Dilute Solution Properties of Poly(benzyl methacrylate) in Ionic Liquids

The static and dynamic properties of a range of molecular weights (2 × 10⁴ to 1.6 × 10⁵ g/mol) of poly(benzyl methacrylate) have been assessed in four different imidazolium- A nd pyrrolidinium-based ionic liquids over a wide temperature range (27-155 °C), primarily using light scattering techniques. All four systems exhibit lower critical solution temperature phase behavior. The relevant structural, dynamic, and thermodynamic parameters were examined as a function of concentration, temperature, and molecular weight. Some interesting observations were revealed. The phase boundaries suggest a shift of the critical composition toward the polymer-rich region, in contrast to the low critical concentrations for polymers commonly observed in polymer solutions. Surprisingly, the second virial coefficient (A₂) remains positive, even at temperatures close to phase separation, where A₂ < 0 is anticipated. Furthermore, A₂ also shows stronger dependence on molecular weight than commonly observed for polymers in good solvents. On the dynamic side, the diffusion virial coefficients (k_d) remained positive over the given temperature range, further corroborating the apparent good solvent behavior of A₂. The excluded volume exponents (ν ≈ 0.53-0.54) obtained from the dependence of hydrodynamic radii on molecular weight also indicate good solvent characteristics.