We present synthesis, Characterization, and gas transport properties of a series of new aromatic polyamides (PAs) containing tri-tert-butylphenol-substituted triphenyl-amine moiety (TPA). The PAs showed a good combination of thermal and mechanical properties (T-g up to 284 degrees C, T-d10 up to 400 and 460 degrees C in air and nitrogen, respectively, and tensile strength up to 68 MPa). Gas transport properties of these membranes were investigated for different gases at 35 degrees C. The PAs showed high gas permeability with moderate gas selectivity [P-CO2 = 119.0, P-O2 = 29.0 barrer and P-CO2/P-CH4 = 37.19, P-O2/P-N2 = 9.67]. The effect of the substituted TPA unit on the gas transport properties of these membranes has been investigated and analyzed using molecular dynamics simulations. A thorough structure/property relationship for this class of materials has been established that may serve as a guide to future design of PA-based gas separation membranes.