Isothermal and non-isothermal cure of a tri-functional epoxy resin (TGAP): A stochastic TMDSC study

The isothermal cure of a highly reactive tri-functional epoxy resin, tri-glycidyl para-amino phenol (TGAP), with diamino diphenyl sulphone (DDS), at two different cure temperatures Tc has been studied by both conventional differential scanning calorimetry (DSC) and by a stochastic temperature modulated DSC technique, TOPEM. From a series of isothermal cure experiments for increasing cure times, the glass transition temperature Tg as a function of isothermal cure time is determined by conventional DSC from a second (non-isothermal) scan, and the vitrification time tv is obtained as the time at which Tg = Tc. In parallel, TOPEM experiments at the same Tc lead directly to the determination of tv from the sigmoidal change in the quasi-static heat capacity. It is not possible to identify the glass transition temperature of the fully cured system, Tg∞, in a third scan by conventional DSC. In contrast, with TOPEM a second (non-isothermal) scan at 2 K/min after the isothermal cure gives rise to three separate transitions: devitrification of the partially cured and vitrified material; almost immediate vitrification as the Tg of the system again rises; finally another devitrification, at a temperature approximating closely to Tg∞. Thus with TOPEM it is possible to obtain a calorimetric measure of the glass transition temperature of this fully cured system.