Study of the degradation of an epoxy/amine resin, 1 photo- and thermo-chemical mechanisms

The degradation of an epoxy/amine resin was studied under photolytic conditions in absence and in presence of oxygen and under thermooxidative conditions. The resin is obtained after curing the diglycidyl ether of bisphenol-A (DGEBA) with a poly(propylene glycol) which is diamine terminated. The mechanisms of degradation of the two separate components before curing were also investigated. Analysis by IR and UV-Vis spectroscopies revealed that the oxidation photoproducts detected during the degradation of the epoxy/amine result from the oxidation of the DGEBA part, of the amine crosslinks and, to a lower extent, of the poly(oxypropylene) units. Their mechanism of formation essentially involves chain scission reactions. During irradiation, the yellowing observed is mainly due to the formation of a quinone methide structure. Thermooxidation generates high discoloration with some products only generated in that case. For all experiments, a detailed analysis of the IR spectra is given with the chemical mechanisms of formation of the degradation products.