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

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.

Can ionic liquid additives be used to extend the scope of poly(styrene)-block-poly(methyl methacrylate) for directed self-assembly?

“…This was attributed to emim NTf 2 being a good solvent for PMMA chains and a poor solvent for the PS. 53 Hence, upon forming a block copolymer/IL blend, the emim NTf 2 preferentially interacts with the PMMA chains and screens the PMMA/PS interactions. This has the effect of decreasing the compatibility of the PMMA and PS chains, which increases the effective χ PS-PMMA parameter.…”

“…Upon incorporation of 10% emim NTf 2 , only a single T g at 106°C could be observed, and this decreased slightly to 104°C for IL concentrations of 25% and 40%. Based on the solubility of PMMA in emim NTf 2 and insolubility of PS in the IL, 53 these results were attributed to the PMMA block being plasticized, and the PS block remaining essentially unaffected. In support of this, Susan et al 55 have shown that blends of PMMA homopolymer and emim NTf 2 have T g values below room temperature for similar degrees of incorporation.…”

Polymers with upper critical solution temperature behavior in alcohol/water solvent mixtures

“…[18] As an alternative, UCST polymers in organic solvents or in water-organic binary solvent mixtures have shown attractive properties. [42][43][44][45][46][47] Ethanol/water solvent mixtures are environmentally friendly solvents that exhibit interesting abnormal properties due to the presence of hydration shells around the ethanol molecules. [48][49][50] For instance, the presence of such hydration shells has been reported to result in solubility maxima for drug molecules in ethanol/water mixtures with certain ratios.…”

Design and Materialization of Ionic Liquids Based on an Understanding of Their Fundamental Properties

“…In this context, we have also conducted fundamental studies on the compatibility and phase behavior of polymers in ILs. 32 Later, we extended out studies of Electrochemistry, 84 (9), 642-653 (2016) polymer electrolytes further to include the combination of taskspecific ILs such as protic ionic liquids (vide infra) and Li + -solvate ionic liquids. 33 The most striking differences of polymer electrolytes of ILs ("ion gels") from polyether electrolytes are the plasticizing effect of the ILs on the polymers and the decoupling of ion transport from the segmental motion of the polymer, enabling fast ion transport that is close to that of ILs themselves.…”