Interpretation of d-spacing determined by wide angle X-ray scattering (WAXS) is of great interest in the study of gas diffusivity or permeability in glassy polymers. Studies of WAXS analysis and of molecular modeling were carried out as a new approach in which to interpret the d-spacings in polyimide synthesized from 2,2-bis (3,4-carboxyphenyl) hexafluoropropane dianhydride (6FDA). The tetramer conformation and the amorphous polymer structure at 25 degrees C were modeled using the semi-empirical molecular orbital method and the molecular dynamics method. The corresponding theoretical X-ray scattering functions were calculated from the atomic coordinates using Debye＇s equation and then compared with the experimental data. The amorphous polymer model was found to be superior to the tetramer conformation model in the predicting experimental X-ray scattering function. It was found that the d-spacing for 6FDA-BAAF polyimide was clearly affected by intramolecular distances containing F atoms. (C)2000 Elsevier Science B.V. All rights reserved.