A series of novel polymer-clay nanocomposites, that is, liquid-crystalline copolyester/montmorillonite (MMT) nanocomposites, were synthesized by the intercalation polycondensation of terephthalic acid, p-acetoxy benzoic acid, and 1,2-diacetoxy benzene in the presence of different organically modified montmorillonites (OMt's). The OMt's were prepared by the ion exchange of MMT with octadecylamine hydrochloride, p-aminobenzoic acid hydrochloride, or lysine hydrochloride. X-ray diffraction and transmission electron microscopy studies indicated that the inorganic cations in the MMT interlayers were already exchanged by organic onium ions and that the OMt intercalated with p-aminobenzoic acid or lysine was good for obtaining more delaminated clay nanocomposites. The glass-transition temperature and modulus of the nanocomposites increased compared with those of the pure polymer, whereas the isotropic temperature decreased. (C) 2003 Wiley Periodicals, Inc.