6FDA‐containing polyimide‐ionene + ionic liquid gas separation membranes

Abstract Polyimides (PI) synthesized from 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with various diamines have been frequently studied as gas separation membranes. The use of 6FDA in polyimides creates a bent structure than can increase fractional free volume (FFV) and gas permeability. Here, we demonstrate that 6FDA is also a useful building block for PI‐ionene materials, which contain cations directly within the polymer backbone. These new 6FDA‐containing PI‐ionenes were combined with several different imidazolium ionic liquids (ILs) to form thin membranes. The thermal properties of all the derivatives were investigated to determine the relationship between regiochemistry and degradation as well as the intermolecular forces that are present within these structures. The gas separation properties of these 6FDA‐containing PI‐ionene + IL materials were investigated, showing modest CO 2 permeabilities similar to other polyimide‐ionenes and CO 2 /CH 4 and CO 2 /N 2 permselectivities that were relatively higher than other polyimide‐ionenes.