Exemplary of such prior art is U.S. Pat. No. 4,031,166 of Bronstert et al, which describes an impact-resistant thermoplastic having a major portion (70-99% by weight) of a styrenic polymer, and a minor portion (from 1 to 30% by weight) of an alpha-olefin polymer, preferably polyethylene, but also including polypropylene, polyisobutylene and copolymers of two or more alpha-olefins, together with co