Effect of p-xylene on the photoinduced formation of polyethylene radicals

Abstract

The effect of p-xylene on the photodegradation of polyethylene (PE) was investigated by analyzing ESR spectra of irradiated samples. The p-xylene-containing PE, irradiated with light of λ > 220 nm at −196°C, showed a spectrum in which a singlet component with a linewidth of 40 G predominated over an eight-line component originating in an alkyl radical of PE. A maximum spectral intensity was recorded at a certain concentration of p-xylene in the PE sample, indicating that an appropriate amount of p-xylene promotes the photoinduced formation of PE radicals. ESR spectra and their changes on warming were compared for p-xylene-containing and phenanthrene-sensitized samples. Thus the singlet component with a line width of 40 G, which was recorded for the former sample, was ascribed to an allyl radical of PE, and the effect of p-xylene on the formation of the allyl radical was very much greater than that of phenanthrene. The mechanism of formation of allyl radical by p-xylene is discussed in terms of the hydrogen-abstracting function of p-xylene radicals.