Showing papers on "Vinyl acetate published in 2004"

Role of molecular weight of atactic poly(vinyl alcohol) (PVA) in the structure and properties of PVA nanofabric prepared by electrospinning

Abstract: Atactic poly(vinyl alcohols) (a-PVAs) having number-average degrees of polymerization [(Pn)s] of 1700 and 4000 were prepared by the solution polymerization of vinyl acetate, which was followed by the saponification of poly(vinyl acetate) to investigate the effects of molecular weights of a-PVA on the characteristics of electrospun a-PVA nanofabrics. A-PVA nanofabrics were prepared by electrospinning with controlling the process parameters including the electrical field, conductivity, tip-to-collector distance, and solution concentration. Through a series of characterization experiments, we identified that the molecular weight of a-PVA had a marked influence on the structure and properties of nanofabrics produced. That is, the higher the molecular weight of PVA, the superior the physical properties of PVA nanofabric. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1638–1646, 2004

Poly(vinyl alcohol) star polymers prepared via MADIX/RAFT polymerisation

Abstract: Poly(vinyl acetate) stars were prepared using MADIX/RAFT polymerisation mediated by xanthates. The polymerisation shows living characteristics with molecular weight increasing with conversion. The subsequent hydrolysis of these three and four arm stars led to the formation of poly(vinyl alcohol) stars.

Substituent Effects in Xanthate-Mediated Polymerization of Vinyl Acetate: Ab Initio Evidence for an Alternative Fragmentation Pathway

Abstract: High-level ab initio calculations have been performed for the addition and fragmentation steps in reversible addition−fragmentation chain transfer (RAFT) polymerization of vinyl acetate. The RAFT agents considered were a series of xanthates of the form SC(O−Z‘)S−R, where Z‘ = methyl, ethyl, iso-propyl, and tert-butyl and R = CH2OCOCH3 and CH3. The results indicate that increasing substitution within the Z‘ group stabilizes the RAFT adduct radical, thereby reducing the rate of fragmentation of the S−R bond. For the model vinyl acetate system, there is an additional substantial reduction in rate for the bulkier iso-propyl and tert-butyl substituents (compared with methyl and ethyl) associated with a sterically induced conformational change in the transition structures. However, the calculated S−R fragmentation rate for Z‘ = tert-butyl is still not low enough to explain the experimentally observed rate retardation in this system. Instead, the rate retardation appears to be the result of the preferred fragmen...

A detailed on-line FT/NIR and 1H NMR spectroscopic investigation into factors causing inhibition in xanthate-mediated vinyl acetate polymerization

Abstract: Potential sources of inhibition have been investigated via in situ Fourier transform - near infra-red (FT-NIR) and off-line H-1 NMR spectroscopy in the RAFT/MADIX bulk polymerization of vinyl acetate (VA) in the presence of an O-isopropyl xanthate, i.e. methyl (isopropoxycarbonothioyl)sulfanyl acetate. The very high reactivity of the vinyl acetate propagating radical makes it very vulnerable to oxygen, by-products generated during the xanthate synthesis, and stabilizers present as impurities. These impurities induce strong and variable inhibition periods in the polymerization. In addition, the MADIX process, using xanthates as reversible chain transfer agents, has been confirmed to be an efficient method for living VA polymerization. Congruent data are obtained when the monomer consumption with time is followed via both H-1 NMR and in situ FT-NIR spetroscopy. The xanthate-mediated polymerization of VA exhibits no retardation effects and excellent control of the molecular weight distribution can be achieved, leading to poly(VA) of molecular weights exceeding 50 000 g . mol(-1) with relatively low polydispersities.

