DIELECTRIC-RELAXATION DURING ISOTHERMAL CURING OF EPOXY-RESIN WITH AN AROMATIC AMINE

The isothermal curing behavior of an epoxy resin system has been monitored by a dielectric measurement whose sensor consisted of a vertical parallel-plate cell based on a three-terminal method. The materials used in the isothermal cure were the diglycidyl ether of bisphenol-A (DGEBA), which was purified from Epon 825 by recrystallization, and 4,4'-diamino diphenyl methane (DDM). A dielectric relaxation was observed during each isothermal cure at temperatures of 70, 80, 90, and 100-degrees-C, which were below the glass transition temperature (T(g)) of the reactive DGEBA-DDM system at the gel point. The relaxation is considered to be caused by the transformation from a liquid state to an ungelled glassy state as a result of an increase in molecular weight because gelation followed by a rubbery state did not exist in the temperature range studied. The dielectric relaxation for the DGEBA-DDM system fits the empirical model of the Havriliak-Negami equation. The T(g) of the DGEBA-DDM system, which was estimated from the dielectric relaxation time, agreed with the one experimentally determined by differential scanning calorimetry (DSC).