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Methylaluminoxane‐free Ethylene Polymerization With In Situ Activated Zirconocene Triisobutylaluminum Catalysts And Silica‐supported Stabilized Borate Cocatalysts
Published 2002 · Chemistry
Heterogenization of tris(pentafluorophenyl)borane [B(C 6 F 5 )3] on a silica support stabilized with chlorotriphenylmethane (ClCPh 3 ) and N,N-dimethylaniline (HNMe 2 Ph) creates the following supported borane cocatalysts: [HNMe 2 Ph] + [B(C 6 F 5 ) 3 -SiO 2 ] and [CPh 3 ] + [B(C 6 F 5 ) 3 -SiO 2 ]. These supported catalysts were reacted with Cp 2 ZrCl 2 TIBA in situ to generate active metallocene species in the reactor. Triisobutylaluminum (TIBA) was a good coactivator for dichloro-zirconocene, acting as the prealkylating agent to generate cationic zirconocene (Cp 2 ZrC 4 H 9 +). The catalytic performances were determined from the kinetics of ethylene-consumption profiles that were independent of the time dedicated to the activation of the catalysts. The scanning electron microscopy-energy dispersive X-ray measurements showed that B(C 6 F 5 ) 3 dispersed uniformly on the silica support. Under our reaction conditions, the [CPh 3 ] + [B(C 6 F 5 ) 3 -SiO 2 ] system had higher productivity and weight-average molecular weight than the [HNMe 2 Ph] + [B(C 6 F 5 ) 3 -SiO 2 ] system. For the [CPh 3 ] + [B(C 6 F 5 ) 3 -SiO 2 ] - system, the productivity increased with the amount catalyst; however, the polydispersity index of polyethylene synthesized did not change. The final shape of polymer particles was a larger-diameter version of the original support particle. The polymer particles synthesized with supported [CPh 3 ] + [B(C 6 F 5 ) 3 -SiO 2 ] - catalysts had larger diameters.