Poly(epsilon-caprolactone)/montmorillonite nanocomposites, prepared by bulk ring-opening polymerization of epsilon-caprolactone in the presence of tin(II) 2-ethylhexanoate as a catalyst and hydroxy groups of ammonium tethers of organoclay acting as chain-growth centers, were characterized by the stretching calorimetry technique. In the range of elastic (reversible) deformations, experimental Young's moduli and linear thermal expansivities of both the intercalated and exfoliated nanocomposites could be fitted to the predictions of Chow's model assuming the apparent aspect ratio of clay nanoparticles of the order of 10. In the range of anelastic deformations, the values of the internal energy increments DeltaU/m for the intercalated nanocomposite lay somewhat below those for the corresponding neat polymer, while the DeltaU/m vs. epsilon plots for the exfoliated nanocomposite and for the corresponding neat polymer were nearly identical both in shape and in absolute values over the entire range of strains, up to the breaking strains epsilon(b). These data suggested higher and lower probabilities of interfacial debonding in the range of anelastic deformations for intercalated and exfoliated samples, respectively. (C) 2004 Elsevier Ltd. All rights reserved.