Nonalternating Chain Walking Polymerization Enables In-Chain Ketone Polyolefin Elastomers

Abstract Millions of tons of polymer waste are generated annually from branched polyethylene-based single-use packaging and agricultural films, constituting a pressing global environmental concern. Nonalternating carbonylative chain walking polymerization offers a promising strategy, whereas fundamentally constrained by the intrinsic kinetic incompatibility between nonalternating insertion and chain walking tendency. Here, we employ an α-imino-ketone nickel platform featuring both electronic asymmetry and axial shielding to circumvent this kinetic challenge, enabling the synthesis of high-molecular-weight (up to 476 kg mol–1), branched polyethylene plastics and elastomers featuring well-defined in-chain ketone functionalities. Nonalternating carbonyl insertion into the branched polyethylene backbone preserves its bulk material properties, while imparting desirable degradability and improving compatibility with polar materials. Notably, the polarity and sufficient branching density render keto-modified polyolefin elastomers as a promising candidate in polar-filler-reinforced polyolefin composites. This work presents a versatile catalyst platform for the synthesis of sustainable polyolefins with tunable properties and degradability.