Showing papers on "Vinyl acetate published in 2020"

Poly(Vinyl Alcohol) Recent Contributions to Engineering and Medicine

Abstract: Poly(vinyl alcohol) (PVA) is a thermoplastic synthetic polymer, which, unlike many synthetic polymers, is not obtained by polymerization, but by hydrolysis of poly(vinyl acetate) (PVAc). Due to the presence of hydroxylic groups, hydrophilic polymers such as PVA and its composites made mainly with biopolymers are used for producing hydrogels that possess interesting morphological and physico-mechanical features. PVA hydrogels and other PVA composites are studied in light of their numerous application for electrical film membranes for chemical separation, element and dye removal, adsorption of metal ions, fuel cells, and packaging. Aside from applications in the engineering field, PVA, like other synthetic polymers, has applications in medicine and biological areas and has become one of the principal objectives of the researchers in the polymer domain. The review presents a few recent applications of PVA composites and contributions related to tissue engineering (repair and regeneration), drug carriers, and wound healing.

Recycling Poly(ethylene-vinyl acetate) with Improved Properties through Dynamic Cross-Linking

Abstract: The low properties of recycled polymers associated with high cost of recycling hinder development of the thermoplastic recycling industry. Dynamic cross-linking of recycled thermoplastics with the ...

Physicochemical Properties of Poly-Vinyl Polymers and Their Influence on Ketoprofen Amorphous Solid Dispersion Performance: A Polymer Selection Case Study.

Abstract: When developing an amorphous solid dispersion (ASD), a prudent choice of polymer is critical to several aspects of ASD performance including: processability, solid state stability and dissolution rate. However, there is little guidance available to formulators to aid judicious polymer selection and a “trial and error” approach is often taken. This study aims to facilitate rational polymer selection and formulation design by generating ASDs using a range of poly-vinyl polymers and ketoprofen as a model active pharmaceutical ingredient (API) and evaluating several aspects of their performance. The molecular weight of the polymer and the ratio of vinyl pyrrolidone to vinyl acetate in the polymer were found to influence the relative humidity at which the relative humidity induced glass transition occurred, as well as the extent of ketoprofen supersaturation achieved during dynamic solubility testing. Interestingly, ASD tablets containing polymers with the vinyl pyrrolidone functional group exhibited higher tensile strengths than those without. This points towards the binder functionality of vinyl pyrrolidone. In conclusion, the physicochemical properties of poly-vinyl polymers greatly influence ketoprofen ASD performance and due regard should be paid to these properties in order to develop an ASD with the desired attributes.

Cobalt(III)-catalyzed ketone-directed C–H vinylation using vinyl acetate

Abstract: Weakly coordinating, ketone-directed C–H vinylation using vinyl acetate is reported here for a wide range of aromatic ketones such as acetophenones, diaryl ketones, chromones and biologically relevant chalcones under cost-effective and air-stable cobalt(III)-catalysis. Regioselective, mono-vinylation occurs for challenging vinyl substitution-free styrenes in moderate to good yields, and this moiety has been used to synthesize functionalized indanone, α-naphthol and an advanced intermediate for bruguierol A synthesis. An acrylate-surrogate provided the corresponding alkenylated product under these vinylation conditions. Detailed mechanistic studies are carried out to support the proposed catalytic cycle.

Poly (1-vinylpyrrolidone-co-vinyl acetate) (PVP-co-VAc) based gel polymer electrolytes for electric double layer capacitors (EDLC)

Abstract: The present work describes the electrochemical performance of gel polymer electrolytes containing two different sodium salts such as sodium trifluoromethanesulfonimide (NaTFSI) and sodium trifluoromethanesulfonate (NaOTF)). Poly (1-vinylpyrrolidone-co-vinyl acetate) P(VP-co-VAc) and the mixture of ethylene carbonate and propylene carbonate (EC: PC) have been employed as the host polymer and plasticizer, respectively. Through electrochemical impedance spectroscopy study, the GPE system containing 50% of NaTFSI (System 1: A5) has achieved higher ionic conductivity (1.79 × 10−3 S cm−1) compared to the GPE system containing 50% of NaOTF (1.21 × 10−3 S cm−1) (System 2: B5). The higher ionic conductivity of System 1: A5 was owing to the larger ionic radius of (TFSI−) anion. Temperature dependent studies affirmed that the ionic conductivity of all samples obeyed Arrhenius behavior. Fourier transform infrared spectroscopy revealed the formation of complex within the GPE systems which indicates the good interaction between the host polymer and the salts. X-ray diffraction analysis demonstrated the reduction in crystallinity of System 1: A5 is greater than that of System 2: B5. The maximum specific capacitance achieved by the EDLC employing System 1: A5 and System 2: B5 was 13.44 F/g (67% capacitance retention) and 13.33 F/g (4.2% capacitance retention), respectively.

