Novel 6FDA-based polyimides derived from sterically hindered Tröger's base diamines: Synthesis and gas permeation properties

Two novel Tröger's base-based di-o-substituted diamine monomers were synthesized and used to prepare two intrinsically microporous 6FDA-based polyimides (PIM-PI-TB-1 and PIM-PI-TB-2) with high molecular weight, high thermal stability and excellent solubility in common organic solvents. Compared to previously reported methods for preparing TB-based diamines, which are based on reduction of dimerized nitro-substituted anilines or condensation of phenylenediamine derivatives with dianhydrides, the novel protocol can be used to prepare different functionalized TB-based diamine monomers from a wide variety of aniline derivatives. PIM-PI-TB-1 (made from 6FDA and dibromo-tetramethyl-substituted TB diamine) and PIM-PI-TB-2 (made from 6FDA and tetramethyl-substituted TB diamine) are intrinsically microporous polymers with high BET surface areas of 440 m2/g and 580 m2/g, respectively. Pure-gas permeability coefficients of He, H2, N2, O2, CH4, and CO2 were measured at 35 °C and 2 bar for fresh and 180 days aged films. Both TB-based polyimides exhibited high gas permeability with moderate selectivity. The gas permeability dropped significantly coupled with a moderate increase in selectivity after long-term physical aging of 180 days.