SynopsisThe solubility properties of poly(viny1 alcohol) (PVA) vary with the method of preparation of the poly(viny1 acetate) (PVAc) from which it is derived. PVAc was prepared with free-radical catalysts over a range of temperatures from -78 to 90°C. with solvents of varying chain-transfer ability. The corresponding PVA samples varied in their resistance to dissolution in water. Their high-resolution proton nuclear magnetic resonance spectra showed no differences in tacticity. Data on 1,Zdiol content showed only minor differences. Hence, the increase in resistance of PVA to dissolution in water arising from changes in chain-transfer activity of the solvent used in vinyl acetate polymerization is largely attributable to a decrease in molecular weight, and the increase in resistance of PVA to dissolution in water arising from a decrease in the temperature of the vinyl acetate polymerization is largely attributable to a decrease in both long and short branches. Evidently, with polar polymers having small side groups, tacticity is iiot the only factor influencing property variation; that is, variations in stereoregularity influence more the crystallinity of the sample as measured by density or x-ray methods than the ultimate crystallizability under conditions of mechanical and thermal treatment. In this regard polar polymers having small side groiips differ from nonpolar polymers.
It has been postulated (1) that, when heated in solution, lead tetraacetate decomposes monomolecularly to yield lead diacetate and acetyl peroxide or free acetoxy and/or free methyl radicals.
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