Comonomer-controlled synthesis of long-chain branched (LCB)-polyethylene

In this contribution, we disclose the ability of α,ω-diene comonomers, namely 1,7-octadiene and 1–10-undecadiene, as long-chain branching (LCB)/cross-linking promoters in the ethylene polymerization catalyzed by bis(indenyl) and bis(cyclopentadienyl) catalyst systems, namely rac-{EBTHI}ZrCl2 (Zr-1) and (nBuCp)2ZrCl2 (Zr-2). Both under homogeneous and heterogeneous (slurry) conditions, Zr-1-based systems efficiently produced LCB/cross-linked polymers even with very small amounts of diene, as demonstrated by melt rheology measurements. On the other hand, higher co-monomer concentrations were required for the homogeneous Zr-2/MAO system, while only linear PEs were isolated in the presence of its silica-supported version supp-Zr-2 operated under heterogeneous conditions, regardless of the amount of diene employed. Rheological and NMR spectroscopy studies proved that consumption of the diene and formation of LCB/cross-linked structures take place during the early stages of the polymerization. The experimental observations were rationalized by DFT computations.