The hard acrylic ester monomers are selected from alkyl methacrylates containing to 3 carbon atoms in the alkyl group and from non-acrylic monomers such as styrene and substituted styrenes, acrylonitrile, vinyl chloride, and generally any compatible monomer the homopolymer of which has a Tg above 50??? C. Preferred acrylic ester monomers are selected from alkyl methacrylates containing 1 to 2 carb