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Abstract Polyolefins with periodic unsaturation in the backbone chain are sought after for synthesizing chemically recyclable polymers or telechelic polyolefin macromonomers. Here we introduce a bottom‐up synthesis of unsaturated high‐density polyethylene (HDPE) via copolymerization of ethylene with dimethyl 7‐oxabicyclo[2.2.1]hepta‐2,5‐diene‐3,5‐dicarboxylate followed by post‐polymerization retro‐Diels–Alder to unveil hidden double bonds in the polymer backbone. The incorporation of this “Trojan Horse” comonomer was varied and a series of unsaturated HDPE polymers with block lengths of 1.2, 1.9, and 3.5 kDa between double bonds was synthesized. Cross metathesis of unsaturated HDPE samples with 2‐hydroxyethyl acrylate yielded telechelic ester terminated PE macromonomers suitable for the preparation of ester‐linked PE. These materials were depolymerized and repolymerized, making them suitable candidates for chemical recycling. The ester‐linked PE displayed thermal and mechanical properties comparable to commercial HDPE. 

We report the design and synthesis of an α-diimine PdII catalyst that copolymerizes functionalized and long chain α-olefins to produce semicrystalline polyethylene materials. Through a chain-straightening polymerization mechanism, the catalyst afforded high-melting point polymers with Tm values of up to 120 °C. The chain-straightening polymerization operates with high [ω,1]-insertion selectivity at high alkene concentrations and with varying α-olefin chain lengths, including propylene. The Pd catalyst can copolymerize 1-decene and methyl decenoate into semicrystalline ester-functionalized polymers with incorporation percentages proportional to the comonomer ratio (up to 13 mol %). 13C nuclear magnetic resonance and isotope labeling studies revealed that the improved selectivity relative to those of other systems arises from a high selectivity for [2,1]-insertion (96%) coupled with rapid chain-walking for a total of 90 mol % of 1-decene undergoing net [10,1]-insertion.