This work reports the first investigation using the inverse gas chromatography method of a polyimide precursor and the product of its thermal rearrangement (TR polymer), extensively studied earlier. Sorption of gases (CO2, C2H6, C3H8) was studied at the finite dilution regime, while vapors (n-alkanes C-7, C-8, C-10, C-14, C-16) were investigated at infinite dilution. It was demonstrated that thermal treatment at 450 degrees C results in a significant increase in the solubility coefficients S for large gas molecules. The absolute values observed for the TR polymer solubility coefficients of solutes are significant and comparable with those for the polymer of intrinsic microporosity (PIM-1), the polymer known by the greatest S values among all of the polymers studied. Sorption thermodynamics in the TR polymer is distinguished by very large and negative mixing parameters: enthalpy (h) over bar (E,infinity)(1) and entropy (s) over bar (E,infinity)(1).