; Wang, Wenjie; Liu, Ying; Liu, Gang

    2015-04-14

    This work reports a facile novel approach to prepare asymmetric poly(vinylidene fluoride)/polystyrene (PVDF/PS) composite latex particles with controllable morphologies using one-step soap-free seeded emulsion polymerization, i.e., surface-initiated single electron transfer radical polymerization (SET-RP) of styrene (St) at the surface of PVDF seed particles. It was observed that the morphology was influenced mainly by the St/PVDF feed ratio, the polymerization temperature, and the length of the catalyst Cu(0) wire (Φ 1.00 mm). When the feed ratio was St/PVDF = 5.0 g/1.0 g, snowman-like Janus particles were exclusively obtained. Raspberry-like and popcorn-like composite particles were observed at a higher reaction temperature or a shorter length of the catalyst wire. The reaction kinetics plots demonstrated some unique features. The formation of nonspherical composite nanoparticles can be ascribed to the surface nucleation of PS bulges following the SET-RP.

  6. Selective radical addition with a designed heterobifunctional halide: a primary study toward sequence-controlled polymerization upon template effect.

    PubMed

    Ida, Shohei; Terashima, Takaya; Ouchi, Makoto; Sawamoto, Mitsuo

    2009-08-12

    A ruthenium(II)-catalyzed, highly selective, quantitative radical addition of an alkene, methacrylic acid (MAA), has been achieved by using a template halide (2) containing a built-in amine group as a recognition site for the carboxyl group of the substrate. The specific ionic binding of MAA by the amine template (1:1 molar ratio) led to preferential formation of the 1:1 MAA-2 adduct, whereas a similar halide without a template induced MAA oligomerization even in the presence of an externally added amine. A competitive radical addition of MAA versus its ester form [methyl methacrylate (MMA)] on the halide further demonstrated that the substrate selectivity [k'(MAA)/k'(MMA)] for 2 is enhanced more than 10 times by the intramolecular introduction of the template relative to the result for the nontemplate halide. These specificities are most likely triggered by the specific interaction (recognition) of the carboxyl group in MAA via the acid-selective template amine, which is implanted in the close vicinity of the radical addition site in 2. These results intimate possibility of control over the repeat-unit sequence in precision polymerization.

  7. ’Living’ Radical Polymerization. 1. Possibilities and Limitations

    DTIC Science & Technology

    1994-06-30

    AD-A281 042 OFFICE OF NAVAL RESEARCH / CONTRACT N00014-94-1-0l01 R&T Code 31321075 Technical Report No. 16 " LIVING " RADICAL POLYMERIZATION. I...Report # 16 4. TITLE AND SUBTITLE S. FUNDING NUMBERS " Living " Radical Polymerization. I. Possibilities and Limitations N00014-94-1-0101 6. AUTHOR(S) D...preparation of polymers with controlled macromolecular structure in a " living " radical process requires low stationary concentration of growing radicals

  8. Radicals contributing to preirradiation graft polymerization onto porous polyethylene

    NASA Astrophysics Data System (ADS)

    Uezu, Kazuya; Saito, Kyoichi; Furusaki, Shintaro; Sugo, Takanobu; Ishigaki, Isao

    Porous polyethylene hollow fiber was irradiated by an electron beam at 160 kGy and 8 kGy/min. The concentrations of the radicals such as alkyl, allyl and peroxy were determined by analyzing an integral form of ESR spectra. The comparison of the decay of the radicals with and without contact with air demonstrated that the key radical contributing to the preirradiation graft polymerization is the alkyl radical. The decay of the alkyl radical was simulated by the diffusion-controlled model in the spherical crystallites of polyethylene.

  9. Micropatterned Surfaces for Atmospheric Water Condensation via Controlled Radical Polymerization and Thin Film Dewetting.

    PubMed

    Wong, Ian; Teo, Guo Hui; Neto, Chiara; Thickett, Stuart C

    2015-09-30

    Inspired by an example found in nature, the design of patterned surfaces with chemical and topographical contrast for the collection of water from the atmosphere has been of intense interest in recent years. Herein we report the synthesis of such materials via a combination of macromolecular design and polymer thin film dewetting to yield surfaces consisting of raised hydrophilic bumps on a hydrophobic background. RAFT polymerization was used to synthesize poly(2-hydroxypropyl methacrylate) (PHPMA) of targeted molecular weight and low dispersity; spin-coating of PHPMA onto polystyrene films produced stable polymer bilayers under appropriate conditions. Thermal annealing of these bilayers above the glass transition temperature of the PHPMA layer led to complete dewetting of the top layer and the formation of isolated PHPMA domains atop the PS film. Due to the vastly different rates of water nucleation on the two phases, preferential dropwise nucleation of water occurred on the PHPMA domains, as demonstrated by optical microscopy. The simplicity of the preparation method and ability to target polymers of specific molecular weight demonstrate the value of these materials with respect to large-scale water collection devices or other materials science applications where patterning is required.

  10. Stereo-, Temporal and Chemical Control through Photoactivation of Living Radical Polymerization: Synthesis of Block and Gradient Copolymers.

    PubMed

    Shanmugam, Sivaprakash; Boyer, Cyrille

    2015-08-12

    Nature has developed efficient polymerization processes, which allow the synthesis of complex macromolecules with a perfect control of tacticity as well as molecular weight, in response to a specific stimulus. In this contribution, we report the synthesis of various stereopolymers by combining a photoactivated living polymerization, named photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) with Lewis acid mediators. We initially investigated the tolerance of two different photoredox catalysts, i.e., Ir(ppy)3 and Ru(bpy)3, in the presence of a Lewis acid, i.e., Y(OTf)3 and Yb(OTf)3, to mediate the polymerization of N,N-dimethyl acrylamide (DMAA). An excellent control of tacticity as well as molecular weight and dispersity was observed when Ir(ppy)3 and Y(OTf)3 were employed in a methanol/toluene mixture, while no polymerization or poor control was observed with Ru(bpy)3. In comparison to a thermal system, a lower amount of Y(OTf)3 was required to achieve good control over the tacticity. Taking advantage of the temporal control inherent in our system, we were able to design complex macromolecular architectures, such as atactic block-isotactic and isotactic-block-atactic polymers in a one-pot polymerization approach. Furthermore, we discovered that we could modulate the degree of tacticity through a chemical stimulus, by varying [DMSO]0/[Y(OTf)3]0 ratio from 0 to 30 during the polymerization. The stereochemical control afforded by the addition of a low amount of DMSO in conjunction with the inherent temporal control enabled the synthesis of stereogradient polymer consisting of five different stereoblocks in one-pot polymerization.

  11. From Living Carbocationic to Living Radical Polymerization.

    DTIC Science & Technology

    1994-06-30

    C 1 -OFFICE OF NAVAL RESEARCH CONTRACT N00014-94-1-0101 R&T Code 31321075 Technical Report No. 18 FROM " LIVING " CARBOCATIONIC TO " LIVING " RADICAL...NUMBERS "From Living " Carbocationic to " Living " ’jical Polymerization N00014-94-1-01I01 6. AUTHOR(S) Krzysztof Matyjaszewski 7. PERFORMING ORGANIZATION NAME...1994) 1Za. DISTRIBUTION I AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE 13. ABSTRACT (Maximum 200 words) " Living " carbocationic polymerization is

  12. Modeling the free radical polymerization of acrylates

    NASA Astrophysics Data System (ADS)

    Günaydin, Hakan; Salman, Seyhan; Tüzün, Nurcan Şenyurt; Avci, Duygu; Aviyente, Viktorya

    Acrylates have gained importance because of their ease of conversion to high-molecular-weight polymers and their broad industrial use. Methyl methacrylate (MMA) is a well-known monomer for free radical polymerization, but its α-methyl substituent restricts the chemical modification of the monomer and therefore the properties of the resulting polymer. The presence of a heteroatom in the methyl group is known to increase the polymerizability of MMA. Methyl α-hydroxymethylacrylate (MHMA), methyl α-methoxymethylacrylate (MC1MA), methyl α-acetoxymethylacrylate (MAcMA) show even better conversions to high-molecular-weight polymers than MMA. In contrast, the polymerization rate is known to decrease as the methyl group is replaced by ethyl in ethyl α-hydroxymethylacrylate (EHMA) and t-butyl in t-butyl α-hydroxymethylacrylate (TBHMA). In this study, quantum mechanical tools (B3LYP/6-31G*) have been used in order to understand the mechanistic behavior of the free radical polymerization reactions of acrylates. The polymerization rates of MMA, MHMA, MC1MA, MAcMA, EHMA, TBHMA, MC1AN (α-methoxymethyl acrylonitrile), and MC1AA (α-methoxymethyl acrylic acid) have been evaluated and rationalized. Simple monomers such as allyl alcohol (AA) and allyl chloride (AC) have also been modeled for comparative purposes.

  13. Spatial control over brush growth through sunlight-induced atom transfer radical polymerization using dye-sensitized TiO2 as a photocatalyst.

    PubMed

    Li, Bin; Yu, Bo; Zhou, Feng

    2014-07-01

    Simulated-sunlight induced atom transfer radical polymerization is used for spatial control over polymer brush growth by in situ photo-generation of the Cu(I) /L activator complex from its higher oxidation state Cu(II) /L deactivator complex using dye sensitized titanium dioxide nano-particles. The polymerization is well controlled under sunlight irradiation. Another attractive feature of this method is the possibility of creating various patterned surfaces of brushes using photomasks. When a nanoporous alumina oxide membrane is used as the template for confinement diffusion of photogenerated Cu(I) /L catalyst, patterns with sub-50 nm resolution are obtained. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Nanostructured hybrid hydrogels prepared by a combination of atom transfer radical polymerization and free radical polymerization

    PubMed Central

    Bencherif, Sidi A.; Siegwart, Daniel J.; Srinivasan, Abiraman; Horkay, Ferenc; Hollinger, Jeffrey O.; Washburn, Newell R.; Matyjaszewski, Krzysztof

    2012-01-01

    A new method to prepare nanostructured hybrid hydrogels by incorporating well-defined poly(oligo (ethylene oxide) monomethyl ether methacrylate) (POEO300MA) nanogels of sizes 110–120 nm into a larger three-dimensional (3D) matrix was developed for drug delivery scaffolds for tissue engineering applications. Rhodamine B isothiocyanate-labeled dextran (RITC-Dx) or fluorescein isothiocyanate-labeled dextran (FITC-Dx)-loaded POEO300MA nanogels with pendant hydroxyl groups were prepared by activators generated electron transfer atom transfer radical polymerization (AGET ATRP) in cyclohexane inverse miniemulsion. Hydroxyl-containing nanogels were functionalized with methacrylated groups to generate photoreactive nanospheres. 1H NMR spectroscopy confirmed that polymerizable nanogels were successfully incorporated covalently into 3D hyaluronic acid-glycidyl methacrylate (HAGM) hydrogels after free radical photo-polymerization (FRP). The introduction of disulfide moieties into the polymerizable groups resulted in a controlled release of nanogels from cross-linked HAGM hydrogels under a reducing environment. The effect of gel hybridization on the macroscopic properties (swelling and mechanics) was studied. It is shown that swelling and nanogel content are independent of scaffold mechanics. In-vitro assays showed the nanostructured hybrid hydrogels were cytocompatible and the GRGDS (Gly–Arg–Gly–Asp–Ser) contained in the nanogel structure promoted cell–substrate interactions within 4 days of incubation. These nanostructured hydrogels have potential as an artificial extracellular matrix (ECM) impermeable to low molecular weight biomolecules and with controlled pharmaceutical release capability. Moreover, the nanogels can control drug or biomolecule delivery, while hyaluronic acid based-hydrogels can act as a macroscopic scaffold for tissue regeneration and regulator for nanogel release. PMID:19592087

  15. Polymeric nanocapsules with controllable crosslinking degree via combination of surface-initiated atom transfer radical polymerisation and photocrosslinking techniques.

    PubMed

    Liu, Peng; Mu, Bin; Du, Pengcheng; Hong, Zhilai

    2013-06-01

    The crosslinked polystyrene nanocapsules with controllable crosslinking degree have been prepared by the ultraviolet (UV)-induced photocrosslinking of the polystyrene grafted silica nanoparticles (SN-PS), which was obtained by the surface-initiated atom transfer radical polymerisation of styrene from the modified silica nanoparticle templates, after the silica templates were etched with hydrofluoric acid. The effect of the UV-irradiating time on the inner diameter of the nanocapsules, and the degree of crosslinking and the thickness of the shells was investigated. The dynamic light scattering results showed that the degree of crosslinking of the obtained nanocapsules increased with the prolongation of the UV-irradiation time, therefore the inner diameter of the nanocapsules increased. However, the percentage of grafting of the crosslinked polymer shells decreased with increasing the UV-irradiation time because of the photodecomposition of the polystyrene grafted during the UV-irradiated crosslinking process, according to the thermogravimetric analysis.

  16. ATOM TRANSFER RADICAL POLYMERIZATION OF N-BUTYL METHACRYLATE IN AQUEOUS DISPERSED SYSTEMS: A MINIEMULSION APPROACH. (R826735)

    EPA Science Inventory

    Ultrasonication was applied in combination with a hydrophobe for the copper-mediated atom transfer radical polymerization of n-butyl methacrylate in an aqueous dispersed system. A controlled polymerization was successfully achieved, as demonstrated by a linear correlation between...

  17. ATOM TRANSFER RADICAL POLYMERIZATION OF N-BUTYL METHACRYLATE IN AQUEOUS DISPERSED SYSTEMS: A MINIEMULSION APPROACH. (R826735)

    EPA Science Inventory

    Ultrasonication was applied in combination with a hydrophobe for the copper-mediated atom transfer radical polymerization of n-butyl methacrylate in an aqueous dispersed system. A controlled polymerization was successfully achieved, as demonstrated by a linear correlation between...

  18. Hemoglobin and red blood cells catalyze atom transfer radical polymerization.

    PubMed

    Silva, Tilana B; Spulber, Mariana; Kocik, Marzena K; Seidi, Farzad; Charan, Himanshu; Rother, Martin; Sigg, Severin J; Renggli, Kasper; Kali, Gergely; Bruns, Nico

    2013-08-12

    Hemoglobin (Hb) is a promiscuous protein that not only transports oxygen, but also catalyzes several biotransformations. A novel in vitro catalytic activity of Hb is described. Bovine Hb and human erythrocytes were found to display ATRPase activity, i.e., they catalyzed the polymerization of vinyl monomers under conditions typical for atom transfer radical polymerization (ATRP). N-isopropylacrylamide (NIPAAm), poly(ethylene glycol) methyl ether acrylate (PEGA), and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were polymerized using organobromine initiators and the reducing agent ascorbic acid in acidic aqueous solution. In order to avoid chain transfer from polymer radicals to Hb's cysteine residues, the accessible cysteines were blocked by a reaction with a maleimide. The formation of polymers with bromine chain ends, relatively low polydispersity indices (PDI), first order kinetics and an increase in the molecular weight of poly(PEGA) and poly(PEGMA) upon conversion indicate that control of the polymerization by Hb occurred via reversible atom transfer between the protein and the growing polymer chain. For poly(PEGA) and poly(PEGMA), the reactions proceeded with a good to moderate degree of control. Sodium dodecyl sulfate (SDS) gel electrophoresis, circular dichroism spectroscopy, and time-resolved ultraviolet-visible (UV-vis) spectroscopy revealed that the protein was stable during polymerization, and only underwent minor conformational changes. As Hb and erythrocytes are readily available, environmentally friendly, and nontoxic, their ATRPase activity is a useful tool for synthetic polymer chemistry. Moreover, this novel activity enhances the understanding of Hb's redox chemistry in the presence of organobromine compounds.

  19. Surface-active and stimuli-responsive polymer--Si(100) hybrids from surface-initiated atom transfer radical polymerization for control of cell adhesion.

    PubMed

    Xu, F J; Zhong, S P; Yung, L Y L; Kang, E T; Neoh, K G

    2004-01-01

    A simple two-step method was developed for the covalent immobilization of atom-transfer radical polymerization (ATRP) initiators on the hydrogen-terminated Si(100) (Si-H) surface. Well-defined functional polymer-Si hybrids, consisting of covalently tethered brushes of poly(ethylene glycol) monomethacrylate (PEGMA) polymer, N-isopropylacrylamide (NIPAAm) polymer, and NIPAAm-PEGMA copolymers and block copolymers on Si-H surfaces, were prepared via surface-initiated ATRP. Kinetics study revealed that the chain growth from the silicon surface was consistent with a "controlled" process. Surface cultures of the cell line 3T3-Swiss albino on the hybrids were evaluated. The PEGMA graft-polymerized silicon [Si-g-P(PEGMA)] surface is very effective in preventing cell attachment and growth. At 37 degrees C [above the lower critical solution temperature (LCST, approximately 32 degrees C) of NIPAAm], the seeded cells adhered, spread, and proliferated on the NIPAAm graft polymerized silicon [Si-g-P(NIPAAm)] surface. Below the LCST, the cells detached from the Si-g-P(NIPAAm) surface spontaneously. Incorporation of PEGMA units into the NIPAAm chains of the Si-g-P(NIPAAm) surface via copolymerization resulted in more rapid cell detachment during the temperature transition. The "active" chain ends on the Si-g-P(PEGMA) and Si-g-P(NIPAAm) hybrids were also used as the macroinitiators for the synthesis of diblock copolymer brushes. Thus, not only are the hybrids potentially useful as stimuli-responsive adhesion modifiers for cells in silicon-based biomedical microdevices but also the active chain ends on the hybrid surfaces offer opportunities for further surface functionalization and molecular design.

  20. Radical Ring-Opening Polymerization: Scope, Limitations, and Application to (Bio)Degradable Materials.

    PubMed

    Tardy, Antoine; Nicolas, Julien; Gigmes, Didier; Lefay, Catherine; Guillaneuf, Yohann

    2017-02-08

    Cyclic monomers bearing either vinyl or exomethylene groups have the ability to be polymerized through a radical pathway via a ring-opening mechanism (addition-fragmentation process), leading to the introduction of functionalities in the polymer backbone. Radical ring-opening polymerization (rROP) combines the advantages of both ring-opening polymerization and radical polymerization, that is the preparation of polymers bearing heteroatoms in the backbone but with the ease and robustness of a radical process. This current review presents a comprehensive description of rROP by detailing: (i) the various monomers that polymerize through rROP; (ii) the main parameters that govern the rROP mechanism; (iii) the copolymerization by conventional or controlled/living radical polymerization between rROP monomers and traditional vinyl monomers to obtain copolymers with advanced properties; (iv) the different applications (low shrinkage materials and preparation of (bio)degradable materials) of rROP monomer-containing materials, and (v) the main alternatives to rROP to induce degradability to materials obtained by a radical polymerization.

  1. Microwave-assisted radical polymerization of dialkyl fumarates

    NASA Astrophysics Data System (ADS)

    Cortizo, M. Susana; Laurella, Sergio; Alessandrini, José Luis

    2007-07-01

    Free radical polymerization of dialkyl fumarates (R:isopropyl, cyclohexyl, 2-ethylhexyl, 2-phenylethyl) under microwave irradiation was investigated. The polymerizations were carried out at different powers of irradiation and initiator concentrations (benzoyl peroxide, BP) and the effect of the monomer structure on the conversion, average molecular weights and the polydispersity index ( Mw/ Mn) was analyzed. A significant enhancement of the rates of polymerization was found, as compared with those obtained under thermal conditions.

  2. Application of living free radical polymerization for nucleic acid delivery.

    PubMed

    Chu, David S H; Schellinger, Joan G; Shi, Julie; Convertine, Anthony J; Stayton, Patrick S; Pun, Suzie H

    2012-07-17

    Therapeutic gene delivery can alter protein function either through the replacement of nonfunctional genes to restore cellular health or through RNA interference (RNAi) to mask mutated and harmful genes. Researchers have investigated a range of nucleic acid-based therapeutics as potential treatments for hereditary, acquired, and infectious diseases. Candidate drugs include plasmids that induce gene expression and small, interfering RNAs (siRNAs) that silence target genes. Because of their self-assembly with nucleic acids into virus-sized nanoparticles and high transfection efficiency in vitro, cationic polymers have been extensively studied for nucleic acid delivery applications, but toxicity and particle stability have limited the clinical applications of these systems. The advent of living free radical polymerization has improved the quality, control, and reproducibility of these synthesized materials. This process yields well-defined, narrowly disperse materials with designed architectures and molecular weights. As a result, researchers can study the effects of polymer architecture and molecular weight on transfection efficiency and cytotoxicity, which will improve the design of next-generation vectors. In this Account, we review findings from structure-function studies that have elucidated key design motifs necessary for the development of effective nucleic acid vectors. Researchers have used robust methods such as atom transfer radical polymerization (ATRP), reverse addition-fragmentation chain transfer polymerization (RAFT), and ring-opening metastasis polymerization (ROMP) to engineer materials that enhance extracellular stability and cellular specificity and decrease toxicity. In addition, we discuss polymers that are biodegradable, form supramolecular structures, target specific cells, or facilitate endosomal release. Finally, we describe promising materials with a range of in vivo applications from pulmonary gene delivery to DNA vaccines.

  3. pH-responsive controlled-release fertilizer with water retention via atom transfer radical polymerization of acrylic acid on mussel-inspired initiator.

    PubMed

    Ma, Zhi-yuan; Jia, Xin; Zhang, Guo-xiang; Hu, Jia-mei; Zhang, Xiu-lan; Liu, Zhi-yong; Wang, He-yun; Zhou, Feng

    2013-06-12

    This work reports a polydopamine-graft-poly(acrylic acid) (Pdop-g-PAA)-coated controlled-release multi-element compound fertilizer with water-retention function by a combination of mussel-inspired chemistry and surface-initiated atom transfer radical polymerization (SI-ATRP) techniques for the first time. The morphology and composition of the products were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), gel permeation chromatography (GPC), and inductively coupled plasma (ICP) emission spectrometry. The results revealed that the stimuli-responsive layer formed by a Pdop inner layer and a PAA outer corona exhibit outstanding selective permeability to charged nutrients and the release rate of encapsulated elements can be tailored by the pH values. At low pH, the Pdop-g-PAA layer can reduce nutrient loss, and at high pH, the coating restrains transportation of negative nutrients but favors the release of cations. Moreover, PAA brushes provide good water-retention property. This Pdop-graft-polymer brushes coating will be effective and promising in the research and development of multi-functional controlled-release fertilizer.

  4. Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes.

    PubMed

    Zoppe, Justin O; Ataman, Nariye Cavusoglu; Mocny, Piotr; Wang, Jian; Moraes, John; Klok, Harm-Anton

    2017-02-08

    The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

  5. Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst.

    PubMed

    Theriot, Jordan C; Ryan, Matthew D; French, Tracy A; Pearson, Ryan M; Miyake, Garret M

    2016-04-22

    A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The procedure is performed under an inert atmosphere using air- and water-exclusion techniques. The outcome of the polymerization is affected by the ratios of monomer, initiator, and catalyst used as well as the reaction concentration, solvent, and nature of the light source. Temporal control over the polymerization can be exercised by turning the visible light source off and on. Low dispersities of the resultant polymers as well as the ability to chain-extend to form block copolymers suggest control over the polymerization, while chain end-group analysis provides evidence supporting an atom-transfer radical polymerization mechanism.

  6. Development of materials from copolyacrylates via atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Jones, Melody Mersadez

    Homopolymerization of 2-(trimethylsilyl)ethyl acrylate, 3,3-dimethylbutyl acrylate, methyl acrylate, and methyl methacrylate using atom transfer radical polymerization (ATRP) is reported. In addition, polymethyl acrylate and polymethyl methacrylate were used as macroinitiators for diblock copolymerizations (via ATRP) with various monomers to yield pMA-b-TMSEA, pMMA-b-TMSEA, and pMMA-b-GMA copolymers; these results are also reported. Controlled polymerizations were performed using the CuBr/hexamethyltriethylenetetramine catalyst system in combination with methyl bromopropionate as the initiator. The protected acid block copolymers pMA-b-TMSEA and pMMA-b-TMSEA were deprotected to afford acrylic and meth acrylic acid block copolymers pMA-b-AA and pMMA-b-AA. Methylene chloride was used to micellize the amphiphilic copolymers in order to obtain the critical micelle concentration of the polymers (CMCpMA-b-AA = 10 mg/mL, CMCpMMA-b-AA = 0.4 mg/mL). The majority of polymerization were done in bulk; however, since poly(trimethylsilyl)ethyl acrylate displayed polydispersity (Mn = 11459, PDI = 1.437) on the high end of the acceptable range, various solvents were utilized to decrease the polymerization rate and afford low polydispersity materials. This differs from the ATRP of polymethyl acrylate or polymethyl methacrylate using this catalytic system, which do not require the addition of a solvent to obtain well-defined polymers. Also, for this polymerization system three different temperatures (60°C, 90°C, and 120°C) were used, in order to reduce the concentration of radicals and the contribution of termination. The homopolymers and protected acid block copolymers were characterized by gel permeation chromatography to determine the relative molecular weights. Differential scanning calorimetry was used to obtain the glass transition temperature of all polymers. Characterization using NMR (1H and 13C) and FTIR confirmed homopolymerization of 3,3-dimethylbutyl acrylate, 2

  7. Temperature-controlled flow switching in nanocapillary array membranes mediated by poly(N-isopropylacrylamide) polymer brushes grafted by atom transfer radical polymerization.

    PubMed

    Lokuge, Ishika; Wang, Xuejun; Bohn, Paul W

    2007-01-02

    We report actively controlled transport that is thermally switchable and size-selective in a nanocapillary array membrane (NCAM) prepared by grafting poly(N-isopropylacrylamide) (PNIPAAm) brushes onto the exterior surface of a Au-coated polycarbonate track-etched membrane. A smooth Au layer on the membrane surface, which is key to obtaining a uniform polymer film, was prepared by thermal evaporation of approximately 50 nm Au on both exterior surfaces. After evaporation, the inner diameter of the pore is reduced slightly, but the NCAM retains a narrow pore size distribution. PNIPPAm brushes with 10-30 nm (dry film) thickness were grafted onto the Au surface through surface-initiated atom transfer radical polymerization (ATRP) using a disulfide initiator, (BrC(CH3)2COO(CH2)11S)2. Molecular transport through the PNIPAAm polymer brush-modified NCAMs was investigated by real-time fluorescence measurements using fluorescein isothiocyanate (FITC)-labeled dextrans ranging from 4.4 to 282 kDa in membranes with variable initial pore diameters (80, 100, and 200 nm) and different PNIPAAm thicknesses. Manipulating the temperature of the NCAM through the PNIPAAm lower critical solution temperature (LCST) causes large, size-dependent changes in the transport rates. Over specific ranges of probe size, transport is completely blocked below the LCST but strongly allowed above the LCST. The combination of the highly uniform PNIPAAm brush and the monodisperse pore size distribution is critical in producing highly reproducible switching behavior. Furthermore, the reversible nature of the switching raises the possibility of using them as actively controlled filtration devices.

  8. Preparing polymer brushes on polytetrafluoroethylene films by free radical polymerization

    NASA Astrophysics Data System (ADS)

    Sun, Wei; Chen, Yiwang; Deng, Qilan; Chen, Lie; Zhou, Lang

    2006-11-01

    Films of polytetrafluoroethylene (PTFE) were exposed to sodium naphthalenide (Na/naphtha) etchant so as to defluorinate the surface for obtaining hydroxyl functionality. Surface-initiators were immobilized on the PTFE films by esterification of 4,4‧-azobis(4-cyanopentanoic acid) (ACP) and the hydroxyl groups covalently linked to the surface. Grafting of polymer brushes on the PTFE films was carried out by the surface-initiated free radical polymerization. Homopolymers brushes of methyl methacrylate (MMA) were prepared by free radical polymerization from the azo-functionalized PTFE surface. The chemical composition and topography of the graft-functionalized PTFE surfaces were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IR spectroscopy and atomic force microscopy (AFM). Water contact angles on PTFE films were reduced by surface grafting of MMA.

  9. Novel Patterned Films by Free-Radical Polymerization Techniques

    NASA Astrophysics Data System (ADS)

    Ward, Jennifer H.; Peppas, Nicholas A.

    2000-03-01

    We have developed novel techniques for the preparation of micropatterned structures by the block copolymerization of thin layers using UV free-radical polymerizations. The process involves polymerizing the first layer in the presence of an iniferter (initiator-transfer agent-terminator) with a dithiocarbamate group to make a photosensitive polymer. Upon application of a second monomer layer on the first polymer layer and irradiation, a copolymer is formed between the two layers. Patterns are created on the films by applying a mask and selectively irradiating the surface. Applications of this type of material are in biomaterials and biosensors for the selective adhesion of cells and proteins. We have successfully polymerized poly(ethylene glycol) (PEG) onto a layer of poly(methyl methacrylate) (PMMA) in the presence of tetraethylthiuran disulfide. Cells will adhere to the exposed PMMA areas but not to the PEG surfaces. This work has been supported by National Science Foundation grant No. DGE-9972770.

  10. Biodegradable and radically polymerized elastomers with enhanced processing capabilities.

    PubMed

    Ifkovits, Jamie L; Padera, Robert F; Burdick, Jason A

    2008-09-01

    The development of biodegradable materials with elastomeric properties is beneficial for a variety of applications, including for use in the engineering of soft tissues. Although others have developed biodegradable elastomers, they are restricted by their processing at high temperatures and under vacuum, which limits their fabrication into complex scaffolds. To overcome this, we have modified precursors to a tough biodegradable elastomer, poly(glycerol sebacate) (PGS) with acrylates to impart control over the crosslinking process and allow for more processing options. The acrylated-PGS (Acr-PGS) macromers are capable of crosslinking through free radical initiation mechanisms (e.g., redox and photo-initiated polymerizations). Alterations in the molecular weight and % acrylation of the Acr-PGS led to changes in formed network mechanical properties. In general, Young's modulus increased with % acrylation and the % strain at break increased with molecular weight when the % acrylation was held constant. Based on the mechanical properties, one macromer was further investigated for in vitro and in vivo degradation and biocompatibility. A mild to moderate inflammatory response typical of implantable biodegradable polymers was observed, even when formed as an injectable system with redox initiation. Moreover, fibrous scaffolds of Acr-PGS and a carrier polymer, poly(ethylene oxide), were prepared via an electrospinning and photopolymerization technique and the fiber morphology was dependent on the ratio of these components. This system provides biodegradable polymers with tunable properties and enhanced processing capabilities towards the advancement of approaches in engineering soft tissues.

  11. Pickering emulsion templated interfacial atom transfer radical polymerization for microencapsulation.

    PubMed

    Li, Jian; Hitchcock, Adam P; Stöver, Harald D H

    2010-12-07

    This Article describes a new microencapsulation method based on a Pickering emulsion templated interfacial atom transfer radical polymerization (PETI-ATRP). Cationic LUDOX CL nanoparticles were coated electrostatically with an anionic polymeric ATRP initiator, poly(sodium styrene sulfonate-co-2-(2-bromoisobutyryloxy)ethyl methacrylate) (PSB), prepared by radical copolymerization of sodium styrene sulfonate and 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM). The resulting PSB-modified CL particles were surface active and could be used to stabilize oil-in-water Pickering emulsions. ATRP of water-soluble cross-linking monomers, confined to the oil-water interface by the surface-bound PSB, then led to nanoparticle/polymer composite shells. This method allowed encapsulation of core solvents (xylene, hexadecane, perfluoroheptane) with different solubility parameters. The microcapsule (MC) wall chemistry could accommodate different monomers, demonstrating the versatility of this method. Double-walled MCs were formed by sequentially carrying out PETI-ATRP and in situ polymerization of encapsulated monomers. The double-walled structure was verified by both transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM).

  12. Horseradish peroxidase mediated free radical polymerization of methyl methacrylate.

    PubMed

    Kalra, B; Gross, R A

    2000-01-01

    This paper reports the free radical polymerization of methyl methacrylate (MMA) catalyzed by horseradish peroxidase (HRP). A novel method was developed whereby MMA polymerization can be carried out at ambient temperatures in the presence of low concentrations of hydrogen peroxide and 2,4-pentanedione in a mixture of water and a water-miscible solvent. Polymers of MMA formed were highly stereoregular with predominantly syndiotactic sequences (syn-dyad fractions from 0.82 to 0.87). Analyses of the chloroform-soluble fraction of syndio-PMMA products by GPC showed that they have number-average molecular weights, Mn, that range from 7500 to 75,000. By using 25% v/v of the cosolvents dioxane, tetrahydrofuran, acetone, and dimethylformamide, 85, 45, 7 and 2% product yields, respectively, resulted after 24 h. Increasing the proportion of dioxane to water from 1:3 to 1:1 and 3:1 resulted in a decrease in polymer yield from 45 to 38 and 7%, respectively. Increase in the enzyme concentration from 70 to 80 and 90 mg/mL resulted in increased reaction kinetics. By adjustment of the molar ratio of 2,4-pentanedione to hydrogen peroxide between 1.30:1.0 and 1.45:1.0, the product yields and Mn values were increased. On the basis of the catalytic properties of HRP and studies herein, we believe that the keto-enoxy radicals from 2,4-pentanedione are the first radical species generated. Then, initiation may take place through this radical or by the radical transfer to another molecule.

  13. Fluorescent dye-labelled polymer synthesis by nitroxide mediated radical polymerization

    NASA Astrophysics Data System (ADS)

    Kollár, Jozef; Chmela, Štefan; Hrčková, Ľudmila; Hrdlovič, Pavol

    2012-07-01

    New applications of polymers at advanced technologies demand increased requirements on their properties. These properties are influenced by molecular as well as supramolecular structure. Controlled radical polymerization mediated by stable nitroxides (NMP) or substituted alkoxyamines offers simple method for preparation of polymers with programmable structure of macromolecules which possess remarkable better physical as well as chemical properties. They can be used as a macro initiators for the synthesis of block copolymers. At the present time it has been generally accepted that the extent of "livingness" is high for all conversions [1-4]. To verify this statement a series of fluorescent dye-labelled regulators has been synthesized, spectrally characterized and used as the mediators of styrene and n-butyl acrylate polymerization. Direct quantification of dormant species concentration (extent of livingness) and calculation of molar mass of marked polymers was performed by absorption and/or emission spectroscopy. Controlled radical polymerization mediated by stable nitroxides bearing fluorescence mark represents unconventional approach for monitoring and evaluation of mechanism and kinetics of polymerization process. Results indicate that the extent of livingness is strongly influenced by conversion as well as mediator concentration. There is a clear tendency toward to decreasing amount of dormant species with increasing monomer conversion. Moreover, lower mediator concentration decreases livingness of polymerization process.

  14. Ambiguous anti-fouling surfaces: Facile synthesis by light-mediated radical polymerization

    SciTech Connect

    Pester, Christian W.; Poelma, Justin E.; Narupai, Benjaporn; Patel, Shrayesh N.; Su, Gregory M.; Mates, Thomas E.; Luo, Yingdong; Ober, Christopher K.; Hawker, Craig J.; Kramer, Edward J.

    2015-08-06

    In an attempt to create a polymer brush-based platform for the systematic study for anti-biofouling surfaces, the benefits of surface initiated, visible light-mediated radical polymerization are utilized to fabricate well-defined, chemically ambiguously patterned surfaces. A variety of analytical tools are used to illustrate the precise tuning of surface chemistry and thoroughly characterize spatially well-defined, hydrophilic/hydrophobic surfaces composed of poly(ethylene glycol methacrylate) and poly(trifluoroethyl methacrylate) with chemical definition on the micron scale. Advantages of both visible light-mediated photopolymerization and traditional copper-catalyzed atom transfer radical polymerization are combined to achieve both high spatial control and expanded monomer tolerance.

  15. Biocompatible Polymeric Analogues of DMSO Prepared by Atom Transfer Radical Polymerization.

    PubMed

    Li, Sipei; Chung, Hee Sung; Simakova, Antonina; Wang, Zongyu; Park, Sangwoo; Fu, Liye; Cohen-Karni, Devora; Averick, Saadyah; Matyjaszewski, Krzysztof

    2017-02-13

    The synthesis of a sulfoxide-based water-soluble polymer, poly(2-(methylsulfinyl)ethyl acrylate) (polyMSEA), a polymeric analogue of DMSO, by atom transfer radical polymerization (ATRP) is reported. Well-defined linear polymers were synthesized using relatively low amounts of copper catalyst (1000 or 100 ppm). Two types of star polymers were synthesized by either an "arm-first" approach or a "core-first" approach using a biodegradable β-cyclodextrin core. The glass transition temperatures of both the linear polymer (16 °C) and star polymer (32 °C) were determined by differential scanning calorimetry (DSC). The lower critical solution temperature (LCST) of poly(MSEA) was estimated to be ca. 140 °C by extrapolating the LCST of a series of copolymers with NIPAM. Cytotoxicity tests revealed that both the linear and star polymers have low toxicity, even at concentrations up to 3 mg/mL.

  16. Surface modification of electrospun fibres for biomedical applications: A focus on radical polymerization methods.

    PubMed

    Duque Sánchez, Lina; Brack, Narelle; Postma, Almar; Pigram, Paul J; Meagher, Laurence

    2016-11-01

    The development of electrospun ultrafine fibres from biodegradable and biocompatible polymers has created exciting opportunities for biomedical applications. Fibre meshes with high surface area, suitable porosity and stiffness have been produced. Despite desirable structural and topographical properties, for most synthetic and some naturally occurring materials, the nature of the fibre surface chemistry has inhibited development. Hydrophobicity, undesirable non-specific protein adsorption and bacterial attachment and growth, coupled with a lack of surface functionality in many cases and an incomplete understanding of the myriad of interactions between cells and extracellular matrix (ECM) proteins have impeded the application of these systems. Chemical and physical treatments have been applied in order to modify or control the surface properties of electrospun fibres, with some success. Chemical modification using controlled radical polymerization, referred to here as reversible-deactivation radical polymerization (RDRP), has successfully introduced advanced surface functionality in some fibre systems. Atom transfer radical polymerization (ATRP) and reversible addition fragmentation chain transfer (RAFT) are the most widely investigated techniques. This review analyses the practical applications of electrospinning for the fabrication of high quality ultrafine fibres and evaluates the techniques available for the surface modification of electrospun ultrafine fibres and includes a detailed focus on RDRP approaches.

  17. Radical polymerization of vinyl acetate with bis(tetramethylheptadionato)cobalt(II): coexistence of three different mechanisms.

    PubMed

    Santhosh, Kumar; Gnanou, Yves; Champouret, Yohan; Daran, Jean-Claude; Poli, Rinaldo

    2009-01-01

    The complex [Co(II)(tmhd)(2)] (4; tmhd = 2,2,6,6-tetramethylhepta-3,5-dionato) has been investigated as a mediator for controlled radical polymerization of vinyl acetate (VAc) and compared with the analogue [Co(II)(acac)(2)] (1; acac = acetylacetonato). A relatively well controlled process occurs, after an induction time, with 2,2'-azobis(4-methoxyl-2,4-dimethylvaleronitrile) (V-70) as radical initiator at 30 degrees C. However, whereas the polymerization essentially stops after about six initiator half-lives in the presence of 1, it continues with a first-order rate law in the presence of 4. The successful simulation of the kinetic data shows that 4 operates simultaneously by associative (degenerative transfer, DT) and dissociative (organometallic radical polymerization, OMRP) mechanisms. The occurrence of OMRP was confirmed by an independent polymerization experiment starting from an isolated and purified [Co(tmhd)(2)](PVAc) macroinitiator. The polymer molecular weight evolves linearly with conversion in accordance with the expected values for one chain per Co atom when DT is the predominant mechanism and also during the pure OMRP process; however, observation of stagnating molecular weights at long reaction times with concomitant breakdown of the first-order rate law for monomer consumption indicates a competitive chain-transfer process catalyzed by an increasing amount of Co(II). In the presence of external donors L (water, pyridine, triethylamine) the DT pathway is blocked and the OMRP pathway is accelerated, and polymerization with complex 4 is then about five times slower than with complex 1. The reversal of relative effective OMRP rate constants k(eff) (4>1 in the absence of external donors, 4<1 in their presence) is rationalized through competitive steric effects on Co(III)-C and Co(II)-L bond strengths. These propositions are supported by (1)H NMR studies and by DFT calculations.

  18. Radical Chain Polymerization Catalyzed by Graphene Oxide and Cooperative Hydrogen Bonding.

    PubMed

    Zhu, Zhongcheng; Shi, Shengjie; Wang, Huiliang

    2016-01-01

    Graphene oxide (GO) is effective in catalyzing a wide variety of organic reactions and a few types of polymerization reactions. No radical chain polymerizations catalyzed by GO have been reported. In this article, we probe the catalytic role and acceleration effect of GO for self-initiated radical chain polymerizations of acrylic acid (AA) in the presence of GO and a pre-existing polymer, poly(N-vinylpyrrolidone) (PVP), from a calorimetric perspective. Gelation experiments and DSC studies show that GO can function as a catalyst to accelerate the radical chain polymerization of AA. Isothermal polymerization kinetic data shows that the addition of GO diminishes the induction periods and increases the polymerization rates, as indicated by the much enhanced overall kinetic rate constants and lowered activation energies. The catalytic effect of GO for the polymerization of AA is attributed to the acidity of GO and the hydrogen bonding interactions between GO and monomer molecules and/or polymers.

  19. Introduction of Living Polymerization. Living and/or Controlled Polymerization

    DTIC Science & Technology

    1994-06-30

    separated into kinetic and synthetic. The intention of this paper is not to review existing and proclaimed living systems but to discuss the essence of a...o1 OFFICE OF NAVAL RESEARCH S4 CONTRACT N00014-94-1-0101 I R&T Code 31321075 Technical Report No. 10 INTRODUCTION TO LIVING POLYMERIZATION. LIVING ...TITLE AND SUBTITLE S. FUNDING NUMBERS Introduction to Living Polymerization. Living and/or Controlled Polymerization N00014-94-1-0101 6. AUTHOR(S

  20. Organometallic mediated radical polymerization of vinyl acetate using bis(imino)pyridine vanadium trichloride complexes.

    PubMed

    Perry, Mitchell R; Allan, Laura E N; Decken, Andreas; Shaver, Michael P

    2013-07-07

    The synthesis and characterization of one novel proligand and six novel vanadium(III) trichloride complexes is described. The controlled radical polymerization activity towards vinyl acetate of these, and eight other bis(imino)pyridine vanadium trichloride complexes previously reported, is investigated. Those complexes possessing variation at the N-aryl para-position with no steric protection offered by ortho-substituents (4 examples) result in poor control over poly(vinyl acetate) polymerization. Control is improved with increasing steric bulk at the ortho-position of the N-aryl substituent (4 examples) although attempts to increase steric bulk past isopropyl were unsuccessful. Synthesizing bis(imino)pyridine vanadium trichloride complexes with substituted imine backbones restores polymerization control when aliphatic substituents are used (4 examples) but ceases to make any drastic improvements on catalyst lifetime. Modification of the polymerization conditions is also investigated, in an attempt to improve the catalyst lifetime. Expansion of the monomer scope to include other vinyl esters, particularly those derived from renewable resources, shows promising results.

  1. Cobalt-Mediated Radical Polymerization of Vinyl Acetate and Acrylonitrile in Supercritical Carbon Dioxide.

    PubMed

    Kermagoret, Anthony; Chau, Ngoc Do Quyen; Grignard, Bruno; Cordella, Daniela; Debuigne, Antoine; Jérôme, Christine; Detrembleur, Christophe

    2016-03-01

    Cobalt-mediated radical polymerization (CMRP) of vinyl acetate (VAc) is successfully achieved in supercritical carbon dioxide (scCO2). CMRP of VAc is conducted using an alkyl-cobalt(III) adduct that is soluble in scCO2. Kinetics studies coupled to visual observations of the polymerization medium highlight that the melt viscosity and PVAc molar mass (Mn) are key parameters that affect the CMRP in scCO2. It is noticed that CMRP is controlled for Mn up to 10 000 g mol(-1), but loss of control is progressively observed for higher molar masses when PVAc precipitates in the polymerization medium. Low molar mass PVAc macroinitiator, prepared by CMRP in scCO2, is then successfully used to initiate the acrylonitrile polymerization. PVAc-b-PAN block copolymer is collected as a free flowing powder at the end of the process although the dispersity of the copolymer increases with the reaction time. Although optimization is required to decrease the dispersity of the polymer formed, this CMRP process opens new perspectives for macromolecular engineering in scCO2 without the utilization of fluorinated comonomers or organic solvents.

  2. Development of Initiation Strategies for the Optimization and Stabilization of Brushes Formed by Surface-Initiated Radical Polymerization

    NASA Astrophysics Data System (ADS)

    Bain, Erich D.

    Three challenges facing the continued development of the surface-initiated (SI) polymerization field are addressed. The first challenge is that surface-initiated free radical polymerization (SI-FRP) is currently under-represented in literature reports, despite the fact that SI-FRP offers several important advantages over surface-initiated controlled radical polymerization (SI-CRP) and represents a complementary approach. Recognizing that simple, efficient, and safer approaches to synthesizing effective surface free radical initiators are needed, we present a novel synthetic route to an azo type free radical initiator that forms self-assembled monolayers on oxide coated surfaces such as silicon and glass. The yield of the novel synthetic approach is approximately double that of the previous method, and the usage of cyanide is reduced dramatically. We characterize the decomposition kinetics of the initiator using differential scanning calorimetry, comparing it with other similar initiators. We characterize the surface properties of initiator layers on silicon using ellipsometry, water contact angle measurements, and x-ray photoelectron spectroscopy (XPS). We demonstrate the use of the initiator for SI-FRP as well as SI-CRP mechanisms including reverse atom transfer radical polymerization (RATRP) and reversible addition-fragmentation transfer (RAFT) polymerization. A second challenge facing the field of SI polymerization involves the stability of grafted polymer brushes in aqueous environments and under tension, both of which are commonly encountered in many applications. We hypothesize that the mechanism of brush degrafting involves hydrolysis of ester backbone units in the initiator, which are ubiquitous in surface-bound polymerization initiator systems. The novel initiator described herein is unique in that its backbone consists of a chemically stable alkane chain, free of esters or other easily hydrolysable groups. We present results of experiments demonstrating

  3. Recent developments in atom transfer radical polymerization (ATRP): methods to reduce metal catalyst concentrations.

    PubMed

    Lou, Qin; Shipp, Devon A

    2012-10-08

    Atom transfer radical polymerization (ATRP) was initially developed in the mid-1990s, and with continued refinement and use has led to significant discoveries in new materials. However, metal contamination of the polymer product is an issue that has proven detrimental to widespread industrial application of ATRP. The laboratories of K. Matyjaszewski have made significant progress towards removing this impediment, leading the development of "activators regenerated by electron transfer" ATRP (ARGET ATRP) and electrochemically mediated ATRP (eATRP) technologies. These variants of ATRP allow polymers to be produced with great molecular weight and functionality control but at significantly reduced catalyst concentrations, typically at parts per million levels. This Concept examines these polymerizations in terms of their mechanism and outcomes, and is aimed at giving the reader an overview of recent developments in the field of ATRP. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Electrically controlled polymeric gel actuators

    DOEpatents

    Adolf, D.B.; Shahinpoor, M.; Segalman, D.J.; Witkowski, W.R.

    1993-10-05

    Electrically controlled polymeric gel actuators or synthetic muscles are described capable of undergoing substantial expansion and contraction when subjected to changing pH environments, temperature, or solvent. The actuators employ compliant containers for the gels and their solvents. The gels employed may be cylindrical electromechanical gel fibers such as polyacrylamide fibers or a mixture of poly vinyl alcohol-polyacrylic acid arranged in a parallel aggregate and contained in an electrolytic solvent bath such as salt water. The invention includes smart, electrically activated devices exploiting this phenomenon. These devices are capable of being manipulated via active computer control as large displacement actuators for use in adaptive structure such as robots. 11 figures.

  5. Electrically controlled polymeric gel actuators

    DOEpatents

    Adolf, Douglas B.; Shahinpoor, Mohsen; Segalman, Daniel J.; Witkowski, Walter R.

    1993-01-01

    Electrically controlled polymeric gel actuators or synthetic muscles capable of undergoing substantial expansion and contraction when subjected to changing pH environments, temperature, or solvent. The actuators employ compliant containers for the gels and their solvents. The gels employed may be cylindrical electromechanical gel fibers such as polyacrylamide fibers or a mixture of poly vinyl alcohol-polyacrylic acid arranged in a parallel aggregate and contained in an electrolytic solvent bath such as salt water. The invention includes smart, electrically activated devices exploiting this phenomenon. These devices are capable of being manipulated via active computer control as large displacement actuators for use in adaptive structure such as robots.

  6. Optically active helical vinylterphenyl polymers: chiral teleinduction in radical polymerization and tunable stereomutation.

    PubMed

    Wang, Rong; Zhang, Jie; Wan, Xinhua

    2015-04-01

    Helical vinyl aromatic polymers are emerging as interesting chiral materials due to their dynamic tailorability, synthetic simplicity, and outstanding chemical and physical stabilities. This Personal Account discusses long-range chirality transfer in the radical polymerization of vinylterphenyl monomers and tunable stereomutation of the resultant polymers. It begins with a general introduction to the design, synthesis, and characterization of helical poly{(+)-2,5-bis[4'-((S)-2-methylbutyloxy)phenyl]styrene}, the first one of this series of polymers. Then, long-range chirality transfer during radical polymerization of terphenyl-based vinyl monomers is explained. After that, the chiroptical property control of the resultant polymers by means of the transition from kinetically controlled conformation to thermodynamically controlled conformation and external stimulus is described. This Personal Account concludes by discussing the advantages and disadvantages of the strategy of using vinylterphenyls to obtain optically active helical polymers and providing a short outlook, especially emphasizing the importance of tacticity on the chiroptical properties of polymers. Copyright © 2015 The Chemical Society of Japan and Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Facile Soap-Free Miniemulsion Polymerization of Methyl Methacrylate via Reverse Atom Transfer Radical Polymerization.

    PubMed

    Zhu, Gaohua; Zhang, Lifen; Pan, Xiangqiang; Zhang, Wei; Cheng, Zhenping; Zhu, Xiulin

    2012-12-21

    A facile soap-free miniemulsion polymerization of methyl methacrylate (MMA) was successfully carried out via a reverse ATRP technique, using a water-soluble potassium persulfate (KPS) or 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50) both as the initiator and the stabilizer, and using an oil-soluble N,N-n-butyldithiocarbamate copper (Cu(S2CN(C4H9)2)2) as the catalyst without adding any additional ligand. Polymerization results demonstrated the "living"/controlled characteristics of ATRP and the resultant latexes showed good colloidal stability with average particle size around 300-700 nm in diameter. The monomer droplet nucleation mechanism was proposed. NMR spectroscopy and chain-extension experiments under UV light irradiation confirmed the attachment and livingness of UV light sensitive -S-C(=S)-N(C4H9)2 group in the chain end.

  8. Compositional Controls on Melt Polymerization

    NASA Astrophysics Data System (ADS)

    Brugger, C.; Hammer, J.

    2005-12-01

    The structure and rheology of silicate melts are strongly controlled by composition, namely the concentrations of network-forming and -modifying cations. Melt viscosity is implicated in kinetic theories of phase transformations as a proxy for component mobility, which partly controls rates of crystal and bubble nucleation and growth. To anticipate reaction kinetics in magmas and focus experimental work on key variables, compositional controls on melt structure are systematically investigated using NBO/T (Mysen, 1988), the ratio of non-bridging oxygens to tetrahedrally coordinated cations. Silicon, ferric iron, and aluminum are network-formers, whereas alkalis and divalent cations are network-modifiers unless needed to charge-balance trivalent cations in tetrahedral coordination. NBO/T calculations are performed over 4D composition space (alkalis, silica, divalent and trivalent cations), in which 3 components are varied independently, creating a cube. We assess the effects of individual components using slices through the cube contoured for NBO/T. Ratios are also calculated for naturally occurring liquids and MELTS-generated liquid lines of descent derived from basalts with similar silica contents but varying in alkalis. Naturally occurring melts are highly polymerized (NBO/T of 0-1) compared to silicate minerals (0-4). Calculations show that replacing network-modifiers with network-formers decreases NBO/T; conversely, replacing formers with modifiers increases the ratio. However, polymerization increases when alumina replaces silica or when alkalis replace divalent cations. Natural alkali-rich melts tend to have fewer divalent cations than alkali-poor melts at similar silica contents, thus they are more polymerized and have higher viscosities. Contrary to common perception, the lower viscosities of highly differentiated alkalic melts (e.g. trachytes, phonolites) compared to silica-rich rhyolites are attributed to lower silica rather than greater alkalis. In fact

  9. Free Radical Polymerization of Styrene: A Radiotracer Experiment

    ERIC Educational Resources Information Center

    Mazza, R. J.

    1975-01-01

    Describes an experiment designed to acquaint the chemistry student with polymerization reactions, vacuum techniques, liquid scintillation counting, gas-liquid chromatography, and the handling of radioactive materials. (MLH)

  10. Free Radical Polymerization of Styrene: A Radiotracer Experiment

    ERIC Educational Resources Information Center

    Mazza, R. J.

    1975-01-01

    Describes an experiment designed to acquaint the chemistry student with polymerization reactions, vacuum techniques, liquid scintillation counting, gas-liquid chromatography, and the handling of radioactive materials. (MLH)

  11. Sequence-regulated copolymers via tandem catalysis of living radical polymerization and in situ transesterification.

    PubMed

    Nakatani, Kazuhiro; Ogura, Yusuke; Koda, Yuta; Terashima, Takaya; Sawamoto, Mitsuo

    2012-03-07

    Sequence regulation of monomers is undoubtedly a challenging issue as an ultimate goal in polymer science. To efficiently produce sequence-controlled copolymers, we herein developed the versatile tandem catalysis, which concurrently and/or sequentially involved ruthenium-catalyzed living radical polymerization and in situ transesterification of methacrylates (monomers: RMA) with metal alkoxides (catalysts) and alcohols (ROH). Typically, gradient copolymers were directly obtained from the synchronization of the two reactions: the instantaneous monomer composition in feed gradually changed via the transesterification of R(1)MA into R(2)MA in the presence of R(2)OH during living polymerization to give R(1)MA/R(2)MA gradient copolymers. The gradient sequence of monomers along a chain was catalytically controlled by the reaction conditions such as temperature, concentration and/or species of catalysts, alcohols, and monomers. The sequence regulation of multimonomer units was also successfully achieved in one-pot by monomer-selective transesterification in concurrent tandem catalysis and iterative tandem catalysis, providing random-gradient copolymers and gradient-block counterparts, respectively. In contrast, sequential tandem catalysis via the variable initiation of either polymerization or in situ transesterification led to random or block copolymers. Due to the versatile adaptability of common and commercially available reagents (monomers, alcohols, catalysts), this tandem catalysis is one of the most efficient, convenient, and powerful tools to design tailor-made sequence-regulated copolymers.

  12. Polyacrylamide grafting of modified graphene oxides by in situ free radical polymerization

    SciTech Connect

    Tang, Mingyi; Xu, Xiaoyang; Wu, Tao; Zhang, Sai; Li, Xianxian; Li, Yi

    2014-12-15

    Highlights: • Graphene oxide (GO) was modified by chemical reactions to functionalized GO (FGO). • The FGOs and the GO were then subjected to in situ free radical polymerization. • Hydroxyl groups of GO were the most reactive grafting sites. - Abstract: Graphene oxide (GO) was modified using chemical reactions to obtain three types of functionalized GO sheets (FGO). The FGO sheets and the GO were then subjected to in situ free radical polymerization in order to study the grafting polymerization. The FGO and grafted-.FGO were analyzed with Fourier transform infrared spectroscopy, scanning electronic microscopy, thermo-gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The grafting percentages in the materials were calculated using the TGA and XPS results. The FGO sheets with different functional groups exhibited different grafting abilities, and hydroxyl groups were proven to be the most reactive grafting sites for the in situ free radical grafting polymerization of polyacrylamide.

  13. Free Radical Polymerization of Styrene and Methyl Methacrylate in Various Room Temperature Ionic Liquids

    SciTech Connect

    Zhang, Hongwei; Hong, Kunlun; Mays, Jimmy

    2005-01-01

    Conventional free radical polymerization of styrene and methyl methacrylate was carried out in various room temperature ionic liquids (RTILs). The RTILs used in this research encompass a wide range of cations and anions. Typical cations include imidazolium, phosphonium, pyridinium, and pyrrolidinium; typical anions include amide, borate, chloride, imide, phosphate, and phosphinate. Reactions are faster and polymers obtained usually have higher molecular weights when compared to polymerizations carried out in volatile organic solvents under the same conditions. This shows that rapid rates of polymerization and high molecular weights are general features of conventional radical polymerizations in RTILs. Attempts to correlate the polarities and viscosities of the RTILs with the polymerization behavior fail to yield discernible trends.

  14. Free-radical solution-polymerization of trifluoronitrosomethane with tetrafluoroethylene

    NASA Technical Reports Server (NTRS)

    Gdickman, S. A.

    1972-01-01

    Heavy-walled glass reactor, equipped with aerosol-compatible couplings and needle valve and charged with solvent and initiator, is utilized for polymerization. Polymer conversions and reactor/vessel operation are discussed.

  15. Metal-Free Atom Transfer Radical Polymerization of Methyl Methacrylate with ppm Level of Organic Photocatalyst.

    PubMed

    Huang, Zhicheng; Gu, Yu; Liu, Xiaodong; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

    2016-10-28

    It is well known that the recently developed photoinduced metal-free atom transfer radical polymerization (ATRP) has been considered as a promising methodology to completely eliminate transition metal residue in polymers. However, a serious problem needs to be improved, namely, large amount of organic photocatalysts should be used to keep the controllability over molecular weights and molecular weight distributions. In this work, a novel photocatalyst 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) with strong excited state reduction potential is successfully used to mediate a metal-free ATRP of methyl methacrylate just with parts per million (ppm) level usage under irradiation of blue light emitting diode at room temperature, using ethyl α-bromophenyl-acetate as a typical initiator with high initiator efficiency. The polymerization kinetic study, multiple controlled "on-off" light switching cycle regulation, and chain extension experiment confirm the "living"/controlled features of this promising photoinduced metal-free ATRP system with good molecular weight control in the presence of ppm level photocatalyst 4CzIPN.

  16. On the role of oil-soluble initiators in the radical polymerization of micellar systems.

    PubMed

    Capek, I

    2001-05-25

    Polymerization in micellar systems is a technique which allows the preparation of ultrafine as well as coarse latex particles. This article presents a review of the current literature in the field of radical polymerization of classical monomers in micellar systems initiated by oil-soluble initiators. Besides a short introduction to some of the kinetic aspects of emulsion polymerization initiated by water-soluble initiators, we mainly focus on the kinetics and the mechanism of radical polymerization in o/w and w/o micellar systems initiated by classical oil-soluble initiators. The initiation of emulsion polymerization of an unsaturated monomer (styrene, butyl acrylate,...) by a water-soluble initiator (ammonium peroxodisulfate) is well understood. It starts in the aqueous phase and the initiating radicals enter the monomer-swollen micelle. The formed oligomeric radicals are surface active and increase the colloidal stability of the disperse system. Besides, the charged initiating radicals might experience the energetic barrier when entering the charged particle surface. The locus of initiation with oil-soluble initiators is more complex. It can partition between the aqueous-phase and the oil-phase. Besides, the surface-active oil-soluble initiator can penetrate into the interfacial layer. The dissolved oil-soluble initiator in the monomer droplet can experience the cage effect. The small fraction of the oil-soluble initiator dissolved in the aqueous phase takes part in the formation of radicals. The oligomeric radicals formed are uncharged and therefore, they do not experience the energetic barrier when entering the polymer particles. We summarize and discuss the experimental data of radical polymerization of monomers initiated by oil-soluble initiators in terms of partitioning an initiator among the different domains of the multiphase system. The inhibitor approach is used to model the formation of radicals and their history during the polymerization. The nature of

  17. A novel solid state photocatalyst for living radical polymerization under UV irradiation.

    PubMed

    Fu, Qiang; McKenzie, Thomas G; Ren, Jing M; Tan, Shereen; Nam, Eunhyung; Qiao, Greg G

    2016-02-11

    This study presents the development of a novel solid state photocatalyst for the photoinduced controlled radical polymerization of methacrylates under mild UV irradiation (λmax ≈ 365 nm) in the absence of conventional photoinitiators, metal-catalysts or dye sensitizers. The photocatalyst design was based on our previous finding that organic amines can act in a synergistic photochemical reaction with thiocarbonylthio compounds to afford well controlled polymethacrylates under UV irradiation. Therefore, in the current contribution an amine-rich polymer was covalently grafted onto a solid substrate, thus creating a heterogeneous catalyst that would allow for facile removal, recovery and recyclability when employed for such photopolymerization reactions. Importantly, the polymethacrylates synthesized using the solid state photocatalyst (ssPC) show similarly excellent chemical and structural integrity as those catalysed by free amines. Moreover, the ssPC could be readily recovered and re-used, with multiple cycles of polymerization showing minimal effect on the integrity of the catalyst. Finally, the ssPC was employed in various photo-"click" reactions, permitting high yielding conjugations under photochemical control.

  18. A novel solid state photocatalyst for living radical polymerization under UV irradiation

    PubMed Central

    Fu, Qiang; McKenzie, Thomas G.; Ren, Jing M.; Tan, Shereen; Nam, Eunhyung; Qiao, Greg G.

    2016-01-01

    This study presents the development of a novel solid state photocatalyst for the photoinduced controlled radical polymerization of methacrylates under mild UV irradiation (λmax ≈ 365 nm) in the absence of conventional photoinitiators, metal-catalysts or dye sensitizers. The photocatalyst design was based on our previous finding that organic amines can act in a synergistic photochemical reaction with thiocarbonylthio compounds to afford well controlled polymethacrylates under UV irradiation. Therefore, in the current contribution an amine-rich polymer was covalently grafted onto a solid substrate, thus creating a heterogeneous catalyst that would allow for facile removal, recovery and recyclability when employed for such photopolymerization reactions. Importantly, the polymethacrylates synthesized using the solid state photocatalyst (ssPC) show similarly excellent chemical and structural integrity as those catalysed by free amines. Moreover, the ssPC could be readily recovered and re-used, with multiple cycles of polymerization showing minimal effect on the integrity of the catalyst. Finally, the ssPC was employed in various photo-“click” reactions, permitting high yielding conjugations under photochemical control. PMID:26863939

  19. A novel solid state photocatalyst for living radical polymerization under UV irradiation

    NASA Astrophysics Data System (ADS)

    Fu, Qiang; McKenzie, Thomas G.; Ren, Jing M.; Tan, Shereen; Nam, Eunhyung; Qiao, Greg G.

    2016-02-01

    This study presents the development of a novel solid state photocatalyst for the photoinduced controlled radical polymerization of methacrylates under mild UV irradiation (λmax ≈ 365 nm) in the absence of conventional photoinitiators, metal-catalysts or dye sensitizers. The photocatalyst design was based on our previous finding that organic amines can act in a synergistic photochemical reaction with thiocarbonylthio compounds to afford well controlled polymethacrylates under UV irradiation. Therefore, in the current contribution an amine-rich polymer was covalently grafted onto a solid substrate, thus creating a heterogeneous catalyst that would allow for facile removal, recovery and recyclability when employed for such photopolymerization reactions. Importantly, the polymethacrylates synthesized using the solid state photocatalyst (ssPC) show similarly excellent chemical and structural integrity as those catalysed by free amines. Moreover, the ssPC could be readily recovered and re-used, with multiple cycles of polymerization showing minimal effect on the integrity of the catalyst. Finally, the ssPC was employed in various photo-“click” reactions, permitting high yielding conjugations under photochemical control.

  20. Phenyl Benzo[b]phenothiazine as a Visible Light Photoredox Catalyst for Metal-Free Atom Transfer Radical Polymerization.

    PubMed

    Dadashi-Silab, Sajjad; Pan, Xiangcheng; Matyjaszewski, Krzysztof

    2016-12-23

    This paper reports use of phenyl benzo[b]phenothiazine (Ph-benzoPTZ) as a visible light-induced metal-free atom transfer radical polymerization (ATRP) photoredox catalyst. Well-controlled polymerizations of various methacrylate monomers were conducted under a 392 nm visible light LED using Ph-benzoPTZ to activate different alkyl halides. The use of the photocatalyst enabled temporal control over the growth of polymer chains during intermittent on/off periods. The polymerization was initiated and progressed only under stimulation by light and completely stopped in the absence of light. Block copolymers were synthesized to demonstrate high retention of chain end fidelity in the polymers and livingness of the process.

  1. Polar, Functional Diene-Based Materials: Free Radical Polymerization of 2-Cyanomethyl-1,3-Butadiene

    SciTech Connect

    Jing, Y

    2000-09-12

    This thesis presented here focuses on the synthesis of 2-cyanomethyl-l ,3-butadiene and the free-radical polymerization of this monomer. In addition to the bulk, solution and emulsion polymerizations,, copolymerization with styrene and acrylonitrile will also be discussed. The comonomers were chosen due to the potential applications mentioned above. Furthermore, the thermal properties and rnicrostructures of the homopolymers and the copolymers are examined.

  2. Free-Radical Polymerization Using the Rotating-Sector Method.

    ERIC Educational Resources Information Center

    Moss, Stephen J.

    1982-01-01

    Discusses principles of a particular approach in teaching elementary kinetics of polymerization. Although the treatment discussed is more difficult for students to grasp, problems may be reduced using a computer program. The program, written in Applesoft Basic, is available from the author together with sample output. (JN)

  3. Facile synthesis of thermally stable poly(N-vinylpyrrolidone)-modified gold surfaces by surface-initiated atom transfer radical polymerization.

    PubMed

    Liu, Xiaoli; Sun, Kai; Wu, Zhaoqiang; Lu, Jianhong; Song, Bo; Tong, Weifang; Shi, Xiujuan; Chen, Hong

    2012-06-26

    Well-controlled polymerization of N-vinylpyrrolidone (NVP) on Au surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP) was carried out at room temperature by a silanization method. Initial attempts to graft poly(N-vinylpyrrolidone) (PVP) layers from initiators attached to alkanethiol monolayers yielded PVP films with thicknesses less than 5 nm. The combined factors of the difficulty in the controllable polymerization of NVP and the instability of alkanethiol monolayers led to the difficulty in the controlled polymerization of NVP on Au surfaces. Therefore, the silanization method was employed to form an adhesion layer for initiator attachment. This method allowed well-defined ATRP polymerization to occur on Au surfaces. Water contact angle, X-ray photoelectron spectroscopy (XPS), and reflectance Fourier transform infrared (reflectance FTIR) spectroscopy were used to characterize the modified surfaces. The PVP-modified gold surface remained stable at 130 °C for 3 h, showing excellent thermal stability. Thus, postfunctionalization of polymer brushes at elevated temperatures is made possible. The silanization method was also applied to modify SPR chips and showed potential applications in biosensors and biochips.

  4. Structural features of macrocyclic cobalt complexes - catalysts of chain transfer to a monomer in radical polymerization

    SciTech Connect

    Gridnev, A.A.; Lampeka, Ya.D.; Smirnov, B.R.; Yatsimirskii, K.B.

    1987-11-01

    Data are given on the catalytic activity of a series of cobalt coordination compounds with macrocyclic and acyclic ligsnds of different structures in radical polymerization reactions of methacrylic monomers. The influence of various factors (especially the structure of the ligand) on the manifestation of catalytic properties of the compounds studied is discussed.

  5. Ionic Liquids as Catalysts for the Radical Acrylate Polymerization Co-initiated by Imine Bases

    NASA Astrophysics Data System (ADS)

    Polenz, I.; Spange, S.

    2014-08-01

    The catalysis of the imine base acrylate (IBA) polymerization by Ionic Liquids (ILs) is reported. Addition of IL traces (~10-50 mM) to an imine base / acrylate mixture leads to both a significant decrease of the activation temperature (40 °C) required for the IBA polymerization process and an increase in the polymerization rate by a factor of 5-40 depending on the IL species. The radical character of the polymerization is proved by copolymerization experiments using methyl methacrylate (MMA) and methacrylonitrile (MAN) and comparison with literature known values of copolymerization parameters rMMA and rMAN of these co-monomers. The influence of the IL on the polymerization kinetics is quantified by the polymerization rate law; the order referring to the IL is 1 indicating its crucial impact on the monomer activation. The IBA activation properties are strongly dependent on the IL interaction strengths with the IBA components verified by the KAMELT-TAFT hydrogen bond donating ability α. The stronger the interaction (higher α) is, the less the IBA polymerization activation. The temperature dependence of four different IL catalysed IBA polymerization is investigated, allows a classification and anomalous non-ARRHENIUS regimes are discussed. Activation energies EA,P span over 20 and 50 kJ·mol-1, which is between the values of thermal- (~80 kJ·mol-1) and photo-initiation (~20 kJ·mol-1).

  6. Cytocompatible Polymer Grafting from Individual Living Cells by Atom-Transfer Radical Polymerization.

    PubMed

    Kim, Ji Yup; Lee, Bong Soo; Choi, Jinsu; Kim, Beom Jin; Choi, Ji Yu; Kang, Sung Min; Yang, Sung Ho; Choi, Insung S

    2016-12-05

    A cytocompatible method of surface-initiated, activator regenerated by electron transfer, atom transfer radical polymerization (SI-ARGET ATRP) is developed for engineering cell surfaces with synthetic polymers. Dopamine-based ATRP initiators are used for both introducing the ATRP initiator onto chemically complex cell surfaces uniformly (by the material-independent coating property of polydopamine) and protecting the cells from radical attack during polymerization (by the radical-scavenging property of polydopamine). Synthetic polymers are grafted onto the surface of individual yeast cells without significant loss of cell viability, and the uniform and dense grafting is confirmed by various characterization methods including agglutination assay and cell-division studies. This work will provide a strategic approach to the generation of living cell-polymer hybrid structures and open the door to their application in multitude of areas, such as sensor technology, catalysis, theranostics, and cell therapy. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Advancing Polymer-Supported Ionogel Electrolytes Formed via Radical Polymerization

    NASA Astrophysics Data System (ADS)

    Visentin, Adam F.

    fabricated. In addition to developing an understanding of UV-polymerized systems, a rapid 10 to 20 second, microwave-assisted polymerization method was developed as a novel means to create ionogels. These ionogels exhibited comparable mechanical response and ionic conductivity levels to those gels fabricated by the UV method. Lastly, an EDLC prototype was fabricated using a UV-polymerized ionogel formed in situ between two high-surface area carbon electrodes. The device performance metrics were comparable to commercial EDLCs, and functioned for several thousand cycles with limited loss in capacitance.

  8. Surface-initiated atom transfer radical polymerization from chitin nanofiber macroinitiator film.

    PubMed

    Yamamoto, Kazuya; Yoshida, Sho; Kadokawa, Jun-Ichi

    2014-11-04

    This paper reports the preparation of chitin nanofiber-graft-poly(2-hydroxyethyl acrylate) (CNF-g-polyHEA) films by surface-initiated atom transfer radical polymerization (ATRP) of HEA monomer from a CNF macroinitiator film. First, a CNF film was prepared by regeneration from a chitin ion gel with an ionic liquid. Then, acylation of the CNF surface with α-bromoisobutyryl bromide was carried out to obtain the CNF macroinitiator film having the initiating moieties (α-bromoisobutyrate group). The surface-initiated graft polymerization of HEA from the CNF macroinitiator film by ATRP was performed to produce the CNF-g-polyHEA film. The IR, XRD, and SEM measurements of the resulting film indicated the progress of the graft polymerization of HEA on surface of CNFs. The molecular weights of the grafted polyHEAs increased with prolonged polymerization times, which affected the mechanical properties of the films under tensile mode.

  9. The fabrication of superlow protein absorption zwitterionic coating by electrochemically mediated atom transfer radical polymerization and its application.

