Polymerization Of Vinyl Acetate Research Articles

Finite Element Analysis of Cushioned Diabetic Footwear Using Ethylene Vinyl Acetate Polymer.

With the development of societies, diabetic foot ulcers have become one of the most common diseases requiring lower extremity amputation. The early treatment and prevention of diabetic foot ulcers can considerably reduce the possibility of amputation. Using footwear to redistribute and relieve plantar pressure is one of the important measures for the treatment and prevention of diabetic foot ulcers. Thus, the evaluation and prediction of the distribution of plantar pressure play an important role in designing footwears. Herein, the finite element method was used to study plantar pressure under two kinds of foot models, namely, the skeletal structure foot model and the whole foot model, to explore the influence of human bones on the pressure of the soles of the feet and obtain accurate foot pressure. Simulation results showed that under the two models, the plantar pressure and the pressure from the footwear with ethylene vinyl acetate were all reduced. The total deformation demonstrated a slight increase. These stresses are very useful as they enable the design of suitable orthotic footwear that reduces the amount of stress in individuals with diabetic foot ulcers.

Electromagnetic wave absorption of inexpensive C/ZnO composites derived from zinc-based acrylate resins

Based on the abundant and low-cost zinc-based acrylate resins, C/ZnO composites were fabricated via one-step carbonization at 700 °C in a N2 atmosphere for 2 h. Zinc-based acrylate resins, which were synthesized by free-radical polymerization of butyl acrylate (BA), acrylic acid (AA) and vinyl acetate (VAc) and dehydration condensation of Zn(OH)2, provided a common source for carbon and ZnO. These materials demonstrate enhanced electromagnetic wave absorption (EMWA) behavior with tunable microwave absorption bands at 2–18 GHz, which is related to the molar ratio (mol%) of Zn(OH)2 to acrylate monomers in zinc-based acrylate resins. Remarkably, the 0.11 mol% C/ZnO composite exhibits outstanding absorption properties: the minimum reflection loss (RLmin) at 16.7 wt% loading of −34.66 dB is observed at 3.0 mm and 10.32 GHz, and an RLmin of −24.83 dB is observed at a small thickness of 1.5 mm with an effective absorption bandwidth (EAB) of 3.61 GHz. Moreover, the EAB (RL ≤ −10 dB) from the C band to Ku band is achieved by simply adjusting the thickness of the absorbers, which are superior to the other hybrids of organic carbon and ZnO. These results provide a new strategy for the preparation of carbon-based composites containing metal oxides and their application in high-performance microwave absorption.

Organo-Cobalt Complexes in Reversible-Deactivation Radical Polymerization.

Cobalt complexes have played an essential role in different chemical reactions. One of them that has attracted substantial attention in polymer science is cobalt mediated radical polymerization (CMRP), which is famous for its remarkable efficiency in controlling the radical polymerization of vinyl acetate (VAc) and other less active monomers (LAMs). Two pathways, reversible termination (RT) and degenerative transfer (DT), were recognized to control the polymerization in CMRP and could be further used to rationalize the mechanism of other RDRP methods. These control mechanisms were then found to be correlated to the redox potential of cobalt complexes and thus could be judged more quantitatively. The control of polymer composition and tacticity could also be achieved by using CMRP. The hybridization of CMRP and atom transfer radical polymerization (ATRP) could directly synthesize the vinyl acetate/methyl methacrylate and vinyl acetate/styrene block copolymers in one pot. The copolymer of acrylates and 1-octene could be obtained by visible-light-induced CMRP. With the addition of bulky Lewis acid, CMRP of N,N-dimethylacrylamide (DMA) showed high isotacticities with the contents of meso dyads (m) and meso triads (mm) up to 94 % and 87 %, respectively, and generated the crystalline PDMA with Tm as high as 276 °C. This personal account reviewed the development of CMRP with the mechanistic understanding, the control of composition and stereoselectivity of the polymeric products, and its perspective.

