Showing papers on "Vinyl acetate published in 2008"

Effect of Silica Nanoparticles on the Local Segmental Dynamics in Poly(vinyl acetate)

Abstract: The effect of nanosized silica particles on the properties of poly(vinyl acetate) (PVAc) was investigated for a range of silica concentrations encompassing the percolation threshold. The quantity of polymer adsorbed to the particles (“bound rubber”) increased systematically with silica content and was roughly equal to the quantity shielded from shear stresses (“occluded rubber”). This bound and occluded polymer attained a level of ∼12% at a silica volume content of 28%; nevertheless, the glass transition properties of the PVAc, including the glass transition temperature, local segmental relaxation function and relaxation times, and the changes in thermal expansion coefficient and heat capacity at Tg, were unaffected by the interfacial material. That is, there is no indication that the local segmental dynamics of the chains adjacent to silica particles differ from the motions of the bulk chains. Interestingly, the volume sensitivity of the segmental dynamics, as determined from the scaling exponent γ in th...

Glassy Dynamics in Thin Polymer Layers Having a Free Upper Interface

Abstract: The molecular dynamics in thin polymer layers having a free upper interface is investigated by means of Broadband Dielectric Spectroscopy and AC-calorimetry Down to film thicknesses of ∼10 nm no shifts in the average relaxation time and no broadening of the dynamic glass transition are detected for polystyrene, poly(methyl methacrylate), poly(vinyl acetate), poly(γ-benzyl-l-glutamate) and poly(2-vinyl pyridine) This experimental finding restricts to a few nanometers the length-scale of a possible alteration of the polymer mobility in the vicinity of free interfaces

Graft block copolymers of propargyl methacrylate and vinyl acetate via a combination of RAFT/MADIX and click chemistry: Reaction analysis

Abstract: Propargyl methacrylate with its acetylene function protected with a silyl group is polymerized via the reversible addition fragmentation chain transfer (RAFT) process, using cyanoisopropyl dithiobenzoate (CPDB) as RAFT agent, and subsequently deprotected to afford a polymer backbone where each repeated unit is decorated with an acetylene functionality (1000 < Mn < 13,600 g mol-1, 1.07 < PDI < 1.29). In parallel, an azide functionalized xanthate (ethoxythiocarbonylsulfanyl-acetic acid 3-azido-propyl ester) was employed to prepare narrow polydisperse poly(vinyl acetate) (M n = 850 g mol-1, PDI = 1.20). The two polymers are conjugated by Huisgen 1,3-dipolar cycloaddition to afford narrow polydisperse comb polymer (1.12 < PDI < 1.18, 3400 < Mn < 12,500 g mol-1, based on linear polystyrene calibration, 4500 < M n theo < 15,600 g mol-1). The study places special emphasis on following the copper catalyzed 1,3-dipolar cycloaddition via Fourier Transform Infrared Spectroscopy (FTIR) as well as via on-line UV-Vis photospectrometry on several model compounds, i.e. the nonmonomer inserted azido-xanthate RAFT/MADLX. agent as well as a 2-propargyl-2-bromopropionate and 3-azidopropyl-2-bromopropionate model compounds. A suitable absorption band in the VIS at 666 nm (tentatively assigned to a charge transfer complex between copper(I) and the forming triazole moieties) is identified as a promising sensor for following the click reaction kinetics, thus allowing for the rapid assessment of reaction completion in an on-line fashion. © 2007 Wiley Periodicals, Inc.

