High resolution solid-state C-13-NMR study of As-cured and irradiated epoxy resins

This article presents the effects of strong ionizing radiations on the phys ico-chemical modifications of aliphatic or aromatic amine-cured epoxy rest. ns based on diglycidyl ether of bisphenol A (DGEBA). Such epoxy resins hav e a considerable number of applications in the nuclear industrial field and are known to be very stable under moderate irradiation conditions. Using extensively high resolution solid-state C-13-NMR spectroscopy we show that the aliphatic amine-cured resin (DGEBA-TETA) appears much more sensit ive to gamma rays than the aromatic amine-cured one (DGEBA-DDM). On the one hand, qualitative analyses of the high resolution solid-state C-13-NMR spe ctra of both epoxy resins, irradiated under similar conditions (8.5 MGy), r eveal almost no change in the aromatic amine-cured resin whereas new resona nces are observed for the aliphatic amine-cured resin. These new peaks were interpreted as the formation of new functional groups such as amides, acid s and/or esters and to alkene groups probably formed in the aliphatic amine skeleton. On the other hand, molecular dynamics of these polymers are inve stigated by measuring the relaxation times, T-CH, T-1 rhoH and T-1C, before and after irradiation. The study of relaxation data shows the formation, u nder irradiation, of a more rigid network, especially for the aliphatic ami ne-cured system and confirms that aromatic amine-cured resin [DGEBA-4,4'-di aminodiphenylmethane(DDM)] is much less affected by ionizing radiations tha n the aliphatic amine-cured resin [DGEBA-triethylenetetramine(TETA)]. Moreo ver, it has been shown that the molecular modifications generated by irradi ation on the powder of the aliphatic-amine-cured resin appear to be homogen eously distributed inside the polymers as no phase separations can be deduc ed from the above analyses. Copyright (C) 2001 John Wiley & Sons, Ltd.