Copolymerization of terephthalaldehyde with pyrrole, indole and carbazole gives microporous POFs functionalized with unpaired electrons
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bio-inspired↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Copolymerization of CO 2 and meso epoxides using enantioselective β-diiminate catalysts: a route to highly isotactic polycarbonates
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Ellis, W. Chadwick↗
One-pot single-step copolymerization of aromatic trifluorovinyl ethers toward perfluorocyclobutyl (PFCB) segmented copolymers
A segmented PFCB aryl ether copolymer was synthesized directly from two aryl TFVE monomers having different reactivities and the blocky copolymer structure was confirmed by 19 F NMR spectroscopic data.
Park, Jiyoung↗
Initiation precursors and initiators in laser-induced copolymerization of styrene and maleic anhydride in acetone
The initiation step of photopolymerized styrene/maleic anhydride copolymer was investigated at 365 nm. UV absorption measurements provide decisive evidence that the styrene/maleic anhydride charge transfer complex is the sole absorbing species; however, key laser experiments suggest intermediate reactions lead to a monoradical initiating species. A mechanism for the photoinitiation step of the copolymer is proposed.
Miner, Gilda A.↗
Relative Rates for Plasma Homo- and Copolymerizations of Olefins in a Homologous Series of Fluorinated Ethylenes
The relative rates of plasma (co)polymerizations of ethylene, vinyl fluoride, vinylidene fluoride, trifluoroethylene and tetrafluoroethylene (VF(sub x); x = 0-4, respectively) were determined in an rf, capacitively coupled, tubular reactor with external electrodes using identical plasma parameters. The averages of deposition rates obtained by both microgravimetry and ellipsometry were plotted versus the F/C ratios of the monomers or monomer blends. The deposition rates for VF(sub x)(x = 1-3) and 20 monomer blends were all located above a straight line joining the rates for VF(sub 0) and VF(sub 4), following a concave-downward plot of deposition rate versus F/C ratio similar to that reported previously for VF(sub 0)/VF(sub 4) blends. The deposition rates for VF(sub m)/VF(sub n) blends (m = 3 or 4; n = 0-2) were all greater than expected for non-interacting monomers; those for VF(sub 0)/VF(sub 2) and VF(sub 1)/VF(sub 2) blends were all lower than expected; while those for VF(sub 0)/VF(sub 1) and VF(sub 3)/VF(sub 4) blends fen on a straightline plot versus F/C ratio, indicative of apparent non-interaction between monomers. The mechanisms for plasma (co)polymerizations of VF(sub x) monomers responsible for the wide range of relative deposition rates remain to be elucidated.
Golub, Morton A.↗
Random copolymerization of macromonomers as a versatile strategy to synthesize mixed-graft block copolymers
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99 GENERAL AND MISCELLANEOUS↗
Synthesis and Characterization of Chitosan-Grafted-Poly(2-Hydroxyaniline) Microstructures for Water Decontamination
Chitosan as a biopolymer, biodegradable, safe, non-toxic and widely abundant in nature was grafted with poly(2-hydroxyaniline) (P2-HA) through aqueous chemical oxidative copolymerization using ammonium persulphate in acetic acid medium. The grafting conditions were studied by varying grafting parameters. The effect of oxidant, 2-hydroxyaniline (2-HA) and acetic acid concentrations on the rate of copolymerization was studied. The synthesized graft characterized using UV–Vis, FTIR, TGA, XRD, and scanning electron microscope and compared with chitosan and P2-HA. The grafting enhances the thermal properties of chitosan. The effect of temperature on the rate of grafting copolymerization reaction was studied. The apparent activation energy (Ea) of the copolymerization reaction found to be 21.1116 kJ/mol. Also, ΔH{sup *} and ΔS{sup *}, were calculated and found to 22.8630 kJ/mol and −109.4290 J/mol K respectively. The mechanism of the grafting copolymerization reaction discussed. Chitosan, P2-HA and chitosan-graft-P2-HA used for the removal of Cr, Fe, Mn, Cu and Zn divalent ions from a contaminated water samples. The adsorption isotherm parameters are given.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions
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 over 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. Lastly, controlled copolymerization therefore expands the parameter space for molecular and materials design.
