Abstract: In this paper, free radical melt-grafting of the multi monomer system for maleic anhydride(MAH)/styrene(St) onto polypropylene(PP) has been studied by means of a single screw extruder. The influences of St concentration and initiator concentration on the grafting reaction were investigated. It was shown that the addition of St as a co monomer could significantly enhance MAHgrafting level on PP. The maximum MAHgrafting degree was obtained when the molar ratio of MAHto St was approximately 1∶1, but the melt flow rate(MFR) of the grafted PPwas the highest at this ratio. It was proposed that the interaction and reaction between MAHand St monomers played an important role in the grafting reaction. St improved grafting reactivity of MAHor reacted with MAHto form St MAHcopolymer(SMA) before the two monomers grafted onto PP. Grafting of SMAgreatly improved the grafting degree of MAH. When molar ratio of MAHto St is 1∶1, main grafting reaction in the system is the grafting of SMAtoward PP, therefore, the grafting degree of the grafted PPis the highest. When the concentration of MAHis higher than that of St, some MAHmonomer reacts with St to form SMA, others can directly grafts onto PPmacroradicals. When the amount of St added is higher than that of MAH, part of St monomer may preferentially react with PPmacroradicals to form more stable styryl macroradicals, while others copolymerize with MAH, yielding SMA. MFRof the grafted PPis lower in this case. It is considered that MFRof the grafted PPis decided by concentration of free monomers, or, number of grafting reactive species. FTIRanalysis confirmed the above mechanism.

Key words: Polypropylene, Melt-grafting, Maleic anhydride, Styrene