A statistical thermodynamic modeling of the formation of polymer/clay intercalation and nanocomposites was developed. The key factor in determining intercalation was an exothermic heat of mixing between polymer chains and the organically modified silicate surface. This was found to agree with previous experimental results in the literature including halogenated polymers and acrylonitrile copolymers. (c) 2006 Wiley Periodicals, Inc.