(161am) Effects of Impregnation Conditions on Catalyst Distribution in Metallocene Catalyzed Olefin Polymerization

The immobilization of metallocene catalyst on porous silica microparticles allow for the catalyst to retain its high activity and adds controllability of polymer particle morphology and its properties. However, the performances of silica-supported catalysts are often inconsistent due to the intrinsic heterogeneity of the solid support material itself and the variations in catalyst preparation by impregnation techniques. A typical silica-supported metallocene catalyst is prepared by several stages including silica conditioning, coactivator (MAO, methylaluminoxane) immobilization via reactions with surface silanol groups, and finally the formation of MAO-metallocene complex. During the impregnation process, these catalytically active compounds diffuse into the tortuous pores of a support material and the fine structure of the pore itself can be altered and affect the ultimate performance of the catalyst. In this work, we have investigated the effects of catalyst impregnation conditions on the distribution of catalytic components on the pore surfaces, catalyst activity, and catalyst fragmentation. Elemental mapping of transition metals has been made using electron probe micro-analysis to determine the penetration depth of the catalyst prepared by various catalyst preparation techniques while ICP-MS analysis was performed to determine the overall composition. It was revealed that metallocene preferentially binds to areas of high MAO concentrations, the locations of which depend on the pore structure of the support. These areas of higher MAO-metallocene complexes lead to different parts of the silica-supported catalyst fragmenting more rapidly than areas of low complex concentration during polymer growth. The contact time during the impregnation process influences the formation of these complexes and leads to a peak in catalyst activities. More experimental and theoretical modeling results will be presented at the meeting.