Chemical process design

Abstract: Integrated Process Design Process Synthesis by Hierarchical Approach Synthesis of Separation System Reactor / Separation / Recycle Systems Phenol Hydrogenation to Cyclohexanone Alkylation of Benzene by Propylene to Cumene Vinyl Chloride Monomer Process Fatty-Ester Synthesis by Catalytic Distillation Isobutane Alkylation Vinyl Acetate Monomer Process Acrylonitrile by Propene Ammoxidation Biochemical Process for NOx Removal PVC Manufactoring by Suspension Polymerization Biodiesel Manufacturing Bioethanol Manufacturing

Preparation of a xanthate‐terminated dextran by click chemistry: Application to the synthesis of polysaccharide‐coated nanoparticles via surfactant‐free ab initio emulsion polymerization of vinyl acetate

Abstract: Stable monodisperse poly(vinyl acetate) (PVAc) submicronic latex particles were synthesized by ab initio batch emulsion polymerization using a dextran derivative from renewable resource as an efficient steric stabilizer. The dextranend-functionalized by a xanthate moiety was synthesized by Huisgen's 1,3-dipolar cycloaddition (click chemistry). It was applied as a macromolecular RAFT (reversible addition fragmentation chain transfer) agent in surfactant-free emulsion polymerization of vinyl acetate to form in situ an amphiphilic block copolymer able to efficiently stabilize the latex particles. The method afforded the preparation of high solids content (27%) latices coated by dextran. Both the kinetic study and the molar mass analyses confirmed the involvement of the dithiocarbonate group in the emulsion polymerization process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2845–2857, 2008

Organo-Cobalt Mediated Living Radical Polymerization of Vinyl Acetate

Abstract: Vinyl acetate polymerization initiated by azo radical sources in the presence of cobalt(II) tetramesitylporphyrin ((TMP)CoII) shows an induction period followed by an organo-cobalt mediated living radical polymerization (LRP). The induction period corresponds to converting (TMP)CoII to an organo-cobalt porphyrin derivative (organo-Co(TMP)). Living character at low vinyl acetate conversion is demonstrated by a linear increase in molecular weight with conversion, relatively low polydispersity homopolymers, and formation of block copolymers with methyl acrylate ((TMP)Co-PVAc-b-PMA). Deviations from ideal LRP occur by radical termination and chain transfer events at moderate conversion of vinyl acetate (VAc). Mechanistic studies demonstrate that the VAc radical polymerization is controlled by a degenerative transfer mechanism that utilizes organo-cobalt complexes as the transfer agent. Kinetic studies are utilized in comparing radical polymerization of vinyl acetate and methyl acrylate that are mediated by or...

Exchange of Organic Radicals with Organo-Cobalt Complexes Formed in the Living Radical Polymerization of Vinyl Acetate

Abstract: Exchange of organic radicals between solution and organo-cobalt complexes is experimentally observed and the reaction pathway is probed through DFT calculations. Cyanoisopropyl radicals from AIBN (2,2′-azobisisobutyronitrile) enter solutions of cobalt(II) tetramesityl porphyrin ((TMP)CoII•, 1) and vinyl acetate (VAc) in benzene and react to produce transient hydride (TMP)Co−H and radicals (•CH(OAc)CH2C(CH3)2CN (R1•)) that proceed on to form organo-cobalt complexes (TMP)Co−CH(OAc)CH3 (4, Co−R2) and (TMP)Co−CH(OAc)CH2C(CH3)2CN (3, Co−R1), respectively. Rate constants for cyanoisopropyl radical addition with vinyl acetate and hydrogen atom transfer to (TMP)CoII• are reported through kinetic studies for the formation and transformation of organo-cobalt species in this system. Rate constants for near-degenerate exchanges of radicals in solution with organo-cobalt complexes are deduced from 1H NMR studies and kinetic modeling. DFT computations revealed formation of an unsymmetrical adduct of (TMP)Co−CH(OAc)CH3 ...

Copolymers as Flow Improvers for Mexican Crude Oils

Abstract: A series of copolymers derived from styrene (S), n-butyl acrylate (BuA), and vinyl acetate (VA) monomers were prepared by emulsion polymerization to improve some physical properties of Mexican crude oils (MCOs). Once obtained, the copolymers were characterized by Fourier transform infrared (FTIR) spectroscopy, size-exclusion chromatography (SEC), and thermogravimetric analysis (TGA). Later, they were dissolved in toluene and were added to both light and heavy MCOs; the pour point temperature and apparent viscosity of these mixtures were carefully evaluated. Results indicate that styrene and vinyl acetate (SVA) copolymers show a good pour point depressant performance for both types of crude oils. The apparent viscosity dependence on temperature for light and heavy crude oils, mixed with copolymers, was also established. It was observed that, in general, the addition of copolymers decreases the apparent viscosity of both light and heavy crude oils above 35 °C.

