ESR spin trapping determination of the hydroperoxide concentration in polyethylene oxide (PEO) in aqueous solution

Initial hydroperoxide (ROOH), which exists even in freshly produced polymers, acts as an initiator for the oxidative degradation of the polymer. Electron spin resonance (ESR) with the spin trapping agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) was used to investigate the presence of 'initial ROOH' in a polyethylene oxide (PEO) sample. The degradation of PEO was investigated by heating or irradiating mixtures of PEO/DMPO/H2O with or without dissolved oxygen by ultraviolet-visible (UV-vis, λ > 250 nm) and visible (λ > 350 nm) light. The concentration of 'initial ROOH' and the photolysis and thermolysis rate constants were estimated from the concentrations of the DMPO-H, DMPO-C-PEO, and DMPO-OH spin adducts. Knowledge of the oxidative degradation mechanism of polymers allows the 'initial ROOH' concentration to be used as a quality control indicator for polymers.