Using High-Pressure Infrared Spectroscopy to Study the Interactions between Triblock Copolymers and Ionic Liquids

Abstract

In this study, we used high-pressure infrared spectroscopy to probe the local structures formed between the ionic liquid [BMI][PF6] and the triblock PEO–PPO–PEO copolymer 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 the relative band intensities of the signals for the imidazolium moieties occurred upon compression. Upon increasing the pressure, the ether C–O–C stretching band underwent dramatic changes, with a shoulder peak appearing near 1097 cm–1 with relatively increasing intensity. It appears that high pressures somehow stabilize the hydrogen bonds formed between [BMI] and P123, possibly forcing the P123 molecules to dissociate the clusters of ionic liquid through enhanced hydrogen bonding with the imidazolium C–H units. Analogous to temperature-dependent behavior, we suggest the possibility of pressure-induced association of P123 molecules through elevation of pressure.