With differential scanning calorimetry, we have demonstrated a peculiar behavior under equilibrium conditions of neat poly(epsilon-caprolactone) and its organophilic montmorillonite nanocomposites. In particular, in the determination of the equilibrium melting temperature by the extrapolation of the data of the melting temperature (T-m) versus the crystallization temperature (T-c), a bimodal trend has been observed. At the lower T-c's, the data of T-m follow a constant trend, whereas at the higher ones, the usual increasing trend has been obtained. Morphological observations by atomic force microscopy (AFM) have provided evidence of two different crystalline morphologies for the lower and higher T-c ranges. Moreover, AFM has shown that the thermal treatments strongly influence the clay dispersion in the polymer matrix. (c) 2005 Wiley Periodicals, Inc.