The present invention provides a method of forming comb or star copolymers. The comb or star copolymers are useful in surface modification of thermoplastic materials or as surfactants. The method is aimed at attaching a polymeric side chain differing in polarity and chemical structure from the backbone and forming a comb or star copolymer structure. In particular the process comprises polymerizing in a first step a polymer backbone from epoxy and nitroxylether group containing monomers and in a second step polymerizing under controlled radical conditions a comb or star structure onto this backbone. The epoxy group containing monomers are for example of the formula (II) ##STR00001##