ABSTRACTThe largest commercial application of carbon nanotubes (CNT) are their polymer nanocomposites (PNCs). This motivates detailed studies of the interactions between CNTs and polymers and the ways the CNTs influence the crystallization behavior and structure of PNCs. We have chosen isotactic polypropylene (iPP) as one of the best model systems because of its ability to form a smectic liquid crystal phase. We studied iPP/CNT nanocomposites with CNT concentrations ranging from 0.01 to 5% per weight. We prepared films by compression molding and quenching in a mixture of isopropyl alcohol and dry ice. Some of the formed smectic liquid crystalline (LC) phase of iPP/CNT PNCs persisted to temperatures higher than the last melting temperature for iPP crystals. By means of differential scanning calorimetry we corroborated the existence of the LC phase in the nanocomposites and studied the impact of multi-walled carbon nanotubes on its melting and re-crystallization. We used a polarizing optical microscopy to reconfirm our DSC data.