The instant invention relates to a composition of a thermoplastic polymer and a triblock-copolymer or grafted comb copolymer, with enhanced melt flow during processing. Further aspects of the invention are the triblock-copolymers or grafted comb polymers itself, a method for their production and their use as compatibilizers and meltflow enhancing additives. Yet another aspect of the invention are functional alkoxyamines, which are useful for the preparation of the triblock-copolymers or grafted comb polymers.