Single-Step Grafting of a Thermoresponsive RAFT Polymer from Nanocellulose by Radical Decarboxylation

The grafting of polymers in a single step from TEMPO-oxidized nanocellulose (TOCN) via controlled radical polymerization is reported here for the first time. Reversible addition-fragmentation chain-transfer (RAFT) polymerization is achieved through silver-mediated radical decarboxylation on the surface of the cellulose fibers in the presence of a RAFT precursor in a primarily water-based mixture. Electrochemical studies were performed to tune the redox properties of the silver-ligand complex and achieve an extremely high monomer conversion and grafting efficiency. This led to the grafting of a thermoresponsive polymer with low dispersity and controlled molecular weight, which in turn allowed for the tuning of the thermal properties of the nanocellulose-polymer composite. SANS analysis of the materials provides a clear model to explain the effect of the polymer molecular weight on the thermoresponsive and gelation properties of PNIPAM-g-CNF, where a lower polymer molecular weight results in an ordered assembly of bundled fibers above the critical temperature.