For the purpose of increasing the mobility of residual bisphenol A dicyanate ester (BADCY) during the final stage of curing and achieving a complete reaction of cyanate groups, a small quantity of monofunctional phenol was added to BADCY to form an imidocarbonate, or a small quantity of monofunctional cyanate esters was added to form cyanate ester copolymers. The proposed structures were confirmed with Fourier transform infrared, elemental analysis, mass spectrometry, and NMR spectroscopy. The thermal properties of the cured cyanate esters were measured with dynamic mechanical analysis, thermogravimetric analysis, and dielectric analysis. These data were compared with those for the cured BADCY resin. The cured modified cyanate esters exhibited a lower dielectric constant, a lower dissipation factor, and lower moisture absorption than the cured BADCY system. (C) 2004 Wiley Periodicals, Inc.