Showing papers on "Vinyl acetate published in 1999"

The Overgrowth of Calcium Carbonate on Poly(vinyl chloride-co-vinyl acetate-co-maleic acid)

Abstract: Poly(vinyl chloride-co-vinyl acetate-co-maleic acid) (vinyl chloride 83%, vinyl acetate 13%, carboxylated 1%) was found to be a substrate favoring the deposition of vaterite crystals from stable supersaturated solutions at pH 8.50 and 25 °C. Induction times preceding calcium carbonate precipitation were inversely proportional to the solution supersaturation, and a surface energy of 23 mJm-2 was calculated according to classical nucleation theory. The relatively low value may be attributed to the heterogeneous character of vaterite nucleation. The linear dependence of the rates of vaterite formation on the solution supersaturation, in which the crystallization took place, in combination with the independence of the measured rates on the fluid dynamics, suggested that vaterite overgrowth was controlled by surface diffusion. This finding was in agreement with the results obtained for the crystallization of vaterite on cholesterol. Our results suggest that the kinetics of overgrowth may be very important for ...

Enzyme-Mediated Regioselective Acylations of Sophorolipids.

Abstract: Enzymatic synthesis of well-defined sophorolipid analogues for evaluation of their bioactivities and as new building blocks for the preparation of glycolipid-based amphiphilic polymers is described. Lipase Novozym 435 from Candida antarctica has been shown to be an efficient catalyst for acylation of sophorolipids esters. A mixture of sophorolipids produced by Torulopsis bombicola was esterified by reaction with sodium alcoxide. The alkyl esters of sophorose lipids were subjected to Novozym 435 catalyzed acylation in dry tetrahydrofuran (THF) with vinyl acrylate and vinyl acetate to diacyl derivatives. The reactions were highly regioselective, and exclusive acylation of the hydroxyl groups on C-6‘ and C-6‘ ‘ took place. Methyl ester in the absence of the acylating agent, or with the agent at a concentration less than equimolar, gave sophorolactone (9). Careful analysis of the spectral data revealed it to be a synthetic analogue of microbially produced macrolactone. Sophorolactone (9) differs in the site a...

Polymerization of vinyl acetate promoted by iron complexes

Abstract: Polymerization of vinyl acetate (VOAc) was carried out using CCl4 as the initiator in the presence of the Fe(OAc)2/PMDETA (PMDETA = N,N,N‘,N‘‘,N‘‘-pentamethyldiethylenetriamine) complex. Poly(vinyl...

Block Copolymerizations of Vinyl Acetate by Combination of Conventional and Atom Transfer Radical Polymerization

Abstract: Four different methods of block copolymerization, combining atom transfer radical polymerization (ATRP) and conventional radical polymerization, were studied. The first two methods employed azo compounds containing activated halogen atoms. 2,2‘-Azobis[2-methyl-N-(2-(4-chloromethylbenzoyloxy)ethyl)propionamide] (AMCBP) was used to initiate the polymerization of vinyl acetate (VAc) at 90 °C. The resulting pVAc with a Cl terminal group (Mn = 47 900; Mw/Mn = 2.21) was subsequently used as a macroinitiator for styrene (St) to yield pVAc-b-pSt (Mn = 91 600; Mw/Mn = 1.80). In the second method, 2,2‘-azobis[2-methyl-N-(2-(2-bromoisobutyryloxy)ethyl)propionamide] (AMBEP) was first used to polymerize n-butyl acrylate (BA) at 30 °C in the presence of CuBr/tris[2-(dimethylamino)ethyl]amine (Me6-TREN). The pBA (Mn = 7500; Mw/Mn = 1.15) with the preserved central azo unit was dissolved in VAc and extended to a block copolymer (Mn = 41 800; Mw/Mn = 3.56). Alternatively, ATRP has been combined with a redox initiated syst...

Process for the production of vinyl acetate

Abstract: A process for the production of vinyl acetate which comprises contacting ethylene, acetic acid and an oxygen-containing gas with a supported palladium catalyst prepared by a process comprising the steps of (a) impregnating a catalyst support with a palladium compound, (b) converting the palladium compound to substantially metallic palladium, and (c) sintering the supported palladium at a temperature of greater than 500° C.

