| 摘要 |
"Partial" polyvinyl acetals (i.e. those containing only acetal and hydroxyl groups) are prepared by treating at about 60 DEG C. an anhydrous alcoholic solution of a polyvinyl ester simultaneously with an inorganic acid, e.g. anhydrous hydrochloric or sulphuric acids, and an amount of aldehyde less than that equivalent to the alcoholysis product, and treating the reaction product with alkali, e.g. alcoholic sodium hydroxide. Polyvinyl esters specified are those of aliphatic acids, e.g. polyvinyl formate, acetate, propionate, or butyrate, or of inorganic acids, e.g. polyvinyl halides. Aldehydes specified are straight-chain saturated aliphatic aldehydes containing at least three carbon atoms, e.g. propionaldehyde, butyraldehyde, 2 - ethyl butyraldehyde, n-hexaldehyde, 2-ethylhexaldehyde; also benzaldehyde, formaldehyde, acetaldehyde, crotonaldehyde, isomers of vinyl crotonaldehyde, e.g. hexadienal; or mixtures thereof. The solvent alcohol may be any lower aliphatic alcohol, e.g. methyl, ethyl, iso-propyl, or butyl alcohol. Products containing 25--80 per cent, especially those with 60 to 75 per cent of acetal groups, may be used as interlayers in safety glass. In examples: a methyl-alcoholic solution of polyvinyl acetate was simultaneously treated with n-butyraldehyde and (a) anhydrous hydrochloric acid, (b) anhydrous sulphuric acid, and the acetal precipitated with water and treated with alcoholic sodium hydroxide. The products are soluble in ethyl alcohol, in glycol monoalkyl ethers, and in methyl alcohol containing less than 10 per cent of water; and are compatible with ester plasticizers, e.g. diethyl phthalate. |
