Using the methodology and workflow established in the previous sections, in this section we explore a broader range of PIM-based polymers with a view to establish structure-property patterns in their behavior. A widely recognized behavior of transport properties is that permeability often correlates with FFV. In Fig. (d), we plot the CO 2 permeability with respect to the calculated FFV from simulations. Although the relationship is not strictly linear, a clear trend indicates that permeability is generally proportional to FFV. This outcome is expected, as FFV essentially governs the available free pathways for gas molecules. This finding also confirms that one of the well documented experimental trends is reproducible within the simulation framework. exhibit both the highest (PIM-PI-9) and lowest (PIM-1) permeability among the membranes tested. This observation suggests that simply increasing solubility does not necessarily lead to higher permeability. In some cases, the opposite may occur. It also suggests that diffusivity is a strong function of the solubility; or, in other words, it depends on how gas molecules interact with the surface of the polymer. This observation is in line with our previous findings on the relation between the perm-selectivity and sorption selectivity using lattice model and Dynamic Mean Field Theory. Fig. (f) presents the perm-selectivity as a function of sorption selectivity. According to the solution diffusion model, the gradient of this plot is the diffusion selectivity, α i/j = D i D j S i S j . For all the cases, the diffusion selectivity is below 1, below the parity plot shown by the black line, meaning that CO 2 molecules diffuses slower than N 2 for all the polymeric membranes tested. As we have discussed previously, the strong gas-membrane interaction is slowing down the diffusion of CO 2 , even though that CO 2 is smaller than N 2 in its molecular size. Another point emerging from this figure is that the perm-selectivity is approximately proportional to sorption selectivity. To enhance selectivity as a design strategy, these observation would suggest developing membranes with stronger CO 2 binding, e.g. by introducing functional groups that attract CO 2 ; and indeed these approaches have been reported in the literature. While no clear trend is observed for permeability, increasing sorption selectivity indeed enhances perm-selectivity.