Degradation of poly(2-hydroxyethyl methacrylate) by gamma irradiation

Electron Spin Resonance (ESR) spectroscopy has been utilised to examine the effect of high energy radiation on poly(2-hydroxyethyl methacrylate) PHEMA. Radiation chemical yields (G-values) for radicals were 1.7 and 1.2 for γ-irradiation at 77 K and ambient temperature, respectively. The ESR spectra at 77 and 300 K were simulated. The ESR spectrum at 77 K is a combination of six types of radicals ·CH, ·CHCHOH, COOCHCHOH, ·COO-, -CH- and ·CHO. However, after room temperature irradiation, the spectrum is a combination of methacrylate main chain scission radical and -CH-. The high stability of this radical at room temperature indicates the system is very rigid as a result of hydrogen bonding from the inherent side chain structure and radiation induced crosslinking due to labile hydrogen atoms in the side chain