Spherical polypropylene (PP) granules of high porosity were synthesized using a spherical high yield TiCl4

／MgCl2 supported catalyst．As much as 50 wt％ of styrene (St)／benzoyl peroxide (BPO) mixture (based on PP weight) was adsorbed into the PP granules

and solid phase graft polymerization of St was conducted under different conditions. Effects of various reaction parameters

such as St／PP weight ratio

BPO／St ratio

reaction temperature

and reaction time on the amount of grafted PS in PP

graft efficiency

and the molecular weight of product were investigated．The structure and phase morphology of the produced PP/PP-g-PS alloy was characterized by infrared (FTIR)

differential scanning calorimetry (DSC)

GPC

viscometry and polarized microscope (PLM)．The results showed that solid phase graft polymerization of St in PP granule produced PP/PP-g-PS／PS alloy with high amount of grafted PS (maximum 24.3 wt％ of PS based on PP／PP-g-PS) and high graft efficiency (maximum 56.7％)．The size of PP crystals was greatly reduced after grafting PS on PP．The final product is still in the form of regular spherical granules

which is beneficial to industrial process．Under the studied conditions

there was slight degradation of the PP chains in the graft reaction．