The thermal degradation of vinyl polyperoxides, poly(styrene peroxide) (PSP), poly(α-methylstyrene peroxide) (PAMSP) and poly(α-phenylstyrene peroxide) (PAPSP), was carried out at different temperatures in toluene. The time evolution of molecular weight distributions (MWDs) was determined by gel permeation chromatography (GPC). A continuous distribution model was used to evaluate the random chain degradation rate coefficients. The activation energies, determined from the temperature dependence of the rate coefficients, suggest that thermal degradation of polyperoxides is controlled by the dissociation of the O-O bonds in the backbone of the polymer chain. Among the three polyperoxides investigated, the thermal stability is the highest for PAPSP and the lowest for PAMSP. © 2002 Elsevier Science Ltd. All rights reserved.