Journal of Polymer Science Part A: Polymer Chemistry, Vol.40, No.19, 3240-3248, 2002
Methylaluminoxane-free ethylene polymerization with in situ activated zirconocene triisobutylaluminum catalysts and silica-supported stabilized borate cocatalysts
Heterogenization of tris(pentafluorophenyl)borane [B(C6F5)(3)] on a silica support stabilized with chlorotriphenylmethane (CICPh3) and NN-dimethylaniline (HNMe2Ph) creates the following supported borane cocatalysts: [HNMe2Ph](+) [B(C6F5)(3) -SiO2](-) and [CPh3](+) [B(C6F5)(3)-SiO2](-). These supported catalysts were reacted with Cp2ZrCl2 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 (Cp2ZrC4H9+). 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,F,),, dispersed uniformly on the silica support. Under our reaction conditions, the [CPh3](+) [B(C6F5)(3) -SiO2- system had higher productivity and weight-average molecular weight than the [HNMe2Ph](+) [B(C6F5)(3)- SiO2 - system. For the [CPh3](+)- [B(C6F5)(3)-SiO2](-) - 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 [CPh3](+) [B(C6F5)(3)-SiO2 - catalysts had larger diameters.