Copolymers having a K-value of 5 to 80, measured as a 0.5 weight percent solution in isopropanol at 25.degree. C., prepared in the presence of polymerization initiators by the radical polymerization of:
- A) 20 to 80 weight percent, based on the total weight of monomers (A) and (B), of at least one olefinic unsaturated polyoxyalkylene alcohol adduct or polyester alcohol adduct;
- B) 80 to 20 weight percent, based on the total weight of monomers (A) and (B), of at least one vinyl monomer selected from the group consisting of N-vinyl-formamide, N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-2-caprolactam, N-vinyl-2-propylene urea;
- C) 0 to 40 weight percent, based on 100 parts by weight of monomers (A) and (B), of glycidyl acrylate, glycidyl methacrylate or mixtures thereof;
- D) 0 to 10 parts by weight based on 100 parts per weight of monomers (A) and (B) of at least one a,b-monoolefinic unsaturated acid and;
- E) 0 to 30 parts by weight based on 100 parts per weight of monomers (A) and (B) of at least one olefinic unsaturated carboxylic acid amide, and/or olefinic unsaturated carboxylic acid ester and/or styrene.