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

We report a lower critical solution temperature (LCST) behavior of binary systems consisting of poly­(benzyl methacrylate) (PBnMA) and solvate ionic liquids: equimolar mixtures of triglyme (G3) or tetraglyme (G4) and lithium bis­(trifluoromethanesulfonyl)­amide. We evaluated the critical temperatures (<i>T</i>_cs) using transmittance measurements. The stability of the glyme–Li⁺ complex ([Li­(G3 or G4)]⁺) in the presence of PBnMA was confirmed using Raman spectroscopy, pulsed-field gradient spin–echo NMR (PGSE-NMR), and thermogravimetric analysis to demonstrate that the complex was not disrupted. The interaction between glyme–Li⁺ complex and PBnMA was investigated via ⁷Li NMR chemical shifts. Upfield shifts originating from the ring-current effect of the aromatic ring within PBnMA were observed with the addition of PBnMA, indicating localization of the glyme–Li⁺ complex above and below the benzyl group of PBnMA, which may be a reason for negative mixing entropy, a key requirement of the LCST

Micellization/Demicellization Self-Assembly Change of ABA Triblock Copolymers Induced by a Photoswitchable Ionic Liquid with a Small Molecular Trigger

To date, the demonstration of photoinduced micellization/demicellization of ABA-type triblock copolymers in ionic liquids (ILs) has been based on photoresponsive polymers. Herein, rather than the photoresponsive polymers, a small molecular trigger, an azobenzene-based IL, is employed for the first time to achieve a photocontrollable micellization. ABA-type triblock copolymers were synthesized in which the A block (either poly­(2-phenylethyl methacrylate) or poly­(benzyl methacrylate)) has a lower critical solution temperature (LCST) in imidazolium-based ILs, while the B block (poly­(methyl methacrylate)) is compatible with ILs; these triblock copolymers are denoted as PMP and BMB, respectively. Solutions of the azobenzene-based IL containing the copolymers exhibited different micellization temperatures in the dark and under UV irradiation. For PMP, at a temperature between the two micellization temperatures, UV irradiation induced a “unimer-to-micelle” transition, while for BMB, UV irradiation induced a “micelle-to-unimer” transition. The main difference in the chemical structures of the copolymers is the number of methylene spacers (1 or 2) between the aromatic ring and ester of the A blocks. NMR analysis showed that the chemical shifts of the ILs were shifted in opposite directions on UV irradiation, indicating that azobenzene isomerization can affect the solvation interactions between the polymers and the ILs

Adsorption of Polyether Block Copolymers at Silica–Water and Silica–Ethylammonium Nitrate Interfaces

Atomic force microscope (AFM) force curves and images are used to characterize the adsorbed layer structure formed by a series of diblock copolymers with solvophilic poly­(ethylene oxide) (PEO) and solvophobic poly­(ethyl glycidyl ether) (PEGE) blocks at silica–water and silica–ethylammoniun nitrate (EAN, a room temperature ionic liquid (IL)) interfaces. The diblock polyethers examined are EGE₁₀₉EO₅₄, EGE₁₁₃EO₁₁₅, and EGE₁₀₄EO₁₇₈. These experiments reveal how adsorbed layer structure varies as the length of the EO block varies while the EGE block length is kept approximately constant; water is a better solvent for PEO than EAN, so higher curvature structures are found at the interface of silica with water than with EAN. At silica–water interfaces, EGE₁₀₉EO₅₄ forms a bilayer and EGE₁₁₃EO₁₁₅ forms elongated aggregates, while a well-ordered array of spheres is present for EGE₁₀₄EO₁₇₈. EGE₁₀₉EO₅₄ does not adsorb at the silica–EAN interface because the EO chain is too short to compete with the ethylammonium cation for surface adsorption sites. However, EGE₁₁₃EO₁₁₅ and EGE₁₀₄EO₁₇₈ do adsorb and form a bilayer and elongated aggregates, respectively

Microscopic Structure of Solvated Poly(benzyl methacrylate) in an Imidazolium-Based Ionic Liquid: High-Energy X‑ray Total Scattering and All-Atom MD Simulation Study

We report a new approach for investigating polymer structures in solution systems, including polymer–solvent interactions at the molecular level. The solvation structure of poly­(benzyl methacrylate) (PBnMA) in an imidazolium-based ionic liquid (IL) has been investigated at the molecular level using high-energy X-ray total scattering (HEXTS) with the aid of all-atom molecular dynamics (MD) simulations. The X-ray radial distribution functions derived from both experimental HEXTS and theoretical MD (<i>G</i>^exp(<i>r</i>) and <i>G</i>^MD(<i>r</i>), respectively) were in good agreement in the present PBnMA/IL system. The <i>G</i>(<i>r</i>) functions were successfully separated into two components for the inter- and intramolecular contributions. Here, the former corresponds to polymer solvation (or polymer–solvent interactions) and the latter to polymer structure, such as conformation and interactions between side chains (benzyl groups) in PBnMA. The intermolecular <i>G</i>^MD_inter(<i>r</i>) revealed that the side chains are preferentially solvated by imidazolium cations rather than anions. On the other hand, the intramolecular <i>G</i>^MD_intra(<i>r</i>) suggested that PBnMA is also stabilized by interactions among the aromatic side chains (π–π stacking). Thus, polymer (benzyl group)–cation interactions and benzyl group stacking within a PBnMA chain coexist in the PBnMA/IL system to give a more ordered solution structure. This behavior might be ascribed to negative mixing entropy in the solution state, which is key to the lower critical solution temperature (LCST)-type phase behavior in the PBnMA/IL solutions