Effect of vinyl acetate content and silicate loading on EVA nanocomposites under shear and extensional flow

Abstract: In this study, three EVAs (ethylene-vinyl acetate co-polymers) with different vinyl contents (VA) ranging from 9 wt% to 28 wt% (EVA9, EVA18 and EVA28) were melt blended with organo-clay to obtain polymer layered silicate nanocomposites. Filler intercalation and exfoliation were evidenced by X-ray diffraction. The melt state viscoelastic properties of EVA nanocomposites were studied to examine the influence of clay in altering the flow properties of these polymeric nanocomposites. The EVA18 and EVA28 nanocomposites exhibited remarkable difference in dynamic and steady shear properties compared to neat polymers. On the other hand, EVA9-5% nanocomposite did not exfoliate and exhibited rheological behaviour very similar to that of the neat polymer. Furthermore, the first normal stress difference was found to be dependent on the silicate loadings when measured at low shear stresses. The uniaxial extensional viscosity measurement indicated that the strain hardening was weaker in EVA nanocomposites compared to neat polymers. Environmental scanning electron (ESE)-microscopy elucidated a possible reason for reduced strain hardening in these systems.

A Novel, Facile Method for the Preparation of Uniform, Reactive Maleic Anhydride/Vinyl Acetate Copolymer Micro- and Nanospheres

Abstract: A novel, stabilizer-free dispersion polymerization with alkyl esters as reaction media gives uniform alternating microspheres of maleic anhydride (MAn)/vinyl acetate (VAc) copolymer. The diameter of the copolymer microspheres could be precisely controlled from 80 to 750 nm by changing the monomer concentration or feed ratio. Moreover, this new type of copolymer microspheres with reactive anhydride groups on the surface has good solubility in common nontoxic solvents such as water and ethanol.

Poly(ethylene glycol)-lipase complexes that are highly active and enantioselective in ionic liquids.

Abstract: Lipase-catalyzed alcoholysis between vinyl acetate and 2-phenyl-1-propanol was investigated in dialkylimidazolium-based ionic liquids. Although native lipase powder exhibited very low activity in an ionic liquid, forming a poly(ethylene glycol) (PEG)-lipase complex improved the lipase activity in the ionic liquid. The activity of the PEG-lipase complex was higher in ionic liquids than in common organic solvents (n-hexane, isooctane and dimethylsulfoxide). Fluorescence measurements using 4-aminophthalimide revealed that the ionic liquids were more hydrophilic than the organic solvents used for non-aqueous enzymology. A kinetic study of lipase-catalyzed alcoholysis in an ionic liquid ([Bmim][PF6]) revealed that the Michaelis constant (Km) for 2-phenyl-1-propanol in the ionic liquid was half that in n-hexane, suggesting that the ionic liquid stabilized the enzyme-substrate complex. Finally, we carried out enantioselective alcoholysis of 1-phenylethanol in ionic liquids employing the PEG-lipase complex, and obtained high enantioselectivity, comparable to that in n-hexane.

Vinyl acetate formation by the reaction of ethylene with acetate species on oxygen-covered Pd(111).

Abstract: The reaction pathway of vinyl acetate synthesis is scrutinized by reacting gas-phase ethylene (at an effective pressure of 1 × 10-4 Torr) with η2-acetate species (with a coverage of 0.31 ± 0.02 monolayer) on a Pd(111)−O(2×2) model catalyst surface in ultrahigh vacuum. It is found that the 1414 cm-1 infrared feature due to the symmetric OCO stretching mode of the acetate species decreases in intensity due to reaction with gas-phase ethylene, while temperature-programmed desorption experiments demonstrate that vinyl acetate is formed. The formation of ethylidyne species is detected when almost all of the acetate species have been removed. The experimental removal kinetics are reproduced by a model in which adsorbed acetates react with an ethylene-derived (possibly ethylene or vinyl) species, where ethylene adsorption is blocked by the acetate present on the surface.

Nonwoven binders with high wet/dry tensile strength ratio

Abstract: This invention is directed to an improved nonwoven product comprising a nonwoven web of fibers bonded together with a sufficient amount of binder comprised of a polymer comprised of vinyl acetate, ethylene, and a crosslinking monomer to form a self-sustaining web. The improvement in the nonwoven product resides in the use of a polymer having a crystalline melting point (T m ) ranging from 35 to 90° C., preferably 50 to 80° C.; measured at a heat rate of 20° C./minute. The polymer should have a crystalline heat of fusion (H f ), which typically range from about 2 to about 50 joules per gram and a low glass transition temperature (T g ), e.g., from 10 to −40° C., typically −15 to −35° C.