36 MATERIALS SCIENCE↗
Introducing Low-Cost Pyrazine Unit into Terpolymer Enables High-Performance Polymer Solar Cells with Efficiency of 18.23%
Recently, a random ternary copolymerization strategy has become a promising and efficient approach to develop high-performance polymer donors for polymer solar cells (PSCs). Here, in this study, a low-cost electron-withdrawing unit, 2,5-bis(4-(2-ethylhexyl)thiophen-2-yl)pyrazine (PZ-T), is incorporated into the polymer backbone of PM6 as the third component, and three D-A 1 -D-A 2 type terpolymers PMZ-10, PMZ-20, and PMZ-30 are synthesized by the random copolymerization strategy, with the PZ-T proportion of 10%, 20%, and 30%, respectively. The terpolymers exhibit downshifted highest occupied molecular orbital energy levels than PM6, which is beneficial for obtaining higher open-circuit voltage (V oc ) of the PSCs with the polymer as a donor. Importantly, the PSCs based on PMZ-10:Y6 demonstrate efficient exciton dissociation, higher and balanced electron/hole mobilities, desirable aggregation, and high power conversion efficiency of 18.23%, which is the highest efficiency among the terpolymer-based PSCs so far. The results indicate that the ternary copolymerization strategy with PZ-T as the second A-unit is an efficient approach to further improve the photovoltaic performance and reduce the synthetic cost of the D-A copolymer donors.
36 MATERIALS SCIENCE↗
Supramolecular Arene‐Perfluoroarene Assembly Enhances Photoiniferter Polymerization Kinetics
Ultra-high-molecular-weight (UHMW, >106 Da) polymers have unique thermomechanical properties due to their large number of physical entanglements. Producing UHMW styrenic polymers is challenging because of their prohibitively slow homopolymerization kinetics. In this report, we show that alternating photoiniferter copolymerization between methoxy-functionalized styrenic monomers and pentafluorostyrene can circumvent this limitation under conditions where arene–perfluoroarene (AP) interactions contribute to favorable monomer association and accelerate copolymerization. Increasing methoxy substitution on the styrene arene ring leads to pronounced rate enhancements that correlate with electronic complementarity between the styrenic comonomers. Density functional theory calculations reveal increasingly favorable AP interaction energies across the series, consistent with monomer association contributing to faster propagation. The result is up to 2000% enhancement in propagation rate in copolymerizations compared to styrene homopolymerization. Despite these rate enhancements, the resulting materials retain broadly similar glass-transition temperatures and network-like thermomechanical behavior, with only modest softening across the series. Here, we then leverage the approach to produce UHMW trialkoxystyrene copolymers bearing sterically encumbered pendants, which are ultrasoft (Young's modulus of 8 kPa) and highly extensible (560%). These results establish that designed supramolecular association between styrenics is a powerful tool for controlling reactivity in radical polymerization and generating otherwise difficult-to-obtain materials.
Marquez, Joshua D. [University of Florida, Gainesv↗
Laccase-mediated synthesis of lignin-core hyperbranched copolymers
Lignin, one of the major chemical constituents of woody biomass, is the second most abundant biopolymer found in nature. The pulp and paper industry has long produced lignin on the scale of millions of tons annually as a by-product of the pulping process, and the dawn of cellulosic ethanol production has further contributed to this amount. Historically, lignin has been perceived as a waste material and burned as a fuel for the pulping process. But, recent research has been geared toward developing cost-effective technologies to convert lignin into valuable commodities. Attributing to the polyphenolic structure of lignin, enzymatic modification of its surface using laccases (benzenediol:oxygen oxidoreductases, EC 1.10.3.2) has demonstrated to be highly successful. The current study aims at developing lignin-core hyperbranched copolymers via the laccase-assisted copolymerization of kraft lignin with methylhydroquinone and a trithiol. Based on the physical properties of the resulting material, it is likely that crosslinking reactions have taken place during the drying process to produce a copolymeric network rather than discrete hyperbranched copolymers, with NMR data providing evidence of covalent bonding between monomers. A preliminary thermal analysis data reveals that the copolymeric material possesses a moderate glass transition temperature and exhibits good thermostability, thus may have potential application as a lignin-based thermoplastic. Scanning electron microscopy images confirm the smooth, glossy surface of the material and that it is densely packed. Our results are a sustainable, ecofriendly, economic method to create an exciting novel biomaterial from a renewable feedstock while further enhancing lignin valorization.
