Supramolecular hydrogels based on hydrogen bonding: Impact of ionic comonomers

The polymerization of N-acryloyl glycineamide (NAGA) in water results in the creation of robust supramolecular hydrogels, exhibiting a network structure through inter-chain crosslinking formed by hydrogen bonds between NAGA units. The stability of these hydrogen bonds in water is based on the aggregation of NAGA units into microdomains or clusters, thereby effectively shielding the hydrogen bonds from the surrounding aqueous medium. Beyond the inherent water absorption characteristics of these hydrogels, the unique ability for the dissociation and re-association of their physical crosslinks imparts features such as reversible swelling and shrinking as well as self-healing and remolding capabilities. In this study, we synthesize a series of supramolecular hydrogels through copolymerization of NAGA and ionic sodium acrylate comonomers for a dual purpose: first, to regulate water absorption levels, and second, to introduce a salt partitioning effect into the hydrogels during their swelling in salt solution. Our findings indicate that the properties of these hydrogels are intricately influenced by the volume fraction of the solid network, the concentration of ionic units, and temperature. Notably, supramolecular samples with ionic units exhibit a 16% salt rejection in a single cycle of salt partitioning during their swelling in a 1 g·L⁻¹ sodium chloride solution.