Abstract: Impact modified copolymers of vinyl aromatic, ethylenically unsaturated nitrile and, optionally, methyl methacrylate monomer, wherein the impact modifier comprises (a) large grafted rubber particles of a rubbery alkyl acrylate polymer having a particle size from about 0.5.mu. to 0.8.mu., 0.04 to 0.5 percent by weight of a polymerized crosslinking monomer and from 0.5 to 40 percent grafted rigid phase, and (b) small grafted rubber particles of a rubbery alkyl acrylate polymer having a particle size from about 0.05.mu. to about 0.20.mu., 0.25 to about 2.0 percent of a crosslinking monomer, provided that the weight percentage of crosslinking monomer is at least twice the weight percentage of the crosslinking monomer in the large particle, and from about 15 to about 60 percent by weight grafted rigid phase.