Free-radical melt-grafting of the dual-monomer systems glycidyl methacrylate-styrene (GMA-St0 and hydroxyethyl methacrylate-styrene (HEMA-St) onto polypropylene (PP) has been studied using a single-screw extruder. For single monomer grafting systems, degradation of PP was unavoidable and deterioration of the mechanical properties of the grafted PP subsequently occurred because of β-scission of PP chains during the free-radical melt-grafting process. However, for the dual-monomer systems, it is shown that the addition of styrene as a comonomer can significantly enhance the GMA or HEMA grafting levels on PP and reduce the extent of βscission of PP backbone. It has been found that the grafting degree of deal-monomer melt-grafted PP, such as PP-g-(GMA-co-St) or PP-g-(HEMA-co-St), is about quadruple that or single-monomer grafted PP for the same monomer and dicumyl peroxide concentrations. Moreover, the melt flow rate of the dual-monomer grafted PP not only was endowed with higher polarity, but also kept its good mechanical properties. 2000 Society of Chemical Industry.