Super-tough and rapidly self-recoverable multi-bond network hydrogels facilitated by 2-ureido-4[1H]-pyrimidone dimers

Multi-bond network (MBN) hydrogels contain hierarchical dynamic bonds with different bond association energy as energy dissipation units, enabling super-tough mechanical properties. In this work, we copolymerize a protonated 2-ureido-4[1H]-pyrimidone (UPy)-contained monomer with acrylic acid in HCl solution. After removing excess HCl, UPy motifs are deprotonated and from dimers, thus generating an UPy-contained MBN hydrogel. The obtained MBN hydrogels (75 wt% water content) exhibit super-tough mechanical properties (0.39 MPa to 2.51 MPa tensile strength), with tremendous amount of energy (1.68 MJ/m3 to 11.1 MJ/m3) dissipated by the dissociation of UPy dimers. The introduction of ionic bonds can further improve the mechanical properties. Moreover, owing to their dynamic nature, both UPy dimers and ionic bonds can re-associate after being dissociated, resulting in excellent self-recovery ability (around 90% recovery efficiency within only 1 h). The excellent self-recovery ability mainly originates from the re-association of UPy dimers based on the high dimerization constant of UPy motifs