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Facile Synthesis of a Hydroxyl-Functionalized Tröger’s Base Diamine: A New Building Block for High-Performance Polyimide Gas Separation Membranes

Ma, Xiaohua, Abdulhamid, Mahmoud, Miao, Xiaohe, Pinnau, Ingo
Macromolecules 2017 v.50 no.24 pp. 9569-9576
anhydrides, carbon dioxide, condensation reactions, hydrogen, hydrogen bonding, methane, moieties, nitrogen, permeability, porous media, solvents, temperature, thermal stability
Two intrinsically microporous polyimides (PIM-PIs) were synthesized by the polycondensation reaction of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3,3′,3′-tetramethylspirobisindane-6,7,6′,7′-tetracarboxylic dianhydride (SBI) with a newly designed o-hydroxyl-functionalized Tröger’s base diamine, 1,7-diamino-6H,12H-5,11-methanodibenzo[1,5]diazocine-2,8-diol (HTB). Both amorphous PIM-PIs were soluble in aprotic solvents and showed excellent thermal stability with onset decomposition temperature of ∼380 °C. SBI-HTB displayed a higher CO₂ permeability (466 vs 67 barrer) than 6FDA-HTB but a significantly lower selectivity for CO₂/CH₄ (29 vs 73), H₂/CH₄ (29 vs 181), O₂/N₂ (4.6 vs 6.0), and N₂/CH₄ (1 vs 2.5). 6FDA-HTB displayed the highest gas-pair permselectivity values of all reported OH-functionalized PIM-PIs to date. The high permselectivity of 6FDA-HTB resulted primarily from exceptional diffusion selectivity due to strong size-sieving properties caused by hydrogen bonding between the proton of the hydroxyl group and the nitrogen atoms in the tertiary amine of the Tröger’s base (O–H···N).