The effect of end groups on the thermal degradation of poly(methyl methacrylate)

The thermal degradation of poly(methyl methacrylate) was studied using a system of thiols as initiators. Depolymerization is the dominant reaction in the thermal degradation of such polymers, according to thermal analysis. The degradation mechanism involves only main-chain scission. Three methods of degradation were applied to elucidate the thermal degradation behaviour. The activation energy for the degradation of PMMA-thiols is 170 kJ/mol, higher than that of PMMA-AIBN (60 kJ/mol), as measured by the Flynn method. According to Ozawa's method, the activation energy is 210 kJ/mol higher than that of an AIBN-initiated polymer (148-151 kJ/mol). By Kissinger's measurement method, this system has a frequency factor (∼ 10¹⁰) five orders of magnitude higher than the ordinary PMMA (∼ 10⁵). The observed results are explained as a "blocking effect".