Poly(epsilon-caprolactone)/montmorillonite nanocomposites were prepared maintaining a constant inorganic content with three means: melt blending of poly(E-caprolactone) with natural or organomodified clays, in situ polymerization of epsilon-caprolactone in the presence of organomodified clays, and initiation of epsilon-caprolactone polymerization from the silicate layer with appropriate organomodified montmorillonites and activator. In this last case, the polymer chains were grafted to the silicate layers and it was possible to tune up the grafting density. The presence of clays did not modify the polymer crystallinity. It was shown that the in situ polymerization process from the clay surface improved the clay dispersion. The gas barrier properties of the different composite systems were discussed both as a function of the clay dispersion and of the matrix/clay interactions. The highest barrier properties were obtained for an exfoliated morphology and the highest grafting density. Similar evolution of the permeability and the diffusion coefficients was observed. (C) 2004 Wiley Periodicals, Inc.