Specific solubility behavior of quaternary ammonium-based poly(ionic liquid) particles by changing counter anion

The solubility behavior of poly(ionic liquid) (PIL) particles, which were prepared by dispersion polymerization of ([2-(methacryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)amide), [MTMA][TFSA], was observed in detail. The solubility of PILs was varied by changing the counter anion. A PIL with [TFSA] anion does not dissolve in polar solvents such as ethanol; however, a PIL with Br anions does dissolve in ethanol. Upon the addition of LiBr to ethanol solution at high concentrations (>2.5 wt.%), the PIL particles dissolved from their outer surface and the counter anions [TFSA] were replaced with Br anions on the particle surfaces. On the other hand, in the case of the ethanol solutions at low LiBr concentrations (<2.5 wt.%), a specific solubility behavior was observed: domains inside the PIL particles were generated before their dissolution, most likely due to osmotic pressure. Moreover, PIL particles having hollow structures were prepared using this specific solubility behavior.

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► The solubility behavior of poly(ionic liquid) (PIL) particles was observed by changing the counter anion.
► At low salt concentrations (<2.5 wt.%), domains inside the PIL particles were generated before their dissolution.
► This solubility behavior was caused by differences in osmotic pressure between the PIL particles and salt solutions.
► PIL particles having hollow structure were prepared utilizing osmotic phenomena.