Aromatic polyimide derived from 2,2’-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 3,3’-di-aminodiphenylsulfone (m-DDS) has been synthesized to facilitate the study of relationships between the polymer structure and the gas transport properties (permeability and selectivity). The gas permeability and selectivity of CO2, O-2, N-2, and CH4 for the 6FDA-m-DDS membranes cured at 150, 200, and 250 degrees C have been determined at 35 degrees C and at pressures up to 760 cmHg. The packing density and the fluorescence intensity of the 6FDA-m-DDS polyimide increased sharply with the increasing curing temperature. We propose that this behavior is associated with an increase in intermolecular and/or intramolecular interactions by a charge transfer complex formed in 6FDA-m-DDS containing an alternating sequence of electron donor and electron acceptor molecules. The effect of the microstructure of the thermally cured 6FDA-m-DDS membranes on their gas transport properties is discussed.