Decoupling of Fatigue Properties and High Modulus in Dynamic Covalent Polymers

Maintaining a high modulus to simultaneously withstand deformation and increase fatigue resistance to restrict crack propagation in a material presents a significant challenge. In this work, a straightforward strategy was developed to address this issue in polymers. A dynamic network was incorporated into a permanent one prior to the formation of the latter, and two incompatible polymer networks were created to prevent common phase separation. The mechanical and fatigue resistance properties were substantially enhanced by the exact modulation of the soft and hard phase distribution by the precise control over the densities of dynamic and permanent networks as well as the number of reprocessing steps. The experimental results demonstrated a nearly nine-fold increase in the fatigue life of polyurethane compared with traditional design methods, and a 2.5 times increase in modulus. This strategy shows potential for the design of fatigue-resistant thermosetting and thermoplastic materials. The results offer new insight for the development of durable, high-performance materials that are reprocessable and compatible.