    PubMed

    Hu, Yichuan; Yang, Guang; Liang, Bo; Fang, Lu; Ma, Guanglong; Zhu, Qin; Chen, Shengfu; Ye, Xuesong

    2015-02-01

    A well-controllable electrochemically mediated surface-initiated atom transfer radical polymerization (e-siATRP) method for the fabrication of superlow protein absorption zwitterionic hydrogel coatings based on poly(sulbetaine methacrylate) (pSBMA) was developed in this work. The effects of the electric condition on polymerization as well as its antifouling performances both in vitro and in vivo were also investigated. Different potentials (-0.08 V, -0.15 V and -0.22 V) and polymerization times (from 8 to 48 h) were chosen to study the polymerization procedure. X-ray photoelectron spectroscopy, atomic force microscopy and ellipsometry measurements were used to characterize the properties of the polymer layers. Ellipsometry measurements showed that a higher potential provided faster polymerization and thicker polymer layers; however, the protein absorption experiments showed that the best polymerization condition was under a constant potential of -0.15 V and 32 h, under which the protein absorption was 0.8% in an enzyme-linked immunosorbent assay (compared to a bare gold electrode). The electrodes with a pSBMA coating effectively deduced the current sensitivity decay both in undiluted serum and in vivo. The usage of the commercially available polymerization monomer of SBMA, the simple convenient synthesis process regardless of the presence of oxygen and the excellent controllability of e-siATRP make it a very promising and universal technique in the preparation of zwitterionic polymer coatings, especially in the development of biocompatible material for implantable devices such as neural and biosensor electrodes.

  10. Chemical control of rate and onset temperature of nadimide polymerization

    NASA Technical Reports Server (NTRS)

    Lauver, R. W.

    1985-01-01

    The chemistry of norbornenyl capped imide compounds (nadimides) is briefly reviewed with emphasis on the contribution of Diels-Alder reversion in controlling the rate and onset of the thermal polymerization reaction. Control of onset temperature of the cure exotherm by adjusting the concentration of maleimide is demonstrated using selected model compounds. The effects of nitrophenyl compounds as free radical retarders on nadimide reactivity are discussed. A simple copolymerization model is proposed for the overall nadimide cure reaction. An approximate numerical analysis is carried out to demonstrate the ability of the model to simulate the trends observed for both maleimide and nitrophenyl additions.

  11. Radical polymerization in holographic grating formation in PQ-PMMA photopolymer part I: Short exposure

    NASA Astrophysics Data System (ADS)

    Yu, Dan; Liu, Hongpeng; Geng, Yaohui; Wang, Weibo; Zhao, Yuanyuan

    2014-11-01

    Photochemical radical polymerization in phenathrenequinone doped poly(methyl methacrylate) photopolymer are investigated theoretically and experimentally at short exposure. In experiments, the dynamic evolution of diffraction efficiency in grating formation is measured. Based on the rate equations of chemical reactions, the analytical expressions of components evolution are deduced to compare the contributions of several photochemical processes to the grating formation. The percentages of these radical polymerizations, namely the polymerization of one PQ with one matrix molecule, the bimolecular combination of MMA molecules, and the disproportionation of MMA molecules, are extracted quantitatively by nonlinear fitting experimental curves. Furthermore, the kinetics parameters, quantum yield Φ and molar absorption coefficient ε of photosensitizers, are determined to demonstrate the rationality of chemical processes. The theoretical results indicate that the polymerization of PQ with matrix is primary photochemical process which dominated the grating formation at short exposure. The contribution of chain polymerization of MMA molecules on the grating can be neglected. This investigation can provide a significant foundation for improving holographic characteristics by photochemical mechanism.

  12. Hydrolyzable Poly[Poly(Ethylene Glycol) Methyl Ether Acrylate]-Colistin Prodrugs through Copper-Mediated Photoinduced Living Radical Polymerization.

    PubMed

    Zhu, Chongyu; Schneider, Elena K; Nikolaou, Vasiliki; Klein, Tobias; Li, Jian; Davis, Thomas P; Whittaker, Michael R; Wilson, Paul; Kempe, Kristian; Velkov, Tony; Haddleton, David M

    2017-07-19

    Through the recently developed copper-mediated photoinduced living radical polymerization (CP-LRP), a novel and well-defined polymeric prodrug of the antimicrobial lipopeptide colistin has been developed. A colistin initiator (Boc5-col-Br2) was synthesized through the modification of colistin on both of its threonine residues using a cleavable initiator linker, 2-(2-bromo-2-methylpropanoyloxy) acetic acid (BMPAA), and used for the polymerization of acrylates via CP-LRP. Polymerization proceeds from both sites of the colistin initiator, and through the polymerization of poly(ethylene glycol) methyl ether acrylate (PEGA480), three water-soluble polymer-colistin conjugates (col-PPEGA, having degrees of polymerization of 5, 10, and 20) were achieved with high yield (conversion of ≥93%) and narrow dispersities (Đ < 1.3) in 2-4 h. Little or no effect on the structure and activity of the colistin was observed during the synthesis, and most of the active colistin can be recovered from the conjugates in vitro within 2 days. Furthermore, in vitro biological analyses including disk diffusion, broth microdilution, and time-kill studies suggested that all of the conjugates have the ability to inhibit the growth of multidrug-resistant (MDR) Gram-negative bacteria, of which col-PPEGA DP5 and DP10 showed similar or better antibacterial performance compared to the clinically relevant colistin prodrug CMS, indicating their potential as an alternative antimicrobial therapy. Moreover, considering the control over the polymerization, the CP-LRP technique has the potential to provide an alternative platform for the development of polymer bioconjugates.

  13. Synthesis and characterization of carbon fibers functionalized with poly (glycidyl methacrylate) via atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Wu, Yongwei; Xiong, Lei; Qin, Xiaokang; Wang, Zhengyue; Ding, Bei; Ren, Huan; Pi, Xiaolong

    2015-07-01

    In this work, polyacrylonitrile (PAN)-based carbon fibers (CF) were chemically modified with poly (glycidyl methacrylate) (PGMA) via atom transfer radical polymerization (ATRP) to improve the interaction between the CF and polymer matrix. The FT-IR, TGA, and XPS were used to determine the chemical structure of the resulting products and the quantities of PGMA chains grafted from the CF surface. The experimental results confirm that the CF surface was functionalized and glycidyl methacrylate was graft-polymerized onto the CF, and the grafting content of polymer could reach 10.2%.

  14. Functionalization of nylon membranes via surface-initiated atom-transfer radical polymerization.

    PubMed

    Xu, F J; Zhao, J P; Kang, E T; Neoh, K G; Li, J

    2007-07-31

    The ability to manipulate and control the surface properties of nylons is of crucial importance to their widespread applications. In this work, surface-initiated atom-transfer radical polymerization (ATRP) is employed to tailor the functionality of the nylon membrane and pore surfaces in a well-controlled manner. A simple two-step method, involving the activation of surface amide groups with formaldehyde and the reaction of the resulting N-methylol polyamide with 2-bromoisobutyryl bromide, was first developed for the covalent immobilization of ATRP initiators on the nylon membrane and its pore surfaces. Functional polymer brushes of 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol)monomethacrylate (PEGMA) were prepared via surface-initiated ATRP from the nylon membranes. A kinetics study revealed that the chain growth from the membranes was consistent with a "controlled" process. The dormant chain ends of the grafted HEMA polymer (P(HEMA)) and PEGMA polymer (P(PEGMA)) on the nylon membranes could be reactivated for the consecutive surface-initiated ATRP to produce the corresponding nylon membranes functionalized by P(HEMA)-b-P(PEGMA) and P(PEGMA)-b-P(HEMA) diblock copolymer brushes. In addition, membranes with grafted P(HEMA) and P(PEGMA) brushes exhibited good resistance to protein adsorption and fouling under continuous-flow conditions.

  15. Exploiting Metalloporphyrins for Selective Living Radical Polymerization Tunable over Visible Wavelengths.

    PubMed

    Shanmugam, Sivaprakash; Xu, Jiangtao; Boyer, Cyrille

    2015-07-22

    The use of metalloporphyrins has been gaining popularity particularly in the area of medicine concerning sensitizers for the treatment of cancer and dermatological diseases through photodynamic therapy (PDT), and advanced materials for engineering molecular antenna for harvesting solar energy. In line with the myriad functions of metalloporphyrins, we investigated their capability for photoinduced living polymerization under visible light irradiation over a broad range of wavelengths. We discovered that zinc porphyrins (i.e., zinc tetraphenylporphine (ZnTPP)) were able to selectively activate photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of trithiocarbonate compounds for the polymerization of styrene, (meth)acrylates and (meth)acrylamides under a broad range of wavelengths (from 435 to 655 nm). Interestingly, other thiocarbonylthio compounds (dithiobenzoate, dithiocarbamate and xanthate) were not effectively activated in the presence of ZnTPP. This selectivity was likely attributed to a specific interaction between ZnTPP and trithiocarbonates, suggesting novel recognition at the molecular level. This interaction between the photoredox catalyst and trithiocarbonate group confers specific properties to this polymerization, such as oxygen tolerance, enabling living radical polymerization in the presence of air and also ability to manipulate the polymerization rates (kp(app) from 1.2-2.6 × 10(-2) min(-1)) by varying the visible wavelengths.

  16. Atom transfer radical polymerization (ATRP) and organometallic mediated radical polymerization (OMRP) of styrene mediated by diaminobis(phenolato)iron(II) complexes: a DFT study.

    PubMed

    Poli, Rinaldo; Shaver, Michael P

    2014-07-21

    This study has addressed the radical polymerization of styrene mediated by the diaminobis(phenolate) complexes [Fe(O-2,4-Y2C6H2-5-CH2)2NCH2CH2NMe2], abbreviated as [Fe(II)]. The system is known to be well controlled when Y = Cl but not when Y = alkyl. The control was proposed to occur by a dual ATRP+OMRP mechanism. We have used DFT calculations to address the Y = Cl and Y = CH3 systems. The growing radical chain, ATRP dormant chain, and OMRP dormant chain were simplified to PhCH(CH3)(•), PhCH(CH3)-Cl, and [PhCH(CH3)-Fe(III)]. The idealized ATRP activation/deactivation equilibrium involves [Fe(III)-Cl] (I(Y)) and PhCH(CH3)(•) on the active side and [Fe(II)] (II(Y)) and PhCH(CH3)-Cl on the dormant side, whereas the OMRP activation/deactivation relates [Fe(II)] and PhCH(CH3)(•) with [PhCH(CH3)-Fe(III)] (III(Y)). A benchmarking of various functionals against the known spin properties of alkylporphyriniron(III) shows B3PW91* to be a suitable functional. For the purpose of bond dissociation energy calculations, a dispersion correction was made (B3PW91*-D3). For both Y systems, the ground state is a spin sextet for I, a spin quintet for II, and a spin quartet for III. The calculations show a greater energy cost for the ATRP activation process involving Cl atom addition to II(Cl) to yield I(Cl) (7.2 kcal/mol) relative to the process transforming II(Me) to I(Me) (2.1 kcal/mol). On the other hand, the alkyl addition transforming II to III provides slightly greater stabilization for II(Cl) (27.1 kcal/mol) than for II(Me) (26.1 kcal/mol). As a result, both ATRP and OMRP trapping processes provide greater stabilization for the Y = Cl system, in agreement with the observed better control. The charge analysis attributes these minor but determining energy differences to the inductive electron withdrawing effect of the phenolato Cl substituents. The ATRP and OMRP activation/deactivation pathways have been analyzed in relation to the spin state change; they show in each case

  17. In Situ Investigation of Electrochemically Mediated Surface-Initiated Atom Transfer Radical Polymerization by Electrochemical Surface Plasmon Resonance.

    PubMed

    Chen, Daqun; Hu, Weihua

    2017-03-28

    Electrochemically mediated atom transfer radical polymerization (eATRP) initiates/controls the controlled/living ATRP chain propagation process by electrochemically generating (regenerating) the activator (lower-oxidation-state metal complex) from deactivator (higher-oxidation-state metal complex). Despite successful demonstrations in both of homogeneous polymerization and heterogeneous system (namely, surface-initiated ATRP, SI-ATRP), the eATRP process itself has never been in situ investigated, and important information regarding this process remains unrevealed. In this work, we report the first investigation of the electrochemically mediated SI-ATRP (eSI-ATRP) by rationally combining electrochemical technique with real-time surface plasmon resonance (SPR). In the experiment, the potential of a SPR gold chip modified by self-assembled monolayer of ATRP initiator was controlled to electrochemically reduce the deactivator to activator to initiate the SI-ATRP, and the whole process was simultaneously monitored by SPR with a high time resolution of 0.1 s. It is found that it is feasible to electrochemically trigger/control the SI-ATRP and the polymerization rate is correlated to the potential applied to the gold chip. This work reveals important kinetic information on eSI-ATRP, and offers a powerful platform for in situ investigation of such complicated processes.

  18. Polymerization Induced Self-Assembly of Alginate Based Amphiphilic Graft Copolymers Synthesized by Single Electron Transfer Living Radical Polymerization.

    PubMed

    Kapishon, Vitaliy; Whitney, Ralph A; Champagne, Pascale; Cunningham, Michael F; Neufeld, Ronald J

    2015-07-13

    Alginate-based amphiphilic graft copolymers were synthesized by single electron transfer living radical polymerization (SET-LRP), forming stable micelles during polymerization induced self-assembly (PISA). First, alginate macroinitiator was prepared by partial depolymerization of native alginate, solubility modification and attachment of initiator. Depolymerized low molecular weight alginate (∼12 000 g/mol) was modified with tetrabutylammonium, enabling miscibility in anhydrous organic solvents, followed by initiator attachment via esterification yielding a macroinitiator with a degree of substitution of 0.02, or 1-2 initiator groups per alginate chain. Then, methyl methacrylate was polymerized from the alginate macroinitiator in mixtures of water and methanol, forming poly(methyl methacrylate) grafts, prior to self-assembly, of ∼75 000 g/mol and polydispersity of 1.2. PISA of the amphiphilic graft-copolymer resulted in the formation of micelles with diameters of 50-300 nm characterized by light scattering and electron microscopy. As the first reported case of LRP from alginate, this work introduces a synthetic route to a preparation of alginate-based hybrid polymers with a precise macromolecular architecture and desired functionalities. The intended application is the preparation of micelles for drug delivery; however, LRP from alginate can also be applied in the field of biomaterials to the improvement of alginate-based hydrogel systems such as nano- and microhydrogel particles, islet encapsulation materials, hydrogel implants, and topical applications. Such modified alginates can also improve the function and application of native alginates in food and agricultural applications.

  19. Oseltamivir-conjugated polymeric micelles prepared by RAFT living radical polymerization as a new active tumor targeting drug delivery platform.

    PubMed

    Kapishon, Vitaliy; Allison, Stephanie; Whitney, Ralph A; Cunningham, Michael F; Szewczuk, Myron R; Neufeld, Ronald J

    2016-03-01

    Targeted drug delivery using polymeric nanostructures has been at the forefront of cancer research, engineered for safer, more efficient and effective use of chemotherapy. Here, we designed a new polymeric micelle delivery system for active tumor targeting followed by micelle-drug internalization via receptor-induced endocytosis. We recently reported that oseltamivir phosphate targets and inhibits Neu1 sialidase activity associated with receptor tyrosine kinases such as epidermal growth factor receptors (EGFRs) which are overexpressed in cancer cells. By decorating micelles with oseltamivir, we investigated whether they actively targeted human pancreatic PANC1 cancer cells. Amphiphilic block copolymers with oseltamivir conjugated at the hydrophilic end, oseltamivir-pPEGMEMA-b-pMMA (oseltamivir-poly(polyethylene glycol methyl ether methacrylate)-block-poly(methyl methacrylate), were synthesized using reversible addition-fragmentation chain transfer (RAFT) living radical polymerization. Oseltamivir-conjugated micelles have self-assembling properties to give worm-like micellar structures with molecular weight of 80 000 g mol(-1). Oseltamivir-conjugated water soluble pPEGMEMA, dose dependently, both inhibited sialidase activity associated with Neu1, and reduced viability of PANC1 cells. In addition, oseltamivir-conjugated micelles, labelled with a hydrophobic fluorescent dye within the micelle core, were subsequently internalized by PANC1 cells. Blocking cell surface Neu1 with anti-Neu1 antibody, reduced internalization of oseltamivir-conjugated micelles, demonstrating that Neu1 binding linked to sialidase inhibition were prerequisite steps for subsequent internalization of the micelles. The mechanism of internalization is likely that of receptor-induced endocytosis demonstrating potential as a new nanocarrier system for not only targeting a tumor cell, but also for directly reducing viability through Neu1 inhibition, followed by intracellular delivery of hydrophobic

  20. Controlled polymerization of protic ionic liquid monomer by ARGET-ATRP and TERP.

    PubMed

    Nakamura, Yasuyuki; Nakanishi, Kouji; Yamago, Shigeru; Tsujii, Yoshinobu; Takahashi, Kenichi; Morinaga, Takashi; Sato, Takaya

    2014-03-01

    The direct synthesis of structurally well-defined protic polymeric ionic liquid (PIL) with controlled molecular weight and molecular weight distribution is examined using N,N-diethyl-N-(2-methacryloylethyl) ammonium bis(tri-fluoromethylsulfonyl)imide (DEMH-TFSI) as a monomer. Three polymerization methods, namely, atom transfer radical polymerization (ATRP), activators regenerated by electron transfer (ARGET)-ATRP, and organotellurium-mediated living radical polymerization (TERP) are employed in this study. While the polymerization by ATRP is slow and does not reach high monomer conversion that under ARGET-ATRP and TERP proceeds smoothly and affords structurally well-defined poly(DEMH-TFSI)s. TERP is especially efficient for the control and poly(DEMH-TFSI)s with low to high molecular weights (M¯(n) = 49 100-392 500) and narrow molecular weight distributions (M¯(w)/M¯(n) = 1.17-1.46) are obtained. These results represent the first example of synthesis of a structurally well-defined protic, ammonium PIL by direct polymerization of the protic ionic liquid monomer. The polymerization of N,N-diethyl-N-(2-methacryloylethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide (DEMM-TFSI), which possesses a quaternary ammonium salt, also proceeds in a highly controlled manner under TERP conditions. A diblock copolymer, polystyrene-block-poly(DEMH-TFSI), is also successfully synthesized by TERP. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. UV-triggered dopamine polymerization: control of polymerization, surface coating, and photopatterning.

    PubMed

    Du, Xin; Li, Linxian; Li, Junsheng; Yang, Chengwu; Frenkel, Nataliya; Welle, Alexander; Heissler, Stefan; Nefedov, Alexei; Grunze, Michael; Levkin, Pavel A

    2014-12-17

    UV irradiation is demonstrated to initiate dopamine polymerization and deposition on different surfaces under both acidic and basic pH. The observed acceleration of the dopamine polymerization is explained by the UV-induced formation of reactive oxygen species that trigger dopamine polymerization. The UV-induced dopamine polymerization leads to a better control over polydopamine deposition and formation of functional polydopamine micropatterns. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Preparation and characterization of optical-functional diblock copolymer brushes on hollow sphere surface via atom transfer radical polymerization

    SciTech Connect

    Wang, Li-Ping; Li, Wen-Zhi; Zhao, Li-Min; Zhang, Chun-Juan; Wang, Yan-Dong; Kong, Li-Li; Li, Ling-Ling

    2010-09-15

    The optical-functional poly(methyl methacrylate)-block-Tb complex diblock copolymer brushes grafted from hollow sphere surface via atom transfer radical polymerization were investigated in this work. A sufficient amount of azo initiator was introduced onto hollow sphere surface firstly. Then the monomer methyl methacrylate was polymerized via surface-initiated reverse atom transfer radical polymerization using azo group modified hollow sphere as initiator. Following, the poly(methyl methacrylate) modified hollow sphere was used as maroinitiator for surface-initiated atom transfer radical polymerization of Tb complex. The samples were characterized by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance, gel permeation chromatographer and transmission electron microscopy, respectively. The results indicated that the poly(methyl methacrylate) had grafted from hollow sphere surface and the average diameter of hollow core was about 1 {mu}m. The optical properties of the poly(methyl methacrylate)-block-Tb copolymer modified hollow sphere were also reported.

  3. Controlled polymerization of acrylonitrile proceeded along with the Belousov-Zhabotinsky oscillator by changing its stirring conditions

    NASA Astrophysics Data System (ADS)

    Furue, Yuuka; Okano, Kunihiko; Banno, Taisuke; Asakura, Kouichi

    2016-02-01

    Chemical oscillations of the manganese-ion catalyzed Belousov-Zhabotinsky (BZ) reaction system were found to be controlled by changing its stirring conditions. The oscillation stopped at a high stirring rate, while it reappeared immediately by reducing the stirring rate. It is known in the BZ reaction system, that the radical polymerization takes place along with the oscillation when acrylic monomers are added. By the addition of acrylonitrile to the system stirred at a high stirring rate, the oscillation as well as the polymerization of acrylonitrile stopped. The radical polymerization of acrylonitrile by the BZ oscillator is thus found to be made controllable by changing the mixing conditions.

  4. Facile "living" radical polymerization of methyl methacrylate in the presence of iniferter agents: homogeneous and highly efficient catalysis from copper(II) acetate.

    PubMed

    Jiang, Hongjuan; Zhang, Lifen; Jiang, Xiaowu; Bao, Xiaoguang; Cheng, Zhenping; Zhu, Xiulin

    2014-08-01

    A facile homogeneous polymerization system involving the iniferter agent 1-cyano-1-methylethyl diethyldithiocarbamate (MANDC) and copper(II) acetate (Cu(OAc)2 ) is successfully developed in bulk using methyl methacylate (MMA) as a model monomer. The detailed polymerization kinetics with different molar ratios (e.g., [MMA]0 /[MANDC]0 /[Cu(OAc)2 ]0 = 500/1/x (x = 0.1, 0.2, 0.5, 1.0)) demonstrate that this system has the typical "living"/controlled features of "living" radical polymerization, even with ppm level catalyst Cu(OAc)2 , first order polymerization kinetics, a linear increase in molecular weight with monomer conversion and narrow molecular weight distributions for the resultant PMMA. (1) H NMR spectra and chain-extension experiments further confirm the "living" characteristics of this process. A plausible mechanism is discussed.

  5. Radical polymerization by a supramolecular catalyst: cyclodextrin with a RAFT reagent

    PubMed Central

    Koyanagi, Kohei; Takashima, Yoshinori; Nakamura, Takashi; Yamaguchi, Hiroyasu

    2016-01-01

    Supramolecular catalysts have received a great deal of attention because they improve the selectivity and efficiency of reactions. Catalysts with host molecules exhibit specific reaction properties and recognize substrates via host–guest interactions. Here, we examined radical polymerization reactions with a chain transfer agent (CTA) that has α-cyclodextrin (α-CD) as a host molecule (α-CD-CTA). Prior to the polymerization of N,N-dimethylacrylamide (DMA), we investigated the complex formation of α-CD with DMA. Single X-ray analysis demonstrated that α-CD includes DMA inside its cavity. When DMA was polymerized in the presence of α-CD-CTA using 2,2'-azobis[2-(2-imidazolin-2-yl)propane dihydrochloride (VA-044) as an initiator in an aqueous solution, poly(DMA) was obtained in good yield and with narrow molecular weight distribution. In contrast, the polymerization of DMA without α-CD-CTA produced more widely distributed polymers. In the presence of 1,6-hexanediol (C6 diol) which works as a competitive molecule by being included in the α-CD cavity, the reaction yield was lower than that without C6 diol. PMID:28144318

  6. Vapor-Phase Free Radical Polymerization in the Presence of Ionic Liquids

    NASA Astrophysics Data System (ADS)

    Gupta, Malancha

    2011-03-01

    Ionic liquids (ILs) have recently attracted significant interest as an environmentally-friendly alternative to traditional volatile organic solvents because ILs are non-volatile, non-flammable, and can be easily recycled. ILs can be exploited in many ways to improve the selectivity and kinetics of chemical reactions, including polymer synthesis. Ionic liquids have negligible vapor pressure and are therefore stable under vacuum. A few studies have investigated ILs as substrates in inorganic vacuum deposition processes, but to our knowledge ILs have not been used in vapor phase polymerization systems. We have recently introduced ionic liquids into the initiated chemical vapor deposition (iCVD) process for the first time. The iCVD polymerization process occurs via a free-radical mechanism, and the deposited polymeric films are compositionally analogous to solution-phase polymers. Despite the wide range of polymers that have been synthesized using iCVD, it has proven difficult to polymerize monomers with low surface concentrations such as styrene and low propagation rates such as methyl methacrylate and it is difficult to produce block copolymers. In this talk, we will show that our novel ILiCVD system can address some of these shortcomings. We will explain the effects of deposition time, temperature, and monomer solubility on the morphology of the polymer and the molecular weight of the polymer chains.

  7. Instantaneous Directional Growth of Block Copolymer Nanowires During Heterogeneous Radical Polymerization (HRP).

    PubMed

    Lu, Chunliang; Urban, Marek W

    2016-04-13

    Polymeric nanowires that consist of ultrahigh molecular weight block copolymers were instantaneously prepared via one-step surfactant-free heterogeneous radical polymerization (HRP). Under heterogeneous reaction and initiator-starvation conditions, the sequential copolymerization of hydrophilic and hydrophobic monomers facilitates the formation of amphiphilic ultrahigh molecular weight block copolymers, which instantaneously assemble to polymeric nanowires. As polymerization progresses, initially formed nanoparticles exhibit the directional growth due to localized repulsive forces of hydrophilic blocks and confinement of the hydrophobic blocks that adopt favorable high aspect ratio nanowire morphologies. Using one-step synthetic approach that requires only four ingredients (water as a solvent, two polymerizable monomers (one hydrophilic and one hydrophobic), and water-soluble initiator), block copolymer nanowires ∼70 nm in diameter and hundreds of microns in length are instantaneously grown. For example, when 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and styrene (St) were copolymerized, high aspect ratio nanowires consist of ultrahigh (>10(6) g/mol) molecular weight pDMAEMA-b-St block copolymers and the presence of temperature responsive pDMAEMA blocks facilitates nanowire diameter changes as a function of temperature. These morphologies may serve as structural components of the higher order biological constructs at micro and larger length scales, ranging from single strand nanowires to engineered biomolecular networks capable of responding to diverse and transient environmental signals, and capable of dimensional changes triggered by external stimuli.

  8. Beta-sheet side chain polymers synthesized by atom-transfer radical polymerization.

    PubMed

    Ayres, Lee; Adams, P Hans H M; Löwik, Dennis W P M; van Hest, Jan C M

    2005-01-01

    Silks are a widely studied class of naturally occurring structural proteins. Dragline spider silk, in particular, is considered to be nature's high-performance material due to its remarkable combination of strength and toughness. These mechanical properties stem from the protein secondary structure, a combination of well-defined beta-sheets in a less well-defined glycine-rich matrix. The translation of this structure into a synthetic polymer was the aim of this investigation. To achieve this, a peptide-based monomer containing the sequence alanine-glycine-alanine-glycine, a well-known beta-sheet-forming sequence found in silk, was synthesized. Using atom-transfer radical polymerization and a bifunctional initiator, a well-defined peptide-based polymer was prepared. This was then used as the macroinitiator for the polymerization of methyl methacrylate. The resulting well-defined triblock copolymer was analyzed using IR spectroscopy, which clearly showed beta-sheet secondary structure had been introduced.

  9. Water soluble and heat resistant polymers by free radical polymerization of lactic acid-based monomers

    NASA Astrophysics Data System (ADS)

    Tanaka, Hitoshi; Kibayashi, Tatsuya; Niwa, Miki

    2013-08-01

    Tactic heat resistant polymer was prepared by free radical polymerization of lactic acid-based monomers, i.e. chiral 2-isopropyl-5-methylene-1,3-dioxolan-4-ones (1). The polymerization of 1 proceeded smoothly without ring-opening to give a polymer with high isotacticity (mm) of 29.7~100% and glass transition temperature (Tg) of 172~213°C. 1 also showed high reactivity in the copolymerization with styrene and methyl methacrylate, and the incorporation of 1 unit in the copolymer structure increased Tg of each polymer. In addition, hydrolysis of poly(1) produced a new type of water soluble poly(lactic acid), i.e. poly(α-hydroxy acrylate), and poly(α-hydroxy acrylate-co-divinyl benzene) hydrogel absorbed water as high as 1000 times of the original polymer weight.

  10. The radical trap in atom transfer radical polymerization need not be thermodynamically stable. A study of the MoX(3)(PMe(3))(3) catalysts.

    PubMed

    Maria, Sébastien; Stoffelbach, François; Mata, José; Daran, Jean-Claude; Richard, Philippe; Poli, Rinaldo

    2005-04-27

    The molybdenum(III) coordination complexes MoX(3)(PMe(3))(3) (X = Cl, Br, and I) are capable of controlling styrene polymerization under typical atom transfer radical polymerization (ATRP) conditions, in conjunction with 2-bromoethylbenzene (BEB) as an initiator. The process is accelerated by the presence of Al(OPr(i))(3) as a cocatalyst. Electrochemical and synthetic studies aimed at identifying the nature of the spin trap have been carried out. The cyclic voltammogram of MoX(3)(PMe(3))(3) (X = Cl, Br, I) shows partial reversibility (increasing in the order Cl < Br < I) for the one-electron oxidation wave. Addition of X(-) changes the voltammogram, indicating the formation of MoX(4)(PMe(3))(3) for X = Cl and Br. On the other hand, I(-) is more easily oxidized than the MoI(3)(PMe(3))(3) complex; thus, the putative MoI(4)(PMe(3))(3) complex is redox unstable. Electrochemical studies of MoI(3)(PMe(3))(3) in the presence of X(-) (X = Cl or Br) reveal the occurrence of facile halide-exchange processes, leading to the conclusion that the MoI(3)X(PMe(3))(3) products are also redox unstable. The oxidation of MoX(3)(PMe(3))(3) with (1)/(2)Br(2) yields MoX(3)Br(PMe(3))(3) (X = Cl, Br), whose molecular nature is confirmed by single-crystal X-ray analyses. On the other hand, the oxidation of MoI(3)(PMe(3))(3) by I(2) slowly yields a tetraiodomolybdate(III) salt of iodotrimethylphosphonium, [Me(3)PI][MoI(4)(PMe(3))(3)], as confirmed by an X-ray study. This product has no controlling ability in radical polymerization. The redox instability of MoI(3)X(PMe(3))(3) can be reconciled with its involvement as a radical trapping species in the MoI(3)(PMe(3))(3)-catalyzed ATRP, given the second-order nature of its decomposition rate.

  11. Fixed Point Transformations Based Iterative Control of a Polymerization Reaction

    NASA Astrophysics Data System (ADS)

    Tar, József K.; Rudas, Imre J.

    As a paradigm of strongly coupled non-linear multi-variable dynamic systems the mathematical model of the free-radical polymerization of methyl-metachrylate with azobis (isobutyro-nitrile) as an initiator and toluene as a solvent taking place in a jacketed Continuous Stirred Tank Reactor (CSTR) is considered. In the adaptive control of this system only a single input variable is used as the control signal (the process input, i.e. dimensionless volumetric flow rate of the initiator), and a single output variable is observed (the process output, i.e. the number-average molecular weight of the polymer). Simulation examples illustrate that on the basis of a very rough and primitive model consisting of two scalar variables various fixed-point transformations based convergent iterations result in a novel, sophisticated adaptive control.

  12. Facile synthesis of brush poly(phosphoamidate)s via one-pot tandem ring-opening metathesis polymerization and atom transfer radical polymerization.

    PubMed

    Ding, Liang; Qiu, Jun; Wei, Jun; Zhu, Zhenshu

    2014-09-01

    Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA)-based brush poly(phosphoamidate)s are successfully synthesized by a combination of ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP) following either a commutative two-step procedure or a straightforward one-pot process using Grubbs ruthenium-based catalysts for tandem catalysis. Compared with the traditional polymerization method, combining ROMP and ATRP in a one-pot process allows the preparation of brush copolymers characterized by a relatively moderate molecular weight distribution and quantitative conversion of monomer. Moreover, the surface morphologies and aggregation behaviors of these polymers are studied by AFM and TEM measurements.

  13. An ultra-sensitive microfluidic immunoassay using living radical polymerization and porous polymer monoliths.

    SciTech Connect

    Abhyankar, Vinay V.; Singh, Anup K.; Hatch, Anson V.

    2010-07-01

    We present a platform that combines patterned photopolymerized polymer monoliths with living radical polymerization (LRP) to develop a low cost microfluidic based immunoassay capable of sensitive (low to sub pM) and rapid (<30 minute) detection of protein in 100 {micro}L sample. The introduction of LRP functionality to the porous monolith allows one step grafting of functionalized affinity probes from the monolith surface while the composition of the hydrophilic graft chain reduces non-specific interactions and helps to significantly improve the limit of detection.

  14. Recent Developments in the Synthesis of Biomacromolecules and their Conjugates by Single Electron Transfer-Living Radical Polymerization.

    PubMed

    Lligadas, Gerard; Grama, Silvia; Percec, Virgil

    2017-04-10

    Single electron transfer-living radical polymerization (SET-LRP) represents a robust and versatile tool for the synthesis of vinyl polymers with well-defined topology and chain end functionality. The crucial step in SET-LRP is the disproportionation of the Cu(I)X generated by activation with Cu(0) wire, powder, or nascent Cu(0) generated in situ into nascent, extremely reactive Cu(0) atoms and nanoparticles and Cu(II)X2. Nascent Cu(0) activates the initiator and dormant chains via a homogeneous or heterogeneous outer-sphere single-electron transfer mechanism (SET-LRP). SET-LRP provides an ultrafast polymerization of a plethora of monomers (e.g., (meth)-acrylates, (meth)-acrylamides, styrene, and vinyl chloride) including hydrophobic and water insoluble to hydrophilic and water soluble. Some advantageous features of SET-LRP are (i) the use of Cu(0) wire or powder as readily available catalysts under mild reaction conditions, (ii) their excellent control over molecular weight evolution and distribution as well as polymer chain ends, (iii) their high functional group tolerance allowing the polymerization of commercial-grade monomers, and (iv) the limited purification required for the resulting polymers. In this Perspective, we highlight the recent advancements of SET-LRP in the synthesis of biomacromolecules and of their conjugates.

  15. All-polymeric control of nanoferronics.

    PubMed

    Xu, Beibei; Li, Huashan; Hall, Asha; Gao, Wenxiu; Gong, Maogang; Yuan, Guoliang; Grossman, Jeffrey; Ren, Shenqiang

    2015-12-01

    In the search for light and flexible nanoferronics, significant research effort is geared toward discovering the coexisting magnetic and electric orders in crystalline charge-transfer complexes. We report the first example of multiferroicity in centimeter-sized crystalline polymeric charge-transfer superstructures that grow at the liquid-air interface and are controlled by the regioregularity of the polymeric chain. The charge order-driven ferroic mechanism reveals spontaneous and hysteretic polarization and magnetization at the donor-acceptor interface. The charge transfer and ordering in the ferroic assemblies depend critically on the self-organizing and molecular packing of electron donors and acceptors. The invention described here not only represents a new coupling mechanism of magnetic and electric ordering but also creates a new class of emerging all-organic nanoferronics.

  16. All-polymeric control of nanoferronics

    PubMed Central

    Xu, Beibei; Li, Huashan; Hall, Asha; Gao, Wenxiu; Gong, Maogang; Yuan, Guoliang; Grossman, Jeffrey; Ren, Shenqiang

    2015-01-01

    In the search for light and flexible nanoferronics, significant research effort is geared toward discovering the coexisting magnetic and electric orders in crystalline charge-transfer complexes. We report the first example of multiferroicity in centimeter-sized crystalline polymeric charge-transfer superstructures that grow at the liquid-air interface and are controlled by the regioregularity of the polymeric chain. The charge order–driven ferroic mechanism reveals spontaneous and hysteretic polarization and magnetization at the donor-acceptor interface. The charge transfer and ordering in the ferroic assemblies depend critically on the self-organizing and molecular packing of electron donors and acceptors. The invention described here not only represents a new coupling mechanism of magnetic and electric ordering but also creates a new class of emerging all-organic nanoferronics. PMID:26824068

  17. A Mechanochemical Switch to Control Radical Intermediates

    PubMed Central

    2015-01-01

    B12-dependent enzymes employ radical species with exceptional prowess to catalyze some of the most chemically challenging, thermodynamically unfavorable reactions. However, dealing with highly reactive intermediates is an extremely demanding task, requiring sophisticated control strategies to prevent unwanted side reactions. Using hybrid quantum mechanical/molecular mechanical simulations, we follow the full catalytic cycle of an AdoB12-dependent enzyme and present the details of a mechanism that utilizes a highly effective mechanochemical switch. When the switch is “off”, the 5′-deoxyadenosyl radical moiety is stabilized by releasing the internal strain of an enzyme-imposed conformation. Turning the switch “on,” the enzyme environment becomes the driving force to impose a distinct conformation of the 5′-deoxyadenosyl radical to avoid deleterious radical transfer. This mechanochemical switch illustrates the elaborate way in which enzymes attain selectivity of extremely chemically challenging reactions. PMID:24846280

  18. A mechanochemical switch to control radical intermediates.

    PubMed

    Brunk, Elizabeth; Kellett, Whitney F; Richards, Nigel G J; Rothlisberger, Ursula

    2014-06-17

    B₁₂-dependent enzymes employ radical species with exceptional prowess to catalyze some of the most chemically challenging, thermodynamically unfavorable reactions. However, dealing with highly reactive intermediates is an extremely demanding task, requiring sophisticated control strategies to prevent unwanted side reactions. Using hybrid quantum mechanical/molecular mechanical simulations, we follow the full catalytic cycle of an AdoB₁₂-dependent enzyme and present the details of a mechanism that utilizes a highly effective mechanochemical switch. When the switch is "off", the 5'-deoxyadenosyl radical moiety is stabilized by releasing the internal strain of an enzyme-imposed conformation. Turning the switch "on," the enzyme environment becomes the driving force to impose a distinct conformation of the 5'-deoxyadenosyl radical to avoid deleterious radical transfer. This mechanochemical switch illustrates the elaborate way in which enzymes attain selectivity of extremely chemically challenging reactions.

  19. Study on the role of active radicals on plasma sterilization inside small diameter flexible polymeric tubes

    NASA Astrophysics Data System (ADS)

    Mstsuura, Hiroto; Fujiyama, Takatomo; Okuno, Yasuki; Furuta, Masakazu; Okuda, Shuichi; Takemura, Yuichiro

    2015-09-01

    Recently, atmospheric pressure discharge plasma has gathered attention in various fields. Among them, plasma sterilization with many types of plasma source has studied for decades and its mechanism is still an open question. If active radicals produced in plasma has main contribution of killing bacterias, direct contact of the so-called plasma flame might not be necessary. To confirm this, sterilization inside small diameter flexible polymeric tubes is studied in present work. DBD type plasma jet is produce by flowing helium gas in a glass tube. A long polymeric tube is connected and plasma jet is introduced into it. Plasma flame length depends on helium gas flow rate, but limited to about 10 cm in our experimental condition. E.colis set at the exit plasma source is easily killed during 10 min irradiation. At the tube end (about 20 cm away from plasma source exit), sterilization is possible with 30 min operation. This result shows that active radical is produced with helium plasma and mist contained in sample, and it can be transferred more than 20 cm during it life time. More plasma diagnostic data will also be shown at the conference. This work was partially supported by the ''ZE Research Program, IAE(ZE27B-4).

  20. Synthesis of Poly(Sorbitan Methacrylate) Hydrogel by Free-Radical Polymerization

    NASA Astrophysics Data System (ADS)

    Jeong, Gwi-Taek; Lee, Kyoung-Min; Yang, Hee-Seung; Park, Seok-Hwan; Park, Jae-Hee; Sunwoo, Changshin; Ryu, Hwa-Won; Kim, Doman; Lee, Woo-Tae; Kim, Hae-Sung; Cha, Wol-Seog; Park, Don-Hee

    Hydrogels are materials with the ability to swell in water through the retention of significant fractions of water within their structures. Owing to their relatively high degree of biocompatibility, hydrogels have been utilized in a host of biomedical applications. In an attempt to determine the optimum conditions for hydrogel synthesis by the free-radical polymerization of sorbitan methacrylate (SMA), the hydrogel used in this study was well polymerized under the following conditions: 50% (w/v) SMA as monomer, 1% (w/w) α, α'-azo-bis(isobutyro-nitrile) as thermal initiator, and 1% (w/w) ethylene glycol dimethacrylate as cross-liking agent. Under these conditions, the moisture content of the polymerized SMA hydrogel was higher than in the other conditions. Moreover, the moisture content of the poly(SMA) hydrogel was also found to be higher than that of the poly(methyl methacrylate [MMA]) hydrogel. When the Fourier transform-infrared spectrum of poly(SMA) hydrogel was compared with that of poly(MMA) hydrogel, we noted a band at 1735-1730/cm, which did not appear in the Fourier transform-infrared spectrum of poly(MMA). The surface of the poly(SMA) hydrogel was visualized through scanning electron microscopy, and was uniform and clear in appearance.

  1. Grafting-from cellulose nanocrystals via photoinduced Cu-mediated reversible-deactivation radical polymerization.

    PubMed

    Hatton, Fiona L; Kedzior, Stephanie A; Cranston, Emily D; Carlmark, Anna

    2017-02-10

    In this work we describe the grafting of cellulose nanocrystals (CNCs) by surface-initiated photoinduced Cu-mediated reversible-deactivation radical polymerization (RDRP). Initially, CNCs obtained through sulfuric acid hydrolysis were functionalized with a tertiary bromo-ester moiety as an initiating group for the subsequent RDRP of methyl acrylate, targeting three different degrees of polymerization for the polymer grafts: 50, 300 and 600. The polymerizations proceeded in DMSO in the presence of CuBr2 and Me6TREN as the catalytic system utilizing a UV source (λmax≈360nm). The technique proved highly versatile for the modification of CNCs with poly(methyl acrylate), where considerably high grafting was achieved in short reaction times (90min), with simple purification steps. CNC morphology was maintained and polymer grafts were evident through FT-IR spectroscopy, thermal analysis, contact angle measurements, X-ray photoelectron microscopy and x-ray diffraction. Copyright © 2016 Elsevier Ltd. All rights reserved.

  2. Synthesis of poly(sorbitan methacrylate) hydrogel by free-radical polymerization.

    PubMed

    Jeong, Gwi-Taek; Lee, Kyoung-Min; Yang, Hee-Seung; Park, Seok-Hwan; Park, Jae-Hee; Sunwoo, Changshin; Ryu, Hwa-Won; Kim, Doman; Lee, Woo-Tae; Kim, Hae-Sung; Cha, Wol-Seog; Park, Don-Hee

    2007-04-01

    Hydrogels are materials with the ability to swell in water through the retention of significant fractions of water within their structures. Owing to their relatively high degree of biocompatibility, hydrogels have been utilized in a host of biomedical applications. In an attempt to determine the optimum conditions for hydrogel synthesis by the free-radical polymerization of sorbitan methacrylate (SMA), the hydrogel used in this study was well polymerized under the following conditions: 50% (w/v) SMA as monomer, 1% (w/w) alpha, alpha'-azo-bis(isobutyro-nitrile) as thermal initiator, and 1% (w/w) ethylene glycol dimethacrylate as cross-liking agent. Under these conditions, the moisture content of the polymerized SMA hydrogel was higher than in the other conditions. Moreover, the moisture content of the poly(SMA) hydrogel was also found to be higher than that of the poly(methyl methacrylate [MMA]) hydrogel. When the Fourier transform-infrared spectrum of poly(SMA) hydrogel was compared with that of poly(MMA) hydrogel, we noted a band at 1735-1730/cm, which did not appear in the Fourier transform-infrared spectrum of poly(MMA). The surface of the poly(SMA) hydrogel was visualized through scanning electron microscopy, and was uniform and clear in appearance.

  3. Influence of ultrasonic condition on phase transfer catalyzed radical polymerization of methyl methacrylate in two phase system - A kinetic study.

    PubMed

    Marimuthu, Elumalai; Murugesan, Vajjiravel

    2016-08-25

    An ultrasonic condition assisted phase transfer catalyzed radical polymerization of methyl methacrylate was investigated in an ethyl acetate/water two phase system at 60±1°C and 25kHz, 300W under inert atmosphere. The influence of monomer, initiator, catalyst and temperature, volume fraction of aqueous phase on the rate of polymerization was examined in detail. The reaction order was found to be unity for monomer, initiator and catalyst. Generally, the reaction rate was relatively fast in two phase system, when a catalytic amount of phase transfer catalyst was used. The combined approach, use of ultrasonic and PTC condition was significantly enhances the rate of polymerization. An ultrasonic and phase transfer catalyzed radical polymerization of methyl methacrylate has shown about three fold enhancements in the rate compared with silent polymerization of MMA using cetyltrimethylammonium bromide as PTC. The resultant kinetics was evaluated with silent polymerization and an important feature was discussed. The activation energy and other thermodynamic parameters were computed. Based on the obtained results an appropriate radical mechanism has been derived. TGA showed the polymer was stable up to 150°C. The FT-IR and DSC analysis validates the atactic nature of the obtained polymer. The XRD pattern reveals the amorphous nature of polymer was dominated.

  4. Light-Mediated Atom Transfer Radical Polymerization of Semi-Fluorinated (Meth)acrylates: Facile Access to Functional Materials.

    PubMed

    Discekici, Emre H; Anastasaki, Athina; Kaminker, Revital; Willenbacher, Johannes; Truong, Nghia P; Fleischmann, Carolin; Oschmann, Bernd; Lunn, David J; Read de Alaniz, Javier; Davis, Thomas P; Bates, Christopher M; Hawker, Craig J

    2017-04-26

    A highly efficient photomediated atom transfer radical polymerization protocol is reported for semi-fluorinated acrylates and methacrylates. Use of the commercially available solvent, 2-trifluoromethyl-2-propanol, optimally balances monomer, polymer, and catalyst solubility while eliminating transesterification as a detrimental side reaction. In the presence of UV irradiation and ppm concentrations of copper(II) bromide and Me6-TREN (TREN = tris(2-aminoethyl amine)), semi-fluorinated monomers with side chains containing between three and 21 fluorine atoms readily polymerize under controlled conditions. The resulting polymers exhibit narrow molar mass distributions (Đ ≈ 1.1) and high end group fidelity, even at conversions greater than 95%. This level of control permits the in situ generation of chain-end functional homopolymers and diblock copolymers, providing facile access to semi-fluorinated macromolecules using a single methodology with unprecedented monomer scope. The results disclosed herein should create opportunities across a variety of fields that exploit fluorine-containing polymers for tailored bulk, interfacial, and solution properties.

  5. Development of new atom transfer radical polymerization system by iron (III)-metal salts without using any external initiator and reducing agent.

    PubMed

    Khan, Mohd Yusuf; Chen, Xiangxiong; Lee, Seung Woo; Noh, Seok Kyun

    2013-08-01

    Atom transfer radical polymerization (ATRP) catalyzed by high oxidation state metal salts of FeX3 is developed for the first time in the absence of both external initiator and reducing agent. Methyl methacrylate (MMA) and styrene are polymerized successfully using FeX3 /Phosphorous ligands with well-controlled molecular weight distributions (=1.5). The molecular weight of the polymers increases with monomer consumption with the progress of time and the polymerization behaviors show a decent ATRP trend. Activators and initiators are suggested to generate in situ by the addition reaction of MMA and one equivalent of FeX3 . The PMMA synthesized from without-initiator system is characterized by (1) H, (13) C and DEPT (distortionless enhancement by polarization transfer nuclear magnetic resonance) nuclear magnetic resonance spectroscopy. Chain extension and copolymerization experiments prove the livingness of the obtained polymer. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Electrochemically mediated atom transfer radical polymerization from a substrate surface manipulated by bipolar electrolysis: fabrication of gradient and patterned polymer brushes.

    PubMed

    Shida, Naoki; Koizumi, Yuki; Nishiyama, Hiroki; Tomita, Ikuyoshi; Inagi, Shinsuke

    2015-03-23

    We report the first ever use of electrochemically mediated atom transfer radical polymerization (eATRP) employing a bipolar electrochemical method for the fabrication of both gradient and patterned polymer brushes. A potential gradient generated on a bipolar electrode allowed the formation of a concentration gradient of a Cu(I) polymerization catalyst through the one-electron reduction of Cu(II) , resulting in the gradient growth of poly(NIPAM) brushes from an initiator-modified substrate surface set close to a bipolar electrode. These polymer brushes could be fabricated in three-dimensional gradient shapes with control over thickness, steepness, and modified area by varying the electrolytic conditions. Moreover, by site-selective application of potential during bipolar electrolysis, a polymer brush with a circular pattern was successfully formed. Polymerization was achieved using both a polar monomer (NIPAM) and a nonpolar monomer (MMA) with the eATRP system.

  7. [Preparation of a novel polymer monolith using atom transfer radical polymerization method for solid phase extraction].

    PubMed

    Shen, Ying; Qi, Li; Qiao, Juan; Mao, Lanqun; Chen, Yi

    2013-04-01

    In this study, a novel polymer monolith based solid phase extraction (SPE) material has been prepared by two-step atom transfer radical polymerization (ATRP) method. Firstly, employing ethylene glycol dimethacrylate (EDMA) as a cross-linker, a polymer monolith filled in a filter head has been in-situ prepared quickly under mild conditions. Then, the activators generated by electron transfer ATRP (ARGET ATRP) was used for the modification of poly(2-(dimethylamino)ethyl-methacrylate) (PDMAEMA) on the monolithic surface. Finally, this synthesized monolith for SPE was successfully applied in the extraction and enrichment of steroids. The results revealed that ATRP can be developed as a facile and effective method with mild reaction conditions for monolith construction and has the potential for preparing monolith in diverse devices.

  8. Modification of jute fibers with polystyrene via atom transfer radical polymerization.

    PubMed

    Plackett, David; Jankova, Katja; Egsgaard, Helge; Hvilsted, Søren

    2005-01-01

    Atom transfer radical polymerization (ATRP) was investigated as a method of covalently bonding polystyrene to jute (Corchorus capsularis) and as a possible approach to fiber composites with enhanced properties. Jute fibers were modified with a brominated initiator and subsequently ATRP modified to attach polystyrene and then examined using SEM, DSC, TGA, FTIR, XPS, elemental analysis, and Py-GC-MS. These techniques confirmed that polystyrene had been covalently bound to the fibers and consequently ATRP-modified jute fiber mats were used to prepare hot-pressed polystyrene composites. Composite specimens were tensile tested and fracture surfaces examined using SEM. Although SEM examination suggested different fracture modes between unmodified fiber and ATRP-modified samples, the tensile strength of modified samples was slightly lower on average than that of unmodified samples. For fiber composite applications, we conclude that further optimization of the ATRP method is required, possibly targeting higher and more uniform loading of polystyrene on the fibers.

  9. Encapsidated atom-transfer radical polymerization in Qβ virus-like nanoparticles.

    PubMed

    Hovlid, Marisa L; Lau, Jolene L; Breitenkamp, Kurt; Higginson, Cody J; Laufer, Burkhardt; Manchester, Marianne; Finn, M G

    2014-08-26

    Virus-like particles (VLPs) are unique macromolecular structures that hold great promise in biomedical and biomaterial applications. The interior of the 30 nm-diameter Qβ VLP was functionalized by a three-step process: (1) hydrolytic removal of endogenously packaged RNA, (2) covalent attachment of initiator molecules to unnatural amino acid residues located on the interior capsid surface, and (3) atom-transfer radical polymerization of tertiary amine-bearing methacrylate monomers. The resulting polymer-containing particles were moderately expanded in size; however, biotin-derivatized polymer strands were only very weakly accessible to avidin, suggesting that most of the polymer was confined within the protein shell. The polymer-containing particles were also found to exhibit physical and chemical properties characteristic of positively charged nanostructures, including the ability to easily enter mammalian cells and deliver functional small interfering RNA.

  10. Encapsidated Atom-Transfer Radical Polymerization in Qβ Virus-like Nanoparticles

    PubMed Central

    2015-01-01

    Virus-like particles (VLPs) are unique macromolecular structures that hold great promise in biomedical and biomaterial applications. The interior of the 30 nm-diameter Qβ VLP was functionalized by a three-step process: (1) hydrolytic removal of endogenously packaged RNA, (2) covalent attachment of initiator molecules to unnatural amino acid residues located on the interior capsid surface, and (3) atom-transfer radical polymerization of tertiary amine-bearing methacrylate monomers. The resulting polymer-containing particles were moderately expanded in size; however, biotin-derivatized polymer strands were only very weakly accessible to avidin, suggesting that most of the polymer was confined within the protein shell. The polymer-containing particles were also found to exhibit physical and chemical properties characteristic of positively charged nanostructures, including the ability to easily enter mammalian cells and deliver functional small interfering RNA. PMID:25073013

  11. Mucoadhesive polymeric platforms for controlled drug delivery.

    PubMed

    Andrews, Gavin P; Laverty, Thomas P; Jones, David S

    2009-03-01

    The process of mucoadhesion involving a polymeric drug delivery platform is a complex one that includes wetting, adsorption and interpenetration of polymer chains amongst various other processes. The success and degree of mucoadhesion bonding is influenced by various polymer-based properties such as the degree of cross-linking, chain length and the presence of various functional groupings. The attractiveness of mucosal-targeted controlled drug delivery of active pharmaceutical ingredients (APIs), has led formulation scientists to engineer numerous polymeric systems for such tasks. Formulation scientists have at their disposal a range of in vitro and in vivo mucoadhesion testing setups in order to select candidate adhesive drug delivery platforms. As such, mucoadhesive systems have found wide use throughout many mucosal covered organelles for API delivery for local or systemic effect. Evolution of such mucoadhesive formulations has transgressed from first-generation charged hydrophilic polymer networks to more specific second-generation systems based on lectin, thiol and various other adhesive functional groups.

  12. Uranium recovery from seawater: development of fiber adsorbents prepared via atom-transfer radical polymerization

    SciTech Connect

    Saito, Tomonori; Brown, Suree; Chatterjee, Sabornie; Kim, Jungseung; Tsouris, Costas; Mayes, Richard T.; Kuo, Li-Jung; Gill, Gary; Oyola, Yatsandra; Janke, Christopher J.; Dai, Sheng

    2014-08-04

    We developed a novel adsorbent preparation method using atom-transfer radical polymerization (ATRP) combined with radiation-induced graft polymerization (RIGP) in order to synthesize an adsorbent for uranium recovery from seawater. Furthermore, the ATRP method allowed a much higher degree of grafting on the adsorbent fibers (595 2818%) than that allowed by RIGP alone. The adsorbents were prepared with varied composition of amidoxime groups and hydrophilic acrylate groups. The successful preparation revealed that both ligand density and hydrophilicity were critical for optimal performance of the adsorbents. Adsorbents synthesized in this study showed a relatively high performance (141 179 mg/g at 49 62 % adsorption) in laboratory screening tests using a uranium concentration of ~6 ppm. This performance is much higher than that of known commercial adsorbents. However, actual seawater experiment showed impeded performance compared to the recently reported high-surface-area-fiber adsorbents, due to slow adsorption kinetics. The impeded performance motivated an investigation of the effect of hydrophilic block addition on the graft chain terminus. The addition of hydrophilic block on the graft chain terminus nearly doubled the uranium adsorption capacity in seawater, from 1.56 mg/g to 3.02 mg/g. Our investigation revealed the importance of polymer chain conformation, in addition to ligand and hydrophilic group ratio, for advanced adsorbent synthesis for uranium recovery from seawater.

  13. Surface modification of nanodiamond through metal free atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Zeng, Guangjian; Liu, Meiying; Shi, Kexin; Heng, Chunning; Mao, Liucheng; Wan, Qing; Huang, Hongye; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2016-12-01

    Surface modification of nanodiamond (ND) with poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] has been achieved by using metal free surface initiated atom transfer radical polymerization (SI-ATRP). The ATRP initiator was first immobilized on the surface of ND through direct esterification reaction between hydroxyl group of ND and 2-bromoisobutyryl bromide. The initiator could be employed to obtain ND-poly(MPC) nanocomposites through SI-ATRP using an organic catalyst. The final functional materials were characterized by 1H nuclear magnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermo gravimetric analysis in detailed. All of these characterization results demonstrated that ND-poly(MPC) have been successfully obtained via metal free photo-initiated SI-ATRP. The ND-poly(MPC) nanocomposites shown enhanced dispersibility in various solvents as well as excellent biocompatibility. As compared with traditional ATRP, the metal free ATRP is rather simple and effective. More importantly, this preparation method avoided the negative influence of metal catalysts. Therefore, the method described in this work should be a promising strategy for fabrication of polymeric nanocomposites with great potential for different applications especially in biomedical fields.

  14. Simultaneous interpenetrating silicone hydrogel based on radical/addition polymerization for extended release of ocular therapeutics.

    PubMed

    Xu, Jinku; Zhang, Leilei; Zhang, Yongchun; Li, Tianduo; Huo, Guanghua

    2014-01-01

    Hydrogels with interpenetrating network (IPN) can overcome thermodynamic incompatibility and obtain transparent materials with limited phase separation. In this report, hydroxyl-grafting polysiloxane (HPSO) was synthesized and transparent silicone hydrogels with interpenetrating network were simultaneously prepared based on radical polymerization of methacrylic monomer of 3-methacryloxypropyl tris(trimethylsiloxy)silane/N,N-dimethylacrylamide and addition polymerization of HPSO/isophorone diisocyanate. The silicone hydrogels were characterized by dehydration kinetics, tensile tester, light transmittance, ion permeability, oxygen permeability, and lysozyme deposition. The results show that increasing the proportion of hydrophobic network of HPSO in the IPN silicone hydrogel decreases equilibrium swelling ratio, ion permeability, Young's modulus, and lysozyme deposition; on the contrary, increased tensile strength, elongation at break and oxygen permeability. Puerarin and ketoconazole were used as models to evaluate the drug loading and in vitro release behavior of the silicone hydrogels. It is revealed that the amount of loaded drugs in the hydrogel decreases with the increase of HPSO network in the hydrogels. All the silicone hydrogels exhibit extended release behavior, especially for ketoconazole, the in vitro release is divided into two phases corresponding to the rapid release at initial 24 h and relatively slow release from 125 to 360 h.

  15. Multifunctional Giant Amphiphiles via simultaneous copper(I)-catalyzed azide-alkyne cycloaddition and living radical polymerization.

    PubMed

    Daskalaki, Eleftheria; Le Droumaguet, Benjamin; Gérard, David; Velonia, Kelly

    2012-02-01

    A novel class of chemically addressable, multifunctional Giant Amphiphiles was synthesized in excellent yields and polydispersity following simultaneous or sequential living radical polymerization and the click, copper(I)-catalysed azide-alkyne cycloaddition (CuAAC). This new approach allows chemical tailoring of the biomacromolecules and in situ formation of nanocontainers. This journal is © The Royal Society of Chemistry 2012

  16. Synthesis of selenium nano-composite (t-Se@PS) by surface initiated atom transfer radical polymerization.

    PubMed

    Wang, Michael C P; Gates, Byron D

    2012-09-04

    Selenium nanostructures, which are otherwise susceptible to oxidative damage, were encapsulated with a thin layer of polystyrene. The thin layer of polystyrene was grafted onto the surfaces of selenium by a surface initiated atom transfer radical polymerization reaction. These encapsulated nanostructures demonstrate an enhanced resistance towards corrosion.

  17. Radical polymerization in holographic grating formation in PQ-PMMA photopolymer part II: Consecutive exposure and dark decay

    NASA Astrophysics Data System (ADS)

    Yu, Dan; Liu, Hongpeng; Geng, Yaohui; Wang, Weibo; Zhao, Yuanyuan

    2014-11-01

    Photochemical radical polymerization in phenathrenequinone doped poly(methyl methacrylate) photopolymer are investigated theoretically and experimentally under consecutive exposure. The detailed photochemical mechanisms are analyzed. Based on the rate equations of photochemical reactions, the diffusion models with nonlocal response are proposed to describe the kinetic process of radical polymerization and the significance of photochemical processes for the grating formation. In experiments, the temporal evolution of diffraction efficiency in grating formation is measured under consecutive exposure and after exposure. The percentages of these radical polymerizations, namely the polymerization of PQ with matrix, the bimolecular combination of MMA molecules, and the disproportionation of MMA molecules, are extracted quantitatively by comparing theory with experiments. It is indicated that the polymerization of PQ with matrix is primary photochemical process which dominated the grating formation under consecutive exposure. In this period, the contribution of chain polymerization of MMA radicals is weak for the grating formation. After reaching the peak values of grating strength, the influence of the free MMA molecules and photoproduct macromolecules on the grating decay is discussed in a long-term period. The diffusion coefficients of MMA and photoproduct are extracted by fitting the curves using double exponential function. MMA’s diffusion contributed to the fast decay process of grating after exposure and photoproduct’s diffusion contributed to the slow and long decay of grating. The results break previous understanding about the diffusion of single photoproduct macromolecules lead to the dark decay of grating. This investigation can provide a significant foundation for improving modulation depth and long-term stability by photochemical mechanism.

  18. Controlled release polymeric ocular delivery of acyclovir.

    PubMed

    Deshpande, Praful Balavant; Dandagi, Panchaxari; Udupa, Nayanabhirama; Gopal, Shavi V; Jain, Samata S; Vasanth, Surenalli G

    2010-01-01

    The aim of the present study was to formulate and evaluate controlled release polymeric ocular delivery of acyclovir. Reservoir-type ocular inserts were fabricated by sandwiching hydroxypropyl methylcellulose (HPMC) matrix film containing acyclovir between two rate controlling membranes of cellulose acetate phthalate (CAP). The solubility and dissolution rate of poorly soluble acyclovir was enhanced by preparing binary systems with beta-cyclodextrin and then incorporated into HPMC matrix. Nine formulations (AB-1 to AB-9) with varying ratio of HPMC (drug matrix) and CAP (rate controlling membrane) were developed and sterilized by gamma radiation. The formulations were subjected to various physico-chemical evaluations. The in vitro release profile of all the formulations showed a steady, controlled drug release up to 20 h with non-Fickian diffusion behavior. A high correlation coefficient found between in vitro/in vivo release rate studies. Formation of acyclovir complex was confirmed by differential scanning calorimetry. In addition, dissolution rate studies revealed improved solubility of acyclovir when complexed with beta-cyclodextrin. Stability studies showed that the ocular inserts could be stored safely at study storage conditions. In conclusion, the present study demonstrated controlled release formulation of acyclovir inserts for ocular delivery using biodegradable polymers.

  19. Quantitative investigation of free radicals in bio-oil and their potential role in condensed-phase polymerization.

    PubMed

    Kim, Kwang Ho; Bai, Xianglan; Cady, Sarah; Gable, Preston; Brown, Robert C

    2015-03-01

    We report on the quantitative analysis of free radicals in bio-oils produced from pyrolysis of cellulose, organosolv lignin, and corn stover by EPR spectroscopy. Also, we investigated their potential role in condensed-phase polymerization. Bio-oils produced from lignin and cellulose show clear evidence of homolytic cleavage reactions during pyrolysis that produce free radicals. The concentration of free radicals in lignin bio-oil was 7.5×10(20)  spin g(-1), which was 375 and 138 times higher than free-radical concentrations in bio-oil from cellulose and corn stover. Pyrolytic lignin had the highest concentration in free radicals, which could be a combination of carbon-centered (benzyl radicals) and oxygen-centered (phenoxy radicals) organic species because they are delocalized in a π system. Free-radical concentrations did not change during accelerated aging tests despite increases in molecular weight of bio-oils, suggesting that free radicals in condensed bio-oils are stable.

  20. Chain conformation and nano-patterning of polymer brushes prepared by surface-initiated atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Gao, Xiang

    Over the past decade, the development of surface-initiated living polymerization methods has brought a breakthrough to surface modification owing to their control ability. Surface-initiated atom transfer radical polymerization (si-ATRP), as the most popular one, has been widely employed to give novel polymer structures and functionalities to various surfaces for the purposes of tailoring surface properties, introducing new functions, or preparing so-called "smart surfaces", which can respond to external stimuli such as solvent type, pH, temperature, electric and magnetic fields etc. In this thesis, the mechanistic study of the si-ATRP was first carried out through modeling to gain good understanding of si-ATRP. Si-ATRP was then employed to prepare different types of polymer brushes to produce "smart surfaces". The kinetic model was developed using the method of moment. Combined with experimental data, a quantitative analysis was carried out for the si-ATRP mechanism. All information of grafted polymer chains, including active chain concentration, radical concentration, chain length, polydispersity, was illustrated. A new radical termination mechanism, termed as migration-termination, was proposed for si-ATRP. Si-ATRP was then employed to graft poly(oligo(ethylene glycol) methacrylate) (POEGMA) block poly(methyl methacrylate) (PMMA) brushes on silicon wafer surfaces. Simple solvent treatment gave nanoscale patterns via the phase segregation of POEGMA and PMMA segments. Various patterns including spherical aggregates, wormlike aggregates, stripe patterns, perforated layers and complete overlayers, were obtained by adjusting the upper block layer thickness. Furthermore, these nanopatterns had a unique stimuli-responsive property, i.e., switching between different morphologies reversibly after being treated with selective solvents. POEGMA-block-poly(2-(methacryloyloxy)ethyl trimethylammonium chloride) (PMETAC) brushes, having two hydrophilic segments, were synthesized

  1. Two-dimensional organic molecules for two-photon absorption, aluminum alkyl complexes initiated polymerizations, and unimolecular living radical polymerization initiators

    NASA Astrophysics Data System (ADS)

    Bi, Xiangdong

    A study of structure-property relationship on two-photon absorbing chromophores showed that highly symmetric and conjugated molecular structures exhibited larger two-photon absorption cross-section in comparison to their counterparts with lower symmetry. A number of symmetric two-photon absorbing chromophores were developed. Measurements of their optical properties showed that cross-sections were further enhanced upon (i) attachment of electron donating groups, such as substituted amino groups, to the symmetric structures; (ii) extension of the conjugation length; and (iii) replacement of conjugated pi center with an sp3 hybridized nitrogen atom. Two-photon absorbing polymers and a dendritic structure of symmetric molecules were also synthesized and characterized. A series of bulky aluminum complexes were synthesized and characterized. For the first time, they were found to be active initiators towards the polymerization of acrylates. Coordination of methyl acrylate to aluminum complexes was observed by variable-temperature nuclear magnetic resonance spectroscopy. Adducts of methyl acrylate to aluminum complexes were isolated and characterized by both 1H and 13C nuclear magnetic resonance spectroscopy. The proposed mechanism involved a radical process where the radicals were produced by an assisted homolysis of the Al-alkyl bond. A kinetic study of the methyl acrylate polymerization initiated by bulky aluminum complex showed that the rate of polymerization was first-order with respect to the monomer concentration and half-order with respect to the concentration of aluminum initiator. Further investigation showed bulky aluminum complexes were also active in the initiation of the polymerization of styrene and some other monomers. A facile one-step synthesis of an unimolecular initiator, 2,3-dimethyl-4-phenyl-4-(2 ',2',6',6' -tetramethylpiperidinoxy)butanitrile, was developed for "living" radical polymerization study. A "living" polymerization of styrene was observed

  2. Radical-initiated controlled synthesis of homo- and copolymers based on acrylonitrile

    NASA Astrophysics Data System (ADS)

    Grishin, D. F.; Grishin, I. D.

    2015-07-01

    Data on the controlled synthesis of polyacrylonitrile and acrylonitrile copolymers with other (meth)acrylic and vinyl monomers upon radical initiation and metal complex catalysis are analyzed. Primary attention is given to the use of metal complexes for the synthesis of acrylonitrile-based (co)polymers with defined molecular weight and polydispersity in living mode by atom transfer radical polymerization. The prospects for using known methods of controlled synthesis of macromolecules for the preparation of acrylonitrile homo- and copolymers as carbon fibre precursors are estimated. The major array of published data analyzed in the review refers to the last decade. The bibliography includes 175 references.

  3. Controlled Polymerization by Incarceration of Monomers in Nanochannels

    NASA Astrophysics Data System (ADS)

    Uemura, Takashi; Kitagawa, Susumu

    Porous Coordination Polymers (PCPs) composed of transition metal ions and bridging organic ligands have been extensively studied. The characteristic features of PCPs are highly regular channel structures, controllable channel sizes approximating molecular dimensions, designable surface potentials and functionality, and flexible frameworks responsive to guest molecules. Owing to these advantages, successful applications of PCPs range from molecular storage and separation to heterogeneous catalysts. In particular, use of their regulated and tunable nanochannels in the field of polymerization has allowed multi-level control of polymerization via control of stereoregularlity, molecular weight, etc. In this chapter, we focus on recent progress in polymerization utilizing the nanochannels of PCPs, and demonstrate why this polymerization system is attractive and promising from the viewpoint of precision control of polymeric structures.

  4. Controlled polymerization by incarceration of monomers in nanochannels.

    PubMed

    Uemura, Takashi; Kitagawa, Susumu

    2010-01-01

    Porous Coordination Polymers (PCPs) composed of transition metal ions and bridging organic ligands have been extensively studied. The characteristic features of PCPs are highly regular channel structures, controllable channel sizes approximating molecular dimensions, designable surface potentials and functionality, and flexible frameworks responsive to guest molecules. Owing to these advantages, successful applications of PCPs range from molecular storage and separation to heterogeneous catalysts. In particular, use of their regulated and tunable nanochannels in the field of polymerization has allowed multi-level control of polymerization via control of stereoregularlity, molecular weight, etc. In this chapter, we focus on recent progress in polymerization utilizing the nanochannels of PCPs, and demonstrate why this polymerization system is attractive and promising from the viewpoint of precision control of polymeric structures.

  5. Preparation of Transparent Bulk TiO2/PMMA Hybrids with Improved Refractive Indices via an in Situ Polymerization Process Using TiO2 Nanoparticles Bearing PMMA Chains Grown by Surface-Initiated Atom Transfer Radical Polymerization.

    PubMed

    Maeda, Satoshi; Fujita, Masato; Idota, Naokazu; Matsukawa, Kimihiro; Sugahara, Yoshiyuki

    2016-12-21

    Transparent TiO2/PMMA hybrids with a thickness of 5 mm and improved refractive indices were prepared by in situ polymerization of methyl methacrylate (MMA) in the presence of TiO2 nanoparticles bearing poly(methyl methacrylate) (PMMA) chains grown using surface-initiated atom transfer radical polymerization (SI-ATRP), and the effect of the chain length of modified PMMA on the dispersibility of modified TiO2 nanoparticles in the bulk hybrids was investigated. The surfaces of TiO2 nanoparticles were modified with both m-(chloromethyl)phenylmethanoyloxymethylphosphonic acid bearing a terminal ATRP initiator and isodecyl phosphate with a high affinity for common organic solvents, leading to sufficient dispersibility of the surface-modified particles in toluene. Subsequently, SI-ATRP of MMA was achieved from the modified surfaces of the TiO2 nanoparticles without aggregation of the nanoparticles in toluene. The molecular weights of the PMMA chains cleaved from the modified TiO2 nanoparticles increased with increases in the prolonging of the polymerization period, and these exhibited a narrow distribution, indicating chain growth controlled by SI-ATRP. The nanoparticles bearing PMMA chains were well-dispersed in MMA regardless of the polymerization period. Bulk PMMA hybrids containing modified TiO2 nanoparticles with a thickness of 5 mm were prepared by in situ polymerization of the MMA dispersion. The transparency of the hybrids depended significantly on the chain length of the modified PMMA on the nanoparticles, because the modified PMMA of low molecular weight induced aggregation of the TiO2 nanoparticles during the in situ polymerization process. The refractive indices of the bulk hybrids could be controlled by adjusting the TiO2 content and could be increased up to 1.566 for 6.3 vol % TiO2 content (1.492 for pristine PMMA).

  6. Morphological control of conductive polymers utilized electrolysis polymerization technique: trial of fabricating biocircuit.

    PubMed

    Onoda, Mitsuyoshi

    2014-10-01

    Conductive polymers are a strong contender for making electronic circuits. The growth pattern in conductive polymer synthesis by the electrolysis polymerization method was examined. The growth pattern is deeply related to the coupling reaction of the radical cation and the deprotonation reaction following it and changes suddenly depending on the kind and concentration of the supporting electrolyte and the solvent used. That is, when the electrophilic substitution coupling reaction becomes predominant, the three-dimensional growth form is observed, and when the radical coupling reaction becomes predominant, the two-dimensional growth morphology is observed. In addition, the growth pattern can be comparatively easily controlled by changing the value of the polymerization constant current, and it is considered that the indicator and development for biocircuit research with neuron-type devices made of conjugated polymers was obtained.

  7. Characterization of silver/polystyrene nanocomposites prepared by in situ bulk radical polymerization

    SciTech Connect

    Vukoje, Ivana D.; Vodnik, Vesna V.; Džunuzović, Jasna V.; Džunuzović, Enis S.; Marinović-Cincović, Milena T.; Jeremić, Katarina; Nedeljković, Jovan M.

