Tough, Photoluminescent, Self-Healing Waterborne Polyurethane Elastomers Resulting from Synergistic Action of Multiple Dynamic Bonds

Polymers that integrate multiple functions into one system broaden the application range of materials, but it remains a great challenge to obtain polymer materials with simultaneously high strength, high toughness, and high self-healing rate. In this work, we prepared waterborne polyurethane (WPU) elastomers using Schiff bases containing disulfide and acylhydrazone bonds (PD) as chain extenders. Acylhydrazone forming a hydrogen bond not only acts as a physical cross-linking point, which promotes the microphase separation of polyurethane to increase the thermal stability, tensile strength, and toughness of the elastomer, but also serves as a "clip" to integrate various dynamic bonds together to synergistically reduce the activation energy of the polymer chain movement and endow the molecular chain with faster fluidity. Therefore, WPU-PD exhibits excellent mechanical properties at room temperature, such as a tensile strength and a fracture energy of 25.91 MPa and 121.66 kJ m^-2, respectively, and a high self-healing efficiency of 93.7% in a short time under moderate heating conditions. In addition, the photoluminescence property of WPU-PD enables us to track its self-healing process by monitoring change of the fluorescence intensity at the cracks, which helps to avoid the accumulation of cracks and improve the reliability of the elastomer. This self-healing polyurethane has a great potential application value in optical anticounterfeiting, flexible electronics devices, functional automobile protective films, and so on.

Tough, Self-Healing Hydrogels Capable of Ultrafast Shape Changing

Achieving multifunctional shape-changing hydrogels with synergistic and engineered material properties is highly desirable for their expanding applications, yet remains an ongoing challenge. The synergistic design of multiple dynamic chemistries enables new directions for the development of such materials. Herein, a molecular design strategy is proposed based on a hydrogel combining acid-ether hydrogen bonding and imine bonds. This approach utilizes simple and scalable chemistries to produce a doubly dynamic hydrogel network, which features high water uptake, high strength and toughness, excellent fatigue resistance, fast and efficient self-healing, and superfast, programmable shape changing. Furthermore, deformed shapes can be memorized due to the large thermal hysteresis. This new type of shape-changing hydrogel is expected to be a key component in future biomedical, tissue, and soft robotic device applications.