Showing papers on "Vinyl acetate published in 2015"

Poly[(maleic anhydride)-alt-(vinyl acetate)]: A Pure Oxygenic Nonconjugated Macromolecule with Strong Light Emission and Solvatochromic Effect

Abstract: Organic luminescent materials carrying no phenyl rings have attracted much interest from researchers due to their excellent biocompatibility and good biodegradability, which make them available for...

Comparative Study of Different Methods for the Prediction of Drug-Polymer Solubility

Abstract: In this study, a comparison of different methods to predict drug-polymer solubility was carried out on binary systems consisting of five model drugs (paracetamol, chloramphenicol, celecoxib, indomethacin, and felodipine) and polyvinylpyrrolidone/vinyl acetate copolymers (PVP/VA) of different monomer weight ratios. The drug-polymer solubility at 25 °C was predicted using the Flory-Huggins model, from data obtained at elevated temperature using thermal analysis methods based on the recrystallization of a supersaturated amorphous solid dispersion and two variations of the melting point depression method. These predictions were compared with the solubility in the low molecular weight liquid analogues of the PVP/VA copolymer (N-vinylpyrrolidone and vinyl acetate). The predicted solubilities at 25 °C varied considerably depending on the method used. However, the three thermal analysis methods ranked the predicted solubilities in the same order, except for the felodipine-PVP system. Furthermore, the magnitude of the predicted solubilities from the recrystallization method and melting point depression method correlated well with the estimates based on the solubility in the liquid analogues, which suggests that this method can be used as an initial screening tool if a liquid analogue is available. The learnings of this important comparative study provided general guidance for the selection of the most suitable method(s) for the screening of drug-polymer solubility.

Interfacial Interactions and Segmental Dynamics of Poly(vinyl acetate)/Silica Nanocomposites

Abstract: We investigate the interfacial interactions and segmental dynamics of hydrophilic and hydrophobic (calcined) silica nanoparticle (NP) filled poly(vinyl acetate) (PVAc) composites via a combination of Fourier transform infrared spectroscopy (FTIR) and broadband dielectric spectroscopy measurements. For hydrophilic silica NP filled composites, an increase in the amount of bound carbonyl groups with increasing silica loading can be noted due to hydrogen bonding interactions with hydroxyls on the NP surfaces and carbonyl groups of PVAc. It is surprising that the apparent glass transition temperature (Tg) increases very slightly (∼1 K) compared to pure PVAc, but the glass transition process becomes much broader, indicating the existence of a slower relaxation mode. In addition to the bulklike α-relaxation assigned to polymer segments away from the NP surfaces, the nanocomposites also exhibit a slower interfacial α′-relaxation by 3–4 orders of magnitude compared to bulk polymers. However, in the case of hydroph...

Photocatalyst-Free and Blue Light-Induced RAFT Polymerization of Vinyl Acetate at Ambient Temperature.

Abstract: Vinyl acetate is polymerized in the living way under the irradiation of blue light-emitting diodes (LEDs) or sunlight without photocatalyst at ambient temperature. 2-(Ethoxycarbonothioyl)sulfanyl propanoate is exclusively added and acts as initiator and chain transfer agent simultaneously in the current system. Poly(vinyl acetate) with well-regulated molecular weight and narrow molecular weight distribution (Đ < 1.30) is synthesized. Near quantitative end group fidelity of polymer is demonstrated by nuclear magnetic resonance (NMR) and matrix-assisteed laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).

Influence of Processing Conditions on Properties of Poly (Vinyl acetate)/Cellulose Nanocrystal Nanocomposites

Abstract: We investigated how different processing methods affect the morphology and mechanical properties of nanocomposites made from poly(vinyl acetate) (PVAc) and cellulose nanocrystals (CNCs). Homogeneously mixed reference PVAc/CNC nanocomposites of various compositions were first prepared by solution casting. These materials were post-processed by mixing in a roller blade mixer (RBM) or a twin-screw extruder (TSE) and subsequent compression molding. Transmission electron microscopy was used to elucidate the dispersion and size distribution of the CNCs and these data were correlated with the materials' mechanical properties. While RBM processed composites are virtually indistinguishable from the solution-cast reference materials, TSE processing led to mechanical degradation of the CNCs and resulted materials with inferior mechanical properties. Direct RBM mixing of PVAc and CNCs was also explored. This process afforded materials that are much stiffer than the neat matrix, but did not reach the levels of the reference series.

