PHOTOOXIDATION OF POLY(PHENYLENE ETHER) - A REEXAMINATION OF THE MECHANISM

An analytical and kinetic study of the photochemistry which occurs in poly(phenylene ether) (PPE) in the solid state is reported. Oxidation photoproducts formed by irradiation in the range 254-365 nm were investigated by FTIR spectroscopy. Specific chemical treatments were developed in order to identify the photoproducts. Hydroperoxides formed on aromatic rings appeared as primary oxidation products. These photo-unstable hydroperoxides were transformed into many oxidized products such as phenolic groups and quinone-methide forms. The most outstanding feature was related to the localization of photo-oxidative transformations in the surface layers of solid PPE samples (e < 11-mu-m). Photoproduct profiles were observed in accelerated photo-oxidation experiments and in outdoor exposures. In the highly oxidized surface layer, ring scissions occurred leading to saturated acids observed at 1714 cm-1. The profile revealed that an irradiated film of PPE was a heterogeneous reactor whose core was not oxidized. Kinetics are consequently largely dependent upon such heterogeneities.