Synthesis of dual-sensitive nanocrystalline cellulose-grafted block copolymers of N-isopropylacrylamide and acrylic acid by reversible addition-fragmentation chain transfer polymerization

A core-shell structure of crosslinked poly(2-hydroxyethylmethacrylate) as corona and nanocrystalline cellulose (NCC) as core was synthesized by distillation precipitation polymerization. Then, it was reacted with a chain transfer agent of S-(thiobenzoylthioglycolic) acid to obtain NCC-RA. Homopolymers of N-isopropylacrylamide (NIPAAm) and acrylic acid (AA) as temperature-and pH-sensitive materials, as well as their dual-sensitive block copolymers, were grafted at the surface of NCC-RA by an in situ reversible addition-fragmentation chain transfer polymerization method via R-group approach. Grafting of chain transfer agent and polymer chains at the surface of nanocrystals was studied by X-ray photoelectron (XPS), Fourier transform infrared, and Raman spectroscopies. Thermogravimetric analysis and XPS were also used to study the graft content of chain transfer agent and polymers. Sensitivity of the polymer-grafted NCCs to temperature and pH were studied by UV-visible spectroscopy. By the addition of poly(N-isopropylacrylamide) block to the poly(acrylic acid)-grafted nanocrystals, phase transition is observed at 32 degrees C. When the poly(acrylic acid) block is the outer layer, phase transition is observed at higher temperatures and pH-responsivity is observed at pH 7.0-10.0. Finally, morphology of the neat and polymer-grafted NCCs was studied by scanning and transmission electron microscopies.