Thermoresponsive Copolymer Poly(N-Vinylcaprolactam) Grafted Cellulose Nanocrystals: Synthesis, Structure, and Properties

A novel thermoresponsive copolymer poly(N-vinylcaprolactam) grafted cellulose nanocrystals (PVCL-g-CNCs) was synthesized using surface-initiated atom transfer radical polymerization, and its temperature responsive behavior was studied in this work. The chemical structure characterization by Fourier transform infrared spectroscopy, solid-state CP/MAS 13C NMR spectroscopy, and X-ray photoelectron spectroscopy confirmed the presence of covalently grafting PVCL chains on the CNC surface. The crystalline structure and nanorod-shaped morphology of CNCs were well preserved after polymerization. Transmission electron microscope results indicated that the surface of CNCs was covered with grafted PVCL brushes. The viscoelastic properties of PVCL-g-CNC aqueous suspensions (1.0 wt %) by dynamic rheology measurements confirmed the thermally induced phase transition behavior. The work presented herein paves the way to design CNC-based advanced functional materials benefiting both from the intrinsic characteristics of CNCs and the new properties imparted by the temperature sensitive grafted polymer chains.