Toughening shape-memory epoxy resins via sacrificial hydrogen bonds

Abstract

The demand for composites with long anti-fatigue lifetimes and stable performance in extreme environments has created requirements for both high strength and toughness when it comes to epoxy matrices. However, for thermosets, promoting maximum elongation and extensibility without sacrificing mechanical strength remains challenging. Herein, via introducing hydrogen bonds and flexible segments into the crosslinked network simultaneously, a shape-memory epoxy resin with good mechanical properties was prepared. The long flexible chains provide the network with good mobility and toughness, while the existence of reversible hydrogen bonds leads to a cooperative effect in terms of both increased cross-linking density and anchor points for chain-restriction. Benefiting from the rigid–flexible integrated structure in this system, the typical resin exhibits high tensile strength (73.66 MPa) with large elongation at break (9.42%). In addition, this epoxy network also shows good thermally induced shape-memory effects. Therefore, as all aspects of its superior performance are mainly based on the presence of sacrificial bonds in the network, a similar strategy can be used to toughen rigid polymers, and using this approach can allow a favorable combination of high strength and extensibility to be realized.