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.