For example, from the results obtained earlier, the permeability of CO 2 in PIM-PI-8 is k CO 2 =13900±5375 Barrer, and the solubility S CO 2 =54.05±1.50 cm 3 (STP)/(cm 3 bar). Using these values, the diffusivity of CO 2 is calculated as D CO 2 = 1.93±0.75×10 -10 m 2 /s. Similarly, for N 2 , the transport diffusivity from the solution diffusion model is