Aqueous solutions or aqueous emulsions of copolymers are obtainable by copolymerization of (a) from 20 to 95 mol % of at least one monoethylenically unsaturated C4-C12-dicarboxylic acid or the anhydride thereof with (b) from 5 to 80 mol % of at least one branched oligomer or polymer which has a vinyl, vinylidene or alkylvinylene terminal group and is of at least 9 carbon atoms and (c) from 0 to 50 mol % of at least one further monoethylenically unsaturated compound which is copolymerizable with the monomers (a) and (b) and contain from 0.5 to 70% by weight, based on the total amount of the solutions or emulsions, of these copolymers. These copolymer solutions or emulsions are suitable as leather assistants and as dispersants for pigments.