Photo-oxidation of phenoxy resins at long and short wavelengths - II. Mechanisms of formation of photoproducts

Products resulting from the photo-oxidation of phenoxy resin were identified and reported in the preceding paper; mechanisms that account for formation of the photoproducts are proposed in the present paper. Results show that the dominant photo-oxidative pathway is a photo-induced oxidation implying hydroperoxidation. In the first steps of the oxidation induced by long wavelengths (lambda > 300 nm), the main reactions involve the methylene groups in the alpha position to the ether groups. Photo-unstable hydroperoxides are transformed into phenyl formate end-groups. By contrast, no phenyl formate end-groups have been found under short-wavelength exposure (lambda = 254 nm); it is believed that hydrogen abstraction of hydroperoxides formed in alpha positions to ether is more likely to occur than the anticipated homolysis. (C) 1997 Elsevier Science Limited.