Spectroscopic investigation of cure reaction in a bisphenol-A dicyanate ester thermosetting resin

The objective of the dissertation was to develop an intrinsic UV and luminescence cure monitoring technique and to provide insight in understanding the cure chemistry of polycyanate resins. UV-visible spectrum of a bisphenol A dicyanate ester (BPADCY) monomer during the cure reaction supported that the cyclotrimerization of cyanate esters to form triazine rings is the principal reaction.^ A very strong luminescence emission was found during the cure reaction of BPADCY monomer. As the cure reaction proceeded, the fluorescence emission intensity around 420 nm first increased and then decreased accompanied by a small bathochromic shift. Eleven cure related model compounds representing reactants, intermediates and products were chosen, and their UV-Visible and fluorescence behaviors were characterized in solution and in the solid state. Fluorescence behavior during cyclotrimerization of a monofunctional cyanate ester was also characterized. The model compound study indicated that the aromatic substituted triazines formed during the cure reaction and their inner filter effect were responsible for the emission around 420 nm and the observed trend in intensity. Fluorescence emission intensity of polycyanate resins heavily depended upon the measurement temperatures. Both bisphenol A as an impurity in monomer and cobalt acetylacetonate/nonyl phenol catalysts did not interfere with the emission at 420 nm. In situ fluorescence characterization was attempted for the cure reaction of cobalt acetylacetonate/nonyl phenol catalyzed BPADCY system. The phosphorescence emission wavelength of polycyanate resins appeared at about 20 nm longer than that of fluorescence. Phosphorescence lifetime was found to be about 20 ms at room temperature and remained relatively unchanged throughout the cure reaction.^ FTIR in situ cure kinetics of BPADCY monomer indicated that the cure reaction in air was a little faster than in argon. A linear relationship was found between the consumption rate of cyanate ester groups and the formation rate of substituted triazine rings.