Poly vinyl acetate dispersions

Poly(vinyl acetate) dispersions are more sensitive to hydrolysis but have good color retention and resistance to grease and oil. 

FIG. 13.14 Critical flocculation temperature of aqueous poly(vinyl acetate) dispersion stabilized by poly(oxyethylene) indicated by a sharp change in absorbance with temperature. (Redrawn with permission from D. H. Napper, in Colloid and Interface Science (M. Kerker, R. L. Rowell, and A. C. Zettlemoyer, Eds.), Academic Press, New York, 1977.)... 

Ballantine (4) observed that the y-induced emulsion polymerization of styrene is about 100 times faster and yields higher molecular weights (up to 2 X 10 ) than the y-induced bulk polymerization. He explains the large difference in reaction rates by the high radical yield (G/ value) of water, as compared with the G/j value of styrene. An over-all activation energy of 3.7 kcal. per mole was calculated from the temperature dependence of the reaction. Allen et al. (1) prepared and grafted polystyrene and poly (vinyl acetate) dispersions under the influence of y-radiation. Mezhirova et al. (28) found a temperature-independent reaction rate of the y-induced emulsion polymerization of styrene. 

Preparation of a Stable Poly (vinyl acetate) Dispersion. 246... 

Mowicoll Hoechst Poly(vinyl acetate) dispersions... 

Poly(vinyl ester) dispersions are quantitatively more important than solid resins. Homopolymer and copolymer dispersions are used for binders in emulsion (dispersion) paints, plastic-bonded plasters, and water-thinnable adhesives. Poly(vinyl acetate) dispersions are less important than vinyl acetate copolymer dispersions. The most important comonomers of vinyl acetate are vinyl laurate, dibutyl maleate, Versatic Acid esters (VeoVa, Shell), ethylene, vinyl chloride, and butyl acrylate. Poly(vinyl propionate) and copolymers of vinyl propionate with butyl acrylate, styrene, or vinyl chloride are also marketed and used as dispersions. 

Poly(vinyl acetate) dispersions form lightfast, dry, hard, brittle films. Plasticizers therefore have to be used (external plasticization), which are, however, volatile and lead to embrittlement of the films after a relatively short time. Internally plasticized dispersions of copolymers of vinyl acetate with vinyl laurate, butyl maleate, Versatic Acid esters, or ethylene form permanently flexible, nonaging films that are not, however, always sufficiently resistant to hydrolysis. Terpolymer (vinyl acetate-ethylene-vinyl chloride) dispersions form films that are more resistant to hydrolysis than homopolymer and copolymer dispersions. The films also have a higher mechanical strength and lower flammability. The glass transition temperature of the terpolymer can be varied within wide limits and properties can be matched to requirements by using a suitable choice of comonomers. The same is true of vinyl propionate copolymer dispersions. 

Adhesives, poly(vinyl acetate) dispersions, drying oils, cross-linking, NMR spectroscopy... 

The PVAc formulations currently available on the adhesives market are rather complex systems comprising a poly(vinyl acetate) dispersion, a film forming promoter, a cross-linking agent and/or a hardener. The use of modified poly(vinyl acetate) dispersions generally requires a thermal treatment to obtain the best results and the use of a specific cross-linking comonomer, such as N-methylolacrylamide (NMA), may cause a lower shelf-life of adhesives as well as formaldehyde emissions. 

TABLE 7.2 Some Poly(Vinyl Acetate) Dispersions Used in Conservation ... 

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