Influence of the addition of an aliphatic epoxide as reactive diluent on the cure kinetics of epoxy/amine formulations

The cure kinetics of two different diepoxy prepolymers and their mixtures with a single diamine was analyzed using size exclusion chromatography (SEC). One of the diepoxy prepolymers was based on bisphenol‐A diglycidyl ether (DGEBA), while the other one was the diglycidyl ether of 1,4‐butanediol (DGEBD), which is a typical reactive diluent. They were used either alone or as a 50% mixture (in equivalents). The cycloaliphatic diamine 4,4′‐diamino‐3,3′‐dimethyldicyclo‐hexylmethane (3DCM) was used in stoichiometric proportions in every formulation. SEC could be used to follow the conversion of each type of epoxy groups as a function of time, in the pre‐gel stage. The reaction rate followed an autocatalytic behavior (catalysis by OH groups) in every case. DGEBD was less reactive than DGEBA. Mixing of both diepoxy prepolymers led to an increase in the specific rate constant for DGEBD and a decrease of the one for DGEBA. This can be explained by the influence of the polarity of the reaction medium on the polymerization rate and the presence of chlorine impurities.