Browsing by Author "Quijada, Raul"
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- Hafnocene catalyst for polyethylene and its nanocomposites with SBA-15 by in situ polymerization: immobilization approaches, catalytic behavior and properties evaluationPublication . Ferreira, Ana E.; Cerrada, María L.; Pérez, Ernesto; Lorenzo, Vicente; Cramail, Henri; Lourenço, J. P.; Quijada, Raul; Ribeiro, M. RosárioA hafnocene catalyst combined with methylaluminoxane (MAO) has been used as catalytic complex for the preparation of a set of polyethylene homopolymers by in situ polymerization under homogenous conditions and of different nanocomposites with mesoporous SBA- 15 particles, the latter playing the dual role of catalyst support and nanofiller. Distinct immobilization approaches have been explored for obtainment of these nanocomposites. Moreover, catalytic features, thermal stability, melting and crystallization transitions and mechanical behavior have been evaluated for those materials.
- Preparation of polypropylene-based nanocomposites using nanosized MCM-41 as support and in situ polymerizationPublication . Gonzalez, Dario M.; Quijada, Raul; Yazdani-Pedram, Mehrdad; Lourenço, J. P.; Ribeiro, M. RosárioMCM-41 nanoparticles were used for preparing nanocomposites through the in situ polymerization of propylene. The performance of the catalytic system and the final properties of the materials obtained are highly dependent on the methodology used for impregnation of the catalyst onto the support particles, and therefore an optimization study for the impregnation methodology of the catalyst (Me2Si(Ind)(2)ZrCl2) was carried out. Two different methodologies were used; the results in terms of catalytic activity and polymer molecular masses indicated that the most promising one involved the pre-activation of the catalyst with the cocatalyst, methylaluminoxane, followed by impregnation onto the MCM-41 nanoparticles. Thus, an optimized route for the preparation of polypropylene nanocomposites achieving significant improvements in catalyst activity was developed. The nanocomposite materials were characterized by GPC, TGA and DSC. The dispersion state and the size of the nanoparticles incorporated in the polypropylene matrix were investigated by transmission electron microcopy. Additionally, this methodology allows simultaneous control of the desired amount of support and the concentration of catalyst to be used in the in situ polymerization. (c) 2015 Society of Chemical Industry