| 摘要 |
The stability of resin prepared by condensation of polyvinyl alcohol or a hydrolyzed polyvinyl ester with a substance containing a reactive carbonyl group in the presence of sulphuric acid is improved by subjecting the resin to an hydrolysis or alcoholysis so mild as not appreciably to affect the acetal groups or ester groups if present. Hydrolysis may be effected by very dilute acids (other than sulphuric acid), e.g. monobasic acids such as hydrochloric, hydrobromic or perchloric acids or by dilute solutions of acid-reacting salts, e.g. ammonium or zinc chlorides. Alcohols specified for the alcoholysis are methyl, ethyl, and iso-propyl alcohols. Where the acetals are derived from aldehydes, there may be included bodies capable of reacting therewith, e.g. urea or other amides, or primary or secondary amines. The resin need not be isolated before treatment: the sulphuric acid present may be neutralized, e.g. by sodium acetate, hydroxide, or phosphate, ammonia, or amines and the hydrolytic agent then added; or the reaction mixture may be poured into a solution of a soluble salt, e.g. sodium chloride, the sulphuric acid being neutralized and liberating the hydrolytic agent. The resins before or after stabilization, may be neutralized by alkalies, alkali salts, or organic bases, e.g. by sodium acetate, carbonate, or hydroxide, ammonia, or amines. The treatment may be carried out in the presence of a water-miscible swelling agent for the resin, e.g. acetic acid, dioxane or alcohols. In examples: polyvinyl acetaldehyde, formaldehydebutyraldehyde, or formaldehyde-acetaldehyde acetal resins are treated with very dilute hydrochloric acid at room temperature; a polyvinyl acetaldehyde acetal resin is treated with the same at 100 DEG C.; with an aqueous-isopropyl alcoholic solution of sodium acetate (with or without hydrochloric acid), with an aqueous solution of sodium chloride, or with a tert.-butyl alcoholic solution of hydrogen chloride; a polyvinyl butyraldehyde acetal resin is treated with a dilute aqueous solution of acetic and hydrochloric acids. |
