Effect of premelting temperatures and molecular weight on the crystallization behavior of syndiotactic polystyrene/montmorillonite nanocomposites

X-ray diffraction methods and differential scanning calorimetry (DSC) have been used to investigate the crystalline structure and crystallization kinetics of syndiotactic polystyrene (sPS)/montmorillonite (MMT) nanocomposites. X-ray diffraction data show the presence of polymorphism in sPS/MMT nanocomposites, which is strongly dependent on the premelting temperatures (T-maxs), MMT content and molecular weight of sPS (referred to as HsPS for higher molecular weight sPS and LsPS for lower molecular weight sPS). This result indicates that the T-maxs, MMT content, and cooling rates all affect the alpha/beta crystalline formation of HsPS/MMT nanocomposites, but T-maxs the dominant factor for the crystalline formation of LsPS/MMT nanocomposites; the latter is probably due to the presence of only stable beta crystalline forms of LsPS if treated at T(maxs)greater than or equal to280degreesC. We also studied the nonisothermal melt-crystallization kinetics, melting behavior, and crystalline structure of sPS/MMT nanocomposites at various cooling rates. The results indicate that the addition of a small amount of MMT into the sPS causes a change of the mechanism of nucleation and growth of sPS crystallites.