Curing kinetics of phase separating thermosets studied by DSC, TMDSC and dielectric relaxation spectroscopy

Differential scanning calorimetry (DSC), temperature-modulated DSC (TMDSC) and dielectric relaxation spectroscopy have been performed during isotherma l curing of an epoxy network (diglycidylether of bisphenol A cross-linked w ith diaminodiphenyl methane) and of thermoplast modified epoxy resins ("sem i-interpenetrating polymer networks") consisting of the epoxy network compo nent and different amounts (10 and 20 wt%) of a linear high T-g-polymer (po lyethersulfone). During reaction the homogeneous mixtures phase separate in to an epoxy-rich and a linear polymer-rich phase. The time dependent change s in the complex dielectric permittivity are described by a simple two phas e model based on two Havriliak-Negami functions combined with Vogel-Fulcher equations for the description of the curing time dependence of the relaxat ion times. The time increase of the relaxation times in the two phases duri ng isothermal curing is incorporated by time-dependent Vogel-temperatures. The latter are related to the time evolution of the glass transition temper atures T-g in the two phases measured independently by calorimetry. With TM DSC it was possible to resolve T-g for both phases since the curing time ev olution of the heat capacity could be separated from the heat of reaction. In the conventional DSC the T-g Of the linear polymer rich phase was masked by the heat of reaction. In addition, with TMDSC the vitrification during isothermal curing could be monitored. (C) 1999 Elsevier Science B.V. All ri ghts reserved.