FLUORESCENCE MONITORING OF POLARITY CHANGE AND GELATION DURING EPOXY CURE

The fluorescence spectrum of -(4-dimethylaminophenyl)-6-phenyl-1,3,5-h exatriene (DMA-DPH) dissolved in a stoichiometric mixture of diglycidy l ether of bisphenol A and diethylene triamine was measured as a funct ion of cure time at various cure temperatures. The frequency of the fl uorescence maximum for DMA-DPH increased during the curing reactions b ecause of the change in the polarity of the epoxy resin. In an isother mal cure, the fluorescence frequency increased linearly with the cure time until the gelation occurred. The total change in fluorescence fre quency that occurred from the beginning of the isothermal cure to the gelation time was 1000 cm-1 and was independent of the cure temperatur e, implying that the chemical structure of the infinite network at the gelation time was independent of the cure temperature. The rate const ant, K(T), for the polarity change during an isothermal cure of the ep oxy resin, defined as the rate constant for the linear increase in flu orescence frequency, was determined. The activation energy of K(T), wa s estimated to be 60 kJ mol-1.