Cationic and polymeric radicals of vinyl monomers in halogenated matrices: An ESR and SCF MO study

The vinyl monomers methyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, and β-methylstyrene were dissolved in CF3CCl3, x-irradiated at 4 or 77 K, and investigated by ESR spectroscopy. The molecular cation of methyl acrylate has no resolved hyperfine structure, indicating that the unpaired electron is localized on the carbonyl oxygen. Evidence that a two-stage photoinduced reaction gives rise to a propagating radical was obtained. Propagating radicals were observed also with methyl methacrylate, acrylic acid, and methacrylic acid as solutes. The positive ion of β-methylstyrene has been prepared and characterized. The experimental data have been compared with molecular orbital calculations at different levels of approximation.