Silica supported zirconocenes and Al‐based cocatalysts: surface metal loading and catalytic activity

Abstract

The Z r surface loading from Cp2ZrC1, toluene solutions on different kinds of cornmer-cia1 silicas (Grace 948, 952 and 956) was determined by Rutherford backscattering spectrometry. In all silicas, a saturation trend was observed with increasing amount of metal in the initial solution, the largest Zr loading value (1 wt.-%) being observed for silica Grace 948. Solid surface areas were determined by the BET method before and after metallocene immobilization, revealing that the values do not change after zirconocene impregnation. Two different kinds of cocatalyst were used, methylaluminoxane and trimethylaluminium. The aluminium loading on silica Grace 948 was determined using the 27Al(p,y)28Si nuclear reaction and titrometry, both showing that methylaluminoxane leads to an 'A1 grafting' four times more efficient than does trimethylaluminium. Finally, the catalytic activity of these systems was tested in the polymerization of ethylene. The supported catalysts were shown to be active, specially using the low cost trimethylaluminium as a cocatalyst. The polymers obtained with the supported systems exhibited a higher molecular weight than those obtained with the homogeneous system.

Linear low-density polyethylene synthesis promoted by homogeneous and supported catalysts

“…28 Chien and He 29 reported that [Ind] 2 ZrCl 2 was not retained directly on the silica surface, leading consequently to no activity in ethylene±propylene copolymerization, while it could be grafted onto an MAO/SiO 2 support. In previous work, 12,13 we have already veri®ed that grafting (nBuCp) 2 ZrCl 2 on dehydroxylated silica afforded supported catalyst systems which were active in ethylene homopoymerization. In the present work, we have veri®ed that such a catalytic system is also active in ethylene and 1-hexene copolymerization, producing LLDPE having a narrow molecular weight distribution (1.8±2.6), indicating /homogeneity in the nature of the surface active species.…”

“…The resulting solid was washed with 12 Â 2.0 mL of toluene and dried under vacuum for 4 h. The resultant catalysts contained 0.85 wt% Zr/SiO 2 determined by Rutherford backscattering spectrometry. 12,13 Polymerization Ethylene copolymerizations were performed in 0.3 L of toluene in a 1.0 L Pyrex glass reactor connected to a constant temperature circulator, equipped with a mechanical stirrer, and inlets for argon and the monomer. MAO was used as co-catalyst in an Al/Zr molar ratio of 2500.…”

“…In previous works, 12,13 we studied the in¯uence of several parameters in the immobilization of (nBuCp) 2 ZrCl 2 on silica, taking into account the grafted metal content, together with the ethylene polymerization activity. Based on a series of results we were able to develop an optimized (nBuCp) 2 ZrCl 2 supported catalyst.…”

Copolymerization of ethylene and 1-hexene with supported metallocene catalysts: Effect of support treatment

“…The Al content in SMAO, reported by WITCO, is 24.4 wt.-%. The Al content for MAO-treated silica was estimated to be approximately 7 wt.-%, based on values published in the literature for a similar supporting procedure 11) . Bridged or non-bridged zirconium or hafnium catalysts were individually supported onto these three supports.…”

Catalisadores metalocênicos suportados para a produção de poliolefinas: revisão das estratégias de imobilização

“…Devido ao MAO ser um componente volumoso, ele apresenta ainda um efeito estérico sobre os grupos hidroxila residuais da superfície, impedindo uma reação subsequente. Diferentes metalocenos têm sido suportados sobre sí-lica modificada com MAO ou TMA, 82 sempre exibindo uma menor atividade catalítica em relação ao sistema homogêneo devido, provavelmente, ao número reduzido de sítios ativos. Complementarmente, Novokshonova et al 24 verificaram que a sílica, tratada previamente com MAO, apresenta uma redução da disponibilidade de metilas reativas para a ativação do catalisador, uma vez que parte deles foi consumida na reação com os grupos hidroxilas do suporte.…”