Styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) and styrene-b-(ethylene-co-propylene) (SEP, SEPSEP) block copolymers with different styrene contents and different numbers of blocks in the copolymer chain were functionalized by melt radical grafting with glycidyl methacrylate (GMA) and employed as compatibilizers for PET-based blends. Binary blends of PET with both functionalized (SEBS-g-GMA, SEP-g-GMA, SEPSEP-g-GMA) and neat (SEBS, SEP, SEPSEP) copolymers (75 : 25 w/w) and ternary blends of PET and PP (75 : 25 w/w) with various amounts (2.5-10 phr) of both modified and unmodified copolymers were prepared in an internal mixer, and their properties were evaluated by SEM, DSC, melt viscosimetry, and tensile and impact tests. The roles of the chemical structure, grafting degree, and concentration of the various copolymers on blend compatibilization was investigated. The blends with the grafted copolymers showed a neat improvement of phase dispersion and interfacial adhesion compared to the blends with nonfunctionalized copolymers. The addition of grafted copolymers resulted in a marked increase in melt viscosity, which was accounted for by the occurrence of chemical reactions between the epoxide groups of GMA and the carboxyl/hydroxyl end groups of PET during melt mixing. Blends with SEPSEP-g-GMA and SEBS-g-GMA, at concentrations of 5-10 phr, showed a higher compatibilizing effect with enhanced elongation at break and impact resistance. The effectiveness of GMA-functionalized SEBS was then compared to that of maleic anhydride-grafted SEBS. (c) 2005 Wiley Periodicals, Inc.