A Facile Strategy to Construct Stretchable and Thermoreversible Double Network Hydrogels with Low Hysteresis and High Toughness Based on Entanglement and Hydrogen Bond Networks.

High toughness and low hysteresis are of great significance for stretchable hydrogels to strengthen their reliability and practicability for cycle-loaded applications. Whereas, it is still challenging to simultaneously gain mutually repulsive properties due to the existence of dissipation structure. Here, stretchable and recoverable double network (DN) hydrogels comprising highly entangled network structure and temperature-induced dense hydrogen bond (HB)-associated network structure are synthesized, in which slidable entanglements and dense HBs act as the effective crosslinking in first and second networks, respectively. Moveable entanglements and stable HB structures endow hydrogels with high stretchability (999%), high tensile strength (0.82 MPa) and high fracture toughness (4.51 MJ·m-3) through stress transmission along long chains and HB clusters energy dissipation. Moreover, the imposed energy on hydrogels can saved in oriented polymer chains by disentanglement as an entropy loss, thus ensuring the low hysteresis (6.2% at 100% tensile strain) of hydrogels. In addition, deformed hydrogel can be well remodeled and recovered (stress recovery of 95.5%) by temperature-triggered sol-gel transition of HB network. By means of entanglement and hydrogen bond strategies, stretchable DN hydrogels not only equilibrate the conflict of low hysteresis and high toughness, but also provides a new perspective to design high-property hydrogels for cycle-loaded applications.