The construction of the polymer membranes closely follows the methodology detailed in previous studies. For more information, readers are referred to the original article. Briefly, the process begins by constructing polymer chains using the Force Field Assisted Linear Self-Avoiding Random Walk application in PySIMM. Each chain is constrained to a maximum of approximately 800 heavy atoms (excluding hydrogen), keeping the chain length constant and independent of the monomer size. The constructed chains are then packed together using Packmol. For most cases, the membrane thickness is set to 6 nm, and the total number of atoms is about 20,000. For fixing the membrane thickness in z-direction at 6 nm, rigid walls are placed in the x, y planes of the membrane. To avoid interactions between periodic images in z-direction, a vacuum layer with a thickness of 5 nm is placed at each side of the polymer membrane. To provide a concrete example, PIM-PI-8 system contains 16 polymer chains of 11 monomers each, with 1199 atoms per chain and total 19184 atoms in the system. Details of all systems under consideration are provided in Supplementary Tables and. The structural characteristics of polymer membranes determine their behavior and separation performance. To explore these properties, we use bulk polymer systems that have been relaxed under the N P T ensemble and apply Poreblazer 56 to determine their density, fractional free volume (FFV) and pore size distribution. The results reported in Tab. 1 and in the SI are averaged over three independent configurations to ensure statistical reliability.