Dynamic Poly(disulfide) Interphase Enhances Ductility and Toughness of Covalent Adaptable Network Composite without Loss of Stiffness

Abstract Covalent adaptable networks (CANs) offer recyclability and reprocessability, yet bond-exchange dynamics can reduce mechanical strength and toughness. Although the composite formation of CAN provides benefits in both aspectsstrengthening the CAN and adding recyclability to the compositeit still faces a stiffness−ductility trade-off that limits material usefulness. Here, we demonstrate a CAN composite design in which silica nanoparticle incorporation, combined with interfacial chemical structure, enhances ductility and toughness in a highly crosslinked matrix without compromising the high elastic modulus. Introducing poly(disulfide) dynamic covalent bonding chains into the network and at the filler interface significantly increases ductility, toughness, and stress at break. Together with a comparison to composites with permanent interfacial bonding, these results underscore the important role of interfacial chemistry. Based on these comparative experiments, the observed toughness enhancement is proposed to arise from energy dissipation via reorganization at the interphase through stress-activated disulfide exchange and network topological rearrangement. The resulting stress-responsive viscoelasticity enables stable deformation and allows CAN-based composites to overcome the stiffness−ductility trade-off.