Measurements of sorption isotherms and diffusion coefficients by means of a magnetic suspension balance

Abstract: Sorption equilibrium and diffusion coefficients of solvents in a polymer were determined by use of a magnetic suspension balance (MSB). The binary systems poly(vinyl acetate)–methanol and poly(vinyl acetate)–toluene at 20, 40 and 60 °C were investigated. The solvent activity was calculated with the Flory–Huggins and UNIFAC-FV model and the diffusion coefficient with the free-volume theory. The measured values are compared with literature data and Flory–Huggins interaction parameters and free-volume parameters were adapted to the measured data.

The effects of ageing a bimetallic catalyst under industrial conditions: a study of fresh and used Pd-Au-K/silica vinyl acetate synthesis catalysts

Abstract: The effects of ageing under industrial conditions commercial Pd-Au-K/SiO 2 vinyl acetate (VA) synthesis catalysts was studied by XRD, HREM/EDX, XPS, DRIFTS and temperature-programmed oxidation (TPO). The fresh catalysts contain palladium in two forms: Pd–Au alloy particles 4–5 nm in diameter and a very highly dispersed Pd metal component. As a consequence, the alloy particles are far more Au rich than predicted on the basis of the metal loadings (60% Au versus 18% Au). Usage resulted in both pronounced sintering of the Pd–Au alloy particles and the appearance of a Pd acetate component, but without significant change in composition of the alloy particles. Thus, the migration of palladium acetate species does not contribute significantly to sintering. DRIFT spectra revealed the presence of palladium acetate, acetic acid and silyl ester species on the aged sample, in addition to the KOAc also observed on the fresh samples. A further band observed at 1730 cm −1 on the aged sample is assigned to a monodentate “ester-like” palladium acetate species, previously postulated as a key reaction intermediate in vinyl acetate monomer (VAM) formation.

A comparative study of UV aging characteristics of poly(ethylene‐co‐vinyl acetate) and poly(ethylene‐co‐vinyl acetate)/carbon black mixture

Abstract: In this comparative study, the effect of carbon black (CB) on the thermal ageing characteristics of poly(ethylene-co-vinyl acetate) (EVA) was investigated. EVA, containing 13% vinyl acetate (VA), and poly(ethylene-co-vinyl acetate)/carbon black mixture (EVA/CB) containing 13% VA and 1% CB were aged at 85°C in air up to 30 weeks. Sol-gel analysis experiments were made to determine the percentage gelation of both virgin and aged samples. FT-IR measurements were performed to follow the chemical changes which took place in the samples during ageing. Dynamic and isothermal thermogravimetric studies were performed for determination of the thermal stabilities of virgin and aged samples. Sol-gel analysis results showed that EVA itself has a tendency to form a gel under thermal treatment, whereas EVA/CB never becomes a gel when being thermally aged under the same conditions. As a result of FT-IR measurements, some oxidation products such as ketone, lactone and vinyl species were observed through thermal ageing of EVA. It is also clear that these kind of oxidation products did not appear to a considerable extent in EVA/CB. Thermal analysis experiments exhibit that thermal stability of EVA decreased through thermal ageing; whereas that of EVA/CB remained almost unchanged. Copyright © 2004 John Wiley & Sons, Ltd.

Enantioselective transesterification using lipase-displaying yeast whole-cell biocatalyst.

