Chemorheology of epoxy resin - Part II Polyurethane-cross-linked epoxy resin cured with a tertiary amine

A secondary hydroxyl group containing epoxy resin was reacted and cross-linked with polyurethane (PU). This PU-cross-linked epoxy resin was cured with a tertiary amine and the viscosity and dynamic mechanical properties were determined by a cone-and-plate rheometer. A dual Arrhenius viscosity model was modified to predict the viscosity profile with time before gelation during non-isothermal curing, and the calculated values coincided with the experimental data. The activation energy of this system (NCO/OH ratio=30 mol%) calculated by the modified model was 13kcal mol^-1 for the initial region, and 16.8 kcal mol^-1 for the final region. After gelation, the dynamic complex modulus was correlated to the reaction kinetics according to the rubber elasticity theory, and the activation energy calculated was 5.2 kcal mol^-1. These activation energies are all lower than those of the unmodified epoxy resin system. Consequently, the reaction rate of the PU-cross-linked epoxide system was less affected by temperature than that of the unmodified epoxide system. It was also found that the rate of increase of viscosity and dynamic moduli decreased with increasing PU content. The gelling point was estimated by rheological measurements.