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

In situ synthesis of topologically modified linear polyethylenes (PEs) using single-site polymerization catalysis is a challenging task that enables the production advanced materials with tailored properties. We describe here our investigations aimed at an efficient generation long-chain branches (LCB) in PEs discrete B-, Al- and Zn-alkenyl co-reagents combination homogeneous rac-{EBTHI}ZrCl2 (1)/ or (nBuCp)ZrCl2 (2)/MAO catalytic systems. As corroborated by extensive rheological studies 13C NMR spectroscopy, Al-and Zn-based reagents promote LCB formation via two-step mechanism involving both vinylic group insertion M → Zr transmetallation steps. striking contrast, B-alkenyl species was found to form hydrolytically stable B-centred cross-linked PE structures. The Mg-based reagent appeared be reluctant towards Mg reaction, providing only products insertion, which after hydrolysis afforded short-chain branched (SCB) PEs. experimental observations were rationalized DFT computations.