Proposed mechanism for the curing of epoxy resins with amine‐lewis acid complexes or salts

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Abstract
The common assumption in the literature is that amine complexes of Lewis acids (particularly boron trifluoride) cure epoxy resins by virtue of their dissociation to liberate the Lewis acid which then functions as the “true” catalyst. Evidence is presented to indicate that this picture of amine–Lewis acid complex curing may be incorrect. Another mechanism is proposed which is consistent with (a) lack of correlation between adduct stability and reactivity, (b) a similarity in reactivity of BF3 adducts and the corresponding fluoroborate salts, (c) the relationship between reactivity of BF3 and PF5 adducts, (d) a correlation between reactivity and structure of the amine in the complex, and (e) the effect of the anion on reactivity of amine salts. The relative reactivity of the catalysts has been equated with the temperature at which gelation occurs on heating at a fairly constant rate.
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