Synthesis of Novel Well-Defined Poly(vinyl acetate)-b-poly(acrylonitrile) and Derivatized Water-Soluble Poly(vinyl alcohol)-b-poly(acrylic acid) Block Copolymers by Cobalt-Mediated Radical Polymerization

Abstract: Poly(vinyl acetate)−Co(acac)2 macroinitiators, prepared by cobalt-mediated radical polymerization of vinyl acetate (VAc), were used to synthesize well-defined poly(vinyl acetate)-b-poly(acrylonitrile) (PVAc-b-PAN) block copolymers. Different solvents and temperatures were tested for the polymerization of the acrylonitrile segment by cobalt-mediated radical polymerization (CMRP), and copolymers with low polydispersity were obtained provided that dimethylformamide was used as solvent at 0 °C. The mechanism of control was assumed to change from a degenerative chain transfer mechanism for the VAc polymerization to a reversible-termination process for the AN polymerization. The hydrolysis of the ester groups of the PVAc block and the nitrile groups of the PAN sequence of the copolymer by potassium hydroxide in an ethanol/water mixture provided the double hydrophilic and pH-responsive poly(vinyl alcohol)-b-poly(acrylic acid) block copolymer. Finally, the pH responsiveness of these copolymers was demonstrated by...

Two Calorimetric Glass Transitions in Miscible Blends Containing Poly(ethylene oxide)

Abstract: Miscible blends containing poly(ethylene oxide) (PEO) have been examined over the entire composition range using differential scanning calorimetry to explore further the reported presence of two glass transitions. Three systems, poly(ethylene oxide)−dimethyl ether (PEO−DME)/poly(methyl methacrylate) (PMMA), PEO/poly(lactide) (PLA), and PEO/poly(vinyl acetate) (PVAc), were chosen in order to study the effects of end-group chemistry, annealing time, and crystallinity on the calorimetric behavior of the blends. The molecular weight of PEO was kept low to minimize the interference due to crystallization. Two distinct glass transitions were observed in the mid-composition range for all three systems. The glass transition temperatures varied smoothly with blend composition between the glass transition temperatures of the two homopolymer components. It was found that the self-concentration model describes the composition dependence of these glass transitions well. Further investigation on selected PEO/PVAc blend...

Non-isothermal crystallization and melting of ethylene-vinyl acetate copolymers with different vinyl acetate contents

Abstract: Non-isothermal crystallization and subsequent melting of three grades of ethylene-vinyl acetate copolymer were investigated by differential scanning calorimetry (DSC) technique. The DSC crystallization curves show that vinyl acetate (VAc) content has the same effect on the onset, peak and final crystallization temperatures, and these copolymers have almost the same spacing of thermal windows under identical crystallization condition. Subsequent melting DSC results suggest that EVA14 (14 wt% VAc) has the narrowest distribution of lamellar thickness and the most perfect crystals. Though the instantaneous nucleation was preferred, non-isothermal crystallization kinetics shows that EVA14 could form tridimensional crystallites, whereas EVA18 (18 wt% VAc) and EVA28 (28 wt% VAc) are prone to crystallize two-dimen- sionally, as a result of more noncrystallizable VAc co-monomers introduced in the crystallizable ethylene segments. The growth rate falls on the following sequence: EVA14>EVA18>EVA28. Moreover, the kinetic crystallizability G also well characterizes the variation of the non-isothermal crystallization of these EVA materials, in the view of structural impedi- ment caused by the VAc content.

