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 ( 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][TfN] ionene + IL hybrids having [Cmim][TfN] and [Bnmim][TfN] ILs offered mechanically stable matrixes with high CO affinity. The permeability of CO was increased by factors of 2 and 3 for Cmim and Bnmim hybrids (2.15 to 6.32 barrers), respectively, compared to the neat [6FDA I4A pXy][TfN] without sacrificing their permselectivity for CO/CH and CO/N gas pairs.