Multimodal Polypropylene Synthesis Using Cyclic Borane Cocatalyst

A strategy for synthesizing bimodal isotactic polypropylene (iPP) using a C₂-symmetric zirconocene catalyst is reported. Unlike conventional multimodal polymerization methods requiring multireactor systems or multiple catalysts, our approach exploits multiple counteranions derived from a boron-based cocatalyst 1. Propylene polymerization using zirconocene 2 produced polypropylene with a bimodal molecular weight distribution when combined with cocatalyst 1 without losing stereospecificity. Chain-end analyses of the polymer obtained by using 1 confirmed different chain propagation and termination propensities compared with the polymer from a conventional borane activator, B(C₆F₅)₃, explaining the observed bimodal nature. Notably, this molecular weight distribution could be tuned by the polymerization temperature and solvent, highlighting the potential for the control of these termination reactions.