A hyperbranched polysilane-based, borane cocatalyst for the metallocene-catalyzed polymerization of propylene

The synthesis of a vinyl-terminated, hyperbranched polysilane and the additional hydroboration with bis(pentafluorophenyl) borohydride are reported. Quantitative transformation was proved by ¹H NMR and FT-IR analysis. The polymeric borane was tested as cocatalyst in the metallocene-catalyzed polymerization of propylene. The corresponding catalyst system comprising rac-[1-(9-η⁵-fluorenyl)-2-(5,6-cyclopenta-2-methyl-1- η⁵-indenyl)ethane]zirconocene dichloride and the polymeric borane was activated in situ in the presence of triisobutylaluminum (TIBA). Polymerizations were performed at temperatures of 30 and 50°C with a propylene concentration of 3 mol/L in toluene solution using various cocatalyst: catalyst ratios (10:1, 50:1, and 100:1). This polymer-supported catalyst system produces polypropylenes with excellent activities and good molecular weights. These results were compared with an additional set of polymerization experiments using molecular dispersed B(C₆F₅)₃ as cocatalyst, resulting in significantly reduced polymerization activities. This indicates a hindered catalyst mobility inside the hyperbranched cocatalyst matrix, leading to a higher concentration of active species within the hyperbranched nanostructure.