Al-alkenyl-induced formation of long-chain branched polyethylene via coordinative tandem insertion and chain-transfer polymerization using (nBuCp)2ZrCl2/MAO systems: An experimental and theoretical study

Recently, we have identified the Al-alkenyl species iBuAl(oct-7-en-1-yl)2 (Al-1) as a promising long-chain branching (LCB) promoter in ethylene polymerization catalyzed by rac-{EBTHI}ZrCl2-based systems, proposing incorporation of its alkenyl moiety into growing polyethylene (PE) chain crucial step for LCB formation. The success process was attributed to high copolymerization ability selected catalyst. In present contribution, aimed at probing efficiency Al-1 combination with catalyst systems based on unbridged metallocene (nBuCp)2ZrCl2 (Zr-1), namely homogeneous Zr-1/MAO or heterogeneous MAO silica-supported-Zr-1/TIBAL (supp-Zr-1/TIBAL); literature, such are claimed be less efficient catalysts compared bridged (i.e. rac-{EBTHI}ZrCl2). fact, while supported produces only purely linear PEs, branched structures were obtained presence congener homogenous system. Remarkably, qualitative rheological data suggest that extent formation samples is comparable PEs synthesized under similar reaction conditions EBTHI/MAO/Al-1 This testifies suitable promoter, even metallocenes having quite different (at least series). rationalized considering Zr/Al heterobimetallic facilitating via coordinative tandem insertion and chain-transfer mechanism, previous study, new DFT computations.