Thermosensitive Phase Separation Behavior of Poly(benzyl methacrylate)/Solvate Ionic Liquid Solutions

Area of Science:

• Polymer Science
• Materials Chemistry
• Physical Chemistry

Background:

• Lower critical solution temperature (LCST) behavior in polymer solutions is crucial for applications like smart materials and drug delivery.
• Solvate ionic liquids offer unique solvation properties and tunable characteristics.
• Understanding polymer-solvate interactions is key to controlling phase behavior.

Purpose of the Study:

• To investigate the LCST behavior of poly(benzyl methacrylate) (PBnMA) in binary systems with solvate ionic liquids.
• To elucidate the role of glyme-lithium cation complex stability and interactions with PBnMA.
• To determine the factors contributing to the observed phase transition.

Main Methods:

• Preparation and characterization of binary systems of PBnMA and solvate ionic liquids (equimolar mixtures of triglyme (G3) or tetraglyme (G4) and lithium bis(trifluoromethanesulfonyl)amide).
• Determination of critical temperatures (Tc) using transmittance measurements.
• Assessment of glyme-Li+ complex stability using Raman spectroscopy, pulsed-field gradient spin-echo NMR (PGSE-NMR), and thermogravimetric analysis.
• Investigation of PBnMA-glyme-Li+ complex interactions via 7Li NMR chemical shifts.

Main Results:

• The binary systems exhibited clear lower critical solution temperature (LCST) behavior.
• Raman spectroscopy, PGSE-NMR, and TGA confirmed the stability of the glyme-Li+ complex in the presence of PBnMA.
• 7Li NMR chemical shifts indicated specific interactions, with the glyme-Li+ complex localizing near the aromatic benzyl group of PBnMA.
• Observed upfield shifts suggest a negative mixing entropy, a prerequisite for LCST.

Conclusions:

• The study demonstrates LCST behavior in PBnMA/solvate ionic liquid systems.
• The glyme-Li+ complex remains stable and interacts favorably with PBnMA through localization around the benzyl group.
• This specific interaction and resulting negative mixing entropy are identified as key factors driving the observed LCST phenomenon.