Keto-Polyethylene Material from Pd(II)-Catalyzed Copolymerization with Continuous Carbon Monoxide Feed

Pd(II) phosphinosulfonate catalysts were employed in the nonalternating copolymerization of ethylene and carbon monoxide to produce keto-polyethylenes with high-density polyethylene-like materials properties. The different reactivities of the two monomers were addressed with a customized reactor setup that allows the feeding of ethylene and CO at very different feed ratios and automatic repressurization to replenish consumed monomers upon reaching a pressure threshold. Four literature-known catalysts were screened and the keto group microstructure of the resulting keto-PEs aligned well with the activation free energy differences (ΔΔG‡) of the alternating and nonalternating pathways, calculated via density functional theory. Pd-2 with a 2′,6′-dimethoxy-1,1′-biphenyl-substituted phosphine motif was the most active catalyst, yielding copolymers with the highest molecular weight (around 30-40 kg mol-1). Consequently, Pd-2 was subjected to further optimization of the E/CO copolymerization to obtain HDPE-like materials. Tensile-testing specimens of keto-PEs with 0.5 and 1.4 mol % of keto groups were obtained via melt pressing and exhibited mechanical properties on par with the HDPE reference material.