Octa-functional POSS: An Epoxy Filler or Co-monomer?

Particle tethering with the matrix permits property manipulation depending on the respective architecture and chemistry. However, integration of highly reactive moieties into epoxy networks may detrimentally affect the reaction stoichiometry. In this study, octa glycidyl polyhedral oligomeric silsesquioxane (OG POSS) was incorporated into an epoxy matrix (a) by considering it as a co-monomer (requiring stoichiometric compensation) and (b) by considering it as a silica-based filler (simple addition without compensation). The simple addition of OG POSS resulted in a considerable glass transition temperature (T
_g
) decrease due to impaired stoichiometry, while the stoichiometric addition moderated this effect. These results, supported by the dielectric data, demonstrate that OG POSS is better considered as a co-monomer.