Thin films of high impact polystyrene (HIPS 8350) and styrene-butadienestyrene triblock. copolymers (SBS) were exposed to polychromatic light for different time intervals in SEPAP 12/24 at 55 degrees C in atmospheric air. The photooxidized samples were analyzed by C-13-NMR spectroscopy in the liquid state. Epoxides and alcohols were photoproducts in the SBS. Epoxides were not observed in the HIPS. The morphological changes of the solution cast HIPS and SBS films caused by irradiation were studied by scanning electron microscopy. The property deterioration was explained in terms of scission reactions in the HIPS and SBS matrix. The micrographs indicate that both materials are of a two phasic system.