| Abstract: | ESR spectra of gamma irradiated annealed and quenched forms of polypropylene film have been studied at the temperatures used for post-irradiation grafting experiments with butadiene, described in Part I. On warming from low temperature there is radical loss by termination and some radical transformation to radicals with optimum stability in annealed polypropylene at approximately 45°C. These radicals, which may be allyl type, are sited at the crystal faces, and decay more rapidly at higher temperatures in annealed polypropylene; in quenced polypropylene their concentration never exceeds one third the optimum observed in annealed polypropylene. Correlation with the grafting experiments suggests that allyl radicals are important for long-term grafting. Effects on the ESR spectrum of adding butadiene to the system show that in the long-term butadiene adds exclusively to the allyl radicals and that alkyl radicals still present at that stage are precursors to the allyl radicals. They do not react directly with butadiene presumably because they are sited in the inaccessible crystal core. Experiments at lower temperature show that butadiene does react with alkyl radicals in accessible regions. |
