| 摘要 |
Polyvinyl alcohol is prepared by the alcoholysis with excess methanol of a solid, finely-divided polyvinyl ester of an unsubstituted lower aliphatic monocarboxylic acid, such as polyvinyl formate, acetate, propionate, or butyrate, under vigorous agitation in the presence of an alkaline catalyst, such as sodium or potassium hydroxide or alcoholate, and a liquid solvent modifier, such as oil of turpentine, petroleum fractions, and coal tar naphthas freed from benzene and toluene, which is at least partially miscible with methanol, and in which the polyvinyl alcohol is insoluble and the polyvinyl ester is not more than sparingly soluble; the volume ratio of methanol to liquid solvent modifier is within the range of 20 : 1 to 0.2 : 1, the ratio being such that the rate of solution of the polyvinyl ester in the mixture is less than the rate of alcoholysis. The process is preferably carried out at room temperature, either batchwise or continuously, and the polyvinyl alcohol may be separated from the alcoholysis medium by filtration or centrifuging to provide a polyvinyl alcohol of low ester content which gives a clear solution when dissolved in water. Specification 512,001 is referred to. |
