Various analyses were used to characterize polypropylene films grafted with poly(acrylic acid) : infra-red spectroscopy (by means of transmission, total attenuated reflection and microscopic techniques), permeation and optical microscopy on coloured samples. We have compared the results obtained when the film to be modified was initially treated to eliminate incorporated additives with those obtained when the additives were not removed. In addition to the progressive propagation of the grafting previously evidenced, we have shown that the solubility parameter plays the major part in the transport of the monomer molecules from the surface to the bulk.