Electron Spin Resonance Study of Radicals in Photopolymerized Di(meth)acrylate Network

ESR spectra of free radicals trapped in photopolymerized HDDA (1,6-hexanediol diacrylate) and HDDMA (1,6-hexanediol dimethacrylate) were (re)examined. Careful analyses of the spectral patterns, the hyperfine structures due to β-protons, revealed that the radicals in the polymethacrylate are the propagation radicals of the conformation with the least strain energy (trans form) and those in the polyacrylate are the midchain radicals resulting from the Ca-Hacleavage at diad sectors of the conformation with the highest strain energy (gauche-gauche form). When both polymers were formed on an inert high-surface-area substrate and exposed to oxygen at low temperature (-18 °C), instant conversion of the radicals to the peroxy radicals ROO' was observed. The resulting peroxy radicals decayed rapidly at room temperature (t1/2= ~3 min). © 1989, American Chemical Society. All rights reserved.