Polymers in Ionic Liquids: Dawn of Neoteric Solvents and Innovative Materials

Abstract

Abstract In this paper, we review recent advances in the use of polymers in ionic liquids (ILs) from the view point of the “dawn of neoteric solvents and innovative materials.” The first part of this paper presents a brief review of the solubility parameters of ILs, which are expected to serve as a qualitative guide for predicting polymer solubility in ILs; however, this concept cannot be used to rationalize a number of cases in which strong Coulombic interactions dominate the solubility parameters of the ILs. Thus, solubility of 24 different common synthetic polymers is experimentally demonstrated under dilute conditions (3 wt %) in four different common ILs. It is found that the Lewis basicities of the counter anions in the ILs play an important role in determining the solubility of the polymers. ILs can also be used as good solvents for low-solubility biopolymers and as good dispersion media of carbon nanotubes, which contributes to the fields of biorefinery processes and advanced materials. Certain combinations of polymers in ILs undergo phase separations as the temperature of the solutions is varied. The solubility of a nonionic polymer in water generally decreases with increasing temperature, and certain combinations exhibit lower critical solution temperature (LCST) phase separation, whereas the solubility of a polymer in an organic solvent generally increases with increasing temperature and in some cases upper critical solution temperature (UCST) phase separation is observed. Interestingly, both LCST and UCST phase separations are observed for certain polymers in ILs. After presenting possible explanations of the solubility of polymers in ILs, recent developments in the field of thermosensitive polymers in ILs are discussed from the perspective of materials science, where such phase separations are exploited to trigger abrupt changes in polymer properties. The final part of this review describes the thermosensitive self-assembly of block copolymers in ILs. Similar to conventional molecular solvents, block copolymers in ILs exhibit variable self-assemblies in solution and in the bulk.