An improved process for the production of powders of maleic acid anhydride/1-olefin copolymers by suspension polymerization in the presence of special dispersion agents which are obtained by the reaction of a copolymer of maleic acid anhydride and a 1-olefin with an aliphatic monohydric alcohol or an aliphatic monoamine or a mixture thereof, at least 30 mol % of the anhydride groups being esterified to semi-esters or amidated to semi-amides. The copolymer powders obtained have a surprisingly narrowparticle size distribution and can be used without grinding or sifting as reactive fillers for natural and synthetic rubbers. They also can be used for the production of paper coating agents as they dissolve easily and without residue in alkalis, ammonia or amines.