High Toughness Polyurethane toward Artificial Muscles, Tuned by Mixing Dynamic Hard Domains

Developing multiphase polyurethanes (PUs) with loosely packed domains containing dynamic linkages and appropriately crystallized soft phases composed of polycaprolactone diol (PCL) segments is effective for the trade-off between toughness and self-healing. Here, we proposed a new strategy based on mixed dynamic hard segments to achieve the goal and improve self-healing behavior and mechanical performance. The designed polyurethanes comprise a microphase-separated structure with polycaprolactone diol as soft segments, which are facilitated to store entropy energy under strain. The aromatic disulfides together with aliphatic chain extenders were selected as hard segments to adjust the hierarchical structures, including microphase separation and crystallinity. The reversible hydrogen bonds and disulfide bonds distributed in the polymer network contribute to enhancing stretchability and self-healing performance. In this research, the robust polyurethanes with uniform microphase separation structures and insufficient crystallinity were designed by mixing a dynamic hard domain, which exhibits the potential application in the field of flexible conductors and synthetic muscles; the recovery efficiency at 90 °C is 93.8% and the ultimate stress/strain are 18.7 ± 0.2 MPa/2253 ± 149.2%. This work confirmed that the feasibility of synthetic PUs by changing the mole ratio of dual chain extenders simply, which is also expected to inspire the related fields of engineering, may require polymers with excellent self-healing efficiency and extraordinary robustness simultaneously.