Substituent engineering of dynamic covalent bonds enables simultaneous enhancement of performance and recyclability

A central challenge in designing recyclable polymers lies in the trade-off between recyclability and performance. State-of-the-art strategies leveraging supramolecular interactions or dynamic covalent bonds (DCBs), either individually or in orthogonal combination, mostly end up improving one property with the compromise of the other. Here, we present a unified molecular design strategy based on substituent engineering of DCBs to simultaneously enhance service-life performance and end-of-life recyclability. By introducing a β-ketoester substituent into dynamic oxime-urethane (OU) linkages, intermolecular hydrogen bonding is strengthened while bond thermodynamics are biased toward dissociation. We show that the engineered poly(OU)s exhibit improved mechanical and thermomechanical properties (e.g., 38 vs. 24 MPa in tensile strength; 360 vs. 169 MPa in Young's modulus; 36 vs. 20 °C in T _g) compared to the control sample lacking the β-ketoester moieties. Meanwhile, efficient depolymerization is achieved under mild conditions (140 °C), enabling recovery of the constituent components in high yields via simple vacuum distillation, particularly with an isocyanate yield of 87%, in contrast to only 14% for the depolymerization of normal poly(OU). The materials are also thermally reprocessable and enable closed-loop recycling of carbon fiber-reinforced composites. This work establishes substituent engineering of DCBs as a general strategy to decouple recyclability and performance, offering a pathway toward high-performance circular polymer materials.