What is claimed are copolymers consisting essentially of from 1 to 90% by weight of the repetitive structural unit of the formula (1) in which R1 is hydrogen or methyl, Z is a C1-C4-alkylene group and X is hydrogen, an alkali metal or ammonium, from 10 to 99% by weight of a repetitive structural unit which is derived from olefinically unsaturated comonomers containing at least one oxygen, nitrogen, sulfur or phosphorus atom and from 0 to 20% by weight of crosslinking structures originating from monomers having at least two olefinic double bonds. These copolymers are suitable for use as drift control agents for crop protection compositions.