Cosolvency-Induced UCST/LCST Dual Phase Separation of Poly(2-hydroxyethyl methacrylate) in Nonaqueous Organic Solvent Mixtures
Koki Takasu, Natsuki Inaba, Shu Takeuchi, Keitaro Matsuoka, Kazuki Sada
Abstract
Mixed solvents as media are a widely used strategy for achieving UCST/LCST dual phase separation. However, due to the difficulty in controlling the solvation/desolvation of polymer chains, this phenomenon has been realized only in water and water-miscible organic solvents. Herein, we demonstrate UCST/LCST dual phase separation in nonaqueous mixed organic solvents. The ternary polymer solution consists of poly(2-hydroxyethyl methacrylate), aliphatic alcohols, and aprotic less-polar poor solvents. Systematic variation of the mixing ratio realized that UCST-type phase separation occurs in alcohol-rich mixed solvents, while LCST-type phase separation emerges in poor-solvent-rich mixed solvents. This behavior was consistently observed across 15 different mixed solvents. The phase diagrams indicate that the emergence of a completely miscible region due to the cosolvency effect is crucial for achieving UCST/LCST dual phase separation, in agreement with trends observed in water/organic solvent systems. This study expands the diversity of media available for designing UCST/LCST dual phase separation.