Biobased Poly(lactide)/ethylene-co-vinyl Acetate Thermoplastic Vulcanizates: Morphology Evolution, Superior Properties, and Partial Degradability

Abstract: Partially biobased thermoplastic vulcanizates (TPV) with novel morphology, superior properties and partial degradability were prepared by dynamic cross-link of saturated poly(lactide) and ethylene-co-vinyl acetate (PLA/EVA) blends using 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (AD) as a free radical initiator. EVA showed higher reactivity with free radicals in comparison with PLA, leading to much higher gel content of the EVA phase (Gf-EVA) than that of the PLA phase (Gf-PLA). However, the Gf-PLA increased more steeply at AD content larger than 1 wt % where the reaction of EVA approached to a saturation point. The competing reaction changed the viscosity ratio of the two components (ηPLA/ηEVA) that resulted in a novel morphology evolution of the TPV, i.e., from sea–island-type morphology to phase inversion via a dual-continuous network-like transition and finally cocontinuity again with increasing the AD content. The cross-link and phase inversion considerably enhanced the melt viscosity (η*), elastici...

A well-defined, versatile photoinitiator (salen)Co–CO2CH3 for visible light-initiated living/controlled radical polymerization

Abstract: The control of the polymerization of a wide range of monomers under mild conditions by a single catalyst remains a major challenge in polymer science. We report a versatile, well-defined organocobalt salen complex to control living radical polymerization of different categories of monomers, including acrylates, acrylamides and vinyl acetate, under visible light irradiation at ambient temperature. Both household light and sunlight were effectively applied in the synthesis of polymers with controlled molecular weights and narrow polydispersities. Narrowly dispersed block copolymers (Mw/Mn < 1.2) were obtained under various conditions. The structures of the polymers were analyzed by 1H NMR, 2D NMR, 13C NMR, GPC, MALDI-TOF-MS and isotopic labeling experiments, which showed that the ω and α ends of the polymer chains were capped with (salen)Co and -CO2CH3 segments, respectively, from the photoinitiator (salen)Co-CO2CH3. The ω end was easily functionalized through oxygen insertion followed by hydrolysis from 18O2 to -18OH. This robust system can proceed without any additives, and offers a versatile and green way to produce well-defined homo and block copolymers.

Enhanced Solubility of Polyvinyl Esters in scCO 2 by Means of Vinyl Trifluorobutyrate Monomer

Abstract: The novel monomer, vinyl trifluorobutyrate (VTFBu), when polymerized in a controlled fashion by RAFT/MADIX polymerization with a xanthate transfer agent, yields poly(vinyl ester)s with improved solubility in supercritical carbon dioxide. The thermodynamic parameters controlling the solubility of VTFBu/vinyl acetate statistical copolymers are discussed based on ab initio calculations, glass transition temperatures of the copolymers, and surface tension measurements. The enhanced solubility of this new class of CO2-philic polymer combined with its good chemical stability render it attractive for the preparation of next-generation macromolecular surfactants for the formation of water–scCO2 emulsions.

Synthesis and Free Radical Copolymerization of a Vinyl Monomer from Soybean Oil

Abstract: A one-step method that converts soybean oil into (acryloylamino)ethyl soyate, a new vinyl monomer of free radical polymerization, was developed. The synthesized monomer combines a vinyl double bond (acryloyl functional group) and nonconjugated (isolated) double bonds of fatty acids. The double bond of the acryloyl group is reactive in a free radical chain polymerization that yields linear macromolecules containing isolated double bonds in side chains. Monomer reactivity ratios (r1, r2) in copolymerization of the new soybean oil-based acrylic monomer (SBA) with styrene, methyl methacrylate, and vinyl acetate, as well as the Q–e parameters of the SBA, were determined. The obtained results indicate that copolymerization can be described with the classical Mayo–Lewis equation. In terms of polymerizability, the SBA can be classified as an acrylic monomer. The double bonds of the fatty acid chains remain mainly unaffected during the free radical polymerization. The remaining unsaturated fragments in the side ch...

