Copolymers prepared by copolymerization of (a) a total of from 3.5 to 20% by weight of at least one polymerizable acid selected from (a1) ethylenically unsaturated C3-C10-monocarboxylic acid and (a2) ethylenically unsaturated C4-C10-dicarboxylic acid or their anhydrides, (b) from 4 to 10% by weight of at least one compound of the general formula I the sum of (a) and (b) being in the range from 7.5 to 24% by weight, (c) from 60 to 92.5% by weight of at least one compound of the general formula II (d) from 0 to 0.5% by weight of at least one compound of the general formula III (e) from 0 to 10% by weight of (meth)acrylonitrile, (f) from 0 to 10% by weight of at least one conjugated diolefin, (g) from 0 to 10% by weight of at least one vinylaromatic compound of the general formula IV the variables being defined as follows: R1 and R2 are identical or different and are selected from hydrogen and C1-C10-alkyl, R3 and R4 are identical or different and are selected from hydrogen, C1-C20-alkyl, phenyl, or R3 and R4 together are C2-C10-alkylene, substituted or unsubstituted, R5 is selected from C1-C20-alkyl and phenyl, R6, R7, R8, R9, R10 and R11 are identical or different and are selected from hydrogen and C1-C10-alkyl, x is an integer in the range from 0 to 12, y is selected from 0 and 1, x being chosen to be not equal to 0 when y is 1, k is an integer in the range from 0 to 3, it being possible for the copolymers to be completely or partly neutralized with alkali or ammonium and data in % by weight being based in each case on the total copolymer.