    2014-01-01

    Graphical abstract: - Highlights: • Synthesis and characterization of polystyrene nanocomposites based on Ag nanoparticles. • The glass transition temperature decreased in nanocomposites with respect to the pure polymer. • Resistance of the polymer to thermal degradation enhanced with Ag nanoparticles content. - Abstract: Nanocomposites (NCs) with different content of silver nanoparticles (Ag NPs) embeded in polystyrene (PS) matrix were prepared by in situ bulk radical polymerization. The nearly monodisperse Ag NPs protected with oleylamine were synthesized via organic solvo-thermal method and further used as a filler. The as-prepared spherical Ag NPs with diameter of 7.0 ± 1.5 nm were well dispersed in the PS matrix. The structural properties of the resulting Ag/PS NCs were characterized by transmission electron microscope (TEM) and Fourier transform infrared (FTIR) spectroscopy, while optical properties were characterized using optical absorption measurements. The gel permeation chromatography (GPC) measurements showed that the presence of Ag NPs stabilized with oleylamine has no influence on the molecular weight and polydispersity of the PS matrix. The influence of silver content on the thermal properties of Ag/PS NCs was investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results indicated that resistance of PS to thermal degradation was improved upon incorporation of Ag NPs. The Ag/PS NCs have lower glass transition temperatures than neat PS because loosely packed oleylamine molecules at the interface caused the increase of free volume and chain segments mobility near the surface of Ag NPs.

  8. Removal of dye by carboxymethyl cellulose, acrylamide and graphene oxide via a free radical polymerization process.

    PubMed

    Varaprasad, Kokkarachedu; Jayaramudu, Tippabattini; Sadiku, Emmanuel Rotimi

    2017-05-15

    Carboxymethyl cellulose has been used for the design of novel engineered hydrogels in order to obtain effective three-dimensional structures for industrial applications. In this work, dye removal carboxymethyl cellulose-acrylamide-graphene oxide (CMC-AM-GO) hydrogels were prepared by a free-radical polymerization method. The GO was developed by the modified Hummers method. The CMC-AM-GO and GO were characterized by FTIR, XRD and SEM. The swelling and swelling kinetics were calculated using gravimetric process. The kinetic parameter, swelling exponent values [n=0.59-0.7507] explained the fact that the CMC-AM-GO hydrogles have super Case II diffusion transport mechanism. CMCx-AM-GO (x=1-4) and CMC-AM hydrogels were used for removal of Acid Blue-133. The result explains that composite hydrogels significantly removed the acid blue when compared to the neat hydrogel. The maximum AB absorption (185.45mg/g) capacity was found in the case of CMC2-AM-GO hydrogel. Therefore, cellulose-based GO hydrogels can be termed as smart systems for the abstraction of dye in water purification applications.

  9. Surface initiated atom transfer radical polymerization grafting of sodium styrene sulfonate from titanium and silicon substrates

    PubMed Central

    Foster, Rami N.; Keefe, Andrew J.; Jiang, Shaoyi; Castner, David G.

    2013-01-01

    This study investigates the grafting of poly-sodium styrene sulfonate (pNaSS) from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate functionalized Si and Ti substrates by atom transfer radical polymerization (ATRP). The composition, molecular structure, thickness, and topography of the grafted pNaSS films were characterized with x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), variable angle spectroscopic ellipsometry (VASE), and atomic force microscopy (AFM), respectively. XPS and ToF-SIMS results were consistent with the successful grafting of a thick and uniform pNaSS film on both substrates. VASE and AFM scratch tests showed the films were between 25 and 49 nm thick on Si, and between 13 and 35 nm thick on Ti. AFM determined root-mean-square roughness values were ∼2 nm on both Si and Ti substrates. Therefore, ATRP grafting is capable of producing relatively smooth, thick, and chemically homogeneous pNaSS films on Si and Ti substrates. These films will be used in subsequent studies to test the hypothesis that pNaSS-grafted Ti implants preferentially adsorb certain plasma proteins in an orientation and conformation that modulates the foreign body response and promotes formation of new bone. PMID:24482558

  10. Understanding atom transfer radical polymerization: effect of ligand and initiator structures on the equilibrium constants.

    PubMed

    Tang, Wei; Kwak, Yungwan; Braunecker, Wade; Tsarevsky, Nicolay V; Coote, Michelle L; Matyjaszewski, Krzysztof

    2008-08-13

    Equilibrium constants in Cu-based atom transfer radical polymerization (ATRP) were determined for a wide range of ligands and initiators in acetonitrile at 22 degrees C. The ATRP equilibrium constants obtained vary over 7 orders of magnitude and strongly depend on the ligand and initiator structures. The activities of the Cu(I)/ligand complexes are highest for tetradentate ligands, lower for tridentate ligands, and lowest for bidentate ligands. Complexes with tripodal and bridged ligands (Me6TREN and bridged cyclam) tend to be more active than those with the corresponding linear ligands. The equilibrium constants are largest for tertiary alkyl halides and smallest for primary alkyl halides. The activities of alkyl bromides are several times larger than those of the analogous alkyl chlorides. The equilibrium constants are largest for the nitrile derivatives, followed by those for the benzyl derivatives and the corresponding esters. Other equilibrium constants that are not readily measurable were extrapolated from the values for the reference ligands and initiators. Excellent correlations of the equilibrium constants with the Cu(II/I) redox potentials and the carbon-halogen bond dissociation energies were observed.

  11. Adsorption of perfluorinated compounds on aminated rice husk prepared by atom transfer radical polymerization.

    PubMed

    Deng, Shubo; Niu, Li; Bei, Yue; Wang, Bin; Huang, Jun; Yu, Gang

    2013-04-01

    Adsorption is considered as an effective method to remove perfluorinated compounds (PFCs) from aqueous solution. In this study, an aminated rice husk (RH) adsorbent was successfully prepared through surface-initiated atom transfer radical polymerization (ATRP) and subsequent amination reaction, and it was used to remove perfluorooctanoate (PFOA), perfluorobutanoic acid (PFBA) and perfluorooctane sulfonate (PFOS) from aqueous solution. Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) analysis verified the presence of grafted polymer brushes and amine groups on the RH surface. The zero point of zeta potential of aminated RH was 8.5, which facilitated the sorption of anionic PFCs on the positively charged adsorbent at pH below 8.5. The sorption equilibria of PFOA, PFBA and PFOS were achieved within 5 h, 3 h and 9 h, respectively, faster than the reported porous adsorbents. Sorption isotherms showed that the adsorption capacities of PFOA, PFBA and PFOS on the aminated RH at pH 5.0 were 2.49, 1.70 and 2.65 mmol g(-1), respectively. Sorption behavior and X-ray photoelectron spectroscopy (XPS) analysis confirmed that the electrostatic and hydrophobic interactions were involved in the sorption process, and the micelles and hemi-micelles of PFOA and PFOS may form on the adsorbent surface.

  12. Removal of cefalexin using yeast surface-imprinted polymer prepared by atom transfer radical polymerization.

    PubMed

    Li, Xiuxiu; Pan, Jianming; Dai, Jiangdong; Dai, Xiaohui; Ou, Hongxiang; Xu, Longcheng; Li, Chunxiang; Zhang, Rongxian

    2012-10-01

    The first use of yeast as a support in the molecular imprinting field combined with atom transfer radical polymerization was described. Then, the as-prepared molecularly imprinted polymers were characterized by Fourier transmission infrared spectrometry, scanning electron microscope, thermogravimetric analysis, and elemental analysis. The obtained imprinted polymers demonstrated elliptical-shaped particles with the thickness of imprinting layer of 0.63 μm. The batch mode experiments were adopted to investigate the adsorption equilibrium, kinetics, and selectivity. The kinetic properties of imprinted polymers were well described by the pseudo-second-order kinetic equation, indicating the chemical process was the rate-limiting step for the adsorption of cefalexin (CFX). The equilibrium data were well fitted by the Freundlich isotherm, and the multimolecular layers adsorption capacity of imprinted polymers was 34.07 mg g(-1) at 298 K. The selectivity analysis suggested that the imprinted polymers exhibited excellent selective recognition for CFX in the presence of other compounds with related structure. Finally, the analytical method based on the imprinted polymers extraction coupled with high-performance liquid chromatograph was successfully used for CFX analysis in spiked pork and water samples.

  13. Novel multi-responsive P2VP-block-PNIPAAm block copolymers via nitroxide-mediated radical polymerization

    PubMed Central

    Corten, Cathrin; Kretschmer, Katja

    2010-01-01

    Summary Linear soluble multi-responsive block copolymers are able to form so called schizophrenic micelles in aqueous solution. Here, such polymers are prepared via nitroxide-mediated radical polymerization (NMRP). In a first step nitroxide-terminated poly(2-vinylpyridine) (P2VP) was prepared with different molecular weights and narrow molecular weight distributions. The best reaction conditions, optimized by kinetic studies, were bulk polymerization at 110 °C. Using P2VP as a macroinitiator, the synthesis of new soluble linear block copolymers of P2VP and poly(N-isopropylacrylamide) (PNIPAAm) (P2VP-block-PNIPAAm) was possible. The nitroxide terminated polymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, size exclusion chromatography (SEC) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Thermal properties were investigated by the differential scanning calorimetry (DSC). Block copolymers showed pH- and temperature-responsive solubility in aqueous media. By increasing the P2VP content, the phase transition temperature shifted to lower temperatures (e.g. 26 °C for P2VP114-block-PNIPAAm180). Depending on the resulting block length, temperature and pH value of aqueous solution, the block copolymers form so called schizophrenic micelles. The hydrodynamic radius R h of these micelles associated with pH values and temperature was analyzed by dynamic light scattering (DLS). Such kind of block copolymers has potential for many applications, such as controlled drug delivery systems. PMID:20978627

  14. Coating and dispersion of ceramic nanoparticles by UV-ozone etching assisted surface-initiated living radical polymerization.

    PubMed

    Arita, Toshihiko

    2010-10-01

    Commercially available unmodified ceramic nanoparticles (NPs) in dry powder state were surface-modified and dispersed in almost single-crystal size. The surface-initiated living radical polymerization after just UV-ozone soft etching enables one to graft polymers onto the surface of ceramic NPs and disperse them in solvents. Furthermore, a number of NPs were dispersed with single-crystal sizes. The technique developed here could be applied to almost all ceramic NPs including metal nitrides.

  15. Expanded corn starch as a versatile material in atom transfer radical polymerization (ATRP) of styrene and methyl methacrylate.

    PubMed

    Bansal, Ankushi; Kumar, Arvind; Latha, Patnam Padma; Ray, Siddharth Sankar; Chatterjee, Alok Kumar

    2015-10-05

    Polymerization of styrene (St) and methyl methacrylate (MMA) was performed by surface initiated (SI) and activator generated by electron transfer (AGET) systems of atom transfer radical polymerization (ATRP) using renewable expanded corn starch (ECS) as a support. This prepared ECS is found to have V type crystallinity with 50 m(2)g(-1) surface area (<1m(2)g(-1) for corn starch (CS)) and average pore volume of 0.43 cm(3)g(-1) (<0.1cm(3)g(-1) for CS). In SI-ATRP, hydroxyl groups on ECS were converted into macro-initiator by replacing with 2-bromoisobutyryl bromide (BIBB) with a 0.06 degree of substitution determined from NMR. In AGET-ATRP, CuBr2/ligand complex get adsorbed on ECS (Cu(II)/ECS=10 wt.%) to catalyze the polymerization. Synthesized PS/PMMA was characterized by SEM, FT-IR, (1)H NMR.

  16. Chain Reaction Polymerization.

    ERIC Educational Resources Information Center

    McGrath, James E.

    1981-01-01

    The salient features and importance of chain-reaction polymerization are discussed, including such topics as the thermodynamics of polymerization, free-radical polymerization kinetics, radical polymerization processes, copolymers, and free-radical chain, anionic, cationic, coordination, and ring-opening polymerizations. (JN)

  17. Chain Reaction Polymerization.

    ERIC Educational Resources Information Center

    McGrath, James E.

    1981-01-01

    The salient features and importance of chain-reaction polymerization are discussed, including such topics as the thermodynamics of polymerization, free-radical polymerization kinetics, radical polymerization processes, copolymers, and free-radical chain, anionic, cationic, coordination, and ring-opening polymerizations. (JN)

  18. Copper(II)/tertiary amine synergy in photoinduced living radical polymerization: accelerated synthesis of ω-functional and α,ω-heterofunctional poly(acrylates).

    PubMed

    Anastasaki, Athina; Nikolaou, Vasiliki; Zhang, Qiang; Burns, James; Samanta, Shampa R; Waldron, Christopher; Haddleton, Alice J; McHale, Ronan; Fox, David; Percec, Virgil; Wilson, Paul; Haddleton, David M

    2014-01-22

    Photoinduced living radical polymerization of acrylates, in the absence of conventional photoinitiators or dye sensitizers, has been realized in "daylight'"and is enhanced upon irradiation with UV radiation (λ(max) ≈ 360 nm). In the presence of low concentrations of copper(II) bromide and an aliphatic tertiary amine ligand (Me6-Tren; Tren = tris(2-aminoethyl)amine), near-quantitative monomer conversion (>95%) is obtained within 80 min, yielding poly(acrylates) with dispersities as low as 1.05 and excellent end group fidelity (>99%). The versatility of the technique is demonstrated by polymerization of methyl acrylate to a range of chain lengths (DP(n) = 25-800) and a number of (meth)acrylate monomers, including macromonomer poly(ethylene glycol) methyl ether acrylate (PEGA480), tert-butyl acrylate, and methyl methacrylate, as well as styrene. Moreover, hydroxyl- and vic-diol-functional initiators are compatible with the polymerization conditions, forming α,ω-heterofunctional poly(acrylates) with unparalleled efficiency and control. The control retained during polymerization is confirmed by MALDI-ToF-MS and exemplified by in situ chain extension upon sequential monomer addition, furnishing higher molecular weight polymers with an observed reduction in dispersity (Đ = 1.03). Similarly, efficient one-pot diblock copolymerization by sequential addition of ethylene glycol methyl ether acrylate and PEGA480 to a poly(methyl acrylate) macroinitiator without prior workup or purification is also reported. Minimal polymerization in the absence of light confers temporal control and alludes to potential application at one of the frontiers of materials chemistry whereby precise spatiotemporal "on/off" control and resolution is desirable.

  19. Thermoresponsive Melamine Sponges with Switchable Wettability by Interface-Initiated Atom Transfer Radical Polymerization for Oil/Water Separation.

    PubMed

    Lei, Zhiwen; Zhang, Guangzhao; Deng, Yonghong; Wang, Chaoyang

    2017-03-15

    Here we have obtained a temperature responsive melamine sponge with a controllable wettability between superhydrophilicity and superhydrophobicity by grafting the octadecyltrichlorosilane and thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) onto the surface of melamine sponge skeletons. The whole process included the silanization in which step the rough surface with low surface energy and the NH2 were provided, and the atom transfer radical polymerization which ensured the successful grafting of PNIPAAm onto the skeleton's surface. The product exhibits a good reversible switch between superhydrophilicity and superhydrophobicity by changing the temperature below or above the lower critical solution temperature (LCST, about 32 °C) of PNIPAAm, and the modified sponge still retains a good responsiveness after undergoing two temperature switches for 20 cycles. Simultaneously, the functionalized sponges could be used to absorb the oil under water at 37 °C, and they released the absorbed oil in various ways under water at 20 °C, showing wide potential applications including oil/water separation.

  20. Preparation of hydrophilic polymer-grafted polystyrene beads for hydrophilic interaction chromatography via surface-initiated atom transfer radical polymerization.

    PubMed

    Dai, Xiaojun; He, Yuan; Wei, Yinmao; Gong, Bolin

    2011-11-01

    A one-step procedure based on surface-initiated atom transfer radical polymerization (SI-ATRP) to hydrophilize monodisperse poly(chloromethylstyrene-co-divinylbenzene) beads has been presented in this work, using 2-hydroxyl-3-[4-(hydroxymethyl)-1H-1,2,3-triazol-1-yl]propyl 2-methylacrylate (HTMA) as a monomer. The chain length of the grafted poly(HTMA) was controlled via varying the ratio of HTMA to initiator on the surface of the beads. When using the grafted beads as a stationary phase in hydrophilic interaction chromatography (HILIC), good resolution for nucleobases/nucleosides was obtained with acetonitrile aqueous solution as an eluent; while for phenolic acids and glycosides, they could be eluted and separated in the presence of TFA. The retention time of the solutes increased with the amount of the grafted HTMA. The retention mechanisms of solutes were investigated by the effects of mobile phase composition and buffer pH on the retention of solutes. The results illustrated that the retention behaviors of the tested solutes were dominated by hydrogen bonding interaction and electrostatic interaction. From the chemical structure of the ligands, the modified beads could not only be used as a stationary phase in HILIC, but also act as a useful building block to develop new stationary phases for other chromatographic modes such as affinity media. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Cationic Polymerization of Vinyl Ethers Controlled by Visible Light.

    PubMed

    Kottisch, Veronika; Michaudel, Quentin; Fors, Brett P

    2016-12-07

    Photoinitiated cationic polymerizations are widely used in industrial processes; however, gaining photocontrol over chain growth would expand the utility of these methods and facilitate the design of novel complex architectures. We report herein a cationic polymerization regulated by visible light. This polymerization proceeds under mild conditions: a combination of a metal-free photocatalyst, a chain-transfer agent, and light irradiation enables the synthesis of various poly(vinyl ether)s with good control over molecular weight and dispersity as well as excellent chain-end fidelity. Significantly, photoreversible cation formation in this system enables efficient control over polymer chain growth with light.

  2. Atom transfer radical polymerization preparation and photophysical properties of polypyridylruthenium derivatized polystyrenes.

    PubMed

    Fang, Zhen; Ito, Akitaka; Keinan, Shahar; Chen, Zuofeng; Watson, Zoe; Rochette, Jason; Kanai, Yosuke; Taylor, Darlene; Schanze, Kirk S; Meyer, Thomas J

    2013-08-05

    A ruthenium containing polymer featuring a short carbonyl-amino-methylene linker has been prepared by atom transfer radical polymerization (ATRP). The polymer was derived from ATRP of the N-hydroxysuccinimide (NHS) derivative of p-vinylbenzoic acid, followed by an amide coupling reaction of the NHS-polystyrene with Ru(II) complexes derivatized with aminomethyl groups (i.e., [Ru(bpy)2(CH3-bpy-CH2NH2)](2+) where bpy is 2,2'-bipyridine, and CH3-bpy-CH2NH2 is 4-methyl-4'-aminomethyl-2,2'-bipyridine). The Ru-functionalized polymer structure was confirmed by using nuclear magnetic resonance and infrared spectroscopy, and the results suggest that a high loading ratio of polypyridylruthenium chromophores on the polystyrene backbone was achieved. The photophysical properties of the polymer were characterized in solution and in rigid ethylene glycol glasses. In solution, emission quantum yield and lifetime studies reveal that the polymer's metal-to-ligand charge transfer (MLCT) excited states are quenched relative to a model Ru complex chromophore. In rigid media, the MLCT-ground state band gap and lifetime are both increased relative to solution with time-resolved emission measurements revealing fast energy transfer hopping within the polymer. Molecular dynamics studies of the polymer synthesized here as well as similar model systems with various spatial arrangements of the pendant Ru complex chromophores suggest that the carbonyl-amino-methylene linker probed in our target polymer provides shorter Ru-Ru nearest-neighbor distances leading to an increased Ru*-Ru energy hopping rate, compared to those with longer linkers in counterpart polymers.

  3. Synergistic effect of ultrasonication and phase transfer catalysts in radical polymerization of methyl methacrylate - A kinetic study.

    PubMed

    Prabha, J; Susan Jemima, W; Jayaprada, M; Umapathy, M J

    2017-03-01

    Methyl methacrylate (MMA) has been polymerized to poly methyl methacrylate (PMMA) by employing three different phase transfer catalysts (PTC) such as 1,4-bis(dimethylhexyl)ethylenediammoniumbromide (DMHEDAB), 1,4bis(dimethylheptyl)ethylenediammoniumbromide (DMH1EDAB) and 1,4-bis(dimethyloctyl)ethylenediammonium bromide (DMOEDAB) under the influence of ultrasound radiation. The radical polymerization was performed under unstirred condition at a temperature of 60±1°C in an oxygen free atmosphere employing water soluble K2S2O8 as initiator. Various parameters such as role of [Monomer], [Initiator], [PTC], solvent and temperature were investigated on rate of polymerization (Rp) and the synergic efficacy of ultrasound wave variation and phase transfer catalysts were also assessed. It was found that the rate of polymerization (Rp) increased drastically for all the three catalyst under the influence of ultrasound and the order of efficiency was found to be [Formula: see text] This increase may be due to the number of carbon chain attached to the polar group which facilitate and accelerate the rate of polymerization.

  4. Surface modification of glycidyl-containing poly(methyl methacrylate) microchips using surface-initiated atom-transfer radical polymerization.

    PubMed

    Sun, Xuefei; Liu, Jikun; Lee, Milton L

    2008-02-01

    Fabrication of microfluidic systems from polymeric materials is attractive because of simplicity and low cost. Unfortunately, the surfaces of many polymeric materials can adsorb biological samples. Therefore, it is necessary to modify their surfaces before these polymeric materials can be used for separation and analysis. Oftentimes it is difficult to modify polymeric surfaces because of their resistance to chemical reaction. Recently, we introduced a surface-reactive acrylic polymer, poly(glycidyl methacrylate-co-methyl methacrylate) (PGMAMMA), which can be modified easily and is suitable for fabrication of microfluidic devices. Epoxy groups on the surface can be activated by air plasma treatment, hydrolysis, or aminolysis. In this work, the resulting hydroxyl or amino groups were reacted with 2-bromoisobutylryl bromide to introduce an initiator for surface-initiated atom-transfer radical polymerization (SI-ATRP). Polyethylene glycol (PEG) layers grown on the surface using this method were uniform, hydrophilic, stable, and resistant to protein adsorption. Contact angle measurement and X-ray photoelectron spectroscopy (XPS) were used to characterize activated polymer surfaces, initiator-bound surfaces, and PEG-grafted surfaces. We obtained excellent capillary electrophoresis (CE) separations of proteins and peptides with the PEG-modified microchips. A separation efficiency of 4.4 x 10(4) plates for a 3.5 cm long separation channel was obtained.

  5. Visible-light organic photocatalysis for latent radical-initiated polymerization via 2e⁻/1H⁺ transfers: initiation with parallels to photosynthesis.

    PubMed

    Aguirre-Soto, Alan; Lim, Chern-Hooi; Hwang, Albert T; Musgrave, Charles B; Stansbury, Jeffrey W

    2014-05-21

    We report the latent production of free radicals from energy stored in a redox potential through a 2e(-)/1H(+) transfer process, analogous to energy harvesting in photosynthesis, using visible-light organic photoredox catalysis (photocatalysis) of methylene blue chromophore with a sacrificial sterically hindered amine reductant and an onium salt oxidant. This enables light-initiated free-radical polymerization to continue over extended time intervals (hours) in the dark after brief (seconds) low-intensity illumination and beyond the spatial reach of light by diffusion of the metastable leuco-methylene blue photoproduct. The present organic photoredox catalysis system functions via a 2e(-)/1H(+) shuttle mechanism, as opposed to the 1e(-) transfer process typical of organometallic-based and conventional organic multicomponent photoinitiator formulations. This prevents immediate formation of open-shell (radical) intermediates from the amine upon light absorption and enables the "storage" of light-energy without spontaneous initiation of the polymerization. Latent energy release and radical production are then controlled by the subsequent light-independent reaction (analogous to the Calvin cycle) between leuco-methylene blue and the onium salt oxidant that is responsible for regeneration of the organic methylene blue photocatalyst. This robust approach for photocatalysis-based energy harvesting and extended release in the dark enables temporally controlled redox initiation of polymer syntheses under low-intensity short exposure conditions and permits visible-light-mediated synthesis of polymers at least 1 order of magnitude thicker than achievable with conventional photoinitiated formulations and irradiation regimes.

  6. Visible-Light Organic Photocatalysis for Latent Radical-Initiated Polymerization via 2e–/1H+ Transfers: Initiation with Parallels to Photosynthesis

    PubMed Central

    2015-01-01

    We report the latent production of free radicals from energy stored in a redox potential through a 2e–/1H+ transfer process, analogous to energy harvesting in photosynthesis, using visible-light organic photoredox catalysis (photocatalysis) of methylene blue chromophore with a sacrificial sterically hindered amine reductant and an onium salt oxidant. This enables light-initiated free-radical polymerization to continue over extended time intervals (hours) in the dark after brief (seconds) low-intensity illumination and beyond the spatial reach of light by diffusion of the metastable leuco-methylene blue photoproduct. The present organic photoredox catalysis system functions via a 2e–/1H+ shuttle mechanism, as opposed to the 1e– transfer process typical of organometallic-based and conventional organic multicomponent photoinitiator formulations. This prevents immediate formation of open-shell (radical) intermediates from the amine upon light absorption and enables the “storage” of light-energy without spontaneous initiation of the polymerization. Latent energy release and radical production are then controlled by the subsequent light-independent reaction (analogous to the Calvin cycle) between leuco-methylene blue and the onium salt oxidant that is responsible for regeneration of the organic methylene blue photocatalyst. This robust approach for photocatalysis-based energy harvesting and extended release in the dark enables temporally controlled redox initiation of polymer syntheses under low-intensity short exposure conditions and permits visible-light-mediated synthesis of polymers at least 1 order of magnitude thicker than achievable with conventional photoinitiated formulations and irradiation regimes. PMID:24786755

  7. Localized surface plasmon resonance nanosensing of C-reactive protein with poly(2-methacryloyloxyethyl phosphorylcholine)-grafted gold nanoparticles prepared by surface-initiated atom transfer radical polymerization.

    PubMed

    Kitayama, Yukiya; Takeuchi, Toshifumi

    2014-06-03

    Highly sensitive and selective protein nanosensing based on localized surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) on which polymerized specific ligands were grafted as an artificial protein recognition layer for the target protein were demonstrated. As a model, optical nanosensing for C-reactive protein (CRP), a known biomarker for chronic inflammation that predicts the risk of arteriosclerosis or heart attacks, was achieved by measuring the shift of LSPR spectra derived from the change of permittivity of poly(2-methacryloyloxyethyl phosphorylcholine)-grafted AuNPs (PMPC-g-AuNPs) upon interacting with CRP, in which the PMPC-g-AuNPs layer were grafted on AuNPs by surface-initiated atom transfer radical polymerization (ATRP). This nanosensing system was effective even for detecting CRP concentrations in a human serum solution diluted to 1% (w/w), at which point a limit of detection was ~50 ng/mL and nonspecific adsorption of other proteins was negligible. The nanosensing system using specific ligand-grafted AuNPs has several strengths, such as low preparation cost, avoiding the need for expensive instruments, no necessary complex pretreatments, and high stability, because it does not contain biobased molecules. We believe this novel synthetic route for protein nanosensors, composed of AuNPs and a polymerized specific ligand utilizing surface-initiated controlled/living radical polymerization, will provide a foundation for the design and synthesis of nanosensors targeting various other biomarker proteins, paving the way for future advances in the field of biosensing.

  8. Porous polymers by controlling phase separation during vapor deposition polymerization.

    PubMed

    Tao, Ran; Anthamatten, Mitchell

    2013-11-01

    A template-free method is described to fabricate continuous-phase, porous polymer films by simultaneous phase separation during vapor deposition polymerization. The technique involves concurrent polymerization, crosslinking, and phase separation of condensed species and reaction products. Deposited films form open-cell, macroporous structures consisting of crosslinked and glassy poly(glycidyl methacrylate). By limiting phase separation during vapor phase deposition, spatially dependent morphologies, such as layered morphologies, can be grown. Results show that combining vapor deposition polymerization with phase separation establishes morphological control, which may be applied to applications including cellular scaffolds, thin cushions and vibration dampers, and membranes for separations.

  9. Room temperature optically detected magnetic resonance (photoluminescence detected magnetic resonance) of radical ion pairs induced by vacuum ultraviolet in thin polymeric films

    SciTech Connect

    Verkhovlyuk, V. N. Anisimov, O. A.; Fedotov, K. Yu.

    2016-05-15

    A setup for recording optically detected electron paramagnetic resonance spectra of radical ions involved in geminate recombination and generated by vacuum ultraviolet is described. The setup allows registration of EPR spectra from short-lived radical ions in polymeric films at room temperature by recombination fluorescence modulated by a resonance microwave field.

  10. Radical and ion molecule mechanisms in the polymerization of hydrocarbons and chlorosilanes in RF plasmas at low pressures ( 1.0 torr)

    NASA Technical Reports Server (NTRS)

    Avni, R.; Carmi, U.; Inspektor, A.; Rosenthal, I.

    1984-01-01

    The ion-molecule and the radical-molecule mechanisms are responsible for the dissociation of hydrocarbons, and chlorosilane monomers and the formation of polymerized species, respectively, in the plasma state of a RF discharge. In the plasma, of a mixture of monomer with Ar, the rate determining step for both dissociation and polymerization is governed by an ion-molecular type interaction. Additions of H2 or NH3 to the monomer Ar(+) mixture transforms the rate determining step from an ion-molecular interaction to a radical-molecule type interaction for both monomer dissociation and polymerization processes.

  11. Surface modification of carbon nanotubes via combination of mussel inspired chemistry and chain transfer free radical polymerization

    NASA Astrophysics Data System (ADS)

    Wan, Qing; Tian, Jianwen; Liu, Meiying; Zeng, Guangjian; Huang, Qiang; Wang, Ke; Zhang, Qingsong; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2015-08-01

    In this work, a novel strategy for surface modification of carbon nanotubes (CNTs) was developed via combination of mussel inspired chemistry and chain transfer free radical polymerization. First, pristine CNTs were functionalized with polydopamine (PDA), which is formed via self-polymerization of dopamine in alkaline conditions. These PDA functionalized CNTs can be further reacted with amino-terminated polymers (named as PDMC), which was synthesized through chain transfer free radical polymerization using cysteamine hydrochloride as chain transfer agent and methacryloxyethyltrimethyl ammonium chloride as the monomer. PDMC perfectly conjugated with CNT-PDA was ascertained by a series of characterization techniques including transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The dispersibility of obtained CNT nanocomposites (named as CNT-PDA-PDMC) was further examined. Results showed that the dispersibility of CNT-PDA-PDMC in aqueous and organic solutions was obviously enhanced. Apart from PDMC, many other amino-terminated polymers can also be used to functionalization of CNTs via similar strategy. Therefore, the method described in this work should be a general strategy for fabrication various polymer nanocomposites.

  12. Diffusion-regulated phase-transfer catalysis for atom transfer radical polymerization of methyl methacrylate in an aqueous/organic biphasic system.

    PubMed

    Ding, Mingqiang; Jiang, Xiaowu; Peng, Jinying; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

    2015-03-01

    A concept based on diffusion-regulated phase-transfer catalysis (DRPTC) in an aqueous-organic biphasic system with copper-mediated initiators for continuous activator regeneration is successfully developed for atom transfer radical polymerization (ICAR ATRP) (termed DRPTC-based ICAR ATRP here), using methyl methacrylate (MMA) as a model monomer, ethyl α-bromophenylacetate (EBrPA) as an initiator, and tris(2-pyridylmethyl)amine (TPMA) as a ligand. In this system, the monomer and initiating species in toluene (organic phase) and the catalyst complexes in water (aqueous phase) are simply mixed under stirring at room temperature. The trace catalyst complexes transfer into the organic phase via diffusion to trigger ICAR ATRP of MMA with ppm level catalyst content once the system is heated to the polymerization temperature (75 °C). It is found that well-defined PMMA with controlled molecular weights and narrow molecular weight distributions can be obtained easily. Furthermore, the polymerization can be conducted in the presence of limited amounts of air without using tedious degassed procedures. After cooling to room temperature, the upper organic phase is decanted and the lower aqueous phase is reused for another 10 recycling turnovers with ultra low loss of catalyst and ligand loading. At the same time, all the recycled catalyst complexes retain nearly perfect catalytic activity and controllability, indicating a facile and economical strategy for catalyst removal and recycling. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Protein adsorption resistance of PVP-modified polyurethane film prepared by surface-initiated atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Yuan, Huihui; Qian, Bin; Zhang, Wei; Lan, Minbo

    2016-02-01

    An anti-fouling surface of polyurethane (PU) film grafted with Poly(N-vinylpyrrolidone) (PVP) was prepared through surface-initiated atom transfer radical polymerization (SI-ATRP). And the polymerization time was investigated to obtain PU films with PVP brushes of different lengths. The surface properties and protein adsorption of modified PU films were evaluated. The results showed that the hydrophilicity of PU-PVP films were improved with the increase of polymerization time, which was not positive correlation with the surface roughness due to the brush structure. Additionally, the protein resistance performance was promoted when prolonging the polymerization time. The best antifouling PU-PVP (6.0 h) film reduced the adsoption level of bovine serum albumin (BSA), lysozyme (LYS), and brovin serum fibrinogen (BFG) by 93.4%, 68.3%, 85.6%, respectively, compared to the unmodified PU film. The competitive adsorption of three proteins indicated that LYS preferentially adsorbed on the modified PU film, while BFG had the lowest adsorption selectivity. And the amount of BFG on PU-PVP (6.0 h) film reduced greatly to 0.08 μg/cm2, which was almost one-tenth of its adsorption from the single-protein system. Presented results suggested that both hydrophilicity and surface roughness might be the important factors in all cases of protein adsorption, and the competitive or selective adsorption might be related to the size of the proteins, especially on the non-charged films.

  14. Bottom-Up Fabrication of Nanopatterned Polymers on DNA Origami by In Situ Atom-Transfer Radical Polymerization.

    PubMed

    Tokura, Yu; Jiang, Yanyan; Welle, Alexander; Stenzel, Martina H; Krzemien, Katarzyna M; Michaelis, Jens; Berger, Rüdiger; Barner-Kowollik, Christopher; Wu, Yuzhou; Weil, Tanja

    2016-05-04

    Bottom-up strategies to fabricate patterned polymers at the nanoscale represent an emerging field in the development of advanced nanodevices, such as biosensors, nanofluidics, and nanophotonics. DNA origami techniques provide access to distinct architectures of various sizes and shapes and present manifold opportunities for functionalization at the nanoscale with the highest precision. Herein, we conduct in situ atom-transfer radical polymerization (ATRP) on DNA origami, yielding differently nanopatterned polymers of various heights. After cross-linking, the grafted polymeric nanostructures can even stably exist in solution without the DNA origami template. This straightforward approach allows for the fabrication of patterned polymers with low nanometer resolution, which provides access to unique DNA-based functional hybrid materials.

  15. Surface-initiated reverse atom transfer radical polymerization (SI-RATRP) for blood-compatible polyurethane substrates

    NASA Astrophysics Data System (ADS)

    Lu, Chunyan; Zhou, Ninglin; Xu, Dong; Tang, Yida; Jin, Suxing; Wu, Yue; Shen, Jian

    2011-10-01

    A well-defined polymer brushes (2-(methacryloyloxy) ethyl phosphorylcholine, MPC) grafted from the polyurethane (PU) substrate by surface-initiated reverse atom transfer radical polymerization (SI-RATRP) was studied. In this work, a kind of silane coupling agent (3-chloropropyltrimethoxysilane, CPTM) was adopted to serve as a coupling agent as well as a ligand for the first time. Surface structure, wettability, morphology of the PU substrates before and after modification were characterized by Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy measurement (XPS), Atomic force microscope (AFM), Water contact angle measurement, respectively. The results showed that zwitterionic brushes were successfully fabricated on the PU surfaces, and the content of the grafted layer increased gradually with the polymerization time. The blood compatibility of the PU substrates was evaluated by protein adsorption tests and platelet adhesion tests in vitro. It was found that all the PU functionalized with zwitterionic brush showed improved resistance to nonspecific protein adsorption and platelet adhesion.

  16. Nanoengineered analytical immobilized metal affinity chromatography stationary phase by atom transfer radical polymerization: Separation of synthetic prion peptides

    PubMed Central

    McCarthy, P.; Chattopadhyay, M.; Millhauser, G.L.; Tsarevsky, N.V.; Bombalski, L.; Matyjaszewski, K.; Shimmin, D.; Avdalovic, N.; Pohl, C.

    2010-01-01

    Atom transfer radical polymerization (ATRP) was employed to create isolated, metal-containing nanoparticles on the surface of non-porous polymeric beads with the goal of developing a new immobilized metal affnity chromatography (IMAC) stationary phase for separating prion peptides and proteins. Transmission electron microscopy was used to visualize nanoparticles on the substrate surface. Individual ferritin molecules were also visualized as ferritin–nanoparticle complexes. The column's resolving power was tested by synthesizing peptide analogs to the copper binding region of prion protein and injecting mixtures of these analogs onto the column. As expected, the column was capable of separating prion-related peptides differing in number of octapeptide repeat units (PHGGGWGQ), (PHGGGWGQ)2, and (PHGGGWGQ)4. Unexpectedly, the column could also resolve peptides containing the same number of repeats but differing only in the presence of a hydrophilic tail, Q → A substitution, or amide nitrogen methylation. PMID:17481564

  17. One-Pot Synthesis of Double Poly(Ionic Liquid) Block Copolymers by Cobalt-Mediated Radical Polymerization-Induced Self-Assembly (CMR-PISA) in Water.

    PubMed

    Cordella, Daniela; Debuigne, Antoine; Jérôme, Christine; Kochovski, Zdravko; Taton, Daniel; Detrembleur, Christophe

    2016-07-01

    Amphiphilic double poly(ionic liquid) (PIL) block copolymers are directly prepared by cobalt-mediated radical polymerization induced self-assembly (CMR-PISA) in water of N-vinyl imidazolium monomers carrying distinct alkyl chains. The cobalt-mediated radical polymerization of N-vinyl-3-ethyl imidazolium bromide (VEtImBr) is first carried out until high conversion in water at 30 °C, using an alkyl bis(acetylacetonate)cobalt(III) adduct as initiator and controlling agent. The as-obtained hydrophilic poly(N-vinyl-3-ethyl imidazolium bromide) (PVEtImBr) is then used as a macroinitiator for the CMR-PISA of N-vinyl-3-octyl imidazolium bromide (VOcImBr). Self-assembly of the amphiphilic PVEtImBr-b-PVOcImBr block copolymer, i.e., of PIL-b-PIL-type, rapidly takes place in water, forming polymer nanoparticles consisting of a hydrophilic PVEtImBr corona and a hydrophobic PVOcImBr core. Preliminary investigation into the effect of the size of the hydrophobic block on the dimension of the nanoparticles is also described. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Advances in light-induced polymerizations: I. Shadow cure in free radical photopolymerizations II. Experimental and modeling studies of photoinitiator systems for effective polymerizations with LEDs

    NASA Astrophysics Data System (ADS)

    Kitano, Hajime

    Photopolymerization has become the standard for many coating and printing applications that require rapid curing at room temperature due to its potential to reduce volatile organic compound (VOC) emissions while providing a means for efficient manufacturing processes. These advantages could be useful in a variety of emerging applications, such as anisotropic conductive films (ACF) if photopolymerization could extend into relatively narrow shadow regions which are not directly illuminated, and if visible wavelengths that are not absorbed by polyimide films could be used to trigger the reaction. The broad objectives of this research are i) to examine the factors that determine the attainable extent of shadow cure in free radical polymerizations, and ii) to develop initiator systems effective for polymerization using visible light and light emitting diode (LED) lamps. Project I: Shadow Cure in Free Radical Photopolymerizations. In this project, the extent of shadow cure in visible-light-induced free radical photopolymerization is investigated. A number of effective methods such as adding additives, utilizing a reflective stage, and increasing the light intensity are introduced. In addition, the use of fluorescent dyes in multi-component photoinitiator systems proved to be very effective for shadow cure because the fluorescent light emitted from the dye could irradiate the shadow region. When considering practical resins, mixtures of oligomers and monomers, the viscosity is the major barrier that must be overcome in order to achieve high conversion in the shadow regions using visible-light-induced multi-component photoinitiator systems. Hence, instead of using multi-component systems, a commercial visible-light-induced single-component photoinitiator is investigated. As a result, a high conversion in shadow regions of the viscous oligomer containing resin is achieved. Project II: Experimental and Modeling Studies of Photoinitiator Systems for Effective Polymerizations

  19. Activators generated by electron transfer for atom transfer radical polymerization of styrene in the presence of mesoporous silica nanoparticles

    SciTech Connect

    Khezri, Khezrollah; Roghani-Mamaqani, Hossein

    2014-11-15

    Graphical abstract: Effect of mesoporous silica nanoparticles (MCM-41) on the activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP) is investigated. Decrement of conversion and number average molecular weight and also increment of polydispersity index (PDI) values are three main results of addition of MCM-41 nanoparticles. Incorporation of MCM-41 nanoparticles in the polystyrene matrix can clearly increase thermal stability and decrease glass transition temperature of the nanocomposites. - Highlights: • Spherical morphology, hexagonal structure, and high surface area with regular pore diameters of the synthesized MCM-41 nanoparticles are examined. • AGET ATRP of styrene in the presence of MCM-41 nanoparticles is performed. • Effect of MCM-41 nanoparticles addition on the polymerization rate, conversion and molecular weights of the products are discussed. • Improvement in thermal stability of the nanocomposites and decreasing T{sub g} values was also observed by incorporation of MCM-41 nanoparticles. - Abstract: Activator generated by electron transfer for atom transfer radical polymerization was employed to synthesize well-defined mesoporous silica nanoparticles/polystyrene composites. Inherent features of spherical mesoporous silica nanoparticles were evaluated by nitrogen adsorption/desorption isotherm, X-ray diffraction and scanning electron microscopy analysis techniques. Conversion and molecular weight evaluations were carried out using gas and size exclusion chromatography respectively. By the addition of only 3 wt% mesoporous silica nanoparticles, conversion decreases from 81 to 58%. Similarly, number average molecular weight decreases from 17,116 to 12,798 g mol{sup −1}. However, polydispersity index (PDI) values increases from 1.24 to 1.58. A peak around 4.1–4.2 ppm at proton nuclear magnetic resonance spectroscopy results clearly confirms the living nature of the polymerization. Thermogravimetric

  20. Microgel coating of magnetic nanoparticles via bienzyme-mediated free-radical polymerization for colorimetric detection of glucose

    NASA Astrophysics Data System (ADS)

    Wu, Qing; Wang, Xia; Liao, Chuanan; Wei, Qingcong; Wang, Qigang

    2015-10-01

    This study describes a new strategy for the fabrication of magnetic core-shell microgels by free-radical polymerization triggered by the cascade reaction of glucose oxidase (GOx) and horseradish peroxidase (HRP). The mild polymerization around the interface of the magnetic nanoparticles permits the mild coating of the microgel layer with excellent characteristics for various applications in biocatalysis and medical diagnostics, as well as in clinical fields. The immobilized bienzyme within the microgel has a largely retained activity relative to the non-immobilized one. The confining effect of the microgel and the well designed distance between the two enzymes can benefit the diffusion of intermediates to the HRP active site. The final microgels can be incontestably employed as sensitive biosensors for colorimetric glucose detection.This study describes a new strategy for the fabrication of magnetic core-shell microgels by free-radical polymerization triggered by the cascade reaction of glucose oxidase (GOx) and horseradish peroxidase (HRP). The mild polymerization around the interface of the magnetic nanoparticles permits the mild coating of the microgel layer with excellent characteristics for various applications in biocatalysis and medical diagnostics, as well as in clinical fields. The immobilized bienzyme within the microgel has a largely retained activity relative to the non-immobilized one. The confining effect of the microgel and the well designed distance between the two enzymes can benefit the diffusion of intermediates to the HRP active site. The final microgels can be incontestably employed as sensitive biosensors for colorimetric glucose detection. Electronic supplementary information (ESI) available: Experimental details and ESI figures. See DOI: 10.1039/c5nr05716g

  1. Beyond Traditional RAFT: Alternative Activation of Thiocarbonylthio Compounds for Controlled Polymerization

    PubMed Central

    McKenzie, Thomas G.; Fu, Qiang; Uchiyama, Mineto; Satoh, Kotaro; Xu, Jiangtao

    2016-01-01

    Recent developments in polymerization reactions utilizing thiocarbonylthio compounds have highlighted the surprising versatility of these unique molecules. The increasing popularity of reversible addition–fragmentation chain transfer (RAFT) radical polymerization as a means of producing well‐defined, ‘controlled’ synthetic polymers is largely due to its simplicity of implementation and the availability of a wide range of compatible reagents. However, novel modes of thiocarbonylthio activation can expand the technique beyond the traditional system (i.e., employing a free radical initiator) pushing the applicability and use of thiocarbonylthio compounds even further than previously assumed. The primary advances seen in recent years are a revival in the direct photoactivation of thiocarbonylthio compounds, their activation via photoredox catalysis, and their use in cationic polymerizations. These synthetic approaches and their implications for the synthesis of controlled polymers represent a significant advance in polymer science, with potentially unforeseen benefits and possibilities for further developments still ahead. This Research News aims to highlight key works in this area while also clarifying the differences and similarities of each system. PMID:27711266

  2. STIR: Redox-Switchable Olefin Polymerization Catalysis: Electronically Tunable Ligands for Controlled Polymer Synthesis

    DTIC Science & Technology

    2013-03-28

    REPORT Final Report: STIR: Redox-Switchable Olefin Polymerization Catalysis : Electronically Tunable Ligands for Controlled Polymer Synthesis 14...2211 15. SUBJECT TERMS Catalysis , Redox-Switchable, Polymerization, Polyolefins Brian K. Long University of Tennessee at Knoxville Office of Research...Polymerization Catalysis : Electronically Tunable Ligands for Controlled Polymer Synthesis Report Title ABSTRACT Olefin polymerization catalysts containing

  3. A new approach to network heterogeneity: Polymerization Induced Phase Separation in photo-initiated, free-radical methacrylic systems

    PubMed Central

    Szczepanski, Caroline R.; Pfeifer, Carmem S.; Stansbury, Jeffrey W.

    2012-01-01

    Non-reactive, thermoplastic prepolymers (poly- methyl, ethyl and butyl methacrylate) were added to a model homopolymer matrix composed of triethylene glycol dimethacrylate (TEGDMA) to form heterogeneous networks via polymerization induced phase separation (PIPS). PIPS creates networks with distinct phase structure that can partially compensate for volumetric shrinkage during polymerization through localized internal volume expansion. This investigation utilizes purely photo-initiated, free-radical systems, broadening the scope of applications for PIPS since these processing conditions have not been studied previously. The introduction of prepolymer into TEGDMA monomer resulted in stable, homogeneous monomer formulations, most of which underwent PIPS upon photo-irradiation, creating heterogeneous networks. During polymerization the presence of prepolymer enhanced autoacceleration, allowing for a more extensive ambient cure of the material. Phase separation, as characterized by dynamic changes in sample turbidity, was monitored simultaneously with monomer conversion and either preceded or was coincident with network gelation. Dynamic mechanical analysis shows a broadening of the tan delta peak and secondary peak formation, characteristic of phase-separated materials, indicating one phase rich in prepolymer and another depleted form upon phase separation. In certain cases, PIPS leads to an enhanced physical reduction of volumetric shrinkage, which is attractive for many applications including dental composite materials. PMID:23109733

  4. A new approach to network heterogeneity: Polymerization Induced Phase Separation in photo-initiated, free-radical methacrylic systems.

    PubMed

    Szczepanski, Caroline R; Pfeifer, Carmem S; Stansbury, Jeffrey W

    2012-09-28

    Non-reactive, thermoplastic prepolymers (poly- methyl, ethyl and butyl methacrylate) were added to a model homopolymer matrix composed of triethylene glycol dimethacrylate (TEGDMA) to form heterogeneous networks via polymerization induced phase separation (PIPS). PIPS creates networks with distinct phase structure that can partially compensate for volumetric shrinkage during polymerization through localized internal volume expansion. This investigation utilizes purely photo-initiated, free-radical systems, broadening the scope of applications for PIPS since these processing conditions have not been studied previously.The introduction of prepolymer into TEGDMA monomer resulted in stable, homogeneous monomer formulations, most of which underwent PIPS upon photo-irradiation, creating heterogeneous networks. During polymerization the presence of prepolymer enhanced autoacceleration, allowing for a more extensive ambient cure of the material. Phase separation, as characterized by dynamic changes in sample turbidity, was monitored simultaneously with monomer conversion and either preceded or was coincident with network gelation. Dynamic mechanical analysis shows a broadening of the tan delta peak and secondary peak formation, characteristic of phase-separated materials, indicating one phase rich in prepolymer and another depleted form upon phase separation. In certain cases, PIPS leads to an enhanced physical reduction of volumetric shrinkage, which is attractive for many applications including dental composite materials.

  5. A review of our development of dental adhesives--effects of radical polymerization initiators and adhesive monomers on adhesion.

    PubMed

    Ikemura, Kunio; Endo, Takeshi

    2010-03-01

    This paper reviews the development of dental adhesives by collating information of related studies from original scientific papers, reviews, and patent literatures. Through our development, novel radical polymerization initiators, adhesive monomers, and microcapsules were synthesized, and their effects on adhesion were investigated. It was found that 5-monosubstituted barbituric acid (5-MSBA)-containing ternary initiators in conjunction with adhesive monomers contributed to effective adhesion with good polymerization reactivity. Several kinds of novel adhesive monomers bearing carboxyl group, phosphonic acid group or sulfur-containing group were synthesized, and investigated their multi-purpose bonding functions. It was suggested that the flexible methylene chain in the structure of adhesive monomers played a pivotal role in their enhanced bonding durability. It was found that the combination of acidic monomers with sulfur-containing monomer markedly improved adhesion to enamel, dentin, porcelain, alumina, zirconia, non-precious metals and precious metals. A new poly(methyl methacrylate) (PMMA)-type adhesive resin comprising microencapsulated polymerization initiators was also found to exhibit both good formulation stability and excellent adhesive property.

  6. Preparation of a novel polymer monolith with functional polymer brushes by two-step atom-transfer radical polymerization for trypsin immobilization.

    PubMed

    Li, Nan; Zheng, Wei; Shen, Ying; Qi, Li; Li, Yaping; Qiao, Juan; Wang, Fuyi; Chen, Yi

    2014-12-01

    Novel porous polymer monoliths grafted with poly{oligo[(ethylene glycol) methacrylate]-co-glycidyl methacrylate} brushes were fabricated via two-step atom-transfer radical polymerization and used as a trypsin-based reactor in a continuous flow system. This is the first time that atom-transfer radical polymerization technique was utilized to design and construct polymer monolith bioreactor. The prepared monoliths possessed excellent permeability, providing fast mass transfer for enzymatic reaction. More importantly, surface properties, which were modulated via surface-initiated atom-transfer radical polymerization, were found to have a great effect on bioreactor activities based on Michaelis-Menten studies. Furthermore, three model proteins were digested by the monolith bioreactor to a larger degree within dramatically reduced time (50 s), about 900 times faster than that by free trypsin (12 h). The proposed method provided a platform to prepare porous monoliths with desired surface properties for immobilizing various enzymes.

  7. Using Living Radical Polymerization to Enable Facile Incorporation of Materials in Microfluidic Cell Culture Devices

    PubMed Central

    Simms, Helen M.; Bowman, Christopher M.; Anseth, Kristi S.

    2008-01-01

    High throughput screening tools are expediting cell culture studies with applications in drug discovery and tissue engineering. This contribution demonstrates a method to incorporate 3D cell culture sites into microfluidic devices and enables the fabrication of high throughput screening tools with uniquely addressable culture environments. Contact Lithographic Photopolymerization (CLiPP) was used to fabricate microfluidic devices with two types of 3D culture sites: macroporous rigid polymer cell scaffolds and poly(ethylene glycol) (PEG) encapsulated cell matrices. Cells were cultured on-device with both types of culture sites, demonstrating material cytocompatibility. Multilayer microfluidic devices were fabricated with channels passing the top and bottom sides of a series of rigid porous polymer scaffolds. Cells were seeded and cultured on-device, demonstrating the ability to deliver cells and culture cells on multiple scaffolds along the length of a single channel. Flow control through these rigid porous polymer scaffolds was demonstrated. Finally, devices were modified by grafting of PEG methacrylate from surfaces to prevent non-specific protein adsorption and ultimately cell adhesion to channel surfaces. The living radical component of this CLiPP device fabrication platform enables facile incorporation of 3D culture sites into microfluidic cell culture devices, which can be utilized for high throughput screening of cell material interactions. PMID:18294686

  8. Insights into relevant mechanistic aspects about the induction period of Cu(0)/Me(6)TREN-mediated reversible-deactivation radical polymerization.

    PubMed

    Gao, Yongsheng; Zhao, Tianyu; Zhou, Dezhong; Greiser, Udo; Wang, Wenxin

    2015-10-04

    There is a controversial debate about the mechanism of the Cu(0)-catalyzed radical polymerization. Herein, a comparative analysis of a series of reactions catalyzed by different valent copper shows that the induction period and the subsequent autoaccelerated polymerization of a Cu(0)/Me6TREN-catalyzed system originate from the accumulation of soluble copper species, and Cu(I) is still a powerful activator under its disproportionation favored conditions.

  9. Cyclic Multiblock Copolymers via Combination of Iterative Cu(0)-Mediated Radical Polymerization and Cu(I)-Catalyzed Azide-Alkyne Cycloaddition Reaction.

    PubMed

    Xiao, Lifen; Zhu, Wen; Chen, Jiqiang; Zhang, Ke

    2017-02-01

    Cyclic multiblock polymers with high-order blocks are synthesized via the combination of single-electron transfer living radical polymerization (SET-LRP) and copper-catalyzed azide-alkyne cycloaddition (CuAAC). The linear α,ω-telechelic multiblock copolymer is prepared via SET-LRP by sequential addition of different monomers. The SET-LRP approach allows well control of the block length and sequence as A-B-C-D-E, etc. The CuAAC is then performed to intramolecularly couple the azide and alkyne end groups of the linear copolymer and produce the corresponding cyclic copolymer. The block sequence and the cyclic topology of the resultant cyclic copolymer are confirmed by the characterization of (1) H nuclear magnetic resonance spectroscopy, gel permeation chromatography, Fourier transform infrared spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

  10. Synthesis and characterization of TiO2/poly(methyl methacrylate) nanocomposites via surface thiol-lactam initiated radical polymerization.

    PubMed

    Bach, Long Giang; Islam, M Rafiqul; Gal, Yeong Soon; Lim, Kwon Taek

    2012-07-01

    An approach to the surface modification of TiO2 nanoparticles was described based on the thiol functionalization of TiO2 followed by thiol-lactam initiated radical polymerization (TLIRP) of methyl methacrylate (MMA). FT-IR, XRD and XPS analyses confirmed the grafting of the polymer on the TiO2 surface. TGA analysis revealed superior thermal stability of PMMA-g-TiO2 compared with PMMA. TEM measurements and time-dependent phase monitoring suggested much higher colloidal stability of PMMA-g-TiO2 than TiO2 in toluene. The controlled nature of the TLIRP of MMA from the surface of TiO2 was determined by GPC analysis.

  11. Surface modification of dense membranes using radical graft polymerization enhanced by monomer filtration.

    PubMed

    Bernstein, Roy; Belfer, Sofia; Freger, Viatcheslav

    2010-07-20

    Surface graft polymerization is a promising way to modify membranes for improved performance. Redox-initiated graft polymerization of vinyl monomers is a facile and inexpensive method carried out at room temperature in aqueous media; however, its use is often limited by slow kinetics, low surface specificity, and excessive consumption of chemicals on undesired homopolymerization. It is shown that in the case of RO or NF membranes these drawbacks may be eliminated by utilizing the selectivity of the membranes toward monomers and carrying out the polymerization while applying pressure, i.e., under filtration conditions. Concentration polarization that ensues raises the concentration of reagents near the membrane surface and thereby drastically increases the rate of reaction and preferentially directs it towards surface grafting. Grafting experiments using 2-hydroxyethyl methacrylate and other monomers and characterization of modified membranes using permeability measurements, ATR-FTIR, AFM, XPS, and contact angle demonstrate that the required monomer concentrations can be drastically reduced, particularly when a small fraction of a cross-linker is added. As an additional benefit, this approach enables broadening the spectrum of utilizable monomers to sparingly soluble hydrophobic, charged, and macro-monomers, as was demonstrated using sparingly soluble ethyl methacrylate and 2-ethoxyethyl methacrylate and other monomers. Even though the kinetics of the process is substantially complicated by evolution and concentration polarization of oligomeric and polymeric species, especially in the presence of a cross-linker, it is well offset by the benefits of higher rate, specificity, and reduced monomer consumption.

  12. Functional Degradable Polymers by Radical Ring-Opening Copolymerization of MDO and Vinyl Bromobutanoate: Synthesis, Degradability and Post-Polymerization Modification.

    PubMed

    Hedir, Guillaume G; Bell, Craig A; O'Reilly, Rachel K; Dove, Andrew P

    2015-07-13

    The synthesis of vinyl bromobutanoate (VBr), a new vinyl acetate monomer derivative obtained by the palladium-catalyzed vinyl exchange reaction between vinyl acetate (VAc) and 4-bromobutyric acid is reported. The homopolymerization of this new monomer using the RAFT/MADIX polymerization technique leads to the formation of novel well-defined and controlled polymers containing pendent bromine functional groups able to be modified via postpolymerization modification. Furthermore, the copolymerization of vinyl bromobutanoate with 2-methylene-1,3-dioxepane (MDO) was also performed to deliver a range of novel functional degradable copolymers, poly(MDO-co-VBr). The copolymer composition was shown to be able to be tuned to vary the amount of ester repeat units in the polymer backbone, and hence determine the degradability, while maintaining a control of the final copolymers' molar masses. The addition of functionalities via simple postpolymerization modifications such as azidation and the 1,3-dipolar cycloaddition of a PEG alkyne to an azide is also reported and proven by (1)H NMR spectroscopy, FTIR spectroscopy, and SEC analyses. These studies enable the formation of a novel class of hydrophilic functional degradable copolymers using versatile radical polymerization methods.

  13. Surface grafting of Eu(3+) doped luminescent hydroxyapatite nanomaterials through metal free light initiated atom transfer radical polymerization for theranostic applications.

    PubMed

    Zeng, Guangjian; Liu, Meiying; Jiang, Ruming; Heng, Chunning; Huang, Qiang; Mao, Liucheng; Hui, Junfeng; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2017-08-01

    We reported a simple and efficient method to prepare the hydrophilic luminescent HAp polymer nanocomposites through the combination of ligand exchange and metal free light initiated surface-initiated atom transfer radical polymerization (SI-ATRP) using 10-phenylphenothiazine (PTH) as organic catalyst and 2-methacryloyloxyethyl phosphorylcholine (MPC) and itaconic acid (IA) as monomers. The biological imaging and drug delivery performance of HAp-poly(MPC-IA) nanorods were examined to evaluate their potential for biomedical applications. Results suggested that hydrophilic HAp-poly(MPC-IA) nanorods can be successfully prepared. More importantly, the HAp-poly(MPC-IA) exhibited excellent water dispersibility, desirable biocompatibility and good performance for biological imaging and controlled drug delivery applications. As compared with other controlled living polymerization reactions, the metal free light initiated SI-ATRP displayed many advantages such as easy for handle, mild reaction conditions, toxicity and fluorescence quenching from metal catalysts. Therefore, we believe that this strategy should be a useful and effective strategy for preparation of HAp nanomaterials for biomedical applications. Copyright © 2017 Elsevier B.V. All rights reserved.

  14. Thermally-initiated free radical polymerization for reproducible production of stable linear polyacrylamide coated capillaries, and their application to proteomic analysis using capillary zone electrophoresis-mass spectrometry.

    PubMed

    Zhu, Guijie; Sun, Liangliang; Dovichi, Norman J

    2016-01-01

    Proteomic analysis using capillary zone electrophoresis (CZE) typically is performed with linear polyacrylamide (LPA) coated capillaries. These capillaries both minimize the adsorption of peptides and proteins to the inner wall of the capillary and decrease electroosmosis, which increases the separation capacity. LPA coating protocols were first reported by Hjerten in 1985. Conventional LPA production is based on the use of tetramethylethylenediamine (TEMED) to catalyze the free-radical polymerization that couples acrylamide to a capillary wall that has been pretreated with γ-methacryloxypropyltrimethoxysilane. The treated capillary is filled with a mixture of monomer, TEMED, and ammonium persulfate; free radical polymerization forms the LPA coating. Over many years, we have observed significant variation in the electroosmotic properties of commercial LPA coated capillaries both along the capillary length and between lots. We believe this variation is due to differences in the time between initiation of the reaction and the filling of the capillary. Here, we report a simple method for the generation of very stable and reproducible coatings. In this protocol, the monomer mixture and an ammonium persulfate initiator are introduced into the capillary without TEMED initiator. The mixture is stable and does not begin polymerization at room temperature. The filled capillary is then heated in a water bath to initiate polymerization in a well-controlled manner. A mixture of four standard proteins was used to evaluate the coating performance. Compared with commercialized LPA capillaries, our LPA capillaries generate much better separation performance and superior protein peak shape in CZE analysis. We also analyzed an intact antibody (MW 150K) by CZE-MS with the new LPA capillary in triplicate runs. The intact antibody generated a Gaussian-shaped electrophoresis peak with 1.2% relative standard deviation in migration time and 8.5% in base peak intensity. An automated CZE

  15. Thermal Polymerization of Styrene in the Presence of Stable Radicals and Inhibitors

    DTIC Science & Technology

    1994-06-30

    35(1), 778 (1994) Carnegie Mellon University Department of Chemistry D TlC 4400 Fifth Avenue /,D T IC Pittsburgh, PA 15213 f ELECTE’ ’JUN "’k IW41 June...Nitroxyl radicals (like TEMPO) give the best results. Acknowledgments However a classic picryl hydrazyl radical ( DPPH ), acts in a similar way. Galvinoxyl...4.367 1.31 78 irntidazolfintiuans-lI-yloxy miethyl sulfate DPPH 3,444 1.76 36 ______________ Galvinoxyl 43,157 1.5 57 Classic inhibitors based on the

  16. A Visible Light Initiating System for Free Radical Promoted Cationic Polymerization

    DTIC Science & Technology

    1994-02-02

    bis-(4, 4’-dimethylaminoihenyl)methane as the main product and crystal violet, methyl violet, as well as the leuco rorms of these dyes as minor...cation in chain polymerization is reported. The system is based on electron transfer photoreduction of xanthene dye triplets by aromatic amines...Previously, Crivello and Lam 9 had reported attempts to use visible light absorbing dyes to sensitize the decomposition of iodonium salts to initiate

  17. Radical graft polymerization of an Allyl Monomer onto Hydrophilic Polymers and their antibacterial nanofibrous membranes

    USDA-ARS?s Scientific Manuscript database

    Hydrophilic poly (vinyl alcohol-co-ethylene) (PVA-co-PE) copolymers with 27 mol %, 32 mol % and 44 mol % ethylene were functionalized by melt radical graft copolymerization with 2,4-diamino-6-diallylamino-1,3,5-triazine (NDAM) using reactive extrusion. This functionalization imparts antibacterial pr...

  18. Degradable and comb-like PEG-based copolymers by nitroxide-mediated radical ring-opening polymerization.

    PubMed

    Delplace, Vianney; Tardy, Antoine; Harrisson, Simon; Mura, Simona; Gigmes, Didier; Guillaneuf, Yohann; Nicolas, Julien

    2013-10-14

    Three cyclic ketene acetals, 2-methylene-1,3-dioxepane (MDO), 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), and 2-methylene-4-phenyl-1,3-dioxolane (MPDL), have been copolymerized with oligo(ethylene glycol) methyl ether methacrylate and a small amount of acrylonitrile (or styrene) at 90 °C by nitroxidemediated radical ring-opening polymerization, as a convenient way to prepare degradable PEG-based copolymers for biomedical applications. MPDL was the best candidate, enabling high monomer conversions to be reached and well-defined PEG-based copolymers with adjustable amount of ester groups in the main chain to be synthesized, leading to nearly complete hydrolytic degradation (5% KOH aqueous solution, ambient temperature). The noncytotoxicity of the obtained copolymers was shown on three different cell lines (i.e., fibroblasts, endothelial cells and macrophages), representing a promising approach for the design of degradable precursors for PEGylation and bioconjugation via the NMP technique.

  19. Crystalline TiO 2 grafted with poly(2-methacryloyloxyethyl phosphorylcholine) via surface-initiated atom-transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Zhao, Yuancong; Tu, Qiufen; Wang, Jin; Huang, Qiongjian; Huang, Nan

    2010-12-01

    Crystalline TiO 2 films were prepared by unbalanced magnetron sputtering and the structure was confirmed by XRD. An organic layer of 11-hydroxyundecylphosphonic acid (HUPA) was prepared on the TiO 2 films by self-assembling, and the HUPA on TiO 2 films was confirmed by FTIR analysis. Simultaneously, hydroxyl groups were introduced in the phosphonic acid molecules to provide a functionality for further chemical modification. 2-Methacryloyloxyethyl phosphorylcholine (MPC), a biomimetic monomer, was chemically grafted on the HUPA surfaces at room temperature by surface-initiated atom-transfer radical polymerization. The surface characters of TiO 2 films modified by poly-MPC were confirmed by FTIR, XPS and SEM analysis. Platelet adhesion experiment revealed that poly-MPC modified surface was effective to inhibit platelet adhesion in vitro.

  20. Highly selective capture of nucleosides with boronic acid functionalized polymer brushes prepared by atom transfer radical polymerization.

    PubMed

    Cheng, Ting; Zhu, Shuqiang; Zhu, Bin; Liu, Xiaoyan; Zhang, Haixia

    2016-04-01

    The nucleoside or modified nucleoside level in biological fluids reflects the pathological or physiological state of the body. Boronate affinity absorbents are widely used to selectively extract nucleosides from complex samples. In this work, a novel functionalized absorbent was synthesized by attaching 4-mercaptophenylboronic acid to gold nanoparticles on modified attapulgite. The surface of the attapulgite was modified by poly(acryloyloxyethyltrimethyl ammonium chloride) by atom transfer radical polymerization, creating many polymer brushes on the surface. The resultant material exhibited superior binding capacity (30.83 mg/g) for adenosine and was able to capture cis-diol nucleosides from 1000-fold interferences. Finally, to demonstrate its potential for biomolecule extraction, this boronate affinity material was used to preconcentrate nucleosides from human urine and plasma. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. First multi-reactive dextran-based inisurf for atom transfer radical polymerization in miniemulsion.

    PubMed

    Wu, Man; Forero Ramirez, Laura M; Rodriguez Lozano, Ana; Quémener, Damien; Babin, Jérôme; Durand, Alain; Marie, Emmanuelle; Six, Jean-Luc; Nouvel, Cécile

    2015-10-05

    A multi-reactive polysaccharide-based inisurf (acting both as initiator and stabilizer) has been designed for the first time from dextran with the aim of preparing dextran-covered nanoparticles with covalent linkage between core and coverage. This inisurf was used for polymerizing butyl acrylate in miniemulsion by AGET-ATRP. Both hydrophobic phenoxy groups and initiator groups (bromoisobutyryl ester) were introduced within hydrophilic dextran chain, conferring it amphiphilic and macroinitiator characters. Amphiphilic properties of dextran inisurfs have been evidenced as well as their ability to stabilize the direct miniemulsion of n-butyl acrylate. After optimization of polymerization conditions with model studies, assays were successfully realized with dextran-based inisurfs. Because of their amphiphilic character, inisurfs migrated at oil/water interface and initiated polymerization from bromoisobutyryl ester groups. Therefore graft copolymers were produced at oil/water interface, due to the multifunctional character of these inisurfs and constituted the particle inner core with covalent links to the dextran coverage.

  2. Peculiar aspects of the free-radical polymerization of 1-vinylimidazole

    NASA Astrophysics Data System (ADS)

    Chapiro, Adolphe

    The polymerization of 1-vinylimidazole (VI) exhibits several unusual features. The reaction is auto-accelerated in bulk and in solution, an observation attributed to a "matrix" effect. Abnormal orders are found with respect to monomer concentration and to rate of initiation and these are dependent on the monomer content in the reaction mixture. Molecular monomer-monomer and monomer-solvent associations were characterized in these systems, suggesting a gradual change in the reactivity of the monomer upon dilution. A cross-linked gel arises in systems which generate a concentrated polymer solution in the monomer. It is assumed that growing polymer chains can add onto double bonds of the imidazole rings in the polymer but this reaction is slow and only occurs significantly under the conditions stated above. A complicated process takes place when benzoyl peroxide is used to initiate the reaction. A rapid polymerization takes place at very low temperatures leading to low molecular weight polymers and to other addition products. G(R rad ) values were derived from experiments with gamma-ray initiation by combining polymerization rate and molecular weight data. The estimated value for pure VI is G(R rad )=2.2. The monomer was found to "protect" water and methanol in their radiolysis, being itself "sensitized" by CCL 4.

  3. Atom transfer radical polymerization to fabricate monodisperse poly[glycidyl methacrylate-co-poly (ethylene glycol) methacrylate] microspheres and its application for protein affinity purification.

    PubMed

    Yu, Ling; Shi, Zhuan Zhuan; Li, Chang Ming

    2015-09-01

    Poly[glycidyl methacrylate-co-poly (ethylene glycol) methacrylate] microspheres for the first time were successfully synthesized by atom transfer radical polymerization (ATRP) method at room temperature. The co-polymerization approach was investigated to delicately control the microsphere morphology and size-distribution by reaction conditions including solvent percentage, monomer loading and rotation speed. The results show that the average size of the microspheres is ∼5.7 μm with coexistence of epoxy, hydroxyl and ether groups, which provide plentiful functional sites for protein anchoring. The mechanism of the microsphere formation is proposed. The microsphere successfully demonstrates its unique application for affinity purification of proteins, in which the functional epoxy group facilitates a simple and efficient protein covalent immobilization to purify immunoglobulin G on the microspheres, while the hydrophilic poly (ethylene glycol) motif can repulse nonspecific protein adsorption for good specificity. This microspheres can be used in broad protein biosensors due to their abundant functional groups and high surface to volume ratio.

  4. Fuzzy ternary particle systems by surface-initiated atom transfer radical polymerization from layer-by-layer colloidal core-shell macroinitiator particles.

    PubMed

    Fulghum, Timothy M; Patton, Derek L; Advincula, Rigoberto C

    2006-09-26

    We report the synthesis of ternary polymer particle material systems composed of (a) a spherical colloidal particle core, coated with (b) a polyelectrolyte intermediate shell, and followed by (c) a grafted polymer brush prepared by surface-initiated polymerization as the outer shell. The layer-by-layer (LbL) deposition process was utilized to create a functional intermediate shell of poly(diallyl-dimethylammonium chloride)/poly(acrylic acid) multilayers on the colloid template with the final layer containing an atom transfer radical polymerization (ATRP) macroinitiator polyelectrolyte. The intermediate core-shell architecture was analyzed with FT-IR, electrophoretic mobililty (zeta-potential) measurements, atomic force microscopy, and transmission electron microscopy (TEM) techniques. The particles were then utilized as macroinitiators for the surface-initiated ATRP grafting process for poly(methyl methacrylate) polymer brush. The polymer grafting was confirmed with thermo gravimetric analysis, FT-IR, and TEM. The polymer brush formed the outermost shell for a ternary colloidal particle system. By combining the LbL and surface-initiated ATRP methods to produce controllable multidomain core-shell architectures, interesting functional properties should be obtainable based on independent polyelectrolyte and polymer brush behavior.

  5. Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization from Chlorinated Polypropylene and Polyethylene Trunk Fibers

    DOE PAGES

    Brown, Suree; Chatterjee, Sabornie; Li, Meijun; ...

