A facile method to fabricate hydrogels from DMSO polymer gels via solvent exchange

A mixture of the bipyridine, phenyl and/or cyclohexanediamine-based building blocks 1, 2, and/or 3, having hydrazide, aldehyde or amine moieties, respectively, formed DMSO polymer gels by the hydrazone reaction under acidic conditions. These DMSO gels were transformed into hydrogels without a change in shape by solvent exchange. Interestingly, G′ and G′′ values of the hydrogels increased 9–12-fold due to the formation of a three-dimensional network structure by intermolecular hydrogen bonding interactions. In sweep measurements, the γ values of the hydrogels prepared without NaCl were enhanced from 18.5% to 46–55%, which was attributed to the three-dimensional network with additional intermolecular hydrogen-bonding interactions. Furthermore, a gel-to-quasi-liquid transition was completely reversible, where the G′ and G′′ values were recovered rapidly within 60 s. This reversibility was a thixotropic response.