Showing papers on "Vinyl acetate published in 1996"

Solubility of Polymers and Copolymers in Supercritical CO2

Abstract: Cloud-point data to temperatures of 270 °C and 3000 bar are presented for CO2 with the family of poly(acrylates) including methyl, ethyl, propyl, butyl, ethylhexyl, and octadecyl, with poly(butyl methacrylate), with poly(vinyl acetate), with statistically random copolymers of poly(ethylene-co-methyl acrylate) with 41, 31, and 18 mol % acrylate, with poly(tetrafluoroethylene-co-hexafluoropropylene) and poly(vinylidene-co-hexafluoropropylene) copolymers, each with ∼20 mol % hexafluoropropylene, and with Teflon AF. Over the same range of conditions, CO2 cannot dissolve polyethylene, poly(acrylic acid), poly(methyl methacrylate), poly(ethyl methacrylate), polystyrene, poly(vinyl fluoride), or poly(vinylidene fluoride). CO2 is a weak solvent that exhibits the temperature-sensitive characteristics observed with polar solvents. The solubility of a nonpolar hydrocarbon polymer or a copolymer in CO2 can be increased by at least partially fluorinating the polymer or by incorporating some polar groups into the backb...

Heterogeneous vinylacetate/ethylene dispersion

Abstract: A copolymer in dispersion or redispersible powder form which is stabilized by a protective colloid and has a glass transition temperature of -40° to 10° C. and an ethylene content of at least 30% by weight, based on the total amount of monomers, with a heterogeneous build-up of the copolymer particles, including a first polymer phase, which includes vinyl acetate and >40% by weight of ethylene, based on the total amount of monomers in this phase, and a last copolymer phase, which includes vinyl acetate and 5 to 40% by weight of ethylene, based on the total amount of monomers in this phase, is suitable, for example, as a binder in building materials.

Adhesive testing at the Canadian Conservation Institute-an evaluation of selected poly(vinyl acetate) and acrylic adhesives

Abstract: In 1983 the Canadian Conservation Institute (CCI) initiated a project to evaluate 27 poly(vinyl acetate) (PVAC) and 25 acrylic adhesives on the basis of pH, emission of harmful volatiles, flexibility/strength and yellowing upon dark aging at room temperature and fluorescent light aging. Measurement of the pH of extracts showed that the PVAC adhesives were more acidic than the acrylic adhesives and that light aging tended to decrease the pH of both classes. The PVAC homopolymers generally were more acidic than the PVAC copolymers and many acrylic adhesives containing butyl acrylate were found to be neutral. The analysis of volatile compounds from the PVAC and acrylic adhesives showed that they emitted various ester and residual solvent compounds but only the PVAC adhesives released appreciable quantities of acetic acid. The results indicated that, after an initial curing period of several weeks, the evolution of acetic acid from the PVAC adhesives should not pose an acute hazard. In general, both P...

Lipase-catalyzed second-order asymmetric transformations as resolution and synthesis strategies for chiral 5-(acyloxy)-2(5H)-furanone and pyrrolinone synthons

Abstract: By use of lipase R (Amano, Penicillium roqueforti) immobilized on Hyflo Super Cell it is possible to convert at ambient temperature 5-hydroxy-5H-furan-2-one (5) to acetic acid 5-oxo-2,5-dihydrofuran-2-yl ester (1b) by acylation with vinyl acetate in 1:1 cyclohexane−butyl acetate. At 90% conversion the enantiomeric excess of 1b is 100%. This is an example of an enzyme-catalyzed second-order transformation whereby the unreactive enantiomer of 5 racemizes during reaction, allowing up to 100% conversion and obtainment of high enantiomeric excesses. The method is even more effective with 5-(acyloxy)-2(5H)-pyrrolinones. Racemic acetic acid 1-acetyl-5-oxo-2,5-dihydro-1H-pyrrol-2-yl ester (2) when treated with the lipase from Candida antarctica at ambient temperature in 3:1 n-hexane−butanol undergoes exactly 50% conversion to afford (+)-2 in >99% enantiomeric excess. This is the unreactive enantiomer. The (−)-enantiomer is converted to the 5-hydroxy derivative 6, which with Candida antarctica in 1:1 n-hexane−viny...

Effect of Solvent Size on Solvent Self-Diffusion in Polymer−Solvent Systems

Abstract: The free-volume theory for solvent self-diffusion coefficients in polymer−solvent systems is modified to include a more general analysis of the effects of solvent size. The predictions of the theory are compared with self-diffusion data for a diverse set of solvents and four polymers, polystyrene, poly(vinyl acetate), poly(methyl methacrylate), and poly(p-methylstyrene). The new prediction of size effects is based on the consideration of the asymmetry of solvent molecules.

