An investigation was conducted on the effects of photodegradation of multilayer films based on PET copolymers. The films were composed by different layers with PET, PET/PEN, and PET/PEI copolymers with a total thickness of 23 mu m. The films produced by coextrusion followed by a biaxial orientation in an industrial equipment were exposed to the ultraviolet radiation in the laboratory for periods of up to 600 h. The samples were investigated by FTIR-ATR, UV/visible spectroscopy, fluorescence spectroscopy, size exclusion chromatography, mechanical properties, and scanning electron microscopy. The results showed that the photooxidation is concentrated at the surface layers and that coextruded films were more sensitive to the UV radiation effects. The deterioration in mechanical properties with exposure and the fracture behavior were shown to be consistent with the amount of degradation that occurred in the films. (c) 2007 Wiley Periodicals, Inc.