Variations of the dielectric properties of epoxy resins during microwave curing

The curing of a particular epoxy resin (diglycidylether of bisphenol-A) by three amino hardeners (4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulphone and 4,4′-diaminodiphenylether) is followed by dielectric measurements performed under microwave heating. The formation on heating of a molecular association, is suggested by the analysis of the dielectric variations on the basis of an additive contribution of all the known constituents in the mixture. The reversibility of this molecular association is demonstrated. Two possible interpretations are proposed and discussed. Dielectric constant variations during curing provide evidence that microwave heating is a very efficient way of energy transfer and for monitoring chemical processes, such as the cross-linking of epoxy resins.