Voltammetric Characterization of Soluble Polyacetylene Derivatives Obtained from the Ring-Opening Metathesis Polymerization (ROMP) of Substituted Cyclooctatetraenes

DTIC Science & Technology

1993-01-15

emct ,t ,n electrochemical cis-trans isomerization on the first voltammetric sweep through either reductive or doping. Spectroelectrochemical studies...predominantly- cis poly-RCOT films was irreversible, and indicated the presence of an electrochemical cis-trans isomerization on the first voltammetric sweep ...electrochemical measurements were performed under N2(g) in a Vacuum Atmospheres dry box. Cyclic voltametry was performed using a 3-electrode configuration in a l

Thermoset polymers via ring opening metathesis polymerization of functionalized oils

DOEpatents

Larock, Richard C; Henna, Phillip H; Kessier, Michael R

2012-11-27

The invention provides a method for producing a thermosetting resin from renewable oils, the method comprising supplying renewable oil molecules containing strained ring alkene moieties; reacting the alkene moieties with cyclic alkenes to create a polymer; and repeating the above two steps until the resin having desired characteristics are obtained. Also provided is a thermoset resin comprising functionalized renewable oil polymerized with a co-monomer.

Modeling random methyl branching in ethylene/ propylene copolymers using metathesis chemistry: synthesis and thermal behavior.

PubMed

Sworen, John C; Smith, Jason A; Wagener, Kenneth B; Baugh, Lisa S; Rucker, Steven P

2003-02-26

The structure of random ethylene/propylene (EP) copolymers has been modeled using step polymerization chemistry. Six ethylene/propylene model copolymers have been prepared via acyclic diene metathesis (ADMET) polymerization and characterized for primary and higher level structure using in-depth NMR, IR, DSC, WAXD, and GPC analysis. These copolymers possess 1.5, 7.1, 13.6, 25.0, 43.3, and 55.6 methyl branches per 1000 carbons. Examination of these macromolecules by IR and WAXD analysis has demonstrated the first hexagonal phase in EP copolymers containing high ethylene content (90%) without the influence of sample manipulation (temperature, pressure, or radiation). Thermal behavior studies have shown that the melting point and heat of fusion decrease as the branch content increases. Further, comparisons have been made between these random ADMET EP copolymers, random EP copolymers made by typical chain addition techniques, and precisely branched ADMET EP copolymers.

Surface-initiated ring-opening metathesis polymerization (SI-ROMP) to attach a tethered organic corona onto CdSe/ZnS core/shell quantum dots

PubMed Central

Vatansever, Fatma; Hamblin, Michael R.

2016-01-01

Core–shell CdSe/ZnS quantum dots (QDs) are useful as tunable photostable fluorophores for multiple applications in industry, biology, and medicine. However, to achieve the optimum optical properties, the surface of the QDs must be passivated to remove charged sites that might bind extraneous substances and allow aggregation. Here we describe a method of growing an organic polymer corona onto the QD surface using the bottom-up approach of surface-initiated ring-opening metathesis polymerization (SI-ROMP) with Grubbs catalyst. CdSe/ZnS QDs were first coated with mercaptopropionic acid by displacing the original trioctylphosphine oxide layer, and then reacted with 7-octenyl dimethyl chlorosilane. The resulting octenyl double bonds allowed the attachment of ruthenium alkylidene groups as a catalyst. A subsequent metathesis reaction with strained bicyclic monomers (norbornene-dicarbonyl chloride (NDC), and a mixture of NDC and norbornenylethylisobutyl-polyhedral oligomeric silsesquioxane (norbornoPOSS)) allowed the construction of tethered organic homo-polymer or co-polymer layers onto the QD. Compounds were characterized by FT-IR, 1H-NMR, X-ray photoelectron spectroscopy, differential scanning calorimetry, and transmission electron microscopy. Atomic force microscopy showed that the coated QDs were separate and non-aggregated with a range of diameter of 48–53 nm. PMID:28360819

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Tao; Chatterjee, Sabornie; Mahurin, Shannon M.

Amidoxime-functionalized polydimethylsiloxane (AO-PDMSPNB) membranes with various amidoxime compositions were synthesized via ring-opening metathesis polymerization followed by post-polymerization modification. Compared to other previously reported PDMS-based membranes, the amidoxime-functionalized membranes show enhanced CO 2 permeability and CO 2/N 2 selectivity. The overall gas separation performance (CO 2 permeability 6800 Barrer; CO 2/N 2 selectivity 19) of the highest performing membrane exceeds the Robeson upper bound line, and the excellent permeability of the copolymer itself provides great potential for real world applications where huge volumes of gases are separated. This study details how tuning the CO 2-philicity within rubbery polymer matrices influences gasmore » transport properties. Key parameters for tuning gas transport properties are discussed, and the experimental results show good consistency with theoretical calculations. Finally, this study provides a roadmap to enhancing gas separation performance in rubbery polymers by tuning gas solubility selectivity.« less

Healing efficiency of epoxy-based materials for structural application

NASA Astrophysics Data System (ADS)

Raimondo, Marialuigia; Guadagno, Liberata

2012-07-01

This paper describes a self-healing composite exhibiting high levels of healing efficiency under working conditions typical of aeronautic applications. The self-healing material is composed of a thermosetting epoxy matrix in which a catalyst of Ring Opening Metathesis Polymerization (ROMP) and nanocapsules are dispersed. The nanocapsules contain a monomer able to polymerize via ROMP. The preliminary results demonstrate an efficient self-repair function which is also active at very low temperatures.

End-functionalized ROMP polymers for Biomedical Applications

PubMed Central

Madkour, Ahmad E.; Koch, Amelie H. R.; Lienkamp, Karen; Tew, Gregory N.

2010-01-01

We present two novel allyl-based terminating agents that can be used to end-functionalize living polymer chains obtained by ring-opening metathesis polymerization (ROMP) using Grubbs’ third generation catalyst. Both terminating agents can be easily synthesized and yield ROMP polymers with stable, storable activated ester groups at the chain-end. These end-functionalized ROMP polymers are attractive building blocks for advanced polymeric materials, especially in the biomedical field. Dye-labeling and surface-coupling of antimicrobially active polymers using these end-groups were demonstrated. PMID:21499549

Impact of tuning CO 2-philicity in polydimethylsiloxane-based membranes for carbon dioxide separation

DOE PAGES

Hong, Tao; Chatterjee, Sabornie; Mahurin, Shannon M.; ...

2017-02-22

Amidoxime-functionalized polydimethylsiloxane (AO-PDMSPNB) membranes with various amidoxime compositions were synthesized via ring-opening metathesis polymerization followed by post-polymerization modification. Compared to other previously reported PDMS-based membranes, the amidoxime-functionalized membranes show enhanced CO 2 permeability and CO 2/N 2 selectivity. The overall gas separation performance (CO 2 permeability 6800 Barrer; CO 2/N 2 selectivity 19) of the highest performing membrane exceeds the Robeson upper bound line, and the excellent permeability of the copolymer itself provides great potential for real world applications where huge volumes of gases are separated. This study details how tuning the CO 2-philicity within rubbery polymer matrices influences gasmore » transport properties. Key parameters for tuning gas transport properties are discussed, and the experimental results show good consistency with theoretical calculations. Finally, this study provides a roadmap to enhancing gas separation performance in rubbery polymers by tuning gas solubility selectivity.« less

Catalysts and methods for ring opening metathesis polymerization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schrock, Richard Royce; Autenrieth, Benjamin

The present invention, among other things, provides highly syndiotactic poly(dicyclopentadiene) and/or hydrogenated poly(dicyclopentadiene), compositions thereof, and compounds and methods for preparing the same. In some embodiments, a provided compound is a compound of formula I, II or III. In some embodiments, a provided method comprises providing a compound of formula I, II or III.

Ionomers and methods of making same and uses thereof

DOEpatents

Coates, Geoffrey W.; Kostalik, IV, Henry A.; Clark, Timothy J.; Robertson, Nicholas J.

2016-11-15

Ionomers comprising ionic groups such as, for example, tetraalkylammonium groups and methods of making such ionomers. For example, the ionomers can be produced by ring opening metathesis polymerization of alkene-containing monomers with tetraalkylammonium groups and, optionally, alkene-containing monomers without tetraalkylammonium groups. The ionomers can be used in applications such as, for example, fuel cell applications.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Tao; Niu, Zhenbin; Hu, Xunxiang

The development of high performance materials for CO 2 separation and capture will significantly contribute to a solution for climate change. In this work, (bicycloheptenyl) ethyl terminated polydimethylsiloxane (PDMSPNB) membranes with varied cross-link densities were synthesized via ring-opening metathesis polymerization. The developed polymer membranes show higher permeability and better selectivity than those of conventional cross-linked PDMS membrane. The achieved performance (CO 2 permeability ~ 6800 Barrer and CO 2/N 2 selectivity ~ 14) is very promising for practical applications. The key to achieving this high performance is the use of an in-situ cross-linking method of the difunctional PDMS macromonomers, whichmore » provides lightly cross-linked membranes. By combining positron annihilation lifetime spectroscopy, broadband dielectric spectroscopy and gas solubility measurements, we have elucidated the key parameters necessary for achieving their excellent performance.« less

Synthesis of interlocked molecules by olefin metathesis

NASA Astrophysics Data System (ADS)

Clark, Paul Gregory

A large body of work in the Grubbs group has focused on the development of functional-group tolerant ruthenium alkylidene catalysts that perform a number of olefin metathesis reactions. These catalysts have seen application in a wide range of fields, including classic total synthesis as well as polymer and materials chemistry. One particular family of compounds, interlocked molecules, has benefitted greatly from these advances in catalyst stability and activity. This thesis describes several elusive and challenging interlocked architectures whose syntheses have been realized through the utilization of different types of ruthenium-catalyzed olefin metathesis reactions. Ring-closing olefin metathesis has enabled the synthesis of a [c2]daisy-chain dimer with the ammonium binding site near the cap of the dimer. A deprotonated DCD possessing such a structural attribute will more forcefully seek to restore coordinating interactions upon reprotonation, enhancing its utility as a synthetic molecular actuator. Dimer functionalization facilitated incorporation into linear polymers, with a 48% size increase of an unbound, extended analogue of the polymer demonstrating slippage of the dimer units. Ongoing work is directed at further materials studies, in particular, exploring the synthesis of macroscopic networks containing the DCD units and analyzing the correlation between molecular-scale extension-contraction manipulations and resulting macro-scale changes. A "clipping" approach to a polycatenated cyclic polymer, a structure that resembles a molecular "charm bracelet", has been described. The use of ring-opening metathesis polymerization of a carbamate monomer in the presence of a chain transfer agent allowed for the synthesis of a linear polymer that was subsequently functionalized and cyclized to the corresponding cyclic analogue. This cyclic polymer was characterized through a variety of techniques, and subjected to further functionalization reactions, affording a cyclic polyammonium scaffold. Diolefin polyether fragments were coordinated and "clipped" around the ammonium sites within the polymer backbone using ring-closing olefin metathesis, giving the molecular "charm bracelet". Confirmation of the interlocked nature of the product was achieved via 1H NMR spectroscopy and two-dimensional diffusion ordered NMR spectroscopy. A simple strategy for a one-pot, multi-component synthesis of polyrotaxanes using acyclic diene metathesis polymerization was developed. The polyrotaxanes were characterized by traditional 1H NMR spectroscopy as well as size exclusion chromatography, and the interlocked topology was confirmed using two-dimension diffusion-ordered NMR spectroscopy. The dynamic, self-correcting nature of the ADMET polymerization was also explored through the equilibration of a capped polyammonium polymer in the presence of dibenzo-24-crown-8 ether and olefin metathesis catalysts. The efficiency and ease with which these mechanically interlocked macromolecules can be assembled should facilitate rapid modulation to achieve versatile polyrotaxane architectures. Flexible, switchable [c2]daisy-chain dimers (DCDs) were synthesized, where the macromer ammonium binding site was adjacent to the crown-type recognition structure and separated from the cap by an alkyl chain. A DCD of this topology is expected to have an extended structure in the bound conformation (when the ammonium was coordinated to the crown). Several different macromer candidates were designed to allow access to DCDs with flexible alkyl chains between the ammonium binding site and the cap, and a number of synthetic routes were explored in an effort to access these challenging materials. While the first generation DCD structure proved to be unstable due to a labile ester linkage, work is continuing toward the development of several cap structures in an effort to replace the ester linkage with an ether linkage, which, in the second generation model systems, has proven much more stable to the acidic and basic conditions necessary to induce switching of the dimeric architecture. One of the efforts in our lab is directed at the synthesis of 18F-labeled nanoparticles to be used as tumor imaging agents in positron emission tomography. We have been working to optimize fluorine incorporation while minimizing NP crosslinking. Because of evidence of NP side-reactions with the potassium carbonate base, we have begun to use potassium benzoate solid-state beads. To analyze the fluorinated NPs, various sorbents were explored. It was found that silica sorbents rapidly reacted and bound to the NPs, while the NPs remained unreactive and mobile on alumina. Further analysis of the NPs has been accomplished using 2D-DOSY NMR spectroscopy. Future work with the NPs will involve a systematic evaluation of the role of water on the extent of fluorination, as well as functionalization of the NPs with Cy5.5 dye for use in studies on eyes to be done in collaboration with researchers at the Mayo Clinic.

Computational study of productive and non-productive cycles in fluoroalkene metathesis.

PubMed

Rybáčková, Markéta; Hošek, Jan; Šimůnek, Ondřej; Kolaříková, Viola; Kvíčala, Jaroslav

2015-01-01

A detailed DFT study of the mechanism of metathesis of fluoroethene, 1-fluoroethene, 1,1-difluoroethene, cis- and trans-1,2-difluoroethene, tetrafluoroethene and chlorotrifluoroethene catalysed with the Hoveyda-Grubbs 2(nd) generation catalyst was performed. It revealed that a successful metathesis of hydrofluoroethenes is hampered by a high preference for a non-productive catalytic cycle proceeding through a ruthenacyclobutane intermediate bearing fluorines in positions 2 and 4. Moreover, the calculations showed that the cross-metathesis of perfluoro- or perhaloalkenes should be a feasible process and that the metathesis is not very sensitive to stereochemical issues.

Biocatalytic synthesis and polymerization via ROMP of new biobased phenolic monomers: a greener process towards sustainable antioxidant polymers

NASA Astrophysics Data System (ADS)

Diot-Néant, Florian; Migeot, Loïs; Hollande, Louis; Reano, Felix A.; Domenek, Sandra; Allais, Florent

2017-12-01

Antioxidant norbornene-based monomers bearing biobased sterically hindered phenols (SHP) - NDF (norbornene dihydroferulate) and NDS (norbornene dihydrosinapate) - have been successfully prepared through biocatalysis from naturally occurring ferulic and sinapic acids, respectively, in presence of Candida antarctica Lipase B (Cal-B). The ring opening metathesis polymerization (ROMP) of these monomers was investigated according to ruthenium catalyst type (GI) vs. (HGII) and monomer to catalyst molar ratio ([M]/[C]). The co-polymerization of antioxidant functionalized monomer (NDF or NDS) and non-active norbornene (N) has also been performed in order to adjust the number of SHP groups present per weight unit and tune the antioxidant activity of the copolymers. The polydispersity of the resulting copolymers was readily improved by a simple acetone wash to provide antioxidant polymers with well-defined structures. After hydrogenation with p-toluenesulfonylhydrazine (p-TSH), the radical scavenging ability of the resulting saturated polymers was evaluated using α,α-diphenyl-β-picrylhydrazyl (DPPH) analysis. Results demonstrated that polymers bearing sinapic acid SHP exhibited higher antiradical activity than the polymer bearing ferulic acid SHP. In addition it was also shown that only a small SHP content was needed in the copolymers to exhibit a potent antioxidant activity.

Gold Nanoparticles with Externally Controlled, Reversible Shifts of Local Surface Plasmon Resonance Bands

PubMed Central

Yavuz, Mustafa S.; Jensen, Gary C.; Penaloza, David P.; Seery, Thomas A. P.; Pendergraph, Samuel A.; Rusling, James F.; Sotzing, Gregory A.

2010-01-01

We have achieved reversible tunability of local surface plasmon resonance in conjugated polymer functionalized gold nanoparticles. This property was facilitated by the preparation of 3,4-ethylenedioxythiophene (EDOT) containing polynorbornene brushes on gold nanoparticles via surface-initiated ring-opening metathesis polymerization. Reversible tuning of the surface plasmon band was achieved by electrochemically switching the EDOT polymer between its reduced and oxidized states. PMID:19839619

Effect of cross-link density on carbon dioxide separation in polydimethylsiloxane-norbornene membranes

DOE PAGES

Hong, Tao; Niu, Zhenbin; Hu, Xunxiang; ...

2015-10-20

The development of high performance materials for CO 2 separation and capture will significantly contribute to a solution for climate change. In this work, (bicycloheptenyl) ethyl terminated polydimethylsiloxane (PDMSPNB) membranes with varied cross-link densities were synthesized via ring-opening metathesis polymerization. The developed polymer membranes show higher permeability and better selectivity than those of conventional cross-linked PDMS membrane. The achieved performance (CO 2 permeability ~ 6800 Barrer and CO 2/N 2 selectivity ~ 14) is very promising for practical applications. The key to achieving this high performance is the use of an in-situ cross-linking method of the difunctional PDMS macromonomers, whichmore » provides lightly cross-linked membranes. By combining positron annihilation lifetime spectroscopy, broadband dielectric spectroscopy and gas solubility measurements, we have elucidated the key parameters necessary for achieving their excellent performance.« less

Poly(1-Vinyl-1,2,4-triazolium) Poly(Ionic Liquid)s: Synthesis and the Unique Behavior in Loading Metal Ions.

PubMed

Zhang, Weiyi; Yuan, Jiayin

2016-07-01

Herein, the synthesis of a series of poly(4-alkyl-1-vinyl-1,2,4-triazolium) poly(ionic liquid)s is reported either via straightforward free radical polymerization of their corresponding ionic liquid monomers or via anion metathesis of the polymer precursors bearing halide as counter anion. The ionic liquid monomers are first prepared via N-alkylation reaction of commercially available 1-vinyl-1,2,4-triazole with alkyl iodides, followed by anion metathesis with targeted fluorinated anions. The thermal properties and solubilities of these poly(ionic liquid)s have been systematically investigated. Interestingly, it is found that the poly(4-ethyl-1-vinyl-1,2,4-triazolium) poly(ionic liquid) exhibited an improved loading capacity of transition metal ions in comparison with its imidazolium counterpart. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Statistical Ring Opening Metathesis Copolymerization of Norbornene and Cyclopentene by Grubbs' 1st-Generation Catalyst.

PubMed

Nikovia, Christiana; Maroudas, Andreas-Philippos; Goulis, Panagiotis; Tzimis, Dionysios; Paraskevopoulou, Patrina; Pitsikalis, Marinos

2015-08-27

Statistical copolymers of norbornene (NBE) with cyclopentene (CP) were prepared by ring-opening metathesis polymerization, employing the 1st-generation Grubbs' catalyst, in the presence or absence of triphenylphosphine, PPh₃. The reactivity ratios were estimated using the Finemann-Ross, inverted Finemann-Ross, and Kelen-Tüdos graphical methods, along with the computer program COPOINT, which evaluates the parameters of binary copolymerizations from comonomer/copolymer composition data by integrating a given copolymerization equation in its differential form. Structural parameters of the copolymers were obtained by calculating the dyad sequence fractions and the mean sequence length, which were derived using the monomer reactivity ratios. The kinetics of thermal decomposition of the copolymers along with the respective homopolymers was studied by thermogravimetric analysis within the framework of the Ozawa-Flynn-Wall and Kissinger methodologies. Finally, the effect of triphenylphosphine on the kinetics of copolymerization, the reactivity ratios, and the kinetics of thermal decomposition were examined.

In situ formation of pyridyl-functionalized poly(3-hexylthiophene)s via quenching of the Grignard metathesis polymerization: Toward ligands for semiconductor quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kochemba, William Michael; Pickel, Deanna L.; Sumpter, Bobby G.

The synthesis of well-defined, end-functional poly(3-hexylthiophene)s (P3HTs) by in situ quenching of the Grignard metathesis (GRIM) polymerization is complicated by the extreme tendency to favor difunctional products in all but a few cases. A facile one-pot method for preparing 2-pyridyl and 3-pyridyl P3HTs with high abundance of monofunctional products is established via an examination of the kinetics of the end-functionalization quenching reaction with lithium chloride complexes of 2- and 3-pyridyl Grignard reagents. Density functional theory calculations guide the selection of pyridine as the end group, which provides the capacity to ligate cadmium selenide (CdSe) nanocrystals and arrests aggregation upon thermalmore » annealing when dispersed in a P3HT matrix. The relative abundances of various end-functional products, as ascertained by high-resolution matrix assisted laser desorption ionization time-of-flight mass spectrometry, can be altered through the use of 1-pentene as an additive: GRIM polymerizations quenched with 3-pyridyl and 2-pyridyl Grignard reagents show 5% and 18% abundances of difunctional, pyridyl-capped P3HTs, respectively, when 1-pentene is present at 1000:1 relative to the nickel catalyst. This represents a significant improvement compared to quenching with aryl Grignard reagents, where difunctional products predominate. Furthermore, the ability to manipulate end group compositions coupled with the propensity of pyridyl-functionalized P3HTs to ligate semiconductor quantum dots (SQDs) opens new possibilities for tuning the morphology of conjugated polymer/SQD blends.« less

Highly Permeable Oligo(ethylene oxide)- co-poly(dimethylsiloxane) Membranes for Carbon Dioxide Separation

DOE PAGES

Hong, Tao; Lai, Sophia C.; Mahurin, Shannon Mark; ...

2017-12-27

Here, a series of cross–linked, freestanding oligo(ethylene oxide)– co–(polydimethylsiloxane–norbornene) membranes with varied composition is synthesized via in situ ring–opening metathesis polymerization. These membranes show remarkably high CO 2 permeabilities (3400 Barrer) and their separation performance approaches the Robeson upper bound. The excellent permeability of these copolymer membranes provides great potential for real–world applications where enormous volumes of gases must be separated. The gas transport properties of these films are found to be directly proportional to oligo(ethylene oxide) content incorporation, which stems from the increased solubility selectivity change within the copolymer matrix. This work provides a systematic study of how gasmore » separation performance in rubbery membranes can be enhanced by tuning the CO 2–philicity of their constituent monomeric subunits.« less

In situ crosslinking of surface-initiated ring opening metathesis polymerization of polynorbornene for improved stability.

PubMed

Fursule, Ishan A; Abtahi, Ashkan; Watkins, Charles B; Graham, Kenneth R; Berron, Brad J

2018-01-15

In situ crosslinking is expected to increase the solvent stability of coatings formed by surface-initiated ring opening metathesis polymerization (SI ROMP). Solvent-associated degradation limits the utility of SI ROMP coatings. SI ROMP coatings have a unique capacity for post-functionalization through reaction of the unsaturated site on the polymer backbone. Any post-reaction scheme which requires a liquid solvent has the potential to degrade the coating and lower the thickness of the resulting film. We designed a macromolecular crosslinking group based on PEG dinorbornene. The PEG length is tailored to the expected mean chain to chain distance during surface-initiated polymerization. This crosslinking macromer is randomly copolymerized with norbornene through SI ROMP on a gold coated substrate. The solvent stability of polynorbornene coatings with and without PEG dinorbornene is quantitatively determined, and the mechanism of degradation is further supported through XPS and AFM analyses. The addition of the 0.25mol% PEG dinorbornene significantly increases the solvent stability of the SI ROMP coatings. The crosslinker presence in the more stable films is supported with observable PEG absorbances by FTIR and an increase in contact angle hysteresis when compared to non-crosslinked coatings. The oxidation of the SI ROMP coatings is supported by the observation of carbonyl oxygen in the polynorbornene coatings. The rapid loss of the non-crosslinked SI ROMP coating corresponds to nanoscale pitting across the surface and micron-scale regions of widespread film loss. The crosslinked coatings have uniform nanoscale pitting, but the crosslinked films show no evidence of micron-scale film damage. In all, the incorporation of minimal crosslinking content is a simple strategy for improving the solvent stability of SI ROMP coatings. Copyright © 2017 Elsevier Inc. All rights reserved.

Single Turnover at Molecular Polymerization Catalysts Reveals Spatiotemporally Resolved Reactions.

PubMed

Easter, Quinn T; Blum, Suzanne A

2017-10-23

Multiple active individual molecular ruthenium catalysts have been pinpointed within growing polynorbornene, thereby revealing information on the reaction dynamics and location that is unavailable through traditional ensemble experiments. This is the first single-turnover imaging of a molecular catalyst by fluorescence microscopy and allows detection of individual monomer reactions at an industrially important molecular ruthenium ring-opening metathesis polymerization (ROMP) catalyst under synthetically relevant conditions (e.g. unmodified industrial catalyst, ambient pressure, condensed phase, ca. 0.03 m monomer). These results further establish the key fundamentals of this imaging technique for characterizing the reactivity and location of active molecular catalysts even when they are the minor components. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Increased functionality of methyl oleate using alkene metathesis

USDA-ARS?s Scientific Manuscript database

A series of alkene cross metathesis reactions were performed using a homogeneous ruthenium based catalyst. Using this technology, a variety of functional groups can be incorporated into the biobased starting material, methyl oleate. Trans-stilbene, styrene, methyl cinnamate and hexen-3-ol were all s...

Tandem ring-closing metathesis/transfer hydrogenation: practical chemoselective hydrogenation of alkenes.

PubMed

Connolly, Timothy; Wang, Zhongyu; Walker, Michael A; McDonald, Ivar M; Peese, Kevin M

2014-09-05

An operationally simple chemoselective transfer hydrogenation of alkenes using ruthenium metathesis catalysts is presented. Of great practicality, the transfer hydrogenation reagents can be added directly to a metathesis reaction and effect hydrogenation of the product alkene in a single pot at ambient temperature without the need to seal the vessel to prevent hydrogen gas escape. The reduction is applicable to a range of alkenes and can be performed in the presence of aryl halides and benzyl groups, a notable weakness of Pd-catalyzed hydrogenations. Scope and mechanistic considerations are presented.

Methods for suppressing isomerization of olefin metathesis products

DOEpatents

Firth, Bruce E.; Kirk, Sharon E.

2015-10-27

A method for suppressing isomerization of an olefin metathesis product produced in a metathesis reaction includes adding an isomerization suppression agent that includes nitric acid to a mixture that includes the olefin metathesis product and residual metathesis catalyst from the metathesis reaction under conditions that are sufficient to passivate at least a portion of the residual metathesis catalyst. Methods of refining a natural oil are described.

Polyphosphoester-Camptothecin Prodrug with Reduction-Response Prepared via Michael Addition Polymerization and Click Reaction.

PubMed

Du, Xueqiong; Sun, Yue; Zhang, Mingzu; He, Jinlin; Ni, Peihong

2017-04-26

Polyphosphoesters (PPEs), as potential candidates for biocompatible and biodegradable polymers, play an important role in material science. Various synthetic methods have been employed in the preparation of PPEs such as polycondensation, polyaddition, ring-opening polymerization, and olefin metathesis polymerization. In this study, a series of linear PPEs has been prepared via one-step Michael addition polymerization. Subsequently, camptothecin (CPT) derivatives containing disulfide bonds and azido groups were linked onto the side chain of the PPE through Cu(I)-catalyzed azidealkyne cyclo-addition "click" chemistry to yield a reduction-responsive polymeric prodrug P(EAEP-PPA)-g-ss-CPT. The chemical structures were characterized by nuclear magnetic resonance spectroscopy, gel permeation chromatography, Fourier transform infrared, ultraviolet-visible spectrophotometer, and high performance liquid chromatograph analyses, respectively. The amphiphilic prodrug could self-assemble into micelles in aqueous solution. The average particle size and morphology of the prodrug micelles were measured by dynamic light scattering and transmission electron microscopy, respectively. The results of size change under different conditions indicate that the micelles possess a favorable stability in physiological conditions and can be degraded in reductive medium. Moreover, the studies of in vitro drug release behavior confirm the reduction-responsive degradation of the prodrug micelles. A methyl thiazolyl tetrazolium assay verifies the good biocompatibility of P(EAEP-PPA) not only for normal cells, but also for tumor cells. The results of cytotoxicity and the intracellular uptake about prodrug micelles further demonstrate that the prodrug micelles can efficiently release CPT into 4T1 or HepG2 cells to inhibit the cell proliferation. All these results show that the polyphosphoester-based prodrug can be used for triggered drug delivery system in cancer treatment.

Preparation of actinide boride materials via solid-state metathesis reactions and actinide dicarbollide precursors

NASA Astrophysics Data System (ADS)

Lupinetti, Anthony J.; Fife, Julie; Garcia, Eduardo; Abney, Kent D.

2000-07-01

Information gaps exist in the knowledge base needed for choosing among the alternate processes to be used in the safe conversion of fissile materials to optimal forms for safe interim storage, long-term storage, and ultimate disposition. The current baseline storage technology for various wastes uses borosilicate glasses.1 The focus of this paper is the synthesis of actinide-containing ceramic materials at low and moderate temperatures (200 °C-1000 °C) using molecular and polymeric actinide borane and carborane complexes.

Synthesis and Purification of Tunable High Tg Electro-Optical Polymers by Ring Opening Metathesis Polymerization

DTIC Science & Technology

2011-09-01

The amic acid was dissolved in DMF (100 mL) at 100 °C. Acetic anhydride (14.8 g, 0.145 mol) and anhydrous sodium acetate (0.8 g, 0.01 mol) were...exo-N-[(E)-2-(ethyl(4-((4-nitrophenyl)diazenyl)phenyl)amino)ethyl benzoate ] nadimide (5). DPTS (0.44 g, 1.41 mmol), exo-N-(p-Carboxyphenyl...agent for a Ru-based catalyst when extracted with aqueous sodium bicarbonate (28, 29). We reasoned that MNA could enhance the solubility of the

Synthesis of Side Chain Liquid Crystal Polymers by Living Ring Opening Metathesis Polymerization. 3. Influence of Molecular Weight, Interconnecting Unit and Substituent on the Mesomorphic behavior of Polymers with Laterally Attached Mesogens

DTIC Science & Technology

1992-04-08

polymethylsiloxanes, 6 -7 polyacrylates ,2,4,5 polymethacrylates, 1 ,3 and polychloroacrylates, 5 exhibit only nematic mesophases regardless of the...corresponding carboxyl chloride. Potassium bicyclo[2.2.1]hept-2-ene-5- carboxylate was prepared by titrating a methanolic solution of the carboxylic acid...Esterification of the Corresponding Benzyl Bromides. Monomers 1I-n were prepared in 47-88% yield using the following procedure. A mixture of potassium bicyclo

Near-Infrared Chromophore Functionalized Soft Actuator with Ultrafast Photoresponsive Speed and Superior Mechanical Property.

PubMed

Liu, Li; Liu, Mei-Hua; Deng, Lin-Lin; Lin, Bao-Ping; Yang, Hong

2017-08-23

In this Communication, we develop a two-step acyclic diene metathesis in situ polymerization/cross-linking method to synthesize uniaxially aligned main-chain liquid crystal elastomers with chemically bonded near-infrared absorbing four-alkenyl-tailed croconaine-core cross-linkers. Because of the extraordinary photothermal conversion property, such a soft actuator material can raise its local temperature from 18 to 260 °C in 8 s, and lift up burdens 5600 times heavier than its own weight, under 808 nm near-infrared irradiation.

Micromechanical characterization of single-walled carbon nanotube reinforced ethylidene norbornene nanocomposites for self-healing applications

NASA Astrophysics Data System (ADS)

Aïssa, B.; Haddad, E.; Jamroz, W.; Hassani, S.; Farahani, R. D.; Merle, P. G.; Therriault, D.

2012-10-01

We report on the fabrication of self-healing nanocomposite materials, consisting of single-walled carbon nanotube (SWCNT) reinforced 5-ethylidene-2-norbornene (5E2N) healing agent—reacted with ruthenium Grubbs catalyst—by means of ultrasonication, followed by a three-roll mixing mill process. The kinetics of the 5E2N ring opening metathesis polymerization (ROMP) was studied as a function of the reaction temperature and the SWCNT loads. Our results demonstrated that the ROMP reaction was still effective in a large temperature domain ( - 15-45 °C), occurring at very short time scales (less than 1 min at 40 °C). On the other hand, the micro-indentation analysis performed on the SWCNT/5E2N nanocomposite material after its ROMP polymerization showed a clear increase in both the hardness and the Young modulus—up to nine times higher than that of the virgin polymer—when SWCNT loads range only from 0.1 to 2 wt%. The approach demonstrated here opens new prospects for using carbon nanotube and healing agent nanocomposite materials for self-repair functionality, especially in a space environment.

Methods for suppressing isomerization of olefin metathesis products

DOEpatents

Firth, Bruce E.; Kirk, Sharon E.; Gavaskar, Vasudeo S.

2015-09-22

A method for suppressing isomerization of an olefin metathesis product produced in a metathesis reaction includes adding an isomerization suppression agent to a mixture that includes the olefin metathesis product and residual metathesis catalyst from the metathesis reaction under conditions that are sufficient to passivate at least a portion of the residual metathesis catalyst. The isomerization suppression agent is phosphorous acid, a phosphorous acid ester, phosphinic acid, a phosphinic acid ester or combinations thereof. Methods of refining natural oils are described.

Self-healing of polymeric materials: The effect of the amount of DCPD confined within microcapsules

NASA Astrophysics Data System (ADS)

Chipara, Dorina M.; Perez, Alma; Lozano, Karen; Elamin, Ibrahim; Villarreal, Jahaziel; Salinas, Alfonso; Chipara, Mircea

2013-03-01

The self-healing SH) of polymers is based on the dispersion of a catalyst and of microcapsules filled with monomer within the polymeric matrix. Sufficiently large external stresses will rupture the microcapsule, releasing the monomer which will diffuse through the polymer and eventually will reach a catalyst particle igniting a polymerization reaction. The classical SH system includes first generation Grubbs catalyst and poly-urea formaldehyde microcapsules filled with DCPD. The polymerization reaction is a ring-opening metathesis. The size and the mechanical features of microcapsules are critical in controlling the SH process. Research was focused on the effect of DCPD on the size and thickness of microcapsules. Microscopy was used to determine the size of microcapsules (typically in the range of 10-4 m) and the thickness of the microcapsules (ranging between 10-6 to 10-8 m). Research revealed a thick disordered layer over a thin and more compact wall. Raman spectroscopy confirmed the confinement of DCPD, TGA measurements aimed to a better understanding of the degradation processes in inert atmosphere, and mechanical tests supported the ignition of self-healing properties. This research has been supported by National Science Foundation under DMR (PREM) grant 0934157.

Ruthenium-catalyzed metathesis reactions of ortho- and meta-dialkenyl-carboranes: efficient ring-closing and acyclic diene polymerization reactions.

PubMed

Guron, Marta; Wei, Xiaolan; Carroll, Patrick J; Sneddon, Larry G

2010-07-05

The ruthenium-catalyzed metathesis reactions of dialkenyl-substituted ortho- and meta-carboranes provide excellent routes to both cyclic-substituted o-carboranes and new types of main-chain m-carborane polymers. The adjacent positions of the two olefins in the 1,2-(alkenyl)(2)-o-carboranes strongly favor the formation of ring-closed (RCM) products with the reactions of 1,2-(CH(2)=CHCH(2))(2)-1,2-C(2)B(10)H(10) (1), 1,2-(CH(2)=CH(CH(2))(3)CH(2))(2)-1,2-C(2)B(10)H(10) (2), 1,2-(CH(2)=CHSiMe(2))(2)-1,2-C(2)B(10)H(10) (3), 1,2-(CH(2)=CHCH(2)SiMe(2))(2)-1,2-C(2)B(10)H(10) (4), and 1,2-[CH(2)=CH(CH(2))(4)SiMe(2)](2)-1,2-C(2)B(10)H(10) (5) affording 1,2-(-CH(2)CH=CHCH(2)-)-C(2)B(10)H(10) (10), 1,2-[-CH(2)(CH(2))(3)CH=CH(CH(2))(3)CH(2)-]-1,2-C(2)B(10)H(10) (11), 1,2-[-SiMe(2)CH=CHSiMe(2)-]-1,2-C(2)B(10)H(10) (12), 1,2-[-SiMe(2)CH(2)CH=CHCH(2)SMe(2)-]-C(2)B(10)H(10) (13), and 1,2-[-SiMe(2)(CH(2))(4)CH=CH(CH(2))(4)SiMe(2)-]-C(2)B(10)H(10) (14), respectively, in 72-97% yields. On the other hand, the reaction of 1,2-(CH(2)-CHCH(2)OC(=O))(2)-1,2-C(2)B(10)H(10) (6) gave cyclo-[1,2-(1',8'-C(=O)OCH(2)CH=CHCH(2)OC(=O))-1,2-C(2)B(10)H(10)](2) (15a) and polymer 15b resulting from intermolecular metathesis reactions. The nonadjacent positions of the alkenyl groups in the 1,7-(alkenyl)(2)-m-carboranes, 1,7-(CH(2)=CHCH(2))(2)-1,7-C(2)B(10)H(10) (7), 1,7-(CH(2)=CH(CH(2))(3)CH(2))(2)-1,7-C(2)B(10)H(10) (8), and 1,7-(CH(2)=CHCH(2)SiMe(2))(2)-1,7-C(2)B(10)H(10) (9), disfavor the formation of RCM products, and in these cases, acyclic diene metathesis polymerizations (ADMET) produced new types of main chain m-carborane polymers. The structures of 3, 9, 11, 12, 13, and 15a were crystallographically confirmed.

Soluble, Highly Conjugated Derivatives of Polyacetylene from the Ring-Opening Metathesis Polymerization of Monosubstituted Cyclooctatetraenes: Synthesis and the Relationship Between Polymer Structure and Physical Properties

DTIC Science & Technology

1993-01-15

through a pad of Celite into a flask equipped with a sidearm stopcock and the volume of the solution was not adjusted. Neopentyl lithium was...The resonance at 2.5 ppm (A) was irradiated and both this resonance and the resonance at 2.8 ppm (B) were integrated. An ethylene glycol temperature...angles for different side groups in model compound S (MM2 results, C3 = cyclopropyl, Np = neopentyl ). Figure 14. Values of torsion angle el at 10 fs

Second and third order nonlinear optical properties of conjugated molecules and polymers

NASA Technical Reports Server (NTRS)

Perry, Joseph W.; Stiegman, Albert E.; Marder, Seth R.; Coulter, Daniel R.; Beratan, David N.; Brinza, David E.

1988-01-01

Second- and third-order nonlinear optical properties of some newly synthesized organic molecules and polymers are reported. Powder second-harmonic-generation efficiencies of up to 200 times urea have been realized for asymmetric donor-acceptor acetylenes. Third harmonic generation chi(3)s have been determined for a series of small conjugated molecules in solution. THG chi(3)s have also been determined for a series of soluble conjugated copolymers prepared using ring-opening metathesis polymerization. The results are discussed in terms of relevant molecular and/or macroscopic structural features of these conjugated organic materials.

Synthesis and molecular structures of phenylamides of magnesium, calcium, strontium, and barium--from molecular to polymeric structures.

PubMed

Gärtner, Martin; Görls, Helmar; Westerhausen, Matthias

2007-09-03

Several preparative procedures for the synthesis of the THF complexes of the alkaline earth metal bis(phenylamides) of Mg (1), Ca (2), Sr (3), and Ba (4) are presented such as metalation of aniline with strontium and barium, metathesis reactions of MI2 with KN(H)Ph, and metalation of aniline with arylcalcium compounds or dialkylmagnesium. The THF content of these compounds is rather low and an increasing aggregation is observed with the size of the metal atom. Thus, tetrameric [(THF)2Ca{mu-N(H)Ph}2]4 (2) and polymeric [(THF)2Sr{mu-N(H)Ph}2]infinity and {[(THF)2Ba{mu-N(H)Ph}2]2[(THF)Ba{mu-N(H)Ph}2]2}infinity show six-coordinate metal atoms with increasing interactions to the pi systems of the phenyl groups with increasing the radius of the alkaline earth metal atom.

Activating catalysts with mechanical force.

PubMed

Piermattei, Alessio; Karthikeyan, S; Sijbesma, Rint P

2009-05-01

Homogeneously catalysed reactions can be 'switched on' by activating latent catalysts. Usually, activation is brought about by heat or an external chemical agent. However, activation of homogeneous catalysts with a mechanical trigger has not been demonstrated. Here, we introduce a general method to activate latent catalysts by mechanically breaking bonds between a metal and one of its ligands. We have found that silver(I) complexes of polymer-functionalized N-heterocyclic carbenes, which are latent organocatalysts, catalyse a transesterification reaction when exposed to ultrasound in solution. Furthermore, ultrasonic activation of a ruthenium biscarbene complex with appended polymer chains results in catalysis of olefin metathesis reactions. In each case, the catalytic activity results from ligand dissociation, brought about by transfer of mechanical forces from the polymeric substituents to the coordination bond. Mechanochemical catalyst activation has potential applications in transduction and amplification of mechanical signals, and mechanically initiated polymerizations hold promise as a novel repair mechanism in self-healing materials.

Tandem enyne metathesis-Diels-Alder reaction for construction of natural product frameworks.

PubMed

Rosillo, Marta; Domínguez, Gema; Casarrubios, Luis; Amador, Ulises; Pérez-Castells, Javier

2004-03-19

Enynes connected through aromatic rings are used as substrates for metathesis reactions. The reactivity of three ruthenium carbene complexes is compared. The resulting 1,3-dienes are suitable precursors of polycyclic structures via a Diels-Alder process. Some domino RCM-Diels-Alder reactions are performed, suggesting a possible beneficial effect of the ruthenium catalyst in the cycloaddition process. Other examples require Lewis acid cocatalyst. When applied to aromatic ynamines or enamines, a new synthesis of vinylindoles is achieved. Monitorization of several metathesis reactions with NMR shows the different behavior for ruthenium catalysts. New carbenic species are detected in some reactions with an important dependence on the solvent used.

Optimal Hydrophobicity in Ring-Opening Metathesis Polymerization-Based Protein Mimics Required for siRNA Internalization.

PubMed

deRonde, Brittany M; Posey, Nicholas D; Otter, Ronja; Caffrey, Leah M; Minter, Lisa M; Tew, Gregory N

2016-06-13

Exploring the role of polymer structure for the internalization of biologically relevant cargo, specifically siRNA, is of critical importance to the development of improved delivery reagents. Herein, we report guanidinium-rich protein transduction domain mimics (PTDMs) based on a ring-opening metathesis polymerization scaffold containing tunable hydrophobic moieties that promote siRNA internalization. Structure-activity relationships using Jurkat T cells and HeLa cells were explored to determine how the length of the hydrophobic block and the hydrophobic side chain compositions of these PTDMs impacted siRNA internalization. To explore the hydrophobic block length, two different series of diblock copolymers were synthesized: one series with symmetric block lengths and one with asymmetric block lengths. At similar cationic block lengths, asymmetric and symmetric PTDMs promoted siRNA internalization in the same percentages of the cell population regardless of the hydrophobic block length; however, with 20 repeat units of cationic charge, the asymmetric block length had greater siRNA internalization, highlighting the nontrivial relationships between hydrophobicity and overall cationic charge. To further probe how the hydrophobic side chains impacted siRNA internalization, an additional series of asymmetric PTDMs was synthesized that featured a fixed hydrophobic block length of five repeat units that contained either dimethyl (dMe), methyl phenyl (MePh), or diphenyl (dPh) side chains and varied cationic block lengths. This series was further expanded to incorporate hydrophobic blocks consisting of diethyl (dEt), diisobutyl (diBu), and dicyclohexyl (dCy) based repeat units to better define the hydrophobic window for which our PTDMs had optimal activity. High-performance liquid chromatography retention times quantified the relative hydrophobicities of the noncationic building blocks. PTDMs containing the MePh, diBu, and dPh hydrophobic blocks were shown to have superior siRNA internalization capabilities compared to their more and less hydrophobic counterparts, demonstrating a critical window of relative hydrophobicity for optimal internalization. This better understanding of how hydrophobicity impacts PTDM-induced internalization efficiencies will help guide the development of future delivery reagents.

In Silico Olefin Metathesis with Ru-Based Catalysts Containing N-Heterocyclic Carbenes Bearing C60 Fullerenes.

PubMed

Martínez, Juan Pablo; Vummaleti, Sai Vikrama Chaitanya; Falivene, Laura; Nolan, Steven P; Cavallo, Luigi; Solà, Miquel; Poater, Albert

2016-05-04

Density functional theory calculations have been used to explore the potential of Ru-based complexes with 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) ligand backbone (A) being modified in silico by the insertion of a C60 molecule (B and C), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A, B, and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron-withdrawing N-heterocyclic carbene improves the performance of unannulated complex A. The efficiency of complex B is only surpassed by complex A when the backbone of the N-heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic-donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A. Overall, this study indicates that such Ru-based complexes B and C might have the potential to be effective olefin metathesis catalysts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Alkene metathesis: the search for better catalysts.

PubMed

Deshmukh, Prashant H; Blechert, Siegfried

2007-06-28

Alkene metathesis catalyst development has made significant progress over recent years. Research in metathesis catalyst design has endeavoured to tackle three key issues: those of (i) catalyst efficiency and activity, (ii) substrate scope and selectivity--particularly stereoselective metathesis reactions--and (iii) the minimization of metal impurities and catalyst recycling. This article describes a brief history of metathesis catalyst development, followed by a survey of more recent research, with a particular emphasis on ruthenium catalysts.

Cross enyne metathesis of para-substituted styrenes: a kinetic study of enyne metathesis.

PubMed

Giessert, Anthony J; Diver, Steven T

2005-01-20

[Reaction: see text] The intermolecular enyne metathesis between alkynes and styrene derivatives was developed to study electronic effects in enyne metathesis. A Hammett plot for the overall reaction, catalyst initiation and vinyl carbene turnover was determined with the second generation Grubbs ruthenium carbene catalyst.

Synthesis and Side Chain Liquid Crystal Polymers by Living Ring Opening Metathesis Polymerization. 5. Influence of Mesogenic Group and Interconnecting Group on the Thermotropic Behavior of the Resulting Polymers

DTIC Science & Technology

1992-07-22

Scheme I. The first nucleophilic displacement of halide of an n-haloalkan-l-ol with 4-cyano-4’-hydroxybiphenyl employed potassium carbonate in...21 𔃼 polysiloxanes, 23.24 and polyacrylates . 2- All these polymers exhibit an odd-even effect. If one considers the total number of atoms between the...0.019 mol) and 4’-methoxy-4-hydroxybiphenyl (4.0g, 0.020 tool) were heated at 100°C in 40 mL of dimethylformamide in the presence of potassium carbonate

Synthetic Mimic of Antimicrobial Peptide with Nonmembrane-Disrupting Antibacterial Properties

PubMed Central

2008-01-01

Polyguanidinium oxanorbornene (PGON) was synthesized from norbornene monomers via ring-opening metathesis polymerization. This polymer was observed to be strongly antibacterial against Gram-negative and Gram-positive bacteria as well as nonhemolytic against human red blood cells. Time-kill studies indicated that this polymer is lethal and not just bacteriostatic. In sharp contrast to previously reported SMAMPs (synthetic mimics of antimicrobial peptides), PGON did not disrupt membranes in vesicle-dye leakage assays and microscopy experiments. The unique biological properties of PGON, in same ways similar to cell-penetrating peptides, strongly encourage the examination of other novel guanidino containing macromolecules as powerful and selective antimicrobial agents. PMID:18850741

Catalyst system comprising a first catalyst system tethered to a supported catalyst

DOEpatents

Angelici, Robert J.; Gao, Hanrong

1998-08-04

The present invention provides new catalyst formats which comprise a supported catalyst tethered to a second and different catalyst by a suitable tethering ligand. A preferred system comprises a heterogeneous supported metal catalyst tethered to a homogeneous catalyst. This combination of homogeneous and heterogeneous catalysts has a sufficient lifetime and unusually high catalytic activity in arene hydrogenations, and potentially many other reactions as well, including, but not limited to hydroformylation, hydrosilation, olefin oxidation, isomerization, hydrocyanation, olefin metathesis, olefin polymerization, carbonylation, enantioselective catalysis and photoduplication. These catalysts are easily separated from the products, and can be reused repeatedly, making these systems very economical.

Catalyst system comprising a first catalyst system tethered to a supported catalyst

DOEpatents

Angelici, R.J.; Gao, H.

1998-08-04

The present invention provides new catalyst formats which comprise a supported catalyst tethered to a second and different catalyst by a suitable tethering ligand. A preferred system comprises a heterogeneous supported metal catalyst tethered to a homogeneous catalyst. This combination of homogeneous and heterogeneous catalysts has a sufficient lifetime and unusually high catalytic activity in arene hydrogenations, and potentially many other reactions as well, including, but not limited to hydroformylation, hydrosilication, olefin oxidation, isomerization, hydrocyanidation, olefin metathesis, olefin polymerization, carbonylation, enantioselective catalysis and photoduplication. These catalysts are easily separated from the products, and can be reused repeatedly, making these systems very economical. 2 figs.

Computational Elucidation of Selectivities and Mechanisms Performed by Organometallic and Bioinorganic Catalysts

NASA Astrophysics Data System (ADS)

Grandner, Jessica Marie

Computational methods were used to determine the mechanisms and selectivities of organometallic-catalyzed reactions. The first half of the dissertation focuses on the study of metathesis catalysts in collaboration with the Grubbs group at CalTech. Chapter 1 describes the studies of the decomposition modes of several ruthenium-based metathesis catalysts. These studies were performed to better understand the decomposition of such catalysts in order to prevent decomposition (Chapter 1.2) or utilize decomposed catalysts for alternative reactions (Chapter 1.1). Chapter 2.1 describes the computational investigation of the origins of stereoretentive metathesis with ruthenium-based metathesis catalysts. These findings were then used to computationally design E-selective metathesis catalysts (Chapter 2.2). While the first half of the dissertation was centered around ruthenium catalysts, the second half of the dissertation pertains to iron-catalyzed reaction, in particular, iron-catalyzed reactions by P450 enzymes. The elements of Chapter 3 concentrate on the stereo- and chemo-selectivity of P450-catalyzed C-H hydroxylations. By combining multiple computational methods, the inherent activity of the iron-oxo catalyst and the influence of the active site on such reactions were illuminated. These discoveries allow for the engineering of new substrates and mutant enzymes for tailored C-H hydroxylation. While the mechanism of C-H hydroxylations catalyzed by P450 enzymes has been well studied, there are several P450-catalyzed transformations for which the mechanism is unknown. The components of Chapter 4 describe the use of computations to determine the mechanisms of complex, multi-step reactions catalyzed by P450s. The determination of these mechanisms elucidates how these enzymes react with various functional groups and substrate architectures and allows for a better understanding of how drug-like compounds may be broken down by human P450s.

Cellular Delivery of Nanoparticles Revealed with Combined Optical and Isotopic Nanoscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Proetto, Maria T.; Anderton, Christopher R.; Hu, Dehong

Synthetic drug-carrying nanomaterials offer great potential as targeted cellular delivery vehicles. Typically, their size, morphology, surface chemistry and stability are optimized in order to control their effect on drug release kinetics, cellular uptake pathways, efficiency and site of action. However, methods to track the carriers and their cargo independently at the micro- and nanoscale have been severely underutilized preventing the correlation between structure and function. Here we show that by using combined optical and isotopic nanoscopy we can track the uptake in cancer cells and subsequent drug release of a Pt(II)-loaded anticancer nanoparticle (NP) system. We found that by directlymore » polymerizing an oxaliplatin analogue containing a norbornyl moiety amenable to polymerization via ring opening metathesis polymerization (ROMP) we could generate amphiphiles in one pot. Spontaneous self-assembly of the drug-containing polymers in aqueous solution led to well-defined NPs in a reproducible manner. Our results demonstrate that the covalently loaded NPs are equipotent with free oxaliplatin and are taken up intact via endocytic pathways before release of the cytotoxic cargo. This was confirmed by super resolution fluorescence structured illumination microscopy (SIM) and nanoscale secondary ion mass spectrometry (NanoSIMS). We anticipate that this type of multimodal cellular tracking of NP and drug will bridge the knowledge gap between particle structure and performance for the vast array of currently generalizable systems in the literature. Furthermore, the use of covalently loaded NP drug systems should allow development of more stable, reproducible and site specific nanodelivery agents.« less

Cyclic alkyl amino carbene (CAAC) ruthenium complexes as remarkably active catalysts for ethenolysis

DOE PAGES

Marx, Vanessa M.; Sullivan, Alexandra H.; Melaimi, Mohand; ...

2014-12-17

In this paper, an expanded family of ruthenium-based metathesis catalysts bearing cyclic alkyl amino carbene (CAAC) ligands was prepared. These catalysts exhibited exceptional activity in the ethenolysis of the seed-oil derivative methyl oleate. In many cases, catalyst turnover numbers (TONs) of more than 100,000 were achieved, at a catalyst loading of only 3 ppm. Remarkably, the most active catalyst system was able to achieve a TON of 340 000, at a catalyst loading of only 1 ppm. Finally, this is the first time a series of metathesis catalysts has exhibited such high performance in cross-metathesis reactions employing ethylene gas, withmore » activities sufficient to render ethenolysis applicable to the industrial-scale production of linear α-olefins (LAOs) and other terminal-olefin products.« less

Adhesion strength of norbornene-based self-healing agents to an amine-cured epoxy

NASA Astrophysics Data System (ADS)

Huang, Guang Chun; Lee, Jong Keun; Kessler, Michael R.; Yoon, Sungho

2009-07-01

Self-healing is triggered by crack propagation through embedded microcapsules in an epoxy matrix, which then release the liquid healing agent into the crack plane. Subsequent exposure of the healing agent to the chemical catalyst initiates ring-opening metathesis polymerization (ROMP) and bonding of the crack faces. In order to improve self-healing functionality, it is necessary to enhance adhesion of polymerized healing agent within the crack to the matrix resin. In this study, shear bond strength between different norbornene-based healing agents and an amine-cured epoxy resin was evaluated using the single lap shear test method (ASTM D3163, modified). The healing agents tested include endodicyclopentadiene (endo-DCPD), 5-ethylidene-2-norbornene (ENB) and DCPD/ENB blends. 5-Norbornene-2-methanol (NBM) was used as an adhesion promoter, containing hydroxyl groups to form hydrogen bonds with the amine-cured epoxy. A custom synthesized norbornene-based crosslinking agent was also added to improve adhesion for ENB by increasing the crosslinking density of the adhesive after ROMP. The healing agents were polymerized with varying loadings of the 1st generation Grubbs' catalyst at different reaction times and temperatures.

Single chain technology: Toward the controlled synthesis of polymer nanostructures

NASA Astrophysics Data System (ADS)

Lyon, Christopher

A technique for fabricating advanced polymer nanostructures enjoying recent popularity is the collapse or folding of single polymer chains in highly dilute solution mediated by intramolecular cross-linking. We term the resultant structures single-chain nanoparticles (SCNP). This technique has proven particularly valuable in the synthesis of nanomaterials on the order of 5 -- 20 nm. Many different types of covalent and non-covalent chemistries have been used to this end. This dissertation investigates the use of so-called single-chain technology to synthesize nanoparticles using modular techniques that allow for easy incorporation of functionality or special structural or characteristic features. Specifically, the synthesis of linear polymers functionalized with pendant monomer units and the subsequent intramolecular polymerization of these monomer units is discussed. In chapter 2, the synthesis of SCNP using alternating radical polymerization is described. Polymers functionalized with pendant styrene and stilbene groups are synthesized via a modular post-polymerization Wittig reaction. These polymers were exposed to radical initiators in the presence (and absence) of maleic anhydride and other electron deficient monomers in order to form intramolecular cross-links. Chapter 3 discusses templated acyclic diene metathesis (ADMET) polymerization using single-chain technology, starting with the controlled ring-opening polymerization of a glycidyl ether functionalized with an ADMET monomer. This polymer was then exposed to Grubbs' catalyst to polymerize the ADMET monomer units. The ADMET polymer was hydrolytically cleaved from the template and separated. Upon characterization, it was found that the daughter ADMET polymer had a similar degree of polymerization, but did not retain the low dispersity of the template. Chapter 4 details the synthesis of aldehyde- and diol-functionalized polymers toward the synthesis of SCNP containing dynamic, acid-degradable acetal cross-links. SCNP fabrication with these materials is beyond the scope of this dissertation.

Sequence Effects in Conjugated Donor-Acceptor Trimers and Polymers.

PubMed

Zhang, Shaopeng; Hutchison, Geoffrey R; Meyer, Tara Y

2016-06-01

To investigate the sequence effect on donor-acceptor conjugated oligomers and polymers, the trimeric isomers PBP and BPP, comprising dialkoxy phenylene vinylene (P), benzothiadiazole vinylene (B), and alkyl endgroups with terminal olefins, are synthesized. Sequence effects are evident in the optical/electrochemical properties and thermal properties. Absorption maxima for PBP and BPP differ by 41 nm and the electrochemical band gaps by 0.1 V. The molar emission intensity is five times greater in PBP than BPP. Both trimers are crystalline and the melting points differ by 17 °C. The PBP and BPP trimers are used as macromonomers in an acyclic diene metathesis polymerization to give PolyPBP and PolyBPP. The optical and electrochemical properties are similar to those of their trimer precursors-sequence effects are still evident. These results suggest that sequence is a tunable variable for electronic materials and that the polymerization of oligomeric sequences is a useful approach to introducing sequence into polymers. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of terminal alkenes from internal alkenes and ethylene via olefin metathesis

DOEpatents

Schrodi, Yann [Agoura Hills, CA

2011-11-29

This invention relates generally to olefin metathesis, and more particularly relates to the synthesis of terminal alkenes from internal alkenes using a cross-metathesis reaction catalyzed by a selected olefin metathesis catalyst. In one embodiment of the invention, for example, a method is provided for synthesizing a terminal olefin, the method comprising contacting an olefinic substrate comprised of at least one internal olefin with ethylene, in the presence of a metathesis catalyst, wherein the catalyst is present in an amount that is less than about 1000 ppm relative to the olefinic substrate, and wherein the metathesis catalyst has the structure of formula (II) ##STR00001## wherein the various substituents are as defined herein. The invention has utility, for example, in the fields of catalysis, organic synthesis, and industrial chemistry.

Synthesis of terminal alkenes from internal alkenes and ethylene via olefin metathesis

DOEpatents

Schrodi, Yann

2013-07-09

This invention relates generally to olefin metathesis, and more particularly relates to the synthesis of terminal alkenes from internal alkenes using a cross-metathesis reaction catalyzed by a selected olefin metathesis catalyst. In one embodiment of the invention, for example, a method is provided for synthesizing a terminal olefin, the method comprising contacting an olefinic substrate comprised of at least one internal olefin with ethylene, in the presence of a metathesis catalyst, wherein the catalyst is present in an amount that is less than about 1000 ppm relative to the olefinic substrate, and wherein the metathesis catalyst has the structure of formula (II) ##STR00001## wherein the various substituents are as defined herein. The invention has utility, for example, in the fields of catalysis, organic synthesis, and industrial chemistry.

Synthesis of terminal alkenes from internal alkenes and ethylene via olefin metathesis

DOEpatents

Schrodi, Yann

2016-02-09

This invention relates generally to olefin metathesis, and more particularly relates to the synthesis of terminal alkenes from internal alkenes using a cross-metathesis reaction catalyzed by a selected olefin metathesis catalyst. In one embodiment of the invention, for example, a method is provided for synthesizing a terminal olefin, the method comprising contacting an olefinic substrate comprised of at least one internal olefin with ethylene, in the presence of a metathesis catalyst, wherein the catalyst is present in an amount that is less than about 1000 ppm relative to the olefinic substrate, and wherein the metathesis catalyst has the structure of formula (II) ##STR00001## wherein the various substituents are as defined herein. The invention has utility, for example, in the fields of catalysis, organic synthesis, and industrial chemistry.

Synthesis of terminal alkenes from internal alkenes and ethylene via olefin metathesis

DOEpatents

Schrodi, Yann

2015-09-22

This invention relates generally to olefin metathesis, and more particularly relates to the synthesis of terminal alkenes from internal alkenes using a cross-metathesis reaction catalyzed by a selected olefin metathesis catalyst. In one embodiment of the invention, for example, a method is provided for synthesizing a terminal olefin, the method comprising contacting an olefinic substrate comprised of at least one internal olefin with ethylene, in the presence of a metathesis catalyst, wherein the catalyst is present in an amount that is less than about 1000 ppm relative to the olefinic substrate, and wherein the metathesis catalyst has the structure of formula (II) ##STR00001## wherein the various substituents are as defined herein. The invention has utility, for example, in the fields of catalysis, organic synthesis, and industrial chemistry.

Mapping Optimal Charge Density and Length of ROMP-Based PTDMs for siRNA Internalization.

PubMed

Caffrey, Leah M; deRonde, Brittany M; Minter, Lisa M; Tew, Gregory N

2016-10-10

A fundamental understanding of how polymer structure impacts internalization and delivery of biologically relevant cargoes, particularly small interfering ribonucleic acid (siRNA), is of critical importance to the successful design of improved delivery reagents. Herein we report the use of ring-opening metathesis polymerization (ROMP) methods to synthesize two series of guanidinium-rich protein transduction domain mimics (PTDMs): one based on an imide scaffold that contains one guanidinium moiety per repeat unit, and another based on a diester scaffold that contains two guanidinium moieties per repeat unit. By varying both the degree of polymerization and, in effect, the relative number of cationic charges in each PTDM, the performances of the two ROMP backbones for siRNA internalization were evaluated and compared. Internalization of fluorescently labeled siRNA into Jurkat T cells demonstrated that fluorescein isothiocyanate (FITC)-siRNA internalization had a charge content dependence, with PTDMs containing approximately 40 to 60 cationic charges facilitating the most internalization. Despite this charge content dependence, the imide scaffold yielded much lower viabilities in Jurkat T cells than the corresponding diester PTDMs with similar numbers of cationic charges, suggesting that the diester scaffold is preferred for siRNA internalization and delivery applications. These developments will not only improve our understanding of the structural factors necessary for optimal siRNA internalization, but will also guide the future development of optimized PTDMs for siRNA internalization and delivery.

Nobel Chemistry in the Laboratory: Synthesis of a Ruthenium Catalyst for Ring-Closing Olefin Metathesis--An Experiment for the Advanced Inorganic or Organic Laboratory

ERIC Educational Resources Information Center

Greco, George E.

2007-01-01

An experiment for the upper-level undergraduate laboratory is described in which students synthesize a ruthenium olefin metathesis catalyst, then use the catalyst to carry out the ring-closing metathesis of diethyl diallylmalonate. The olefin metathesis reaction was the subject of the 2005 Nobel Prize in chemistry. The catalyst chosen for this…

Group 1 and group 2 metal complexes supported by a bidentate bulky iminopyrrolyl ligand: synthesis, structural diversity, and ε-caprolactone polymerization study.

PubMed

Kottalanka, Ravi K; Harinath, A; Rej, Supriya; Panda, Tarun K

2015-12-14

We report here a series of alkali and alkaline earth metal complexes, each with a bulky iminopyrrolyl ligand [2-(Ph3CN=CH)C4H3NH] (1-H) moiety in their coordination sphere, synthesized using either alkane elimination or silylamine elimination methods or the salt metathesis route. The lithium salt of molecular composition [Li(2-(Ph3CN=CH)C4H3N)(THF)2] (2) was prepared using the alkane elimination method, and the silylamine elimination method was used to synthesize the dimeric sodium and tetra-nuclear potassium salts of composition [(2-(Ph3CN=CH)C4H3N)Na(THF)]2 (3) and [(2-(Ph3CN=CH)C4H3N)K(THF)0.5]4 (4) respectively. The magnesium complex of composition [(THF)2Mg(CH2Ph){2-(Ph3CN=CH)C4H3N}] (5) was synthesized through the alkane elimination method, in which [Mg(CH2Ph)2(OEt2)2] was treated with the bulky iminopyrrole ligand 1-H in 1 : 1 molar ratio, whereas the bis(iminopyrrolyl)magnesium complex [(THF)2Mg{2-(Ph3CN=CH)C4H3N}2] (6) was isolated using the salt metathesis route. The heavier alkaline earth metal complexes of the general formula {(THF)nM(2-(Ph3CN=CH)C4H3N)2} [M = Ca (7), Sr (8), and n = 2; M = Ba (9), n = 3] were prepared in pure form using two synthetic methods: in the first method, the bulky iminopyrrole ligand 1-H was directly treated with the alkaline earth metal precursor [M{N(SiMe3)2}2(THF)n] (where M = Ca, Sr and Ba) in 2 : 1 molar ratio in THF solvent at ambient temperature. The complexes 7-9 were also obtained using the salt metathesis reaction, which involves the treatment of the potassium salt (4) with the corresponding metal diiodides MI2 (M = Ca, Sr and Ba) in 2 : 1 molar ratio in THF solvent. The molecular structures of all the metal complexes (1-H, 2-9) in the solid state were established through single-crystal X-ray diffraction analysis. The complexes 5-9 were tested as catalysts for the ring-opening polymerization of ε-caprolactone. High activity was observed in the heavier alkaline earth metal complexes 7-9, with a very narrow polydispersity index in comparison to that of magnesium complexes 5 and 6.

Metathesis of alkanes and related reactions.

PubMed

Basset, Jean-Marie; Copéret, Christophe; Soulivong, Daravong; Taoufik, Mostafa; Cazat, Jean Thivolle

2010-02-16

The transformation of alkanes remains a difficult challenge because of the relative inertness of the C-H and C-C bonds. The rewards for asserting synthetic control over unfunctionalized, saturated hydrocarbons are considerable, however, because converting short alkanes into longer chain analogues is usually a value-adding process. Alkane metathesis is a novel catalytic and direct transformation of two molecules of a given alkane into its lower and higher homologues; moreover, the process proceeds at relatively low temperature (ambient conditions or higher). It was discovered through the use of a silica-supported tantalum hydride, ([triple bond]SiO)(2)TaH, a multifunctional catalyst with a single site of action. This reaction completes the story of the metathesis reactions discovered over the past 40 years: olefin metathesis, alkyne metathesis, and ene-yne cyclizations. In this Account, we examine the fundamental mechanistic aspects of alkane metathesis as well as the novel reactions that have been derived from its study. The silica-supported tantalum hydride catalyst was developed as the result of systematic and meticulous studies of the interaction between oxide supports and organometallic complexes, a field of study denoted surface organometallic chemistry (SOMC). A careful examination of this surface-supported tantalum hydride led to the later discovery of alumina-supported tungsten hydride, W(H)(3)/Al(2)O(3), which proved to be an even better catalyst for alkane metathesis. Supported tantalum and tungsten hydrides are highly unsaturated, electron-deficient species that are very reactive toward the C-H and C-C bonds of alkanes. They show a great versatility in various other reactions, such as cross-metathesis between methane and alkanes, cross-metathesis between toluene and ethane, or even methane nonoxidative coupling. Moreover, tungsten hydride exhibits a specific ability in the transformation of isobutane into 2,3-dimethylbutane as well as in the metathesis of olefins or the selective transformation of ethylene into propylene. Alkane metathesis represents a powerful tool for making progress in a variety of areas, perhaps most notably in the petroleum and petrochemical fields. Modern civilization is currently confronting a host of problems that relate to energy production and its effects on the environment, and judicious application of alkane metathesis to the processing of fuels such as crude oil and natural gas may well afford solutions to these difficulties.

