An aqueous solution of a water soluble polymer, such as poly ethylene glycol (PEG), when mixed with an aqueous solution of another water soluble polymer such as dextran or an organic or inorganic salt, separate into two phases. Liquid-liquid extraction utilizing these aqueous twophase systems (ATPSs) has been used to separate and purify biological products from the complex mixtures in which they are produced [1 ,2]. Similar to the simple electrolytes, hydrophi lic ILs based aqueous two-phase systems are formed when a hydrophilic IL and a certain salt or a certain water solub le polymer are combined with each other in aqueous solution. Although IL-salt aqueous two-phase systems have been studied extensively in recent years, however the information about the IL-polymer aqueous two-phase systems is very scarce in the literature [3]. In this work, we present our results on density and sound velocity measurements of ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate ([C4mirn][HS04]) in water and in aqueous solutions ofpoly(propylene glycol) 400 (PPG400), poly( ethylene glycol) 400 (PEG400) and 2000 (PEG2000) over a range of temperatures at atmospheric pressure that have not been previously published. The effects of polymer and temperature on the apparent molar volume and isentropic compressibility of[ C4mirn Jl HS04J are studied.
