Thermal and mechanical properties of epoxy/monofunctional and epoxy/multifunctional POSS nanocomposites

The thermal and mechanical properties of diglycidyl ether of bisphenol-A (DGEBA) copolymerized with two types of polyhedral oligomeric silsesquioxane (POSS) nanophases, namely, monofunctional POSS-epoxide macromer (MoPOSS) and multifunctional POSS-epoxide macromer (MuPOSS) cured with polyoxypropylene diamine were investigated. The glass transition temperature, T_g, measured by DSC increased with an increasing weight fraction of the MoPOSS. For the MuPOSS series, the T_g of the composite containing 3.0 wt.% MuPOSS increased; however, the T_g's of the composites containing equal to or greater than 5.0 wt.% MuPOSS decreased because of a reduced cross-linking density and a plasticization effect from the excess curing agent. The curing of the MoPOSS systems followed first-order kinetics with lower activation energies and frequency factors. TGA experiments indicated that both types of the POSS provided enhancement in the thermal stabilities compared to the epoxy network. Fracture analysis showed that the POSS-incorporated epoxy network glasses had higher fracture toughness values than the neat epoxy resin.