An electron spin resonance study of the radiation chemistry of poly(hydroxybutyrate)

The spectra of the radical species resulting from gamma irradiation of poly(hydroxybutyrate) and its copolymers with hydroxyvalerate have been obtained after radiolysis at 77 and 303 K, and the corresponding radiation chemical yields have been calculated. Photobleaching and annealing experiments have allowed the major radical species to be identified and their reactivities to be assessed. Radical anions, as well as neutral radicals, were observed to be present at 77 K, but the radial anions were found to decay to neutral radicals at temperatures around 140K. Above about 250 K a multi-line component of the spectrum was lost, but the radical associated with this spectral change has not been unequivocally assigned, though it is believed to be a radical resulting from chain scission. Annealing over the temperature range 300-350 K resulted in the loss of a triplet, which accounts for most of the radicals present. This triplet has been assigned to a radical located on the carbon atom adjacent to the carbonyl group. This radical is believed to exist in two possible conformations. All of the radicals decayed at temperatures above 400 K. (author)