Preparation and Morphology Control of Poly(ionic liquid) Particles

Poly(ionic liquid)s (PILs) are prepared by the polymerization of ionic liquid (IL) monomers that have polymerizable groups on their cationic or anionic component. PILs also share many of the characteristic properties of ILs and can be used in various materials such as CO2 sorbents, polymer electrolytes, dispersants, and microwave-absorbing materials. In this feature article, we survey our research, focusing on the preparation of PILs in the particulate state (PIL particles) and on the morphological control of the PIL particles, including (1) the preparation of PIL particles by dispersion polymerization and emulsion polymerization, (2) control of the morphology of composite particles consisting of a PIL and poly(methyl methacrylate) (PMMA), (3) the preparation of hollow particles with a PIL shell, and (4) the preparation of PIL particles containing reduced graphene oxide (rGO). The size of the obtained PIL particles could be controlled through a modification of the synthesis conditions and the mode of polymerization (i.e., dispersion polymerization or emulsion polymerization). The obtained PIL particles maintained the characteristic properties of the corresponding ILs; moreover, the solubility of the PIL particles could be easily modified by changing their counteranion. Using seeded polymerization, we prepared PMMA/PIL composite polymer particles and subsequently demonstrated that their morphology can be manipulated to yield a core–shell or Janus structure. Hollow particles consisting of a PIL shell were also prepared, and modification of the polarity and penetration behavior of the shell through anion exchange was demonstrated.