Synthesis and Performance of 6FDA-Based Polyimide-Ionenes and Composites with Ionic Liquids as Gas Separation Membranes

Three new isomeric 6FDA-based polyimide-ionenes, with imidazolium moieties and varying regiochemistry (para-, meta-, and ortho- connectivity), and composites with three different ionic liquids (ILs) have been developed as gas separation membranes. The structural-property relationships and gas separation behaviors of the newly developed 6FDA polyimide-ionene + IL composites have been extensively studied. All the 6FDA-based polyimide-ionenes exhibited good compatibility with the ILs and produced homogeneous hybrid membranes with the high thermal stability of ~380 °C. Particularly, [6FDA I4A pXy][Tf(2)N] ionene + IL hybrids having [C(4)mim][Tf(2)N] and [Bnmim][Tf(2)N] ILs offered mechanically stable matrixes with high CO(2) affinity. The permeability of CO(2) was increased by factors of 2 and 3 for C(4)mim and Bnmim hybrids (2.15 to 6.32 barrers), respectively, compared to the neat [6FDA I4A pXy][Tf(2)N] without sacrificing their permselectivity for CO(2)/CH(4) and CO(2)/N(2) gas pairs.