Methylaluminoxane-free ethylene polymerization with in situ activated zirconocene triisobutylaluminum catalysts and silica-supported stabilized borate cocatalysts

Abstract

Heterogenization of tris(pentafluorophenyl)borane [B(C6F5)3] on a silica support stabilized with chlorotriphenylmethane (CICPh3) and N,N-dimethylaniline (HNMe2Ph) creates the following supported borane cocatalysts: [HNMe2Ph]+[B(C6 F5)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(C6F5)3 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(C6 F5)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.