Alkaline monomer for mechanical enhanced and self-healing hydrogels based on dynamic borate ester bonds

Abstract Hydrogels based on borate ester bonds enable fast, multiple repairs with their dynamically reversible covalent bonds at room temperature. However, these materials could only be healed with alkaline additives to control the pH values right now which results in the limited healing and mechanical performance. In this research, dimethylaminoethyl methacrylate (DMAEMA) is employed as an alkaline monomer and randomly copolymerize with N-methylol acrylamide (NAM) to form a mechanical enhanced and self-healing hydrogel at room temperature. The hydrogels exhibit a dramatic fracture stress of as much as 368 kPa and fracture strain of 542%. Besides, the anti-fatigue properties of the hydrogels (slight residual deformation after stretch-release cycles at strain of 200%) have been proved as well. Moreover, the as-prepared hydrogels successfully achieve 91% of the fracture stress recovery within 1 h at room temperature and 100% repair of the fracture strain after 24 h. At last, the healing mechanism has been discussed. This work provides a novel system for the borate ester bonds-based self-healing materials with improved healing and mechanical performance by the simple and efficient method which would expand the range of applications in smart materials.