Water-Enabled Room-Temperature Self-Healing and Recyclable Polyurea Materials with Super-Strong Strength, Toughness, and Large Stretchability.

The synthesis of polymeric materials that simultaneously possess multiple excellent mechanical properties and high-efficient self-healability at room temperature is always a huge challenge. Here, we report the synthesis of a transparent polyurea material that can self-heal at room temperature with the aid of water and, meanwhile, has multiple remarkable mechanical performances, including super-high strength, excellent toughness, and large stretchability. Thanks to the synergistic enhancement of both dynamic imine bonds and hierarchical hydrogen bonds within the networks, the resulting polyureas have a world-record tensile strength of 41.2 MPa when compared with other polyurethanes that can self-heal at room temperature and, at the same time, a large breaking strain of 823.0% and a superior toughness of 127.2 MJ/m3. Besides the influence of imine bonds, the mechanical properties of the polyureas are also strongly related to the density and strength of the hierarchical hydrogen bonds within the polyurea networks, and these two factors could be finely controlled by adjusting the mass ratio of the soft segments with different chain lengths and the types of diisocyanates used for polyurea synthesis, respectively. More importantly, the highly dynamic characteristic of both imine bonds and hierarchical hydrogen bonds within the polyureas endows the materials with repeated water-enabled room-temperature self-healing capacity with a high healing efficiency of 92.2%. Moreover, the polyureas can also be recycled or remolded under mild conditions by the hot-pressing or dissolution/casting process. The synthesized polyureas also show great potential in damping applications with a loss factor larger than 0.3 over the temperature range from 12 to 75 °C. It is believed that polyureas with super-high and well-tunable mechanical properties and high-efficient room-temperature self-healing ability have great potential to substitute traditional irreparable polymers in diverse practical applications.