A synthetic scheme was developed to prepare cationically polymerizable octafunctional monomers with silsesquioxane (T-8) cores. Epoxy and 1-propenoxy functional groups were attached to the core by the hydrosilation of T-8(H) with an appropriate precursor. The steric constraints and the requirements for the hydrosilation reaction are discussed. The monomers were fully characterized and then polymerized by exposure to ultraviolet irradiation in the presence of onium salt photoinitiators. The polymerization conditions for the monomers were optimized and compared with each other using real-time infrared spectroscopy. Thermal analysis was also performed on the resulting crosslinked polymers.