| 摘要 |
In a process for the manufacture of solid polyvinyl alcohol, a polyvinyl ester of a carboxylic acid having 1 to 10 carbon atoms is hydrolysed within the temperature range 10 DEG to 120 DEG C. with 0,01 to 10% by weight of the reaction mixture of a strong acid as catalyst and 0,5 to 15% by weight of the reaction mixture of water, the balance being a mixture of 1 to 50% by weight of said ester and 99 to 50% by weight of a water-miscible and acid-miscible solvent for the polyvinyl ester but non-solvent for the polyvinyl alcohol and, under the reaction conditions does not form an ester with the carboxylic acid radical of the polyvinyl ester, whereby polyvinyl alcohol is precipitated in powdery form and recovered from the reaction mixture. The polyvinyl ester may be polyvinyl acetate, propionate or formate. The solvent may be acetone, methyl ethyl ketone, diethyl ketone, t-butanol, methyl acetate or tetrahydrofuran and mixtures thereof with aromatic hydrocarbons. The acid may be hydrochloric, sulphuric, phosphoric, perchloric or a sulphonic acid. The hydrolysis may be interrupted to give partially hydrolysed products, or such products may be obtained by selection of appropriate reactants and conditions. Specification 818,294 is referred to. |