    2015-12-10

    Seawater contains a large amount of uranium (~4.5 billion tons) which can serve as a limitless supply of an energy source. However, in order to make the recovery of uranium from seawater economically feasible, lower manufacturing and deployment costs are required, and thus, solid adsorbents must have high uranium uptake, reusability, and high selectivity toward uranium. In this study, atom-transfer radical polymerization (ATRP), without the radiation-induced graft polymerization (RIGP), was used for grafting acrylonitrile (AN) and tert-butyl acrylate (tBA) from a new class of trunk fibers, forming adsorbents in a readily deployable form. The new class of trunk fibers wasmore » prepared by the chlorination of PP round fiber, hollow-gear-shaped PP fiber, and hollow-gear-shaped PE fiber. During ATRP, degrees of grafting (d.g.) varied according to the structure of active chlorine sites on trunk fibers and ATRP conditions, and the d.g. as high as 2570% was obtained. Resulting adsorbent fibers were evaluated in U-spiked simulated seawater and the maximum adsorption capacity of 146.6 g U/kg, much higher than that of a standard adsorbent JAEA fiber (75.1 g/kg), was obtained. This new type of trunk fibers can be used for grafting a variety of uranium-interacting ligands, including designed ligands that are highly selective toward uranium.« less

  6. Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization from Chlorinated Polypropylene and Polyethylene Trunk Fibers

    SciTech Connect

    Brown, Suree; Chatterjee, Sabornie; Li, Meijun; Yue, Yanfeng; Tsouris, Costas; Janke, Christopher J.; Saito, Tomonori; Dai, Sheng

    2015-12-10

    Seawater contains a large amount of uranium (~4.5 billion tons) which can serve as a limitless supply of an energy source. However, in order to make the recovery of uranium from seawater economically feasible, lower manufacturing and deployment costs are required, and thus, solid adsorbents must have high uranium uptake, reusability, and high selectivity toward uranium. In this study, atom-transfer radical polymerization (ATRP), without the radiation-induced graft polymerization (RIGP), was used for grafting acrylonitrile (AN) and tert-butyl acrylate (tBA) from a new class of trunk fibers, forming adsorbents in a readily deployable form. The new class of trunk fibers was prepared by the chlorination of PP round fiber, hollow-gear-shaped PP fiber, and hollow-gear-shaped PE fiber. During ATRP, degrees of grafting (d.g.) varied according to the structure of active chlorine sites on trunk fibers and ATRP conditions, and the d.g. as high as 2570% was obtained. Resulting adsorbent fibers were evaluated in U-spiked simulated seawater and the maximum adsorption capacity of 146.6 g U/kg, much higher than that of a standard adsorbent JAEA fiber (75.1 g/kg), was obtained. This new type of trunk fibers can be used for grafting a variety of uranium-interacting ligands, including designed ligands that are highly selective toward uranium.

  7. Reverse atom transfer radical polymerization (RATRP) for anti-clotting PU-LaCl3-g-P(MPC) films

    NASA Astrophysics Data System (ADS)

    Lu, Chunyan; Zhou, Ninglin; Xiao, Yinghong; Tang, Yida; Jin, Suxing; Wu, Yue; Shen, Jian

    2013-01-01

    Low grafting density is a disadvantage both in reverse atom transfer radical polymerization (RATRP) and ATRP. In this work, the surfaces of polyurethane (PU) were treated by LaCl3·6H2O to obtain modified surfaces with hydrated layers. The reaction of surface-initiated RATRP was carried out easily, which may be attributed to the enriched hydroxyl groups on the hydrated layers. An innovation found in this work is that some free lanthanum ions (La3+) reacted with the silane coupling agent (CPTM) and the product served as mixed ligand complex. The mixed ligand complex instead of conventional 2,2‧-bipyridine was adopted to serve as a ligand in the process of RATRP. As a result, PU surfaces grafted with well-defined polymer brushes (MPC) were obtained. PU substrates before and after modification were characterized by FTIR, XPS, AFM, SEM, SCA, respectively. The results showed that zwitterionic brushes were successfully fabricated on the PU surfaces (P(MPC)), and the content of the grafted layer increased gradually with polymerization time with the grafting density as high as 97.9%. The blood compatibility of the PU substrates was evaluated by plasma recalcification profiles test and platelet adhesion tests in vitro. It was found that all PU functionalized with zwitterionic brush showed improved resistance to nonspecific protein adsorption and platelet adhesion.

  8. Effect of Surface Charge on Surface-Initiated Atom Transfer Radical Polymerization from Cellulose Nanocrystals in Aqueous Media.

    PubMed

    Zoppe, Justin O; Xu, Xingyu; Känel, Cindy; Orsolini, Paola; Siqueira, Gilberto; Tingaut, Philippe; Zimmermann, Tanja; Klok, Harm-Anton

    2016-04-11

    Cellulose nanocrystals (CNCs) with different charge densities were utilized to examine the role of electrostatic interactions on surface-initiated atom transfer radical polymerization (SI-ATRP) in aqueous media. To this end, growth of hydrophilic uncharged poly(N,N-dimethylacrylamide) (PDMAM) brushes was monitored by electrophoresis, (1)H NMR spectroscopy, and dynamic light scattering (DLS). Molecular weight and polydispersity of PDMAM brushes was determined by GPC analysis of hydrolytically cleaved polymers. Initiator and polymer brush grafting densities, and thus, initiator efficiencies were derived from elemental analysis. Higher initiator efficiency of polymer brush growth was observed for CNCs with higher anionic surface sulfate half-ester group density, but at the expense of high polydispersity caused by inefficient deactivation. PDMAM grafts with number-average molecular weights up to 530 kDa and polydispersity indices <1.5 were obtained under highly diluted monomer concentrations. The role of surface chemistry on the growth of neutral polymer brushes from CNCs in water is emphasized and a model of the interfacial region at the onset of polymerization is proposed. The results presented here could have implications for other substrates that present surface charges and for the assumption that the kinetics of Cu-mediated SI-CRP are analogous to those conducted in solution.

  9. PREPARATION OF BLOCK COPOLYMERS OF POLY(STYRENE) AND POLY(T-BUTYL ACRYLATE) OF VARIOUS MOLECULAR WEIGHTS AND ARCHITECTURES BY ATOM TRANSFER RADICAL POLYMERIZATION. (R826735)

    EPA Science Inventory

    Block copolymers of polystyrene and poly(t-butyl acrylate) were prepared using atom transfer radical polymerization techniques. These polymers were synthesized with a CuBr/N,N,N,NPREPARATION OF BLOCK COPOLYMERS OF POLY(STYRENE) AND POLY(T-BUTYL ACRYLATE) OF VARIOUS MOLECULAR WEIGHTS AND ARCHITECTURES BY ATOM TRANSFER RADICAL POLYMERIZATION. (R826735)

    EPA Science Inventory

    Block copolymers of polystyrene and poly(t-butyl acrylate) were prepared using atom transfer radical polymerization techniques. These polymers were synthesized with a CuBr/N,N,N,NFree Radical Addition Polymerization Kinetics without Steady-State Approximations: A Numerical Analysis for the Polymer, Physical, or Advanced Organic Chemistry Course

    ERIC Educational Resources Information Center

    Iler, H. Darrell; Brown, Amber; Landis, Amanda; Schimke, Greg; Peters, George

    2014-01-01

    A numerical analysis of the free radical addition polymerization system is described that provides those teaching polymer, physical, or advanced organic chemistry courses the opportunity to introduce students to numerical methods in the context of a simple but mathematically stiff chemical kinetic system. Numerical analysis can lead students to an…

  10. Free Radical Addition Polymerization Kinetics without Steady-State Approximations: A Numerical Analysis for the Polymer, Physical, or Advanced Organic Chemistry Course

    ERIC Educational Resources Information Center

    Iler, H. Darrell; Brown, Amber; Landis, Amanda; Schimke, Greg; Peters, George

    2014-01-01

    A numerical analysis of the free radical addition polymerization system is described that provides those teaching polymer, physical, or advanced organic chemistry courses the opportunity to introduce students to numerical methods in the context of a simple but mathematically stiff chemical kinetic system. Numerical analysis can lead students to an…

  11. Skylab D024 thermal control coatings and polymeric films experiment

    NASA Technical Reports Server (NTRS)

    Lehn, William L.; Hurley, Charles J.

    1992-01-01

    The Skylab D024 Thermal Control Coatings and Polymeric Films Experiment was designed to determine the effects of the external Skylab space environment on the performance and properties of a wide variety of selected thermal control coatings and polymeric films. Three duplicate sets of thermal control coatings and polymeric films were exposed to the Skylab space environment for varying periods of time during the mission. The specimens were retrieved by the astronauts during extravehicular activities (EVA) and placed in hermetically sealed return containers, recovered, and returned to the Wright Laboratory/Materials Laboratory/WPAFB, Ohio for analysis and evaluation. Postflight analysis of the three sets of recovered thermal control coatings indicated that measured changes in specimen thermo-optical properties were due to a combination of excessive contamination and solar degradation of the contaminant layer. The degree of degradation experienced over-rode, obscured, and compromised the measurement of the degradation of the substrate coatings themselves. Results of the analysis of the effects of exposure on the polymeric films and the contamination observed are also presented. The D024 results were used in the design of the LDEF M0003-5 Thermal Control Materials Experiment. The results are presented here to call to the attention of the many other LDEF experimenters the wealth of directly related, low earth orbit, space environmental exposure data that is available from the ten or more separate experiments that were conducted during the Skylab mission. Results of these experiments offer data on the results of low altitude space exposure on materials recovered from space with exposure longer than typical STS experiments for comparison with the LDEF results.

  12. Preparation of a thick polymer brush layer composed of poly(2-methacryloyloxyethyl phosphorylcholine) by surface-initiated atom transfer radical polymerization and analysis of protein adsorption resistance.

    PubMed

    Inoue, Yuuki; Onodera, Yuya; Ishihara, Kazuhiko

    2016-05-01

    The purpose of this study was to prepare a thick polymer brush layer composed of poly(2-methacryloyloxyethyl phosphorylcholine (MPC)) and assess its resistance to protein adsorption from the dissolved state of poly(MPC) chains in an aqueous condition. The thick poly(MPC) brush layer was prepared through the surface-initiated atom transfer radical polymerization (SI-ATRP) of MPC with a free initiator from an initiator-immobilized substrate at given [Monomer]/[Free initiator] ratios. The ellipsometric thickness of the poly(MPC) brush layers could be controlled by the polymerization degree of the poly(MPC) chains. The thickness of the poly(MPC) brush layer in an aqueous medium was larger than that in air, and this tendency became clearer when the polymerization degree of the poly(MPC) increased. The maximum thickness of the poly(MPC) brush layer in an aqueous medium was around 110 nm. The static air contact angle of the poly(MPC) brush layer in water indicated a reasonably hydrophilic nature, which was independent of the thickness of the poly(MPC) brush layer at the surface. This result occurred because the hydrated state of the poly(MPC) chains is not influenced by the environment surrounding them. Finally, as measured with a quartz crystal microbalance, the amount of protein adsorbed from a fetal bovine serum solution (10% in phosphate-buffered saline) on the original substrate was 420 ng/cm(2). However, the poly(MPC) brush layer reduced this value dramatically to less than 50 ng/cm(2). This effect was independent of the thickness of the poly(MPC) brush layer for thicknesses between 20 nm and about 110 nm. These results indicated that the surface covered with a poly(MPC) brush layer is a promising platform to avoid biofouling and could also be applied to analyze the reactions of biological molecules with a high signal/noise ratio.

  13. MAPLE deposited polymeric blends coatings for controlled drug delivery

    NASA Astrophysics Data System (ADS)

    Paun, Irina Alexandra; Ion, Valentin; Moldovan, Antoniu; Dinescu, Maria

    2012-07-01

    We report on the use of Matrix Assisted Pulsed Laser Evaporation (MAPLE) for producing coatings of polymer blends for controlled drug delivery. The coatings consisting of blends of polyethylene glycol: poly(lactide-co-glycolide) (PEG: PLGA blends) are compared with those consisting of individual polymers (PEG, PLGA) in terms of chemical composition, morphology, hydrophilicity and optical constants. The release kinetics of an anti-inflammatory drug (indomethacin) through the polymeric coatings is monitored and possible mechanisms of the drug release are discussed. Furthermore, the compatibility of the polymeric coatings with blood constituents is investigated. Finally, the perspectives for employing MAPLE for producing coatings of polymer blends to be used in implants that deliver drugs in a controlled manner, along with the routes to be followed for elucidating the mechanism of drug release, are revealed.

  14. Kinetics of a methyl methacrylate polymerization initiated by the stable free radicals in irradiated polytetrafluoroethylene and properties of the resultant graft polymer

    SciTech Connect

    Donato, K.A.E.

    1987-01-01

    The kinetics of the polymerization of methyl methacrylate (MMA) initiated by the stable free radicals in commercially available irradiated polytetrafluoroethylene micropowder and the rheological, thermal, chemical, and mechanical properties of the resultant graft polymer are described. Test tube runs using different ratios of MMA to PTFE were made to determine the feasibility of the reaction and optimum reaction conditions. The amount of graft produced was equal to the weight gain of the solids after removal of the adventitious homopolymer by extraction in acetone. Test quantities of material were produced in a 500 milliliter agitated reactor. A higher ratio of PTFE to excess MMA and longer reaction times result in higher conversion in test tubes. A kinetic model was developed to relate the original concentration of PTFE free radical to the amount of MMA polymer. Graft polymer containing PTFE micropowder, PMMA graft, and PMMA homopolymer in a ratio of 18:5:1 was used for property characterization. The graft material extrudes well at 513K and has a viscosity comparable to that of PMMA homopolymer. The material is stable upon re-extrusion. DSC thermograms show that the heat of transition of the PTFE melting peak is proportional to the amount of PTFE in the sample. Good solvents for PMMA are detrimental to the structural integrity of the graft extrudate; heat treatment improves the chemical resistance. The PTFE block controls the mechanical properties of the graft.

  15. Regiochemical control of monolignol radical coupling: a new paradigm for lignin and lignan biosynthesis

    NASA Technical Reports Server (NTRS)

    Gang, D. R.; Costa, M. A.; Fujita, M.; Dinkova-Kostova, A. T.; Wang, H. B.; Burlat, V.; Martin, W.; Sarkanen, S.; Davin, L. B.; Lewis, N. G.

    1999-01-01

    BACKGROUND: Although the lignins and lignans, both monolignol-derived coupling products, account for nearly 30% of the organic carbon circulating in the biosphere, the biosynthetic mechanism of their formation has been poorly understood. The prevailing view has been that lignins and lignans are produced by random free-radical polymerization and coupling, respectively. This view is challenged, mechanistically, by the recent discovery of dirigent proteins that precisely determine both the regiochemical and stereoselective outcome of monolignol radical coupling. RESULTS: To understand further the regulation and control of monolignol coupling, leading to both lignan and lignin formation, we sought to clone the first genes encoding dirigent proteins from several species. The encoding genes, described here, have no sequence homology with any other protein of known function. When expressed in a heterologous system, the recombinant protein was able to confer strict regiochemical and stereochemical control on monolignol free-radical coupling. The expression in plants of dirigent proteins and proposed dirigent protein arrays in developing xylem and in other lignified tissues indicates roles for these proteins in both lignan formation and lignification. CONCLUSIONS: The first understanding of regiochemical and stereochemical control of monolignol coupling in lignan biosynthesis has been established via the participation of a new class of dirigent proteins. Immunological studies have also implicated the involvement of potential corresponding arrays of dirigent protein sites in controlling lignin biopolymer assembly.

  16. Regiochemical control of monolignol radical coupling: a new paradigm for lignin and lignan biosynthesis

    NASA Technical Reports Server (NTRS)

    Gang, D. R.; Costa, M. A.; Fujita, M.; Dinkova-Kostova, A. T.; Wang, H. B.; Burlat, V.; Martin, W.; Sarkanen, S.; Davin, L. B.; Lewis, N. G.

    1999-01-01

    BACKGROUND: Although the lignins and lignans, both monolignol-derived coupling products, account for nearly 30% of the organic carbon circulating in the biosphere, the biosynthetic mechanism of their formation has been poorly understood. The prevailing view has been that lignins and lignans are produced by random free-radical polymerization and coupling, respectively. This view is challenged, mechanistically, by the recent discovery of dirigent proteins that precisely determine both the regiochemical and stereoselective outcome of monolignol radical coupling. RESULTS: To understand further the regulation and control of monolignol coupling, leading to both lignan and lignin formation, we sought to clone the first genes encoding dirigent proteins from several species. The encoding genes, described here, have no sequence homology with any other protein of known function. When expressed in a heterologous system, the recombinant protein was able to confer strict regiochemical and stereochemical control on monolignol free-radical coupling. The expression in plants of dirigent proteins and proposed dirigent protein arrays in developing xylem and in other lignified tissues indicates roles for these proteins in both lignan formation and lignification. CONCLUSIONS: The first understanding of regiochemical and stereochemical control of monolignol coupling in lignan biosynthesis has been established via the participation of a new class of dirigent proteins. Immunological studies have also implicated the involvement of potential corresponding arrays of dirigent protein sites in controlling lignin biopolymer assembly.

  17. Controlled release of ethylene via polymeric films for food packaging

    NASA Astrophysics Data System (ADS)

    Pisano, Roberto; Bazzano, Marco; Capozzi, Luigi Carlo; Ferri, Ada; Sangermano, Marco

    2015-12-01

    In modern fruit supply chain a common method to trigger ripening is to keep fruits inside special chambers and initiate the ripening process through administration of ethylene. Ethylene is usually administered through cylinders with inadequate control of its final concentration in the chamber. The aim of this study is the development of a new technology to accurately regulate ethylene concentration in the atmosphere where fruits are preserved: a polymeric film, containing an inclusion complex of α-cyclodextrin with ethylene, was developed. The complex was prepared by molecular encapsulation which allows the entrapment of ethylene into the cavity of α-cyclodextrin. After encapsulation, ethylene can be gradually released from the inclusion complex and its release rate can be regulated by temperature and humidity. The inclusion complex was dispersed into a thin polymeric film produced by UV-curing. This method was used because is solvent-free and involves low operating temperature; both conditions are necessary to prevent rapid release of ethylene from the film. The polymeric films were characterized with respect to thermal behaviour, crystalline structure and kinetics of ethylene release, showing that can effectively control the release of ethylene within confined volume.

  18. Reticulated Nanoporous Polymers by Controlled Polymerization-Induced Microphase Separation

    SciTech Connect

    Seo, Myungeun; Hillmyer, Marc A.

    2013-04-08

    Materials with percolating mesopores are attractive for applications such as catalysis, nanotemplating, and separations. Polymeric frameworks are particularly appealing because the chemical composition and the surface chemistry are readily tunable. We report on the preparation of robust nanoporous polymers with percolating pores in the 4- to 8-nanometer range from a microphase-separated bicontinuous precursor. We combined polymerization-induced phase separation with in situ block polymer formation from a mixture of multifunctional monomers and a chemically etchable polymer containing a terminal chain transfer agent. This marriage results in microphase separation of the mixture into continuous domains of the etchable polymer and the emergent cross-linked polymer. Precise control over pore size distribution and mechanical integrity renders these materials particularly suited for various advanced applications.

  1. Application of advanced polymeric materials for controlled release pesticides

    NASA Astrophysics Data System (ADS)

    Rahim, M.; Hakim, M. R.; Haris, H. M.

    2016-08-01

    The objective of this work was to study the capability of advanced polymeric material constituted by chitosan and natural rubber matrices for controlled release of pesticides (1-hydroxynaphthalene and 2-hydroxynaphthalene) in aqueous solution. The released amount of pesticides was measured spectrophotometrically from the absorbance spectra applying a standardized curve. The release of the pesticides was studied into refreshing and non-refreshing neutral aqueous media. Interestingly, formulation successfully indicated a consistent, controlled and prolonged release of pesticides over a period of 35 days.

  2. Biocompatible polymeric implants for controlled drug delivery produced by MAPLE

    NASA Astrophysics Data System (ADS)

    Paun, Irina Alexandra; Moldovan, Antoniu; Luculescu, Catalin Romeo; Dinescu, Maria

    2011-10-01

    Implants consisting of drug cores coated with polymeric films were developed for delivering drugs in a controlled manner. The polymeric films were produced using matrix assisted pulsed laser evaporation (MAPLE) and consist of poly(lactide-co-glycolide) (PLGA), used individually as well as blended with polyethylene glycol (PEG). Indomethacin (INC) was used as model drug. The implants were tested in vitro (i.e. in conditions similar with those encountered inside the body), for predicting their behavior after implantation at the site of action. To this end, they were immersed in physiological media (i.e. phosphate buffered saline PBS pH 7.4 and blood). At various intervals of PBS immersion (and respectively in blood), the polymeric films coating the drug cores were studied in terms of morphology, chemistry, wettability and blood compatibility. PEG:PLGA film exhibited superior properties as compared to PLGA film, the corresponding implant being thus more suitable for internal use in the human body. In addition, the implant containing PEG:PLGA film provided an efficient and sustained release of the drug. The kinetics of the drug release was consistent with a diffusion mediated mechanism (as revealed by fitting the data with Higuchi's model); the drug was gradually released through the pores formed during PBS immersion. In contrast, the implant containing PLGA film showed poor drug delivery rates and mechanical failure. In this case, fitting the data with Hixson-Crowell model indicated a release mechanism dominated by polymer erosion.

  3. REVERSIBILITY OF RADICAL-OLEFIN REACTIONS.

    DTIC Science & Technology

    ALKENES, *STYRENES, *POLYVINYL CHLORIDE, CHEMICAL EQUILIBRIUM, POLYMERIZATION, POLYMERIZATION, FREE RADICALS , MOLECULAR ISOMERISM, TRACER STUDIES, CHEMICAL REACTIONS, DECOMPOSITION, SYNTHESIS(CHEMISTRY).

  4. Radical graft polymerization of an allyl monomer onto hydrophilic polymers and their antibacterial nanofibrous membranes.

    PubMed

    Wang, Dong; Xu, Weilin; Sun, Gang; Chiou, Bor-Sen

    2011-08-01

    Hydrophilic poly (vinyl alcohol-co-ethylene) (PVA-co-PE) copolymers with 27 mol %, 32 mol % and 44 mol % ethylene were functionalized by melt radical graft copolymerization with 2,4-diamino-6-diallylamino-1,3,5-triazine (NDAM) using reactive extrusion. This functionalization imparts antibacterial properties. The covalent attachments of the NDAM as side chains onto the PVA-co-PE polymer backbones were confirmed. The effects of initiator concentrations and ethylene contents in PVA-co-PE polymers on grafting of NDAM were studied. The chain scissions of PVA-co-PE polymers during reactive extrusion were investigated by monitoring changes in the melt torque and FTIR spectra. The NDAM grafted PVA-co-PE polymers were successfully fabricated into hydrophilic nanofibers and nanofibrous membranes with sufficient surface exposure of the grafted NDAM. The hydrophilicity of the PVA-co-PE polymers and the large specific surface area offered by the nanofiber membranes significantly facilitated the chlorine activation process, enhanced the active chlorine contents of the grafted PVA-co-PE nanofiber membranes, and therefore led to their superior antibacterial properties.

  5. Three-dimensionally ordered macroporous nitroxide polymer brush electrodes prepared by surface-initiated atom transfer polymerization for organic radical batteries.

    PubMed

    Lin, Chun-Hao; Chou, Wei-Jen; Lee, Jyh-Tsung

    2012-01-01

    The synthesis and electrochemical performance of three-dimensionally ordered macroporous (3DOM) nitroxide polymer brush electrodes for organic radical batteries are reported. The 3DOM electrodes are synthesized via polystyrene colloidal crystal templating with electropolymerization of polypyrrole, modification of surface initiator, and surface-initiated atom transfer radical polymerization. The discharge capacity of the 3DOM electrodes is proportional to the thickness of the inverse opal. The discharge capacity of the 3DOM electrode at a discharge rate of 5 C is 40 times higher than that of the planar electrode; its cycle-life performance exhibits 96.1% retention after 250 cycles.

  6. In situ development of self-reinforced cellulose nanocrystals based thermoplastic elastomers by atom transfer radical polymerization.

    PubMed

    Yu, Juan; Wang, Chunpeng; Wang, Jifu; Chu, Fuxiang

    2016-05-05

    Recently, the utilization of cellulose nanocrystals (CNCs) as a reinforcing material has received a great attention due to its high elastic modulus. In this article, a novel strategy for the synthesis of self-reinforced CNCs based thermoplastic elastomers (CTPEs) is presented. CNCs were first surface functionalized with an initiator for surface-initiated atom transfer radical polymerization (SI-ATRP). Subsequently, SI-ATRP of methyl methacrylate (MMA) and butyl acrylate (BA) was carried out in the presence of sacrificial initiator to form CTPEs in situ. The CTPEs together with the simple blends of CNCs and linear poly(MMA-co-BA) copolymer (P(MMA-co-BA)) were characterized for comparative study. The results indicated that P(MMA-co-BA) was successfully grafted onto the surface of CNCs and the compatibility between CNCs and the polymer matrix in CTPEs was greatly enhanced. Specially, the CTPEs containing 2.15wt% CNCs increased Tg by 19.2°C and tensile strength by 100% as compared to the linear P(MMA-co-BA). Copyright © 2016 Elsevier Ltd. All rights reserved.

  7. UV-Induced Radical Photo-Polymerization: A Smart Tool for Preparing Polymer Electrolyte Membranes for Energy Storage Devices.

    PubMed

    Nair, Jijeesh R; Chiappone, Annalisa; Destro, Matteo; Jabbour, Lara; Meligrana, Giuseppina; Gerbaldi, Claudio

    2012-10-17

    In the present work, the preparation and characterization of quasi-solid polymer electrolyte membranes based on methacrylic monomers and oligomers, with the addition of organic plasticizers and lithium salt, are described. Noticeable improvements in the mechanical properties by reinforcement with natural cellulose hand-sheets or nanoscale microfibrillated cellulose fibers are also demonstrated. The ionic conductivity of the various prepared membranes is very high, with average values approaching 10-3 S cm-1 at ambient temperature. The electrochemical stability window is wide (anodic breakdown voltages > 4.5 V vs. Li in all the cases) along with good cyclability in lithium cells at ambient temperature. The galvanostatic cycling tests are conducted by constructing laboratory-scale lithium cells using LiFePO4 as cathode and lithium metal as anode with the selected polymer electrolyte membrane as the electrolyte separator. The results obtained demonstrate that UV induced radical photo-polymerization is a well suited method for an easy and rapid preparation of easy tunable quasi-solid polymer electrolyte membranes for energy storage devices.

  8. UV-Induced Radical Photo-Polymerization: A Smart Tool for Preparing Polymer Electrolyte Membranes for Energy Storage Devices.

    PubMed

    Nair, Jijeesh R; Chiappone, Annalisa; Destro, Matteo; Jabbour, Lara; Zeng, Juqin; Di Lupo, Francesca; Garino, Nadia; Meligrana, Giuseppina; Francia, Carlotta; Gerbaldi, Claudio

    2012-06-19

    In the present work, the preparation and characterization of quasi-solid polymer electrolyte membranes based on methacrylic monomers and oligomers, with the addition of organic plasticizers and lithium salt, are described. Noticeable improvements in the mechanical properties by reinforcement with natural cellulose hand-sheets or nanoscale microfibrillated cellulose fibers are also demonstrated. The ionic conductivity of the various prepared membranes is very high, with average values approaching 10-3 S cm-1 at ambient temperature. The electrochemical stability window is wide (anodic breakdown voltages > 4.5 V vs. Li in all the cases) along with good cyclability in lithium cells at ambient temperature. The galvanostatic cycling tests are conducted by constructing laboratory-scale lithium cells using LiFePO4 as cathode and lithium metal as anode with the selected polymer electrolyte membrane as the electrolyte separator. The results obtained demonstrate that UV induced radical photo-polymerization is a well suited method for an easy and rapid preparation of easy tunable quasi-solid polymer electrolyte membranes for energy storage devices.

  9. Ultrasound assisted free radical polymerization of glycidyl methacrylate by a new disite phase-transfer catalyst system: A kinetic study.

    PubMed

    Sankar, Kavitha; Rajendran, Venugopal

    2012-11-01

    The kinetics of multi-site phase-transfer catalyzed free radical polymerisation of glycidyl methacrylate (GMA) using potassium peroxy disulphate (PDS) as water soluble initiator and newly synthesized 1,4-dihexadecylpyrazine-1,4-diium dibromide as multi-site phase-transfer catalyst (MPTC) has been investigated in ethyl acetate/water two phase system at constant temperature 65±1°C under nitrogen atmosphere and ultrasound irradiation conditions. The rate of polymerization increases with an increase in concentrations of GMA, PDS and MPTC. The order with respect to monomer, initiator and MPTC were found to be 1.0, 0.5 and 1.0, respectively. The comparative study reveals that the Rp of GMA determined in the presence of PTC combined with ultrasound has shown more enhancements in the activity than PTC alone. Based on the observed results a suitable mechanism has been proposed to account for the experimental observations and its significance was discussed. Copyright © 2012 Elsevier B.V. All rights reserved.

  10. Superparamagnetic lysozyme surface-imprinted polymer prepared by atom transfer radical polymerization and its application for protein separation.

    PubMed

    Gai, Qing-Qing; Qu, Feng; Liu, Zong-Jian; Dai, Rong-Ji; Zhang, Yu-Kui

    2010-07-30

    Molecular imprinting as a promising and facile separation technique has received much attention because of their high selectivity for target molecules. In this study, the superparamagnetic lysozyme surface-imprinted polymer was prepared by a novel fabricating protocol, the grafting of the imprinted polymer on magnetic particles in aqueous media was done by atom transfer radical polymerization (ATRP), and the properties of the imprinted polymer were characterized in detail. Its high selective adsorption and recognition to lysozyme demonstrated the separation ability of the magnetic imprinted material to template molecule, and it has been used for quick and direct separation of lysozyme from the mixture of standard proteins and real egg white samples under an external magnetic field. Furthermore, the elution of lysozyme from the imprinted material was achieved by PEG/sulphate aqueous two-phase system, which caused lysozyme not only desorption from the imprinted materials but also redistribution in the top and bottom phase of aqueous two-phase system. The aqueous two-phase system exhibited some of the extraction and enrichment effect to desorbed lysozyme. Our results showed that ATRP is a promising method for the protein molecularly imprinted polymer preparation.

  11. Hydrogel brushes grafted from stainless steel via surface-initiated atom transfer radical polymerization for marine antifouling

    NASA Astrophysics Data System (ADS)

    Wang, Jingjing; Wei, Jun

    2016-09-01

    Crosslinked hydrogel brushes were grafted from stainless steel (SS) surfaces for marine antifouling. The brushes were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-methacryloyloxyethyl phosphorylcholine (MPC) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) respectively with different fractions of crosslinker in the feed. The grafted layers prepared with different thickness were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), ellipsometry and water contact angle measurements. With the increase in the fraction of crosslinker in the feed, the thickness of the grafted layer increased and the surface became smooth. All the brush-coated SS surfaces could effectively reduce the adhesion of bacteria and microalgae and settlement of barnacle cyprids, as compared to the pristine SS surface. The antifouling efficacy of the PEGMA polymer (PPEGMA)-grafted surface was higher than that of the MPC polymer (PMPC)-grafted surfaces. Furthermore, the crosslinked hydrogel brush-grafted surfaces exhibited better fouling resistance than the non-crosslinked polymer brush-grafted surfaces, and the antifouling efficacy increased with the crosslinking density. These hydrogel coatings of low toxicity and excellent anti-adhesive characteristics suggested their useful applications as environmentally friendly antifouling coatings.

  12. Synthesis of zwitterionic polymer-based amphiphilic triblock copolymers by atom transfer radical polymerization for production of extremely stable nanoemlusions

    NASA Astrophysics Data System (ADS)

    Lee, Jin Yong; Kim, Ji Eun; Kim, Jin Woong

    2015-03-01

    In fields of soft matter, there have been growing interests in utilizing amphiphilic block copolymers due to their intriguing properties, such as surface activity as well as self-assembly. In this work, we synthesize a series of poly (2-(methacryloyloxy) ethyl phosphorylcholine)- b-poly (ɛ-caprolactone)- b-poly (2-(methacryloyloxy) ethyl phosphorylcholine) (PMPC- b-PCL- b-PMPC) triblock copolymers by using atom transfer radical polymerization (ATRP). We have a particular interest in using poly (2-(methacryloyloxy) ethyl phosphorylcholine) (PMPC) as a hydrophilic block, since it can have both electrostatic repulsion and steric repulsion in complex fluid systems. Assembling them at the oil-water interface by using the phase inversion method enables production of highly stable nanoemulsions. From the analyses of the crystallography and self-assembly behavior, we have found that the triblock copolymers assemble to form a flexible but tough molecular thin film at the interface, which is essential for the remarkable improvement in the emulsion stability.

  13. Protein-resistant polyurethane via surface-initiated atom transfer radical polymerization of oligo(ethylene glycol) methacrylate.

    PubMed

    Jin, Zhilin; Feng, Wei; Zhu, Shiping; Sheardown, Heather; Brash, John L

    2009-12-15

    Protein-resistant polyurethane (PU) surfaces were prepared by surface-initiated simultaneous normal and reverse atom transfer radical polymerization (s-ATRP) of poly(oligo(ethylene glycol) methacrylate) (poly (OEGMA)). Oxygen plasma treatment was employed for initial activation of the PU surface. The grafted polymer chain length was adjusted by varying the molar ratio of monomer to sacrificial initiator in solution from 5:1 to 200:1. The modified PU surfaces were characterized by water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Protein adsorption experiments from tris-buffered saline (TBS) and plasma were carried out to evaluate the protein-resistance of the surfaces. Adsorption from single and binary protein solutions as well as from plasma was significantly reduced after modification. Adsorption decreased with increasing poly(OEGMA) chain length. Fibrinogen (Fg) adsorption on the 200:1 monomer/initiator surface was in the range of 3-33 ng/cm(2) representing 96-99% reduction compared with the unmodified PU. Fg adsorption from 0.01-10% plasma was as low as 1-5 ng/cm(2). Moreover, binary protein adsorption experiments using Fg and lysozyme (Lys) showed that protein size is a factor in the protein resistance of these surfaces.

  14. UV-Induced Radical Photo-Polymerization: A Smart Tool for Preparing Polymer Electrolyte Membranes for Energy Storage Devices

    PubMed Central

    Nair, Jijeesh R.; Chiappone, Annalisa; Destro, Matteo; Jabbour, Lara; Zeng, Juqin; Lupo, Francesca Di; Garino, Nadia; Meligrana, Giuseppina; Francia, Carlotta; Gerbaldi, Claudio

    2012-01-01

    In the present work, the preparation and characterization of quasi-solid polymer electrolyte membranes based on methacrylic monomers and oligomers, with the addition of organic plasticizers and lithium salt, are described. Noticeable improvements in the mechanical properties by reinforcement with natural cellulose hand-sheets or nanoscale microfibrillated cellulose fibers are also demonstrated. The ionic conductivity of the various prepared membranes is very high, with average values approaching 10−3 S cm−1 at ambient temperature. The electrochemical stability window is wide (anodic breakdown voltages > 4.5 V vs. Li in all the cases) along with good cyclability in lithium cells at ambient temperature. The galvanostatic cycling tests are conducted by constructing laboratory-scale lithium cells using LiFePO4 as cathode and lithium metal as anode with the selected polymer electrolyte membrane as the electrolyte separator. The results obtained demonstrate that UV induced radical photo-polymerization is a well suited method for an easy and rapid preparation of easy tunable quasi-solid polymer electrolyte membranes for energy storage devices. PMID:24958178

  15. UV-Induced Radical Photo-Polymerization: A Smart Tool for Preparing Polymer Electrolyte Membranes for Energy Storage Devices

    PubMed Central

    Nair, Jijeesh R.; Chiappone, Annalisa; Destro, Matteo; Jabbour, Lara; Meligrana, Giuseppina; Gerbaldi, Claudio

    2012-01-01

    In the present work, the preparation and characterization of quasi-solid polymer electrolyte membranes based on methacrylic monomers and oligomers, with the addition of organic plasticizers and lithium salt, are described. Noticeable improvements in the mechanical properties by reinforcement with natural cellulose hand-sheets or nanoscale microfibrillated cellulose fibers are also demonstrated. The ionic conductivity of the various prepared membranes is very high, with average values approaching 10-3 S cm-1 at ambient temperature. The electrochemical stability window is wide (anodic breakdown voltages > 4.5 V vs. Li in all the cases) along with good cyclability in lithium cells at ambient temperature. The galvanostatic cycling tests are conducted by constructing laboratory-scale lithium cells using LiFePO4 as cathode and lithium metal as anode with the selected polymer electrolyte membrane as the electrolyte separator. The results obtained demonstrate that UV induced radical photo-polymerization is a well suited method for an easy and rapid preparation of easy tunable quasi-solid polymer electrolyte membranes for energy storage devices. PMID:24958425

  16. Rational preparation of dibenzothiophene-imprinted polymers by surface imprinting technique combined with atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Yang, Wenming; Liu, Lukuan; Zhou, Zhiping; Liu, Hong; Xie, Binze; Xu, Wanzhen

    2013-10-01

    A computational simulation method is introduced to simulate the dibenzothiophene-monomer pre-assembly system of molecular imprinted polymers. The interaction type and intensity between dibenzothiophene and monomer are discussed from the binding energy and spatial position distribution. The simulation and analysis results indicate that the amount of the function monomer is not the more the better in preparing molecular imprinted polymers. Based on the above results, a novel dibenzothiophene-imprinted polymers with the favorable specific adsorption effect was prepared by surface imprinting technique combined with atom transfer radical polymerization. This combined technologies are used for preparing a desulfurization adsorbent for the first time. Various measures were selected to characterize the structure and morphology of the prepared adsorbent. The characterization results show that the adsorbent has suitable features for further adsorption process. A series of static adsorption experiments were conducted to analyze its adsorption performance. The adsorption process follows Elovich model by the kinetic analysis and Sips equation by the isothermal analysis. The approach we described will provide another opportunity in the deep desulfurization field.

  17. Metal-centered polymers: Using controlled polymerization methodologies for the generation of responsive materials

    NASA Astrophysics Data System (ADS)

    Johnson, Robert Matthew

    Controlled polymerization methods were used to prepare highly modular polymeric metal complexes via convergent and divergent strategies. In these materials, the metal center provides a versatile hub for preparing diverse architectures through coordinative bonds. Moreover, the metal complex introduces various properties to the polymer such as luminescence, magnetism, or electroactivity. Suitably functionalized metal complexes have been used for the atom transfer radical polymerization of acrylate and methacrylate monomers by metalloinitiation to generate luminescent biocompatible materials through a divergent synthesis. By cleaving the tert-butyl groups from poly(tert -butyl acrylate), water soluble [Ru(bpyPAA2)3] 2+ has been prepared as well as the amphiphilic star block copolymer [Ru{bpy(PLA-PAA)2}3]2+ (PLA = poly(lactic acid), PAA = poly(acrylic acid) Bipyridine-centered polymeric macroligands may be chelated to a variety of metal salts. The polymer size greatly influences the formation of [Fe(bpy) 3]2+ centered polymers. As the molecular weight increases (> ˜25 kDa) tris complex formation decreases. Tris(bpy) synthesis is also impacted by chemical composition. BpyPtBA2 (PtBA = poly(tert-butyl acrylate) generates an iron mono(bpy) complex before giving rise to the bis(bpy) iron complex; no tris complex is observed. In contrast, the combination of bpyPEG2 (3 equiv) (PEG = (poly(ethylene glycol)) results in the formation of some iron tris(bpy) compound; however, complete tris(bpy) product formation is suppressed, presumably because of the chelating ability of the PEG chains. These examples contrast with other polymeric macroligands such as bpyPS2, bpyPMMA2, bpyPCL2 and bpyPLA 2 (PS = polystyrene; PMMA = poly(methyl methacrylate); PCL = poly(epsilon-caprolactone); PLA = poly(DL-lactic acid)) for which chelation reactions are facile for low molecular weight macroligands (<15 kDa), with chelation efficiencies (defined as (epsilonPMC/epsilonbpy) x 100%) only declining

  18. New Cobalt-Mediated Radical Polymerization (CMRP) of Methyl Methacrylate Initiated by Two Single-Component Dinuclear β-Diketone Cobalt (II) Catalysts

    PubMed Central

    Bao, Feng; Feng, Lingling; Gao, Jie; Tan, Zhifang; Xing, Bin; Ma, Rui; Yan, Chunjie

    2010-01-01

    Two dinuclear cobalt complexes based on bis-diketonate ligands (ligand 1: 3,3′-(1,3-phenylene)bis(1-phenylpropane-1,3-dione); ligand 2: 3,3′-(1,4-phenylene)bis(1-phenylpropane-1,3-dione)) were successfully synthesized. The two neutral catalysts all showed satisfactory activities in the cobalt-mediated radical polymerization (CMRP) of methyl methacrylate (MMA) with the common initiator of azodiisobutyronitrile (AIBN). The resulting polymerizations have all of the characteristics of a living polymerization and displayed linear semilogarithmic kinetic plots, a linear correlation between the number-average molecular weight and the monomer conversion, and low polydispersities. Mono- or dicomponent low polydispersity polymers could be obtained by using the two dinuclear catalysts under proper reaction conditions. All these improvements facilitate the implementation of the acrylate CMRP and open the door to the scale-up of the syntheses and applications of the multicomponent low polydispersity polymers. PMID:21049027

  19. Controlled RAFT Polymerization of 2-Vinyl-4,4-Dimethylazlactone (VDMA): A Facile Route to Bio-Inspired Polymer Surfaces

    SciTech Connect

    Lokitz, Bradley S; Messman, Jamie M; Hinestrosa Salazar, Juan Pablo; Alonzo Calderon, Jose E; Verduzco, Rafael; Brown, Rebecca H; Osa, Masashi; Ankner, John Francis; Kilbey, II, S Michael

    2009-01-01

    We report the controlled radical polymerization of 2-vinyl-4,4-dimethyl azlactone (VDMA), a 2-alkenyl-2-oxazolin-5-one monomer that contains a polymerizable vinyl moiety as well as a highly reactive, pendant azlactone as well as solution characterizations and surface attachment and functionaliztion. Reversible addition fragmentation chain transfer (RAFT) was used to polymerize of VDMA in benzene at 65 C using either 2-(2-cyanopropyl) dithiobenzoate (CPDB) or 2-dodecylsulfanylthiocarbonyl-sulfanyl-2-methylpropionic acid (DMP) as RAFT chain transfer agents (CTAs). The pseudo first order kinetics and resultant well-defined polymers of low polydispersity indicate that both CTAs afford control over the RAFT polymerization of VDMA. Dynamic and static light scattering and small angle neutron scattering were performed to determine the dn/dc, weight-average molecular weight, radius of gyration, and second virial coefficient of VDMA homopolymers in THF. Additionally, well-defined polymers of VDMA containing carboxyl end groups were covalently attached to epoxy modified silicon wafers via esterification to produce polymeric scaffolds that could be subsequently functionalized for various bio-inspired applications.

  20. ESR studies of semicontinuous emulsion polymerization

    SciTech Connect

    Lau, W.; Westmoreland, D.G.

    1993-12-31

    Electron spin resonance (ESR) is used in the detection and quantification of propagating radicals during a semicontinuous emulsion polymerization. The propagating radical concentration is crucial for the determination of kinetic parameters of the emulsion polymerization process. A flow reactor was built which involves a closed-loop flow system that circulates latex from the polymerization reactor through the ESR cavity for free-radical measurements and back to the reactor. With the continuous measurement of the radical concentrations during a polymerization of methyl methacrylate (MMA), {bar n} (average number of radicals per particle) and k{sub p} (propagating rate constant), are measured throughout the entire polymerization. For the polymerization of the MMA system studied, the authors observed a gradual increased in n and decrease in k{sub p} during the run, suggesting a diffusionally controlled process and that the polymerization is not occurring homogeneously throughout the polymer particles. In the glassy pMMA matrix, radicals can be {open_quotes}trapped{close_quotes} within a minimum volume and remain unterminated.

  1. Control over Colloidal Particle Morphology by Dispersion Polymerization

    NASA Astrophysics Data System (ADS)

    Peng, B.

    2013-03-01

    The main subject of this thesis is the structure and morphology control of colloidal polymer particles, in particular, poly(methyl methacrylate) (PMMA) particles, by dispersion polymerization in polar solvents. The structure control, ranging from surface morphology and internal structure to shape manipulation of polymer particles, was attempted through copolymerization of monomers with various types of materials, such as cross-linkers, dyes, and colloidal silica spheres or rods. The obtained spherical or non-spherical particles are interesting as model systems as they mimic molecules at colloidal scales. Their phase behavior can be studied in the presence or absence of external fields (like electric and gravity fields). Additionally, they can be used for various applications, such as photonic crystals

  2. A strategy for sequence control in vinyl polymers via iterative controlled radical cyclization

    PubMed Central

    Hibi, Yusuke; Ouchi, Makoto; Sawamoto, Mitsuo

    2016-01-01

    There is a growing interest in sequence-controlled polymers toward advanced functional materials. However, control of side-chain order for vinyl polymers has been lacking feasibility in the field of polymer synthesis because of the inherent feature of chain-growth propagation. Here we show a general and versatile strategy to control sequence in vinyl polymers through iterative radical cyclization with orthogonally cleavable and renewable bonds. The proposed methodology employs a repetitive and iterative intramolecular cyclization via a radical intermediate in a one-time template with a radical-generating site at one end and an alkene end at the other, each of which is connected to a linker via independently cleavable and renewable bonds. The unique design specifically allowed control of radical addition reaction although inherent chain-growth intermediate (radical species) was used, as well as the iterative cycle and functionalization for resultant side chains, to lead to sequence-controlled vinyl polymers (or oligomers). PMID:26996881

  3. Combination of electrografting and atom-transfer radical polymerization for making the stainless steel surface antibacterial and protein antiadhesive.

    PubMed

    Ignatova, Milena; Voccia, Samuel; Gilbert, Bernard; Markova, Nadya; Cossement, Damien; Gouttebaron, Rachel; Jérôme, Robert; Jérôme, Christine

    2006-01-03

    A two-step "grafting from" method has been successfully carried out, which is based on the electrografting of polyacrylate chains containing an initiator for the atom transfer radical polymerization (ATRP) of 2-(tert-butylamino)ethyl methacrylate (TBAEMA) or copolymerization of TBAEMA with either monomethyl ether of poly(ethylene oxide) methacrylate (PEOMA) or acrylic acid (AA) or styrene. The chemisorption of this type of polymer brushes onto stainless steel surfaces has potential in orthopaedic surgery. These films have been characterized by ATR-FTIR, Raman spectroscopy, atomic force microscopy (AFM), and measurement of contact angles of water. The polymer formed in solution by ATRP and that one detached on purpose from the surface have been analyzed by size exclusion chromathography (SEC) and (1)H NMR spectroscopy. The strong adherence of the films onto stainless steel has been assessed by peeling tests. AFM analysis has shown that addition of hydrophilic comonomers to the grafted chains decreases the surface roughness. According to dynamic quartz crystal microbalance experiments, proteins (e.g., fibrinogen) are more effectively repelled whenever copolymer brushes contain neutral hydrophilic (PEOMA) co-units rather than negatively charged groups (PAA salt). Moreover, a 2- to 3-fold decrease in the fibrinogen adsorption is observed when TBAEMA is copolymerized with either PEOMA or AA rather than homopolymerized or copolymerized with styrene. Compared to the bare stainless steel surface, brushes of polyTBAEMA, poly(TBAEMA-co-PEOMA) and poly(TBAEMA-co-AA) decrease the bacteria adhesion by 3 to 4 orders of magnitude as revealed by Gram-positive bacteria S. aureus adhesion tests.

  4. p-Hydroxyphenyl (H) Units Lower the Degree of Polymerization in Lignin: Chemical Control in Lignin Biosynthesis

    SciTech Connect

    Sangha, A. K.; Parks, J. M.; Davis, M. F.; Smith, J. C.

    2013-01-01

    Lignin, composed predominantly of p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) subunits, is a major component of plant cell walls that imparts resistance toward chemical and microbial deconstruction of plant biomass, rendering its conversion inefficient and costly. Previous studies have shown that alterating lignin composition, i.e., the relative abundance of H, G and S subunits, promises more efficient extraction of sugars from plant biomass. Smaller and less branched lignin chains are more easily extracted during pretreatment, making cellulose more readily degradable. Here, using density functional theory calculations, we show that the incorporation of H subunits into lignin via b-b and b-5 interunit linkages reduces the degree of polymerization in lignin. Frontier molecular orbital analyses of lignin dimers and trimers show that H as a terminal subunit on a growing lignin polymer linked via b-b and b-5 linkage cannot undergo radical formation, preventing further chain growth by endwise polymerization resulting in lignin polymers with lower degree of polymerization. These results indicate that, for endwise polymerization in lignin synthesis, there exists a chemical control that may lay a significant role in determining the structure of lignin.

  5. Morphology Control of Multicomponent Polymeric Surfactants Using Pressure

    NASA Astrophysics Data System (ADS)

    Cho, Junhan

    The development of nanoscale morphologies for a molten polymeric surfactant under pressure is investigated by using a recently formulated self-consistent field theory. A linear ABC block copolymer is taken as our model system that allows a disparity in the propensities for curved interfaces and pressure responses of ij-pairs. The interplay of those features lead the copolymer to new morphologies at a moderate segregation level and at ambient condition such as networks and pillars of 2-dimensional array. It is shown that pressure is an effective means of morphology control and identification for those new structures. The role of volume fluctuations in the development of those structures is discussed. J.C. acknowledges the support from Center for Photofunctional Energy Materials through Gyeonggi Regional Research Program.

  6. Preparation of PEGylated polymeric nanoprobes with aggregation-induced emission feature through the combination of chain transfer free radical polymerization and multicomponent reaction: Self-assembly, characterization and biological imaging applications.

    PubMed

    Wan, Qing; Liu, Meiying; Mao, Liucheng; Jiang, Ruming; Xu, Dazhuang; Huang, Hongye; Dai, Yanfeng; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2017-03-01

    Self-assembly of amphiphilic luminescent copolymers is a general route to fabricate fluorescent polymeric microparticles (FPMs). In this work, the FPMs with aggregation-induced emission (AIE) feature were fabricated via the combination of the chain transfer free radical polymerization and "one-pot" multicomponent reaction, which conjugated the aldehyde-containing AIE active dye AIE (CHO-An-CHO) and amino-terminated hydrophilic polymer (ATPPEGMA) using mercaptoacetic acid (MTA) as the "lock" molecule. The structure, chemical compositions, optical properties as well as biological properties of the PPEGMA-An-PPEGMA FPMs were characterized and investigated by means of a series of techniques and experiments in detail. We demonstrated the final copolymers showed amphiphilic properties, strong yellow fluorescence and high water dispersibility. Biological evaluation suggested that PPEGMA-An-PPEGMA FPMs possess low cytotoxicity and can be used for cell imaging. More importantly, many other AIE active FPMs are expected to be fabricated using the similar strategy because of the good substrate and monomer applicability of the multicomponent reaction and chain transfer living radical polymerization. Therefore, we could conclude that the strategy described in this work should be of great interest for fabrication of multifunctional AIE active nanoprobes for biomedical applications.

  7. Radical Reaction Control in the AdoMet Radical Enzyme CDG Synthase (QueE): Consolidate, Destabilize, Accelerate

    PubMed Central

    2016-01-01

    Abstract Controlling radical intermediates and thus catalysing and directing complex radical reactions is a central feature of S‐adensosylmethionine (SAM)‐dependent radical enzymes. We report ab initio and DFT calculations highlighting the specific influence of ion complexation, including Mg2+, identified as a key catalytic component on radical stability and reaction control in 7‐carboxy‐7‐deazaguanine synthase (QueE). Radical stabilisation energies (RSEs) of key intermediates and radical clock‐like model systems of the enzyme‐catalysed rearrangement of 6‐carboxytetrahydropterin (CPH4), reveals a directing role of Mg2+ in destabilising both the substrate‐derived radical and corresponding side reactions, with the effect that the experimentally‐observed rearrangement becomes dominant over possible alternatives. Importantly, this is achieved with minimal disruption of the thermodynamics of the substrate itself, affording a novel mechanism for an enzyme to both maintain binding potential and accelerate the rearrangement step. Other mono and divalent ions were probed with only dicationic species achieving the necessary radical conformation to facilitate the reaction. PMID:27859789

  8. Reactions of hydrated electron with various radicals: spin factor in diffusion-controlled reactions.

    PubMed

    Ichino, Takatoshi; Fessenden, Richard W

    2007-04-05

    The reactions of hydrated electron (eaq-) with various radicals have been studied in pulse radiolysis experiments. These radicals are hydroxyl radical (*OH), sulfite radical anion (*SO3-), carbonate radical anion (CO3*-), carbon dioxide radical anion (*CO2-), azidyl radical (*N3), dibromine radical anion (Br2*-), diiodine radical anion (I2*-), 2-hydroxy-2-propyl radical (*C(CH3)2OH), 2-hydroxy-2-methyl-1-propyl radical ((*CH2)(CH3)2COH), hydroxycyclohexadienyl radical (*C6H6OH), phenoxyl radical (C6H5O*), p-methylphenoxyl radical (p-(H3C)C6H4O*), p-benzosemiquinone radical anion (p-OC6H4O*-), and phenylthiyl radical (C6H5S*). The kinetics of eaq- was followed in the presence of the counter radicals in transient optical absorption measurements. The rate constants of the eaq- reactions with radicals have been determined over a temperature range of 5-75 degrees C from the kinetic analysis of systems of multiple second-order reactions. The observed high rate constants for all the eaq- + radical reactions have been analyzed with the Smoluchowski equation. This analysis suggests that many of the eaq- + radical reactions are diffusion-controlled with a spin factor of 1/4, while other reactions with *OH, *N3, Br2*-, I2*-, and C6H5S* have spin factors significantly larger than 1/4. Spin dynamics for the eaq-/radical pairs is discussed to explain the different spin factors. The reactions with *OH, *N3, Br2*-, and I2*- have also been found to have apparent activation energies less than that for diffusion control, and it is suggested that the spin factors for these reactions decrease with increasing temperature. Such a decrease in spin factor may reflect a changing competition between spin relaxation/conversion and diffusive escape from the radical pairs.

  9. Adhesion controls bacterial actin polymerization-based movement

    PubMed Central

    Soo, Frederick S.; Theriot, Julie A.

    2005-01-01

    As part of its infectious life cycle, the bacterial pathogen Listeria monocytogenes propels itself through the host-cell cytoplasm by triggering the polymerization of host-cell actin near the bacterial surface, harnessing the activity of several cytoskeletal proteins used during actin-based cell crawling. To distinguish among several classes of biophysical models of actin-based bacterial movement, we used a high-throughput tracking technique to record the movement of many individual bacteria during temperature shifts. The speed of each bacterium varied strongly with temperature, closely following the Arrhenius rate law. Among bacteria, the prefactor A of the Arrhenius dependence unexpectedly varied exponentially with apparent activation energy, Ea, over a wide range (8–21 kcal/mol), reminiscent of the “rate compensation effect” of classical catalytic reactions. Average Ea were increased for mutant bacteria deficient in binding Ena/VASP proteins and bacteria moving in diluted extract. These two effects were additive. The observed temperature and rate compensation effects are consistent with a class of simple kinetic models in which the bacterium advances through the thermally driven, cooperative breakage of groups of adhesive bonds on its surface. The estimated number of coupled adhesive bonds N on the bacterial surface varies between 10 and 40 bonds. In contrast to other models, this model correctly predicts an experimentally observed negative correlation between bacterial speed and actin gel density. The idea that speed depends on adhesion, rather than polymerization, suggests several alternative mechanisms by which known cytoskeletal regulatory proteins could control cellular movement. PMID:16251274

  10. Use of a Reliable Homemade Dilatometer To Study the Kinetics of the Radical Chain Polymerization of PMMA: An Undergraduate Polymer Chemistry Laboratory Kinetics Experiment

    NASA Astrophysics Data System (ADS)

    Mendicuti, Francisco; Martín, Olga; Tarazona, Maria Pilar

    1998-11-01

    In this laboratory experiment, a simple, reliable homemade dilatometer was used to study the kinetics of the radical chain polymerization of PMMA. The reaction was carried out in toluene with benzoyl peroxide as the initiator at a temperature of 80 °C. Each student studied the kinetics at a different initiator concentration constant. Pseudo-first-order plots permit students to obtain kapp and to demonstrate order 1 with respect to the monomer concentration. Finally, a log-log plot of kapp versus the initiator concentration from the data collected by each student demonstrates order 0.5 with respect to the initiator concentration. Results also agree with the rate constants of the process implicated in this type of polymerization.

  11. Control of polymeric nanoparticle size to improve therapeutic delivery.

    PubMed

    Hickey, John W; Santos, Jose Luis; Williford, John-Michael; Mao, Hai-Quan

    2015-12-10

    As nanoparticle (NP)-mediated drug delivery research continues to expand, understanding parameters that govern NP interactions with the biological environment becomes paramount. The principles identified from the study of these parameters can be used to engineer new NPs, impart unique functionalities, identify novel utilities, and improve the clinical translation of NP formulations. One key design parameter is NP size. New methods have been developed to produce NPs with increased control of NP size between 10 and 200nm, a size range most relevant to physical and biochemical targeting through both intravascular and site-specific deliveries. Three notable techniques best suited for generating polymeric NPs with narrow size distributions are highlighted in this review: self-assembly, microfluidics-based preparation, and flash nanoprecipitation. Furthermore, the effect of NP size on the biological fate and transport properties at the molecular scale (protein-NP interactions) and the tissue and systemic scale (convective and diffusive transport of NPs) are analyzed here. These analyses underscore the importance of NP size control in considering clinical translation and assessment of therapeutic outcomes of NP delivery vehicles.

  12. Stable polymeric carbon radicals. Part 2: Attempts at the preparation of polyradicals of the triphenylmethyl type linked by P-phenylene units

    NASA Technical Reports Server (NTRS)

    Braun, D.; Lehmann, P.

    1985-01-01

    As starting materials for the preparation of polyradicals of triphenylmethyl type linked by p-phenylene units bis(4-iodophenylmethane) and bis(4-iodo-2,5-dimethyl-phenylmethane) were synthesized by a Sandmeyer reaction from the corresponding diamino compounds and subsequently transformed into the corresponding polymeric hydrocarbons 6a and 6b by an Ullmann condensation. In the following step 6a and 6b were brominated at the tert. carbon atom by means of N-bromosuccinimide. The reaction of the resulting poly (4,4'-biphenylylen-alpha-bromobenzylidene)s (7a and 7b) with mercury afforded the corresponding radicals, the ESR spectra of which were recorded. From the methyl substituted polymer 7b poly (2,2'5,5-tetramethyl-4,4'-bi-phenylylen)phenylmethylidyne was formed, whereas the unsubstituted product 7a was transformed into a para-quinoide polymer with radical properties.

  13. Covalent immobilization of glucose oxidase on well-defined poly(glycidyl methacrylate)-Si(111) hybrids from surface-initiated atom-transfer radical polymerization.

    PubMed

    Xu, F J; Cai, Q J; Li, Y L; Kang, E T; Neoh, K G

    2005-01-01

    A simple one-step procedure was employed for the covalent immobilization of an atom-transfer radical polymerization (ATRP) initiator, via the robust Si-C bond, on the hydrogen-terminated Si(111) surface (Si-H surface). Well-defined poly(glycidyl methacrylate) [P(GMA)] brushes, tethered directly on the (111)-oriented single-crystal silicon surface, were prepared via surface-initiated ATRP. Kinetics study on the surface-initiated ATRP of glycidyl methacrylate revealed that the chain growth from the silicon surface was consistent with a "controlled" process. A relatively high concentration of glucose oxidase (GOD; above 0.2 mg/cm2) could be coupled directly to the well-defined P(GMA) brushes via the ring-opening reaction of the epoxide groups with the amine moieties of the enzyme. The resultant GOD-functionalized P(GMA) brushes, with the accompanying hydroxyl groups from the ring-opening reaction of the epoxide groups, serves as an effective spacer to provide the GOD with a higher degree of conformational freedom and a more hydrophilic environment. An equivalent enzyme activity above 1.6 units/cm2 [micromoles of beta-D-(+)-glucose oxidized to d-gluconolactone per minute per square centimeter] and a corresponding relative activity of about 60% could be readily achieved. The immobilized GOD also exhibited an improved stability during storage over that of the free enzyme. The GOD-functionalized silicon substrates are potentially useful to the development of silicon-based glucose biosensors.

  14. Fabrication of polymeric scaffolds with a controlled distribution of pores.

    PubMed

    Capes, J S; Ando, H Y; Cameron, R E

    2005-12-01

    The design of tissue engineering scaffolds must take into account many factors including successful vascularisation and the growth of cells. Research has looked at refining scaffold architecture to promote more directed growth of tissues through well-defined anisotropy in the pore structure. In many cases it is also desirable to incorporate therapeutic ingredients, such as growth factors, into the scaffold so that their release occurs as the scaffold degrades. Therefore, scaffold fabrication techniques must be found to precisely control, not only the overall porosity of scaffolds, but also the pore size, shape and spatial distribution. This work describes the use of a regularly shaped porogen, sugar spheres, to manufacture polymeric scaffolds. Results show that pre-assembling the spheres created scaffolds with a constant porosity of 60%, but with varying pores sizes from 200-800 microm, leading to a variation in the surface area and likely degradation rate of the scaffolds. Employing different polymer impregnation techniques tailored the number of pores present with a diameter of less than 100 microm to suit different functions, and altering the packing structure of the sugar spheres created scaffolds with novel layered porosity. Replacing sugar spheres with sugar strands formed scaffolds with pores aligned in one direction.

  15. Polymeric surfaces exhibiting photocatalytic activity and controlled anisotropic wettability

    NASA Astrophysics Data System (ADS)

    Anastasiadis, Spiros H.; Frysali, Melani A.; Papoutsakis, Lampros; Kenanakis, George; Stratakis, Emmanuel; Vamvakaki, Maria; Mountrichas, Grigoris; Pispas, Stergios

    2015-03-01

    In this work we focus on surfaces, which exhibit controlled, switchable wettability in response to one or more external stimuli as well as photocatalytic activity. For this we are inspired from nature to produce surfaces with a dual-scale hierarchical roughness and combine them with the appropriate inorganic and/or polymer coating. The combination of the hierarchical surface with a ZnO coating and a pH- or temperature-responsive polymer results in efficient photo-active properties as well as reversible superhydrophobic / superhydrophilic surfaces. Furthermore, we fabricate surfaces with unidirectional wettability variation. Overall, such complex surfaces require advanced design, combining hierarchically structured surfaces with suitable polymeric materials. Acknowledgment: This research was partially supported by the European Union (European Social Fund, ESF) and Greek national funds through the ``ARISTEIA II'' Action (SMART-SURF) of the Operational Programme ``Education and Lifelong Learning,'' NSRF 2007-2013, via the General Secretariat for Research & Technology, Ministry of Education and Religious Affairs, Greece.

  16. Role of Radical Species in Salicylaldiminato Ni(II) Mediated Polymer Chain Growth: A Case Study for the Migratory Insertion Polymerization of Ethylene in the Presence of Methyl Methacrylate.

    PubMed

    Ölscher, Franz; Göttker-Schnetmann, Inigo; Monteil, Vincent; Mecking, Stefan

    2015-11-25

    To date, an inconclusive and partially contradictive picture exists on the behavior of neutral Ni(II) insertion polymerization catalysts toward methyl methacrylate (MMA). We shed light on this issue by a combination of comprehensive mechanistic NMR and EPR studies, isolation of a key Ni(I) intermediate, and pressure reactor studies with ethylene and MMA, followed by detailed polymer analysis. An interlocking mechanistic picture of an insertion and a free radical polymerization is revealed. Both polymerizations run simultaneously (25 bar ethylene, neat MMA, 70 °C); however, the chain growth cycles are independent of each other, and therefore exclusively a physical mixture of homo-PE and homo-PMMA is obtained. A Ni-C bond cleavage was excluded as a free radical source. Rather a homolytic P-C bond cleavage in the labile aryl phosphine ligand and the reaction of low-valent Ni(0/I) species with specific iodo substituted N^O (Ar-I) ligands were shown to initiate radical MMA polymerizations. Several reductive elimination decomposition pathways of catalyst precursor or active intermediates were shown to form low-valent Ni species. One of those pathways is a bimolecular reductive coupling via intermediate (N^O)Ni(I) formation. These intermediate Ni(I) species can be prevented from ultimate decomposition by capturing with organic radical sources, forming insertion polymerization active [(N^O)Ni(II)-R] species and prolonging the ethylene polymerization activity.

  17. Sulphur-radical control on petroleum formation rates

    USGS Publications Warehouse

    Lewan, M.D.

    1998-01-01

    Most petroleum is formed through the partial decomposition of kerogen (an insoluble sedimentary organic material) in response to thermal stress during subsurface burial in a sedimentary basin. Knowing the mechanisms and kinetics of this process allows the determination of the extent and timing of petroleum formation, which, in turn, are critical for evaluating the potential for petroleum occurrences within a sedimentary basin. Kinetic models of petroleum generation are derived mainly from pyrolysis experiments, in which it is usually assumed that formation rates are controlled by the strength of the bonds within the precursor compounds: this agrees with the observation that petroleum formation rates increase with increasing sulphur content of thermally immature kerogen, C-S bonds being weaker than C-C bonds. However, this explanation fails to account for the overall composition of petroleum. Here I argue, on the basis of pyrolysis experiments, that it is the presence of sulphur radicals, rather than the relative weakness of C-S bonds, that controls petroleum formation rates. My findings suggest that the rate of petroleum formation depends critically on the concentration of sulphur radicals generated during the initial stages of thermal maturation. The proposed mechanism appears to provide a realistic explanation for both the overall composition of petroleum and the observed variation in formation rates.

  18. Etching radical controlled gas chopped deep reactive ion etching

    DOEpatents

    Olynick, Deidre; Rangelow, Ivo; Chao, Weilun

    2013-10-01

    A method for silicon micromachining techniques based on high aspect ratio reactive ion etching with gas chopping has been developed capable of producing essentially scallop-free, smooth, sidewall surfaces. The method uses precisely controlled, alternated (or chopped) gas flow of the etching and deposition gas precursors to produce a controllable sidewall passivation capable of high anisotropy. The dynamic control of sidewall passivation is achieved by carefully controlling fluorine radical presence with moderator gasses, such as CH.sub.4 and controlling the passivation rate and stoichiometry using a CF.sub.2 source. In this manner, sidewall polymer deposition thicknesses are very well controlled, reducing sidewall ripples to very small levels. By combining inductively coupled plasmas with controlled fluorocarbon chemistry, good control of vertical structures with very low sidewall roughness may be produced. Results show silicon features with an aspect ratio of 20:1 for 10 nm features with applicability to nano-applications in the sub-50 nm regime. By comparison, previous traditional gas chopping techniques have produced rippled or scalloped sidewalls in a range of 50 to 100 nm roughness.

  19. Surface initiated supplemental activator and reducing agent atom transfer radical polymerization (SI-SARA-ATRP) of 4-vinylpyridine on poly(ethylene terephthalate).

    PubMed

    Maaz, Mohamad; Elzein, Tamara; Bejjani, Alice; Barroca-Aubry, Nadine; Lepoittevin, Bénédicte; Dragoe, Diana; Mazerat, Sandra; Nsouli, Bilal; Roger, Philippe

    2017-08-15

    Poly(ethylene terephthalate) (PET) substrates were modified by means of surface-initiated supplemental activator and reducing agent atom transfer radical polymerization (SI-SARA-ATRP) of 4-vinylpyridine (4VP). Substrates were pretreated in order to graft chloromethylbenzene (CMB) units capable of initiating the radical polymerization reaction of 4VP units. Surface characterization techniques, including Water Contact Angle (WCA), Attenuated Total Reflection (ATR), X-ray photoelectron spectroscopy (XPS), Atomic Force Microscopy (AFM) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) showed a successful grafting of a stable, smooth and homogenous layer of p4VP. This process offers the advantages of a rapid, simplified and low cost strategy to chemically modify polymer substrates with covalently bonded layer of the pH responsive p4VP for different applications. Moreover, by using TOF-SIMS profiling, we were able to track a density gradient along the z-axis generated by the interpenetrating phases of the different layers of the final modified surface. Fact that we correlated to the various positions of initiation sites within the polyethylenimine (PEI) used for PET aminolysis prior to CMB grafting. Our strategy will be used in future work to graft other polymers for different applications where industrial scale viable options are needed. Copyright © 2017 Elsevier Inc. All rights reserved.

  20. Synthesis and characterization of TiO 2/Ag/polymer ternary nanoparticles via surface-initiated atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Park, Jung Tae; Koh, Joo Hwan; Seo, Jin Ah; Cho, Yong Soo; Kim, Jong Hak

    2011-08-01

    We report on the novel ternary hybrid materials consisting of semiconductor (TiO 2), metal (Ag) and polymer (poly(oxyethylene methacrylate) (POEM)). First, a hydrophilic polymer, i.e. POEM, was grafted from TiO 2 nanoparticles via the surface-initiated atom transfer radical polymerization (ATRP) technique. These TiO 2-POEM brush nanoparticles were used to template the formation of Ag nanoparticles by introduction of a AgCF 3SO 3 precursor and a NaBH 4 aqueous solution for reduction process. Successful grafting of polymeric chains from the surface of TiO 2 nanoparticles and the in situ formation of Ag nanoparticles within the polymeric chains were confirmed using transmission electron microscopy (TEM), UV-vis spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). FT-IR spectroscopy also revealed the specific interaction of Ag nanoparticles with the C dbnd O groups of POEM brushes. This study presents a simple route for the in situ synthesis of both metal and polymer confined within the semiconductor, producing ternary hybrid inorganic-organic nanomaterials.

  1. Effects of LDEF flight exposure on selected polymeric films and thermal control coatings

    NASA Technical Reports Server (NTRS)

    Slemp, Wayne S.; Young, Philip R.; Shen, James Y.

    1991-01-01

    The characterization of polymeric films and thermal control coatings which were exposed for five years and ten months to the low-Earth environment is reported. Changes in solar absorptance, thermal emittance, and transmission are compared to laboratory control specimens. Sputter-deposited metallic coatings are shown to eliminate atomic oxygen erosion of resin matrix composite materials. The effects of long-term atomic oxygen exposure to metallized FEP Teflon film is characterized. Chemical characterization of polymeric films indicates that although surface erosion occurs, the molecular structure of the basic polymeric film has not changed significantly in response to this exposure.

  2. Fabrication of contrast agents for magnetic resonance imaging from polymer-brush-afforded iron oxide magnetic nanoparticles prepared by surface-initiated living radical polymerization.

    PubMed

    Ohno, Kohji; Mori, Chizuru; Akashi, Tatsuki; Yoshida, Shinichi; Tago, Yoshiyuki; Tsujii, Yoshinobu; Tabata, Yasuhiko

    2013-10-14

    The aim of this study is to fabricate a contrast agent for magnetic resonance imaging (MRI) by using hybrid particles composed of a core of iron oxide magnetite (Fe3O4) nanoparticles and a shell of hydrophilic polymer brush synthesized by surface-initiated (SI) living radical polymerization. To achieve this, Fe3O4 nanoparticles were surface-modified with initiating groups for atom transfer radical polymerization (ATRP) via a ligand-exchange reaction in the presence of a triethoxysilane derivative having an ATRP initiation site. The ATRP-initiator-functionalized Fe3O4 nanoparticles were used for performing the SI-ATRP of methyl methacrylate to demonstrate the ability of the synthesized nanoparticles to produce well-defined polymer brushes on their surfaces. The polymerization proceeded in a living fashion so as to produce graft polymers with targeted molecular weights and narrow molecular weight distribution. The average graft density was estimated to be as high as 0.7 chains/nm(2), which indicates the formation of so-called concentrated polymer brushes on the Fe3O4 nanoparticles. Dynamic light scattering and transmission electron microscope observations of the hybrid nanoparticles revealed their uniformity and dispersibility in solvents to be excellent. A similar polymerization process was conducted using a hydrophilic monomer, poly(ethylene glycol) methyl ether methacrylate (PEGMA), to prepare Fe3O4 nanoparticles grafted with poly(PEGMA) brushes. The resultant hybrid nanoparticles showed excellent dispersibility in aqueous media including physiological conditions without causing any aggregations. The blood clearance and biodistribution of the hybrid particles were investigated by intravenously injecting particles labeled with a radio isotope, (125)I, into mice. It was found that some hybrid particles exhibited an excellently prolonged circulation lifetime in the blood with a half-life of about 24 h. When such hybrid particles were injected intravenously into a

  3. Quality control of residual solvent content in polymeric microparticles.

    PubMed

    Dixit, Kalpana; Athawale, Rajani B; Singh, Sarabjit

    2015-01-01

    Organic solvents are the innate part of pharmaceutical industry, playing vital role in the bulk drug substance as well as finished product manufacturing. Even though they are used for various crucial purposes, they still lack therapeutic beneficial effect and can be toxic if present in unacceptable limits in final product. Hence, their concentration must be regulated in the final pharmaceutical formulation. With the major development in the market of polymeric microparticles in past few decades, drug product manufacturers are paying more attention towards the development of new techniques for reducing residual solvent content of microparticles. This article sheds light on the importance of removal of organic volatile impurities from the formulation and its regulatory aspects. It also highlights how residual solvent affects various physicochemical characteristics of polymeric microparticles and suggests certain solutions as per the current state of art for limiting organic solvent content in the final product.

