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.

We investigated the solvated structure of cellulose in a phosphonate-based ionic liquid (IL) solution utilizing scattering experiments and all-atom molecular dynamics (MD) simulations. Based on the high-energy Xray total scattering experiment and MD simulations, a predominant interaction between cellulose and the IL was established, i.e., hydrogen bonding between the IL anion species and hydroxyl groups of cellulose. In addition, it was found that intramolecular hydrogen bonds existed within cellulose molecules, even when dissolved in the IL. Furthermore, the conformation of cellulose chains in the IL was investigated by a small-angle X-ray scattering experiment. As a result, it was found that cellulose molecules were dispersed at the molecular level and existed as rigid-rod-like polymers because of the intramolecular hydrogen bonds within the cellulose molecules. In dynamic light scattering experiments, a speckle pattern was observed for concentrated cellulose solutions. This indicated the existence of a physical-gel-like frozen inhomogeneity.

A series of critical clusters was prepared by mixing two different kinds of tetra-functional poly(ethylene glycol) (PEG) prepolymers carrying complementary end-groups. The structures of these critical clusters were investigated by small angle neutron scattering (SANS) in different dilution levels. Scaling laws for semidilute polymer solutions were observed in the solution of critical polymer clusters for q < ξ −1 , where q is the scattering vector and ξ is the correlation length. The fractal dimension of the critical clusters was estimated to be approximately 2.0, irrespective of the preparation condition of the critical clusters. For q > ξ −1 , the size distribution of the critical clusters influenced the scattering intensity. Assuming the validity of the scattering theory for the dilute solution of critical polymer clusters in the q-range q > ξ −1 , the Fisher exponent was estimated to be 1.90−2.25, which was found to depend on the preparation condition of the critical clusters.

We have utilized small-angle neutron scattering (SANS) to quantitatively characterize the LCST-type phase behavior of the poly(benzyl methacrylate) (PBnMA) derivative poly(2-phenylethyl methacrylate) (PPhEtMA) in the deuterated ionic liquid (IL) d8-1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (d8-[C2mIm(+)][TFSA(-)]). The SANS curves showed a discontinuous change from those characteristics of dispersed polymer chains to those of large aggregates of PPhEtMA chains suspended in the IL solution, indicating that phase separation occurs discontinuously at Tc. Furthermore, we evaluated the enthalpic and entropic contributions to the effective interaction parameter χeff of PPhEtMA in [C2mIm(+)][TFSA(-)] and compared them with those of PBnMA. The absolute value of the enthalpic contribution observed for PPhEtMA was smaller than that for PBnMA. This difference in the enthalpic term can be attributed to the unfavorable interaction between the IL and the alkyl group in the side chain of PPhEtMA. In addition, the temperature dependence of χeff was smaller than the previously reported value for a thermo-responsive polymer in an aqueous system. It was found out that the strong dependence of Tc on the chemical structure in IL systems originated from the relatively smaller temperature dependence of χeff.