AbstractThe influences of heat treating of PVC on photooxidation were studied by spectroscopy. PVC containing thermal stabilizers selected from metal stearates, dibutyltin compounds and mercaptide were heat treated and then irradiated by a weatherometer at 0°C. Stabilizing action of metal stearate for photooxidation of PVC is decreased by heat treating prior to irradiation. Dibutyltin compounds show good photostability, especially, dibutyltin benzylmaleate is enhanced by heat treating. Mercaptide shows weak photostability, and stability is decreased furthermore by heat treating. Binding energy of sulphur was measured by XPS spectrometry. Divalent sulphur is oxidized to hexavalent in irradiated PVC films