This work reports the formation and detailed characterization of the γ‐cyclodextrin (γ‐CD) inclusion compounds (ICs) formed with two poly (vinyl chloride) samples with different isotactic content. The ICs were characterized by X‐ray diffraction, solid state 13C‐NMR, solution 1H‐NMR, FT‐infrared, differential scanning calorimetry, and thermogravimetric analysis. Experimental evidence of the inclusion of the guest polymer chains into the narrow channels created by the γ‐CD crystalline host lattice has been obtained. Examination of coalesced poly (vinyl chlorides) (PVCs) obtained after the host γ‐CD is removed reveals different characteristics specifically for the coalesced PVC sample with higher isotactic content. An increase in Tg was observed by DSC for this PVC. To the contrary, the Tg of the coalesced PVC sample with lower isotactic content is almost the same as that of the as‐synthesized sample. Thermogravimetric analysis indicated that coalesced PVC with higher isotactic content acquires a degree of stabilization after modification by threading into and being extracted from its γ‐CD IC. The results suggest that an irreversible conformational change takes place when PVC forms ICs with a solid host lattice like γ‐CD. The PVC molecules extend and reorganize into a more stable conformation in the IC, consequently improving the properties of the coalesced sample. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2503–2513, 2007 Inclusion compound (ICs) were prepared from γ‐cyclodextrin (γ‐CD) and two poly (vinylchloride) (PVC) samples with different isotactic content. Fourier transform infrared (FTIR) spectroscopy, wide‐angle X‐ray diffraction (WAXD), and solid state 13C‐NMR have been used to verify the formation and successfully characterize all inclusion compounds. The coalesced PVC reveals different characteristics specifically for the coalesced PVC sample with higher isotactic content. The results suggest that an irreversible conformational change takes place when PVC forms ICs with a solid host lattice like γ‐CD, wich explains, perfectly, the variation in the properties in the coalesced polymer sample, specially the improvement of the global process of thermal degradation.