09 BIOMASS FUELS↗
Synthesis and Characterization of Lignin-grafted-poly(ε-caprolactone) from Different Biomass Sources
Modification of lignin with poly(ε-caprolactone) is a promising approach to valorize industrial low-value lignins and to advance the bioeconomy. We have synthesized lignin grafted poly(ε-caprolactone) (lignin-g-PCL) copolymers via ring-opening polymerization of ε-caprolactone with different types of lignins of varying botanical sources (G-type pine lignin, S/G-type poplar lignin, and C-type Vanilla seeds lignin) and lignin extraction methods (Kraft and ethanol organosolv pulping). The lignin-g-PCL copolymer showed remarkably improved compatibility and dispersion in acetone, chloroform, and toluene in comparison to non-modified lignins. The structure and thermal properties of the lignin-g-PCL were investigated using Fourier-transform infrared spectroscopy (FTIR), 31 P nuclear magnetic resonance (NMR), 2D heteronuclear single quantum correlation (HSQC) NMR, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Furthermore, we have found that all the technical lignins were reactive to the copolymerization reaction regardless of their plant source and isolation methods. The molecular weights of the synthesized lignin-g-PCL copolymers were positively correlated with the content of aliphatic lignin hydroxyls, suggesting that the copolymerization reaction tends to occur preferentially at the aliphatic hydroxyls rather than the phenolic hydroxyls of lignin. Thermal analyses of the lignin-g-PCL copolymers were studied, and in general, a reduction of melting temperature and crystallinity percentage in comparison to the neat PCL was observed. However, the thermal behavior of lignin-g-PCL copolymers varied depending on the lignin feedstocks employed in the copolymerization reaction.
59 BASIC BIOLOGICAL SCIENCES↗
Methods for polymer synthesis
The present invention provides methods for reducing induction periods in epoxide-CO.sub.2 copolymerizations. In certain embodiments, the methods include the step of contacting an epoxide with CO.sub.2 in the presence of two catalysts: an epoxide hydrolysis catalyst and an epoxide CO.sub.2 copolymerization catalyst. In another aspect, the invention provides catalyst compositions comprising a mixture of an epoxide hydrolysis catalyst and an epoxide CO.sub.2 copolymerization catalyst.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Methods for polymer synthesis
The present invention provides methods for reducing induction periods in epoxide-CO2 copolymerizations. In certain embodiments, the methods include the step of contacting an epoxide with CO2 in the presence of two catalysts: an epoxide hydrolysis catalyst and an epoxide CO2 copolymerization catalyst. In another aspect, the invention provides catalyst compositions comprising a mixture of an epoxide hydrolysis catalyst and an epoxide CO2 copolymerization catalyst.
36 MATERIALS SCIENCE↗
Amorphous fluorinated copolymer gas separation membranes
Membranes having a permselective active layer of a copolymerized perfluorinated monomer and an non-fluorinated alkylvinylester monomer demonstrate superior selective permeability performance for separating gas mixtures compared to membranes of exclusively perfluorinated polymers. Preferred active layer compositions are copolymers of perfluoro-2,2-dimethyl-1,3 dioxole (PDD) copolymerized with an alkylvinyl ester such as vinyl acetate, and vinyl pivalate, and with alkylvinyl esters that are substantially hydrolyzed to provide copolymerized vinyl alcohol functionality. The membranes can have a thin, high diffusion rate, “gutter layer” of a fluorinated polymer highly permeable to nitrogen positioned between the active layer and a porous support layer. A novel copolymer effective in selectively permeable membranes is a copolymer of PDD and an alkylvinyl ester compound having the formula H2C═CHOC(O)R1 in which R1 is a linear or branched alkyl group of from 2 to 5 carbon atoms.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Europium-doped aluminum oxide phosphors as indicators for frontal polymerization dynamics
In this study, we present an inexpensive and practical method that allows the monitoring and visualization of front polymerization, propagation, and dynamics. Commercially available europium-doped aluminum oxide powders were combined with video imaging to visualize free-radical propagating polymer fronts. In order to demonstrate the applicability of this method, frontal copolymerization reactions of propoxylated glycerin triacrylate (EB53), pentaerythritol triacrylate (PETA), and pentaerythritol tetra-acrylate (PETEA) with 1,1-Bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane (Luperox 231®) as an initiator were studied and compared to the results obtained by IR imaging. Systems exhibiting higher filler loading, higher EB53 content, and less acrylated monomers showed a marked decrease in front velocity, while those with more acrylated monomers and higher crosslinking density showed a marked increase in front velocity. Finally, in order to show the potential of the imaging technique, we studied fronts propagating in planar and spherical geometries.
