Oligomeric and Polymeric Ionic Liquids: Engineering Architecture and Morphology

Abstract

The series of amphiphilic anionic protic hyperbranched oligomeric and polymeric ionic liquids (HBP-OILs) with different terminal groups and an adjustable hydrophilic-hydrophobic balance which are sensitive to pH and ionic strength changes was obtained by neutralizing the carboxylic and sulfonic terminal acid groups of aliphatic hyperbranched core with N-methylimidazole (Im) and 1,2,4-1H-triazole (Tr). The introduction of long hydrophobic aliphatic tails to starting hydrophobic hyperbranched core influences more significantly on the size of micellar assemblies than the introduction of ionic groups does. The assembly of these compounds into core-corona micelles in aqueous media in a wide range of pH and ionic conditions was established. Regulation of HBP-OILs amphiphilicity can be realized by varying the extent of ionization of terminal groups by changing pH or ionic strength. The synthesis of the thermally responsive protic anionic hyperbranched poly(ionic liquid)s (HBP-PILs) was based on partial (50%) and full neutralization of carboxyl groups of aliphatic polyester core by monoamine-terminated poly(N-isopropylacrylamide)s (PNIPAM). Its linear oligoester analog was synthesized in a similar way. These compounds possess low critical solution temperature (LCST) behavior with a narrow LCST window and amorphous state in condensed matter. We found that HBP-PILs form smaller in comparison with linear analogues spherical micelles and their aggregates of different morphologies depending on the content of PNIPAM. When temperature is higher than LCST the formation of spherical micelles, network-like aggregates and large vesicles is observed. In opposite to initial cores prone to form spherical domains the thermally responsive compounds are able to self-assemble into elongated unimolecular nanodomain. The complex self-assembling behavior and diverse morphology of resultant supramolecular assamblies of HBP-OILs and HBP-PILs might lead to unique ionic transport properties as a key point for creation of nanomaterials with tunable ion transport characteristics.