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

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 Troger's base (TB)-containing ionene polymers for enhanced CO2 separation. The two diimidazole-functionalized Troger's base monomers synthesized from ortho- and para-substituted imidazole anilines were polymerized with equimolar amounts of two different aromatic and aliphatic comonomers (alpha,alpha'-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 Troger'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.