Patent ID: 6870009

Claim:
A low molecular weight polyvinyl acetal with a solution viscosity of from 2 to 12 mPas measured in accordance with DIN 53015, Höppler method, 10% by weight solution in ethanol, and with a degree of polymerization P w less than 200, said low molecular weight polyvinyl acetal obtained by hydrolyzing a vinyl ester polymer and then acetalizing the resultant polyvinyl alcohol using one or more aldehydes selected from the group consisting of aliphatic and aromatic aldehydes having from 1 to 15 carbon atoms, wherein a vinyl ester polymer obtained by polymerizing one or more vinyl esters of optionally branched C 1-15 alkylcarboxylic acids, and optionally, one or more co-monomers selected from the group consisting of ethylenically unsaturated mono- and dicarboxylic acids, ethylenically unsaturated carboxamides and carbonitriles, monoesters of fumaric acid and maleic acid and salts thereof, (meth)acrylates of C 1-15 alcohols, monoolefins, dienes, vinylaromatics and vinyl halides, and optionally, from 0.02 to 20% by weight based on the weight of the vinyl ester polymer of one or more polyethylenically unsaturated precrosslinking monomers, and from 0.02 to 20% by weight of one or more post-crosslinking monomers selected from the group consisting of acrylamidoglycolic acid, methyl methacrylamidoglycolate, N-methylolacrylamide, N-methylolmethacrylamide, allyl N-methylolcarbamate, alkyl ethers and esters of N-methylolacrylamide, alkyl ethers and esters of N-methylolmethacrylamide and alkyl ethers and esters of allyl N-methylolcarbamate, said vinyl ester polymer having a solution viscosity of from 1.0 to 1.6 mPas measured in accordance with DIN 53015, Höppler method, 10% by weight solution in ethyl acetate, is hydrolyzed, the hydrolysis proceeds until the content of vinyl alcohol units is ≧50 mol %, and the resulting polyvinyl alcohol has a solution viscosity is from 1.0 to 2.0 mPas measured in accordance with DIN 53015, Höppler method, 4% by weight solution in water.