E.S.R. Spectra of Free Radicals Relevant to Methacrylate Polymerization

Carbon-based free radicals were generated by thermal cleavage of the tetraester Me2C(COOME)-CH2-CMe( COOMe )- CMe ( COOMe )-CH2-C( COOMe )Me2 which is a model for head-to-head units in a poly(methyl methacrylate ) chain. The resulting electron spin resonance spectrum had higher resolution than the 'nine-line' spectrum previously reported; this enabled identification of the component radicals. In the present case, the spectrum was well matched by a summation of spectra of the Me2C(COOME)-CH2-CMe( COOMe ) radical and the 1-methoxycarbonyl-1-methylethyl radical Me2-C-COOMe derived from it by loss of methyl methacrylate. Both of these radicals were generated in separate experiments. Radicals were also generated from starting materials containing a CD3 group in place of the single CH3.