| 摘要 |
1,231,532. Polyvinyl alcohol. E. I. DU PONT DE NEMOURS & CO. 24 Feb., 1969 [23 Feb., 1968], No. 9819/69. Heading C3P. In a method for the production of polyvinyl alcohol in which a solution of a polyvinyl ester in a hydrolytic alcohol is continuously fed to an alcoholysis mixture containing an alcoholysis catalyst and from which mixture there is continuously withdrawn a slurry of the polyvinyl alcohol in a solvent mixture of the alcohol and the by-product ester of the alcohol with the residue acid of said polyvinyl ester, said solution of the polyvinyl ester is fed to said alcoholysis mixture at a rate such that the concentration of soluble polymer in said alcoholysis mixture does not exceed about 1 % of the weight of said alcoholysis mixture and the alcoholysis mixture is maintained at a temperature not exceeding 35� C., whereby the product polyvinyl alcohol obtained is 97 to 98�5 % alcoholysed and an aqueous solution thereof is gel-resistant at room temperature. Polyvinyl acetate is alcoholysed in a mixture of methyl alcohol and methyl acetate using sodium methylate. The polyvinyl acetate is preferably pre-alcoholysed to 10-40%. |
