THERMAL-DEGRADATION CHEMISTRY OF POLY(DIPHENOXYPHOSPHAZENE)

The thermal degradation of poly(diphenoxyphosphazene) has been reexamined with emphasis on the roles of P-Cl and P-OH weak links. The polymers studied had residual chlorine contents of < 0.05%, 2.4%, and 9.9%. Thermal degradations were performed either in a dynamic mode on the direct insertion probe of a mass spectrometer or under isothermal conditions in sealed ampoules at temperatures up to 440-degrees-C. Several model compounds (products observed from the dynamic degradation of the polymers) were also subjected to isothermal degradation in order to better distinguish between primary and secondary products. The primary degradation products included chlorine-containing cyclic trimer and tetramer species, which were themselves too unstable to be observed in isothermal degradation studies. Triphenyl phosphate was formed as a secondary product from the degradation of the cyclic oligomers rather than as a primary product from polymer chain ends, as had been previously suggested. Hydrolysis of P-Cl weak links was obtained only with difficulty, requiring steam treatment. Steam hydrolysis reduced the thermal stability of polymers with high initial P-Cl contents.