The thermoset epoxy systems of diglycidyl ether of bisphenol-A (DGEBA) and different imidazoles (unsubstituted imidazole, N-methyl-im., 2-methyl-im., 4(5)-methyl-im., 2-ethyl,4-methyl-im., 2-ethyl-im., 2-phenyl-im.) as catalytical curing agents were characterized. From microcalorimetric experiments it was deduced that each molecule of imidazole induces more than 20 epoxy groups to undergo polyaddition. Therefore, optimum glass transition temperature-ranges can be obtained with 0.025 to 0.05 mol of catalyst/equivalent of epoxy. The different alkyl-and aryl-substituted imidazoles show rather similar catalytic effects, with the kinetics differing by a factor of 3 at most. Mechanical properties (flexural modulus and strength, ultimate strain and fracture toughness) at ambient temperature do not correlate with the crosslinking density of the polymer network.
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J. Vogt (1987) studied this question.
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