Using High-Pressure Infrared Spectroscopy to Studythe Interactions between Triblock Copolymers and Ionic Liquids.

In this study, we used high-pressureinfrared spectroscopy to probe the local structures formed betweenthe ionic liquid [BMI][PF6] and the triblock PEO–PPO–PEOcopolymer P123. The signals for the imidazolium C–H units of[BMI][PF6] underwent anomalous frequency shifts upon dilution,induced by order-to-order transitions. Appreciable changes in therelative band intensities of the signals for the imidazolium moietiesoccurred upon compression. Upon increasing the pressure, the etherC–O–C stretching band underwent dramatic changes, witha shoulder peak appearing near 1097 cm–1with relativelyincreasing intensity. It appears that high pressures somehow stabilizethe hydrogen bonds formed between [BMI] and P123, possibly forcingthe P123 molecules to dissociate the clusters of ionic liquid throughenhanced hydrogen bonding with the imidazolium C–H units. Analogousto temperature-dependent behavior, we suggest the possibility of pressure-inducedassociation of P123 molecules through elevation of pressure. [ABSTRACT FROM AUTHOR]