Butyl acrylate (BA) with acrylated castor oil (ACO) was grafted onto porous polypropylene (PP) granules by grafting polymerization. Crosslinked copolymer microdomains which functioned as rubber phase to improve the toughness of PP were filled into the pores of PP granules. The sizes of crosslinked copolymer microdomains were controlled in the range of 0.1-1 mu m in PP matrix. The results of fourier transform infrared spectroscopy and scanning electron microscope of PP-g-(BA-co-ACO) after extracted by acetone confirmed that BA and ACO were grafted onto PP successfully. The effects of comonomer ratio, initiator content and comonomer content on grafting percentage (GP) and grafting efficiency (GE) were investigated. The GP of PP-g-(BA-co-ACO) could be up to 21.3% with the comonomer content increasing to 25%. The crosslinked copolymer decreased the melting flow index and the relative crystallinity of PP. Dynamic mechanical thermal analysis showed that the glass transition temperature of PP decreased slightly from 22 degrees C to 15 degrees C. The addition of 5% comonomer content led to an increase of notched impact strength from 1.96 to 3.81 kJ/m(2) (nearly doubled) and a marginal decrease in the tensile strength of PP. Then with further addition of comonomer, the notched impact strength increased to 8.98 kJ/m(2) while the tensile strength was 29.37 MPa. (c) 2017 Society of Plastics Engineers