Compatibilization and Characterization of Polylactide and Biopolyethylene Binary Blends by Non-Reactive and Reactive Compatibilization Approaches.

Abstract: In this study, different compatibilizing agents were used to analyze their influence on immiscible blends of polylactide (PLA) and biobased high-density polyethylene (bioPE) 80/20 (wt/wt). The compatibilizing agents used were polyethylene vinyl acetate (EVA) with a content of 33% of vinyl acetate, polyvinyl alcohol (PVA), and dicumyl peroxide (DPC). The influence of each compatibilizing agent on the mechanical, thermal, and microstructural properties of the PLA-bioPE blend was studied using different microscopic techniques (i.e., field emission electron microscopy (FESEM), transmission electron microscopy (TEM), and atomic force microscopy with PeakForce quantitative nanomechanical mapping (AFM-QNM)). Compatibilized PLA-bioPE blends showed an improvement in the ductile properties, with EVA being the compatibilizer that provided the highest elongation at break and the highest impact-absorbed energy (Charpy test). In addition, it was observed by means of the different microscopic techniques that the typical droplet-like structure is maintained, but the use of compatibilizers decreases the dimensions of the dispersed droplets, leading to improved interfacial adhesion, being more pronounced in the case of the EVA compatibilizer. Furthermore, the incorporation of the compatibilizers caused a very marked decrease in the crystallinity of the immiscible PLA-bioPE blend.

Efficient and Stable Magnetic Chitosan-Lipase B from Candida Antarctica Bioconjugates in the Enzymatic Kinetic Resolution of Racemic Heteroarylethanols.

Abstract: Lipase B from Candida antarctica immobilized by covalent binding on sebacoyl-activated chitosan-coated magnetic nanoparticles proved to be an efficient biocatalyst (49.2-50% conversion in 3-16 h and >96% enantiomeric excess) for the enzymatic kinetic resolution of some racemic heteroarylethanols through transesterification with vinyl acetate. Under optimal conditions (vinyl acetate, n-hexane, 45 °C), the biocatalyst remains active after 10 cycles.

Controlled-Release from High-Loaded Reservoir-Type Systems—A Case Study of Ethylene-Vinyl Acetate and Progesterone

Abstract: Reservoir systems (drug-loaded core surrounded by drug-free membrane) provide long-term controlled drug release. This is especially beneficial for drug delivery to specific body regions including the vagina. In this study, we investigated the potential of reservoir systems to provide high drug release rates over several weeks. The considered model system was an intra-vaginal ring (IVR) delivering progesterone (P4) in the mg/day range using ethylene-vinyl acetate (EVA) as release rate-controlling polymers. To circumvent the high material needs associated with IVR manufacturing, we implemented a small-scale screening procedure that predicts the drug release from IVRs. Formulations were designed based on the solubility and diffusivity of P4 in EVAs with varying vinyl acetate content. High in-vitro P4 release was achieved by i) high P4 solubility in the core polymer; ii) high P4 partition coefficient between the membrane and the core; and/or iii) low membrane thicknesses. It was challenging for systems designed to release comparatively high fractions of P4 at early times to retain a constant drug release over a long time. P4 crystal dissolution in the core could not counterbalance drug diffusion through the membrane and drug crystal dissolution was found to be the rate-limiting step. Overall, high P4 release rates can be achieved from EVA-based reservoir systems.

Highly Porous Magnetic Janus Microparticles with Asymmetric Surface Topology.