Thermal degradation of ethylene (vinyl acetate)

Abstract: Ethylene (vinyl acetate), EVA, is a copolymer which is thermally degraded at high temperatures, with acetic acid release at approximately 620 K. This release can be studied by using thermal methods, and in particular thermogravimetric analysis.

Catalyst, method of its production and its use for the production of vinyl acetate monomer

Abstract: A catalyst and method of its production for use in making vinyl acetate monomer. The carrier is impregnated with a basic solution and a solution containing gold salts and palladium salts and finally impregnated with alkali acetate. The activity and selectivity of the catalyst, its mechanical strength, the noble-metal adhesion and the dispersion of noble metal on the carrier can be improved if the carrier is impregnated in a pretreatment with salts containing as cation elements of groups IA, IIA, IIIA and IVB of the periodic table and as anions elements of group VIIA or complex anions such as nitrate, sulfate or anions of organic acids such as acetate and lactate and is subsequently dried and calcined at temperatures of at least 160° C.

Lipase-Catalyzed Transesterification of Aryl-Substituted Alkanols in an Organic Solvent

Abstract: Lipase-catalyzed transesterifications of aryl-substituted alcohols with vinyl acetate in organic solvents have been investigated. Vmax of (R)-1-phenylethanol is much larger than its (S)-counterpart, although their Kms are similar each other. It is proposed that a lipase from Pseudomonas cepacia can form a complex easily with each enantiomer, although the complex with the (S)-enantiomer is abortive. Enantioselectivity for the ortho-substituted 1-phenylethanol is smaller than those for the others. A three-dimensional model for the active domain of the lipase has been proposed to explain the enantioselectivity and substrate selectivity of the lipase.

Real-time analysis of ethylene vinyl acetate random copolymers using near infrared spectroscopy during extrusion

Abstract: Poly(ethylene vinyl acetate) (EVA) is a very common polymer used in hot melt adhesives. The rheological and thermal-mechanical properties of these adhesives are strongly related to the content of vinyl acetate (VA) incorporated into this random copolymer during polymerization. Results of in-line monitoring of VA content in flowing molten EVA polymers, using fiberoptic near infrared spectroscopy, shall be discussed in detail. In-line monitoring is not only desired for its numerous advantages (such as high quality products, lower waste, lower developmental cycle time, and lower costs) but also because it eliminates the sample handling concerns associated with molten polymers.

Heat capacity spectroscopy compared to other linear response methods at the dynamic glass transition in poly(vinyl acetate)

Abstract: Heat capacity spectroscopy measurements in the frequency range from 1.25 to 12 600 rad/s at the dynamic glass transition in poly(vinyl acetate) are reported. The data are compared to results of dielectric and shear spectroscopy in a comparable frequency range on the same sample. The peaks of the different imaginary parts do not have the same position across the main transition zone. The sequence of the peaks with increasing frequency is as follows: dielectric compliance, entropy compliance, and shear modulus. The distances between the different peaks are 0.3 ± 0.4 and 1.0 ± 0.4 frequency decades, respectively.

Alkyl-fumarate-vinyl acetate copolymer as flow improver for high waxy Indian crude oils

Abstract: A number of alkyl fumarate−vinyl acetate copolymers having a wide range of molecular weights were prepared by solution polymerization using a variety of solvents. The efficacy of these copolymers as flow improvers (FI)/pour point depressants (PPD) was tested on Indian crude oils having similar wax (<12%) and asphaltene (<0.5%) contents. The results indicate that the performance of the additives is dependent on the molecular weight of the polymer. The highest molecular weight copolymer is the best additive for crude oils that have a broad range of normal paraffins and lower average carbon numbers. The addition of the lowest molecular weight copolymer resulted in the best efficacy for crude oils containing a narrow range of normal paraffins with higher average carbon numbers. Intermediate molecular weight copolymers are best for crude oils containing a broad range of normal paraffins and higher average carbon number. The peak shear stress and steady shear stress of gelled Bombay High (BH) crude oil (at 16 °...

Process for the production of supported palladium-gold catalysts

Abstract: An improved process for producing high activity and high selectivity supported palladium-gold catalysts is provided. The process involves calcining the support impregnated with a palladium salt and gold salt in a non-reducing atmosphere and at a temperature ranging from 100° C. to 600° C. prior to reducing the metals. Catalysts of the invention are useful for the production of vinyl acetate in the vapor phase by reaction of ethylene, acetic acid and oxygen.

