Strong and Tough Poly(2-Isopropenyl-2-Oxazoline) Hydrogels with Terpyridine as Dual Orthogonal Covalent and...

Developing simple and efficient methods to mechanically reinforce single-network hydrogels for practical applications remains an important challenge. This study presents a strategy for preparing poly(2-isopropenyl-2-oxazoline) (PiPOx) hydrogels using a dicarboxylic acid functionalized terpyridine (TPy) dual orthogonal crosslinker that acts as both a permanent covalent crosslinker and a dynamic non-covalent crosslinker upon metal complexation. In this dual orthogonal crosslinking approach, PiPOx is first crosslinked with the dicarboxylic acid functionalized TPy in DMSO to form a stable covalent network, followed by solvent exchange to water, drying and the introduction of reversible coordination bonds through swelling in an aqueous zinc(II) ion solution. This orthogonal dual crosslinking strategy results in high compressive strength (26.6 MPa) and tough (5.28 MJ·m^-3) single-network hydrogels. This is attributed to the fact that the hydrogel combines thermodynamically stable primary permanent crosslinks and dynamic secondary reversible crosslinks in the same dual crosslinker, leading to polymer network contraction, thereby providing a novel and simple approach for the preparation of strong and tough dual orthogonal crosslinked single network hydrogels.