Products from both the thermal and photooxidation of polybutadiene have been studied using various analytical techniques such as infrared and ultraviolet spectroscopy, gas—liquid chromatography, phosphorescence emission, and phosphorescence excitation spectroscopy. Analyses have allowed a plausible mechanism to be formulated for the photooxidation of this polymer, consistent with all the observed physical and chemical changes. Both photo- and thermal oxidative polymer degradation initially result in the formation of α,β-unsaturated carbonyls which, under photo-degrading conditions, are subsequently photolysed to yield the observed final products.