Patent ID: 8153740

Claim:
An ampholytic copolymer obtained by free-radical copolymerization of a) at least one compound with a free-radically polymerizable, α,β-ethylenically unsaturated double bond and at least one anionogenic and/or anionic group per molecule selected from the group consisting of acrylic acid, methacrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, b) 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 selected from the group consisting of vinylimidazole, tert.-butylaminoethyl methacrylate and mixtures thereof, and, c) at least one α,β-ethylenically unsaturated amide-group-containing compound selected from the group consisting of acrylamide, methacrylamide, N- vinylpyrrolidone, N-vinylcaprolactam, N-vinylformamide, N-vinylacetamide and mixtures thereof, where the quantitative molar ratio of compounds a) to compounds b) is from 0.5:1 to less than 2:1.