Using maleic anhydride grafted polyethylene as blend component in blends with thermoplastic polyurethanes (TPU), the particle size was reduced dramatically in comparison to the non-reactive case. In addition, phase adhesion was observed and the mechanical properties were improved, These improvements are due to the chemical reaction, as well as to the influence of the lower viscosity ratio of the reactive blend system. Ethylene copolymers with different contents of acrylic acid were added as compatibilizer to TPU / polypropylene blends. The ethylene copolymers ape not miscible with the blend components and no reaction with the TPU was found. Nevertheless, the particle size of tile blends was reduced. Additionally, the morphology was stabilized against coalescence in quiescent melt and under processing conditions. The mechanical properties were improved. These results are due Po the steric suppression of coalescence.