Radiochemical ageing of an amine cured epoxy network. Part II: kinetic modelling

The radiochemical ageing (doses up to 70 MGy at a temperature of 120 °C in air) of an aromatic rich epoxide-amine stoichiometric network was studied by DMA (determination of the glass transition temperature), NMR (consumption of aliphatic CH groups) and ESR (radical decay). The number of chain scissions on elastically active chains is derived from T_g decreasing using the Di Marzio's theory. Then, a two steps mechanistic scheme is proposed, in which chain scissions occur in the initiation step but radicals partly recombine in the termination step. A kinetic model is derived from this scheme and its elementary rate constants are determined from NMR (initiation) and ESR (termination) measurements. It appears that the termination is diffusion controlled, which leaded us to introduce a time dependent termination rate constant using the Waite's theory. The model predictions are in acceptable agreement with experimental data in the range 0-70 MGy.