Abstract: An enantioselective transesterification in non-aqueous organic solvent was developed by utilizing a lipase-displaying yeast whole cell biocatalyst constructed in our previous study. As a model reaction, optical resolution of (RS)-1-phenylethanol, which serves as one of chiral building blocks, was carried out by enantioselective transesterification with vinyl acetate. Recombinant Rhizopus oryzae lipase displayed on the yeast cell surface retained its activity in hexane, heptane, cyclohexane and octane. The effective amount of whole-cell biocatalyst in the reaction mixture was 10 mg/ml solvent. In a reaction mixture incubated for 36 h with molecular sieves 4A, the concentration of (R)-1-phenylethyl acetate reached 39.8 mM (97.3% yield) with high enantiomeric excess (93.3%ee). In contrast, a reaction mixture incubated without molecular sieves 4A produced little (R)- and (S)-1-phenylethyl acetate. The results obtained in this study demonstrate the applicability of the lipase-displaying yeast whole cell biocatalyst to bioconversion processes in non-aqueous organic solvents.

Synthesis and Solubility of Linear Poly(tetrafluoroethylene-co-vinyl acetate) in Dense CO2: Experimental and Molecular Modeling Results

Abstract: Supercritical carbon dioxide was used as a reaction medium to synthesize statistically random (i.e., no specific correlation between the location of the monomers on the polymer) copolymers of tetrafluoroethylene (TFE) and vinyl acetate (VAc) with similar molar mass and 11.6−63.3 mol % TFE content. The solubility of the copolymers at 25 °C in CO2 reduced after reaching a maximum value at a TFE molar concentration of 19.3 mol %. The 46.7 mol % TFE copolymer only dissolved in CO2 at elevated temperatures, whereas the 63.3 mol % TFE copolymer did not dissolve in CO2 even at temperatures in excess of 144 °C and pressures of 210 MPa. The molecular modeling results show that the interaction of CO2 with acetate side group was not affected by presence of fluorine in the polymer backbone; therefore, the enhanced solubility of the semifluorinated copolymers is attributable to the enhanced binding between CO2 and the semifluorinated backbone of the copolymer when the CO2 molecule can access both the fluorinated (Lewi...

Study of cobalt(II)-chitosan coordination polymer and its catalytic activity and selectivity for vinyl monomer polymerization

Abstract: A cobalt(II)-chitosan coordination polymer has been prepared by soaking a chitosan film in CoCl2 aqueous solution. The results have been investigated by means of X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared FT-IR spectroscopy, thermal analysis and electrical conductivity measurements. The XPS and FT-IR spectra reveal that the chitosan coordinated with cobalt(II) through both oxygen and nitrogen atoms in the chitosan chain. The XPS results show that the coordination polymer possess the same shake-up peaks with CoCl2, indicating that the cobalt(II)-chitosan coordination polymer is high spin and the coordination number of cobalt(II) centers is four, and the electrical conductivity measurements confirm this result. Also, cobalt(II) coordination polymer can be used as a catalyst, and the polymerization of vinyl acetate was carried out in the presence of the coordination polymer/Na2SO3/H2O at pH 7 and normal temperature. The polyvinyl acetate possessed a random structure. Copyright © 2004 John Wiley & Sons, Ltd.

Adsorption of poly(vinyl alcohol) from water to a hydrophobic surface: effects of molecular weight, degree of hydrolysis, salt, and temperature.

Abstract: The adsorption of poly(vinyl alcohol) (PVOH) from aqueous solutions to a silicon-supported fluoroalkyl monolayer is described. Thickness, wettability, and roughness of adsorbed films are studied as a function of polymer molecular weight, degree of hydrolysis (from the precursor, poly(vinyl acetate)), polymer concentration, salt type and concentration, and temperature. The data suggest a two-stage process for adsorption of the polymer: physisorption due to a hydrophobic effect (decrease in interfacial free energy) and subsequent stabilization of the adsorbed layer due to crystallization of the polymer. Adsorption of lower-molecular-weight polymers results in thicker films than those prepared with a higher molecular weight; this is ascribed to better crystallization of more mobile short chains. Higher contents of unhydrolyzed acetate groups on the poly(vinyl alcohol) chain lead to thicker adsorbed films. Residual acetate groups partition to the outermost surface of the films and determine wettability. Salts, including sodium chloride and sodium sulfate, promote adsorption, which results in thicker films; at the same time, their presence over a wide concentration range leads to formation of rough coatings. Sodium thiocyanate has little effect on PVOH adsorption, only slightly reducing the thickness in a 2 M salt solution. Increased temperature promotes adsorption in the presence of salt, but has little effect on salt-free solutions. Evidently, higher temperatures favor adsorption but cause crystallization to be less thermodynamically favorable. These competing effects result in the smoothest coatings being formed in an intermediate temperature range.

