Grafting light-, temperature, and CO2-responsive copolymers from cellulose nanocrystals by atom transfer radical polymerization for adsorption of nitrate ions

Cellulose nanocrystal (CNC)-grafted and free block copolymers of 2-dimethylaminoethyl methacrylate (DMAEMA) and coumarin were successfully synthesized via atom transfer radical polymerization. Copolymers were designed in different chain lengths and block ratios and used in ion adsorption from aqueous solutions. The copolymers are responsive to CO2, pH, temperature, and also light. By inserting CO2 to the system, the protonated amine groups of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) caused nitrate ion adsorption by electrostatic forces. The LCST of PDMAEMA blocks has been increased by inserting of CO2, which results in their higher solubility and therefore higher possibility of ion-adsorption. Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance, and thermogravimetric analysis were used for structural and thermal characterization of the synthesized free and CNC-grafted copolymers. UV-Vis spectroscopy was used for study of nitrate ion-adsorption from the aqueous solution. Responsivity of the free copolymers to temperature, CO2, and light was evaluated by dynamic light scattering. By increasing the PDMAEMA length, ion-adsorption capacity has been increased. CO2 helps for ion-adsorption by protonation of the amine groups and increasing the LCST of PDMAEMA block. However, the temperature and light stimuli can be used in regeneration process by the squeezing and crosslinking processes.