High Water-Content Thermoresponsive Hydrogels via Electrostatic Macrocrosslinking of Cellulose Nanofibrils

Atom transfer radical polymerization (ATRP) has been utilized to synthesize tri- and star-block copolymers of poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) and quaternized poly(2-(dimethylamino) ethyl methacrylate) (qPDMAEMA). The block copolymers, all with a minimum of two cationically charged blocks, were sequentially used for electrostatic macrocrosslinking of a dilute dispersion of anionic TEMPO-oxidized cellulose nanofibrils (CNF, 0.3 wt%), forming free-standing hydrogels. The cationic block copolymers adsorbed irreversibly to the CNF, enabling the formation of ionically crosslinked hydrogels, with a storage modulus of up to 2.9 kPa. The ability of the block copolymers to adsorb CNF was confirmed by quartz crystal microbalance with dissipation monitoring (QCM-D) and infrared spectroscopy (FT-IR), and the thermoresponsive properties of the hydrogels were investigated by rheological stress and frequency sweep, and gravimetric measurements. This method was shown to be promising for the facile production of thermoresponsive hydrogels based on CNF. (C) 2016 Wiley Periodicals, Inc.