Rigid epoxy networks with very high intrinsic fracture toughness using a piperazine-based in-situ polymerization strategy

Various fillers and thermoplastics are often added to thermoset epoxies to improve toughness, but this may compromise their other properties or make synthesis difficult. In this study, brittle crosslinked epoxy networks are significantly toughened through in-situ polymerization of epoxy using piperazine, which reacts at moderately low temperatures in a catalyst-free one-pot method. Dynamic mechanical properties and nanoscale morphology suggest the mechanism for improved toughness is higher yielding near the crack tip due to increased molecular weight between crosslinks. The resulting toughness (K_IC ∼ 2.12 MPa√m, G_IC ∼ 1.96 kJ/m²) is higher than any other unfilled all-epoxy materials found in the literature.