Butyl acrylate/vinyl acetate copolymer latex synthesis using ultrasound as an initiator

Abstract: The polymerization of oil-in-water (o/w) emulsions of monomeric species has been performed at 30°C (±5°C) under ultrasonic irradiation, in the absence of any added chemical initiators. Emulsions of butyl acrylate and vinyl acetate as well as emulsified mixtures of the two monomers have been reacted in this way. In all cases, the radicals formed as a result of the ultrasonic cavitation were sufficient to cause polymerization. Stable blue-white or white dispersions of polymer latex particles were obtained. The kinetics of the copolymerization process were monitored. The data obtained here show that the polymerization rate depends strongly upon the monomer concentration dissolved in the aqueous phase and on its vapor pressure. The more volatile of the monomers examined, vinyl acetate, was seen to have a markedly lower polymerization rate at equivalent monomer concentrations when compared to the butyl acrylate. This was attributed to monomer evaporation into the cavities formed by the ultrasound, causing a dampening of the cavitation process and hence a lower radical density. Data of particle sizes and polymer molecular weights for the latex samples support this hypothesis.

Polymer Viscoelastic Properties Measured by Friction Force Microscopy

Abstract: Using the contact diameter as the velocity-to-frequency conversion length, we suggest a correlation between the friction in films of poly(ethylene terephtalate), poly(vinyl alcohol), poly(vinyl acetate) and gelatin with their known α and/or β relaxation process. This method potetially enables aaassignment of frictional mechanisms, which are due to viscoelastic relaxati, on a nanometer scale

Dynamics of Poly(vinyl acetate) in Bulk and on Silica

Abstract: Quadrupole echo deuterium NMR has been used to probe the dynamics of poly(vinyl acetate-d3) in bulk and at saturation coverage (from toluene) on silica at the solid−air interface In bulk and at lo

Significant effect of acyl groups on enantioselectivity in lipase-catalyzed transesterifications

Abstract: The effect of the acyl group of acylating agents on the enantioselectivity in the lipase-catalyzed transesterifications of racemic 2-[( N , N -dimethylcarbamoyl)methyl]-3-cyclopenten-1-ol in diisopropyl ether was found to be significant. The enantioselectivity was enhanced markedly by changing the acylating agent from vinyl acetate to vinyl butyrate, and dropped substantially with longer acyl donors. Other acyl donors were also examined.

Preparation and thermal characterization of block copolymers by macroazonitriles having glycidyl azide and epichlorohydrin moieties

Abstract: Poly(glycidyl azide) (PGA) an energetic polymer and polyepichlorohydrin (PECH) were condensed with 4,4′ azobis(4-cyanopentanoyl chloride) (ACPC) to prepare macro-azo-initiators. Block copolymers containing each of these polyethers as a block segment combined with polystyrene (PS) or poly(vinyl acetate) (PVAc) have been drived by the polymerization of monomers initiated with this macro-azo-initiators. Thermal properties of block copolymers were investigated with differential scanning calorimetry (DSC) and thermogravimetry. DSC traces showed single glass transition temperatures in between the related segments of copolymers. Dynamic thermogravimetric analysis revealed the individual degradation behaviors of block segments © 1996 John Wiley & Sons, Inc.

Production of vinyl acetate-based polymer, production of saponified vinyl acetate-based polymer and resin composition

Abstract: PROBLEM TO BE SOLVED: To obtain the subject polymer slightly causing coloring or gel-like stone in molding after saponification and useful as a raw material of saponified polymer for fibers, etc., by adding a specific conjugated polyene compound after polymerization of monomer containing vinyl acetate. SOLUTION: A monomer (mixture) containing vinyl acetate is polymerized in the presence of a polymerization catalyst having =20 deg.C, preferably a boiling point higher than a boiling point of vinyl acetate (e.g. 1-bromo-1, 3-butadiene, myrcene, farnesene).

Miscibility, morphology and fracture toughness of epoxy resin/poly(vinyl acetate) blends

Abstract: Diglycidylether of bisphenol A (DGEBA)/poly(vinyl acetate) (PVAc) blends cured with 4,4′-diaminodiphenylmethane (DDM) were prepared. The miscibility and phase behavior were investigated by means of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). The study results indicate that the epoxy precursor (DGEBA)/PVAc blends are clearly miscible at the entire composition and theTg values experimentally obtained are in a good agreement with those predicted by Fox equation. Cured at elevated temperature, all the DDM-cured blends underwent phase separation and display two-phase morphology. When PVAc content is more than 10 wt%, the thermoplastics-modified resins began to show a co-continuous phase structure. It is the cocontinuous structure that leads to a significantly-improved toughness inKic. Morphologic investigation of the surfaces of fracture mechanic measurement specimens indicates that the toughening effect of the thermoplastics-modified epoxy resins may arise mainly from the ductile yielding of PVAc.