This article concerns the in situ compatibilization of immiscible isotatic polypropylene/ styrene-butadiene-styrene triblock copolymer blends (i-PP/SBS) by use of a reactive mixture. For this purpose, maleated PP (PP-MAH) and SBS (SBS-MAH) were used as functionalized polymers and 4,4'-diaminediphenylmethane was used as a coupling agent between maleated polymers, resulting in a graft copolymer. Binary blends of i-PP/SBS, nonreactive ternary blends of i-PP/PP-MAH/SBS, and reactive ternary blends of i-PP/PP-MAH/SBS-MAH with varying diamine/anhydride molar ratios were prepared. The mechanical properties of the blends were determined by tensile and impact-resistance tests. The optimum improvement in the mechanical properties was found when the diamine/anhydride molar ratio in the ternary reactive blends was 0.5/1. (C) 2002 Wiley Periodicals, Inc.873516522