Theoretical Study on the Mechanism of Formation of Cyanate Resins

Ab initio calculations of a formation reaction of a triazine ring were performed. From the model substrate, methyl cyanate, a concerted association path with C(3)(h)() symmetry was first examined. In terms of energy changes, this path was found to be unlikely. Second, a stepwise path assisted by a water cluster was tested. But, this path was found to be of a relatively high amount of activation energy in the first additional step. Third, a zinc formate was used as a catalyst, and the reaction was computed to have a reasonable stepwise route for formation of the six-membered triazine ring. Fourth, the reaction promoted by a hydronium ion was shown to generate a ring-closure mechanism similar to that caused by the zinc catalyst. Thus, the crucial role of catalysts coordinated to the sigma lone-pair orbital of the cyanate nitrogen atom was verified.