Partially crosslinked plastics materials having a melt flow index of from 0.1 to 100 g/10 min at 230.degree. C. and under a weight of 2.16 kg, containinga) a polymer of from 25 to 97% by weight of a propylene copolymer (I) which contains from 0.1 to 15% by weight of polymerized C.sub.2 -C.sub.10 -alk-1-enes and of from 3 to 75% by weight of a further propylene copolymer (II) which contains from 15 to 80% by weight of polymerized C.sub.2 -C.sub.10 -alk-1-enes andb) an organosilane compound of the following formula (I)A.sub.4-n SiR.sub.n (I)where the radicals A are identical or different and are each an acrylate or methacrylate or vinyl, the radicals R are identical or different and are each C.sub.1 -C.sub.8 -alkoxy or C.sub.1 -C.sub.8 -acetoxy and n is 1, 2 or 3,are obtainable by reacting the polymer a) with the organosilane compound b) in the presence of a free radical initiator and a condensation catalyst at from 180 to 280.degree. C. and from 1 to 100 bar and in the course of average residence times of the reaction mixture of from 0.2 to 10 minutes.The novel plastics materials have in particular improved processibility and thermoformability, a lower sealing temperature and better white fracture behavior.