In situ FTIR and DSC investigation on cure reaction of liquid aromatic dicyanate ester with different types of epoxy resin

Abstract

Cure reactions of a liquid aromatic dicyanate ester [1,1'-bis(4-cyanatophenyl) ethane, DiCy] associated with a liquid cycloaliphatic epoxy ester (3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane-carboxylate, EPC) and with liquid bisphenol A epoxide [2,2-bis(4-glycidyloxyphenyl)propane, EPA] were studied through a cross-reference between in situ FTIR and DSC dynamic scanning. DiCy can act here as a latent catalyst to cure EPC and EPA resins. Reaction mechanisms were found to be different for both curing systems (EPC/DiCy and EPA/DiCy). Two significantly separated exotherms were observed in the DSC thermograms in each system. The reaction mechanism of the EPA/DiCy system was found to follow mainly Bauer pathways. We postulate a new sequence of the mechanism in this system due to the presence of an oxazoline structure during the progression of the curing process. In the curing system of EPC/ DiCy, however, another five principle reaction paths, rather than Bauer pathways, are suggested: (1) polycyclotrimerization of DiCy, (2) formation of oxazoline, (3) insertion of EPC into cyanurate, (4) formation oftetrahydro-oxazolo-oxazole, and (5) ring cleavage and reformation of oxazoline to form the insertion structure of cyanurate. The lower temperature peak in the DSC thermogram is primarily contributed by the former three reaction paths, whereas the higher temperature peak can mainly be attributed to the reaction paths 4 and 5.