A tandem cross-metathesis/semipinacol rearrangement reaction.

PubMed

Plummer, Christopher W; Soheili, Arash; Leighton, James L

2012-05-18

An efficient and (E)-selective synthesis of a 6-alkylidenebicyclo[3.2.1]octan-8-one has been developed. The key step is a tandem cross-metathesis/semipinacol rearrangement reaction, wherein the Hoveyda-Grubbs II catalyst, or more likely a derivative thereof, serves as the Lewis acid for the rearrangement. Despite the fact that both the starting alkene and the cross-metathesis product are viable rearrangement substrates, only the latter rearranges, suggesting that the Lewis acidic species is generated only after the cross-metathesis reaction is complete.

Enhanced control of end-group composition in poly(3-hexylthiophene)s prepared by GRIM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kochemba, William Michael; Kilbey, II, S Michael; Pickel, Deanna L

The ability to prepare well-defined semiconducting polymers is essential for understanding the link between structure and function in organic photovoltaic devices. A general method for enhanced control of the degree of functionality of end-functionalized poly(3-hexylthiophene)s (P3HT) prepared by Grignard Metathesis (GRIM) polymerization has been developed. In the absence of additives, the degree of functionality of end-functional P3HTs prepared by quenching of the GRIM polymerization with a Grignard reagent is dependent on the Grignard reagent utilized. In this study, additives such as styrene and 1-pentene are shown to alter the end-group composition of tolyl-functionalized P3HTs as determined by MALDI-TOF MS. Inmore » particular, when quenching the GRIM polymerization with tolylmagnesium bromide a modest decrease in the difunctional product is observed, and the yield of the monofunctional product increases significantly. Temperature and lithium chloride (LiCl) addition also play impactful roles. Monofunctional P3HT is found to be the major product (65%) when the functionalization is done in the presence of LiCl and styrene at 0oC, whereas in the absence of additives the monofunctional product is present at only 20%.« less

Richard Schrock, Robert Grubbs, and Metathesis Method in Organic Synthesis

Science.gov Websites

Organic Synthesis Resources with Additional Information Richard R. Schrock of the Massachusetts Institute Nobel Prize in Chemistry "for the development of the metathesis method in organic synthesis" ] Chauvin, Grubbs and Schrock "for the development of the metathesis method in organic synthesis,"

Prosodically Driven Metathesis in Mutsun

ERIC Educational Resources Information Center

Butler, Lynnika

2013-01-01

Among the many ways in which sounds alternate in the world's languages, changes in the order of sounds (metathesis) are relatively rare. Mutsun, a Southern Costanoan language of California which was documented extensively before the death of its last speaker in 1930, displays three patterns of synchronic consonant-vowel (CV) metathesis. Two of…

Evidence for Dynamic Chemical Kinetics at Individual Molecular Ruthenium Catalysts.

PubMed

Easter, Quinn T; Blum, Suzanne A

2018-02-05

Catalytic cycles are typically depicted as possessing time-invariant steps with fixed rates. Yet the true behavior of individual catalysts with respect to time is unknown, hidden by the ensemble averaging inherent to bulk measurements. Evidence is presented for variable chemical kinetics at individual catalysts, with a focus on ring-opening metathesis polymerization catalyzed by the second-generation Grubbs' ruthenium catalyst. Fluorescence microscopy is used to probe the chemical kinetics of the reaction because the technique possesses sufficient sensitivity for the detection of single chemical reactions. Insertion reactions in submicron regions likely occur at groups of many (not single) catalysts, yet not so many that their unique kinetic behavior is ensemble averaged. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Recent advances in heterobimetallic catalysis across a "transition metal-tin" motif.

PubMed

Das, Debjit; Mohapatra, Swapna Sarita; Roy, Sujit

2015-06-07

Heterobimetallic catalysts, bearing a metal-metal bond between a transition metal (TM) and a tin atom, are very promising due to their ability in mediating a wide variety of organic transformations. Indeed the utilization of such catalysts is a challenging and evolving area in the field of homogeneous catalysis. Catalysis across a 'TM-Sn' motif is an emerging area in the broader domain of multimetallic catalysis. The present review apprises the chemists' community of the past, present and future scope of this versatile catalytic motif. The TM-Sn catalyzed reactions presented include, among others, Friedel-Crafts alkylation, carbonylation, polymerization, cyclization, olefin metathesis, Heck coupling, hydroarylation Michael addition and tandem coupling. The mechanistic aspects of the reactions have been highlighted as well.

Labelling Polymers and Micellar Nanoparticles via Initiation, Propagation and Termination with ROMP

PubMed Central

Thompson, Matthew P.; Randolph, Lyndsay M.; James, Carrie R.; Davalos, Ashley N.; Hahn, Michael E.

2014-01-01

In this paper we compare and contrast three approaches for labelling polymers with functional groups via ring-opening metathesis polymerization (ROMP). We explored the incorporation of functionality via initiation, termination and propagation employing an array of novel initiators, termination agents and monomers. The goal was to allow the generation of selectively labelled and well-defined polymers that would in turn lead to the formation of labelled nanomaterials. Norbornene analogues, prepared as functionalized monomers for ROMP, included fluorescent dyes (rhodamine, fluorescein, EDANS, and coumarin), quenchers (DABCYL), conjugatable moieties (NHS esters, pentafluorophenyl esters), and protected amines. In addition, a set of symmetrical olefins for terminally labelling polymers, and for the generation of initiators in situ is described. PMID:24855496

Facially Amphipathic Glycopolymers Inhibit Ice Recrystallization.

PubMed

Graham, Ben; Fayter, Alice E R; Houston, Judith E; Evans, Rachel C; Gibson, Matthew I

2018-05-02

Antifreeze glycoproteins (AFGPs) from polar fish are the most potent ice recrystallization (growth) inhibitors known, and synthetic mimics are required for low-temperature applications such as cell cryopreservation. Here we introduce facially amphipathic glycopolymers that mimic the three-dimensional structure of AFGPs. Glycopolymers featuring segregated hydrophilic and hydrophobic faces were prepared by ring-opening metathesis polymerization, and their rigid conformation was confirmed by small-angle neutron scattering. Ice recrystallization inhibition (IRI) activity was reduced when a hydrophilic oxo-ether was installed on the glycan-opposing face, but significant activity was restored by incorporating a hydrophobic dimethylfulvene residue. This biomimetic strategy demonstrates that segregated domains of distinct hydrophilicity/hydrophobicity are a crucial motif to introduce IRI activity, which increases our understanding of the complex ice crystal inhibition processes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murphy, Timothy A; Tupy, Michael J; Abraham, Timothy W

A wax comprises a metathesis product and/or a product that resembles, at least in part, a product which may be formed from a metathesis reaction. The wax may be used to form articles for example, candles (container candles, votive candles, and/or a pillar candles), crayons, fire logs or tarts. The wax commonly includes other components in addition to the metathesis product.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murphy, Timothy A.; Tupy, Michael J.; Abraham, Timothy W.

A wax comprises a metathesis product and/or a product that resembles, at least in part, a product which may be formed from a metathesis reaction. The wax may be used to form articles, for example, candles (container candles, votive candles, and/or a pillar candles), crayons, fire logs, or tarts. The wax commonly includes other components in addition to the metathesis product.

Learning metathesis: Evidence for syllable structure constraints.

PubMed

Finley, Sara

2017-02-01

One of the major questions in the cognitive science of language is whether the perceptual and phonological motivations for the rules and patterns that govern the sounds of language are a part of the psychological reality of grammatical representations. This question is particularly important in the study of phonological patterns - systematic constraints on the representation of sounds, because phonological patterns tend to be grounded in phonetic constraints. This paper focuses on phonological metathesis, which occurs when two adjacent sounds switch positions (e.g., ca st pronounced as ca ts ). While many cases of phonological metathesis appear to be motivated by constraints on syllable structure, it is possible that these metathesis patterns are merely artifacts of historical change, and do not represent the linguistic knowledge of the speaker (Blevins & Garrett, 1998). Participants who were exposed to a metathesis pattern that can be explained in terms of structural or perceptual improvement were less likely to generalize to metathesis patterns that did not show the same improvements. These results support a substantively biased theory in which phonological patterns are encoded in terms of structurally motivated constraints.

Learning metathesis: Evidence for syllable structure constraints

PubMed Central

Finley, Sara

2016-01-01

One of the major questions in the cognitive science of language is whether the perceptual and phonological motivations for the rules and patterns that govern the sounds of language are a part of the psychological reality of grammatical representations. This question is particularly important in the study of phonological patterns – systematic constraints on the representation of sounds, because phonological patterns tend to be grounded in phonetic constraints. This paper focuses on phonological metathesis, which occurs when two adjacent sounds switch positions (e.g., cast pronounced as cats). While many cases of phonological metathesis appear to be motivated by constraints on syllable structure, it is possible that these metathesis patterns are merely artifacts of historical change, and do not represent the linguistic knowledge of the speaker (Blevins & Garrett, 1998). Participants who were exposed to a metathesis pattern that can be explained in terms of structural or perceptual improvement were less likely to generalize to metathesis patterns that did not show the same improvements. These results support a substantively biased theory in which phonological patterns are encoded in terms of structurally motivated constraints. PMID:28082764

Methods for treating a metathesis feedstock with metal alkoxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cohen, Steven A.; Anderson, Donde R.; Wang, Zhe

Various methods are provided for treating and reacting a metathesis feedstock. In one embodiment, the method includes providing a feedstock comprising a natural oil, chemically treating the feedstock with a metal alkoxide under conditions sufficient to diminish catalyst poisons in the feedstock, and, following the treating, combining a metathesis catalyst with the feedstock under conditions sufficient to metathesize the feedstock.

A general approach to medium ring alkynes by using metathesis of cobalt hexacarbonyl containing dienes.

PubMed

Young, David G J; Burlison, Joseph A; Peters, Ulf

2003-05-02

The assembly of medium sized rings (7-9) was achieved by using the metathesis of dienes linked by a cobalt hexacarbonyl complexed alkyne with either Grubbs' or Schrock's catalysts. The products of metathesis were subjected to transformations involving the dicobalt hexacarbonyl complexes, for example, decomplexation to liberate cyclic alkynes or Pauson-Khand reaction.

Synthesis of (+)-Didemniserinolipid B: Application of a 2-Allyl-4-fluorophenyl Auxiliary for Relay Ring-Closing Metathesis

PubMed Central

Marvin, Christopher C.; Voight, Eric A.; Suh, Judy M.; Paradise, Christopher L.; Burke, Steven D.

2009-01-01

The synthesis of didemniserinolipid B utilizing a ketalization/ring-closing metathesis (K/RCM) strategy is described. In the course of this work, a novel 2-allyl-4-fluorophenyl auxiliary for relay ring-closing metathesis (RRCM) was developed which increased the yield of the RCM. The resulting 6,8-dioxabicyclo[3.2.1]octene core was selectively functionalized by complimentary dihydroxylation and epoxidation routes to install the C10 axial alcohol. This bicyclic ketal core was further functionalized by etherification and an alkene cross metathesis with an unsaturated α-phenylselenyl ester en route to completing the total synthesis. PMID:18811201

Poly(sophorolipid) structural variation: effects on biomaterial physical and biological properties.

PubMed

Peng, Yifeng; Munoz-Pinto, Dany J; Chen, Mingtao; Decatur, John; Hahn, Mariah; Gross, Richard A

2014-11-10

Diacetylated lactonic sophorolipids (polyLSL[6'Ac,6″Ac]), a biosurfactant, can be efficiently polymerized by ring-opening metathesis polymerization (ROMP). In this paper, enzyme-mediated chemical transformations are developed to regioselectively modify LSL[6'Ac,6″Ac] at sophorose primary hydroxyl positions (6' and 6″). The resulting modified LSLs were polymerized to expand polyLSL structural diversity, that is, polyLSL[6'OH,6″Ac], polyLSL[6'OH,6″OH], polyLSL[6'Bu,6″Ac], polyLSL[6'N3,6″Ac], and polyLSL[6'MA,6″Ac]. Controlled placement of azide and methacrylate at sophorolipid moieties enables the use of "click" reactions to introduce bioactive groups. Thermal analyses of polyLSLs showed that the acylation pattern at sugar moieties has a remarkable effect on chain stiffness and crystallinity. Films of polyLSL[6'Ac,6″Ac], polyLSL[6'OH,6″Ac], and polyLSL[6'Bu,6″Ac] exhibited nonbrittle behaviors with compressive elastic moduli ranging from ∼1.5 to ∼4.9 MPa. PolyLSLs were cytocompatible with human mesenchymal stem cells (h-MSCs), and examination of material-induced osteogenic cell lineage progression uncovered a dependence on polyLSL substitution at sophorose 6'-sites. This research reveals opportunities to regulate polyLSL physical properties and cell response behaviors by variation in substituents at polyLSL sophorolipid moieties.

Three-dimensional organization of block copolymers on "DNA-minimal" scaffolds.

PubMed

McLaughlin, Christopher K; Hamblin, Graham D; Hänni, Kevin D; Conway, Justin W; Nayak, Manoj K; Carneiro, Karina M M; Bazzi, Hassan S; Sleiman, Hanadi F

2012-03-07

Here, we introduce a 3D-DNA construction method that assembles a minimum number of DNA strands in quantitative yield, to give a scaffold with a large number of single-stranded arms. This DNA frame is used as a core structure to organize other functional materials in 3D as the shell. We use the ring-opening metathesis polymerization (ROMP) to generate block copolymers that are covalently attached to DNA strands. Site-specific hybridization of these DNA-polymer chains on the single-stranded arms of the 3D-DNA scaffold gives efficient access to DNA-block copolymer cages. These biohybrid cages possess polymer chains that are programmably positioned in three dimensions on a DNA core and display increased nuclease resistance as compared to unfunctionalized DNA cages. © 2012 American Chemical Society

Electronic Interactions of n-Doped Perylene Diimide Groups Appended to Polynorbornene Chains: Implications for Electron Transport in Organic Electronics.

PubMed

Nguyen, Minh T; Biberdorf, Joshua D; Holliday, Bradley J; Jones, Richard A

2017-11-01

A polymer consisting of a polynorbornene backbone with perylene diimide (PDI) pendant groups on each monomeric unit is synthesized via ring opening metathesis polymerization. The PDI pendant groups along the polymer backbone, studied by UV-vis absorption, fluorescence emission, and electron paramagnetic resonance spectroscopy in addition to electrochemical methods, show evidence of molecular aggregation and corresponding electronic coupling with neighboring groups, which forms pathways for efficient electron transport from one group to another in a specific reduced form. When n-doped, the title polymer shows redox conductivity of 5.4 × 10 -3 S cm -1 , comparable with crystalline PDI materials, and is therefore a promising material for use in organic electronics. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Methods of refining natural oils, and methods of producing fuel compositions

DOEpatents

Firth, Bruce E.; Kirk, Sharon E.

2015-10-27

A method of refining a natural oil includes: (a) providing a feedstock that includes a natural oil; (b) reacting the feedstock in the presence of a metathesis catalyst to form a metathesized product that includes olefins and esters; (c) passivating residual metathesis catalyst with an agent that comprises nitric acid; (d) separating the olefins in the metathesized product from the esters in the metathesized product; and (e) transesterifying the esters in the presence of an alcohol to form a transesterified product and/or hydrogenating the olefins to form a fully or partially saturated hydrogenated product. Methods for suppressing isomerization of olefin metathesis products produced in a metathesis reaction, and methods of producing fuel compositions are described.

Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C 2-symmetric building block: a strategy for the synthesis of decanolide natural products.

PubMed

Schmidt, Bernd; Kunz, Oliver

2013-01-01

Starting from the conveniently available ex-chiral pool building block (R,R)-hexa-1,5-diene-3,4-diol, the ten-membered ring lactones stagonolide E and curvulide A were synthesized using a bidirectional olefin-metathesis functionalization of the terminal double bonds. Key steps are (i) a site-selective cross metathesis, (ii) a highly diastereoselective extended tethered RCM to furnish a (Z,E)-configured dienyl carboxylic acid and (iii) a Ru-lipase-catalyzed dynamic kinetic resolution to establish the desired configuration at C9. Ring closure was accomplished by macrolactonization. Curvulide A was synthesized from stagonolide E through Sharpless epoxidation.

Artificial Informational Polymers and Nanomaterials from Ring-Opening Metathesis Polymerization

NASA Astrophysics Data System (ADS)

James, Carrie Rae

Inspired by naturally occurring polymers (DNA, polypeptides, polysaccharides, etc.) that can self-assemble on the nanoscale into complex, information-rich architectures, we have synthesized nucleic acid based polymers using ROMP. These polymers were synthesized using a graft-through strategy, whereby nucleic acids bearing a strained cyclic olefin were directly polymerized. This is the first example of the graft-through polymerization of nucleic acids. Our approach takes advantage of non-charged peptide nucleic acids (PNAs) as elements to incorporate into ROMP polymer backbones. PNA is a synthetic nucleic acid analogue known for its increased affinity and specificity for complementary DNA or RNA. To accomplish the graft-through polymerization of PNA, we conjugated PNA to strained cyclic olefins using solid phase peptide conjugation chemistry. These PNA monomers were then directly polymerized into homo and block copolymers forming brushes, or comb-like arrangements, of information. Block copolymer amphiphiles of these materials, where the PNA brush served as the hydrophilic portion, were capable of self-assembly into spherical nanoparticles (PNA NPs). These PNA NPs were then studied with respect to their ability to hybridize complementary DNA sequences, as well as their ability to undergo cellular internalization. PNA NPs consisting of densely packed brushes of nucleic acids possessed increased thermal stability when mixed with their complementary DNA sequence, indicating a greater DNA binding affinity over their unpolymerized PNA counterparts. In addition, by arranging the PNA into dense brushes at the surface of the nanoparticle, Cy5.5 labeled PNA NPs were able to undergo cellular internalization into HeLa cells without the need for an additional cellular delivery device. Importantly, cellular internalization of PNA has remained a significant challenge in the literature due to the neutrally charged amino-ethyl glycine backbone of PNA. Therefore, this represents a novel way of facilitating cellular uptake of PNA. This materials strategy represents the first direct polymerization of nucleic acids, and presents a novel method for arranging biological information on the nanoscale at high density in order to confer novel attributes.

Homobimetallic Ruthenium-N-Heterocyclic Carbene Complexes For Olefin Metathesis

NASA Astrophysics Data System (ADS)

Sauvage, Xavier; Demonceau, Albert; Delaude, Lionel

In this chapter, the synthesis and catalytic activity towards olefin metathesis of homobimetallic ruthenium (Ru)-alkylidene, -cyclodiene or -arene complexes bearing phosphine or N-heterocyclic carbene (NHC) ligands are reviewed. Emphasis is placed on the last category of bimetallic compounds. Three representatives of this new type of molecular scaffold were investigated. Thus, [(p-cymene)Ru(m-Cl)3RuCl (h2-C2H4)(L)] complexes with L = PCy3 (15a), IMes (16a), or IMesCl2 (16b) were prepared. They served as catalyst precursors for cross-metathesis (CM) of various styrene derivatives. These experiments revealed the outstanding aptitude of complex 16a (and to a lesser extent of 16b) to catalyze olefin metathesis reactions. Contrary to monometallic Ru-arene complexes of the [RuCl2(p-cymene)(L)] type, the new homobimetallic species did not require the addition of a diazo compound nor visible light illumination to initiate the ring-opening metathesis of norbornene or cyclooctene. When diethyl 2,2-diallylmalonate and N,N-diallyltosylamide were exposed to 16a,b, a mixture of cycloisomerization and ring-closing metathesis (RCM) products was obtained in a nonselective way. Addition of phenylacetylene enhanced the metathetical activity while completely repressing the cycloisomerization process.

Metathesis Activity Encoded in the Metallacyclobutane Carbon-13 NMR Chemical Shift Tensors

PubMed Central

2017-01-01

Metallacyclobutanes are an important class of organometallic intermediates, due to their role in olefin metathesis. They can have either planar or puckered rings associated with characteristic chemical and physical properties. Metathesis active metallacyclobutanes have short M–Cα/α′ and M···Cβ distances, long Cα/α′–Cβ bond length, and isotropic 13C chemical shifts for both early d0 and late d4 transition metal compounds for the α- and β-carbons appearing at ca. 100 and 0 ppm, respectively. Metallacyclobutanes that do not show metathesis activity have 13C chemical shifts of the α- and β-carbons at typically 40 and 30 ppm, respectively, for d0 systems, with upfield shifts to ca. −30 ppm for the α-carbon of metallacycles with higher dn electron counts (n = 2 and 6). Measurements of the chemical shift tensor by solid-state NMR combined with an orbital (natural chemical shift, NCS) analysis of its principal components (δ11 ≥ δ22 ≥ δ33) with two-component calculations show that the specific chemical shift of metathesis active metallacyclobutanes originates from a low-lying empty orbital lying in the plane of the metallacyclobutane with local π*(M–Cα/α′) character. Thus, in the metathesis active metallacyclobutanes, the α-carbons retain some residual alkylidene character, while their β-carbon is shielded, especially in the direction perpendicular to the ring. Overall, the chemical shift tensors directly provide information on the predictive value about the ability of metallacyclobutanes to be olefin metathesis intermediates. PMID:28776018

Direct synthesis of Z-alkenyl halides through catalytic cross-metathesis

PubMed Central

Koh, Ming Joo; Nguyen, Thach T.; Zhang, Hanmo; Schrock, Richard R.; Hoveyda, Amir H.

2016-01-01

Olefin metathesis has made a significant impact on modern organic chemistry, but important shortcomings remain: for example, the lack of efficient processes that can be used to generate acyclic alkenyl halides. Halo-substituted ruthenium carbene complexes decompose rapidly or deliver low activity and/or minimal stereoselectivity, and our understanding of the corresponding high-oxidation-state systems is very limited. In this manuscript, we show that previously unknown halo-substituted molybdenum alkylidene species are exceptionally reactive and are able to participate in high-yielding olefin metathesis reactions that afford acyclic 1,2-disubstituted Z-alkenyl halides. Transformations are promoted by small amounts of an in situ-generated catalyst with unpurified, commercially available and easy-to-handle liquid 1,2-dihaloethene reagents and proceed to high conversion at ambient temperature within four hours. Many alkenyl chlorides, bromides and fluorides can be obtained in up to 91 percent yield and complete Z selectivity. This method can be used to easily synthesize biologically active compounds and to perform the site- and stereoselective fluorination of other organic compounds. PMID:27008965

Concise Syntheses of Insect Pheromones Using Z-Selective Cross Metathesis**

PubMed Central

Herbert, Myles B.; Marx, Vanessa M.; Pederson, Richard L.; Grubbs, Robert H.

2013-01-01

The shortest synthetic routes to nine cis-pheromones containing a variety of functionality, including an unconjugated (E,Z) diene, are reported. These lepidopteran pheromones are used extensively for pest control, and were easily prepared using ruthenium-based Z-selective cross metathesis, highlighting the advantages of this method over less efficient ways to form Z-olefins. Important insight into the mechanism of Z-selective metathesis was uncovered during experimentation and subsequently explored. PMID:23055437

An electronic rationale for observed initiation rates in ruthenium-mediated olefin metathesis: charge donation in phosphine and N-heterocyclic carbene ligands.

PubMed

Getty, Kendra; Delgado-Jaime, Mario Ulises; Kennepohl, Pierre

2007-12-26

Ru K-edge XAS data indicate that second generation ruthenium-based olefin metathesis precatalysts (L = N-heterocyclic carbene) possess a more electron-deficient metal center than in the corresponding first generation species (L = tricyclohexylphosphine). This surprising effect is also observed from DFT calculations and provides a simple rationale for the slow phosphine dissociation kinetics previously noted for second-generation metathesis precatalysts.

Nonproductive events in ring-closing metathesis using ruthenium catalysts.

PubMed

Stewart, Ian C; Keitz, Benjamin K; Kuhn, Kevin M; Thomas, Renee M; Grubbs, Robert H

2010-06-30

The relative TONs of productive and nonproductive metathesis reactions of diethyl diallylmalonate are compared for eight different ruthenium-based catalysts. Nonproductive cross metathesis is proposed to involve a chain-carrying ruthenium methylidene. A second more-challenging substrate (dimethyl allylmethylallylmalonate) that forms a trisubstituted olefin product is used to further delineate the effect of catalyst structure on the relative efficiencies of these processes. A steric model is proposed to explain the observed trends.

Process for the synthesis of unsaturated alcohols

DOEpatents

Maughon, Bob R.; Burdett, Kenneth A.; Lysenko, Zenon

2007-02-13

A process of preparing an unsaturated alcohol (olefin alcohol), such as, a homo-allylic mono-alcohol or homo-allylic polyol, involving protecting a hydroxy-substituted unsaturated fatty acid or fatty acid ester, such as methyl ricinoleate, derived from a seed oil, to form a hydroxy-protected unsaturated fatty acid or fatty acid ester; homo-metathesizing or cross-metathesizing the hydroxy-protected unsaturated fatty acid or fatty acid ester to produce a product mixture containing a hydroxy-protected unsaturated metathesis product; and deprotecting the hydroxy-protected unsaturated metathesis product under conditions sufficient to prepare the unsaturated alcohol. Preferably, methyl ricinoleate is converted by cross-metathesis or homo-metathesis into the homo-allylic mono-alcohol 1-decene-4-ol or the homo-allylic polyol 9-octadecene-7,12-diol, respectively.

New developments using carbon dioxide as a solvent: Monolayers and nanocomposites. 1. Reactions of organosilanes with oxidized silicon surfaces in carbon dioxide. 2. Polymer/polymer nanocomposites synthesized in carbon dioxide

NASA Astrophysics Data System (ADS)

Cao, Chuntao

The aim of this research was to explore new directions for carbon dioxide. The first project emphasized silyl monolayer synthesis. Silylation reactions were performed in both liquid and supercritical carbon dioxide. Different monofunctional organosilanes reacted with silica surfaces, forming covalently attached monolayers. These monolayers were characterized using contact angle measurements, X-ray photoelectron spectroscopy, and ellipsometry. Reaction kinetics were established, and compared with silylations in organic solvents. The reaction rate in CO2 is higher than that in conventional solvents while the final coverage is slightly lower than the optimized conditions for conventional solvents. Other multi-functional silanes were also studied. The silylation of nanoporous silica surfaces showed bonding densities almost as high as the maximum value reported in literature for small-pore substrates. Overall, CO2 is a good solvent for silylations on silica surfaces. The second project was to synthesize polymer/polymer nanocomposites using a CO2-assisted templating method. Semicrystalline polymers are composed of tens-of-nanometer thick crystalline lamellae and an amorphous matrix. CO2 normally swells only the amorphous and interlamellar regions. The goal of this research was to selectively bring monomers to the amorphous and interlamellar regions with the help of CO2. In situ polymerization and precipitation fixes the structure, replicating the nano-structure of the semicrystalline polymer substrate. Ring-opening metathesis polymerization was performed inside of CO2-swollen poly(4-methyl-1-pentene) (PMP) of high crystallinity. Several polymer/polymer nanocomposites were successfully produced using this method. They were characterized by a variety of techniques, such as transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and wide angle X-ray diffraction (WAXD). Infrared studies and TEM indicated that one type of composite, polynorbomene/PMP, had a gradient distribution of polynorbornene inside of the PMP matrix. Another composite, polyoctenamer/PMP prepared by cis-cyclooctene polymerization, exhibited very interesting mechanical properties. The poly(dicyclopentadiene)/PMP composites are unique nanometer-scale blends of a highly crosslinked thermoset with a thermoplastic polymer.

Ruthenium Grubbs' catalyst nanostructures grown by UV-excimer-laser ablation for self-healing applications

NASA Astrophysics Data System (ADS)

Aïssa, B.; Nechache, R.; Haddad, E.; Jamroz, W.; Merle, P. G.; Rosei, F.

2012-10-01

A self healing composite material consisting of 5-Ethylidene-2-Norbornene (5E2N) monomer reacted with Ruthenium Grubbs' Catalyst (RGC) was prepared. First, the kinetics of the 5E2N ring opening metathesis polymerization (ROMP) reaction RGC was studied as a function of temperature. We show that the polymerization reaction is still effective in a large temperature range (-15 to 45 °C), occurring at short time scales (less than 1 min at 40 °C). Second, the amount of RGC required for ROMP reaction significantly decreased through its nanostructuration by means of a UV-excimer laser ablation process. RGC nanostructures of few nanometers in size where successfully obtained directly on silicon substrates. The X-ray photoelectron spectroscopy data strongly suggest that the RGC still keep its original stoichiometry after nanostructuration. More importantly, the associated ROMP reaction was successfully achieved at an extreme low RGC concentration equivalent to (11.16 ± 1.28) × 10-4 Vol.%, occurring at very short time reaction. This approach opens new prospects for using healing agent nanocomposite materials for self-repair functionality, thereby obtaining a higher catalytic efficiency per unit mass.

Stereoselectivity of supported alkene metathesis catalysts: a goal and a tool to characterize active sites.

PubMed

Copéret, Christophe

2011-01-05

Stereoselectivity in alkene metathesis is a challenge and can be used as a tool to study active sites under working conditions. This review describes the stereochemical relevance and problems in alkene metathesis (kinetic vs. thermodynamic issues), the use of (E/Z) ratio at low conversions as a tool to characterize active sites of heterogeneous catalysts and finally to propose strategies to improve catalysts based on the current state of the art.

Methods of refining natural oils and methods of producing fuel compositions

DOEpatents

Firth, Bruce E; Kirk, Sharon E; Gavaskar, Vasudeo S

2015-11-04

A method of refining a natural oil includes: (a) providing a feedstock that includes a natural oil; (b) reacting the feedstock in the presence of a metathesis catalyst to form a metathesized product that includes olefins and esters; (c) passivating residual metathesis catalyst with an agent selected from the group consisting of phosphorous acid, phosphinic acid, and a combination thereof; (d) separating the olefins in the metathesized product from the esters in the metathesized product; and (e) transesterifying the esters in the presence of an alcohol to form a transesterified product and/or hydrogenating the olefins to form a fully or partially saturated hydrogenated product. Methods for suppressing isomerization of olefin metathesis products produced in a metathesis reaction, and methods of producing fuel compositions are described.

Design of water-soluble, thiol-reactive polymers of controlled molecular weight: a novel multivalent scaffold

NASA Astrophysics Data System (ADS)

Carrillo, Alvaro; Gujraty, Kunal V.; Rai, Prakash R.; Kane, Ravi S.

2005-07-01

Multivalent molecules, i.e. scaffolds presenting multiple copies of a suitable ligand, constitute an emerging class of nanoscale therapeutics. We present a novel approach for the design of multivalent ligands, which allows the biofunctionalization of polymers with proteins or peptides in a controlled orientation. It consists of the synthesis of water-soluble, activated polymer scaffolds of controlled molecular weight, which can be biofunctionalized with various thiolated ligands in aqueous media under mild conditions. These polymers were synthesized by ring-opening metathesis polymerization (ROMP) and further modified to make them water-soluble. The incorporation of chloride groups activated the polymers to react with thiol-containing peptides or proteins, and the formation of multivalent ligands in aqueous media was demonstrated. This strategy represents a convenient route for synthesizing multivalent ligands of controlled dimensions and valency.

Decarboxylative alkenylation

NASA Astrophysics Data System (ADS)

Edwards, Jacob T.; Merchant, Rohan R.; McClymont, Kyle S.; Knouse, Kyle W.; Qin, Tian; Malins, Lara R.; Vokits, Benjamin; Shaw, Scott A.; Bao, Deng-Hui; Wei, Fu-Liang; Zhou, Ting; Eastgate, Martin D.; Baran, Phil S.

2017-04-01

Olefin chemistry, through pericyclic reactions, polymerizations, oxidations, or reductions, has an essential role in the manipulation of organic matter. Despite its importance, olefin synthesis still relies largely on chemistry introduced more than three decades ago, with metathesis being the most recent addition. Here we describe a simple method of accessing olefins with any substitution pattern or geometry from one of the most ubiquitous and variegated building blocks of chemistry: alkyl carboxylic acids. The activating principles used in amide-bond synthesis can therefore be used, with nickel- or iron-based catalysis, to extract carbon dioxide from a carboxylic acid and economically replace it with an organozinc-derived olefin on a molar scale. We prepare more than 60 olefins across a range of substrate classes, and the ability to simplify retrosynthetic analysis is exemplified with the preparation of 16 different natural products across 10 different families.

Peptide/protein-polymer conjugates: synthetic strategies and design concepts.

PubMed

Gauthier, Marc A; Klok, Harm-Anton

2008-06-21

This feature article provides a compilation of tools available for preparing well-defined peptide/protein-polymer conjugates, which are defined as hybrid constructs combining (i) a defined number of peptide/protein segments with uniform chain lengths and defined monomer sequences (primary structure) with (ii) a defined number of synthetic polymer chains. The first section describes methods for post-translational, or direct, introduction of chemoselective handles onto natural or synthetic peptides/proteins. Addressed topics include the residue- and/or site-specific modification of peptides/proteins at Arg, Asp, Cys, Gln, Glu, Gly, His, Lys, Met, Phe, Ser, Thr, Trp, Tyr and Val residues and methods for producing peptides/proteins containing non-canonical amino acids by peptide synthesis and protein engineering. In the second section, methods for introducing chemoselective groups onto the side-chain or chain-end of synthetic polymers produced by radical, anionic, cationic, metathesis and ring-opening polymerization are described. The final section discusses convergent and divergent strategies for covalently assembling polymers and peptides/proteins. An overview of the use of chemoselective reactions such as Heck, Sonogashira and Suzuki coupling, Diels-Alder cycloaddition, Click chemistry, Staudinger ligation, Michael's addition, reductive alkylation and oxime/hydrazone chemistry for the convergent synthesis of peptide/protein-polymer conjugates is given. Divergent approaches for preparing peptide/protein-polymer conjugates which are discussed include peptide synthesis from synthetic polymer supports, polymerization from peptide/protein macroinitiators or chain transfer agents and the polymerization of peptide side-chain monomers.

ROMP-based thermosetting polymers from modified castor oil with various cross-linking agents

NASA Astrophysics Data System (ADS)

Ding, Rui

Polymers derived from bio-renewable resources are finding an increase in global demand. In addition, polymers with distinctive functionalities are required in certain advanced fields, such as aerospace and civil engineering. In an attempt to meet both these needs, the goal of this work aims to develop a range of bio-based thermosetting matrix polymers for potential applications in multifunctional composites. Ring-opening metathesis polymerization (ROMP), which recently has been explored as a powerful method in polymer chemistry, was employed as a unique pathway to polymerize agricultural oil-based reactants. Specifically, a novel norbornyl-functionalized castor oil alcohol (NCA) was investigated to polymerize different cross-linking agents using ROMP. The effects of incorporating dicyclopentadiene (DCPD) and a norbornene-based crosslinker (CL) were systematically evaluated with respect to curing behavior and thermal mechanical properties of the polymers. Isothermal differential scanning calorimetry (DSC) was used to investigate the conversion during cure. Dynamic DSC scans at multiple heating rates revealed conversion-dependent activation energy by Ozawa-Flynn-Wall analysis. The glass transition temperature, storage modulus, and loss modulus for NCA/DCPD and NCA/CL copolymers with different cross-linking agent loading were compared using dynamic mechanical analysis. Cross-link density was examined to explain the very different dynamic mechanical behavior. Mechanical stress-strain curves were developed through tensile test, and thermal stability of the cross-linked polymers was evaluated by thermogravimetric analysis to further investigate the structure-property relationships in these systems.

Low Catalyst Loadings in Olefin Metathesis: Synthesis of Nitrogen Heterocycles by Ring Closing Metathesis

PubMed Central

Kuhn, Kevin M.; Champagne, Timothy M.; Hong, Soon Hyeok; Wei, Wen-Hao; Nickel, Andrew; Lee, Choon Woo; Virgil, Scott C.; Grubbs, Robert H.; Pederson, Richard L.

2010-01-01

(eq 1) A series of ruthenium catalysts have been screened under ring closing metathesis (RCM) conditions to produce five-, six-, and seven-membered carbamate-protected cyclic amines. Many of these catalysts demonstrated excellent RCM activity and yields with as low as 500 ppm catalyst loadings. RCM of the five-membered carbamate-series could be run neat, the six-membered carbamate-series could be run at 1.0 M concentrations and the seven-membered carbamate-series worked best at 0.2 M to 0.05 M concentrations. PMID:20141172

Highly efficient conversion of plant oil to bio-aviation fuel and valuable chemicals by combination of enzymatic transesterification, olefin cross-metathesis, and hydrotreating.

PubMed

Wang, Meng; Chen, Mojin; Fang, Yunming; Tan, Tianwei

2018-01-01

The production of fuels and chemicals from renewable resources is increasingly important due to the environmental concern and depletion of fossil fuel. Despite the fast technical development in the production of aviation fuels, there are still several shortcomings such as a high cost of raw materials, a low yield of aviation fuels, and poor process techno-economic consideration. In recent years, olefin metathesis has become a powerful and versatile tool for generating new carbon-carbon bonds. The cross-metathesis reaction, one kind of metathesis reaction, has a high potential to efficiently convert plant oil into valuable chemicals, such as α-olefin and bio-aviation fuel by combining with a hydrotreatment process. In this research, an efficient, four-step conversion of plant oil into bio-aviation fuel and valuable chemicals was developed by the combination of enzymatic transesterification, olefin cross-metathesis, and hydrotreating. Firstly, plant oil including oil with poor properties was esterified to fatty acid methyl esters by an enzyme-catalyzed process. Secondly, the fatty acid methyl esters were partially hydrotreated catalytically to transform poly-unsaturated fatty acid such as linoleic acid into oleic acid. The olefin cross-metathesis then transformed the oleic acid methyl ester (OAME) into 1-decene and 1-decenoic acid methyl ester (DAME). The catalysts used in this process were prepared/selected in function of the catalytic reaction and the reaction conditions were optimized. The carbon efficiency analysis of the new process illustrated that it was more economically feasible than the traditional hydrotreatment process. A highly efficient conversion process of plant oil into bio-aviation fuel and valuable chemicals by the combination of enzymatic transesterification, olefin cross-metathesis, and hydrotreatment with prepared and selected catalysts was designed. The reaction conditions were optimized. Plant oil was transformed into bio-aviation fuel and a high value α-olefin product with high carbon utilization.

Design of Heterogeneous Hoveyda-Grubbs Second-Generation Catalyst-Lipase Conjugates.

PubMed

Neville, Anthony; Iniesta, Javier; Palomo, Jose M

2016-12-06

Heterogeneous catalysts have been synthesi zed by the conjugation of Hoveyda-Grubbs second-generation catalyst with a lipase. The catalytic properties of the organometallic compound in solution were firstly optimized, evaluating the activity of Ru in the ring-closing metathesis of diethyldiallymalonate at 25 °C at different solvents and in the presence of different additives. The best result was found using tetrahydrofuran as a solvent. Some additives such as phenylboronic acid or polyetheneglycol slightly improved the activity of the Ru catalyst whereas others, such as pyridine or dipeptides affected it negatively. The organometallic compound immobilized on functionalized-surface materials activated with boronic acid or epoxy groups (around 50-60 µg per mg support) and showed 50% conversion at 24 h in the ring-closing metathesis. Cross-linked enzyme aggregates (CLEA's) of the Hoveyda-Grubbs second-generation catalyst with Candida antarctica lipase (CAL-B) were prepared, although low Ru catalyst was found to be translated in low conversion. Therefore, a sol-gel preparation of the Hoveyda-Grubbs second-generation and CAL-B was performed. This catalyst exhibited good activity in the metathesis of diethyldiallymalonate in toluene and in aqueous media. Finally, a new sustainable approach was used by the conjugation lipase-Grubbs in solid phase in aqueous media. Two strategies were used: one using lipase previously covalently immobilized on an epoxy-Sepharose support (hydrophilic matrix) and then conjugated with grubbs; and in the second, the free lipase was incubated with organometallic in aqueous solution and then immobilized on epoxy-Sepharose. The different catalysts showed excellent conversion values in the ring-closing metathesis of diethyldiallymalonate in aqueous media at 25 °C.

Synthesis and Properties of a Precision Sulfonated Trimethylene-Styrene Polyelectrolyte

NASA Astrophysics Data System (ADS)

Kennemur, Justin; Neary, William; Bohlmann, Michele; Kendrick, Aaron

We recently reported successful ring-opening metathesis polymerization of 4-phenylcyclopentene to afford a precision ethylene-styrene type copolymer with a phenyl branch at exactly every fifth carbon along the backbone following mild hydrogenation of the backbone olefins. (http://dx.doi.org/10.1002/marc.201600121) Compared to polystyrene, this material shows a markedly reduced glass transition temperature (Tg 17 °C) and remains amorphous. We have now extended the function of this polymer via sulfonation of the phenyl branches to produce a precision polyelectrolyte with an ionic charge spacing at every fifth carbon along the chain. The reduced yet precise charge density coupled with the low Tg of the native material translates into a variety of properties that are unique to this system and potentially useful as an addition to the limited set of available polyelectrolyte materials. Synthetic aspects in addition to thermal and mechanical properties will be discussed. Graduate Student.

Molecular Blends of Methylated-Poly(ethylenimine) and Amorphous Porous Organic Cages for SO 2 Adsorption

DOE PAGES

Zhu, Guanghui; Carrillo, Jan-Michael Y.; Sujan, Achintya; ...

2018-05-30

Porous organic cages (POCs) are emerging porous materials that exhibit intriguing properties in the areas of self-assembly, host-guest interaction, and solution processability. Here in this work, we explore the applicability of POCs as molecular porous supports for polymeric amines. We find that primary amines in poly(ethylenimine) (PEI) can undergo metathesis with the imine bonds present in POCs, resulting in non-porous products. This problem can be overcome by transforming the primary amines in PEI to tertiary amines via methylation. The methylated PEI (mPEI) forms homogeneous composites with amorphous scrambled porous organic cages (ASPOCs) without undesired reactions or phase separation. The microscopicmore » structure of the composites is studied using molecular dynamics simulations. Finally, these composite materials are evaluated as adsorbents for low concentration SO2 (200 ppm) adsorption and show good thermal and cyclic stability.« less

Antimicrobial Polymers Prepared by ROMP with Unprecedented Selectivity: A Molecular Construction Kit Approach

PubMed Central

Lienkamp, Karen; Madkour, Ahmad E.; Musante, Ashlan; Nelson, Christopher F.; Nüsslein, Klaus

2014-01-01

Synthetic Mimics of Antimicrobial Peptides (SMAMPs) imitate natural host-defense peptides, a vital component of the body’s immune system. This work presents a molecular construction kit that allows the easy and versatile synthesis of a broad variety of facially amphiphilic oxanorbornene-derived monomers. Their ring-opening metathesis polymerization (ROMP) and deprotection provide several series of SMAMPs. Using amphiphilicity, monomer feed ratio, and molecular weight as parameters, polymers with 533 times higher selectivitiy (selecitviy = hemolytic concentration/minimum inhibitory concentration) for bacteria over mammalian cells were discovered. Some of these polymers were 50 times more selective for Gram-positive over Gram-negative bacteria while other polymers surprisingly showed the opposite preference. This kind of “double selectivity” (bacteria over mammalian and one bacterial type over another) is unprecedented in other polymer systems and is attributed to the monomer’s facial amphiphilicity. PMID:18593128

A facile route to ketene-functionalized polymers for general materials applications

NASA Astrophysics Data System (ADS)

Leibfarth, Frank A.; Kang, Minhyuk; Ham, Myungsoo; Kim, Joohee; Campos, Luis M.; Gupta, Nalini; Moon, Bongjin; Hawker, Craig J.

2010-03-01

Function matters in materials science, and methodologies that provide paths to multiple functionality in a single step are to be prized. Therefore, we introduce a robust and efficient strategy for exploiting the versatile reactivity of ketenes in polymer chemistry. New monomers for both radical and ring-opening metathesis polymerization have been developed, which take advantage of Meldrum's acid as both a synthetic building block and a thermolytic precursor to dialkyl ketenes. The ketene-functionalized polymers are directly detected by their characteristic infrared absorption and are found to be stable under ambient conditions. The inherent ability of ketenes to provide crosslinking via dimerization and to act as reactive chemical handles via addition, provides simple methodology for application in complex materials challenges. Such versatile characteristics are illustrated by covalently attaching and patterning a dye through microcontact printing. The strategy highlights the significant opportunities afforded by the traditionally neglected ketene functional group in polymer chemistry.

Molecular Blends of Methylated-Poly(ethylenimine) and Amorphous Porous Organic Cages for SO 2 Adsorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Guanghui; Carrillo, Jan-Michael Y.; Sujan, Achintya

Porous organic cages (POCs) are emerging porous materials that exhibit intriguing properties in the areas of self-assembly, host-guest interaction, and solution processability. Here in this work, we explore the applicability of POCs as molecular porous supports for polymeric amines. We find that primary amines in poly(ethylenimine) (PEI) can undergo metathesis with the imine bonds present in POCs, resulting in non-porous products. This problem can be overcome by transforming the primary amines in PEI to tertiary amines via methylation. The methylated PEI (mPEI) forms homogeneous composites with amorphous scrambled porous organic cages (ASPOCs) without undesired reactions or phase separation. The microscopicmore » structure of the composites is studied using molecular dynamics simulations. Finally, these composite materials are evaluated as adsorbents for low concentration SO2 (200 ppm) adsorption and show good thermal and cyclic stability.« less

Block copolymer with simultaneous electric and ionic conduction for use in lithium ion batteries

DOEpatents

Javier, Anna Esmeralda K; Balsara, Nitash Pervez; Patel, Shrayesh Naran; Hallinan, Jr., Daniel T

2013-10-08

Redox reactions that occur at the electrodes of batteries require transport of both ions and electrons to the active centers. Reported is the synthesis of a block copolymer that exhibits simultaneous electronic and ionic conduction. A combination of Grignard metathesis polymerization and click reaction was used successively to synthesize the block copolymer containing regioregular poly(3-hexylthiophene) (P3HT) and poly(ethylene oxide) (PEO) segments. The P3HT-PEO/LiTFSI mixture was then used to make a lithium battery cathode with LiFePO.sub.4 as the only other component. All-solid lithium batteries of the cathode described above, a solid electrolyte and a lithium foil as the anode showed capacities within experimental error of the theoretical capacity of the battery. The ability of P3HT-PEO to serve all of the transport and binding functions required in a lithium battery electrode is thus demonstrated.

The Influence of the Anionic Counter-Ion on the Activity of Ammonium Substituted Hoveyda-Type Olefin Metathesis Catalysts in Aqueous Media

NASA Astrophysics Data System (ADS)

Gułajski, Łukasz; Grela, Karol

Polar olefin metathesis catalysts, bearing an ammonium group are presented. The electron withdrawing ammonium group not only activates the catalysts electronically, but at the same time makes the catalysts more hydrophilic. Catalysts can be therefore efficiently used not only in traditional media, such as methylene chloride and toluene, but also in technical-grade alcohols, alcohol— water mixtures and in neat water. Finally, in this overview the influence of the anionic counter-ion on the activity of ammonium substituted Hoveyda-type olefin metathesis catalysts in aqueous media is presented.

Tailoring Pore Size and Chemical Interior of near 1 nm Sized Pores in a Nanoporous Polymer Based on a Discotic Liquid Crystal

PubMed Central

2017-01-01

A triazine based disc shaped molecule with two hydrolyzable units, imine and ester groups, was polymerized via acyclic diene metathesis in the columnar hexagonal (Colhex) LC phase. Fabrication of a cationic nanoporous polymer (pore diameter ∼1.3 nm) lined with ammonium groups at the pore surface was achieved by hydrolysis of the imine linkage. Size selective aldehyde uptake by the cationic porous polymer was demonstrated. The anilinium groups in the pores were converted to azide as well as phenyl groups by further chemical treatment, leading to porous polymers with neutral functional groups in the pores. The pores were enlarged by further hydrolysis of the ester groups to create ∼2.6 nm pores lined with −COONa surface groups. The same pores could be obtained in a single step without first hydrolyzing the imine linkage. XRD studies demonstrated that the Colhex order of the monomer was preserved after polymerization as well as in both the nanoporous polymers. The porous anionic polymer lined with −COOH groups was further converted to the −COOLi, −COONa, −COOK, −COOCs, and −COONH4 salts. The porous polymer lined with −COONa groups selectively adsorbs a cationic dye, methylene blue, over an anionic dye. PMID:28416888

High-performance vitrimers from commodity thermoplastics through dioxaborolane metathesis

NASA Astrophysics Data System (ADS)

Röttger, Max; Domenech, Trystan; van der Weegen, Rob; Breuillac, Antoine; Nicolaÿ, Renaud; Leibler, Ludwik

2017-04-01

Windmills, cars, and dental restoration demand polymer materials and composites that are easy to process, assemble, and recycle while exhibiting outstanding mechanical, thermal, and chemical resistance. Vitrimers, which are polymer networks able to shuffle chemical bonds through exchange reactions, could address these demands if they were prepared from existing plastics and processed with fast production rates and current equipment. We report the metathesis of dioxaborolanes, which is rapid and thermally robust, and use it to prepare vitrimers from polymers as different as poly(methyl methacrylate), polystyrene, and high-density polyethylene that, although permanently cross-linked, can be processed multiple times by means of extrusion or injection molding. They show superior chemical resistance and dimensional stability and can be efficiently assembled. The strategy is applicable to polymers with backbones made of carbon-carbon single bonds.

Catalytic metathesis of carbon dioxide with heterocumulenes mediated by titanium isopropoxide.

PubMed

Ghosh, Rajshekhar; Samuelson, Ashoka G

2005-04-21

The insertion of an isopropoxide ligand of titanium isopropoxide into heterocumulenes gives a product that carries out metathesis at elevated temperatures by undergoing insertion of a second heterocumulene in a head to head fashion, followed by an extrusion reaction.

Water-Free Rare Earth-Prussian Blue Type Analogues: Synthesis, Structure, Computational Analysis, and Magnetic Data of {Ln[superscript III](DMF)[subscript 6]Fe[superscript III](CN)[subcsript 6]}[subscript infinity] (Ln = Rare Earths Excluding Pm)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilson, Duane C.; Liu, Shengming; Chen, Xuenian

2009-11-04

Water-free rare earth(III) hexacyanoferrate(III) complexes, {l_brace}Ln(DMF){sub 6}({mu}-CN){sub 2}Fe(CN){sub 4}{r_brace}{sub {infinity}} (DMF = N,N-dimethylformamide; Ln = Sm, 1; Eu, 2; Gd, 3; Tb, 4; Dy, 5; Ho, 6; Er, 7; Tm, 8; Yb, 9; Lu, 10; Y, 11; La, 12; Ce, 13; Pr, 14; Nd, 15), were synthesized in dry DMF through the metathesis reactions of [(18-crown-6)K]{sub 3}Fe(CN){sub 6} with LnX{sub 3}(DMF){sub n} (X = Cl or NO{sub 3}). Anhydrous DMF solutions of LnX{sub 3}(DMF){sub n} were prepared at room temperature from LnCl{sub 3} or LnX{sub 3} {center_dot} nH{sub 2}O under a dynamic vacuum. All compounds were characterized by IR, X-raymore » powder diffraction (except for 10), and single crystal X-ray diffraction (except for 2, 7, 10). Infrared spectra reveal that a monotonic, linear relationship exists between the ionic radius of the lanthanide and the {nu}{sub {mu}-CN} stretching frequency of 1-10, 12-15 while 11 deviates slightly from the ionic radius relationship. X-ray powder diffraction data are in agreement with powder patterns calculated from single crystal X-ray diffraction results, a useful alternative for bulk sample confirmation when elemental analysis data are difficult to obtain. Eight-coordinate Ln(III) metal centers are observed for all structures. trans-cyanide units of [Fe(CN){sub 6}]{sup 3-} formed isocyanide linkages to Ln(III) resulting in one-dimensional polymeric chains. Structures of compounds 1-9 and 11 are isomorphous, crystallizing in the space group C2/c. Structures of compounds 12-15 are also isomorphous, crystallizing in the space group P2/n. One unique polymeric chain exists in the structures of 1-9 and 11 while two unique polymeric chains exist in structures of 12-15. One of the polymeric chains of 12-15 is similar to that observed for 1-9, 11 while the other is more distorted and has a shorter Ln-Fe distance. Magnetic susceptibility measurements for compounds 3-6, 8, 11 were performed on polycrystalline samples of the compounds.« less

Accuracy of a new ring-opening metathesis elastomeric dental impression material with spray and immersion disinfection.

PubMed

Kronström, Mats H; Johnson, Glen H; Hompesch, Richard W

2010-01-01

A new elastomeric impression material has been formulated with a ring-opening metathesis chemistry. In addition to other properties of clinical significance, the impression accuracy must be confirmed. The purpose of this study was to compare the accuracy of the new elastomeric impression material with vinyl polysiloxane and polyether following both spray and immersion disinfection. Impressions of a modified dentoform with a stainless steel crown preparation in the lower right quadrant were made, and type IV gypsum working casts and dies were formed. Anteroposterior (AP), cross-arch (CA), buccolingual (BL), mesiodistal (MD), occlusogingivobuccal (OGB), and occlusogingivolingual (OGL) dimensions were measured using a microscope. Working cast and die dimensions were compared to those of the master model. The impression materials were a newly formulated, ring-opening metathesis-polymerization impression material (ROMP Cartridge Tray and ROMP Volume Wash), vinyl polysiloxane (VPS, Aquasil Ultra Monophase/LV), and a polyether (PE, Impregum Penta Soft/Permadyne Garant L). Fifteen impressions with each material were made, of which 5 were disinfected by spray for 10 minutes (CaviCide), 5 were disinfected by immersion for 90 minutes (ProCide D), and 5 were not disinfected. There were significant cross-product interactions with a 2-way ANOVA, so a 1-way ANOVA and Dunnett's T3 multiple comparison test were used to compare the dimensional changes of the 3 impression materials, by disinfection status and for each location (alpha=.05). For ROMP, there were no significant differences from the master, for any dimension, when comparing the control and 2 disinfectant conditions. No significant differences were detected among the 3 impression materials for CA, BL, and MD. The working die dimensions of OGB and OGL for VPS with immersion disinfection were significantly shorter than with PE and ROMP (P<.05). Overall, the AP dimension was more accurate than CA, and the BL of working dies was 0.040 mm greater in diameter than MD. The accuracy of gypsum working casts and working dies from the new and 2 existing types of impression material were similar, for both spray and immersion disinfection. Judicious application of a die spacer can compensate for the small differences observed. VPS may require additional laboratory accommodation to compensate for a shorter working die. Copyright 2010 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

A stereoselective synthesis of (+)-physoperuvine using a tandem aza-Claisen rearrangement and ring closing metathesis reaction.

PubMed

Zaed, Ahmed M; Swift, Michael D; Sutherland, Andrew

2009-07-07

A stereoselective synthesis of (+)-physoperuvine, a tropane alkaloid from Physalis peruviana Linne has been developed using a one-pot tandem aza-Claisen rearrangement and ring closing metathesis reaction to form the key amino-substituted cycloheptene ring.

Metathesis process for preparing an alpha, omega-functionalized olefin

DOEpatents

Burdett, Kenneth A.; Mokhtarzadeh, Morteza; Timmers, Francis J.

2010-10-12

A cross-metathesis process for preparing an .alpha.,.omega.-functionalized olefin, such as methyl 9-decenoate, and an .alpha.-olefin having three or more carbon atoms, such as 1-decene. The process involves contacting in a first reaction zone an .alpha.-functionalized internal olefin, such as methyl oleate, and an .alpha.-olefinic monomer having three or more carbon atoms, such as 1-decene, with a first metathesis catalyst to prepare an effluent stream containing the .alpha.,.omega.-functionalized olefin, such as methyl 9-decenoate, an unfunctionalized internal olefin, such as 9-octadecene, unconverted reactant olefins, and optionally, an .alpha.,.omega.-difunctionalized internal olefinic dimer, such as dimethyl 9-octadecen-1,18-dioate; separating said effluent streams; then contacting in a second reaction zone the unfunctionalized internal olefin with ethylene in the presence of a second metathesis catalyst to obtain a second product effluent containing the .alpha.-olefinic monomer having three or more carbon atoms; and cycling a portion of the .alpha.-olefinic monomer stream(s) to the first zone.

Ruthenium-catalyzed intramolecular metathesis of dienes and its application in the synthesis of bridged and spiro azabicycles

NASA Astrophysics Data System (ADS)

Kuznetsov, N. Yu; Bubnov, Yu N.

2015-07-01

The review presents a historical excursion into catalytic alkene metathesis, covering the problems of history of the discovery of this process, as well as investigations on the properties, structure and reactivity of the most popular ruthenium catalysts for metathesis, mechanism of their action and decomposition. The main part covers studies devoted to the syntheses of bridged azabicyclic and 1-azaspirocyclic compounds comprising the intramolecular metathesis of dienes as the key step. The formation of a bicyclic skeleton of a series of natural bridged (cocaine, ferruginine, calystegines, and anatoxin-a) and spiro (pinnaic acids, halichlorine, hystrionicotoxin, and cephalotaxine) azabicycles, as well as their analogues and compounds with larger rings is demonstrated. The methods for the synthesis of diene precursors and the conditions for final assembling of the bicyclic compounds are considered in detail. The generalization of the literature data allows one to efficiently carry out the mentioned process taking into account the most important features. The bibliography includes 129 references.

Synthesis of E- and Z-trisubstituted alkenes by catalytic cross-metathesis

NASA Astrophysics Data System (ADS)

Nguyen, Thach T.; Koh, Ming Joo; Mann, Tyler J.; Schrock, Richard R.; Hoveyda, Amir H.

2017-12-01

Catalytic cross-metathesis is a central transformation in chemistry, yet corresponding methods for the stereoselective generation of acyclic trisubstituted alkenes in either the E or the Z isomeric forms are not known. The key problems are a lack of chemoselectivity—namely, the preponderance of side reactions involving only the less hindered starting alkene, resulting in homo-metathesis by-products—and the formation of short-lived methylidene complexes. By contrast, in catalytic cross-coupling, substrates are more distinct and homocoupling is less of a problem. Here we show that through cross-metathesis reactions involving E- or Z-trisubstituted alkenes, which are easily prepared from commercially available starting materials by cross-coupling reactions, many desirable and otherwise difficult-to-access linear E- or Z-trisubstituted alkenes can be synthesized efficiently and in exceptional stereoisomeric purity (up to 98 per cent E or 95 per cent Z). The utility of the strategy is demonstrated by the concise stereoselective syntheses of biologically active compounds, such as the antifungal indiacen B and the anti-inflammatory coibacin D.

Synthesis of E- and Z-trisubstituted alkenes by catalytic cross-metathesis.

PubMed

Nguyen, Thach T; Koh, Ming Joo; Mann, Tyler J; Schrock, Richard R; Hoveyda, Amir H

2017-12-20

Catalytic cross-metathesis is a central transformation in chemistry, yet corresponding methods for the stereoselective generation of acyclic trisubstituted alkenes in either the E or the Z isomeric forms are not known. The key problems are a lack of chemoselectivity-namely, the preponderance of side reactions involving only the less hindered starting alkene, resulting in homo-metathesis by-products-and the formation of short-lived methylidene complexes. By contrast, in catalytic cross-coupling, substrates are more distinct and homocoupling is less of a problem. Here we show that through cross-metathesis reactions involving E- or Z-trisubstituted alkenes, which are easily prepared from commercially available starting materials by cross-coupling reactions, many desirable and otherwise difficult-to-access linear E- or Z-trisubstituted alkenes can be synthesized efficiently and in exceptional stereoisomeric purity (up to 98 per cent E or 95 per cent Z). The utility of the strategy is demonstrated by the concise stereoselective syntheses of biologically active compounds, such as the antifungal indiacen B and the anti-inflammatory coibacin D.

Refining of plant oils to chemicals by olefin metathesis.

PubMed

Chikkali, Samir; Mecking, Stefan

2012-06-11

Plant oils are attractive substrates for the chemical industry. Their scope for the production of chemicals can be expanded by sophisticated catalytic conversions. Olefin metathesis is an example, which also illustrates generic issues of "biorefining" to chemicals. Utilization on a large scale requires high catalyst activities, which influences the choice of the metathesis reaction. The mixture of different fatty acids composing a technical-grade plant oil substrate gives rise to a range of products. This decisively determines possible process schemes, and potentially provides novel chemicals and intermediates not employed to date. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Design and Stereoselective Preparation of a New Class of Chiral Olefin Metathesis Catalysts and Application to Enantioselective Synthesis of Quebrachamine: Catalyst Development Inspired by Natural Product Synthesis

PubMed Central

Sattely, Elizabeth S.; Meek, Simon J.; Malcolmson, Steven J.; Schrock, Richard R.; Hoveyda, Amir H.

2010-01-01

A total synthesis of the Aspidosperma alkaloid quebrachamine in racemic form is first described. A key catalytic ring-closing metathesis of an achiral triene is used to establish the all-carbon quaternary stereogenic center and the tetracyclic structure of the natural product; the catalytic transformation proceeds with reasonable efficiency through the use of existing achiral Ru or Mo catalysts. Ru- or Mo-based chiral olefin metathesis catalysts have proven to be inefficient and entirely nonselective in cases where the desired product is observed. In the present study, the synthesis route thus serves as a platform for the discovery of new olefin metathesis catalysts that allow for efficient completion of an enantioselective synthesis of quebrachamine. Accordingly, on the basis of mechanistic principles, stereogenic-at-Mo complexes bearing only monodentate ligands have been designed. The new catalysts provide significantly higher levels of activity than observed with the previously reported Ru- or Mo-based complexes. Enantiomerically enriched chiral alkylidenes are generated through diastereoselective reactions involving achiral Mo-based bispyrrolides and enantiomerically pure silyl-protected binaphthols. Such chiral catalysts initiate the key enantioselective ring-closing metathesis step in the total synthesis of quebrachamine efficiently (1 mol % loading, 22 °C, 1 h, >98% conversion, 84% yield) and with high selectivity (98:2 er, 96% ee). PMID:19113867

Synthesis of the carbocyclic core of the cornexistins by ring-closing metathesis.

PubMed

Clark, J Stephen; Marlin, Frederic; Nay, Bastien; Wilson, Claire

2003-01-09

An advanced intermediate in the synthesis of the phytotoxins cornexistin and hydroxycornexistin has been synthesized. Sequential palladium-mediated sp(2)-sp(3) fragment coupling and ring-closing diene metathesis have been used to construct the nine-membered carbocyclic core found in the natural products. [reaction--see text

Recent advances in the development of alkyne metathesis catalysts

PubMed Central

Wu, Xian

2011-01-01

Summary The number of well-defined molybdenum and tungsten alkylidyne complexes that are able to catalyze alkyne metathesis reactions efficiently has been significantly expanded in recent years.The latest developments in this field featuring highly active imidazolin-2-iminato- and silanolate–alkylidyne complexes are outlined in this review. PMID:21286398

Omega-functionalized fatty acids, alcohols, and ethers via olefin metathesis

USDA-ARS?s Scientific Manuscript database

Methyl 17-hydroxy stearate was converted to methyl octadec-16-enoate using copper sulfate adsorbed on silica gel. This compound, possessing unsaturation at the opposite end of the chain from the carboxylate, served as a useful substrate for the olefin metathesis reaction. As a result, several fatt...

A two-color fluorogenic carbene complex for tagging olefins via metathesis reaction

NASA Astrophysics Data System (ADS)

Wirtz, Marcel; Grüter, Andreas; Heib, Florian; Huch, Volker; Zapp, Josef; Herten, Dirk-Peter; Schmitt, Michael; Jung, Gregor

2015-12-01

We describe a fluorogenic ruthenium (II) carbene complex in which the chromophore is directly connected to the metal center. The compound introduces a boron dipyrromethene (BODIPY) moiety into target double bonds by metathesis. Tagging of terminal double bonds is demonstrated on immobilized styrene units on a glass surface. We also show that two compounds with distinguishable fluorescence properties are formed in the model reaction with styrene. The outcome of the metathesis reaction is characterized by 19F-NMR, optical spectroscopy, and, finally, single-molecule trajectories. This labeling scheme, in our perception, is of particular interest in the fields of interfacial science and biorthogonal ligation in combination with super-resolution imaging.

Methods for the synthesis of olefins and derivatives

DOEpatents

Burk, Mark J; Pharkya, Priti; Van Dien, Stephen J; Burgard, Anthony P; Schilling, Christophe H

2013-06-04

The invention provides a method of producing acrylic acid. The method includes contacting fumaric acid with a sufficient amount of ethylene in the presence of a cross-metathesis transformation catalyst to produce about two moles of acrylic acid per mole of fumaric acid. Also provided is an acrylate ester. The method includes contacting fumarate diester with a sufficient amount of ethylene in the presence of a cross-metathesis transformation catalyst to produce about two moles of acrylate ester per mole of fumarate diester. An integrated process for process for producing acrylic acid or acrylate ester is provided which couples bioproduction of fumaric acid with metathesis transformation. An acrylic acid and an acrylate ester production also is provided.

Methods for the synthesis of olefins and derivatives

DOEpatents

Burk, Mark J [San Diego, CA; Pharkya, Priti [San Diego, CA; Van Dien, Stephen J [Encinitas, CA; Burgard, Anthony P [Bellefonte, PA; Schilling, Christophe H [San Diego, CA

2011-09-27

The invention provides a method of producing acrylic acid. The method includes contacting fumaric acid with a sufficient amount of ethylene in the presence of a cross-metathesis transformation catalyst to produce about two moles of acrylic acid per mole of fumaric acid. Also provided is an acrylate ester. The method includes contacting fumarate diester with a sufficient amount of ethylene in the presence of a cross-metathesis transformation catalyst to produce about two moles of acrylate ester per mole of fumarate diester. An integrated process for process for producing acrylic acid or acrylate ester is provided which couples bioproduction of fumaric acid with metathesis transformation. An acrylic acid and an acrylate ester production also is provided.

Methods for synthesis of olefins and derivatives

DOEpatents

Burk, Mark J.; Pharkya, Priti; Van Dien, Stephen J.; Burgard, Anthony P.; Schilling, Christophe H.

2016-06-14

The invention provides a method of producing acrylic acid. The method includes contacting fumaric acid with a sufficient amount of ethylene in the presence of a cross-metathesis transformation catalyst to produce about two moles of acrylic acid per mole of fumaric acid. Also provided is an acrylate ester. The method includes contacting fumarate diester with a sufficient amount of ethylene in the presence of a cross-metathesis transformation catalyst to produce about two moles of acrylate ester per mole of fumarate diester. An integrated process for process for producing acrylic acid or acrylate ester is provided which couples bioproduction of fumaric acid with metathesis transformation. An acrylic acid and an acrylate ester production also is provided.

