Multistimuli-Responsive Antiprotein-Fouling Benzimidazolium Poly(zwitterionic ionic liquid)s with Tunable UCST for Dispersion of Carbon Nanotubes and Cross-Linked Hydrogels

Poly(zwitterionic ionic liquid) (PZIL) refers to a polymeric architecture with an ionic liquid moiety also capable of being zwitterionic in each repeating unit, which has not been explored so far in the literature. Owing to their versatile structures and interesting properties, nowadays they are attracting much interest in industrial and biomedical applications. Thus, this work demonstrates the design and synthesis of two styryl-based homopolymers containing repeating units comprising carboxyalkylbenzimidazolium bromide functionalities, employing RAFT polymerization in water. These PZILs exist as poly(zwitterion)s and form pH-tunable aggregated nanostructures, appearing as turbid suspensions in water at pH 4.1. The transformation of a turbid suspension to a transparent solution on heating and vice versa on cooling suggests a clear upper critical solution temperature (UCST)-type phase behavior of the PZILs in water, and the derived cloud points (T_cps) are found to be tunable with pH and PZIL concentrations, as well. Below the isoelectric point (pI), at any pH, the PZILs also exhibit a reversible UCST-type transition from one-phase to two-phase in the presence of different Hofmeister anions in water, with T_cps tunable with anion and PZIL concentrations. In this pH range, these PZILs behave as cationic poly(ionic liquid)s and are found to be very effective in dispersing multiwalled carbon nanotubes (MWCNTs) in water. The aqueous dispersions of MWCNT-PZIL composites are responsive toward different stimuli such as temperature, pH, and anions. Both PZILs exhibit antiprotein-fouling activities by preventing nonspecific aggregation of bovine serum albumin in water at pH 7 (beyond the pI). The zwitterionic hydrogel derived from zwitterionic ionic liquid monomers shows multistimuli-responsive behavior and exhibits excellent water-uptake ability in water and aqueous NaCl solutions, with % equilibrium swelling of ∼123 and ∼320, respectively.