36 MATERIALS SCIENCE↗
Chemically Recyclable Analogs of Styrene–Butadiene Copolymers Enabling Perfectly Linear Ethylene–Styrene Materials with Random Phenyl Distribution
Copolymerization of cyclopentene (CP) and 4-phenylcyclopentene (4PCP) at a full range of comonomer feed ratios is reported using Ru-based ring-opening metathesis polymerization (ROMP) yielding homogeneous copolymers analogous to poly(styrene-ran-1,4-butadiene) and poly(ethylene-ran-styrene) copolymers following hydrogenation under mild conditions. In all cases, total monomer conversions of 86%–92% yielded copolymers with compositions within 4% of monomer feeds. Analysis of equilibrium copolymerization thermodynamics, rarely performed on two cycloolefin monomers with low ring strain energies, provides rational design strategies for negotiating two monomers with different equilibrium monomer concentrations. Inverse-gated decoupled 13 C NMR analysis of dyad sequences on the resulting copolymer microstructures concludes a near-random distribution of comonomer units. The copolymers produced from ROMP have number-average molar masses up to 60 kg mol –1 , moderate dispersities (1.5 ± 0.1), and high trans olefin content (86% ± 2%) while glass-transitions temperatures follow the Fox equation and span the full range between homopolymer extremities of PCP (−96 °C) and P4PCP (17 °C). Unlike most prevulcanized elastomers, these materials undergo facile chemical recycling to monomer, producing complete ring-closing metathesis depolymerization (RCMD) of the polymer back to the CP comonomers. Quantitative olefin hydrogenation produced perfectly linear polyethylene with 4%–16% of the backbone carbons containing a phenyl pendant, analogous to ES copolymers with up to 71.5% w/w styrene units but with random distribution of the aromatic pendants. Thermal properties of these materials are discussed, which span from semicrystalline to amorphous, and with T g values notably less than the reported ES copolymer analogs at similar compositions.
animal feed↗
Synthesis and Reactivity of Palladium(II) Alkyl Complexes that Contain Phosphine-cyclopentanesulfonate Ligands
The synthesis of the phosphine-cyclopentanesulfonate pro-ligands Li/K[2-PPh 2 -cyclopentanesulfonate] (Li/K[2a]), Li/K[2-P(2-OMe-Ph) 2 -cyclopentanesulfonate] (Li/K[2b]), and H[2b], and the corresponding Pd(II) alkyl complexes (κ 2 - P , O -2a)PdMe(pyridine) (3a) and (κ 2 - P , O -2b)PdMe(pyridine) (3b) is described herein. The sulfonate-bridged base-free dimer {(2b)PdMe} 2 (4b) was synthesized by abstraction of pyridine from 3b using B(C 6 F 5 ) 3 . The borane-coordinated base-free dimer [{2b·B(C 6 F 5 ) 3 }PdMe] 2 (5b), in which B(C 6 F 5 ) 3 binds to a sulfonate oxygen, was prepared by addition of 1 equiv of B(C 6 F 5 ) 3 per Pd to 4b or addition of 2 equiv of B(C 6 F 5 ) 3 to 3b. Compounds 3b, 4b, and 5b polymerize ethylene with low activity (up to 210 kg mol –1 h –1 at 250 psi and 80 °C) to linear polyethylene ( M n = 1950–5250 Da) with predominantly internal olefin placements. 3b and 4b copolymerize ethylene with methyl acrylate to linear copolymers that contain up to 11.7 mol % methyl acrylate, which is incorporated as –CH 2 CH(CO 2 Me)CH 2 – (80%) in-chain units and –CH 2 CH(CO 2 Me)Me (8%) and –CH 2 CH=CH(CO 2 Me) (12%) chain-end units. 3b and 4b also copolymerize ethylene with vinyl fluoride to linear copolymers that contain up to 0.41 mol % vinyl fluoride, which is incorporated as –CH 2 CHFCH 2 – (~80%) in-chain units and –CH 2 CF 2 H (7%), –CH 2 CHFCH 3 (5%), and –CH 2 CH 2 F (8%) chain-end units. Complexes 3b and 4b are more stable and active in ethylene polymerization than analogous (PAr 2 - CH 2 CH 2 SO 3 )PdR catalysts, but are less active than analogous (PAr 2 - arene sulfonate)PdR catalysts. Low-temperature NMR studies show that 4b reacts with ethylene below -10 °C to form the ethylene adduct cis - P , R -(2b)PdMe(ethylene) (7b), which undergoes ethylene insertion at 5 °C. DFT calculations for a model (PMe 2 -cyclopentanesulfonate)Pd(Pr)(ethylene) species show that ethylene insertion proceeds by cis - P , R / trans - P , R isomerization followed by migratory insertion, and that the lower activity of 3b and 4b vis-à-vis analogous (PAr 2 -arenesulfonate)PdR catalysts results from a higher barrier for migratory insertion of the trans - P , R isomer.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