A graft polymer obtained by free radically polymerizing:(A) a monomer or monomer mixture comprising:(a) from 10-100% by weight of a N-vinylcarboxamide of the formula: ##STR1## where R.sup.1 and R.sup.2 are each H or C.sub.1 -C.sub.6 -alkyl, (b) from 0-90% by weight of at least one other monoethylenically unsaturated monomer which is copolymerizable with (a), and(c) from 0-5% by weight of at least one monomer having at least two ethylenically unsaturated nonconjugated double bonds in the molecule, in the presence of(B) a polytetrahydrofuran or a polymer which contains at least 3 units of a C.sub.2 -C.sub.4 alkylene oxide and is a hornopolymer of C.sub.2-4 -alkylene oxide having two free terminal OH groups or random or block copolymers of C.sub.2-4 -alkylene oxides having two free terminal OH groups or the reaction products of C.sub.2-4 -alkylene oxides with phenols, amines or fatty carboxylic acids, in a weight ratio (A):(B) ranging from 95:5 to 10:80, some or all of the amide groups having been eliminated by hydrolysis.