Titanium dioxide nano-ceramic filler in solid polymer electrolytes: Strategy towards suppressed dendrite formation and enhanced electrochemical performance for safe lithium ion batteries

Solid polymer electrolytes (SPEs) in lithium-ion batteries (LIBs) are emerging as promising alternative for liquid electrolytes. However, one of the drawbacks of SPEs is incompatibility between lithium metal anode/electrolyte that leads to the low ionic conductivity and lower cycling performance of LIBs. The present study show that fabrication of free-standing flexible hybrid solid polymer electrolyte (HSPE) based on poly(vinylidene fluoride-co-hexafluoro propylene)/poly(vinyl acetate) polymer blend electrolyte with TiO2 nano-ceramic filler (NCF). The incorporation of TiO2-NCF aids in simultaneous improvements of the ionic conductivity and mechanical properties of host matrix. HSPE with 7.5 wt% TiO2 exhibits highest ionic conductivity of 2.69 × 10−3 S cm−1 at 30 °C, which is ~2.5 time higher than ceramic free HSPE. In addition, the incorporation of TiO2 enhances the high thermal stability (thermal degradation at 350 °C) and mechanical strength (stress 8.4 MPa) of the HSPE. Remarkably, HSPE with 7.5 wt% TiO2-NCF possess large Li+ transference number (0.53) with extended electrochemical stability window (5.4 V) and superior compatibility with lithium metal which is highly desirable for high voltage LIBs. The Li/HSPE/LiFePO4 cell showed superior charge discharge properties, cycling stability and rate capability. Suppression of growth and proliferation of Li dendrites was demonstrated by time dependent impendence analysis. Furthermore, density functional theory (DFT) calculations confirm the mutual interactions between TFSI− and ions in electrolytes and that between TiO2 segments and polymer segments. This work exemplifies the significant role of TiO2-NCF in enhanced electrochemical performance of polymer based free standing flexible HSPE.

백금계 촉매와 Hydrosilane 개시제를 이용한 아세트산 비닐 합성

In this work, a series of hydrosilanes including phenylsilane, diphenylsilane, triethylsilane (TES), and tris(trimethylsilyl)silane combined with catalytical amount of platinum complex such as dichloro(1,5-cyclooctadiene) platinum (COD) and dichloro(dicyclopentadienyl)platinum have been used to initiate the polymerization of vinyl acetate (VAc) at 70-95 ℃. An ultrahigh molecular weight PVAc with number-average molecular weight (M<SUB>n</SUB>) up to 1.17×10<SUP>6</SUP> Da and polydispersity index (PDI) of 2.59 has been synthesized using TES as an initiator in the presence of 9.7 ppm of COD. A kinetic study indicates that the polymerization at VAc/TES/COD molar ratio = 3.0×10<SUP>5</SUP> : 60 : 1 smoothly reached 81.0% conversion in 28.0 h at 85 ℃, producing PVAc with M<SUB>n</SUB> increasing linearly from 1.41×105 to 6.01×10<SUP>5</SUP> Da with the increase of monomer conversion. A mechanistic investigation revealed that COD was firstly reduced by reductive TES, producing Pt nanoparticles and corresponding silane radicals to initiate the polymerization of VAc.

Green Polymerization of Vinyl Acetate Using Maghnite-Na+, an Exchanged Montmorillonite Clay, as an Ecologic Catalyst

In this work, the green polymerization of vinyl acetate is carried out by a new method which consists in the use of clay called Maghnite-Na+ as an ecological catalyst, non-toxic, inexpensive and recyclable by a simple filtration. X-ray diffraction and scanning electron microscopy showed that Maghnite-Na+ is successfully obtained after cationic treatment (sodium) on crude maghnite. It is an effective alternative to replace toxic catalysts such as benzoyl peroxide and azobisisobutyronitrile which are mostly used during the synthesis of polyvinyl acetate (PVAc) making the polymerization reaction less problematic for the environment. The synthesis reaction is less energetic by the use of recycled polyurethane as a container for the reaction mixture and is considered as a renewable material and a good thermal insulator maintaining the temperature of 273 K for 6 h. The reaction in bulk is also preferred to avoid the use of a solvent and therefore to stay in the context of green chemistry. In these conditions, the structure of obtained polymer is established by 1H NMR and 13C NMR. Infrared spectroscopy (FT-IR) was also used to confirm the structure of PVAc. Thermogravimetric analysis showed that it is thermally stable and starts to degrade at 603 K while differential scanning calorimetry showed that this polymer has a glass transition temperature Tg of 323 K.

