Mechanisms of Solidification of Epoxy-Amine Resins During Cure

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Previous workers have studied the solidification mechanism of curing epoxy resin systems. It is generally believed that addition polymerization systems in which the average functionality of the reactants is greater than 2, solidify through the formation of an infinite network. Statistical analysis of the reaction system allows the prediction of the degree of reaction at which the infinite network can be observed. Analysis of the scaling properties of systems approaching the critical degree of reaction have predicted that certain scaling laws should be observed near the critical degree of reaction. The scaling predictions tested were the observation, near the solidification point, of a power law dependence of G' and G" on frequency obtained near the time when G' and G" are equal, for which the power exponent was 0.7 ± 0.02, and a scaling law involving a reaction coordinate, ƞ ∼ ε−k. with k = 1.3 ± 0.2. However, gelation at the predicted point in the reaction and the predicted scaling were observed only in isolated cases. This work addresses the difference between systems that exhibit scaling as predicted and those which do not exhibit scaling. Work reported here shows, in a system for which the scaling predictions are observed, solidification occurs at the degree of reaction predicted by the simple statistical theory. This solidification mechanism appears to be observed only for those systems and cure conditions where the cure reaction is carried out at a temperature above the highest attainable glass transition temperature for the fully cured system. For the majority of epoxy systems, solidification does not occur near the predicted degree of reaction but may occur before or after the predicted point. For these systems the scaling properties predicted are not observed. © 1994, American Chemical Society. All rights reserved.

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