The time dependence of the thermooxidative degradation was measured within the temperature range of 100 -150OC. The extent of degradation was characterized by monitoring the content of hydroperoxy, hydroxyl, carbonyl, and quinone groups. Moreover, oxygen absorption, weight changes, and carbon dioxide formation were followed. Calculations of material balance were carried out on the basis of weight changes, oxygen absorption, and analytically determined concentration of oxidation products. The photooxidation was also characterized by the content of hydroperoxy groups and the formation of hydroxyl, ester, and carbonyl groups. A semiquantitative method was employed to determine the concentration of carboxyl groups. In both cases the presence of xanthone moieties was observed. In samples subjected to photooxidation also a small amount of peracids and peresters was found. The mechanism of the degradation processes is discussed in some details.