  4. Synthesis of Novel μ-Star Copolymers with Poly(N-Octyl Benzamide) and Poly(ε-Caprolactone) Miktoarms through Chain-Growth Condensation Polymerization, Styrenics-Assisted Atom Transfer Radical Coupling, and Ring-Opening Polymerization.

    PubMed

    Huang, Chih-Feng; Aimi, Junko; Lai, Kuan-Yu

    2017-02-01

    Star copolymers are known to phase separate on the nanoscale, providing useful self-assembled morphologies. In this study, the authors investigate synthesis and assembly behavior of miktoarm star (μ-star) copolymers. The authors employ a new strategy for the synthesis of unprecedented μ-star copolymers presenting poly(N-octyl benzamide) (PBA) and poly(ε-caprolactone) (PCL) arms: a combination of chain-growth condensation polymerization, styrenics-assisted atom transfer radical coupling, and ring-opening polymerization. Gel permeation chromatography, mass-analyzed laser desorption/ionization mass spectrometry, and (1) H NMR spectroscopy reveal the successful synthesis of a well-defined (PBA11 )2 -(PCL15 )4 μ-star copolymer (Mn,NMR ≈ 12 620; Đ = 1.22). Preliminary examination of the PBA2 PCL4 μ-star copolymer reveals assembled nanofibers having a uniform diameter of ≈20 nm. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Polymer@MOF@MOF: "grafting from" atom transfer radical polymerization for the synthesis of hybrid porous solids.

    PubMed

    McDonald, Kyle A; Feldblyum, Jeremy I; Koh, Kyoungmoo; Wong-Foy, Antek G; Matzger, Adam J

    2015-08-04

    The application of a core-shell architecture allows the formation of a polymer-coated metal-organic framework (MOF) maintaining high surface area (2289-2857 m(2) g(-1)). The growth of a MOF shell from a MOF core was used to spatially localize initiators by post-synthetic modification. The confinement of initiators ensures that polymerization is restricted to the outer shell of the MOF.

  6. Preparation of Mg(OH)2 hybrid pigment by direct precipitation and graft onto cellulose fiber via surface-initiated atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Wang, Xiao; Zhang, Yue; Lv, Lihua; Cui, Yongzhu; Wei, Chunyan; Pang, Guibing

    2016-02-01

    Mg(OH)2 flame retardant hybrid pigment is synthesized through simultaneous solution precipitation and adsorption of anionic dyes (C.I. Acid Red 6). The Mg(OH)2 hybrid pigment bearing vinyl groups after surface silane modification is immobilized onto the surface of bromo end-functional cellulose fiber by atom transfer radical polymerization (ATRP). The morphology and structure of Mg(OH)2 pigments and cellulose fibers grafted with modified pigments are characterized. The thermal properties, flammability and color fastness of cellulose fibers grafted with modified pigments are measured. The results reveal that anionic dye molecules are adsorbed onto Mg(OH)2 crystals and affect the formation of lamella-like Mg(OH)2 crystals. The cellulose fiber grafted with modified Mg(OH)2 hybrid pigment absorbs about four times heat more than original cellulose fiber with about 4% immobilization ratio of pigment, which shortens nearly half of afterflame time and afterglow time.

  7. Fabrication of an ionic liquid-based macroporous polymer monolithic column via atom transfer radical polymerization for the separation of small molecules.

    PubMed

    Zhang, Hang; Bai, Ligai; Wei, Zhen; Liu, Sha; Liu, Haiyan; Yan, Hongyuan

    2016-01-01

    A polymer monolithic column was prepared in a stainless steel column (50×4.6mm i.d.) via atom transfer radical polymerization technique using triallyl isocyanurate and ionic liquid (1-allyl-3-methylimidazolium chloride) as co-monomers, ethylene dimethacrylate as cross linking agent, polyethylene glycol 200, 1,4-butanediol, and N, N- dimethylformamide as porogen system, CCl4 as initiator, and FeCl2 as catalyst. The optimized polymer columns were characterized by scanning electron microscope, nitrogen adsorption-desorption instrument, mercury intrusion porosimetry, infrared spectrometer, and thermogravimetric analysis technique. Respectively, all of these factors above could illustrate that the optimized columns had relative uniform macroporous structure and high thermal stability. A series of basic and acidic small molecules, isomers, and homologues were used to evaluate the performance of these monoliths and enhanced column efficiency was obtained. Copyright © 2015 Elsevier B.V. All rights reserved.

  8. Precision synthesis of poly(ionic liquid)-based block copolymers by cobalt-mediated radical polymerization and preliminary study of their self-assembling properties.

    PubMed

    Coupillaud, Paul; Fèvre, Maréva; Wirotius, Anne-Laure; Aissou, Karim; Fleury, Guillaume; Debuigne, Antoine; Detrembleur, Christophe; Mecerreyes, David; Vignolle, Joan; Taton, Daniel

    2014-02-01

    A poly(ionic liquid)-based block copolymer (PIL BCP), namely, poly(vinyl acetate)-b-poly(N-vinyl-3-butylimidazolium bromide), PVAc-b-PVBuImBr, is synthesized by sequential cobalt-mediated radical polymerization (CMRP). A PVAc precursor is first prepared at 30 °C in bulk by CMRP of VAc, using bis(acetylacetonato)cobalt(II), Co(acac)2, and a radical source (V-70). Growth of PVBuImBr from PVAc-Co(acac)2 is accomplished by CMRP in DMF/MeOH (2:1, v/v). This PIL BCP self-assembles in the sub-micron size range into aggregated core-shell micelles in THF, whereas polymeric vesicles are observed in water, as evidenced by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Thin-solid sample cut from raw materials analyzed by TEM shows an ordered lamellar organization by temperature-dependent synchrotron small-angle X-ray scattering (SAXS). Anion exchange can be accomplished to achieve the corresponding PIL BCP with bis(trifluorosulfonyl)imide (Tf2 N(-)) anions, which also gives rise to an ordered lamellar phase in bulk samples. A complete suppression of SAXS second-order reflection suggests that this compound has a symmetric volume fraction (f ≈ 0.5). SAXS characterization of both di- and triblock PIL BCP analogues previously reported also shows a lamellar phase of very similar behavior, with only an increase of the period by about 8% at 60 °C.

  9. Controlled Bioactive Molecules Delivery Strategies for Tendon and Ligament Tissue Engineering using Polymeric Nanofibers.

    PubMed

    Hiong Teh, Thomas Kok; Hong Goh, James Cho; Toh, Siew Lok

    2015-01-01

    The interest in polymeric nanofibers has escalated over the past decade given its promise as tissue engineering scaffolds that can mimic the nanoscale structure of the native extracellular matrix. With functionalization of the polymeric nanofibers using bioactive molecules, localized signaling moieties can be established for the attached cells, to stimulate desired biological effects and direct cellular or tissue response. The inherently high surface area per unit mass of polymeric nanofibers can enhance cell adhesion, bioactive molecules loading and release efficiencies, and mass transfer properties. In this review article, the application of polymeric nanofibers for controlled bioactive molecules delivery will be discussed, with a focus on tendon and ligament tissue engineering. Various polymeric materials of different mechanical and degradation properties will be presented along with the nanofiber fabrication techniques explored. The bioactive molecules of interest for tendon and ligament tissue engineering, including growth factors and small molecules, will also be reviewed and compared in terms of their nanofiber incorporation strategies and release profiles. This article will also highlight and compare various innovative strategies to control the release of bioactive molecules spatiotemporally and explore an emerging tissue engineering strategy involving controlled multiple bioactive molecules sequential release. Finally, the review article concludes with challenges and future trends in the innovation and development of bioactive molecules delivery using polymeric nanofibers for tendon and ligament tissue engineering.

  10. Cu(II)-mediated atom transfer radical polymerization of methyl methacrylate via a strategy of thermo-regulated phase-separable catalysis in a liquid/liquid biphasic system: homogeneous catalysis, facile heterogeneous separation, and recycling.

    PubMed

    Pan, Jinlong; Zhang, Bingjie; Jiang, Xiaowu; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

    2014-09-01

    A strategy of thermo-regulated phase-separable catalysis (TPSC) is applied to the Cu(II)-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in a p-xylene/PEG-200 biphasic system. Initiators for continuous activator regeneration ATRP (ICAR ATRP) are used to establish the TPSC-based ICAR ATRP system using water-soluble TPMA as a ligand, EBPA as an initiator, CuBr2 as a catalyst, and AIBN as a reducing agent. By heating to 70 °C, unlimited miscibility of both solvents is achieved and the polymerization can be carried out under homogeneous conditions; then on cooling to 25 °C, the mixture separates into two phases again. As a result, the catalyst complex remains in the PEG-200 phase while the obtained polymers stay in the p-xylene phase. The catalyst can therefore be removed from the resultant polymers by easily separating the two different layers and can be reused again. It is important that well-defined PMMA with a controlled molecular weight and narrow molecular weight distribution could be obtained using this TPSC-based ICAR ATRP system. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Encapsulation of Fe 3O 4 magnetic nanoparticles with poly(methyl methacrylate) via surface functionalized thiol-lactam initiated radical polymerization

    NASA Astrophysics Data System (ADS)

    Bach, Long Giang; Islam, Md. Rafiqul; Kim, Jong Tae; Seo, SungYong; Lim, Kwon Taek

    2012-01-01

    Poly(methyl methacrylate) (PMMA) was grafted onto Fe3O4 magnetic nanoparticles (MNPs) by using a thiol-lactam initiated radical polymerization (TLIRP) via grafting from approach. The surface of the MNPs was treated with the (3-mercaptopropyl)trimethoxysilane coupling agent to give thiol functionalized MNPs (MNPs-SH). Subsequently, the polymerization of MMA performed in the presence of the MNPs-SH and butyrolactam efficiently afforded PMMA-g-MNPs. The grafting of PMMA on the surface of the MNPs was investigated by FT-IR, 1H NMR, TGA, XPS, and EDX analyses. The morphology of the core/shell type PMMA-g-MNPs was confirmed by HR-TEM. GPC analysis showed that the molecular weight of PMMA and monomer conversion increased with the reaction time. The amount of the grafted polymer on the surface of the MNPs was found to be ca. 82.5% as estimated from TGA analysis. The MNPs and PMMA-g-MNPs were subjected to magnetic property investigation by SQUID, and the PMMA-g-MNPs showed relatively high saturated magnetization (53.3 emu/g) without any remanence or coercivity, which made the nanocomposites easily separable from solid-liquid phases suggesting their superparamagnetic character. The magnetic nanocomposites had an exceptionally good dispersibility in organic solvents as demonstrated by UV-Vis spectroscopy as well as time-dependent digital photographic monitoring.

  12. Preparation of high-capacity, weak anion-exchange membranes by surface-initiated atom transfer radical polymerization of poly(glycidyl methacrylate) and subsequent derivatization with diethylamine

    NASA Astrophysics Data System (ADS)

    Qian, Xiaolei; Fan, Hua; Wang, Chaozhan; Wei, Yinmao

    2013-04-01

    Ion-exchange membrane is of importance for the development of membrane chromatography. In this work, a high-capacity anion-exchange membrane was prepared by grafting of glycidyl methacrylate (GMA) onto the surface of regenerated cellulose (RC) membranes via surface-initiated atom transfer radical polymerization (SI-ATRP) and subsequent derivatization with diethylamine. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterize changes in the chemical functionality, surface topography and pore morphology of the modified membranes. The static capacity of the prepared anion-exchange membrane was evaluated with bovine serum albumin (BSA) as a model protein. The results indicated that the anion-exchange membrane which could reach a maximum capacity of 96 mg/mL for static adsorption possesses a higher adsorption capacity, and the adsorption capacity increases with the polymerization time. The effect of pH and salt concentration confirmed that the adsorption of BSA followed ion-exchange mechanism. The established method would have potential application in the preparation of anion-exchange membrane.

  13. Synthesis of poly(poly(ethylene glycol) methacrylate)-polyisobutylene ABA block copolymers by the combination of quasiliving carbocationic and atom transfer radical polymerizations.

    PubMed

    Szabó, Ákos; Szarka, Györgyi; Iván, Béla

    2015-01-01

    Systematic investigations are carried out on the synthesis of a series of new, unique ABA-type triblock copolymers consisting of the hydrophobic and chemically inert polyisobutylene (PIB) inner and the hydrophilic comb-shaped poly(poly(ethylene glycol) methacrylate) (PPEGMA) polymacromonomer as an outer block. Telechelic PIB macroinitiators with narrow molecular weight distributions (MWD) are synthesized by quasiliving carbocationic polymerization of isobutylene with a bifunctional initiator followed by quantitative chain end derivatizations. Atom transfer radical polymerization (ATRP) of PEGMAs with various molecular weights is investigated by using these macroinitiators. It is found that CuBr is an inefficient ATRP catalyst, while CuCl leads to high, nearly complete conversions of the PEGMA macromonomers. Gel permeation chromatography (GPC) analyses reveal slow initiation of PEGMA at relatively high PIB/PEGMA ratios or with PEGMAs of higher molecular weights due to steric hindrance between the macroinitiator and macromonomer. The occurrence of slow initiation, and not permanent termination, is proven by highly efficient ATRP of a low-molecular-weight monomer, methyl methacrylate, with the block copolymers as macroinitiators. Successful synthesis of PPEGMA-PIB-PPEGMA ABA block copolymers is obtained by using either low-molecular-weight PEGMA or relatively low macroinitiator/macromonomer ratios. Differential scanning calorimetry (DSC) indicates phase separation and significant suppression of the crystallinity of the pendant poly(ethylene glycol) (PEG) chains in these new block copolymers. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Improving the drug delivery characteristics of graphene oxide based polymer nanocomposites through the "one-pot" synthetic approach of single-electron-transfer living radical polymerization

    NASA Astrophysics Data System (ADS)

    Gao, Peng; Liu, Meiying; Tian, Jianwen; Deng, Fengjie; Wang, Ke; Xu, Dazhuang; Liu, Liangji; Zhang, Xiaoyong; Wei, Yen

    2016-08-01

    Graphene oxide (GO) based polymer nanocomposites have attracted extensive research interest recently for their outstanding physicochemical properties and potential applications. However, surface modification of GO with synthetic polymers has demonstrated to be trouble for most polymerization procedures are occurred under non-aqueous solution, which will in turn lead to the restacking of GO. In this work, a facile and efficient "one-pot" strategy has been developed for surface modification of GO with synthetic polymers through single-electron-transfer living radical polymerization (SET-LRP). The GO based polymer nanocomposites were obtained via SET-LRP in aqueous solution using poly(ethylene glycol) methyl ether methacrylate (PEGMA) as the monomer and 11-bromoundecanoic acid as the initiator, which could be effectively adsorbed on GO through hydrophobic interaction. The successful preparation of GO based polymer nanocomposites was confirmed by a series of characterization techniques such as 1H nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. The resultant products exhibit high water disperisibility, excellent biocompatibility and high efficient drug loading capability, making these PEGylated GO nanocomposites promising candidates for biomedical applications.

  15. "Near perfect" amphiphilic conetwork based on end-group cross-linking of polydimethylsiloxane triblock copolymer via atom transfer radical polymerization.

    PubMed

    Xu, Jianfeng; Qiu, Ming; Ma, Bomou; He, Chunju

    2014-09-10

    Novel amphiphilic conetworks (APCNs) with uniform channel size were synthesized through end-cross-linking of well-defined amphiphilic triblock copolymers via atom transfer radical polymerization (ATRP). A new ditelechelic polydimethylsiloxane macroinitiator was synthesized to initiate the polymerization of N,N-dimethylacrylamide. The resulting triblock copolymers show well-defined molecular weight with narrow polydisperisty, which are telechelic modified by allylamine and fully cross-linked with polyhydrosiloxanes through hydrosilylation. Transmission electron microscopy shows that the APCN has the behavior of microphase separation with small channel size and uniform phase domain. The resulting APCNs with idealized microstructure exhibit a combination of excellent properties, i.e., superhigh mechanical strength (4 ± 1 MPa) and elongation ratio (175 ± 25%), outstanding oxygen permeability (350 ± 150 barrers), a high water uptake property, and excellent biocompatibility, indicating that in this way, "near perfect" networks are obtained. These results are better than those reported in the literature, suggesting a promising semipermeable barrier for islet encapsulation in relative biomaterial fields.

  16. Controllable synthesis of new polymerizable macrosurfactants via CCTP and RAFT techniques and investigation of their performance in emulsion polymerization.

    PubMed

    Chen, Li; Yan, Lili; Li, Qing; Wang, Caifeng; Chen, Su

    2010-02-02

    We reported herein the synthesis of poly(methacrylic acid)-b-poly(butyl acrylate) (PMAA-b-PBA) block copolymers (surfmers) and their performance as novel polymerizable macrosurfactants in emulsion polymerization. The surfmers bearing terminal unsaturated carbon-carbon double bonds were first successfully designed and sythesized via catalytic chain transfer polymerization (CCTP) and radical addition-fragmentation polymerization (RAFT) techniques. The structures of surfmers were characterized by Raman spectra, nuclear magnetic resonance ((1)H NMR), and gel permeation chromatography (GPC). The critical micelle concentration of surfmers was determined. Subsequently, the surfmers were used as emulsifier to prepare polyacrylate latexes (PA-surf). The influence of the surfmer concentration as well as PMAA and PBA chain segment ratios of surfmer on their performance in emulsion polymerization was discussed thoroughly. The particle size, amount of coagulum, and stability against electrolyte solutions of the latexes were evaluated. Also, the relations between monomer conversion in emulsion polymerization, polymerization rate, emulsion particle size, surface tension, and reaction time were investigated, which showed some interesting information for the probable mechanism underlying this emulsion polymerization system. Atomic force microscopy (AFM) and attenuated total reflection Fourier transform infrared spectra (ATR FT-IR) were performed to investigate the surface morphology and component distribution of the latex films. The results show high efficiency of these surfmers in emulsion polymerization, suggesting that the resultant PMAA-b-PBA block copolymers act not only as the emulsifier but also as the stabilizer of monomer droplets as well as the so-called comonomer.

  17. Near-monodisperse poly(2-(methacryloyloxy)ethyl phosphorylcholine)-based macromonomers prepared by atom transfer radical polymerization and thiol-ene click chemistry: novel reactive steric stabilizers for aqueous emulsion polymerization.

    PubMed

    Warren, Nicholas J; Muise, Carl; Stephens, Alex; Armes, Steven P; Lewis, Andrew L

    2012-02-07

    Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) macromonomers have been prepared by the atom transfer radical polymerization (ATRP) of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) using a bifunctional disulfide-based initiator. To attach a terminal polymerizable methacrylate group, the central disulfide bond was cleaved and the resulting thiols were conjugated to 3-(acryloyloxy)-2-hydroxypropyl methacrylate using tris(2-carboxyethyl)phosphine (TCEP) in water. Here TCEP serves as both the disulfide cleavage agent and also the catalyst for the subsequent Michael addition, which is highly selective for the acrylate group. The resulting methacrylate-terminated macromonomers were used as a reactive steric stabilizer for the aqueous emulsion polymerization of styrene, yielding near-monodisperse PMPC-stabilized polystyrene (PS) latexes of around 100-200 nm in diameter. As a comparison, the disulfide-containing PMPC homopolymer precursor and the intermediate thiol-functional PMPC homopolymer (PMPC-SH) were also evaluated as potential steric stabilizers. Interestingly, near-monodisperse latexes were also obtained in each case. These three sterically-stabilized latexes, prepared using either PMPC macromonomer, disulfide-based PMPC homopolymer, or PMPC-SH homopolymer as a reactive steric stabilizer, remained colloidally stable after both freeze-thaw experiments and the addition of an electrolyte, indicating that a coronal layer of PMPC chains prevented flocculation in each case. In contrast, both a charge-stabilized PS latex prepared in the absence of any steric stabilizer and a PS latex prepared in the presence of a nonfunctional PMPC homopolymer exhibited very poor colloidal stability when subjected to a freeze-thaw cycle or the addition of an electrolyte, as expected.

  18. Chromatographic assessment of two hybrid monoliths prepared via epoxy-amine ring-opening polymerization and methacrylate-based free radical polymerization using methacrylate epoxy cyclosiloxane as functional monomer.

    PubMed

    Wang, Hongwei; Ou, Junjie; Lin, Hui; Liu, Zhongshan; Huang, Guang; Dong, Jing; Zou, Hanfa

    2014-11-07

    Two kinds of hybrid monolithic columns were prepared by using methacrylate epoxy cyclosiloxane (epoxy-MA) as functional monomer, containing three epoxy moieties and one methacrylate group. One column was in situ fabricated by ring-opening polymerization of epoxy-MA and 1,10-diaminodecane (DAD) using a porogenic system consisting of isopropanol (IPA), H2O and ethanol at 65°C for 12h. The other was prepared by free radical polymerization of epoxy-MA and ethylene dimethacrylate (EDMA) using 1-propanol and 1,4-butanediol as the porogenic solvents at 60°C for 12h. Two hybrid monoliths were investigated on the morphology and chromatographic assessment. Although two kinds of monolithic columns were prepared with epoxy-MA, their morphologies looked rather different. It could be found that the epoxy-MA-DAD monolith possessed higher column efficiencies (25,000-34,000plates/m) for the separation of alkylbenzenes than the epoxy-MA-EDMA monolith (12,000-13,000plates/m) in reversed-phase nano-liquid chromatography (nano-LC). Depending on the remaining epoxy or methacrylate groups on the surface of two pristine monoliths, the epoxy-MA-EDMA monolith could be easily modified with 1-octadecylamine (ODA) via ring-opening reaction, while the epoxy-MA-DAD monolith could be modified with stearyl methacrylate (SMA) via free radical reaction. The chromatographic performance for the separation of alkylbenzenes on SMA-modified epoxy-MA-DAD monolith was remarkably improved (42,000-54,000 plates/m) when compared with that on pristine epoxy-MA-DAD monolith, while it was not obviously enhanced on ODA-modified epoxy-MA-EDMA monolith when compared with that on pristine epoxy-MA-EDMA monolith. The enhancement of the column efficiency of epoxy-MA-DAD monolith after modification might be ascribed to the decreased mass-transfer resistence. The two kinds of hybrid monoliths were also applied for separations of six phenols and seven basic compounds in nano-LC.

  19. Cysteine Methylation Controls Radical Generation in the Cfr Radical AdoMet rRNA Methyltransferase

    PubMed Central

    Challand, Martin R.; Salvadori, Enrico; Driesener, Rebecca C.; Kay, Christopher W. M.; Roach, Peter L.; Spencer, James

    2013-01-01

    The ‘radical S-adenosyl-L-methionine (AdoMet)’ enzyme Cfr methylates adenosine 2503 of the 23S rRNA in the peptidyltransferase centre (P-site) of the bacterial ribosome. This modification protects host bacteria, notably methicillin-resistant Staphylococcus aureus (MRSA), from numerous antibiotics, including agents (e.g. linezolid, retapamulin) that were developed to treat such organisms. Cfr contains a single [4Fe-4S] cluster that binds two separate molecules of AdoMet during the reaction cycle. These are used sequentially to first methylate a cysteine residue, Cys338; and subsequently generate an oxidative radical intermediate that facilitates methyl transfer to the unreactive C8 (and/or C2) carbon centres of adenosine 2503. How the Cfr active site, with its single [4Fe-4S] cluster, catalyses these two distinct activities that each utilise AdoMet as a substrate remains to be established. Here, we use absorbance and electron paramagnetic resonance (EPR) spectroscopy to investigate the interactions of AdoMet with the [4Fe-4S] clusters of wild-type Cfr and a Cys338 Ala mutant, which is unable to accept a methyl group. Cfr binds AdoMet with high (∼ 10 µM) affinity notwithstanding the absence of the RNA cosubstrate. In wild-type Cfr, where Cys338 is methylated, AdoMet binding leads to rapid oxidation of the [4Fe-4S] cluster and production of 5'-deoxyadenosine (DOA). In contrast, while Cys338 Ala Cfr binds AdoMet with equivalent affinity, oxidation of the [4Fe-4S] cluster is not observed. Our results indicate that the presence of a methyl group on Cfr Cys338 is a key determinant of the activity of the enzyme towards AdoMet, thus enabling a single active site to support two distinct modes of AdoMet cleavage. PMID:23861844

  20. Controllable surface morphology and properties via mist polymerization on a plasma-treated polymethyl methacrylate surface.

    PubMed

    Wan, S J; Wang, L; Xu, X J; Zhao, C H; Liu, X D

    2014-02-14

    Surface modification by grafting polymers on solid materials is an important strategy used to improve surface properties. This article reports that under appropriate conditions, very thin layers with desired morphologies may be constructed on a plasma-treated substrate by feeding a small quantity of a monomer with a mist stream carrying droplets produced from monomer solutions. We investigate the effects of process parameters that affect layer morphology, including exposure time to the mist stream, concentration of the monomer solution, and solvent selectivity. For a methyl methacrylate solution in ethanol, nanoparticles are uniformly grown with increasing monomer concentration or exposure time and finally form a porous layer at 3.65 mol L(-1) for 30 min. Decreasing solvent polarity not only affects surface morphology, but also increases hydrophobicity of the resulting surface. With 2,2,3,4,4,4-hexafluorobutyl methacrylate as the monomer, SEM and AFM micrographs indicated that mist polymerization results in numerous microspheres on the activated surface. These experimental results were interpreted by a mechanism in terms of an in situ polymerization accompanied by a phase transformation of the resulting polymer. Specifically, plasma treatment provides highly active cations and radicals to initiate very rapid polymerization, and the resulting polymers are consequently deposited from the liquid onto the surface under phase transition mechanisms.

  1. Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization (ATRP) from Poly(vinyl chloride)- co -chlorinated Poly(vinyl chloride) (PVC- co -CPVC) Fiber

    DOE PAGES

    Brown, Suree; Yue, Yanfeng; Kuo, Li-Jung; ...

    2016-03-11

    The need to secure future supplies of energy attracts researchers in several countries to a vast resource of nuclear energy fuel: uranium in seawater (estimated at 4.5 billion tons in seawater). In this study, we developed effective adsorbent fibers for the recovery of uranium from seawater via atom-transfer radical polymerization (ATRP) from a poly-(vinyl chloride)-co-chlorinated poly(vinyl chloride) (PVC-co-CPVC) fiber. ATRP was employed in the surface graft polymerization of acrylonitrile (AN) and tert-butyl acrylate (tBA), precursors for uranium-interacting functional groups, from PVC-co-CPVC fiber. The [tBA]/[AN] was systematically varied to identify the optimal ratio between hydrophilic groups (from tBA) and uranyl-binding ligandsmore » (from AN). The best performing adsorbent fiber, the one with the optimal [tBA]/[AN] ratio and a high degree of grafting (1390%), demonstrated uranium adsorption capacities that are significantly greater than those of the Japan Atomic Energy Agency (JAEA) reference fiber in natural seawater tests (2.42 3.24 g/kg in 42 days of seawater exposure and 5.22 g/kg in 49 days of seawater exposure, versus 1.66 g/kg in 42 days of seawater exposure and 1.71 g/kg in 49 days of seawater exposure for JAEA). Lastly, adsorption of other metal ions from seawater and their corresponding kinetics were also studied. The grafting of alternative monomers for the recovery of uranium from seawater is now under development by this versatile technique of ATRP.« less

  2. Accessing conjugated polymers with precisely controlled heterobisfunctional chain ends via post-polymerization modification of the OTf group and controlled Pd(0)/t-Bu3P-catalyzed Suzuki cross-coupling polymerization

    DOE PAGES

    Hu, Qiao -Sheng; Hong, Kunlun; Zhang, Hong -Hai

    2015-08-12

    In this study, a general strategy toward the synthesis of well-defined conjugated polymers with controlled heterobisfunctional chain ends via combination of controlled Pd(0)/t-Bu3P Suzuki cross-coupling polymerization with the post-polymerization modification of the triflate (OTf) group was disclosed.

  3. Accessing conjugated polymers with precisely controlled heterobisfunctional chain ends via post-polymerization modification of the OTf group and controlled Pd(0)/t-Bu3P-catalyzed Suzuki cross-coupling polymerization

    SciTech Connect

    Hu, Qiao -Sheng; Hong, Kunlun; Zhang, Hong -Hai

    2015-08-12

    In this study, a general strategy toward the synthesis of well-defined conjugated polymers with controlled heterobisfunctional chain ends via combination of controlled Pd(0)/t-Bu3P Suzuki cross-coupling polymerization with the post-polymerization modification of the triflate (OTf) group was disclosed.

  4. Protein Kinase D Controls Actin Polymerization and Cell Motility through Phosphorylation of Cortactin*

    PubMed Central

    Eiseler, Tim; Hausser, Angelika; De Kimpe, Line; Van Lint, Johan; Pfizenmaier, Klaus

    2010-01-01

    We here identify protein kinase D (PKD) as an upstream regulator of the F-actin-binding protein cortactin and the Arp actin polymerization machinery. PKD phosphorylates cortactin in vitro and in vivo at serine 298 thereby generating a 14-3-3 binding motif. In vitro, a phosphorylation-deficient cortactin-S298A protein accelerated VCA-Arp-cortactin-mediated synergistic actin polymerization and showed reduced F-actin binding, indicative of enhanced turnover of nucleation complexes. In vivo, cortactin co-localized with the nucleation promoting factor WAVE2, essential for lamellipodia extension, in the actin polymerization zone in Heregulin-treated MCF-7 cells. Using a 3-dye FRET-based approach we further demonstrate that WAVE2-Arp and cortactin prominently interact at these structures. Accordingly, cortactin-S298A significantly enhanced lamellipodia extension and directed cell migration. Our data thus unravel a previously unrecognized mechanism by which PKD controls cancer cell motility. PMID:20363754

  5. Preparation of methacrylamide-functionalized crosslinked chitosan by free radical polymerization for the removal of lead ions.

    PubMed

    Sutirman, Zetty Azalea; Sanagi, Mohd Marsin; Abd Karim, Khairil Juhanni; Wan Ibrahim, Wan Aini

    2016-10-20

    A new poly(methacrylamide) grafted crosslinked chitosan was prepared for removal of lead, Pb(II) ion from aqueous solution. Crosslinked chitosan, in beads form, was grafted with methacrylamide (MAm) using ammonium persulfate (APS) as free radical initiator. Evidence of grafting was determined by comparing FTIR, TGA, SEM and (13)C NMR analyses of chitosan and graft copolymer. The optimal conditions for grafting reaction were as follow: crosslinked chitosan beads (1g), MAm (17.62×10(-1)M), APS (2.63×10(-1)M), reaction time (3h) and temperature (60°C). The modified chitosan bead was then used in laboratory batch experiments to evaluate the removal of Pb(II) ion from water samples. The Langmuir and Freundlich adsorption models were also applied to describe the equilibrium isotherms. The results revealed that the adsorption of Pb(II) ions onto the beads fitted very well with the Langmuir model with the maximum capacity (qmax) of 250mgg(-1).

  6. Methylenelactide: vinyl polymerization and spatial reactivity effects

    PubMed Central

    Britner, Judita

    2016-01-01

    The first detailed study on free-radical polymerization, copolymerization and controlled radical polymerization of the cyclic push–pull-type monomer methylenelactide in comparison to the non-cyclic monomer α-acetoxyacrylate is described. The experimental results revealed that methylenelactide undergoes a self-initiated polymerization. The copolymerization parameters of methylenelactide and styrene as well as methyl methacrylate were determined. To predict the copolymerization behavior with other classes of monomers, Q and e values were calculated. Further, reversible addition fragmentation chain transfer (RAFT)-controlled homopolymerization of methylenelactide and copolymerization with N,N-dimethylacrylamide was performed at 70 °C in 1,4-dioxane using AIBN as initiator and 2-(((ethylthio)carbonothioyl)thio)-2-methylpropanoic acid as a transfer agent. PMID:28144306

  7. Green polymer chemistry: investigating the mechanism of radical ring-opening redox polymerization (R3P) of 3,6-dioxa-1,8-octanedithiol (DODT).

    PubMed

    Rosenthal-Kim, Emily Q; Puskas, Judit E

    2015-04-13

    The mechanism of the new Radical Ring-opening Redox Polymerization (R3P) of 3,6-dioxa-1,8-octanedithiol (DODT) by triethylamine (TEA) and dilute H2O2 was investigated. Scouting studies showed that the formation of high molecular weight polymers required a 1:2 molar ratio of DODT to TEA and of DODT to H2O2. Further investigation into the chemical composition of the organic and aqueous phases by 1H-NMR spectroscopy and mass spectrometry demonstrated that DODT is ionized by two TEA molecules (one for each thiol group) and thus transferred into the aqueous phase. The organic phase was found to have cyclic disulfide dimers, trimers and tetramers. Dissolving DODT and TEA in water before the addition of H2O2 yielded a polymer with Mn = 55,000 g/mol, in comparison with Mn = 92,000 g/mol when aqueous H2O2 was added to a DODT/TEA mixture. After polymer removal, MALDI-ToF MS analysis of the residual reaction mixtures showed only cyclic oligomers remaining. Below the LCST for TEA in water, 18.7 °C, the system yielded a stable emulsion, and only cyclic oligomers were found. Below DODT/TEA and H2O2 1:2 molar ratio mostly linear oligomers were formed, with <20% cyclic oligomers. The findings support the proposed mechanism of R3P.

  8. Inorganic-organic hybrid coatings on stainless steel by layer-by-layer deposition and surface-initiated atom-transfer-radical polymerization for combating biocorrosion.

    PubMed

    Yuan, S J; Pehkonen, S O; Ting, Y P; Neoh, K G; Kang, E T

    2009-03-01

    To improve the biocorrosion resistance of stainless steel (SS) and to confer the bactericidal function on its surface for inhibiting bacterial adhesion and biofilm formation, well-defined inorganic-organic hybrid coatings, consisting of the inner compact titanium oxide multilayers and outer dense poly(vinyl-N-hexylpyridinium) brushes, were successfully developed. Nanostructured titanium oxide multilayer coatings were first built up on the SS substrates via the layer-by-layer sol-gel deposition process. The trichlorosilane coupling agent, containing the alkyl halide atom-transfer-radical polymerization (ATRP) initiator, was subsequently immobilized on the titanium oxide coatings for surface-initiated ATRP of 4-vinylpyridine (4VP). The pyridium nitrogen moieties of the covalently immobilized 4VP polymer, or P(4VP), brushes were quaternized with hexyl bromide to produce a high concentration of quaternary ammonium salt on the SS surfaces. The excellent antibacterial efficiency of the grafted polycations, poly(vinyl-N-pyridinium bromide), was revealed by viable cell counts and atomic force microscopy images of the surface. The effectiveness of the hybrid coatings in corrosion protection was verified by the Tafel plot and electrochemical impedance spectroscopy measurements.

  9. Grafting of antibacterial polymers on stainless steel via surface-initiated atom transfer radical polymerization for inhibiting biocorrosion by Desulfovibrio desulfuricans.

    PubMed

    Yuan, S J; Xu, F J; Pehkonen, S O; Ting, Y P; Neoh, K G; Kang, E T

    2009-06-01

    To enhance the biocorrosion resistance of stainless steel (SS) and to impart its surface with bactericidal function for inhibiting bacterial adhesion and biofilm formation, well-defined functional polymer brushes were grafted via surface-initiated atom transfer radical polymerization (ATRP) from SS substrates. The trichlorosilane coupling agent, containing the alkyl halide ATRP initiator, was first immobilized on the hydroxylated SS (SS-OH) substrates for surface-initiated ATRP of (2-dimethylamino)ethyl methacrylate (DMAEMA). The tertiary amino groups of covalently immobilized DMAEMA polymer or P(DMAEMA), brushes on the SS substrates were quaternized with benzyl halide to produce the biocidal functionality. Alternatively, covalent coupling of viologen moieties to the tertiary amino groups of P(DMAEMA) brushes on the SS surface resulted in an increase in surface concentration of quaternary ammonium groups, accompanied by substantially enhanced antibacterial and anticorrosion capabilities against Desulfovibrio desulfuricans in anaerobic seawater, as revealed by antibacterial assay and electrochemical studies. With the inherent advantages of high corrosion resistance of SS, and the good antibacterial and anticorrosion capabilities of the viologen-quaternized P(DMAEMA) brushes, the functionalized SS is potentially useful in harsh seawater environments and for desalination plants. Copyright 2009 Wiley Periodicals, Inc.

  10. Antibacterial inorganic-organic hybrid coatings on stainless steel via consecutive surface-initiated atom transfer radical polymerization for biocorrosion prevention.

    PubMed

    Yuan, S J; Pehkonen, S O; Ting, Y P; Neoh, K G; Kang, E T

    2010-05-04

    To enhance the corrosion resistance of stainless steel (SS) and to impart its surface with antibacterial functionality for inhibiting biofilm formation and biocorrosion, well-defined inorganic-organic hybrid coatings, consisting of a polysilsesquioxane inner layer and quaternized poly(2-(dimethyamino)ethyl methacrylate) (P(DMAEMA)) outer blocks, were prepared via successive surface-initiated atom transfer radical polymerization (ATRP) of 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). The cross-linked P(TMASPMA), or polysilsesquioxane, inner layer provided a durable and resistant coating to electrolytes. The pendant tertiary amino groups of the P(DMAEMA) outer block were quaternized with alkyl halide to produce a high concentration of quaternary ammonium groups with biocidal functionality. The so-synthesized inorganic-organic hybrid coatings on the SS substrates exhibited good anticorrosion and antibacterial effects and inhibited biocorrosion induced by sulfate-reducing bacteria (SRB) in seawater media, as revealed by antibacterial assay and electrochemical analyses, and they are potentially useful to steel-based equipment under harsh industrial and marine environments.

  11. Functionalized cotton via surface-initiated atom transfer radical polymerization for enhanced sorption of Cu(II) and Pb(II).

    PubMed

    Zheng, Y Q; Deng, Shubo; Niu, Li; Xu, F J; Chai, M Y; Yu, Gang

    2011-09-15

    The surface-initiated atom transfer radical polymerization (ATRP) was used to successfully prepare the aminated cotton and polyacrylic acid sodium (P(AA-Na))-grafted cotton for the efficient removal of Cu(II) and Pb(II) from aqueous solution in this study. The modified cotton surfaces were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The grafted long polymers with high density of amine and carboxyl groups on the cotton surfaces were responsible for the enhanced adsorption of heavy metals. The sorption behaviors including sorption kinetics, isotherms and pH effect were investigated. The sorption equilibrium of Cu(II) and Pb(II) was achieved within 1h on the P(AA-Na)-grafted cotton, much faster than 8h on the aminated cotton. According to the Langmuir fitting, the maximum sorption capacities of Cu(II) and Pb(II) on the P(AA-Na)-grafted cotton were 2.45 and 2.44 mmol/g, respectively, higher than many adsorbents reported in the literature. The P(AA-Na)-grafted cotton had better adsorption behaviors for Cu(II) and Pb(II) than the aminated cotton.

  12. A poly(acrylonitrile)-functionalized porous aromatic framework synthesized by atom-transfer radical polymerization for the extraction of uranium from seawater

    SciTech Connect

    Yue, Yanfeng; Zhang, Chenxi; Tang, Qing; Mayes, Richard T.; Liao, Wei -Po; Liao, Chen; Tsouris, Costas; Stankovich, Joseph J.; Chen, Jihua; Hensley, Dale K.; Abney, Carter W.; Jiang, De-en; Brown, Suree; Dai, Sheng

    2015-10-30

    In order to ensure a sustainable reserve of fuel for nuclear power generation, tremendous research efforts have been devoted to developing advanced sorbent materials for extracting uranium from seawater. In this work, a porous aromatic framework (PAF) was surface-functionalized with poly(acrylonitrile) through atom-transfer radical polymerization (ATRP). Batches of this adsorbent were conditioned with potassium hydroxide (KOH) at room temperature or 80 °C prior to contact with a uranium-spiked seawater simulant, with minimal differences in uptake observed as a function of conditioning temperature. A maximum capacity of 4.81 g-U/kg-ads was obtained following 42 days contact with uranium-spiked filtered environmental seawater, which demonstrates a comparable adsorption rate. A kinetic investigation revealed extremely rapid uranyl uptake, with more than 80% saturation reached within 14 days. Furthermore, relying on the semiordered structure of the PAF adsorbent, density functional theory (DFT) calculations reveal cooperative interactions between multiple adsorbent groups yield a strong driving force for uranium binding.

  13. Experimental design and analysis of activators regenerated by electron transfer-atom transfer radical polymerization experimental conditions for grafting sodium styrene sulfonate from titanium substrates

    PubMed Central

    Foster, Rami N.; Johansson, Patrik K.; Tom, Nicole R.; Koelsch, Patrick; Castner, David G.

    2015-01-01

    A 24 factorial design was used to optimize the activators regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP) grafting of sodium styrene sulfonate (NaSS) films from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate (ester ClSi) functionalized titanium substrates. The process variables explored were: (1) ATRP initiator surface functionalization reaction time; (2) grafting reaction time; (3) CuBr2 concentration; and (4) reducing agent (vitamin C) concentration. All samples were characterized using x-ray photoelectron spectroscopy (XPS). Two statistical methods were used to analyze the results: (1) analysis of variance with α=0.05, using average Ti XPS atomic percent as the response; and (2) principal component analysis using a peak list compiled from all the XPS composition results. Through this analysis combined with follow-up studies, the following conclusions are reached: (1) ATRP-initiator surface functionalization reaction times have no discernable effect on NaSS film quality; (2) minimum (≤24 h for this system) grafting reaction times should be used on titanium substrates since NaSS film quality decreased and variability increased with increasing reaction times; (3) minimum (≤0.5 mg cm−2 for this system) CuBr2 concentrations should be used to graft thicker NaSS films; and (4) no deleterious effects were detected with increasing vitamin C concentration. PMID:26396463

  14. Self-assemblies of γ-CDs with pentablock copolymers PMA-PPO-PEO-PPO-PMA and endcapping via atom transfer radical polymerization of 2-methacryloyloxyethyl phosphorylcholine

    PubMed Central

    Lin, Jing; Kong, Tao; Ye, Lin; Zhang, Ai-ying

    2015-01-01

    Summary Pentablock copolymers PMA-PPO-PEO-PPO-PMA synthesized via atom transfer radical polymerization (ATRP) were self-assembled with varying amounts of γ-CDs to prepare poly(pseudorotaxanes) (PPRs). When the concentration of γ-CDs was lower, the central PEO segment served as a shell of the micelles and was preferentially bent to pass through the γ-CD cavity to construct double-chain-stranded tight-fit PPRs characterized by a channel-like crystal structure. With an increase in the amount of γ-CDs added, they began to accommodate the poly(methyl acrylate) (PMA) segments dissociated from the core of the micelles. When more γ-CDs were threaded and slipped over the segments, the γ-CDs were randomly distributed along the pentablock copolymer chain to generate single-chain-stranded loose-fit PPRs and showed no characteristic channel-like crystal structure. All the self-assembly processes of the pentablock copolymers resulted in the formation of hydrogels. After endcapping via in situ ATRP of 2-methacryloyloxyethyl phosphorylcholine (MPC), these single-chain-stranded loose-fit PPRs were transformed into conformational identical polyrotaxanes (PRs). The structures of the PPRs and PRs were characterized by means of 1H NMR, GPC, 13C CP/MAS NMR, 2D 1H NOESY NMR, FTIR, WXRD, TGA and DSC analyses. PMID:26732122

  15. Synthesis and Characterization of Surface Grafted Poly(N-isopropylacrylamide) and Poly(Carboxylic Acid)– Iron Particles via Atom Transfer Radical Polymerization for Biomedical Applications

    PubMed Central

    Sutrisno, Joko; Fuchs, Alan; Evrensel, Cahit

    2014-01-01

    This research relates to the preparation and characterization of surface grafted poly(N-isopropylacrylamide) and poly(carboxylic acid)–micron-size iron particles via atom transfer radical polymerization (ATRP). The surface grafted polymers–iron particles result in multifunctional materials which can be used in biomedical applications. The functionalities consist of cell targeting, imaging, drug delivery, and immunological response. The multifunctional materials are synthesized in two steps. First, surface grafting is used to place polymer molecules on the iron particles surface. The second step, is conjugation of the bio-molecules onto the polymer backbone. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy were used to confirm the presence of polymers on the iron particles. The thickness of the grafted polymers and glass transition temperature of the surface grafted polymers were determined by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The covalent bond between grafted polymers and iron particles caused higher glass transition temperature as compared with non-grafted polymers. The ability to target the bio-molecule and provide fluorescent imaging was simulated by conjugation of rat immunoglobulin and fluorescein isothiocyanate (FITC) labeled anti-rat. The fluorescence intensity was determined using flow cytometry and conjugated IgG-FITC anti-rat on iron particles which was imaged using a fluorescence microscopy. PMID:25382869

  16. Grafting N-Isopropyl Acrylamide) from Poly(vinylidene Fluoride) Mirofiltration, Membranes via Direct Surface-Initiated Atom Transfer Radical Polymerization, and Temperature Sensitivity

    NASA Astrophysics Data System (ADS)

    Chen, Yiwang; Xiao, Jichun; Zhou, Weihua; Deng, Qilan; Nie, Huarong; Wan, Meixiang; Bai, Fenglian

    Well-defined poly(N-isopropyl acrylamide) (PNIPAAm) brushes on commercial hydrophobic poly(vinylidene fluoride) (PVDF) microfiltration membrane surfaces were prepared, via direct atom transfer radical polymerization (ATRP) with the secondary fluorinated site of PVDF as initiator and water as solvent at 80°C. The effect of solvents on the ATRP was studied in detail. The water as reaction solvent was in favor of surface-initiated ATRP of N-isopropyl acrylamide (NIPAAm) from secondary fluoride of PVDF membranes. The chemical composition and structure of the modified PVDF membrane surfaces were determined by attenuated total reflectance (ATR) Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface and cross-section morphology of membranes were studied by scanning electron microscopy (SEM). The pore sizes of the pristine PVDF membrane and the PNIPAAm-grafted PVDF membranes were measured using micro-image analysis and process software. The introduction of the well-defined PNIPAAm on the PVDF membrane gave rise to hydrophilicity. Water contact angles of PVDF membranes reduced after the surface grafting of PNIPAAm. Water fluxes and protein solution permeation experiments revealed that the PNIPAAm-grafted PVDF membranes exhibited temperature-responsive permeability. The unique microstructure of PNIPAAm brushes facilitated hydrophilicity below the lower critical solution temperature.

  17. Using the Interior Cavity of the P22 Capsid for Site Specific Initiation of Atom Transfer Radical Polymerization with Tremendously Increased Cargo Loading

    PubMed Central

    Lucon, Janice; Qazi, Shefah; Uchida, Masaki; Bedwel, Gregory J.; LaFrance, Ben; Prevelige, Peter E.; Douglas, Trevor

    2013-01-01

    Virus-like particles (VLPs) have emerged as important and versatile architectures for chemical manipulation in the development of functional hybrid nanostructures. Here we have successfully demonstrated the site selective initiation of atom transfer radical polymerization (ATRP) reactions to form an addressable polymer constrained within the interior cavity of a VLP. This protein-polymer hybrid, of P22 and crosslinked poly(2-aminoethyl methacrylate), is potentially useful as a new high-density delivery vehicle for encapsulation and delivery of small molecule cargos. In particular, the encapsulated polymer can act as a scaffold for the attachment of primary amine reactive molecules of interest, such as a fluorescein dye or a Gd-DTPA MRI contrast agent. Using this approach, a significant increase in labeling density of the VLP, compared to previous modifications of VLPs, can be achieved. These results highlight the use of multimeric protein-polymer conjugates for their potential utility in the development of VLP-based MRI contrast agents with the possibility of loading other cargos. PMID:23000990

  18. A poly(acrylonitrile)-functionalized porous aromatic framework synthesized by atom-transfer radical polymerization for the extraction of uranium from seawater

    DOE PAGES

    Yue, Yanfeng; Zhang, Chenxi; Tang, Qing; ...

    2015-10-30

    In order to ensure a sustainable reserve of fuel for nuclear power generation, tremendous research efforts have been devoted to developing advanced sorbent materials for extracting uranium from seawater. In this work, a porous aromatic framework (PAF) was surface-functionalized with poly(acrylonitrile) through atom-transfer radical polymerization (ATRP). Batches of this adsorbent were conditioned with potassium hydroxide (KOH) at room temperature or 80 °C prior to contact with a uranium-spiked seawater simulant, with minimal differences in uptake observed as a function of conditioning temperature. A maximum capacity of 4.81 g-U/kg-ads was obtained following 42 days contact with uranium-spiked filtered environmental seawater, whichmore » demonstrates a comparable adsorption rate. A kinetic investigation revealed extremely rapid uranyl uptake, with more than 80% saturation reached within 14 days. Furthermore, relying on the semiordered structure of the PAF adsorbent, density functional theory (DFT) calculations reveal cooperative interactions between multiple adsorbent groups yield a strong driving force for uranium binding.« less

  19. Experimental design and analysis of activators regenerated by electron transfer-atom transfer radical polymerization experimental conditions for grafting sodium styrene sulfonate from titanium substrates.

    PubMed

    Foster, Rami N; Johansson, Patrik K; Tom, Nicole R; Koelsch, Patrick; Castner, David G

    2015-09-01

    A 2(4) factorial design was used to optimize the activators regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP) grafting of sodium styrene sulfonate (NaSS) films from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate (ester ClSi) functionalized titanium substrates. The process variables explored were: (1) ATRP initiator surface functionalization reaction time; (2) grafting reaction time; (3) CuBr2 concentration; and (4) reducing agent (vitamin C) concentration. All samples were characterized using x-ray photoelectron spectroscopy (XPS). Two statistical methods were used to analyze the results: (1) analysis of variance with [Formula: see text], using average [Formula: see text] XPS atomic percent as the response; and (2) principal component analysis using a peak list compiled from all the XPS composition results. Through this analysis combined with follow-up studies, the following conclusions are reached: (1) ATRP-initiator surface functionalization reaction times have no discernable effect on NaSS film quality; (2) minimum (≤24 h for this system) grafting reaction times should be used on titanium substrates since NaSS film quality decreased and variability increased with increasing reaction times; (3) minimum (≤0.5 mg cm(-2) for this system) CuBr2 concentrations should be used to graft thicker NaSS films; and (4) no deleterious effects were detected with increasing vitamin C concentration.

  20. Self-assemblies of γ-CDs with pentablock copolymers PMA-PPO-PEO-PPO-PMA and endcapping via atom transfer radical polymerization of 2-methacryloyloxyethyl phosphorylcholine.

    PubMed

    Lin, Jing; Kong, Tao; Ye, Lin; Zhang, Ai-Ying; Feng, Zeng-Guo

    2015-01-01

    Pentablock copolymers PMA-PPO-PEO-PPO-PMA synthesized via atom transfer radical polymerization (ATRP) were self-assembled with varying amounts of γ-CDs to prepare poly(pseudorotaxanes) (PPRs). When the concentration of γ-CDs was lower, the central PEO segment served as a shell of the micelles and was preferentially bent to pass through the γ-CD cavity to construct double-chain-stranded tight-fit PPRs characterized by a channel-like crystal structure. With an increase in the amount of γ-CDs added, they began to accommodate the poly(methyl acrylate) (PMA) segments dissociated from the core of the micelles. When more γ-CDs were threaded and slipped over the segments, the γ-CDs were randomly distributed along the pentablock copolymer chain to generate single-chain-stranded loose-fit PPRs and showed no characteristic channel-like crystal structure. All the self-assembly processes of the pentablock copolymers resulted in the formation of hydrogels. After endcapping via in situ ATRP of 2-methacryloyloxyethyl phosphorylcholine (MPC), these single-chain-stranded loose-fit PPRs were transformed into conformational identical polyrotaxanes (PRs). The structures of the PPRs and PRs were characterized by means of (1)H NMR, GPC, (13)C CP/MAS NMR, 2D (1)H NOESY NMR, FTIR, WXRD, TGA and DSC analyses.

  1. Adsorption of fibrinogen and lysozyme on silicon grafted with poly(2-methacryloyloxyethyl phosphorylcholine) via surface-initiated atom transfer radical polymerization.

    PubMed

    Feng, Wei; Zhu, Shiping; Ishihara, Kazuhiko; Brash, John L

    2005-06-21

    Surfaces based on grafted poly(2-methacryloyloxyethyl phosphorylcholine) (poly(MPC)) "brushes" with a constant graft density of 0.39 chain/nm2 and chain length from 5 to 200 monomer units were prepared by surface-initiated atom transfer radical polymerization (ATRP) on silicon wafers. The chain length and layer thickness of the poly(MPC) grafts were varied via the ratio of MPC to sacrificial initiator. The surfaces were characterized by water contact angle, XPS, and AFM. The effect of poly(MPC) chain length on fibrinogen and lysozyme adsorption was studied in TBS buffer at pH 7.4. The adsorption of both proteins on the poly(MPC)-grafted surfaces was greatly reduced compared to the unmodified silicon. Adsorption decreased with increasing chain length of the poly(MPC) grafts. Grafts of chain length 200 (MW 59 000) gave adsorption levels of 7 and 2 ng/cm2, respectively, for fibrinogen and lysozyme at 1 mg/mL protein concentration, corresponding to reductions of greater than 98% compared to the unmodified silicon. Adsorption experiments using mixtures of the two proteins showed that the suppression of protein adsorption on the poly(MPC)-grafted surfaces was not strongly dependent on protein size or charge.

  2. The Effect of Intensive Education On Urinary Incontinence Following Radical Prostatectomy: A Randomized Control Trial.

    PubMed

    Novick, Besma Jassani; Angie, Michelle; Walker, Esteban; Kitay, Renee; Monday, Kathryn; Albert, Nancy M

    2014-01-01

    Intense bladder control education failed to improve bladder control among patients who underwent a radical prostatectomy as treatment of their prostate cancer. Despite this educational intervention, participants continued to experience post-operative bladder control problems. Nurses need to develop and implement novel interventions that might enhance bladder control.

  3. Multi input single output model predictive control of non-linear bio-polymerization process

    SciTech Connect

    Arumugasamy, Senthil Kumar; Ahmad, Z.

    2015-05-15

    This paper focuses on Multi Input Single Output (MISO) Model Predictive Control of bio-polymerization process in which mechanistic model is developed and linked with the feedforward neural network model to obtain a hybrid model (Mechanistic-FANN) of lipase-catalyzed ring-opening polymerization of ε-caprolactone (ε-CL) for Poly (ε-caprolactone) production. In this research, state space model was used, in which the input to the model were the reactor temperatures and reactor impeller speeds and the output were the molecular weight of polymer (M{sub n}) and polymer polydispersity index. State space model for MISO created using System identification tool box of Matlab™. This state space model is used in MISO MPC. Model predictive control (MPC) has been applied to predict the molecular weight of the biopolymer and consequently control the molecular weight of biopolymer. The result shows that MPC is able to track reference trajectory and give optimum movement of manipulated variable.

  4. Multi input single output model predictive control of non-linear bio-polymerization process

    NASA Astrophysics Data System (ADS)

    Arumugasamy, Senthil Kumar; Ahmad, Z.

    2015-05-01

    This paper focuses on Multi Input Single Output (MISO) Model Predictive Control of bio-polymerization process in which mechanistic model is developed and linked with the feedforward neural network model to obtain a hybrid model (Mechanistic-FANN) of lipase-catalyzed ring-opening polymerization of ɛ-caprolactone (ɛ-CL) for Poly (ɛ-caprolactone) production. In this research, state space model was used, in which the input to the model were the reactor temperatures and reactor impeller speeds and the output were the molecular weight of polymer (Mn) and polymer polydispersity index. State space model for MISO created using System identification tool box of Matlab™. This state space model is used in MISO MPC. Model predictive control (MPC) has been applied to predict the molecular weight of the biopolymer and consequently control the molecular weight of biopolymer. The result shows that MPC is able to track reference trajectory and give optimum movement of manipulated variable.

  5. Epoxide Activated Anionic Polymerization: Application to the Synthesis of (Co)Polyethers with Controlled Structure and Tuned Properties

    NASA Astrophysics Data System (ADS)

    Labbe, Amelie; Rejsek, Virginie; Carlotti, Stephane; Deffieux, Alain

    A ring opening polymerization process allowing the fast and controlled anionic polymerization of epoxide monomers is described and applied to the synthesis of (co)polyethers with novel structure and composition. The approach is based on the simultaneous formation of complexes between an organometallic Lewis acid additive with both the anionic initiator and the monomer. In conjunction with the use of tetraalkylammonium or phosphonium salts as initiators, the addition of such additive allows the synthesis of polyethers and block copolyethers with controlled molar masses and narrow polydispersities, in hydrocarbon media, at low temperature, and in short reaction times. The low nucleophilic character of the propagating species involved in the polymerization avoids transfer to monomer, a side reaction which is often predominant in conventional anionic polymerizations. This also allows the controlled polymerization of functional epoxides such as glycidyl methacrylate and epichlorohydrin. Properties and potential applications of these new polyethers and copolyethers are also reported.

  6. Polymeric enteral diets as primary treatment of active Crohn's disease: a prospective steroid controlled trial.

    PubMed Central

    González-Huix, F; de León, R; Fernández-Bañares, F; Esteve, M; Cabré, E; Acero, D; Abad-Lacruz, A; Figa, M; Guilera, M; Planas, R

    1993-01-01

    Thirty two patients with active Crohn's disease were included in a controlled randomised trial to determine the efficacy and safety of polymeric enteral nutrition compared with steroids, to achieve and maintain clinical remission. The polymeric diet was administered through a fine bore nasogastric tube by continuous, pump assisted infusion (2800 (SEM 120) kcal/day). The steroid group received 1 mg/kg/day of prednisone. Both treatments were effective in inducing clinical remission: 15 of the 17 patients given steroids and 12 of the 15 patients assigned to the polymeric diet went into clinical remission (defined by a Van Hees index < 120) within four weeks of treatment. The percentage reduction of the Van Hees index was 34.8 (4.9)% for steroids and 32.3 (5)% for enteral nutrition (mean difference 2.5%; 95% CI--11.8% to +16.8%). Mean time elapsed to achieve remission was similar in both groups (2.0 (1) v 2.4 (1.2) weeks). Tolerance of the enteral diet was excellent. Four patients in the steroid group had mild complications attributable to this treatment. Ten patients (66.6%) in the steroid group and five (41.6%) in the enteral nutrition group relapsed within a year of discharge, but no differences were found in the cumulative probability of relapse during the follow up period. These results suggest that polymeric enteral nutrition is as safe and effective as steroids in inducing short term remission in active Crohn's disease. PMID:8314510

  7. STATISTICAL, GRADIENT, BLOCK AND GRAFT COPOLYMERS BY CONTROLLED/LIVING RADICAL POLYMERIZATIONS. (R829580)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  8. CONTROLLED/LIVING RADICAL POLYMERIZATION: THE NEXT FRONTIER IN POLYMER SCIENCE? (R826735)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  9. CONTROLLED/LIVING RADICAL POLYMERIZATION APPLIED TO WATER-BORNE SYSTEMS. (R826735)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  10. CONTROLLED/LIVING RADICAL POLYMERIZATION: THE NEXT FRONTIER IN POLYMER SCIENCE? (R826735)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  11. CONTROLLED/LIVING RADICAL POLYMERIZATION APPLIED TO WATER-BORNE SYSTEMS. (R826735)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  12. Surface Treatment of Polymeric Materials Controlling the Adhesion of Biomolecules

    PubMed Central

    Poncin-Epaillard, Fabienne; Vrlinic, Tjasa; Debarnot, Dominique; Mozetic, Miran; Coudreuse, Arnaud; Legeay, Gilbert; El Moualij, Benaïssa; Zorzi, Willy

    2012-01-01

    This review describes different strategies of surface elaboration for a better control of biomolecule adsorption. After a brief description of the fundamental interactions between surfaces and biomolecules, various routes of surface elaboration are presented dealing with the attachment of functional groups mostly thanks to plasma techniques, with the grafting to and from methods, and with the adsorption of surfactants. The grafting of stimuli-responsive polymers is also pointed out. Then, the discussion is focused on the protein adsorption phenomena showing how their interactions with solid surfaces are complex. The adsorption mechanism is proved to be dependent on the solid surface physicochemical properties as well as on the surface and conformation properties of the proteins. Different behaviors are also reported for complex multiple protein solutions. PMID:24955631

  13. Fabrication and control of CT number through polymeric composites based on coronary plaque CT phantom applications

    PubMed Central

    Hoy, Carlton F. O.; Naguib, Hani E.; Paul, Narinder

    2016-01-01

    Abstract. Biomedical phantoms are commonly used for various medical imaging modalities to improve imaging quality and procedures. Current biomedical phantoms fabricated commercially are high in cost and limited in the specificity of human environments and structures that can be mimicked. This study aimed to control the measurable computed tomography (CT) number in Hounsfield units through polymeric biomedical phantom materials using controlled amounts of hydroxyapatite (hA). The purpose was to fabricate CT phantoms capable of mimicking various coronary plaque types while introducing a fabrication technique and basis for a numerical model to which the technique may be applied. The CT number is tunable based on the controlled material properties of electron density and atomic numbers. Three different polymeric matrices of polyethylene (PE), thermoplastic polyurethane (TPU), and polyvinylidene fluoride (PVDF) were selected due to their varied specific densities and ease of fabrication acting as integral properties for CT phantom fabrication. These polymers were processed together with additions of hA in mass percentages of 2.5, 5, 10, and 20% hA as well as a 0% hA as a control for each polymeric material. By adding hA to PE, TPU, and PVDF an increasing trend was exhibited between CT number and weight percent of hA. PMID:26958580

  14. Fabrication and control of CT number through polymeric composites based on coronary plaque CT phantom applications.

    PubMed

    Hoy, Carlton F O; Naguib, Hani E; Paul, Narinder

    2016-01-01

    Biomedical phantoms are commonly used for various medical imaging modalities to improve imaging quality and procedures. Current biomedical phantoms fabricated commercially are high in cost and limited in the specificity of human environments and structures that can be mimicked. This study aimed to control the measurable computed tomography (CT) number in Hounsfield units through polymeric biomedical phantom materials using controlled amounts of hydroxyapatite (hA). The purpose was to fabricate CT phantoms capable of mimicking various coronary plaque types while introducing a fabrication technique and basis for a numerical model to which the technique may be applied. The CT number is tunable based on the controlled material properties of electron density and atomic numbers. Three different polymeric matrices of polyethylene (PE), thermoplastic polyurethane (TPU), and polyvinylidene fluoride (PVDF) were selected due to their varied specific densities and ease of fabrication acting as integral properties for CT phantom fabrication. These polymers were processed together with additions of hA in mass percentages of 2.5, 5, 10, and 20% hA as well as a 0% hA as a control for each polymeric material. By adding hA to PE, TPU, and PVDF an increasing trend was exhibited between CT number and weight percent of hA.

  15. How to polymerize ethylene in a highly controlled fashion?

    PubMed

    Kempe, Rhett

    2007-01-01

    Very fast, reversible, polyethylene (PE) chain transfer or complex-catalysed "Aufbaureaktion" describes a "living" chain-growing process on a main-group metal or zinc atom; this process is catalysed by an organo-transition-metal or lanthanide complex. PE chains are transferred very fast between the two metal sites and chain growth takes place through ethylene insertion into the transition-metal- or lanthanide-carbon bond-coordinative chain-transfer polymerisation (CCTP). The transferred chains "rest" at the main-group or zinc centre, at which chain-termination processes like beta-H transfer/elimination are of low significance. Such protocols can be used to synthesise very narrowly distributed PE materials (M(w)/M(n)<1.1 up to a molecular weight of about 4000 g mol(-1)) with differently functionalised end groups. Higher molecular-weight polymers can be obtained with a slightly increased M(w)/M(n), since diffusion control and precipitation of the polymers influences the chain-transfer process. Recently, a few transition-metal- or lanthanide-based catalyst systems that catalyse such a highly reversible chain-growing process have been described. They are summarised and compared within this contribution.

  16. Enhanced and selective adsorption of mercury ions on chitosan beads grafted with polyacrylamide via surface-initiated atom transfer radical polymerization.

    PubMed

    Li, Nan; Bai, Renbi; Liu, Changkun

    2005-12-06

    Enhanced and selective removal of mercury ions was achieved with chitosan beads grafted with polyacrylamide (chitosan-g-polyacrylamide) via surface-initiated atom transfer radical polymerization (ATRP). The chitosan-g-polyacrylamide beads were found to have significantly greater adsorption capacities and faster adsorption kinetics for mercury ions than the chitosan beads. At pH 4 and with initial mercury concentrations of 10-200 mg/L, the chitosan-g-polyacrylamide beads can achieve a maximum adsorption capacity of up to 322.6 mg/g (in comparison with 181.8 mg/g for the chitosan beads) and displayed a short adsorption equilibrium time of less than 60 min (compared to more than 15 h for the chitosan beads). Coadsorption experiments with both mercury and lead ions showed that the chitosan-g-polyacrylamide beads had excellent selectivity in the adsorption of mercury ions over lead ions at pH < 6, in contrast to the chitosan beads, which did not show clear selectivity for either of the two metal species. Mechanism study suggested that the enhanced mercury adsorption was due to the many amide groups grafted onto the surfaces of the beads, and the selectivity in mercury adsorption can be attributed to the ability of mercury ions to form covalent bonds with the amide. It was found that adsorbed mercury ions on the chitosan-g-polyacrylamide beads can be effectively desorbed in a perchloric acid solution, and the regenerated beads can be reused almost without any loss of adsorption capacity.

  17. Surface polyPEGylation of Eu3+ doped luminescent hydroxyapatite nanorods through the combination of ligand exchange and metal free surface initiated atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Zeng, Guangjian; Liu, Meiying; Heng, Chunning; Huang, Qiang; Mao, Liucheng; Huang, Hongye; Hui, Junfeng; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2017-03-01

    The Eu3+ doped luminescent hydroxyapatite (HAp) nanorods with uniform size and morphology can be synthesized by hydrothermal route. However, these HAp nanorods are coated by hydrophobic oleylamine, which makes them difficult to be dispersed in aqueous solution and impede their biomedical applications. In this work, Eu3+ doped luminescent polymers functionalized HAp nanorods were prepared through the combination of ligand exchange reaction and metal free surface initiated atom transfer radical polymerization (ATRP) method. In this procedure, the amino group functionalized HAp nanorods were first prepared by ligand exchange reaction using adenosine monophosphate (AMP) as ligand. Then the Br-containing initiators (HAp-Br) were introduced onto the surface of HAp-AMP nanorods through the amidation reaction. Finally, polymers functionalized HAp nanorods were prepared by metal free ATRP method using poly(ethylene glycol) methacrylate (PEGMA) as monomer and 10-phenylphenothiazine (PTH) as organic photocatalyst. The properties of these obtained HAp nanocomposites (HAP-polyPEGMA nanorods) were characterized by means of transmission electron microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis in detail. The cell imaging of these HAP-polyPEGMA nanorods was examined using laser scanning confocal microscope to evaluate their biomedical applications. We demonstrated for the first time that hydrophobic luminescent HAp nanorods can be functionalized with polyPEGMA through the combination of ligand exchange reaction and metal free surface initiated ATRP. As compared with the traditional ATRP, the metal free ATRP can overcome the toxic and fluorescence quenching effects of metal catalysts such as copper ions. More importantly, the strategy described in this work should also be utilized for fabrications of many other luminescent polymer nanocomposites due to its good monomer adoptability.

  18. L-Arabinose (pyranose and furanose rings)-branched poly (vinylalcohol): enzymatic synthesis of the sugar esters followed by free radical polymerization.

    PubMed

    Rodrigues Borges, Maurício; Balaban, Rosangela de Carvalho

    2014-12-20

    Herein this study reports the successful synthesis of a new poly(vinyl alcohol) (PVA), containing L-arabinose (L-arabinopyranose and arabinofuranose isomers) branched in only two steps: (1) production of polymerizable monomers of L-arabinose isomers (pyranose and furanose forms) through enzymatic synthesis using alkaline protease from Bacillus subtilis as catalyst and two substrates: L-arabinose and Divinyl Adipate (DVA) in N,N-dimethylformamide (DMF); (2) radical polymerization of the monomers, using an initiator system consisting of potassium persulfate and hydrogen peroxide in water. The transesterification of DVA with L-arabinose was monitored via qualitative analysis by TLC, confirming the formation of the vinyl sugar ester. The acylation occurred on the two different cyclic conformations of the L-arabinose which coexist in equilibrium: (α/β) arabinofuranose and (α/β) arabinopyranose. The acylation positions and the chemical structure of the 5-O-vinyl adipoyl L-arabinofuranose and 4-O-vinyl adipolyl L-arabinopyranose formed were determined by 13C NMR. The surface activity of the L-arabinose esters mixture (monomers) was compared with a commercial product based on phenol formaldehyde polyoxyalkylene polyamine, largely used as surfactant in many industries. FTIR spectroscopy of the sugar ester monomers and the respective polymer were compared revealing the disappearance of the vinyl group in the polymer spectrum. The polymer number-average molar mass (Mn) and the weight-average molar mass (Mw) were determined by gel permeation chromatography (GPC) presenting the following results: 2.9 × 10(4) Da and 7.2 × 10(4) Da, respectively, and polydispersity (Mw/Mn) equal to 2.48.

  19. Control of surface charges by radicals as a principle of antistatic polymers protecting electronic circuitry.

    PubMed

    Baytekin, H Tarik; Baytekin, Bilge; Hermans, Thomas M; Kowalczyk, Bartlomiej; Grzybowski, Bartosz A

    2013-09-20

    Even minute quantities of electric charge accumulating on polymer surfaces can cause shocks, explosions, and multibillion-dollar losses to electronic circuitry. This paper demonstrates that to remove static electricity, it is not at all necessary to "target" the charges themselves. Instead, the way to discharge a polymer is to remove radicals from its surface. These radicals colocalize with and stabilize the charges; when they are scavenged, the surfaces discharge rapidly. This radical-charge interplay allows for controlling static electricity by doping common polymers with small amounts of radical-scavenging molecules, including the familiar vitamin E. The effectiveness of this approach is demonstrated by rendering common polymers dust-mitigating and also by using them as coatings that prevent the failure of electronic circuitry.

  20. Nanoparticle Control of Void Formation and Expansion in Polymeric and Composite Systems

    DTIC Science & Technology

    2007-02-01

    particulate phase into a polymeric matrix. Initially, this methodology was applied to neat thermoplastic resin systems. It was soon adapted for...were no significant effects of the blowing agent and surfactant on the foam morphology. Foam Density Density of the traditional epoxy matrix (control...34Rheological and Morphological Properties of VARTM (Vacuum Assisted Resin Transfer Molding ) Epoxy Resin/ Clay Nanocomposites," Society of Plastics

  1. Micro-electro-mechanics of ionic polymeric gels as electrically controllable artificial muscles

    SciTech Connect

    Shahinpoor, M.

    1994-12-31

    A polymer gel is defined as a cross-linked polymer network swollen in a liquid medium. These gels possess an ionic structure in the sense that they are generally composed of a number of fixed ions pertaining to sites of various polymer cross-links and segments and mobile ions (counter ions) due to the presence of a solvent which is electrolytic. Ionic polymeric gels are three-dimensional networks of cross-linked macromolecular polyelectrolytes that swell or shrink in aqueous solutions on addition of alkali or acids, respectively. Linear reversible dilation and contraction of the order of more than 1,000 percent have been observed in the laboratory for polyacrylonitrile (PAN) fibers. Furthermore, it has been experimentally observed that swelling and shrinking of ionic gels can also be induced electrically. Thus, direct computer control of large expansions and contractions of ionic polymeric gels by means of a voltage gradient appears to be possible. A mechanism is presented for the reversible nonhomogeneous large deformations and in particular bending of strips of ionic polymeric gels in the presence of an electric field. Exact expressions are given relating the deformation characteristics of the gel to the electric field strength or voltage gradient, gel dimensions and other physical parameters such as the resistance and the capacitance of the gel strip. It is concluded that direct voltage control of such nonhomogeneous large deformations in ionic polymeric gels is possible. These electrically controlled deformations may find unique applications in robotics, artificial muscles, large motion actuator designs, drug delivery systems and smart materials, adaptive structures and systems.

