| 摘要 |
Partial polyvinyl acetal resins are manufactured by bringing about the incomplete reaction of polyvinyl alcohol with an aldehyde, in the presence of an inorganic acidic substance as catalyst, under such reaction conditions that from about 2,5 to about 7, preferably 2,5 to 4, molecular proportions of polyvinyl alcohol (calculated as the monomeric substance) are caused to combine with one out: (a) by reacting an aldehyde with an aqueous solution of polyvinyl alcohol; (b) by reacting an aldehyde with a suspension of polyvinyl alcohol in a suitable solvent for the resin to be made; or preferably (c) by conducting the reaction in a liquid medium of which the composition is adjusted as the reaction proceeds so that a solid phase is never present. In examples: (1) and (2) butyraldehyde is stirred with an aqueous solution of polyvinyl alcohol and hydrochloric acid is added; (3) n-hexaldehyde is similarly reacted; (4) various proportions of propionaldehyde are reacted with polyvinyl alcohol in aqueous hydrochloric acid solution, the equilibrium ratio of polyvinyl alcohol to aldehyde being 4 mols. to 1 in each case; (5) polyvinyl alcohol damp with methyl alcohol is dissolved in isopropyl alcohol and the solution is stirred with butyraldehyde and hydrochloric acid and then allowed to stand, whereby about 3,5 mols. of polyvinyl alcohol react with one of aldehyde; (6) as in (5) but using more aldehyde, about 2,5 mols. of polyvinyl alcohol reacting with one of aldehyde; (7) the reaction of (5) is effected in the presence of n-butyl alcohol instead of isopropyl alcohol; (8) and (9) butyraldehyde is added gradually to an aqueous solution of polyvinyl alcohol containing hydrochloric acid, and isopropyl alcohol is added as the reaction proceeds so as to prevent the formation of a precipitate; (10) butyraldehyde and hydrochloric acid, both dissolved in isopropyl alcohol, are added alternately to an aqueous solution of polyvinyl alcohol. Other aldehydes specified are: formaldehyde and paraformaldehyde, acetaldehyde and paraldehyde, 2-ethylhexaldehyde, 3-heptaldehyde, crotonaldehyde, 2-vinylcrotonaldehyde, hexadien-2 : 4-al-1, 2 : 3-ethylpropylacrolein, 2 : 3-isobutylaryl acrolein and benzaldehyde. Mixtures of aldehydes may also be used. Specification 351,082* is referred to. 2 : 3-Isobutylamylacrolein is obtainable by reacting hexaldehyde with isohexaldehyde. Hexadien-2 : 4-al-1 is obtainable by condensing acetaldehyde with crotonaldehyde. |
