The radiation chemistry of poly(arylene ether phosphine oxide)s

Abstract

Electron spin resonance spectroscopy (ESR) was used to study the free radicals produced on γ-irradiation of selected poly(arylene ether phosphine oxide)s (PEPO). Both neutral and anionic free radicals were detected after irradiation at 77K. Thermal annealing of the radicals resulted in the identification of two decay regions; between 77 and 200K and above 240K, corresponding to the decay of radical anions and neutral radicals respectively. Photolysis with visible wavelengths was used to detrap, and so identify, anionic radicals. The presence of two species of radical anions was inferred by inspection of the radical decay curves and the spectra of the radicals lost on photolysis. The neutral free radicals detected were identified as phenoxyl-type radicals formed by the homolytic scission of ether bonds in the polymer. 31P NMR of the polymers after irradiation showed broadening of the main peak to higher chemical shift, suggesting crosslinking, probably at the phenyl side-chain. Viscosity measurements showed a slight decrease in the limiting viscosity numbers for solutions in dichloromethane, and therefore in the molecular weight of the polymers, with increasing dose. Main chain scission and crosslinking occur simultaneously in the polymers, with chain scission dominant over crosslinking [G(S)>4G(X)]. At 77K the radical yield incieased with dose in a similar fashion for all three polymers, but at room temperature the radical yields for a given dose increased in order of the ratio of ether bonds to aromatic groups in the polymer, that is, in the order biphenol<bisphenol-A<hydroquinone PEPO.