Thermal degradation of polycyclopentadiene polymer (PCPD) was investigated by pyrolysis gas chromatography (PGC) in the temperature range of 500-950 degrees C. The nature and composition of the pyrolyzates at various temperatures are presented, and the mechanism of degradation is explained. The activation energy of decomposition (E-a) was obtained from an Arrhenius-type plot using the concentration of the product ethylene (C-2) at different pyrolysis temperatures and the value was found to be 138 kJ mol(-1). Thermo-oxidative degradation of PCPD in the presence of ammonium perchlorate (AP), the most commonly used oxidizer for polymeric fuel binders, was studied at a pyrolysis temperature of 700 degrees C. The compositions of the products with varying amounts of AP are given, and the exothermicity of oxidative decomposition reactions is evaluated. The energetics of the degradation processes are compared with those of polybutadiene type polymers. (C) 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 635-641, 2000.