Closed‐Loop Chemical Recyclable Guanidinium‐Imine Covalent Adaptable Networks With Exceptional Mechanical Strength and Chemical Stability

Abstract Thermosetting polymers face significant challenges in recyclability and environmental sustainability due to their permanently cross‐linked structures. Covalent adaptable networks (CANs) offer a promising solution by incorporating dynamic covalent bonds (DCBs), yet they often suffer from a trade‐off between recyclability and chemical stability. Herein, we report a mechanically robust and chemically stable guanidinium‐based CAN through the synergistic integration of dynamic imine bonds and robust hydrogen‐bonds. By employing triaminoguanidinium chloride (TGCl) as a dynamic cross‐linker, a poly(urethane‐guanidinium‐imine) (PUGI) network bearing adjacent dynamic covalent and noncovalent bonds within one chemical moiety, thereby overcoming the trade‐off between recyclability and chemical stability. This synergetic polymer network endows the PUGI CAN with exceptional mechanical strength (tensile strength up to 117.8 MPa), outstanding chemical stability against aggressive media (including strong acids, bases, and saline solutions), and efficient physical recyclability via hot‐pressing. Critically, the inherent reversibility of guanidinium‐based imine bonds enables the PUGI CAN closed‐loop chemical recyclability while retaining its mechanical properties. This work provides a versatile molecular paradigm for designing high‐performance, recyclable thermosets with potential applications in extreme environments and contributes to the development of a circular economy for advanced polymers.