A mixed polymorphic morphology of intercalated/exfoliated structure was observed in syndiotactic polystyrene (sPS)/clay nanocomposites, which were successfully prepared by solution intercalation technique using 1,1,2,2-tetrachloroethane (TCE) as a solvent. Furthermore, X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses were used to examine the effect of montmorillonite clays (MMT, in pristine or organo-modified forms) in isothermally melt-crystallized sPS at several available crystallization temperatures (T-c) in a competitive environment of coexisting alpha- and beta-crystals. A significant change in polymorphism of sPS was observed by the inclusion of different clays and the temperature regime of the a-crystal formation in sPS was found to increase considerably up to 250 degreesC by the presence of the organo-clay. Pristine clay (Na-MMT) was found to induce the beta-crystal of sPS at all T(c)(')s studied in this work. The overall thermodynamics of crystallization remained unchanged as the P-phases were found in major proportion at higher temperature of crystallization (similar to 260 degreesC), irrespective of the nature of the clays. The dispersibility of the clays in sPS matrix is assumed to play the pivotal role in modifying the crystalline structures, which was further corroborated by the polarized optical microscopy (POM). The spherulitic morphology clearly indicates differences in crystallites as affected by the nano-clays. Incorporation of organo-clay with nanoscale dispersibility through the intercalation of sPS molecules into the clay galleries was found to promote rapid formation of alpha-forms, which develops into spherulites of smaller dimension as compared to those of the beta-forms. The alteration in melting behavior of sPS is attributed to the different crystallite structures that lead to formation of different kind of spherulites. (C) 2004 Elsevier Ltd. All rights reserved.