THERMAL OXIDATIVE-DEGRADATION OF POLY(METHYL METHACRYLATE)

The oxidative degradation of poly(methyl methacrylate), PMMA, has been investigated at temperatures up to 320-degrees-C. Molecular oxygen protects PMMA against depolymerization at temperatures below about 220-degrees-C. At higher temperatures oxidative main-chain scission becomes very important as evidenced by molar mass determinations. By GC-MS analysis it was found that the condensable volatile products contained as major compounds, apart from monomer, 2-methyl-oxirane carbonic acid methyl ester (I), methyl pyruvate (II), dimethyl itaconate (V) and acetaldehyde. According to our proposed mechanisms the formation of I is indicative of main-chain scissions due to the decomposition of oxyl-radicals which are formed by H-abstraction from backbone carbons and the subsequent reaction of the carbon-centered radicals with O2. II is traced back to oxy-radicals formed by reaction of O2 with carbon-centered terminal radicals generated by cleavage of C-C bonds in the backbone. The rather high product yield ratio I/II almost-equal-to 6 indicates that at T < 320-degrees-C and in the presence of O2 main-chain cleavage is mainly due to H-abstraction from backbone carbons.