Ultra-tough and stress-free two-way shape memory polyurethane induced by polymer segment "spring"

Two-way shape memory polymers (2WSMP) are highly desired for artificial muscles, soft actuators and sensors, while the stress-free 2WSMP greatly expands the practical potential of shape memory polymers. However, traditional 2WSMP cannot show high strength or good mechanical properties, which limited its practical application. It is important to create a new reversible polymer system in order to obtain more intricate movements, precise control and great mechanical properties. Herein, a two-way shape memory polyurethane was created using a new molecular strategy, which shows great properties, i.e., 2342% super stretch strain, 591 MPa true tensile strength, 708.04 J/kg of energy density, and 667.96 W/kg of power density. In addition, the 2WSMP could achieve a maximum 24.53% reversible transformation under 1 MPa stress, and 13.7% two-way shape change without external stress, respectively. In this polyurethane, the great mechanical properties and stress-free two-way shape memory effect are caused by the elastic polybutadiene (PB) segments, which acts as a "molecular spring." Furthermore, this 2WSMP could simulate reversible muscle-like motion, and be employed in ligaments. Consequently, this polyurethane offers a fresh design concept for stress-free two-way performance memory polymers and has a wide range of potential applications in the field of artificial muscles, soft actuators and ligaments.