The effect of polymerisation conditions on the kinetics and mechanism of the thermal degradation of PMMA

A large number of kinetic studies have been carried out over the past 60 years on the thermal degradation of poly(methyl methacrylate), PMMA, but these have lead to the publication of widely varying kinetic rate parameters with little correlation between them. In this paper, an attempt has been made to explain these observations in terms of the structural differences of the PMMA produced by the polymerisation scheme adopted. Some PMMA samples polymerised by free radical initiators degrade in two steps separated by temperature, the lower degradation being initiated from weak links produced by head to head addition termination of the propagating radicals, while the upper is initiated from chain ends and by random scission. The first had an activation energy approximately half that of the second. Other samples do not exhibit this low temperature degradation although polymerised by free radical initiators, and are as stable as anionic polymerised PMMA. Some doubts are cast on the nature of these weak links. (C) 2002 Elsevier Science Ltd. All rights reserved.