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