UV, luminescence, and FTIR characterization of cure reaction in bisphenol A dicyanate ester resin

To develop cure monitoring techniques for bisphenol A dicyanate ester (BPADCY) resin, UV, fluorescence, phosphorescence, and IR spectra were investigated. UV-vis spectra during the cure reaction indicates that the cyclotrimerization of cyanate esters to form triazine rings is the principal reaction, as supported by IR spectroscopic results. During the cure reaction, very strong luminescence emission has been found. Fluorescence emission intensity around 420 nm first increases, followed by decrease with a small red shift as the cure reaction proceeds. The aromatically substituted cyanurates formed during the cure reaction and their inner filter effect are responsible for the observed emission and its trend in intensity. In-situ fluorescence characterization showed similar results for the catalyzed cure reaction with cobalt acetylacetonate/nonylphenol as well as bisphenol A catalyzed resin in comparison to purified BPADCY, except for the faster rate in fluorescence spectral change. Phosphorescence emission of polycyanate resins appears at a 440 nm, which is about 20 run longer than that of fluorescence. The phosphorescence lifetime has been found to be about 20 ms at room temperature and remains relatively unchanged throughout the cure reaction. FTIR in situ cure studies of BPADCY monomer indicates a linear relationship between the consumption rate of cyanate ester groups and the formation rate of the substituted triazine rings. Fluorescence changes are correlated to the extent of cure by IR technique.