Recruiting the Students to Fight Cancer: Total Synthesis of Goniothalamin

ERIC Educational Resources Information Center

Nahra, Fady; Riant, Olivier

2015-01-01

A modified total synthesis of (S)-goniothalamin is described for an advanced course in organic chemistry. This experiment gives students an opportunity to handle organometallic reagents and perform an enzymatic kinetic resolution and a metathesis reaction, all in the same synthesis. Furthermore, students learn flame-drying techniques for the…

Entrapped Single Tungstate Site in Zeolite for Cooperative Catalysis of Olefin Metathesis with Brønsted Acid Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Pu; Ye, Lin; Sun, Zhenyu

Industrial olefin metathesis catalysts generally suffer from low reaction rates and require harsh reaction conditions for moderate activities. This is due to their inability to prevent metathesis active sites (MAS) from aggregation and their intrinsic poor adsorption and activation of olefin molecules. Here, isolated tungstate species as single molecular MAS is immobilized inside zeolite pores by Bronsted acid sites (BAS) on the inner surface. It is demonstrated for the first time that unoccupied BAS in atomic proximity to MAS enhance olefin adsorption and greatly facilitate the formation of metallocycle intermediates in a stereospecific manner. Thus, effective cooperative catalysis takes placemore » over the BAS-MAS pair. In consequence, for the cross-metathesis of ethene and trans-2-butene to propene, under the same mild reaction conditions, the propene production rate over WOx/USY is ca. 7,300 times that over the industrial WO3/SiO2 based catalyst. A propene yield up to 79% (80% selectivity) without observable deactivation was obtained over WOx/USY for a wide range of reaction conditions.« less

Unearthing a Well-Defined Highly Active Bimetallic W/Ti Precatalyst Anchored on a Single Silica Surface for Metathesis of Propane.

PubMed

Samantaray, Manoja K; Kavitake, Santosh; Morlanés, Natalia; Abou-Hamad, Edy; Hamieh, Ali; Dey, Raju; Basset, Jean-Marie

2017-03-08

Two compatible organometallic complexes, W(Me) 6 (1) and TiNp 4 (2), were successively anchored on a highly dehydroxylated single silica support (SiO 2-700 ) to synthesize the well-defined bimetallic precatalyst [(≡Si-O-)W(Me) 5 (≡Si-O-)Ti(Np) 3 ] (4). Precatalyst 4 was characterized at the molecular level using advanced surface organometallic chemistry (SOMC) characterization techniques. The strong autocorrelation observed between methyl of W and Ti in 1 H- 1 H multiple-quantum NMR spectra demonstrates that W and Ti species are in close proximity to each other. The bimetallic precatalyst 4, with a turnover number (TON) of 9784, proved to be significantly more efficient than the silica-supported monometallic catalyst [(≡Si-O-)W(Me) 5 ] (3), with a TON of 98, for propane metathesis at 150 °C in a flow reactor. The dramatic improvement in the activity signifies the cooperativity between Ti and W and indicates that the key step of alkane metathesis (C-H bond activation followed by β-H elimination) occurs on Ti, followed by olefin metathesis, which occurs on W. We have demonstrated the influence and importance of proximity of Ti to W for achieving such a significantly high activity. This is the first report demonstrating the considerably high activity (TON = 9784) in propane metathesis at moderate temperature (150 °C) using a well-defined bimetallic system prepared via the SOMC approach.

Bimolecular Coupling as a Vector for Decomposition of Fast-Initiating Olefin Metathesis Catalysts.

PubMed

Bailey, Gwendolyn A; Foscato, Marco; Higman, Carolyn S; Day, Craig S; Jensen, Vidar R; Fogg, Deryn E

2018-06-06

The correlation between rapid initiation and rapid decomposition in olefin metathesis is probed for a series of fast-initiating, phosphine-free Ru catalysts: the Hoveyda catalyst HII, RuCl 2 (L)(═CHC 6 H 4 - o-O i Pr); the Grela catalyst nG (a derivative of HII with a nitro group para to O i Pr); the Piers catalyst PII, [RuCl 2 (L)(═CHPCy 3 )]OTf; the third-generation Grubbs catalyst GIII, RuCl 2 (L)(py) 2 (═CHPh); and dianiline catalyst DA, RuCl 2 (L)( o-dianiline)(═CHPh), in all of which L = H 2 IMes = N,N'-bis(mesityl)imidazolin-2-ylidene. Prior studies of ethylene metathesis have established that various Ru metathesis catalysts can decompose by β-elimination of propene from the metallacyclobutane intermediate RuCl 2 (H 2 IMes)(κ 2 -C 3 H 6 ), Ru-2. The present work demonstrates that in metathesis of terminal olefins, β-elimination yields only ca. 25-40% propenes for HII, nG, PII, or DA, and none for GIII. The discrepancy is attributed to competing decomposition via bimolecular coupling of methylidene intermediate RuCl 2 (H 2 IMes)(═CH 2 ), Ru-1. Direct evidence for methylidene coupling is presented, via the controlled decomposition of transiently stabilized adducts of Ru-1, RuCl 2 (H 2 IMes)L n (═CH 2 ) (L n = py n' ; n' = 1, 2, or o-dianiline). These adducts were synthesized by treating in situ-generated metallacyclobutane Ru-2 with pyridine or o-dianiline, and were isolated by precipitating at low temperature (-116 or -78 °C, respectively). On warming, both undergo methylidene coupling, liberating ethylene and forming RuCl 2 (H 2 IMes)L n . A mechanism is proposed based on kinetic studies and molecular-level computational analysis. Bimolecular coupling emerges as an important contributor to the instability of Ru-1, and a potentially major pathway for decomposition of fast-initiating, phosphine-free metathesis catalysts.

Casting Molding of PDCPD Material for Purpose of Car’s Power Steering Body

NASA Astrophysics Data System (ADS)

Grabowski, L.; Baier, A.; Sobek, M.

2018-01-01

The growing industry of polymer and composite materials is facing new challenges posed by the automotive industry. In this industry, traditional materials such as steel and aluminum are widely replaced with plastic materials, including polymers. In the past, such behavior concerned design and interior elements, but more and more often plastics are used in the case of load-bearing elements, i.e. those that require high strength and durability nowadays. This kind of materials are also often used in safety systems or driver assistance systems. Therefore, the aim of the activities described in this article are to carry out an innovative process of injection of cold polymeric material, PDCPD (Polidicyclopentadiene), polymerizing with the use of Metathesis reaction, which in 2005 was awarded the Nobel Prize. This injection applies to the worm gear components of the system, supports the power steering system of the passenger car. Also the process of selecting the appropriate parameters to carry out this process, guaranteeing the best quality of the obtained elements is necessary. The aim of the activities was to achieve a fully useful power steering support system, using a polymer body, which is replacing the aluminum. These activities were aimed at reducing the costs and weight of the final product. The injection process and the way to achieve the finished product were carried out in an innovative way, never used in industry before.

The Acquisition of Consonant Feature Sequences: Harmony, Metathesis, and Deletion Patterns in Phonological Development

ERIC Educational Resources Information Center

Gerlach, Sharon Ruth

2010-01-01

This dissertation examines three processes affecting consonants in child speech: harmony (long-distance assimilation) involving major place features as in "coat" [kouk]; long-distance metathesis as in "cup" [p[wedge]k]; and initial consonant deletion as in "fish" [is]. These processes are unattested in adult phonology, leading to proposals for…

Synthesis and Catalytic Activity of Ruthenium-Indenylidene Complexes for Olefin Metathesis: Microscale Experiments for the Undergraduate Inorganic or Organometallic Laboratories

ERIC Educational Resources Information Center

Pappenfus, Ted M.; Hermanson, David L.; Ekerholm, Daniel P.; Lilliquist, Stacie L.; Mekoli, Megan L.

2007-01-01

A series of experiments for undergraduate laboratory courses (e.g., inorganic, organometallic or advanced organic) have been developed. These experiments focus on understanding the design and catalytic activity of ruthenium-indenylidene complexes for olefin metathesis. Included in the experiments are the syntheses of two ruthenium-indenylidene…

Ring-Closing Metathesis: An Advanced Guided-Inquiry Experiment for the Organic Laboratory

ERIC Educational Resources Information Center

Schepmann, Hala G.; Mynderse, Michelle

2010-01-01

The design and implementation of an advanced guided-inquiry experiment for the organic laboratory is described. Grubbs's second-generation catalyst is used to effect the ring-closing metathesis of diethyl diallylmalonate. The reaction is carried out under an inert atmosphere at room temperature and monitored by argentic TLC. The crude reaction is…

Decoupling of ion conductivity from segmental dynamics in oligomeric ethylene oxide functionalized oxanorbornene dicarboximide homopolymers

DOE PAGES

Adams, Marisa; Richmond, Victoria; Smith, Douglas; ...

2017-03-24

Here, in order to design more effective solid polymer electrolytes, it is important to decouple ion conductivityfrom polymer segmental motion. To that end, novel polymers based on oxanorbornene dicarboximidemonomers with varying lengths of oligomeric ethylene oxide side chains have been synthesized usingring opening metathesis polymerization. These unique polymers have a fairly rigid and bulky backboneand were used to investigate the decoupling of ion motion from polymer segmental dynamics. Ionconductivity was measured using broadband dielectric spectroscopy for varying levels of added lithiumsalt. The conductivity data demonstrate six to seven orders of separation in timescale of ion conductivityfrom polymer segmental motion formore » polymers with shorter ethylene oxide side chains. However,commensurate changes in the glass transition temperatures T g reduce the effect of decoupling in ionconductivity and lead to lower conductivity at ambient conditions. These results suggest that both anincrease in decoupling and a reduction in T g might be required to develop solid polymer electrolytes withhigh ion conductivity at room temperature.« less

Covalently-bonded grafting of [Ln3(Benzimidazole)4]-arrayed (Ln = Tb, Nd, Yb or Er) complex monomers into PNBE (poly(norbornene)) with highly luminous color-purity green-light or efficient NIR luminescence

NASA Astrophysics Data System (ADS)

Liu, Lin; Fu, Guorui; Feng, Heini; Guan, Jiaqing; Li, Fengping; Lü, Xingqiang; Wong, Wai-Kwok; Jones, Richard A.

2017-07-01

Within series of Ln3-grafted polymers Poly({[Ln3(L)4(NO3)6]·(NO3)·(H3O)2}-co-NBE) (Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3; Ln = Nd, 4; Ln = Yb, 5; Ln = Er, 6 or Ln = Gd, 7) obtained from ring-opening metathesis polymerization (ROMP) of norbornene (NBE) with each of allyl-functionalized complex monomers {[Ln3(L)4(NO3)6]·(NO3)·(H3O)2} (HL = 4-allyl-2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol), PNBE-assisted effective energy transfer renders Poly(3-co-NBE) Tb3+-centered highly luminous color-purity green-light with an attractive quantum yield of 87% and efficient near-infrared (NIR) luminescence (ΦNdL = 0.61%; ΦYbL = 1.47% and ΦErL = 0.03%) for Nd3+-, Yb3+- or Er3+-grafted polymers.

Determination of airborne, volatile amines from polyurethane foams by sorption onto a high-capacity cation-exchange resin based on poly(succinic acid).

PubMed

Seeber, G; Buchmeiser, M R; Bonn, G K; Bertsch, T

1998-06-05

A high-capacity carboxylic acid-functionalized resin prepared by ring-opening metathesis polymerization based on cross-linked endo,endo-poly(norborn-2-ene-5,6-dicarboxylic acid) was used for the sampling of volatile, airborne amines from polyurethane (PU) foams. Six tertiary amines which represent commonly used promotors for the formation of PUs from diisocyanates and polyols, namely pentamethyldiethylenetriamine, diazabicyclooctane, N-methylmorpholine, N-ethylmorphine, 1,4-dimethylpiperazine and N,N-dimethylethanolamine, were sorbed onto the new resin. The sorption behavior of the new material was investigated in terms of loading capacities, the influence of concentration, flow-rate as well as of the amount of resin. Breakthrough curves were recorded from each single component as well as of mixtures thereof. Finally, the resin was used for the sampling of amines evaporating from PU foams applied in buildings. Further information about time dependent concentration profiles were obtained using a combination of GC-MS and Fourier transform IR spectroscopy.

Assessing synthetic strategies: total syntheses of (+/-)-neodolabellane-type diterpenoids.

PubMed

Valente, Cory; Organ, Michael G

2008-01-01

Two strategies, namely a cross-metathesis/ring-closing metathesis and Pd-catalyzed Stille allylation/Nozaki-Hiyama-Kishi coupling, are examined for the preparation of neodolabellane-type diterpenoids 1 and 2. Whereas the first approach possessed synthetic limitations, the latter was successfully employed to provide compounds 1 and 2 in 8.8% (14 steps) and 8% (15 steps) overall yields, respectively.

Methods of making organic compounds by metathesis

DOEpatents

Abraham, Timothy W.; Kaido, Hiroki; Lee, Choon Woo; Pederson, Richard L.; Schrodi, Yann; Tupy, Michael John

2015-09-01

Described are methods of making organic compounds by metathesis chemistry. The methods of the invention are particularly useful for making industrially-important organic compounds beginning with starting compositions derived from renewable feedstocks, such as natural oils. The methods make use of a cross-metathesis step with an olefin compound to produce functionalized alkene intermediates having a pre-determined double bond position. Once isolated, the functionalized alkene intermediate can be self-metathesized or cross-metathesized (e.g., with a second functionalized alkene) to produce the desired organic compound or a precursor thereto. The method may be used to make bifunctional organic compounds, such as diacids, diesters, dicarboxylate salts, acid/esters, acid/amines, acid/alcohols, acid/aldehydes, acid/ketones, acid/halides, acid/nitriles, ester/amines, ester/alcohols, ester/aldehydes, ester/ketones, ester/halides, ester/nitriles, and the like.

Functionalized linear and cyclic polyolefins

DOEpatents

Tuba, Robert; Grubbs, Robert H.

2018-02-13

This invention relates to methods and compositions for preparing linear and cyclic polyolefins. More particularly, the invention relates to methods and compositions for preparing functionalized linear and cyclic polyolefins via olefin metathesis reactions. Polymer products produced via the olefin metathesis reactions of the invention may be utilized for a wide range of materials applications. The invention has utility in the fields of polymer and materials chemistry and manufacture.

Catalytic Enantioselective Olefin Metathesis in Natural Product Synthesis. Chiral Metal-Based Complexes that Deliver High Enantioselectivity and More

PubMed Central

Malcolmson, Steven J.; Meek, Simon J.; Zhugralin, Adil R.

2012-01-01

Chiral olefin metathesis catalysts enable chemists to access enantiomerically enriched small molecules with high efficiency; synthesis schemes involving such complexes can be substantially more concise than those that would involve enantiomerically pure substrates and achiral Mo alkylidenes or Ru-based carbenes. The scope of research towards design and development of chiral catalysts is not limited to discovery of complexes that are merely the chiral versions of the related achiral variants. A chiral olefin metathesis catalyst, in addition to furnishing products of high enantiomeric purity, can offer levels of efficiency, product selectivity and/or olefin stereoselectivity that are unavailable through the achiral variants. Such positive attributes of chiral catalysts (whether utilized in racemic or enantiomerically enriched form) should be considered as general, applicable to other classes of transformations. PMID:19967680

Solution-Phase Dynamic Assembly of Permanently Interlocked Aryleneethynylene Cages through Alkyne Metathesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Qi; Yu, Chao; Long, Hai

2015-05-08

Highly stable permanently interlocked aryleneethynylene molecular cages were synthesized from simple triyne monomers using dynamic alkyne metathesis. The interlocked complexes are predominantly formed in the reaction solution in the absence of any recognition motif and were isolated in a pure form using column chromatography. This study is the first example of the thermodynamically controlled solution-phase synthesis of interlocked organic cages with high stability.

Ruthenium indenylidene “1st generation” olefin metathesis catalysts containing triisopropyl phosphite

PubMed Central

Guidone, Stefano; Nahra, Fady; Slawin, Alexandra M Z

2015-01-01

Summary The reaction of triisopropyl phosphite with phosphine-based indenylidene pre-catalysts affords “1st generation” cis-complexes. These have been used in olefin metathesis reactions. The cis-Ru species exhibit noticeable differences with the trans-Ru parent complexes in terms of structure, thermal stability and reactivity. Experimental data underline the importance of synergistic effects between phosphites and L-type ligands. PMID:26425210

Metathesis-mediated synthesis of (R)-10-methyl-2-tridecanone, the southern corn rootworm pheromone.

PubMed

Shikichi, Yasumasa; Mori, Kenji

2012-01-01

(R)-10-Methyl-2-tridecanone, the female sex pheromone of the southern corn rootworm (Diabrotica undecimpunctata howardi Barber), was synthesized in 9 steps from methyl (S)-3-hydroxy-2-methylpropanoate in a 15.7% overall yield. Olefin cross metathesis between (R)-6-methyl-1-nonene and 5-hexen-2-one employing Grubbs' first-generation catalyst was the key step of the synthesis.

Assessment of density functional methods for the study of olefin metathesis catalysed by ruthenium alkylidene complexes

NASA Astrophysics Data System (ADS)

Śliwa, Paweł; Handzlik, Jarosław

2010-06-01

Performance of 31 DFT methods in thermochemistry of olefin metathesis involving the model catalyst (PH 3) 2(Cl) 2Ru dbnd CH 2 is studied using the CCSD(T) reference energies. The best methods are M06, ωB97X-D and PBE0, followed by MPW1B95, LC-ωPBE, M05-2X and B1B95. Among 20 functionals tested in reproduction of experimental PCy 3 dissociation energy for the Grubbs catalyst (H 2IMes)(PCy 3)(Cl) 2Ru dbnd CHPh, the M06-class and M05-2X methods are most accurate. ωB97X-D overestimates the dissociation energy, whereas MPW1B95, LC-ωPBE, PBE0 and B1B95 underestimate it, similarly to other methods, which give larger errors. LC-ωPBE, B1B95, MPW1B95 and PBE0 provide the best geometries.

Synthesis of Side-Chain Oxysterols and their Enantiomers through Cross-Metathesis Reactions of Δ22 Steroids

PubMed Central

Brownholland, David P.

2017-01-01

A synthetic route that utilizes a cross-metathesis reaction with Δ22 steroids has been developed to prepare sterols with varying C-27 side-chains. Natural sterols containing hydroxyl groups at the 25 and (25R)-26 positions were prepared. Enantiomers of cholesterol and (3β,25R)-26-hydroxycholesterol (27-hydroxycholesterol) trideuterated at C-19 were prepared for future biological studies. PMID:28300584

Molybdenum chloride catalysts for Z-selective olefin metathesis reactions

NASA Astrophysics Data System (ADS)

Koh, Ming Joo; Nguyen, Thach T.; Lam, Jonathan K.; Torker, Sebastian; Hyvl, Jakub; Schrock, Richard R.; Hoveyda, Amir H.

2017-01-01

The development of catalyst-controlled stereoselective olefin metathesis processes has been a pivotal recent advance in chemistry. The incorporation of appropriate ligands within complexes based on molybdenum, tungsten and ruthenium has led to reactivity and selectivity levels that were previously inaccessible. Here we show that molybdenum monoaryloxide chloride complexes furnish higher-energy (Z) isomers of trifluoromethyl-substituted alkenes through cross-metathesis reactions with the commercially available, inexpensive and typically inert Z-1,1,1,4,4,4-hexafluoro-2-butene. Furthermore, otherwise inefficient and non-stereoselective transformations with Z-1,2-dichloroethene and 1,2-dibromoethene can be effected with substantially improved efficiency and Z selectivity. The use of such molybdenum monoaryloxide chloride complexes enables the synthesis of representative biologically active molecules and trifluoromethyl analogues of medicinally relevant compounds. The origins of the activity and selectivity levels observed, which contradict previously proposed principles, are elucidated with the aid of density functional theory calculations.

From a Decomposition Product to an Efficient and Versatile Catalyst: The [Ru(η5-indenyl)(PPh3)2Cl] Story

PubMed Central

2014-01-01

Conspectus One of the most important challenges in catalyst design is the synthesis of stable promoters without compromising their activity. For this reason, it is important to understand the factors leading to decomposition of such catalysts, especially if side-products negatively affect the activity and selectivity of the starting complex. In this context, the understanding of termination and decomposition processes in olefin metathesis is receiving significant attention from the scientific community. For example, the decomposition of ruthenium olefin metathesis precatalysts in alcohol solutions can occur during either the catalyst synthesis or the metathesis process, and such decomposition has been found to be common for Grubbs-type precatalysts. These decomposition products are usually hydridocarbonyl complexes, which are well-known to be active in several transformations such as hydrogenation, terminal alkene isomerization, and C–H activation chemistry. The reactivity of these side products can be unwanted, and it is therefore important to understand how to avoid them and maybe also important to keep an open mind and think of ways to use these in other catalytic reactions. A showcase of these decomposition studies is reported in this Account. These reports analyze the stability of ruthenium phenylindenylidene complexes, highly active olefin metathesis precatalysts, in basic alcohol solutions. Several different decomposition processes can occur under these conditions depending on the starting complex and the alcohol used. These indenylidene-bearing metathesis complexes display a completely different behavior compared with that of other metathesis precatalysts and show an alternative competitive alcoholysis pathway, where rather than forming the expected hydrido carbonyl complexes, the indenylidene fragment is transformed into a η1-indenyl, which then rearranges to its η5-indenyl form. In particular, [RuCl(η5-(3-phenylindenylidene)(PPh3)2] has been found to be extremely active in numerous transformations (at least 20) as well as compatible with a broad range of reaction conditions, rendering it a versatile catalytic tool. It should be stated that the η5-phenyl indenyl ligand shows enhanced catalytic activity over related half-sandwich ruthenium complexes. The analogous half-sandwich (cyclopentadienyl and indenyl) ruthenium complexes show lower activity in transfer hydrogenation and allylic alcohol isomerization reactions. In addition, this catalyst allows access to new phenylindenyl ruthenium complexes, which can be achieved in a very straightforward manner and have been successfully used in catalysis. This Account provides an overview of how mechanistic insights into decomposition and stability of a well-known family of ruthenium metathesis precatalysts has resulted in a series of novel and versatile ruthenium complexes with unexpected reactivity. PMID:25264626

Synthesis of side-chain oxysterols and their enantiomers through cross-metathesis reactions of Δ22 steroids.

PubMed

Brownholland, David P; Covey, Douglas F

2017-05-01

A synthetic route that utilizes a cross-metathesis reaction with Δ 22 steroids has been developed to prepare sterols with varying C-27 side-chains. Natural sterols containing hydroxyl groups at the 25 and (25R)-26 positions were prepared. Enantiomers of cholesterol and (3β,25R)-26-hydroxycholesterol (27-hydroxycholesterol) trideuterated at C-19 were prepared for future biological studies. Copyright © 2017 Elsevier Inc. All rights reserved.

Application of Ring-Closing Metathesis to Grb2 SH3 Domain-Binding Peptides | Center for Cancer Research

Cancer.gov

In silico-generated hypothetical interactions of a ring-closing metathesis-macrocylized peptide bound to the amino terminal SH3 domain of the growth factor receptor bound protein 2 (Grb2). The complex was derived from the NMR solution structure of the bound parent peptide, Ac-V-P-P-P-V-P-P-R-R-R-amide (Protein Data Bank: 3GBQ). The protein surface is shown as electrostatic

``Effect of Polyalkylthiophene Microstructure on Physical and Optoelectronic Properties''

NASA Astrophysics Data System (ADS)

Minkler, Michael J., Jr.; Beckingham, Bryan S.

Conjugated polymers have been of widespread interest as flexible semiconductors for organic electronic devices such as solar cells, field effect transistor,s and light-emitting diodes. Of particular interest have been alkyl-substituted polythiophenes due to their well-controlled synthesis, favorable optoelectronic properties, and solubility in organic solvents. Importantly, relatively small changes to the chemical microstructure in poly(3-alkylthiophenes) (P3ATs) can have a significant effect on the resulting physical and optoelectronic properties. For instance, the addition of aliphatic side chains onto unsubstituted polythiophene provides solubility but also greatly decreases conductivity in comparison to unsubstituted polythiophene (PT). In this work, we use Grignard metathesis polymerization to synthesize poly(3-hexylthiophene) (P3HT), PT, and statistical copolymers (P[3HT-co-T]) over a range of compositions. We examine the physical properties (melting temperature, crystallinity, etc) by differential scanning calorimetry and wide angle X-ray scattering, optoelectronic properties by UV/Vis spectroscopy, and solubility in organic solvents of these copolymers in order to gain insights into the interplay of microstructure and properties in this class of materials.

Construction of Well-Defined Redox-Responsive CO2 -Based Polycarbonates: Combination of Immortal Copolymerization and Prereaction Approach.

PubMed

Liu, Shunjie; Zhao, Xun; Guo, Hongchen; Qin, Yusheng; Wang, Xianhong; Wang, Fosong

2017-05-01

Due to the axial group initiation in traditional (salen)CoX/quaternary ammonium catalyst system, it is difficult to construct single active center propagating polycarbonates for copolymerization of CO 2 /epoxides. Here a redox-responsive poly(vinyl cyclohexene carbonate) (PVCHC) with detachable disulfide-bond backbone is synthesized in a controllable manner using (salen)CoTFA/[bis(triphenylphosphine)iminium, [PPN]TFA binary catalyst, where the axial group initiation is depressed by judiciously choosing 3,3'-dithiodipropionic acid as starter. While for those comonomers failing to obtain polycarbonate with unimodal gel permeation chromatography (GPC) curve, a versatile method is developed by combination of immortal copolymerization and prereaction approach, and functional aliphatic polycarbonates having well-defined architecture and narrow polydispersity can be prepared. The resulting PVCHC can be further functionalized with alkenes by versatile cross-metathesis reaction to tune the physicochemical properties. The combination of immortal polymerization and prereaction approach creates a powerful platform for controllable synthesis of functional CO 2 -based polycarbonates. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular Diversity by Olefin Cross-Metathesis on Solid Support. Generation of Libraries of Biologically Promising β-Lactam Derivatives.

PubMed

Méndez, Luciana; Poeylaut-Palena, Andrés A; Mata, Ernesto G

2018-05-16

The application of the reagent-based diversification strategy for generation of libraries of biologically promising β-lactam derivatives is described. Key features are the versatility of the linker used and the cross-metathesis functionalization at the cleavage step. From an immobilized primary library, diversity was expanded by applying different cleavage conditions, leading to a series of cholesterol absorption inhibitor analogues together with interesting hybrid compounds through incorporation of a chalcone moiety.

Stereoselective protecting group free synthesis of D,L-gulose ethyl glycoside via multicomponent enyne cross metathesis--hetero Diels-Alder reaction.

PubMed

Castagnolo, Daniele; Botta, Lorenzo; Botta, Maurizio

2009-07-27

An efficient and stereoselective synthesis of D,L-gulose was described. The key step of the synthetic route is represented by a multicomponent enyne cross metathesis-hetero Diels-Alder reaction which allows the formation of the pyran ring from cheap and commercially available substrates in a single synthetic step. The synthesis of D,L-gulose was accomplished without the use of protecting groups making this approach highly desirable also in terms of atom economy.

Fluorinated bottlebrush polymers based on poly(trifluoroethyl methacrylate): Synthesis and characterizations

DOE PAGES

Xu, Yuewen; Wang, Weiyu; Wang, Yangyang; ...

2015-11-25

Bottlebrush polymers are densely grafted polymers with long side-chains attached to a linear polymeric backbone. Their unusual structures endow them with a number of unique and potentially useful properties in solution, in thin films, and in bulk. Despite the many studies of bottlebrushes that have been reported, the structure–property relationships for this class of materials are still poorly understood. In this contribution, we report the synthesis and characterization of fluorinated bottlebrush polymers based on poly(2,2,2-trifluoroethyl methacrylate). The synthesis was achieved by atom transfer radical polymerization (ATRP) using an α-bromoisobutyryl bromide functionalized norbornene initiator, followed by ring-opening metathesis polymerization (ROMP) usingmore » a third generation Grubbs’ catalyst (G3). Rheological characterization revealed that the bottlebrush polymer backbones remained unentangled as indicated by the lack of a rubbery plateau in the modulus. By tuning the size of the backbone of the bottlebrush polymers, near-spherical and elongated particles representing single brush molecular morphologies were observed in a good solvent as evidenced by TEM imaging, suggesting a semi-flexible nature of their backbones in dilute solutions. Thin films of bottlebrush polymers exhibited noticeably higher static water contact angles as compared to that of the macromonomer reaching the hydrophobic regime, where little differences were observed between each bottlebrush polymer. Further investigation by AFM revealed that the surface of the macromonomer film was relatively smooth; in contrast, the surface of bottlebrush polymers displayed certain degrees of nano-scale roughness (R q = 0.8–2.4 nm). The enhanced hydrophobicity of these bottlebrushes likely results from the preferential enrichment of the fluorine containing end groups at the periphery of the molecules and the film surface due to the side chain crowding effect. Furthermore, our results provide key information towards the design of architecturally tailored fluorinated polymers with desirable properties.« less

Dynamic Covalent Synthesis of Aryleneethynylene Cages through Alkyne Metathesis: Dimer, Tetramer, or Interlocked Complex?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Qi; Yu, Chao; Zhang, Chenxi

A dynamic covalent approach towards rigid aryleneethynylene covalent organic polyhedrons (COPs) was explored. Our study on the relationship of the COP structures and the geometry of their building blocks reveals that the topology of aryleneethynylene COPs strongly depends on the size of the building blocks. A tetramer (D2h symmetric), dimer, or interlocked complex can be formed from monomers with the same face-to-edge angle but in different sizes. As alkyne metathesis is a self-exchange reaction and non-directional, the cyclooligomerization of multi-alkyne monomers involves both intramolecular cyclization and intermolecular metathesis reaction, resulting in complicated thermodynamic process disturbed by kinetic competition. Although amore » tetrahedron-shaped tetramer (Td symmetric) has comparable thermodynamic stability to a D2h symmetric tetramer, its formation is kinetically disfavored and was not observed experimentally. Aryleneethynylene COPs consist of purely unsaturated carbon backbones and exhibit large internal cavities, which would have interesting applications in host-guest chemistry and development of porous materials.« less

Tandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium–arene complexes

PubMed Central

Borguet, Yannick; Sauvage, Xavier; Zaragoza, Guillermo; Demonceau, Albert

2010-01-01

Summary The tandem catalysis of ring-closing metathesis/atom transfer radical reactions was investigated with the homobimetallic ruthenium–indenylidene complex [(p-cymene)Ru(μ-Cl)3RuCl(3-phenyl-1-indenylidene)(PCy3)] (1) to generate active species in situ. The two catalytic processes were first carried out independently in a case study before the whole sequence was optimized and applied to the synthesis of several polyhalogenated bicyclic γ-lactams and lactones from α,ω-diene substrates bearing trihaloacetamide or trichloroacetate functionalities. The individual steps were carefully monitored by 1H and 31P NMR spectroscopies in order to understand the intimate details of the catalytic cycles. Polyhalogenated substrates and the ethylene released upon metathesis induced the clean transformation of catalyst precursor 1 into the Ru(II)–Ru(III) mixed-valence compound [(p-cymene)Ru(μ-Cl)3RuCl2(PCy3)], which was found to be an efficient promoter for atom transfer radical reactions under the adopted experimental conditions. PMID:21160564

REDUCTION OF PLUTONIUM TO Pu$sup +3$ BY SODIUM DITHIONITE IN POTASSIUM CARBONATE

DOEpatents

Miller, D.R.; Hoekstra, H.R.

1958-12-16

Plutonium values are reduced in an alkaline aqueous medlum to the trlvalent state by means of sodium dlthionite. Plutonlum values are also separated from normally assoclated contaminants by metathesizing a lanthanum fluoride carrier precipitate containing plutonium with a hydroxide solution, performing the metathesis in the presence of about 0.2 M sodium dithionite at a temperature of between 40 and 90 icient laborato C.

Synthesis of Cyclic Porphyrin Trimers through Alkyne Metathesis Cyclooligomerization and Their Host–Guest Binding Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Chao; Long, Hai; Jin, Yinghua

2016-06-17

Cyclic porphyrin trimers were synthesized through one-step cyclooligomerization via alkyne metathesis from diyne monomers. These macrocycles show interesting host-guest binding interactions with fullerenes, selectively binding C70 (6 x 103 M-1) over C60 and C84 (no binding observed). The fullerene-encapsulated host-guest complex can undergo guest or host exchange in the presence of another guest (2,4,6-tri(4-pyridyl)-1,3,5-triazine) or host (cage COP5) molecule with higher binding affinity.

Pharmacophore mapping in the laulimalide series: total synthesis of a vinylogue for a late-stage metathesis diversification strategy.

PubMed

Wender, Paul A; Hilinski, Michael K; Skaanderup, Philip R; Soldermann, Nicolas G; Mooberry, Susan L

2006-08-31

An efficient synthesis of the macrocyclic core of laulimalide with a pendant vinyl group at C20 is described, allowing for late-stage introduction of various side chains through a selective and efficient cross metathesis diversification step. Representative analogues reported herein are the first to contain modifications to only the side chain dihydropyran of laulimalide and des-epoxy laulimalide. This step-economical strategy enables the rapid synthesis of new analogues using alkenes as an inexpensive, abundantly available diversification feedstock.

Formation of polycyclic lactones through a ruthenium-catalyzed ring-closing metathesis/hetero-Pauson-Khand reaction sequence.

PubMed

Finnegan, David F; Snapper, Marc L

2011-05-20

Processes that form multiple carbon-carbon bonds in one operation can generate molecular complexity quickly and therefore be used to shorten syntheses of desirable molecules. We selected the hetero-Pauson-Khand (HPK) cycloaddition and ring-closing metathesis (RCM) as two unique carbon-carbon bond-forming reactions that could be united in a tandem ruthenium-catalyzed process. In doing so, complex polycyclic products can be obtained in one reaction vessel from acyclic precursors using a single ruthenium additive that can catalyze sequentially two mechanistically distinct transformations.

Metathesis depolymerizable surfactants

DOEpatents

Jamison, Gregory M [Albuquerque, NM; Wheeler, David R [Albuquerque, NM; Loy, Douglas A [Tucson, AZ; Simmons, Blake A [San Francisco, CA; Long, Timothy M [Evanston, IL; McElhanon, James R [Manteca, CA; Rahimian, Kamyar [Albuquerque, NM; Staiger, Chad L [Albuquerque, NM

2008-04-15

A class of surfactant molecules whose structure includes regularly spaced unsaturation in the tail group and thus, can be readily decomposed by ring-closing metathesis, and particularly by the action of a transition metal catalyst, to form small molecule products. These small molecules are designed to have increased volatility and/or enhanced solubility as compared to the original surfactant molecule and are thus easily removed by solvent extraction or vacuum extraction at low temperature. By producing easily removable decomposition products, the surfactant molecules become particularly desirable as template structures for preparing meso- and microstructural materials with tailored properties.

Highly efficient molybdenum-based catalysts for enantioselective alkene metathesis

PubMed Central

Malcolmson, Steven J.; Meek, Simon J.; Sattely, Elizabeth S.; Schrock, Richard R.; Hoveyda, Amir H.

2009-01-01

Discovery of efficient catalysts is one of the most compelling objectives of modern chemistry. Chiral catalysts are in particularly high demand, as they facilitate synthesis of enantiomerically enriched small molecules that are critical to developments in medicine, biology and materials science1. Especially noteworthy are catalysts that promote—with otherwise inaccessible efficiency and selectivity levels—reactions demonstrated to be of great utility in chemical synthesis. Here we report a class of chiral catalysts that initiate alkene metathesis1 with very high efficiency and enantioselectivity. Such attributes arise from structural fluxionality of the chiral catalysts and the central role that enhanced electronic factors have in the catalytic cycle. The new catalysts have a stereogenic metal centre and carry only monodentate ligands; the molybdenum-based complexes are prepared stereoselectively by a ligand exchange process involving an enantiomerically pure aryloxide, a class of ligands scarcely used in enantioselective catalysis2,3. We demonstrate the application of the new catalysts in an enantioselective synthesis of the Aspidosperma alkaloid, quebrachamine, through an alkene metathesis reaction that cannot be promoted by any of the previously reported chiral catalysts. PMID:19011612

Methods of refining and producing dibasic esters and acids from natural oil feedstocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snead, Thomas E.; Cohen, Steven A.; Gildon, Demond L.

Methods and systems for making dibasic esters and/or dibasic acids using metathesis are generally disclosed. In some embodiments, the methods comprise reacting a terminal olefin ester with an internal olefin ester in the presence of a metathesis catalyst to form a dibasic ester and/or dibasic acid. In some embodiments, the terminal olefin ester or the internal olefin ester are derived from a renewable feedstock, such as a natural oil feedstock. In some such embodiments, the natural oil feedstock, or a transesterified derivative thereof, is metathesized to make the terminal olefin ester or the internal olefin ester.

Stereoselective synthesis of functionalized cyclic amino acid derivatives via a [2,3]-Stevens rearrangement and ring-closing metathesis.

PubMed

Nash, Aaron; Soheili, Arash; Tambar, Uttam K

2013-09-20

Unnatural cyclic amino acids are valuable tools in biomedical research and drug discovery. A two-step stereoselective strategy for converting simple glycine-derived aminoesters into unnatural cyclic amino acid derivatives has been developed. The process includes a palladium-catalyzed tandem allylic amination/[2,3]-Stevens rearrangement followed by a ruthenium-catalyzed ring-closing metathesis. The [2,3]-rearrangement proceeds with high diastereoselectivity through an exo transition state. Oppolzer's chiral auxiliary was utilized to access an enantiopure cyclic amino acid by this approach, which will enable future biological applications.

Highly Z- and Enantioselective Ring-Opening/Cross-Metathesis Reactions Catalyzed by Stereogenic-at-Mo Adamantylimido Complexes

PubMed Central

Ibrahem, Ismail; Yu, Miao; Schrock, Richard R.; Hoveyda, Amir H.

2009-01-01

The first highly Z- and enantioselective class of ring-opening/cross-metathesis (ROCM) reactions is presented. Transformations are promoted in the presence of <2 mol % of chiral stereogenic-at-Mo monoaryloxide complexes, which bear an adamantylimido ligand and are prepared and used in situ. Reactions involve meso oxabicyclic substrates and afford the desired pyrans in 50–85% yield and in up to >98:<2 enantiomer ratio (er). Importantly, the desired chiral pyrans are thus obtained bearing a Z olefin either exclusively (>98:<2 Z:E) or predominantly (≥87:13 Z:E). PMID:19249833

Synthesis and Structure of Fully Conjugated Block Copolymers Utilized in Organic Photovoltaics

NASA Astrophysics Data System (ADS)

Lee, Youngmin; Aplan, Melissa; Wang, Qing; Gomez, Enrique D.

2015-03-01

Fully conjugated block copolymers have the potential to overcome many of the limitations of mixtures and blends as photoactive layers in solar cells; furthermore, they may serve as model systems to study fundamental questions regarding optoelectric properties and charge transfer. However, the synthesis of fully conjugated block copolymers remains a challenging issue in the fieldchallenge. We have optimized the two-step synthesis of P3HT-b-PFTBT, which is composed comprised of Grignard metathesis for polymerization of P3HT followed by chain extension through a Suzuki-Miyaura polycondenstation. We find that the concentration of the Grignard reagent is critical for end-group control such that P3HT is terminated by H at one end and Br at the other. Furthermore, we can utilize an asymmetric feed ratio of monomers for the Suzuki-Miyaura reaction to minimize the amount of uncoupled homopolymers and to control the molecular weight of the second block. We investigated the chemical composition, structure and electrical characteristics of the polymers prepared by the different synthetic methods, and demonstrate that we can utilize these strategies for the synthesis of block copolymers beyond P3HT-b-PFTBT.

Synthesis and redox activity of "clicked" triazolylbiferrocenyl polymers, network encapsulation of gold and silver nanoparticles and anion sensing.

PubMed

Rapakousiou, Amalia; Deraedt, Christophe; Irigoyen, Joseba; Wang, Yanlan; Pinaud, Noël; Salmon, Lionel; Ruiz, Jaime; Moya, Sergio; Astruc, Didier

2015-03-02

The design of redox-robust polymers is called for in view of interactions with nanoparticles and surfaces toward applications in nanonetwork design, sensing, and catalysis. Redox-robust triazolylbiferrocenyl (trzBiFc) polymers have been synthesized with the organometallic group in the side chain by ring-opening metathesis polymerization using Grubbs-III catalyst or radical polymerization and with the organometallic group in the main chain by Cu(I) azide alkyne cycloaddition (CuAAC) catalyzed by [Cu(I)(hexabenzyltren)]Br. Oxidation of the trzBiFc polymers with ferricenium hexafluorophosphate yields the stable 35-electron class-II mixed-valent biferrocenium polymer. Oxidation of these polymers with Au(III) or Ag(I) gives nanosnake-shaped networks (observed by transmission electron microscopy and atomic force microscopy) of this mixed-valent Fe(II)Fe(III) polymer with encapsulated metal nanoparticles (NPs) when the organoiron group is located on the side chain. The factors that are suggested to be synergistically responsible for the NP stabilization and network formation are the polymer bulk, the trz coordination, the nearby cationic charge of trzBiFc, and the inter-BiFc distance. For instance, reduction of such an oxidized trzBiFc-AuNP polymer to the neutral trzBiFc-AuNP polymer with NaBH4 destroys the network, and the product flocculates. The polymers easily provide modified electrodes that sense, via the oxidized Fe(II)Fe(III) and Fe(III)Fe(III) polymer states, respectively, ATP(2-) via the outer ferrocenyl units of the polymer and Pd(II) via the inner Fc units; this recognition works well in dichloromethane, but also to a lesser extent in water with NaCl as the electrolyte.

Novel self-healing materials chemistries for targeted applications

NASA Astrophysics Data System (ADS)

Wilson, Gerald O.

Self-healing materials of the type developed by White and co-workers [1] were designed to autonomically heal themselves when damaged, thereby extending the lifetime of various applications in which such material systems are employed. The system was based on urea-formaldehyde microcapsules containing dicyclopentadiene (DCPD) and Grubbs' catalyst particles embedded together in an epoxy matrix. When a crack propagates through the material, it ruptures the microcapsules, releasing DCPD into the crack plane, where it comes in contact and reacts with the catalyst to initiate a ring opening metathesis polymerization (ROMP), bonding the crack and restoring structural continuity. The present work builds on this concept in several ways. Firstly, it expands the scope and versatility of the ROMP self-healing chemistry by incorporation into epoxy vinyl ester matrices. Major technical challenges in this application include protection of the catalyst from deactivation by aggressive curing agents, and optimization of the concentration of healing agents in the matrix. Secondly, new ruthenium catalysts are evaluated for application in ROMP-based self-healing materials. The use of alternative derivatives of Grubbs' catalyst gave rise to self-healing systems with improved healing efficiencies and thermal properties. Evaluation of the stability of these new catalysts to primary amine curing agents used in the curing of common epoxy matrices also led to the discovery and characterization of new ruthenium catalysts which exhibited ROMP initiation kinetics superior to those of first and second generation Grubbs' catalysts. Finally, free radical polymerization was evaluated for application in the development of bio-compatible self-healing materials. [1] White, S. R.; Sottos, N. R.; Geubelle, P. R.; Moore, J. S.; Kessler, M. R.; Sriram, S. R.; Brown, E. N.; Viswanathan, S. Nature 2001, 409, 794.

Molecular Syntheses of Extended Materials

NASA Astrophysics Data System (ADS)

Paley, Daniel W.

Bottom-up molecular synthesis is a route to chemically and crystallographically uniform polymers and solid-state materials. Through the use of molecular precursors, we gain atomic-level control of functionality and fine-tuning of the collective properties of materials. This dissertation presents two studies that demonstrate this approach. Ring-opening alkyne metathesis polymerization is a possible approach to monodisperse conjugated polymers, but its applications have been limited by difficult syntheses and high air sensitivity of known organometallic ROAMP initiators. We designed a dimeric, air-stable molybdenum alkylidyne with a tris(phenolate) supporting ligand. The precatalyst is activated by addition of methanol and polymerizes cyclooctynes with excellent chemical selectivity and functional group tolerance. The Nuckolls and Roy groups have introduced a new family of solid-state compounds synthesized from cobalt chalcogenide clusters Co6Q 8(PR3)6 and fullerenes. The first examples of these materials crystallized in superatom lattices with the symmetry of simple inorganic solids CdI2 (P-3m1) and NaCl (Fm-3m). This dissertation reveals that further members of the family feature extraordinary diversity of structure, including a pseudo-trigonal array of fulleride dimers in [Co 6Te8(PEt3)6]2[C140 ][C70]2 and a heterolayered van der Waals cocrystal [Co6Se8(PEt2phen)6][C 60]5. In addition to these unusual crystal structures, this dissertation presents a method for assigning redox states from crystallographic data in Co6Q8 clusters. Finally, a detailed guide to the collection and solution of single-crystal X-ray data is presented. The guide is intended for independent study by new crystallographers.

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush.

PubMed

Lin, Tzu-Pin; Chang, Alice B; Luo, Shao-Xiong; Chen, Hsiang-Yun; Lee, Byeongdu; Grubbs, Robert H

2017-11-28

Grafting density is an important structural parameter that exerts significant influences over the physical properties of architecturally complex polymers. In this report, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization. ω-Norbornenyl poly(d,l-lactide) and polystyrene macromonomers were copolymerized with discrete comonomers in different feed ratios, enabling precise control over both the grafting density and molecular weight. Small-angle X-ray scattering experiments demonstrate that these graft block polymers self-assemble into long-range-ordered lamellar structures. For 17 series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ∼ N bb α ) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z (System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, not segregation effects. A model is proposed in which the characteristic ratio (C ∞ ), a proxy for the backbone stiffness, scales with N bb as a function of the grafting density: C ∞ ∼ N bb f(z) . The scaling behavior disclosed herein provides valuable insights into conformational changes with grafting density, thus introducing opportunities for block polymer and material design.

Methods of refining and producing dibasic esters and acids from natural oil feedstocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snead, Thomas E; Cohen, Steven A; Gildon, Demond L

2015-04-07

Methods are provided for refining natural oil feedstocks and producing dibasic esters and/or dibasic acids. The methods comprise reacting a terminal olefin with an internal olefin in the presence of a metathesis catalyst to form a dibasic ester and/or dibasic acid. In certain embodiments, the olefin esters are formed by reacting the feedstock in the presence of a metathesis catalyst under conditions sufficient to form a metathesized product comprising olefins and esters, separating the olefins from the esters in the metathesized product, and transesterifying the esters in the presence of an alcohol to form a transesterified product having olefin esters.

Methods of refining and producing dibasic esters and acids from natural oil feedstocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snead, Thomas E.; Cohen, Steven A.; Gildon, Demond L.

2016-03-15

Methods are provided for refining natural oil feedstocks and producing dibasic esters and/or dibasic acids. The methods comprise reacting a terminal olefin with an internal olefin in the presence of a metathesis catalyst to form a dibasic ester and/or dibasic acid. In certain embodiments, the olefin esters are formed by reacting the feedstock in the presence of a metathesis catalyst under conditions sufficient to form a metathesized product comprising olefins and esters, separating the olefins from the esters in the metathesized product, and transesterifying the esters in the presence of an alcohol to form a transesterified product having olefin esters.

Synthesis of all-hydrocarbon stapled α-helical peptides by ring-closing olefin metathesis.

PubMed

Kim, Young-Woo; Grossmann, Tom N; Verdine, Gregory L

2011-06-01

This protocol provides a detailed procedure for the preparation of stapled α-helical peptides, which have proven their potential as useful molecular probes and as next-generation therapeutics. Two crucial features of this protocol are (i) the construction of peptide substrates containing hindered α-methyl, α-alkenyl amino acids and (ii) the ring-closing olefin metathesis (RCM) of the resulting resin-bound peptide substrates. The stapling systems described in this protocol, namely bridging one or two turns of an α-helix, are highly adaptable to most peptide sequences, resulting in favorable RCM kinetics, helix stabilization and promotion of cellular uptake.

Phosphate Tether-Mediated Ring-Closing Metathesis for the Generation of P-Stereogenic, Z-Configured Bicyclo[7.3.1]- and Bicyclo[8.3.1]phosphates.

PubMed

Markley, Jana L; Maitra, Soma; Hanson, Paul R

2016-02-05

A phosphate tether-mediated ring-closing metathesis (RCM) study to the synthesis of Z-configured, P-stereogenic bicyclo[7.3.1]- and bicyclo[8.3.1]phosphates is reported. Investigations suggest that C3-substitution, olefin substitution, and proximity of the forming olefin to the bridgehead carbon of the bicyclic affect the efficiency and stereochemical outcome of the RCM event. This study demonstrates the utility of phosphate tether-mediated desymmetrization of C2-symmetric, 1,3-anti-diol-containing dienes in the generation of macrocyclic phosphates with potential synthetic and biological utility.

Ring-rearrangement metathesis of nitroso Diels-Alder cycloadducts.

PubMed

Vincent, Guillaume; Kouklovsky, Cyrille

2011-03-01

Strained nitroso Diels-Alder bicyclo[2.2.1] or [2.2.2] adducts functionalized with alkene side chains of diverse length undergo a ring-rearrangement metathesis process with external alkenes and Grubbs II or Hoveyda-Grubbs II ruthenium catalysts, under microwave irradiation or classical heating, to deliver cis-fused bicycles of various ring sizes, which contain a N-O bond. These scaffolds are of synthetic relevance for the generation of molecular diversity and to the total synthesis of alkaloids. The observation of unexpected reactions, such as epimerization or one-carbon homologation of the alkene side chain, is also reported. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Low-temperature synthesis of actinide tetraborides by solid-state metathesis reactions

DOEpatents

Lupinetti, Anthony J [Los Alamos, NM; Garcia, Eduardo [Los Alamos, NM; Abney, Kent D [Los Alamos, NM

2004-12-14

The synthesis of actinide tetraborides including uranium tetraboride (UB.sub.4), plutonium tetraboride (PuB.sub.4) and thorium tetraboride (ThB.sub.4) by a solid-state metathesis reaction are demonstrated. The present method significantly lowers the temperature required to .ltoreq.850.degree. C. As an example, when UCl.sub.4 is reacted with an excess of MgB.sub.2, at 850.degree. C., crystalline UB.sub.4 is formed. Powder X-ray diffraction and ICP-AES data support the reduction of UCl.sub.3 as the initial step in the reaction. The UB.sub.4 product is purified by washing water and drying.

Rapid Solid-State Metathesis Routes to Nanostructured Silicon-Germainum

NASA Technical Reports Server (NTRS)

Rodriguez, Marc (Inventor); Kaner, Richard B. (Inventor); Bux, Sabah K. (Inventor); Fleurial, Jean-Pierre (Inventor)

2014-01-01

Methods for producing nanostructured silicon and silicon-germanium via solid state metathesis (SSM). The method of forming nanostructured silicon comprises the steps of combining a stoichiometric mixture of silicon tetraiodide (SiI4) and an alkaline earth metal silicide into a homogeneous powder, and initating the reaction between the silicon tetraiodide (SiI4) with the alkaline earth metal silicide. The method of forming nanostructured silicon-germanium comprises the steps of combining a stoichiometric mixture of silicon tetraiodide (SiI4) and a germanium based precursor into a homogeneous powder, and initiating the reaction between the silicon tetraiodide (SiI4) with the germanium based precursors.

A DFT Study of Tungsten-Methylidene Formation on a W/ZSM-5 Zeolite: The Metathesis Active Site.

PubMed

Maihom, Thana; Probst, Michael; Limtrakul, Jumras

2015-10-26

Tungsten-methylidene formation from ethene on either the W(IV) , W(V) , or W(VI) active sites of a W/ZSM-5 zeolite is investigated by using the M06-L functional. The reaction is assumed to proceed in two steps; the first step is the [2+2] cycloaddition between ethene and the W-O active site to form an oxametallacycle intermediate. The intermediate is then decomposed to produce the W-methylidene active site from the metathesis reaction. The overall activation barrier of the reaction on W(VI) (27.3 kcal mol(-1) ) is considerably lower than the ones for W(IV) and W(V) (69.4 and 37.1 kcal mol(-1) , respectively). Moreover, the reaction involving the W(VI) site also stabilizes intermediates and products to a larger extent than the ones on the W(IV) and W(V) sites. As a result, we have demonstrated that the reaction of the W-methylidene metathesis active site is both kinetically and thermodynamically favored to occur on the W(VI) active site of the zeolite. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Low Temperature Activation of Supported Metathesis Catalysts by Organosilicon Reducing Agents

PubMed Central

2016-01-01

Alkene metathesis is a widely and increasingly used reaction in academia and industry because of its efficiency in terms of atom economy and its wide applicability. This reaction is notably responsible for the production of several million tons of propene annually. Such industrial processes rely on inexpensive silica-supported tungsten oxide catalysts, which operate at high temperatures (>350 °C), in contrast with the mild room temperature reaction conditions typically used with the corresponding molecular alkene metathesis homogeneous catalysts. This large difference in the temperature requirements is generally thought to arise from the difficulty in generating active sites (carbenes or metallacyclobutanes) in the classical metal oxide catalysts and prevents broader applicability, notably with functionalized substrates. We report here a low temperature activation process of well-defined metal oxo surface species using organosilicon reductants, which generate a large amount of active species at only 70 °C (0.6 active sites/W). This high activity at low temperature broadens the scope of these catalysts to functionalized substrates. This activation process can also be applied to classical industrial catalysts. We provide evidence for the formation of a metallacyclopentane intermediate and propose how the active species are formed. PMID:27610418

Rational approach to polymer-supported catalysts: synergy between catalytic reaction mechanism and polymer design.

PubMed

Madhavan, Nandita; Jones, Christopher W; Weck, Marcus

2008-09-01

Supported catalysis is emerging as a cornerstone of transition metal catalysis, as environmental awareness necessitates "green" methodologies and transition metal resources become scarcer and more expensive. Although these supported systems are quite useful, especially in their capacity for transition metal catalyst recycling and recovery, higher activity and selectivity have been elusive compared with nonsupported catalysts. This Account describes recent developments in polymer-supported metal-salen complexes, which often surpass nonsupported analogues in catalytic activity and selectivity, demonstrating the effectiveness of a systematic, logical approach to designing supported catalysts from a detailed understanding of the catalytic reaction mechanism. Over the past few decades, a large number of transition metal complex catalysts have been supported on a variety of materials ranging from polymers to mesoporous silica. In particular, soluble polymer supports are advantageous because of the development of controlled and living polymerization methods that are tolerant to a wide variety of functional groups, including controlled radical polymerizations and ring-opening metathesis polymerization. These methods allow for tuning the density and structure of the catalyst sites along the polymer chain, thereby enabling the development of structure-property relationships between a catalyst and its polymer support. The fine-tuning of the catalyst-support interface, in combination with a detailed understanding of catalytic reaction mechanisms, not only permits the generation of reusable and recyclable polymer-supported catalysts but also facilitates the design and realization of supported catalysts that are significantly more active and selective than their nonsupported counterparts. These superior supported catalysts are accessible through the optimization of four basic variables in their design: (i) polymer backbone rigidity, (ii) the nature of the linker, (iii) catalyst site density, and (iv) the nature of the catalyst attachment. Herein, we describe the design of polymer supports tuned to enhance the catalytic activity or decrease, or even eliminate, decomposition pathways of salen-based transition metal catalysts that follow either a monometallic or a bimetallic reaction mechanism. These findings result in the creation of some of the most active and selective salen catalysts in the literature.

Metal- and Reagent-Free Anodic C-C Cross-Coupling of Phenols with Benzofurans leading to a Furan Metathesis.

PubMed

Lips, Sebastian; Frontana-Uribe, Bernardo Antonio; Dörr, Maurice; Schollmeyer, Dieter; Franke, Robert; Waldvogel, Siegfried R

2018-04-20

Heterobiaryls consisting of a phenol and a benzofuran motif are of significant importance for pharmaceutical applications. An attractive sustainable, metal- and reagent-free, electrosynthetic, and highly efficient method, that allows access to (2-hydroxyphenyl)benzofurans is presented. Upon the electrochemical dehydrogenative C-C cross-coupling reaction, a metathesis of the benzo moiety at the benzofuran occurs. This gives rise to a substitution pattern at the hydroxyphenyl moiety which would not be compatible by a direct coupling process. The single-step protocol is easy to conduct in an undivided electrolysis cell, therefore scalable, and inherently safe. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Biofuel by isomerizing metathesis of rapeseed oil esters with (bio)ethylene for use in contemporary diesel engines

PubMed Central

Pfister, Kai F.; Baader, Sabrina; Baader, Mathias; Berndt, Silvia; Goossen, Lukas J.

2017-01-01

Rapeseed oil methyl ester (RME) and (bio)ethylene are converted into biofuel with an evenly rising boiling point curve, which fulfills the strict boiling specifications prescribed by the fuel standard EN 590 for modern (petro)diesel engines. Catalyzed by a Pd/Ru system, RME undergoes isomerizing metathesis in a stream of ethylene gas, leading to a defined olefin, monoester, and diester blend. This innovative refining concept requires negligible energy input (60°C) and no solvents and does not produce waste. It demonstrates that the pressing challenge of increasing the fraction of renewables in engine fuel may be addressed purely chemically rather than by motor engineering. PMID:28630908

Biofuel by isomerizing metathesis of rapeseed oil esters with (bio)ethylene for use in contemporary diesel engines.

PubMed

Pfister, Kai F; Baader, Sabrina; Baader, Mathias; Berndt, Silvia; Goossen, Lukas J

2017-06-01

Rapeseed oil methyl ester (RME) and (bio)ethylene are converted into biofuel with an evenly rising boiling point curve, which fulfills the strict boiling specifications prescribed by the fuel standard EN 590 for modern (petro)diesel engines. Catalyzed by a Pd/Ru system, RME undergoes isomerizing metathesis in a stream of ethylene gas, leading to a defined olefin, monoester, and diester blend. This innovative refining concept requires negligible energy input (60°C) and no solvents and does not produce waste. It demonstrates that the pressing challenge of increasing the fraction of renewables in engine fuel may be addressed purely chemically rather than by motor engineering.

First Principles Simulations of Hydrocarbon Conversion Processes in Functionalized Zeolitic Materials

NASA Astrophysics Data System (ADS)

Mazar, Mark Nickolaus

With increasing demand for chemicals and fuels, and finite traditional crude oil resources, there is a growing need to invent, establish, or optimize chemical processes that convert gasifiable carbon-based feedstocks (e.g., coal, natural gas, oil sands, or biomass) into the needed final products. Catalysis is central to almost every industrial chemical process, including alkane metathesis (AM) and the methanol-to-hydrocarbons (MTH) process, which represent final steps in a sequence of hydrocarbon conversion reactions. An in depth understanding of AM and MTH is essential to the selective production of the desired end products. In this dissertation, ab initio density functional theory simulations provide unique mechanistic and thermodynamic insight of specific elementary steps involved in AM and MTH as performed on zeolite supports. Zeolites have been employed throughout the petroleum industry because of their ability to perform acid-catalyzed reactions (e.g., cracking or MTH). The crystalline structure of zeolites imparts regular microporous networks and, in turn, the selective passage of molecules based on shape and functionality. Many different elements can be grafted onto or substituted into zeolites, resulting in a broad range of catalytic behavior. However, due to the variety of competing and secondary reactions that occur at experimental conditions, it is often difficult to extract quantitative information regarding individual elementary steps. ab initio calculations can be particularly useful for this purpose. Alkane metathesis (i.e., the molecular redistribution or chain length averaging of alkanes) is typically performed by transition metal hydrides on amorphous alumina or silica supports. In Chapter 3, the feasibility of AM in zeolites is assessed by using a grafted Ta-hydride complex to explore the full catalytic cycle in the self-metathesis of ethane. The decomposition of a Ta-metallacyclobutane reaction intermediate that forms during olefin metathesis is responsible for the largest activation energy of the catalytic cycle. This assessment is similar to the findings of alkane metathesis studies on alumina/silica supports and indicates that the entire AM cycle can be performed in zeolites by isolated single-atom transition metal hydrides. Performed over acid form zeolites, MTH is used in the conversion of methanol into a broad range of hydrocarbons, including alkenes, alkanes, and aromatics. For reasons that are not yet rigorously quantified, product selectivities vary dramatically based on the choice of catalyst and reaction conditions. The methylation of species containing double bonds (i.e., co-catalysts) is central to the overall process. Distinct structure-function relationships were found with respect to the elementary steps in the methylation and beta-scission of olefins. In Chapter 4, the role of zeolite topology in the step-wise methylation of ethene by surface methoxides is investigated. Elementary steps are studied across multiple frameworks (i.e., BEA, CHA, FER, MFI, and MOR) constituting a wide variety of confinement environments. The reaction of surface methoxides with ethene is found to require a transition state containing a primary carbocation. The barrier height is found to decrease nearly monotonically with respect to the degree of dispersion interactions stabilizing the primary carbocationic species in the transition state. In addition, quantification of the ``local'' dispersion energy indicates that confinement effects can not be simply correlated to pore size. The beta-scission of olefins plays an important role in the product selectivities of many important chemical processes, including MTH. In Chapter 5, beta-scission modes involving C6 and C8 isomers are investigated at a single, isolated Bronsted acid site within H-ZSM-5. We find that the relative enthalpic barriers of beta-scission elementary steps can be rationalized by the substitution order of the two different carbocationic carbon atoms that are present in the reactant (C+) and transition states (betaC). In fact, the increase in charge required by the betaC atom to go from the physi/chemi-sorbed reactant state to the beta-scission transition state (+0.23e-0.33e) is found to correlate almost linearly with the intrinsic activation energy (89-233 kJ mol-1). The charge of the betaC atom depends, to a large extent, on the substitution order of both the C+ and betaC atoms and, therefore, each beta-scission mode is a sub-category onto itself. Isomerization reactions, which are fast with respect to beta-scission, enable reactant hydrocarbons to explore and find low barrier beta-scission pathways. Selectivities predicted on the basis of the relative barrier heights of beta-scission modes accessible to C6 and C8 species indicate general agreement with experimental observations.

Controlling the hydrogenolysis of silica-supported tungsten pentamethyl leads to a class of highly electron deficient partially alkylated metal hydrides

DOE PAGES

Maity, Niladri; Barman, Samir; Callens, Emmanuel; ...

2015-11-30

The well-defined single-site silica-supported tungsten complex [(Si–O–)W(Me) 5], 1, is an excellent precatalyst for alkane metathesis. The unique structure of 1 allows the synthesis of unprecedented tungsten hydrido methyl surface complexes via a controlled hydrogenolysis. Specifically, in the presence of molecular hydrogen, 1 is quickly transformed at -78 °C into a partially alkylated tungsten hydride, 4, as characterized by 1H solid-state NMR and IR spectroscopies. Species 4, upon warming to 150 °C, displays the highest catalytic activity for propane metathesis yet reported. DFT calculations using model systems support the formation of [(Si–O–)WH 3(Me) 2], as the predominant species at -78more » °C following several elementary steps of hydrogen addition (by σ-bond metathesis or α-hydrogen transfer). Rearrangement of 4 occuring between -78 °C and room temperature leads to the formation of an unique methylidene tungsten hydride [(Si–O–)WH 3(CH 2)], as determined by solid-state 1H and 13C NMR spectroscopies and supported by DFT. Thus for the first time, a coordination sphere that incorporates both carbene and hydride functionalities has been observed.« less

Platform Chemicals from an Oilseed Biorefinery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tupy, Mike; Schrodi Yann

2006-11-06

The US chemical industry is $460 billion in size where a $150 billion segment of which is non-oxygenated chemicals that is sourced today via petroleum but is addressable by a renewable feedstock if one considers a more chemically reduced feedstock such as vegetable oils. Vegetable oil, due to its chemical functionality, provides a largely untapped opportunity as a renewable chemical source to replace petroleum-derived chemicals and produce platform chemicals unavailable today. This project examined the fertile intersection between the rich building blocks provided by vegetable oils and the enhanced chemical modification capability provided by metathesis chemistry. The technology advanced inmore » this study is the process of ethylene cross-metathesis (referred to as ethenolysis) with vegetable oil and vegetable oil derivatives to manufacture the platform-chemical 9-decenoic acid (or 9DA) and olefin co-products. The project team meet its goals of demonstrating improved catalyst efficiencies of several multiples, deepening the mechanistic understanding of metathesis, synthesis and screening of dozens of new catalysts, designing and modeling commercial processes, and estimating production costs. One demonstrable result of the study was a step change improvement in catalyst turnover number in the ethenolysis of methyl oleate as reported here. We met our key measurable of producing 100 lbs of 9DA at the pilot-scale, which demonstrated ability to scale-up ethenolysis. DOE Project funding had significant positive impact on development of metathetically modified vegetable oils more broadly as the Cargill/Materia partnership, that was able to initiate primarily due to DOE funding, has succeeded in commercializing products, validating metathesis as a platform technology, and expanding a diverse products portfolio in high value and in large volume markets. Opportunities have expanded and business development has gained considerable momentum and enabled further expansion of the Materia/Cargill relationship. This project exceeded expectations and is having immediate impact on DOE success by replacing petroleum products with renewables in a large volume application today.« less

Retraction Note: Catalytic living ring-opening metathesis polymerization

NASA Astrophysics Data System (ADS)

Nagarkar, Amit A.; Kilbinger, Andreas F. M.

2018-05-01

We the authors are retracting this Article because of our failure to reproduce the molecular weight dispersities (PDI) shown in Fig. 4 using the chain-transfer agent described in the paper (CTA1). While the degenerate chain-transfer mechanism described in Fig. 3 is correct, the best molecular weight dispersities that could be reproduced with the chain-transfer agent shown in the Article are much larger (PDI > 2.0) than reported.We have since studied the kinetics of CTA1 in comparison with several other chain-transfer agents we are currently investigating and we now understand that the reactivity of CTA1 towards propagating ruthenium alkylidene complexes is very low. Very long monomer addition times would therefore have been necessary to gain control over the molecular weight distribution. Such long addition times would exceed the lifetime of the Grubbs catalyst in solution. Faster addition of the monomer has since repeatedly been shown to broaden the molecular weight dispersity.Additionally, the best chain-transfer agents we are currently investigating are orders of magnitude more reactive than CTA1 but give broader molecular weight dispersities than reported in Fig. 4. Molecular weight and dispersity control as shown in Fig. 4 is therefore an inappropriate claim for CTA1.The authors deeply regret these errors and apologize to the community.

Mesoporous Polymer Frameworks from End-Reactive Bottlebrush Copolymers

DOE PAGES

Altay, Esra; Nykypanchuk, Dmytro; Rzayev, Javid

2017-08-07

Reticulated nanoporous materials generated by versatile molecular framework approaches are limited to pore dimensions on the scale of the utilized rigid molecular building blocks (<5 nm). The inherent flexibility of linear polymers precludes their utilization as long framework connectors for the extension of this strategy to larger length scales. We report a method for the fabrication of mesoporous frameworks by using bottlebrush copolymers with reactive end blocks serving as rigid macromolecular interconnectors with directional reactivity. End-reactive bottlebrush copolymers with pendant alkene functionalities were synthesized by a combination of controlled radical polymerization and polymer modification protocols. Ru-catalyzed cross-metathesis cross-linking of bottlebrushmore » copolymers with two reactive end blocks resulted in the formation of polymer frameworks where isolated cross-linked domains were interconnected with bottlebrush copolymer bridges. The resulting materials were characterized by a continuous network pore structure with average pore sizes of 9–50 nm, conveniently tunable by the length of the utilized bottlebrush copolymer building blocks. As a result, the materials fabrication strategy described in this work expands the length scale of molecular framework materials and provides access to mesoporous polymers with a molecularly tunable reticulated pore structure without the need for templating, sacrificial component etching, or supercritical fluid drying.« less

Presidential Green Chemistry Challenge: 2012 Small Business Award

EPA Pesticide Factsheets

Presidential Green Chemistry Challenge 2012 award winner, Elevance Renewable Sciences, used Nobel-prize-winning metathesis catalysis to produce high-value difunctional chemicals from renewable feedstocks including natural oils.

