The physical and mechanical properties of annealed (PPA) and quenched (PPQ) forms of isotactic polypropylene film modified by 7-irradiation in the presence of gaseous 1,3-butadiene (BDI have been studied. BD was chemically bound to the film in amounts up to 16.3 mass o. Gel contents were considerably greater than after corresponding in vacuo irradiations. To was reduced by up to 14 C after 5 and 15 Mrad but increased after 50 Mrad Melting and crystallization behaviour was similar to that of samples after corresponding in vacuo irradiations suggesting that BD was incorporated mainly in non-crystalline regions. However, residues from extractions in refluxing xylene also melted and crystallized showing that light cross-linking must have occurred in the crystalline regions, probably at the lamellar surfaces. Compared with in vacuo irradiations the initial modulus and the yield stress of PPA were reduced after 5 and 15 Mrad such that the samples could be drawn beyond both yield point and the necking process without rupture. After 50 Mrad this improvement was lost probably because the more extensive cross-linking had counteracted the increased flexibility due to the incorporated BD. The elastic nature of the incorporated BD resulted in a reduction in the extent of the necking process in all samples. After 50 Mrad both PPA and PPQ exhibited good elastic complex moduli above the melting point.