Hybrid materials obtained by in situ polymerization based on polypropylene and mesoporous SBA-15 silica particles: Catalytic aspects, crystalline details and mechanical behavior

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°C. 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.

Hybrid materials obtained by in situ polymerization based on polypropylene and mesoporous SBA-15 silica particles: Catalytic aspects, crystalline details and mechanical behavior Articles