Ethenolysis: A Green Catalytic Tool to Cleave Carbon-Carbon Double Bonds.

PubMed

Bidange, Johan; Fischmeister, Cédric; Bruneau, Christian

2016-08-22

Remarkable innovations have been made in the field of olefin metathesis due to the design and preparation of new catalysts. Ethenolysis, which is cross-metathesis with ethylene, represents one catalytic transformation that has been used with the purpose of cleaving internal carbon-carbon double bonds. The objectives were either the ring opening of cyclic olefins to produce dienes or the shortening of unsaturated hydrocarbon chains to degrade polymers or generate valuable shorter terminal olefins in a controlled manner. This Review summarizes several aspects of this reaction: the catalysts, their degradation in the presence of ethylene, some parameters driving their productivity, the side reactions, and the applications of ethenolysis in organic synthesis and in potential industrial applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Tzu-Pin; Chang, Alice B.; Luo, Shao-Xiong

Grafting density is an important structural parameter that imparts significant influences over the physical properties of architecturally complex polymers. In this paper, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization (ROMP). ω-norbornenyl poly(D,L-lactide) (PLA) and polystyrene (PS) macromonomers were copolymerized with discrete co-monomers in different feed ratios, enabling precise control over the grafting density. Small-angle X-ray scattering (SAXS) experiments demonstrate that these graft block polymers can self-assemble into long-range-orderedmore » lamellar structures. For seventeen series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ~ N bb α) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z (System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, instead of segregation strengths. A model is pro-posed in which the characteristic ratio (C ∞), a proxy for the backbone stiffness, scales with N bb as a function of the grafting density: C ∞ ~ N bb f(z). To the best of our knowledge, this report represents the first study of scaling behavior for the self-assembly of block polymers with variable grafting density. Lastly, the relationships disclosed herein provide valuable insights into conformational changes with grafting density, thus introducing new opportunities for future block polymer design.« less

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

DOE PAGES

Lin, Tzu-Pin; Chang, Alice B.; Luo, Shao-Xiong; ...

2017-10-26

Grafting density is an important structural parameter that imparts significant influences over the physical properties of architecturally complex polymers. In this paper, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization (ROMP). ω-norbornenyl poly(D,L-lactide) (PLA) and polystyrene (PS) macromonomers were copolymerized with discrete co-monomers in different feed ratios, enabling precise control over the grafting density. Small-angle X-ray scattering (SAXS) experiments demonstrate that these graft block polymers can self-assemble into long-range-orderedmore » lamellar structures. For seventeen series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ~ N bb α) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z (System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, instead of segregation strengths. A model is pro-posed in which the characteristic ratio (C ∞), a proxy for the backbone stiffness, scales with N bb as a function of the grafting density: C ∞ ~ N bb f(z). To the best of our knowledge, this report represents the first study of scaling behavior for the self-assembly of block polymers with variable grafting density. Lastly, the relationships disclosed herein provide valuable insights into conformational changes with grafting density, thus introducing new opportunities for future block polymer design.« less

Efficient and selective degradation of polyethylenes into liquid fuels and waxes under mild conditions.

PubMed

Jia, Xiangqing; Qin, Chuan; Friedberger, Tobias; Guan, Zhibin; Huang, Zheng

2016-06-01

Polyethylene (PE) is the largest-volume synthetic polymer, and its chemical inertness makes its degradation by low-energy processes a challenging problem. We report a tandem catalytic cross alkane metathesis method for highly efficient degradation of polyethylenes under mild conditions. With the use of widely available, low-value, short alkanes (for example, petroleum ethers) as cross metathesis partners, different types of polyethylenes with various molecular weights undergo complete conversion into useful liquid fuels and waxes. This method shows excellent selectivity for linear alkane formation, and the degradation product distribution (liquid fuels versus waxes) can be controlled by the catalyst structure and reaction time. In addition, the catalysts are compatible with various polyolefin additives; therefore, common plastic wastes, such as postconsumer polyethylene bottles, bags, and films could be converted into valuable chemical feedstocks without any pretreatment.

On the track to silica-supported tungsten oxo metathesis catalysts: input from 17O solid-state NMR.

PubMed

Merle, Nicolas; Girard, Guillaume; Popoff, Nicolas; De Mallmann, Aimery; Bouhoute, Yassine; Trébosc, Julien; Berrier, Elise; Paul, Jean-François; Nicholas, Christopher P; Del Rosal, Iker; Maron, Laurent; Gauvin, Régis M; Delevoye, Laurent; Taoufik, Mostafa

2013-09-03

The grafting of an oxo chloro trisalkyl tungsten derivative on silica dehydroxylated at 700 °C was studied by several techniques that showed reaction via W-Cl cleavage, to afford a well-defined precatalyst for alkene metathesis. This was further confirmed by DFT calculations on the grafting process. (17)O labeling of the oxo moiety of a series of related molecular and supported tungsten oxo derivatives was achieved, and the corresponding (17)O MAS NMR spectra were recorded. Combined experimental and theoretical NMR studies yielded information on the local structure of the surface species. Assessment of the (17)O NMR parameters also confirmed the nature of the grafting pathway by ruling out other possible grafting schemes, thanks to highly characteristic anisotropic features arising from the quadrupolar and chemical shift interactions.

Amorphous and nanocrystalline luminescent Si and Ge obtained via a solid-state chemical metathesis synthesis route

NASA Astrophysics Data System (ADS)

McMillan, Paul F.; Gryko, Jan; Bull, Craig; Arledge, Richard; Kenyon, Anthony J.; Cressey, Barbara A.

2005-03-01

A new solid-state metathesis synthesis route was applied to obtain bulk samples of amorphous or microcrystalline Si and Ge. The method involves reaction of Zintl phases such as NaSi or NaGe, with ammonium or metal (e.g., CuCl, CoBr 2) halides. The driving force for the solid-state reaction is provided by the formation of alkali halides and the transition metals or metal silicides, or gaseous ammonia and hydrogen. The semiconductors were purified by washing to remove other solid products. The amorphous semiconductors were obtained in bulk form from reactions carried out at 200-300 °C. Syntheses at higher temperatures gave rise to microcrystalline semiconductors, or to micro-/nanocrystalline particles contained within the amorphous material. Similar crystalline/amorphous composites were obtained after heat treatment of bulk amorphous materials.

Synthesis of densely functionalized enantiopure indolizidines by ring-closing metathesis (RCM) of hydroxylamines from carbohydrate-derived nitrones

PubMed Central

Bonanni, Marco; Marradi, Marco; Cardona, Francesca; Cicchi, Stefano; Goti, Andrea

2007-01-01

Background Indolizidine alkaloids widely occur in nature and display interesting biological activity. This is the reason for which their total synthesis as well as the synthesis of non-natural analogues still attracts the attention of many research groups. To establish new straightforward accesses to these molecules is therefore highly desirable. Results The ring closing metathesis (RCM) of enantiopure hydroxylamines bearing suitable unsaturated groups cleanly afforded piperidine derivatives in good yields. Further cyclization and deprotection of the hydroxy groups gave novel highly functionalized indolizidines. The synthesis of a pyrroloazepine analogue is also described. Conclusion We have developed a new straightforward methodology for the synthesis of densely functionalized indolizidines and pyrroloazepine analogues in 6 steps and 30–60% overall yields from enantiopure hydroxylamines obtained straightforwardly from carbohydrate-derived nitrones. PMID:18076753

Synthesis of ω-Oxo Amino Acids and trans-5-Substituted Proline Derivatives Using Cross-Metathesis of Unsaturated Amino Acids.

PubMed

Salih, Nabaz; Adams, Harry; Jackson, Richard F W

2016-09-16

A range of 7-oxo, 8-oxo, and 9-oxo amino acids, analogues of 8-oxo-2-aminodecanoic acid, one of the key components of the cyclic tetrapeptide apicidin, have been prepared by a three-step process involving copper-catalyzed allylation of serine-, aspartic acid-, and glutamic acid-derived organozinc reagents, followed by cross-metathesis of the resulting terminal alkenes with unsaturated ketones and hydrogenation. The intermediate 7-oxo-5-enones underwent a highly diastereoselective (dr ≥96:4) acid-catalyzed aza-Michael reaction to give trans-2,5-disubstituted pyrrolidines, 5-substituted proline derivatives. The aza-Michael reaction was first observed when the starting enones were allowed to stand in solution in deuterochloroform but can be efficiently promoted by catalytic amounts of dry HCl.

Efficient and selective degradation of polyethylenes into liquid fuels and waxes under mild conditions

PubMed Central

Jia, Xiangqing; Qin, Chuan; Friedberger, Tobias; Guan, Zhibin; Huang, Zheng

2016-01-01

Polyethylene (PE) is the largest-volume synthetic polymer, and its chemical inertness makes its degradation by low-energy processes a challenging problem. We report a tandem catalytic cross alkane metathesis method for highly efficient degradation of polyethylenes under mild conditions. With the use of widely available, low-value, short alkanes (for example, petroleum ethers) as cross metathesis partners, different types of polyethylenes with various molecular weights undergo complete conversion into useful liquid fuels and waxes. This method shows excellent selectivity for linear alkane formation, and the degradation product distribution (liquid fuels versus waxes) can be controlled by the catalyst structure and reaction time. In addition, the catalysts are compatible with various polyolefin additives; therefore, common plastic wastes, such as postconsumer polyethylene bottles, bags, and films could be converted into valuable chemical feedstocks without any pretreatment. PMID:27386559

Dispersing Zwitterions into Comb Polymers for Nonviral Transfection: Experiments and Molecular Simulation.

PubMed

Ghobadi, Ahmadreza F; Letteri, Rachel; Parelkar, Sangram S; Zhao, Yue; Chan-Seng, Delphine; Emrick, Todd; Jayaraman, Arthi

2016-02-08

Polymer-based gene delivery vehicles benefit from the presence of hydrophilic groups that mitigate the inherent toxicity of polycations and that provide tunable polymer-DNA binding strength and stable complexes (polyplexes). However, hydrophilic groups screen charge, and as such can reduce cell uptake and transfection efficiency. We report the effect of embedding zwitterionic sulfobetaine (SB) groups in cationic comb polymers, using a combination of experiments and molecular simulations. Ring-opening metathesis polymerization (ROMP) produced comb polymers with tetralysine (K4) and SB pendent groups. Dynamic light scattering, zeta potential measurements, and fluorescence-based experiments, together with coarse-grained molecular dynamics simulations, described the effect of SB groups on the size, shape, surface charge, composition, and DNA binding strength of polyplexes formed using these comb polymers. Experiments and simulations showed that increasing SB composition in the comb polymers decreased polymer-DNA binding strength, while simulations indicated that the SB groups distributed throughout the polyplex. This allows polyplexes to maintain a positive surface charge and provide high levels of gene expression in live cells. Notably, comb polymers with nearly 50 mol % SB form polyplexes that exhibit positive surface charge similarly as polyplexes formed from purely cationic comb polymers, indicating the ability to introduce an appreciable amount of SB functionality without screening surface charge. This integrated simulation-experimental study demonstrates the effectiveness of incorporating zwitterions in polyplexes, while guiding the design of new and effective gene delivery vectors.

Synthesis of amide-functionalized cellulose esters by olefin cross-metathesis.

PubMed

Meng, Xiangtao; Edgar, Kevin J

2015-11-05

Cellulose esters with amide functionalities were synthesized by cross-metathesis (CM) reaction of terminally olefinic esters with different acrylamides, catalyzed by Hoveyda-Grubbs 2nd generation catalyst. Chelation by amides of the catalyst ruthenium center caused low conversions using conventional solvents. The effects of both solvent and structure of acrylamide on reaction conversion were investigated. While the inherent tendency of acrylamides to chelate Ru is governed by the acrylamide N-substituents, employing acetic acid as a solvent significantly improved the conversion of certain acrylamides, from 50% to up to 99%. Homogeneous hydrogenation using p-toluenesulfonyl hydrazide successfully eliminated the α,β-unsaturation of the CM products to give stable amide-functionalized cellulose esters. The amide-functionalized product showed higher Tg than its starting terminally olefinic counterpart, which may have resulted from strong hydrogen bonding interactions of the amide functional groups. Copyright © 2015 Elsevier Ltd. All rights reserved.

Amorphous and nanocrystalline luminescent Si and Ge obtained via a solid-state chemical metathesis synthesis route

DOE Office of Scientific and Technical Information (OSTI.GOV)

McMillan, Paul F.; Gryko, Jan; Bull, Craig

A new solid-state metathesis synthesis route was applied to obtain bulk samples of amorphous or microcrystalline Si and Ge. The method involves reaction of Zintl phases such as NaSi or NaGe, with ammonium or metal (e.g., CuCl, CoBr{sub 2}) halides. The driving force for the solid-state reaction is provided by the formation of alkali halides and the transition metals or metal silicides, or gaseous ammonia and hydrogen. The semiconductors were purified by washing to remove other solid products. The amorphous semiconductors were obtained in bulk form from reactions carried out at 200-300{sup o}C. Syntheses at higher temperatures gave rise tomore » microcrystalline semiconductors, or to micro-/nanocrystalline particles contained within the amorphous material. Similar crystalline/amorphous composites were obtained after heat treatment of bulk amorphous materials.« less

Polymer performance in cooling water: The influence of process variables

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amjad, Z.; Pugh, J.; Zibrida, J.

1997-01-01

The key to the efficacy of phosphate and phosphonates in stabilized phosphate and all-organic cooling water treatment (CWT) programs is the presence and performance of polymeric inhibitors/dispersants. The performance of polymeric additives used in CWT programs can be adversely impacted by the presence of iron, phosphonate, or cationic polymer and influenced by a variety of process variables including system pH and temperature. In this article, the performance of several polymeric additives is evaluated under a variety of stressed conditions.

Polymer performance in cooling water: The influence of process variables

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amjad, Z.; Pugh, J.; Zibrida, J.

1996-12-01

The key to the efficacy of phosphate and phosphonates in stabilized phosphate and all-organic cooling water treatment (CWT) programs is the presence and performance of polymeric inhibitors/dispersants. The performance of polymeric additives used in CWT programs can be adversely impacted by the presence of iron, phosphonate, or cationic polymer and influenced by a variety of process variables including system pH and temperature. In this paper, the performance of several polymeric additives is evaluated under a variety of stressed conditions.

Measuring the Electro-Optic Coefficients of Bulk-poled Polymers

DTIC Science & Technology

2012-09-01

polymethylmethacrylate (PMMA) was produced by CYRO Industries (Acrylite H15) and distributed by AMCO Plastics. All other chemicals were obtained from Sigma...nitrostyryl) benzene) PMMA polymethylmethacrylate RMS root-mean-square ROMP ring-opening metathesis polymer Tg glass transition temperature

Synthesis of (±)-Tetrapetalone A-Me Aglycon**

PubMed Central

Carlsen, Peter N.; Mann, Tyler J.; Hoveyda, Amir H.

2014-01-01

The first synthesis of (±)-tetrapetalone A-Me aglycon is described. Key bond-forming reactions include Nazarov cyclization, a ring-closing metathesis (RCM) promoted with complete diastereoselectivity by a chiral Mo-based complex, tandem conjugate reduction-intramolecular aldol cyclization, and oxidative dearomatization. PMID:25045072

Synthesis by ring-closing alkyne metathesis with selective hydrogenation, and olfactory comparison of (7E)- and (7Z)-cyclohexadec-7-enone (Aurelione(®) ).

PubMed

Mathys, Marion; Kraft, Philip

2014-10-01

Both C=C-bond isomers of cyclohexadec-7-enone (6, Aurelione(®) ) were selectively synthesized via cyclohexadec-7-ynol (16) by ring-closing alkyne metathesis of icosa-2,18-diyn-9-ol (15), employing an in situ-formed catalyst from Mo(CO)6 and 4-(trifluoromethyl)phenol. Pyridinium chlorochromate (PCC) oxidation and subsequent Lindlar hydrogenation afforded the (7Z)-configured isomer (7Z)-6, while hydrosilylation of the intermediate cyclohexadec-7-ynone (17), followed by desilylation, provided the (7E)-configured cyclohexadec-7-enone ((7E)-6). The substrate for the alkyne metathesis was prepared from cycloheptanone (7) by cycloaddition of chloromethylcarbene to its trimethylsilyl enol ether 8, and subsequent ring enlargement of the adduct 9 under rearrangement to 2-methylcyclooct-2-enone (10), which was subjected to Weitz-Scheffer epoxidation and Eschenmoser-Ohloff fragmentation to non-7-ynal (12). Its reaction with the Grignard reagent of 11-bromoundec-2-yne (14), prepared from the corresponding alcohol 13 by Appel-Lee bromination, furnished the icosa-2,18-diyn-9-ol (15). While both isomers of cyclohexadec-7-enone (6) possess warm and powdery musk odors with tobacco-type ambery accents, (7Z)-6 is more animalic and waxy, whereas (7E)-6 was found to be more floral, sweet, and hay-like in tonality. Interestingly, however, with odor detection thresholds of 2.0 ng/l air and 2.3 ng/l air, respectively, both (7Z)-6 and (7E)-6 were found to be almost identical in their odor strength, with the (7Z)-6 being only very slightly more powerful. Copyright © 2014 Verlag Helvetica Chimica Acta AG, Zürich.

Enzymatic glycosylation, inhibitor design, and synthesis and formation of glyco-self assembled monolayers for simulation of recognition.

PubMed

Scheppokat, Angela M; Gerber, Agnes; Schroven, Andreas; Meinke, Sebastian; Kopitzki, Sebastian; Beketow, Eugen; Thimm, Julian; Thiem, Joachim

2010-01-01

Glycosyltransferases from the albumen gland of Helix pomatia could be used in tandem mode for the chemoenzymatic synthesis of beta,1-3/beta,1-6-linked oligogalactans. By employing recombinant trans-sialidase of Trypanosoma cruzi (TcTS) the formation of a range of modified Galbeta,1-3GalNAc derivatives could be terminally alpha,2-3 sialylated. Biacore studies indicated the binding of these modified trisaccharides to myelin-associated glycoprotein (MAG). Using an eight-step synthetic route N-acyl-modified sialyl donor structures could be obtained. TcTS was used to transfer these structures to an isolactoside, and Michaelis constants of the donors indicated the kind and size of modifications allowed at the 5-nitrogen site. A number of sialic acid C-glycosides could be obtained via the C-allyl sialoside and subsequent metathesis. Biacore measurements showed derivatives substituted with aromatic residues to give K(D) values in the mM range. Benzaldehyde-functionalized glycosides of mono and disaccharides were synthesized by metathesis and could be used for the formation of novel glyco-self assembled monolayers (glyco-SAMs) employing various tether structures and attached to gold surfaces. Initial experiments were performed with concanavalin A and manno-SAMs. By atomic force microscopic measurements of tethered glycosides attached to gold-coated tips and surfaces weak forces in the nN range could be detected. Structure activity correlation of forces suggested rationales for complex interactions of various glycosides including minor stereochemical variations. Copyright (c) 2009 Elsevier GmbH. All rights reserved.

Melt Miscibility in Block Copolymers Containing Polyethylene and Substituted Polynorbornenes

NASA Astrophysics Data System (ADS)

Mulhearn, William; Register, Richard

Very few polymer species exist with a sufficiently weak repulsive interaction against polyethylene (PE), characterized by a low Flory parameter χ or interaction energy density X, to be useful for preparing PE-containing block copolymers with disordered melts at high molecular weights. Most suitably miscible polymers are chemically similar to PE, such as copolymers of ethylene with a minority content of an α-olefin, and so are only marginally useful for property modification due to similar physical properties like the glass transition temperature (Tg) . However, the family of polymers consisting of substituted norbornenes prepared via ring-opening metathesis polymerization (ROMP) and subsequent hydrogenation is unique in that many of its members exhibit very low X against PE (comparable with the interaction energy between poly(ethylene-alt-propylene) and PE), and some of these also exhibit high Tg. The miscibility between PE and a substituted, hydrogenated ROMP polynobornene, or between two dissimilar hydrogenated polynorbornenes, is a strong function of the substituent appended to the norbornene monomer. The mixing thermodynamics of this polymer series are irregular, in that the interaction energies do not follow X = (δ1 - δ2)2 where δ is the solubility parameter. However, other systematic trends do apply and we develop a set of mixing rules to quantitatively describe the experimental miscibility behavior. We also investigate statistical copolymerization of two norbornene monomers as a means to continuously tune miscibility with a homopolymer of a third monomer.

Design of aromatic-containing cell-penetrating peptide mimics with structurally modified π electronics.

PubMed

deRonde, Brittany M; Birke, Alexander; Tew, Gregory N

2015-02-09

Cell-penetrating peptides (CPPs) and their synthetic mimics (CPPMs) represent a class of molecules that facilitate the intracellular delivery of various cargo. Previous studies indicated that the presence of aromatic functionalities improved CPPM activity. Given that aromatic functionalities play prominent roles in membrane biology and participate in various π interactions, we explored whether these interactions could be optimized for improved CPPM activity. CPPMs were synthesized by ring-opening metathesis polymerization by using monomers that contained aromatic rings substituted with electron-donating and electron-withdrawing groups and covered an electrostatic potential range from -29.69 to +15.57 kcal mol(-1) . These groups altered the quadrupole moments of the aromatic systems and were used to test if such structural modifications changed CPPM activity. CPPMs were added to dye-loaded vesicles and the release of carboxyfluorescein was monitored as a function of polymer concentration. Changes in the effective polymer concentration to release 50% of the dye (effective concentration, EC50 ) were monitored. Results from this assay showed that the strength of the electron-donating and electron-withdrawing groups incorporated in the CPPMs did not alter polymer EC50 values or activity. This suggests that other design parameters may have a stronger impact on CPPM activity. In addition, these results indicate that a wide range of aromatic groups can be incorporated without negatively impacting polymer activity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Counit Inclusion in Hydrogenated Polynorbornene Copolymer Crystals

NASA Astrophysics Data System (ADS)

Burns, Adam; Showak, Michael; Stella, Andrew; Register, Richard

2014-03-01

Crystallization in poly(A-co-B) random copolymers, where homopolymer A is crystalline but B is not, is dictated by the degree to which crystals of A can include B units. Typically, B units are strongly excluded from the A crystals, drastically reducing the degree of crystallinity wc and crystal thickness tc even at modest comonomer contents. However, in some cases, B units can be incorporated into the crystals as defects, significantly diminishing the counits' impact on wc and tc. The extent and consequences of counit inclusion have been investigated in hydrogenated polynorbornene (hPN) with alkylnorbornene counits, synthesized by living ring-opening metathesis polymerization followed by hydrogenation. In the case of 5-hexylnorbornene (HxN) counits, a steep decline in wc and tc with counit content is found, indicative of strong exclusion. In contrast, when the counits are 5-methylnorbornene (MeN), extensive inclusion of MeN units into the crystals is observed. hP(N-co-MeN) copolymers maintain appreciable crystallinity above 30 mol% MeN, and the dependence of the melting point Tm on tc tracks that of the hPN homopolymer. Four times as much MeN as HxN (molar basis) is required to produce a comparable drop in wc. Therefore, copolymerization with MeN can be used to tune Tm without drastically reducing wc. Additionally, hPN exhibits a polymorphic transition to a rotationally disordered (RD) crystal at temperature Tcc

Polymeric Materials for Aerospace Power and Propulsion: Overview of Polymer Research at NASA Glenn

NASA Technical Reports Server (NTRS)

Meador, Michael A.

2007-01-01

Weight, durability and performance are all major concerns for any NASA mission. Use of lightweight materials, such as fiber reinforced polymer matrix composites can lead to significant reductions in vehicle weight and improvements in vehicle performance. Research in the Polymeric Materials Branch at NASA Glenn is focused on improving the durability, properties, processability and performance of polymeric materials by utilizing both conventional polymer science and engineering as well as nanotechnology and bioinspired approaches. This presentation will provide an overview of these efforts and highlight recent progress.

Association of Ions and Fractional Crystallization.

ERIC Educational Resources Information Center

Scaife, Charles W. J.; Dubs, Richard L.

1983-01-01

Presents an experiment in which color is used as an additional characteristic when purifying and identifying crystals of two soluble salts obtained from a metathesis reaction. Indicates that the experiment has been used with both nonmajors and inorganic chemistry students in at least their third term. (JN)

Synthesis and Characterization of Polyfunctional Polyhedral Silsesquioxane Cages

NASA Astrophysics Data System (ADS)

Sulaiman, Santy

Recent studies on octameric polyhedral silsesquioxanes, (RSiO1.5 )8, indicate that the silsesquioxane cage is not just a passive component but appears to be involved in electron delocalization with conjugated organic tethers in the excited state. This dissertation presents the synthesis and characterization of (RSiO1.5)8 molecules with unique photophysical properties that provide support for the existence of conjugation that involves the (RSiO1.5)8 cage. The dissertation first discusses the elaboration of octavinylsilsesquioxane via cross-metathesis to form styrenyl-functionalized octasilsesquioxane molecules. Subsequent Heck coupling reactions of p-bromostyrenyl derivative provides vinylstilbene-functionalized octasilsesquioxane. The amino derivative, NH2VinylStilbeneOS, show highly red-shifted emission spectrum (100 nm from the simple organic analog p-vinylstilbene) and high two-photon absorption (TPA) cross-section value (100 GM/moiety), indicating charge-transfer processes involving the silsesquioxane cage as the electron acceptor. The unique photophysical properties of polyfunctional luminescent cubic silsesquioxanes synthesized from ortho-8-, (2,5)-16-, and 24-brominated octaphenylsilsesquioxane (OPS) via Heck coupling show how the steric interactions of the organic tethers at the silsesquioxane cage corner affect conjugation with the silsesquioxane cage. Furthermore, the high TPA cross-section (10 GM/moiety) and photoluminescence quantum yield (20%) of OPS functionalized with 24 acetoxystyrenyl groups suggest that the existence excited states in these molecules with similar energies and decay rates: normal radiative pi- pi* transition and charge transfer involving the silsesquioxane cage. The fluoride ion-catalyzed rearrangement reactions of cage and polymeric silsesquioxanes provide a convenient route to a mixture of deca- and dodecameric silsesquioxane molecules in high yields, giving us the opportunity to investigate the effect of silsesquioxane cage geometry on their photophysical properties. The ability to recycle polymeric silsesquioxane resins, byproducts from cubic silsesquioxane syntheses, into useful cage silsesquioxane molecules adds another advantage. Lastly, we present the synthesis of octa(aminophenyl)silsesquioxane-based epoxy resins with coefficient of thermal expansion (CTE) as low as 25°C/ppm without ceramic fillers. The CTEs of these resins can be tailored over an order of magnitude by choosing epoxy crosslinking agents having different flexibilities.

Cooperative Metal+Ligand Oxidative Addition and Sigma-Bond Metathesis: A DFT Study

DOE PAGES

Lopez, Kent G.; Cundari, Thomas R.; Gary, J. Brannon

2018-01-17

A computational study of the experimentally proposed mechanism of alkyne diboration by a PDICo complex yielded two fundamental catalytic steps that undergo remarkable electronic changes, PDI = bis(imino)-pyridine. The reactions are envisaged via DFT (density functional theory) and MCSCF (multi-configuration self-consistent field) simulations as (i) a cooperative metal+ligand oxidative addition, and (ii) a sigma-bond metathesis induced ligand-to-metal charge transfer. Analysis of the bonding of pertinent intermediates/TSs also yielded important insight that may be illuminating with regards to the larger field of green catalysis that seeks to ennoble base metals through synergy with potentially redox non-innocent (RNI) ligands. For the presentmore » case, massive changes in electronic structure do not incur massive energetic penalties. Finally, in conjunction with previous research, one may postulate that structural and energetic “fluidity” among several electronic states of RNI-M 3d along the reaction coordinate is an essential signature of redox cooperativity and thus ennoblement.« less

DFT computations support the σ-complex assisted metathesis (σ-CAM) mechanism for the 1,4-Rh shift of Cp*Rh(III)-(η(1)-β-styryl) complexes.

PubMed

Li, Yougui; He, Gang; Kantchev, Eric Assen B

2014-11-28

DFT calculations support the σ-complex assisted metathesis (σ-CAM) mechanism recently proposed for the first 1,4-Rh shift of a Rh(III) complex rather than the oxidative addition/reductive elimination pathway characteristic of Rh(i). A single, concerted TS (ΔG(‡) = 27-34 kcal mol(-1)) was found and its electronic structure characterized by Bader's AIM analysis. The 4-centered TS is characterized by a enhanced charge separation (Rh and H atoms - positive, both C atoms - negative) relative to the σ-vinyl Rh starting material and the σ-aryl-Rh product. The AIM topological analysis of the electron density reveals a network of interactions: Rh with H as well as both Rh and H with both C(vinyl) and C(aryl) in the TS and confirms the C(vinyl)-Rh agnostic interaction observed experimentally in the σ-aryl-Rh product.

Function-oriented synthesis: biological evaluation of laulimalide analogues derived from a last step cross metathesis diversification strategy.

PubMed

Mooberry, Susan L; Hilinski, Michael K; Clark, Erin A; Wender, Paul A

2008-01-01

Laulimalide is a potent microtubule stabilizing agent and a promising anticancer therapeutic lead. The identification of stable, efficacious and accessible analogues is critical to clinically exploiting this novel lead. To determine which structural features of laulimalide are required for beneficial function and thus for accessing superior clinical candidates, a series of side chain analogues were prepared through a last step cross metathesis diversification strategy and their biological activities were evaluated. Five analogues, differing in potency from 233 nM to 7.9 muM, effectively inhibit cancer cell proliferation. Like laulimalide, they retain activity against multidrug resistant cells, stabilize microtubules and cause the formation of aberrant mitotic spindles, mitotic accumulation, Bcl-2 phosphorylation and initiation of apoptosis. Structural modifications in the C 23-C 27 dihydropyran side chain can be made without changing the overall mechanism of action, but it is clear that this subunit has more than a bystander role.

Z-Selective Catalytic Olefin Cross-Metathesis

PubMed Central

Meek, Simon J.; O’Brien, Robert V.; Llaveria, Josep; Schrock, Richard R.; Hoveyda, Amir H.

2011-01-01

Alkenes are found in a great number of biologically active molecules and are employed in numerous transformations in organic chemistry. Many olefins exist as E or higher energy Z isomers. Catalytic procedures for stereoselective formation of alkenes are therefore valuable; nonetheless, methods for synthesis of 1,2-disubstituted Z olefins are scarce. Here we report catalytic Z-selective cross-metathesis reactions of terminal enol ethers, which have not been reported previously, and allylic amides, employed thus far only in E-selective processes; the corresponding disubstituted alkenes are formed in up to >98% Z selectivity and 97% yield. Transformations, promoted by catalysts that contain the highly abundant and inexpensive molybdenum, are amenable to gram scale operations. Use of reduced pressure is introduced as a simple and effective strategy for achieving high stereoselectivity. Utility is demonstrated by syntheses of anti-oxidant C18 (plasm)-16:0 (PC), found in electrically active tissues and implicated in Alzheimer’s disease, and the potent immunostimulant KRN7000. PMID:21430774

Syntheses and structures of alkaline earth metal bis(diphenylamides).

PubMed

Gärtner, Martin; Fischer, Reinald; Langer, Jens; Görls, Helmar; Walther, Dirk; Westerhausen, Matthias

2007-06-11

Various preparative procedures are employed in order to synthesize alkaline earth metal bis(diphenylamides) such as (i) metalation of HNPh2 with the alkaline earth metal M, (ii) metalation of HNPh2 with MPh2, (iii) metathesis reaction of MI2 with KNPh2, (iv) metalation of HNPh2 with PhMI in THF, and (v) metathesis reaction of PhMI with KNPh2 followed by a dismutation reaction yielding MPh2 and M(NPh2)2. The magnesium compounds [(diox)MgPh2]infinity (1) and (thf)2Mg(NPh2)2 (2) show tetracoordinate metal atoms, whereas in (dme)2Ca(NPh2)2 (3), (thf)4Sr(NPh2)2 (4), and (thf)4Ba(NPh2)2 (5) the metals are 6-fold coordinated. Additional agostic interactions between an ipso-carbon of one of the phenyl groups of the amide ligand and the alkaline earth metal atom lead to unsymmetric coordination of the NPh2 anions with two strongly different M-N-C angles in 3-5.

Cooperative Metal+Ligand Oxidative Addition and Sigma-Bond Metathesis: A DFT Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lopez, Kent G.; Cundari, Thomas R.; Gary, J. Brannon

A computational study of the experimentally proposed mechanism of alkyne diboration by a PDICo complex yielded two fundamental catalytic steps that undergo remarkable electronic changes, PDI = bis(imino)-pyridine. The reactions are envisaged via DFT (density functional theory) and MCSCF (multi-configuration self-consistent field) simulations as (i) a cooperative metal+ligand oxidative addition, and (ii) a sigma-bond metathesis induced ligand-to-metal charge transfer. Analysis of the bonding of pertinent intermediates/TSs also yielded important insight that may be illuminating with regards to the larger field of green catalysis that seeks to ennoble base metals through synergy with potentially redox non-innocent (RNI) ligands. For the presentmore » case, massive changes in electronic structure do not incur massive energetic penalties. Finally, in conjunction with previous research, one may postulate that structural and energetic “fluidity” among several electronic states of RNI-M 3d along the reaction coordinate is an essential signature of redox cooperativity and thus ennoblement.« less

Alkaline earth metallocenes coordinated with ester pendants: synthesis, structural characterization, and application in metathesis reactions.

PubMed

Li, Heng; Zhang, Wen-Xiong; Xi, Zhenfeng

2013-09-16

A variety of ester-substituted cyclopentadiene derivatives have been synthesized by one-pot reactions of 1,4-dilithio-1,3-butadienes, CO, and acid chlorides. Direct deprotonation of the ester-substituted cyclopentadienes with Ae[N(SiMe3 )2 ]2 (Ae=Ca, Sr, Ba) efficiently generated members of a new class of heavier alkaline earth (Ca, Sr, Ba) metallocenes in good to excellent yields. Single-crystal X-ray structural analysis demonstrated that these heavier alkaline earth metallocenes incorporated two intramolecularly coordinated ester pendants and multiply-substituted cyclopentadienyl ligands. The corresponding transition metal metallocenes, such as ferrocene derivatives and half-sandwich cyclopentadienyl tricarbonylrhenium complexes, could be generated highly efficiently by metathesis reactions. The multiply-substituted cyclopentadiene ligands bearing an ester pendant, and the corresponding heavier alkaline earth and transition-metal metallocenes, may have further applications in coordination chemistry, organometallic chemistry, and organic synthesis. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In situ chemical oxidative polymerization preparation of poly(3,4-ethylenedioxythiophene)/graphene nanocomposites with enhanced thermoelectric performance.

PubMed

Xu, Kongli; Chen, Guangming; Qiu, Dong

2015-05-01

Three different in situ chemical oxidative polymerization routes, that is, (A) spin-coating and subsequent liquid layer polymerization, (B) spin-coating followed by vapor phase polymerization, and (C) in situ polymerization and then post-treatment by immersion in ethylene glycol (EG), have been developed to achieve poly(3,4-ethylenedioxythiophene)/reduced graphene oxide (PEDOT/rGO) nanocomposites. As demonstrated by scanning electron microscopic and energy-dispersive X-ray spectroscopic techniques, PEDOT has been successfully coated on the surface of the rGO nanosheets by each of the three preparation routes. Importantly, all of the nanocomposites display a greatly enhanced thermoelectric performance (power factors) relative to those of the corresponding neat PEDOT. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Superwettability-Induced Confined Reaction toward High-Performance Flexible Electrodes.

PubMed

Xiong, Weiwei; Liu, Hongliang; Zhou, Yahong; Ding, Yi; Zhang, Xiqi; Jiang, Lei

2016-05-18

To find a general strategy to realize confinement of the conductive layer for high-performance flexible electrodes, with improved interfacial adhesion and high conductivity, is of important scientific significance. In this work, superwettability-induced confined reaction is used to fabricate high-performance flexible Ag/polymer electrodes, showing significantly improved silver conversion efficiency and interfacial adhesion. The as-prepared flexible electrodes by superhydrophilic polymeric surface under oil are highly conductive with an order of magnitude higher than the Ag/polymer electrodes obtained from original polymeric surface. The high conductivity achieved via superhydrophilic confinement is ascribed to the fact that the superhydrophilic polymeric surface can enhance the reaction rate of silver deposition and reduce the size of silver nanoparticles to achieve the densest packing. This new approach will provide a simple method to fabricate flexible and highly conductive Ag/polymer electrodes with excellent adhesion between the conductive layer and the substrate, and can be extended to other metal/polymeric electrodes or alloy/polymeric electrodes.

Polymeric Coating of Supporting Substrates Facilities: New Source Performance Standards (NSPS)

EPA Pesticide Factsheets

Learn more about the New Source Performance Standards (NSPS) rule for polymeric coating by reading the rule summary, rule history and the code of federal regulations subpart. Information on related rules is also on this page.

Shell Higher Olefins Process.

ERIC Educational Resources Information Center

Lutz, E. F.

1986-01-01

Shows how olefin isomerization and the exotic olefin metathesis reaction can be harnessed in industrial processes. Indicates that the Shell Higher Olefins Process makes use of organometallic catalysts to manufacture alpha-olefins and internal carbon-11 through carbon-14 alkenes in a flexible fashion that can be adjusted to market needs. (JN)

Recent advances and developments in composite dental restorative materials.

PubMed

Cramer, N B; Stansbury, J W; Bowman, C N

2011-04-01

Composite dental restorations represent a unique class of biomaterials with severe restrictions on biocompatibility, curing behavior, esthetics, and ultimate material properties. These materials are presently limited by shrinkage and polymerization-induced shrinkage stress, limited toughness, the presence of unreacted monomer that remains following the polymerization, and several other factors. Fortunately, these materials have been the focus of a great deal of research in recent years with the goal of improving restoration performance by changing the initiation system, monomers, and fillers and their coupling agents, and by developing novel polymerization strategies. Here, we review the general characteristics of the polymerization reaction and recent approaches that have been taken to improve composite restorative performance.

Recent Advances and Developments in Composite Dental Restorative Materials

PubMed Central

Cramer, N.B.; Stansbury, J.W.; Bowman, C.N.

2011-01-01

Composite dental restorations represent a unique class of biomaterials with severe restrictions on biocompatibility, curing behavior, esthetics, and ultimate material properties. These materials are presently limited by shrinkage and polymerization-induced shrinkage stress, limited toughness, the presence of unreacted monomer that remains following the polymerization, and several other factors. Fortunately, these materials have been the focus of a great deal of research in recent years with the goal of improving restoration performance by changing the initiation system, monomers, and fillers and their coupling agents, and by developing novel polymerization strategies. Here, we review the general characteristics of the polymerization reaction and recent approaches that have been taken to improve composite restorative performance. PMID:20924063

Sieving polymer synthesis by reversible addition fragmentation chain transfer polymerization.

PubMed

Nai, Yi Heng; Jones, Roderick C; Breadmore, Michael C

2013-12-01

Replaceable sieving polymers are the fundamental component for high resolution nucleic acids separation in CE. The choice of polymer and its physical properties play significant roles in influencing separation performance. Recently, reversible addition fragmentation chain transfer (RAFT) polymerization has been shown to be a versatile polymerization technique capable of yielding well defined polymers previously unattainable by conventional free radical polymerization. In this study, a high molecular weight PDMA at 765 000 gmol-1 with a PDI of 1.55 was successfully synthesized with the use of chain transfer agent - 2-propionic acidyl butyl trithiocarbonate (PABTC) in a multi-step sequential RAFT polymerization approach. This study represents the first demonstration of RAFT polymerization for synthesizing polymers with the molecular weight range suitable for high resolution DNA separation in sieving electrophoresis. Adjustment of pH in the reaction was found to be crucial for the successful RAFT polymerization of high molecular weight polymer as the buffered condition minimizes the effect of hydrolysis and aminolysis commonly associated with trithiocarbonate chain transfer agents. The separation efficiency of PABTC-PDMA was found to have marginally superior separation performance compared to a commercial PDMA formulation, POP™-CAP, of similar molecular weight range.

Immobilization of molecular catalysts in supported ionic liquid phases.

PubMed

Van Doorslaer, Charlie; Wahlen, Joos; Mertens, Pascal; Binnemans, Koen; De Vos, Dirk

2010-09-28

In a supported ionic liquid phase (SILP) catalyst system, an ionic liquid (IL) film is immobilized on a high-surface area porous solid and a homogeneous catalyst is dissolved in this supported IL layer, thereby combining the attractive features of homogeneous catalysts with the benefits of heterogeneous catalysts. In this review reliable strategies for the immobilization of molecular catalysts in SILPs are surveyed. In the first part, general aspects concerning the application of SILP catalysts are presented, focusing on the type of catalyst, support, ionic liquid and reaction conditions. Secondly, organic reactions in which SILP technology is applied to improve the performance of homogeneous transition-metal catalysts are presented: hydroformylation, metathesis reactions, carbonylation, hydrogenation, hydroamination, coupling reactions and asymmetric reactions.

Nucleation of polystyrene latex particles in the presence of gamma-methacryloxypropyltrimethoxysilane: functionalized silica particles.

PubMed

Bourgeat-Lami, Elodie; Insulaire, Mickaelle; Reculusa, Stéphane; Perro, Adeline; Ravaine, Serge; Duguet, Etienne

2006-02-01

Silica/polystyrene nanocomposite particles with different morphologies were synthesized through emulsion polymerization of styrene in the presence of silica particles previously modified by gamma-methacryloxypropyltrimethoxysilane (MPS). Grafting of the silane molecule was performed by direct addition of MPS to the aqueous silica suspension in the presence of an anionic surfactant under basic conditions. The MPS grafting density on the silica surface was determined using the depletion method and plotted against the initial MPS concentration. The influence of the MPS grafting density, the silica particles size and concentration and the nature of the surfactant on the polymerization kinetics and the particles morphology was investigated. When the polymerization was performed in the presence of an anionic surfactant, transmission electron microscopy images showed the formation of polymer spheres around silica for MPS grafting densities lower than typically 1 micromole x m(-2) while the conversion versus time curves indicated a strong acceleration effect under such conditions. In contrast, polymerizations performed in the presence of a larger amount of MPS moieties or in the presence of a non ionic emulsifier resulted in the formation of "excentered" core-shell morphologies and lower polymerization rates. The paper identifies the parameters that allow to control particles morphology and polymerization kinetics and describes the mechanism of formation of the nanocomposite colloids.

Variable Effect during Polymerization

ERIC Educational Resources Information Center

Lunsford, S. K.

2005-01-01

An experiment performing the polymerization of 3-methylthiophene(P-3MT) onto the conditions for the selective electrode to determine the catechol by using cyclic voltammetry was performed. The P-3MT formed under optimized conditions improved electrochemical reversibility, selectivity and reproducibility for the detection of the catechol.

Nucleotide Selectivity in Abiotic RNA Polymerization Reactions.

PubMed

Coari, Kristin M; Martin, Rebecca C; Jain, Kopal; McGown, Linda B

2017-09-01

In order to establish an RNA world on early Earth, the nucleotides must form polymers through chemical rather than biochemical reactions. The polymerization products must be long enough to perform catalytic functions, including self-replication, and to preserve genetic information. These functions depend not only on the length of the polymers, but also on their sequences. To date, studies of abiotic RNA polymerization generally have focused on routes to polymerization of a single nucleotide and lengths of the homopolymer products. Less work has been done the selectivity of the reaction toward incorporation of some nucleotides over others in nucleotide mixtures. Such information is an essential step toward understanding the chemical evolution of RNA. To address this question, in the present work RNA polymerization reactions were performed in the presence of montmorillonite clay catalyst. The nucleotides included the monophosphates of adenosine, cytosine, guanosine, uridine and inosine. Experiments included reactions of mixtures of an imidazole-activated nucleotide (ImpX) with one or more unactivated nucleotides (XMP), of two or more ImpX, and of XMP that were activated in situ in the polymerization reaction itself. The reaction products were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify the lengths and nucleotide compositions of the polymerization products. The results show that the extent of polymerization, the degree of heteropolymerization vs. homopolymerization, and the composition of the polymeric products all vary among the different nucleotides and depend upon which nucleotides and how many different nucleotides are present in the mixture.

Nucleotide Selectivity in Abiotic RNA Polymerization Reactions

NASA Astrophysics Data System (ADS)

Coari, Kristin M.; Martin, Rebecca C.; Jain, Kopal; McGown, Linda B.

2017-09-01

In order to establish an RNA world on early Earth, the nucleotides must form polymers through chemical rather than biochemical reactions. The polymerization products must be long enough to perform catalytic functions, including self-replication, and to preserve genetic information. These functions depend not only on the length of the polymers, but also on their sequences. To date, studies of abiotic RNA polymerization generally have focused on routes to polymerization of a single nucleotide and lengths of the homopolymer products. Less work has been done the selectivity of the reaction toward incorporation of some nucleotides over others in nucleotide mixtures. Such information is an essential step toward understanding the chemical evolution of RNA. To address this question, in the present work RNA polymerization reactions were performed in the presence of montmorillonite clay catalyst. The nucleotides included the monophosphates of adenosine, cytosine, guanosine, uridine and inosine. Experiments included reactions of mixtures of an imidazole-activated nucleotide (ImpX) with one or more unactivated nucleotides (XMP), of two or more ImpX, and of XMP that were activated in situ in the polymerization reaction itself. The reaction products were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify the lengths and nucleotide compositions of the polymerization products. The results show that the extent of polymerization, the degree of heteropolymerization vs. homopolymerization, and the composition of the polymeric products all vary among the different nucleotides and depend upon which nucleotides and how many different nucleotides are present in the mixture.

Measurement and Analysis of in vitro Actin Polymerization

PubMed Central

Doolittle, Lynda K.; Rosen, Michael K.; Padrick, Shae B.

2014-01-01

Summary The polymerization of actin underlies force generation in numerous cellular processes. While actin polymerization can occur spontaneously, cells maintain control over this important process by preventing actin filament nucleation and then allowing stimulated polymerization and elongation by several regulated factors. Actin polymerization, regulated nucleation and controlled elongation activities can be reconstituted in vitro, and used to probe the signaling cascades cells use to control when and where actin polymerization occurs. Introducing a pyrene fluorophore allows detection of filament formation by an increase in pyrene fluorescence. This method has been used for many years and continues to be broadly used, owing to its simplicity and flexibility. Here we describe how to perform and analyze these in vitro actin polymerization assays, with an emphasis on extracting useful descriptive parameters from kinetic data. PMID:23868594

In situ metathesis reaction combined with liquid-phase microextraction based on the solidification of sedimentary ionic liquids for the determination of pyrethroid insecticides in water samples.

PubMed

Hu, Lu; Zhang, Panjie; Shan, Wanyu; Wang, Xuan; Li, Songqing; Zhou, Wenfeng; Gao, Haixiang

2015-11-01

A novel dispersion liquid-liquid microextraction method based on the solidification of sedimentary ionic liquids (SSIL-DLLME), in which an in situ metathesis reaction forms an ionic liquid (IL) extraction phase, was developed to determine four pyrethroid insecticides (i.e., permethrin, cyhalothrin, fenpropathrin, and transfluthrin) in water followed by separation using high-performance liquid chromatography. In the developed method, in situ DLLME was used to enhance the extraction efficiency and yield. After centrifugation, the extraction solvent, tributyldodecylphosphonium hexafluorophosphate ([P44412][PF6]), was easily collected by solidification in the bottom of the tube. The effects of various experimental parameters, the quantity of tributyldodecylphosphonium bromide ([P44412]Br), the molar ratio of [P44412]Br to potassium hexafluorophosphate (KPF6), the ionic strength, the temperature of the sample solution, and the centrifugation time, were optimized using a Plackett-Burman design to identify the significant factors that affected the extraction efficiency. These significant factors were then optimized using a central composite design. Under the optimized conditions, the recoveries of the four pyrethroid insecticides at four spiked levels ranged from 87.1% to 101.7%, with relative standard deviations (RSDs) ranging from 0.1% to 5.5%. At concentration levels between 1 and 500 µg/L, good linearity was obtained, with coefficients of determination greater than 0.9995. The limits of detection (LODs) for the four pyrethroid insecticides were in the range of 0.71-1.54 µg/L. The developed method was then successfully used for the determination of pyrethroid insecticides in environmental samples. Copyright © 2015 Elsevier B.V. All rights reserved.

Facile and Reliable in Situ Polymerization of Poly(Ethyl Cyanoacrylate)-Based Polymer Electrolytes toward Flexible Lithium Batteries.

PubMed

Cui, Yanyan; Chai, Jingchao; Du, Huiping; Duan, Yulong; Xie, Guangwen; Liu, Zhihong; Cui, Guanglei

2017-03-15

Polycyanoacrylate is a very promising matrix for polymer electrolyte, which possesses advantages of strong binding and high electrochemical stability owing to the functional nitrile groups. Herein, a facile and reliable in situ polymerization strategy of poly(ethyl cyanoacrylate) (PECA) based gel polymer electrolytes (GPE) via a high efficient anionic polymerization was introduced consisting of PECA and 4 M LiClO 4 in carbonate solvents. The in situ polymerized PECA gel polymer electrolyte achieved an excellent ionic conductivity (2.7 × 10 -3 S cm -1 ) at room temperature, and exhibited a considerable electrochemical stability window up to 4.8 V vs Li/Li + . The LiFePO 4 /PECA-GPE/Li and LiNi 1.5 Mn 0.5 O 4 /PECA-GPE/Li batteries using this in-situ-polymerized GPE delivered stable charge/discharge profiles, considerable rate capability, and excellent cycling performance. These results demonstrated this reliable in situ polymerization process is a very promising strategy to prepare high performance polymer electrolytes for flexible thin-film batteries, micropower lithium batteries, and deformable lithium batteries for special purpose.

Compatibility between dental adhesive systems and dual-polymerizing composite resins.

PubMed

Michaud, Pierre-Luc; MacKenzie, Alexandra

2016-10-01

Information is lacking about incompatibilities between certain types of adhesive systems and dual-polymerizing composite resins, and universal adhesives have yet to be tested with these resins. The purpose of this in vitro study was to investigate the bonding outcome of dual-polymerizing foundation composite resins by using different categories of adhesive solutions and to determine whether incompatibilities were present. One hundred and eighty caries-free, extracted third molar teeth were allocated to 9 groups (n=20), in which 3 different bonding agents (Single Bond Plus [SB]), Scotchbond Multi-purpose [MP], and Scotchbond Universal [SU]) were used to bond 3 different composite resins (CompCore AF [CC], Core Paste XP [CP], and Filtek Supreme Ultra [FS]). After restorations had been fabricated using an Ultradent device, the specimens were stored in water at 37°C for 24 hours. The specimens were tested under shear force at a rate of 0.5 mm/min. The data were analyzed with Kruskal-Wallis tests and post hoc pairwise comparisons (α=.05). All 3 composite resins produced comparable shear bond strengths when used with MP (P=.076). However, when either SB or SU was used, the light-polymerized composite resin (FS) and 1 dual-polymerized foundation composite resin (CC) bonded significantly better than the other dual-polymerized foundation composite resin (CP) (P<.005). Both FS and CC performed best with SU but had acceptable results with all of the bonding agents. CP only performed acceptably with MP (P=.023) and had poor results with both other agents. Dual-polymerizing composite resins can obtain equally good bond strengths as light-polymerizing alternatives. However, not all dual-polymerizing composite resins perform well with all bonding systems; some incompatibilities exist between different products. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Effect of polymer type on characterization and filtration performances of multi-walled carbon nanotubes (MWCNT)-COOH-based polymeric mixed matrix membranes.

PubMed

Sengur-Tasdemir, Reyhan; Mokkapati, Venkata R S S; Koseoglu-Imer, Derya Y; Koyuncu, Ismail

2018-05-01

Multi-walled carbon nanotubes (MWCNTs) can be used for the fabrication of mixed matrix polymeric membranes that can enhance filtration perfomances of the membranes by modifying membrane surface properties. In this study, detailed characterization and filtration performances of MWCNTs functionalized with COOH group, blended into polymeric flat-sheet membranes were investigated using different polymer types. Morphological characterization was carried out using atomic force microscopy, scanning electron microscopy and contact angle measurements. For filtration performance tests, protein, dextran, E. coli suspension, Xanthan Gum and real activated sludge solutions were used. Experimental data and analyses revealed that Polyethersulfone (PES) + MWCNT-COOH mixed matrix membranes have superior performance abilities compared to other tested membranes.

Synthesis of an Epoxide Carbonylation Catalyst: Exploration of Contemporary Chemistry for Advanced Undergraduates

ERIC Educational Resources Information Center

Getzler, Yutan D. Y. L.; Schmidt, Joseph A. R.; Coates, Geoffrey W.

2005-01-01

A class of highly active, well-defined compounds for the catalytic carbonylation of epoxides and aziridines to beta-lactones and beta-lactams are introduced. The synthesis of one of the catalysts involves a simple imine condensation to form the ligand followed by air-sensitive metalation and salt metathesis steps.

Synthesis and Characterization of Cerium(IV) Metallocenes

DOE PAGES

Sutton, Andrew; Clark, David Lewis; Scott, Brian Lindley; ...

2015-12-11

In this study, by applying a salt metathesis approach between Ce(OtBu 3) 2(NO 3) 2(THF) 2 and the potassium salts of mono- and ditrimethylsilyl substituted cyclopentadienes, we were able to isolate two new Ce(IV) metallocenes, including to the best of our knowledge, the first structurally characterized bis-cyclopentadiene Ce(IV) compound.

A synthetic approach to the fusicoccane A-B ring fragment based on a Pauson-Khand cycloaddition/Norrish type 1 fragmentation.

PubMed

Dake, Gregory R; Fenster, Erik E; Patrick, Brian O

2008-09-05

A synthetic approach to the A-B ring system within the fusicoccane family of diterpenes is presented. Key steps in this approach are a diastereoselective Pauson-Khand reaction, a Norrish 1 photofragmentation, a Charette cyclopropanation, and a ring-closing metathesis process.

Development of Improved Chemicals and Plastics from Oilseeds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nugent, Patricia A.; Lysenko, Zenon

2006-11-09

The overall objective of this program was to develop technology that can be applied to the production of various chemicals and plastics from seed oils. This research and development program included activities in all four key barrier areas identified in the US DOE Technology Roadmap for Plant/Crop-Based Renewable Resources, namely Plant Science, Production, Processing, and Utilization. Participants in the project included The Dow Chemical Company, Castor Oil, Inc., and the USDA Western Regional Research Center (WRRC). The objective of this production task was to evaluate and develop metathesis catalyst technology as a means of utilizing seed oils as feedstocks formore » the chemical industry. Specifically, ethenolysis of fatty acid methyl esters, FAME’s, leads to functionalized derivatives. These serve as valuable starting points for materials which cascade into a variety of applications, many of which have a current market presence. The relatively recent discovery and commercial availability of a family of metathesis catalysts which are tolerant of polar functional groups and the acquisition and implementation of high throughput synthesis and screening infrastructure led to a prime opportunity to investigate this project area.« less

Hydride oxidation from a titanium–aluminum bimetallic complex: insertion, thermal and electrochemical reactivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Alexandra C.; Altman, Alison B.; Lohrey, Trevor D.

We report the synthesis and reactivity of paramagnetic heterometallic complexes containing a Ti(III)-μ-H-Al(III) moiety. Combining different stoichiometries amounts of Cp 2TiCl and KH 3AlC(TMS) 3 (Cp = cyclopentadienyl, TMS = trimethylsilyl) resulted in the formation of either bimetallic Cp 2Ti(μ-H) 2(H)AlC(TMS) 3 (2) or trimetallic (Cp 2Ti) 2(μ-H) 3(H)AlC(TMS) 3 (3) via salt metathesis pathways. While these complexes were indefinitely stable at room temperature, the bridging hydrides were readily activated upon exposure to heteroallenes, heating, or electrochemical oxidation. In each case, formal hydride oxidation occurred, but the isolated product maintained the +3 oxidation state at both metal centers. The naturemore » of this reactivity was explored using deuterium labelling experiments and Density Functional Theory (DFT) calculations. It was found that while C–H activation from the Ti(III) bimetallic may occur through a σ-bond metathesis pathway, chemical oxidation to Ti(IV) promotes bimolecular reductive elimination of dihydrogen to form a Ti(III) product.« less

Hydride oxidation from a titanium–aluminum bimetallic complex: insertion, thermal and electrochemical reactivity

DOE PAGES

Brown, Alexandra C.; Altman, Alison B.; Lohrey, Trevor D.; ...

2017-05-31

We report the synthesis and reactivity of paramagnetic heterometallic complexes containing a Ti(III)-μ-H-Al(III) moiety. Combining different stoichiometries amounts of Cp 2TiCl and KH 3AlC(TMS) 3 (Cp = cyclopentadienyl, TMS = trimethylsilyl) resulted in the formation of either bimetallic Cp 2Ti(μ-H) 2(H)AlC(TMS) 3 (2) or trimetallic (Cp 2Ti) 2(μ-H) 3(H)AlC(TMS) 3 (3) via salt metathesis pathways. While these complexes were indefinitely stable at room temperature, the bridging hydrides were readily activated upon exposure to heteroallenes, heating, or electrochemical oxidation. In each case, formal hydride oxidation occurred, but the isolated product maintained the +3 oxidation state at both metal centers. The naturemore » of this reactivity was explored using deuterium labelling experiments and Density Functional Theory (DFT) calculations. It was found that while C–H activation from the Ti(III) bimetallic may occur through a σ-bond metathesis pathway, chemical oxidation to Ti(IV) promotes bimolecular reductive elimination of dihydrogen to form a Ti(III) product.« less

Hydrogenation catalysts were derived from Mo(Co)/sub 6//alumina

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowman, R.G.

1979-01-01

Alumina hydrogenation catalysts were derived from mo(CO)/sub 6//alumina with characteristics dependent upon the activation temperature, degree of alumina hydroxylation, and carrier gas used. Decomposition of Mo(CO)/sub 6/ at 100/sup 0/C on partially hydroxylated alumina in helium or hydrogen yielded Mo(CO)/sub 3//alumina, which catalyzed olefin metathesis in helium carrier and both metathesis and hydrogenation in hydrogen carrier. Decomposition of Mo(CO)/sub 6/ on dehydroxylated alumina at 100/sup 0/C in helium and in hydrogen resulted in complete decarbonylation and partial oxidation of molybdenum; this catalyst was 10 times as active as Mo(CO)/sub 3//alumina for hydrogenation. Decomposition of Mo(CO)/sub 6/ on dehydroxylated alumina atmore » 500/sup 0/C in helium gave essentially Mo(0)/alumina, which catalyzed hydrogenation, methanation, and hydrogenolysis in hydrogen. Catalysts activated on dehydroxylated alumina were ten times more active for methanation at 300/sup 0/C than catalyst activated on partially hydroxylated alumina and showed differences in selectivity for cyclopropane hydrogenolysis at 100/sup 0/C.« less

A study on an unusual SN2 mechanism in the methylation of benzyne through nickel-complexation.

PubMed

Hatakeyama, Makoto; Sakamoto, Yuki; Ogata, Koji; Sumida, Yuto; Sumida, Tomoe; Hosoya, Takamitsu; Nakamura, Shinichiro

2017-10-11

In this study, three reaction mechanisms of a benzyne-nickel (Ni) complex ([Ni(C 6 H 4 )(dcpe)]) with iodomethane during the methylation process were investigated, namely (a) S N 2 reaction of the benzyne-Ni complex with iodomethane, (b) concerted σ-bond metathesis during the bond breaking/forming processes, and (c) oxidative addition of iodomethane to the Ni-center and the subsequent reductive elimination process. DFT calculations revealed that the reaction barrier of the S N 2 reaction is slightly lower than those of the other mechanisms. The results of orbital analyses suggest that [Ni(C 6 H 4 )(dcpe)] forms a metallacycle structure between benzyne and the Ni II (3d 8 ) center instead of the η 2 -structure with the Ni 0 (3d 10 ) center. The metallacycle structures became inappropriate as the intermediates of oxidative addition in the formation of the Ni II -Me bond, avoiding further oxidation to the high-valent Ni IV . The high free energy along σ-bond metathesis was generated from the steric hindrance, thus invoking methylation and Ni-I bond formation concertedly.

Copper(I)-induced amplification of a [2]catenane in a virtual dynamic library of macrocyclic alkenes.

PubMed

Berrocal, José Augusto; Nieuwenhuizen, Marko M L; Mandolini, Luigi; Meijer, E W; Di Stefano, Stefano

2014-08-28

Olefin cross-metathesis of diluted dichloromethane solutions (≤0.15 M) of the 28-membered macrocyclic alkene C1, featuring a 1,10-phenanthroline moiety in the backbone, as well as of catenand 1, composed of two identical interlocked C1 units, generates families of noninterlocked oligomers Ci. The composition of the libraries is strongly dependent on the monomer concentration, but independent of whether C1 or 1 is used as feedstock, as expected for truly equilibrated systems. Accordingly, the limiting value 0.022 M approached by the equilibrium concentration of C1 when the total monomer concentration approaches the critical value, as predicted by the Jacobson-Stockmayer theory, provides a reliable estimate of the thermodynamically effective molarity. Catenand 1 behaves as a virtual component of the dynamic libraries, in that there is no detectable trace of its presence in the equilibrated mixtures, but becomes the major component - in the form of its copper(I) complex - when olefin cross-metathesis is carried out in the presence of a copper(I) salt.

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

PubMed Central

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

2016-01-01

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. PMID:27166728

Porous Structure Design of Polymeric Membranes for Gas Separation

DOE PAGES

Zhang, Jinshui; Schott, Jennifer Ann; Mahurin, Shannon Mark; ...

2017-04-04

High-performance polymeric membranes for gas separation are of interest for molecular-level separations in industrial-scale chemical, energy and environmental processes. To overcome the inherent trade-off relationship between permeability and selectivity, the creation of permanent microporosity in polymeric matrices is highly desirable because the porous structures can provide a high fractional free volume to facilitate gas transport through the dense layer. In this feature article, recent developments in the formation of porous polymeric membranes and potential strategies for pore structure design are reviewed.

A Review on Surface Stress-Based Miniaturized Piezoresistive SU-8 Polymeric Cantilever Sensors

NASA Astrophysics Data System (ADS)

Mathew, Ribu; Ravi Sankar, A.

2018-06-01

In the last decade, microelectromechanical systems (MEMS) SU-8 polymeric cantilevers with piezoresistive readout combined with the advances in molecular recognition techniques have found versatile applications, especially in the field of chemical and biological sensing. Compared to conventional solid-state semiconductor-based piezoresistive cantilever sensors, SU-8 polymeric cantilevers have advantages in terms of better sensitivity along with reduced material and fabrication cost. In recent times, numerous researchers have investigated their potential as a sensing platform due to high performance-to-cost ratio of SU-8 polymer-based cantilever sensors. In this article, we critically review the design, fabrication, and performance aspects of surface stress-based piezoresistive SU-8 polymeric cantilever sensors. The evolution of surface stress-based piezoresistive cantilever sensors from solid-state semiconductor materials to polymers, especially SU-8 polymer, is discussed in detail. Theoretical principles of surface stress generation and their application in cantilever sensing technology are also devised. Variants of SU-8 polymeric cantilevers with different composition of materials in cantilever stacks are explained. Furthermore, the interdependence of the material selection, geometrical design parameters, and fabrication process of piezoresistive SU-8 polymeric cantilever sensors and their cumulative impact on the sensor response are also explained in detail. In addition to the design-, fabrication-, and performance-related factors, this article also describes various challenges in engineering SU-8 polymeric cantilevers as a universal sensing platform such as temperature and moisture vulnerability. This review article would serve as a guideline for researchers to understand specifics and functionality of surface stress-based piezoresistive SU-8 cantilever sensors.[Figure not available: see fulltext.

Directed evolution of artificial metalloenzymes for in vivo metathesis

NASA Astrophysics Data System (ADS)

Jeschek, Markus; Reuter, Raphael; Heinisch, Tillmann; Trindler, Christian; Klehr, Juliane; Panke, Sven; Ward, Thomas R.

2016-09-01

The field of biocatalysis has advanced from harnessing natural enzymes to using directed evolution to obtain new biocatalysts with tailor-made functions. Several tools have recently been developed to expand the natural enzymatic repertoire with abiotic reactions. For example, artificial metalloenzymes, which combine the versatile reaction scope of transition metals with the beneficial catalytic features of enzymes, offer an attractive means to engineer new reactions. Three complementary strategies exist: repurposing natural metalloenzymes for abiotic transformations; in silico metalloenzyme (re-)design; and incorporation of abiotic cofactors into proteins. The third strategy offers the opportunity to design a wide variety of artificial metalloenzymes for non-natural reactions. However, many metal cofactors are inhibited by cellular components and therefore require purification of the scaffold protein. This limits the throughput of genetic optimization schemes applied to artificial metalloenzymes and their applicability in vivo to expand natural metabolism. Here we report the compartmentalization and in vivo evolution of an artificial metalloenzyme for olefin metathesis, which represents an archetypal organometallic reaction without equivalent in nature. Building on previous work on an artificial metallohydrolase, we exploit the periplasm of Escherichia coli as a reaction compartment for the ‘metathase’ because it offers an auspicious environment for artificial metalloenzymes, mainly owing to low concentrations of inhibitors such as glutathione, which has recently been identified as a major inhibitor. This strategy facilitated the assembly of a functional metathase in vivo and its directed evolution with substantially increased throughput compared to conventional approaches that rely on purified protein variants. The evolved metathase compares favourably with commercial catalysts, shows activity for different metathesis substrates and can be further evolved in different directions by adjusting the workflow. Our results represent the systematic implementation and evolution of an artificial metalloenzyme that catalyses an abiotic reaction in vivo, with potential applications in, for example, non-natural metabolism.

Kinetically E-selective macrocyclic ring-closing metathesis

NASA Astrophysics Data System (ADS)

Shen, Xiao; Nguyen, Thach T.; Koh, Ming Joo; Xu, Dongmin; Speed, Alexander W. H.; Schrock, Richard R.; Hoveyda, Amir H.

2017-01-01

Macrocyclic compounds are central to the development of new drugs, but preparing them can be challenging because of the energy barrier that must be surmounted in order to bring together and fuse the two ends of an acyclic precursor such as an alkene (also known as an olefin). To this end, the catalytic process known as ring-closing metathesis (RCM) has allowed access to countless biologically active macrocyclic organic molecules, even for large-scale production. Stereoselectivity is often critical in such cases: the potency of a macrocyclic compound can depend on the stereochemistry of its alkene; alternatively, one isomer of the compound can be subjected to stereoselective modification (such as dihydroxylation). Kinetically controlled Z-selective RCM reactions have been reported, but the only available metathesis approach for accessing macrocyclic E-olefins entails selective removal of the Z-component of a stereoisomeric mixture by ethenolysis, sacrificing substantial quantities of material if E/Z ratios are near unity. Use of ethylene can also cause adventitious olefin isomerization—a particularly serious problem when the E-alkene is energetically less favoured. Here, we show that dienes containing an E-alkenyl-B(pinacolato) group, widely used in catalytic cross-coupling, possess the requisite electronic and steric attributes to allow them to be converted stereoselectively to E-macrocyclic alkenes. The reaction is promoted by a molybdenum monoaryloxide pyrrolide complex and affords products at a yield of up to 73 per cent and an E/Z ratio greater than 98/2. We highlight the utility of the approach by preparing recifeiolide (a 12-membered-ring antibiotic) and pacritinib (an 18-membered-ring enzyme inhibitor), the Z-isomer of which is less potent than the E-isomer. Notably, the 18-membered-ring moiety of pacritinib—a potent anti-cancer agent that is in advanced clinical trials for treating lymphoma and myelofibrosis—was prepared by RCM carried out at a substrate concentration 20 times greater than when a ruthenium carbene was used.

