Polyhedral oligomeric silsesquioxane (POSS)-based epoxy nanocomposite involving a reversible Diels–Alder-type network as a self-healing material

Epoxy-polyhedral oligomeric silsesquioxane (POSS) nanocomposites were prepared by incorporating POSS nanofiller into the epoxy-amine network. The monofunctional epoxy-POSS monomer or nonfunctional octaphenyl POSS unit were applied to reinforce the epoxy network by producing the nanocomposite with chemically bound pendant POSS or physically admixed POSS. The combination of reactive and unreactive POSS, leads to a synergistic effect and to the most efficient reinforcement of the epoxy network. Both polymer-POSS and POSS–POSS interactions are present in the system and lead to a strong physical crosslinking through the path polymer-bound POSS-unbound POSS domain. The nanocomposite was modified by incorporation of the thermoreversible Diels–Alder (DA) type network. The produced interpenetrating network composed of the irreversible reinforced epoxy and the reversible DA networks exhibits an efficient self-healing capability. This strong nanocomposite, showing a modulus of 800 MPa at room temperature, was healed with an efficiency of 61%. The developed stiff nanocomposite is shown to be a promising material because self-healing of strong thermosets is still a big challenge. With the increasing content of POSS nanofiller and heterogeneity of the nanocomposite, however, the healing efficiency diminishes. The insufficient contact of crack surfaces due to involved inhomogeneities results in a worse sealing of the material crack.