Ultra-Strong 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, ultra-strong strength and highly efficient recyclability is still a large challenge. Here, we are the first to synthesize novel hyperbranched epoxy resins (Bn, n = 6, 12, 24) containing an imide structure 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. We have successfully resolved the two conflicts between strength and toughness and between high performance during service and high efficiency during degradation. These findings provide a route for designing ultra-strong, tough and recyclable thermoset epoxy resins. This article is protected by copyright. All rights reserved.