Porous Sulfonated PVA Microspheres for Controlled Molecules Delivery: A Methylene Blue Study

Functionalized PVA microspheres are commonly used as drug carriers in the fields of pharmacy and medicine. With this aim, we obtained and test novel PVA-PVAc-AMPS sulfonated microspheres by free radical suspension polymerization of vinyl acetate (VAc) and 2-acrylamido-2-methyl-1-propanesulfonic sodium salt acid (AMPS), followed by saponification. The microspheres exhibited a porous core-shell structure with excellent sphericity, a mean size of 171 µm, and elasticity modulus comparable with commercial particles currently used in medical applications. Methylene blue (MB) which has shown similar adherence properties as the cytostatic drug doxorubicin was used as a model drug to study the drug loading/release characteristics of the sulfonated microspheres prepared in this work. 20.7 mg g-1 MB per gram of microspheres was the maximum adsorption capacity in two hours using UV-Vis absorption spectroscopy. The experimental data on adsorption were well described by the pseudo-second order kinetic model. The in vitro release profile of loaded MB microspheres showed rapid desorption in the first hour followed by slower MB release, reaching 8.6% elution at four hours. The diffusion process was found to be dominant in the MB desorption from the PVA-PVAc-AMPS microspheres.

Backbone-Degradable Vinyl Acetate Latex: Coatings for Single-Use Paper Products.

We report an approach to waterborne and degradable latex polymers. Emulsion polymerization of vinyl acetate (VA) with the cyclic ketene acetal 2-methylene-1,3-dioxepane (MDO) yields polymer particles and latex-based coatings that are hydrolytically degradable due to the presence of backbone ester groups. Polymerization under mildly basic conditions (pH 8) and at low temperature (40 °C) is critical: if the in-process pH is too acidic or the temperature too high, MDO is lost to hydrolysis, but when the media is too alkaline, VA monomer rapidly hydrolyzes. When coated onto commercial paper, films of these degradable particle dispersions show excellent oil and grease resistance as compared to non-degradable, VA-only compositions. This new class of latex is therefore well-suited for the design of next-generation, biodegradable and compostable single-use food service products, as well as for other applications where the erosion or degradation of polymer-based films and coatings is required.

“One-pot direct synthesis of novel antibacterial diblock copolymers-based-vinyl acetate via RAFT polymerization”

The one-pot route has been adopted for direct synthesis of novel Poly(vinyl acetate-co-1,3-divinyltetramethyldisiloxane), Poly(vinyl acetate-co-4-vinylbenzyl chloride) and Poly(vinyl acetate-co-vinyltriphenylphosphonium bromide) diblock copolymers via reversible addition-fragmentation chain transfer (RAFT) polymerization of vinyl acetate with a variety of comonomers such as 1,3-divinyltetramethyldisiloxane, 4-vinylbenzyl chloride and vinyltriphenyl phosphonium bromide using cyanomethylmethyl(phenyl) carbamodithioate as RAFT agent. These RAFT copolymers have been characterized by standard spectroscopic methods viz. FTIR, 13C-NMR, UV–visible absorption spectroscopy and gel permeation chromatography. The multi instruments studies of obtained diblock copolymers show that these are successfully formed as a result of RAFT. Their thermal stabilities have been investigated by thermogravimetric analyses and differential scanning calorimetry. The physio-chemical properties of each copolymer such as ionic conductivity, density, and intrinsic viscosity have also been evaluated. Further, they are tested in vitro, using disc diffusion and broth dilution methods against two Gram positive (S. aureus and B. subtilus) bacteria and three Gram negative bacteria (S. typhi, E. coli and P. aeruginosa). A broad spectrum and strongest antibacterial activity suggested that these RAFT copolymers have potential as antibacterial agents.

