Thermally Responsive Hyperbranched Poly(ionic liquid)s: Assembly and Phase Transformations

A library of linear and branched amphiphilic poly­(ionic liquid)­s based on hydrophobic cores and peripheral thermally sensitive shells was synthesized and studied with regard to their ability to form stimuli-responsive, organized assemblies in aqueous media. The thermally responsive derivatives of poly­(ionic liquid)­s were synthesized by neutralizing 32 terminal carboxyl groups of functionalized polyester cores by amine-terminated poly­(<i>N</i>-isopropyl­acrylamide)­s (PNIPAM) (50% and 100%). We observed that these hyperbranched poly­(ionic liquid)­s possessed a narrow low critical solution transition (LCST) window with LCST for hyperbranched compounds being consistently lower than that for linear PNIPAM containing counterparts. We found that the poly­(ionic liquid)­s form spherical micellar assemblies with diverse morphologies, such as micelles and their aggregates, depending on the terminal compositions with reduced sizes for hyperbranched poly­(ionic liquid)­s. Increasing temperature above LCST promoted formation of network-like aggregates, large vesicles, and spherical micelles. Moreover, all PNIPAM-terminated compounds exhibited distinct unimolecular prolate nanodomain morphology in contrast to common spherical domains of initial cores. We proposed a multilength scale organized morphology to describe the thermoresponsive poly­(ionic liquid)­s micellar assemblies and discussed their morphological transformations during phase transitions associated with changes in hydrophobic–hydrophilic balance of poly­(ionic liquid)­s with distinct hydrophobic cores and variable peripheral shells

Assembly of Amphiphilic Hyperbranched Polymeric Ionic Liquids in Aqueous Media at Different pH and Ionic Strength

We demonstrated the assembly of amphiphilic hyperbranched protic ionic liquids (HBP-ILs) based on aliphatic hyperbranched polyester (HBP) in aqueous media in a wide range of pH and ionic conditions. The series of new branched polyionic liquids with different terminal groups, HBP-ILs, was synthesized by neutralization of carboxylic and sulfonic terminal acid groups of hypebranched core with <i>N</i>-methyl­imidazole (Im) and 1,2,4-1<i>H</i>-triazole (Tr). HBP-IL compounds with triazole and imidazole counterions form 12–16 nm core–corona micelles at pH 11.6. We found that the introduction of long hydrophobic terminal groups such as <i>n</i>-octadecylurethane tails to initial hydrophobic HBP core has larger effect on the size of micellar assemblies than the introduction of ionic terminals groups. Furthermore, tuning the hydrophilic/hydrophobic balance of HBP-ILs can be achieved by changing the degree of ionization of terminal groups and counterions by reducing pH from 11.6 to 5.2 or ionic strength to 0.1 M. These changes caused the formation of much larger micellar aggregates with the size of 150–200 nm due to reduced ionization of carboxylic groups. At the same time, for sulfonate-containing HBP-ILs the micelle size increased modestly (to 25–40 nm) because of the higher degree of ionization of sulfonate terminal groups. The diverse aggregation behavior of these branched polymeric ionic liquids enables control over their micellar morphologies in solution and bulk states