We describe the LCST-type phase behavior of poly(ethylene oxide) (PEO) dissolved in imidazolium-based tetrafluoroborate ionic liquids (ILs). Phase diagrams were determined by a combination of small-angle neutron scattering (SANS) and cloud point (CP) measurements. Unlike typical LCST phase diagrams of polymer solutions, the PEO/IL phase diagram is either roughly symmetric with a critical composition near 50% polymer or asymmetric with a critical composition shifted to an even higher concentration of PEO. As the molecular weight decreases from 20 500 to 4200 g/mol, the critical temperature (T c) increases slightly (∼10 °C). However, a larger increase in T c (27 °C) was observed as the molecular weight decreases from 4200 to 2100 g/mol, likely due to the increasing importance of hydrogen bonds between the −OH end groups of PEO and the fluorine atoms of the anions. This inference is supported by the strong dependence of the phase diagram on the identity of the PEO end groups (hydroxy vs methoxy). Furthermore, replacing the most acidic proton of the imidazolium ring (in the C2 position) with a methyl group lowers the T c and changes the shape of the phase diagram significantly, suggesting that the hydrogen bonds between the H atoms on the C2 position of the imidazolium ring and the O atoms of PEO play an important role in determining the LCST phase behavior of this system.

We describe the LCST-type phase behavior of poly(ethylene oxide) (PEO) (M = 5000 and 20000) dissolved in 1,3-dialkylimidazolium tetrafluoroborate ionic liquids. The phase transition temperatures were identified using cloud point measurements. In these PEO/ionic liquid systems, liquid−liquid phase separation is observed in the temperature range from 130 to 170 °C. We report unusual temperature−composition phase diagrams in which the cloud point curves are strongly asymmetric, with the critical composition (w c) shifted to high concentrations of PEO. The critical temperature (T c) and the critical composition (w c) of these systems are not a strong function of the molecular weight of PEO. In addition, the values of the LCST increase as the length of the alkyl chain in the imidazolium cation increases. By using ionic liquid blends as solvents, the LCSTs can be tuned by varying the mixing ratio of two ionic liquids.

We describe the lower critical solution temperature (LCST)-type phase behavior of poly(n-butyl methacrylate) (PnBMA) (M =13,000 and 48,000) dissolved in 1-alkyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl}amide ionic liquids (ILs). The temperature-composition phase diagrams of these PnBMA/IL systems are strongly asymmetric with the critical composition shifted to low concentrations of PnBMA. As the molecular weight increases from 13,000 to 48,000, the critical temperature decreases by 20 °C, and the critical composition shifts to a lower concentration. On the basis of the LCST of PnBMA, we designed a thermosensitive poly(n-butyl methacrylate)-poly(ethylene oxide) (PnBMA-PEO) diblock copolymer that exhibits a free chain/micelle transition in an IL as the temperature increases above the lower critical micellization temperature (LCMT). Furthermore, using IL blends as solvents, both the LCST of PnBMA and the LCMT of PnBMA-PEO can be tuned over a wide range by mixing two different alkyl methylimidazolium ILs without modifying the chemical structure of the polymers.

The viscosity (η) of [EMIM][BF 4 ] was measured on an ARES rheometer using 50 mm parallel plates. A nominal gap of 1 mm was employed, and the gap was adjusted at each temperature to keep an even sample loading. The samples were enclosed in a nitrogen convection oven, maintaining the temperature within ± 0.5 °C. The viscosity was measured