The primary steps involved in the degradation of polybenzyl at temperatures between 140 and 220OC. in the presence of air or pure oxygen has been found to be an attack a t the methylene linkages to give benzhydrol and benzophenone linkages. Kinetic evaluation of the rate of benzophenone-type carbonyl ingrowth indicated an apparent initial activation energy for the oxidation yocess of 14.5 f 3.5 kcal. Vapor-phase chromatographic analysis of the volatile products of the reaction indicate that the formation of benzoic acid and benzophenone are the major products of oxidation, along with smaller amounts of benzene, toluene, water, and carbon dioxide. It must be concluded that the initial oxidation of polybenzyl closely parallels the oxidation of phenolic resins and other closely related activated methylene polymers. Secondary degradation reactions which produce chain scission are generally equitable t o further oxidation a t both the benzhydrol and benzophenone linkages. The appearance and spectral substantiation of the formation of benzoic anhydride linkages from thermal dehydration of benzoic acid most adequately accounts for the formation of the secondary reaction products giving new but minor infrared bands in the early and intermediate stages of the degradation.