| 摘要 |
Polyvinyl acetals are prepared by adding with agitation polyvinyl alcohol, dissolved in a preponderantly aqueous solvent, to an aldehyde containing at least two carbon atoms, in the presence of an acid catalyst, at least 0.08 mols. of aldehyde being present per mol. of polyvinyl alcohol, in such a way that rapid dispersion of the polyvinyl alcohol is obtained, and maintaining the reaction mixture under agitation until acetalization has proceeded to the predetermined degree. In a modification of the process, the polyvinyl alcohol solution and the aldehyde may be introduced into a reaction vessel simultaneously in proportionate amounts under vigorous agitation. The polyvinyl alcohol may be added to the aldehyde contained in a reaction vessel and, if desired, a further quantity of aldehyde may be added to the reaction mixture. Small amounts of dispersing agents, e.g. gelatine, monomyristine, monostearine or a fatty alcohol sulphate, may be added to the polyvinyl alcohol solution. In examples: (1) a 10 per cent aqueous solution of polyvinyl alcohol containing sulphuric acid catalyst is added to butyraldehyde under agitation, a further portion of butyraldehyde is added and the mixture held at 50-55 DEG C.; and (2) an aqueous solution containing polyvinyl alcohol, sulphuric acid and methanol and butyraldehyde are introduced simultaneously into a mixing vessel in proportionate amounts, the mixture is maintained under agitation for an hour at 50 DEG C. when, on cooling, the polyvinyl butyral resin separates out. Resins are obtained, having constitutions by weight of polyvinyl ester 0-10 per cent, polyvinyl alcohol 15-22 per cent and polyvinyl acetal 85-77 per cent. Examples are given of the use of acetaldehyde, butyraldehyde, isobutyraldehyde, paraldehyde, propionaldehyde, benzaldehyde, 2.4-dimethyl pentanal, and mixtures of aldehydes. Specification 566,004 is referred to. |