Development of octreotide-conjugated polymeric prodrug of bufalin for targeted delivery to somatostatin receptor 2 overexpressing breast cancer in vitro and in vivo

PubMed Central

Liu, Tao; Jia, Tingting; Yuan, Xia; Liu, Cheng; Sun, Jian; Ni, Zhenhua; Xu, Jian; Wang, Xuhui; Yuan, Yi

2016-01-01

Background Development of polymeric prodrugs of small molecular anticancer drugs has become one of the most promising strategies to overcome the intrinsic shortcomings of small molecular anticancer drugs and improve their anticancer performance. Materials and methods In the current work, we fabricated a novel octreotide (Oct)-modified esterase-sensitive tumor-targeting polymeric prodrug of bufalin (BUF) and explored its anticancer performance against somatostatin receptor 2 overexpressing breast cancer. Results The obtained tumor-targeting polymeric prodrug of BUF, P(oligo[ethylene glycol] monomethyl ether methacrylate [OEGMA]-co-BUF-co-Oct), showed a nanosize dimension and controlled drug release features in the presence of esterase. It was demonstrated by in vitro experiment that P(OEGMA-co-BUF-co-Oct) showed enhanced cytotoxicity, cellular uptake, and apoptosis in comparison with those of free BUF. In vivo experiment further revealed the improved accumulation of drugs in tumor tissues and enhanced anticancer performance of P(OEGMA-co-BUF-co-Oct). Conclusion Taken together, this study indicated that polymeric prodrug of BUF holds promising potential toward the treatment of somatostatin receptor 2 overexpressing breast cancer. PMID:27284243

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rohde, Brian J.; Le, Kim Mai; Krishnamoorti, Ramanan

The mechanical properties of two chemically distinct and complementary thermoset polymers were manipulated through development of thermoset blends. The thermoset blend system was composed of an anhydride-cured diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin, contributing high tensile strength and modulus, and polydicyclopentadiene (PDCPD), which has a higher toughness and impact strength as compared to other thermoset polymers. Ultra-small-angle and small-angle X-ray scattering analysis explored the morphology of concurrently cured thermoset blends, revealing a macroscopically phase separated system with a surface fractal structure across blended systems of varying composition. The epoxy resin rich and PDCPD rich phases exhibited distinct glassmore » transitions (Tg’s): the Tg observed at higher temperature was associated with the epoxy resin rich phase and was largely unaffected by the presence of PDCPD, whereas the PDCPD rich phase Tg systematically decreased with increasing epoxy resin content due to inhibition of dicyclopentadiene ring-opening metathesis polymerization. The mechanical properties of these phase-separated blends were in reasonable agreement with predictions by the rule of mixtures for the blend tensile strength, modulus, and fracture toughness. Scanning electron microscopy analysis of the tensile and fracture specimen fracture surfaces showed an increase in energy dissipation mechanisms, such as crazing, shear banding, and surface roughness, as the fraction of the more ductile component, PDPCD, increased. These results present a facile method to tune the mechanical properties of a toughened thermoset network, in which the high modulus and tensile strength of the epoxy resin can be largely retained at high epoxy resin content in the blend, while increasing the fracture toughness.« less

First-Principles Studies of Structure-Property Relationships: Enabling Design of Functional Materials

NASA Astrophysics Data System (ADS)

Zhou, Qunfei

First-principles calculations based on quantum mechanics have been proved to be powerful for accurately regenerating experimental results, uncovering underlying myths of experimental phenomena, and accelerating the design of innovative materials. This work has been motivated by the demand to design next-generation thermionic emitting cathodes and techniques to allow for synthesis of photo-responsive polymers on complex surfaces with controlled thickness and patterns. For Os-coated tungsten thermionic dispenser cathodes, we used first-principles methods to explore the bulk and surface properties of W-Os alloys in order to explain the previously observed experimental phenomena that thermionic emission varies significantly with W-Os alloy composition. Meanwhile, we have developed a new quantum mechanical approach to quantitatively predict the thermionic emission current density from materials perspective without any semi-empirical approximations or complicated analytical models, which leads to better understanding of thermionic emission mechanism. The methods from this work could be used to accelerate the design of next-generation thermionic cathodes. For photoresponsive materials, we designed a novel type of azobenzene-containing monomer for light-mediated ring-opening metathesis polymerization (ROMP) toward the fabrication of patterned, photo-responsive polymers by controlling ring strain energy (RSE) of the monomer that drives ROMP. This allows for unprecedented remote, noninvasive, instantaneous spatial and temporal control of photo-responsive polymer deposition on complex surfaces.This work on the above two different materials systems showed the power of quantum mechanical calculations on predicting, understanding and discovering the structures and properties of both known and unknown materials in a fast, efficient and reliable way.

Polymeric additive performance in closed whitewater systems

Treesearch

T. H. Wegner

1984-01-01

“With more stringent requirements on discharge water quality and with escalating water treatment costs, water recycling within the paper mill is of growing importance. A serious problem resulting from more white-water recycling is reduced drainage and fiber or fines retention because of diminished polymeric additive performance. To provide better insight for overcoming...

First-principles study of pollutant molecules absorbed on polymeric adsorbents using the vdW-DF2 functional

NASA Astrophysics Data System (ADS)

Zhu, Jinguo; Wang, Yapeng; Tian, Ting; Zhang, Qianfan

2018-03-01

Polymeric adsorbents have been attracting increasing attention because of their favorable structrual properties and effectiveness of solving small molecules contaminants. However, due to the absence of deep insight into the adsorption mechanism of polymeric adsorbents, researches on new polymeric adsorbents can only be carried out by repeated experiments and tests, which is extremely inefficient. Therefore, investigating the adsorption process of polymeric adsorbents, especially the mechanism of adsorbing various air pollutant molecules by materials modelling and simulation, is of great significance. Here in this work, we systematically studied the adsorption mechanism by first-principles computation with van der Waals interaction. It demonstrates that the adsorption between them was pure physisorption originating from the hydrogen bond and intermolecular forces consisting of Keesom force, Debye force and London dispersion force. The proportions of these forces varied according to different adsorption systems. The adsorption effects were determined by the polymers’ dipole moment and polarizability. The adsorption performance of some polymers with special structures was also investigated to explore their possibility as potential adsorbents. The results of our simulation can provide some guidance for developing new polymeric adsorbents with better performance.

High-speed vibration-milling-promoted synthesis of symmetrical frameworks containing two or three pyrrole units

PubMed Central

Leonardi, Marco; Villacampa, Mercedes

2017-01-01

The pseudo-five-component reaction between β-dicarbonyl compounds (2 molecules), diamines and α-iodoketones (2 molecules), prepared in situ from aryl ketones, was performed efficiently under mechanochemical conditions involving high-speed vibration milling with a single zirconium oxide ball. This reaction afforded symmetrical frameworks containing two pyrrole or fused pyrrole units joined by a spacer, which are of interest in the exploration of chemical space for drug discovery purposes. The method was also extended to the synthesis of one compound containing three identical pyrrole fragments via a pseudo-seven-component reaction. Access to compounds having a double bond in their spacer chain was achieved by a different approach involving the homodimerization of 1-allyl- or 1-homoallylpyrroles by application of cross-metathesis chemistry. PMID:29062414

Synthesis of (+)-dumetorine and congeners by using flow chemistry technologies.

PubMed

Riva, Elena; Rencurosi, Anna; Gagliardi, Stefania; Passarella, Daniele; Martinelli, Marisa

2011-05-23

An efficient total synthesis of the natural alkaloid (+)-dumetorine by using flow technology is described. The process entailed five separate steps starting from the enantiopure (S)-2-(piperidin-2-yl)ethanol 4 with 29% overall yield. Most of the reactions were carried out by exploiting solvent superheating and by using packed columns of immobilized reagents or scavengers to minimize handling. New protocols for performing classical reactions under continuous flow are disclosed: the ring-closing metathesis reaction with a novel polyethylene glycol-supported Hoveyda catalyst and the unprecedented flow deprotection/Eschweiler-Clarke methylation sequence. The new protocols developed for the synthesis of (+)-dumetorine were applied to the synthesis of its simplified natural congeners (-)-sedamine and (+)-sedridine. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Anionic polymerization of p-(2,2'-diphenylethyl)styrene and applications to graft copolymers.

PubMed

Huang, Minglu; Han, Bingyong; Lu, Jianmin; Yang, Wantai; Fu, Zhifeng

2017-01-01

Well-controlled anionic polymerization of an initiator-functionalized monomer, p -(2,2'-diphenylethyl)styrene (DPES), was achieved for the first time. The polymerization was performed in a mixed solvent of cyclohexane and tetrahydrofuran (THF) at 40 °C with n -BuLi as initiator. When the volume ratio of cyclohexane to THF was 20, the anionic polymerization of DPES showed living polymerization characteristics, and well-defined block copolymer PDPES- b -PS was successfully synthesized. Furthermore, radical polymerization of methyl methacrylate in the presence of PDPES effectively afforded a graft copolymer composed of a polystyrene backbone and poly(methyl methacrylate) branches. The designation of analogous monomers and polymers was of great significance to synthesize a variety of sophisticated copolymer and functionalize polymer materials.

Pentadienyl chemistry of the heavy alkaline-earth metals revisited.

PubMed

Reiners, Matthias; Fecker, Ann Christin; Freytag, Matthias; Jones, Peter G; Walter, Marc D

2014-05-14

Open-metallocenes of the heavy alkaline-earth metals [(η(5)-Pdl')2M(thf)n] (M = Ca (1), Sr (2), n = 1; M = Ba (3), n = 2; Pdl' = 2,4-tBu2C5H5) are readily prepared by salt-metathesis between MI2 and KPdl' and characterized by NMR spectroscopy and X-ray diffraction studies.

Electrochromic Salts, Solutions, and Devices

DOEpatents

Burrell, Anthony K.; Warner, Benjamin P.; McClesky, T. Mark

2008-11-11

Electrochromic salts. Electrochromic salts of dicationic viologens such as methyl viologen and benzyl viologen associated with anions selected from bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide, and tris(trifluoromethylsulfonyl)methide are produced by metathesis with the corresponding viologen dihalide. They are highly soluble in molten quarternary ammonium salts and together with a suitable reductant provide electrolyte solutions that are used in electrochromic windows.

Electrochromic salts, solutions, and devices

DOEpatents

Burrell, Anthony K [Los Alamos, NM; Warner, Benjamin P [Los Alamos, NM; McClesky,7,064,212 T. Mark

2006-06-20

Electrochromic salts. Electrochromic salts of dicationic viologens such as methyl viologen and benzyl viologen associated with anions selected from bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide, and tris(trifluoromethylsulfonyl)methide are produced by metathesis with the corresponding viologen dihalide. They are highly soluble in molten quarternary ammonium salts and together with a suitable reductant provide electrolyte solutions that are used in electrochromic windows.

Electrochromic Salts, Solutions, and Devices

DOEpatents

Burrell, Anthony K.; Warner, Benjamin P.; McClesky, T. Mark

2008-10-14

Electrochromic salts. Electrochromic salts of dicationic viologens such as methyl viologen and benzyl viologen associated with anions selected from bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide, and tris(trifluoromethylsulfonyl)methide are produced by metathesis with the corresponding viologen dihalide. They are highly soluble in molten quarternary ammonium salts and together with a suitable reductant provide electrolyte solutions that are used in electrochromic windows.

Intrinsic embedded sensors for polymeric mechatronics: flexure and force sensing.

PubMed

Jentoft, Leif P; Dollar, Aaron M; Wagner, Christopher R; Howe, Robert D

2014-02-25

While polymeric fabrication processes, including recent advances in additive manufacturing, have revolutionized manufacturing, little work has been done on effective sensing elements compatible with and embedded within polymeric structures. In this paper, we describe the development and evaluation of two important sensing modalities for embedding in polymeric mechatronic and robotic mechanisms: multi-axis flexure joint angle sensing utilizing IR phototransistors, and a small (12 mm), three-axis force sensing via embedded silicon strain gages with similar performance characteristics as an equally sized metal element based sensor.

Intrinsic Embedded Sensors for Polymeric Mechatronics: Flexure and Force Sensing

PubMed Central

Jentoft, Leif P.; Dollar, Aaron M.; Wagner, Christopher R.; Howe, Robert D.

2014-01-01

While polymeric fabrication processes, including recent advances in additive manufacturing, have revolutionized manufacturing, little work has been done on effective sensing elements compatible with and embedded within polymeric structures. In this paper, we describe the development and evaluation of two important sensing modalities for embedding in polymeric mechatronic and robotic mechanisms: multi-axis flexure joint angle sensing utilizing IR phototransistors, and a small (12 mm), three-axis force sensing via embedded silicon strain gages with similar performance characteristics as an equally sized metal element based sensor. PMID:24573310

Analytical methods for the measurement of polymerization kinetics and stresses of dental resin-based composites: A review

PubMed Central

Ghavami-Lahiji, Mehrsima; Hooshmand, Tabassom

2017-01-01

Resin-based composites are commonly used restorative materials in dentistry. Such tooth-colored restorations can adhere to the dental tissues. One drawback is that the polymerization shrinkage and induced stresses during the curing procedure is an inherent property of resin composite materials that might impair their performance. This review focuses on the significant developments of laboratory tools in the measurement of polymerization shrinkage and stresses of dental resin-based materials during polymerization. An electronic search of publications from January 1977 to July 2016 was made using ScienceDirect, PubMed, Medline, and Google Scholar databases. The search included only English-language articles. Only studies that performed laboratory methods to evaluate the amount of the polymerization shrinkage and/or stresses of dental resin-based materials during polymerization were selected. The results indicated that various techniques have been introduced with different mechanical/physical bases. Besides, there are factors that may contribute the differences between the various methods in measuring the amount of shrinkages and stresses of resin composites. The search for an ideal and standard apparatus for measuring shrinkage stress and volumetric polymerization shrinkage of resin-based materials in dentistry is still required. Researchers and clinicians must be aware of differences between analytical methods to make proper interpretation and indications of each technique relevant to a clinical situation. PMID:28928776

Tuning preparation conditions towards optimized separation performance of thermally polymerized organo-silica monolithic columns in capillary liquid chromatography.

PubMed

Gharbharan, Deepa; Britsch, Denae; Soto, Gabriela; Weed, Anna-Marie Karen; Svec, Frantisek; Zajickova, Zuzana

2015-08-21

Tuning of preparation conditions, such as variations in the amount of a porogen, concentration of an aqueous acid catalyst, and adjustment in polymerization temperature and time, towards optimized chromatographic performance of thermally polymerized monolithic capillaries prepared from 3-(methacryloyloxy)propyltrimethoxysilane has been carried out. Performance of capillary columns in reversed-phase liquid chromatography was assessed utilizing various sets of solutes. Results describing hydrophobicity, steric selectivity, and extent of hydrogen bonding enabled comparison of performance of hybrid monolithic columns prepared under thermal (TSG) and photopolymerized (PSG) conditions. Reduced amounts of porogen in the polymerization mixture, and prolonged reaction times were necessary for the preparation of monolithic columns with enhanced retention and column efficiency that reached to 111,000 plates/m for alkylbenzenes with shorter alkyl chains. Both increased concentration of catalyst and higher temperature resulted in faster polymerization but inevitably in insufficient time for pore formation. Thermally polymerized monoliths produced surfaces, which were slightly more hydrophobic (a methylene selectivity of 1.28±0.002 TSG vs 1.20±0.002 PSG), with reduced number of residual silanols (a caffeine/phenol selectivity of 0.13±0.001 TSG vs 0.17±0.003 PSG). However, steric selectivity of 1.70±0.01 was the same for both types of columns. The batch-to-batch repeatability was better using thermal initiation compared to monolithic columns prepared under photopolymerized conditions. RSD for retention factor of benzene was 3.7% for TSG capillaries (n=42) vs. 6.6% for PSG capillaries (n=18). A similar trend was observed for columns prepared within the same batch. Copyright © 2015 Elsevier B.V. All rights reserved.

Reactive molecular dynamics of network polymers: Generation, characterization and mechanical properties

NASA Astrophysics Data System (ADS)

Shankar, Chandrashekar

The goal of this research was to gain a fundamental understanding of the properties of networks created by the ring opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) used in self-healing materials. To this end we used molecular simulation methods to generate realistic structures of DCPD networks, characterize their structures, and determine their mechanical properties. Density functional theory (DFT) calculations, complemented by structural information derived from molecular dynamics simulations were used to reconstruct experimental Raman spectra and differential scanning calorimetry (DSC) data. We performed coarse-grained simulations comparing networks generated via the ROMP reaction process and compared them to those generated via a RANDOM process, which led to the fundamental realization that the polymer topology has a unique influence on the network properties. We carried out fully atomistic simulations of DCPD using a novel algorithm for recreating ROMP reactions of DCPD molecules. Mechanical properties derived from these atomistic networks are in excellent agreement with those obtained from coarse-grained simulations in which interactions between nodes are subject to angular constraints. This comparison provides self-consistent validation of our simulation results and helps to identify the level of detail necessary for the coarse-grained interaction model. Simulations suggest networks can classified into three stages: fluid-like, rubber-like or glass-like delineated by two thresholds in degree of reaction alpha: The onset of finite magnitudes for the Young's modulus, alphaY, and the departure of the Poisson ration from 0.5, alphaP. In each stage the polymer exhibits a different predominant mechanical response to deformation. At low alpha < alphaY it flows. At alpha Y < alpha < alphaP the response is entropic with no change in internal energy. At alpha > alphaP the response is enthalpic change in internal energy. We developed graph theory-based network characterizations to correlate between network topology and the simulated mechanical properties. (1) Eigenvector centrality (2) Graph fractal dimension, (3) Fiedler partitioning, and (4) Cross-link fraction (Q3+Q4). Of these quantities, the Fiedler partition is the best characteristic for the prediction of Young's Modulus. The new computational tools developed in this research are of great fundamental and practical interest.

In vivo polymerization of poly(3,4-ethylenedioxythiophene) in the living rat hippocampus does not cause a significant loss of performance in a delayed alternation task

NASA Astrophysics Data System (ADS)

Ouyang, Liangqi; Shaw, Crystal L.; Kuo, Chin-chen; Griffin, Amy L.; Martin, David C.

2014-04-01

After extended implantation times, traditional intracortical neural probes exhibit a foreign-body reaction characterized by a reactive glial sheath that has been associated with increased system impedance and signal deterioration. Previously, we have proposed that the local in vivo polymerization of an electronically and ionically conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), might help to rebuild charge transport pathways across the glial scar between the device and surrounding parenchyma (Richardson-Burns et al 2007 J. Neural Eng. 4 L6-13). The EDOT monomer can be delivered via a microcannula/electrode system into the brain tissue of living animals followed by direct electrochemical polymerization, using the electrode itself as a source of oxidative current. In this study, we investigated the long-term effect of local in vivo PEDOT deposition on hippocampal neural function and histology. Rodent subjects were trained on a hippocampus-dependent task, delayed alternation (DA), and implanted with the microcannula/electrode system in the hippocampus. The animals were divided into four groups with different delay times between the initial surgery and the electrochemical polymerization: (1) control (no polymerization), (2) immediate (polymerization within 5 min of device implantation), (3) early (polymerization within 3-4 weeks after implantation) and (4) late (polymerization 7-8 weeks after polymerization). System impedance at 1 kHz was recorded and the tissue reactions were evaluated by immunohistochemistry. We found that under our deposition conditions, PEDOT typically grew at the tip of the electrode, forming an ˜500 µm cloud in the tissue. This is much larger than the typical width of the glial scar (˜150 µm). After polymerization, the impedance amplitude near the neurologically important frequency of 1 kHz dropped for all the groups; however, there was a time window of 3-4 weeks for an optimal decrease in impedance. For all surgery-polymerization time intervals, the polymerization did not cause significant deficits in performance of the DA task, suggesting that hippocampal function was not impaired by PEDOT deposition. However, GFAP+ and ED-1+ cells were also found at the deposition two weeks after the polymerization, suggesting potential secondary scarring. Therefore, less extensive deposition or milder deposition conditions may be desirable to minimize this scarring while maintaining decreased system impedance.

In vivo polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) in living rat hippocampus does not cause a significant loss of performance in a delayed alternation (DA) task

PubMed Central

Ouyang, Liangqi; Shaw, Crystal L.; Kuo, Chin-chen; Griffin, Amy L.; Martin, David C.

2014-01-01

After extended implantation times, traditional intracortical neural probes exhibit a foreign body reaction characterized by a reactive glial sheath that has been associated with increased system impedance and signal deterioration. Previously, we have proposed that the local in vivo polymerization of an electronically and ionically conducting polymer, poly(3,4 ethylene dioxythiophene) (PEDOT), might help to rebuild charge transport pathways across the glial scar between the device and surrounding parenchyma (Richardson-Burns, Hendricks, & Martin, 2007). The EDOT monomer can be delivered via a microcannula/electrode system into the brain tissue of living animals followed by direct electrochemical polymerization, using the electrode itself as a source of oxidative current. In this study we investigated the long-term effect of local in vivo PEDOT deposition on hippocampal neural function and histology. Rodent subjects were trained on a hippocampus-dependent task, Delayed Alternation (DA), and implanted with the microcannula/electrode system in the hippocampus. The animals were divided into four groups with different delay times between the initial surgery and the electrochemical polymerization: (1) Control (no polymerization), (2) Immediate (polymerization within 5 minutes of device implantation), (3) Early (polymerization within 3–4 weeks after implantation), and (4) Late (polymerization 7–8 weeks after polymerization). System impedance at 1 kHz was recorded and the tissue reactions were evaluated by immunohistochemistry. We found that under our deposition conditions, PEDOT typically grew at the tip of the electrode, forming a ~500 μm cloud into the tissue. This is much larger than the typical width of the glial scar (~150 μm). After polymerization, the impedance amplitude near the neurologically important frequency of 1 kHz dropped for all the groups, however, there was a time window of 3–4 weeks for optimal decrease in impedance. For all surgery-polymerization time intervals, the polymerization did not cause significant deficits in performance of the DA task, suggesting that hippocampal function was not impaired by PEDOT deposition. However, GFAP+ and ED-1+ cells were also found at the deposition 2 weeks after the polymerization, suggesting potential secondary scarring. Therefore less extensive deposition or milder deposition conditions may be desirable to minimize this scarring while maintaining decreased system impedance. PMID:24503720

Polymeric Janus Nanoparticles: Recent Advances in Synthetic Strategies, Materials Properties, and Applications.

PubMed

Fan, Xiaoshan; Yang, Jing; Loh, Xian Jun; Li, Zibiao

2018-06-13

Polymeric Janus nanoparticles with two sides of incompatible chemistry have received increasing attention due to their tunable asymmetric structure and unique material characteristics. Recently, with the rapid progress in controlled polymerization combined with novel fabrication techniques, a large array of functional polymeric Janus particles are diversified with sophisticated architecture and applications. In this review, the most recently developed strategies for controlled synthesis of polymeric Janus nanoparticles with well-defined size and complex superstructures are summarized. In addition, the pros and cons of each approach in mediating the anisotropic shapes of polymeric Janus particles as well as their asymmetric spatial distribution of chemical compositions and functionalities are discussed and compared. Finally, these newly developed structural nanoparticles with specific shapes and surface functions orientated applications in different domains are also discussed, followed by the perspectives and challenges faced in the further advancement of polymeric Janus nanoparticles as high performance materials. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pentavalent uranium trans-dihalides and -pseudohalides.

PubMed

Lewis, Andrew J; Nakamaru-Ogiso, Eiko; Kikkawa, James M; Carroll, Patrick J; Schelter, Eric J

2012-05-21

Pentavalent uranium complexes of the formula U(V)X(2)[N(SiMe(3))(2)](3) (X = F(-), Cl(-), Br(-), N(3)(-), NCS(-)) are accessible from the oxidation of U(III)[N(SiMe(3))(2)](3) through two sequential, one-electron oxidation reactions (halides) and substitution through salt metathesis (pseudohalides). Uranium(v) mixed-halides are also synthesized by successive one-electron oxidation reactions.

Total synthesis of (+)-antroquinonol and (+)-antroquinonol D.

PubMed

Sulake, Rohidas S; Chen, Chinpiao

2015-03-06

The first total synthesis of (+)-antroquinonol and (+)-antroquinonol D, two structurally unique quinonols with a sesquiterpene side chain, is described. The route features an iridium-catalyzed olefin isomerization-Claisen rearrangement reaction (ICR), lactonization, and Grubbs olefin metathesis. The requisite α,β-unsaturation was achieved via the selenylation/oxidation protocol and elimination of β-methoxy group to provide two natural products from a common intermediate.

Enantioselective modular synthesis of cyclohexenones: total syntheses of (+)-crypto- and (+)-infectocaryone.

PubMed

Franck, Géraldine; Brödner, Kerstin; Helmchen, Günter

2010-09-03

A modular synthesis of cyclohexenones is described and applied to the first enantioselective total syntheses of (+)-crypto- and (+)-infectocaryone. Key steps in the synthesis of cyclohexenones are an iridium-catalyzed allylic alkylation, nucleophilic allylation, and ring-closing metathesis. On the way to (+)-cryptocaryone, a catch and release strategy involving an iodolactonization/elimination and a regioselective C-acylation were used.

Synthesis of alkyl-substituted six-membered lactones through ring-closing metathesis of homoallyl acrylates. An easy route to pyran-2-ones, constituents of tobacco flavor.

PubMed

D'Annibale, Andrea; Ciaralli, Laura; Bassetti, Mauro; Pasquini, Chiara

2007-08-03

The ring-closing metathesis (RCM) reactions of homoallylic acrylates bearing alkyl substituents on various positions of their skeleton afford the corresponding pentenolides in the presence of carbene ruthenium catalysts. For R3 = R4 = H, or R3 = Me, R4 = H, the reactions are catalyzed by complex [RuCl2(PCy3)2(=CHPh)], while a second-generation Grubbs catalyst is required when R3 = H and R4 = Me, R3 = R4 = Me, or R3 = i-Pr and R4 = H. Alkyl substitution at the homoallylic carbon (R1, R2) increases the yield of the reaction when both the acrylic and/or homoallylic double bonds are methyl-substituted. The interaction of the catalyst with the substrate in the initiation stage involves the homoallylic double bond rather than the acrylic moiety, and the resulting alkylidene species from the first-generation Grubbs catalyst can be observed by 1H and 31P NMR. The racemic tobacco constituents 4-isopropyl-5,6-dihydropyran-2-one and 4-isopropyltetrahydropyran-2-one are prepared via a short reaction sequence, involving the RCM reaction as the key transformation.

Dual functions of imidazole-based polymeric ionic liquid (PIL) on the anticorrosive performance of graphene-based waterborne epoxy coatings

NASA Astrophysics Data System (ADS)

Liu, Chengbao; Du, Peng; Nan, Feng; Zhao, Haichao; Wang, Liping

2018-06-01

Dispersion of graphene nanosheets in a water and polymer matrix has been rarely achieved due to graphene’s hydrophobicity, which thus impedes its potential anticorrosive application. In this study, stable graphene aqueous dispersion was obtained by using imidazole-based polymeric ionic liquid (PIL) as the dispersant with ultrasonic vibration. Stacked graphene sheets were exfoliated to a few layers via cation-π interaction between PIL and graphene nanosheets. Electrochemical impedance measurements were taken to investigate the anticorrosion performance of epoxy coatings with or without polymeric ionic liquid–graphene (PIL–G) hybrids. Results indicated that the PIL–G hybrid significantly enhanced the long-term protective performance of epoxy coatings, which was attributed to the synergistic effects of the corrosion-inhibitive PIL and impermeable graphene nanosheets.

Targeted polymeric nanoparticles for cancer gene therapy

PubMed Central

Kim, Jayoung; Wilson, David R.; Zamboni, Camila G.; Green, Jordan J.

2015-01-01

In this article, advances in designing polymeric nanoparticles for targeted cancer gene therapy are reviewed. Characterization and evaluation of biomaterials, targeting ligands, and transcriptional elements are each discussed. Advances in biomaterials have driven improvements to nanoparticle stability and tissue targeting, conjugation of ligands to the surface of polymeric nanoparticles enable binding to specific cancer cells, and the design of transcriptional elements has enabled selective DNA expression specific to the cancer cells. Together, these features have improved the performance of polymeric nanoparticles as targeted non-viral gene delivery vectors to treat cancer. As polymeric nanoparticles can be designed to be biodegradable, non-toxic, and to have reduced immunogenicity and tumorigenicity compared to viral platforms, they have significant potential for clinical use. Results of polymeric gene therapy in clinical trials and future directions for the engineering of nanoparticle systems for targeted cancer gene therapy are also presented. PMID:26061296

Tubulin polymerization-stimulating activity of Ganoderma triterpenoids.

PubMed

Kohno, Toshitaka; Hai-Bang, Tran; Zhu, Qinchang; Amen, Yhiya; Sakamoto, Seiichi; Tanaka, Hiroyuki; Morimoto, Satoshi; Shimizu, Kuniyoshi

2017-04-01

Tubulin polymerization is an important target for anticancer therapies. Even though the potential of Ganoderma triterpenoids against various cancer targets had been well documented, studies on their tubulin polymerization-stimulating activity are scarce. This study was conducted to evaluate the effect of Ganoderma triterpenoids on tubulin polymerization. A total of twenty-four compounds were investigated using an in vitro tubulin polymerization assay. Results showed that most of the studied triterpenoids exhibited microtuble-stabilizing activity to different degrees. Among the investigated compounds, ganoderic acid T-Q, ganoderiol F, ganoderic acid S, ganodermanontriol and ganoderic acid TR were found to have the highest activities. A structure-activity relationship (SAR) analysis was performed. Extensive investigation of the SAR suggests the favorable structural features for the tubulin polymerization-stimulating activity of lanostane triterpenes. These findings would be helpful for further studies on the potential mechanisms of the anticancer activity of Ganoderma triterpenoids and give some indications on the design of tubulin-targeting anticancer agents.

Experiments of the Essential Amino Acids at high temperature and high pressure using DAC

NASA Astrophysics Data System (ADS)

Kubo, K.; Okamoto, K.

2017-12-01

Amino acids are organic compounds that form the fundamental part of life. Proteins are formed by peptide binding and polymerization of amino acids. Amino acids are polymerized in the ridge hydrothermal field, formed proteins, and might be evolved into life. Experimental studies on the polymerization of amino acids in hydrothermal environments have been conducted. However, they were hydrothermal experiments and after the experiments. All run products (amid-acids) were observed at ambient condition. Few in-situ observations of amino acids were done in experiments in hydrothermal condition. In order to perform in-situ observation of the polymerization of amino acids, we have conducted the DAC experiments. Amino acids were filled in the DAC, pressures were applied, then heated to high temperature with Raman analysis. In preliminary experiment using glycine, polymerization forming diglycine, were completed. Investigation amino acids polymerization under hydrothermal condition would shed light for new view of early life science.

Evaluation of metal-polymeric fixed partial prosthesis using optical coherence tomography

NASA Astrophysics Data System (ADS)

Sinescu, C.; Negrutiu, M. L.; Duma, V. F.; Marcauteanu, C.; Topala, F. I.; Rominu, M.; Bradu, A.; Podoleanu, A. Gh.

2013-11-01

Metal-Polymeric fixed partial prosthesis is the usual prosthetic treatment for many dental patients. However, during the mastication the polymeric component of the prosthesis is fractured and will be lost. This fracture is caused by the material defects or by the fracture lines trapped inside the esthetic components of the prosthesis. This will finally lead to the failure of the prosthetic treatment. Nowadays, there is no method of identification and forecast for the materials defects of the polymeric materials. The aim of this paper is to demonstrate the capability of Optical Coherence Tomography (OCT) as a non-invasive clinical method that can be used for the evaluation of metal-polymeric fixed partial prostheses. Twenty metal-polymeric fixed partial prostheses were used for this study. The esthetic component of the prostheses has been Adoro (Ivoclar). Optical investigations of the metal prostheses have revealed no material defects or fracture lines. All the prostheses were temporary cemented in the oral cavities of the patients for six month. The non-invasive method used for the investigations was OCT working in Time Domain mode at 1300 nm. The evaluations of the prostheses were performed before and after their cementation in the patient mouths. All the imagistic results were performed in 2D and than in 3D, after the reconstruction. The results obtained after the OCT evaluation allowed for the identification of 4 metal-polymeric fixed partial prostheses with material defects immediately after finishing the technological procedures. After 6 month in the oral environment other 3 fixed partial prostheses revealed fracture lines. In conclusion, OCT proved to be a valuable tool for the noninvasive evaluation of the metal-polymeric fixed partial prostheses.

Magnetic record support

NASA Technical Reports Server (NTRS)

Nakayama, M.; Morita, H.; Tokuoka, Y.; Izumi, T.; Fukuda, K.; Kubota, Y.

1984-01-01

The magnetic layer of a magnetic record support is coated with a thin film of a polymer with a siloxane bond. The magnetic layer consists of a thin film obtained by vacuum metallization, cathode sputtering or dispersion of a ferromagnetic metal powder in a binder. The polymer with a siloxane bond is produced by the polymerization of an organic silicon compound which inherently contains or is able to form this bond. Polymerization is preferably performed by plasma polymerization.

FT-IR Investigation of Hoveyda-Grubbs'2{sup nd} Generation Catalyst in Self-Healing Epoxy Mixtures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guadagno, Liberata; Naddeo, Carlo; Vittoria, Vittoria

The development of smart composites capable of self-repair on aeronautical structures is still at the planning stage owing to complex issues to overcome. A very important issue to solve concerns the components' stability of the proposed composites which are compromised at the cure temperatures necessary for good performance of the composite. In this work we analyzed the possibility to apply Hoveyda Grubbs' second generation catalyst (HG2) to develop self-healing systems. Our experimental results have shown critical issues in the use of epoxy precursors in conjunction with Hoveyda-Grubbs II metathesis catalyst. However, an appropriate curing cycle of the self-healing mixture permitsmore » to overcome the critical issues making possible high temperatures for the curing process without deactivating self-repair activity.« less

Method for forming polymerized microfluidic devices

DOEpatents

Sommer, Gregory J [Livermore, CA; Hatch, Anson V [Tracy, CA; Wang, Ying-Chih [Pleasanton, CA; Singh, Anup K [Danville, CA; Renzi, Ronald F [Tracy, CA; Claudnic, Mark R [Livermore, CA

2011-11-01

Methods for making a micofluidic device according to embodiments of the present invention include defining a cavity. Polymer precursor solution is positioned in the cavity, and exposed to light to begin the polymerization process and define a microchannel. In some embodiments, after the polymerization process is partially complete, a solvent rinse is performed, or fresh polymer precursor introduced into the microchannel. This may promote removal of unpolymerized material from the microchannel and enable smaller feature sizes. The polymer precursor solution may contain an iniferter. Polymerized features therefore may be capped with the iniferter, which is photoactive. The iniferter may aid later binding of a polyacrylamide gel to the microchannel surface.

Method for forming polymerized microfluidic devices

DOEpatents

Sommer, Gregory J.; Hatch, Anson V.; Wang, Ying-Chih; Singh, Anup K.; Renzi, Ronald F.; Claudnic, Mark R.

2013-03-12

Methods for making a microfluidic device according to embodiments of the present invention include defining.about.cavity. Polymer precursor solution is positioned in the cavity, and exposed to light to begin the polymerization process and define a microchannel. In some embodiments, after the polymerization process is partially complete, a solvent rinse is performed, or fresh polymer precursor introduced into the microchannel. This may promote removal of unpolymerized material from the microchannel and enable smaller feature sizes. The polymer precursor solution may contain an iniferter. Polymerized features therefore may be capped with the iniferter, which is photoactive. The iniferter may aid later binding of a polyacrylamide gel to the microchannel surface.

Mixo-IBR BP1A Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahrens, Toby; Van der Meulen, Leslie

The objective of the initial budget period was to determine whether BioProcess Algae (BPA) had all of the data, information, facilities, and agreements presented in its proposal response to DE-FOA-0000739. BPA was to demonstrate heterotrophic lipid production, demonstrate the production of fuels by metathesis of algal oils, and develop data to justify the scale-up effort proposed for the Pilot Mixotrophic Algae Integrated Biorefinery.

Synthesis of 5/7-, 5/8- and 5/9-bicyclic lactam templates as constraints for external beta-turns.

PubMed

Duggan, Heather M E; Hitchcock, Peter B; Young, Douglas W

2005-06-21

The 5/7-, 5/8- and 5/9-bicyclic lactams 3, 17, 5 and 6 have been synthesised as single diastereoisomers by a route involving ring closing olefin metathesis. The X-ray crystal structure of the amino acid hydrochloride has been carried out and compared to that of the saturated external beta-turn constraint 18.

The first total synthesis of sporiolide A.

PubMed

Du, Yuguo; Chen, Qi; Linhardt, Robert J

2006-10-27

The first total synthesis of the natural cytotoxic agent sporiolide A has been accomplished from D-glucal in 16 steps with 6.1% overall yield. Carbohydrates were applied as the chiral templates to manipulate the absolute configuration during the synthesis. Pyridinium chlorochromate (PCC)-promoted transformation of the cyclic enol-ether to lactone, followed by Yamaguchi esterification and intramolecular ring closure metathesis, greatly facilitates synthesis of the target compound.

Novel Energetic Materials for Counter WMD Applications

DTIC Science & Technology

2011-09-01

insensitive dianionic dinitrourea salts: The CN4ol · anion paired with nitrogen-rich cations C. Energetic ionic liquids based on anionic rare earth nitrate ...and their derivatives as energetic materials by click chemistry 1-Pentafluorosulfanyl acetylene and its derivatives react with azide or diazomethane...extended to the syntheses and characterization often DNU dianionic salts by the metathesis oftetrazolium and guanidinium sulfates with in situ

Nanoporous poly(3-hexylthiophene) thin film structures from self-organization of a tunable molecular bottlebrush scaffold

DOE PAGES

Ahn, Suk-kyun; Carrillo, Jan-Michael Y.; Keum, Jong K.; ...

2017-04-07

The ability to widely tune the design of macromolecular bottlebrushes provides access to self-assembled nanostructures formed by microphase segregation in melt, thin film and solution that depart from structures adopted by simple linear copolymers. A series of random bottlebrush copolymers containing poly(3-hexylthiophene) (P3HT) and poly(D,L-lactide) (PLA) side chains grafted on a poly(norbornene) backbone were synthesized via ring-opening metathesis polymerization (ROMP) using the grafting through approach. P3HT side chains induce a physical aggregation of the bottlebrush copolymers upon solvent removal by vacuum drying, primarily driven by attractive π–π interactions; however, the amount of aggregation can be controlled by adjusting side chainmore » composition or by adding linear P3HT chains to the bottlebrush copolymers. Coarse-grained molecular dynamics simulations reveal that linear P3HT chains preferentially associate with P3HT side chains of bottlebrush copolymers, which tends to reduce the aggregation. The nanoscale morphology of microphase segregated thin films created by casting P3HT–PLA random bottlebrush copolymers is highly dependent on the composition of P3HT and PLA side chains, while domain spacing of nanostructures is mainly determined by the length of the side chains. The selective removal of PLA side chains under alkaline conditions generates nanoporous P3HT structures that can be tuned by manipulating molecular design of the bottlebrush scaffold, which is affected by molecular weight and grafting density of the side chains, and their sequence. Furthermore, the ability to exploit the unusual architecture of bottlebrushes to fabricate tunable nanoporous P3HT thin film structures may be a useful way to design templates for optoelectronic applications or membranes for separations.« less

Nanoporous poly(3-hexylthiophene) thin film structures from self-organization of a tunable molecular bottlebrush scaffold

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, Suk-kyun; Carrillo, Jan-Michael Y.; Keum, Jong K.

The ability to widely tune the design of macromolecular bottlebrushes provides access to self-assembled nanostructures formed by microphase segregation in melt, thin film and solution that depart from structures adopted by simple linear copolymers. A series of random bottlebrush copolymers containing poly(3-hexylthiophene) (P3HT) and poly(D,L-lactide) (PLA) side chains grafted on a poly(norbornene) backbone were synthesized via ring-opening metathesis polymerization (ROMP) using the grafting through approach. P3HT side chains induce a physical aggregation of the bottlebrush copolymers upon solvent removal by vacuum drying, primarily driven by attractive π–π interactions; however, the amount of aggregation can be controlled by adjusting side chainmore » composition or by adding linear P3HT chains to the bottlebrush copolymers. Coarse-grained molecular dynamics simulations reveal that linear P3HT chains preferentially associate with P3HT side chains of bottlebrush copolymers, which tends to reduce the aggregation. The nanoscale morphology of microphase segregated thin films created by casting P3HT–PLA random bottlebrush copolymers is highly dependent on the composition of P3HT and PLA side chains, while domain spacing of nanostructures is mainly determined by the length of the side chains. The selective removal of PLA side chains under alkaline conditions generates nanoporous P3HT structures that can be tuned by manipulating molecular design of the bottlebrush scaffold, which is affected by molecular weight and grafting density of the side chains, and their sequence. Furthermore, the ability to exploit the unusual architecture of bottlebrushes to fabricate tunable nanoporous P3HT thin film structures may be a useful way to design templates for optoelectronic applications or membranes for separations.« less

Design of new disulfide-based organic compounds for the improvement of self-healing materials.

PubMed

Matxain, Jon M; Asua, José M; Ruipérez, Fernando

2016-01-21

Self-healing materials are a very promising kind of materials due to their capacity to repair themselves. Among others, diphenyl disulfide-based compounds (Ph2S2) appear to be among the best candidates to develop materials with optimum self-healing properties. However, few is known regarding both the reaction mechanism and the electronic structure that make possible such properties. In this vein, theoretical approaches are of great interest. In this work, we have carried out theoretical calculations on a wide set of different disulfide compounds, both aromatic and aliphatic, in order to elucidate the prevalent reaction mechanism and the necessary electronic conditions needed for improved self-healing properties. Two competitive mechanisms were considered, namely, the metathesis and the radical-mediated mechanism. According to our calculations, the radical-mediated mechanism is the responsible for this process. The formation of sulfenyl radicals strongly depends on the S-S bond strength, which can be modulated chemically by the use of proper derivatives. At this point, amino derivatives appear to be the most promising ones. In addition to the S-S bond strength, hydrogen bonding between disulfide chains seems to be relevant to favour the contact among disulfide units. This is crucial for the reaction to take place. The calculated hydrogen bonding energies are of the same order of magnitude as the S-S bond energies. Finally, reaction barriers have been analysed for some promising candidates. Two reaction mechanisms were compared, namely, the [2+2] metathesis reaction mechanism and the [2+1] radical-mediated mechanism. No computational evidence for the existence of any transition state for the metathesis mechanism was found, which indicates that the radical-mediated mechanism is the one responsible in the self-healing process of these materials. Interestingly, the calculated reaction barriers are around 10 kcal mol(-1) regardless the substituent employed. All these results suggest that the radical formation and the structural role of the hydrogen bonding prevale over kinetics. Having this in mind, as a conclusion, some new compounds are proposed for the design of future self-healing materials with improved features.

Simultaneous measurement of polymerization stress and curing kinetics for photo-polymerized composites with high filler contents.

PubMed

Wang, Zhengzhi; Landis, Forrest A; Giuseppetti, Anthony A M; Lin-Gibson, Sheng; Chiang, Martin Y M

2014-12-01

Photopolymerized composites are used in a broad range of applications with their performance largely directed by reaction kinetics and contraction accompanying polymerization. The present study was to demonstrate an instrument capable of simultaneously collecting multiple kinetics parameters for a wide range of photopolymerizable systems: degree of conversion (DC), reaction exotherm, and polymerization stress (PS). Our system consisted of a cantilever beam-based instrument (tensometer) that has been optimized to capture a large range of stress generated by lightly-filled to highly-filled composites. The sample configuration allows the tensometer to be coupled to a fast near infrared (NIR) spectrometer collecting spectra in transmission mode. Using our instrument design, simultaneous measurements of PS and DC are performed, for the first time, on a commercial composite with ≈80% (by mass) silica particle fillers. The in situ NIR spectrometer collects more than 10 spectra per second, allowing for thorough characterization of reaction kinetics. With increased instrument sensitivity coupled with the ability to collect real time reaction kinetics information, we show that the external constraint imposed by the cantilever beam during polymerization could affect the rate of cure and final degree of polymerization. The present simultaneous measurement technique is expected to provide new insights into kinetics and property relationships for photopolymerized composites with high filler content such as dental restorative composites. Published by Elsevier Ltd.

Simultaneous Measurement of Polymerization Stress and Curing Kinetics for Photo-polymerized Composites with High Filler Contents

PubMed Central

Wang, Zhengzhi; Landis, Forrest A.; Giuseppetti, Anthony A.M.; Lin-Gibson, Sheng; Chiang, Martin Y.M.

2015-01-01

Objectives Photopolymerized composites are used in a broad range of applications with their performance largely directed by reaction kinetics and contraction accompanying polymerization. The present study was to demonstrate an instrument capable of simultaneously collecting multiple kinetics parameters for a wide range of photopolymerizable systems: degree of conversion (DC), reaction exotherm, and polymerization stress (PS). Methods Our system consisted of a cantilever beam-based instrument (tensometer) that has been optimized to capture a large range of stress generated by lightly-filled to highly-filled composites. The sample configuration allows the tensometer to be coupled to a fast near infrared (NIR) spectrometer collecting spectra in transmission mode. Results Using our instrument design, simultaneous measurements of PS and DC are performed, for the first time, on a commercial composite with ≈ 80 % (by mass) silica particle fillers. The in situ NIR spectrometer collects more than 10 spectra per second, allowing for thorough characterization of reaction kinetics. With increased instrument sensitivity coupled with the ability to collect real time reaction kinetics information, we show that the external constraint imposed by the cantilever beam during polymerization could affect the rate of cure and final degree of polymerization. Significance The present simultaneous measurement technique is expected to provide new insights into kinetics and property relationships for photopolymerized composites with high filler content such as dental restorative composites. PMID:25443160

Effect of polymerization technique and glass fiber addition on the surface roughness and hardness of PMMA denture base material.

PubMed

Gad, Mohammed M; Rahoma, Ahmed; Al-Thobity, Ahmad M

2018-06-20

The current study evaluated the effects of autoclave polymerization both with and without glass fiber (GF) reinforcement on the surface roughness and hardness of acrylic denture base material. Ninety disc specimens (30×2.5 mm) were prepared from Vertex resin and divided according to polymerization techniques into a water bath, short and long autoclave polymerization groups. Tested groups were divided into three subgroups according to the GF concentration (0, 2.5, and 5 wt%). Profilometer and Vickers hardness tests were performed to measure surface roughness and hardness. ANOVA and Tukey-Kramer multiple comparison tests analyzed the results, and p≤0.05 was considered statistically significant. Autoclave polymerization significantly decreased the surface roughness and increased the hardness of acrylic resin without GF reinforcement (p<0.05). However, 5 wt% GF addition significantly increased surface roughness and decreased hardness of the autoclave polymerized denture base resin (p<0.05). Surface properties of Polymethyl methacrylate (PMMA) denture base material improved with autoclave polymerization and negatively affected with GFs addition.

Pentacene-based organic thin film transistors, integrated circuits, and active matrix displays on polymeric substrates

NASA Astrophysics Data System (ADS)

Sheraw, Christopher Duncan

2003-10-01

Organic thin film transistors are attractive candidates for a variety of low cost, large area commercial electronics including smart cards, RF identification tags, and flat panel displays. Of particular interest are high performance organic thin film transistors (TFTs) that can be fabricated on flexible polymeric substrates allowing low-cost, lightweight, rugged electronics such as flexible active matrix displays. This thesis reports pentacene organic thin film transistors fabricated on flexible polymeric substrates with record performance, the fastest photolithographically patterned organic TFT integrated circuits on polymeric substrates reported to date, and the fabrication of the organic TFT backplanes used to build the first organic TFT-driven active matrix liquid crystal display (AMLCD), also the first AMLCD on a flexible substrate, ever reported. In addition, the first investigation of functionalized pentacene derivatives used as the active layer in organic thin film transistors is reported. A low temperature (<110°C) process technology was developed allowing the fabrication of high performance organic TFTs, integrated circuits, and large TFT arrays on flexible polymeric substrates. This process includes the development of a novel water-based photolithographic active layer patterning process using polyvinyl alcohol that allows the patterning of organic semiconductor materials for elimination of active layer leakage current without causing device degradation. The small molecule aromatic hydrocarbon pentacene was used as the active layer material to fabricate organic TFTs on the polymeric material polyethylene naphthalate with field-effect mobility as large as 2.1 cm2/V-s and on/off current ratio of 108. These are the best values reported for organic TFTs on polymeric substrates and comparable to organic TFTs on rigid substrates. Analog and digital integrated circuits were also fabricated on polymeric substrates using pentacene TFTs with propagation delay as low as 38 musec and clocked digital circuits that operated at 1.1 kHz. These are the fastest photolithographically patterned organic TFT circuits on polymeric substrates reported to date. Finally, 16 x 16 pentacene TFT pixel arrays were fabricated on polymeric substrates and integrated with polymer dispersed liquid crystal to build an AMLCD. The pixel arrays showed good optical response to changing data signals when standard quarter-VGA display waveforms were applied. This result marks the first organic TFT-driven active matrix liquid crystal display ever reported as well as the first active matrix liquid crystal display on a flexible polymeric substrate. Lastly, functionalized pentacene derivatives were used as the active layer in organic thin film transistor materials. Functional groups were added to the pentacene molecule to influence the molecular ordering so that the amount of pi-orbital overlap would be increased allowing the potential for improved field-effect mobility. The functionalization of these materials also improves solubility allowing for the possibility of solution-processed devices and increased oxidative stability. Organic thin film transistors were fabricated using five different functionalized pentacene active layers. Devices based on the pentacene derivative triisopropylsilyl pentacene were found to have the best performance with field-effect mobility as large as 0.4 cm 2/V-s.

Occurrence and Speciation of Polymeric Chromium(III), Monomeric Chromium(III) and Chromium(VI) in Environmental Samples

PubMed Central

HU, LIGANG; CAI, YONG; JIANG, GUIBIN

2016-01-01

Laboratory experiments suggest that polymeric Cr(III) could exist in aqueous solution for a relative long period of time. However, the occurrence of polymeric Cr(III) has not been reported in environmental media due partially to the lack of method for speciating polymeric Cr. We observed an unknown Cr species during the course of study on speciation of Cr in the leachates of chromated-copper-arsenate (CCA)-treated wood. Efforts were made to identify structure of the unknown Cr species. Considering the forms of Cr existed in the CCA-treated woods, we mainly focused our efforts to determine if the unknown species were polymeric Cr(III), complex of Cr/As or complex of Cr with dissolved organic matter (DOM). In order to evaluate whether polymeric Cr(III) largely exist in wood leachates, high performance liquid chromatography coupled with inductively coupled mass spectrometry (HPLC-ICPMS was used) for simultaneous speciation of monomeric Cr(III), polymeric Cr(III), and Cr(VI). In addition to wood leachates where polymeric Cr (III) ranged from 39.1 to 67.4 %, occurrence of the unknown Cr species in other environmental matrices, including surface waters, tap and waste waters, was also investigated. It was found that polymeric Cr(III) could exist in environmental samples containing μg/L level of Cr, at a level up to 60% of total Cr, suggesting that polymeric Cr(III) could significantly exist in natural environments. Failure in quantifying polymeric Cr(III) would lead to the underestimation of total Cr and bias in Cr speciation. The environmental implication of the presence of polymeric Cr(III) species in the environment deserves further study. PMID:27156211

Thin Coatings of Polymeric Carbon and Carbon Nanotubes for Corrosion Protection

DTIC Science & Technology

2009-02-01

Thin Coatings of Polymeric Carbon and Carbon Nanotubes for Corrosion Protection Zafar Iqbal Department of Chemistry and Environmental Science New...Department of Chemistry and Environmental Science ,Newark,NJ,07102 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND

Polymeric molecular sieve membranes via in situ cross-linking of non-porous polymer membrane templates.

PubMed

Qiao, Zhen-An; Chai, Song-Hai; Nelson, Kimberly; Bi, Zhonghe; Chen, Jihua; Mahurin, Shannon M; Zhu, Xiang; Dai, Sheng

2014-04-16

High-performance polymeric membranes for gas separation are attractive for molecular-level separations in industrial-scale chemical, energy and environmental processes. Molecular sieving materials are widely regarded as the next-generation membranes to simultaneously achieve high permeability and selectivity. However, most polymeric molecular sieve membranes are based on a few solution-processable polymers such as polymers of intrinsic microporosity. Here we report an in situ cross-linking strategy for the preparation of polymeric molecular sieve membranes with hierarchical and tailorable porosity. These membranes demonstrate exceptional performance as molecular sieves with high gas permeabilities and selectivities for smaller gas molecules, such as carbon dioxide and oxygen, over larger molecules such as nitrogen. Hence, these membranes have potential for large-scale gas separations of commercial and environmental relevance. Moreover, this strategy could provide a possible alternative to 'classical' methods for the preparation of porous membranes and, in some cases, the only viable synthetic route towards certain membranes.

Relationship between Leakage Current and Pollution Deposits on the Surface of Polymeric Insulator

NASA Astrophysics Data System (ADS)

Miyake, Takuma; Seo, Yuya; Sakoda, Tatsuya; Otsubo, Masahisa

Application of polymeric materials used for housing insulators is considered. However, because polymeric insulator is organic matter, the aged deterioration is anxious. The lifetime of polymeric insulator is influenced by environmental conditions such as ultraviolet, acid rain, and polluted deposits. A change of the surface condition of polymeric material causes the dry band arc discharge and the discharge may lower the insulation strength. To investigate the relationship between insoluble pollution and occurrence of dry band arc discharge, we performed a salt-fog test with ethylene vinyl acetate (EVA) samples. The results showed that the heavy erosion caused by frequent dry band arc discharges occurred even in the case of a light polluted condition. Additionally, a very characteristic increase tendency in leakage current with a period of about 5 h was observed during the mist period.

Frontal Polymerization of Dicyclopentadiene: A Numerical Study.

PubMed

Goli, Elyas; Robertson, Ian D; Geubelle, Philippe H; Moore, Jeffrey S

2018-04-26

As frontal polymerization is being considered as a faster and more energy efficient manufacturing technique for polymer-matrix fiber-reinforced composites, we perform a finite-element-based numerical study of the initiation and propagation of a polymerization front in dicyclopentadiene (DCPD). The transient thermochemical simulations are complemented by an analytical study of the steady-state propagation of the polymerization front, allowing to draw a direct link between the cure kinetics model and the key characteristics of the front, i.e., front velocity and characteristic length scales. The second part of this study focuses on the prediction of the temperature spike associated with the merger of two polymerization fronts. The thermal peak, which might be detrimental to the properties of the polymerized material, is due to the inability of the heat associated with the highly exothermic reaction to be dissipated when the two fronts merge. The analysis investigates how the amplitude of the thermal spike is affected by the degree of cure at the time of the front merger.

Antimicrobial Polymeric Materials with Quaternary Ammonium and Phosphonium Salts

PubMed Central

Xue, Yan; Xiao, Huining; Zhang, Yi

2015-01-01

Polymeric materials containing quaternary ammonium and/or phosphonium salts have been extensively studied and applied to a variety of antimicrobial-relevant areas. With various architectures, polymeric quaternary ammonium/phosphonium salts were prepared using different approaches, exhibiting different antimicrobial activities and potential applications. This review focuses on the state of the art of antimicrobial polymers with quaternary ammonium/phosphonium salts. In particular, it discusses the structure and synthesis method, mechanisms of antimicrobial action, and the comparison of antimicrobial performance between these two kinds of polymers. PMID:25667977

A simple method for determining polymeric IgA-containing immune complexes.

PubMed

Sancho, J; Egido, J; González, E

1983-06-10

A simplified assay to measure polymeric IgA-immune complexes in biological fluids is described. The assay is based upon the specific binding of a secretory component for polymeric IgA. In the first step, multimeric IgA (monomeric and polymeric) immune complexes are determined by the standard Raji cell assay. Secondly, labeled secretory component added to the assay is bound to polymeric IgA-immune complexes previously fixed to Raji cells, but not to monomeric IgA immune complexes. To avoid false positives due to possible complement-fixing IgM immune complexes, prior IgM immunoadsorption is performed. Using anti-IgM antiserum coupled to CNBr-activated Sepharose 4B this step is not time-consuming. Polymeric IgA has a low affinity constant and binds weakly to Raji cells, as Scatchard analysis of the data shows. Thus, polymeric IgA immune complexes do not bind to Raji cells directly through Fc receptors, but through complement breakdown products, as with IgG-immune complexes. Using this method, we have been successful in detecting specific polymeric-IgA immune complexes in patients with IgA nephropathy (Berger's disease) and alcoholic liver disease, as well as in normal subjects after meals of high protein content. This new, simple, rapid and reproducible assay might help to study the physiopathological role of polymeric IgA immune complexes in humans and animals.

Actin Polymerization: An Event Regulated by Tyrosine Phosphorylation During Buffalo Sperm Capacitation.

PubMed

Naresh, S; Atreja, S K

2015-12-01

In the female reproductive tract, the spermatozoa undergo a series of physiological and biochemical changes, prior to gaining the ability to fertilize, that result to capacitation. However, the actin polymerization and protein tyrosine phosphorylation are the two necessary steps for capacitation. In this study, we have demonstrated the actin polymerization and established the correlation between protein tyrosine phosphorylation and actin reorganization during in vitro capacitation in buffalo (Bubalus bubalis) spermatozoa. Indirect immunofluorescence and Western blot techniques were used to detect actin polymerization and tyrosine phosphorylation. The time-dependent fluorimetric studies revealed that the actin polymerization starts from the tail region and progressed towards the head region of spermatozoa during capacitation. The lysophosphatidyl choline (LPC)-induced acrosome reaction (AR) stimulated quick actin depolymerization. The inhibitor cytochalasin D (CD) blocked the in vitro capacitation by inhibiting the actin polymerization. In addition, we also performed different inhibitor (Genistein, H-89, PD9809 and GF-109) and enhancer (dbcAMP, H(2)O(2) and vanadate) studies on actin tyrosine phosphorylation and actin polymerization. The inhibitors of tyrosine phosphorylation inhibit actin tyrosine phosphorylation and polymerization, whereas enhancers of tyrosine phosphorylation stimulate F-actin formation and tyrosine phosphorylation. These observations suggest that the tyrosine phosphorylation regulates the actin polymerization, and both are coupled processes during capacitation of buffalo spermatozoa. © 2015 Blackwell Verlag GmbH.

The autowave modes of solid phase polymerization of metal-containing monomers in two- and three-dimensional fiberglass-filled matrices

NASA Astrophysics Data System (ADS)

Barelko, V. V.; Pomogailo, A. D.; Dzhardimalieva, G. I.; Evstratova, S. I.; Rozenberg, A. S.; Uflyand, I. E.

1999-06-01

The phenomenon of autowave (frontal) solid phase polymerization of metal-containing monomers based on metal-acrylamide complexes is considered. The comparison of the features of autowave processes realized in both the single-component matrices of the monomer and the matrices filled by the fiberglass materials is performed. The unstable regimes of the polymerization wave as well as the conditions for the stabilization of the flat front in the filled matrices are described. The peculiarities of the frontal regimes in the three- and two-dimensional media are studied. Some possibilities for using of autowave polymerization in the fabrication of the polymer-fiberglass composites and composition prepregs are discussed.

Polymeric Materials for Aerospace Power and Propulsion-NASA Glenn Overview

NASA Technical Reports Server (NTRS)

Meador, Michael A.

2008-01-01

Use of lightweight materials in aerospace power and propulsion components can lead to significant reductions in vehicle weight and improvements in performance and efficiency. Polymeric materials are well suited for many of these applications, but improvements in processability, durability and performance are required for their successful use in these components. Polymers Research at NASA Glenn is focused on utilizing a combination of traditional polymer science and engineering approaches and nanotechnology to develop new materials with enhanced processability, performance and durability. An overview of these efforts will be presented.

The First Total Synthesis of Sporiolide A

PubMed Central

Chen, Qi; Linhardt, Robert J.

2014-01-01

The first total synthesis of the natural cytotoxic agent sporiolide A has been accomplished from D-glucal in 16 steps with 6.1% overall yield. Carbohydrates were applied as the chiral templates to manipulate the absolute configuration during the synthesis. Pyridinium chlorochromate (PCC)-promoted transformation of the cyclic enol-ether to lactone, followed by Yamaguchi esterification and intramolecular ring closure metathesis, greatly facilitates synthesis of the target compound. PMID:17064018

DISSOLUTION OF PLUTONIUM CONTAINING CARRIER PRECIPITATE BY CARBONATE METATHESIS AND SEPARATION OF SULFIDE IMPURITIES THEREFROM BY SULFIDE PRECIPITATION

DOEpatents

Duffield, R.B.

1959-07-14

A process is described for recovering plutonium from foreign products wherein a carrier precipitate of lanthanum fluoride containing plutonium is obtained and includes the steps of dissolving the carrier precipitate in an alkali metal carbonate solution, adding a soluble sulfide, separating the sulfide precipitate, adding an alkali metal hydroxide, separating the resulting precipitate, washing, and dissolving in a strong acid.

Inorganic Halogen Oxidizer Research.

DTIC Science & Technology

1982-04-21

Hexafluorophosphate , High Detonation Pressure Explosives. 20. (Continued) (71.7 weight %). The formation and decomposition mechanism of NF4+ salts was...low-tern- Reaction of NFSbF, with CsBrF 4 0. Although CsBrF[O perature metathesis using a cesium salt is superior to a lithium reacts with HF...yield of perchloryl fluoride (97%) is achieved with a mixture of fluorosulfonic acid and SbF 5 as fluorinating medium. Potassium, sodium, lithium

Grubbs's Cross Metathesis of Eugenol with cis-2-butene-1, 4-diol to Make a Natural Product: An Organometallic Experiment for the Undergraduate Lab

ERIC Educational Resources Information Center

Taber, Douglass F.; Frankowski, Kevin J.

2006-01-01

A modified experimental procedure for the one-step synthesis that is suitable for the undergraduate organic lab is presented. In the course of work towards the more routine use of air-sensitive organometallic complexes such as the Grubb's catalyst, the natural product (E)-4-(4-hydroxy-3-methoxyphenyl) but-2-en-ol, 4, was synthesized.

Ionic Liquids as Energetic Materials

DTIC Science & Technology

2007-03-01

triazolium halide that can be synthesized from the electrophilic fluorination and quaternization of the amino-substituted triazole. Metathesis with a...silver salt such as silver nitrate forms the nitrate salt. By electrophilic difluoroamination of 1 -alkyl-3-nitro- 1,2,4-triazole, 1,4-dialkyl-3-nitro...nonaromatic salts (1-7) described in Table 1. The presence of small amounts of fluorine in the substituent arm contributes to the thermal stability and has

Splitting a C-O bond in dialkylethers with bis(1,2,4-tri-t-butylcyclopentadienyl) cerium-hydride does not occur by a sigma-bond metathesis pathway: a combined experimental and DFT computational study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Werkema, Evan; Yahia, Ahmed; Maron, Laurent

2010-04-06

Addition of diethylether to [1,2,4(Me3C)3C5H2]2CeH, abbreviated Cp'2CeH, gives Cp'2CeOEt and ethane. Similarly, di-n-propyl- or di-n-butylether gives Cp'2Ce(O-n-Pr) and propane or Cp'2Ce(O-n-Bu) and butane, respectively. Using Cp'2CeD, the propane and butane contain deuterium predominantly in their methyl groups. Mechanisms, formulated on the basis of DFT computational studies, show that the reactions begin by an alpha or beta-CH activation with comparable activation barriers but only the beta-CH activation intermediate evolves into the alkoxide product and an olefin. The olefin then inserts into the Ce-H bond forming the alkyl derivative, Cp'2CeR, that eliminates alkane. The alpha-CH activation intermediate is in equilibrium with themore » starting reagents, Cp'2CeH and the ether, which accounts for the deuterium label in the methyl groups of the alkane. The one-step sigma-bond metathesis mechanism has a much higher activation barrier than either of the two-step mechanisms.« less

Enhanced photoluminescence of SrWO{sub 4}:Eu{sup 3+} red phosphor synthesized by mechanochemically assisted solid state metathesis reaction method at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peter, Anthuvan John, E-mail: quantajohn@gmail.com; Banu, I. B. Shameem

2015-06-24

Optically efficient europium activated alkaline earth metal tungstate nano phosphor (SrWO{sub 4}) with different doping concentrations have been synthesized by mechanochemically assisted solid state metathesis reaction at room temperature for the first time. The XRD and Raman spectra results indicated that the prepared powders exhibit a scheelite-type tetragonal structure. FTIR spectra exhibited a high absorption band situated at around 854 cm{sup −1}, which was ascribed to the W–O antisymmetric stretching vibrations into the [WO{sub 4}]{sup 2−} tetrahedron groups. Analysis of the emission spectra with different Eu{sup 3+} concentrations revealed that the optimum dopant concentration for SrWO{sub 4}: x Eu{sup 3+} phosphormore » is about 8 mol% of Eu{sup 3+}.The red emission intensity of the SSM prepared SrWO{sub 4}: 0.08Eu{sup 3+} phosphors are 2 times greater than that of the commercial Y{sub 2}O{sub 2}S: Eu{sup 3+} red phosphor prepared by the conventional solid state reaction method. All the results indicate that the phosphor is a promising red phosphor pumped by NUV InGaN chip for fabricating WLED.« less

Product Distribution from Precursor Bite Angle Variation in Multitopic Alkyne Metathesis: Evidence for a Putative Kinetic Bottleneck.

PubMed

Moneypenny, Timothy P; Yang, Anna; Walter, Nathan P; Woods, Toby J; Gray, Danielle L; Zhang, Yang; Moore, Jeffrey S

2018-05-02

In the dynamic synthesis of covalent organic frameworks and molecular cages, the typical synthetic approach involves heuristic methods of discovery. While this approach has yielded many remarkable products, the ability to predict the structural outcome of subjecting a multitopic precursor to dynamic covalent chemistry (DCC) remains a challenge in the field. The synthesis of covalent organic cages is a prime example of this phenomenon, where precursors designed with the intention of affording a specific product may deviate dramatically when the DCC synthesis is attempted. As such, rational design principles are needed to accelerate discovery in cage synthesis using DCC. Herein, we test the hypothesis that precursor bite angle contributes significantly to the energy landscape and product distribution in multitopic alkyne metathesis (AM). By subjecting a series of precursors with varying bite angles to AM, we experimentally demonstrate that the product distribution, and convergence toward product formation, is strongly dependent on this geometric attribute. Surprisingly, we discovered that precursors with the ideal bite angle (60°) do not afford the most efficient pathway to the product. The systematic study reported here illustrates how seemingly minor adjustments in precursor geometry greatly affect the outcome of DCC systems. This research illustrates the importance of fine-tuning precursor geometric parameters in order to successfully realize desirable targets.

