Dielectric monitoring of curing of liquid oligomer-modified epoxy matrices

Dielectric measurements were performed in 'real-time' at several temperatures to follow polymerization reactions on blends of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin with 4, 4 ' -diaminodiphenylmethane (DDM) hardener and different amounts of polyoxypropylenetriamine (POPTA) oligomer. These systems exhibit phase separation induced by molar mass increasing through curing of the resin. Monitoring of phase separation and vitrification (related to the alpha -relaxation) was performed by this technique. The results are compared with those for the unmodified resin-hardener mixture. The change of the main a-relaxation with cure time, cure temperature, and amount of modifier was measured for the mixtures. This change of the main relaxation through curing in the frequency domain was indicative of the cure reaction advancement, because of its dependence on the viscosity of the medium. The change of the ionic conductivity during curing was also analysed, showing its dependence upon cure temperature. (C) 2001 Society of Chemical Industry.