Photodegradation and photostabilization of poly(p-phenylene sulfide). Part 2. UV induced physicochemical changes

The photodegradation of PPS as a result of UV irradiation manifests itself not only in yellowing and color-darkening, but also surface oxidation (conversion of S to S(O)x), IR and UV-visible spectral changes, and partial loss of solubility (in hot 1-chloronaphthalene). The formation of insoluble fractions and the size exclusion chromatography (SEC) analysis of soluble fractions strongly suggest that crosslinking, rather than chain scission, is a major outcome of the photolysis. The effects of various factors on photocoloration have been examined; these include resin purity, morphology, molecular weight, nature of end group, presence of oligomers, oxygen vs inert atmosphere, and spectral region of excitation. While the presence of extractable oligomers in PPS does not affect the magnitude of its photocoloration, oxygen in the ambient atmosphere accelerates the process considerably. The color changes of crystalline translucent films are generally higher than those of transparent amorphous films. The estimated short lifetime of the PPS singlet excited state suggests that the degradation arising from it would not be easily controllable by quenchers. Attempts at photostabilization of PPS based on a screening mechanism should focus on maximum spectral overlap between the screener and the polymer in the near-UV region (300–380 nm).