  2. The Radical Press and the Beginning of the Birth Control Movement in the United States.

    ERIC Educational Resources Information Center

    Goldstein, Cynthia

    The American birth control movement was born among radicals, mostly socialist women, early in the twentieth century. Although some information about birth control had circulated in medical journals, books and advertising in the nineteenth century, the passage in 1873 of a federal obscenity law known as the Comstock law resulted in the absence of…

  3. The Radical Press and the Beginning of the Birth Control Movement in the United States.

    ERIC Educational Resources Information Center

    Goldstein, Cynthia

    The American birth control movement was born among radicals, mostly socialist women, early in the twentieth century. Although some information about birth control had circulated in medical journals, books and advertising in the nineteenth century, the passage in 1873 of a federal obscenity law known as the Comstock law resulted in the absence of…

  4. Comparative Effectiveness of Cancer Control and Survival after Robot-Assisted versus Open Radical Prostatectomy.

    PubMed

    Hu, Jim C; O'Malley, Padraic; Chughtai, Bilal; Isaacs, Abby; Mao, Jialin; Wright, Jason D; Hershman, Dawn; Sedrakyan, Art

    2017-01-01

    Robot-assisted surgery has been rapidly adopted in the U.S. for prostate cancer. Its adoption has been driven by market forces and patient preference, and debate continues regarding whether it offers improved outcomes to justify the higher cost relative to open surgery. We examined the comparative effectiveness of robot-assisted vs open radical prostatectomy in cancer control and survival in a nationally representative population. This population based observational cohort study of patients with prostate cancer undergoing robot-assisted radical prostatectomy and open radical prostatectomy during 2003 to 2012 used data captured in the SEER (Surveillance, Epidemiology, and End Results)-Medicare linked database. Propensity score matching and time to event analysis were used to compare all cause mortality, prostate cancer specific mortality and use of additional treatment after surgery. A total of 6,430 robot-assisted radical prostatectomies and 9,161 open radical prostatectomies performed during 2003 to 2012 were identified. The use of robot-assisted radical prostatectomy increased from 13.6% in 2003 to 2004 to 72.6% in 2011 to 2012. After a median followup of 6.5 years (IQR 5.2-7.9) robot-assisted radical prostatectomy was associated with an equivalent risk of all cause mortality (HR 0.85, 0.72-1.01) and similar cancer specific mortality (HR 0.85, 0.50-1.43) vs open radical prostatectomy. Robot-assisted radical prostatectomy was also associated with less use of additional treatment (HR 0.78, 0.70-0.86). Robot-assisted radical prostatectomy has comparable intermediate cancer control as evidenced by less use of additional postoperative cancer therapies and equivalent cancer specific and overall survival. Longer term followup is needed to assess for differences in prostate cancer specific survival, which was similar during intermediate followup. Our findings have significant quality and cost implications, and provide reassurance regarding the adoption of more

  5. Controlled drug release through a plasma polymerized tetramethylcyclo-tetrasiloxane coating barrier.

    PubMed

    Osaki, Shigemasa; Chen, Meng; Zamora, Paul O

    2012-01-01

    A plasma polymerized tetramethylcyclo-tetrasiloxane (TMCTS) coating was deposited onto a metallic biomaterial, 316 stainless steel, to control the release rate of drugs, including daunomycin, rapamycin and NPC-15199 (N-(9-fluorenylmethoxy-carbonyl)-leucine), from the substrate surface. The plasma-state polymerized TMCTS thin film was deposited in a vacuum plasma reactor operated at a radio-frequency of 13.56 MHz, and was highly adhesive to the stainless steel, providing a smooth and hard coating layer for drugs coated on the substrate. To investigate the influence of plasma coating thickness on the drug diffusion profile, coatings were deposited at various time lengths from 20 s to 6 min, depending on the type of drug. Atomic force spectroscopy (AFM) was utilized to characterize coating thickness. Drug elution was measured using a spectrophotometer or high-performance liquid chromatography (HPLC) system. The experimental results indicate that plasma polymerized TMCTS can be used as an over-coating to control drug elution at the desired release rate. The drug-release rate was also found to be dependent on the molecular weight of the drug with plasma coating barrier on top of it. The in vitro cytotoxicity test result suggested that the TMCTS plasma coatings did not produce a cytotoxic response to mammalian cells. The non-cytotoxicity of TMCTS coating plus its high thrombo-resistance and biocompatibility are very beneficial to drug-eluting devices that contact blood.

  6. Rapid Prototyping of Polymeric Nanopillars by 3D Direct Laser Writing for Controlling Cell Behavior.

    PubMed

    Buch-Månson, Nina; Spangenberg, Arnaud; Gomez, Laura Piedad Chia; Malval, Jean-Pierre; Soppera, Olivier; Martinez, Karen L

    2017-08-23

    Mammalian cells have been widely shown to respond to nano- and microtopography that mimics the extracellular matrix. Synthetic nano- and micron-sized structures are therefore of great interest in the field of tissue engineering, where polymers are particularly attractive due to excellent biocompatibility and versatile fabrication methods. Ordered arrays of polymeric pillars provide a controlled topographical environment to study and manipulate cells, but processing methods are typically either optimized for the nano- or microscale. Here, we demonstrate polymeric nanopillar (NP) fabrication using 3D direct laser writing (3D DLW), which offers a rapid prototyping across both size regimes. The NPs are interfaced with NIH3T3 cells and the effect of tuning geometrical parameters of the NP array is investigated. Cells are found to adhere on a wide range of geometries, but the interface depends on NP density and length. The Cell Interface with Nanostructure Arrays (CINA) model is successfully extended to predict the type of interface formed on different NP geometries, which is found to correlate with the efficiency of cell alignment along the NPs. The combination of the CINA model with the highly versatile 3D DLW fabrication thus holds the promise of improved design of polymeric NP arrays for controlling cell growth.

  7. Industrial application of Raman spectroscopy for control and optimization of vinyl acetate resin polymerization.

    PubMed

    Frauendorfer, Eric; Hergeth, Wolf-Dieter

    2017-01-01

    Monitoring and control of resin polymerizations is essential for high process safety, high product quality, and competitive production costs. Vinyl acetate resins created by bulk and solution polymerization usually have a high molecular weight and viscosity, making sample extraction for analysis a cumbersome process. In-process analytical methods, like Raman spectroscopy, enable not only the measurement of monomer and polymer composition during the reaction without complex mathematical calibrations but also the determination of final product properties. The latter is also possible in conjunction with other process data like temperatures and feed rates and with a multivariate approach. An overview of challenges, necessary considerations, and results is given. Graphical abstract Prediction of product quality parameter viscosity using online-Raman spectroscopy data vs. reference data (Hoeppler viscosity measured in the lab after sample extraction) using partial least squares modelling.

  8. Anchoring energy enhancement and pretilt angle control of liquid crystal alignment on polymerized surfaces

    NASA Astrophysics Data System (ADS)

    Weng, Libo; Liao, Pei-Chun; Lin, Chen-Chun; Ting, Tien-Lun; Hsu, Wen-Hao; Su, Jenn-Jia; Chien, Liang-Chy

    2015-09-01

    We demonstrate enhanced surface anchoring energy and control of pretilt angle in a nematic liquid crystal cell with vertical alignment and polymerized surfaces (PS-VA). The polymerized surfaces are formed by ultraviolet (UV) irradiation-induced phase separation of a minute amount of a reactive monomer in the vertical-aligned nematic liquid crystal. By introducing a bias voltage during UV curing, surface-localized polymer protrusions with a dimension of 100nm and a field-induced pretilt angle are observed. Experimental evidences and theoretical analyses validate that PS-VA has increased surface anchoring strength by two folds and pretilt angle has been changed from 89° to 86° compared to those of a VA cell. The enabling PS-VA cell technique with excel electro-optical properties such as very good dark state, high optical contrast, and fast rise and decay times may lead to development of a wide range of applications.

  9. Anchoring energy enhancement and pretilt angle control of liquid crystal alignment on polymerized surfaces

    SciTech Connect

    Weng, Libo; Chien, Liang-Chy; Liao, Pei-Chun; Lin, Chen-Chun; Ting, Tien-Lun; Hsu, Wen-Hao; Su, Jenn-Jia

    2015-09-15

    We demonstrate enhanced surface anchoring energy and control of pretilt angle in a nematic liquid crystal cell with vertical alignment and polymerized surfaces (PS-VA). The polymerized surfaces are formed by ultraviolet (UV) irradiation-induced phase separation of a minute amount of a reactive monomer in the vertical-aligned nematic liquid crystal. By introducing a bias voltage during UV curing, surface-localized polymer protrusions with a dimension of 100nm and a field-induced pretilt angle are observed. Experimental evidences and theoretical analyses validate that PS-VA has increased surface anchoring strength by two folds and pretilt angle has been changed from 89° to 86° compared to those of a VA cell. The enabling PS-VA cell technique with excel electro-optical properties such as very good dark state, high optical contrast, and fast rise and decay times may lead to development of a wide range of applications.

  10. Polymethyl methacrylate-co-methacrylic acid coatings with controllable concentration of surface carboxyl groups: A novel approach in fabrication of polymeric platforms for potential bio-diagnostic devices

    NASA Astrophysics Data System (ADS)

    Hosseini, Samira; Ibrahim, Fatimah; Djordjevic, Ivan; Koole, Leo H.

    2014-05-01

    The generally accepted strategy in development of bio-diagnostic devices is to immobilize proteins on polymeric surfaces as a part of detection process for diseases and viruses through antibody/antigen coupling. In that perspective, polymer surface properties such as concentration of functional groups must be closely controlled in order to preserve the protein activity. In order to improve the surface characteristics of transparent polymethacrylate plastics that are used for diagnostic devices, we have developed an effective fabrication procedure of polymethylmetacrylate-co-metacrylic acid (PMMA-co-MAA) coatings with controlled number of surface carboxyl groups. The polymers were processed effectively with the spin-coating technique and the detailed control over surface properties is here by demonstrated through the variation of a single synthesis reaction parameter. The chemical structure of synthesized and processed co-polymers has been investigated with nuclear magnetic resonance spectroscopy (NMR) and matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-ToF-MS). The surface morphology of polymer coatings have been analyzed with atomic force microscopy (AFM) and scanning electron microscopy (SEM). We demonstrate that the surface morphology and the concentration of surface -COOH groups (determined with UV-vis surface titration) on the processed PMMA-co-MAA coatings can be precisely controlled by variation of initial molar ratio of reactants in the free-radical polymerization reaction. The wettability of developed polymer surfaces also varies with macromolecular structure.

  11. Methyl Methacrylate Polymerization in Nanoporous Matrix: Reactivity and Molecular Weight

    NASA Astrophysics Data System (ADS)

    Zhao, Haoyu; Simon, Sindee

    2011-03-01

    The influence of nanoconfinement on the free radical polymerization of methyl methacrylate is investigated. Nanoporous controlled pore glass (CPG) is used as a nanoconfining matrix for the polymerization. The reaction is followed by measuring heat flow as a function of reaction time during isothermal polymerization using differential scanning calorimetry (DSC). Preliminary results indicate several interesting effects for polymerization in 110 nm diameter pores: the induction time increases under nanoconfinement, the effective reaction rate constant increases, the effective activation energy is unchanged, and the gel effect or autoaccleration occurs at earlier times after induction. The latter result concerning the gel effect is presumably due to the decrease in diffusivity under nanoconfinement which results in a decrease in the termination rate of free radicals. The cause of the longer induction times and accelerated reaction rates just after induction are under investigation. The influence of nanoconfinement on molecular weight will also be examined.

  12. Profilin Regulates Apical Actin Polymerization to Control Polarized Pollen Tube Growth.

    PubMed

    Liu, Xiaonan; Qu, Xiaolu; Jiang, Yuxiang; Chang, Ming; Zhang, Ruihui; Wu, Youjun; Fu, Ying; Huang, Shanjin

    2015-12-07

    Pollen tube growth is an essential step during flowering plant reproduction, whose growth depends on a population of dynamic apical actin filaments. Apical actin filaments were thought to be involved in the regulation of vesicle fusion and targeting in the pollen tube. However, the molecular mechanisms that regulate the construction of apical actin structures in the pollen tube remain largely unclear. Here, we identify profilin as an important player in the regulation of actin polymerization at the apical membrane in the pollen tube. Downregulation of profilin decreased the amount of filamentous actin and induced disorganization of apical actin filaments, and reduced tip-directed vesicle transport and accumulation in the pollen tube. Direct visualization of actin dynamics revealed that the elongation of actin filaments originating at the apical membrane decreased in profilin mutant pollen tubes. Mutant profilin that is defective in binding poly-L-proline only partially rescues the actin polymerization defect in profilin mutant pollen tubes, although it fully rescues the actin turnover phenotype. We propose that profilin controls the construction of actin structures at the pollen tube tip, presumably by favoring formin-mediated actin polymerization at the apical membrane.

  13. Electrospun regenerated cellulose nanofibrous membranes surface-grafted with polymer chains/brushes via the atom transfer radical polymerization method for catalase immobilization.

    PubMed

    Feng, Quan; Hou, Dayin; Zhao, Yong; Xu, Tao; Menkhaus, Todd J; Fong, Hao

    2014-12-10

    In this study, an electrospun regenerated cellulose (RC) nanofibrous membrane with fiber diameters of ∼200-400 nm was prepared first; subsequently, 2-hydroxyethyl methacrylate (HEMA), 2-dimethylaminoethyl methacrylate (DMAEMA), and acrylic acid (AA) were selected as the monomers for surface grafting of polymer chains/brushes via the atom transfer radical polymerization (ATRP) method. Thereafter, four nanofibrous membranes (i.e., RC, RC-poly(HEMA), RC-poly(DMAEMA), and RC-poly(AA)) were explored as innovative supports for immobilization of an enzyme of bovine liver catalase (CAT). The amount/capacity, activity, stability, and reusability of immobilized catalase were evaluated, and the kinetic parameters (Vmax and Km) for immobilized and free catalase were determined. The results indicated that the respective amounts/capacities of immobilized catalase on RC-poly(HEMA) and RC-poly(DMAEMA) nanofibrous membranes reached 78 ± 3.5 and 67 ± 2.7 mg g(-1), which were considerably higher than the previously reported values. Meanwhile, compared to that of free CAT (i.e., 18 days), the half-life periods of RC-CAT, RC-poly(HEMA)-CAT, RC-poly(DMAEMA)-CAT, and RC-poly(AA)-CAT were 49, 58, 56, and 60 days, respectively, indicating that the storage stability of immobilized catalase was also significantly improved. Furthermore, the immobilized catalase exhibited substantially higher resistance to temperature variation (tested from 5 to 70 °C) and lower degree of sensitivity to pH value (tested from 4.0 and 10.0) than the free catalase. In particular, according to the kinetic parameters of Vmax and Km, the nanofibrous membranes of RC-poly(HEMA) (i.e., 5102 μmol mg(-1) min(-1) and 44.89 mM) and RC-poly(DMAEMA) (i.e., 4651 μmol mg(-1) min(-1) and 46.98 mM) had the most satisfactory biocompatibility with immobilized catalase. It was therefore concluded that the electrospun RC nanofibrous membranes surface-grafted with 3-dimensional nanolayers of polymer chains/brushes would be

  14. Hierarchical supramolecular ordering with biaxial orientation of a combined main-chain/side-chain liquid-crystalline polymer obtained from radical polymerization of 2-vinylterephthalate.

    PubMed

    Xie, He-Lou; Jie, Chang-Kai; Yu, Zhen-Qiang; Liu, Xuan-Bo; Zhang, Hai-Liang; Shen, Zhihao; Chen, Er-Qiang; Zhou, Qi-Feng

    2010-06-16

    The liquid-crystalline (LC) phase structures and transitions of a combined main-chain/side-chain LC polymer (MCSCLCP) 1 obtained from radical polymerization of a 2-vinylterephthalate, poly(2,5-bis{[6-(4-butoxy-4'-oxybiphenyl) hexyl]oxycarbonyl}styrene), were studied using differential scanning calorimetry, one- and two-dimensional wide-angle X-ray diffraction (1D and 2D WAXD), and polarized light microscopy. We have found that 1 with sufficiently high molecular weight can self-assemble into a hierarchical structure with double orderings on the nanometer and subnanometer scales at low temperatures. The main chains of 1, which are rodlike as a result of the "jacketing" effect generated by the central rigid portion of the side chains laterally attached to every second carbon atom along the polyethylene backbone, form a 2D centered rectangular scaffold. The biphenyl-containing side chains fill the space between the main chains, forming a smectic E (SmE)-like structure with the side-chain axis perpendicular to that of the main chain. This biaxial orientation of 1 was confirmed by our 2D WAXD experiments through three orthogonal directions. The main-chain scaffold remains when the SmE-like packing is melted at elevated temperatures. Further heating leads to a normal smectic A (SmA) structure followed by the isotropic state. We found that when an external electric field was applied, the main-chain scaffold greatly inhibited the motion of the biphenyls. While the main chains gain a sufficiently high mobility in the SmA phase, macroscopic orientation of 1 can be achieved using a rather weak electric field, implying that the main and side chains with orthogonal directions can move cooperatively. Our work demonstrates that when two separate components, one offering the "jacketing" effect to the normally flexible backbone and the other with mesogens that form surrounding LC phases, are introduced simultaneously into the side chains, the polymer obtained can be described as an

  15. Of Radicals and DREAMers: Harnessing Exceptionality to Challenge Immigration Control

    ERIC Educational Resources Information Center

    Heredia, Luisa Laura

    2015-01-01

    This article contributes to the literature on undocumented youth activism and citizenship by assessing undocumented youth's challenges to a growing regime of migration control in the US. It uses Doug McAdam's tactical interaction as an analytical lens to explore two consecutive high-risk campaigns, ICE infiltrations and expulsion/re-entry. In this…

  16. Of Radicals and DREAMers: Harnessing Exceptionality to Challenge Immigration Control

    ERIC Educational Resources Information Center

    Heredia, Luisa Laura

    2015-01-01

    This article contributes to the literature on undocumented youth activism and citizenship by assessing undocumented youth's challenges to a growing regime of migration control in the US. It uses Doug McAdam's tactical interaction as an analytical lens to explore two consecutive high-risk campaigns, ICE infiltrations and expulsion/re-entry. In this…

  17. Supramolecular polymerization of a prebiotic nucleoside provides insights into the creation of sequence-controlled polymers

    SciTech Connect

    Wang, Jun; Bonnesen, Peter V; Rangel, E.; Vallejo, E.; Sanchez-Castillo, Ariadna; Cleaves, II, H. James; Baddorf, Arthur P; Sumpter, Bobby G; Pan, Minghu; Maksymovych, Petro; Fuentes-Cabrera, Miguel A

    2016-01-04

    The self-assembly of a nucleoside on Au(111) was studied to ascertain whether polymerization on well-defined substrates constitutes a promising approach for making sequence-controlled polymers. Scanning tunneling microscopy and density functional theory were used to investigate the self-assembly on Au(111) of (RS)-N9-(2,3-dihydroxypropyl)adenine (DHPA), a plausibly prebiotic nucleoside analog of adenosine. It is found that DHPA molecules self-assemble into a hydrogen-bonded polymer that grows almost exclusively along the herringbone reconstruction pattern, has a two component sequence that is repeated over hundreds of nanometers, and is erasable with electron-induced excitation. Although the sequence is simple, more complicated ones are envisioned if two or more nucleoside types are combined. Because polymerization occurs on a substrate in a dry environment, the success of each combination can be gauged with high-resolution imaging and accurate modeling techniques. The resulting characteristics make nucleoside self-assembly on a substrate an attractive approach for designing sequence-controlled polymers. Moreover, by choosing plausibly prebiotic nucleosides, insights may be provided into how nature created the first sequence-controlled polymers capable of storing information. Such insights, in turn, can inspire new ways of synthesizing sequence-controlled polymers.

  18. Supramolecular polymerization of a prebiotic nucleoside provides insights into the creation of sequence-controlled polymers

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Bonnesen, Peter V.; Rangel, E.; Vallejo, E.; Sanchez-Castillo, Ariadna; James Cleaves, H., II; Baddorf, Arthur P.; Sumpter, Bobby G.; Pan, Minghu; Maksymovych, Petro; Fuentes-Cabrera, Miguel

    2016-01-01

    Self-assembly of a nucleoside on Au(111) was studied to ascertain whether polymerization on well-defined substrates constitutes a promising approach for making sequence-controlled polymers. Scanning tunneling microscopy and density functional theory were used to investigate the self-assembly on Au(111) of (RS)-N9-(2,3-dihydroxypropyl)adenine (DHPA), a plausibly prebiotic nucleoside analog of adenosine. It is found that DHPA molecules self-assemble into a hydrogen-bonded polymer that grows almost exclusively along the herringbone reconstruction pattern, has a two component sequence that is repeated over hundreds of nanometers, and is erasable with electron-induced excitation. Although the sequence is simple, more complicated ones are envisioned if two or more nucleoside types are combined. Because polymerization occurs on a substrate in a dry environment, the success of each combination can be gauged with high-resolution imaging and accurate modeling techniques. These characteristics make nucleoside self-assembly on a substrate an attractive approach for designing sequence-controlled polymers. Further, by choosing plausibly prebiotic nucleosides, insights may be provided into how nature created the first sequence-controlled polymers capable of storing information. Such insights, in turn, can inspire new ways of synthesizing sequence-controlled polymers.

  19. Supramolecular polymerization of a prebiotic nucleoside provides insights into the creation of sequence-controlled polymers

    PubMed Central

    Wang, Jun; Bonnesen, Peter V.; Rangel, E.; Vallejo, E.; Sanchez-Castillo, Ariadna; James Cleaves II, H.; Baddorf, Arthur P.; Sumpter, Bobby G.; Pan, Minghu; Maksymovych, Petro; Fuentes-Cabrera, Miguel

    2016-01-01

    Self-assembly of a nucleoside on Au(111) was studied to ascertain whether polymerization on well-defined substrates constitutes a promising approach for making sequence-controlled polymers. Scanning tunneling microscopy and density functional theory were used to investigate the self-assembly on Au(111) of (RS)-N9-(2,3-dihydroxypropyl)adenine (DHPA), a plausibly prebiotic nucleoside analog of adenosine. It is found that DHPA molecules self-assemble into a hydrogen-bonded polymer that grows almost exclusively along the herringbone reconstruction pattern, has a two component sequence that is repeated over hundreds of nanometers, and is erasable with electron-induced excitation. Although the sequence is simple, more complicated ones are envisioned if two or more nucleoside types are combined. Because polymerization occurs on a substrate in a dry environment, the success of each combination can be gauged with high-resolution imaging and accurate modeling techniques. These characteristics make nucleoside self-assembly on a substrate an attractive approach for designing sequence-controlled polymers. Further, by choosing plausibly prebiotic nucleosides, insights may be provided into how nature created the first sequence-controlled polymers capable of storing information. Such insights, in turn, can inspire new ways of synthesizing sequence-controlled polymers. PMID:26725380

  20. Supramolecular polymerization of a prebiotic nucleoside provides insights into the creation of sequence-controlled polymers

    DOE PAGES

    Wang, Jun; Bonnesen, Peter V; Rangel, E.; ...

    2016-01-04

    The self-assembly of a nucleoside on Au(111) was studied to ascertain whether polymerization on well-defined substrates constitutes a promising approach for making sequence-controlled polymers. Scanning tunneling microscopy and density functional theory were used to investigate the self-assembly on Au(111) of (RS)-N9-(2,3-dihydroxypropyl)adenine (DHPA), a plausibly prebiotic nucleoside analog of adenosine. It is found that DHPA molecules self-assemble into a hydrogen-bonded polymer that grows almost exclusively along the herringbone reconstruction pattern, has a two component sequence that is repeated over hundreds of nanometers, and is erasable with electron-induced excitation. Although the sequence is simple, more complicated ones are envisioned if two ormore » more nucleoside types are combined. Because polymerization occurs on a substrate in a dry environment, the success of each combination can be gauged with high-resolution imaging and accurate modeling techniques. The resulting characteristics make nucleoside self-assembly on a substrate an attractive approach for designing sequence-controlled polymers. Moreover, by choosing plausibly prebiotic nucleosides, insights may be provided into how nature created the first sequence-controlled polymers capable of storing information. Such insights, in turn, can inspire new ways of synthesizing sequence-controlled polymers.« less

  1. Sustainable polymerizations in recoverable microemulsions.

    PubMed

    Chen, Zhenzhen; Yan, Feng; Qiu, Lihua; Lu, Jianmei; Zhou, Yinxia; Chen, Jiaxin; Tang, Yishan; Texter, John

    2010-03-16

    Free radical and atom-transfer radical polymerizations were conducted in monomer/ionic liquid microemulsions. After the polymerization and isolation of the resultant polymers, the mixture of the catalyst and ionic liquids (surfactant and continuous phase) can be recovered and reused, thereby dramatically improving the environmental sustainability of such chemical processing. The addition of monomer to recovered ionic liquid mixtures regenerates transparent, stable microemulsions that are ready for the next polymerization cycle upon addition of initiator. The method combines the advantages of IL recycling and microemulsion polymerization and minimizes environmental disposable effects from surfactants and heavy metal ions.

  2. Preparations and properties of a tunable void with shell thickness SiO2@SiO2 core-shell structures via activators generated by electron transfer for atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Ren, Yi-xian; Zhou, Guo-wei; Cao, Pei

    2016-02-01

    Core-shell structure nanoparticles are attracting considerable attention because of their applications in drug delivery, catalysis carrier, and nanomedicine. In this study, SiO2@SiO2 core-shell structure with tunable void and shell thickness was successfully prepared for the first time using SiO2-poly(buty acrylate) (PBA)-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) (SiO2-PBA-b-PDMAEMA) as the template and tetraethoxysilane (TEOS) as the silica source. An amphiphilic copolymer PBA-b-PDMAEMA was first grafted onto the SiO2 nanosphere surface through activators regenerated by electron transfer for atom transfer radical polymerization. TEOS was hydrolyzed along with the PDMAEMA chain through hydrogen bonding, and the core-shell structure of SiO2@SiO2 was obtained through calcination to remove the copolymer. The gradient hydrophilicity of the PBA-b-PDMAEMA copolymer template facilitated the hydrolysis of TEOS molecules along the PDMAEMA to PBA segments, thereby tuning the voids between the SiO2 core and SiO2 shell, as well as the SiO2 shell thickness. The voids were about 10-15 nm and the shell thicknesses were about 4-11 nm when adding different amounts of DMAEMA monomer. SiO2@SiO2 core-shell structures with tunable void and shell thickness were employed as supports for the loading and release of doxorubicin hydrochloride (DOX) in PBS (pH 4.0). The samples demonstrated good loading capacity and controlled release rate of DOX.

  3. Well-defined iron complexes as efficient catalysts for "green" atom-transfer radical polymerization of styrene, methyl methacrylate, and butyl acrylate with low catalyst loadings and catalyst recycling.

    PubMed

    Nakanishi, So-Ichiro; Kawamura, Mitsunobu; Kai, Hidetomo; Jin, Ren-Hua; Sunada, Yusuke; Nagashima, Hideo

    2014-05-05

    Environmentally friendly iron(II) catalysts for atom-transfer radical polymerization (ATRP) were synthesized by careful selection of the nitrogen substituents of N,N,N-trialkylated-1,4,9-triazacyclononane (R3 TACN) ligands. Two types of structures were confirmed by crystallography: "[(R3 TACN)FeX2 ]" complexes with relatively small R groups have ionic and dinuclear structures including a [(R3 TACN)Fe(μ-X)3 Fe(R3 TACN)](+) moiety, whereas those with more bulky R groups are neutral and mononuclear. The twelve [(R3 TACN)FeX2 ]n complexes that were synthesized were subjected to bulk ATRP of styrene, methyl methacrylate (MMA), and butyl acrylate (BA). Among the iron complexes examined, [{(cyclopentyl)3 TACN}FeBr2 ] (4 b) was the best catalyst for the well-controlled ATRP of all three monomers. This species allowed easy catalyst separation and recycling, a lowering of the catalyst concentration needed for the reaction, and the absence of additional reducing reagents. The lowest catalyst loading was accomplished in the ATRP of MMA with 4 b (59 ppm of Fe based on the charged monomer). Catalyst recycling in ATRP with low catalyst loadings was also successful. The ATRP of styrene with 4 b (117 ppm Fe atom) was followed by precipitation from methanol to give polystyrene that contained residual iron below the calculated detection limit (0.28 ppm). Mechanisms that involve equilibria between the multinuclear and mononuclear species were also examined. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Sequence-controlled methacrylic multiblock copolymers via sulfur-free RAFT emulsion polymerization

    NASA Astrophysics Data System (ADS)

    Engelis, Nikolaos G.; Anastasaki, Athina; Nurumbetov, Gabit; Truong, Nghia P.; Nikolaou, Vasiliki; Shegiwal, Ataulla; Whittaker, Michael R.; Davis, Thomas P.; Haddleton, David M.

    2016-10-01

    Translating the precise monomer sequence control achieved in nature over macromolecular structure (for example, DNA) to whole synthetic systems has been limited due to the lack of efficient synthetic methodologies. So far, chemists have only been able to synthesize monomer sequence-controlled macromolecules by means of complex, time-consuming and iterative chemical strategies such as solid-state Merrifield-type approaches or molecularly dissolved solution-phase systems. Here, we report a rapid and quantitative synthesis of sequence-controlled multiblock polymers in discrete stable nanoscale compartments via an emulsion polymerization approach in which a vinyl-terminated macromolecule is used as an efficient chain-transfer agent. This approach is environmentally friendly, fully translatable to industry and thus represents a significant advance in the development of complex macromolecule synthesis, where a high level of molecular precision or monomer sequence control confers potential for molecular targeting, recognition and biocatalysis, as well as molecular information storage.

  5. Sequence-controlled methacrylic multiblock copolymers via sulfur-free RAFT emulsion polymerization

    NASA Astrophysics Data System (ADS)

    Engelis, Nikolaos G.; Anastasaki, Athina; Nurumbetov, Gabit; Truong, Nghia P.; Nikolaou, Vasiliki; Shegiwal, Ataulla; Whittaker, Michael R.; Davis, Thomas P.; Haddleton, David M.

    2017-02-01

    Translating the precise monomer sequence control achieved in nature over macromolecular structure (for example, DNA) to whole synthetic systems has been limited due to the lack of efficient synthetic methodologies. So far, chemists have only been able to synthesize monomer sequence-controlled macromolecules by means of complex, time-consuming and iterative chemical strategies such as solid-state Merrifield-type approaches or molecularly dissolved solution-phase systems. Here, we report a rapid and quantitative synthesis of sequence-controlled multiblock polymers in discrete stable nanoscale compartments via an emulsion polymerization approach in which a vinyl-terminated macromolecule is used as an efficient chain-transfer agent. This approach is environmentally friendly, fully translatable to industry and thus represents a significant advance in the development of complex macromolecule synthesis, where a high level of molecular precision or monomer sequence control confers potential for molecular targeting, recognition and biocatalysis, as well as molecular information storage.

  6. Actin polymerization as a key innate immune effector mechanism to control Salmonella infection.

    PubMed

    Man, Si Ming; Ekpenyong, Andrew; Tourlomousis, Panagiotis; Achouri, Sarra; Cammarota, Eugenia; Hughes, Katherine; Rizzo, Alessandro; Ng, Gilbert; Wright, John A; Cicuta, Pietro; Guck, Jochen R; Bryant, Clare E

    2014-12-09

    Salmonellosis is one of the leading causes of food poisoning worldwide. Controlling bacterial burden is essential to surviving infection. Nucleotide-binding oligomerization domain-like receptors (NLRs), such as NLRC4, induce inflammasome effector functions and play a crucial role in controlling Salmonella infection. Inflammasome-dependent production of IL-1β recruits additional immune cells to the site of infection, whereas inflammasome-mediated pyroptosis of macrophages releases bacteria for uptake by neutrophils. Neither of these functions is known to directly kill intracellular salmonellae within macrophages. The mechanism, therefore, governing how inflammasomes mediate intracellular bacterial-killing and clearance in host macrophages remains unknown. Here, we show that actin polymerization is required for NLRC4-dependent regulation of intracellular bacterial burden, inflammasome assembly, pyroptosis, and IL-1β production. NLRC4-induced changes in actin polymerization are physically manifested as increased cellular stiffness, and leads to reduced bacterial uptake, production of antimicrobial molecules, and arrested cellular migration. These processes act in concert to limit bacterial replication in the cell and dissemination in tissues. We show, therefore, a functional link between innate immunity and actin turnover in macrophages that underpins a key host defense mechanism for the control of salmonellosis.

  7. Radical Decisions in Cancer: Redox Control of Cell Growth and Death

    PubMed Central

    Sainz, Rosa M.; Lombo, Felipe; Mayo, Juan C.

    2012-01-01

    Free radicals play a key role in many physiological decisions in cells. Since free radicals are toxic to cellular components, it is known that they cause DNA damage, contribute to DNA instability and mutation and thus favor carcinogenesis. However, nowadays it is assumed that free radicals play a further complex role in cancer. Low levels of free radicals and steady state levels of antioxidant enzymes are responsible for the fine tuning of redox status inside cells. A change in redox state is a way to modify the physiological status of the cell, in fact, a more reduced status is found in resting cells while a more oxidative status is associated with proliferative cells. The mechanisms by which redox status can change the proliferative activity of cancer cells are related to transcriptional and posttranscriptional modifications of proteins that play a critical role in cell cycle control. Since cancer cells show higher levels of free radicals compared with their normal counterparts, it is believed that the anti-oxidative stress mechanism is also increased in cancer cells. In fact, the levels of some of the most important antioxidant enzymes are elevated in advanced status of some types of tumors. Anti-cancer treatment is compromised by survival mechanisms in cancer cells and collateral damage in normal non-pathological tissues. Though some resistance mechanisms have been described, they do not yet explain why treatment of cancer fails in several tumors. Given that some antitumoral treatments are based on the generation of free radicals, we will discuss in this review the possible role of antioxidant enzymes in the survival mechanism in cancer cells and then, its participation in the failure of cancer treatments. PMID:24213319

  8. Supramolecular Architectures Based no Dehydro[24]annulenes: Toward the Controlled Synthesis of pi-Conjugated Nanotubular Materials via Topochemical Polymerization

    NASA Astrophysics Data System (ADS)

    Suzuki, Mitsuharu

    Chapter 1 overviews currently available synthetic methodologies of carbon nanomaterials. Conventional syntheses, stepwise chemical syntheses, and seeding/cloning approaches are described. Problems associated with each methodology are pointed out. Chapter 2 begins with introductions to the dehydroannulene-based synthesis of carbon nanomaterials and topochemical polymerization of butadiynes. This chapter then describes a new approach to achieve the controlled synthesis of tubular nanocarbon materials, namely multifold topochemical polymerization of dehydroannulenes. An extensive crystal-engineering study leads to successful formation of supramolecular nanotubes based on dehydro[24]annulenes. The obtained structures possess preferable packing parameters for the intended multifold topochemical polymerization. Chapter 3 explores on-surface self-assemblies of dehydro[24]annulenes. The relationship between the molecular structure and self-assembling behavior of is examined with the aid of scanning tunnel microscopy. This study paves the way for the topochemical polymerization of these compounds within surface-confined self-assemblies.

  9. Control of polymerization shrinkage and stress in nanogel-modified monomer and composite materials

    PubMed Central

    Moraes, Rafael R.; Garcia, Jeffrey W.; Barros, Matthew D.; Lewis, Steven H.; Pfeifer, Carmem S.; Liu, JianCheng; Stansbury, Jeffrey W.

    2011-01-01

    Objectives This study demonstrates the effects of nano-scale prepolymer particles as additives to model dental monomer and composite formulations. Methods Discrete nanogel particles were prepared by solution photopolymerization of isobornyl methacrylate and urethane dimethacrylate in the presence of a chain transfer agent, which also provided a means to attach reactive groups to the prepolymer. Nanogel was added to triethylene glycol dimethacrylate (TEGDMA) in increments between 5 and 40 wt% with resin viscosity, reaction kinetics, shrinkage, mechanical properties, stress and optical properties evaluated. Maximum loading of barium glass filler was determined as a function of nanogel content and composites with varied nanogel content but uniform filler loading were compared in terms of consistency, conversion, shrinkage and mechanical properties. Results High conversion, high molecular weight internally crosslinked and cyclized nanogel prepolymer was efficiently prepared and redispersed into TEGDMA with an exponential rise in viscosity accompanying nanogel content. Nanogel addition at any level produced no deleterious effects on reaction kinetics, conversion or mechanical properties, as long as reactive nanogels were used. A reduction in polymerization shrinkage and stress was achieved in proportion to nanogel content. Even at high nanogel concentrations, the maximum loading of glass filler was only marginally reduced relative to the control and high strength composite materials with low shrinkage were obtained. Significance The use of reactive nanogels offers a versatile platform from which resin and composite handling properties can be adjusted while the polymerization shrinkage and stress development that challenge the adhesive bonding of dental restoratives are controllably reduced. PMID:21388669

  10. Heteroscorpionate rare-earth initiators for the controlled ring-opening polymerization of cyclic esters.

    PubMed

    Otero, Antonio; Lara-Sánchez, Agustín; Fernández-Baeza, Juan; Alonso-Moreno, Carlos; Márquez-Segovia, Isabel; Sánchez-Barba, Luis F; Castro-Osma, José A; Rodríguez, Ana M

    2011-05-07

    A series of neutral rare-earth metal amides containing different achiral and chiral heteroscorpionate ligands was synthesized and characterized and these compounds were employed in the polymerization of cyclic esters. Thus, treatment of [Ln{N(SiHMe(2))(2)}(3)(thf)(2)] (Ln = Nd, Sm) with acetamide or thioacetamide heteroscorpionate ligands for 2 h at 0 °C afforded the α-agostic silylamido dimeric rare-earth compounds [Ln{N(SiHMe(2))(2)}(NNE)](2) (Ln = Nd and Sm; NNE = heteroscorpionate ligands, E = O, S) (1-8), some as enantiopure complexes. Complexes 1-8 contain dianionic heteroscorpionate pseudoallyl ligands resulting from C-H activation of the bridging methine group of the bis(pyrazol-1-yl)methane moiety and subsequent coordination to the metal center. However, when the reaction was carried out for 1 h at lower temperature new bis(silylamido) dimeric lanthanide compounds [Ln{N(SiHMe(2))(2)}(2)(NNE)](2) (Ln = Nd and Sm; E = O) (9 and 10) were obtained. The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structures of 1, and 4 were also established. Neodymium complexes are active initiators for the ring-opening polymerization (ROP) of lactide (LA) and lactones, giving rise to medium-high molar mass polymers under mild conditions and with narrow polydispersities. These complexes were well suited for achieving well-controlled polymerization through an insertion-coordination mechanism. Achiral and racemic complexes did not affect stereocontrol in the polymerizarion of rac-LA but the enantiomerically pure complex 1 was found to exhibit a homosteric preference for one of the two enantiomers of rac-LA at low conversions.

  11. Polymers based on stable phenoxyl radicals for the use in organic radical batteries.

    PubMed

    Jähnert, Thomas; Häupler, Bernhard; Janoschka, Tobias; Hager, Martin D; Schubert, Ulrich S

    2014-05-01

    Polymers with pendant phenoxyl radicals are synthesized and the electrochemical properties are investigated in detail. The monomers are polymerized using ring-opening metathesis polymerization (ROMP) or free-radical polymerization methods. The monomers and polymers, respectively, are oxidized to the radical either before or after the polymerization. These phenoxyl radicals containing polymers reveal a reversible redox behavior at a potential of -0.6 V (vs Ag/AgCl). Such materials can be used as anode-active material in organic radical batteries (ORBs).

  12. Anisotropic nanoparticles with controllable morphologies from non-cross-linked seeded emulsion polymerization.

    PubMed

    Niu, Qun; Pan, Mingwang; Yuan, Jinfeng; Liu, Xiao; Wang, Xiaomei; Yu, Haifeng

    2013-09-01

    A simple and elegant approach to fabricate anisotropic P(VC-co-AAEM)/PS nanoparticles with controllable morphologies via emulsifier-free seeded emulsion polymerization is presented. Non-cross-linked P(VC-co-AAEM) seeds with hydrophilic surface are first synthesized through copolymerization of vinyl chloride (VC) and acetoacetoxyethyl methacrylate (AAEM), which are used to prepare P(VC-co-AAEM)/PS NPs with multiple bulges by SEP of styrene. Electron microscopy observation indicates that the content of AAEM in seeds is crucial to control the phase separation and morphology of the composite NPs. Moreover, the thermodynamic immiscibility between PVC and PS is the driving force for the formation of PS bulges onto the P(VC-co-AAEM) seeds. The resultant anisotropic NPs with non-cross-linked feature may promisingly serve as compatibilizers for further polymer processing. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Preparation of acetylsalicylic acid-acylated chitosan as a novel polymeric drug for drug controlled release.

    PubMed

    Liu, Changkun; Wu, Yiguang; Zhao, Liyan; Huang, Xinzheng

    2015-01-01

    The acetylsalicylic acid-acylated chitosan (ASACTS) with high degree of substitution (DS) was successfully synthesized, and characterized with FTIR, (1)H NMR and elemental analysis methods. The optimum synthesis conditions were obtained which gave the highest DS (about 60%) for ASACTS. Its drug release experiments were carried out in simulated gastric and intestine fluids. The results show that the drugs in the form of acetylsalicylic acid (ASA) and salicylic acid (SA) were released in a controlled manner from ASACTS only in simulated gastric fluid. The release profile can be best fitted with logistic and Weibull model. The research results reveal that ASACTS can be a potential polymeric drug for the controlled release of ASA and SA in the targeted gastric environment.

  14. Formation of hematite nanoparticle monolayers of controlled coverage and structure at polymeric microparticles.

    PubMed

    Sadowska, Marta; Adamczyk, Zbigniew; Nattich-Rak, Małgorzata

    2017-11-01

    The deposition of hematite nanoparticles (22nm and 29nm in diameter) on negatively charged polystyrene microspheres (820nm in diameter) was studied by micro-electrophoretic measurements and AFM. The influence of ionic strength, varied between 10(-4) and 10(-2)M, was determined. Initially, the electrophoretic mobility change of microspheres upon the addition of controlled amount of hematite nanoparticles were measured. These dependencies were quantitatively interpreted in terms of the general electrokinetic model. This allowed to determine the coverage of nanoparticles on microspheres under in situ conditions, which increased with ionic strength attaining 0.35 for the ionic strength of 10(-2)M and 29 in diameter hematite particles. This effect, attributed to the decreasing range of lateral electrostatic repulsion among deposited particles, was accounted for by the random sequential adsorption model. However, the coverages attained for lower ionic strength exceeded the theoretical predictions. This effect was interpreted in terms of an additional electrostatic screening due to polymeric chains present at the microparticle surface. The acid base properties of the hematite monolayers were also acquired by applying thorough micro-electrophoretic measurements. The obtained results confirmed a feasibility of preparing hematite nanoparticle monolayers on polymeric carrier microspheres having well-defined coverage and structure. Copyright © 2017 Elsevier Inc. All rights reserved.

  15. Temporal Control of Gelation and Polymerization Fronts Driven by an Autocatalytic Enzyme Reaction.

    PubMed

    Jee, Elizabeth; Bánsági, Tamás; Taylor, Annette F; Pojman, John A

    2016-02-05

    Chemical systems that remain kinetically dormant until activated have numerous applications in materials science. Herein we present a method for the control of gelation that exploits an inbuilt switch: the increase in pH after an induction period in the urease-catalyzed hydrolysis of urea was used to trigger the base-catalyzed Michael addition of a water-soluble trithiol to a polyethylene glycol diacrylate. The time to gelation (minutes to hours) was either preset through the initial concentrations or the reaction was initiated locally by a base, thus resulting in polymerization fronts that converted the mixture from a liquid into a gel (ca. 0.1 mm min(-1)). The rate of hydrolytic degradation of the hydrogel depended on the initial concentrations, thus resulting in a gel lifetime of hours to months. In this way, temporal programming of gelation was possible under mild conditions by using the output of an autocatalytic enzyme reaction to drive both the polymerization and subsequent degradation of a hydrogel.

  16. Temporal Control of Gelation and Polymerization Fronts Driven by an Autocatalytic Enzyme Reaction

    PubMed Central

    Jee, Elizabeth; Bánsági, Tamás

    2016-01-01

    Abstract Chemical systems that remain kinetically dormant until activated have numerous applications in materials science. Herein we present a method for the control of gelation that exploits an inbuilt switch: the increase in pH after an induction period in the urease‐catalyzed hydrolysis of urea was used to trigger the base‐catalyzed Michael addition of a water‐soluble trithiol to a polyethylene glycol diacrylate. The time to gelation (minutes to hours) was either preset through the initial concentrations or the reaction was initiated locally by a base, thus resulting in polymerization fronts that converted the mixture from a liquid into a gel (ca. 0.1 mm min−1). The rate of hydrolytic degradation of the hydrogel depended on the initial concentrations, thus resulting in a gel lifetime of hours to months. In this way, temporal programming of gelation was possible under mild conditions by using the output of an autocatalytic enzyme reaction to drive both the polymerization and subsequent degradation of a hydrogel. PMID:27478280

  17. Temporal Control of Gelation and Polymerization Fronts Driven by an Autocatalytic Enzyme Reaction

    PubMed Central

    Jee, Elizabeth; Bánsági, Tamás

    2016-01-01

    Abstract Chemical systems that remain kinetically dormant until activated have numerous applications in materials science. Herein we present a method for the control of gelation that exploits an inbuilt switch: the increase in pH after an induction period in the urease‐catalyzed hydrolysis of urea was used to trigger the base‐catalyzed Michael addition of a water‐soluble trithiol to a polyethylene glycol diacrylate. The time to gelation (minutes to hours) was either preset through the initial concentrations or the reaction was initiated locally by a base, thus resulting in polymerization fronts that converted the mixture from a liquid into a gel (ca. 0.1 mm min−1). The rate of hydrolytic degradation of the hydrogel depended on the initial concentrations, thus resulting in a gel lifetime of hours to months. In this way, temporal programming of gelation was possible under mild conditions by using the output of an autocatalytic enzyme reaction to drive both the polymerization and subsequent degradation of a hydrogel. PMID:26732469

  18. Correlating Thin-Film Radical Density with Charge Transport in Open-Shell Conducting Macromolecules

    NASA Astrophysics Data System (ADS)

    Hay, Martha; Jergens, Elizabeth; Boudouris, Bryan

    Within the class of radical polymers, stable open-shell species serve as the medium for charge transport by undergoing oxidation-reduction (redox) reactions. The kinetics of these reactions are rapid enough that they are not considered rate-limiting in the electronic interactions of these materials. Rather, the proximity of these radical sites is paramount as a synthetic handle. Unfortunately, controlling the density of radicals has proven challenging in radical polymer systems. Often radical functionality is imparted to a polymer, rather than polymerizing a radical-containing monomer unit. This can prove troublesome as longer reaction times, in the interest of higher radical functionality, can lead to the elimination of radicals. Thus, the consequential altering of the radical electronic interactions is not well understood. We have synthesized a series of polynorbornene-based radical monomers at controlled radical loadings such that the radical density was preserved from monomer to polymer synthesis. As such, we attribute any change in the macroscopic transport properties to a change in the spacing between radical sites. These results elucidate the role of radical site distribution on the electronic performance of nitroxide-based radical polymers.

  19. Design of a self-tuning regulator for temperature control of a polymerization reactor.

    PubMed

    Vasanthi, D; Pranavamoorthy, B; Pappa, N

    2012-01-01

    The temperature control of a polymerization reactor described by Chylla and Haase, a control engineering benchmark problem, is used to illustrate the potential of adaptive control design by employing a self-tuning regulator concept. In the benchmark scenario, the operation of the reactor must be guaranteed under various disturbing influences, e.g., changing ambient temperatures or impurity of the monomer. The conventional cascade control provides a robust operation, but often lacks in control performance concerning the required strict temperature tolerances. The self-tuning control concept presented in this contribution solves the problem. This design calculates a trajectory for the cooling jacket temperature in order to follow a predefined trajectory of the reactor temperature. The reaction heat and the heat transfer coefficient in the energy balance are estimated online by using an unscented Kalman filter (UKF). Two simple physically motivated relations are employed, which allow the non-delayed estimation of both quantities. Simulation results under model uncertainties show the effectiveness of the self-tuning control concept. Copyright © 2011 ISA. Published by Elsevier Ltd. All rights reserved.

  20. Acupuncture for Preventing Complications after Radical Hysterectomy: A Randomized Controlled Clinical Trial

    PubMed Central

    Yi, Wei-min; Chen, Qing; Liu, Chang-hao; Hou, Jia-yun; Chen, Liu-dan; Wu, Wei-kang

    2014-01-01

    We aimed to investigate the preventive effects of acupuncture for complications after radical hysterectomy. A single-center randomized controlled single-blinded trial was performed in a western-style hospital in China. One hundred and twenty patients after radical hysterectomy were randomly allocated to two groups and started acupuncture from sixth postoperative day for five consecutive days. Sanyinjiao (SP6), Shuidao (ST28), and Epangxian III (MS4) were selected with electrical stimulation and Zusanli (ST36) without electrical stimulation for thirty minutes in treatment group. Binao (LI14) was selected as sham acupuncture point without any stimulation in control group. The main outcome measures were bladder function and prevalence of postoperative complications. Compared with control group, treatment group reported significantly improved bladder function in terms of maximal cystometric capacity, first voiding desire, maximal flow rate, residual urine, and bladder compliance, and decreased bladder sensory loss, incontinence, and urinary retention on fifteenth and thirtieth postoperative days. Treatment group showed significant advantage in reduction of urinary tract infection on thirtieth postoperative day. But no significant difference between groups was observed for lymphocyst formation. By improving postoperative bladder function, early intervention of acupuncture may provide a valuable alternative method to prevent bladder dysfunctional disorders and urinary tract infection after radical hysterectomy. PMID:24839455

  1. Production of cold formaldehyde molecules for study and control of chemical reaction dynamics with hydroxyl radicals

    SciTech Connect

    Hudson, Eric R.; Ticknor, Christopher; Sawyer, Brian C.; Taatjes, Craig A.; Lewandowski, H. J.; Bochinski, J. R.; Bohn, J. L.; Ye Jun

    2006-06-15

    We propose a method for controlling a class of low temperature chemical reactions. Specifically, we show the hydrogen abstraction channel in the reaction of formaldehyde (H{sub 2}CO) and the hydroxyl radical (OH) can be controlled through either the molecular state or an external electric field. We also outline experiments for investigating and demonstrating control over this important reaction. To this end, we report the first Stark deceleration of H{sub 2}CO. We have decelerated a molecular beam of H{sub 2}CO essentially to rest, producing molecules at 100 mK with a density of {approx}10{sup 6} cm{sup -3}.

  2. Non-polymeric coatings to control drug release from metallic coronary stents

    NASA Astrophysics Data System (ADS)

    Gupta, Celia Edith Macias

    Percutaneous transluminal coronary angiography (PTCA) is a procedure used to re-open narrowed coronary arteries. During PTCA, a coronary stent is expanded inside a diseased vessel and serves as a scaffold to keep the artery open. The major drawback of stenting is restenosis---a re-narrowing of the vessel resulting from the hyperproliferation of smooth muscle cells. Drug eluting stents (DES) reduce the rate of restenosis compared to bare metal stents. Paclitaxel (PAT) is commonly used in DES for its ability to prevent restenosis. However, DES have been associated with thrombosis due to the polymer carrier that controls drug delivery. Therefore, there is a need to change the drug delivery mechanisms to eliminate the need of polymers. The goal of this dissertation is to develop a novel polymer-free drug eluting stent that controls drug release using nanoscale metal coatings. The coating was designed to release PAT as the metal slowly degrades in biological conditions. Once all the Paclitaxel has eluted from the surface, the coating will continue to degrade until the final result is a bare metal stent. The results of this study include a novel non-polymeric drug delivery system using nanoscale coatings that release Paclitaxel at a rate similar to commercial stents, as well as the biocompatibility and efficacy of these coatings. The non-polymeric drug delivery system described here achieved a Paclitaxel release profile equivalent to clinically available Paclitaxel-eluting stents and effectively inhibits smooth muscle cell proliferation, thereby completely eliminating the need for polymers to control drug release from coronary stents.

  3. Electroassisted Functionalization of Nitinol Surface, a Powerful Strategy for Polymer Coating through Controlled Radical Surface Initiation.

    PubMed

    Arrotin, Bastien; Delhalle, Joseph; Dubois, Philippe; Mespouille, Laetitia; Mekhalif, Zineb

    2017-03-28

    Coating Nitinol (NiTi) surfaces with a polymer layer has become very appealing in the past few years owing to its increased attraction in the biomedical field. Although its intrinsic properties helped ensure its popularity, its extensive implementation is still hampered by its nickel inclusion, making it sensitive to pitting corrosion and therefore leading to the release of carcinogenic Ni(2+) ions. Among all recent ways to modify NiTi surfaces, elaboration of self-assembled monolayers is of great interest as their high order confers a reinforcement of the metal surface corrosion resistance and brings new functionalities to the metal for postmodification processes. In this work, we compare the electroassisted and thermally assisted self-assembling of 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid (BUPA) to the classical immersion process on NiTi surfaces initially submitted to a hydrothermal treatment. Among all tested conditions, the electroassisted grafting of BUPA at room temperature appears to be the most promising alternative, as it allows grafting in very short times (5-10 min), thus preventing its degradation. The thus-formed layer has been proven to be sufficient to enable the surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-(dimethylamino)ethyl methacrylate.

  4. Novel Diblock Copolymer-Grafted Multiwalled Carbon Nanotubes via a combination of Living and Controlled/Living Surface Polymerizations

    SciTech Connect

    Priftis, Dimitrios; Sakellariou, Georgios; Mays, Jimmy; Hadjichristidis, Nikos

    2010-01-01

    Diels Alder cycloaddition reactions were used to functionalize multiwalled carbon nanotubes (MWNTs) with 1-benzocylcobutene-10-phenylethylene (BCB-PE) or 4-hydroxyethylbenzocyclobutene (BCB-EO). The covalent functionalization of the nanotubes with these initiator precursors was verified by FTIR and thermogravimetric analysis (TGA). After appropriate transformations/additions, the functionalized MWNTs were used for surface initiated anionic and ring opening polymerizations of ethylene oxide and e-caprolactone (e-CL), respectively. The OH-end groups were transformed to isopropylbromide groups by reaction with 2-bromoisobutyryl bromide, for subsequent atom transfer radical polymerization of styrene or 2-dimethylaminoethyl methacrylate to afford the final diblock copolymers. 1H NMR, differential scanning calorimetry (DSC), TGA, and transmission electron microscopy (TEM) were used for the characterization of the nanocomposite materials. TEM images showed the presence of a polymer layer around the MWNTs as well as the dissociation of MWNT bundles. Consequently, this general methodology, employing combinations of different polymerization techniques, increases the diversity of diblocks that can be grafted from MWNTs.

  5. Chromatographic efficiency comparison of polyhedral oligomeric silsesquioxanes-containing hybrid monoliths via photo- and thermally-initiated free-radical polymerization in capillary liquid chromatography for small molecules.

    PubMed

    Wang, Hongwei; Ou, Junjie; Liu, Zhongshan; Lin, Hui; Peng, Xiaojun; Zou, Hanfa

    2015-09-04

    Monolithic poly(methacrylate epoxy cyclosiloxane-co-polyhedral oligomeric silsesquioxanes) (epoxy-MA-POSS) capillary columns have been prepared via either photo- or thermally-initiated polymerization of the corresponding monomers using a 1-propanol/PEG 400 mixture as porogens. Photochemical polymerization was accomplished by irradiation of the UV-transparent capillary for 10min at room temperature, while thermal polymerization was performed at 55°C, 60°C or 65°C for 18h. The evaluation of chromatographic property for two hybrid epoxy-MA-POSS monoliths was carried out. The results indicate that hybrid monoliths fabricated by photochemical initiation exhibit higher column efficiency (97,000-98,400plates/m) than those synthesized by thermal polymerization (41,100-48,000plates/m) in cLC. The higher efficiency of photo-initiated hybrid monoliths is closely related to lower eddy dispersion (A-term) and mass transfer resistance (C-term).

  6. Morphological control of multihollow polymer latex particles through a controlled phase separation in the seeded emulsion polymerization.

    PubMed

    Li, Bingxin; Xu, Yongfei; Wang, Mozhen; Ge, Xuewu

    2013-12-03

    In this work, we first reported that the phase separation can take place both inside and outside of a multihollow-structured cross-linked seed microspheres swollen by styrene monomers in water during the radiation-induced seeded emulsion polymerization. The phase separation process in these two opposite directions will determine the morphology of final latex particles. First, sulfonated cross-linked polystyrene (SCPS) seed microspheres were swollen by styrene in water. Water will permeate into the SCPS seed microspheres during the swelling process, forced by the osmotic pressure produced by the strong hydrophilicity of the sulfonic acid groups. New aqueous phases are created and stabilized by the hydrophilic -SO3H groups, resulting in a multihollow structure of swollen SCPS seed microspheres. When the polymerization of styrene is induced by (60)Co γ-ray radiation, the phase separation of newly formed polystyrene phase will occur at the seed microsphere-water interface inside and/or outside of the SCPS seed microspheres through adjusting the diameter of seed microsphere, the content of cross-link agent, and the sulfonation degree of SCPS seed microspheres. As a result, SCPS latex particles with a variety of special morphologies, such as spherical multihollow, plum-like, and walnut-like latex particles were obtained. The results of this study provide not only a simple and interesting way to design and synthesize multihollow polymer latex particles with controllable surface morphologies but also a better understanding on phase separation mechanism during the swelling and polymerization of monomers in cross-linked amphiphilic polymer networks.

  7. Pulsed plasma polymerization for controlling shrinkage and surface composition of nanopores.

    PubMed

    Asghar, Waseem; Ilyas, Azhar; Deshmukh, Rajendra R; Sumitsawan, Sulak; Timmons, Richard B; Iqbal, Samir M

    2011-07-15

    Solid-state nanopores have emerged as sensors for single molecules and these have been employed to examine the biophysical properties of an increasingly large variety of biomolecules. Herein we describe a novel and facile approach to precisely adjust the pore size, while simultaneously controlling the surface chemical composition of the solid-state nanopores. Specifically, nanopores fabricated using standard ion beam technology are shrunk to the requisite molecular dimensions via the deposition of highly conformal pulsed plasma generated thin polymeric films. The plasma treatment process provides accurate control of the pore size as the conformal film deposition depends linearly on the deposition time. Simultaneously, the pore and channel chemical compositions are controlled by appropriate selection of the gaseous monomer and plasma conditions employed in the deposition of the polymer films. The controlled pore shrinkage is characterized with high resolution AFM, and the film chemistry of the plasma generated polymers is analyzed with FTIR and XPS. The stability and practical utility of this new approach is demonstrated by successful single molecule sensing of double-stranded DNA. The process offers a viable new advance in the fabrication of tailored nanopores, in terms of both the pore size and surface composition, for usage in a wide range of emerging applications.

  8. Control of molecular weight of polystyrene using the reverse iodine transfer polymerization (RITP)-emulsion technique.

    PubMed

    Oh, Hyeong Geun; Shin, Hongcheol; Jung, Hyejun; Lee, Byung Hyung; Choe, Soonja

    2011-01-15

    The RITP-emulsion polymerization of styrene in the presence of molecular iodine has been successfully performed using potassium persulfate (KPS) as an initiator and 1-hexadecanesulfonate as an emulsifier under argon atmosphere at 80°C for 7 hrs in the absence of light. The effects of the iodine concentration, molar ratio between KPS and iodine, and solid contents on the molecular weight of polystyrene (PS) were studied. As the iodine concentration increased from 0.05 to 0.504 mmol under the fixed [KPS]/[I(2)] ratio at 4.5, the weight-average molecular weight of PS substantially decreased from 126,120 to 35,690 g/mol, the conversion increased from 85.0% to 95.2%, and the weight-average particle diameter decreased from 159 to 103 nm. In addition, as the ratio of [KPS]/[I(2)] increased from 0.5 to 6.0 at the fixed [I(2)] of 0.504 mmol, the weight-average molecular weight of PS decreased from 72,170 to 30,640 g/mol with high conversion between 81.7% and 96.5%. Moreover, when the styrene solid content increased from 10 to 40 wt.% at the fixed [KPS]/[I(2)] ratio of 4.5, the weight-average molecular weight of PS varied between 33,500 and 37,200 g/mol, the conversion varied between 94.9% and 89.7% and the weight-average diameter varied from 122 to 205 nm. Thus, the control of molecular weight of PS less than 100,000g/mol with high conversion (95%) and particle stability of up to 40 wt.% solid content were easily achieved through the usage of iodine with suitable ratio of [KPS]/[I(2)] in the RITP-emulsion polymerization technique, which is of great industrial importance.

  9. Regulation of actin polymerization by tropomodulin-3 controls megakaryocyte actin organization and platelet biogenesis.

    PubMed

    Sui, Zhenhua; Nowak, Roberta B; Sanada, Chad; Halene, Stephanie; Krause, Diane S; Fowler, Velia M

    2015-07-23

    The actin cytoskeleton is important for platelet biogenesis. Tropomodulin-3 (Tmod3), the only Tmod isoform detected in platelets and megakaryocytes (MKs), caps actin filament (F-actin) pointed ends and binds tropomyosins (TMs), regulating actin polymerization and stability. To determine the function of Tmod3 in platelet biogenesis, we studied Tmod3(-/-) embryos, which are embryonic lethal by E18.5. Tmod3(-/-) embryos often show hemorrhaging at E14.5 with fewer and larger platelets, indicating impaired platelet biogenesis. MK numbers are moderately increased in Tmod3(-/-) fetal livers, with only a slight increase in the 8N population, suggesting that MK differentiation is not significantly affected. However, Tmod3(-/-) MKs fail to develop a normal demarcation membrane system (DMS), and cytoplasmic organelle distribution is abnormal. Moreover, cultured Tmod3(-/-) MKs exhibit impaired proplatelet formation with a wide range of proplatelet bud sizes, including abnormally large proplatelet buds containing incorrect numbers of von Willebrand factor-positive granules. Tmod3(-/-) MKs exhibit F-actin disturbances, and Tmod3(-/-) MKs spreading on collagen fail to polymerize F-actin into actomyosin contractile bundles. Tmod3 associates with TM4 and the F-actin cytoskeleton in wild-type MKs, and confocal microscopy reveals that Tmod3, TM4, and F-actin partially colocalize near the membrane of proplatelet buds. In contrast, the abnormally large proplatelets from Tmod3(-/-) MKs show increased F-actin and redistribution of F-actin and TM4 from the cortex to the cytoplasm, but normal microtubule coil organization. We conclude that F-actin capping by Tmod3 regulates F-actin organization in mouse fetal liver-derived MKs, thereby controlling MK cytoplasmic morphogenesis, including DMS formation and organelle distribution, as well as proplatelet formation and sizing. © 2015 by The American Society of Hematology.

  10. Preparation of micrometer-sized polymer particles with control of initiator dissociation during soap-free emulsion polymerization.

    PubMed

    Nagao, Daisuke; Sakamoto, Tatsuro; Konno, Hiroyuki; Gu, Shunchao; Konno, Mikio

    2006-12-19

    A previously proposed method of soap-free emulsion polymerization employing an amphoteric initiator, 2,2'-azobis [N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate (VA-057), was extended to synthesize micrometer-sized polystyrene particles with low polydispersity in an acidic region of pH from 3.3 to 4.6. A buffer system of CH3COOH/CH3COONa was used for the adjustment of pH, which was aimed at effective promotion of particle coagulation in early stage of the polymerization. In these experiments, CH3COOH concentration was varied from 20 to 360 mM at a CH3COONa concentration of 10 mM. Polymer particles with an average size of 1.8 microm and low polydispersity were obtained at the CH3COOH concentration of 40 mM for the concentrations of 1.1 M styrene monomer and 10 mM initiator. To more precisely control dispersion stability of particles, experiments in which pH was stepwisely changed during the polymerization were also carried out. This polymerization method could enhance the average size of particles to 2.2 microm while retaining the monodispersity of particles. Furthermore, combination of pH stepwise change and monomer addition during the polymerization could produce particles with an average size of 3.0 microm and low polydispersity.

  11. Controlling Structure and Function of Polymeric Drug Delivery Nanoparticles Using Microfluidics.

    PubMed

    Bains, Aman; Cao, Yimeng; Kly, Sundiata; Wulff, Jeremy E; Moffitt, Matthew G

    2017-08-07

    We demonstrate control of multiscale structure and drug delivery function for paclitaxel (PAX)-loaded polycaprolactone-block-poly(ethylene oxide) (PCL-b-PEO) polymeric nanoparticles (PNPs) via synthesis and flow-directed shear processing in a two-phase gas-liquid microfluidic reactor. This strategy takes a page from the engineering of commodity plastics, where processing rather than polymer chemistry provides an experimental handle on properties and function. PNPs formed from copolymers with three different PCL block lengths show sizes, morphologies, and loading efficiencies that depend on both the PCL block length and the microfluidic flow rate. By varying flow rate and comparing with a conventional bulk method of PNP preparation, we show that flow-variable shear processing provides control of PNP sizes and morphologies and enables slower PAX release times (up to 2 weeks) compared to bulk-prepared PNPs. Antiproliferative effects against cultured MCF-7 breast cancer cells were greatest for PNPs formed at an intermediate flow rate, corresponding to small and low-polydispersity spheres formed uniquely at this flow condition. Formation and flow-directed nanoscale shear processing in gas-liquid microfluidic reactors provides a manufacturing platform for drug delivery PNPs that could enable more effective and selective nanomedicines through multiscale structural control.

  12. Osteoclast radicals.

    PubMed

    Silverton, S

    1994-11-01

    In biological research, new ideas arise and quickly spread to encompass the entire field. Thus, the evolution of molecular biology has significantly changed our methods of approaching our research. A similar far-reaching finding has been the advent of radical reactions into biology. Although radical chemistry has been utilized for many technological advances that affect our daily lives, the appreciation of this same process within our cells has opened an unexplored arena for research enquiry. As cellular messengers, radical molecules seem whimsically designed: they are evanescent, rapidly and apparently indiscriminately reactive, and barely detectable by most biological methods. Yet, our initial probing of these reactive agents in cells and organisms has led us to postulate a virtually undescribed system of communication within and among cells which may have significant effects in multiple organs. In bone, radical reactants have been attributed with an important role in the control of bone resorption.

  13. Controllable Chemoselectivity in Visible-Light Photoredox Catalysis: Four Diverse Aerobic Radical Cascade Reactions.

    PubMed

    Liu, Xinfei; Ye, Xinyi; Bureš, Filip; Liu, Hongjun; Jiang, Zhiyong

    2015-09-21

    Reported is the controllable selectivity syntheses of four distinct products from the same starting materials by visible-light photoredox catalysis. By employing a dicyanopyrazine-derived chromophore (DPZ) as photoredox catalyst, an aerobic radical mechanism has been developed, and allows the reactions of N-tetrahydroisoquinolines (THIQs) with N-itaconimides to through four different pathways, including addition-cyclization, addition-elimination, addition-coupling, and addition-protonation, with satisfactory chemoselectivity. The current strategy provide straightforward access to four different but valuable N-heterocyclic adducts in moderate to excellent yields. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Synthesis of biodegradable poly-epsilon-caprolactone microspheres by dispersion ring-opening polymerization in supercritical carbon dioxide.

    PubMed

    Grignard, Bruno; Stassin, Fabrice; Calberg, Cédric; Jérôme, Robert; Jérôme, Christine

    2008-11-01

    A series of fluorinated diblock and triblock copolymers of poly(epsilon-caprolactone) and poly(heptadecafluorodecylacrylate) were prepared by combining ring-opening polymerization of epsilon-CL and atom transfer radical polymerization of the acrylate. These copolymers with well-controlled molecular weight and composition were characterized by (1)H NMR spectroscopy and used as stabilizers for the dispersion ring-opening polymerization of epsilon-CL in supercritical carbon dioxide. The effect of composition and architecture of the polymeric stabilizers on the stabilization of PCL microspheres was investigated. Finally, purification of PCL was successfully implemented by reactive supercritical fluid extraction of the tin catalyst.

  15. Growth control of budding yeast cells by oxygen-radical treatment

    NASA Astrophysics Data System (ADS)

    Ohta, Takayuki; Hashizume, Hiroshi; Ito, Masafumi; Takeda, Keigo; Hori, Masaru

    2013-09-01

    Microorganisms respond to stimuli or stresses such as chemicals, nutrition, pressure, heat and so on. Those stimuli lead to cell activation, inactivation or cell death, such as apoptosis and necrosis. Reactive oxygen species possibly affect cell growth as well as inactivation depending on stimuli. In this study, we investigated effects of oxygen-radical treatment on not only inactivation but also promoted/repressed cell growth of budding yeast by varying dose of atomic oxygen produced from an atmospheric-pressure oxygen radical source. Dose of atomic oxygen was estimated based on treatment time and oxygen flux. Cell growth was promoted with atomic oxygen between 0 and 2.1 ×1019 cm-2 dose of atomic oxygen. The treated cells were grown about 10 percent more proliferously than the control cells. Moreover, 64 percent of the treated cells to the control ones were inactivated at more than 4.2 ×1020 cm-2. These results, therefore, suggested that atomic-oxygen dose had a potential to control mitotic promotion and repression, and inactivation of yeast cell growth.

  16. Controlled Release Inhalable Polymeric Microspheres for Treatment of Pulmonary Arterial Hypertension.

    PubMed

    Saigal, Aparna; Ng, Wai Kiong; Tan, Reginald B H; Chan, Sui Yung

    2015-01-01

    Pulmonary arterial hypertension (PAH) is a chronic ailment of the lungs, exhibiting elevated arterial pressure and vascular resistance; with a mean arterial pressure above 25 mmHg at rest and above 30 mmHg during exercise. It is associated with poor prognosis, and its prevalence is estimated to be 15 cases per one million. The current treatment options for PAH are discussed with the prostanoid class of drugs being the most effective. The latter drugs act by dilating systemic and pulmonary arterial vascular beds and, with sustained long-term usage, altering pulmonary remodelling. They are administered as IV infusions or inhalation solutions. Despite their clinical effectiveness, prostanoids have short half-lives requiring frequent administration of 6-9 times daily and thus suffer from poor compliance. Controlled release inhalation delivery systems for treatment of PAH, ranging from liposomes, biodegradable nano- and microparticles, formation of co-precipitates and complexation with cyclodextrins, are explored. Arising from these formulation strategies, we developed novel polymeric microspheres for inhalation to reduce dosing frequency and improve medication compliance. These microspheres are designed with release modifiers, to reside in the lung which is the site of drug action for a longer duration so as to release the drug slowly and consistently over a prolonged period. This could lead to the development of the first commercially available controlled release inhalation product.

  17. Using polymeric materials to control stem cell behavior for tissue regeneration.

    PubMed

    Zhang, Nianli; Kohn, David H

    2012-03-01

    Patients with organ failure often suffer from increased morbidity and decreased quality of life. Current strategies of treating organ failure have limitations, including shortage of donor organs, low efficiency of grafts, and immunological problems. Tissue engineering emerged about two decades ago as a strategy to restore organ function with a living, functional engineered substitute. However, the ability to engineer a functional organ is limited by a limited understanding of the interactions between materials and cells that are required to yield functional tissue equivalents. Polymeric materials are one of the most promising classes of materials for use in tissue engineering, due to their biodegradability, flexibility in processing and property design, and the potential to use polymer properties to control cell function. Stem cells offer potential in tissue engineering because of their unique capacity to self-renew and differentiate into neurogenic, osteogenic, chondrogenic, and myogenic lineages under appropriate stimuli from extracellular components. This review examines recent advances in stem cell-polymer interactions for tissue regeneration, specifically highlighting control of polymer properties to direct adhesion, proliferation, and differentiation of stem cells, and how biomaterials can be designed to provide some of the stimuli to cells that the natural extracellular matrix does.

  18. Controlled nanopatterning of a polymerized ionic liquid in a strong electric field

    DOE PAGES

    Bocharova, Vera; Agapov, Alexander L.; Tselev, Alexander; ...