Well-Defined PIII-Terminated Polymers from Phosphorylated Carbodithioate RAFT Agents

Five S-alkyl di-tert-butylphosphorylated carbodithioates, Z–C(S)SR, were studied as chain transfer agents (CTAs) in the RAFT polymerization of vinyl monomers. These phosphorus-containing CTAs involve new PIII and PV moieties in the Z group (phosphine-borane or free phosphine). Two of them, with an S-bonded 1-methoxycarbonylethyl group as leaving group, have not previously been described. The CTAs with a PV Z group provide good control over the polymerization of styrene (St) and n-butyl acrylate (nBA). Molar masses are close to theoretical values, and dispersities are consistently low during polymerization. The monitoring of polymerization by 31P NMR spectroscopy supports the controlled character and the integrity of the polymer chain ends. Conversely, they inhibit the polymerization of the less-activated monomer vinyl acetate (VAc). The reactivity of the CTAs with a PIII Z group mainly depends on the reaction medium, and their performance for St, nBA, and VAc was surprising and unexpected. Theoretical calculations were carried out to rationalize their behavior. Finally, an innovative strategy was developed to obtain well-controlled polymers with free phosphine ω-chain ends.

Process Characterization of Polyvinyl Acetate Emulsions Applying Inline Photon Density Wave Spectroscopy at High Solid Contents.

The high solids semicontinuous emulsion polymerization of polyvinyl acetate using poly (vinyl alcohol-co-vinyl acetate) as protective colloid is investigated by optical spectroscopy. The suitability of Photon Density Wave (PDW) spectroscopy as inline Process Analytical Technology (PAT) for emulsion polymerization processes at high solid contents (>40% (w/w)) is studied and evaluated. Inline data on absorption and scattering in the dispersion is obtained in real-time. The radical polymerization of vinyl acetate to polyvinyl acetate using ascorbic acid and sodium persulfate as redox initiator system and poly (vinyl alcohol-co-vinyl acetate) as protective colloid is investigated. Starved–feed radical emulsion polymerization yielded particle sizes in the nanometer size regime. PDW spectroscopy is used to monitor the progress of polymerization by studying the absorption and scattering properties during the synthesis of dispersions with increasing monomer amount and correspondingly decreasing feed rate of protective colloid. Results are compared to particle sizes determined with offline dynamic light scattering (DLS) and static light scattering (SLS) during the synthesis.

The effect of styrene-butadiene rubber and ethylene vinyl acetate polymers on the mechanical properties of Engineered Cementitious Composites

Nowadays, the application of the Engineered Cementitious Composites (ECC) is increasing. An alternative way to use un-oiled fibers in ECC is the coating fibers with hydrophobic oil. Coating of fibers with hydrophobic oil in high volumes of concrete is not practical and is almost impossible. In this study, to increase the mechanical properties of ECC with the use of unoiled fibers, the polymers of styrene butadiene rubber (SBR) and ethylene vinyl acetate (EVA) were used. The cement was replaced by the polymers in order to strengthen the tensile and flexural properties. In sum, 7 mix proportions were prepared for the intended tests. The ECC for compressive strength, the uniaxial tensile and three-point bending were examined and tested. The results of the present research indicated that the use of polymers boosts the tensile and flexural properties of the ECC with unoiled fibers. The tensile strain in this study increased by more than 3% after the application of the polymers. Furthermore, the compressive strength increased by more than 47 MPa, and the deflection at the mid-span reached more than 9 mm in the bending test. On the other hand, these results also proved that the SBR latex is more compatible with the use of ECC in comparison of EVA powder.

Stereospecific cationic RAFT polymerization of bulky vinyl ethers and stereoblock poly(vinyl alcohol) via mechanistic transformation to radical RAFT polymerization of vinyl acetate

The simultaneous control of molecular weight and tacticity in cationic polymerization remains challenging. Here, we propose a new approach for stereospecific living cationic polymerization by combining cationic reversible addition-fragmentation chain transfer (RAFT) polymerization with thiocarbonylthio compounds and stereospecific cationic polymerization of bulky vinyl ethers with Lewis acid catalysts. In this combined system, the molecular weight was controlled by the RAFT process between the growing cationic and dormant dithiocarbamate chain ends, whereas the tacticity was controlled by stereospecific propagation based on the steric hindrance of bulky side groups and counteranions derived from the Lewis acid catalysts. Herein, we demonstrate the availability of this approach in the cationic polymerization of various bulky vinyl ethers, such as tert‑butyl, benzyl, trimethylsilyl, and tert‑butyldimethylsilyl vinyl ether, using dithiocarbamates and BF3•OEt2 or EtAlCl2 in toluene at –78 °C. Isotactic-rich poly(vinyl ether)s with controlled molecular weights and dithiocarbamate chain-end groups were obtained from a series of bulky vinyl ethers and were converted into molecular-weight-controlled isotactic poly(vinyl alcohol) (mm ≥ 70%) with a high melting temperature (Tm ~ 230 °C). Furthermore, isotactic-b-atactic stereoblock PVA (mm/mr/rr = 75/25/5 and 23/48/29, Tm ~ 210 °C) was synthesized by mechanistic transformation from the stereospecific cationic RAFT polymerization of trimethylsilyl vinyl ether into the radical RAFT polymerization of vinyl acetate using diphenyl dithiocarbamate as the common RAFT agent followed by simultaneous deprotection of the silyl and acetyl groups.

