Synthesis of Polyethylenes with In-Chain Isolated Carbonyls from CO2 and Ethylene via a Tandem Photoreduction/Polymerization Protocol

Aiming at accessing polyethylene-bearing in-chain degradable functionality, copolymerization of carbon dioxide (CO2) with ethylene has long been recognized as a significant but highly challenging transformation. Nevertheless, most trials have resulted in ethylene homopolymerization because of the endothermic property and high energy barriers of CO2 insertion during polymer chain propagation. Here we report an unprecedented tandem reaction protocol for the synthesis of polyethylenes with in-chain carbonyls from CO2 and ethylene by the combination of photocatalytic CO2 reduction and palladium-catalyzed coordination/insertion polymerization. This protocol provides an easy way to adjust the carbonyl content (from 0.13 to 12 mol %) and insertion selectivity (up to 99% isolated carbonyls) of the polyethylene copolymers, which enables the polymers to maintain the main properties of high density polyethylene and simultaneously endows them with good photodegradability. In addition, besides apolar polyethylene copolymers, polar-functionalized polyethylenes with in-chain isolated carbonyls can also be synthesized from CO2, ethylene and a polar monomer using the same protocol. We believe our present work sheds new light on the synthesis of degradable polyethylenes by employing CO2 as a green carbonyl source.