(415c) Behavior of Homopolymers and Block Copolymers In Ionic Liquids: Glass Transitions, Viscoelasticity and Critical Micelle Concentrations

Ionic liquids (ILs) are a relatively new class of solvents composed exclusively of ions. Specific advantages that they offer over traditional solvents include negligible volatility, tailorable solubilization, and high thermal and chemical stability, allowing them to be used as a liquid phase over very large temperatures ranges. Initially, polymer scientists took advantage of their solvating properties for use as polymerization media, and more recently, for their potential to create composite materials for diverse applications such as dielectric materials for thin-film transistors and solid-state polymer electrolytes for electrochemical devices. In terms of more dilute systems, homopolymers in ILs have been proposed as designer solvents, while block copolymers in ionic liquids have been studied for their micelle- and vesicle-forming capabilities with potential applications as vessels for transport and extraction within biphasic systems. With this increasing focus on their materials applications, it is important to gain a complete understanding of the basic phase behavior of polymers and IL solvent systems.

First, we examine the behavior of a model polymer-IL system over the range of compositions from dilute polymer to pure polymer. Specifically, we study the glass transition and viscoelastic properties of poly(methyl methacrylate) in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide over the temperature range from -180 to 230 ºC. Secondly, we discuss the critical micelle concentrations (CMCs) of block copolymers in IL systems as functions of block copolymer and IL composition. These results are related to the balance of solvophobic and solvophilic interactions induced by the different copolymer and cation/anion combinations. Overall CMC values were found to be over four orders of magnitude greater than those measured in aqueous systems, in accord with the lower solvophobicity of ILs. Finally, we explore the effect of temperature on these systems at concentrations near the CMC.