Rheological characterization of ethylene vinyl acetate copolymers

Abstract: A series of ethylene vinyl acetate (EVA) copolymers was studied by dynamic mechanical spectroscopy to understand the relative influence of composition, structure, and molecular weight distribution on their rheological behavior in the melt. The examination of their viscoelastic properties in a large temperature range showed that the glass transition temperature is nearly independent on their composition because of the statistical nature of the copolymers, though some long sequence of polyethylene homopolymer may exist at low vinyl acetate (VA) content. The successful use of the time temperature superposition for oscillatory experiments in the melt confirmed the previous remarks, because the application of the Williams Landel Ferry (WLF) equation leads to a unique set of WLF coefficient, whatever the composition of the EVA. This enables the comparison of the rheological behavior in the melt at the same temperature, in the same free volume condition, and at last it was shown that in the terminal zone, the molecular weight distribution is more influent on the behavior of EVA copolymers than their composition. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2625–2630, 1999

Phase Structure of Poly(3-hydroxy butyrate)/Poly(vinyl acetate) Blends Probed by Small-Angle X-ray Scattering

Abstract: The semicrystalline morphology of poly(3-hydroxy butyrate) (PHB)/poly(vinyl acetate) (PVAc) blends at four crystallization temperatures (Tc = 70, 90, 110, and 125 °C) was probed by small-angle X-ray scattering (SAXS). Morphological parameters including the crystal thickness (lc) and the amorphous layer thickness (la) were deduced from the interphase distribution function. Blending with PVAc thickened the PHB crystals. The amorphous layers were also swollen upon blending, but la displayed a maximum in its variation with PVAc composition. A zero-angle scattering was observed in the Lorentz-corrected SAXS profiles of PHB/PVAc 60/40 blend crystallized at 110 and 125 °C and 50/50 composition crystallized at 90−125 °C. Such a zero-angle scattering was attributed to the presences of amorphous domains between the lamellar stacks so as to generate gaps in the sequential stacking of lamellae. These amorphous domains were generated by the interfibrillar segregation of PVAc, where PVAc was expelled beyond several lay...

A spectroscopic study of the homogeneous catalytic conversion of ethylene to vinyl acetate by palladium acetate

Abstract: We have studied the various aspects of the homogeneous acetoxylation of ethylene to vinyl acetate by palladium acetate using ultraviolet−visible (UV/vis), Raman, and infrared spectroscopic methods. Vibrational assignments for the Raman and the infrared spectra of crystalline palladium acetate have been made. Density functional theoretical calculations were used to help with our assignments. Raman spectroscopy demonstrated that Pd acetate solvated in glacial acetic acid maintains a trimeric structure, similar to that of the crystal. Upon addition of potassium acetate in concentrations between 0.10 and 0.20 M, the palladium acetate trimers decompose to dimers. It remains, however, an open question whether monomers, or perhaps dimers that are fully coordinated by acetate ligands, form with increasing potassium acetate concentration. In the presence of ethylene, dimeric species appear to form by decomposition of the trimers, and it is the dimers which are the catalytically active and selective species in the ...

High damping material composition

Abstract: A high damping material composition useful as a vibration damper and an acoustic insulating material such as a sound insulating wall for an acoustic room, a sound insulating partition for a construction structure and a soundproofing wall for a vehicle. The high damping material composition of the present invention containing the following components (A) and (B); (A) a polymer having in the molecular chain thereof a chemical structural unit derived from the following (a); (a) at least one selected from the group consisting of an acrylic monomer, a methacrylic monomer, an ethylene-acrylic copolymer, an ethylene-methacrylic copolymer and vinyl acetate; (B) at least one damping property imparting agent selected from the group consisting of a hindered phenol compound, a phosphite ester compound, a phosphate ester compound, a basic compound containing nitrogen and a hindered amine compound. The combined use of the component (A) and (B) makes an interaction therebetween homogeneous and appropriate, so that the component (B) is homogeneously dispersed in the component (A), resulting in exhibition of a high tan δ. Moreover, the homogeneous dispersion can be maintained for a long period thereby to prevent a declined of tan δ with time. The compositions have a tan δ peak temperature of approximately room temperature, which makes the compositions suitable for use in a room temperature atmosphere.

Nonisothermal crystallization and melting behavior of poly(?-hydroxybutyrate)-Poly(vinyl-acetate) blends

Abstract: Nonisothermal crystallization and melting behavior of poly(P-hydroxybutyrate) (PHB)-poly(vinyl acetate) (PVAc) blends from the melt were investigated by differential scanning calorimetry using various cooling rates. The results show that crystallization of PHB from the melt in the PHB-PVAc blends depends greatly upon cooling rates and blend compositions. For a given composition, the crystallization process begins at higher temperatures when slower scanning rates are used. At a given cooling rate, the presence of PVAc reduces the overall PHB crystallization rate. The Avrami analysis modified by Jeziorny and a new method were used to describe the nonisothermal crystallization process of PHB-PVAc blends very well. The double-melting phenomenon is found to be caused by crystallization during heating in DSC. (C) 1999 John Wiley & Sons, Inc.

