Steric and Electronic Effects Manipulate Cyanoguanidine Urea Networks to Achieve Ultrastrength, Toughness, and Malleability: Structural Design, Synthesis, and Performances
Yanlin Liu, Zhen Yu*, Yajin Fang, Jinping Ni, Junping Zhang*, Zhaobin Tang*
Although the development of covalent adaptive networks has opened up the possibility of recycling thermosets, the relentless pursuit of such materials must still reconcile the contradiction between comprehensive performance, particularly the contradiction between ultrahigh mechanical strength and malleability or recyclability. To address this issue, a molecular design strategy utilizing synergistic steric and electronic effects in the cyanoguanidine urea (CGUA) network was developed in this work. The dipole–dipole interaction enhances the cohesive energy density and mechanical enhancement, whereas tailored steric hindrance modulates the dynamic bond activation barrier. This yields CGUA networks exhibiting unprecedented mechanical properties, including as tensile strength of up to 150.6 MPa, modulus exceeding 1821 MPa, and toughness surpassing 2996 J m–2, while retaining malleability at 160 and 180 °C. By varying the steric and electronic properties of substituents within the guanidine urea structure, tunable control over polymerization, network dynamics, and mechanical properties can be achieved. This work provides a novel strategy to decouple mechanical robustness from dynamic functionality in recyclable polymers.