Reversible-deactivation radical polymerization of vinyl acetate mediated by tralen, an organomediator

An organic compound, tralen, has been developed as a mediator to control the radical polymerization of vinyl acetate, methyl acrylate, and N-vinyl pyrrolidone via the reversible termination mechanism.

Manganese(ii) Schiff-base-mediated reversible deactivation controlled radical polymerization of vinyl acetate

The manganese Schiff-base complexes were applied in the OMRP of vinyl acetate.

Facile Synthesis of Ultrahigh Molecular Weight Poly(Methyl Methacrylate) by Organic Halides in the Presence of Palladium Nanoparticles.

A facile and versatile approach for the synthesis of ultrahigh molecular weight poly(methyl methacrylate) (PMMA) at mild conditions was developed. Certain organic halides combined with a catalytical amount of palladium nanoparticles (Pd NPs) were found to be very effective in initiating polymerizations of methyl methacrylate (MMA), methyl acrylate, vinyl acetate and other vinyl monomers. An ultrahigh molecular weight PMMA with a number-average molecular weight of 4.65 × 106 Da and a weight-average molecular weight of 8.08 × 106 Da was synthesized at 70 °C using 2-bromoisobutyric acid ethyl ester (EBiB) as an initiator in the presence of catalytical amount (10.1 ppm) of Pd NPs. A kinetic investigation found that the orders of polymerization with respect to EBiB, Pd NP and MMA were 0.23, 0.50, and 0.58, respectively. Proton nuclear magnetic resonance (1H NMR) combined with matrix-assisted laser desorption ionization time of flight mass spectroscopy (MALDI-TOF) and gel permeation chromatography (GPC) were used to prove that the macromolecular chain had an end-group of EBiB residue. The electron spin resonance (ESR), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) results reveal that the reaction of EBiB with Pd NPs caused a bromo atom (Br) transfer from EBiB to Pd NPs and resulted in the generation of EBiB residue radical to initiate the polymerization of MMA and the formation of PdIIBr2 on the surface of Pd nanoparticles.

Cobalt(II) complexes of α-diimine derived from cycloalkylamines as controlling agents for organometallic mediated radical polymerization of vinyl acetate

A series of cobalt(II)-α-diimine complexes derived from cycloalkylamines (cycloalkyl = cyclopentyl (1a), cyclohexyl (1b), cycloheptyl (1c), and cyclooctyl (1d)) were synthesized: [CoCl2(Pent-DAB)] (2a), [CoCl2(Hex-DAB)] (2b), [CoCl2(Hept-DAB)] (2c), and [CoCl2(Oct-DAB)] (2d). The α-diimines 1a-d were characterized by FTIR, UV–Vis, and 1H- and 13C NMR spectroscopy, while their respective cobalt(II) complexes (2a-d) were characterized by elemental analysis, FTIR, UV–Vis, EPR, and computational studies. The ability of complexes 2a-d to mediate the vinyl acetate (VAc) polymerization initiated by AIBN, according to a cobalt-mediated radical polymerization (CMRP) mechanism, was explored. A mechanistic investigation of radical trapping based on the combination of theoretical and experimental results for CMRP using 2a-d was conducted. This study shows that the activation/deactivation equilibrium exerted by 2a-d occurs by only one of the faces of the complexes via reversible-termination mechanism. The molecular weight increased in direct proportion to the monomer conversion in the early stages of polymerization for complexes 2a and 2b, while uncontrolled polymerization was observed for 2c and 2d. The molecular weights indicate that the steric effect operated by the cycloalkyl substituents plays an important role in the polymerization control, and that a greater steric hindrance disfavors the dormant state for CMRP equilibrium.

