Grafting of polypropylene (PP) by reactive processing in the presence and absence of styrene (ST) was performed to assess the effect of each one of the copolymers obtained in the compatibilization of poly(ethylene terephthalate) and (propyleneethylene) copolymer blends, PET/EP copolymer (80/20). Grafting reactions of maleic anhydride and ST onto PP were conducted according to an experimental design where the concentrations of maleic anhydride and ST were varied. The amount of reacted maleic anhydride and the extent of degradation in PP were determined by means of Fourier-transformed infrared spectroscopy and melt-flow index, respectively. The PET/EP copolymer blends were obtained in a co-rotating twin-screw extruder. The effect of grafted copolymer type, PP-g-MA (PP grafted with maleic anhydride) or PP-g-MAST (PP grafted with maleic anhydride and styrene) in the compatibilization of PET/EP copolymer blends was assessed through mechanical (tensile test), morphological (scanning electron microscopy), and rheological properties. The presence of ST in the grafting reaction of maleic anhydride onto PP showed to significantly increase the amount of reacted maleic anhydride and reduce PP degradation. However, increasing ST concentration in the reaction mass affected the investigated variables only when maleic anhydride concentration was at its lowest level. Results of the PET/EP blends showed that both graft copolymers improved polymer interface adhesion, however, PP-g-MAST showed improved performance for the same level of compatibilizer used. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013