Mechanistic Insights into Cationic [P,O]-Pd-Catalyzed Chain-Transfer Copolymerization of Ethylene with Carbon Monoxide

The copolymerization of olefins with carbon monoxide (CO) affords aliphatic polyketones, which exhibit excellent mechanical strength, crystallinity, photodegradability, hydrophilicity, and surface and barrier properties. The chain-transfer copolymerization of ethylene with CO has offered an available method to regulate the molecular weight of polyketones that are amenable to conventional injection molding and extrusion. In this study, we investigated the copolymerization pathway using the [P,O]-Pd catalyst in a protonic environment. The key chain-propagating species are identified by state-of-the-art electrospray ionization mass spectrometry. These findings indicate that the copolymerization can be performed in different protonic solvents in a chain-transfer fashion; thus, the molecular weight of polyketone products can be regulated over the range of 8.13–238 kg/mol. In particular, such a chain-transfer method renders the formation of novel telechelic structures having a ketone backbone and diester chain ends selectively. The differences between [P,O]-Pd and diphosphine–Pd catalysts have been disclosed, and this study provides insights into the discovery and design of novel catalysts for this interesting copolymerization reaction.