Vinyl Alcohol Content Research Articles

Determination of molecular weight for poly(vinyl butyral) using size exclusion chromatography/low‐angle laser light scattering (SEC/LALLS) in hexafluoroisopropanol

AbstractSize exclusion chromatography/low‐angle laser light‐scattering (SEC/LALLS) determinations of molecular weight for poly(vinyl butyral) (PVB) using hexafluoroisopropanol (HFIP) as the polymer solvent and chromatographic mobile phase are described. The use of HFIP provided aggregate‐free SEC/LALLS chromatograms from which molecular weight distribution averages were calculated. Comparison of SEC/LALLS molecular weights determined in HFIP with similar data obtained using tetrahydrofuran as the polymer solvent and chromatographic mobile phase indicated that the former is more generally applicable for PVB of different vinyl alcohol content.

Study of the melting and crystallization behaviour of poly(ethylene oxide)-poly(vinyl alcohol) blends

The melting and crystallization behaviour of blends of poly(ethylene oxide) and poly(vinyl alcohol) has been analysed. Hoffman-Weeks plots of the observed melting points versus crystallization temperatures are constructed. From these plots, melting-point depressions have been found. However, measurements of glass transition temperatures by dynamic mechanical thermal analysis have shown no changes for poly(ethylene oxide). Crystallization kinetics became slower as the poly(vinyl alcohol) content was increased.

Synthesis and transport properties of poly(vinyl alcohol) acrylonitrile/2-hydroxyethyl methacrylate membranes—I. Synthesis of poly(vinyl alcohol) acrylonitrile 2-hydroxyethyl methacrylate graft copolymer

The graft copolymerization of acrylonitrile and hydroxyethyl methacrylate monomers onto poly(vinyl alcohol) backbone using the ceric ion technique was investigated in detail and a high percentage grafting of the monomers onto the backbone was obtained. Another backbone which was investigated was a blend of poly(vinyl alcohol) and polyacrylic acid (PVA-PA). The grafting onto the poly(vinyl alcohol) was found to depend on the concentration of the ceric ion and its acidity and the poly(vinyl alcohol) content. Grafting was observed to proceed very smoothly onto the poly(vinyl alcohol) but was much slower in the poly(vinyl alcohol)/poly(acrylic acid) system. The graft copolymerization was interpreted in terms of an emulsion polymerization in the case of the poly(vinyl alcohol) system. However, grafting did not proceed very readily in the poly(vinyl alcohol)/poly(acrylic acid) blend system, explained by a coagulation which caused the system to react more slowly.

Spectrophotometric determination of poly(vinyl alcohol) in cadmium hydroxide pastes

A colorimetric method has been developed to spectrophotometrically determine the poly(vinyl alcohol) (PVA) content of aqueous Cd(OH)/sub 2/ pastes. The method, which is based upon the formation of a blue PVA-iodine-boric acid complex, can quantitatively determine PVA in aqueous solution concentrations of 2-40 mg/L corresponding to PVA levels within the paste as low as 0.02%. Solution absorbance of the complex, however, depends upon the concentration of Cd/sup 2 +/ in solution necessitating cognizance of this level for routine quantitative analysis.

Miscibility of mixtures from partially hydrolyzed poly(vinyl acetate) and poly(N‐vinyl‐2‐pyrrolidone)

AbstractPolymers with different compositions of vinyl alcohol and vinyl acetate units (P(VA‐VAc)), obtained by alcoholysis of poly(vinyl acetate) with sodium methoxide, were mixed with poly(N‐vinyl‐2‐pyrrolidone) (PVP). The miscibility was studied observing glass transition temperatures by differential scanning calorimetry (DSC). The calorimetric results indicate that for vinyl alcohol unit contents in P(VA‐VAc) of roughly 70 wt.‐% or more, P(VA‐VAc)/PVP blends are fully miscible, whereas blends obtained from P(VA‐VAc) with vinyl alcohol contents lower than the above mentioned values are only partially miscible or even immiscible. The miscibility is attributed to hydrogen bond interactions between hydroxyl groups in P(VA‐VAc) and the carbonyl group of PVP.

Dielectric and dynamic-mechanical behaviour of ethylene-vinyl alcohol copolymers

Dynamic-mechanical and dielectric measurements on ethylene-vinyl alcohol copolymers with two different vinyl alcohol contents and, for comparison on polyvinylalcohol and low density polyethylene, have been carried out in order to clarify the nature of the relaxation peak. The relaxation peak observable in the dielectric loss curves of the copolymers has been assigned to the interfacial polarization, MWS type, occurring between hydrogen bonded hydroxyl groups and the apolar polyethylene segments. The shoulder also present in the ε″-T curves of the copolymers seems to correspond to the glass transition peak which is hidden since the dielectric loss curve increases quickly because of the MWS polarization peak. The frequencytemperature map confirms this opinion.

