Vitrification and dielectric relaxation during the isothermal curing of an epoxy–amine resin

Abstract

The isothermal curing of an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) with a diamine based on 4,4′-diamino-3,3′-dimethyldicyclohexylmethane (3DCM) was analysed by dielectric relaxation spectroscopy (DRS), conventional differential scanning calorimetry (DSC) and temperature modulated DSC (TMDSC). The chemical kinetics corresponds to an autocatalytic model with an apparent activation energy of 58 kJ mol −1. The vitrification was analysed by TMDSC, between 40 and 140 °C, using the modulus of the complex heat capacity, |C p ∗|. A mobility factor based on the evolution of |C p ∗| was used to study the reaction step controlled by diffusion. The permittivity and loss factor were measured by DRS as a function of time in the frequency range between 10 Hz and 100 kHz. The dipolar relaxation, analysed by the peak of the maximum loss factor, was correlated with the vitrification determined by TMDSC. The analysis of the logarithm of the frequency against the conversion degree allows the characterisation of the molecular dynamics of the crosslinking reaction up until the vitrification of the system.