Ultrahigh Branching of Main‐Chain‐Functionalized Polyethylenes by Inverted Insertion Selectivity

Branched polyolefin microstructures resulting from so‐called “chain walking” are a fascinating feature of late transition metal catalysts; however, to date it has not been demonstrated how desirable branched polyolefin microstructures can be generated thereby. We demonstrate how highly branched polyethylenes with methyl branches (220 Me/1000 C) exclusively and very high molecular weights (ca. 10⁶ g mol^?1), reaching the branch density and microstructure of commercial ethylene–propylene elastomers, can be generated from ethylene alone. At the same time, polar groups on the main chain can be generated by in‐chain incorporation of methyl acrylate. Key to this strategy is a novel rigid environment in an α‐diimine Pd^II catalyst with a steric constraint that allows for excessive chain walking and branching, but restricts branch formation to methyl branches, hinders chain transfer to afford a living polymerization, and inverts the regioselectivity of acrylate insertion to a 1,2‐mode.