Reactivity, viscoelastic behaviour and mechanical performances of hybrid systems based on epoxy resins and reactive polyhedral oligosilsequioxanes

An epoxy resin was modified by adding an epoxy functionalized polyhedral oligomeric silsesquioxane (POSS). FT-NIR measurements demonstrated that the epoxy groups of POSS were almost as reactive as those of the DGEBA in the curing stage, while in the post-curing a lower reactivity of the latter was found. The dynamic-mechanical analysis showed an increase in the storage modulus and a decrease of Tg and T² with POSS content. The viscoelastic analysis showed that the addition of POSS enhanced the free volume and the tendency of the network to undergo thermal expansion. In particular, the ² transition was made increasingly localized by increasing the POSS content. With respect to mechanical performances, the yield process was facilitated by incorporation of the POSS nanocages within the network, possibly due to an enhancement of the chain mobiliy. Fracture measurements showed an improvement of the parameters Kc and Gc up to 5 wt% of POSS, after which a decrease of toughness was observed. These results were supported by a fractographic analysis.