Bio-based poly(lactide)/ethylene-co-vinyl acetate thermoplastic vulcanizates by dynamic crosslinking: structure vs. property

Abstract: Bio-based thermoplastic vulcanizates (TPV) from poly(lactide) (PLA) and ethylene-co-vinyl acetate rubber (EVA) were fabricated using dicumyl peroxide (DCP) as a curing agent; it is the first time that the application of PLA in elastic materials is demonstrated. A two-stage competing reaction mechanism as a function of peroxide content is revealed via gel analysis. The crosslinking of EVA is dominant at low DCP content (<1 wt%), which levels off when the DCP content exceeds 1 wt%. The gel fractions of the EVA and PLA phases can be tuned by the DCP content and fabrication technique. A desirable phase inversion of the PLA/EVA blends due to selective dynamic curing was monitored by both atomic force microscopy (AFM) and dynamic mechanical analysis (DMA). Consequently, PLA/EVA thermoplastic vulcanizates with high strength, high elongation at break, low tensile set and intermediate hardness were obtained. Moreover, their mechanical properties can be tuned by the DCP content and plasticization. The correlation between their structures and properties was investigated.

Acrylamide modified poly(vinyl alcohol): crystalline and enhanced water solubility

Abstract: Acrylamide (AAm) modified polyvinyl alcohol (PVA) with enhanced water solubility and tunable tacticity and crystallinity was prepared by alcoholysis of vinyl acetate (VAc) and acrylamide copolymers. The chemical structures and performance of VAc–AAm copolymers and AAm-modified PVA were measured by FTIR, UV-vis, XRD, elemental analysis as well as rheometry. FTIR and XRD analysis reveals that AAm units in PVA chain can reduce the stereoregularity effectively, and suppress the crystallinity. And a decreasing linear relationship between crystallinity and AAm mole fractions is observed. Furthermore, the influence of AAm modification on the water solubility of PVA was studied, and a significant enhancement either at low temperature (30 °C) or at high temperature (70 °C) was achieved through AAm modification. Moreover, the rheological investigation suggested that the relative strength of the hydrogen bonding interactions existing between PVA chains was weakened, while those between PVA chains and water molecules, to some extent, were enhanced after AAm modification. The method presented is an easy but promising way to prepare PVA that can have good water solubility even at low temperature while exhibiting high degrees of alcoholysis.

Evaluation of CO2-philicity of poly(vinyl acetate) and poly(vinyl acetate-alt-maleate) copolymers through molecular modeling and dissolution behavior measurement.

Abstract: Multiscale molecular modeling and dissolution behavior measurement were both used to evaluate the factors conclusive on the CO2-philicity of poly(vinyl acetate) (PVAc) homopolymer and poly(vinyl acetate-alt-maleate) copolymers. The ab initio calculated interaction energies of the candidate CO2-philic molecule models with CO2, including vinyl acetate dimer (VAc), dimethyl maleate (DMM), diethyl maleate (DEM), and dibutyl maleate (DBM), showed that VAc was the most CO2-philc segment. However, the cohesive energy density, solubility parameter, Flory–Huggins parameter, and radial distribution functions calculated by using the molecular dynamics simulations for the four polymer and polymer–CO2 systems indicated that poly(VAc-alt-DBM) had the most CO2-philicity. The corresponding polymers were synthesized by using free radical polymerization. The measurement of cloud point pressures of the four polymers in CO2 also demonstrated that poly(VAc-alt-DBM) had the most CO2-philicity. Although copolymerization of male...

Visible-Light-Induced Living Radical Polymerization (LRP) Mediated by (salen)Co(II)/TPO at Ambient Temperature

Abstract: Visible-light-induced living radical polymerization of acrylates (MA, nBA, tBA), acrylamides (DMA, AMO), and vinyl acetate (VAc) at ambient temperature mediated by (salen)Co(II)/TPO was described. Effects of light intensity, feeding ratio of monomer and equivalent of TPO for the polymerization of MA were investigated. Well-defined homopolymers and block polymers with predetermined molecular weight and narrow polydispersity were obtained under mild conditions. The mechanism of the polymerization was proposed based on polymerization behavior and polymer structure analysis. The (salen)Co(II)/TPO system was suitable for both conjugated and unconjugated monomers under mild conditions.

Production of Catalyst-Free Hyperpolarised Ethanol Aqueous Solution via Heterogeneous Hydrogenation with Parahydrogen.

Abstract: An experimental approach for the production of catalyst-free hyperpolarised ethanol solution in water via heterogeneous hydrogenation of vinyl acetate with parahydrogen and the subsequent hydrolysis of ethyl acetate was demonstrated. For an efficient hydrogenation, liquid vinyl acetate was transferred to the gas phase by parahydrogen bubbling and almost completely converted to ethyl acetate with Rh/TiO2 catalyst. Subsequent dissolution of ethyl acetate gas in water containing OH− ions led to the formation of catalyst- and organic solvent-free hyperpolarised ethanol and sodium acetate. These results represent the first demonstration of catalyst- and organic solvent-free hyperpolarised ethanol production achieved by heterogeneous hydrogenation of vinyl acetate vapour with parahydrogen and the subsequent ethyl acetate hydrolysis.

