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It is a great challenge for polyimide to increase its permeability and at the same time to maintain its high selectivity. In this work, Tröger’s Base (TB)-based polyimides through polymerizing Tröger’s Base diamines with two kinds of anhydrides were successfully synthesized to enhance the permeability of polyimides for gas separation. The TB-polyimide membranes exhibited greatly improved gas separation performance for H 2 /CH 4, H 2 /N 2, He/CH 4, and CO 2 /CH 4 gas pairs, among which the separation performance of 6-FDA-based TB-polyimides approaches or slightly exceeds the 2008 Robeson upper bound. Our results revealed that the TB unit with rigid and in-built amine structure plays an important role for increasing the permeability of polyimides and simultaneously maintaining high selectivity. In addition, the TB-based polyimide membranes exhibited extremely high solubility selectivity for the CO 2 /N 2 gas pair up to 62.7 due to a strong affinity between CO 2 and nitrogen atoms of tertiary amine in TB.
Wang et al. (Tue,) studied this question.