    2014-12-17

    Nanolithography has become a driving force in advancements of the modern day's electronics, allowing for miniaturization of devices and a steady increase of the calculation, power, and storage densities. Among various nanofabrication approaches, scanning probe techniques, including atomic force microscopy (AFM), are versatile tools for creating nanoscale patterns utilizing a range of physical stimuli such as force, heat, or electric field confined to the nanoscale. In this study, the potential of using the electric field localized at the apex of an AFM tip to induce and control changes in the mechanical properties of an ion containing polymer—a polymerized ionic liquidmore » (PolyIL)—on a very localized scale is explored. In particular, it is demonstrated that by means of AFM, one can form topographical features on the surface of PolyIL-based thin films with a significantly lower electric potential and power consumption as compared to nonconductive polymer materials. Lastly,, by tuning the applied voltage and ambient air humidity, control over dimensions of the formed structures is reproducibly achieved.« less

  19. Using Polymeric Materials to Control Stem Cell Behavior for Tissue Regeneration

    PubMed Central

    Zhang, Nianli; Kohn, David H.

    2017-01-01

    Patients with organ failure often suffer from increased morbidity and decreased quality of life. Current strategies of treating organ failure have limitations, including shortage of donor organs, low efficiency of grafts, and immunological problems. Tissue engineering emerged about two decades ago as a strategy to restore organ function with a living, functional engineered substitute. However, the ability to engineer a functional organ substitute is limited by a limited understanding of the interactions between materials and cells that are required to yield functional tissue equivalents. Polymeric materials are one of the most promising classes of materials for use in tissue engineering due to their biodegradability, flexibility in processing and property design, and the potential to use polymer properties to control cell function. Stem cells offer potential in tissue engineering because of their unique capacity to self renew and differentiate into neurogenic, osteogenic, chondrogenic, myogenic lineages under appropriate stimuli from extracellular components. This review examines recent advances in stem cell-polymer interactions for tissue regeneration, specifically highlighting control of polymer properties to direct adhesion, proliferation, and differentiation of stem cells, and how biomaterials can be designed to provide some of the stimuli to cells that the natural extracellular matrix does. PMID:22457178

  20. Controlling the thickness of hollow polymeric microspheres prepared by electrohydrodynamic atomization

    PubMed Central

    Chang, Ming-Wei; Stride, Eleanor; Edirisinghe, Mohan

    2010-01-01

    In this study, the ability to control the shell thickness of hollow polymeric microspheres prepared using electrohydrodynamic processing at ambient temperature was investigated. Polymethylsilsesquioxane (PMSQ) was used as a model material for the microsphere shell encapsulating a core of liquid perfluorohexane (PFH). The microspheres were characterized by Fourier transform infrared spectroscopy and optical and electron microscopy, and the effects of the processing parameters (flow-rate ratio, polymer concentration and applied voltage) on the mean microsphere diameter (D) and shell thickness (t) were determined. It was found that the mean diameters of the hollow microspheres could be controlled in the range from 310 to 1000 nm while the corresponding mean shell thickness varied from 40 to 95 nm. The results indicate that the ratio D : t varied with polymer concentration, with the largest value of approximately 10 achieved with a solution containing 18 wt% of the polymer, while the smallest value (6.6) was obtained at 36 wt%. For polymer concentrations above 63 wt%, hollow microspheres could not be generated, but instead PMSQ fibres encapsulating PFH liquid were obtained. PMID:20519216

  1. Controlling the cell adhesion property of silk films by graft polymerization.

    PubMed

    Dhyani, Vartika; Singh, Neetu

    2014-04-09

    We report here a graft polymerization method to improve the cell adhesion property of Bombyx mori silk fibroin films. B. mori silk has evolved as a promising material for tissue engineering because of its biocompatibility and biodegradability. However, silk's hydrophobic character makes cell adhesion and proliferation difficult. Also, the lack of sufficient reactive amino acid residues makes biofunctionalization via chemical modification challenging. Our study describes a simple method that provides increased chemical handles for tuning of the surface chemistry of regenerated silk films (SFs), thus allowing manipulation of their bioactivity. By grafting pAAc and pHEMA via plasma etching, we have increased carboxylic acid and hydroxyl groups on silk, respectively. These modifications allowed us to tune the hydrophilicity of SFs and provide functional groups for bioconjugation. Our strategy also allowed us to develop silk-based surface coatings, where spatial control over cell adhesion can be achieved. This control over cell adhesion in a particular region of the SFs is difficult to obtain via existing methods of modifying the silk fibroin instead of the SF surface. Thus, our strategy will be a valuable addition to the toolkit of biofunctionalization for enhancing SFs' tissue engineering applications.

  2. Controlled nanopatterning of a polymerized ionic liquid in a strong electric field

    SciTech Connect

    Bocharova, Vera; Agapov, Alexander L.; Tselev, Alexander; Kumar, Rajeev; Berdzinski, Stefan; Strehmel, Veronika; Kisliuk, Alexander; Kravchenko, Ivan I.; Sumpter, Bobby G.; Sokolov, Alexei P.; Kalinin, Sergei V.; Strelcov, Evgheni; Collins, Liam

    2014-12-17

    Nanolithography has become a driving force in advancements of the modern day's electronics, allowing for miniaturization of devices and a steady increase of the calculation, power, and storage densities. Among various nanofabrication approaches, scanning probe techniques, including atomic force microscopy (AFM), are versatile tools for creating nanoscale patterns utilizing a range of physical stimuli such as force, heat, or electric field confined to the nanoscale. In this study, the potential of using the electric field localized at the apex of an AFM tip to induce and control changes in the mechanical properties of an ion containing polymer—a polymerized ionic liquid (PolyIL)—on a very localized scale is explored. In particular, it is demonstrated that by means of AFM, one can form topographical features on the surface of PolyIL-based thin films with a significantly lower electric potential and power consumption as compared to nonconductive polymer materials. Lastly,, by tuning the applied voltage and ambient air humidity, control over dimensions of the formed structures is reproducibly achieved.

  3. Persistent free radicals, heavy metals and PAHs generated in particulate soot emissions and residue ash from controlled combustion of common types of plastic.

    PubMed

    Valavanidis, Athanasios; Iliopoulos, Nikiforos; Gotsis, George; Fiotakis, Konstantinos

    2008-08-15

    The production and use of polymeric materials worldwide has reached levels of 150 million tonnes per year, and the majority of plastic materials are discarded in waste landfills where are burned generating toxic emissions. In the present study we conducted laboratory experiments for batch combustion/burning of commercial polymeric materials, simulating conditions of open fire combustion, with the purpose to analyze their emissions for chemical characteristics of toxicological importance. We used common types of plastic materials: poly(vinyl chloride) (PVC), low and high density poly(ethylene) (LDPE, HDPE), poly(styrene) (PS), poly(propylene) (PP) and poly(ethylene terephthalate) (PET). Samples of particulate smoke (soot) collected on filters and residue solid ash produced by controlled burning conditions at 600-750 degrees C are used for analysis. Emissions of particulate matter, persistent free radicals embedded in the carbonaceous polymeric matrix, heavy metals, other elements and PAHs were determined in both types of samples. Results showed that all plastics burned easily generating charred residue solid ash and black airborne particulate smoke. Persistent carbon- and oxygen-centered radicals, known for their toxic effects in inhalable airborne particles, were detected in both particulate smoke emissions and residue solid ash. Concentrations of heavy metals and other elements (determined by Inductively Coupled Plasma Emission Spectrometry, ICP, method) were measured in the airborne soot and residue ash. Toxic heavy metals, such as Pb, Zn, Cr, Ni, and Cd were relatively at were found at low concentrations. High concentrations were found for some lithophilic elements, such as Na, Ca, Mg, Si and Al in particulate soot and residue solid ash. Measurements of PAHs showed that low molecular weight PAHs were at higher concentrations in the airborne particulate soot than in the residue solid ash for all types of plastic. Higher-ringed PAHs were detected at higher

  4. Microtransfer printing of metal ink patterns onto plastic substrates utilizing an adhesion-controlled polymeric donor layer

    NASA Astrophysics Data System (ADS)

    Park, Ji-Sub; Choi, Jun-Chan; Park, Min-Kyu; Bae, Jeong Min; Bae, Jin-Hyuk; Kim, Hak-Rin

    2016-06-01

    We propose a method for transfer-printed electrode patterns onto flexible/plastic substrates, specifically intended for metal ink that requires a high sintering temperature. Typically, metal-ink-based electrodes cannot be picked up for microtransfer printing because the adhesion between the electrodes and the donor substrate greatly increases after the sintering process due to the binding materials. We introduced a polymeric donor layer between the printed electrodes and the donor substrate and effectively reduced the adhesion between the Ag pattern and the polymeric donor layer by controlling the interfacial contact area. After completing a wet-etching process for the polymeric donor layer, we obtained Ag patterns supported on the fine polymeric anchor structures; the Ag patterns could be picked up onto the stamp surface even after the sintering process by utilizing the viscoelastic properties of the elastomeric stamp with a pick-up velocity control. The proposed method enables highly conductive metal-ink-based electrode patterns to be applied on thermally weak plastic substrates via an all-solution process. Metal electrodes transferred onto a film showed superior electrical and mechanical stability under the bending stress test required for use in printed flexible electronics.

  5. Controlled radical fluorination of poly(meth)acrylic acids in aqueous solution.

    PubMed

    Dong, Yucheng; Wang, Zhentao; Li, Chaozhong

    2017-08-17

    Fluorinated alkenes exhibit very poor reactivity in copolymerization with non-fluorinated polar monomers such as acrylates. Herein we describe a convenient method for the synthesis of poly(vinyl fluoride-co-acrylic acid) and poly(2-fluoropropene-co-methacrylic acid) copolymers. Thus, the silver-catalyzed decarboxylative radical fluorination of poly(acrylic acid) with Selectfluor in water at room temperature affords poly(vinyl fluoride-co-acrylic acid) copolymers in high yields with well-defined molecular weights and polydispersities. A linear correlation is observed between the extent of fluorination and the amount of Selectfluor, indicating that the copolymer of virtually any monomer ratio can be readily accessed by controlling the amount of Selectfluor. This controlled decarboxylative fluorination is extended to poly(methacrylic acid), leading to well-defined poly(2-fluoropropene-co-methacrylic acid) copolymers.Fluorinated alkenes have very poor reactivity in copolymerizations with non-fluorinated polar monomers. Here the authors show silver-catalyzed decarboxylative radical fluorination of poly(acrylic acid) with Selectfluor in water at room temperature to form poly(vinyl fluoride-co-acrylic acid) copolymers.

  6. SYNTHESIS AND IN VITRO CHARACTERIZATION OF HYDROXYPROPYL METHYLCELLULOSE-GRAFT-POLY (ACRYLIC ACID/2-ACRYLAMIDO-2-METHYL-1-PROPANESULFONIC ACID) POLYMERIC NETWORK FOR CONTROLLED RELEASE OF CAPTOPRIL.

    PubMed

    Furqan Muhammad, Iqbal; Mahmood, Ahmad; Aysha, Rashid

    2016-01-01

    A super-absorbent hydrogel was developed by crosslinking of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and acrylic acid with hydroxypropyl methylcellulose (HPMC) for controlled release drug delivery of captopril, a well known antihypertensive drug. Acrylic acid and AMPS were polymerized and crosslinked with HPMC by free radical polymerization, a widely used chemical crosslinking method. N,N'-methylenebisacrylamide (MBA) and potassium persulfate (KPS) were added as cross-linker and initiator, respectively. The hydrogel formulation was loaded with captopril (as model drug). The concentration of captopril was monitored at 205 nm using UV spectrophotometer. Equilibrium swelling ratio was determined at pH 2, 4.5 and 7.4 to evaluate the pH responsiveness of the formed hydrogel. The super-absorbent hydrogels were evaluated by FTIR, SEM, XRD, and thermal analysis (DSC and TGA). The formation of new copolymeric network was determined by FTIR, XRD, TGA and DSC analysis. The hydrogel formulations with acrylic acid and AMPS ratio of 4: 1 and lower amounts of crosslinker had shown maximum swelling. Moreover, higher release rate of captopril was observed at pH 7.4 than at pH 2, because of more swelling capacity of copolymer with increasing pH of the aqueous medium. The present research work confirms the development of a stable hydrogel comprising of HPMC with acrylic acid and AMPS. The prepared hydrogels exhibited pH sensitive behav-ior. This superabsorbent composite prepared could be a successful drug carrier for treating hypertension.

  7. Control of Microcellular Structure in Polymeric Foams via Nanofiller Size and Surface Chemistry

    NASA Astrophysics Data System (ADS)

    Goren, Kerem; Schadler, Linda; Ozisik, Rahmi

    2008-03-01

    Polymeric foams are used in many applications, where thermal insulation, selective sound inhibition or low density materials are needed. They are generally produced by blending polymer with a chemical blowing agent, which releases inert gas at processing temperatures. There are two major drawbacks to this process: chemical residues that form during the decomposition of blowing agent and formation of large (macroscopic) pores that weaken the material. To overcome these drawbacks, supercritical carbon dioxide (scCO2) is used. Use of scCO2 along with nanofillers provide heterogeneous nucleation, and present the opportunity to control pore size and pore distribution. In the current study, the effect of silica size and silica-scCO2 interaction on microcellular structure was investigated. Two different silica fillers were synthesized: 15 and 150 nm. These silica nanofillers were surface modified with tridecafluoro-1,1,2,2-tetrahydrooctyl triethoxysilanes. Dynamic Light Scattering, FT-IR, TGA, and SEM were used to characterize the samples. Results indicate that there is a strong correlation between surface chemistry, and hence scCO2 and filler interaction on pore size and size distribution.

  8. Polymerization Initiated at the Sidewalls of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Tour, James M.; Hudson, Jared L.

    2011-01-01

    A process has been developed for growing polymer chains via anionic, cationic, or radical polymerization from the side walls of functionalized carbon nanotubes, which will facilitate greater dispersion in polymer matrices, and will greatly enhance reinforcement ability in polymeric material.

  9. Controlling the dissociation dynamics of acetophenone radical cation through excitation of ground and excited state wavepackets

    NASA Astrophysics Data System (ADS)

    Moore Tibbetts, Katharine; Tarazkar, Maryam; Bohinski, Timothy; Romanov, Dmitri A.; Matsika, Spiridoula; Levis, Robert J.

    2015-08-01

    Time-resolved measurements of the acetophenone radical cation prepared via adiabatic ionization with strong field 1270 nm excitation reveal coupled wavepacket dynamics that depend on the intensity of the 790 nm probe pulse. At probe intensities below 7× {10}11 W cm-2, out of phase oscillations between the parent molecular ion and the benzoyl fragment ion are shown to arise from a one-photon excitation from the ground D0 ionic surface to the D1 and/or D2 excited surfaces by the probe pulse. At higher probe intensities, a second set of wavepacket dynamics are observed that couple the benzoyl ion to the phenyl, butadienyl, and acylium fragment ions. Equation of motion coupled cluster calculations of the ten lowest lying ionic surfaces and the dipole couplings between the ground ionic surface D0 and the nine excited states enable elucidation of the dissociation pathways and deduction of potential dissociation mechanisms. The results can lead to improved control schemes for selective dissociation of the acetophenone radical cation.

  10. Design of pervaporation membrane for organic-liquid separation based on solubility control by plasma-graft filling polymerization technique

    SciTech Connect

    Yamaguchi, Takeo; Nakao, Shinichi; Kimura, Shoji )

    1993-05-01

    Pervaporation performance through the membranes showed the same tendency as solubility results. The authors have prepared the filling-polymerized membrane for pervaporation of organic-liquid mixtures by the plasma-graft polymerization technique. The membrane is composed of two different polymers: a porous substrate which can suppress membrane swelling and a grafted polymer which forms in the pores of the substrate and exhibits selectivity due to its solubility. The objectives of the present study are to design a suitable membrane for an organic-mixture system by the control of the filling-polymer solubility. Specifically, a porous high-density polyethylene membrane and poly(methylacrylate/acrylamide) copolymer were employed as the porous substrate and grafted polymer, respectively, and grafted copolymer solubility was predicted by Hansen solubility parameters (HSP). The grafted polymer composition and its solubility behavior could be controlled by varying the monomer composition, and the solubility change was in accordance with the prediction by HSP. Pervaporation performance through the membranes showed the same tendency as solubility results. The authors concluded that an optimum pervaporation membrane can be designed on the basis of solubility control through use of these techniques for polymerization and prediction.

  11. A Model-based B2B (Batch to Batch) Control for An Industrial Batch Polymerization Process

    NASA Astrophysics Data System (ADS)

    Ogawa, Morimasa

    This paper describes overview of a model-based B2B (batch to batch) control for an industrial batch polymerization process. In order to control the reaction temperature precisely, several methods based on the rigorous process dynamics model are employed at all design stage of the B2B control, such as modeling and parameter estimation of the reaction kinetics which is one of the important part of the process dynamics model. The designed B2B control consists of the gain scheduled I-PD/II2-PD control (I-PD with double integral control), the feed-forward compensation at the batch start time, and the model adaptation utilizing the results of the last batch operation. Throughout the actual batch operations, the B2B control provides superior control performance compared with that of conventional control methods.

  12. Polymerization of a Photocleavable Monomer Using Visible Light.

    PubMed

    Bagheri, Ali; Yeow, Jonathan; Arandiyan, Hamidreza; Xu, Jiangtao; Boyer, Cyrille; Lim, May

    2016-06-01

    The polymerization of the photocleavable monomer, o-nitrobenzyl methacrylate (NBMA), is investigated using photoinduced electron/energy transfer reversible addition-fragmentation chain transfer polymerization. The polymerizations under visible red (λ max = 635 nm, 0.7 mW cm(-2) ) and yellow (λ max = 560 nm, 9.7 mW cm(-2) ) light are performed and demonstrate rational evidence of a controlled/living radical polymerization process. Well-defined poly(o-nitrobenzyl methacrylate) (PNBMA) homopolymers with good control over the molecular weight and polymer dispersity are successfully synthesized by varying the irradiation time and/or targeted degree of polymerization. Chain extension of a poly(oligo(ethylene glycol) methyl ether methacrylate) macro-chain transfer agent with NBMA is carried out to fabricate photocleavable amphiphilic block copolymers (BCP). Finally, these self-assembled BCP rapidly dissemble under UV light suggesting the photoresponsive character of NBMA is not altered during the polymerization under yellow or red light. Such photoresponsive polymers can be potentially used for the remote-controlled delivery of therapeutic compounds.

  13. Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization (ATRP) from Poly(vinyl chloride)- co -chlorinated Poly(vinyl chloride) (PVC- co -CPVC) Fiber

    SciTech Connect

    Brown, Suree; Yue, Yanfeng; Kuo, Li-Jung; Mehio, Nada; Li, Meijun; Gill, Gary; Tsouris, Costas; Mayes, Richard T.; Saito, Tomonori; Dai, Sheng

    2016-03-11

    The need to secure future supplies of energy attracts researchers in several countries to a vast resource of nuclear energy fuel: uranium in seawater (estimated at 4.5 billion tons in seawater). In this study, we developed effective adsorbent fibers for the recovery of uranium from seawater via atom-transfer radical polymerization (ATRP) from a poly-(vinyl chloride)-co-chlorinated poly(vinyl chloride) (PVC-co-CPVC) fiber. ATRP was employed in the surface graft polymerization of acrylonitrile (AN) and tert-butyl acrylate (tBA), precursors for uranium-interacting functional groups, from PVC-co-CPVC fiber. The [tBA]/[AN] was systematically varied to identify the optimal ratio between hydrophilic groups (from tBA) and uranyl-binding ligands (from AN). The best performing adsorbent fiber, the one with the optimal [tBA]/[AN] ratio and a high degree of grafting (1390%), demonstrated uranium adsorption capacities that are significantly greater than those of the Japan Atomic Energy Agency (JAEA) reference fiber in natural seawater tests (2.42 3.24 g/kg in 42 days of seawater exposure and 5.22 g/kg in 49 days of seawater exposure, versus 1.66 g/kg in 42 days of seawater exposure and 1.71 g/kg in 49 days of seawater exposure for JAEA). Lastly, adsorption of other metal ions from seawater and their corresponding kinetics were also studied. The grafting of alternative monomers for the recovery of uranium from seawater is now under development by this versatile technique of ATRP.

  14. Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization (ATRP) from Poly(vinyl chloride)- co -chlorinated Poly(vinyl chloride) (PVC- co -CPVC) Fiber

    SciTech Connect

    Brown, Suree; Yue, Yanfeng; Kuo, Li-Jung; Mehio, Nada; Li, Meijun; Gill, Gary; Tsouris, Costas; Mayes, Richard T.; Saito, Tomonori; Dai, Sheng

    2016-04-20

    The need to secure future supplies of energy attracts researchers in several countries to a vast resource of nuclear energy fuel: uranium in seawater (estimated at 4.5 billion tons in seawater). In this study, we developed effective adsorbent fibers for the recovery of uranium from seawater via atom-transfer radical polymerization (ATRP) from a poly- (vinyl chloride)-co-chlorinated poly(vinyl chloride) (PVC-co-CPVC) fiber. ATRP was employed in the surface graft polymerization of acrylonitrile (AN) and tert-butyl acrylate (tBA), precursors for uranium-interacting functional groups, from PVC-co-CPVC fiber. The [tBA]/[AN] was systematically varied to identify the optimal ratio between hydrophilic groups (from tBA) and uranyl-binding ligands (from AN). The best performing adsorbent fiber, the one with the optimal [tBA]/[AN] ratio and a high degree of grafting (1390%), demonstrated uranium adsorption capacities that are significantly greater than those of the Japan Atomic Energy Agency (JAEA) reference fiber in natural seawater tests (2.42-3.24 g/kg in 42 days of seawater exposure and 5.22 g/kg in 49 days of seawater exposure, versus 1.66 g/kg in 42 days of seawater exposure and 1.71 g/kg in 49 days of seawater exposure for JAEA). Adsorption of other metal ions from seawater and their corresponding kinetics were also studied. The grafting of alternative monomers for the recovery of uranium from seawater is now under development by this versatile technique of ATRP.

  15. Molecular weight control in organochromium olefin polymerization catalysis by hemilabile ligand-metal interactions.

    PubMed

    Mark, Stefan; Wadepohl, Hubert; Enders, Markus

    2016-01-01

    A series of Cr(III) complexes based on quinoline-cyclopentadienyl ligands with additional hemilabile side arms were prepared and used as single-site catalyst precursors for ethylene polymerization. The additional donor functions interact with the metal centers only after activation with the co-catalyst. Evidence for this comes from DFT-calculations and from the differing behavior of the complexes in ethylene polymerization. All complexes investigated show very high catalytic activity and the additional side arm minimizes chain-transfer reactions, leading to increase of molecular weights of the resulting polymers.

  16. Molecular weight control in organochromium olefin polymerization catalysis by hemilabile ligand–metal interactions

    PubMed Central

    Mark, Stefan; Wadepohl, Hubert

    2016-01-01

    Summary A series of Cr(III) complexes based on quinoline-cyclopentadienyl ligands with additional hemilabile side arms were prepared and used as single-site catalyst precursors for ethylene polymerization. The additional donor functions interact with the metal centers only after activation with the co-catalyst. Evidence for this comes from DFT-calculations and from the differing behavior of the complexes in ethylene polymerization. All complexes investigated show very high catalytic activity and the additional side arm minimizes chain-transfer reactions, leading to increase of molecular weights of the resulting polymers. PMID:27559387

  17. Controlled aniline polymerization strategies for polyaniline micro- and nano self-assembling into practical electronic devices.

    PubMed

    Yunus, Sami; Attout, Anne; Bertrand, Patrick

    2009-02-03

    Electroless polymerization of aniline on platinum is investigated for polyaniline micro- and nanostructuring into practical electronic devices. This type of reaction is adapted to estimate its usefulness in a lithographic process. For practical electronic device fabrication, electroless polymerization of aniline can be used to electrically bridge initially independent platinum electrodes. As this application requires a polyaniline bridge to form over a nonconductive material before an electrical contact is obtained, polyaniline growth using chemical oxidative reaction is investigated on substrates presenting surface-tension contrast patterns.

  18. Ultrahigh Molecular Weight Linear Block Copolymers: Rapid Access by Reversible-Deactivation Radical Polymerization and Self- Assembly into Large Domain Nanostructures

    SciTech Connect

    Mapas, Jose Kenneth D.; Thomay, Tim; Cartwright, Alexander N.; Ilavsky, Jan; Rzayev, Javid

    2016-05-05

    Block copolymer (BCP) derived periodic nanostructures with domain sizes larger than 150 nm present a versatile platform for the fabrication of photonic materials. So far, the access to such materials has been limited to highly synthetically involved protocols. Herein, we report a simple, “user-friendly” method for the preparation of ultrahigh molecular weight linear poly(solketal methacrylate-b-styrene) block copolymers by a combination of Cu-wire-mediated ATRP and RAFT polymerizations. The synthesized copolymers with molecular weights up to 1.6 million g/mol and moderate dispersities readily assemble into highly ordered cylindrical or lamella microstructures with domain sizes as large as 292 nm, as determined by ultra-small-angle x-ray scattering and scanning electron microscopy analyses. Solvent cast films of the synthesized block copolymers exhibit stop bands in the visible spectrum correlated to their domain spacings. The described method opens new avenues for facilitated fabrication and the advancement of fundamental understanding of BCP-derived photonic nanomaterials for a variety of applications.

  19. Polymeric microspheres

    DOEpatents

    Walt, David R.; Mandal, Tarun K.; Fleming, Michael S.

    2004-04-13

    The invention features core-shell microsphere compositions, hollow polymeric microspheres, and methods for making the microspheres. The microspheres are characterized as having a polymeric shell with consistent shell thickness.

  20. act up controls actin polymerization to alter cell shape and restrict Hedgehog signaling in the Drosophila eye disc.

    PubMed

    Benlali, A; Draskovic, I; Hazelett, D J; Treisman, J E

    2000-04-28

    Cells in the morphogenetic furrow of the Drosophila eye disc undergo a striking shape change immediately prior to their neuronal differentiation. We have isolated mutations in a novel gene, act up (acu), that is required for this shape change. acu encodes a homolog of yeast cyclase-associated protein, which sequesters monomeric actin; we show that acu is required to prevent actin filament polymerization in the eye disc. In contrast, profilin promotes actin filament polymerization, acting epistatically to acu. However, both acu and profilin are required to prevent premature Hedgehog-induced photoreceptor differentiation ahead of the morphogenetic furrow. These findings suggest that dynamic changes in actin filaments alter cell shape to control the movement of signals that coordinate a wave of differentiation.

  1. Regio- and Stereochemical Control in Ocimene Polymerization by Half-Sandwich Rare-Earth Metal Dialkyl Complexes.

    PubMed

    Peng, Deqian; Du, Gaixia; Zhang, Pengfei; Yao, Bo; Li, Xiaofang; Zhang, Shaowen

    2016-06-01

    The polymerization of ocimene has been first achieved by half-sandwich rare-earth metal dialkyl complexes in combination with activator and Al(i) Bu3 . The regio- and stereoselectivity in the ocimene polymerization can be controlled by tuning the cyclopentadienyl ligand and the central metal of the complex. The chiral cyclopentadienyl-ligated Sc complex 1 prepares syndiotactic cis-1,4-polyocimene (cis-1,4-selectivity up to 100%, rrrr = 100%), while the corresponding Lu, Y, and Dy complexes 2-4 and the achiral pentamethylcyclopentadienyl Sc, Lu, and Y complexes 5-7 afford isotactic trans-1,2-polyocimenes (trans-1,2-selectivity up to 100%, mm = 100%).

  2. Free radical generation and concentration in a plasma polymer: the effect of aromaticity.

    PubMed

    Ershov, Sergey; Khelifa, Farid; Lemaur, Vincent; Cornil, Jérôme; Cossement, Damien; Habibi, Youssef; Dubois, Philippe; Snyders, Rony

    2014-08-13

    Plasma polymer films (PPF) have increasing applications in many fields due to the unique combination of properties of this class of materials. Among notable features arising from the specifics of plasma polymerization synthesis, a high surface reactivity can be advantageously used when exploited carefully. It is related to the presence of free radicals generated during the deposition process through manifold molecular bond scissions in the energetic plasma environment. In ambient atmosphere, these radicals undergo autoxidation reactions resulting in undesired polymer aging. However, when the reactivity of surface radicals is preserved and they are put in direct contact with a chemical group of interest, a specific surface functionalization or grafting of polymeric chains can be achieved. Therefore, the control of the surface free radical density of a plasma polymer is crucially important for a successful grafting. The present investigation focuses on the influence of the hydrocarbon precursor type, aromatic vs aliphatic, on the generation and concentration of free radicals on the surface of the PPF. Benzene and cyclohexane were chosen as model precursors. First, in situ FTIR analysis of the plasma phase supplemented by density functional theory calculations allowed the main fragmentation routes of precursor molecules in the discharge to be identified as a function of energy input. Using nitric oxide (NO) chemical labeling in combination with X-ray photoelectron spectroscopy analysis, a quantitative evaluation of concentration of surface free radicals as a function of input power has been assessed for both precursors. Different evolutions of the surface free radical density for the benzene- and cyclohexane-based PPF, namely, a continuous increase versus stabilization to a plateau, are attributed to different plasma polymerization mechanisms and resulting structures as illustrated by PPF characterization findings. The control of surface free radical density can be

  3. Real-time Detection of Polymerization Reactions with Hyperpolarized Xenon at Low Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Glöggler, Stefan; Blümich, Bernhard; Appelt, Stephan

    2011-03-01

    For process control it is desirable to develop simple devices for studying polymerization reactions in real-time and in-situ. We are demonstrating an approach using NMR at fields as low as 35 G and hyperpolarized xenon, which allows us to observe polymerization reactions in real-time. The investigated reaction is a free radical polymerization with the initiator azobisisobutyronitrile (AIBN) and the monomer methyl methacrylate (MMA). AIBN and MMA are mixed together in a sample tube under noble gas atmosphere, and the reaction is started by irradiation with UV light (360 nm). As the reaction goes on, xenon NMR spectra are acquired. They show increasing line broadening and a variation of the chemical shift depending on the state of polymerization. This observation gives rise to the idea that a single-sided high resolution NMR sensor can be developed with which at least light induced polymerization reactions can be studied in-situ and in real-time.

  4. Fabrication of a polymer with three-dimensional structure by the ion beam graft polymerization method

    NASA Astrophysics Data System (ADS)

    Taniike, Akira; Kida, Yasutomo; Furuyama, Yuichi; Kitamura, Akira

    2011-12-01

    The graft polymerization method is one of the most effective techniques to produce a new polymer with unique function. To produce the polymer, we conducted experiments on radiation graft polymerization using ion beams of several hundred keV energy. A high density polyethylene (PE) film was irradiated with H + beams, then, graft polymerization with monomer solution such as acrylic acid or acrylonitrile was conducted. Radicals generated by the interaction between the beam ions and the PE molecules become the starting point of the graft polymerization. Since the range in PE depends on ion energy, the density distribution of the graft chain can be controlled by the ion energy. Using a mask which restricts the ion beam incidence, PE sheets containing graft chains only in the unmasked area were obtained. Multiple ion beam graft polymerization can produce a polymer which has some functional bases at specified position. We have demonstrated the production of a polymer film with a three-dimensional structure.

  5. Antagonistic regulation of F-BAR protein assemblies controls actin polymerization during podosome formation.

    PubMed

    Tsujita, Kazuya; Kondo, Akihiro; Kurisu, Shusaku; Hasegawa, Junya; Itoh, Toshiki; Takenawa, Tadaomi

    2013-05-15

    FBP17, an F-BAR domain protein, has emerged as a crucial factor linking the plasma membrane to WASP-mediated actin polymerization. Although it is well established that FBP17 has a powerful self-polymerizing ability that promotes actin nucleation on membranes in vitro, knowledge of inhibitory factors that counteract this activity in vivo is limited. Here, we demonstrate that the assembly of FBP17 on the plasma membranes is antagonized by PSTPIP2, another F-BAR protein implicated in auto-inflammatory disorder. Knockdown of PSTPIP2 in macrophage promotes the assembly of FBP17 as well as subsequent actin nucleation at podosomes, resulting in an enhancement of matrix degradation. This phenotype is rescued by expression of PSTPIP2 in a manner dependent on its F-BAR domain. Time-lapse total internal reflection fluorescence (TIRF) microscopy observations reveal that the self-assembly of FBP17 at the podosomal membrane initiates actin polymerization, whereas the clustering of PSTPIP2 has an opposite effect. Biochemical analysis and live-cell imaging show that PSTPIP2 inhibits actin polymerization by competing with FBP17 for assembly at artificial as well as the plasma membrane. Interestingly, the assembly of FBP17 is dependent on WASP, and its dissociation by WASP inhibition strongly induces a self-organization of PSTPIP2 at podosomes. Thus, our data uncover a previously unappreciated antagonism between different F-BAR domain assemblies that determines the threshold of actin polymerization for the formation of functional podosomes and may explain how the absence of PSTPIP2 causes auto-inflammatory disorder.

  6. Surface functionalized SiO2 nanoparticles with cationic polymers via the combination of mussel inspired chemistry and surface initiated atom transfer radical polymerization: Characterization and enhanced removal of organic dye.

    PubMed

    Huang, Qiang; Liu, Meiying; Mao, Liucheng; Xu, Dazhuang; Zeng, Guangjian; Huang, Hongye; Jiang, Ruming; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2017-03-28

    Monodispersed SiO2 particles functionalized with cationic polymers poly-((3-acrylamidopropyl)trimethylammonium chloride) (PAPTCl) were prepared using mussel inspired surface modification strategy and surface initiated atom transfer radical polymerization (SI-ATRP). Fourier transform infrared spectroscopy, transmission electron microscope, thermogravimetric analysis, X-ray photoelectron spectroscopy, and zeta potential were employed to characterize these SiO2 samples. The adsorption performance of the functionalized SiO2 (donated as SiO2-PDA-PAPTCl) towards anionic organic dye Congo red (CR) was investigated to evaluate their potential environmental applications. We demonstrated that the surface of SiO2 particles can be successfully functionalized with cationic PAPTCl. The adsorption capability of as-prepared SiO2 was found to increases from 28.70 and 106.65mg/g after surface grafted with cationic polymers. The significant enhancement in the adsorption capability of SiO2-PDA-PAPTCl is mainly attributed to the introduction of cationic polymers. More importantly, this strategy is expected to be promising for fabrication of many other functional polymer nanocomposites for environmental applications due to the universality of mussel inspired chemistry and well designability and good monomer adaptability of SI-ATRP.

  7. Induction heating vs conventional heating for the hydrothermal treatment of nitinol and its subsequent 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate coating by surface-initiated atom transfer radical polymerization.

    PubMed

    Devillers, S; Barthélémy, B; Delhalle, J; Mekhalif, Z

    2011-10-01

    Nitinol is an alloy of great interest in general and especially in the biomedical field where many researches are aimed to improve both its corrosion resistance and its biocompatibility. In this work, we report on the advantage of an induction heating treatment in pure water compared to a conventional hydrothermal procedure. Both treatments lead to a hydroxylation of the surface, a decrease of the nickel amount in the outer part of the oxide layer, and a drastically decreased corrosion current density. However, the amount of surface hydroxyl groups is higher in the case of the induction heating treatment, which in turn leads to a denser grafting of atom transfer radical polymerization initiators and ultimately to a thicker 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate (MPC) polymer layer than in the case of conventional heating treatments. X-ray photoelectron spectroscopy (XPS), static contact angle, and polarization curves measurements as well as scanning electron microscopy (SEM) have been used to characterize the obtained modified surfaces. © 2011 American Chemical Society

  8. Characterization of pH-Responsive Hydrogels of Poly(Itaconic acid-g-Ethylene Glycol) Prepared by UV-Initiated Free Radical Polymerization as Biomaterials for Oral Delivery of Bioactive Agents

    PubMed Central

    Betancourt, Tania; Pardo, Juan; Soo, Ken; Peppas, Nicholas A.

    2009-01-01

    Effective oral delivery of proteins is impeded by steep pH gradients and proteolytic enzymes in the gastrointestinal tract, as well as low absorption of the proteins into the bloodstream due to their size, charge or solubility. In the present work, pH-responsive complexation hydrogels of poly(itaconic acid) with poly(ethylene glycol) grafts were synthesized for applications in oral drug delivery. These hydrogels were expected to be in collapsed configuration at low pH due to hydrogen bonding between poly(itaconic acid) carboxyl groups and poly(ethylene glycol), and to swell with increasing pH because of charge repulsion between deprotonated carboxylic acid groups. Hydrogels were prepared by UV-initiated free radical polymerization using tetraethylene glycol as the crosslinking agent and Irgacure® 2959 as the initiator. The effect of monomer ratios, crosslinking ratio and solvent amount on the properties of the hydrogels were investigated. The composition of the hydrogels was confirmed by FTIR. Equilibrium swelling studies in the pH range of 1.2 to 7 revealed that the extent of swelling increased with increasing pH up to a pH of about 6, when no further carboxylic acid deprotonation occurred. Studies in Caco-2 colorectal carcinoma cells confirmed the cytocompatibility of these materials at concentrations of up to 5 mg/ml. PMID:19536838

  9. Determination of melamine and cyromazine in milk by high performance liquid chromatography coupled with online solid-phase extraction using a novel cation-exchange restricted access material synthesized by surface initiated atom transfer radical polymerization.

    PubMed

    Zhang, Yingying; Lin, Shen; Jiang, Ping; Zhu, Xudong; Ling, Jing; Zhang, Wen; Dong, Xiangchao

    2014-04-11

    A novel strong-cation-exchange restricted access material has been synthesized by atom transfer radical polymerization (ATRP). In the synthesis, poly(3-sulfopropyl methacrylate-co-ethylene dimethacrylate), [p(SPM/EDMA)] was grafted on the silica by surface-initiated ATRP first. The poly(glycerol mono-methacrylate) [pGMMA] was then immobilized on the external surface, which created a chemical diffusion barrier for protein exclusion. The resulting Sil-g-p(SPM/EDMA)-g-pGMMA has both functions of protein exclusion and cation exchange, exhibiting the property of cation-exchange restricted access material. The application of Sil-g-p(SPM/EDMA)-g-pGMMA has been studied by the determination of melamine and cyromazine in bovine milk using the online solid-phase extraction/HPLC method. In the process, the Sil-g-p(SPM/EDMA)-g-pGMMA was used for the sample pre-treatment and a HILIC column was employed as the analytical column. The method has shown good accuracy, precision and low limits of detections. The result demonstrated that the Sil-g-p(SPM/EDMA)-g-pGMMA can be used for the cation extraction from biological samples by direct HPLC injection.

  10. Well-Defined High Molecular Weight Polystyrene with High Rates and High Livingness Synthesized via Two-Stage RAFT Emulsion Polymerization.

    PubMed

    Yan, Kun; Gao, Xiang; Luo, Yingwu

    2015-07-01

    A highly living polymer with over 100 kg mol(-1) molecular weight is very difficult to achieve by controlled radical polymerization since the unavoidable side reactions of irreversible radical termination and radical chain transfer to monomer reaction become significant. It is reported that over 500 kg mol(-1) polystyrene with high livingness and low dispersity could be synthesized by a facile two-stage reversible addition-fragmentation transfer emulsion polymerization. The monomer conversion reaches 90% within 10 h. High livingness of the product is ascribed to the extremely low initiator concentration and the chain transfer constant for monomer unexpectedly much lower than the well-accepted values in the conventional radical polymerization. The two-stage monomer feeding policy much decreases the dispersity of the product.

  11. Evaluation of Thermal Control Coatings and Polymeric Materials Exposed to Ground Simulated Atomic Oxygen and Vacuum Ultraviolet Radiation

    NASA Technical Reports Server (NTRS)

    Kamenetzky, R. R.; Vaughn, J. A.; Finckenor, M. M.; Linton, R. C.

    1995-01-01

    Numerous thermal control and polymeric samples with potential International Space Station applications were evaluated for atomic oxygen and vacuum ultraviolet radiation effects in the Princeton Plasma Physics Laboratory 5 eV Neutral Atomic Oxygen Facility and in the MSFC Atomic Oxygen Drift Tube System. Included in this study were samples of various anodized aluminum samples, ceramic paints, polymeric materials, and beta cloth, a Teflon-impregnated fiberglass cloth. Aluminum anodizations tested were black duranodic, chromic acid anodize, and sulfuric acid anodize. Paint samples consisted of an inorganic glassy black paint and Z-93 white paint made with the original PS7 binder and the new K2130 binder. Polymeric samples evaluated included bulk Halar, bulk PEEK, and silverized FEP Teflon. Aluminized and nonaluminized Chemfab 250 beta cloth were also exposed. Samples were evaluated for changes in mass, thickness, solar absorptance, and infrared emittance. In addition to material effects, an investigation was made comparing diffuse reflectance/solar absorptance measurements made using a Beckman DK2 spectroreflectometer and like measurements made using an AZ Technology-developed laboratory portable spectroreflectometer.

  12. In vitro, in vivo and pharmacokinetic assessment of amikacin sulphate laden polymeric nanoparticles meant for controlled ocular drug delivery

    NASA Astrophysics Data System (ADS)

    Sharma, Upendra Kumar; Verma, Amita; Prajapati, Sunil Kuamr; Pandey, Himanshu; Pandey, Avinash C.

    2015-02-01

    The rationale of current exploration was to formulate positively charged amikacin-loaded polymeric nanoparticles providing a controlled release attribute. Amikacin sulphate-loaded nanoparticles were prepared by w/o/w emulsification solvent evaporation approach succeeded by high-pressure homogenization. Two bioadhesive positively charged polymers, Eudragit® RS 100 and Eudragit® RL 100, were used in the blend, with variable ratios of drug and polymer. The formulations were assessed in terms of particle size and zeta potential. Thermal gravimetric analysis was brought out on the samples of drug, polymer and drug polymer complex. Drug loading and release attributes of the nanoparticles were scrutinized and antimicrobial activity in contrast to Staphylococcus aureus was appraised. Ocular irritation test, in vivo ocular retention study, in vivo release profile (permeation study) and in vivo antibacterial activity of polymeric nanosuspensions were executed. No rupture consequence but a lengthened drug release was contemplated from all formulations. Amikacin sulphate release from the polymeric nanoparticles reflected a better fit with Korsmeyer-Peppas model. In the course of the antibacterial activity of nanoparticles against S. aureus, formulation AE1 displays the most prominent inhibitory effect as compared with marketed formulation of amikacin sulphate.

  13. Polymerization as a Model Chain Reaction

    ERIC Educational Resources Information Center

    Morton, Maurice

    1973-01-01

    Describes the features of the free radical, anionic, and cationic mechanisms of chain addition polymerization. Indicates that the nature of chain reactions can be best taught through the study of macromolecules. (CC)

  14. Polymerization as a Model Chain Reaction

    ERIC Educational Resources Information Center

    Morton, Maurice

    1973-01-01

    Describes the features of the free radical, anionic, and cationic mechanisms of chain addition polymerization. Indicates that the nature of chain reactions can be best taught through the study of macromolecules. (CC)

  15. N-Heterocyclic carbene-mediated zwitterionic polymerization of N-substituted N-carboxyanhydrides toward poly(α-peptoid)s: kinetic, mechanism, and architectural control.

    PubMed

    Guo, Li; Lahasky, Samuel H; Ghale, Kushal; Zhang, Donghui

    2012-06-06

    N-Heterocyclic carbene (NHC)-mediated polymerizations of N-butyl N-carboxyanhydride (Bu-NCA) to produce cyclic poly(N-butyl glycine)s (c-NHC-PNBGs) have been investigated in various solvents with NHCs having differing steric and electronic properties. Control over the polymer molecular weight (MW) and polymerization rate is strongly dependent on the solvent and the NHC structure. Kinetic studies reveal that the propagating intermediates for the polymerization in low dielectric solvents (e.g., THF or toluene) maintain cyclic architectures with two chain ends in close contact through Coulombic interaction. The NHCs not only initiate the polymerization, but also mediate the chain propagation as intramolecular counterions. Side reactions are significantly suppressed in low dielectric solvents due to the reduced basicity and nucleophilicity of the negatively charged chain ends of the zwitterions, resulting in quasi-living polymerization behavior. By contrast, the two charged chain ends of the zwitterionic species are fully dissociated in high dielectric solvents. The chain propagation proceeds as in conventional anionic polymerizations, wherein side reactions (e.g., transamidation) compete with chain propagation, resulting in significantly diminished control over polymer MW. The cyclic zwitterionic propagating species can be converted into their linear polymeric analogues (l-NHC-PNBGs) by end-capping with electrophiles (e.g., acetyl chloride) or the NHC-free cyclic analogues (c-PNBGs) by treatment with NaN(TMS)(2), as evidenced by MALDI-TOF MS, NMR, and SEC analysis.

  16. The role of weak interactions in lignin polymerization.

    PubMed

    Sánchez-González, Ángel; Martín-Martínez, Francisco J; Dobado, J A

    2017-03-01

    Lignin is the most abundant natural polymer composed by aromatic moieties. Its chemical composition and its abundance have focused efforts to unlock its potential as a source of aromatic compounds for many years. The lack of a proper way for lignin de-polymerization has hampered its success as a natural solution for commodity aromatic chemicals, which is also due to the lack of understanding of the underlying mechanisms of lignin polymerization. A fuller fundamental understanding of polymerization mechanisms could lead to improvements in de-polymerization strategies, and therefore a proper methodology and a predictive theoretical framework are required for such purpose. This work presents a complete computational study on some of the key steps of lignin polymerization mechanisms. Density functional theory (DFT) calculations have been performed to evaluate the most appropriate methodology and to compute the chemical structures and reaction enthalpies for the monolignol dimerization, the simplest key step that controls the polymerization. Quantum theory of atoms in molecules (QTAIM) has been applied to understand the coupling reaction mechanisms, for which the radical species and transition states (TSs) involved have been characterized. The coupling that leads to the formation of the β-O-4 linkage has been theoretically reproduced according to proposed mechanisms, for which weak interactions have been found to play a key role in the arrangement of reactants. The hydrogen bond formed between the oxygen of the phenoxy radical, and the alcohol of the aliphatic chain, together with the interaction between aromatic rings, locates the reactants in a position that favors such β-O-4 linkage. Graphical Abstract QTAIM analysis of the complex between coumaryl and coniferyl alcohols. It emphasizes the importance of weak interactions during the formation of beta-O-4 linkages in the polymerization of lignin.

  17. Polycomb group protein ezh2 controls actin polymerization and cell signaling.

    PubMed

    Su, I-hsin; Dobenecker, Marc-Werner; Dickinson, Ephraim; Oser, Matthew; Basavaraj, Ashwin; Marqueron, Raphael; Viale, Agnes; Reinberg, Danny; Wülfing, Christoph; Tarakhovsky, Alexander

    2005-05-06

    Polycomb group protein Ezh2, one of the key regulators of development in organisms from flies to mice, exerts its epigenetic function through regulation of histone methylation. Here, we report the existence of the cytosolic Ezh2-containing methyltransferase complex and tie the function of this complex to regulation of actin polymerization in various cell types. Genetic evidence supports the essential role of cytosolic Ezh2 in actin polymerization-dependent processes such as antigen receptor signaling in T cells and PDGF-induced dorsal circular ruffle formation in fibroblasts. Revealed function of Ezh2 points to a broader usage of lysine methylation in regulation of both nuclear and extra-nuclear signaling processes.

  18. Controlled Ring-Opening Metathesis Polymerization by Molybdenum and Tungsten Alkylidene Complexes

    DTIC Science & Technology

    1988-07-29

    weights and low polydispersities (as low as 1.03) consistent with a living catalyst system employing 50, 100, 200, and 400 eq of monomer. The reactions are...secondary metathesis of polymer chains Bulky alkoxide ligands Wittig-like reaction Ring-opening metathesis polymerization (ROMP) Feast monomer Cyclic...olefins Retro Diels-Alder reaction Norbornene (NBE) Low temperature column chromatography Endo-,endo-5,6-dicarbomethoxynorbornene Discrete, soluble

  19. Nano Particle Control of Void Formation and Expansion in Polymeric and Composite Systems

    DTIC Science & Technology

    2009-05-01

    ES) 8. PERFORMING ORGANIZATION REPORT NUMBER Glocal Network Corporation 3131 Western Avenue Ste M-526 Seattle, WA 98121...Scientific Research Arlington, VA 22203-1954 Principal Investigator Dr. James C. Seferis Polymeric Composites Laboratory GloCal Network...F.R.E.E.D.O.M., with the flexibility of a profit research and development organization, GloCal Network Corporation, with both entities doing business as the

  20. Tankyrase Polymerization Is Controlled by Its Sterile Alpha Motif and Poly(ADP-Ribose) Polymerase Domains

    PubMed Central

    De Rycker, Manu; Price, Carolyn M.

    2004-01-01

    Tankyrases are novel poly(ADP-ribose) polymerases that have SAM and ankyrin protein-interaction domains. They are found at telomeres, centrosomes, nuclear pores, and Golgi vesicles and have been shown to participate in telomere length regulation. Their other function(s) are unknown, and it has been difficult to envision a common role at such diverse cellular locations. We have shown that tankyrase 1 polymerizes through its sterile alpha motif (SAM) domain to assemble large protein complexes. In vitro polymerization is reversible and still allows interaction with ankyrin-domain binding proteins. Polymerization can also occur in vivo, with SAM-dependent association of overexpressed tankyrase leading to formation of large tankyrase-containing vesicles, disruption of Golgi structure, and inhibition of apical secretion. Finally, tankyrase polymers are dissociated efficiently by poly(ADP-ribosy)lation. This disassembly is prevented by mutation of the PARP domain. Our findings indicate that tankyrase 1 has the unique capacity to promote both assembly and disassembly of large protein complexes. Thus, tankyrases appear to be master scaffolding proteins that regulate the formation of dynamic protein networks at different cellular locations. This implies a common scaffolding function for tankyrases at each location, with specific tankyrase interaction partners conferring location-specific roles to each network, e.g., telomere compaction or regulation of vesicle trafficking. PMID:15509784

  1. Taming the free radical shrew - learning to control homolytic reactions at higher heteroatoms.

    PubMed

    Schiesser, Carl H

    2006-10-21

    Free radical chemistry has come a long way in a relatively short period of time. Armed with mechanistic and rate constant data, the synthetic practitioner can now apply free radical chemistry to the synthesis of many different classes of target molecule with confidence. This Feature Article highlights progress made in the understanding and application of free radical reactions at main group higher heteroatoms and demonstrates how this knowledge can be used to construct interesting higher heterocycles, many of which exhibit biological activity, through the use of intramolecular homolytic substitution chemistry.

  2. Global Model of Time-Modulated Electronegative Discharges for Neutral Radical and Electron Temperature Control

    NASA Astrophysics Data System (ADS)

    Kim, Sungjin; Lieberman, M. A.; Lichtenberg, A. J.

    2003-10-01

    Control and reduction of neutral radical flux/ion flux ratio and electron temperature Te is required for next generation etching in the microelectronics industry. We investigate time-modulated power for these purposes using a volume-averaged (global) oxygen discharge model, We consider pressures of 10-50 mTorr and plasma densities of 10^10-10^11 cm-3. In this regime, the discharge is found to be weakly electronegative. The modulation period and the duty ratio (on-time/period) are varied to determine the optimum conditions for reduction of FR= O-atom flux/ion flux and T_e. Two chambers with different height/diameter ratios (<< 1, and unity) are examined to determine the influence of the surface-area/volume ratio. At a fixed duty ratio, both FR and Te are found to have minimum values as the pulse period is varied, with the minimum value decreasing as the duty ratio decreases. Significant reductions in FR and Te are found. Support provided by Lam Research, NSF Grant ECS-0139956, California industries, and UC-SMART Contract SM99-10051.

  3. Urinary Incontinence and Erectile Dysfunction After Robotic Versus Open Radical Prostatectomy: A Prospective, Controlled, Nonrandomised Trial.

    PubMed

    Haglind, Eva; Carlsson, Stefan; Stranne, Johan; Wallerstedt, Anna; Wilderäng, Ulrica; Thorsteinsdottir, Thordis; Lagerkvist, Mikael; Damber, Jan-Erik; Bjartell, Anders; Hugosson, Jonas; Wiklund, Peter; Steineck, Gunnar

    2015-08-01

    Robot-assisted laparoscopic radical prostatectomy (RALP) has become widely used without high-grade evidence of superiority regarding long-term clinical outcomes compared with open retropubic radical prostatectomy (RRP), the gold standard. To compare patient-reported urinary incontinence and erectile dysfunction 12 mo after RALP or RRP. This was a prospective, controlled, nonrandomised trial of patients undergoing prostatectomy in 14 centres using RALP or RRP. Clinical-record forms and validated patient questionnaires at baseline and 12 mo after surgery were collected. Odds ratios (ORs) were calculated with logistic regression and adjusted for possible confounders. The primary end point was urinary incontinence (change of pad less than once in 24h vs one time or more per 24h) at 12 mo. Secondary end points were erectile dysfunction at 12 mo and positive surgical margins. Of 2625 eligible men, 2431 (93%) could be evaluated for the primary end point. At 12 mo after RALP, 366 men (21.3%) were incontinent, as were 144 (20.2%) after RRP. The adjusted OR was 1.08 (95% confidence interval [CI], 0.87-1.34). Erectile dysfunction was observed in 1200 men (70.4%) 12 mo after RALP and 531 (74.7%) after RRP. The adjusted OR was 0.81 (95% CI, 0.66-0.98). The frequency of positive surgical margins did not differ significantly between groups: 21.8% in the RALP group and 20.9% in the RRP group (adjusted OR: 1.09; 95% CI, 0.87-1.35). The nonrandomised design is a limitation. In a Swedish setting, RALP for prostate cancer was modestly beneficial in preserving erectile function compared with RRP, without a statistically significant difference regarding urinary incontinence or surgical margins. We compared patient-reported urinary incontinence after prostatectomy with two types of surgical technique. There was no statistically significant improvement in the rate of urinary leakage, but there was a small improvement regarding erectile function after robot-assisted operation. Copyright

  4. Control of Asymmetry in the Radical Addition Approach to Chiral Amine Synthesis

    PubMed Central

    Friestad, Gregory K.

    2014-01-01

    The state-of-the-science in asymmetric free radical additions to imino compounds is presented, beginning with an overview of methods involving stereocontrol by various chiral auxiliary approaches. Chiral N-acylhydrazones are discussed with respect to their use as radical acceptors for Mn-mediated intermolecular additions, from design to scope surveys to applications to biologically active targets. A variety of aldehydes and ketones serve as viable precursors for the chiral hydrazones, and a variety of alkyl iodides may be employed as radical precursors, as discussed in a critical review of the functional group compatibility of the reaction. Applications to amino acid and alkaloid synthesis are presented to illustrate the synthetic potential of these versatile stereocontrolled carbon–carbon bond construction reactions. Asymmetric catalysis is discussed, from seminal work on the stereocontrol of radical addition to imino compounds by non-covalent interactions with stoichiometric amounts of catalysts, to more recent examples demonstrating catalyst turnover. PMID:24085561

  5. Robotic Assisted Radical Cystectomy with Extracorporeal Urinary Diversion Does Not Show a Benefit over Open Radical Cystectomy: A Systematic Review and Meta-Analysis of Randomised Controlled Trials.

    PubMed

    Tan, Wei Shen; Khetrapal, Pramit; Tan, Wei Phin; Rodney, Simon; Chau, Marisa; Kelly, John D

    2016-01-01

    The number of robotic assisted radical cystectomy (RARC) procedures is increasing despite the lack of Level I evidence showing any advantages over open radical cystectomy (ORC). However, several systematic reviews with meta-analyses including non-randomised studies, suggest an overall benefit for RARC compared to ORC. We performed a systematic review with meta-analysis of randomised controlled trials (RCTs) to evaluate the perioperative morbidity and efficacy of RARC compared to ORC in patients with bladder cancer. Literature searches of Medline/Pubmed, Embase, Web of Science and clinicaltrials.gov databases up to 10th March 2016 were performed. The inclusion criteria for eligible studies were RCTs which compared perioperative outcomes of ORC and RARC for bladder cancer. Primary objective was perioperative and histopathological outcomes of RARC versus ORC while the secondary objective was quality of life assessment (QoL), oncological outcomes and cost analysis. Four RCTs (from 5 articles) met the inclusion criteria, with a total of 239 patients all with extracorporeal urinary diversion. Patient demographics and clinical characteristics of RARC and ORC patients were evenly matched. There was no significant difference between groups in perioperative morbidity, length of stay, positive surgical margin, lymph node yield and positive lymph node status. RARC group had significantly lower estimated blood loss (p<0.001) and wound complications (p = 0.03) but required significantly longer operating time (p<0.001). QoL was not measured uniformly across trials and cost analysis was reported in one RCTs. A test for heterogeneity did highlight differences across operating time of trials suggesting that surgeon experience may influence outcomes. This study does not provide evidence to support a benefit for RARC compared to ORC. These results may not have inference for RARC with intracorporeal urinary diversion. Well-designed trials with appropriate endpoints conducted by equally

  6. Voltage-responsive reversible self-assembly and controlled drug release of ferrocene-containing polymeric superamphiphiles.

    PubMed

    Chang, Xueyi; Cheng, Zhiyu; Ren, Biye; Dong, Renfeng; Peng, Jun; Fu, Shiyu; Tong, Zhen

    2015-10-14

    A new type of voltage-responsive comb-like superamphiphilic block polymer PEG113-b-PAA30/FTMA was prepared by the electrostatic interactions of an ionic ferrocenyl surfactant (FTMA) and an oppositely charged double-hydrophilic block polyelectrolyte poly-(ethylene glycol)-b-poly(acrylic acid) (PEG113-b-PAA30) in aqueous solution. An in situ electrochemical redox system was designed to research its electrochemical activity in aqueous solution. The polymeric superamphiphile PEG113-b-PAA30/FTMA could reversibly aggregate to form spherical micelles of 20-30 nm diameter in aqueous solution, and also disaggregate into irregular fragments by an electrochemical redox reaction when its concentration is in the range of the critical aggregation concentration (cacred) of the reduction state to its cacox of the oxidation state. Interestingly, above cacox, the superamphiphile can aggregate into spherical micelles of 20-30 nm diameter, which can be transformed into larger spherical micelles of 40-120 nm diameter after electrochemical oxidation, and reversibly recover initial sizes after electrochemical reduction. Moreover, this reversible self-assembly process can be electrochemically controlled just by changing its electrochemical redox extent without adding any other chemical reagent. Further, rhodamine 6G (R6G)-loaded polymeric superamphiphile aggregates have been successfully used for the voltage-controlled release of loaded molecules based on their voltage-responsive self-assembly, and the release rate of R6G could be mediated by changing electrochemical redox potentials and the concentrations of polymeric superamphiphiles. Our observations witness a new strategy to construct a voltage-responsive reversible self-assembly system.

  7. Numerical Simulation of Temperature Controlled Solid Phase Forming Process of Polymeric Plate

    NASA Astrophysics Data System (ADS)

    Liu, Haipeng; Hu, Ping; Fu, Zhengchun; Yan, Yue; Zhang, Guanli

    2005-08-01

    In this paper, a new forming process of polymeric plate called stretch-forming was simulated by adopting the thermo-elasto-visco-plastic large deformation finite element formulation based on Updated Lagrangian method. Some details of this forming process were also studied. It was shown that temperature has important effect on the forming process. Slide contact was assumed in the simulation. Friction force was ignored due to good lubrication. The adopted algorithm is verified by analyzing a thermoforming problem provided in a NUMIFORM'98 paper and comparing simulation results with experimental measures in that paper.

  8. Free radicals and antioxidant enzymes in older adults after regular senior elastic band exercising: an experimental randomized controlled pilot study.

    PubMed

    Liao, Lin Yu; Chung, Wei Sheng; Chen, Kuei Min

    2017-01-01

    The aim of this study was to pilot test the effects of regular senior elastic band exercises on the generation of free radicals and antioxidant enzyme activities in older adults. Long-term regular exercises have positive health promotion outcomes. On the contrary, high-intensity, high-speed and short-term exercises in older adults may increase free radicals and cause chronic disease and ageing effect. A prospective randomized controlled pilot study. Data were collected during 2012. Twenty-five older adults were recruited from a community care centre, southern Taiwan and were randomly assigned to either an experimental or control group. Twenty-two participants completed the study: experimental group (n = 10) and control group (n = 12). The experimental group performed 6-month senior elastic band exercises while the control group kept regular daily routines. Both groups received blood tests (thiobarbituric acid-reacting substances and glutathione peroxidase) 30 minutes before the study began and 1 hour after the final intervention treatment. At the end of the 6-month senior elastic band exercises, no statistically significant differences in thiobarbituric acid-reacting substances and glutathione peroxidase values between the experimental and control groups. No significant differences existed in both thiobarbituric acid-reacting substances and glutathione peroxidase values before and after the 6-month senior elastic band exercises either. Regular senior elastic band exercises did not increase the generation of free radicals and antioxidant enzyme activities. Senior elastic band exercises have the potential to be promoted among older adults in the community as an exercise option without adverse effects on free radicals and have potential for mitigating ageing and increasing disease control. © 2016 John Wiley & Sons Ltd.

  9. Kinetic resolution of racemic α-olefins with ansa-zirconocene polymerization catalysts: Enantiomorphic site vs. chain end control

    PubMed Central

    Byers, Jeffery A.; Bercaw, John E.

    2006-01-01

    Copolymerization of racemic α-olefins with ethylene and propylene was carried out in the presence of enantiopure C1-symmetric ansa metallocene, {1,2-(SiMe2)2(η5-C5H-3,5-(CHMe2)2)(η5-C5H3)}ZrCl2 to probe the effect of the polymer chain end on enantioselection for the R- or S-α-olefin during the kinetic resolution by polymerization catalysis. Copolymerizations with ethylene revealed that the polymer chain end is an important factor in the enantioselection of the reaction and that for homopolymerization, chain end control generally works cooperatively with enantiomorphic site control. Results from propylene copolymerizations suggested that chain end control arising from a methyl group at the β carbon along the main chain can drastically affect selectivity, but its importance as a stereo-directing element depends on the identity of the olefin. PMID:17032768

  10. Encapsulation of the synthetic retinoids Am80 and LE540 into polymeric micelles and the retinoids' release control.

    PubMed

    Satoh, Taku; Higuchi, Yuriko; Kawakami, Shigeru; Hashida, Mitsuru; Kagechika, Hiroyuki; Shudo, Koichi; Yokoyama, Masayuki

    2009-06-19

    The objective of this study was to encapsulate two synthetic retinoids Am80 and LE540 into polymeric micelles and to control the retinoids' release rate in vitro. Highly efficient encapsulation yields of these retinoids were obtained for micelles forming from PEG-poly(benzyl aspartate) block copolymers in the wide range of the benzyl substitution degree. The in vitro release examination for LE540 indicated very stable encapsulation of this retinoid owing to its strongly hydrophobic nature. On the other hand, Am80 exhibited a rapid release in Dulbecco's phosphate buffer saline. An addition of a hydrophobic alkyl amine in the Am80-encapsulation process successfully led to significant retardation of the Am80 release rate. A mechanism of the retardation was considered an increase of Am80 hydrophobicity due to an ion-pairing with the alkyl amine. This paper is the first report on release control in the polymeric micelle carrier system through the ion-pairing between an encapsulated drug and an additive.

  11. Low (Sub-1-volt) halfwave voltage polymeric electro-optic modulators achieved by controlling chromophore shape

    PubMed

    Shi; Zhang; Zhang; Bechtel; Dalton; Robinson; Steier

    2000-04-07

    Electro-optic (EO) modulators encode electrical signals onto fiber optic transmissions. High drive voltages limit gain and noise levels. Typical polymeric and lithium niobate modulators operate with halfwave voltages of 5 volts. Sterically modified organic chromophores have been used to reduce the attenuation of electric field poling-induced electro-optic activity caused by strong intermolecular electrostatic interactions. Such modified chromophores, incorporated into polymer hosts, were used to fabricate EO modulators with halfwave voltages of 0.8 volts (at a telecommunications wavelength of 1318 nanometers) and to achieve a halfwave voltage-interaction length product of 2.2 volt-centimeters. Optical push-pull poling and driving were also used to reduce halfwave voltage. This study, together with recent demonstrations of exceptional bandwidths (more than 110 gigahertz) and ease of integration (with very large scale integration semiconductor circuitry and ultra-low-loss passive optical circuitry) demonstrates the potential of polymeric materials for next generation telecommunications, information processing, and radio frequency distribution.

  12. Role of extracellular polymeric substances in bioflocculation of activated sludge microorganisms under glucose-controlled conditions.

    PubMed

    Badireddy, Appala R; Chellam, Shankararaman; Gassman, Paul L; Engelhard, Mark H; Lea, Alan S; Rosso, Kevin M

    2010-08-01

    Extracellular polymeric substances (EPS) secreted by suspended cultures of microorganisms from an activated sludge plant in the presence of glucose were characterized in detail using colorimetry, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. EPS produced by the multi-species community were similar to literature reports of pure cultures in terms of functionalities with respect to C and O but differed subtly in terms of N and P. Hence, it appears that EPS produced by different microorganisms maybe homologous in major chemical constituents but may differ in minor components such as lipids and phosphodiesters. The role of specific EPS constituents on microbial aggregation was also determined. The weak tendency of microorganisms to bioflocculate during the exponential growth phase was attributed to electrostatic repulsion when EPS concentration was low and acidic in nature (higher fraction of uronic acids to total EPS) as well as reduced polymer bridging. However, during the stationary phase, polymeric interactions overwhelmed electrostatic interactions (lower fraction of uronic acids to total EPS) resulting in improved bioflocculation. More specifically, microorganisms appeared to aggregate in the presence of protein secondary structures including aggregated strands, beta-sheets, alpha- and 3-turn helical structures. Bioflocculation was also favored by increasing O-acetylated carbohydrates and overall C-(O,N) and O=C-OH+O=C-OR functionalities. (c) 2010 Elsevier Ltd. All rights reserved.

  13. Role of extracellular polymeric substances in bioflocculation of activated sludge microorganisms under glucose-controlled conditions

    SciTech Connect

    Badireddy, Appala R.; Chellam, Shankararaman; Gassman, Paul L.; Engelhard, Mark H.; Lea, Alan S.; Rosso, Kevin M.

    2010-08-01

    Extracellular polymeric substances (EPS) secreted by suspended cultures of microorganisms from an activated sludge plant in the presence of glucose was characterized in detail using colorimetric analysis, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. EPS produced by the mixed population were similar to literature reports obtained from pure cultures in terms of functionalities with respect to C and O but differed subtly in terms of N and P. Hence, it appears that EPS produced by different microorganisms maybe similar in major chemical constituents but may differ in minor components. The role of specific EPS constituents on microbial aggregation was also determined. The weak tendency of microorganisms to bioflocculate during the exponential growth phase was attributed to electrostatic repulsion when EPS concentration was low and acidic in nature (higher fraction of uronic acids to total EPS). However, during the stationary phase, polymeric interactions overwhelmed electrostatic interactions (lower fraction of uronic acids to total EPS) resulting in greater bioflocculation. More specifically, microorganisms appeared to aggregate in the presence of protein secondary structures including aggregated strands, β-sheets, α- and 3-turn helical structures. Bioflocculation was also favored by increasing O-acetylated carbohydrates and overall C-(O,N) and O=C–OH + O=C–OR functionalities.

  14. Controlled Bulk Properties of Composite Polymeric Solutions for Extensive Structural Order of Honeycomb Polysulfone Membranes

    PubMed Central

    Gugliuzza, Annarosa; Perrotta, Maria Luisa; Drioli, Enrico

    2016-01-01

    This work provides additional insights into the identification of operating conditions necessary to overcome a current limitation to the scale-up of the breath figure method, which is regarded as an outstanding manufacturing approach for structurally ordered porous films. The major restriction concerns, indeed, uncontrolled touching droplets at the boundary. Herein, the bulk of polymeric solutions are properly managed to generate honeycomb membranes with a long-range structurally ordered texture. Water uptake and dynamics are explored as chemical environments are changed with the intent to modify the hydrophilic/hydrophobic balance and local water floatation. In this context, a model surfactant such as the polyoxyethylene sorbitan monolaurate is used in combination with alcohols at different chain length extents and a traditional polymer such as the polyethersufone. Changes in the interfacial tension and kinematic viscosity taking place in the bulk of composite solutions are explored and examined in relation to competitive droplet nucleation and growth rate. As a result, extensive structurally ordered honeycomb textures are obtained with the rising content of the surfactant while a broad range of well-sized pores is targeted as a function of the hydrophilic-hydrophobic balance and viscosity of the composite polymeric mixture. The experimental findings confirm the consistency of the approach and are expected to give propulsion to the commercially production of breath figures films shortly. PMID:27196938

  15. Polymerization Kinetics: Monitoring Monomer Conversion Using an Internal Standard and the Key Role of Sample "t[subscript 0]"

    ERIC Educational Resources Information Center

    Colombani, Olivier; Langelier, Ophelie; Martwong, Ekkachai; Castignolles, Patrice

    2011-01-01

    The use of an internal standard is a conventional and convenient way to monitor the conversion of one or several monomers during a controlled radical polymerization. However, the validity of this technique relies on an accurate determination of the initial monomer-to-internal standard ratio, A[subscript 0], because all subsequent calculations of…

  16. Further evidence for radical-controlled oscillations in the Belousov-Zhabotinskii reaction: Large effects of ultraviolet light and silver ions

    SciTech Connect

    Stuk, L.; Roberts, J.; McCormick, W.D.; Noszticzius, Z. )

    1990-08-23

    We have performed experiments on the Belousov-Zhabotinskii reaction perturbed by ultraviolet light and by silver ions, and over a range of sulfuric acid concentrations, the reaction shows a large sensitivity to these perturbations. Our results support Foersterling and Noszticzius' theory of malonyl radicals as a second control intermediate. Results of perturbation by both ultraviolet light and silver ions at the same time, however, are not adequately explained by either malonyl radical control or bromide control (or both) and suggest a third control intermediate such as bromomalonyl radicals.

  17. 2,2,6,6-Tetramethylpiperydinyl-1-oxyl (TEMPO) Functionalized Benzoxazines Prepared with a One-Pot Synthesis for Reactive/Crosslinkable Initiators of Nitroxide Mediated Polymerization.

    PubMed

    Han, Yi-Jen; Liu, Ying-Ling

    2017-08-01

    In this work, the incorporation of a 2,2,6,6-tetramethylpiperydinyl-1-oxyl (TEMPO) group to a benzoxazine ring is performed using a one-pot synthesis for the preparation of TEMPO-functionalized benzoxazine compounds and polymers as reactive and crosslinkable initiators for nitroxide-mediated polymerization (NMP). The TEMPO-functionalization reaction of benzoxazine, traced with (1) H NMR, is conducted with sequential radical transfer and coupling reactions. Moreover, polystyrene-grafted polybenzoxazine copolymers are prepared with the TEMPO-benzoxazine initiator and NMP of styrene. The polymerization system exhibits the characteristics of controlled radical polymerization, including controlled molecular weights of products and ability for sequential polymerization. Moreover, based on the chemical reactivity and crosslinking ability of benzoxazine groups, the synthesis route developed in this work will widen the scope of the design and synthesis of functional and high-performance polymers. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Radiation-induced graft polymerization of amphiphilic monomers with different polymerization characteristics onto hydrophobic polysilane

    NASA Astrophysics Data System (ADS)

    Tanaka, Hidenori; Iwasaki, Isao; Kunai, Yuichiro; Sato, Nobuhiro; Matsuyama, Tomochika

    2011-08-01

    The structures of poly(methyl-n-propylsilane) (PMPrS) amphiphilically modified through γ-ray-induced graft polymerization were investigated with 1H NMR measurement. By the use of methyl methacrylate (MMA) or diethyl fumarate (DEF) as monomers for the graft polymerization, grafting yield rose with increasing total absorption dose and monomer concentrations, but decreased with increasing dose rate. This result means that grafting yield of modified PMPrS can be controlled by changing irradiation conditions. However, the number of PMMA or PDEF graft chains per PMPrS chain was estimated to be less than 1.0 by analysis of 1H NMR spectra, and this value was lower than that we had expected. To improve graft density, maleic anhydride (MAH), which is known as a non-homopolymerizable monomer in radical polymerization, was used as a monomer for grafting. As a result, high density grafting (one MAH unit for 4.2 silicon atoms) was attained. It demonstrates that the structure of γ-ray-modified polysilane strongly depends on the polymerization characteristics of grafted monomers.

  19. [Light-induced control of polymerization shrinkage of dental composites by generating temporary hardness gradients].

    PubMed

    Sommer, A P; Gente, M

    1999-10-01

    Irradiation of light-curing dental filling materials in a single direction results in a temporary hardness gradient in the direction of the irradiation. The photoactivated polymerisation process begins at the site of the highest light intensity. In the simplest possible model, the polymerizing composites irradiated in a single direction shows three adjacent co-existing phases: an almost hardened, a gelled and a still plastic phase. As long as all three phases are present, any shrinking of the contracting phases can be compensated by the plastic phase. A knowledge of the distribution of these phases and their spatial and temporal modulation by the selection of suitable curing light parameters provides simple techniques for reducing shrinkage gaps around voluminous fillings in large dental cavities.

