“Green Meets Green” – Sustainable solutions of imidazolium and phosphonium ionic liquids with poly(ethylene glycol): Solubility and phase behavior

Liquid–liquid and solid–liquid phase behaviors of the binary solutions of imidazolium [C2mim]+ or trihexyltetradecyl phosphonium [P6,6,6,14]+ ionic liquids having triflate [OTf]−, bistriflamide [NTf2]− or ethyl-sulfate [EtSO4]− anions with poly(ethylene glycol) (PEG) of average molecular mass (Mw) 200, 400 and 2050, were studied. The respective temperature–composition phase diagrams were constructed thus mapping the homogeneous and heterogeneous regions of the studied solutions. The impact of cation, anion and of PEG polymer chain length on the studied phase behavior was investigated and discussed in the terms of the important interactions in the solutions – hydrogen bonds and ion-dipole interactions. Imidazolium cation showed significant advantage over the phosphonium in promoting both liquid–liquid and solid–liquid solubility. On the other hand, the anion effect was found to be dependent on the outcome of the interplay between cation–anion and anion–PEG interactions. As expected, longer PEG chain led to worse solubility with the studied ionic liquids.This study is a first step to explore the possibilities to use the studied (PEG + ionic liquid) solutions as potential sustainable hybrid materials or combined (mixed) solvents of tunable thermophysical properties and/or solvent power.