Synthesis and Gas-Permeation Characterization of a Novel High-Surface Area Polyamide Derived from 1,3,6,8-Tetramethyl-2,7-diaminotriptycene: Towards Polyamides of Intrinsic Microporosity (PIM-PAs)

A triptycene-based diamine, 1,3,6,8-tetramethyl-2,7-diamino-triptycene (TMDAT), was used for the synthesis of a novel solution-processable polyamide obtained via polycondensation reaction with 4,4'-(hexafluoroisopropylidene)bis(benzoic acid) (6FBBA). Molecular simulations confirmed that the tetrasubstitution with ortho-methyl groups in the triptycene building block reduced rotations around the C-N bond of the amide group leading to enhanced fractional free volume. Based on N-2 sorption at 77 K, 6FBBA-TMDAT revealed microporosity with a Brunauer-Emmett-Teller (BET) surface area of 396 m(2) g(-1); to date, this is the highest value reported for a linear polyamide. The aged 6FBBA-TMDAT sample showed moderate pure-gas permeabilities (e.g., 198 barrer for H-2, similar to 109 for CO2, and similar to 25 for O-2) and permselectivities (e.g., alpha H-2/CH4 of similar to 50) that position this polyamide close to the 2008 H-2/CH4 and H-2/N-2 upper bounds. CO2-CH4 mixed-gas permeability experiments at 35 degrees C demonstrated poor plasticization resistance; mixed-gas permselectivity negatively deviated from the pure-gas values likely, due to the enhancement of CH4 diffusion induced by mixing effects.