Monitoring the Cross-Linking of Epoxide Resins by Thermoanalytical Techniques

Abstract

Abstract The curing reaction of bisphenol A diglycidylether with 4,4′-diaminodiphenylmethane (DDM) was studied by thermoanalytical methods. The overall reaction was monitored through the exothermic heat of reaction by differential scanning calorimetry (DSC), and a method is developed for predicting isothermal conversion-time curves over a wide temperature range from the results of two dynamic DSC scans. The reaction mechanism is not specified but it is assumed not to change with conversion, and the rate is assumed to be controlled by a single rate constant of the Arrhenius form. A series of fully cured resins prepared with varying DDM concentration is characterized by penetrometer, thermal expansion, and DSC methods. The Tg's of these resins are compared with those obtained using the stoichiometric quantity of DDM and reacted to different calorimetric degrees of cure. The Tg of the resin increases by about 70[ddot];C in the final 10% of the curing reaction where ΔH measurements are least sensitive, so that the final stages of cure are best monitored by Tg measurements.