REAL-TIME DIELECTRIC STUDIES OF NETWORK FORMATION IN THERMALLY ACTIVATED EPOXY-AMINE AND ISOCYANATE-TRIOL SYSTEMS

Dielectric measurements are reported on the changes that occur in the nature of the dipole relaxation processes during cure of an epoxy-amin e and a diisocyanate-triol system. The epoxy resin forms a vitrified s olid in the final cured state, whereas the urethane retains its elasto meric properties. The initial behaviour for the epoxy resin is dominat ed by ionic conduction processes. Subtraction of the conductivity cont ribution reveals a dipolar relaxation process, which. is analysed usin g the Havriliak-Negami (HN) equation. The characteristic exponent 1 - n of the HN equation changes in a similar manner to that found with ot her epoxy-amine systems. However, the dipolar process in the urethane occurs at very high frequency and a different form of the 1 - n depend ence is observed. Sensitivity of the dielectric method for the detecti on of vitrification and gelation is critically assessed. If the vitrif ication is allowed to occur, then detection of a gel point may not nec essarily be inferred from the dielectric data.