All Poly(ionic liquid)-Based Block Copolymers by Sequential Controlled Radical Copolymerization of Vinylimidazolium Monomers

Abstract: The organometallic-mediated radical polymerization (OMRP) of N-vinyl-3-alkylimidazolium-type monomers, featuring the bis(trifluoromethylsulfonyl)imide counteranion (Tf2N–), in the presence of Co(acac)2 as controlling agent, is reported. Polymerizations of monomers with methyl, ethyl, and butyl substituents are fast, reaching high monomer conversion in ethyl acetate as solvent at 30 °C, and afford structurally well-defined hydrophobic poly(ionic liquid)s (PILs) of N-vinyl type. Block copolymer synthesis is also achieved by sequential OMRP of N-vinyl-3-alkylimidazolium salts carrying different alkyl chains and different counteranions (Tf2N– or Br–). These block copolymerizations are carried out at 30 °C, either under homogeneous solution in methanol or in a biphasic medium consisting of a mixture of ethyl acetate and water. Unprecedented PIL-b-PIL block copolymers are thus prepared under these conditions. However, anion exchange occurs at the early stage of the growth of the second block. Finally, diblock c...

Interception and characterization of catalyst species in rhodium bis(diazaphospholane)-catalyzed hydroformylation of octene, vinyl acetate, allyl cyanide, and 1-phenyl-1,3-butadiene.

Abstract: In the absence of H2, reaction of [Rh(H) (CO)2(BDP)] [BDP = bis(diazaphospholane)] with hydroformylation substrates vinyl acetate, allyl cyanide, 1-octene, and trans-1-phenyl-1,3-butadiene at low temperatures and pressures with passive mixing enables detailed NMR spectroscopic characterization of rhodium acyl and, in some cases, alkyl complexes of these substrates. For trans-1-phenyl-1,3-butadiene, the stable alkyl complex is an η3-allyl complex. Five-coordinate acyl dicarbonyl complexes appear to be thermodynamically preferred over the four-coordinate acyl monocarbonyls at low temperatures and one atmosphere of CO. Under noncatalytic (i.e., no H2 present) reaction conditions, NMR spectroscopy reveals the kinetic and thermodynamic selectivity of linear and branched acyl dicarbonyl formation. Over the range of substrates investigated, the kinetic regioselectivity observed at low temperatures under noncatalytic conditions roughly predicts the regioselectivity observed for catalytic transformations at higher...

Immobilization and characterization of a new regioselective and enantioselective lipase obtained from a metagenomic library.

Abstract: In previous work, a new lipase and its cognate foldase were identified and isolated from a metagenomic library constructed from soil samples contaminated with fat. This new lipase, called LipG9, is a true lipase that shows specific activities that are comparable to those of well-known industrially-used lipases with high activity against long-chain triglycerides. In the present work, LipG9 was co-expressed and co-immobilized with its foldase, on an inert hydrophobic support (Accurel MP1000). We studied the performance of this immobilized LipG9 (Im-LipG9) in organic media, in order to evaluate its potential for use in biocatalysis. Im-LipG9 showed good stability, maintaining a residual activity of more than 70% at 50°C after incubation in n-heptane (log P 4.0) for 8 h. It was also stable in polar organic solvents such as ethanol (log P -0.23) and acetone (log P -0.31), maintaining more than 80% of its original activity after 8 h incubation at 30°C. The synthesis of ethyl esters was tested with fatty acids of different chain lengths in n-heptane at 30 °C. The best conversions (90% in 3 h) were obtained for medium and long chain saturated fatty acids (C8, C14 and C16), with the maximum specific activity, 29 U per gram of immobilized preparation, being obtained with palmitic acid (C16). Im-LipG9 was sn-1,3-specific. In the transesterification of the alcohol (R,S)-1-phenylethanol with vinyl acetate and the hydrolysis of the analogous ester, (R,S)-1-phenylethyl acetate, Im-LipG9 showed excellent enantioselectivity for the R-isomer of both substrates (E> 200), giving an enantiomeric excess (ee) of higher than 95% for the products at 49% conversion. The results obtained in this work provide the basis for the development of applications of LipG9 in biocatalysis.