Thermoresponsive Gels Based on Cross-Linked Polymer-Grafted Cellulose Nanocrystals

Stimuli-responsive nanocomposite hydrogels have garnered significant interest as alternatives to conventional hydrogels, enabling the engineering of stimuli-responsive behavior and network connectivity through composition and architecture. Here, we report thermoresponsive, "one-component" nanocomposite hydrogels composed of copolymer-grafted cellulose nanocrystals (CNCs). Thermoresponsive polyacrylamides or poly(oligoethylene glycol acrylate) copolymers bearing terminal olefin side chains were grafted from the CNC surfaces using atom-transfer radical polymerization, yielding densely grafted hairy nanoparticles (HNPs). The HNPs were cross-linked via UV-mediated thiol-ene click chemistry to form hydrogels. The resulting networks exhibit reversible LCST-type swelling and deswelling, with thermoresponsive and mechanical behavior governed by graft chemistry, architecture, and solvation. Comparative experiments using CNC-free and physically mixed hydrogels show that, at the low CNC loadings employed here, mechanical properties are shaped predominantly by chain entanglement and solvation, rather than by reinforcement from the nanocrystals.