The thermal degradation of poly(propylene oxide), (PPO) and polyepichlorohydrin, (PECH) were studied with the use of direct pyrolysis mass spectrometry. The effects of heating rate and dissociative ionization on fragmentation pattern have also been investigated. It has been determined that PPO degrades via a random cleavage mechanism, the labile C-O bond scissions being preferred, An analogous degradation mechanism can be proposed for PECH. Yet, the elimination of side chains, evolution of HCl and the loss of Cl and CH2Cl were determined to be also effective for this sample. Furthermore, the formation of fragments with cyclic end groups due to consequent intermolecular crosslinking following the loss of side chains have been proposed at the final stages of thermal decomposition of PECH. (C) 2002 Published by Elsevier Science B.V.