“…However, most glassy polymeric membranes, including those noted above, tend to show a size-sieving character in the process of separating CO 2 , and thus diffusivity selectivity is more dominant in the gas separation mechanism. , Therefore, this type of membrane has the following limitations: ,,− (i) low selectivity to penetrant molecules with similar kinetic diameters , (i.e., CO 2 /N 2 and CO 2 /CH 4 separation; CO 2 = 3.30 Å, N 2 = 3.64 Å, and CO 2 = 3.8 Å); (ii) an aging effect where the nonequilibrium free volume contracts over operating time, thereby leading to deterioration of long-term stability; ,, (iii) reduced CO 2 permeability due to the competitive sorption between hydrocarbon (e.g., CH 4 , C 2 H 6 , etc.) and CO 2 within a gas mixture; and (iv) the separation performance of the membranes (i.e., permeability and selectivity) is significantly affected by their film-forming history. , …”