Ethylene polymerization with "constrained-geometry" titanium catalysts over borate-modified silica supports

Two different mesopropus silica materials, Sylopol(R) 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 an dB-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(eta(5):eta(1)-C5Me4SiMe2NR)X-2 (R = Me, Pr-i, Bu-r; 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(eta(5):eta(1)-C5Me4SiMe2NR)X-2/Ph3C+ [B(C6F5)(4)](-), whereas that of the B-MPS5 system was lower. These supported catalysts produced polyethylenes with higher molecular weights ((M) over bar (w) in the range of 106), narrower molecular weight distributions ((M) over bar (w)/(M) over bar (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 wit the B-Sylopol system, while well-shaped polyethylene spheres were formed with the B-MPS5 system.