Supercritical solvent impregnation of poly(ɛ-caprolactone)/poly(oxyethylene-b-oxypropylene-b-oxyethylene) and poly(ɛ-caprolactone)/poly(ethylene-vinyl acetate) blends for controlled release applications

Abstract: Poly(ɛ-caprolactone) blends were successfully impregnated with timolol maleate, an anti-glaucoma drug, using a supercritical solvent impregnation (SSI) technique. Supercritical fluid impregnation efficiency results suggested that the best impregnating conditions were obtained when a cosolvent was used and when specific drug–polymer interactions occurred as a consequence of different chemical structures due to polymer blending. Pressure can be either a favourable factor, when there is enough drug affinity for the polymers, or an unfavourable factor when weaker bonding is involved. In order to determine the relative hydrophilicity/hydrophobicity of the blends, contact angle analysis was performed, while crystallinity determination was also useful to understand the obtained release profiles. Drug loading, heterogeneous/homogeneous dispersion of drug inside the matrix, hydrophilicity, crystallinity, all seem to influence the obtained drug release rates. The “in vitro” release results suggested that a sustained drug release rate can be obtained by changing the SSI operational conditions and by modulating the composition of blends, as a mean to control crystallinity, hydrophilicity and drug affinity for the polymer matrix. After a first day burst release, all samples showed a sustained release profile (1.2–4 μg/(ml day), corresponding to a mass of 3–10 μg/day) which is between the therapeutic and toxic levels of timolol maleate, during a period of 1 month. These drug-loaded polymeric matrices can be a feasible alternative treatment modality for the conventional repeated daily administration of eye drops.

Acoustic backing composition, ultrasonic probe and ultrasonic diagnostic apparatus

Abstract: Disclosed is an acoustic backing composition comprising an ethylene-vinyl acetate copolymer containing 20 to 80% by weight of the vinyl acetate units and a filler contained in the ethylene-vinyl acetate copolymer.

Poly(vinyl acetate), poly((1-O-(vinyloxy) ethyl-2,3,4,6-tetra-O-acetyl-β-d-glucopyranoside) and amorphous poly(lactic acid) are the most CO2-soluble oxygenated hydrocarbon-based polymers

Abstract: Poly(vinyl acetate), PVAc, remains the most CO 2 -soluble non-fluorous polymer identified to date. Small sugar acetates are known to be extraordinarily CO 2 -philic, but cellulose triacetate, a crystalline high molecule weight polymer is CO 2 insoluble. Therefore, an amorphous high molecular weight polymer with pendant sugar acetates was synthesized. This polymer, poly(1- O -(vinyloxy) ethyl-2,3,4,6-tetra- O -acetyl-β- d -glucopyranoside, P(AcGIcVE), was indeed CO 2 -soluble, however cloud point pressures of P(AcGIcVE) at 5 wt% polymer and 298 K were greater than that required for the dissolution of PVAc. Finally, the solubility of amorphous poly(lactic acid), PLA, was determined over a wide range of molecular weight. The corresponding cloud point pressures were much greater than either PVAc or P(AcGIcVE). Ab initio calculations for the CO 2 /PVAc dimer and CO 2 /PLA dimer mixtures were conducted in an attempt to elucidate the dramatic differences in the cloud point values of PVAc and PLA. Our calculations indicate that there is little difference in the average interaction energies for the CO 2 /PLA and the CO 2 /IPA systems. The only indication that PVAc would be expected to be more CO 2 -soluble that PLA was that the vinyl acetate dimer has binding modes that will readily accept multiple CO 2 molecules, whereas the binding modes for the lactic acid dimer can apparently only accommodate a single CO 2 molecule at a time.

