If the elastomer is composed of one or more rigid components (having glass transition temperatures of more than 20??? C.) in addition to the rubber phase, said rigid components are generally prepared by polymerizing styrene, acrylonitrile, methacrylonitrile, ??-methylstyrene, p-methylstyrene, acrylates and methacrylates, such as methyl acrylate, ethyl acrylate and methyl methacrylate, as main mono