Hyperbranched Epoxy Topology Enables Covalent Interphases and Penetration-Locking Thermoset Networks.

The inherent trade-off between high mechanical performance and recyclability in carbon fiber-reinforced epoxy composites (CFREs) remains a fundamental challenge in epoxy resin design. Herein, we introduce a topology engineering strategy based on an imide-containing dual-role hyperbranched platform, which acts simultaneously as reactive tougheners and interfacial coupling agents. Within the matrix, the hyperbranched architecture interpenetrates the linear epoxy network, forming a distinctive dual-phase "penetration-locking" topology that reduces free volume and increases effective cross-link density. At the fiber-matrix interface, thiol-terminated hyperbranched molecules enable covalent interphase formation via thiol-ene click chemistry, enhancing interfacial adhesion and stress transfer. This chemically integrated design enables cost-effective T300-based composites to reach a tensile strength of 740 MPa, comparable to conventional T800-based composites, while T800-based composites achieve up to 1.1 GPa. Importantly, the incorporation of imide and ester linkages introduces chemically addressable cleavage sites, enabling selective depolymerization under mild alkaline methanolysis, recovery of carbon fibers with retained integrity, and upcycling of oligomeric products as curing agents. This work establishes a molecular design framework that couples network topology, interfacial chemistry, and dynamic covalent functionality, providing a versatile platform for high-performance thermoset composites with improved lifecycle sustainability.