Abstract: A description is given of a process for preparing aqueous copolymer dispersions by free-radical polymerization of ethylenically unsaturated monomers in an aqueous solution in which (a) from 10 to 90% by weight of at least one hydrophilic monomer A which has an N-vinyl group and whose polymerisation rate possesses a maximum at pH levels above 7, and (b) from 10 to 90% by weight of at least-one monoethylenically unsaturated hydrophobic monomer B whose polymerisation rate possesses a maximum at pH levels below 7, are copolymerised in the presence of a free-radical initiator system such that in the course of the polymerization the pH falls by from 2 to 5 units. The copolymer dispersions prepared in this way and the copolymers obtainable therefrom are suitable as auxiliaries for pharmaceutical, cosmetic or agrochemical formulations and for preparing paints, coating compositions, sizes, and adhesives.