Poly(2,6-dimethyl-1,4-phenylene oxide) (PPE) films were exposed to monochromatic radiation (254 nm, 365 nm) and to polychromatic radiation (lambda 300 nm, outdoor exposure) in the presence of atmospheric oxygen. Thermooxidation of PPE samples was carried out in the temperature range 100 degrees C-170 degrees C. Products formed in irradiated and thermooxidized films were identified by coupling FTIR spectroscopy to chemical derivatization reactions, physical treatments and gas phase analysis. The nature and the distribution of oxidation products are shown to be different in the two conditions of degradation.