[en] The grafting of styrene onto polypropylene (PP) by simultaneous radiation was carried out. The effects of absorbed dose and the pos radiation period on the grafting yield were investigated. The experiment comprised PP films with 40μm thickness exposed to gamma ionizing radiation at room temperature and nitrogen atmosphere. The films were immersed in styrene/toluene and then irradiated at total dose of 40, 80 and 100 kGy. After irradiation the samples were evaluated at periods of 0, 7, 14, 21 and 28 days at room temperature in order to observe the behavior of grafting degree. Structural, chemical changes and surface morphologies of the modified PP films were characterized by infrared spectroscopic analysis (FTIR), differential scanning calorimetry analysis (DSC), thermogravimetric analysis (TGA) and the degree of grafting (DOG) was gravimetrically determined. The simultaneous radiation indicated the dependency of the percent graft on the absorbed dose. The DOG values are higher when the film was submitted at 100 kGy dose. The thermal stability shows a decrease in the degradation temperature of the modified samples in comparison with the pure polymer. (author)