Dielectric monitoring of curing of liquid oligomer-modified epoxy matrices

Dielectric measurements were performed in 'real-time' at several temperatur es to follow polymerization reactions on blends of a diglycidyl ether of bi sphenol A (DGEBA) epoxy resin with 4, 4 ' -diaminodiphenylmethane (DDM) har dener and different amounts of polyoxypropylenetriamine (POPTA) oligomer. T hese systems exhibit phase separation induced by molar mass increasing thro ugh curing of the resin. Monitoring of phase separation and vitrification ( related to the alpha -relaxation) was performed by this technique. The resu lts are compared with those for the unmodified resin-hardener mixture. The change of the main a-relaxation with cure time, cure temperature, and amoun t of modifier was measured for the mixtures. This change of the main relaxa tion through curing in the frequency domain was indicative of the cure reac tion advancement, because of its dependence on the viscosity of the medium. The change of the ionic conductivity during curing was also analysed, show ing its dependence upon cure temperature. (C) 2001 Society of Chemical Indu stry.