The invention relates to a process for producing molding compositions containing: a) from 55 to 85% by weight of copolymer A composed of vinylaromatic monomer A1 and a,B-unsaturated monomer A2; b) from 15 to 45% by weight of graft copolymer B with particle size from 50 to 550 nm composed of: B1: from 60 to 80% by weight of rubbery graft base B1 composed of: B11: from 80 to 99% by weight of at least one C2-C8-alkyl acrylate, B12: from 0.5 to 2.5% by weight of cyclic crosslinking agent, B13: from 0 to 2% by weight of non-cyclic crosslinking agent, B2: from 20 to 40% by weight of at least one graft shell B2 composed of: B21: from 60 to 75% by weight of a styrene, B22: from 25 to 40% by weight of acrylonitrile, c) from 0 to 10% by weight of additives C; where the reaction time of the polymerization for producing the graft base B1 is in the range from 2 to 5 h, and the addition of the starting materials takes place over at least two chronological segments.