A new approach to the synthesis of reactive organic/inorganic hybrid molecules was developed. Alternating hydrocarbon and 'siloxane" segments were introduced into the arms of radial oligomers using hydrosilation chemistry. Cycloaliphatic and glycidyl epoxy-terminal systems with bisphenol A-based aromatic hydrocarbon cores and siloxane units derived from 1,1,3,3-tetramethyldisiloxane were synthesized and fully characterized (molecules 7 and 6, respectively). The cationic UV and thermal curing behavior of these two new radial hybrid epoxies was investigated using photo- and thermal- differential scanning calorimetry. Hybrid cycloaliphatic epoxy 7 exhibited good UV curing kinetics and photopolymerized to high conversion. The glycidyl analog 6 exhibited poor UV curing kinetics, but was readily cured using 2-ethyl-4-methylimidazole as a nucleophilic curing agent. Both hybrid epoxysiloxanes exhibited extensive thermal cationic cure. The physical properties of cured films of the two new radial epoxysiloxanes were studied and compared with various commercially available hydrocarbon and siloxane benchmark materials. The cured systems exhibited lower moisture uptake and better thermal stability than most hydrocarbon epoxies examined. Several visually compatible blends of the new hybrid molecules with common hydrocarbon resins were identified, and in general organic compatibility was found to be intermediate among selected siloxane-containing benchmarks. Molecules 6 and 7 represent progress towards the goal of synthesizing highly functional organic/inorganic hybrid molecules which combine the best attributes of both hydrocarbon epoxides and siloxane materials. (c) 2007 Wiley Periodicals, Inc.