(696c) Thermally-Rearranged Highly Selective Gas Separation Membranes from Hydroxyl-Functionalized Triptycene-Based Polyimide for Natural Gas Upgrading

Recently, a new polyimide of intrinsic microporosity (TDA1-APAF) prepared from 9,10-dimethyl-2,3,6,7-triptycene tetracarboxylic dianhydride (TDA1) with commercially available 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (APAF) diamine monomer exhibited excellent gas-pair selectivities for O₂/N₂ and CO₂/CH₄ but with moderately high gas permeabilities. To enhance gas permeabilities, conversion of hydroxyl-containing polyimide into polybenzoxazole was used by thermal rearrangement of the aromatic polymer chain with decarboxylation at elevated temperature. TR-TDA1-APAF membrane displayed excellent O₂ permeability of 311 Barrer coupled with O₂/N₂ selectivity of 5.4 and CO₂ permeability of 1328 Barrer coupled with a CO₂/CH₄ selectivity of 27. Gas mixture permeation experiments with a 1:1 CO₂/CH₄ feed mixture demonstrated higher mixed- than pure-gas selectivity (~33) with CO₂ permeability of 1270 Barrer. Interestingly, physical aging over 180 days resulted in an enhanced O₂/N₂ selectivity of 6.3 with O₂ permeability of 185 Barrer and CO₂/CH₄ selectivity of 35 coupled with CO₂ permeability of 699 Barrer. These results suggest that thermally-rearranged membranes from hydroxyl-functionalized triptycene-based polyimides are promising candidate membrane materials for CO₂removal from natural gas and air separation applications.