Tröger's Base-Based Microporous Polyimide Membranes for High-Performance Gas Separation

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 H₂/CH₄, H₂/N₂, He/CH₄, and CO₂/CH₄ 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 CO₂/N₂ gas pair up to 62.7 due to a strong affinity between CO₂ and nitrogen atoms of tertiary amine in TB.