Scaling Analysis and Distribution of the Rotational Correlation Times of a Tracer in Rubbery and Glassy Poly(vinyl acetate): An Electron Spin Resonance Investigation

Abstract: We studied by ESR the rotational motion of a paramagnetic tracer (a deuterated 15 N-enriched nitroxide) in poly(vinyl acetate) (PVAc). The reorientation of the tracer occurs via jumps of about 50° with a heterogeneous distribution of correlation times. Depending on the temperature range, the average correlation time scales as the α, β, and γ relaxation times of PVAc, i.e., = C i i , i = α, β, γ. On cooling, tracks the α relaxation to about the α-β bifurcation temperature and then the β relaxation down to the glass transition. In glassy PVAc / γ = C γ ≃ 1.

Two-Dimensional Fourier Transform Raman Correlation Spectroscopy Study of Composition-Induced Structural Changes in a Series of Ethylene/Vinyl Acetate Copolymers

Abstract: Generalized two-dimensional (2D) FT-Raman correlation spectroscopy has been applied to the study of the composition-induced structural changes in eleven different ethylene/vinyl acetate (EVA) copolymers with vinyl acetate (VA) content varying from 6 to 42 wt % The eleven copolymer samples have been divided into four sets according to their composition range, and 2D correlation analysis has been applied to detect the characteristic bands for each set Throughout the composition range of EVA copolymers, the increase of VA content always causes the crystalline lamellae to shrink, the amorphous interlamellar layers to expand, the all-trans −(CH2)−n conformers to decrease, and the gauche conformers to increase in population In particular, for the EVA with 7 wt % VA, small addition of VA comonomers acts as spacers between adjacent methylene segments and converts the orthorhombic unit cell to the anisotropic unit cell, manifested by the correlation splittings at (1438 cm-1, 1415 cm-1) and (1446 cm-1, 1434 cm-1

Poly(ethylene-co-vinyl acetate) (eva) copolymers as modifiers of oil wax crystallization

Abstract: This work describes the performance of poly(ethylene-co-vinyl acetate) (EVA) copolymers as pour point reducer and organic deposits inhibitor. The molecular weight, molecular weight distribution and vinyl acetate content of the EVA copolymers were determined by gel permeation chromatography and thermogravimetric analyses, respectively. The copolymer with the highest vinyl acetate content (within the range analyzed, 28-41 wt %) exhibited the best performance as organic deposits inhibitor. Results from differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) suggest that the EVA copolymer acts modifying the morphology of the wax crystals.

`Watching' lipase-catalyzed acylations using 1H NMR: competing hydrolysis of vinyl acetate in dry organic solvents

Abstract: Lipase-catalyzed acetylations of 1-phenylethanol with vinyl acetate were monitored in situ by 1 H NMR spectroscopy. Surprisingly, even under dry conditions (no added water) the major reaction was hydrolysis of the vinyl acetate, not acetylation of the substrate. Because this competing hydrolysis consumes water and releases acetic acid, the reaction conditions in lipase-catalyzed acylations are not constant, but vary with the reaction time. Addition of a chiral shift reagent reveals the enantiomeric purity of the starting alcohol and allows calculation of the enantiomeric ratio, E , for the reaction.

Two-Dimensional Near-Infrared Correlation Spectroscopy Studies on Composition-Dependent Spectral Variations in Ethylene/Vinyl Acetate Copolymers: Assignments of Bands Due to Ethylene Units in Amorphous, Disordered, and Orthorhombic Crystalline Phases

Abstract: Generalized two-dimensional (2D) correlation spectroscopy has been applied to the study of the composition-dependent near-infrared (NIR) spectral changes in 11 different ethylene/vinyl acetate (EVA) copolymers with vinyl acetate (VA) content from 6 to 42 wt%. The 2D synchronous correlation analysis of the 11 NIR spectra has separated the bands due to ethylene units from those due to the VA units. The obtained results are consistent with those reached by the calculation of the second derivative and by chemometrics analysis reported in our previous paper. However, the 2D correlation analysis has given clearer evidence for the band separation. Two-dimensional asynchronous correlation analysis has revealed out-of-phase variations between some bands due to ethylene and some bands due to VA and has determined the order of intensity change between them. On the basis of the order of intensity change, the bands of ethylene in the orthorhombic crystalline phase have been discriminated from those in the amorphous and disordered phases. This paper discusses the potentials of three powerful techniques, 2D correlation analysis, the calculation of the second derivatives, and that of regression coefficients in chemometrics, in unraveling rather complicated NIR spectra.

