Robust polyurethane materials with synergistic ionic and metal-ligand crosslinking double networks for specific Cu-ion removal

The development of polymer materials with the harmonious integration of strength, stiffness, and stretchability is important for practical applications; however, this remains a substantial challenge. This work proposes a coupled dynamic bond (CDB) strategy using an ionomer-metal ion-ligand pair, which complements the orthogonal dynamic bonding strategy. It involves the in situ polymerization of acrylic acid (the counter ion) into poly(acrylic acid), resulting in the formation of a second ionic network on the first zinc-imidazole network. The integration of CDBs effectively enhances the stiffness of the material, without affecting its stretchability and strength. The newly synthesized material exhibits well-balanced mechanical properties, with Young's modulus, strength, and toughness of 109 MPa, 32 MPa, and 242 MJm−3, respectively. The Young's modulus and yield strength of double network material are 137% and 100% higher, respectively than those of the material with a metal-coordination single network. The transparent film based on double network material exhibits high potential for application in display films, because of its colorless nature and energy-absorbing impact-protection property. Shear rheological characterization confirms the high melt strength and elasticity of the new CDB-based material, which can be processed by a wide range of techniques, including foam molding. Considering the portable recycling characteristics of dynamic-network materials and their flexible processing attributes, the potential of the foamed material for specific heavy metal-ion removal (for the treatment of lithium-battery wastewater) has been investigated. This research provides valuable insights into the design of complex transition metal-polymer materials, highlighting their exceptional mechanical performance and potential for lightweight applications.