Evaluation of glass fibres, ethylene vinyl acetate and their combination on stone mastic asphalt

ABSTRACT Glass fibre with high tensile strength and Ethylene Vinyl Acetate (EVA) polymer may change Stone Matrix Asphalt (SMA) performance significantly due to its good performance. Therefore, the study’s main objective is to evaluate these two additives’ performances and their combination on SMA. Thus, modified bitumen’s physical properties with 3, 4 and 5% of EVA and mechanical properties of SMA made by 3, 4 and 5% of EVA and 0.1%, 0.2% and 0.3% of glass fibre are investigated. For this purpose, penetration, softening point, rotational viscosity, dynamic shear rheometer, resilient modulus, dynamic creep, and fatigue tests are performed. The results demonstrate that the performance graded of modified bitumen with an optimum value of 4% EVA is improved as two classes, leading to a significant improvement in the SMA performance. However, the performance of SMA containing 0.2% and 0.3% of glass fibre decreases severely due to the fragility of the fibres. The performance of the mixture in 0.1% of the fibres is slightly improved due to the reinforcement of the bitumen mortar and the lack of effect of the fibres on the overall structure of the mixture. Also, only the combination of 4% EVA with 0.1% glass fibre gives an acceptable result.

Justification of binder material selection for carbon particles incorporation into fibrous electromagnetic radiation absorber

The paper presents justification of a binder material for incorporating carbon particles into the interfiber space of electromagnetic radiation absorber. A method for carbon particles incorporation into a fibrous material has been developed. It is based on applying a carbon-containing nanocomposite to the fibrous material’s surface. Previously, the research of carbon particles incorporation into a synthetic material by using an aqueous solution were carried out, which ensured a uniform distribution of carbon particles in the material structure. However, the properties of the material have changed significantly upon mechanical deformation. Therefore, the carbon particles incorporation process was investigated using various nanocomposites obtained on the basis of mixtures of vinyl acetate polymer, or epoxy polymer, or surface-active substance with carbon black. Based on the results of electron microscopic analysis and the reflection and transmission coefficients frequency dependences in the frequency range 0.7–17 GHz, the efficiency of using a nanocomposite based on a mixture of surface-active substance and carbon black to create electromagnetic radiation absorbers was justified. Such electromagnetic radiation absorbers have the transmission coefficient value about –18 dB and reflection coefficient value about –12 dB in the frequency range 7–13 GHz. Carbon-containing electromagnetic radiation absorbers based on fibrous material have thickness less than 3 mm, properties of flexibility and resistance to mechanical deformation. It can be used in various fields, in particular for hiding objects from radio frequency reconnaissance or protecting equipment from external interference.

PET-RAFT copolymerization of vinyl acetate and acrylic acid

Photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization of vinyl acetate (VAc) and acrylic acid (AA) was successfully realized in methanol at room temperature under blue LED (420 nm, 6 mW/cm2) irradiation with xanthate as RAFT agent and fac-[Ir(ppy)3] as the photocatalyst. The well-defined copolymers of poly(VAc-co-AA) with controlled molecular weights (Mn,GPC) and polydispersity index (PDI) were successfully obtained. The polymerization revealed the behaviors of controlled/living polymerization, which was verified by the observed linear relationship of ln([M]0/[M]t) with respect to irradiation time and that of the experimental molecular weights (Mn,GPC) with respect to monomer conversion. GPC curves showed a single peak and shifted to high molecular weights with increasing the irradiation time. The reactivity ratios of VAc and AA were 0.043 and 1.181, respectively in this system. The effect of the amount of fac-[Ir(ppy)3] on PET-RAFT polymerization was investigated. The monomer conversion increased with increasing the amount of fac-[Ir(ppy)3] and the PDI decreased with the increase in the amount of fac-[Ir(ppy)3]. The temporal controllable PET-RAFT polymerization of vinyl acetate (VAc) and acrylic acid (AA) was achieved. The structure of synthesized poly(VAc-co-AA) was characterized by nuclear magnetic resonance spectroscopy (1H NMR) and gel permeation chromatography (GPC), respectively. The extended experiments of poly(VAc-co-AA) with fresh AA was conducted under the irradiation of blue LED, and the results demonstrated that this extension polymerization displayed controlled polymerization behavior. The mechanism was explained in this study.