Phenylselenolate Mercury Alkyl Compounds, PhSeHgMe and PhSeHgEt: Molecular Structures, Protolytic Hg–C Bond Cleavage and Phenylselenolate Exchange‡

PubMed Central

Yurkerwich, Kevin; Quinlivan, Patrick J.; Rong, Yi

2015-01-01

The phenylselenolate mercury alkyl compounds, PhSeHgMe and PhSeHgEt, have been structurally characterized by X-ray diffraction, thereby demonstrating that both compounds are monomeric with approximately linear coordination geometries; the mercury centers do, nevertheless, exhibit secondary Hg•••Se intermolecular interactions that serve to increase the coordination number in the solid state. The ethyl derivative, PhSeHgEt, undergoes facile protolytic cleavage of the Hg–C bond to release ethane at room temperature, whereas PhSeHgMe exhibits little reactivity under similar conditions. Interestingly, the cleavage of the Hg–C bond of PhSeHgEt is also more facile than that of the thiolate analogue, PhSHgEt, which demonstrates that coordination by selenium promotes protolytic cleavage of the mercury-carbon bond. The phenylselenolate compounds PhSeHgR (R = Me, Et) also undergo degenerate exchange reactions with, for example, PhSHgR and RHgCl. In each case, the alkyl groups preserve coupling to the 199Hg nuclei, thereby indicating that the exchange process involves metathesis of the Hg–SePh/Hg–X groups rather than metathesis of the Hg–R/Hg–R groups. PMID:26644634

Phenylselenolate Mercury Alkyl Compounds, PhSeHgMe and PhSeHgEt: Molecular Structures, Protolytic Hg-C Bond Cleavage and Phenylselenolate Exchange.

PubMed

Yurkerwich, Kevin; Quinlivan, Patrick J; Rong, Yi; Parkin, Gerard

2016-01-08

The phenylselenolate mercury alkyl compounds, PhSeHgMe and PhSeHgEt, have been structurally characterized by X-ray diffraction, thereby demonstrating that both compounds are monomeric with approximately linear coordination geometries; the mercury centers do, nevertheless, exhibit secondary Hg•••Se intermolecular interactions that serve to increase the coordination number in the solid state. The ethyl derivative, PhSeHgEt, undergoes facile protolytic cleavage of the Hg-C bond to release ethane at room temperature, whereas PhSeHgMe exhibits little reactivity under similar conditions. Interestingly, the cleavage of the Hg-C bond of PhSeHgEt is also more facile than that of the thiolate analogue, PhSHgEt, which demonstrates that coordination by selenium promotes protolytic cleavage of the mercury-carbon bond. The phenylselenolate compounds PhSeHgR (R = Me, Et) also undergo degenerate exchange reactions with, for example, PhSHgR and RHgCl. In each case, the alkyl groups preserve coupling to the 199 Hg nuclei, thereby indicating that the exchange process involves metathesis of the Hg-SePh/Hg-X groups rather than metathesis of the Hg-R/Hg-R groups.

Synthesis and testing of hypergolic ionic liquids for chemical propulsion

NASA Astrophysics Data System (ADS)

Stovbun, S. V.; Shchegolikhin, A. N.; Usachev, S. V.; Khomik, S. V.; Medvedev, S. P.

2017-06-01

Synthesis of new highly energetic ionic liquids (ILs) is described, and their hypergolic ignition properties are tested. The synthesized ILs combine the advantages of conventional rocket propellants with the energy characteristics of acetylene derivatives. To this end, N-alkylated imidazoles (alkyl = ethyl, butyl) have been synthesized and alkylated with propargyl bromide. The desired ionic liquids have been produced by metathesis using Ag dicyanamide. Modified hypergolic drop tests with white fuming nitric acid have been performed for N-ethyl (IL-1) and N-butyl propargylimidazolium (IL-2) ionic liquids. In the modified drop tests, high-speed shadowgraph imaging is used to visualize the process, and the temperature rise due to ignition is monitored with a two-color photodetector. It is shown that the ignition delay is shorter for IL-1 as compared to IL-2. The ignition of IL-1 occurs in two stages, whereas the combustion of IL-2 proceeds smoothly without secondary flashes.

The effect of photopolymerization on the degree of conversion, polymerization kinetic, biaxial flexure strength, and modulus of self-adhesive resin cements.

PubMed

Aguiar, Thaiane R; de Oliveira, Michele; Arrais, César A G; Ambrosano, Glaucia M B; Rueggeberg, Frederick; Giannini, Marcelo

2015-02-01

Understanding the effect of the degree of conversion on the mechanical properties of auto- and dual-polymerizing self-adhesive resin cements leads to a better estimation of their performance in different clinical scenarios. The purpose of this study was to evaluate the effect of photopolymerization on the degree of conversion (DC) and polymerization kinetic of 4 dual-polymerized resin cements, 20 minutes after mixing, and its effects on the mechanical properties (biaxial flexural strength [FS] and modulus [FM]) after short-term aging. Conventional (RelyX ARC and Clearfil Esthetic Cement) and self-adhesive resin cements (RelyX Unicem and Clearfil SA Cement) were applied to a Fourier infrared spectrometer to assess the DC (n=5) under the following 3 polymerization conditions: direct light exposure (dual-polymerizing mode), exposure through the prepolymerized disk, or autopolymerizing. The polymerization kinetic was recorded for 20 minutes. Then, disk-shaped specimens (n=11) were prepared to evaluate the effect of polymerization on the FS and FM in both extreme polymerization conditions (dual-polymerizing or autopolymerizing). Data were statistically analyzed by 2-way repeated measure ANOVA (DC) and by 2-way ANOVA (FS and FM), followed by the Tukey-Kramer post hoc test (α=.05). Autopolymerizing groups exhibited reduced DC means, whereas intermediate values were observed when resin cements were polymerized through the disk. All groups exhibited higher DC at the end of 20 minutes. The polymerization kinetic revealed a rising curve, and materials, when directly photopolymerized, reached a plateau immediately after light exposure. Regarding the flexural biaxial testing, most of the resin cements were affected by polymerization mode and differences among groups were product dependent. The resin cements achieved immediate higher DC and mechanical properties when photopolymerized. The total absence of photoactivation may still impair their mechanical properties even after short-term aging. Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Highly efficient reversible addition-fragmentation chain-transfer polymerization in ethanol/water via flow chemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Piaoran; Cao, Peng -Fei; Su, Zhe

Here, utilization of a flow reactor under high pressure allows highly efficient polymer synthesis via reversible addition–fragmentation chain-transfer (RAFT) polymerization in an aqueous system. Compared with the batch reaction, the flow reactor allows the RAFT polymerization to be performed in a high-efficiency manner at the same temperature. The adjustable pressure of the system allows further elevation of the reaction temperature and hence faster polymerization. Other reaction parameters, such as flow rate and initiator concentration, were also well studied to tune the monomer conversion and the molar mass dispersity (Ð) of the obtained polymers. Gel permeation chromatography, nuclear magnetic resonance (NMR),more » and Fourier transform infrared spectroscopies (FTIR) were utilized to monitor the polymerization process. With the initiator concentration of 0.15 mmol L –1, polymerization of poly(ethylene glycol) methyl ethermethacrylate with monomer conversion of 52% at 100 °C under 73 bar can be achieved within 40 min with narrow molar mass dispersity (D) Ð (<1.25). The strategy developed here provides a method to produce well-defined polymers via RAFT polymerization with high efficiency in a continuous manner.« less

Shaping the Future of Nanomedicine: Anisotropy in Polymeric Nanoparticle Design

PubMed Central

Meyer, Randall A.; Green, Jordan J.

2015-01-01

Nanofabrication and biomedical applications of polymeric nanoparticles have become important areas of research. Biocompatible polymeric nanoparticles have been investigated for their use as delivery vehicles for therapeutic and diagnostic agents. Although polymeric nanoconstructs have traditionally been fabricated as isotropic spheres, anisotropic, non-spherical nanoparticles have gained interest in the biomaterials community due to their unique interactions with biological systems. Polymeric nanoparticles with different forms of anisotropy have been manufactured utilizing a variety of novel methods in recent years. In addition, they have enhanced physical, chemical, and biological properties compared to spherical nanoparticles, including increased targeting avidity and decreased non-specific in vivo clearance. With these desirable properties, anisotropic nanoparticles have been successfully utilized in many biomedical settings and have performed superiorly to analogous spherical nanoparticles. We summarize the current state-of-the-art fabrication methods for anisotropic polymeric nanoparticles including top-down, bottom-up, and microfluidic design approaches. We also summarize the current and potential future applications of these nanoparticles, including drug delivery, biological targeting, immunoengineering, and tissue engineering. Ongoing research into the properties and utility of anisotropic polymeric nanoparticles will prove critical to realizing their potential in nanomedicine. PMID:25981390

Polymeric endovascular strut and lumen detection algorithm for intracoronary optical coherence tomography images

NASA Astrophysics Data System (ADS)

Amrute, Junedh M.; Athanasiou, Lambros S.; Rikhtegar, Farhad; de la Torre Hernández, José M.; Camarero, Tamara García; Edelman, Elazer R.

2018-03-01

Polymeric endovascular implants are the next step in minimally invasive vascular interventions. As an alternative to traditional metallic drug-eluting stents, these often-erodible scaffolds present opportunities and challenges for patients and clinicians. Theoretically, as they resorb and are absorbed over time, they obviate the long-term complications of permanent implants, but in the short-term visualization and therefore positioning is problematic. Polymeric scaffolds can only be fully imaged using optical coherence tomography (OCT) imaging-they are relatively invisible via angiography-and segmentation of polymeric struts in OCT images is performed manually, a laborious and intractable procedure for large datasets. Traditional lumen detection methods using implant struts as boundary limits fail in images with polymeric implants. Therefore, it is necessary to develop an automated method to detect polymeric struts and luminal borders in OCT images; we present such a fully automated algorithm. Accuracy was validated using expert annotations on 1140 OCT images with a positive predictive value of 0.93 for strut detection and an R2 correlation coefficient of 0.94 between detected and expert-annotated lumen areas. The proposed algorithm allows for rapid, accurate, and automated detection of polymeric struts and the luminal border in OCT images.

A Self-Reporting Photocatalyst for Online Fluorescence Monitoring of High Throughput RAFT Polymerization.

PubMed

Yeow, Jonathan; Joshi, Sanket; Chapman, Robert; Boyer, Cyrille Andre Jean Marie

2018-04-25

Translating controlled/living radical polymerization (CLRP) from batch to the high throughput production of polymer libraries presents several challenges in terms of both polymer synthesis and characterization. Although recently there have been significant advances in the field of low volume, high throughput CLRP, techniques able to simultaneously monitor multiple polymerizations in an "online" manner have not yet been developed. Here, we report our discovery that 5,10,15,20-tetraphenyl-21H,23H-porphine zinc (ZnTPP) is a self-reporting photocatalyst that can mediate PET-RAFT polymerization as well as report on monomer conversion via changes in its fluorescence properties. This enables the use of a microplate reader to conduct high throughput "online" monitoring of PET-RAFT polymerizations performed directly in 384-well, low volume microtiter plates. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photopolymerization of Dienoyl Lipids Creates Planar Supported Poly(lipid) Membranes with Retained Fluidity.

PubMed

Orosz, Kristina S; Jones, Ian W; Keogh, John P; Smith, Christopher M; Griffin, Kaitlyn R; Xu, Juhua; Comi, Troy J; Hall, H K; Saavedra, S Scott

2016-02-16

Polymerization of substrate-supported bilayers composed of dienoylphosphatidylcholine (PC) lipids is known to greatly enhance their chemical and mechanical stability; however, the effects of polymerization on membrane fluidity have not been investigated. Here planar supported lipid bilayers (PSLBs) composed of dienoyl PCs on glass substrates were examined to assess the degree to which UV-initiated polymerization affects lateral lipid mobility. Fluorescence recovery after photobleaching (FRAP) was used to measure the diffusion coefficients (D) and mobile fractions of rhodamine-DOPE in unpolymerized and polymerized PSLBs composed of bis-sorbyl phosphatidylcholine (bis-SorbPC), mono-sorbyl-phosphatidylcholine (mono-SorbPC), bis-dienoyl-phosphatidylcholine (bis-DenPC), and mono-dienoyl phosphatidylcholine (mono-DenPC). Polymerization was performed in both the Lα and Lβ phase for each lipid. In all cases, polymerization reduced membrane fluidity; however, measurable lateral diffusion was retained which is attributed to a low degree of polymerization. The D values for sorbyl lipids were less than those of the denoyl lipids; this may be a consequence of the distal location of polymerizable group in the sorbyl lipids which may facilitate interleaflet bonding. The D values measured after polymerization were 0.1-0.8 of those measured before polymerization, a range that corresponds to fluidity intermediate between that of a Lα phase and a Lβ phase. This D range is comparable to ratios of D values reported for liquid-disordered (Ld) and liquid-ordered (Lo) lipid phases and indicates that the effect of UV polymerization on lateral diffusion in a dienoyl PSLB is similar to the transition from a Ld phase to a Lo phase. The partial retention of fluidity in UV-polymerized PSLBs, their enhanced stability, and the activity of incorporated transmembrane proteins and peptides is discussed.

Photopolymerization of dienoyl lipids creates planar supported poly(lipid) membranes with retained fluidity

PubMed Central

Orosz, Kristina S.; Jones, Ian W.; Keogh, John P.; Smith, Christopher M.; Griffin, Kaitlyn R.; Xu, Juhua; Comi, Troy J.; Hall, H. K.

2016-01-01

Polymerization of substrate-supported bilayers composed of dienoyl phosphatidylcholine (PC) lipids is known to greatly enhance their chemical and mechanical stability, however the effects of polymerization on membrane fluidity have not been investigated. Here planar supported lipid bilayers (PSLBs) composed of dienoyl PCs on glass substrates were examined to assess the degree to which UV-initiated polymerization affects lateral lipid mobility. Fluorescence recovery after photobleaching (FRAP) was used to measure the diffusion coefficients (D) and mobile fractions of rhodamine-DOPE in unpolymerized and polymerized PSLBs composed of bis-sorbyl phosphatidylcholine (bis-SorbPC), mono-sorbyl phosphatidylcholine (mono-SorbPC), bis-dienoyl phosphatidylcholine (bis-DenPC) and mono-dienoyl phosphatidylcholine (mono-DenPC). Polymerization was performed in both the Lα and Lβ phase for each lipid. In all cases, polymerization reduced membrane fluidity, however measurable lateral diffusion was retained which is attributed to a low degree of polymerization. The D values for sorbyl lipids were less than those of the denoyl lipids; this may be a consequence of the distal location of polymerizable group in the sorbyl lipids which may facilitate inter-leaflet bonding. The D values measured after polymerization were 0.1 to 0.8 of those measured before polymerization, a range that corresponds to fluidity intermediate between that of a Lα phase and a Lβ phase. This D range is comparable to ratios of D values reported for liquid-disordered (Ld) and liquid-ordered (Lo) lipid phases, and indicates that the effect of UV polymerization on lateral diffusion in a dienoyl PSLB is similar to the transition from a Ld phase to a Lo phase. The partial retention of fluidity in UV polymerized PSLBs, their enhanced stability, and the activity of incorporated transmembrane proteins and peptides is discussed. PMID:26794208

A multifunctional polymeric nanofilm with robust chemical performances for special wettability.

PubMed

Wang, Yabin; Lin, Feng; Dong, Yaping; Liu, Zhong; Li, Wu; Huang, Yudong

2016-03-07

A multifunctional polymeric nanofilm of a triazinedithiolsilane compound, which can protect metallic substrates and activate the corresponding surface simultaneously, is introduced onto a copper mesh surface via facile solution-immersion approaches. The resultant interface exhibits hydrophilic features due to the existence of silanol groups (SiOH) outward and has the potential to act as a superhydrophilic and underwater superoleophobic material. As the polymeric nanofilm atop the copper mesh is modified with long-chain octadecyltrichlorosilane (OTS), the functionalized surface becomes superhydrophobic and superoleophilic. The OTS-modified polymeric nanofilm shows outstanding chemical durability and stability that are seldom concurrently satisfied for a material with special wettability, owing to its inherent architecture. These textures generate high separation efficiency, durable separation capability and excellent thermal stability. The protective ability, originating from the textures of the underlying cross-linked disulfide units (-SS-) and siloxane networks (SiOSi) on the top of the nanofilm, prolongs the chemical durability. The activating capability stemming from the residual SiOH groups improves the chemical stability as a result of the chemical bonds developed by these sites. The significant point of this investigation lies in enlightening us on the fabrication of multifunctional polymeric nanofilms on different metal surfaces using various triazinedithiolsilane compounds, and on the construction of interfaces with controllable wettable performances in demanding research or industrial applications.

Development, optimisation and application of polyurethane foams as new polymeric phases for stir bar sorptive extraction.

PubMed

Neng, N R; Pinto, M L; Pires, J; Marcos, P M; Nogueira, J M F

2007-11-09

In this contribution, polyurethane foams are proposed as new polymeric phases for stir bar sorptive extraction (SBSE). Assays performed for polyurethane synthesis demonstrated that four series of formulations (P(1), P(2), P(3) and P(4)) present remarkable stability and excellent mechanical resistance to organic solvents. For polymer clean-up treatment, acetonitrile proved to be the best solvent under sonification, ensuring the reduction of the contamination and interferences. SBSE assays performed on these polyurethane polymers followed by liquid desorption and high-performance liquid chromatography-diode array detection (LD-HPLC-DAD) or large volume injection-capillary gas chromatography-mass spectrometry (LD-LVI-GC-MS), showed that P(2) presents the best recovery yields for atrazine, 2,3,4,5-tetrachlorophenol and fluorene, used as model compounds in water samples at a trace level. SBSE(P(2)) assays performed on this polymer mixed up with several adsorbent materials, i.e. activated carbon, a mesoporous material and a calixarene, did not bring any advantages in relation with the polymeric matrix alone. The comparison between assays performed by SBSE(P(2)) and by the conventional SBSE(PDMS) showed much better performance for the former phase on aqueous samples spiked with atrazine, 2,3,4,5-tetrachlorophenol and fluorene, in which the foremost two analytes present recovery values 3- and 10-fold higher, respectively. The polyurethanes proposed as new polymeric phases for SBSE provided powerful capabilities for the enrichment of organic compounds from aqueous matrices, showing to be indicated mainly in the case of the more polar analytes.

Performance impact of novel polymeric dyes in photoresist applications

NASA Astrophysics Data System (ADS)

Lu, Ping-Hung; Mehtsun, Salem; Sagan, John P.; Shan, Jianhui; Gonzalez, Eleazar; Ding, Shuji; Khanna, Dinesh N.

1999-06-01

Dye compounds are commonly used in photoresists as a low cost and effective way to control swing and/or standing wave effect caused by thin film interference as well as reflective notching by reflective light from highly reflective substrate and topography. Convention dyes are typically a monomeric compound with high absorptivity at the wavelength of exposure light and compatible with the resist system selected. Because of the monomeric nature, conventional dyes are relatively low in molecular weight hence their thermal stability and sublimination propensity has always been an issue of concern. We recently synthesize several highly thermal stable diazotized polymeric dyes. Their thermal properties as well as compatibility with resist system were investigated. The impact of polymeric dyes on the resists lithographic performance, swing reduction and reflective notching control are discussed.

The autowave modes of solid phase polymerization of metal-containing monomers in two- and three-dimensional fiberglass-filled matrices.

PubMed

Barelko, V. V.; Pomogailo, A. D.; Dzhardimalieva, G. I.; Evstratova, S. I.; Rozenberg, A. S.; Uflyand, I. E.

1999-06-01

The phenomenon of autowave (frontal) solid phase polymerization of metal-containing monomers based on metal-acrylamide complexes is considered. The comparison of the features of autowave processes realized in both the single-component matrices of the monomer and the matrices filled by the fiberglass materials is performed. The unstable regimes of the polymerization wave as well as the conditions for the stabilization of the flat front in the filled matrices are described. The peculiarities of the frontal regimes in the three- and two-dimensional media are studied. Some possibilities for using of autowave polymerization in the fabrication of the polymer-fiberglass composites and composition prepregs are discussed. (c) 1999 American Institute of Physics.

Conductive cotton prepared by polyaniline in situ polymerization using laccase.

PubMed

Zhang, Ya; Dong, Aixue; Wang, Qiang; Fan, Xuerong; Cavaco-Paulo, Artur; Zhang, Ying

2014-09-01

The high-redox-potential catalyst laccase, isolated from Aspergillus, was first used as a biocatalyst in the oxidative polymerization of water-soluble conductive polyaniline, and then conductive cotton was prepared by in situ polymerization under the same conditions. The polymerization of aniline was performed in a water dispersion of sodium dodecylbenzenesulfonate (SDBS) micellar solution with atmospheric oxygen serving as the oxidizing agent. This method is ecologically clean and permits a greater degree of control over the kinetics of the reaction. The conditions for polyaniline synthesis were optimized. Characterizations of the conducting polyaniline and cotton were carried out using Fourier transform infrared spectroscopy, UV-vis spectroscopy, cyclic voltammetry, the fabric induction electrostatic tester, and the far-field EMC shielding effectiveness test fixture.

Evaluation available encapsulation materials for low-cost long-life silicon photovoltaic arrays

NASA Technical Reports Server (NTRS)

Carmichael, D. C.; Gaines, G. B.; Noel, G. T.; Sliemers, F. A.; Nance, G. P.; Bunk, A. R.; Brockway, M. C.

1978-01-01

Experimental evaluation of selected encapsulation designs and materials based on an earlier study which have potential for use in low cost, long-life photovoltaic arrays are reported. The performance of candidate materials and encapsulated cells were evaluated principally for three types of encapsulation designs based on their potentially low materials and processing costs: (1) polymeric coatings, transparent conformal coatings over the cell with a structural-support substrate; (2) polymeric film lamination, cells laminated between two films or sheets of polymeric materials; and (3) glass-covered systems, cells adhesively bonded to a glass cover (superstrate) with a polymeric pottant and a glass or other substrate material. Several other design types, including those utilizing polymer sheet and pottant materials, were also included in the investigation.

Survey Study of Trunk Materials for Direct ATRP Grafting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saito, Tomonori; Chatterjee, Sabornie; Johnson, Joseph C.

2015-02-01

In previous study, we demonstrated a new method to prepare polymeric fiber adsorbents via a chemical-grafting method, namely atom-transfer radical polymerization (ATRP), and identified parameters affecting their uranium adsorption capacity. However, ATRP chemical grafting in the previous study still utilized conventional radiation-induced graft polymerization (RIGP) to introduce initiation sites on fibers. Therefore, the objective of the present study is to perform survey study of trunk fiber materials for direct ATRP chemical grafting method without RIGP for the preparation of fiber adsorbents for uranium recovery from seawater.

A novel headspace gas chromatographic method for in situ monitoring of monomer conversion during polymerization in an emulsion environment.

PubMed

Chai, Xin-Sheng; Zhong, Jin-Feng; Hu, Hui-Chao

2012-05-18

This paper describes a novel multiple-headspace extraction/gas chromatographic (MHE-GC) technique for monitoring monomer conversion during a polymerization reaction in a water-based emulsion environment. The polymerization reaction of methyl methacrylate (MMA) in an aqueous emulsion is used as an example. The reaction was performed in a closed headspace sample vial (as a mini-reactor), with pentane as a tracer. In situ monitoring of the vapor concentration of the tracer, employing a multiple headspace extraction (sampling) scheme, coupled to a GC, makes it possible to quantitatively follow the conversion of MMA during the early stages of polymerization. Data on the integrated amount of the tracer vapor released from the monomer droplet phase during the polymerization is described by a mathematic equation from which the monomer conversion can be calculated. The present method is simple, automated and economical, and provides an efficient tool in the investigation of the reaction kinetics and effects of the reaction conditions on the early stage of polymerization. Copyright © 2012 Elsevier B.V. All rights reserved.

Radiation-induced controlled polymerization of acrylic acid by RAFT and RAFT-MADIX methods in protic solvents

NASA Astrophysics Data System (ADS)

Sütekin, S. Duygu; Güven, Olgun

2018-01-01

The kinetic investigation of one-pot synthesis of poly(acrylic acid) (PAA) prepared via gamma radiation induced controlled polymerization was reported. PAA homopolymers were prepared by Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization in the presence of trithiocarbonate-based chain transfer agent (CTA) 2-(Dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) and also by Reversible Addition-Fragmentation/Macromolecular Design by Inter-change of Xanthates (RAFT/MADIX) polymerization in the presence of a xanthate based CTA O-ethyl-S-(1-methoxycarbonyl) ethyl dithiocarbonate (RA1). The polymerizations were performed at room temperature by the virtue of ionizing radiation. Protic solvents were used for the RAFT polymerization of AA considering environmental profits. The linear first-order kinetic plot, close control of molecular weight by the monomer/CTA molar ratio supported that the polymerization proceeds in a living fashion. The linear increase in molecular weight with conversion monitored by Size Exclusion Chromatography (SEC) is another proof of controlling of polymerization. [Monomer]/[RAFT] ratio and conversion was controlled to obtain PAA in the molecular weight range of 6900-35,800 with narrow molecular weight distributions. Reaction kinetics and effect of the amount of RAFT agent were investigated in detail. Between two different types of CTA, trithiocarbonate based DDMAT was found to be more efficient in terms of low dispersity (Đ) and linear first-order kinetic behavior for the radiation induced controlled synthesis of PAA homopolymers.

Assessment of surface hardness of acrylic resins submitted to accelerated artificial aging.

PubMed

Tornavoi, D C; Agnelli, J A M; Lepri, C P; Mazzetto, M O; Botelho, A L; Soares, R G; Dos Reis, A C

2012-06-01

The aim of this study was to assess the influence of accelerated artificial aging (AAA) on the surface hardness of acrylic resins. The following three commercial brands of acrylic resins were tested: Vipi Flash (autopolymerized resin), Vipi Wave (microwave heat-polymerized resin) and Vipi Cril (conventional heat-polymerized resin). To perform the tests, 21 test specimens (65x10x3 mm) were made, 7 for each resin. Three surface hardness readings were performed for each test specimen, before and after AAA, and the means were submitted to the following tests: Kolmogorov-Smirnov (P>0.05), Levene Statistic, Two-way ANOVA, Tukey Post Hoc (P<0.05) with the SPSS Statistical Software 17.0. The analysis of the factors showed significant differences in the hardness values (P<0.05). Before aging, the autopolymerized acrylic resin Vipi Flash showed lower hardness values when compared with the heat-polymerized resin Vipi Cril (P=0.001). After aging, the 3 materials showed similar performance when compared among them. The Vipi Cril was the only one affected by AAA and showed lower hardness values after this procedure (Pp=0.003). It may be concluded that accelerated artificial aging influenced surface hardness of heat-polymerized acrylic resin Vipi Cril.

Efficiency of polymerization of bulk-fill composite resins: a systematic review.

PubMed

Reis, André Figueiredo; Vestphal, Mariana; Amaral, Roberto Cesar do; Rodrigues, José Augusto; Roulet, Jean-François; Roscoe, Marina Guimarães

2017-08-28

This systematic review assessed the literature to evaluate the efficiency of polymerization of bulk-fill composite resins at 4 mm restoration depth. PubMed, Cochrane, Scopus and Web of Science databases were searched with no restrictions on year, publication status, or article's language. Selection criteria included studies that evaluated bulk-fill composite resin when inserted in a minimum thickness of 4 mm, followed by curing according to the manufacturers' instructions; presented sound statistical data; and comparison with a control group and/or a reference measurement of quality of polymerization. The evidence level was evaluated by qualitative scoring system and classified as high-, moderate- and low- evidence level. A total of 534 articles were retrieved in the initial search. After the review process, only 10 full-text articles met the inclusion criteria. Most articles included (80%) were classified as high evidence level. Among several techniques, microhardness was the most frequently method performed by the studies included in this systematic review. Irrespective to the "in vitro" method performed, bulk fill RBCs were partially likely to fulfill the important requirement regarding properly curing in 4 mm of cavity depth measured by depth of cure and / or degree of conversion. In general, low viscosities BFCs performed better regarding polymerization efficiency compared to the high viscosities BFCs.

Synergistic effect of graphene oxide on the methanol oxidation for fuel cell application

NASA Astrophysics Data System (ADS)

Siwal, Samarjeet; Ghosh, Sarit; Nandi, Debkumar; Devi, Nishu; Perla, Venkata K.; Barik, Rasmita; Mallick, Kaushik

2017-09-01

Aromatic polypyrene was synthesized by the oxidative polymerization of pyrene with potassium tetrachloropalladate (II), as oxidant. During the polymerization process the palladium salt was reduced to metallic palladium and forms the metal-polymer composite material. Polypyrene stabilized palladium nanoparticles showed electrocatalytic activity toward the oxidation of methanol. The performance of the electrocatalytic activity was substantially improved with the incorporation of graphene oxide to the palladium-polypyrene composite and the synergistic performance was attributed to the electronic and structural properties of the system.

Performance evaluation soil samples utilizing encapsulation technology

DOEpatents

Dahlgran, J.R.

1999-08-17

Performance evaluation soil samples and method of their preparation uses encapsulation technology to encapsulate analytes which are introduced into a soil matrix for analysis and evaluation by analytical laboratories. Target analytes are mixed in an appropriate solvent at predetermined concentrations. The mixture is emulsified in a solution of polymeric film forming material. The emulsified solution is polymerized to form microcapsules. The microcapsules are recovered, quantitated and introduced into a soil matrix in a predetermined ratio to form soil samples with the desired analyte concentration. 1 fig.

Performance evaluation soil samples utilizing encapsulation technology

DOEpatents

Dahlgran, James R.

1999-01-01

Performance evaluation soil samples and method of their preparation using encapsulation technology to encapsulate analytes which are introduced into a soil matrix for analysis and evaluation by analytical laboratories. Target analytes are mixed in an appropriate solvent at predetermined concentrations. The mixture is emulsified in a solution of polymeric film forming material. The emulsified solution is polymerized to form microcapsules. The microcapsules are recovered, quantitated and introduced into a soil matrix in a predetermined ratio to form soil samples with the desired analyte concentration.

Development of cryogenic PRD-49-1 filament-wound tanks

NASA Technical Reports Server (NTRS)

Hoggatt, J. T.

1971-01-01

A high modulus polymeric fiber was evaluated as a reinforcement for filament wound pressure vessels. Winding parameters and design data were established for the fiber with two different epoxy resin systems. Comparison was made between the performance factors of the polymeric fiber and those of S-glass and high modulus graphite vessels.

Asymmetric Synthesis of Apratoxin E.

PubMed

Mao, Zhuo-Ya; Si, Chang-Mei; Liu, Yi-Wen; Dong, Han-Qing; Wei, Bang-Guo; Lin, Guo-Qiang

2016-10-21

An efficient method for asymmetric synthesis of apratoxin E 2 is described in this report. The chiral lactone 8, recycled from the degradation of saponin glycosides, was utilized to prepare the non-peptide fragment 6. In addition to this "from nature to nature" strategy, olefin cross-metathesis (CM) was applied as an alternative approach for the formation of the double bond. Moreover, pentafluorophenyl diphenylphosphinate was found to be an efficient condensation reagent for the macrocyclization.

Z-Selective Metathesis Homocoupling of 1,3-Dienes by Molybdenum and Tungsten Monoaryloxide Pyrrolide (MAP) Complexes

PubMed Central

Townsend, Erik M.; Schrock, Richard R.; Hoveyda, Amir H.

2012-01-01

Molybdenum or tungsten MAP complexes that contain OHIPT as the aryloxide (hexaisopropylterphenoxide) are effective catalysts for homocoupling of simple (E)-1,3-dienes to give (E,Z,E)-trienes in high yield and with high Z selectivities. A vinylalkylidene MAP species was shown to have the expected syn structure in an X-ray study. MAP catalysts that contain OHMT (hexamethylterphenoxide) are relatively inefficient. PMID:22734508

Fundamental Studies on Aluminum Fuels

DTIC Science & Technology

1944-12-01

Isooctr.no 200 C. Additives in the Syster. Aluminum Dilaur- r.te Cyclohexp.ne 201 2. Metathesis (Double Decomposition ) of Aluminum So^pc -ith...changes of hydrolysis -ire reduced (p»47). It has a sharp melting point (p. 88) and x-r:ty diffraotion pattern (p.71 ) and upon partial...of decomposition products. (In the same «ay as by distillation an acaotrope is often produoed and has a constant boiling point). It muat be noted

Highly recoverable pyridinium-tagged Hoveyda-Grubbs pre-catalyst for olefin metathesis. Design of the boomerang ligand toward the optimal compromise between activity and reusability.

PubMed

Rix, Diane; Caïjo, Fréderic; Laurent, Isabelle; Gulajski, Lukasz; Grela, Karol; Mauduit, Marc

2007-09-28

Whereas the boomerang ligand of Hoveyda-Grubbs pre-catalysts can be modified by attachment of a pyridinium tag to its benzylidene moiety, a precise adjustment of the length of the spacer allows the optimum balance to be reached between the activity of the catalyst and its recoverability, exceeding 98% after 6 catalytic runs in the best case.

“Click, Click, Cyclize”: A DOS Approach to Sultams Utilizing Vinyl Sulfonamide Linchpins

PubMed Central

Zhou, Aihua; Rayabarapu, Dinesh; Hanson, Paul R.

2009-01-01

A diversity-oriented synthesis (DOS) strategy termed “Click, Click, Cyclize” is reported. This approach relies on functional group (FG) pairing between a vinyl sulfonamide and an array of functional groups to synthesize skeletally diverse sultams. Several FG pairing pathways on central tertiary vinyl sulfonamide linchpins have been developed including intramolecular Heck, aza-Michael, ring-closing enyne metathesis, Pauson—Khand, and chemoselective oxidation/Baylis—Hillman reactions. PMID:19115841

405 nm diode laser, halogen lamp and LED device comparison in dental composites cure: an "in vitro" experimental trial.

PubMed

Fornaini, C; Lagori, G; Merigo, E; Rocca, J-P; Chiusano, M; Cucinotta, A

2015-12-30

A 405 nm diode laser is indicated for composite materials polymerizing, thanks to the recent evolution in their compositions, absorbing in blue part of the spectrum. The purpose of this research was to evaluate its performance on two different kinds of composite resins. Two different composites were polymerized with a traditional halogen lamp, a LED device and a 405 nm diode laser. The depth of the cure, the volumetric shrinkage, and the degree of the conversion (DC%) of the double bond during the curing process were measured. One-way ANOVA test, Kruskal-Wallis tests, and Dunn comparison tests were used for statistic analysis. Regarding the depth of polymerization, the laser had the worst performance on one composite while on the other, no significant difference with the other devices was observed. The volumetric shrinkage showed that laser produced the lowest change in both of the composites. The DC% measure confirmed these findings. Based on the results of this preliminary study, it is not possible to recommend the 405 nm diode laser for the polymerization of dental composites.

Exploration of ethyl anthranilate-loaded monolithic matrix-type prophylactic polymeric patch.

PubMed

Islam, Johirul; Zaman, Kamaruz; Chakrabarti, Srijita; Bora, Nilutpal Sharma; Pathak, Manash Pratim; Mandal, Santa; Junejo, Julfikar Ali; Chattopadhyay, Pronobesh

2017-10-01

Compromised stability of pharmaceutical formulations loaded with volatiles is a serious problem associated with devices designed to deliver volatile compounds. The present study has been focused to evaluate the stability potential of matrix-type polymeric patches composed of volatile ethyl anthranilate for prophylaxis against vector-borne diseases. Ethyl anthranilate-loaded matrix-type polymeric patches were fabricated by solvent evaporation method on an impermeable backing membrane and attached to temporary release liners. Stability testing of the polymeric patches was performed as per the International Conference on Harmonization (ICH) guidelines for 6 months under accelerated conditions. In addition, the quantification of residual solvents was also performed as per the ICH guidelines. After conducting the stability studies for 6 months, the optimized patches showed the best possible results with respect to uniformity of drug content, physical appearance, and other analytical parameters. Furthermore, the amount of residual solvent was found well below the accepted limit. Thus, the present report outlined the analytical parameters to be evaluated to ensure the stability of a certain devices consisting of volatile compounds. Copyright © 2016. Published by Elsevier B.V.

Graft Polymerization of Acrylic Acid on a Polytetrafluoroethylene Panel by an Inductively Coupled Plasma

NASA Astrophysics Data System (ADS)

Lan, Yan; You, Qingliang; Cheng, Cheng; Zhang, Suzhen; Ni, Guohua; Nagatsu, M.; Meng, Yuedong

2011-02-01

Surface modification on a polytetrafluoroethylene (PTFE) panel was performed with sequential nitrogen plasma treatments and surface-initiated polymerization. By introducing COO- groups to the surface of the PTFE panel through grafting polymerization of acrylic acid (AA), a transparent poly (acrylic acid) (PAA) membrane was achieved from acrylic acid solution. Grafting polymerization initiating from the active groups was achieved on the PTFE panel surface after the nitrogen plasma treatment. Utilizing the acrylic acid as monomers, with COO- groups as cross link sites to form reticulation structure, a transparent poly (acrylic acid) membrane with arborescent macromolecular structure was formed on the PTFE panel surface. Analysis methods, such as fourier transform infrared spectroscopy (FTIR), microscopy and X-ray photoelectron spectroscopy (XPS), were utilized to characterize the structures of the macromolecule membrane on the PTFE panel surface. A contact angle measurement was performed to characterize the modified PTFE panels. The surface hydrophilicities of modified PTFE panels were significantly enhanced after the plasma treatment. It was shown that the grafting rate is related to the treating time and the power of plasma.

The initiating radical yields and the efficiency of polymerization for various dental photoinitiators excited by different light curing units.

PubMed

Neumann, Miguel G; Schmitt, Carla C; Ferreira, Giovana C; Corrêa, Ivo C

2006-06-01

To evaluate the efficiency of the photopolymerization of dental resins it is necessary to know to what extent the light emitted by the light curing units is absorbed by the photoinitiators. On the other hand, the efficiency of the absorbed photons to produce species that launch the polymerization process is also of paramount importance. Therefore, the previously determined PAE (photon absorption efficiency) is used in conjunction with the polymerization quantum yields for the photoinitiators, in order to be able to compare the total process on an equivalent basis. This parameter can be used to identify the best performance for the photochemical process with specific photoinitiators. The efficiency of LED (Ultrablue IS) and QTH (Optilux 401) lamps were tested comparing their performances with the photoinitiators camphorquinone (CQ); phenylpropanedione (PPD); monoacylphosphine oxide (Lucirin TPO); and bisacylphosphine oxide (Irgacure 819). The extent of photopolymerization per absorbed photon was determined from the polymerization quantum yields obtained by using the photoinitiators to polymerize methyl methacrylate, and afterwards combined with the previously determined PAEs. Although CQ presents a rather low polymerization quantum yield, its photopolymerization efficiency is practically the highest when irradiated with the Ultrablue LED. On the other hand, Lucirin is much more efficient than the other photoinitiators when irradiated with a QTH lamp, due to its high quantum yield and the overlap between its absorption spectrum and the output of the visible lamp light. Difference in photopolymerization efficiencies arise when combinations of photoinitiators are used, and when LED sources are used in preference to QTH. Mechanistic understanding is essential to optimal initiator formulation.

Metastable Polymeric Nitrogen: The Ultimate Green High-Energy-Density Material

NASA Astrophysics Data System (ADS)

Ciezak, Jennifer

2007-06-01

High-energy-high-density materials offering increased stability, vulnerability, and environmental safety are being aggressively pursued to meet the requirements of the DoD Joint Visions and Future Force. Nearly two decades ago, it was proposed that polymeric nitrogen would exceed all of these requirements and possess nearly five times the energy of any conventional energetic material in use today. The present study details an investigation into nitrogen polymerization using a novel high-pressure approach utilizing sodium azide as the starting material. Due to the weaker bonding structure of the anionic azide chains in comparison to a N-N triple bond, one expects that the azide chains will create single-covalently bonded polymeric networks more easily than diatomic nitrogen. A polymeric form of sodium azide was synthesized at high pressures, but the material was not metastable at ambient conditions, which precluded performance testing. Quantum chemical calculations have indicated stabilization of the polymeric structure at ambient conditions may be possible with the addition of hydrogen. Vibrational spectroscopic characterization suggests that a meta-stable polymeric form of nitrogen has been synthesized under high-pressure using sodium azide/hydrogen as the starting materials. This material remains stable at ambient conditions upwards of two weeks depending on the storage conditions.

Performance comparison of polarized white light emitting diodes using wire-grid polarizers with polymeric and glass substrates

NASA Astrophysics Data System (ADS)

Su, Jung-Chieh; Chou, Shih-Chieh

2018-03-01

Polarized white light emitting diodes (WLEDs) packaged with reflective metal wire-grid polarizer of polymeric and glass substrates were investigated. The performance comparison of polymeric wire-grid polarizer film (WGF) and nano wire-grid polarizer (NWGP) with glass substrate was evaluated. The transverse electric field (TE) polarization transmittance of WGF is less than that of NWGP due to its smaller grid parameters. Despite of the higher duty cycle of WGF, the angular-dependent extinction ratio (ER) of the polarized WLEDs (PWLEDs) with WGF is higher than that of with NWGP. Regarding increasing drive currents, the PWLEDs with NWGP had better color stability than that with WGF due to better substrate thermal stability. In summary, linewidth, period and substrate material are the crucial factors for the PWLED packaging using wire grid polarizer.

A review of processable high temperature resistant addition-type laminating resins

NASA Technical Reports Server (NTRS)

Serafini, T. T.; Delvigs, P.

1973-01-01

An important finding that resulted from research that was conducted to develop improved ablative resins was the discovery of a novel approach to synthesize processable high temperature resistant polymers. Low molecular weight polyimide prepolymers end-capped with norbornene groups were polymerized into thermo-oxidatively stable modified polyimides without the evolution of void producing volatile materials. This paper reviews basic studies that were performed using model compounds to elucidate the polymerization mechanism of the so-called addition-type polyimides. The fabrication and properties of polyimide/graphite fiber composites using A-type polyimide prepolymer as the matrix are described. An alternate method for preparing processable A-type polyimides by means of in situ polymerization of monomeric reactants on the fiber reinforcement is also described. Polyimide/graphite fiber composite performance at elevated temperatures is presented for A-type polyimides.

Covalently bonded networks through surface-confined polymerization

NASA Astrophysics Data System (ADS)

El Garah, Mohamed; MacLeod, Jennifer M.; Rosei, Federico

2013-07-01

The prospect of synthesizing ordered, covalently bonded structures directly on a surface has recently attracted considerable attention due to its fundamental interest and for potential applications in electronics and photonics. This prospective article focuses on efforts to synthesize and characterize epitaxial one- and two-dimensional (1D and 2D, respectively) polymeric networks on single crystal surfaces. Recent studies, mostly performed using scanning tunneling microscopy (STM), demonstrate the ability to induce polymerization based on Ullmann coupling, thermal dehalogenation and dehydration reactions. The 2D polymer networks synthesized to date have exhibited structural limitations and have been shown to form only small domains on the surface. We discuss different approaches to control 1D and 2D polymerization, with particular emphasis on the surface phenomena that are critical to the formation of larger ordered domains.

New electrochemiluminescent biosensors combining polyluminol and an enzymatic matrix.

PubMed

Sassolas, Audrey; Blum, Loïc J; Leca-Bouvier, Béatrice D

2009-06-01

Performant reagentless electrochemiluminescent (ECL) (bio)sensors have been developed using polymeric luminol as the luminophore. The polyluminol film is obtained by cyclic voltammetry (CV) on a screen-printed electrode either in a commonly used H(2)SO(4) medium or under more original near-neutral buffered conditions. ECL responses obtained after performing polymerization either at acidic pH or at pH 6 have been compared. It appears that polyluminol formed in near-neutral medium gives the best responses for hydrogen peroxide detection. Polymerization at pH 6 by cyclic voltammetry gives a linear range extending from 8 x 10(-8) to 1.3 x 10(-4) M H(2)O(2) concentrations. Based on this performant sensor for hydrogen peroxide detection, an enzymatic biosensor has been developed by associating the polyluminol film with an H(2)O(2)-producing oxidase. Here, choline oxidase (ChOD) has been chosen as a model enzyme. To develop the biosensor, luminol has been polymerized at pH 6 by CV, and then an enzyme-entrapping matrix has been formed on the above modified working electrode. Different biological (chitosan, agarose, and alginate) and chemical (silica gels, photopolymers, or reticulated matrices) gels have been tested. Best performances have been obtained by associating a ChOD-immobilizing photopolymer with the polyluminol film. In this case, choline can be detected with a linear range extending from 8 x 10(-8) to 1.3 x 10(-4) M.

Intramolecular fluorine migration via four-member cyclic transition states

PubMed

Nguyen; Mayer; Morton

2000-11-17

Gaseous CF(3)(+) interchanges F(+) for O with simple carbonyl compounds. CF(3)(+) reacts with propionaldehyde in the gas phase to produce (CH(3))(2)CF(+) via two competing pathways. Starting with 1-(13)C-propionaldehyde, the major pathway (80%) produces (CH(3))(2)CF(+) with the carbon label in one of the methyl groups. The minor pathway (20%) produces (CH(3))(2)CF(+) with the carbon label in the central position. The relative proportions of these two pathways are measured by (19)F NMR analysis of the neutral CH(3)CF=CH(2) produced by deprotonation of (CH(3))(2)CF(+) at <10(-)(3) Torr in an electron bombardment flow (EBFlow) reactor. Formation of alkene in which carbon is directly bonded to fluorine means that (in the minor product, at least) an F(+) for O transposition occurs via adduct formation followed by 1,3-atom transfer and then isomerization of CH(3)CH(2)CHF(+) to the more stable (CH(3))(2)CF(+). Use of CF(4) as a chemical ionization (CI) reagent gas leads to CF(3)(+) adduct ions for a variety of ketones, in addition to isoelectronic transposition of F(+) for O. Metastable ion decompositions of the adduct ions yield the metathesis products. Decompositions of fluorocycloalkyl cations formed in this manner give evidence for the same kinds of rearrangements as take place in CH(3)CH(2)CHF(+). Density functional calculations confirm that F(+) for O metathesis takes place via addition of CF(3)(+) to the carbonyl oxygen followed by transposition via a four-member cyclic transition state. A computational survey of the effects of different substituents in a series of aldehydes and acyclic ketones reveals no systematic variation of the energy of the transition state as a function of thermochemistry, but the Hammond postulate does appear to be obeyed in terms of progress along the reaction coordinate. Bond lengths corresponding to the central barrier correlate with overall thermochemistry of the F(+) for O interchange, but in a sense opposite to what might have been expected: the transition state becomes more product-like as the metathesis becomes increasingly exothermic. This reversal of the naive interpretation of the Hammond postulate is accounted for by the relative positions of the potential energy wells that precede and follow the central barrier.

Polymeric Flexible Immunosensor Based on Piezoresistive Micro-Cantilever with PEDOT/PSS Conductive Layer.

PubMed

Zhao, Rui; Sun, Ying

2018-02-03

In this paper, a fully polymeric micro-cantilever with the surface passivation layer of parylene-C and the strain resistor of poly(3,4-ethylenedioxythiophene)/poly (styrene sulfonate) (PEDOT/PSS) was proposed and demonstrated for immunoassays. By optimizing the design and fabrication of the polymeric micro-cantilever, a square resistance of 220 Ω/□ for PEDOT/PSS conductive layer have been obtained. The experimental spring constant and the deflection sensitivity were measured to be 0.017 N/m and 8.59 × 10 -7 nm -1 , respectively. The biological sensing performances of polymeric micro-cantilever were investigated by the immunoassay for human immunoglobulin G (IgG). The immunosensor was experimentally demonstrated to have a linear behavior for the detection of IgG within the concentrations of 10~100 ng/mL with a limit of detection (LOD) of 10 ng/mL. The experimental results indicate that the proposed polymeric flexible conductive layer-based sensors are capable of detecting trace biological substances.

Hydrophilic crosslinked-polymeric surface capable of effective suppression of protein adsorption

NASA Astrophysics Data System (ADS)

Kamon, Yuri; Inoue, Naoko; Mihara, Erika; Kitayama, Yukiya; Ooya, Tooru; Takeuchi, Toshifumi

2016-08-01

We investigated the nonspecific adsorption of proteins towards three hydrophilic crosslinked-polymeric thin layers prepared by surface-initiated atom transfer radical polymerization using N,N‧-methylenebisacrylamide, 2-(methacryloyloxy)ethyl-[N-(2-methacryloyloxy)ethyl]phosphorylcholine (MMPC), or 6,6‧-diacryloyl-trehalose crosslinkers. Protein binding experiments were performed by surface plasmon resonance with six proteins of different pI values including α-lactalbumin, bovine serum albumin (BSA), myoglobin, ribonuclease A, cytochrome C, and lysozyme in buffer solution at pH 7.4. All of the obtained crosslinked-polymeric thin layers showed low nonspecific adsorption of negatively charged proteins at pH 7.4 such as α-lactalbumin, BSA, and myoglobin. Nonspecific adsorption of positively charged proteins including ribonuclease A, cytochrome C, and lysozyme was the lowest for poly(MMPC). These results suggest poly(MMPC) can effectively reduce nonspecific adsorption of a wide range of proteins that are negatively or positively charged at pH 7.4. MMPC is a promising crosslinker for a wide range of polymeric materials requiring low nonspecific protein binding.

Polymeric Flexible Immunosensor Based on Piezoresistive Micro-Cantilever with PEDOT/PSS Conductive Layer

PubMed Central

Sun, Ying

2018-01-01

In this paper, a fully polymeric micro-cantilever with the surface passivation layer of parylene-C and the strain resistor of poly(3,4-ethylenedioxythiophene)/poly (styrene sulfonate) (PEDOT/PSS) was proposed and demonstrated for immunoassays. By optimizing the design and fabrication of the polymeric micro-cantilever, a square resistance of 220 Ω/□ for PEDOT/PSS conductive layer have been obtained. The experimental spring constant and the deflection sensitivity were measured to be 0.017 N/m and 8.59 × 10−7 nm−1, respectively. The biological sensing performances of polymeric micro-cantilever were investigated by the immunoassay for human immunoglobulin G (IgG). The immunosensor was experimentally demonstrated to have a linear behavior for the detection of IgG within the concentrations of 10~100 ng/mL with a limit of detection (LOD) of 10 ng/mL. The experimental results indicate that the proposed polymeric flexible conductive layer-based sensors are capable of detecting trace biological substances. PMID:29401669

Polymerization model for hydrogen peroxide initiated synthesis of polypyrrole nanoparticles.

PubMed

Leonavicius, Karolis; Ramanaviciene, Almira; Ramanavicius, Arunas

2011-09-06

A very simple, environmentally friendly, one-step oxidative polymerization route to fabricate polypyrrole (Ppy) nanoparticles of fixed size and morphology was developed and investigated. The herein proposed method is based on the application of sodium dodecyl sulfate and hydrogen peroxide, both easily degradable and cheap materials. The polymerization reaction is performed on 24 h time scale under standard conditions. We monitored a polaronic peak at 465 nm and estimated nanoparticle concentration during various stages of the reaction. Using this data we proposed a mechanism for Ppy nanoparticle formation in accordance with earlier emulsion polymerization mechanisms. Rates of various steps in the polymerization mechanism were accounted for and the resulting particles identified using atomic force microscopy. Application of Ppy nanoparticles prepared by the route presented here seems very promising for biomedical applications where biocompatibility is paramount. In addition, this kind of synthesis could be suitable for the development of solar cells, where very pure and low-cost conducting polymers are required. © 2011 American Chemical Society

EFFECT OF CONVENTIONAL AND EXPERIMENTAL GINGIVAL RETRACTION SOLUTIONS ON THE TENSILE STRENGTH AND INHIBITION OF POLYMERIZATION OF FOUR TYPES OF IMPRESSION MATERIALS

PubMed Central

Sábio, Sérgio; Franciscone, Paulo Afonso; Mondelli, José

2008-01-01

In the present study, two types of tests (tensile strength test and polymerization inhibition test) were performed to evaluate the physical and chemical properties of four impression materials [a polysulfide (Permlastic), a polyether (Impregum), a condensation silicone (Xantopren) and a polyvinylsiloxane (Aquasil)] when polymerized in contact with of one conventional (Hemostop) and two experimental (Vislin and Afrin) gingival retraction solutions. For the tensile strength test, the impression materials were mixed and packed into a steel plate with perforations that had residues of the gingival retraction solutions. After polymerization, the specimens were tested in tensile strength in a universal testing machine. For the polymerization inhibition test, specimens were obtained after taking impressions from a matrix with perforations that contained 1 drop of the gingival retraction solutions. Two independent examiners decided on whether or not impression material remnants remained unpolymerized, indicating interference of the chemical solutions. Based on the analysis of the results of both tests, the following conclusions were reached: 1. The tensile strength of the polysulfide decreased after contact with Hemostop and Afrin. 2. None of the chemical solutions inhibited the polymerization of the polysulfide; 3. The polyether presented lower tensile strength after polymerization in contact with the three gingival retraction agents; 4. The polyether had its polymerization inhibited only by Hemostop; 5. None of the chemical solutions affected the tensile strength of the condensation silicone; 6. Only Hemostop inhibited the polymerization of the condensation silicone; 7. The polyvinylsiloxane specimens polymerized in contact with Hemostop had significantly lower tensile strength; 8. Neither of the chemical solutions (Afrin and Vislin) affected the tensile strength of the polyvinylsiloxane and the condensation silicone; 9. Results of the tensile strength and polymerization inhibition tests suggest that Vislin can be used as substance of gingival retraction without affecting the tested properties of four impression materials. PMID:19089261

Effect of conventional and experimental gingival retraction solutions on the tensile strength and inhibition of polymerization of four types of impression materials.

PubMed

Sábio, Sérgio; Franciscone, Paulo Afonso; Mondelli, José

2008-01-01

In the present study, two types of tests (tensile strength test and polymerization inhibition test) were performed to evaluate the physical and chemical properties of four impression materials [a polysulfide (Permlastic), a polyether (Impregum), a condensation silicone (Xantopren) and a polyvinylsiloxane (Aquasil)] when polymerized in contact with of one conventional (Hemostop) and two experimental (Vislin and Afrin) gingival retraction solutions. For the tensile strength test, the impression materials were mixed and packed into a steel plate with perforations that had residues of the gingival retraction solutions. After polymerization, the specimens were tested in tensile strength in a universal testing machine. For the polymerization inhibition test, specimens were obtained after taking impressions from a matrix with perforations that contained 1 drop of the gingival retraction solutions. Two independent examiners decided on whether or not impression material remnants remained unpolymerized, indicating interference of the chemical solutions. Based on the analysis of the results of both tests, the following conclusions were reached: 1. The tensile strength of the polysulfide decreased after contact with Hemostop and Afrin. 2. None of the chemical solutions inhibited the polymerization of the polysulfide; 3. The polyether presented lower tensile strength after polymerization in contact with the three gingival retraction agents; 4. The polyether had its polymerization inhibited only by Hemostop; 5. None of the chemical solutions affected the tensile strength of the condensation silicone; 6. Only Hemostop inhibited the polymerization of the condensation silicone; 7. The polyvinylsiloxane specimens polymerized in contact with Hemostop had significantly lower tensile strength; 8. Neither of the chemical solutions (Afrin and Vislin) affected the tensile strength of the polyvinylsiloxane and the condensation silicone; 9. Results of the tensile strength and polymerization inhibition tests suggest that Vislin can be used as substance of gingival retraction without affecting the tested properties of four impression materials.

ABC Triblock Copolymer Worms: Synthesis, Characterization, and Evaluation as Pickering Emulsifiers for Millimeter-Sized Droplets

PubMed Central

2016-01-01

Polymerization-induced self-assembly (PISA) is used to prepare linear poly(glycerol monomethacrylate)–poly(2-hydroxypropyl methacrylate)–poly(benzyl methacrylate) [PGMA–PHPMA–PBzMA] triblock copolymer nano-objects in the form of a concentrated aqueous dispersion via a three-step synthesis based on reversible addition–fragmentation chain transfer (RAFT) polymerization. First, GMA is polymerized via RAFT solution polymerization in ethanol, then HPMA is polymerized via RAFT aqueous solution polymerization, and finally BzMA is polymerized via “seeded” RAFT aqueous emulsion polymerization. For certain block compositions, highly anisotropic worm-like particles are obtained, which are characterized by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The design rules for accessing higher order morphologies (i.e., worms or vesicles) are briefly explored. Surprisingly, vesicular morphologies cannot be accessed by targeting longer PBzMA blocks—instead, only spherical nanoparticles are formed. SAXS is used to rationalize these counterintuitive observations, which are best explained by considering subtle changes in the relative enthalpic incompatibilities between the three blocks during the growth of the PBzMA block. Finally, the PGMA–PHPMA–PBzMA worms are evaluated as Pickering emulsifiers for the stabilization of oil-in-water emulsions. Millimeter-sized oil droplets can be obtained using low-shear homogenization (hand-shaking) in the presence of 20 vol % n-dodecane. In contrast, control experiments performed using PGMA–PHPMA diblock copolymer worms indicate that these more delicate nanostructures do not survive even these mild conditions. PMID:27795581

Olefin Metathesis in Peptidomimetics, Dynamic Combinatorial Chemistry, and Molecular Imprinting

DTIC Science & Technology

2006-08-01

aryl iodide to the Grignard reagent . Treatment of the magnesium compound with allyl bromide and CuCN·2LiCl afforded benzoate 4-11, which was then...cyclization of a linear peptide by conventional coupling agents to form a new amide bond (Scheme 1-12)36,44 Some common reagents are...dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide (DIC), and expensive reagents such as HATU or PyBroP, which are more efficient.44 Racemization of the chiral

PLUTONIUM CARRIER METATHESIS WITH ORGANIC REAGENT

DOEpatents

Thompson, S.G.

1958-07-01

A method is described for converting a plutonium containing bismuth phosphate carrier precipitate Into a compositton more readily soluble in acid. The method consists of dissolving the bismuth phosphate precipitate in an aqueous solution of alkali metal hydroxide, and adding one of a certaia group of organic compounds, e.g., polyhydric alcohols or a-hydrorycarboxylic acids. The mixture is then heated causiing formation of a bismuth hydroxide precipitate containing plutonium which may be readily dissolved in nitric acid for further processing.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Jinhee; Chen, Ying-Pin; Perry, Zachary

A series of molybdenum- and copper-based MOPs were synthesized through coordination-driven process of a bridging ligand (3,3 -PDBAD, L1) and dimetal paddlewheel clusters. Three conformers of the ligand exist with an ideal bridging angle between the two carboxylate groups of 0° (H2α-L1), 120° (H2β-L1), and of 90° (H2γ-L1), respectively. At ambient or lower temperature, H2L1 and Mo2(OAc)4 or Cu2(OAc)4 were crystallized into a molecular square with γ-L1 and Mo2/Cu2 units. With proper temperature elevation, not only the molecular square with γ-L1 but also a lantern-shaped cage with α-L1 formed simultaneously. Similar to how Watson–Crick pairs stabilize the helical structure ofmore » duplex DNA, the core–shell molecular assembly possesses favorable H-bonding interaction sites. This is dictated by the ligand conformation in the shell, coding for the formation and providing stabilization of the central lantern shaped core, which was not observed without this complementary interaction. On the basis of the crystallographic implications, a heterobimetallic cage was obtained through a postsynthetic metal ion metathesis, showing different reactivity of coordination bonds in the core and shell. As an innovative synthetic strategy, the site-selective metathesis broadens the structural diversity and properties of coordination assemblies.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, J; Chen, YP; Perry, Z

A series of molybdenum- and copper-based MOPs were synthesized through coordination-driven process of a bridging ligand (3,3'-PDBAD, L-1) and dimetal paddlewheel clusters. Three conformers of the ligand exist with an ideal bridging angle between the two carboxylate groups of 0 degrees (H-2 zeta-L(1)), 120 degrees (H-2 beta-L-1), and of 90 degrees (H-2 beta-L-1), respectively. At ambient or lower temperature, (HL1)-L-2 and Mo-2(OAc)(4) or Cu-2(OAc)(4) were crystallized into a molecular square with ?-L-1 and Mo-2/Cu-2 units. With proper temperature elevation, not only the molecular square with ?-L-1 but also a lantern-shaped cage with a-L-1 formed simultaneously. Similar to how Watson-Crick pairsmore » stabilize the helical structure of duplex DNA, the core-shell molecular assembly possesses favorable H-bonding interaction sites. This is dictated by the ligand conformation in the shell, coding for the formation and providing stabilization of the central lantern shaped core, which was not observed without this complementary interaction. On the basis of the crystallographic implications, a heterobimetallic cage was obtained through a postsynthetic metal ion metathesis, showing different reactivity of coordination bonds in the core and shell. As an innovative synthetic strategy, the site-selective metathesis broadens the structural diversity and properties of coordination assemblies.« less

Rapid solid-state metathesis route to transition-metal doped titanias

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coleman, Nathaniel; Perera, Sujith; Gillan, Edward G., E-mail: edward-gillan@uiowa.edu

2015-12-15

Rapid solid-state metathesis (SSM) reactions are often short-lived highly exothermic reactions that yield a molten alkali halide salt that aids in product growth and crystallization. SSM reactions may also produce kinetically stabilized structures due to the short (seconds) reaction times. This report describes the investigation of rapid SSM reactions in the synthesis of transition-metal doped titanias (M–TiO{sub 2}). The dopant targeted compositions were ten mol percent and based on elemental analysis, many of the M–TiO{sub 2} samples were close to this targeted level. Based on surface analysis, some samples showed large enrichment in surface dopant content, particularly chromium and manganesemore » doped samples. Due to the highly exothermic nature of these reactions, rutile structured TiO{sub 2} was observed in all cases. The M–TiO{sub 2} samples are visible colored and show magnetic and optical properties consistent with the dopant in an oxide environment. UV and visible photocatalytic experiments with these visibly colored rutile M–TiO{sub 2} powders showed that many of them are strongly absorbent for methylene blue dye and degrade the dye under both UV and visible light illumination. This work may open up SSM reactions as an alternate non-thermodynamic reaction strategy for dopant incorporation into a wide range of oxide and non-oxides.« less

Evaluation of Polymerization Efficacy in Composite Resins via FT-IR Spectroscopy and Vickers Microhardness Test.

PubMed

Jafarzadeh, Tahereh-Sadat; Erfan, Mohammad; Behroozibakhsh, Marjan; Fatemi, Mostafa; Masaeli, Reza; Rezaei, Yashar; Bagheri, Hossein; Erfan, Yasaman

2015-01-01

Background and aims. Polymerization efficacy affects the properties and performance of composite resin restorations.The purpose of this study was to evaluate the effectiveness of polymerization of two micro-hybrid, two nano-hybrid and one nano-filled ormocer-based composite resins, cured by two different light-curing systems, using Fourier transformation infrared (FT-IR) spectroscopy and Vickers microhardness testing at two different depths (top surface, 2 mm). Materials and methods. For FT-IR spectrometry, five cylindrical specimens (5mm in diameter × 2 mm in length) were prepared from each composite resin using Teflon molds and polymerized for 20 seconds. Then, 70-μm wafers were sectioned at the top surface and at2mm from the top surface. The degree of conversion for each sample was calculated using FT-IR spectroscopy. For Vickers micro-hardness testing, three cylindrical specimens were prepared from each composite resin and polymerized for 20 seconds. The Vickers microhardness test (Shimadzu, Type M, Japan) was performed at the top and bottom (depth=2 mm) surfaces of each specimen. Three-way ANOVA with independent variables and Tukey tests were performed at 95% significance level. Results. No significant differences were detected in degree of conversion and microhardness between LED and QTH light-curing units except for the ormocer-based specimen, CeramX, which exhibited significantly higher DC by LED. All the composite resins showed a significantly higher degree of conversion at the surface. Microhardness was not significantly affected by depth, except for Herculite XRV Ultra and CeramX, which showed higher values at the surface. Conclusion. Composite resins containing nano-particles generally exhibited more variations in degree of conversion and microhardness.

Evaluation of Polymerization Efficacy in Composite Resins via FT-IR Spectroscopy and Vickers Microhardness Test

PubMed Central

Jafarzadeh, Tahereh-Sadat; Erfan, Mohammad; Behroozibakhsh, Marjan; Fatemi, Mostafa; Masaeli, Reza; Rezaei, Yashar; Bagheri, Hossein; Erfan, Yasaman

2015-01-01

Background and aims. Polymerization efficacy affects the properties and performance of composite resin restorations.The purpose of this study was to evaluate the effectiveness of polymerization of two micro-hybrid, two nano-hybrid and one nano-filled ormocer-based composite resins, cured by two different light-curing systems, using Fourier transformation infrared (FT-IR) spectroscopy and Vickers microhardness testing at two different depths (top surface, 2 mm). Materials and methods. For FT-IR spectrometry, five cylindrical specimens (5mm in diameter × 2 mm in length) were prepared from each composite resin using Teflon molds and polymerized for 20 seconds. Then, 70-μm wafers were sectioned at the top surface and at2mm from the top surface. The degree of conversion for each sample was calculated using FT-IR spectroscopy. For Vickers micro-hardness testing, three cylindrical specimens were prepared from each composite resin and polymerized for 20 seconds. The Vickers microhardness test (Shimadzu, Type M, Japan) was performed at the top and bottom (depth=2 mm) surfaces of each specimen. Three-way ANOVA with independent variables and Tukey tests were performed at 95% significance level. Results. No significant differences were detected in degree of conversion and microhardness between LED and QTH light-curing units except for the ormocer-based specimen, CeramX, which exhibited significantly higher DC by LED. All the composite resins showed a significantly higher degree of conversion at the surface. Microhardness was not significantly affected by depth, except for Herculite XRV Ultra and CeramX, which showed higher values at the surface. Conclusion. Composite resins containing nano-particles generally exhibited more variations in degree of conversion and microhardness. PMID:26889359

High performance, durable polymers including poly(phenylene)

DOEpatents

Fujimoto, Cy; Pratt, Harry; Anderson, Travis Mark

2017-02-28

The present invention relates to functionalized polymers including a poly(phenylene) structure. In some embodiments, the polymers and copolymers of the invention include a highly localized concentration of acidic moieties, which facilitate proton transport and conduction through networks formed from these polymers. In addition, the polymers can include functional moieties, such as electron-withdrawing moieties, to protect the polymeric backbone, thereby extending its durability. Such enhanced proton transport and durability can be beneficial for any high performance platform that employs proton exchange polymeric membranes, such as in fuel cells or flow batteries.

Tensile bond strength between auto-polymerized acrylic resin and acrylic denture teeth treated with MF-MA solution.

