Nanocomposites based on polypropylene have been prepared by in situ polymerization of propene in presence of mesoporous SBA-15 silica. Synthetic reactions were carried out with a zirconocene catalyst under either homogenous or supported conditions, the SBA-15 particles being used as carriers, and testing the immobilization of the catalytic system by several approaches. The existence of polypropylene able to crystallize within the mesoporous channels in the resulting materials is initially figured out from the appearance of a small endothermic process on heating calorimetric experiments, located at around 100 ºC. The presence of polypropylene crystallites confined within the SBA-15 mesostructure is thereafter confirmed by SAXS measurements through the intensity variation of the SBA-15 first order reflection, this change being dependent on composition. Accordingly, polypropylene chains can grow up either outside or inside the SBA-15 channels during polymerization and the mesoporous particles maintain their ordered hexagonal arrangement. Mechanical response, as deduced from indentation measurements, improves with SBA-15 incorporation (without varying the final processing temperature). Thus, stiffness increases and deformability is reduced in the nanocomposites as the SBA-15 content rises. Simultaneously, polypropylene amount within channels is enlarged. Amount of SBA-15 is, then, the most important variable.

The main objective of this research is the study of different nanocomposites based on isotactic polypropylene (iPP) and mesoporous SBA-15 silica prepared by melt extrusion, analyzing the possible effect of this filler on the polymorphic behavior of iPP and the eventual observation of confinement effects. Thus, simultaneous Small Angle X-ray Scattering/Wide Angle X-ray Diffraction (SAXS/WAXD) synchrotron experiments at variable temperature have been performed on several iPP nanocomposites with different contents of SBA-15 mesoporous particles. Real-time variable-temperature SAXS measurements turned out a very useful tool to analyze the confinement of iPP crystallites within SBA-15 channels, and also to determine the most probable long spacing of chains located outside the SBA-15 nanospaces. Importance of these structural features is assessed by changes in the mechanical response of the final materials, finding that the presence of mesoporous particles leads to a reinforcing effect and contribute to improve the final dimensional stability.

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