Abstract: Monodispersed magnetic Janus particles composed of a porous polystyrene portion and a nonporous poly(vinyl acetate) portion with embedded oleic acid-coated magnetic nanoparticles were generated using microfluidic emulsification followed by two distinct phase separation events triggered by solvent evaporation. The template droplets were composed of 2 wt % polystyrene, 2 wt % poly(vinyl acetate), and 0.5-2 wt % n-heptane-based magnetic fluid dissolved in dichloromethane (DCM). The porosity of polystyrene compartments was the result of phase separation between a nonvolatile nonsolvent (n-heptane) and a volatile solvent (DCM) within polystyrene-rich phase. The focused ion beam cross-sectioning and scanning electron microscopy (SEM) imaging revealed high surface porosity of polystyrene compartments with negligible porosity of poly(vinyl acetate) parts, which can be exploited to increase the wettability contrast between the two polymers and enhance bubble generation in bubble-driven micromotors. The porosity of the polystyrene portion was controlled by varying the fraction of n-heptane in the dispersed phase. The particle composition was confirmed by scanning electron microscopy-energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The fabricated particles were successfully magnetized when subjected to an external magnetic field, which led to their aggregation into regular 2D assemblies. The particle clusters composed of two to four individual particles could be rotated with a rotating magnetic field. Microfluidic generation of highly porous Janus particles with compositional, topological, and magnetic asymmetry provides a cost-effective, easy-to-implement yet highly robust and versatile strategy for the manufacturing of multifunctional smart particles.

Organoborane Strategy for Polymers Bearing Lactone, Ester, and Alcohol Functionality

Abstract: Vinyl alcohol–methacrylatecopolymers have intriguing functionally rich structures but are synthetically inaccessible from vinyl acetate, the traditional precursor to polyvinyl alcohol. We report a ...

Zinc and Nitrogen-Doped Carbon In-Situ Wrapped ZnO Nanoparticles as a High-Activity Catalyst for Acetylene Acetoxylation

Abstract: Acetylene chemical process, especially catalyzing acetylene acetoxylation for the synthesis of vinyl acetate (VAc), has attracted wide attention in coal-rich countries. Although great efforts have been made to prepare different catalysts to improve the VAc synthesis via acetylene acetoxylation, the acetic acid (HAc) conversion cannot achieve a satisfactory level, much lower than 60%. Herein, ZnO nanoparticles in situ wrapped on zinc-nitrogen-carbon materials (ZnO@ Zn–N–C) have been successfully synthesized. Due to the simultaneous presence of nitrogen and carbon in chitosan, the obtained carbon material achieved in situ nitrogen doping during the high-temperature treatment. Furthermore, the as-obtained ZnO@Zn–N–C exhibits high specific surface area of 1430.1 m2/g and pore volume of 0.92 cm3/g, because Zn composites have the ability to etch carbon to form pores. In particular, ZnO@Zn–N–C displays an amazing catalytic activity for acetylene acetoxylation to synthesize VAc with the HAc conversion high up to 88.8%, which is much higher than those reported in other papers before.

Iodine-Transfer Polymerization (ITP) of Ethylene and Copolymerization with Vinyl Acetate.

Abstract: The first example of a controlled radical polymerization of ethylene using iodine transfer polymerization (ITP) is performed under mild conditions (≤ 100 °C and ≤ 200 bar). Different commercially available, cheap, and non-toxic iodo alkyls (R-I) were used as chain-transfer agents (CTAs) in combination with 2,2'-azobis(2-methylpropionitrile) (AIBN) to investigate the impact of the R-group on the polymerization behaviour. These systems showed no rate retardation and no significant loss of chain ends. The formed well-defined end-capped polyethylene-iodine (PE-I) species is very stable upon storage. Narrow molar-mass distributions with dispersities around 1.6 were obtained up to number average molar masses Mn of 7300 g mol-1. The copolymerization by ITP (ITcoP) of ethylene with vinyl acetate (VAc) to form poly(ethylene-co-vinyl acetate) (EVA) copolymer was also successful. By fine tuning the ethylene pressure and the vinyl acetate content, a broad range of copolymers containing from 0 to 85 mol% of VAc unit was achieved. By reactivating the iodo chain-end, block copolymer structures composed of ethylene and VAc such as poly(ethylene-co-vinyl acetate)-b-polyethylene (EVA-b-PE) or gradient block copopolymers EVA-b-EVA with different content of VAc in the blocks were obtained for the first time using ITP. This highly versatile synthetic platform provides a straightforward access to a diverse range of well-defined PE based polymer materials. Finally, reactivity trends were explored by a theoretical mechanistic study.

Production of vinyl acetate from acetylene

Abstract: The paper presents the "Sol-gel" technology for creation of nanocatalysts, having high efficiency, activity and selectivity for the catalytic acetylating acetylene. The textural characteristics of the catalyst (ZnO)x.(CdO)y(ZrO2)z/keramzite with high activity were studied. Kinetic objective laws of synthesis of vinyl acetate on the created catalyst were investigated, material balance calculated. In addition, advanced technologic scheme of vapor phase synthesis of vinyl acetate was offered.