PubMed

Thongrakard, Ticha; Wiwatwarrapan, Chairat

2016-08-01

This study evaluated the effect of chemical surface treatment using methyl formate-methyl acetate (MF-MA) solution on the tensile bond strength between acrylic denture teeth and auto-polymerized acrylic resin. Seventy maxillary central incisor acrylic denture teeth for each of three different brands (Yamahachi New Ace; Major Dent; Cosmo HXL) were embedded with incisal edge downwards in auto-polymerized resin in polyethylene pipes and ground with silicone carbide paper on their ridge lap surfaces. The teeth of each brand were divided into seven groups (n=10): no surface treatment (control group), MF-MA solution at a ratio of 25:75 (v/v) for 15 seconds, 30 seconds, 60 seconds, 120 seconds, 180 seconds, and MMA for 180 seconds. Auto-polymerized acrylic resin (Unifast Trad) was applied to the ground surface and polymerized in a pressure cooker. A tensile strength test was performed with a universal testing machine. Statistical analysis of the results was performed using two-way analysis of variance (ANOVA) and post-hoc Dunnett T3 test (α=.05). The surface treatment groups had significantly higher mean tensile bond strengths compared with the control group (P<.05) when compared within the same brand. Among the surface treatment groups of each brand, there were no significantly different tensile bond strengths between the MF-MA groups and the MMA 180 second group (P>.05), except for the Yamahachi New Ace MF-MA 180-second group (P<.05). 15-second MF-MA solution can be an alternative chemical surface treatment for repairing a denture base and rebonding acrylic denture teeth with auto-polymerized acrylic resin, for both conventional and cross-linked teeth.

Functional Two-Dimensional Coordination Polymeric Layer as a Charge Barrier in Li-S Batteries.

PubMed

Huang, Jing-Kai; Li, Mengliu; Wan, Yi; Dey, Sukumar; Ostwal, Mayur; Zhang, Daliang; Yang, Chih-Wen; Su, Chun-Jen; Jeng, U-Ser; Ming, Jun; Amassian, Aram; Lai, Zhiping; Han, Yu; Li, Sean; Li, Lain-Jong

2018-01-23

Ultrathin two-dimensional (2D) polymeric layers are capable of separating gases and molecules based on the reported size exclusion mechanism. What is equally important but missing today is an exploration of the 2D layers with charge functionality, which enables applications using the charge exclusion principle. This work demonstrates a simple and scalable method of synthesizing a free-standing 2D coordination polymer Zn 2 (benzimidazolate) 2 (OH) 2 at the air-water interface. The hydroxyl (-OH) groups are stoichiometrically coordinated and implement electrostatic charges in the 2D structures, providing powerful functionality as a charge barrier. Electrochemical performance of the Li-S battery shows that the Zn 2 (benzimidazolate) 2 (OH) 2 coordination polymer layers efficiently mitigate the polysulfide shuttling effects and largely enhance the battery capacity and cycle performance. The synthesis of the proposed coordination polymeric layers is simple, scalable, cost saving, and promising for practical use in batteries.

Novel polymeric monolith materials with a β-cyclodextrin-graphene composite for the highly selective extraction of methyl jasmonate.

PubMed

Yu, Xinhong; Ling, Xu; Zou, Li; Chen, Zilin

2017-04-01

A novel polymeric monolith column with a  β-cyclodextrin-graphene composite was prepared for extraction of methyl jasmonate. A simple, sensitive, and effective polymeric monolith microextraction with high-performance liquid chromatography method has been presented for the determination. To carry out the best microextraction efficiency, several parameters such as sample flow rate, sample volume, and sample pH value were systematically optimized. In addition, the method validation showed a wide linear range of 5-2000 ng/mL, with a good linearity and low limits of detection for methyl jasmonate. The proposed method was successfully applied for the determination of methyl jasmonate in wintersweet flowers with recoveries of 90.67%. The result was confirmed by high-performance liquid chromatography with mass spectrometry. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Poly(ionic liquid) based chemosensors for detection of basic amino acids in aqueous medium

NASA Astrophysics Data System (ADS)

Li, Xinjuan; Wang, Kai; Ma, Nana; Jia, Xianbin

2017-09-01

Naked-eye detection of amino acids in water is of great significance in the field of bio-analytical applications. Herein, polymerized ionic liquids (PILs) with controlled chain length structures were synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization and post-quaternization approach. The amino acids recognition performance of PILs with different alkyl chain lengths and molecular weights was evaluated by naked-eye color change and ultraviolet-visible (UV-vis) spectral studies. These PILs were successfully used for highly sensitive and selective detection of Arg, Lys and His in water. The recognition performance was improved effectively with increased molecular weight of PILs. The biosensitivity of the PILs in water was strongly dependent on their aggregation effect and polarization effect. Highly sensitive and selective detection of amino acids was successfully accomplished by introducing positively charged pyridinium moieties and controlled RAFT radical polymerization.

Extracellular polymeric substances mediate bioleaching/biocorrosion via interfacial processes involving iron(III) ions and acidophilic bacteria.

PubMed

Sand, Wolfgang; Gehrke, Tilman

2006-01-01

Extracellular polymeric substances seem to play a pivotal role in biocorrosion of metals and bioleaching, biocorrosion of metal sulfides for the winning of precious metals as well as acid rock drainage. For better control of both processes, the structure and function of extracellular polymeric substances of corrosion-causing or leaching bacteria are of crucial importance. Our research focused on the extremophilic bacteria Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, because of the "simplicity" and knowledge about the interactions of these bacteria with their substrate/substratum and their environment. For this purpose, the composition of the corresponding extracellular polymeric substances and their functions were analyzed. The extracellular polymeric substances of both species consist mainly of neutral sugars and lipids. The functions of the exopolymers seem to be: (i) to mediate attachment to a (metal) sulfide surface, and (ii) to concentrate iron(III) ions by complexation through uronic acids or other residues at the mineral surface, thus, allowing an oxidative attack on the sulfide. Consequently, dissolution of the metal sulfide is enhanced, which may result in an acceleration of 20- to 100-fold of the bioleaching process over chemical leaching. Experiments were performed to elucidate the importance of the iron(III) ions complexed by extracellular polymeric substances for strain-specific differences in oxidative activity for pyrite. Strains of A. ferrooxidans with a high amount of iron(III) ions in their extracellular polymeric substances possess greater oxidation activity than those with fewer iron(III) ions. These data provide insight into the function of and consequently the advantages that extracellular polymeric substances provide to bacteria. The role of extracellular polymeric substances for attachment under the conditions of a space station and resulting effects like biofouling, biocorrosion, malodorous gases, etc. will be discussed.

Elucidation of a side reaction occurring during nitroxide-mediated polymerization of cyclic ketene acetals by tandem mass spectrometric end-group analysis of aliphatic polyesters.

PubMed

Albergaria Pereira, Bruna de Fátima; Tardy, Antoine; Monnier, Valérie; Guillaneuf, Yohann; Gigmes, Didier; Charles, Laurence

2015-12-15

In order to prevent side reactions while developing new polymerization processes, their mechanism has to be understood and one first key insight is the structure of the end-groups in polymeric by-products. The synthetic method scrutinized here is the nitroxide-mediated polymerization (NMP) of a cyclic ketene acetal, a promising alternative process to the production of polyesters. Polymer end-group characterization was performed by mass spectrometry (MS), combining elemental composition information derived from accurate mass data in the MS mode with fragmentation features recorded in the MS/MS mode. Electrospray was used as the ionization method to ensure the integrity of original chain terminations and a quadrupole time-of-flight (QTOF) instrument was employed for high-resolution mass measurements in both MS and tandem mass spectrometry (MS/MS) modes. Occurrence of side reactions in the studied polymerization method, first evidenced by an unusual increase in dispersity with conversion, was confirmed in MS with the detection of two polymeric impurities in addition to the expected species. Fragmentation rules were first established for this new polyester family in order to derive useful structural information from MS/MS data. In addition to a usual NMP by-product, the initiating group of the second polymeric impurities revealed the degradation of the nitroxide moiety. Unambiguous MS/MS identification of end-groups in by-products sampled from the polymerization medium allowed an unusual side reaction to be identified during the NMP preparation of polyesters. On-going optimization of the polymerization method aims at preventing this undesired process. Copyright © 2015 John Wiley & Sons, Ltd.

Photonic devices based on patterning by two photon induced polymerization techniques

NASA Astrophysics Data System (ADS)

Fortunati, I.; Dainese, T.; Signorini, R.; Bozio, R.; Tagliazucca, V.; Dirè, S.; Lemercier, G.; Mulatier, J.-C.; Andraud, C.; Schiavuta, P.; Rinaldi, A.; Licoccia, S.; Bottazzo, J.; Franco Perez, A.; Guglielmi, M.; Brusatin, G.

2008-04-01

Two and three dimensional structures with micron and submicron resolution have been achieved in commercial resists, polymeric materials and sol-gel materials by several lithographic techniques. In this context, silicon-based sol-gel materials are particularly interesting because of their versatility, chemical and thermal stability, amount of embeddable active compounds. Compared with other micro- and nano-fabrication schemes, the Two Photon Induced Polymerization is unique in its 3D processing capability. The photopolymerization is performed with laser beam in the near-IR region, where samples show less absorption and less scattering, giving rise to a deeper penetration of the light. The use of ultrashort laser pulses allows the starting of nonlinear processes like multiphoton absorption at relatively low average power without thermally damaging the samples. In this work we report results on the photopolymerization process in hybrid organic-inorganic films based photopolymerizable methacrylate-containing Si-nanobuilding blocks. Films, obtained through sol-gel synthesis, are doped with a photo-initiator allowing a radical polymerization of methacrylic groups. The photo-initiator is activated by femtosecond laser source, at different input energies. The development of the unexposed regions is performed with a suitable solvent and the photopolymerized structures are characterized by microscopy techniques.

Performance of selected polymeric materials on LDEF

NASA Technical Reports Server (NTRS)

Young, Philip R.; Slemp, Wayne S.; Stein, Bland A.

1993-01-01

The NASA Long Duration Exposure Facility (LDEF) provided a unique environmental exposure of a wide variety of materials for potential advanced spacecraft application. This paper examines the molecular level response of selected polymeric materials which flew onboard this vehicle. Polymers include epolyimide, polysulfone, and polystyrene film and polyimide, polysulfone, and epoxy matrix resin/graphite fiber reinforced composites. Several promising experimental films were also studied. Most specimens received 5.8 years of low Earth orbital (LEO) exposure on LDEF. Several samples received on 10 months of exposure. Chemical characterization techniques included ultraviolet-visible and infrared spectroscopy, thermal analysis, x-ray photoelectron spectroscopy, and selected solution property measurements. Results suggest that many molecular level effects present during the first 10 months of exposure were not present after 5.8 years of exposure for specimens on or near Row 9. Increased AO fluence near the end of the mission likely eroded away much environmentally induced surface phenomena. The objective of this work is to provide fundamental information for use in improving the performance of polymeric materials for LEO application. A secondary objective is to gain an appreciation for the constraints and limitations of results from LDEF polymeric materials experiments.

Impregnation of β-tricalcium phosphate robocast scaffolds by in situ polymerization.

PubMed

Martínez-Vázquez, Francisco J; Perera, Fidel H; van der Meulen, Inge; Heise, Andreas; Pajares, Antonia; Miranda, Pedro

2013-11-01

Ring-opening polymerization of ε-caprolactone (ε-CL) and L-lactide (LLA) was performed to impregnate β-tricalcium phosphate (β-TCP) scaffolds fabricated by robocasting. Concentrated colloidal inks prepared from β-TCP commercial powders were used to fabricate porous structures consisting of a 3D mesh of interpenetrating rods. ε-CL and LLA were in situ polymerized within the ceramic structure by using a lipase and stannous octanoate, respectively, as catalysts. The results show that both the macropores inside the ceramic mesh and the micropores within the ceramic rods are full of polymer in either case. The mechanical properties of scaffolds impregnated by in situ polymerization (ISP) are significantly increased over those of the bare structures, exhibiting similar values than those obtained by other, more aggressive, impregnation methods such as melt-immersion (MI). ISP using enzymatic catalysts requires a reduced processing temperature which could facilitate the incorporation of growth factors and other drugs into the polymer composition, thus enhancing the bioactivity of the composite scaffold. The implications of these results for the optimization of the mechanical and biological performance of scaffolds for bone tissue engineering applications are discussed. Copyright © 2013 Wiley Periodicals, Inc.

Preparation of activated carbon monolith by application of phenolic resins as carbon precursors

NASA Astrophysics Data System (ADS)

Sajad, Mehran; Kazemzad, Mahmood; Hosseinnia, Azarmidokht

2014-04-01

In the current work, activated carbon monoliths have been prepared by application of different phenolic hydrocarbons namely catechol and resorcinol as carbon precursors. For synthesis of carbon monolith, the precursors have been mixed with Genapol PF-10 as template and then polymerized in the presence of lysine as catalyst. Then the polymerized monolith carbonized in inert atmosphere at 700°C and activated by water steam at 550°C. It was found that resorcinol polymerization is easier than catechol and occurred at 90°C while for polymerization of catechol elevated temperature of 120°C at hydrothermal condition is necessary. The prepared activated carbon samples have been characterized by various analysis methods including scanning electron microscopy (SEM), surface area measurement, and transmission electron microscopy (TEM). The adsorptions of three different aromatic hydrocarbons by the prepared activated carbon samples have also been investigated by high performance liquid chromatography (HPLC) and UV-Vis spectroscopy. It was found that carbon monolith prepared by catechol as carbon precursor has higher adsorpability and strength in comparison with the other sample. The higher performance of carbon monolith prepared by catechol can be associated with its higher active sites in comparison with resorcinol.

Evaluation of shrinkage polymerization and temperature of different acrylic resins used to splinting transfer copings in indirect impression technique

NASA Astrophysics Data System (ADS)

Franco, Ana Paula G. O.; Karam, Leandro Z.; Galvão, José R.; Kalinowski, Hypolito J.

2015-09-01

The aim of the present study was evaluate the shrinkage polymerization and temperature of different acrylic resins used to splinting transfer copings in indirect impression technique. Two implants were placed in an artificial bone, with the two transfer copings joined with dental floss and acrylic resins; two dental resins are used. Measurements of deformation and temperature were performed with Fiber Braggs grating sensor for 17 minutes. The results revealed that one type of resin shows greater values of polymerization shrinkage than the other. Pattern resins did not present lower values of shrinkage, as usually reported by the manufacturer.

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 (Boc 5 -col-Br 2 ) 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 (PEGA 480 ), 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.

Physico-chemical characterization of polymeric micelles loaded with platinum derivatives by capillary electrophoresis and related methods.

PubMed

Oukacine, Farid; Bernard, Stephane; Bobe, Iulian; Cottet, Hervé

2014-12-28

(1,2-diamino-cyclohexane)Platinum(II) ((DACH)Pt) loaded polymeric micelles of poly(ethylene glycol-b-sodium glutamate) (PEG-b-PGlu) are currently studied as a potential candidate to replace oxaliplatin in the treatment of cancers with the aim to reduce side effects like cumulative peripheral distal neurotoxicity and acute dysesthesias. As for all synthetic polymeric drug delivery systems, the characterization of the (co)polymer precursors and of the final drug delivery system (polymeric micelles) is crucial to control the repeatability of the different batches and to get correlation between physico-chemical structure and biological activity. In this work, the use of capillary electrophoresis (CE) and related methods for the characterization of (DACH)Pt-loaded polymeric micelles and their precursor (PEG-b-PGlu copolymer) has been investigated in detail. The separation and quantification of residual PGlu homopolymer in the PEG-b-PGlu sample were performed by free solution capillary zone electrophoresis mode. This mode brought also information on the PEG-b-PGlu copolymer composition and polydispersity. It also permitted to monitor the decomposition of polymeric micelles in the presence of NaCl at room temperature. Interactions between PEG-b-PGlu unimers, on one hand, and polymeric micelles or surfactants, on the other hand, were studied by using the Micellar Electrokinetic Chromatography and Frontal Analysis Capillary Electrophoresis modes. Finally, weight-average hydrodynamic radii of the loaded polymeric micelles and of the PEG-b-PGlu unimers were determined by Taylor Dispersion Analysis (an absolute size determination method that can be easily implemented on CE apparatus). Copyright © 2014 Elsevier B.V. All rights reserved.

Benzoylureas as removable cis amide inducers: synthesis of cyclic amides via ring closing metathesis (RCM).

PubMed

Brady, Ryan M; Khakham, Yelena; Lessene, Guillaume; Baell, Jonathan B

2011-02-07

Rapid and high yielding synthesis of medium ring lactams was made possible through the use of a benzoylurea auxiliary that serves to stabilize a cisoid amide conformation, facilitating cyclization. The auxiliary is released after activation under the mild conditions required to deprotect a primary amine, such as acidolysis of a Boc group in the examples given here. This methodology is a promising tool for the synthesis of medium ring lactams, macrocyclic natural products and peptides.

Enantioselective syntheses of cryptocarya triacetate, cryptocaryolone, and cryptocaryolone diacetate.

PubMed

Smith, Catherine M; O'Doherty, George A

2003-05-29

[reaction: see text] The enantioselective syntheses of three natural products from Cryptocarya latifolia have been achieved in 13-15 steps from ethyl sorbate. The route relies upon an enantio- and regioselective Sharpless dihydroxylation and a palladium-catalyzed reduction to establish the absolute stereochemistry. The route also relies upon a highly (E)-selective olefin cross-metathesis reaction to form trans-delta-hydroxy-1-enoates. The resulting delta-hydroxy-1-enoates were subsequently converted into cryptocarya triacetate, cryptocaryolone, and cryptocaryolone diacetate.

Protodeboronation of ortho- and para-phenol boronic acids and application to ortho and meta functionalization of phenols using boronic acids as blocking and directing groups.

PubMed

Lee, Chun-Young; Ahn, Su-Jin; Cheon, Cheol-Hong

2013-12-06

The first metal-free thermal protodeboronation of ortho- and para-phenol boronic acids in DMSO was developed. The protodeboronation was successfully applied to the synthesis of ortho- and meta-functionalized phenols using the boronic acid moiety as a blocking group and a directing group, respectively. Mechanistic studies suggested that this protodeboronation proceeds through the coordination of water to the boron atom followed by σ-bond metathesis.

One-Pot Isomerization–Cross Metathesis–Reduction (ICMR) Synthesis of Lipophilic Tetrapeptides

PubMed Central

2015-01-01

An efficient, versatile and rapid method toward homologue series of lipophilic tetrapeptide derivatives (herein, the opioid peptides H-TIPP-OH and H-DIPP-OH) is reported. High atom economy and a minimal number of synthetic steps resulted from a one-pot tandem isomerization-cross metathesis-reduction sequence (ICMR), applicable both in solution and solid phase methodology. The broadly applicable synthesis proceeds with short reaction times and simple work-up, as illustrated in this work for alkylated opioid tetrapeptides. PMID:24906051

Stereoselectivity in N-Iminium Ion Cyclization: Development of an Efficient Synthesis of (±)-Cephalotaxine.

PubMed

Liu, Hao; Yu, Jing; Li, Xinyu; Yan, Rui; Xiao, Ji-Chang; Hong, Ran

2015-09-18

A stereoselective N-iminium ion cyclization with allylsilane to construct vicinal quaternary-tertiary carbon centers was developed for the concise synthesis of (±)-cephalotaxine. The current strategy features a TiCl4-promoted cyclization and ring-closure metathesis to furnish the spiro-ring system. The stereochemical outcome in the N-acyliminium ion cyclization was rationalized by the stereoelectronic effect of the Z- or E-allylsilane. Two diastereomers arising from the cyclization were merged into the formal synthesis of (±)-cephalotaxine.

Polymerized phospholipid bilayers as permanent coatings for small amine separations using mixed aqueous/organic capillary zone electrophoresis.

PubMed

Pei, Lei; Lucy, Charles A

2012-12-07

Phospholipid bilayer (SPB) coatings have been used in capillary electrophoresis to reduce the nonspecific adsorption between the capillary wall and cationic analytes. This paper describes the use of the polymerizable lipid 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (Diyne PC) as a permanent capillary coating. A supported phospholipid bilayer was formed on the capillary walls and polymerization was performed in situ using ultraviolet irradiation. The polymerization reaction was monitored by UV-visible absorbance spectroscopy and atomic force microscopy. The EOF of the polymerized Diyne PC coating was moderately suppressed (2.0×10(-4)cm(2)/Vs) compared to a non-polymerized Diyne PC bilayer (0.3×10(-4)cm(2)/Vs), but the stability was improved significantly. Separations of benzylamine, veratrylamine, phenylethylamine and tolyethylamine using a poly Diyne PC coated capillary yielded efficiency of 220,000-370,000 plates/m and peak asymmetry factor 0.48-1.18. Specifically, the poly(Diyne PC) coating provided improved separation resolution in NACE due to the reduced surface adsorption. Copyright © 2012 Elsevier B.V. All rights reserved.

Construction of Nontoxic Polymeric UV-Absorber with Great Resistance to UV-Photoaging

PubMed Central

Huang, Zhong; Ding, Aishun; Guo, Hao; Lu, Guolin; Huang, Xiaoyu

2016-01-01

In this article, we developed a series of new nontoxic polymeric UV-absorbers through covalently attaching a benzophenone derivative onto the main chain of poly(vinyl chloride) (PVC) via mild and quantitative click chemistry. Azide groups were firstly introduced into the backbone of PVC via a nucleophilic reaction without affecting polymeric skeleton. Copper-catalyzed Husigen-Click cycloaddition reaction was performed between the pendant azide groups of PVC and alkynyl of (2-hydroxy-4-(prop-2-ynyloxy)phenyl)(phenyl)methanone at ambient temperature for affording the desired PVC-based UV-absorbers (PVC-UV) with different amounts of benzophenone moieties, which displayed great resistance to photoaging without degradation while exposed to UV irradiation. These polymeric UV-absorbers also showed good solubilities in common organic solvents and no cytotoxicity vs. HaCat cell. Small amounts of PVC-UV were homogeneously mixed with PVC as additive for stabilizing PVC against UV-photoaging without degradation and releasing small molecule even after 200 h while keeping thermal stability. This route of polymeric additive clearly paved an efficient way for solving the puzzle of separation of small molecule additive. PMID:27138547

The fabrication of small molecule organic light-emitting diode pixels by laser-induced forward transfer

NASA Astrophysics Data System (ADS)

Shaw-Stewart, J. R. H.; Mattle, T.; Lippert, T. K.; Nagel, M.; Nüesch, F. A.; Wokaun, A.

2013-01-01

Laser-induced forward transfer (LIFT) is a versatile organic light-emitting diode (OLED) pixel deposition process, but has hitherto been applied exclusively to polymeric materials. Here, a modified LIFT process has been used to fabricate small molecule Alq3 organic light-emitting diodes (SMOLEDs). Small molecule thin films are considerably more mechanically brittle than polymeric thin films, which posed significant challenges for LIFT of these materials. The LIFT process presented here uses a polymeric dynamic release layer, a reduced environmental pressure, and a well-defined receiver-donor gap. The Alq3 pixels demonstrate good morphology and functionality, even when compared to conventionally fabricated OLEDs. The Alq3 SMOLED pixel performances show a significant amount of fluence dependence, not observed with polymerical OLED pixels made in previous studies. A layer of tetrabutyl ammonium hydroxide has been deposited on top of the aluminium cathode, as part of the donor substrate, to improve electron injection to the Alq3, by over 600%. These results demonstrate that this variant of LIFT is applicable for the deposition of functional small molecule OLEDs as well as polymeric OLEDs.

Various aspects of ultrasound assisted emulsion polymerization process.

PubMed

Korkut, Ibrahim; Bayramoglu, Mahmut

2014-07-01

In this paper, the effects of ultrasonic (US) power, pulse ratio, probe area and recipe composition were investigated on two process responses namely, monomer (methyl methacrylate, MMA) conversion and electrical energy consumption per mass of product polymer (PMMA). Pulsed mode US is more suitable than continuous mode US for emulsion polymerization. The probe (tip) area has little effect on the yield of polymerization when comparing 19 and 13 mm probes, 13 mm probe performing slightly better for high conversion levels. Meanwhile, large probe area is beneficial for high conversion efficiency of electric energy to US energy as well as for high radical generation yield per energy consumed. The conversion increased slightly and electrical energy consumption decreased substantially by using a recipe with high SDS and monomer concentrations. Conclusions presented in this paper may be useful for scale-up of US assisted emulsion polymerization. Copyright © 2014 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Hong.

A new technique was developed and demonstrated for combining carbon fibers with aromatic thermoplastic matrices to form a high-quality towpreg. The developed technique utilizes an in-situ electrochemical process (Electrochemical polymerization - ECP) to create the entire polymer matrix surrounding the fiber array by direct polymerization of monomer. Poly-paraxylylene (PPX) and derivatives are successfully polymerized in-situ on carbon fiber surfaces through ECP. A PPX/carbon-fiber towpreg with 40 vol % of matrix is achieved in a fairly short reaction time with a high polymer-coating efficiency. Vapor deposition polymerization (VDP) was also studied. PPX and carbon-fiber towpreg were made successfully by this process.more » A comparison between ECP and VDP was conducted. A study on electrochemical oxidation (ECO) of carbon fibers was also performed. The ECO treatment may be suitable for carbon fibers incorporated in composites with high-temperature curing resins and thermoplastic matrices.« less

Clays as possible catalysts for peptide formation in the prebiotic era

NASA Technical Reports Server (NTRS)

Paecht-Horowitz, M.

1976-01-01

From the point of view of prebiotic synthesis, clays might have performed functions of concentration, catalysis, and protection of molecules. The degrees of polymerization obtained, when amino acid adenylates are added to montmorillonite suspensions in water, are much higher than those obtained by polymerization in the absence of such a clay. In addition, they are of a discrete spectrum, usually multiples of 6 or 7, and reach values of up to 40 mers. In the absence of clay a continuous spectrum of degrees of polymerization is obtained, and usually up to 4-6 mers only. Copolymerization in the absence of clays yields mostly random copolymers, in their presence mostly block copolymers are obtained. Optical density measurements show that after adsorption has taken place on the clay, stacking of its layers occurs. Polymerization starts only after these stacked layers have been formed

Facile preparation of fluorescent layered double hydroxide polymeric composites through the photo-induced surface-initiated controlled living polymerization

NASA Astrophysics Data System (ADS)

Chen, Junyu; Liu, Meiying; Huang, Qiang; Jiang, Ruming; Huang, Hongye; Deng, Fengjie; Wen, Yuanqing; Tian, Jianwen; Zhang, Xiaoyong; Wei, Yen

2018-05-01

(Zn/Al) layered double hydroxide (LDH) based fluorescence probes have been facilely fabricated via photo-induced surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization, which demonstrated green fluorescence, good biocompatibility and excellent dispersion performance in aqueous solution. The as prepared (Zn/Al)LDH polymeric composites were modified with 2-methacryloyloxyethyl phosphorylcholine (MPC), acrylic acid (AA) and diacroloyl-fluorescein (Ac-Fl). Among them, the comonomers MPC and AA were used to endow their water dispersibility, biocompatibility and potential drug carriers, while the Ac-Fl was served both as the fluorescence signal and photocatalyst for RAFT polymerization. A series of characterization methods, including 1H nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, transmission electronic microscopy, thermogravimetric analyses, X-ray photoelectron spectroscopy were employed to conform the successful of surface modification of LDH through photo-induced surface-initiated RAFT polymerization. Besides, UV-vis absorption spectra and fluorescence spectra were adopted to evaluate the optical characteristics of as prepared (Zn/Al)LDH-co-Poly(MPC-AA-Fl) composites, which exhibited high intense green fluorescence. Furthermore, the endocytosis behavior indicates that (Zn/Al)LDH-co-Poly(MPC-AA-Fl) composites could be potentially used in cell imaging and even drug delivery application for their excellent biocompatibility and all advantages described above.

Fabrication and Optimal Design of Biodegradable Polymeric Stents for Aneurysms Treatments

PubMed Central

Han, Xue; Wu, Xia; Kelly, Michael; Chen, Xiongbiao

2017-01-01

An aneurysm is a balloon-like bulge in the wall of blood vessels, occurring in major arteries of the heart and brain. Biodegradable polymeric stent-assisted coiling is expected to be the ideal treatment of wide-neck complex aneurysms. This paper presents the development of methods to fabricate and optimally design biodegradable polymeric stents for aneurysms treatment. Firstly, a dispensing-based rapid prototyping (DBRP) system was developed to fabricate coil and zigzag structures of biodegradable polymeric stents. Then, compression testing was carried out to characterize the radial deformation of the stents fabricated with the coil or zigzag structure. The results illustrated the stent with a zigzag structure has a stronger radial stiffness than the one with a coil structure. On this basis, the stent with a zigzag structure was chosen for the development of a finite element model for simulating the real compression tests. The result showed the finite element model of biodegradable polymeric stents is acceptable within a range of radial deformation around 20%. Furthermore, the optimization of the zigzag structure was performed with ANSYS DesignXplorer, and the results indicated that the total deformation could be decreased by 35.7% by optimizing the structure parameters, which would represent a significant advance of the radial stiffness of biodegradable polymeric stents. PMID:28264515

A common active site of polyhydroxyalkanoate synthase from Bacillus cereus YB-4 is involved in polymerization and alcoholysis reactions.

PubMed

Hyakutake, Manami; Tomizawa, Satoshi; Mizuno, Kouhei; Hisano, Tamao; Abe, Hideki; Tsuge, Takeharu

2015-06-01

Polyhydroxyalkanoate (PHA) synthase from Bacillus cereus YB-4 (PhaRCYB4) catalyzes not only PHA polymerization but also alcoholytic cleavage of PHA chains. The alcoholysis activity of PhaRCYB4 is expressed when a hydroxyacyl-CoA monomer is absent but an alcohol compound is present. In this study, we performed alanine mutagenesis of the putative catalytic triad (Cys(151), Asp(306), and His(335)) in the PhaCYB4 subunit to identify the active site residues for polymerization and alcoholysis activities. Individual substitution of each triad residue with alanine resulted in loss of both polymerization and alcoholysis activities, suggesting that these residues are commonly shared between polymerization and alcoholysis reactions. The loss of activity was also observed following mutagenesis of the triad to other amino acids, except for one PhaRCYB4 mutant with a C151S substitution, which lost polymerization activity but still possessed cleavage activity towards PHA chains. The low-molecular-weight PHA isolated from the PhaRCYB4(C151S)-expressing strain showed a lower ratio of alcohol capping at the P(3HB) carboxy terminus than did that from the wild-type-expressing strain. This observation implies that hydrolysis activity of PhaRCYB4 might be elicited by the C151S mutation.

Structure-property relationships in a series of diglycerol tetraether model lipids and their lyotropic assemblies: the effect of branching topology and chirality.

PubMed

Markowski, Thomas; Drescher, Simon; Meister, Annette; Blume, Alfred; Dobner, Bodo

2014-06-14

Three novel diglycerol tetraether lipids with one membrane-spanning chain have been synthesized. These lipids contain only two or four racemic methyl branches at selected positions of the hydrophobic chains in contrast to natural lipids from archaebacterial membranes with an isoprenoid substitution pattern. The insertion of the methyl moieties was realized starting from either (RS)-citronellyl bromide or the inexpensive methyl malonic acid ethyl ester. For chain elongation the Cu-catalysed Grignard coupling reaction was used. The preparation of diglycerol tetraethers was either performed by condensing suitable blocked monoglycerol diethers by Grubbs metathesis or by reaction of the transmembrane C32-chain with blocked glycerols followed by further alkylation steps. Finally, we could show that the resulting lipids can form closed lipid vesicles comparable to the optically pure counterparts. Therefore, these much simpler lipids compared to the natural lipids from archaebacterial membranes are also suitable for preparation of stable tailored liposomes.

Mixed-Metal Strategy on Metal-Organic Frameworks (MOFs) for Functionalities Expansion: Co Substitution Induces Aerobic Oxidation of Cyclohexene over Inactive Ni-MOF-74.

PubMed

Sun, Dengrong; Sun, Fangxiang; Deng, Xiaoyu; Li, Zhaohui

2015-09-08

Different amounts of Co-substituted Ni-MOF-74 have been prepared via a post-synthetic metal exchange. Inductively coupled plasma mass spectrometry, powder X-ray diffraction (XRD), N2 adsorption/desorption, and extended X-ray absorption fine structure (EXAFS) analyses indicated the successful metathesis between Co and Ni in Ni-MOF-74 to form the solid-solution-like mixed-metal Co/Ni-MOF-74. It was found that introduction of active Co into the Ni-MOF-74 framework enabled the inert Ni-MOF-74 to show activity for cyclohexene oxidation. Since Co was favorably substituted at positions more accessible to the substrate, the mixed-metal Co/Ni-MOF-74 showed superior catalytic performance, compared with pure Co-MOF-74 containing a similar amount of Co. This study provides a facile method to develop solid-solution-like MOFs for heterogeneous catalysis and highlights the great potential of this mixed-metal strategy in the development of MOFs with specific endowed functionalities.

Tough, high performance, addition-type thermoplastic polymers

NASA Technical Reports Server (NTRS)

Pater, Ruth H. (Inventor)

1992-01-01

A tough, high performance polyimide is provided by reacting a triple bond conjugated with an aromatic ring in a bisethynyl compound with the active double bond in a compound containing a double bond activated toward the formation of a Diels-Adler type adduct, especially a bismaleimide, a biscitraconimide, or a benzoquinone, or mixtures thereof. Addition curing of this product produces a high linear polymeric structure and heat treating the highly linear polymeric structure produces a thermally stable aromatic addition-type thermoplastic polyimide, which finds utility in the preparation of molding compounds, adhesive compositions, and polymer matrix composites.

Design and synthesis study of the thermo-sensitive poly (N-vinylpyrrolidone-b- N, N-diethylacrylamide).

PubMed

Zhang, Xiayun; Yang, Zhongduo; Xie, Dengmin; Liu, Donglei; Chen, Zhenbin; Li, Ke; Li, Zhizhong; Tichnell, Brandon; Liu, Zhen

2018-01-01

The reversible addition fragmentation chain transfer (RAFT) polymerization method was adopted here to prepare a series of thermo-sensitive copolymers, poly (N,N-diethyl- acrylamide-b-N-vinylpyrrolidone). Their structures, molecular weight distribution and temperature sensitivity performances were characterized by the nuclear magnetic resonance ( 1 HNMR), the gel permeation chromatography (GPC) and the fluorescence spectrophotometer, respectively. It has been identified that the synthesis reaction of the block copolymer was living polymerization. The thermo-sensitivity study suggested that N-vinylpyrrolidone (NVP), played a key role on the lower critical solution temperature (LCST) performance.

Rapid energy-efficient manufacturing of polymers and composites via frontal polymerization.

PubMed

Robertson, Ian D; Yourdkhani, Mostafa; Centellas, Polette J; Aw, Jia En; Ivanoff, Douglas G; Goli, Elyas; Lloyd, Evan M; Dean, Leon M; Sottos, Nancy R; Geubelle, Philippe H; Moore, Jeffrey S; White, Scott R

2018-05-01

Thermoset polymers and composite materials are integral to today's aerospace, automotive, marine and energy industries and will be vital to the next generation of lightweight, energy-efficient structures in these enterprises, owing to their excellent specific stiffness and strength, thermal stability and chemical resistance 1-5 . The manufacture of high-performance thermoset components requires the monomer to be cured at high temperatures (around 180 °C) for several hours, under a combined external pressure and internal vacuum 6 . Curing is generally accomplished using large autoclaves or ovens that scale in size with the component. Hence this traditional curing approach is slow, requires a large amount of energy and involves substantial capital investment 6,7 . Frontal polymerization is a promising alternative curing strategy, in which a self-propagating exothermic reaction wave transforms liquid monomers to fully cured polymers. We report here the frontal polymerization of a high-performance thermoset polymer that allows the rapid fabrication of parts with microscale features, three-dimensional printed structures and carbon-fibre-reinforced polymer composites. Precise control of the polymerization kinetics at both ambient and elevated temperatures allows stable monomer solutions to transform into fully cured polymers within seconds, reducing energy requirements and cure times by several orders of magnitude compared with conventional oven or autoclave curing approaches. The resulting polymer and composite parts possess similar mechanical properties to those cured conventionally. This curing strategy greatly improves the efficiency of manufacturing of high-performance polymers and composites, and is widely applicable to many industries.

Molecular architecture requirements for polymer-grafted lignin superplasticizers.

PubMed

Gupta, Chetali; Sverdlove, Madeline J; Washburn, Newell R

2015-04-07

Superplasticizers are a class of anionic polymer dispersants used to inhibit aggregation in hydraulic cement, lowering the yield stress of cement pastes to improve workability and reduce water requirements. The plant-derived biopolymer lignin is commonly used as a low-cost/low-performance plasticizer, but attempts to improve its effects on cement rheology through copolymerization with synthetic monomers have not led to significant improvements. Here we demonstrate that kraft lignin can form the basis for high-performance superplasticizers in hydraulic cement, but the molecular architecture must be based on a lignin core with a synthetic-polymer corona that can be produced via controlled radical polymerization. Using slump tests of ordinary Portland cement pastes, we show that polyacrylamide-grafted lignin prepared via reversible addition-fragmentation chain transfer polymerization can reduce the yield stress of cement paste to similar levels as a leading commercial polycarboxylate ether superplasticizer at concentrations ten-fold lower, although the lignin material produced via controlled radical polymerization does not appear to reduce the dynamic viscosity of cement paste as effectively as the polycarboxylate superplasticizer, despite having a similar affinity for the individual mineral components of ordinary Portland cement. In contrast, polyacrylamide copolymerized with a methacrylated kraft lignin via conventional free radical polymerization having a similar overall composition did not reduce the yield stress or the viscosity of cement pastes. While further work is required to elucidate the mechanism of this effect, these results indicate that controlling the architecture of polymer-grafted lignin can significantly enhance its performance as a superplasticizer for cement.

A high-performance renewable thermosetting resin derived from eugenol.

PubMed

Harvey, Benjamin G; Sahagun, Christopher M; Guenthner, Andrew J; Groshens, Thomas J; Cambrea, Lee R; Reams, Josiah T; Mabry, Joseph M

2014-07-01

A renewable bisphenol, 4,4'-(butane-1,4-diyl)bis(2-methoxyphenol), was synthesized on a preparative scale by a solvent-free, Ru-catalyzed olefin metathesis coupling reaction of eugenol followed by hydrogenation. After purification, the bisphenol was converted to a new bis(cyanate) ester by standard techniques. The bisphenol and cyanate ester were characterized rigorously by NMR spectroscopy and single-crystal X-ray diffraction studies. After complete cure, the cyanate ester exhibited thermal stability in excess of 350 °C and a glass transition temperature (Tg ) of 186 °C. As a result of the four-carbon chain between the aromatic rings, the thermoset displayed a water uptake of only 1.8% after a four day immersion in 85 °C water. The wet Tg of the material (167 °C) was only 19 °C lower than the dry Tg , and the material showed no significant degradation as a result of the water treatment. These results suggest that this resin is well suited for maritime environments and provide further evidence that full-performance resins can be generated from sustainable feedstocks. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Incorporation of ionic liquid into porous polymer monoliths to enhance the separation of small molecules in reversed-phase high-performance liquid chromatography.

PubMed

Wang, Jiafei; Bai, Ligai; Wei, Zhen; Qin, Junxiao; Ma, Yamin; Liu, Haiyan

2015-06-01

An ionic liquid was incorporated into the porous polymer monoliths to afford stationary phases with enhanced chromatographic performance for small molecules in reversed-phase high-performance liquid chromatography. The effect of the ionic liquid in the polymerization mixture on the performance of the monoliths was studied in detail. While monoliths without ionic liquid exhibited poor resolution and low efficiency, the addition of ionic liquid to the polymerization mixture provides highly increased resolution and high efficiency. The chromatographic performances of the monoliths were demonstrated by the separations of various small molecules including aromatic hydrocarbons, isomers, and homologues using a binary polar mobile phase. The present column efficiency reached 27 000 plates/m, which showed that the ionic liquid monoliths are alternative stationary phases in the separation of small molecules by high-performance liquid chromatography. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Alternative methods for determining shrinkage in restorative resin composites.

PubMed

de Melo Monteiro, Gabriela Queiroz; Montes, Marcos Antonio Japiassú Resende; Rolim, Tiago Vieira; de Oliveira Mota, Cláudia Cristina Brainer; de Barros Correia Kyotoku, Bernardo; Gomes, Anderson Stevens Leônidas; de Freitas, Anderson Zanardi

2011-08-01

The purpose of this study was to evaluate polymerization shrinkage of resin composites using a coordinate measuring machine, optical coherence tomography and a more widely known method, such as Archimedes Principle. Two null hypothesis were tested: (1) there are no differences between the materials tested; (2) there are no differences between the methods used for polymerization shrinkage measurements. Polymerization shrinkage of seven resin-based dental composites (Filtek Z250™, Filtek Z350™, Filtek P90™/3M ESPE, Esthet-X™, TPH Spectrum™/Dentsply 4 Seasons™, Tetric Ceram™/Ivoclar-Vivadent) was measured. For coordinate measuring machine measurements, composites were applied to a cylindrical Teflon mold (7 mm × 2 mm), polymerized and removed from the mold. The difference between the volume of the mold and the volume of the specimen was calculated as a percentage. Optical coherence tomography was also used for linear shrinkage evaluations. The thickness of the specimens was measured before and after photoactivation. Polymerization shrinkage was also measured using Archimedes Principle of buoyancy (n=5). Statistical analysis of the data was performed with ANOVA and the Games-Howell test. The results show that polymerization shrinkage values vary with the method used. Despite numerical differences the ranking of the resins was very similar with Filtek P90 presenting the lowest shrinkage values. Because of the variations in the results, reported values could only be used to compare materials within the same method. However, it is possible rank composites for polymerization shrinkage and to relate these data from different test methods. Independently of the method used, reduced polymerization shrinkage was found for silorane resin-based composite. Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Polymerization of amino acids under high-pressure conditions: Implication to chemical evolution on the early Earth

NASA Astrophysics Data System (ADS)

Kakegawa, T.; Ohara, S.; Ishiguro, T.; Abiko, H.; Nakazawa, H.

2008-12-01

Prebiotic polymerization of amino acids is the most fundamental reaction to promote the chemical evolution for origin of life. Polymerization of amino acids is the dehydration reaction. This questions as to if submarine hydrothermal conditions, thus hydrated enironments, were appropreate for peptide formations. Our previous experiments implied that non-aqueous and high-pressure environments (more than 20 MPa) would be suitable for polymerization of amino acids (Ohara et al., 2006). This leads to the hypothesis that the first peptides may have formed in the Hadean oceanic crustal environments, where dehydration proceeded with availability of appropriate temperatures and pressures. In the present study, experiments simulating the crustal conditions were performed with various pressures (1-175 MPa) and temperatures (100- 200 C degree) using autoclaves. Purified powders (100 mg) of alanine, glycine, valine and aspartic acid were used in the experiments without mixing water in order to examine the solid-solid reactions. The products were analyzed using HPLC and LC-MS. Results indicate that: (1) longer time is required to form peptide compared to those of previous aqueous experiments; (2) pressure has a role to limit the production of melanoidine and cyclic amino acids, which are inhibitors for elongation of peptides; (3) glycine was polymerized up to 11-mer, which was not formed in any previous experiments without catalyses; (4) valine was polymerized up to 3-mer; and (5) aspartic acid was polymerized to 4-mer, accompanied with production of other amino acids. It is noteworthy that high-pressure environments favor all examined polymerization reactions. Such situations would have happened inside of deep oceanic crusts of the early Earth.

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

Biologically Active Polymeric Coating Materials

DTIC Science & Technology

1975-04-01

unsaturated alkyds , or through a condensation reaction of an organometallic oxide and a resin containing carboxylic acid groups as side chains. The...extend the service life of antifouling coatings by means of polymerization of toxicant into paint resins . The coating binder is so constructed that the...from styrene (s6) and polyester (P54, figure 5) organometallic resins . To date, the antifouling performance of epoxy (WS 52B, figure 6) and

Effect of amine structure on CO2 capture by polymeric membranes.

PubMed

Taniguchi, Ikuo; Kinugasa, Kae; Toyoda, Mariko; Minezaki, Koki

2017-01-01

Poly(amidoamine)s (PAMAMs) incorporated into a cross-linked poly(ethylene glycol) exhibited excellent CO 2 separation properties over H 2 . However, the CO 2 permeability should be increased for practical applications. Monoethanolamine (MEA) used as a CO 2 determining agent in the current CO 2 capture technology at demonstration scale was readily immobilized in poly(vinyl alcohol) (PVA) matrix by solvent casting of aqueous mixture of PVA and the amine. The resulting polymeric membranes can be self-standing with the thickness above 3 μm and the amine fraction less than 80 wt%. The gas permeation properties were examined at 40 °C and under 80% relative humidity. The CO 2 separation performance increased with increase of the amine content in the polymeric membranes. When the amine fraction was 80 wt%, the CO 2 permeability coefficient of MEA containing membrane was 604 barrer with CO 2 selectivity of 58.5 over H 2 , which was much higher than the PAMAM membrane (83.7 barrer and 51.8, respectively) under the same operation conditions. On the other hand, ethylamine (EA) was also incorporated into PVA matrix to form a thin membrane. However, the resulting polymeric membranes exhibited slight CO 2 -selective gas permeation properties. The hydroxyl group of MEA was crucial for high CO 2 separation performance.

Effect of amine structure on CO2 capture by polymeric membranes

PubMed Central

Taniguchi, Ikuo; Kinugasa, Kae; Toyoda, Mariko; Minezaki, Koki

2017-01-01

Abstract Poly(amidoamine)s (PAMAMs) incorporated into a cross-linked poly(ethylene glycol) exhibited excellent CO2 separation properties over H2. However, the CO2 permeability should be increased for practical applications. Monoethanolamine (MEA) used as a CO2 determining agent in the current CO2 capture technology at demonstration scale was readily immobilized in poly(vinyl alcohol) (PVA) matrix by solvent casting of aqueous mixture of PVA and the amine. The resulting polymeric membranes can be self-standing with the thickness above 3 μm and the amine fraction less than 80 wt%. The gas permeation properties were examined at 40 °C and under 80% relative humidity. The CO2 separation performance increased with increase of the amine content in the polymeric membranes. When the amine fraction was 80 wt%, the CO2 permeability coefficient of MEA containing membrane was 604 barrer with CO2 selectivity of 58.5 over H2, which was much higher than the PAMAM membrane (83.7 barrer and 51.8, respectively) under the same operation conditions. On the other hand, ethylamine (EA) was also incorporated into PVA matrix to form a thin membrane. However, the resulting polymeric membranes exhibited slight CO2-selective gas permeation properties. The hydroxyl group of MEA was crucial for high CO2 separation performance. PMID:29383045

Self-organized internal architectures of chiral micro-particles

NASA Astrophysics Data System (ADS)

Provenzano, Clementina; Mazzulla, Alfredo; Pagliusi, Pasquale; De Santo, Maria P.; Desiderio, Giovanni; Perrotta, Ida; Cipparrone, Gabriella

2014-02-01

The internal architecture of polymeric self-assembled chiral micro-particles is studied by exploring the effect of the chirality, of the particle sizes, and of the interface/surface properties in the ordering of the helicoidal planes. The experimental investigations, performed by means of different microscopy techniques, show that the polymeric beads, resulting from light induced polymerization of cholesteric liquid crystal droplets, preserve both the spherical shape and the internal self-organized structures. The method used to create the micro-particles with controlled internal chiral architectures presents great flexibility providing several advantages connected to the acquired optical and photonics capabilities and allowing to envisage novel strategies for the development of chiral colloidal systems and materials.

Surface-initiated graft polymerization on multiwalled carbon nanotubes pretreated by corona discharge at atmospheric pressure.

PubMed

Xu, Lihua; Fang, Zhengping; Song, Ping'an; Peng, Mao

2010-03-01

Surface-initiated graft polymerization on multi-walled carbon nanotubes pretreated with a corona discharge at atmospheric pressure was explored. The mechanism of the corona-discharge-induced graft polymerization is discussed. The results indicate that MWCNTs were encapsulated by poly(glycidyl methacrylate) (PGMA), demonstrating the formation of PGMA-grafted MWCNTs (PGMA-g-MWCNTs), with a grafting ratio of about 22 wt%. The solubility of PGMA-g-MWCNTs in ethanol was dramatically improved compared to pristine MWCNTs, which could contribute to fabricating high-performance polymer/MWCNTs nanocomposites in the future. Compared with most plasma processes, which operate at low pressures, corona discharge has the merit of working at atmospheric pressure.

Porous polymers: enabling solutions for energy applications.

PubMed

Thomas, Arne; Kuhn, Pierre; Weber, Jens; Titirici, Maria-Magdalena; Antonietti, Markus

2009-02-18

A new generation of porous polymers was made for various energy-related applications, e.g., as fuel cell membranes, as electrode materials for batteries, for gas storage, partly from renewable resources. This review intends to catch this emerging field by reporting on a variety of different approaches to make high performing polymers porous. This includes template techniques, polymers with inherent microporosity, polymer frameworks by ionothermal polymerization, and the polymerization of carbon from appropriate precursors and by hydrothermal polymerization. In this process, we try to not only identify the current status of the field, but also point to open question and tasks to identify the potentially relevant progress. Copyright © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Multifaceted Modularity: A Key for Stepwise Building of Hierarchical Complexity in Actinide Metal–Organic Frameworks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dolgopolova, Ekaterina A.; Ejegbavwo, Otega A.; Martin, Corey R.

Growing necessity for efficient nuclear waste management is a driving force for development of alternative architectures towards fundamental understanding of mechanisms involved in actinide integration inside extended structures. In this manuscript, metal-organic frameworks (MOFs) were investigated as a model system for engineering radionuclide containing materials through utilization of unprecedented MOF modularity, which cannot be replicated in any other type of materials. Through the implementation of recent synthetic advances in the MOF field, hierarchical complexity of An-materials were built stepwise, which was only feasible due to preparation of the first examples of actinide-based frameworks with “unsaturated” metal nodes. The first successfulmore » attempts of solid-state metathesis and metal node extension in An-MOFs are reported, and the results of the former approach revealed drastic differences in chemical behavior of extended structures versus molecular species. Successful utilization of MOF modularity also allowed us to structurally characterize the first example of bimetallic An-An nodes. To the best of our knowledge, through combination of solid-state metathesis, guest incorporation, and capping linker installation, we were able to achieve the highest Th wt% in mono- and bi-actinide frameworks with minimal structural density. Overall, combination of a multistep synthetic approach with homogeneous actinide distribution and moderate solvothermal conditions could make MOFs an exceptionally powerful tool to address fundamental questions responsible for chemical behavior of An-based extended structures, and therefore, shed light on possible optimization of nuclear waste administration.« less

Multifaceted Modularity: A Key for Stepwise Building of Hierarchical Complexity in Actinide Metal-Organic Frameworks.

PubMed

Dolgopolova, Ekaterina A; Ejegbavwo, Otega A; Martin, Corey R; Smith, Mark D; Setyawan, Wahyu; Karakalos, Stavros G; Henager, Charles H; Zur Loye, Hans-Conrad; Shustova, Natalia B

2017-11-22

Growing necessity for efficient nuclear waste management is a driving force for development of alternative architectures toward fundamental understanding of mechanisms involved in actinide (An) integration inside extended structures. In this manuscript, metal-organic frameworks (MOFs) were investigated as a model system for engineering radionuclide containing materials through utilization of unprecedented MOF modularity, which cannot be replicated in any other type of materials. Through the implementation of recent synthetic advances in the MOF field, hierarchical complexity of An-materials was built stepwise, which was only feasible due to preparation of the first examples of actinide-based frameworks with "unsaturated" metal nodes. The first successful attempts of solid-state metathesis and metal node extension in An-MOFs are reported, and the results of the former approach revealed drastic differences in chemical behavior of extended structures versus molecular species. Successful utilization of MOF modularity also allowed us to structurally characterize the first example of bimetallic An-An nodes. To the best of our knowledge, through combination of solid-state metathesis, guest incorporation, and capping linker installation, we were able to achieve the highest Th wt % in mono- and biactinide frameworks with minimal structural density. Overall, the combination of a multistep synthetic approach with homogeneous actinide distribution and moderate solvothermal conditions could make MOFs an exceptionally powerful tool to address fundamental questions responsible for chemical behavior of An-based extended structures and, therefore, shed light on possible optimization of nuclear waste administration.

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Alice B.; Lin, Tzu-Pin; Thompson, Niklas B.

Grafting density and graft distribution impact the chain dimensions and physical properties of polymers. However, achieving precise control over these structural parameters presents long-standing synthetic challenges. In this report, we introduce a versatile strategy to synthesize polymers with tailored architectures via grafting-through ring-opening metathesis polymerization (ROMP). One-pot copolymerization of an ω-norbornenyl macromonomer and a discrete norbornenyl co-monomer (diluent) provides opportunities to control the backbone sequence and therefore the side chain distribution. Toward sequence control, the homopolymerization kinetics of 23 diluents were studied, representing diverse variations in the stereochemistry, anchor groups, and substituents. These modifications tuned the homopolymerization rate constants overmore » two orders of magnitude (0.36 M -1 s -1 < k homo < 82 M -1 s -1). Rate trends were identified and elucidated by complementary mechanistic and density functional theory (DFT) studies. Building on this foundation, complex architectures were achieved through copolymerizations of selected diluents with a poly (D,L-lactide) (PLA), polydimethylsiloxane (PDMS), or polystyrene (PS) macromonomer. The cross-propagation rate constants were obtained by non-linear least squares fitting of the instantaneous co-monomer concentrations according to the Mayo-Lewis terminal model. Indepth kinetic analyses indicate a wide range of accessible macromonomer/diluent reactivity ratios (0.08 < r 1/r 2 < 20), corresponding to blocky, gradient, or random backbone sequences. We further demonstrated the versatility of this copolymerization approach by synthesizing AB graft diblock polymers with tapered, uniform, and inverse-tapered molecular “shapes.” Small-angle X-ray scattering analysis of the self-assembled structures illustrates effects of the graft distribution on the domain spacing and backbone conformation. Collectively, the insights provided herein into the ROMP mechanism, monomer design, and homo- and copolymerization rate trends offer a general strategy for the design and synthesis of graft polymers with arbitrary architectures. Controlled copolymerization therefore expands the parameter space for molecular and materials design.« less

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions.

PubMed

Chang, Alice B; Lin, Tzu-Pin; Thompson, Niklas B; Luo, Shao-Xiong; Liberman-Martin, Allegra L; Chen, Hsiang-Yun; Lee, Byeongdu; Grubbs, Robert H

2017-12-06

Grafting density and graft distribution impact the chain dimensions and physical properties of polymers. However, achieving precise control over these structural parameters presents long-standing synthetic challenges. In this report, we introduce a versatile strategy to synthesize polymers with tailored architectures via grafting-through ring-opening metathesis polymerization (ROMP). One-pot copolymerization of an ω-norbornenyl macromonomer and a discrete norbornenyl comonomer (diluent) provides opportunities to control the backbone sequence and therefore the side chain distribution. Toward sequence control, the homopolymerization kinetics of 23 diluents were studied, representing diverse variations in the stereochemistry, anchor groups, and substituents. These modifications tuned the homopolymerization rate constants over 2 orders of magnitude (0.36 M -1 s -1 < k homo < 82 M -1 s -1 ). Rate trends were identified and elucidated by complementary mechanistic and density functional theory (DFT) studies. Building on this foundation, complex architectures were achieved through copolymerizations of selected diluents with a poly(d,l-lactide) (PLA), polydimethylsiloxane (PDMS), or polystyrene (PS) macromonomer. The cross-propagation rate constants were obtained by nonlinear least-squares fitting of the instantaneous comonomer concentrations according to the Mayo-Lewis terminal model. In-depth kinetic analyses indicate a wide range of accessible macromonomer/diluent reactivity ratios (0.08 < r 1 /r 2 < 20), corresponding to blocky, gradient, or random backbone sequences. We further demonstrated the versatility of this copolymerization approach by synthesizing AB graft diblock polymers with tapered, uniform, and inverse-tapered molecular "shapes." Small-angle X-ray scattering analysis of the self-assembled structures illustrates effects of the graft distribution on the domain spacing and backbone conformation. Collectively, the insights provided herein into the ROMP mechanism, monomer design, and homo- and copolymerization rate trends offer a general strategy for the design and synthesis of graft polymers with arbitrary architectures. Controlled copolymerization therefore expands the parameter space for molecular and materials design.

An NMR relaxometry and gravimetric study of gelatin-free aqueous polyacrylamide dosimeters

NASA Astrophysics Data System (ADS)

Babic, Steven; Schreiner, L. John

2006-09-01

In conformal radiation therapy, a high dose of radiation is given to a target volume to increase the probability of cure, and care is taken to minimize the dose to surrounding healthy tissue. The techniques used to achieve this are very complicated and the precise verification of the resulting three-dimensional (3D) dose distribution is required. Polyacrylamide gelatin (PAG) dosimeters with magnetic resonance imaging and optical computed tomography scanning provide the required 3D dosimetry with high spatial resolution. Many basic studies have characterized these chemical dosimeters that polymerize under irradiation. However, the investigation of the fundamental properties of the radiation-induced polymerization in PAG dosimeters is complicated by the presence of the background gelatin matrix. In this work, a gelatin-free model system for the study of the basic radiation-induced polymerization in PAG dosimeters has been developed. Experiments were performed on gelatin-free dosimeters, named aqueous polyacrylamide (APA) dosimeters, containing equal amounts of acrylamide and N,N'-methylene-bisacrylamide. The APA dosimeters were prepared with four different total monomer concentrations (2, 4, 6 and 8% by weight). Nuclear magnetic resonance (NMR) spin-spin and spin-lattice proton relaxation measurements at 20 MHz, and gravimetric analyses performed on all four dosimeters, show a continuous degree of polymerization over the dose range of 0-25 Gy. The developed NMR model explains the relationship observed between the relaxation data and the amount of crosslinked polymer formed at each dose. This model can be extended with gelatin relaxation data to provide a fundamental understanding of radiation-induced polymerization in the conventional PAG dosimeters.

An NMR relaxometry and gravimetric study of gelatin-free aqueous polyacrylamide dosimeters.

PubMed

Babic, Steven; Schreiner, L John

2006-09-07

In conformal radiation therapy, a high dose of radiation is given to a target volume to increase the probability of cure, and care is taken to minimize the dose to surrounding healthy tissue. The techniques used to achieve this are very complicated and the precise verification of the resulting three-dimensional (3D) dose distribution is required. Polyacrylamide gelatin (PAG) dosimeters with magnetic resonance imaging and optical computed tomography scanning provide the required 3D dosimetry with high spatial resolution. Many basic studies have characterized these chemical dosimeters that polymerize under irradiation. However, the investigation of the fundamental properties of the radiation-induced polymerization in PAG dosimeters is complicated by the presence of the background gelatin matrix. In this work, a gelatin-free model system for the study of the basic radiation-induced polymerization in PAG dosimeters has been developed. Experiments were performed on gelatin-free dosimeters, named aqueous polyacrylamide (APA) dosimeters, containing equal amounts of acrylamide and N,N'-methylene-bisacrylamide. The APA dosimeters were prepared with four different total monomer concentrations (2, 4, 6 and 8% by weight). Nuclear magnetic resonance (NMR) spin-spin and spin-lattice proton relaxation measurements at 20 MHz, and gravimetric analyses performed on all four dosimeters, show a continuous degree of polymerization over the dose range of 0-25 Gy. The developed NMR model explains the relationship observed between the relaxation data and the amount of crosslinked polymer formed at each dose. This model can be extended with gelatin relaxation data to provide a fundamental understanding of radiation-induced polymerization in the conventional PAG dosimeters.

Methyleneation of peptides by N,N,N,N-tetramethylethylenediamine (TEMED) under conditions used for free radical polymerization: a mechanistic study.

PubMed

Shirangi, Mehrnoosh; Sastre Toraño, Javier; Sellergren, Börje; Hennink, Wim E; Somsen, Govert W; van Nostrum, Cornelus F

2015-01-21

Free radical polymerization is often used to prepare protein and peptide-loaded hydrogels for the design of controlled release systems and molecular imprinting materials. Peroxodisulfates (ammonium peroxodisulfates (APS) or potassium peroxodisulfates (KPS)) with N,N,N,N-tetramethylethylenediamine (TEMED) are frequently used as initiator and catalyst. However, exposure to these free radical polymerization reagents may lead to modification of the protein and peptide. In this work, we show the modification of lysine residues by ammonium peroxodisulfate (APS)/TEMED of the immunostimulant thymopentin (TP5). Parallel studies on a decapeptide and a library of 15 dipeptides were performed to reveal the mechanism of modification. LC-MS of APS/TEMED-exposed TP5 revealed a major reaction product with an increased mass (+12 Da) with respect to TP5. LC-MS(2) and LC-MS(3) were performed to obtain structural information on the modified peptide and localize the actual modification site. Interpretation of the obtained data demonstrates the formation of a methylene bridge between the lysine and arginine residue in the presence of TEMED, while replacing TEMED with a sodium bisulfite catalyst did not show this modification. Studies with the other peptides showed that the TEMED radical can induce methyleneation on peptides when lysine is next to arginine, proline, cysteine, aspargine, glutamine, histidine, tyrosine, tryptophan, and aspartic acid residues. Stability of peptides and protein needs to be considered when using APS/TEMED in in situ polymerization systems. The use of an alternative catalyst such as sodium bisulfite may preserve the chemical integrity of peptides during in situ polymerization.

α1-antitrypsin polymerizes in alveolar macrophages of smokers with and without α1-antitrypsin deficiency.

PubMed

Bazzan, Erica; Tinè, Mariaenrica; Biondini, Davide; Benetti, Riccardo; Baraldo, Simonetta; Turato, Graziella; Fagiuoli, Stefano; Sonzogni, Aurelio; Rigobello, Chiara; Rea, Federico; Calabrese, Fiorella; Foschino-Barbaro, Maria Pia; Miranda, Elena; Lomas, David A; Saetta, Marina; Cosio, Manuel G

2018-05-12

The deficiency of α 1 -antitrypsin (AAT) is secondary to misfolding and polymerization of the abnormal Z-AAT in liver cells and is associated with lung emphysema. Alveolar macrophages (AM) produce AAT, however it is not known if Z-AAT can polymerize in AM, further decreasing lung AAT and promoting lung inflammation. To investigate if AAT polymerizes in human AM and to study the possible relation between polymerization and degree of lung inflammation. Immunohistochemical analysis with 2C1 monoclonal antibody specific for polymerized AAT was performed in sections of: 9 lungs from individuals with AAT deficiency (AATD) and severe COPD, 35 smokers with normal AAT levels of which 24 with severe COPD and 11 without COPD, and 13 non-smokers. AM positive for AAT polymers were counted and expressed as percentage of total AM in lung. AAT polymerization was detected in [27(4-67)%] of AM from individuals with AATD but also in AM from smokers with normal AAT with [24(0-70)%] and without [24(0-60)%] COPD, but not in AM from non-smokers [0(0-1.5)%] (p<0.0001). The percentage of AM with polymerized AAT correlated with pack-years smoked (r=0.53,p=0.0001), FEV 1 /FVC (r=-0.41,p=0.005), Small Airways Disease (r=0.44,p=0.004), number of CD8+T-cells and neutrophils in alveolar walls (r=0.51,p=0.002; r=0.31,p=0.05 respectively). Polymerization of AAT in alveolar macrophages occurs in lungs of individuals with AATD but also in smokers with normal AAT levels with or without COPD. Our findings highlight the similarities in the pathophysiology of COPD in individuals with and without AATD, adding a potentially important step to the mechanism of COPD. Copyright © 2018. Published by Elsevier Inc.

Two-Dimensional Polymer Synthesized via Solid-State Polymerization for High-Performance Supercapacitors.

PubMed

Liu, Wei; Ulaganathan, Mani; Abdelwahab, Ibrahim; Luo, Xin; Chen, Zhongxin; Rong Tan, Sherman Jun; Wang, Xiaowei; Liu, Yanpeng; Geng, Dechao; Bao, Yang; Chen, Jianyi; Loh, Kian Ping

2018-01-23

Two-dimensional (2-D) polymer has properties that are attractive for energy storage applications because of its combination of heteroatoms, porosities and layered structure, which provides redox chemistry and ion diffusion routes through the 2-D planes and 1-D channels. Here, conjugated aromatic polymers (CAPs) were synthesized in quantitative yield via solid-state polymerization of phenazine-based precursor crystals. By choosing flat molecules (2-TBTBP and 3-TBQP) with different positions of bromine substituents on a phenazine-derived scaffold, C-C cross coupling was induced following thermal debromination. CAP-2 is polymerized from monomers that have been prepacked into layered structure (3-TBQP). It can be mechanically exfoliated into micrometer-sized ultrathin sheets that show sharp Raman peaks which reflect conformational ordering. CAP-2 has a dominant pore size of ∼0.8 nm; when applied as an asymmetric supercapacitor, it delivers a specific capacitance of 233 F g -1 at a current density of 1.0 A g -1 , and shows outstanding cycle performance.

Electrochemical DNA biosensor based on grafting-to mode of terminal deoxynucleoside transferase-mediated extension.

PubMed

Chen, Jinyuan; Liu, Zhoujie; Peng, Huaping; Zheng, Yanjie; Lin, Zhen; Liu, Ailin; Chen, Wei; Lin, Xinhua

2017-12-15

Previously reported electrochemical DNA biosensors based on in-situ polymerization approach reveal that terminal deoxynucleoside transferase (TdTase) has good amplifying performance and promising application in the design of electrochemical DNA biosensor. However, this method, in which the background is significantly affected by the amount of TdTase, suffers from being easy to produce false positive result and poor stability. Herein, we firstly present a novel electrochemical DNA biosensor based on grafting-to mode of TdTase-mediated extension, in which DNA targets are polymerized in homogeneous solution and then hybridized with DNA probes on BSA-based DNA carrier platform. It is surprising to find that the background in the grafting-to mode of TdTase-based electrochemical DNA biosensor have little interference from the employed TdTase. Most importantly, the proposed electrochemical DNA biosensor shows greatly improved detection performance over the in-situ polymerization approach-based electrochemical DNA biosensor. Copyright © 2017 Elsevier B.V. All rights reserved.

Guanidinium ionic liquid-based surfactants as low cytotoxic extractants: Analytical performance in an in-situ dispersive liquid-liquid microextraction method for determining personal care products.

PubMed

Pacheco-Fernández, Idaira; Pino, Verónica; Ayala, Juan H; Afonso, Ana M

2018-07-20

The IL-based surfactant octylguanidinium chloride (C 8 Gu-Cl) was designed and synthetized with the purpose of obtaining a less harmful surfactant: containing guanidinium as core cation and a relatively short alkyl chain. Its interfacial and aggregation behavior was evaluated through conductivity and fluorescence measurements, presenting a critical micelle concentration value of 42.5 and 44.6mmolL -1 , respectively. Cytotoxicity studies were carried out with C 8 Gu-Cl and other IL-based and conventional surfactants, specifically the analogue 1-octyl-3-methylimidazolium chloride (C 8 MIm-Cl), and other imidazolium- (C 16 MIm-Br) and pyridinium- (C 16 Py-Cl) based surfactants, together with the conventional cationic CTAB and the conventional anionic SDS. From these studies, C 8 Gu-Cl was the only one to achieve the classification of low cytotoxicity. An in situ dispersive liquid-liquid microextraction (DLLME) method based on transforming the water-soluble C 8 Gu-Cl IL-based surfactant into a water-insoluble IL microdroplet via a simple metathesis reaction was then selected as the extraction/preconcentration method for a group of 6 personal care products (PCPs) present in cosmetic samples. The method was carried out in combination with high-performance liquid chromatography (HPLC) and diode array detection (DAD). The method was properly optimized, requiring the use of only 30μL of C 8 Gu-Cl for 10mL of aqueous sample with a NaCl content of 8% (w/v) to adjust the ionic strength and pH value of 5. The metathesis reaction required the addition of the anion exchange reagent (bis[(trifluoromethyl)sulfonyl]imide - 1:1 molar ratio), followed by vortex and centrifugation, and dilution of the final microdroplet up to 60μL with acetonitrile before the injection in the HPLC-DAD system. The optimum in situ DLLME-HPLC-DAD method takes ∼10min for the extraction step and ∼22min for the chromatographic separation, with analytical features of low detection limits: down to 0.4μgL -1 ; high reproducibility: with RSD values lower than 10% (intra-day) and 16% (inter-day) for a spiked level of 15μgL -1 ; and an average enrichment factor of 89. The requirement of low volumes (30μL) of a low cytotoxic IL-based surfactant allows the method to be considered less harmful than other common analytical microextraction approaches. Copyright © 2017 Elsevier B.V. All rights reserved.