Investigation of the photodegradation behaviors of an ethylene/vinyl acetate copolymer solar cell encapsulant and effects of antioxidants on the photostability of the material

Abstract: This study concerns the photodegradation and stabilization of a solar cell encapsulating material made from ethylene/vinyl acetate copolymer (EVA). EVA was compounded with various additives in a twin-screw extruder. After that, the extruded film was cured in a hydraulic compression mold before being exposed to ultraviolet (UV) radiation at an ambient temperature for 800 h. The thermal stability of the material was also studied through the aging of the sample at 90°C for 2000 h. The tensile strength of the unstabilized EVA decreased only slightly after the thermal aging. On the other hand, the strength of the material decreased noticeably after the UV irradiation. Fourier transform infrared spectra of various EVA films revealed that there was no deacetylation occurring after the UV irradiation. However, results from the swelling test and swollen-state NMR suggested that the polymer degraded via a chain-scission mechanism. After compounding with some antioxidants, most of the EVA films scarcely degraded after the UV irradiation, with the exception of the EVA compounded with a combination of the aromatic phosphate compound (0.1 phr) and hindered amine light stabilizer (0.1 phr). The results are discussed in light of an antagonism effect that occurred because of the aforementioned combination. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Graft polymerization of vinyl monomers onto cotton fibres pretreated with amines

Abstract: The influence of treating cotton fibres with several amines on the mechanical properties, moisture sorption ability before and after graft polymerization, and on graft yields for various water-soluble and water-insoluble vinyl monomers were analysed. As compared to water, the treatment with amines, ethylenediamine (EDA) in particular, resulted in a decrease in the crystallinity and tensile strength of the cotton fibres, and an increase in the moisture sorption. The graft yields of amine-treated cotton fibres using water-soluble monomers, acrylic acid (AA), methacrylic acid (MAA) and acrylamide (AM) were greater than those observed for water-treated cotton fibres, whereas the graft yields using water-insoluble monomers, methyl acrylate (MA), methyl methacrylate (MMA) and vinyl acetate (VA) were lower. The moisture sorption ability was improved by the graft polymerization with water-soluble monomers. The improvement was enhanced for MA and MAA by treatment with sodium hydroxide to form the corresponding sodium carboxylate derivatives. The tensile strength of EDA-treated cotton was slightly reduced by grafting, while that of the water-activated cotton yarn was barely changed. These results suggest that the graft polymerization of amine-treated cotton fibres with certain vinyl monomers increased the moisture sorption ability without resulting in increased fibre rigidity.

Melt extrusion and spray drying of carbamazepine and dipyridamole with polyvinylpyrrolidone/vinyl acetate copolymers.

Abstract: Aim: Carbamazepine and dipyridamole are class II compounds (BCS) whose oral bioavailability is limited by poor solubility. The use of glass solutions to improve the bioavailability of this class of compound has been an area of research for a number of years. The influence of polymer parameters (Tg, hydrophilicity, solubility parameter, and ability to hydrogen bond) on glass solution properties is investigated. Methods: Carbamazepine and dipyridamole glass solutions are prepared with PVP/VA 64 and PVP/VA 37 by spray drying and melt extrusion. The products are then characterized by XRPD, thermal, and spectroscopic methods. Yield, physical stability, and dissolution profiles are also assessed.Results: The properties of the polymer greatly influenced the ability to produce glass solutions. With decreases in Tg and hydrophilicity, melt extrusion became the more viable of the two preparative techniques. Although glass solutions were successfully prepared, the greater the difference in component solubility param...

New generation layered nanocomposites derived from ethylene‐co‐vinyl acetate and naturally occurring graphite

Abstract: New ethylene-co-vinyl acetate (EVA, with 60% vinyl acetate content) based nanocomposites were prepared with graphites modified by various techniques and a commercially available expanded graphite (EG). The infrared spectra and the surface energy measurements indicated better oxidation and higher surface energy of the graphite modified by mixed acids followed by high temperature treatment (GO). Interlayer space and surface area were increased as a result. EG possessed higher surface area. GO was found to distribute in finer tactoids of average thickness of 25 nm in the matrix, as compared with the unmodified graphite (UG), having average tactoid thickness more than 40 nm along with aggregation. EG also showed finer dispersion in the EVA matrix with some network formation. The dynamic mechanical and the mechanical properties were superior at the 2 wt % concentration of the GO, beyond which the improvement was less, possibly because of aggregation of GO. Greater EVA-GO interaction at 2 wt % concentration was also supported from the swelling analysis, thermal conductivity, and the thermo-oxidative degradation data of the hybrid composites. The melt viscosity was lower at 2 wt % GO concentration. EG based nanocomposites registered similar properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of silica‐based nanofillers on the properties of a low‐density polyethylene/ethylene vinyl acetate copolymer based thermoplastic elastomer

