Ultrastrong and High-Tough Thermoset Epoxy Resins from Hyperbranched Topological Structure and Subnanoscaled Free Volume

The strength and toughness of thermoset epoxy resins are generally mutually exclusive, as are the high performance and rapid recyclability. Experimentally determined mechanical strength values are usually much lower than their theoretical values. The preparation of thermoset epoxy resins with high modulus, high toughness, ultrastrong strength, and highly efficient recyclability is still a challenge. Here, novel hyperbranched epoxy resins (Bn, n = 6, 12, 24) with imide structures by a thiol-ene click reaction. Bn shows an excellent comprehensive function in simultaneously improving the strength, modulus, toughness, low-temperature resistance, and degradability of diglycidyl ether of bisphenol-A (DGEBA). All the mechanical properties first increase and then decrease with minimization of the free volume properties. The improvement is attributable to uniform molecular holes or free volume by a molecular mixture of linear and hyperbranched topological structures. The precise measurement and controllability of the molecular free volume properties of epoxy resins is first discovered, as well as the imide structure degradation of crosslinked epoxy resins. The two conflicts are successfully resolved between strength and toughness and between high performance during service and high efficiency during degradation. These findings provide a route for designing ultrastrong, tough, and recyclable thermoset epoxy resins. This work demonstrates the preparation of high-performance epoxy thermosets from hyperbranched epoxy, overcoming the two conflicts between strength and toughness and between high performance and highly efficient degradation. The in-situ simultaneous reinforcing and toughening mechanism is well investigated, being attributed to a synergistic effect of high crosslinking density, minimization of free volume, narrow free volume distribution, and hyperbranched structure.image

Automated summary

This study presents the preparation of hyperbranched epoxy resins with imide structures, which exhibit excellent comprehensive properties in terms of strength, modulus, toughness, low-temperature resistance, and degradability. By controlling the molecular free volume properties, the conflicts between strength and toughness and between high performance and highly efficient degradation are successfully resolved, providing a new approach for designing ultrastrong, tough, and recyclable thermoset epoxy resins.