  20. Development of an in situ controllable polymerization tool and process for hydrogel used to replace nucleus pulposus

    NASA Astrophysics Data System (ADS)

    Schmocker, Andreas M.; Khoushabi, Azadeh; Bourban, Pierre-Etienne; Schizas, Constantin; Pioletti, Dominique P.; Moser, Christophe

    2015-06-01

    Currently implants or tissue replacements are inserted either as a whole implant or by injecting a liquid which polymerizes to form a solid implant at the appropriate location. This is either highly invasive or not controllable. We developed a tool to perform such surgeries in a minimally invasive and controllable way. It combines photopolymerization and fluorescence spectroscopy in a surgical apparatus. However, to successfully replace tissue such as cartilage or an intervertebral disc, photopolymerizable materials do not only need to be photoactive. They should also be able to withstand the environmental loading conditions after implantation. Therefore we developed a set of in situ and in vitro tests adapted to the evaluation of photopolymerized tissue replacements and implants. In particular in this article, we report on a method, which combines photopolymerization and photorheology to track the current state of polymer during photopolymerization.

  1. Evaluation of polymeric nanoparticle formulations by effective imaging and quantitation of cellular uptake for controlled delivery of doxorubicin.

    PubMed

    Win, Khin Yin; Teng, Choon Peng; Ye, Enyi; Low, Michelle; Han, Ming-Yong

    2015-03-01

    Various polymeric nanoparticles have been extensively engineered for applications in controlled drug release delivery in the last decades. Currently, there is a great demand to develop a strategy to qualitatively and quantitatively evaluate these polymeric nanoparticle formulations for producing innovative delivery systems. In this work, a screening platform is developed using luminescent quantum dots as drug model and imaging label to evaluate nanoparticle formulations incorporating either hydrophilic or hydrophobic drugs and imaging agents. It is validated that there is no influence of the incorporated entities on the cellular uptake profile. The use of quantum dots enables efficient detection and precise quantitation of cellular uptake of particles which occupy 25% of the cell volume. The correlation of quantum dot- and doxorubicin-incorporated nanoparticles is useful to develop an evaluation platform for nanoparticle formulations through imaging and quantitation. This platform is also used to observe the surface properties effect of other polymers such as chitosan and poly(ethylene) glycol on the cellular interaction and uptake. Moreover, quantum dots can be used to study microparticle theranostic delivery formulations by deliberately incorporating as visible ring surrounding the microparticles for their easy identifying and tracing in diagnostic and chemotherapeutic applications.

  2. Fluidic Processing of High-Performance ZIF-8 Membranes on Polymeric Hollow Fibers: Mechanistic Insights and Microstructure Control

    DOE PAGES

    Eum, Kiwon; Rownaghi, Ali; Choi, Dalsu; ...

    2016-06-01

    Recently, a methodology for fabricating polycrystalline metal-organic framework (MOF) membranes has been introduced – referred to as interfacial microfluidic membrane processing – which allows parallelizable fabrication of MOF membranes inside polymeric hollow fibers of microscopic diameter. Such hollow fiber membranes, when bundled together into modules, are an attractive way to scale molecular sieving membranes. The understanding and engineering of fluidic processing techniques for MOF membrane fabrication are in their infancy. Here in this work, a detailed mechanistic understanding of MOF (ZIF-8) membrane growth under microfluidic conditions in polyamide-imide hollow fibers is reported, without any intermediate steps (such as seeding ormore » surface modification) or post-synthesis treatments. A key finding is that interfacial membrane formation in the hollow fiber occurs via an initial formation of two distinct layers and the subsequent rearrangement into a single layer. This understanding is used to show how nonisothermal processing allows fabrication of thinner (5 μm) ZIF-8 films for higher throughput, and furthermore how engineering the polymeric hollow fiber support microstructure allows control of defects in the ZIF-8 membranes. Finally, the performance of these engineered ZIF-8 membranes is then characterized, which have H2/C3H8 and C3H6/C3H8 mixture separation factors as high as 2018 and 65, respectively, and C3H6 permeances as high as 66 GPU.« less

  3. Comparison of release-controlling efficiency of polymeric coating materials using matrix-type casted films and diffusion-controlled coated tablet.

    PubMed

    Piao, Zong-Zhu; Lee, Kyoung-Ho; Kim, Dong-Jin; Lee, Hong-Gu; Lee, Jaehwi; Oh, Kyung Taek; Lee, Beom-Jin

    2010-06-01

    Polymeric coating materials have been widely used to modify release rate of drug. We compared physical properties and release-controlling efficiency of polymeric coating materials using matrix-type casted film and diffusion-controlled coated tablet. Hydroxypropylmethyl cellulose (HPMC) with low or high viscosity grade, ethylcellulose (EC) and Eudragit(R) RS100 as pH-independent polymers and Eudragit S100 for enteric coatings were chosen to prepare the casted film and coated tablet. Tensile strength and contact angle of matrix-type casted film were invariably in the decreasing order: EC> Eudragit S100> HPMC 100000> Eudragit RS100>HPMC 4000. There was a strong linear correlation between tensile strength and contact angle of the casted films. In contrast, weight loss (film solubility) of the matrix-type casted films in three release media (gastric, intestinal fluid and water) was invariably in the increasing order: EC < HPMC 100000 < Eudragit RS100 < HPMC 4000 with an exception of Eudragit S100. The order of release rate of matrix-type casted films was EC > HPMC 100000 > Eudragit RS100 > HPMC 4000 > Eudragit S100. Interestingly, diffusion-controlled coated tablet also followed this rank order except Eudragit S100 although release profiles and lag time were highly dependent on the coating levels and type of polymeric coating materials. EC and Eudragit RS100 produced sustained release while HPMC and Eudragit S100 produced pulsed release. No molecular interactions occurred between drug and coating materials using (1)H-NMR analysis. The current information on release-controlling power of five different coating materials as matrix carrier or diffusion-controlled film could be applicable in designing oral sustained drug delivery.

  4. Dimensional Control and Morphological Transformations of Supramolecular Polymeric Nanofibers Based on Cofacially-Stacked Planar Amphiphilic Platinum(II) Complexes.

    PubMed

    Robinson, Matthew E; Nazemi, Ali; Lunn, David J; Hayward, Dominic W; Boott, Charlotte E; Hsiao, Ming-Siao; Harniman, Robert L; Davis, Sean A; Whittell, George R; Richardson, Robert M; De Cola, Luisa; Manners, Ian

    2017-09-26

    Square-planar platinum(II) complexes often stack cofacially to yield supramolecular fiber-like structures with interesting photophysical properties. However, control over fiber dimensions and the resulting colloidal stability is limited. We report the self-assembly of amphiphilic Pt(II) complexes with solubilizing ancillary ligands based on polyethylene glycol [PEGn, where n = 16, 12, 7]. The complex with the longest solubilizing PEG ligand, Pt-PEG16, self-assembled to form polydisperse one-dimensional (1D) nanofibers (diameters <5 nm). Sonication led to short seeds which, on addition of further molecularly dissolved Pt-PEG16 complex, underwent elongation in a "living supramolecular polymerization" process to yield relatively uniform fibers of length up to ca. 400 nm. The fiber lengths were dependent on the Pt-PEG16 complex to seed mass ratio in a manner analogous to a living covalent polymerization of molecular monomers. Moreover, the fiber lengths were unchanged in solution after 1 week and were therefore "static" with respect to interfiber exchange processes on this time scale. In contrast, similarly formed near-uniform fibers of Pt-PEG12 exhibited dynamic behavior that led to broadening of the length distribution within 48 h. After aging for 4 weeks in solution, Pt-PEG12 fibers partially evolved into 2D platelets. Furthermore, self-assembly of Pt-PEG7 yielded only transient fibers which rapidly evolved into 2D platelets. On addition of further fiber-forming Pt complex (Pt-PEG16), the platelets formed assemblies via the growth of fibers selectively from their short edges. Our studies demonstrate that when interfiber dynamic exchange is suppressed, dimensional control and hierarchical structure formation are possible for supramolecular polymers through the use of kinetically controlled seeded growth methods.

  5. Fundamentals of Atom Transfer Radical Polymerization

    ERIC Educational Resources Information Center

    Coessens, Veerle M. C.; Matyjaszewski, Krzysztof

    2010-01-01

    Today's market increasingly demands sophisticated materials for advanced technologies and high-value applications, such as nanocomposites, optoelectronic, or biomedical materials. Therefore, the demand for well-defined polymers with very specific molecular architecture and properties increases. Until recently, these kinds of polymers could only be…

  6. Fundamentals of Atom Transfer Radical Polymerization

    ERIC Educational Resources Information Center

    Coessens, Veerle M. C.; Matyjaszewski, Krzysztof

    2010-01-01

    Today's market increasingly demands sophisticated materials for advanced technologies and high-value applications, such as nanocomposites, optoelectronic, or biomedical materials. Therefore, the demand for well-defined polymers with very specific molecular architecture and properties increases. Until recently, these kinds of polymers could only be…

  7. Psychotherapy and phosphodiesterase-5 inhibitor in early rehabilitation after radical prostatectomy: a prospective randomised controlled trial.

    PubMed

    Naccarato, A M E P; Reis, L O; Ferreira, U; Denardi, F

    2016-12-01

    The aim of this study was to evaluate the impact of group psychotherapy and the use of a phosphodiesterase-5 inhibitor (PDE-5i) in the early rehabilitation stage of patients with prostate cancer undergoing radical prostatectomy (RP). Fifty-six patients undergoing RP for prostate cancer were randomised into four groups, and 53 completed the protocol: Group 1 - control (n = 11), Group 2 - group psychotherapy (n = 16), Group 3 - lodenafil 80 mg/one tablet per week (n = 12) and Group 4 - group psychotherapy + lodenafil 80 mg/one tablet per week (n = 14). The groups were individually evaluated for erectile function (IIEF-5) and quality of life - QoL (SF-36) weekly, with two meetings held a week apart before the RP and 12 weekly meetings after surgery. The ages ranged from 39 to 76 years, average 61.84. There were no significant medication side effects. Only Group 4 showed improvement in intimacy with a partner and satisfaction with their sex life (P = 0.045 and P = 0.013 respectively), and with no significant worsening of the IIEF-5 (P = 0.250) reported. All groups showed worsening in the final result of the role limitations caused by physical problems (P = 0.009) and role limitations caused by emotional problems (P = 0.002) of the SF-36, but Group 4 had a significantly higher score for the role limitations caused by physical problems (P = 0.009) than the other groups. In conclusion, precocious integral treatment involving group psychotherapy and PDE-5i before and after RP led to less deterioration of erectile function and other domains related to physical aspects (SF-36), with improvement in intimacy with their partner and satisfaction in their sex life, being superior to single treatments. © 2016 Blackwell Verlag GmbH.

  8. Improved Livingness and Control over Branching in RAFT Polymerization of Acrylates: Could Microflow Synthesis Make the Difference?

    PubMed

    Derboven, Pieter; Van Steenberge, Paul H M; Vandenbergh, Joke; Reyniers, Marie-Francoise; Junkers, Thomas; D'hooge, Dagmar R; Marin, Guy B

    2015-12-01

    The superior capabilities of structured microreactors over batch reactors are demonstrated for reversible addition-fragmentation chain transfer (RAFT) solution polymerization of n-butyl acrylate with the aid of simulations, explicitly accounting for the chain length distribution of all macrospecies types. Since perfect isothermicity can be established in a microreactor, less side products due to backbiting and β-scission are formed compared to the batch operation in which ineffective heat removal leads to an undesirable temperature spike. For a given RAFT chain transfer agent (CTA), additional microstructural control results under microflow conditions by optimizing the reaction temperature, lowering the dilution degree, or decreasing the initial molar ratio of monomer to RAFT CTA.

  9. Stimuli-Responsive Polymeric Systems for Controlled Protein and Peptide Delivery: Future Implications for Ocular Delivery.

    PubMed

    Mahlumba, Pakama; Choonara, Yahya E; Kumar, Pradeep; du Toit, Lisa C; Pillay, Viness

    2016-07-30

    Therapeutic proteins and peptides have become notable in the drug delivery arena for their compatibility with the human body as well as their high potency. However, their biocompatibility and high potency does not negate the existence of challenges resulting from physicochemical properties of proteins and peptides, including large size, short half-life, capability to provoke immune responses and susceptibility to degradation. Various delivery routes and delivery systems have been utilized to improve bioavailability, patient acceptability and reduce biodegradation. The ocular route remains of great interest, particularly for responsive delivery of macromolecules due to the anatomy and physiology of the eye that makes it a sensitive and complex environment. Research in this field is slowly gaining attention as this could be the breakthrough in ocular drug delivery of macromolecules. This work reviews stimuli-responsive polymeric delivery systems, their use in the delivery of therapeutic proteins and peptides as well as examples of proteins and peptides used in the treatment of ocular disorders. Stimuli reviewed include pH, temperature, enzymes, light, ultrasound and magnetic field. In addition, it discusses the current progress in responsive ocular drug delivery. Furthermore, it explores future prospects in the use of stimuli-responsive polymers for ocular delivery of proteins and peptides. Stimuli-responsive polymers offer great potential in improving the delivery of ocular therapeutics, therefore there is a need to consider them in order to guarantee a local, sustained and ideal delivery of ocular proteins and peptides, evading tissue invasion and systemic side-effects.

  10. mTORC2 controls actin polymerization required for consolidation of long-term memory

    PubMed Central

    Huang, Wei; Zhu, Ping Jun; Zhang, Shixing; Zhou, Hongyi; Stoica, Loredana; Galiano, Mauricio; Krnjević, Krešimir; Roman, Gregg; Costa-Mattioli, Mauro

    2013-01-01

    A major goal of biomedical research has been the identification of molecular mechanisms that can enhance memory. Here we report a novel signaling pathway that regulates the conversion from short- to long-term memory. The mTOR complex 2 (mTORC2), which contains the key regulatory protein Rictor (Rapamycin-Insensitive Companion of mTOR), was discovered only recently, and little is known about its physiological role. We show that conditional deletion of rictor in the postnatal murine forebrain greatly reduces mTORC2 activity and selectively impairs both long-term memory (LTM) and the late (but not the early) phase of hippocampal long-term potentiation (LTP). Actin polymerization is reduced in the hippocampus of mTORC2-deficient mice and its restoration rescues both L-LTP and LTM. More importantly, a compound that selectively promotes mTORC2 activity converts early-LTP into late-LTP and enhances LTM. These findings indicate that mTORC2 could be a novel therapeutic target for the treatment of cognitive dysfunction. PMID:23455608

  11. Identification of a Distal GLUT4 Trafficking Event Controlled by Actin Polymerization

    PubMed Central

    Lopez, Jamie A.; Burchfield, James G.; Blair, Duncan H.; Mele, Katarina; Ng, Yvonne; Vallotton, Pascal

    2009-01-01

    The insulin-stimulated trafficking of GLUT4 to the plasma membrane in muscle and fat tissue constitutes a central process in blood glucose homeostasis. The tethering, docking, and fusion of GLUT4 vesicles with the plasma membrane (PM) represent the most distal steps in this pathway and have been recently shown to be key targets of insulin action. However, it remains unclear how insulin influences these processes to promote the insertion of the glucose transporter into the PM. In this study we have identified a previously uncharacterized role for cortical actin in the distal trafficking of GLUT4. Using high-frequency total internal reflection fluorescence microscopy (TIRFM) imaging, we show that insulin increases actin polymerization near the PM and that disruption of this process inhibited GLUT4 exocytosis. Using TIRFM in combination with probes that could distinguish between vesicle transport and fusion, we found that defective actin remodeling was accompanied by normal insulin-regulated accumulation of GLUT4 vesicles close to the PM, but the final exocytotic fusion step was impaired. These data clearly resolve multiple steps of the final stages of GLUT4 trafficking, demonstrating a crucial role for actin in the final stage of this process. PMID:19605560

  12. PEG/RGD-modified magnetic polymeric liposomes for controlled drug release and tumor cell targeting.

    PubMed

    Su, Wenya; Wang, Hanjie; Wang, Sheng; Liao, Zhenyu; Kang, Shiyin; Peng, Yao; Han, Lei; Chang, Jin

    2012-04-15

    Polymeric liposomes (PEG/RGD-MPLs), composed of amphiphilic polymer octadecyl-quaternized modified poly (γ-glutamic acid) (OQPGA), PEGylated OQPGA, RGD peptide grafted OQPGA and magnetic nanoparticles, was prepared successfully. These PEG/RGD-MPLs could be used as a multifunctional platform for targeted drug delivery. The results showed that PEG/RGD-MPLs were multilamellar spheres with nano-size (50-70 nm) and positive surface charge (28-42 mV). Compared with magnetic conventional liposomes (MCLs), PEG/RGD-MPLs exhibited sufficient size and zeta potential stability, low initial burst release and less magnetic nanoparticles leakage. The cell uptake results suggested that the PEG/RGD-MPLs (with RGD and magnetic particles) exhibited more drug cellular uptake than non RGD and non magnetism carriers in MCF-7 cells. MTT assay revealed that PEG/RGD-MPLs showed lower in vitro cytotoxicity to GES-1cells at ≤ 100 μg/mL. These data indicated that the multifunctional PEG/RGD-MPLs may be an alternative formulation for drug delivery system. Copyright © 2012 Elsevier B.V. All rights reserved.

  13. Improved Mechanical Performance Fracture Properties and Reliability of Radical-Cured Thermosets

    SciTech Connect

    Redline, Erica Marie; Bolintineanu, Dan S.; Lane, J. Matthew; Stevens, Mark J.; Alam, Todd M.; Celina, Mathias C.

    2016-10-01

    The aim of this study was to alter polymerization chemistry to improve network homogeneity in free-radical crosslinked systems. It was hypothesized that a reduction in heterogeneity of the network would lead to improved mechanical performance. Experiments and simulations were carried out to investigate the connection between polymerization chemistry, network structure and mechanical properties. Experiments were conducted on two different monomer systems - the first is a single monomer system, urethane dimethacrylate (UDMA), and the second is a two-monomer system consisting of bisphenol A glycidyl dimethacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) in a ratio of 70/30 BisGMA/TEGDMA by weight. The methacrylate systems were crosslinked using traditional radical polymeriza- tion (TRP) with azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) as an initiator; TRP systems were used as the control. The monomers were also cross-linked using activator regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) as a type of controlled radical polymerization (CRP). FTIR and DSC were used to monitor reac- tion kinetics of the systems. The networks were analyzed using NMR, DSC, X-ray diffraction (XRD), atomic force microscopy (AFM), and small angle X-ray scattering (SAXS). These techniques were employed in an attempt to quantify differences between the traditional and controlled radical polymerizations. While a quantitative methodology for characterizing net- work morphology was not established, SAXS and AFM have shown some promising initial results. Additionally, differences in mechanical behavior were observed between traditional and controlled radical polymerized thermosets in the BisGMA/TEGDMA system but not in the UDMA materials; this finding may be the result of network ductility variations between the two materials. Coarse-grained molecular dynamics simulations employing a novel model of the CRP reaction were carried out for

  14. Supported neodymium catalysts for isoprene and rac-β-butyrolactone polymerization: modulation of reactivity by controlled grafting.

    PubMed

    Terrier, Michael; Brulé, Emilie; Vitorino, Marta J; Ajellal, Noureddine; Robert, Carine; Gauvin, Régis M; Thomas, Christophe M

    2011-01-17

    A series of hybrid materials, bearing neodymium silylamide initiating groups, have been shown to mediate isoprene polymerization when combined with alkyl aluminum activators [methylaluminoxane, AlEt(2)Cl, Al(iBu)(3)]. The surface species nature and relative distribution were correlated with isoprene polymerization activity and selectivity. This approach to stereocontrol modulation has been extended to racemic β-butyrolactone isoselective ring opening polymerization.

  15. Strategies to control alkoxy radical-initiated relay cyclizations for the synthesis of oxygenated tetrahydrofuran motifs.

    PubMed

    Zhu, Hai; Leung, Joe C T; Sammis, Glenn M

    2015-01-16

    Radical relay cyclizations initiated by alkoxy radicals are a powerful tool for the rapid construction of substituted tetrahydrofurans. The scope of these relay cyclizations has been dramatically increased with the development of two strategies that utilize an oxygen atom in the substrate to accelerate the desired hydrogen atom transfer (HAT) over competing pathways. This has enabled a chemoselective 1,6-HAT over a competing 1,5-HAT. Furthermore, this allows for a chemoselective 1,5-HAT over competing direct cyclizations and β-fragmentations. Oxygen atom incorporation leads to a general increase in cyclization diastereoselectivity over carbon analogues. This chemoselective relay cyclization strategy was utilized in the improved synthesis of the tetrahydrofuran fragment in (−)-amphidinolide K.

  16. Enantiomeric Free Radicals and Enzymatic Control of Stereochemistry in a Radical Mechanism: the Case of Lysine 2,3-aminomutases †

    PubMed Central

    Behshad, E.; Ruzicka, F.J; Mansoorabadi, S.; Chen, D.; Reed, G.H; Frey, P.A.

    2008-01-01

    The product of yjeK in Escherichia coli is a homolog of lysine 2,3-aminomutase (LAM) from Clostridium subterminale SB4, and both enzymes catalyze the isomerization of (S)- but not (R)-α-lysine by radical mechanisms. The turnover number for LAM from E. coli is 5.0 min−1, 0.1% of the value for clostridial LAM. The reaction of E. coli LAM with (S)-α-[3,3,4,4,5,5,6,6- 2H8]lysine proceeds with a kinetic isotope effect of kH/kD = 1.4, suggesting that hydrogen transfer is not rate limiting. The product of the E. coli enzyme is (R)-β-lysine, the enantiomer of the clostridial product. β-Lysine-related radicals are observed in the reactions of both enzymes by electron paramagnetic resonance (EPR). The radical in the reaction of clostridial LAM has the (S)- configuration, whereas that in the reaction of E. coli LAM has the (R)-configuration. Moreover, the conformations of the β-lysine-related radicals at the active sites of E. coli and clostridial LAM are different. The nuclear hyperfine splitting between the C3-hydrogen and the unpaired electron at C2 shows the dihedral angle to be 6°, unlike the 77° reported for the analogous radical bound to the clostridial enzyme. Reaction of (S)-4-thialysine produces a substrate-related radical in the steady state of E. coli LAM, as in the action of the clostridial enzyme. While (S)-β-lysine is not a substrate for E. coli LAM, it undergoes hydrogen abstraction to form an (S)-β-lysine-related radical with the same stereochemistry of hydrogen transfer from C2 of (S)-β-lysine to the 5′-deoxyadenosyl radical as in the action of the clostridial enzyme. The resulting β-lysyl radical has a different conformation than that at the active site of clostridial LAM. All evidence indicates that the opposite stereochemistry displayed by the E. coli LAM is determined by the conformation of the lysine side chain in the active site. Stereochemical models for the actions of LAM from C. subterminale and E. coli are presented. PMID:17042480

  17. Cavity ring-down spectroscopy with an automated control feedback system for investigating nitrate radical surface chemistry reactions.

    PubMed

    Flemmer, Michael M; Ham, Jason E

    2012-08-01

    Nitrate radical (NO(3)(●)) surface chemistry of indoor environments has not been well studied due to the difficulty in generating and maintaining NO(3)(●) at low concentrations for long term exposures. This article presents the Surface Chemistry Reactant Air Delivery and Experiment System (SCRADES), a novel feedback controlled system developed to deliver nitrate radicals at specified concentrations (50-500 ppt, ±30 ppt) and flow rates (500-2000 ml min(-1)) to a variety of indoor surfaces to initiate reaction chemistry for periods of up to 72 h. The system uses a cavity ring-down spectrometer (CRDS), with a detection limit of 1.7 ppt, to measure the concentration of NO(3)(●) supplied to a 24 l experiment chamber. Nitrate radicals are introduced via thermal decomposition of N(2)O(5) and diluted with clean dry air until the desired concentration is achieved. Additionally, this article addresses details concerning NO(3)(●) loss through the system, consistency of the NO(3)(●) concentration delivered, and stability of the CRDS cavity over long exposure durations (72 h).

  18. Cavity ring-down spectroscopy with an automated control feedback system for investigating nitrate radical surface chemistry reactions

    NASA Astrophysics Data System (ADS)

    Flemmer, Michael M.; Ham, Jason E.

    2012-08-01

    Nitrate radical (NO3•) surface chemistry of indoor environments has not been well studied due to the difficulty in generating and maintaining NO3• at low concentrations for long term exposures. This article presents the Surface Chemistry Reactant Air Delivery and Experiment System (SCRADES), a novel feedback controlled system developed to deliver nitrate radicals at specified concentrations (50-500 ppt, ±30 ppt) and flow rates (500-2000 ml min-1) to a variety of indoor surfaces to initiate reaction chemistry for periods of up to 72 h. The system uses a cavity ring-down spectrometer (CRDS), with a detection limit of 1.7 ppt, to measure the concentration of NO3• supplied to a 24 l experiment chamber. Nitrate radicals are introduced via thermal decomposition of N2O5 and diluted with clean dry air until the desired concentration is achieved. Additionally, this article addresses details concerning NO3• loss through the system, consistency of the NO3• concentration delivered, and stability of the CRDS cavity over long exposure durations (72 h).

  19. Cavity ring-down spectroscopy with an automated control feedback system for investigating nitrate radical surface chemistry reactions

    PubMed Central

    Flemmer, Michael M.; Ham, Jason E.

    2015-01-01

    Nitrate radical (NO3•) surface chemistry of indoor environments has not been well studied due to the difficulty in generating and maintaining NO3• at low concentrations for long term exposures. This article presents the Surface Chemistry Reactant Air Delivery and Experiment System (SCRADES), a novel feedback controlled system developed to deliver nitrate radicals at specified concentrations (50–500 ppt, ±30 ppt) and flow rates (500–2000 ml min−1) to a variety of indoor surfaces to initiate reaction chemistry for periods of up to 72 h. The system uses a cavity ring-down spectrometer (CRDS), with a detection limit of 1.7 ppt, to measure the concentration of NO3• supplied to a 24 l experiment chamber. Nitrate radicals are introduced via thermal decomposition of N2O5 and diluted with clean dry air until the desired concentration is achieved. Additionally, this article addresses details concerning NO3• loss through the system, consistency of the NO3• concentration delivered, and stability of the CRDS cavity over long exposure durations (72 h). PMID:22938328

  20. Free-radical-mediated DNA binding.

    PubMed Central

    O'Brien, P J

    1985-01-01

    Free-radical metabolites can be generated metabolically by a one-electron reductase-catalyzed reaction or a "peroxidase" catalyzed oxidation or by photoactivation of a wide variety of aromatic xenobiotics. Radicals may also be generated during lipid peroxidation. Some radicals can react with DNA or bind covalently or noncovalently as a dismutation product or as a dimer, trimer or polymeric product. Modification to the DNA can result in single-strand breaks, loss of template activity, and crosslinking. The binding can prevent enzymic digestion. In some cases, the radicals react with oxygen, resulting before conversion to DNA reactive oxygen species. Most radicals probably do not interact with DNA. PMID:3007090

  1. Fluidic Processing of High-Performance ZIF-8 Membranes on Polymeric Hollow Fibers: Mechanistic Insights and Microstructure Control

    SciTech Connect

    Eum, Kiwon; Rownaghi, Ali; Choi, Dalsu; Bhave, Ramesh R.; Jones, Christopher W.; Nair, Sankar

    2016-06-01

    Recently, a methodology for fabricating polycrystalline metal-organic framework (MOF) membranes has been introduced – referred to as interfacial microfluidic membrane processing – which allows parallelizable fabrication of MOF membranes inside polymeric hollow fibers of microscopic diameter. Such hollow fiber membranes, when bundled together into modules, are an attractive way to scale molecular sieving membranes. The understanding and engineering of fluidic processing techniques for MOF membrane fabrication are in their infancy. Here in this work, a detailed mechanistic understanding of MOF (ZIF-8) membrane growth under microfluidic conditions in polyamide-imide hollow fibers is reported, without any intermediate steps (such as seeding or surface modification) or post-synthesis treatments. A key finding is that interfacial membrane formation in the hollow fiber occurs via an initial formation of two distinct layers and the subsequent rearrangement into a single layer. This understanding is used to show how nonisothermal processing allows fabrication of thinner (5 μm) ZIF-8 films for higher throughput, and furthermore how engineering the polymeric hollow fiber support microstructure allows control of defects in the ZIF-8 membranes. Finally, the performance of these engineered ZIF-8 membranes is then characterized, which have H2/C3H8 and C3H6/C3H8 mixture separation factors as high as 2018 and 65, respectively, and C3H6 permeances as high as 66 GPU.

  2. Controlling the size and morphology of griseofulvin nanoparticles using polymeric stabilizers by evaporation-assisted solvent-antisolvent interaction method

    NASA Astrophysics Data System (ADS)

    Kumar, Raj; Siril, Prem Felix

    2015-06-01

    Griseofulvin (GF) is a potential drug for cancer therapy. However, its application is limited by its poor water solubility. Ultrafine GF nanoparticles were prepared through evaporation-assisted solvent-antisolvent interaction method for improving its solubility. Acetone was used as the solvent and water was used as the antisolvent. It was observed that particle size could be controlled by varying the concentration of GF in acetone. Average particle size was very low, 16 ± 4 and 28 ± 8 nm, when the concentration of GF was 5 and 25 mM, respectively, in acetone. However, the particle size increased drastically to more than 3 µm, when the concentration was increased to 50 mM. Interestingly, the presence of optimized concentration of polyvinylpyrrolidone (PVP) and hydroxypropyl methylcellulose (HPMC) as stabilizers in the antisolvent resulted in significant reduction of particle size. Particle size decreased to less than 40 nm in the presence of the polymeric stabilizers, even when the concentration was 50 mM. Field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy imaging revealed that the polymeric stabilizers encapsulated very small GF particles and thus stabilized them. The solubility of GF-HPMC, GF-PVP, and the bare GF particles that were prepared from 50 mM solution (micro-GF) was nearly 24, 19, and 11 times, respectively, higher than that of raw-GF. In vitro dissolution studies revealed that almost 100 % of the drug was released in 60 min from GF-PVP and GF-HPMC. Fourier transform infrared spectroscopy did not detect any strong interaction between GF and the stabilizers. X-ray diffraction showed that the prepared GF nanoparticles and the micro-GF were in polymorphic form I. Differential scanning calorimetric studies showed that the crystallinity of the nanoformulated GF was only slightly lower than that of raw-GF. Thus, particle size reduction and the presence of stabilizers led to significant enhancement in

  3. Redox-controlled polymerization of lactide catalyzed by bis(imino)pyridine iron bis(alkoxide) complexes.

    PubMed

    Biernesser, Ashley B; Li, Bo; Byers, Jeffery A

    2013-11-06

    Bis(imino)pyridine iron bis(alkoxide) complexes have been synthesized and utilized in the polymerization of (rac)-lactide. The activities of the catalysts were particularly sensitive to the identity of the initiating alkoxide with more electron-donating alkoxides resulting in faster polymerization rates. The reaction displayed characteristics of a living polymerization with production of polymers that exhibited low molecular weight distributions, linear relationships between molecular weight and conversion, and polymer growth observed for up to fifteen sequential additions of lactide monomer to the polymerization reaction. Mechanistic experiments revealed that iron bis(aryloxide) catalysts initiate polymerization with one alkoxide ligand, while iron bis(alkylalkoxide) catalysts initiate polymerization with both alkoxide ligands. Oxidation of an iron(II) catalyst precursor lead to a cationic iron(III) bis-alkoxide complex that was completely inactive toward lactide polymerization. When redox reactions were carried out during lactide polymerization, catalysis could be switched off and turned back on upon oxidation and reduction of the iron catalyst, respectively.

  4. Radical-mediated step-growth: Preparation of hybrid polymer monolithic columns with fine control of nanostructural and chromatographic characteristics.

    PubMed

    Alves, Filipa; Nischang, Ivo

    2015-09-18

    The currently most successful type of porous polymer monoliths utilized in chromatography is prepared by free-radical cross-linking (co)polymerization in porogenic solvents and a single-step molding process. Though such types of materials are well-recognized in the scientific community, they suffer from their multi-scale heterogeneity originating from the nanoscale through to their microscale and ultimately limited performance on their macroscale. This is in particular true when estimating their performance under equilibrium (i.e. isocratic) elution conditions for retained compounds. In this contribution, we study a new concept in the preparation of porous monolithic hybrid materials based on polyhedral oligomeric vinylsilsesquioxanes which undergo radical mediated step-growth cross-linking with thiol-linkers. Fundamental characterization of this new entry of materials is performed via a variety of characterization approaches including infrared and Raman spectroscopies, thermogravimetric analysis, gel fraction, dry-state surface area analysis, and visualization of the capillary-scale porous structure by scanning electron microscopy. This characterization identifies that a rational choice of experimental conditions in monolith preparation leads to destined and desirable materials' properties, in particular with experimentally accessible near-ideal nanoscale network structures. With the obtained structural informations at hand, we finally evidence the monoliths' tailored chromatographic performance by isocratic elution experiments of structurally similar small molecules under reversed-phase type of chromatographic conditions. This validates the fundamental origin for an improved performance of these types of monolithic materials under solvated conditions that has its foundation established in the creation of near-ideal nanoscale networks of material. This identified ideality is manifested in an enhanced and almost retention-insensitive performance in liquid

  5. High mammographic breast density predicts locoregional recurrence after modified radical mastectomy for invasive breast cancer: a case-control study.

    PubMed

    Huang, Yu-Sen; Chen, Jenny Ling-Yu; Huang, Chiun-Sheng; Kuo, Sung-Hsin; Jaw, Fu-Shan; Tseng, Yao-Hui; Ko, Wei-Chun; Chang, Yeun-Chung

    2016-12-01

    We aimed to evaluate the influence of mammographic breast density at diagnosis on the risk of cancer recurrence and survival outcomes in patients with invasive breast cancer after modified radical mastectomy. This case-control study included 121 case-control pairs of women diagnosed with invasive breast cancer between 2004 and 2009, and who had undergone modified radical mastectomy and had mammographic breast density measured before or at diagnosis. Women with known locoregional recurrence or distant metastasis were matched by pathological disease stage, age, and year of diagnosis to women without recurrence. Locoregional recurrence was defined as recurrence in the ipsilateral chest wall, or axillary, internal mammary, or supraclavicular nodes. The median follow-up duration was 84.0 months for case patients and 92.9 months for control patients. Patients with heterogeneously dense (50-75% density) and extremely dense (>75% density) breasts had an increased risk of locoregional recurrence (hazard ratios 3.1 and 5.7, 95% confidence intervals 1.1-9.8 and 1.2-34.9, p = 0.043 and 0.048, respectively) than did women with less dense breasts. Positive margins after surgery also increased the risk of locoregional recurrence (hazard ratio 3.3, 95% confidence interval 1.3-8.3, p = 0.010). Multivariate analysis that included dense breasts (>50% density), positive margin, no adjuvant radiotherapy, and no adjuvant chemotherapy revealed that dense breasts were significant factors for predicting locoregional recurrence risk (hazard ratio 3.6, 95% confidence interval 1.2-11.1, p = 0.025). Our results demonstrate that dense breast tissue (>50% density) increased the risk of locoregional recurrence after modified radical mastectomy in patients with invasive breast cancer. Additional prospective studies are necessary to validate these findings. The study is retrospectively registered with ClinicalTrials.gov, number NCT02771665 , on May 11, 2016.

  6. A strategy for photothermal conversion of polymeric nanoparticles by polyaniline for smart control of targeted drug delivery

    NASA Astrophysics Data System (ADS)

    You, Chaoqun; Wu, Hongshuai; Wang, Mingxin; Wang, Senlin; Shi, Tianyi; Luo, Yanghui; Sun, Baiwang; Zhang, Xiangyang; Zhu, Jin

    2017-04-01

    The near-infrared (NIR)-mediated novel strategy to control the drug release from nanocarriers has developed rapidly in recent decades. Polyaniline as a non-cytotoxic and electroactive material for studying cellular proliferation has attracted great attention in recent years. In the present work, polyaniline-mediated polymeric nanoparticles were developed to target the delivery of cisplatin and release it in a controllable way. The prepared polyaniline nanoparticles displayed a size of 90 ± 1.0 nm, a favorable morphology in water, and could be targeted to tumors through the high affinity between trastuzumab and the overexpressed Her2 in tumor cells. In addition, the developed nanoparticles demonstrated exciting photothermal conversion efficiency induced by NIR light and achieved significant cell inhibition efficiency (93.97%) in vitro when exposed to an 808 nm NIR laser with the power of 1.54 W for 5 min. Therefore, the developed external control release delivery system with excellent specificity and high cytotoxicity exhibited great potential in cell research and our research demonstrated that the polyaniline also has potential in the application of photothermal conversion in biomedicine.

  7. A strategy for photothermal conversion of polymeric nanoparticles by polyaniline for smart control of targeted drug delivery.

    PubMed

    You, Chaoqun; Wu, Hongshuai; Wang, Mingxin; Wang, Senlin; Shi, Tianyi; Luo, Yanghui; Sun, Baiwang; Zhang, Xiangyang; Zhu, Jin

    2017-04-21

    The near-infrared (NIR)-mediated novel strategy to control the drug release from nanocarriers has developed rapidly in recent decades. Polyaniline as a non-cytotoxic and electroactive material for studying cellular proliferation has attracted great attention in recent years. In the present work, polyaniline-mediated polymeric nanoparticles were developed to target the delivery of cisplatin and release it in a controllable way. The prepared polyaniline nanoparticles displayed a size of 90 ± 1.0 nm, a favorable morphology in water, and could be targeted to tumors through the high affinity between trastuzumab and the overexpressed Her2 in tumor cells. In addition, the developed nanoparticles demonstrated exciting photothermal conversion efficiency induced by NIR light and achieved significant cell inhibition efficiency (93.97%) in vitro when exposed to an 808 nm NIR laser with the power of 1.54 W for 5 min. Therefore, the developed external control release delivery system with excellent specificity and high cytotoxicity exhibited great potential in cell research and our research demonstrated that the polyaniline also has potential in the application of photothermal conversion in biomedicine.

  8. Aqueous Copper(II) Photoinduced Polymerization of Acrylates: Low Copper Concentration and the Importance of Sodium Halide Salts.

    PubMed

    Jones, Glen R; Whitfield, Richard; Anastasaki, Athina; Haddleton, David M

    2016-06-15

    Photoinduced metal-mediated radical polymerization is a rapidly developing technique which allows for the synthesis of macromolecules with defined molecular weight and narrow molecular weight distributions, although typically exhibiting significant limitations in aqueous media. Herein we demonstrate that the presence of alkali metal halide salts, in conjunction with low copper concentration and UV irradiation, allows for the controlled polymerization of water-soluble acrylates in aqueous media, yielding narrow molecular weight distributions and high conversions. Despite the aqueous environment which typically compromises polymer end group fidelity, chain extensions have also been successfully performed and different degrees of polymerization were targeted. Importantly, no conversion was observed in the absence of UV light and the polymerization could be switched "on" and "off" upon demand, as demonstrated by intermittent light and dark periods and thus allowing access to spatiotemporal control.

  9. Polymeric nanoparticles

    PubMed Central

    Bolhassani, Azam; Javanzad, Shabnam; Saleh, Tayebeh; Hashemi, Mehrdad; Aghasadeghi, Mohammad Reza; Sadat, Seyed Mehdi

    2014-01-01

    Nanocarriers with various compositions and biological properties have been extensively applied for in vitro/in vivo drug and gene delivery. The family of nanocarriers includes polymeric nanoparticles, lipid-based carriers (liposomes/micelles), dendrimers, carbon nanotubes, and gold nanoparticles (nanoshells/nanocages). Among different delivery systems, polymeric carriers have several properties such as: easy to synthesize, inexpensive, biocompatible, biodegradable, non-immunogenic, non-toxic, and water soluble. In addition, cationic polymers seem to produce more stable complexes led to a more protection during cellular trafficking than cationic lipids. Nanoparticles often show significant adjuvant effects in vaccine delivery since they may be easily taken up by antigen presenting cells (APCs). Natural polymers such as polysaccharides and synthetic polymers have demonstrated great potential to form vaccine nanoparticles. The development of new adjuvants or delivery systems for DNA and protein immunization is an expanding research field. This review describes polymeric carriers especially PLGA, chitosan, and PEI as vaccine delivery systems. PMID:24128651

  10. Robot-assisted laparoscopic prostatectomy versus open radical retropubic prostatectomy: early outcomes from a randomised controlled phase 3 study.

    PubMed

    Yaxley, John W; Coughlin, Geoffrey D; Chambers, Suzanne K; Occhipinti, Stefano; Samaratunga, Hema; Zajdlewicz, Leah; Dunglison, Nigel; Carter, Rob; Williams, Scott; Payton, Diane J; Perry-Keene, Joanna; Lavin, Martin F; Gardiner, Robert A

    2016-09-10

    The absence of trial data comparing robot-assisted laparoscopic prostatectomy and open radical retropubic prostatectomy is a crucial knowledge gap in uro-oncology. We aimed to compare these two approaches in terms of functional and oncological outcomes and report the early postoperative outcomes at 12 weeks. In this randomised controlled phase 3 study, men who had newly diagnosed clinically localised prostate cancer and who had chosen surgery as their treatment approach, were able to read and speak English, had no previous history of head injury, dementia, or psychiatric illness or no other concurrent cancer, had an estimated life expectancy of 10 years or more, and were aged between 35 years and 70 years were eligible and recruited from the Royal Brisbane and Women's Hospital (Brisbane, QLD). Participants were randomly assigned (1:1) to receive either robot-assisted laparoscopic prostatectomy or radical retropubic prostatectomy. Randomisation was computer generated and occurred in blocks of ten. This was an open trial; however, study investigators involved in data analysis were masked to each patient's condition. Further, a masked central pathologist reviewed the biopsy and radical prostatectomy specimens. Primary outcomes were urinary function (urinary domain of EPIC) and sexual function (sexual domain of EPIC and IIEF) at 6 weeks, 12 weeks, and 24 months and oncological outcome (positive surgical margin status and biochemical and imaging evidence of progression at 24 months). The trial was powered to assess health-related and domain-specific quality of life outcomes over 24 months. We report here the early outcomes at 6 weeks and 12 weeks. The per-protocol populations were included in the primary and safety analyses. This trial was registered with the Australian New Zealand Clinical Trials Registry (ANZCTR), number ACTRN12611000661976. Between Aug 23, 2010, and Nov 25, 2014, 326 men were enrolled, of whom 163 were randomly assigned to radical retropubic

  11. Polymerized supramolecular assemblies and biocompatibility

    NASA Astrophysics Data System (ADS)

    O'Brien, David F.

    2001-03-01

    The creation of durable, biomembrane-mimetic coatings for inorganic and polymeric surfaces that are biocompatible, i.e. resistant to nonspecific protein adsorption, remains an important goal that is expected to impact numerous fields. It has already been shown that the physical stability of lipid bilayer vesicles can be dramatically enhanced by cross-linking polymerization of reactive lipids, such as phosphatidylcholines. Bilayers of these same lipids on clean silicon dioxide surfaces can be formed by fusion of small bilayer vesicles with the surface. Radical initiated polymerization of these supported bilayers yields a stable poly(lipid) film that is not perturbed upon exposure to surfactant. Moreover, the cross-linked bilayer film can be removed from water into air with retention of the poly(lipid) bilayer structure. These polymerized bilayer films could be repeatedly transferred from water to air to water with no obvious change in their biocompatibility. The supported bilayer films were equally resistant to non-specific protein adsorption before and after polymerization. This indicates that biocompatible nature of the phosphorylcholine head group of the lipids was not compromised by polymerization of the lipids. The ability to maintain surface biocompatibility of membranes while substantially increasing their stability would appear to extend the technological uses of supramolecular assemblies of lipids.

  12. CO2-responsive polymeric materials: synthesis, self-assembly, and functional applications.

    PubMed

    Darabi, Ali; Jessop, Philip G; Cunningham, Michael F

    2016-08-07

    CO2 is an ideal trigger for switchable or stimuli-responsive materials because it is benign, inexpensive, green, abundant, and does not accumulate in the system. Many different CO2-responsive materials including polymers, latexes, solvents, solutes, gels, surfactants, and catalysts have been prepared. This review focuses on the preparation, self-assembly, and functional applications of CO2-responsive polymers. Detailed discussion is provided on the synthesis of CO2-responsive polymers, in particular using reversible deactivation radical polymerization (RDRP), formerly known as controlled/living radical polymerization (CLRP), a powerful technique for the preparation of well-defined (co)polymers with precise control over molecular weight distribution, chain-end functional groups, and polymer architectural design. Self-assembly in aqueous dispersed media is highlighted as well as emerging potential applications.

  13. High temperature structural, polymeric foams from high internal emulsion polymerization

    SciTech Connect

    Hoisington, M.A.; Duke, J.R.; Apen, P.G.

    1996-02-01

    In 1982, a high internal phase emulsion (HIPE) polymerization process to manufacture microcellular, polymeric foam systems was patented by Unilever. This patent discloses a polymerization process that occurs in a water-in-oil emulsion in which the water represents at least 76% of the emulsion by volume. The oil phase consists of vinyl monomers such as styrene and acrylates that are crosslinked by divinyl monomers during polymerization. After polymerization and drying to remove the water phase, the result is a crosslinked polymer foam with an open cell microstructure that is homogeneous throughout in terms of morphology, density, and mechanical properties. Since 1982, numerous patents have examined various HIPE polymerized foam processing techniques and applications that include absorbents for body fluids, cleaning materials, and ion exchange systems. All the published HIPE polymerized foams have concentrated on materials for low temperature applications. Copolymerization of styrene with maleic anhydride and N-substituted maleimides to produce heat resistant thermoplastics has been studied extensively. These investigations have shown that styrene will free radically copolymerize with N-substituted maleimides to create an alternating thermoplastic copolymer with a Tg of approximately 200{degrees}C. However, there are many difficulties in attempting the maleimide styrene copolymerization in a HIPE such as lower polymerization temperatures, maleimide solubility difficulties in both styrene and water, and difficulty obtaining a stable HIPE with a styrene/maleimide oil phase. This work describes the preparation of copolymer foams from N-ethylmaleimide and Bis(3-ethyl-5-methyl-4-maleimide-phenyl)methane with styrene based monomers and crosslinking agents.

  14. Transient Biocompatible Polymeric Platforms for Long-Term Controlled Release of Therapeutic Proteins and Vaccines

    PubMed Central

    Acar, Handan; Banerjee, Saikat; Shi, Heliang; Jamshidi, Reihaneh; Hashemi, Nastaran; Cho, Michael W.; Montazami, Reza

    2016-01-01

    Polymer-based interpenetrating networks (IPNs) with controllable and programmable degradation and release kinetics enable unique opportunities for physisorption and controlled release of therapeutic proteins or vaccines while their chemical and structural integrities are conserved. This paper presents materials, a simple preparation method, and release kinetics of a series of long-term programmable, biocompatible, and biodegradable polymer-based IPN controlled release platforms. Release kinetics of the gp41 protein was controlled over a 30-day period via tuning and altering the chemical structure of the IPN platforms. Post-release analysis confirmed structural conservation of the gp41 protein throughout the process. Cell viability assay confirmed biocompatibility and non-cytotoxicity of the IPNs. PMID:28546855

  15. Kunststoffe (Polymere)

    NASA Astrophysics Data System (ADS)

    Weißbach, Wolfgang

    Polymere bestehen aus Riesen- oder Makromolekülen, die durch chemische Reaktionen aus einfachen, niedermolekularen Verbindungen entstehen, den Monomeren. Ausgangsstoffe sind überwiegend Kohlenwasserstoffe (KW), die größte Gruppe der C-Verbindungen. Sie müssen reaktionsfähige Stellen besitzen, das sind OH-Gruppen oder Dopppelbindungen.

  16. Dizinc Lactide Polymerization Catalysts: Hyperactivity by Control of Ligand Conformation and Metallic Cooperativity

    PubMed Central

    Thevenon, Arnaud; Romain, Charles; Bennington, Michael S.; White, Andrew J. P.; Davidson, Hannah J.

    2016-01-01

    Abstract Understanding how to moderate and improve catalytic activity is critical to improving degradable polymer production. Here, di‐ and monozinc catalysts, coordinated by bis(imino)diphenylamido ligands, show remarkable activities and allow determination of the factors controlling performance. In most cases, the dizinc catalysts significantly out‐perform the monozinc analogs. Further, for the best dizinc catalyst, the ligand conformation controls activity: the catalyst with “folded” ligand conformation shows turnover frequency (TOF) values up to 60 000 h−1 (0.1 mol % loading, 298 K, [LA]=1 m), whilst that with a “planar” conformation is much slower, under similar conditions (TOF=30 h−1). Dizinc catalysts also perform very well under immortal conditions, showing improved control, and are able to tolerate loadings as low as 0.002 mol % whilst conserving high activity (TOF=12 500 h−1). PMID:27295339

  17. Containerless polymeric microsphere production for biomedical applications

    NASA Technical Reports Server (NTRS)

    Rhim, W. K.; Hyson, M. T.; Chung, S. K.; Colvin, M.; Chang, M.

    1987-01-01

    A containerless method that produces highly uniform microspheres (greater than 50 microns in diameter) from many materials has been developed for biomedical applications. A piezoelectrically vibrated drop generator forms uniform (monodisperse) monomer droplets that are either electrostatistically levitated and polymerized using UV irradiation, or free-radical polymerized. Spheres of 2-hydroxyethyl methacrylate polymer have been produced with diameters of 155 microns + or - 1.57 percent.

  18. Utilization of polymeric smart materials for heterarchical thermal control of spacecrafts systems

    SciTech Connect

    Christiansen, S.; Wiens, M.; Tibbitts, S.; Chave, R.

    1996-03-01

    A passive thermal switch was developed to enable heterarchical (decentralized) thermal control of spacecraft components. The switch utilizes an expansive polymer (paraffin) as the working medium. The thermal switch is a small mechanical stand-off with a variable conductance ranging from 0.015 W/K to 0.45 W/C as the temperature of the component to which it is connected varies from 290 K to 298 K. This device enables accurate, non-electronic thermal control of spacecraft components when used to connect the component-to-be-controlled to a heat sink. Variations in heat load to the component are accommodated by the variable conductance of the switch. The use of the thermal switch as the basis for a heterarchical thermal control strategy is presented. The design and operation of the heat switch is discussed. Results from thermal vacuum testing are presented with a summary of test-derived characteristics. {copyright} {ital 1996 American Institute of Physics.}

  19. Efficacy and oncologic safety of nerve-sparing radical hysterectomy for cervical cancer: a randomized controlled trial

    PubMed Central

    Roh, Ju-Won; Lee, Dong Ock; Lim, Myong Cheol; Seo, Sang-Soo; Chung, Jinsoo; Lee, Sun

    2015-01-01

    Objective A prospective, randomized controlled trial was conducted to evaluate the efficacy of nerve-sparing radical hysterectomy (NSRH) in preserving bladder function and its oncologic safety in the treatment of cervical cancer. Methods From March 2003 to November 2005, 92 patients with cervical cancer stage IA2 to IIA were randomly assigned for surgical treatment with conventional radical hysterectomy (CRH) or NSRH, and 86 patients finally included in the analysis. Adequacy of nerve sparing, radicality, bladder function, and oncologic safety were assessed by quantifying the nerve fibers in the paracervix, measuring the extent of paracervix and harvested lymph nodes (LNs), urodynamic study (UDS) with International Prostate Symptom Score (IPSS), and 10-year disease-free survival (DFS), respectively. Results There were no differences in clinicopathologic characteristics between two groups. The median number of nerve fiber was 12 (range, 6 to 21) and 30 (range, 17 to 45) in the NSRH and CRH, respectively (p<0.001). The extent of resected paracervix and number of LNs were not different between the two groups. Volume of residual urine and bladder compliance were significantly deteriorated at 12 months after CRH. On the contrary, all parameters of UDS were recovered no later than 3 months after NSRH. Evaluation of the IPSS showed that the frequency of long-term urinary symptom was higher in CRH than in the NSRH group. The median duration before the postvoid residual urine volume became less than 50 mL was 11 days (range, 7 to 26 days) in NSRH group and was 18 days (range, 10 to 85 days) in CRH group (p<0.001). No significant difference was observed in the 10-year DFS between two groups. Conclusion NSRH appears to be effective in preserving bladder function without sacrificing oncologic safety. PMID:25872890

  20. Synthesis and characterization of amine-bridged bis(phenolate)lanthanide alkoxides and their application in the controlled polymerization of rac-lactide and rac-β-butyrolactone.

    PubMed

    Nie, Kun; Fang, Lei; Yao, Yingming; Zhang, Yong; Shen, Qi; Wang, Yaorong

    2012-10-15

    A series of neutral lanthanide alkoxides supported by an amine-bridged bis(phenolate) ligand were synthesized, and their catalytic behaviors for the polymerization of rac-lactide (LA) and rac-β-butyrolactone (BBL) were explored. The reactions of (C(5)H(5))(3)Ln(THF) with amine-bridged bis(phenol) LH(2) [L = Me(2)NCH(2)CH(2)N{CH(2)-(2-OC(6)H(2)Bu(t)(2)-3,5)}(2)] in a 1:1 molar ratio in THF for 1 h and then with 1 equiv each of 2,2,2-trifluoroethanol, benzyl alcohol, and 2-propanol gave the neutral lanthanide alkoxides LLn(OCH(2)CF(3))(THF) [Ln = Y (1), Yb (2), Er (3), Sm (4)], LY(OCH(2)Ph)(THF) (5), and LY(OPr(i))(THF) (6), respectively. These lanthanide alkoxides are sensitive to moisture, and the yttrium complex [(LY)(2)(μ-OPr(i))(μ-OH)] (7) was also isolated as a byproduct during the synthesis of complex 6. Complexes 1-6 were well characterized by elemental analyses and IR and NMR spectroscopy in the cases of complexes 1 and 4-6. The definitive molecular structures of all of these complexes were determined by single-crystal X-ray analysis. It was found that complexes 1-6 can initiate efficiently the ring-opening polymerization of rac-LA and rac-BBL in a controlled manner. For rac-LA, polymerization gave polymers with very narrow molecular weight distributions (PDI ≤ 1.12) and very high heterotacticity (P(r) up to 0.99). The observed activity-increasing order is in agreement with the order of the ionic radii, whereas the order for stereoselectivity is in the reverse order. For rac-BBL polymerization, the resultant polymers have narrow molecular distributions (PDI ≤ 1.26) and high syndiotacticity (P(r) up to 0.83). It is worth noting that the activity-decreasing order Yb > Er > Y > Sm is observed for rac-BBL polymerization, which is opposite to the order of ionic radii and to the order of activity for rac-LA polymerization. The ionic radii of lanthanide metals have no obvious effect on the stereoselectivity for rac-BBL polymerization, which is quite

  1. Control of in vivo disposition and immunogenicity of polymeric micelles by adjusting poly(sarcosine) chain lengths on surface

    NASA Astrophysics Data System (ADS)

    Kurihara, Kensuke; Ueda, Motoki; Hara, Isao; Ozeki, Eiichi; Togashi, Kaori; Kimura, Shunsaku

    2017-07-01

    Four kinds of A3B-type amphiphilic polydepsipeptides, (poly(sarcosine))3- b-poly( l-lactic acid) (the degree of polymerization of poly(sarcosine) are 10, 33, 55, and 85; S10 3 , S33 3 , S55 3 , and S85 3 ) were synthesized to prepare core-shell type polymeric micelles. Their in vivo dispositions and stimulations to trigger immune system to produce IgM upon multiple administrations to mice were examined. With increasing poly(sarcosine) chain lengths, the hydrophilic shell became thicker and the surface density at the most outer surface decreased on the basis of dynamic and static light scattering measurements. These two physical elements of polymeric micelles elicited opposite effects on the immune response in light of the chain length therefore to show an optimized poly(sarcosine) chain length existing between 33mer and 55mer to suppress the accelerated blood clearance phenomenon associated with polymeric micelles.

  2. Functionalized Polymeric Membrane with Enhanced Mechanical and Biological Properties to Control the Degradation of Magnesium Alloy.

    PubMed

    Wong, Hoi Man; Zhao, Ying; Leung, Frankie K L; Xi, Tingfei; Zhang, Zhixiong; Zheng, Yufeng; Wu, Shuilin; Luk, Keith D K; Cheung, Kenneth M C; Chu, Paul K; Yeung, Kelvin W K

    2017-04-01

    To achieve enhanced biological response and controlled degradation of magnesium alloy, a modified biodegradable polymer coating called polycaprolactone (PCL) is fabricated by a thermal approach in which the heat treatment neither alters the chemical composition of the PCL membrane nor the rate of magnesium ion release, pH value, or weight loss, compared with the untreated sample. The changes in the crystallinity, hydrophilicity, and oxygen content of heat-treated PCL coating not only improve the mechanical adhesion strength between the coating and magnesium substrate but also enhance the biological properties. Moreover, the thermally modified sample can lead to higher spreading and elongation of osteoblasts, due to the enhanced hydrophilicity and CO to CO functional group ratio. In the analyses of microcomputed tomography from one to four weeks postoperation, the total volume of new bone formation on the heat-treated sample is 10%-35% and 70%-90% higher than that of the untreated and uncoated controls, respectively. Surprisingly, the indentation modulus of the newly formed bone adjacent to the heat-treated sample is ≈20% higher than that of both controls. These promising results reveal the clinical potential of the modified PCL coating on magnesium alloy in orthopedic applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. From the N-Heterocyclic Carbene-Catalyzed Conjugate Addition of Alcohols to the Controlled Polymerization of (Meth)acrylates.

    PubMed

    Ottou, Winnie Nzahou; Bourichon, Damien; Vignolle, Joan; Wirotius, Anne-Laure; Robert, Fredéric; Landais, Yannick; Sotiropoulos, Jean-Marc; Miqueu, Karinne; Taton, Daniel

    2015-06-22

    Among various N-heterocyclic carbenes (NHCs) tested, only 1,3-bis(tert-butyl)imidazol-2-ylidene (NHC(tBu) ) proved to selectively promote the catalytic conjugate addition of alcohols onto (meth)acrylate substrates. This rather rare example of NHC-catalyzed 1,4-addition of alcohols was investigated as a simple means to trigger the polymerization of both methyl methacrylate and methyl acrylate (MMA and MA, respectively). Well-defined α-alkoxy poly(methyl (meth)acrylate) (PM(M)A) chains, the molar masses of which could be controlled by the initial [(meth)acrylate]0/[ROH]0 molar ratio, were ultimately obtained in N,N-dimethylformamide at 25 °C. A hydroxyl-terminated poly(ethylene oxide) (PEO-OH) macro-initiator was also employed to directly access PEO-b-PMMA amphiphilic block copolymers. Investigations into the reaction mechanism by DFT calculations revealed the occurrence of two competitive concerted pathways, involving either the activation of the alcohol or that of the monomer by NHC(tBu) .

  4. Spray-dried powders improve the controlled release of antifungal tioconazole-loaded polymeric nanocapsules compared to with lyophilized products.

    PubMed

    Ribeiro, Roseane Fagundes; Motta, Mariana Heldt; Härter, Andréia Pisching Garcia; Flores, Fernanda Cramer; Beck, Ruy Carlos Ruver; Schaffazick, Scheila Rezende; de Bona da Silva, Cristiane

    2016-02-01

    This work aimed to obtain solid formulations from polymeric nanocapsules and nanoemulsions containing tioconazole, a broad spectrum antifungal drug. Two dehydration methods were used: spray-drying and freeze drying, using lactose as adjuvant (10%, w/v). The liquid formulations had a mean particle size around 206 nm and 182 nm for nanocapsules and nanoemulsions, respectively, and an adequate polydispersity index. Tioconazole content was close to the theoretical amount (1.0 mg/mL). After drying, the content ranged between 98 and 102%with a mean nanometric size of the dried products after redispersion. Scanning electron microscopy showed that the particles are rounded, sphere-shaped for the dried products obtained by spray-drying, and shapeless and irregular shapes for those obtained by freeze-drying. In the microbiological evaluation, all dried products remained active against the yeast Candida albicans when compared to the original systems. The dried products obtained by spray-drying from nanocapsules presented better control of the tioconazole release when compared to the freeze-drying products.

  5. Polymeric hollow spheres assembled from ALG-g-PNIPAM and β-cyclodextrin for controlled drug release.

    PubMed

    Li, Guiying; Yu, Nana; Gao, Yurong; Tao, Qian; Liu, Xunyong

    2016-01-01

    In this paper, thermo-sensitive polymeric hollow spheres assembled from sodium alginate-graft-poly(N-isopropylacrylamide) (ALG-g-PNIPAM) and β-cyclodextrin (β-CD) were prepared for controlled release of 5-fluorouracil (5-FU). In aqueous solutions, β-CD and PNIPAM formed rod-like segments through inclusion complexation interactions and sodium alginate acted as coil segments, which resulted in the formation of hollow structures. The size and wall thickness of assemblies increased with the increase of β-CD in mixtures. The lower critical solution temperature (LCST) of hollow spheres varied in the range of 35-37°C. The hollow spheres exhibited high drug loading efficiency for 5-FU due to the hydrophilic cavities. The initial composition of mixtures, temperature and pH had a significant effect on the inclusion ability and drug release. Increasing temperatures above the LCST or decreasing pH to acidic conditions, a more rapid release rate was observed. Copyright © 2015 Elsevier B.V. All rights reserved.

  6. Controlled synthesis of biodegradable lactide polymers and copolymers using novel in situ generated or single-site stereoselective polymerization initiators.

    PubMed

    Zhong, Zhiyuan; Dijkstra, Pieter J; Feijen, Jan

    2004-01-01

    Polylactides and their copolymers are key biodegradable polymers used widely in biomedical, pharmaceutical and ecological applications. The development of synthetic pathways and catalyst/initiator systems to produce pre-designed polylactides, as well as the fundamental understanding of the polymerization reactions, has continuously been an important topic. Here, we will address the recent advances in the ring-opening polymerization of lactides, with an emphasis on the highly versatile in situ generated initiator systems and single-site stereoselective initiators. The in situ generated initiators including in situ formed yttrium, calcium and zinc alkoxides all have been shown to bring about a rapid and living polymerization of lactides under mild conditions, which facilitated the preparation of a variety of advanced lactide-based biomaterials. For example, well-defined di- and tri-block copolymers consisting of hydrophilic poly(ethylene glycol) blocks and hydrophobic polyester blocks, which form novel biodegradable polymersomes or biodegradable thermosensitive hydrogels, have been prepared. In the past few years, significant progress has also been made in the area of stereoselective polymerization of lactides. This new generation of initiators has enabled the production of polylactide materials with novel microstructures and/or properties, such as heterotactic (--RRSSRRSSRRSS--) polylactide, crystalline syndiotactic (--RSRSRSRSRSRS--) polylactide and isotactic stereoblock (--Rn Sn Rn Sn--) polylactide, exhibiting a high melting temperature. The recently developed polymerizations using in situ generated initiators and stereoselective polymerizations have no doubt opened a brand-new avenue for the design and exploration of polylactides and their copolymers.

  7. Emulsion Polymerization of Butyl Acrylate: Spin Trapping and EPR Study

    NASA Technical Reports Server (NTRS)

    Kim, S.; Westmoreland, D.

    1994-01-01

    The propagating radical in the emulsion polymerization reaction of butyl acrylate was detected by Electron Paramagnetic Resonance spectroscopy using two spin trapping agents, 2-methyl-2nitrosopropane and alpha -N-tert-butylnitrone.

  8. Emulsion Polymerization of Butyl Acrylate: Spin Trapping and EPR Study

    NASA Technical Reports Server (NTRS)

    Kim, S.; Westmoreland, D.

    1994-01-01

    The propagating radical in the emulsion polymerization reaction of butyl acrylate was detected by Electron Paramagnetic Resonance spectroscopy using two spin trapping agents, 2-methyl-2nitrosopropane and alpha -N-tert-butylnitrone.

  9. Metal-insulator transition of valence-controlled VO2 thin film prepared by RF magnetron sputtering using oxygen radical

    NASA Astrophysics Data System (ADS)

    Suetsugu, Takaaki; Shimazu, Yuichi; Tsuchiya, Takashi; Kobayashi, Masaki; Minohara, Makoto; Sakai, Enju; Horiba, Koji; Kumigashira, Hiroshi; Higuchi, Tohru

    2016-06-01

    We have prepared b-axis-oriented VO2 thin films by RF magnetron sputtering using oxygen radicals as the reactive gas. The VO2 thin films consist of a mixed-valence V3+/V4+ state formed by oxygen vacancies. The V3+ ratio strongly depends on the film thickness and the oxygen partial pressure of the radical gun during deposition. The lattice constant of the b-axis increases and the metal-insulator transition (MIT) temperature decreases with decreasing V3+ ratio, although the VO2 thin films with a high V3+ ratio of 42% do not exhibit MIT. The bandwidths and spectral weights of V 3d a1g and \\text{e}\\text{g}σ bands at around the Fermi level, which correspond to the insulating phase at 300 K, are smaller in the VO2 thin films with a low V3+ ratio. These results indicate that the control of the mixed-valence V3+/V4+ state is important for the MIT of b-axis-oriented VO2 thin films.

  10. Controlled release of an osteogenic peptide from injectable biodegradable polymeric composites.

    PubMed

    Hedberg, Elizabeth L; Tang, Andrew; Crowther, Roger S; Carney, Darrell H; Mikos, Antonios G

    2002-12-05

    Poly(D,L-lactic-co-glycolic acid)/poly(ethylene glycol) (PLGA/PEG) blend microparticles loaded with the osteogenic peptide TP508 were added to a mixture of poly(propylene fumarate) (PPF), poly(propylene fumarate)-diacrylate (PPF-DA), and sodium chloride (NaCl) for the fabrication of PPF composite scaffolds that could allow for tissue ingrowth as well as for the controlled release of TP508 when implanted in an orthopedic defect site. In this study, PPF composites were fabricated and the in vitro release kinetics of TP508 were determined. TP508 loading within the PLGA/PEG microparticles, PEG content within the PLGA/PEG microparticles, the microparticle content of the PPF composite polymer component, and the leachable porogen initial mass percent of the PPF composites were varied according to a fractional factorial design and the effect of each variable on the release kinetics was determined for up to 28 days. Each composite formulation released TP508 with a unique release profile. The initial release (release through day 1) of the PLGA/PEG microparticles was reduced upon inclusion in the PPF composite formulations. Day 1 normalized cumulative mass release from PPF composites ranged from 0.14+/-0.01 to 0.41+/-0.01, whereas the release from PLGA/PEG microparticles ranged from 0.31+/-0.02 to 0.58+/-0.01. After 28 days, PPF composites released 53+/-4% to 86+/-2% of the entrapped peptide resulting in cumulative mass releases ranging from 0.14+/-0.01 microg TP508/mm(3) scaffold to 2.46+/-0.05 microg TP508/mm(3) scaffold. The results presented here demonstrate that PPF composites can be used for the controlled release of TP508 and that alterations in the composite's composition can lead to modulation of the TP508 release kinetics. These composites can be used to explore the effects varied release kinetics and dosages on the formation of bone in vivo.

  11. Polymeric Colloidal Nanostructures Fabricated via Highly Controlled Convective Assembly and Their Use for Molecular Imprinting.

    PubMed

    Yang, Jin Chul; Park, Jin Young

    2016-03-23

    In this work, the formation of various polystyrene (PS) colloidal structures on striped PS patterns is demonstrated based on a simple and novel convective assembly method that controls the electrostatic interactions between the PS colloidal particles and sodium dodecyl sulfate (SDS). Under the optimal conditions (different withdrawal speeds, channel dimensions, suspension concentrations, etc.), highly ordered structures such as highly close-packed, zigzag, and linear colloidal aggregates are observed. In addition, these colloidal arrangements are used for development of molecularly imprinted polymer (MIP) sensors with highly improved sensing properties. Using PDMS replicas, three hemispherical poly(methacrylic acid-ethylene glycol dimethacrylate) (poly(MAA-EGDMA)) MIP films, including planar MIP and non-imprinted polymer (NIP) films, are photopolymerized for detection of trace atrazine in an aqueous solution. From gravimetric quartz crystal microbalance (QCM) measurements, a non-close-packed MIP film exhibits highest sensing response (Δf = 932 Hz) to atrazine detection among hemispherical MIP films and shows 6.5-fold higher sensing response than the planar MIP film. In addition, the sensitivity of the MIP sensor is equivalent to -119 Hz/(mol L(-1)). From the ratio of slopes of the calibration curves for the hemispherical MIP and NIP films, the imprinting factor (If) is as high as 11.0. The hemispherical MIP film also shows excellent selectivity in comparison with the sensing responses of other analogous herbicides. As a result, this molecular surface imprinting using PS colloidal arrays is highly efficient for herbicide detection.

  12. Osteoconductive Amine-Functionalized Graphene-Poly(methyl methacrylate) Bone Cement Composite with Controlled Exothermic Polymerization.

    PubMed

    Sharma, Rakesh; Kapusetti, Govinda; Bhong, Sayali Yashwant; Roy, Partha; Singh, Santosh Kumar; Singh, Shikha; Balavigneswaran, Chelladurai Karthikeyan; Mahato, Kaushal Kumar; Ray, Biswajit; Maiti, Pralay; Misra, Nira

    2017-09-20

    Bone cement has found extensive usage in joint arthroplasty over the last 50 years; still, the development of bone cement with essential properties such as high fatigue resistance, lower exothermic temperature, and bioactivity has been an unsolved problem. In our present work, we have addressed all of the mentioned shortcomings of bone cement by reinforcing it with graphene (GR), graphene oxide (GO), and surface-modified amino graphene (AG) fillers. These nanocomposites have shown hypsochromic shifts, suggesting strong interactions between the filler material and the polymer matrix. AG-based nanohybrids have shown greater osteointegration and lower cytotoxicity compared to other nanohybrids as well as pristine bone cement. They have also reduced oxidative stress on cells, resulting in calcification within 20 days of the implantation of nanohybrids into the rabbits. They have significantly reduced the exothermic curing temperature to body temperature and increased the setting time to facilitate practitioners, suggesting that reaction temperature and settling time can be dynamically controlled by varying the concentration of the filler. Thermal stability and enhanced mechanical properties have been achieved in nanohybrids vis-à-vis pure bone cement. Thus, this newly developed nanocomposite can create natural bonding with bone tissues for improved bioactivity, longer sustainability, and better strength in the prosthesis.

  13. Alternating Sequence Controlled Copolymer Synthesis of α-Hydroxy Acids via Syndioselective Ring-Opening Polymerization of O-Carboxyanhydrides Using Zirconium/Hafnium Alkoxide Initiators.

    PubMed

    Sun, Yangyang; Jia, Zhaowei; Chen, Changjuan; Cong, Yong; Mao, Xiaoyang; Wu, Jincai

    2017-08-09

    The ring-opening polymerization (ROP) of O-carboxyanhydrides (OCAs) can give diverse poly(α-hydroxy acid)s (PAHAs) with different functional groups because of easy modification of the side group of OCAs, which can extend applications of PAHAs widely. The stereoselective polymerization of O-carboxyanhydrides and further sequence controlled alternating copolymerization of OCAs were still big challenges until now for lack of suitable catalysts/initiators. In this work, a highly syndioselective ROP of OCAs system as the first stereoselective example in this area is reported using zirconium/hafnium alkoxides as initiators with the highest Pr value up to 0.95. Furthermore, these initiators were successfully applied in the precisely alternating sequence controlled copolymerization of PheOCA and Tyr(Bn)OCA, and alternating copolymerization of LacOCA and PheOCA was also achieved.

  14. Controle de la morphologie d'hydrogels poreux a partir de structures polymeres

    NASA Astrophysics Data System (ADS)

    Esquirol, Anne-Laure

    This master thesis presents a new fabrication method to prepare hydrogels with fully interconnected and tunable macropore networks prepared with co-continuous polymer blends. The main contributions are: (1) a hydrogel fabrication process providing a high control over the average pore size diameter, their volume fraction and their interconnectivity; (2) the microstructural characterization of porous hydrogels with new techniques such as X-ray microtomography and (3) the preparation of porous gels with industrial equipment such as extruders and injection molding presses. The development and improvement of methods and techniques to prepare porous polymers and porous gels have been intensive