Photoinduced acrylamide graft polymerization onto extended hard elastic polypropylene

Hard elastic PP films were graft polymerized with PAAm, using a photoinduction method derived by Tazuke. The graft yield (GY) was measured as a function of extension applied to the PP film during the polymerization. The GY increased stepwise when the extension increased above the yield point. This remarkable increase in GY is due to the fact that the surface of voids created by extension are involved in the graft polymerization. The GY obtained under extensions larger than the yield point was much larger than that ever achieved for the usual PP films. The residual strain after the graft polymerization increased with increase in GY, and the relationship between them changed at about 40% GY, suggesting that some change occurred in the location of grafted PAAm in PP films. The graft ratio, determined after complete extraction of PP and PAAm homopolymers, remained nearly constant with polymerization time, except at the early stage of the polymerization. The effect of extension on the graft ratio implied that the size of the voids may affect the degree of polymerization of graft PAAm when the size is comparatively small.