The effect of cardo fluorene moiety and long-branched aliphatic chain in poly(ether imide) (PEI) membranes on gas transport properties have been investigated. Accordingly, this article reports the synthesis of a new cardo bis(ether amine) monomer with long and branched aliphatic chain namely, 9,9-bis(2-ethylhexyl)-2,7-bis(4-aminophenoxy-3-trifluoromethylphenyl)-9H-fluorene and its polymerization with five different dianhydrides. The monomer and the PEIs were characterized by elemental analysis, H-1-NMR and ATR-FTIR techniques. The polymers showed high molecular weight, glass transition temperature (T-g) up to 248 degrees C, 10% degradation temperature up to 409 degrees C and 437 degrees C under air and nitrogen respectively, tensile strength up to 100 MPa and dielectric constant (epsilon) as low as 2.35. Gas transport properties of these PEI membranes were investigated at three different temperatures (35, 45 and 55 degrees C) using four different gases (e.g., CH4, N-2, O-2 and CO2). The PEIs showed high gas permeability [P(CO2) = 73.91 and P(O-2)=17.12] and permselectivity [alpha(CO2/CH4)=78.24, alpha(O-2/N-2)=20.24] in comparison to many other previously reported PEIs. (C) 2015 Elsevier B.V. All rights reserved.