Mechanistic study on the metallocene-based tandem catalytic coordinative chain transfer polymerization for the synthesis of highly branched polyolefins

Abstract

Creation and control of long-chain branches (LCBs) in coordination polymerization of olefins is an enduring focus of research in both academia and industry. We have recently introduced a tandem catalytic coordinative chain transfer polymerization reaction where upon the concerted function of the polymerization catalyst, the chain transfer agent (CTA), and the displacement catalyst, a highly branched microstructure can be formed. Here we introduce a new tandem catalytic system using Et(Ind)2ZrCl2 as the polymerization catalyst. Despite the optimal reaction temperature for the cooperative function of catalyst components is lower than the ideal temperature for the productivity of the metallocene catalyst, the formation of branches is evident from the decrease and broadening of melting peaks and deviation of rheological properties from characteristic behavior of linear chains in cole–cole plots. Surprisingly, the introduction of the displacement catalyst in CCTP of 1-hexene resulted in low yields and too short polymer chains. Accordingly, we elaborate on the mechanism of this reaction, specifically, we show how the optimal conditions for the (BiPy)2FeEt2 displacement catalyst depend on the monomer type. Namely, the presence of a β–agostic interaction in the bimetallic intermediate formed by the CTA and the displacement catalyst alters the structure of the latter when monomers longer than ethylene are present. This report suggests that our proposed method for the synthesis of branched polyolefins has a great potential for being used in the currently available industrial plants that employ classic metallocene catalysts.