Nanocrystalline cellulose grafted random copolymers of N-isopropylacrylamide and acrylic acid synthesized by RAFT polymerization: effect of different acrylic acid contents on LCST behavior

Abstract

Free and nanocrystalline cellulose (NCC) attached homopolymers of N-isopropylacrylamide and acrylic acid (AA) as temperature- and pH-sensitive materials and also their dual-sensitive copolymers with different contents of AA were synthesized by RAFT polymerization. NCCs were obtained from microcrystalline cellulose by an acid hydrolysis process. Then, the surface of NCC was chemically modified by 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) as chain transfer agent. In situ synthesis of polymers in the presence of 1 wt% of NCC was carried out at 70 °C via the R-group approach. Successful attachment of DDMAT and polymer chains on the backbone of NCC was studied by X-ray photoelectron (XPS), Fourier transform infrared, proton nuclear magnetic resonance, and Raman spectroscopies. Elemental analysis, thermogravimetric analysis, and XPS were also used to evaluate the grafting of DDMAT and polymers. Thermal behaviour of the NCC-attached polymers was also studied by differential scanning calorimetry. The lower critical solution temperatures (LCST) of polymers as phase separation temperatures were measured by the cloud point method using dynamic light scattering. Addition of NCC, AA content, and pH at higher pH values results in increase of LCST. At low pH values, increase of LCST occurred by an increase of NCC and also pH value. The morphology and crystalline structure of polymer-grafted NCCs were examined by transmission electron microscopy and X-ray diffraction respectively.