Group 12 and 13 metal-alkenyl promoted generation of long-chain branching in metallocene-based polyethylene

•Discrete B-, Al-, Mg- and Zn-alkenyl species, namely B(pent-4-enyl)3 (B-2), Al(pent-4-enyl)3 (Al-2), Mg(pent-4-enyl)2 (Mg-2) and Zn(oct-7-enyl)2 (Zn-1), were used as long-chain branching promoters.•Ethylene polymerization with rac-{EBTHI}ZrCl2 (Zr-1) and (nBuCp)2ZrCl2 (Zr-2)/MAO systems in the presence of the M−alkenyl co-reactants was studied.•The use of B-2 and Al-2 induced a change of the rheological behavior of the PEs compatible with the formation of LCB.•PEs obtained with B-2 were characterized as cross-linked structures incorporating hydrolytically stable B-centered branches.•DFT calculations were in agreement with the experimental data.