Polypropylene-g-polyacrylic acid copolymers were prepared by graft polymerization of acrylic acid onto polypropylene (PP) using electron beam preirradiation method. Samples with various graft levels were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The physical structure of grafted PP was significantly affected by the graft content. While XPS revealed an increase in the oxygen content on the PP surface, the crystallinity of the graft copolymer decreased with an increase in the degree of grafting. The heat of fusion as obtained from DSC decreased with the increase in the degree of grafting and was ascribed to the dilution of inherent crystallinity by the incorporation of amorphous polyacrylic acid grafted chains. The thermal stability of graft copolymers was also enhanced as compared to the virgin PP. (c) 2006 Wiley Periodicals, Inc.