Patent ID: 7528192

Claim:
A process for the production of cross-linked polyvinyl acetals, wherein a polymer (A1) is cross-linked, and polymer (A1) contains, relative to its total weight, a) 1.0 to 99.9% by weight of structural units of formula (1) in which R 1 means hydrogen or methyl, b) 0 to 99.0% by weight of structural units of formula (2) in which R 2 represents hydrogen or an alkyl with 1 to 6 carbon atoms, c) 0 to 70.0% by weight of structural units of formula (3) in which R 3 , R 4 , R 5 and R 6 , in each case independently of one another, are each radicals with a molecular weight in the range of 1 to 500 g/mol, d) 0.00001 to 30.0% by weight of structural units of formula (4) in which R 7 and R 8 , in each case independently of one another, are hydrogen, carboxy, alkyl group with 1 to 10 carbon atoms which is optionally substituted by one or more COOH groups, or an optionally substituted aryl group with 6 to 12 carbon atoms, said process comprising in any sequence: (i) reacting polymer (A1) with at least one polyaldehyde of formula (5), R 9 (CHO) n (5) in which R 9 represents a bond or a radical having 1 to 40 carbon atoms, and n is an integer that is greater than or equal to 2, and (ii) partially esterifying groups of formula (1) and formula (4) with one another.