Cyclo-aliphatic epoxy and methacrylate hybrimers were fabricated via the photocationic polymerization of cycloaliphatic epoxy oligosiloxanes and photoradical polymerization of methacrylate oligosiloxanes, respectively. The thermomechanical/thermal properties of these two hybrimers using different photo-polymerization mechanisms were compared. Although both oligosiloxanes showed similar degrees of condensation, siloxane network structures, and sizes, the cycloaliphatic epoxy hybrimer showed improved thermomechanical/thermal properties as compared to the methacrylate hybrimer. This was attributable to a highly crosslinked network structure developing from the living characteristics of photocationic polymerization and the short, compact organic chains of the cycloaliphatic epoxy hybrimer as compared to the methacrylate hybrimer.