Factors affecting water sorption in and solute release from glassy ethylene—vinyl alcohol copolymers

Liquid water sorption kinetics and equilibria in ethylene—vinyl alcohol copolymers of 62, 70 and 72 mole percent vinyl alcohol are characterized at 4° and 25°C. The effect of vinyl alcohol content on both sorption kinetics and equilibria is discussed. Particular attention has been devoted also to the description of the desorption kinetics of ionic solutes which have been previously sorbed and trapped in these glassy polymers. p]Solute diffusion coefficients in the swollen polymer and the relaxation parameters associated with the largely relaxation-controlled swelling of the glass have been measured. Sodium chloride release essentially follows water uptake during the swelling of the glass. Conversely, Fickian desorption patterns have been observed for the release of a highmolecular-weight dye, since complete swelling was achieved rapidly and diffusion-controlled solute release lagged behind the rapid swelling process. Comparison between solute diffusive conductance and the rate of penetration of the advancing swelling fronts leads to predictions of the relative contributions of diffusion and relaxation to the observed release patterns.

A kinetic investigation of thermal degradation of poly(vinyl formals)

AbstractSeveral samples of poly(vinyl formal) having the same vinyl alcohol content (8–9%) but varying contents of vinyl acetate (6–22%) and vinyl formol (70–85%) were prepared and subjected to thermogravimetric analysis, in air and nitrogen atmospheres, employing both isothermal and dynamic methods. Kinetic parameters determined from both the isothermal and dynamic TGA data are compared. The activation energy is seen to be largely dependent on the degree of conversion, implying a complex degradation reaction. The activation energy is also much less for degradation in air than in nitrogen, which can be explained by a reaction with oxygen‐producing structures favoring degradation. The activation energy is less sensitive to variation in polymer composition for degradation in air than in nitrogen. Thus, in the dynamic process, the activation energy value decreases (from 36 to 23 kcal/mole) with increasing acetate content (from 6 to 22%) in nitrogen atmosphere, while in air the activation energy value increases only moderately (from 21 to 27 kcal/mole) with increasing acetate content (from 6 to 22%). The order of reaction is nearly unity, irrespective of the composition of the polymer, both in air and nitrogen.

THE CRYSTALLINITY OF ETHYLENE-VINYLALCOHOL-ACRYLIC ACID TERPOLYMERS

The physical properties and crystal structure of ethylene-vinylalcohol-acrylic acid terpolymer (EVA-AA: 1_??_10mol% AA content) were investigated by X-ray diffraction method and differential scanning calorimetry.Following results were obtained: (1) The degree range of crystallinity of EVA-AA was about 15_??_25% which is lower than that obtained of ethylene-vinyl alcohol copolymer (25_??_50%) notwithstanding their nearly similar vinyl alcohol (VA) content. (2) A crystalline region of EVA-AA was partially decomposed by acrylic acid (AA) units. These AA units localized in the amorphous region of EVA-AA like the AA units in vinyl alcoholacrylic acid and ethylene-acrylic acid copolymer. (3) The data gathered from the melting point, d-spacing and copolymer composition showed that the crystalline region of EVA-AA was composed of VA and Et units and that the VA content of EVA-AA in the crystalline phase differed from the overall VA content of the terpolymer

THE MICRO STRUCTURE OF ETHYLENE VINYL ALCOHOL COPOLYMER

In order to show the relationship between the micro structure of crystalline ethylene vinylalcohol (EVA) copolymer and the copolymer component, the density and the thermal expansion of crystalline part and the behavior of hydroxyl group were studied for the EVA copolymers with various components.The following results were obtained: (1) The crystalline density of EVA copolymer observed by a floatation method was smaller than that evaluated from its unit cell at vinylalcohol (VA) contents under 20 mol%. For the other EVA copolymer with VA contents above 20 mol%, the larger crystalline density compared with the density by calculation from unit cell was always observed, and the VA concentration in the crystalline phase was larger than that of over all copolymer components. (2) According to infra-red spectrum for the hydroxyl group, at VA contents above 30 mol%, the hydrogen bonds were almost formed. (3) The thermal expansion of crystal for EVA copolymer were larger than those of PE and PVA. The expansion of the a axis direction was particularly larger than those of the other directions. From these data, it is reasonable to consider that the hydrogen bond was formed along this direction. (4) The thermal expansion coefficient of EVA copolymers containing VA 20 to 60 mol% was about 2 to 3 times that of EVA copolymer in other ranges of VA contents.

SOLUBILITY OF ETHYLENE-VINYLALCOHOL COPOLYMERS

In order to obtain the basic information of wet and dry spinnings of Ethylene-vinylalcohol copolymers (EVA), their solubility was investigated in many solvents and mixed solvents.The following results were obtained:1. Solubility of various EVA were closely related to solubility parameter (δ) of solvents and were, especially, interpreted with polar component (δp) and hydrogen-bonding component (δh) of the solubility parameter.2. Proton donating solvents such as m-Cresol, Phenol, Ethylene chlorohydrin and Dimethyl sulfoxide showed good solubility to EVA.3. Low vinylalcohol content EVA tended to dissolve in Benzene-Methanol mixed solvents, while high vinylalcohol EVA tended to dissolve in Methanol-Water mixed solvents.4. In case of EVA (vinylalcohol 73.4mol%) in n-Propanol/Water (8/2 vol. ratio), both lower and upper critical solution temperatures (LCST and UCST) were observed.