The effects of nitrous oxide and ethylene on the gas yields and gel formation from γ-irradiated polypropylene

Abstract

Isotactic and atactic polypropylene have been y-irradiated in a vacuum, in nitrous oxide, and in ethylene, and also in the presence of mixtures of these two gases. The y-irradiation of the isotactic polypropylene in a vacuum gives a H2 yield which is non-linear with dose, whereas the CH4 yield is linear with dose. Yields of H2 and CH4 from atactic polypropylene obey a linear relationship with the dose delivered. Both N2O and ethylene depress the G(H2) obtained from vacuum irradiations of isotactic polypropylene, the former due to electron scavenging and the latter to hydrogen atom scavenging. The scavenger studies lead to G(e-) = 0.7�0.1, G(H)thermal = 1.0�0.1, and G(H2)moleculer = 1.86�0.05. ��� Compared to vacuum irradiations, N2O enhances, and ethylene suppresses completely, the crosslinking yield in isotactic polypropylene. In equimolar mixtures of N2O and ethylene the crosslinking yield is suppressed completely. It is suggested that N2O enhances the crosslinking mechanism through an energy transfer and dehydrogenation process and that ethylene interferes by radical scavenging. In mixtures, the results are consistent with ethylene participating in the energy transfer reaction in preference to the N2O and so inhibiting the additional crosslinking that N2O causes through the dehydrogenation reaction. A tentative reaction sequence is proposed.