Polyethylene Incorporating Diels-Alder Comonomers: A "Trojan Horse" Strategy for Chemically Recyclable Polyolefins

Angew Chem Int Ed Engl. 2023 Jul 24;62(30):e202301927. doi: 10.1002/anie.202301927. Epub 2023 Jun 15.

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.

Keywords: Copolymerization; Degradable; Diels-Alder; Polyolefin; Protecting Groups.