The thermal degradation of poly(α-methylstyrene) in solution was investigated at various temperatures (150-225°C) and polymer concentrations (2.00-20.0 g/1) at 6.8 MPa (1000 psig). The molecular weight distributions (MWDs) of the reacted polymer at these conditions were examined at four different residence times. Experimental data indicated that the polymer degraded to its monomer, α-methylstyrene. No other degradation products were observed. Continuous-mixture kinetics was used to examine the MWDs and to obtain the rate coefficient for degradation and its activation energy. The rate was first order in polymer concentration with a rate coefficient at 225°C of 0.01 min 1 and an activation energy of 66.5 kJ/mol (16.0 kcal/mol). The maximum conversion observed at 275°C was 1.2%. Hydrogen-donor solvent, tetralin, had no effect on the degradation. © 1996 Published by Elsevier Science Limited.