Changes of the spectral characteristics of absorption bands depending on the films’ treatment method were registered for polyetherimide Ultem films. The possibility of selection of structural criteria (the ratio of the functional groups absorption bands intensities) showing all conformational changes in elementary unit with metrological processing of the results is shown. It is demonstrated that film formation from chloroform solution leads to elementary unit fragments, Ph–O–Ph′, which have an effect on macromolecule conformation and result in increasing of space between fragments of macromolecules (local polymer matrix packing loosening). Desorption of residual chloroform from films by ethanol or supercritical CO₂ leads to a change of conformers set in Im–Ph–Im′ units. Quantum chemical modeling showed the possibility of convergence of these fragments in neighboring macromolecules, and consequently of interchain π–π interaction (local densification of chain packing of the polymer matrix). After annealing at a temperature higher than glass transition temperature, the polyetherimide film exhibits the most disordered (amorphous) state at all of the fragments. It is demonstrated that the results, obtained by the combination of theoretical and experimental vibrational spectroscopy methods, are in good agreement with data of chain packing ordering found by analysis of gas separation parameters.