title: An EPR, ENDOR and EIE study of gamma-irradiated poly (lactide-co-glycolide) polymers.
abstract: Gamma radiation of poly (lactide-co-glycolide) raw polymers and processed microspheres under vacuum and at 77 K results in the formation of a series of free radicals. The resulting powder electron paramagnetic resonance (EPR) spectrum contains a distribution of several different radicals, depending on the annealing temperature, and is therefore difficult to interpret. By utilising the selectivity of the electron nuclear DOuble resonance (ENDOR) and associated ENDOR induced EPR (EIE) techniques, a more direct approach for the deconvolution of the EPR spectrum can be achieved. Using this approach, the radiolytically induced CH3 *CHC(O)R- chain scission radical was identified at 120 K by simulation of the EIE spectrum. At elevated temperatures (250 K), this radical decays considerably and the more stable radicals -O*CHC(O)-, CH3 *C(OR)C(O)- and CH3 *C(OH)C(O)- predominate. This work demonstrates the utility of the EIE approach to supplement and aid the interpretation of powder EPR spectra of radicals in a polymer matrix.
authors.affiliation: School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK.
authors.forename: James A
authors.initials: JA
authors.lastname: Bushell
authors.forename: Mike
authors.initials: M
authors.lastname: Claybourn
authors.forename: Damien M
authors.initials: DM
authors.lastname: Murphy
authors.forename: Helen E
authors.initials: HE
authors.lastname: Williams
mesh_terms: D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005609:Free Radicals / Q000032:analysis*; D005720:Gamma Rays; D011098:Polyglactin 910 / Q000737:chemistry* / Q000528:radiation effects*; D013696:Temperature
chemical_list: D005609:Free Radicals; D011098:Polyglactin 910