Simultaneous measurements of enthalpy and heat capacity of a thermosetting polymer during the curing process

We report a new microcalorimetric technique which allows simultaneous measurements of the heat capacity and the rate of enthalpy release during the chemical reaction in a substance under quasi‐isothermal conditions. The basic features of the instrument are presented together with brief experimental results on the polymerization of diglycidyl ether of bisphenol A mixed with ethylene diamine. The instrumentation is an advance for studies of both synthetic and biological formation of macromolecules, for now it becomes possible to measure the heat capacity of a time‐variant system and to characterize its vitrification transition occurring at constant temperature, as the growth of the macromolecule by chemical reaction increases the sample’s viscosity. The abrupt decrease observed in the heat capacity curve corresponds to the vitrification transition, which cannot be observed in the corresponding enthalpy release curve. The present calorimeter has an important use in both technological assessment and in unders...