Phenolic cured epoxy reaction mechanism, catalysts

There is considerable evidence for the push-pull concerted effect in the reaction mechanism by using lead salts and DMP-30 salts as catalysts in the phenolic cured epoxy reaction. The complex formation is also supported by Alvey (13) and Son (23). 

Competing ideas drawn from the literature on the catalyzed epoxy-phenolic curing mechanism are reviewed here and will be evaluated in subsequent chapters with regards to the results of experiments carried out in this study the most common catalysts employed are Lewis bases. Many reaction mechanisms have been suggested for the Lewis-base catalysis of the epo -phenolic reaction. " The basic reactions these authors attempted to describe are shown in Rxns 1 and 2. These models differ significantly in their description of which elementaiy molecular reactions occur to achieve the net reaction. In some of these models, the Lewis-base acts as a true catalyst in others, it first forms a complex with one or two of the reactants before the catalytic nature of the complex is activated. 

Epoxy-amine systems follow an addition step-growth polymerisation mechanism. The two principal reactions of primary and secondary amines with epoxy oligomers are shown in Reaction scheme 1 [30]. These reactions are catalysed by acids, phenols and alcohols (e.g. impurities in commercial epoxy resins). The presence of water causes a tremendous acceleration, but does not alter the network structure. The hydroxyl groups formed by the amine-epoxy addition steps are also active catalysts, so that the curing reaction usually shows an accelerating effect in its early stage (autocatalysis). 

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