Abstract
Two different mesoporous silica materials, Sylopol® 948 and MPS5, were used as substrates for the preparation of silica-bound trityl tris(pentafluorophenyl)- borate activators. The borate-modified silica supports, B- Sylopol and B-MPS5, were characterized by solid-state NMR spectroscopy and ICP mass spectrometry, and applied as activators for slurry polymerization of ethylene using constrained-geometry titanium complexes of the formula Ti(η 5 :η 1 -C 5 Me 4 SiMe 2 NR)X 2 (R = Me, i Pr, t Bu; X = Me, Bz, Cl) in the presence of triisobutylaluminium (TIBA). The activity of the B-Sylopol system was higher than that of the corresponding homogeneous catalysts Ti(η 5 :η 1 -C 5 Me 4 SiMe 2 NR)X 2 /Ph 3 C + [B(C 6 F 5 ) 4 ] - , whereas that of the B-MPS5 system was lower. These supported catalysts produced polyethylenes with higher molecular weights (M w in the range of 10 6 ), narrower molecular weight distributions (M w /M n = 1.5-2.3) and higher bulk densities (up to 0.4 g/cm 3 ) compared to those of polyethylenes obtained with the homogeneous system. The resulting polyethylenes were found to replicate the shapes of the supported borate activators. Fine polyethylene particles due to the cracking of the support were observed with the B-Sylopol system, while well-shaped polyethylene spheres were formed with the B-MPS5 system.
Published Version
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