Combination of in situ metathesis reaction with a novel "magnetic effervescent tablet-assisted ionic liquid dispersive microextraction" for the determination of endogenous steroids in human fluids.

PubMed

Wu, Jia; Xu, Zilin; Pan, Yixuan; Shi, Yi; Bao, Xiujie; Li, Jun; Tong, Yu; Tang, Han; Ma, Shuyan; Wang, Xuedong; Lyu, Jianxin

2018-05-01

Herein, a novel magnetic effervescence tablet-assisted microextraction coupled to in situ metathesis reaction of ionic liquid (IS-META-ILDM) is presented for the determination of four endogenous steroids in human urine, pregnant women's blood, and fetal umbilical cord blood. The magnetic effervescent tablets, which were composed of Fe 3 O 4 nanoparticles, sodium carbonate (alkaline source), and tartaric acid (acidic source), were used to disperse the extractant and for convenient magnetic separation. After the effervescent reaction, in situ reaction between NH 4 PF 6 and [C 6 MIM]BF 4 was adopted to change hydrophilic ionic liquid to hydrophobic liquid, which could be separated from the aqueous phase. The newly developed method has three obvious advantages: (1) combination of effervescent dispersion and magnetic nanoparticles' retrieval is cost-effective and the dispersion and collection of the extractant can be completed almost simultaneously; (2) as compared to temperature-controlled ionic liquid dispersive microextraction and cold-induced solidified microextraction, this method avoids a heating and cooling process which significantly reduces the extraction time and energy cost; and (3) the combination of adsorption by magnetic nanoparticles with extraction by in situ metathesis reaction easily produces high recoveries for target analytes. The optimized composition of effervescent tablet and experimental parameters are as follows: 0.64 g mixture of sodium carbonate and tartaric acid, 7 mg of Fe 3 O 4 (20 nm) as magnetic sorbents, 40 μL of [C 6 MIM]BF 4 as the extraction solvent, 0.15 g NH 4 PF 6 , and 300 μL of elution solvent. Under the optimized conditions, the newly developed method provided high extraction recoveries (90.0-118.5%) and low LODs (0.14-0.17 μg L -1 ) in urine and blood samples. In total, this IS-META-ILDM method provided high extraction efficiency, fast and convenient separation, and underutilization of any organic solvent, and thus it has great potential for the determination of trace endogenous steroids in complex human fluids. Graphical abstract The newly developed method has three obvious advantages: combination of effervescent dispersion and magnetic nanoparticles' retrieval is cost-effective and the dispersion and collection of the extractant can be completed almost simultaneously. It avoids a heating and cooling process which significantly reduces the extraction time and energy cost and easily produces high recoveries for target analytes.

Polymeric ionic liquid coatings versus commercial solid-phase microextraction coatings for the determination of volatile compounds in cheeses.

PubMed

Trujillo-Rodríguez, María J; Yu, Honglian; Cole, William T S; Ho, Tien D; Pino, Verónica; Anderson, Jared L; Afonso, Ana M

2014-04-01

The extraction performance of four polymeric ionic liquid (PIL)-based solid-phase microextraction (SPME) coatings has been studied and compared to that of commercial SPME coatings for the extraction of 16 volatile compounds in cheeses. The analytes include 2 free fatty acids, 2 aldehydes, 2 ketones and 10 phenols and were determined by headspace (HS)-SPME coupled to gas chromatography (GC) with flame-ionization detection (FID). The PIL-based coatings produced by UV co-polymerization were more efficient than PIL-based coatings produced by thermal AIBN polymerization. Partition coefficients of analytes between the sample and the coating (Kfs) were estimated for all PIL-based coatings and the commercial SPME fiber showing the best performance among the commercial fibers tested: carboxen-polydimethylsyloxane (CAR-PDMS). For the PIL-based fibers, the highest K(fs) value (1.96 ± 0.03) was obtained for eugenol. The normalized calibration slope, which takes into account the SPME coating thickness, was also used as a simpler approximate tool to compare the nature of the coating within the determinations, with results entirely comparable to those obtained with estimated K(fs) values. The PIL-based materials obtained by UV co-polymerization containing the 1-vinyl-3-hexylimidazolium chloride IL monomer and 1,12-di(3-vinylimiazolium)dodecane dibromide IL crosslinker exhibited the best performance in the extraction of the select analytes from cheeses. Despite a coating thickness of only 7 µm, this copolymeric sorbent coating was capable of quantitating analytes in HS-SPME in a 30 to 2000 µg L(-1) concentration range, with correlation coefficient (R) values higher than 0.9938, inter-day precision values (as relative standard deviation in %) varying from 6.1 to 20%, and detection limits down to 1.6 µg L(-1). Copyright © 2013 Elsevier B.V. All rights reserved.

Effect of hemoglobin polymerization on oxygen transport in hemoglobin solutions.

PubMed

Budhiraja, Vikas; Hellums, J David

2002-09-01

The effect of hemoglobin (Hb) polymerization on facilitated transport of oxygen in a bovine hemoglobin-based oxygen carrier was studied using a diffusion cell. In high oxygen tension gradient experiments (HOTG) at 37 degrees C the diffusion of dissolved oxygen in polymerized Hb samples was similar to that in unpolymerized Hb solutions during oxygen uptake. However, in the oxygen release experiments, the transport by diffusion of dissolved oxygen was augmented by diffusion of oxyhemoglobin over a range of oxygen saturations. The augmentation was up to 30% in the case of polymerized Hb and up to 100% in the case of unpolymerized Hb solution. In experiments performed at constant, low oxygen tension gradients in the range of physiological significance, the augmentation effect was less than that in the HOTG experiments. Oxygen transport in polymerized Hb samples was approximately the same as that in unpolymerized samples over a wide range of oxygen tensions. However, at oxygen tensions lower than 30 mm Hg, there were more significant augmentation effects in unpolymerized bovine Hb samples than in polymerized Hb. The results presented here are the first accurate, quantitative measurements of effective diffusion coefficients for oxygen transport in hemoglobin-based oxygen carriers of the type being evaluated to replace red cells in transfusions. In all cases the oxygen carrier was found to have higher effective oxygen diffusion coefficients than blood.

[Comparative study of polymerization shrinkage and related properties of flowable composites and an unfilled resin].

PubMed

Bukovinszky, Katalin; Molnár, Lilla; Bakó, József; Szalóki, Melinda; Hegedus, Csaba

2014-03-01

The polymerization shrinkage and shrinkage stress of dental composites are in the center of the interest of researchers and manufacturers. It is a great challenge to minimize this important property as low as possible. Many factors are related and are in complicated correlation with each other affecting the polymerization shrinkage. Polymerization shrinkage stress degree of conversion and elasticity has high importance from this aspect. Our aim was to study the polymerization shrinkage and related properties (modulus of elasticity, degree of conversion, shrinkage stress) of three flowable composite (Charisma Opal Flow, SDR, Filtek Ultimate) and an unfilled composite resin. Modulus of elasticity was measured using three point flexure tests on universal testing machine. The polymerization shrinkage stress was determined using bonded-disc technique. The degree of conversion measurements were performed by FT-IR spectroscopy. And the volumetric shrinkage was investigated using Archimedes principle and was measured on analytical balance with special additional equipment. The unfilled resin generally showed higher shrinkage (8,26%), shrinkage stress (0,8 MPa) and degree of conversion (38%), and presented the lowest modulus of elasticity (3047,02MPa). Highest values of unfilled resin correspond to the literature. The lack of fillers enlarges the shrinkage, and the shrinkage stress, but gives the higher flexibility and higher degree of conversion. Further investigations needs to be done to understand and reveal the differences between the composites.

Synthesis and structure of a ferric complex of 2,6-di(1H-pyrazol-3-yl)pyridine and its excellent performance in the redox-controlled living ring-opening polymerization of ε-caprolactone.

PubMed

Fang, Yang-Yang; Gong, Wei-Jie; Shang, Xiu-Juan; Li, Hong-Xi; Gao, Jun; Lang, Jian-Ping

2014-06-14

The reaction of FeCl3 with a pincer ligand, 2,6-di(1H-pyrazol-3-yl)pyridine (bppyH2), produced a mononuclear Fe(III) complex [Fe(bppyH2)Cl3] (1), which could be reduced to the corresponding Fe(II) dichloride complex [Fe(bppyH2)Cl2] (2) by suitable reducing agents such as Cp2Co or Fe powder. 1 and 2 exhibited a reversible transformation from each other with appropriate redox reagents. 1 could be utilized as a pre-catalyst to initiate the ring-opening polymerization of ε-caprolactone in the presence of alcohol but did not work. The 1/alcohol system displayed characteristics of a well-controlled polymerization with the resulting poly(ε-caprolactone) having low molecular weight distributions, a linear tendency of molecular weight evolution with conversion, and polymer growth observed for the sequential additions of ε-caprolactone monomer to the polymerization reaction. The polymerization was completely turned off by the in situ reduction of the catalytic Fe center via Cp2Co and then turned back upon the addition of [Cp2Fe]PF6. The rate of polymerization was modified by switching in situ between the Fe(III) and Fe(II) species.

pH-sensitive Itaconic acid based polymeric hydrogels for dye removal applications.

PubMed

Sakthivel, M; Franklin, D S; Guhanathan, S

2016-12-01

A series of Itaconic Acid (IA) based pH-sensitive polymeric hydrogels were synthesized by condensation polymerization of Itaconic Acid (IA) with Ethylene Glycol (EG) in the presence of an acid medium resulted into pre-polymer. Further, pre-polymer were co-polymerized with Acrylic Acid (AA) through free radical polymerization using Potassium persulphate (KPS). The structural and surface morphological characterizations of the synthesized hydrogels were studied using FT-IR spectroscopy and Scanning Electron Microscope (SEM) respectively. The swelling and swelling equilibrium were performed at varies pH (4.0-10.0). Further, the effects of IA, EG and AA on swelling properties have also been investigated. Thermal stability of synthesized hydrogels have been investigated by TGA, DTA and DSC. The synthesized hydrogels have shown good ability to uptake a Cationic dye. The Methylene blue has been chosen as a model cationic dye. The results of dye removal using IA hydrogels found to have excellent dye removal capacity. Such kind of IA based hydrogels may be recommended for eco-friendly environmental application. viz., removal of dyes and metal ions and sewage water treatment, purification of water etc. Copyright © 2015 Elsevier Inc. All rights reserved.

3D full field strain analysis of polymerization shrinkage in a dental composite.

PubMed

Martinsen, Michael; El-Hajjar, Rani F; Berzins, David W

2013-08-01

The objective of this research was to study the polymerization shrinkage in a dental composite using 3D digital image correlation (DIC). Using 2 coupled cameras, digital images were taken of bar-shaped composite (Premise Universal Composite; Kerr) specimens before light curing and after for 10 min. Three-dimensional DIC was used to assess in-plane and out-of-plane deformations associated with polymerization shrinkage. The results show the polymerization shrinkage to be highly variable with the peak values occurring 0.6-0.8mm away from the surface. Volumetric shrinkage began to significantly decrease at 3.2mm from the specimen surface and reached a minimum at 4mm within the composite. Approximately 25-30% of the strain registered at 5 min occurred after light-activation. Application of 3D DIC dental applications can be performed without the need for assumptions on the deformation field. Understanding the local deformations and strain fields from the initial polymerization shrinkage can lead to a better understanding of the composite material and interaction with surrounding tooth structure, aiding in their further development and clinical prognosis. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Molecularly Oriented Polymeric Thin Films for Space Applications

NASA Technical Reports Server (NTRS)

Fay, Catharine C.; Stoakley, Diane M.; St.Clair, Anne K.

1997-01-01

The increased commitment from NASA and private industry to the exploration of outer space and the use of orbital instrumentation to monitor the earth has focused attention on organic polymeric materials for a variety of applications in space. Some polymeric materials have exhibited short-term (3-5 yr) space environmental durability; however, future spacecraft are being designed with lifetimes projected to be 10-30 years. This gives rise to concern that material property change brought about during operation may result in unpredicted spacecraft performance. Because of their inherent toughness and flexibility, low density, thermal stability, radiation resistance and mechanical strength, aromatic polyimides have excellent potential use as advanced materials on large space structures. Also, there exists a need for high temperature (200-300 C) stable, flexible polymeric films that have high optical transparency in the 300-600nm range of the electromagnetic spectrum. Polymers suitable for these space applications were fabricated and characterized. Additionally, these polymers were molecularly oriented to further enhance their dimensional stability, stiffness, elongation and strength. Both unoriented and oriented polymeric thin films were also cryogenically treated to temperatures below -184 C to show their stability in cold environments and determine any changes in material properties.

Antibacterial performance on plasma polymerized heptylamine films loaded with silver nanoparticles

NASA Astrophysics Data System (ADS)

Lin, Yu-Chun; Lin, Chia-Chun; Lin, Chih-Hao; Wang, Meng-Jiy

2017-01-01

The antibacterial performance of the plasma-polymerized (pp) heptylamine thin films loaded with silver nanoparticles was evaluated against the colonization of Escherichia coli and Staphylococcus aureus. The properties including the thickness and chemical composition of the as deposited HApp films were modulated by adjusting plasma parameters. The acquired results showed that the film thickness was controlled in the range of 20 to 400 nm by adjusting deposition time. The subsequent immersion of the HApp thin films in silver nitrate solutions result in the formation of amine-metal complexes, in which the silver nanoparticles were reduced directly on the matrices to form Ag@HApp. The reduction reaction of silver was facilitated by applying NaBH4 as a reducing agent. The results of physicochemical analyses including morphological analysis and ellipsometry revealed that the silver nanoparticles were successfully reduced on the HApp films, and the amount of reduced silver was closely associated which the thickness of the plasma-polymerized films, the concentration of applied metal ions solutions, and the time of immobilization. Regarding the antibacterial performance, the Ag@HApp films reduced by NaBH4 showed antibacterial abilities of 70.1 and 68.2% against E. coli and S. aureus, respectively.

Polymeric bionanocomposite cast thin films with in situ laccase-catalyzed polymerization of dopamine for biosensing and biofuel cell applications.

PubMed

Tan, Yueming; Deng, Wenfang; Li, Yunyong; Huang, Zhao; Meng, Yue; Xie, Qingji; Ma, Ming; Yao, Shouzhuo

2010-04-22

We report here on the facile preparation of polymer-enzyme-multiwalled carbon nanotubes (MWCNTs) cast films accompanying in situ laccase (Lac)-catalyzed polymerization for electrochemical biosensing and biofuel cell applications. Lac-catalyzed polymerization of dopamine (DA) as a new substrate was examined in detail by UV-vis spectroscopy, cyclic voltammetry, quartz crystal microbalance, and scanning electron microscopy. Casting the aqueous mixture of DA, Lac and MWCNTs on a glassy carbon electrode (GCE) yielded a robust polydopamine (PDA)-Lac-MWCNTs/GCE that can sense hydroquinone with 643 microA mM(-1) cm(-2) sensitivity and 20-nM detection limit (S/N = 3). The DA substrate yielded the best biosensing performance, as compared with aniline, o-phenylenediamine, or o-aminophenol as the substrate for similar Lac-catalyzed polymerization. Casting the aqueous mixture of DA, glucose oxidase (GOx), Lac, and MWCNTs on a Pt electrode yielded a robust PDA-GOx-Lac-MWCNTs/Pt electrode that exhibits glucose-detection sensitivity of 68.6 microA mM(-1) cm(-2). In addition, 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS) was also coimmobilized to yield a PDA-Lac-MWCNTs-ABTS/GCE that can effectively catalyze the reduction of O(2), and it was successfully used as the biocathode of a membraneless glucose/O(2) biofuel cell (BFC) in pH 5.0 Britton-Robinson buffer. The proposed biomacromolecule-immobilization platform based on enzyme-catalyzed polymerization may be useful for preparing many other multifunctional polymeric bionanocomposites for wide applications.

Phosphate Tether-Mediated Approach to the Formal Total Synthesis of (-)-Salicylihalamides A and B

PubMed Central

Chegondi, Rambabu; Tan, Mary M. L.; Hanson, Paul R.

2011-01-01

A concise formal synthesis of the cytotoxic macrolides (-)-salicylihalamides A and B is reported. Key features of the synthetic strategy include a chemoselective hydroboration, highly regio- and diastereoselective methyl cuprate addition, Pd-catalyzed formate reduction, and an E-selective ring-closing metathesis to construct the 12-membered macrocycle subunit. Overall, two routes have been developed from a readily prepared bicyclic phosphate (4-steps), a 13-step route and a more efficient 9-step sequence relying on regioselective esterification of a key diol. PMID:21504150

An Electrochemical and Spectroelectrochemical Study of Substituted Alkylidene Cyclopropabenzenes: 1-(Diphenylmethylene)Cyclopropabenzene in the First Anodic and Cathodic Voltammetric Waves in Acetonitrile.

DTIC Science & Technology

1986-07-30

extracts were washed with water , dried with magnesium sulfate. and N 3 concentrated to an orange oil under reduced pressure. This oil was then passed...prepared from the metathesis of sodium tetrafluoroborate and tetra-n-butylammonium hydrogen sulfate. The crude product was washed with ice water , dissolved...stored in a vacuum oven at 75°C for 24h before use. Acetonitrile was HPLC grade (Baker Chemicals, 0.001% nominal water content) and was used as received

Alkyl complexes of strontium and barium: synthesis and structural characterization of [(Me3Si)2(MeOMe2Si)C]2Sr(THF) and [(Me3Si)2(MeOMe2Si)C]2Ba(MeOCH2CH2OMe).

PubMed

Izod, Keith; Liddle, Stephen T; Clegg, William

2003-06-25

Metathesis between either SrI2 or BaI2 and 2 equiv of {(Me3Si)2(MeOMe2Si)C}K in THF yields the novel heavier alkali metal dialkyls {(Me3Si)2(MeOMe2Si)C}2M(L) [M(L) = Sr(THF) (2), Ba(DME) (3) (DME = 1,2-dimethoxyethane)] after recrystallization.

Extension of the bambus[n]uril family: microwave synthesis and reactivity of allylbambus[n]urils.

PubMed

Rivollier, Julie; Thuéry, Pierre; Heck, Marie-Pierre

2013-02-01

Microwave irradiations allow the preparation of unsaturated bambusurils in 85% yield compared to 20% yield under classical reaction conditions. Five new bambusurils were synthesized including unsaturated derivatives Allyl(8)BU[4] and Allyl(12)BU[6] bearing diallylglycoluril units. The reactivity of Allyl(8)BU[4] was tested in a variety of organic reactions showing that this macrocycle acts as a classical double bond-bearing product. The first monofunctionalized bambusuril Allyl(7)HepBU[4] prepared by a cross metathesis reaction is also reported.

Metal vinylidenes and allenylidenes in catalysis: applications in anti-Markovnikov additions to terminal alkynes and alkene metathesis.

PubMed

Bruneau, Christian; Dixneuf, Pierre H

2006-03-27

The involvement of a catalytic metal vinylidene species was proposed for the first time in 1986 to explain the regioselective formation of vinyl carbamates directly from terminal alkynes, carbon dioxide, and amines. Since this initial report, various metal vinylidenes and allenylidenes, which are key activation intermediates, have proved extremely useful for many alkyne transformations. They have contributed to the rational design of new catalytic reactions. This 20th anniversary is a suitable occasion to present the advancement of organometallic vinylidenes and allenylidenes in catalysis.

The formation mechanism of binary semiconductor nanomaterials: shared by single-source and dual-source precursor approaches.

PubMed

Yu, Kui; Liu, Xiangyang; Zeng, Qun; Yang, Mingli; Ouyang, Jianying; Wang, Xinqin; Tao, Ye

2013-10-11

One thing in common: The formation of binary colloidal semiconductor nanocrystals from single- (M(EEPPh2 )n ) and dual-source precursors (metal carboxylates M(OOCR)n and phosphine chalcogenides such as E=PHPh2 ) is found to proceed through a common mechanism. For CdSe as a model system (31) P NMR spectroscopy and DFT calculations support a reaction mechanism which includes numerous metathesis equilibriums and Se exchange reactions. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Computational chemistry and aeroassisted orbital transfer vehicles

NASA Technical Reports Server (NTRS)

Cooper, D. M.; Jaffe, R. L.; Arnold, J. O.

1985-01-01

An analysis of the radiative heating phenomena encountered during a typical aeroassisted orbital transfer vehicle (AOTV) trajectory was made to determine the potential impact of computational chemistry on AOTV design technology. Both equilibrium and nonequilibrium radiation mechanisms were considered. This analysis showed that computational chemistry can be used to predict (1) radiative intensity factors and spectroscopic data; (2) the excitation rates of both atoms and molecules; (3) high-temperature reaction rate constants for metathesis and charge exchange reactions; (4) particle ionization and neutralization rates and cross sections; and (5) spectral line widths.

Functionalized poly(ethylene glycol) diacrylate microgels by microfluidics: In situ peptide encapsulation for in serum selective protein detection.

PubMed

Celetti, Giorgia; Natale, Concetta Di; Causa, Filippo; Battista, Edmondo; Netti, Paolo A

2016-09-01

Polymeric microparticles represent a robustly platform for the detection of clinically relevant analytes in biological samples; they can be functionalized encapsulating a multiple types of biologics entities, enhancing their applications as a new class of colloid materials. Microfluidic offers a versatile platform for the synthesis of monodisperse and engineered microparticles. In this work, we report microfluidic synthesis of novel polymeric microparticles endowed with specific peptide due to its superior specificity for target binding in complex media. A peptide sequence was efficiently encapsulated into the polymeric network and protein binding occurred with high affinity (KD 0.1-0.4μM). Fluidic dynamics simulation was performed to optimize the production conditions for monodisperse and stable functionalized microgels. The results demonstrate the easy and fast realization, in a single step, of functionalized monodisperse microgels using droplet-microfluidic technique, and how the inclusion of the peptide within polymeric network improve both the affinity and the specificity of protein capture. Copyright © 2016 Elsevier B.V. All rights reserved.

Iron-Based Redox Polymerization of Acrylic Acid for Direct Synthesis of Hydrogel/Membranes, and Metal Nanoparticles for Water Treatment

PubMed Central

Hernández, Sebastián; Papp, Joseph K.; Bhattacharyya, Dibakar

2014-01-01

Functionalized polymer materials with ion exchange groups and integration of nano-structured materials is an emerging area for catalytic and water pollution control applications. The polymerization of materials such as acrylic acid often requires persulfate initiator and a high temperature start. However, is generally known that metal ions accelerate such polymerizations starting from room temperature. If the metal is properly selected, it can be used in environmental applications adding two advantages simultaneously. This paper deals with this by polymerizing acrylic acid using iron as accelerant and its subsequent use for nanoparticle synthesis in hydrogel and PVDF membranes. Characterizations of hydrogel, membranes and nanoparticles were carried out with different techniques. Nanoparticles sizes of 30–60 nm were synthesized. Permeability and swelling measurements demonstrate an inverse relationship between hydrogel mesh size (6.30 to 8.34 nm) and membrane pores (222 to 110 nm). Quantitative reduction of trichloroethylene/chloride generation by Fe/Pd nanoparticles in hydrogel/membrane platforms was also performed. PMID:24954975

Test of the ``radical-like polymerization'' scheme in molecular dynamics on the behavior of polymers under shock loading

NASA Astrophysics Data System (ADS)

Lemarchand, Claire; Bousquet, David; Schnell, Benoît; Pineau, Nicolas

2017-06-01

The behavior of polymer melts under shock loading is a question attracting more and more attention because of applications such as polymer-bonded explosives, light-weight armor and civilian protective equipment, like sports and car equipment. Molecular dynamics (MD) simulations are a very good tool to characterize the microscopic response of the polymer to a shock wave. To do so, the initial configuration of the polymer melt needs to be realistic. The ``radical-like polymerization'' scheme is a method to obtain near equilibrium configurations of a melt of long polymer chains. It consists in adding one neighboring monomer at a time to each growing chain. Between each polymerization step an MD run is performed to relax the new configuration. We test how details of our implementation of the ``radical-like polymerization'' scheme can impact or not Hugoniot curves and changes of chain configuration under shock. We compare our results to other simulation and experimental results on reference polymers.

A Hydrogel of Ultrathin Pure Polyaniline Nanofibers: Oxidant-Templating Preparation and Supercapacitor Application.

PubMed

Zhou, Kun; He, Yuan; Xu, Qingchi; Zhang, Qin'e; Zhou, An'an; Lu, Zihao; Yang, Li-Kun; Jiang, Yuan; Ge, Dongtao; Liu, Xiang Yang; Bai, Hua

2018-05-15

Although challenging, fabrication of porous conducting polymeric materials with excellent electronic properties is crucial for many applications. We developed a fast in situ polymerization approach to pure polyaniline (PANI) hydrogels, with vanadium pentoxide hydrate nanowires as both the oxidant and sacrifice template. A network comprised of ultrathin PANI nanofibers was generated during the in situ polymerization, and the large aspect ratio of these PANI nanofibers allowed the formation of hydrogels at a low solid content of 1.03 wt %. Owing to the ultrathin fibril structure, PANI hydrogels functioning as a supercapacitor electrode display a high specific capacitance of 636 F g -1 , a rate capability, and good cycling stability (∼83% capacitance retention after 10,000 cycles). This method was also extended to the preparation of polypyrrole and poly(3,4-ethylenedioxythiophene) hydrogels. This template polymerization method represents a rational strategy for design of conducing polymer networks, which can be readily integrated in high-performance devices or a further platform for functional composites.

Fabrication of core-shell structured magnetic nanocellulose base polymeric ionic liquid for effective biosorption of Congo red dye.

PubMed

Beyki, Mostafa Hossein; Bayat, Mehrnoosh; Shemirani, Farzaneh

2016-10-01

Ionic liquids are considered to be a class of environmentally friendly compounds as combination of them with bioresource polymeric substances such as; cellulose, constitute emerging coating materials. Biosorption by polymeric ionic liquids exhibits an attractive green way that involves low cost and irrespective of toxicity. As a result, a novel polymeric ionic liquid has been developed by the reaction of one step synthesized Fe3O4-cellulose nanohybrid, epichlorohydrin and 1-methylimidazole and employed as a green sorbent for efficient biosorption of Congo red dye. Effective parameters on dye removing as well as their interactions were determined with response surface methodology (RSM). Congo red adsorption showed fast equilibrium time (11min) with maximum uptake of 131mgg(-1). Isotherm study revealed that Langmuir adsorption model can better describe dye adsorption behavior. Regeneration of the sorbent was performed with a mixture of methanol-acetone-NaOH (3.0molL(-1)) solution. Copyright © 2016 Elsevier Ltd. All rights reserved.

[Evaluation of chromatographic performance of polymerized ionic liquid stationary phase for capillary gas chromatography].

PubMed

Chen, Xiaoyan; Lu, Kai; Qi, Meiling; Fu, Ruonong

2009-11-01

The selectivity and thermal stability of ionic liquids as the stationary phases for capillary gas chromatography (CGC) have attracted much attention of researchers in recent years. In this study, 1-vinyl-3-benzyl imidazolium-bis(trifluoromethane-sulphonyl)imidate (VBIm-NTf2) was synthesized and polymerized (PVBIm-NTf2) in a CGC column. In comparison with VBIm-NTf2, PVBIm-NTf2 exhibits much better thermal stability and chromatographic selectivity, and achieves satisfactory resolution for Grob test mixture, alcohols mixture, esters mixture and aromatics mixture with narrow and symmetric peak shapes. The satisfactory resolution and selectivity of the polymerized column still remain after conditioned at 250 degrees C for 6 h. Additionally, the Abraham solvation parameters of PVBIm-NTf2 were determined and the interactions between the stationary phase and solutes were elucidated. The present work demonstrates that the polymerization is an effective way to improve the selectivity and thermal stability of common ionic liquids as CGC stationary phases.

Analysis of polymeric phenolics in red wines using different techniques combined with gel permeation chromatography fractionation.

PubMed

Guadalupe, Zenaida; Soldevilla, Alberto; Sáenz-Navajas, María-Pilar; Ayestarán, Belén

2006-04-21

A multiple-step analytical method was developed to improve the analysis of polymeric phenolics in red wines. With a common initial step based on the fractionation of wine phenolics by gel permeation chromatography (GPC), different analytical techniques were used: high-performance liquid chromatography-diode array detection (HPLC-DAD), HPLC-mass spectrometry (MS), capillary zone electrophoresis (CZE) and spectrophotometry. This method proved to be valid for analyzing different families of phenolic compounds, such as monomeric phenolics and their derivatives, polymeric pigments and proanthocyanidins. The analytical characteristics of fractionation by GPC were studied and the method was fully validated, yielding satisfactory statistical results. GPC fractionation substantially improved the analysis of polymeric pigments by CZE, in terms of response, repeatability and reproducibility. It also represented an improvement in the traditional vanillin assay used for proanthocyanidin (PA) quantification. Astringent proanthocyanidins were also analyzed using a simple combined method that allowed these compounds, for which only general indexes were available, to be quantified.

Molecular Imprinting of Silica Nanoparticle Surfaces via Reversible Addition-Fragmentation Polymerization for Optical Biosensing Applications

NASA Astrophysics Data System (ADS)

Oluz, Zehra; Nayab, Sana; Kursun, Talya Tugana; Caykara, Tuncer; Yameen, Basit; Duran, Hatice

Azo initiator modified surface of silica nanoparticles were coated via reversible addition-fragmentation polymerization (RAFT) of methacrylic acid and ethylene glycol dimethacrylate using 2-phenylprop 2-yl dithobenzoate as chain transfer agent. Using L-phenylalanine anilide as template during polymerization led molecularly imprinted nanoparticles. RAFT polymerization offers an efficient control of grafting process, while molecularly imprinted polymers shows enhanced capacity as sensor. L-phenylalanine anilide imprinted silica particles were characterized by X-Ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM). Performances of the particles were followed by surface plasmon resonance spectroscopy (SPR) after coating the final product on gold deposited glass substrate against four different analogous of analyte molecules: D-henylalanine anilide, L-tyrosine, L-tryptophan and L-phenylalanine. Characterizations indicated that silica particles coated with polymer layer do contain binding sites for L-phenylalanine anilide, and are highly selective for the molecule of interest. This project was supported by TUBITAK (Project No:112M804).

Chemical characterization of selected LDEF polymeric materials

NASA Technical Reports Server (NTRS)

Young, Philip R.; Slemp, Wayne S.

1991-01-01

Chemical characterization of selected polymeric materials which received exposure on the Long Duration Exposure Facility (LDEF) is reported. The specimens examined include silvered fluorinated ethylene propylene Teflon thermal blanket material, polysulfone, epoxy, polyimide matrix resin/graphite fiber reinforced composites, and several high performance polymer films. These specimens came from numerous LDEF locations, and thus received different environmental exposures. The results to date show no significant change at the molecular level in the polymer that survived exposure. Scanning electron and scanning tunneling microscopes show resin loss and a texturing of some specimens which resulted in a change in optical properties. The potential effect of a silicon-containing molecular contamination on these materials is addressed. The possibility of continued post-exposure degradation of some polymeric films is also proposed.

Advanced moisture modeling of polymer composites.

DOT National Transportation Integrated Search

2014-04-01

Long term moisture exposure has been shown to affect the mechanical performance of polymeric composite structures. This reduction : in mechanical performance must be considered during product design in order to ensure long term structure survival. In...

Electrical Properties and Manufacturability of ITO-MgF2 and Related Transparent Arcproof Spacecraft Coatings

NASA Technical Reports Server (NTRS)

Hambourger, Paul D.

2003-01-01

To investigate the applicability of co-deposited indium tin oxide and magnesium fluoride as a transparent arcproof coating on the exterior of PowerSphere microsatellites. This included testing coating performance after deposition on flexible polymeric substrates, determining whether ultraviolet (UV) radiation present during deposition might affect the UV-curing resin contained in the substrate, and preparation of coated polymeric samples for radiation damage studies by the PowerSphere team.

Rotor vibration reduction with polymeric sectors

NASA Astrophysics Data System (ADS)

Dutt, J. K.; Toi, T.

2003-05-01

This work has been undertaken principally with an idea to improving the dynamic performance of rotor-shaft systems, which often suffer from two major problems (a) resonance and (b) loss of stability, resulting in excessive vibration of such systems. Polymeric material in the form of sectors has been considered in this work as bearing supports. Polymeric material has been considered in this work as both stiffness and loss factor of such materials varies with the frequency of excitation. Stiffness and loss factor have been found out for the proposed support system comprising of polymeric sectors. Depending upon the frequency of excitation the system matrix, in this case, changes and dynamic performance of the rotor-shaft system also changes accordingly. Here in this work avoidance of resonance and application of optimum damping in the support have been investigated by finding out the optimum dimension, i.e., the optimum thickness and optimum length of the sectors. It has been theoretically found that use of such sectors reduces the rotor unbalanced response, increases the stability limit speed for simple rotor-shaft systems and thus improves the dynamic characteristics. Parameters of the system have been presented in terms of non-dimensional quantities. Many examples have been presented in support of the conclusion. The life of such supports, particularly in the presence of chemicals and other reagents has not been investigated.

Polymerization development of "low-shrink" resin composites: Reaction kinetics, polymerization stress and quality of network.

PubMed

Yamasaki, Lilyan C; De Vito Moraes, André G; Barros, Mathew; Lewis, Steven; Francci, Carlos; Stansbury, Jeffrey W; Pfeifer, Carmem S

2013-09-01

To evaluate "low-shrink" composites in terms of polymerization kinetics, stress development and mechanical properties. "Low-shrink" materials (Kalore/KAL, N'Durance/NDUR, and Filtek P90/P90) and one control (Esthet X HD/EHD) were tested. Polymerization stress (PS) was measured using the Instron 5565 tensometer. Volumetric shrinkage (VS) was determined by the ACTA linometer. Elastic modulus (E) and flexural strength (FS) were obtained by a three-point bending test. Degree of conversion (DC) and polymerization rate (Rp) were determined by NIR spectroscopy (6165cm(-1) for dimethacrylates; 4156 and 4071cm(-1) for P90). Photopolymerization was performed at 740mW/cm(2)×27s. Glass transition temperature (Tg), degree of heterogeneity and crosslink density were obtained in a DMA for the fully cured specimens. Analysis of extracts was done by (1)H NMR. Data were analyzed with one-way ANOVA/Tukey's test (α=0.05). The control presented the highest shrinkage and Tg. P90 showed the highest modulus, and NDUR demonstrated the highest conversion. The polymerization rates were comparable for all materials. NDUR and KAL had the highest and the lowest network homogeneity, respectively. The multifunctional P90 had the highest crosslink density, with no difference between other composites. The control had the greatest stress development, similar to NDUR. Crosslinking density and polymer network homogeneity were influenced by degree of conversion and monomer structure. Not all "low-shrink" composites reduced polymerization stress. P90 and NDUR had no leachable monomers, which was also a function of high crosslinking (P90) and high conversion (NDUR). Copyright © 2013 Academy of Dental Materials. All rights reserved.

Construction of dual-functional polymer nanomaterials with near-infrared fluorescence imaging and polymer prodrug by RAFT-mediated aqueous dispersion polymerization.

PubMed

Tian, Chun; Niu, Jinyun; Wei, Xuerui; Xu, Yujie; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

2018-05-31

The performance of functional polymer nanomaterials is a vigorously discussed topic in polymer science. We devoted ourselves to investigating polymer nanomaterials based on near-infrared (NIR) fluorescence imaging and polymer prodrug in this study. Aza-boron dipyrromethene (BODIPY) is an important organic dye, having characteristics such as environmental resistance, light resistance, high molar extinction coefficient, and fluorescence quantum yield. We incorporated it into our target monomer, which can be polymerized without changing its parent structure in a polar solvent and copolymerized with water-soluble monomer to improve the solubility of the dye in an aqueous solution. At the same time, the hydrophobic drug camptothecin (CPT) was designed as a prodrug monomer, and the polymeric nanoparticles (NPs) with NIR fluorescence imaging and prodrug were synthesized in situ in reversible addition-fragmentation chain transfer (RAFT)-mediated aqueous dispersion polymerization. The dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed the final uniform size of the dual-functional polymeric NPs morphology. The dual-functional polymeric NPs had a strong absorption and emission signal in the NIR region (>650 nm) based on the fluorescence tests. In consideration of the long-term biological toxicity, confocal laser scanning microscopy (CLSM) results indicated that the dual-functional NPs with controlled drug content exhibited effective capability of killing HeLa cells. In addition, in vivo imaging of the dual-functional NPs was observed in real time, and the fluorescent signals clearly demonstrated the dynamic process of prodrug transfer.

Crosslinked polymeric ionic liquids as solid-phase microextraction sorbent coatings for high performance liquid chromatography.

PubMed

Yu, Honglian; Merib, Josias; Anderson, Jared L

2016-03-18

Neat crosslinked polymeric ionic liquid (PIL) sorbent coatings for solid-phase microextraction (SPME) compatible with high-performance liquid chromatography (HPLC) are reported for the first time. Six structurally different PILs were crosslinked to nitinol supports and applied for the determination of select pharmaceutical drugs, phenolics, and insecticides. Sampling conditions including sample solution pH, extraction time, desorption solvent, desorption time, and desorption solvent volume were optimized using design of experiment (DOE). The developed PIL sorbent coatings were stable when performing extractions under acidic pH and remained intact in various organic desorption solvents (i.e., methanol, acetonitrile, acetone). The PIL-based sorbent coating polymerized from the IL monomer 1-vinyl-3-(10-hydroxydecyl) imidazolium chloride [VC10OHIM][Cl] and IL crosslinker 1,12-di(3-vinylbenzylimidazolium) dodecane dichloride [(VBIM)2C12] 2[Cl] exhibited superior extraction performance compared to the other studied PILs. The extraction efficiency of pharmaceutical drugs and phenolics increased when the film thickness of the PIL-based sorbent coating was increased while many insecticides were largely unaffected. Satisfactory analytical performance was obtained with limits of detection (LODs) ranging from 0.2 to 2 μg L(-1) for the target analytes. The accuracy of the analytical method was examined by studying the relative recovery of analytes in real water samples, including tap water and lake water, with recoveries varying from 50.2% to 115.9% and from 48.8% to 116.6%, respectively. Copyright © 2016 Elsevier B.V. All rights reserved.

Semi-elemental formula or polymeric formula: is there a better choice for enteral nutrition in acute pancreatitis? Randomized comparative study.

PubMed

Tiengou, Laurent-Eric; Gloro, Romain; Pouzoulet, Julien; Bouhier, Karine; Read, Marie-Hélène; Arnaud-Battandier, Franck; Plaze, Jean-Marie; Blaizot, Xavier; Dao, Thông; Piquet, Marie-Astrid

2006-01-01

Jejunal nutrition is recommended during acute pancreatitis. The use of semi-elemental formulas presents several theoretical advantages over polymeric formulas, but their clinical value has been poorly documented. Our aim was to evaluate in patients with acute pancreatitis the effect of enteral nutrition by a semi-elemental formula compared with a polymeric formula. A randomized prospective pilot study, stratified according to severity, was performed in 30 consecutive patients with acute pancreatitis requiring jejunal nutrition. The semi-elemental group received 35 kcal/kg/d of Peptamen (n = 15), and the polymeric group received the same quantity of Sondalis-Iso (n = 15). Tolerance was evaluated after 7 days of enteral nutrition (D7) on visual analog scale (VAS), stool frequency, and 24-hour steatorrhea/creatorrhea. Outcome was evaluated by weight loss, length of hospital stay, and infection rate. Results were calculated as mean +/- SEM, t-test, or chi2. Patients of the 2 groups were comparable in terms of age, gender, and severity. Tolerance was good in both groups (semi-elemental vs polymeric: VAS, 7.4 +/- 0.6 vs 7.1 +/- 0.6, not significant (NS); number of stools per 24 hours, 1.7 +/- 0.4 vs 1.8 +/- 0.4, NS). Steatorrhea and creatorrhea were lower than normal in both groups. In semi-elemental group, the length of hospital stay was shorter (23 +/- 2 vs 27 +/- 1, p = .006) and weight loss was less marked (1 +/- 1 vs 2 +/- 0, p = .01). One patient in semi-elemental group and 3 patients in polymeric group developed an infection (NS). Semi-elemental and polymeric nutrition are very well tolerated in patients with acute pancreatitis. Nutrition with a semi-elemental formula supports the hypothesis of a more favorable clinical course than nutrition with a polymeric formula, but this conclusion needs to be established in larger adequately powered clinical trials.

Nanocomposite polymeric materials for high density optical storage

NASA Astrophysics Data System (ADS)

Criante, L.; Castagna, R.; Vita, F.; Lucchetta, D. E.; Simoni, F.

2009-02-01

We report the results of an extended investigation performed on composite polymeric materials with the aim of obtaining compounds suitable for holographic recording. In order to investigate the material properties a characterization of holographic reflection gratings at different writing wavelength (514.5, 457 and 405 nm) has been performed. The volume grating presents high diffraction efficiency (>60%), high sensitivity (>103 cm J-1) and refractive index modulation Δn≈0.01 even for writing wavelength in the blue range. We show that following a strategy of two basic components leading to phase separation during the photopolymerization process, most of the requirements for holographic data storage are achieved. The one that needs further improvement concerns long term mechanical stability.

Modeling and sensitivity analysis of mass transfer in active multilayer polymeric film for food applications

NASA Astrophysics Data System (ADS)

Bedane, T.; Di Maio, L.; Scarfato, P.; Incarnato, L.; Marra, F.

2015-12-01

The barrier performance of multilayer polymeric films for food applications has been significantly improved by incorporating oxygen scavenging materials. The scavenging activity depends on parameters such as diffusion coefficient, solubility, concentration of scavenger loaded and the number of available reactive sites. These parameters influence the barrier performance of the film in different ways. Virtualization of the process is useful to characterize, design and optimize the barrier performance based on physical configuration of the films. Also, the knowledge of values of parameters is important to predict the performances. Inverse modeling and sensitivity analysis are sole way to find reasonable values of poorly defined, unmeasured parameters and to analyze the most influencing parameters. Thus, the objective of this work was to develop a model to predict barrier properties of multilayer film incorporated with reactive layers and to analyze and characterize their performances. Polymeric film based on three layers of Polyethylene terephthalate (PET), with a core reactive layer, at different thickness configurations was considered in the model. A one dimensional diffusion equation with reaction was solved numerically to predict the concentration of oxygen diffused into the polymer taking into account the reactive ability of the core layer. The model was solved using commercial software for different film layer configurations and sensitivity analysis based on inverse modeling was carried out to understand the effect of physical parameters. The results have shown that the use of sensitivity analysis can provide physical understanding of the parameters which highly affect the gas permeation into the film. Solubility and the number of available reactive sites were the factors mainly influencing the barrier performance of three layered polymeric film. Multilayer films slightly modified the steady transport properties in comparison to net PET, giving a small reduction in the permeability and oxygen transfer rate values. Scavenging capacity of the multilayer film increased linearly with the increase of the reactive layer thickness and the oxygen absorption reaction at short times decreased proportionally with the thickness of the external PET layer.

Modeling and sensitivity analysis of mass transfer in active multilayer polymeric film for food applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bedane, T.; Di Maio, L.; Scarfato, P.

The barrier performance of multilayer polymeric films for food applications has been significantly improved by incorporating oxygen scavenging materials. The scavenging activity depends on parameters such as diffusion coefficient, solubility, concentration of scavenger loaded and the number of available reactive sites. These parameters influence the barrier performance of the film in different ways. Virtualization of the process is useful to characterize, design and optimize the barrier performance based on physical configuration of the films. Also, the knowledge of values of parameters is important to predict the performances. Inverse modeling and sensitivity analysis are sole way to find reasonable values ofmore » poorly defined, unmeasured parameters and to analyze the most influencing parameters. Thus, the objective of this work was to develop a model to predict barrier properties of multilayer film incorporated with reactive layers and to analyze and characterize their performances. Polymeric film based on three layers of Polyethylene terephthalate (PET), with a core reactive layer, at different thickness configurations was considered in the model. A one dimensional diffusion equation with reaction was solved numerically to predict the concentration of oxygen diffused into the polymer taking into account the reactive ability of the core layer. The model was solved using commercial software for different film layer configurations and sensitivity analysis based on inverse modeling was carried out to understand the effect of physical parameters. The results have shown that the use of sensitivity analysis can provide physical understanding of the parameters which highly affect the gas permeation into the film. Solubility and the number of available reactive sites were the factors mainly influencing the barrier performance of three layered polymeric film. Multilayer films slightly modified the steady transport properties in comparison to net PET, giving a small reduction in the permeability and oxygen transfer rate values. Scavenging capacity of the multilayer film increased linearly with the increase of the reactive layer thickness and the oxygen absorption reaction at short times decreased proportionally with the thickness of the external PET layer.« less

Improvement in glucose biosensing response of electrochemically grown polypyrrole nanotubes by incorporating crosslinked glucose oxidase.

PubMed

Palod, Pragya Agar; Singh, Vipul

2015-10-01

In this paper a novel enzymatic glucose biosensor has been reported in which platinum coated alumina membranes (Anodisc™s) have been employed as templates for the growth of polypyrrole (PPy) nanotube arrays using electrochemical polymerization. The PPy nanotube arrays were grown on Anodisc™s of pore diameter 100 nm using potentiostatic electropolymerization. In order to optimize the polymerization time, immobilization of glucose oxidase (GOx) was first performed using physical adsorption followed by measuring its biosensing response which was examined amperometrically for increasing concentrations of glucose. In order to further improve the sensing performance of the biosensor fabricated for optimum polymerization duration, enzyme immobilization was carried out using cross-linking with glutaraldehyde and bovine serum albumin (BSA). Approximately six fold enhancement in the sensitivity was observed in the fabricated electrodes. The biosensors also showed a wide range of linear operation (0.2-13 mM), limit of detection of 50 μM glucose concentration, excellent selectivity for glucose, notable reliability for real sample detection and substantially improved shelf life. Copyright © 2015 Elsevier B.V. All rights reserved.

Conducting polymer nanowire arrays for high performance supercapacitors.

PubMed

Wang, Kai; Wu, Haiping; Meng, Yuena; Wei, Zhixiang

2014-01-15

This Review provides a brief summary of the most recent research developments in the fabrication and application of one-dimensional ordered conducting polymers nanostructure (especially nanowire arrays) and their composites as electrodes for supercapacitors. By controlling the nucleation and growth process of polymerization, aligned conducting polymer nanowire arrays and their composites with nano-carbon materials can be prepared by employing in situ chemical polymerization or electrochemical polymerization without a template. This kind of nanostructure (such as polypyrrole and polyaniline nanowire arrays) possesses high capacitance, superior rate capability ascribed to large electrochemical surface, and an optimal ion diffusion path in the ordered nanowire structure, which is proved to be an ideal electrode material for high performance supercapacitors. Furthermore, flexible, micro-scale, threadlike, and multifunctional supercapacitors are introduced based on conducting polyaniline nanowire arrays and their composites. These prototypes of supercapacitors utilize the high flexibility, good processability, and large capacitance of conducting polymers, which efficiently extend the usage of supercapacitors in various situations, and even for a complicated integration system of different electronic devices. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Preparation, Characterization and Performances of Powdered Polycarboxylate Superplasticizer with Bulk Polymerization.

PubMed

Liu, Xiao; Wang, Ziming; Zheng, Yunsheng; Cui, Suping; Lan, Mingzhang; Li, Huiqun; Zhu, Jie; Liang, Xu

2014-08-29

A polycarboxylate superplasticizer (PCE) was synthesized in a non-solvent system with bulk polymerization and then was pulverized into powdered form to achieve a rapid transportation and convenient preparation. PCE synthesized by using isopentenyl polyethylene glycol (TPEG) or isobutenyl polyethylene glycol (IPEG) as a macromonomer exhibited the best fluidities and retaining properties at 80 °C and 75 °C, respectively. Besides, azobisisobutyronitrile (AIBN) was suitable as an initiator, and the fumaric acid was suitable as the third monomer. The test results of ¹H nuclear magnetic resonance (¹H NMR) confirmed the occurrences of polymerization, and the measurement results of molecular weight and distribution showed that PCE molecular weight characteristics were in accordance with their fluidity properties in cement paste. The application performances in cement showed that PCEs with the best paste fluidity retentions had the longest final setting time and the shortest setting time interval, and the PCEs with good fluidity properties can obviously delay the hydration process and lower the hydration heat. Accordingly, this is a novel, energy-saving and economical method to prepare powdered PCE in the field of concrete admixtures.

Preparation, Characterization and Performances of Powdered Polycarboxylate Superplasticizer with Bulk Polymerization

PubMed Central

Liu, Xiao; Wang, Ziming; Zheng, Yunsheng; Cui, Suping; Lan, Mingzhang; Li, Huiqun; Zhu, Jie; Liang, Xu

2014-01-01

A polycarboxylate superplasticizer (PCE) was synthesized in a non-solvent system with bulk polymerization and then was pulverized into powdered form to achieve a rapid transportation and convenient preparation. PCE synthesized by using isopentenyl polyethylene glycol (TPEG) or isobutenyl polyethylene glycol (IPEG) as a macromonomer exhibited the best fluidities and retaining properties at 80 °C and 75 °C, respectively. Besides, azobisisobutyronitrile (AIBN) was suitable as an initiator, and the fumaric acid was suitable as the third monomer. The test results of 1H nuclear magnetic resonance (1H NMR) confirmed the occurrences of polymerization, and the measurement results of molecular weight and distribution showed that PCE molecular weight characteristics were in accordance with their fluidity properties in cement paste. The application performances in cement showed that PCEs with the best paste fluidity retentions had the longest final setting time and the shortest setting time interval, and the PCEs with good fluidity properties can obviously delay the hydration process and lower the hydration heat. Accordingly, this is a novel, energy-saving and economical method to prepare powdered PCE in the field of concrete admixtures. PMID:28788184

Characterization of polymerized liposomes using a combination of dc and cyclical electrical field-flow fractionation.

PubMed

Sant, Himanshu J; Chakravarty, Siddharth; Merugu, Srinivas; Ferguson, Colin G; Gale, Bruce K

2012-10-02

Characterization of polymerized liposomes (PolyPIPosomes) was carried out using a combination of normal dc electrical field-flow fractionation and cyclical electrical field-flow fractionation (CyElFFF) as an analytical technique. The constant nature of the carrier fluid and channel configuration for this technique eliminates many variables associated with multidimensional analysis. CyElFFF uses an oscillating field to induce separation and is performed in the same channel as standard dc electrical field-flow fractionation separation. Theory and experimental methods to characterize nanoparticles in terms of their sizes and electrophoretic mobilities are discussed in this paper. Polystyrene nanoparticles are used for system calibration and characterization of the separation performance, whereas polymerized liposomes are used to demonstrate the applicability of the system to biomedical samples. This paper is also the first to report separation and a higher effective field when CyElFFF is operated at very low applied voltages. The technique is shown to have the ability to quantify both particle size and electrophoretic mobility distributions for colloidal polystyrene nanoparticles and PolyPIPosomes.

Surface grafting of Eu3+ 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.

Development and validation of an HPLC method to quantify camptothecin in polymeric nanocapsule suspensions.

PubMed

Granada, Andréa; Murakami, Fabio S; Sartori, Tatiane; Lemos-Senna, Elenara; Silva, Marcos A S

2008-01-01

A simple, rapid, and sensitive reversed-phase column high-performance liquid chromatographic method was developed and validated to quantify camptothecin (CPT) in polymeric nanocapsule suspensions. The chromatographic separation was performed on a Supelcosil LC-18 column (15 cm x 4.6 mm id, 5 microm) using a mobile phase consisting of methanol-10 mM KH2PO4 (60 + 40, v/v; pH 2.8) at a flow rate of 1.0 mL/min and ultraviolet detection at 254 nm. The calibration graph was linear from 0.5 to 3.0 microg/mL with a correlation coefficient of 0.9979, and the limit of quantitation was 0.35 microg/mL. The assay recovery ranged from 97.3 to 105.0%. The intraday and interday relative standard deviation values were < 5.0%. The validation results confirmed that the developed method is specific, linear, accurate, and precise for its intended use. The current method was successfully applied to the evaluation of CPT entrapment efficiency and drug content in polymeric nanocapsule suspensions during the early stage of formulation development.

Polymeric micelles for ocular drug delivery: From structural frameworks to recent preclinical studies.

PubMed

Mandal, Abhirup; Bisht, Rohit; Rupenthal, Ilva D; Mitra, Ashim K

2017-02-28

Effective intraocular drug delivery poses a major challenge due to the presence of various elimination mechanisms and physiological barriers that result in low ocular bioavailability after topical application. Over the past decades, polymeric micelles have emerged as one of the most promising drug delivery platforms for the management of ocular diseases affecting the anterior (dry eye syndrome) and posterior (age-related macular degeneration, diabetic retinopathy and glaucoma) segments of the eye. Promising preclinical efficacy results from both in-vitro and in-vivo animal studies have led to their steady progression through clinical trials. The mucoadhesive nature of these polymeric micelles results in enhanced contact with the ocular surface while their small size allows better tissue penetration. Most importantly, being highly water soluble, these polymeric micelles generate clear aqueous solutions which allows easy application in the form of eye drops without any vision interference. Enhanced stability, larger cargo capacity, non-toxicity, ease of surface modification and controlled drug release are additional advantages with polymeric micelles. Finally, simple and cost effective fabrication techniques render their industrial acceptance relatively high. This review summarizes structural frameworks, methods of preparation, physicochemical properties, patented inventions and recent advances of these micelles as effective carriers for ocular drug delivery highlighting their performance in preclinical studies. Copyright © 2017 Elsevier B.V. All rights reserved.

Evaluation of microhardness, surface roughness, and wear behavior of different types of resin composites polymerized with two different light sources.

PubMed

Topcu, Fulya Toksoy; Erdemir, Ugur; Sahinkesen, Gunes; Yildiz, Esra; Uslan, Ibrahim; Acikel, Cengizhan

2010-02-01

The microhardness, surface roughness and wear resistance of different types of resin composites, polymerized by a Quartz Tungsten Halogen (QTH) or Light Emitting Diode (LED) light curing units (LCU) were evaluated in this in vitro study. Cylindrical blocks were prepared from composites (8 mm in diameter, and 2 mm in thickness) and polymerized by a LED or a QTH LCU. Vickers hardness was measured on the top and bottom surfaces of the specimens. Surface roughness was measured with a surface profilometer on the top of the specimens. For the wear test, specimens were tested in a conventional pin-on-disc tribology machine under 15 N loads. The statistical analyses were performed by one-way analysis of variance (ANOVA) and t-tests, including the Bonferroni correction. Nanocomposite material Clearfil Majesty Posterior showed the highest hardness values in all polymerization types at the top and bottom surfaces (p < 0.05). Microhybrid Clearfil APX and hybrid Quixfil composites demonstrated the greatest surface roughness. Wear resistance of Clearfil Majesty Posterior was found to be the highest among the other tested resin composites. The results indicated that Clearfil Majesty Posterior demonstrated higher microhardness, less surface roughness, and higher wear resistance when compared with the other tested materials for both polymerization types.

Polymeric quantum mechanics and the zeros of the Riemann zeta function

NASA Astrophysics Data System (ADS)

Berra-Montiel, Jasel; Molgado, Alberto

We analyze the Berry-Keating model and the Sierra and Rodríguez-Laguna Hamiltonian within the polymeric quantization formalism. By using the polymer representation, we obtain for both models, the associated polymeric quantum Hamiltonians and the corresponding stationary wave functions. The self-adjointness condition provides a proper domain for the Hamiltonian operator and the energy spectrum, which turned out to be dependent on an introduced scale parameter. By performing a counting of semiclassical states, we prove that the polymer representation reproduces the smooth part of the Riemann-von Mangoldt formula, and also introduces a correction depending on the energy and the scale parameter. This may shed some light on the understanding of the fluctuation behavior of the zeros of the Riemann function from a purely quantum point of view.

Fabrication of submicron proteinaceous structures by direct laser writing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serien, Daniela; Takeuchi, Shoji, E-mail: takeuchi@iis.u-tokyo.ac.jp; ERATO Takeuchi Biohybrid Innovation Project, Japan Science and Technology Agency, 4-6-1 Komaba, Meguro-ku, 153-8505 Tokyo

In this paper, we provide a characterization of truly free-standing proteinaceous structures with submicron feature sizes depending on the fabrication conditions by model-based analysis. Protein cross-linking of bovine serum albumin is performed by direct laser writing and two-photon excitation of flavin adenine dinucleotide. We analyze the obtainable fabrication resolution and required threshold energy for polymerization. The applied polymerization model allows prediction of fabrication conditions and resulting fabrication size, alleviating the application of proteinaceous structure fabrication.

Processable high temperature resistant addition type polyimide laminating resins

NASA Technical Reports Server (NTRS)

Serafini, T. T.; Delvigs, P.

1973-01-01

Basic studies that were performed using model compounds to elucidate the polymerization mechanism of the so-called addition-type (A-type) polyimides are reviewed. The fabrication and properties of polyimide/graphite fiber composites using A-type polyimide prepolymers as the matrix are also reviewed. An alternate method for preparing processable A-type polyimides by means of in situ polymerization of monomer reactants (PMR) on the fiber reinforcement is described. The elevated temperature properties of A-type PMR/graphite fiber composites are also presented.

Frontal Polymerization in Microgravity Summary of Research

NASA Technical Reports Server (NTRS)

Pojman, John A.

2002-01-01

The project began with frontal polymerization (FP). We studied many aspects of FP on the ground and performed two successful weeks of flying on the KC-135. The project evolved into the current flight investigation, Transient Interfacial Phenomena in Miscible Polymer Systems (TIPMPS), as we recognized that an essential question could best be studied using a non-frontal approach. We present detailed results from our ground-based work on FP, KC-135 results and the background, justification and numerical work for the TIPMPS project.

Chiral separation of norlaudanosoline, laudanosoline, laudanosine, chlorthalidone, and three benzoin derivatives using amino acid based molecular micelles.

PubMed

Billiot, Fereshteh H; Billiot, Eugene J; Ng, Yuen Kwun; Warner, Isiah M

2006-02-01

In this study, 18 polymeric single amino acid and dipeptide surfactants are examined, and their performances, in terms of enantioselectivity, are compared for norlaudanosoline, laudanosoline, laudanosine, chlorthalidone, benzoin, benzoin methyl, and benzoin ethyl enantiomers. Several aspects of amino acid-based polymeric surfactants including comparison of single amino acid versus dipeptide, amino acid order, steric effect, and effect of the position of the chiral center of dipeptide surfactants on the chiral selectivity of these optically active compounds are discussed.

Microporous ceramic coated separators with superior wettability for enhancing the electrochemical performance of sodium-ion batteries

NASA Astrophysics Data System (ADS)

Suharto, Yustian; Lee, Yongho; Yu, Ji-Sang; Choi, Wonchang; Kim, Ki Jae

2018-02-01

Finding an alternative to glass fiber (GF) separators is a crucial factor for the fast commercialization of sodium-ion batteries (SIBs), because GF separators are too thick for use in SIBs, thereby decreasing the volumetric and gravimetric energy density. Here we propose a microporous composite separator prepared by introducing a polymeric coating layer of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP co-polymer) with ZrO2 nanoparticles to a polyethylene (PE) separator. The coated separator efficiently enhances the cell performance of SIBs. The ZrO2 nanoparticles, finely dispersed on the polymeric coating layer, induce the formation of many micropores on the polymeric coating layer, suggesting that micropore formation on the coating layer renders the composite separator more open in structure. An ethylene carbonate/propylene carbonate liquid electrolyte for SIBs is not absorbed by PE separators even after 1 h of electrolyte droplet testing, while the proposed separator with many micropores is completely wetted by the electrolyte. Sodium ion migration across the composite separator is therefore effectively enhanced by the formation of ion transfer pathways, which improve ionic conductivity. As a result, the microporous composite separator affords stable cycle performances and excellent specific capacity retention (95.8%) after 50 cycles, comparable to those offered by a SIB with a GF separator.

Rapid analysis of ultraviolet filters using dispersive liquid-liquid microextraction coupled to headspace gas chromatography and mass spectrometry.

PubMed

Pierson, Stephen A; Trujillo-Rodríguez, María J; Anderson, Jared L

2018-05-29

An ionic-liquid-based in situ dispersive liquid-liquid microextraction method coupled to headspace gas chromatography and mass spectrometry was developed for the rapid analysis of ultraviolet filters. The chemical structures of five ionic liquids were specifically designed to incorporate various functional groups for the favorable extraction of the target analytes. Extraction parameters including ionic liquid mass, molar ratio of ionic liquid to metathesis reagent, vortex time, ionic strength, pH, and total sample volume were studied and optimized. The effect of the headspace temperature and volume during the headspace sampling step was also evaluated to increase the sensitivity of the method. The optimized procedure is fast as it only required ∼7-10 min per extraction and allowed for multiple extractions to be performed simultaneously. In addition, the method exhibited high precision, good linearity, and low limits of detection for six ultraviolet filters in aqueous samples. The developed method was applied to both pool and lake water samples attaining acceptable relative recovery values. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Selective sorption of lead, cadmium and zinc ions by a polymeric cation exchanger containing nano-Zr(HPO3S)2.

PubMed

Zhang, Qingrui; Pan, Bingcai; Pan, Bingjun; Zhang, Weiming; Jia, Kun; Zhang, Quanxing

2008-06-01

A novel polymeric hybrid sorbent, namely ZrPS-001, was fabricated for enhanced sorption of heavy metal ions by impregnating Zr(HPO3S)2 (i.e., ZrPS) nanoparticles within a porous polymeric cation exchanger D-001. The immobilized negatively charged groups bound to the polymeric matrix D-001 would result in preconcentration and permeation enhancement of target metal ions prior to sequestration, and ZrPS nanoparticles are expected to sequester heavy metals selectively through an ion-exchange process. Highly effective sequestration of lead, cadmium, and zinc ions from aqueous solution can be achieved by ZrPS-001 even in the presence of competing calcium ion at concentration several orders of magnitude greater than the target species. The exhausted ZrPS-001 beads are amenable to regeneration with 6 M HCI solution for repeated use without any significant capacity loss. Fixed-bed column treatment of simulated waters containing heavy metals at high or trace levels was also performed. The content of heavy metals in treated effluent approached or met the WHO drinking water standard.

Direct laser writing of synthetic poly(amino acid) hydrogels and poly(ethylene glycol) diacrylates by two-photon polymerization.

PubMed

Käpylä, Elli; Sedlačík, Tomáš; Aydogan, Dogu Baran; Viitanen, Jouko; Rypáček, František; Kellomäki, Minna

2014-10-01

The additive manufacturing technique of direct laser writing by two-photon polymerization (2PP-DLW) enables the fabrication of three-dimensional microstructures with superior accuracy and flexibility. When combined with biomimetic hydrogel materials, 2PP-DLW can be used to recreate the microarchitectures of the extracellular matrix. However, there are currently only a limited number of hydrogels applicable for 2PP-DLW. In order to widen the selection of synthetic biodegradable hydrogels, in this work we studied the 2PP-DLW of methacryloylated and acryloylated poly(α-amino acid)s (poly(AA)s). The performance of these materials was compared to widely used poly(ethylene glycol) diacrylates (PEGdas) in terms of polymerization and damage thresholds, voxel size, line width, post-polymerization swelling and deformation. We found that both methacryloylated and acryloylated poly(AA) hydrogels are suitable to 2PP-DLW with a wider processing window than PEGdas. The poly(AA) with the highest degree of acryloylation showed the greatest potential for 3D microfabrication. Copyright © 2014 Elsevier B.V. All rights reserved.

Microfluidic-Assisted Production of Size-Controlled Superparamagnetic Iron Oxide Nanoparticles-Loaded Poly(methyl methacrylate) Nanohybrids.

PubMed

Ding, Shukai; Attia, Mohamed F; Wallyn, Justine; Taddei, Chiara; Serra, Christophe A; Anton, Nicolas; Kassem, Mohamad; Schmutz, Marc; Er-Rafik, Meriem; Messaddeq, Nadia; Collard, Alexandre; Yu, Wei; Giordano, Michele; Vandamme, Thierry F

2018-02-06

In this paper, superparamagnetic iron oxide nanoparticles (SPIONs, around 6 nm) encapsulated in poly(methyl methacrylate) nanoparticles (PMMA NPs) with controlled sizes ranging from 100 to 200 nm have been successfully produced. The hybrid polymeric NPs were prepared following two different methods: (1) nanoprecipitation and (2) nanoemulsification-evaporation. These two methods were implemented in two different microprocesses based on the use of an impact jet micromixer and an elongational-flow microemulsifier. SPIONs-loaded PMMA NPs synthesized by the two methods presented completely different physicochemical properties. The polymeric NPs prepared with the micromixer-assisted nanoprecipitation method showed a heterogeneous dispersion of SPIONs inside the polymer matrix, an encapsulation efficiency close to 100 wt %, and an irregular shape. In contrast, the polymeric NPs prepared with the microfluidic-assisted nanoemulsification-evaporation method showed a homogeneous dispersion, an almost complete encapsulation, and a spherical shape. The properties of the polymeric NPs have been characterized by dynamic light scattering, thermogravimetric analysis, and transmission electron microscope. In vitro cytotoxicity assays were also performed on the nanohybrids and pure PMMA NPs.

Grafting of molecularly imprinted polymer to porous polyethylene filtration membranes by plasma polymerization.

PubMed

Cowieson, D; Piletska, E; Moczko, E; Piletsky, S

2013-08-01

An application of plasma-induced grafting of polyethylene membranes with a thin layer of molecularly imprinted polymer (MIP) was presented. High-density polyethylene (HDPE) membranes, "Vyon," were used as a substrate for plasma grafting modification. The herbicide atrazine, one of the most popular targets of the molecular imprinting, was chosen as a template. The parameters of the plasma treatment were optimized in order to achieve a good balance between polymerization and ablation processes. Modified HDPE membranes were characterized, and the presence of the grafted polymeric layer was confirmed based on the observed weight gain, pore size measurements, and infrared spectrometry. Since there was no significant change in the porosity of the modified membranes, it was assumed that only a thin layer of the polymer was introduced on the surface. The experiments on the re-binding of the template atrazine to the membranes modified with MIP and blank polymers were performed. HDPE membranes which were grafted with polymer using continuous plasma polymerization demonstrated the best result which was expressed in an imprinted factor equal to 3, suggesting that molecular imprinting was successfully achieved.