Selectivity and kinetics of epoxy resin–bisphenol a reaction catalyzed by certain guanidine derivatives

The reaction of bisphenol A with a diglycidyl ether of bisphenol A may lead to linear polymers if a selective catalyst is used. Selective catalysts promote linear polymer formation while nonselective catalysts increase the rate of crosslinking. Selectivity in epoxy resin–bisphenol A reactions depends upon the nature of the catalyst used. In order to understand these catalyst–structure relationships better, we measured the effects of catalysts on the rate of polymerization (k1) and the rate of crosslinking (k2) during epoxy resin cures. The knowledge of the ratio k1/k2 aids in the selection of catalysts specific for the linear polymerization of epoxy resins. We related this specificity to catalysts basicity. We found that less basic catalysts tend to give large k1/k2 values, indicating that little crosslinking occurs with these highly selective catalysts. We demonstrated that the linear polymer obtained from epoxy resin polymerized by triethanolamine, a very selective catalyst, and the linear polymer prepared using 3-p-chlorophenyl-1,1-dimethylurea, a catalyst with low selectivity, are essentially the same. Finally, we caution that quantitative comparisons of selectivity should be restricted to those reactions whose kinetic reaction orders are the same.