Calorimetric measurement of the maximum glass transition temperature in a thermosetting resin

The measurement of the maximum glass transitionT _g∞ of a thermosetting resin is usually performed by differential scanning calorimetry in the second scan (T _g2scan), after a previous scan by heating up the sample to a temperature where the exothermic curing reaction has been completed. However, this method can eventually produce thermal degradation, decreasing the crosslinking density and theT _g of the sample. Values ofT _g2scan between 95? and 102?C were found in an epoxy resin based on DGEBA cured with phthalic anhydride. Thermal degradation effects can be avoided if the measurement is performed by isothermal curing and further determination ofT _g. AT _g∞ value of 109?C is achieved, which is the maximum value ofT _g according to the topological limit of conversion.