Isotactic (iPP) and syndiotactic (sPP) polypropylene composites and their blends containing different amounts of nanosepiolite as cocatalyst support were prepared via in-situ polymerisation using different metallocene catalysts to find out improvements in the mechanical properties in comparison with traditional PP nanocomposites obtained by melt. The results showed that the amount of nanoclay significantly affects the catalytic activity of the C s-symmetry catalyst, obtaining nanocomposites with important microstructural changes: increased molecular weight and syndiotactic sections, narrower molecular weight distributions and increased crystallinity. The particular ordering of the crystalline sections of the sPP observed in the WAXS patterns was the main reason for the dramatic changes in the thermal and mechanical properties of the obtained nanocomposites. Although the nanocomposites obtained with catalyst mixtures maintained certain thermal properties of the iPP, these did not translate into improved mechanical properties due to the loss of crystallinity and the preference for the synthesis of syndiotactic configurations.
