Cure behaviour and structure of dicyanate-epoxy novolac blends

The cure characteristics of bisphenol A dicyanate-novolac epoxy resin blends were investigated by gel time determination and dynamic DSC. The effects of the proportion on the structures of cured blends were investigated by FTIR. In situ FTIR was utilized to study the curing mechanism and curing kinetics. The results indicated the distinct catalytic effects of the novolac epoxy resin on the curing of bisphenol A dicyanate. Due to considerable amounts of unepoxidized phenol present in the novolac epoxy resin, the reactions between phenol and cyanate disturbed the formation of the co-reaction products. The curing reactions of the blends indicated by in situ FTIR did not follow the Bauer mechanism totally. A composite mechanism of triazine-epoxy insertion and epoxy-cyanate reaction indwells in the systems. The authors suggest that most of the oxazolidinone present in the blends is formed by isomerization of oxazoline rather than by insertion of epoxy into isocyanurate. The amount of epoxy resin in the blend did not alter the curing mechanism, but had significant effects on the kinetic behaviour.