Tröger's base-derived dianhydride as a promising contorted building block for polyimide-based membranes for gas separation

Tröger's base-derived dianhydride (TBDA) was prepared and used to synthesize two solution-processable polyimides using 2,3,5,6-tetramethyl-p-phenylenediamine (TMPD) and 1,7-diamino-6H,12H-5,11-methanodibenzo[1,5]diazocine-2,8-diol (HTB). The polyimides TBDA-TMPD and TBDA-HTB demonstrated excellent thermal stability with T_d,5% exceeding 400 °C, and high gas separation performance. A freshly made TBDA-TMPD membrane displayed CO₂ permeability of 1457 barrer and CO₂/CH₄ selectivity of 17. Physical aging over 50 days of TBDA-HTB membrane revealed CO₂ permeability of 61 barrer and CO₂/CH₄ selectivity of 54. Aged TBDA-HTB exhibited notable performance that crossed 2008 upper bound for H₂/CH₄ separation with H₂ permeability of 147 barrer and H₂/CH₄ selectivity of 129. Developing contorted dianhydride provides new scope for designing high-performance polyimide-bearing nitrogen groups in its backbone for different separation applications.