Dipolar relaxations in an epoxy–amine system

Dipolar relaxations in a reactive epoxy–amine system based on diglycidyl ether of bisphenol A with 4,4′-diaminodiphenylsulfone were studied with the Havriliak–Negami function. The system was cured isothermally at 140 °C using simultaneous kinetic and microdielectric studies. The relaxation time was calculated from the frequency fmax of the peak of the loss factor ε′′ versus frequency f. A linear relation exists between the logarithm of the relaxation time τ and the glass transition temperature Tg. Then, logτ follows the Di Benedetto equation revisited by Pascault and Williams allowing the prediction of the relaxation time τ during cure. The unrelaxed permittivity at high frequency εu, the relaxed or static permittivity εs and the skewness parameter β were found independent on the conversion or the curing time. The distribution parameter α decreases as curing time t increases. The difficulty of orientation of dipoles in the electric field due to vitrification is responsible of these behaviours.