Effect of solvent on the rate constants in solution polymerization. Part II. Vinyl acetate

Abstract: Measurements were made of the value of the lumped kinetic constant kp/k of vinyl acetate in different solvents and with different initiators. This quantity was evaluated using the well-known conversion vs. time approach in dilute solutions using both azo-bis-isobutyronitrile and benzoyl peroxide (AIBN and BPO), and two different solvents (toluene and ethyl acetate) at 60°C. As was found for butyl acrylate in Part 1 of this series, it was found that the value of the lumped rate constant depends very strongly on the concentration of monomer in solution, decreasing as the solution becomes more and more dilute. However, unlike butyl acrylate, vinyl acetate is much more susceptible to changes in the solvent type, with toluene acting as a severe retarding agent of polymerization. The results of the present study suggest that at least two separate effects of solvent exist simultaneously in the case of vinyl acetate polymerization, and that both of them must be taken into account when attempting to model this type of system. The number- and weight-average molecular weights of the different polymers were also measured, and excellent agreement was found between the measurements and model predictions. A linear relationship was shown to exist between the value of the lumped constant and the square root of the number-average chain length. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 589–601, 1999

In Situ Observation of Dithiocarbamate-Based Surface Photograft Copolymerization Using Quartz Crystal Microbalance

Abstract: A quartz crystal microbalance (QCM) technique which can detect weight increase in the nanogram order has been employed to continuously monitor the iniferter-based surface photograft polymerization behavior of vinyl monomers. The gold electrodes of the QCM were thinly coated with a photoreactive polystyrene partially derivatized with N,N-diethyldithiocarbamylmethyl groups acting as iniferters. A monotonic decrease in the resonance frequency of the vibrating oscillator of QCM, which was correlated with the weight increase via graft copolymerization initiated on the polystyrene, occurred immediately after ultraviolet light irradiation of the coated electrode surface in a methanolic or aqueous solution of vinyl monomers such as acrylamide (AAm), N,N-dimethylacrylamide (DMAAm), methacrylamide (MAm), methacrylic acid (MA), ethyl acrylate (EA), 2-hydroxyethyl methacrylate (HEMA), 2-(dimethylamino)ethyl methacrylate (DMAEM), N-vinyl-2-pyrrolidone (VP), and styrene (ST), except for vinyl acetate (VA). Upon cessati...

Resin composition and laminate

Abstract: PROBLEM TO BE SOLVED: To obtain a resin composition excellent in external appearances when molded and gas barrier properties by admixing plural saponified products of ethylene/vinyl acetate copolymers in a specific weight ratio with at least one thermoplastic resin in a specific weight ratio. SOLUTION: The resin composition comprises plural saponified products of ethylene/vinyl acetate copolymers (A) and (B), in a component A/component B weight ratio of 90/10-10/90, and further at least one thermoplastic resin (C) selected among a low melting point nylon having a melting point of not higher than 160°C, a partially saponified product of an ethylene/vinyl acetate copolymer and a thermoplastic polyurethane in a components (A+B)/component C weight ratio of 95/5-50/50. The degrees of saponification (mole %) of the components A and B, Sv(A) and Sv(B), respectively, the ethylene contents (mole %) Et(A) and Et(B), and MFR(A) and MFR(B) (g/10 min) satisfy the relations; |SV(A)-Sv(B)|≥1, |Et(A)-Et(B)|≥5, and 4≤MFR(B)/MFR(A). COPYRIGHT: (C)2001,JPO

Enzymatic desymmetrization of meso cis-2,6- and cis,cis-2,4,6-substituted piperidines. Chemoenzymatic synthesis of (5S,9S)-(+)-indolizidine 209D

Abstract: The stereoselective acylation of meso piperidines 3a , b by vinyl acetate (solvent and acyl donor) in the presence of Candida antarctica lipase gave the corresponding (2 S ,6 R ) and (2 S ,4 R ,6 R ) monoesters 2a , b in high enantiomeric purity. (5 S ,9 S )-(+)-Indolizidine 209D was prepared in eight steps from (2 S ,6 R )- 2a .

