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.