A novel cyanate ester, 2,6-dimethyl phenol dipentene cyanate ester (DPCY), was successfully synthesized from cyanogen bromide with 2,6-dimethyl phenol dipentene novolac, which was synthesized from dipentene and 2,6-dimethyl phenol. For the purpose of increasing the mobility of residual DPCY during the final stage of curing and achieving a complete reaction of cyanate groups, a small quantity of a monofunctional cyanate ester, 4-tert-butyl phenol cyanate ester, was added to DPCY to form a cyanate ester copolymer. The thermal properties of the cured cyanate ester resins were studied by dynamic mechanical analysis, dielectric analysis, and thermogravimetric analysis. These data were compared with those of the commercial bisphenol A cyanate ester system. The cured modified cyanate ester exhibited a dielectric constant of 2.59-2.50, a dissipation factor of 0.0055-0.0089, and moisture absorption of 0.91-1.17%; these values were all lower than those of the as-cured bisphenol A dicyanate system. (C) 2004 Wiley Periodicals, Inc.