Design and Synthesis of Imidazolium-Mediated Tröger's Base-Containing Ionene Polymers for Advanced CO 2 Separation Membranes

Abstract

It is highly desirable to integrate the CO 2 solubility benefits of ionic liquids (ILs) in polymeric membrane systems for effective CO 2 separations. Herein, we are exclusively exploring a series of four novel imidazolium-mediated Tröger's base (TB)-containing ionene polymers for enhanced CO 2 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)-C 10 ][Br], respectively). The resulting ionene polymers having halide anions were exchanged with [Tf 2 N] - anions, yielding a novel Tröger's base material [Im-TB(x)-R][Tf 2 N] 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 CO 2 solubility and hence an excellent CO 2 /CH 4 permselectivity of 82.5. The Im-TB-Ionenes also displayed good thermal and mechanical stabilities.