The Effects of Silica Support on Kinetic Behavior and Polymer Properties of Heterogonous Metallocene Catalyst
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The heterogeneous metallocene catalyst is becoming a very competitive industrially due to its ability to produce tailor-made polymers. The main advantage of the metallocene polymer product is the narrow molecular weight distribution (MWD) and the systematic comonomer distribution along the polymer chains. Therefore, the metallocene polymer product has well-defined mechanical and optical properties. The aim of this thesis is to investigate the effects of the silica support on the reaction kinetics and micro properties of the heterogeneous metallocene catalyst system. These investigations include studying the influence of the pore volume, surface area, particle size distribution, and the surface chemical characteristics of silica support on the catalyst performance. The experiments showed that the silica type has an influence on the kinetic behavior. For instance, silica with a lower pore volume shows an induction period when compared with higher pore volume silicas. Moreover, the silica type has a clear influence on catalyst activity and polymer morphology. The smallest silica particles produced the highest activity among the other sizes regardless of silica type. The supported catalysts were characterized and linked to the silica type and size in terms of catalyst activity and polymer morphology. Each catalyst in terms of silica type behaved similarly regardless of type of alkylaluminum used in the formulation. The micro properties of the produced polymers, such as MWD and chemical composition distribution (CCD), were studied to understand the effects of the type and size of silica support and co-catalyst on these properties. The silica types showed no effect on the MWD, but had a slight effect on the CCD. Silica with a high pore volume had a stronger more comonomer response. However, the silica particle size had an influence on the CCD, with less comonomer incorporation observed with smaller silica particles. Finally, triethylauminum was observed to produce polymer with a different MWD when compared with other alkylaluminums. However, all alkylaluminums used in this work had no effect on the CCD of the produced polymer regardless of silica type.