A novel synthetic route for preparing polypropylene-graft-polystyrene (PP-g-PSt) was set up. With this synthetic route, a series of PP-g-PSt copolymers containing different percentages of polystyrene chain were synthesized, based on the different reactivities of two kinds of C-C double bonds on 4-(3-butenyl) styrene. Characterization data, including H-1-NMR, C-13-NMR, GPC, and DSC, demonstrated that the graft copolymers were all very pure. Furthermore, it was also attempted to use this new kind of propylene-styrene graft copolymer as a compatibilizer. DMA and SEM results illustrated that the PP-g-PSt obtained is an efficient compatibilizer for the polypropylene-polystyrene blend. (C) 2004 Wiley Periodicals, Inc.