Multistimuli-Responsive\nAntiprotein-Fouling Benzimidazolium\nPoly(zwitterionic ionic liquid)s with Tunable UCST for Dispersion\nof Carbon Nanotubes and Cross-Linked Hydrogels

Poly(zwitterionic ionic liquid) (PZIL) refers to a polymeric\narchitecture\nwith an ionic liquid moiety also capable of being zwitterionic in\neach repeating unit, which has not been explored so far in the literature.\nOwing to their versatile structures and interesting properties, nowadays\nthey are attracting much interest in industrial and biomedical applications.\nThus, this work demonstrates the design and synthesis of two styryl-based\nhomopolymers containing repeating units comprising carboxyalkylbenzimidazolium\nbromide functionalities, employing RAFT polymerization in water. These\nPZILs exist as poly(zwitterion)s and form pH-tunable aggregated nanostructures,\nappearing as turbid suspensions in water at pH 4.1. The transformation\nof a turbid suspension to a transparent solution on heating and vice\nversa on cooling suggests a clear upper critical solution temperature\n(UCST)-type phase behavior of the PZILs in water, and the derived\ncloud points (<i>T</i><sub>cp</sub>s) are found to be tunable\nwith pH and PZIL concentrations, as well. Below the isoelectric point\n(pI), at any pH, the PZILs also exhibit a reversible UCST-type transition\nfrom one-phase to two-phase in the presence of different Hofmeister\nanions in water, with <i>T</i><sub>cp</sub>s tunable with\nanion and PZIL concentrations. In this pH range, these PZILs behave\nas cationic poly(ionic liquid)s and are found to be very effective\nin dispersing multiwalled carbon nanotubes (MWCNTs) in water. The\naqueous dispersions of MWCNT-PZIL composites are responsive toward\ndifferent stimuli such as temperature, pH, and anions. Both PZILs\nexhibit antiprotein-fouling activities by preventing nonspecific aggregation\nof bovine serum albumin in water at pH 7 (beyond the pI). The zwitterionic\nhydrogel derived from zwitterionic ionic liquid monomers shows multistimuli-responsive\nbehavior and exhibits excellent water-uptake ability in water and\naqueous NaCl solutions, with % equilibrium swelling of ∼123\nand ∼320, respectively.