Triblock copolymers as versatile constituents of double stimuli-responsive ionic-liquid-based aqueous biphasic systems

Abstract

This work proposes the use of triblock copolymers as structurally versatile constituents to develop double stimuli-responsive aqueous biphasic systems (ABS) comprising ionic liquids (ILs). Phase diagrams of ABS comprising cholinium acetate ([Ch][C2O2]) and triblock copolymers composed of polyethylene oxide (PEO) and polypropylene oxide (PPO) with adjustable compositions of PEO, 20% (PE 6200) and 40% (PE 6400), were determined by the cloud point titration method at several temperatures (25–45 °C) and pH (5–7). These ABS present, for all the tested pH conditions, a Lower Critical Solution Temperature (LCST)-like behavior. However, only ABS with PE 6400 copolymer exhibit a simultaneous response to both stimuli. Compared to the homologous homopolymer polypropylene glycol (PPG), and despite their lower capacity to form ABS, copolymers with an adequate content of PEO provide a stronger response to the simultaneous action of pH and temperature. The results obtained highlight the value of an appropriate adjustment of the polymer structure/monomer composition in the development of ABS with double response to temperature and pH. The enhanced tailoring ability of the proposed systems is demonstrated with the simultaneous separation of two dyes by the application of the studied stimuli.