Highly crosslinked nanocomposites of bisphenol A dicyanate (BADCy) containing silica clusters were successfully prepared via the sol-gel process. The silica clusters were generated from various metal alkoxide precursors, including methyltrimethoxysilane (TMOS), 3-glycidoxypropyltrimethoxysilane (GPOS), and 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane (ECOS). The metal alkoxide precursors GPOS and ECOS were, in turn, used as coupling agents. Three kinds of systems involving BADCy/TMOS, BADCy/coupling agent, and BADCy/TMOS/coupling agent were individually prepared and thoroughly investigated using various methods. Each kind of system was of a particular characterization and morphology and had distinct physical and dielectric properties. Isolated silica clusters on a nanoscale were homogenously distributed in the highly crosslinked BADCy/TMOS hybrid system. The characterization of BADCy/TMOS nanocomposites showed improved physical properties, when compared with the neat BADCy network. The particle sizes can be controlled by adding different amounts of TMOS and are slightly increased (in the range of 50-105 nm) with increasing TMOS content. On the other hand, in the highly crosslinked BADCy/coupling agent hybrid system, the silica clusters were tethered to the BADCy matrix by the coupling agent. An oxazoline linkage was detected during the reaction of cyanate groups in BADCy with the epoxide groups in the coupling agent. These nanocomposites exhibited weakened mechanical properties but are of a smaller and more homogenous particle size in the range of 30-50 nm, irrespective of the silica content. Finally, the BADCy/TMOS/coupling agent system was successfully designed to combine the advantages of the two systems mentioned above. (c) 2006 Wiley Periodicals, Inc.