Substructures 1432 and 822, two double-bonded carbons connected to an aromatic ring, define polyacetylenes, which demonstrate some of the highest permeabilities among non-porous polymers in gas separations . By contrast, polar groups generally have negative contributions to gas permeability, as shown in Fig. . For example, double-bonded oxygens (799 and 2706), ethers (1519), and nitrogen atoms (2906) are all inversely correlated with gas permeability. Since most gas molecules are non-polar, the presence of these polar groups generally reduces the solubility of gases, which explains the negative effect.