Gas transport of H-2, CO2, O-2, N-2, and CH4 in a series of cardo polyarylethers were examined over a temperature range of 30 similar to 100 degreesC. These polymers include three poly(aryletherketone)s, two poly(arylethersulfone)s, and one poly(aryletherketoneketone). It was found that the large length/diameter ratio of the polymer repeat unit for cardo polyaryletherketoneketone (PEKK-C) and strong intermolecular interaction in hydrogen-bonded polyarylethersulfone (PES-H) and hydrogen-bonded polyaryletherketone (PEK-H) resulted in a considerable increase in gas permselectivity. Alkyl-substituted polyaryletherketone (PEK-A), bearing a pendant bulky propyl group on the cardo ring, simultaneously exhibited 62.5% higher H-2 permeability and 59.8% higher H-2/N-2 permselectivity than unmodified poly(aryletherketone) (PEK-C). The causes of the trend were interpreted in terms of chain packing density, segmental motion ability, steric factor, and intermolecular interaction of polymers, together with gas kinetic diameter and critical temperature data.