SYNOPSISThe extent of cure for epoxy resin (BADGE) with a small excess of amine hardener (DDM, 4 w/o) was determined by assay of the epoxy groups using near infrared spectroscopy. The importance of the specification of the operational definition of glass transition temperatures is clearly established by comparison of different methods of determining glass transition temperatures.For isothermal cures, there were broad tan 6 loss peaks, while for postcure, there was a large reduction in size of the loss peak at extended times. This suggests that there is a change in network structure that is not related to the extent of reaction of epoxy groups, because X, -0.99 after 30 min at 180°C.

ABSTRACT:The extent of conversion of epoxy groups cured with diaminodiphenyl methane, a diamine, at 100°C was approximately 100%, and the glass-transition temperature (T g i ) was found to be an increasing function of cure time with very large increases with extended postcure treatments at 180°C. However, this considerable increase in the T g with postcure at 180°C was not due to the reactions of epoxy and amine groups. The specific volume reduced with the T g to a minimum at 103°for the cured samples but showed a very slight increase with the T g for the postcured samples. It was also found that the glassy modulus (E g ) was a linear decreasing function of the T g . There were two separate relationships between the E g and the rubbery modulus that depended on the cure conditions and suggested that the "structure" formed due to cure at a temperature of 100°C was different than that at postcure, which was 180°C. The most sensitive structural parameter for these cured epoxy resins was their T g i .

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