Benzophenone-sensitized photo-degradation of polypropylene

Abstract

The effects of benzophenone (BP) on the photo-degradation of polypropylene (PP) were investigated by analyzing the ESR and infrared spectra of the irradiated samples. In the system irradiated with light of λ>300 nm, samples irradiated at both −196°C and room temperature yielded a broad 4-line spectrum with a splitting constant of 24 gauss (alkyl radical), the intensities of which increased with the amount of BP. In the system irradiated with light of λ>220 nm, the sample irradiated at −196°C exhibited the broad 4-line spectrum, on which a sharp 4-line component with a splitting constant of 23 gauss (methyl radical) was superimposed, while the sample irradiated at room temperature mainly showed a singlet spectrum (polyenyl radical). Infrared spectra of the irradiated samples showed that the formation of double bonds on PP is extremely difficult as compared with polyethylene. Thus, it is believed that BP might abstract tertiary hydrogen atoms from the PP substrate to promote the formation of alkyl radicals and the contribution of BP to the formation of polyenyl radicals, which was observed for polyethylene, is small.