Macromolecular mobility changes in virgin and thermally aged epoxies

ABSTRACT Epoxy diamine systems were thermally oxidized at 110°C under air. The impact of ageing on the macromolecular relaxation dynamics was monitored using DMA in multi-frequency multi-temperatures mode, whereas structural changes were sought from sol-gel measurements and Positron Annihilation Lifetime Spectroscopy (PALS) measurements. The analyses lead to the conclusion that chain scissions first occur, but are compensated by crosslinking at long ageing times. Thus, the structural heterogeneity increases, as evidenced from the free volume hole sizes distribution. To estimate the changes of relaxation parameters with ageing, the experimental data were exploited using Williams–Landel–Ferry (WLF) and Vogel–Fulcher–Tammann–Hesse (VTFH) equations, showing respectively that C 2 g increases meanwhile the fragility index (m) decreases. These variations are monotonous despite the dual degradation mechanism. It is assumed that the relaxation dynamics are essentially influenced by the cooperativity drop, resulting from internal crosslinks and antiplasticization.