In Situ Self-growing of Thermoplastics into Strong and Tough Thermosets Based on Dynamic Imidazole-urea Moiety

Abstract

Thermosets are indispensable to our daily life, but their crosslinked structures make them unable to be processed by the melt processing like thermoplastics, which greatly limits their shape designs and applications. Herein, we address this challenge via an in situ self-growing strategy, i.e. utilizing the dynamic imidazole-urea moiety to suck up and integrate epoxy into the materials and making the thermoplastics grow in situ into thermosets. With this strategy, thermosets can be readily processed via hot-melt extrusion molding, including melt spinning and fused deposition modeling 3D printing. More importantly, this strategy simultaneously integrates the flexibility of polyurethane and the robustness of epoxy resin into the resulting thermosets, yielding a mechanical-reinforcing effect to make the material not only strong but also tough (toughness: 99.3 MJ·m⁻³, tensile strength: 38.8 MPa). Moreover, the crosslinking density and modulus of the as-prepared thermosets (from 34.1 MPa to 613.7 MPa) can be readily tuned on demand by changing the growth index. Furthermore, these thermosets exhibited excellent thermal stability and chemical resistance.