Electron resonance spectra of gamma-irradiated polymers: Measurements at 77°K. on polymethacrylic acid and related compounds†

The electron spin resonance (e.s.r.) spectra of free radicals trapped in some addition polymers after gamma-irradiation at 77°K. are described and discussed. When polymethacrylic acid is gamma-irradiated at 77°K., the e.s.r. spectrum at this temperature consists of a symmetrical pattern of seven lines which may be due to dimethyl carboxy methyl radicals, (CH3)2C—CO2H. On warming to 300°K. this spectrum is replaced by the normal “five-plus-four line” spectrum, which has been attributed to trapped propagating radicals. When polymethacrylic acid freed from monomer is gamma-irradiated at 77°K. the e.s.r. spectrum is a single line, probably arising from trapped ·CO2H radicals. A reaction scheme is put forward to account for the production of these radicals. Some observations on polymethyl, polyethyl, poly n-butyl, and poly n-hexyl methacrylates and polydimethyl itaconate are also reported.