CHEMORHEOLOGY OF EPOXY-RESIN .2. POLYURETHANE-CROSS-LINKED EPOXY-RESIN CURED WITH A TERTIARY AMINE

A secondary hydroxyl group containing epoxy resin was reacted and cros s-linked with polyurethane (PU). This PU-cross-linked epoxy resin was cured with a tertiary amine and the viscosity and dynamic mechanical p roperties were determined by a cone-and-plate rheometer. A dual Arrhen ius 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 w as 13 kcal mol-1 for the initial region, and 16.8 kcal mol-1 for the f inal region. After gelation, the dynamic complex modulus was correlate d to the reaction kinetics according to the rubber elasticity theory, and the activation energy calculated was 5.2 kcal mol-1. These activat ion energies are all lower than those of the unmodified epoxy resin sy stem. Consequently, the reaction rate of the PU-cross-linked epoxide s ystem was less affected by temperature than that of the unmodified epo xide system. It was also found that the rate of increase of viscosity and dynamic moduli decreased with increasing PU content. The gelling p oint was estimated by rheological measurements.