Influence of the irradiation parameters on the molecular modifications of an isotactic polypropylene gamma-irradiated under vacuum

Isotactic polypropylene was irradiated under vacuum in a complete set of ex perimental conditions. The influence of the irradiation parameters, total a bsorbed dose, D, and dose rate, I, was analysed in order to verify the theo retical predictions of a simple kinetic model, already presented (Sarcinell i L, Valenza A, Spadaro G. Polymer 1997,38:2307), based on the rates of the main reactions occurring during irradiation, i.e. beta-scission, addition to double bonds and termination. The concentration of free radicals and dou ble bonds formed during irradiation is detected together with a comparison to their dependence on the irradiation parameters. A quantitative determina tion of the "inversion curve", forecasted by the model, i.e. an implicit fu nction of D and I, which gives the dose values enhancing chain branching an d molecular weight increase at fixed dose rate and vice versa, was also per formed. (C) 2000 Elsevier Science Ltd. All rights reserved.