Preparation of Poly(thiol-urethane) Covalent Adaptable Networks Based on Multiple-Types Dynamic Motifs

Strong and Tough Self-Healing Elastomers via BTA-Mediated Microstructure and Metal-ligand Coordination

Creating elastomers with high strength, toughness, and rapid self-healing remains a key challenge. These seemingly contradictory properties require innovative design strategies. Herein, a novel approach is proposed by simultaneously incorporating a unique triple hydrogen bond unit, benzene-1,3,5-tricarboxamide (BTA), and imidazole-Zn2+ dynamic coordination into the elastomer. The BTA forms rigid fibers through self-assembly via triple hydrogen bonding, inducing microphase separation that significantly enhances the material's properties. Hydrogen bonds and coordination interactions provide dynamic reversibility and self-healing, achieving a balance of strength, toughness, and healing capabilities. By varying the BTA content and the degree of coordination crosslinking, the elastomer's strength is tunable within 8.79-2.03 MPa, and it boasts an impressive elongation at a break of up to 700%. Remarkably, it recovers 94.6% of its strength after being cut in half, facilitated by treatment with DMF at 70 °C for 24 h. Furthermore, the integration of carbon nanotubes endows the material with resistance-sensing, enabling real-time monitoring of human movements. Overall, this study lays a theoretical foundation and introduces innovative concepts for the development of high-toughness self-healing elastomers.

Metal Coordination in Polyimine Covalent Adaptable Networks for Tunable Material Properties and Enhanced Creep Resistance

Covalent adaptable networks (CANs) can replace classical thermosets, as their unique dynamic covalent bonds enable recyclable crosslinked polymers. Their creep susceptibility, however, hampers their application. Herein, an efficient strategy to enhance creep resistance of CANs via metal coordination to dynamic covalent imines is demonstrated. Crucially, the coordination bonds not only form additional crosslinks, but also affect the imine exchange. This dual effect results in enhanced glass transition temperature (T_g ), elasticmodulus (G') and creep resistance. The robustness of metal coordination is demonstrated by varying metal ion, counter anion, and coordinating imine ligand. All variations in metal or anion significantly enhance the material properties. The T_g and G' of the CANs are correlated to the coordination bond strength, offering a tunable handle by which choice of metal can steer material properties. Additionally, large differences in T_g and G' are observed for materials with different anions, which are mostly linked to the anion size. This serves as a reminder that for coordination chemistry in the bulk, not only the metal ion is to be considered, but also the accompanying anion. Finally, the reinforcing effect of metal coordination is proved insensitive to the metal-ligand ratio, emphasizing the robustness of the applied method.

Stretchable Self-Healing Plastic Polyurethane with Super-High Modulus by Local Phase-Lock Strategy

In this work, a multiblock polyurethane (PU-Im) consisting of polyether and polyurethane segments with imidazole dangling groups is demonstrated, which can further coordinate with Ni²⁺ . By controlling the ligand content and metal-ligand stoichiometry ratio, PU-Im-Ni complex with vastly different mechanical behavior can be obtained. The elastomer PU-2Im-Ni has extraordinary mechanical strength (61MPa) and excellent toughness (420 MJ m^-3 ), but the plastic PU-4Im-Ni exhibits super-high modulus (515 MPa), strength (63 MPa), and good stretchability (≈800%). The metal-ligand interaction between polyurethane segments and Ni²⁺ is proved by Raman spectra, dynamic mechanical analysis (DMA), and transmission electron microscopy (TEM). The polyurethane segments domain formed by microphase separation is dynamically "locked" by Ni²⁺ coordinated with imidazole, revealing a local phase-lock effect. The phase-locking hard domains reinforce the PU-Im-Ni complex and maintain stimuli-responsive self-healing ability, while the free polyether segments provide stretchability. Primarily, the water environment with plasticization effect serves as an effective and eco-friendly self-healing approach for PU-Im-Ni plastic. With the excellent mechanical performance, thermal/aquatic self-healing ability, and unique damping properties, the PU-Im-Ni complexes show potential applications in self-healing engineering plastic and cushion protection fields.