In situ FT-IR and DSC investigation on the cure reaction of the dicyanate/diepozide/diamine system

Cure reactions of a liquid aromatic dicyanate ester (1,1'-bis(4-cyanatophenyl)ethane, BEDCy) with a liquid bisphenol A epoxide (2,2-bis(4-glycidyloxyphenyl)propane, BADGE) and 4,4'-diaminodiphenyl sulfone (DDS) were studied through correlation of the in situ FT-IR spectroscopy and DSC in dynamic scanning mode. Before this system was examined, cure reactions of precursory systems of BADGE/DDS, BEDCy/BADGE and BEDCy/DDS were investigated separately. Cure reaction paths for each system are proposed. Some reactions in the precursory systems, such as polycyclotrimerization of dicyanate to form sym-triazine and formation of alkyl isocyanurate, were not observed in the combined curing system BEDCy/BADGE/DDS. Four principal reaction paths are proposed for this curing system: (1) formation of oxazoline from the reaction between the epoxide and cyanate group; (2) reaction of epoxide with primary amine to form a hydroxyl group; (3) reaction of epoxide with the hydroxyl group to form an ether linkage; and (4) rearrangement of oxazoline to form oxazolidinone. Two distinct, but somewhat overlapping, exothermic peaks were observed on the DSC thermogram. The lower temperature peak on the DSC thermogram was primarily contributed by the first reaction path, whereas the higher temperature peak can mainly be attributed to the reaction paths 2, 3 and 4. (C) 2001 Society of Chemical Industry.