A series of new aromatic polyamides (PAs) containing 1-adamantanemethoxy substituted triphenylamine has been synthesized for the membrane based gas separation. The PAs were readily soluble and cast into flexible membranes (tensile strengths similar to 104 MPa). All the membranes showed high thermal stability (440 degrees C < T-d10 in air). The permeability of CH4, N-2, O-2 and CO2 through these PA membranes was investigated at 35 degrees C under an applied upstream pressure of 3.5 bar. PA 8b containing hexafluoroisopropylidene moiety exhibited high gas permeability and reasonably good permselectivity in the series (P-CO2=61.5 and P-O2=14.2, P-CO2/P-CH4=51.25 and P-O2/P-N2=10.14), The gas transport properties have been correlated with the polymer structures with respect to their glass transition temperature, fractional free volume (FFV) and dielectric constant values. FFV and free volume distribution were also calculated by the molecular simulation to understand the gas transport properties of the PAs. (C) 2014 Elsevier B.V. All rights reserved