Abstract: In this paper, the chain structure, thermal properties, molecular weight and its distribution of spontaneously polymerized poly(methyl methacrylate) (PMMA) were characterized by nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). Meanwhile, the mechanisms of spontenous polymerization for methyl methylcacrlate (MMA) was disscussed. GPC results indicated that spontenously polymerized PMMA had a higher molecular weight and a wider distribution in comparison of the PMMA polymerized by using initiators. NMR and DSC measurements indicated that the spontenously polymerized PMMA contained peroxy bonds within its chain. These peroxy bonds are thermally instable, and their presence makes the thermal stability of PMMA poor without any effects on its heat resistance. It was also confirmed that the spontenous polymerization of MMA was initiated by the peroxides resulting from the reaction between MMA and oxygen.

Key words: poly（methyl methacrylate）, spontaneous polymerization, polymerization mechamism, thermal property, Peroxide bond