The thermal degradation of a polycyanurate thermosetting material was examined by monitoring glass temperature and weight loss at various temperatures ranging from 180 to 220 degrees C. The effect of the cocatalysts, nonylphenol and copper naphthenate, which are generally used to facilitate curing, were also studied. A decrease in T-g is observed with increasing time at elevated temperatures in the systems containing copper naphthenate, with the onset of degradation occurring sooner with higher concentrations of the copper compound. No change in T-g occurred at long times in systems containing only nonylphenol. Weight loss studies were used to calculate an apparent activation energy of degradation. It was found to be approximately 50 kcal/mol.