How tunable are the coil dimensions of polymers in ionic liquids?

Ionic liquids are emerging as interesting solvents for polymers. The selection of an appropriate cation or anion can alter the properties of ILs, thereby establishing a platform for a wide range of solvation properties. The solvation behavior of polymers in ILs has been investigated through miscibility and phase behavior studies; however, chain dimensions of polymers in ILs remain relatively unexplored. We use small-angle neutron scattering (SANS) to measure the radius of gyration of varying chain lengths of perdeuterated poly(ethylene oxide) in imidazolium-based ILs, which vary in both cation and anion identity. The dependence of coil size on molecular weight yields Flory exponents (v) for 4 different IL-based solvent systems. For all the solvents studied, the exponents lie within 0.55 and 0.6, indicating moderately good to very good solvent behavior. However, greater expansion of d-PEO coils is observed in ILs comprising cations with longer alkyl chains and less basic anions. Interestingly, variation of the anion has a stronger effect on coil dimensions than the cation. Additional relevant parameters such as temperature and lithium salt addition on the coil dimensions of d-PEO chains in ILs are also explored.