Polyvinyl alcohol copolymer film for packaging liquid products and having an improved shelf-life

Abstract: Generally speaking, the present invention is a water-soluble copolymer film comprising a hydrolyzed copolymer of vinyl acetate and a second monomer, the resultant polyvinyl alcohol copolymer having a degree of hydrolysis, expressed as a percentage of vinyl acetate units converted to vinyl alcohol units, of from about 90% to 100%. The second monomer is preferably selected from the group of monomers having carboxylate functionality or sulfonate functionality. The resulting water-soluble copolymer film is disclosed for use in making pouches to contain a unit dose of liquid detergent, such as a liquid laundry detergent. However, it is an aspect of the copolymer film that film solubility to is not significantly affected adversely by the detergent. Such film produces pouches having a greater storage shelf-life over prior art water-soluble film.

Effects of the blend ratio and crosslinking systems on the curing behavior, morphology, and mechanical properties of styrene–butadiene rubber/poly(ethylene‐co‐vinyl acetate) blends

Abstract: Blends of styrene–butadiene rubber (SBR) and poly(ethylene-co-vinyl acetate) (EVA) with different ratios were prepared with a two-roll mixing mill and were vulcanized by three different crosslinking systems, namely, sulfur (S), dicumyl peroxide, and a mixture consisting of S and peroxide (mixed). The vulcanization behavior of the blends was analyzed from the rheographs. The mechanical properties, including stress–strain behavior, tensile strength, elongation at break, modulus, hardness, and abrasion resistance, of the blends were examined. The morphology of the prepared blends was studied with scanning electron microscopy with special reference to the effects of the blend ratio and crosslinking systems. A relatively cocontinuous morphology was observed for the 20/80 SBR/EVA composition. The mechanical properties increased with increasing EVA content up to 60–80%, for all of the vulcanizing modes. The tensile fracture surfaces were analyzed under a scanning electron microscope to understand the failure mechanism. Various theoretical models were applied to explain the properties of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 827–837, 2004

Chemical Recycling of Class A Surface Quality Sheet-Molding Composites

Abstract: This article describes the solvolysis of sheet-molding composites (SMC) consisting of an unsaturated polyester−styrene (UP) thermoset resin associated with glass fibers, filler (calcium carbonate), and a low-profile additive (LPA) (thermoplastic poly(vinyl acetate)). Preliminary studies have shown that glycols, diacids, and bisphenols are poor solvolytic reagents. On the contrary amino alcohols and polyamines allow much higher depolymerization yields, leading to a total digestion of the polymers. Diethylenetriamine (DETA), at boiling temperature (205 °C) was then chosen as solvolytic reagent. Pure poly(vinyl acetate) (PVAc) is readily converted to soluble products. A total dissolution of cured UP requires high yield of ester cleavage. Longer reaction times are needed with styrene content enhancing. The introduction of PVAc in the UP resin does not alter the kinetics of solvolysis of the thermoset but affects the rheological behavior in intermediate states and enhances the viscosity of the final liquid. A ...

Role of the density in the crossover region of o ‐terphenyl and poly(vinyl acetate)

Abstract: The coupling between the reorientation of molecular probes and the density in one low-molar mass glass former [o-terphenyl (OTP)] and one polymer [poly(vinyl acetate )( PVAc)] is studied in the Goldstein’s crossover region where the structural sad and the secondary sbd relaxations bifurcate. The coupling is found to be strong in OTP and virtually absent in PVAc. The probes sense both the a and b relaxations, and locate their splitting accurately. It is concluded that the density affects the relaxation occurring in the crossover region of OTP but not of PVAc at subnanometer length scales. The findings are compared with recent assessments of the role of the molecular packing close and above the glass transition temperature Tg.