Design and Synthesis of Imidazolium-Mediated Tröger's Base-Containing Ionene Polymers for Advanced CO₂ Separation...

It is highly desirable to integrate the CO₂ solubility benefits of ionic liquids (ILs) in polymeric membrane systems for effective CO₂ separations. Herein, we are exclusively exploring a series of four novel imidazolium-mediated Tröger's base (TB)-containing ionene polymers for enhanced CO₂ separation. The two diimidazole-functionalized Tröger's base monomers synthesized from "ortho"- and "para"-substituted imidazole anilines were polymerized with equimolar amounts of two different aromatic and aliphatic comonomers (α,α'-dichloro-p-xylene and 1,10-dibromodecane, respectively) via Menshutkin reactions to obtain four respective ionene polymers ([Im-TB(o&p)-Xy][Cl] and ([Im-TB(o&p)-C₁₀][Br], respectively). The resulting ionene polymers having halide anions were exchanged with [Tf₂N]^- anions, yielding a novel Tröger's base material [Im-TB(x)-R][Tf₂N] or "Im-TB-Ionenes". The structural and physical properties as well as the gas separation behaviors of the copolymers of aromatic and aliphatic Im-TB-Ionenes have been extensively investigated with respect to the regiochemistry of imidazolium groups at the ortho and para positions of the TB unit. The imidazolium-mediated TB-Ionenes showed high CO₂ solubility and hence an excellent CO₂/CH₄ permselectivity of 82.5. The Im-TB-Ionenes also displayed good thermal and mechanical stabilities.