GB482731A - Improvements in the production of synthetic resins and the manufacture of films or sheets therefrom - Google Patents

Abstract

Polyvinyl acetal resins containing 12 to 15 per cent of hydroxyl groups (calculated as polyvinyl alcohol) and at least 10 per cent of ester groups (calculated as polyvinyl ester) are prepared by treating a partially hydrolyzed polyvinyl ester, e.g. polyvinyl acetate, in the presence of a mineral acid catalyst with acetaldehyde under conditions such that acetalysis is not complete. Completion may be prevented by using less than the stoichiometrical quantity of aldehyde or by using excess of water. A polyvinyl ester may be used as starting material and the reaction carried out in the presence of a de-esterifying agent, e.g. water or alcohol, with or without additional solvents, e.g. ethyl acetate or acetone; and the reaction may be carried out under reflux or in a closed vessel, e.g. at 70 DEG C. Suitable catalysts are sulphuric, hydrochloric, or phosphoric acids. The hydroxyl group content of the resins is determined by suspending a sample in pyridine, warming for an hour with a known excess of acetic anhydride, adding water, and titrating the acetic acid produced. The ester group content is determined by suspending a sample in pyridine, warming with a known excess of caustic soda, and titrating. The resins may be made into films by coating a solution of the resin in a solvent, e.g. methyl alcohol with or without acetone, methyl acetate, or both, on to a glass or metal plate or a revolving drum, evaporating, stripping, and curing by heating with warm air. The following examples (in which the parts are by weight) are given. (1) 1300 Parts of polyvinyl acetate and 266,4 parts of paracetaldehyde were dissolved in ethyl alcohol and ethyl acetate and heated for 12 hours at 70 DEG C. in the presence of sulphuric acid. The reaction mixture was then neutralized with ammonium hydroxide precipitated by water and washed. The hydroxyl group content was 13,6 per cent and the acetate content 20,2 per cent. (2) As in (1) but using larger quantities of reactants in the same relative proportions. The hydroxyl group content was 13,5 per cent and the acetate content 20 per cent. (3) As in (1), but using double quantities. The hydroxyl group content was 12,6 per cent and the acetate group content 21,25 per cent. Specifications 351,082* and 477,446 are referred to.