Abstract: Copolymers have a viscosity index VI of more than 160 and compriseA) from 99.0 to 99.99 % by weight of C.sub.2 -C.sub.20 -alk-1-enes andB) from 0.01 to 1.0% by weight of C.sub.5 -C.sub.20 -.alpha.,.omega.-dienes having isolated double bonds.

Abstract: Thermoplastic molding materials compriseA) from 30 to 98% by weight of a graft polymer ofa.sub.K) from 30 to 90% by weight of an elastomeric graft core, obtainable by copolymerization ofa.sub.K /1) from 80 to 99.99% by weight of a C.sub.1 -C.sub.10 -alkyl ester of acrylic acid,a.sub.K /2) from 0.01 to 20% by weight of a crosslinking monomer anda.sub.K /3) from 0 to 40% by weight of one or more further monomers, anda.sub.S) from 10 to 70% by weight of a graft shell ofa.sub.S /1) from 50 to 100% by weight of a styrene compound of the general formula ##STR1## where R.sup.1 and R.sup.2 are each hydrogen or C.sub.1 -C.sub.8 -alkyl, and/or of a C.sub.1 -C.sub.8 -alkyl ester of acrylic acid or methacrylic acid, anda.sub.S /2) from 0 to 50% by weight of one or more further monomers,B) from 1 to 50% by weight of a thermoplastic polymer ofb.sub.1) from 50 to 100% by weight of styrene and/or .alpha.-methylstyrene,b.sub.2) from 0 to 50% by weight of acrylonitrile andb.sub.