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This study investigates the phase behavior and crystallization properties of poly(2-isopropyloxazoline) (PiPrOx) in ionic liquid systems. While PiPrOx is known to exhibit lower critical solution temperature (LCST)-type phase separation in water, our findings reveal that in ionic liquids, PiPrOx displays either LCST- or upper critical solution temperature (UCST)-type transitions depending on the chemical structure of the ionic liquid, particularly the anion. Notably, only under LCST-type conditions does PiPrOx undergo immediate and irreversible crystallization following phase separation. FT-IR spectroscopy shows that PiPrOx adopts a trans-rich conformation in ionic liquids exhibiting LCST-type transitions, even in the dissolved state. This ordered conformation is hypothesized to both lower the entropy of mixing, thereby satisfying the thermodynamic requirement for LCST behavior, and facilitate rapid crystallization. These findings offer new insights into polymer-solvent interactions in ionic liquids and their implications for designing functional polymer materials.

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• cc-by-3.0
  

Keyword: ionic liquid, LCST, crystallization, UCST, phase transition, poly(2-isopropyl-2-oxazoline)

Date published: 2025-04-10

Publisher: Royal Society of Chemistry (RSC)

Journal:

• Chemical Communications (ISSN: 13597345) vol. 61 issue. 49 p. 8843-8846

Funding:

• Japan Society for the Promotion of Science 20H02804
• Japan Society for the Promotion of Science 20K21229
• Japan Society for the Promotion of Science 23H02030

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1039/d5cc01017a

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Updated at: 2025-06-13 12:30:20 +0900

Published on MDR: 2025-06-13 12:22:25 +0900