| Summary: | Fluorinated polyimides incorporated with triptycene units have gained growing attention over the last decade since they present potentially interesting selectivities and a higher free volume with respect to their triptycene-free counterparts. This work examines the transport of single-gas and mixed-gas N<sub>2</sub> and CH<sub>4</sub> in the triptycene-based 6FDA-BAPT homopolyimide and in a block 15,000 g mol<sup>−1</sup>/15,000 g mol<sup>−1</sup> 6FDA-mPDA/BAPT copolyimide by using molecular dynamics (MD) simulations. The void-space analyses reveal that, while the free volume consists of small-to-medium holes in the 6FDA-BAPT homopolyimide, there are more medium-to-large holes in the 6FDA-mPDA/BAPT copolyimide. The single-gas sorption isotherms for N<sub>2</sub> and CH<sub>4</sub> over the 0–70 bar range at 338.5 K show that both gases are more soluble in the block copolyimide, with a higher affinity for methane. CH<sub>4</sub> favours sites with the most favourable energetic interactions, while N<sub>2</sub> probes more sites in the matrices. The volume swellings remain limited since neither N<sub>2</sub> nor CH<sub>4</sub> plasticise penetrants. The transport of a binary-gas 2:1 CH<sub>4</sub>/N<sub>2</sub> mixture is also examined in both polyimides under operating conditions similar to those used in current natural gas processing, i.e., at 65.5 bar and 338.5 K. In the mixed-gas simulations, the solubility selectivities in favour of CH<sub>4</sub> are enhanced similarly in both matrices. Although diffusion is higher in 6FDA-BAPT/6FDA-mPDA, the diffusion selectivities are also close. Both triptycene-based polyimides under study favour, to a similar extent, the transport of methane over that of nitrogen under the conditions studied.
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