Abstract: The thermal degradation behavior of PMMA, which were predecomposed with different time under vacuum condition, were investigated by thermogravimetry (TG)，and the initiation activation energy and activation energy at different weight loss stages were calculated by the methods of Flynn and Flynn-Wall-Ozawa. It showed that, only the PMMA chains with unsaturated ends decomposed during vacuum-predecomposition, and the predecomposing time had not any effect on the molecular weight of them. Those PMMAs after predecomposing were much more thermal stable than original ones, and the less the unsaturated ends on the chain, the better its thermal stability. The reduction of unsaturated ends in the chain could increase the activation energy of the mass loss near 50 %, but had no effect on that at subsequent stages.

Key words: poly(methyl methacrylate), vacuum-predecompoaition, thermal stability, unsaturated end, activation energy