Thermal Degradation of Polyphosphazene Homopolymers and Copolymers Prepared by the Anionic Polymerization of Phosphoranimines

The thermal degradation of poly(bis-trifluoroethoxyphosphazene), as well as random and block copolymers bearing trifluoroethoxy and alkoxyalkoxy groups synthesized by the anionically initiated polymerization of phosphoranimines, has been investigated by TGA. These studies indicate that the thermal stability of the copolymers decreases with incorporation of alkoxyalkoxy groups. There is no direct correlation between the calculated activation energies of decomposition. This has been attributed to entropy differences. Molecular weight vs conversion plots indicate that depolymerization occurs by chain end initiation followed by complete unzipping to cyclic trimer. This is in contrast to polymers prepared by the ring-opening method. This difference has been attributed to a defect-free structure. The primary product of the decomposition of these polymers is the corresponding cyclic trimer.