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

Abstract

High Resolution Image Download MS PowerPoint Slide 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.