Organophilic montmorillonite intercalants were prepared by a cation-exchange process between Na+ ions of montmorillonite and ammonium salt of octadecylamine. Fourier transform infrared (FTIR) spectrometry and X-ray diffraction analyses of the compounds were carried out. The layer spacings of both modified and unmodified montmorillonites were calculated with Bragg's law. FTIR and X-ray profiles showed organophilic characteristics for the modified montmorillonite, the layer spacing of which increased by two orders of magnitude with respect to that of the unmodified montmorillonite. The prepared organo-clay was incorporated into an alkyd-based clear coating, and X-ray profiles showed an exfoliated structure for the organoclay alkyd coating. The application of the prepared organoclay to alkyd-based clear coatings showed a significant enhancement of the hardness and impact strength of the coating film compared with those of unmodified montmorillonite equally incorporated into the coating formulations. (c) 2006 Wiley Periodicals, Inc.