High-Strength, Thermally Activated Shape Memory Hydrogels Based on Hydrogen Bonding between MAAc and NVP

Herein, a facile and novel method is reported for fabricating tough hydrogen-bonded hydrogels through the photoinitiated copolymerization of methacrylic acid (MAAc), N-vinyl pyrrolidone (NVP), and poly(ethylene glycol) methyl ether methacrylate (PEGMA) in an aqueous solution. PEGMA acts as a temporary hydrogen-bonding shielding monomer to prevent the phase separation of MAAc and NVP in an aqueous solution. During polymerization, the shielding effect of the PEGMA weakens, and the stable MAAc-NVP hydrogen-bonding domains, strengthened by the hydrophobic -methyl moieties of MAAc and the five-membered N-heterocycle of NVP, form in situ, endowing the hydrogels with high tensile strength (up to 3.9 MPa), extensibility (up to 600%), and toughness (up to 9 MJ m(-3)). In particular, due to the dynamic nature and temperature sensitivity of hydrogen bonds, the hydrogels also exhibit a fast 100% self-recovery ability and thermally activated shape memory properties. Based purely on the single-fold hydrogen-bonding interactions, a tough supramolecular hydrogel with fascinating properties is successfully developed. These findings may be essential to either the design or practical application of the purely physical hydrogels with high mechanical strength and thermally activated shape memory properties.