Abstract: The effect of pristine silica nanoparticles on a model low-density polyethylene (LDPE)-ethylene vinyl acetate copolymer (EVA) thermoplastic elastomer blend system is explored in this article. Pristine silica nanoparticles were melt-blended with the LDPE-EVA system at 1.5, 3, and 5 wt % loadings through the variation of the sequence of addition. In one of the compositions, coupling agent bis[3-(triethoxysilyl)propyl] tetrasulfide (Si-69) was used to improve the interaction of hydrophilic silica fillers with the polymer matrix. The blends were compression-molded, and their mechanical, dynamic mechanical, and thermal properties, X-ray diffraction patterns, and morphology were evaluated. The properties of the blends were found to be strong functions of the sequence of addition of nanofillers during their preparation. With Si-69 as a coupling agent, the dynamic storage modulus of nanosilica-based composites was found to increase up to 35%. An appreciable improvement in the tension set properties of the thermoplastic elastomer nanocomposites was observed in all the nanosilica-based films. Morphological studies and dynamic properties clearly indicated that the differential properties of these blend systems primarily stemmed from the extent of dispersion and alternation of crystalline morphology, which in turn was a strong function of preferential incorporation in the LDPE or EVA matrix and the agglomeration tendency of the nanofillers.

Synthesis of Poly(vinyl acetate) Nanogels by Xanthate-Mediated Radical Crosslinking Copolymerization

Abstract: Poly(vinyl acetate) (PVAc) nanogels are synthesized by a radical crosslinking copolymerization (RCC) in solution of vinyl acetate and divinyl adipate (DVA) or 2,4,6-tris(allyloxy)-1,3,5-triazine (TAT) as the crosslinker, in the presence of a xanthate as a reversible chain transfer agent. Higher concentrations of crosslinker and lower concentrations of xanthate produce PVAc nanogels of higher molar masses, for a given concentration of xanthate and for a fixed concentration of crosslinker, respectively. The xanthate end-groups allow for the synthesis of ‘second generation’ nanogels through a subsequent RCC from precursors. The chemical cleavage of the crosslinks yields individual poly(vinyl alcohol) chains, which attests that the length of the constitutive chains is controlled by the xanthate.

Theoretical study of the prohibited mechanism for ethylene/vinyl acetate co-polymers to the wax crystal growth.

Abstract: To understand the effect of pour point depressants (PPD) on the wax growth is important for designing PPD additives for use with different oils with high efficiency and good economics. In our current study, molecular mechanics, molecular dynamics, and quantum mechanics calculations were performed to investigate the prohibited mechanism of ethylene/vinyl acetate (EVA) additives on the paraffin deposition in oils. On the wax surface, a single C18 molecule and clusters were preferably deposited on the wax surface (010) in a parallel conformation, which resulted in the formation of large blocks of wax crystal. MD simulation indicated that the linear conformation of EVA was more favorable to be adsorbed onto the carbon backbone of the wax surface (010) with the polar fragments of vinyl acetate staying upside of the surface. Furthermore, four EVA molecules can efficiently optimize the inhibition effect for the deposition of the solute C18 molecules over 10x8 size wax surface (010). According to the simulation results, a simplified rational model was established to estimate the minimum dosage of EVA-type PPD for fuels with different paraffin contents. In a certain degree, this simplified model has provided an effective route to correlate microstructures and the properties of polymer-involving systems, which will shed light on the application of theoretical studies in industries.