Effects of blend ratio, crosslinking systems and fillers on the morphology, curing behavior, mechanical properties, and failure mode of acrylonitrile butadiene rubber and poly(ethylene-co-vinyl acetate) blends

Abstract: Blends of acrylonitrile butadiene rubber (NBR) and poly(ethylene-co-vinyl acetate) (EVA), with varying proportions of the components, were vulcanized using different crosslinking systems, namely, sulfur (S), dicumyl peroxide (DCP), and a mixed system (S + DCP). Mechanical properties, such as stress–strain behavior, tensile strength, elongation at break, Young's modulus, tensile set, and tear strength, were studied. The mixed system exhibited better mechanical performance than other systems. The tensile and tear fracture surfaces were analyzed under the scanning electron microscope in order to understand the failure mechanism. The variation in properties was correlated with the morphology of the system. The effect of high-abrasion furnace black (HAF), semireinforcing furnace black (SRF), silica, and clay on the mechanical properties and failure mechanism of 50/50 blend of NBR–EVA (N50P) has also been studied. The Kraus equation has been applied to analyze the extent of polymer–filler interaction. Applicability of various theoretical models has been investigated to predict the properties of the blend systems. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2335–2364, 1999

Asymmetric Hydroformylation of Olefins in Highly Crosslinked Polymer Matrixes

Abstract: When polymer-immobilized chiral phosphine-phosphite–Rh(I) complexes were used, the asymmetric hydroformylation of styrene gave 2- and 3-phenylpropanals with a substrate/catalyst ratio of 2000, iso/normal ratios of 84/16 to 89/11, and 89% R enantiomeric excess of 2-phenylpropanal; these results were at the highest level in catalytic activity, regio-, and enantioselectivities. Recovery-reuse of the catalyst was examined. Asymmetric hydroformylation of vinyl acetate, (Z)-2-butene, and 3,3,3-trifluoropropene was also successfully performed with the polymer-supported catalysts.

Coatings for biomedical Devices

Abstract: The invention provides devices having gas-phase deposited coatings. Specifically, this invention provides devices, such as biomedical devices, with gas-phase deposited vinyl pyrrolidone, N, N'-dimethylacrlyamide, ethylene glycol, vinyl acetate, vinyl acetic acid, acrylic acid, and 3,3-dimethylacrylic acid coatings that are non-fouling and wettable.

Water-resistant cable

Abstract: The present invention relates to a cable, in particular an optical fibre cable, which is resistant to the radial permeation and to the longitudinal propagation of water. This cable comprises a water-soluble polymer material, characterized in that the said material is a water-swellable and water-soluble material. In particular, this cable is characterized in that, following the ingress of water into this cable, the propagation of water is impeded on account of the combined effect of the swelling of the water-soluble material and the formation of an aqueous solution of the said material which has a predetermined viscosity, so as to impede the passage of the residual water. Preferably, the water-soluble material is chosen from polyacrylamide, modified polyvinyl alcohol, vinyl alcohol/vinyl acetate copolymers, polyvinylpyrrolidone, and mixtures thereof, the material preferably being a vinyl alcohol/vinyl acetate copolymer. The material can advantageously be extruded to form tubular elements for containing optical fibres, for example two-layer tubular elements in which the inner layer is made of water-soluble material and the outer layer is made of a conventional polymer such as PE, PP or PBT.

Catalyst and use thereof in the production of vinyl acetate

Abstract: A catalyst for use in the production of vinyl acetate which comprises (1) a catalyst support, (2) palladium, (3) an acid, (4) at least one acetic acid catalyst promoter and (5) at least one vinyl acetate promoter and/or co-promoter. A process for the production of vinyl acetate from ethylene and an oxygen-containing gas using the catalyst.

Fluid bed vinyl acetate catalyst

Abstract: A catalytically active material useful to prepare vinyl acetate monomer from ethylene, acetic acid, and an oxygen-containing gas under fluid bed conditions comprises a porous microspheroidal support containing catalytically active palladium crystallites finely dispersed within the support. This catalyst material does not require incorporation of gold to maintain activity and selectivity. A process to produce a vinyl acetate fluid bed catalyst in which catalytically active small palladium crystallites are finely dispersed within the support comprises dispersing selected metal species within the support which have an affinity to palladium to form very fine crystallites of palladium. The affinity metal species may be dispersed by impregnation onto a preformed microspheroidal support or may be intimately incorporated within the support before impregnation with a soluble palladium species.