Synthesis and Characterization of a Novel Microporous Dihydroxyl‐Functionalized Triptycene‐Diamine‐Based Polyimide for Natural Gas Membrane Separation

An intrinsically microporous polyimide is synthesized in m‐cresol by a one‐pot high‐temperature condensation reaction of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and newly designed 2,6 (7)‐dihydroxy‐3,7(6)‐diaminotriptycene (DAT1‐OH). The 6FDA‐DAT1‐OH polyimide is thermally stable up to 440 °C, shows excellent solubility in polar solvents, and has moderately high Brunauer‐Teller‐Emmett (BET) surface area of 160 m2 g−1, as determined by nitrogen adsorption at −196 °C. Hydroxyl functionalization applied to the rigid 3D triptycene‐based diamine building block results in a polyimide that exhibits moderate pure‐gas CO2 permeability of 70 Barrer combined with high CO2/CH4 selectivity of 50. Mixed‐gas permeation studies demonstrate excellent plasticization resistance of 6FDA‐DAT1‐OH with impressive performance as potential membrane material for natural gas sweetening with a CO2 permeability of 50 Barrer and CO2/CH4 selectivity of 40 at a typical natural gas well partial pressure of 10 atm.