The characterization of thermoset cure behavior by differential scanning calorimetry. Part I: Isothermal and Dynamic Study

A study of the isothermal cure kinetics of an unsaturated polyester resin by differential scanning calorimetry is described. An autocatalyzed second order kinetic model is adopted to elucidate the cure reaction and also assess the kinetic parameters. The rate constant, the maximum cure rate, the extent of cure, and the degree of conversion at the maximum cure rate, all increase with increasing cure temperature, while the half‐life and the time required to reach the maximum cure rate both decrease. Discrepancies between the experimental results and the predicted values of some of the kinetic parameters, especially at high degrees of conversion, are attributed to the highly different‐controlled cure reaction following the gel point. The activation energy ( E ) and the pre‐exponential factor (1 n A ) of the polyester cure reaction were estimated, using differential graphical techniques, to be 131 ± 4 kJ/mol and 39 ± 1 respectively. An ASTM method (E698) produces erroneously low values of the Arrhenius parameters, suggesting that the assumptions of the method may be overly simplified.