Patent ID: 8034888

Claim:
A copolymer obtained by free-radical polymerization of a monomer mixture M comprising a) 30 to 80% by weight of ethyl methacrylate or 30 to 80% by weight of a mixture of ethyl methacrylate and at least one compound of the general formula (I) different from ethyl methacrylate in which R 1 is H or CH 3 , R 2 is C 1 -C 4 -alkyl, b) 0 to 40% by weight of at least one N-vinyllactam compound, c) 5 to 35% by weight of at least one monoethylenically unsaturated carboxylic acid, d) 0.1 to 30% by weight of at least one compound with a free-radically polymerizable, α,β-ethylenically unsaturated double bond and at least one cationogenic and/or cationic group per molecule, e) 0 to 20% by weight if appropriate of further free-radically polymerizable monomers different from a), b), c) and d), where the fractions of components a) to e) add up to 100% by weight and where the monomer mixture M comprises at least 20% by weight of ethyl methacrylate, wherein the ratio of the total molar amount of the carboxyl and carboxylate groups to the total molar amount of the cationogenic and cationic groups is at least 2.