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 (G exp(r) and G MD(r), respectively) were in good agreement in the present PBnMA/IL system. The G(r) 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 G MD inter(r) revealed that the side chains are preferentially solvated by imidazolium cations rather than anions. On the other hand, the intramolecular G MD intra(r) 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.

Small angle neutron scattering has been used to probe the self-assembled structures formed by novel block copolymers in water and two protic ionic liquids (ILs), ethylammonium nitrate (EAN) and propylammonium nitrate (PAN). The block copolymers consist of solvophilic poly(ethylene oxide) (PEO) tethered to either poly(ethyl glycidyl ether) (PEGE) or poly(glycidyl propyl ether) (PGPrE) solvophobic blocks. Four block copolymers (EGE 109 EO 54 , EGE 113 EO 115 , EGE 104 EO 178 , and GPrE 98 EO 260 ) have been investigated between 10 and 100 °C, showing how aggregate structure changes with increasing the EO block length, by changing the insoluble block from EGE to the more bulky, hydrophobic GPrE block, and with temperature. EO solubility mainly depends on the hydrogen bond network density, and decreases in the order H 2 O, EAN, and then PAN. The solubility of the EGE and GPrE blocks decreases in the order PAN, EAN then water because the large apolar domain of PAN increase the solubility of the solvophobic blocks more effectively than the smaller apolar domains in EAN, and water, which is entirely hydrophilic; GPrE is less soluble than EGE because its larger size hinders solubilization in the IL apolar domains. Large disk-shaped structures were present for EGE 109 EO 54 in all three solvents because short EO chains favor flat structures, while GPrE 98 EO 260 formed spherical structures because long EO chains lead to curved aggregates. The aggregate structures of EGE 113 EO 115 and EGE 104 EO 178 , which have intermediate EO chain lengths, varied depending on the solvent and the temperature. Solubilities also explain trends in critical micelle concentrations (cmc) and temperatures (cmt).

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 (Ts) 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 Li 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.

Instead of the reported photoinduced lower critical solution temperature (LCST) phase transition behavior in ionic liquids (ILs) achieved by photofunctional polymers, this study reports the facile photoinduced LCST phase behavior of nonfunctionalized polymers (poly(benzyl methacrylate) (PBnMA) and poly(2-phenylethyl methacrylate) (PPhEtMA)) in mixed ILs (1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)amide; [C mim][NTf ] and a newly designed functionalized IL containing an azobenzene moiety (1-butyl-3-(4-phenylazobenzyl)imidazolium bis(trifluoromethanesulfonyl)amide; [Azo][NTf ])) as a small-molecular photo trigger. Interestingly, the length of the alkyl spacer between the ester and aryl groups, which is the only structural difference between the two polymers, leads to two different photoresponsive LCST phase transition behaviors. On the basis of spectroscopic studies, the different phase transition behaviors of PBnMA and PPhEtMA may attribute to the different cooperative interactions between the polymers and [C mim][NTf ].

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.