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

Area of Science:

• Polymer Chemistry
• Catalysis
• Materials Science

Background:

• Ethylene and carbon monoxide copolymerization is a key route to functional polyolefins.
• Achieving nonalternating copolymers with desirable material properties requires precise control over monomer reactivity and catalyst performance.

Purpose of the Study:

• To synthesize keto-polyethylenes (keto-PEs) with properties similar to high-density polyethylene (HDPE).
• To investigate the relationship between catalyst structure, monomer reactivity, and copolymer microstructure.
• To optimize the copolymerization process for producing HDPE-like materials.

Main Methods:

• Screening of four Pd(II) phosphinosulfonate catalysts for ethylene and carbon monoxide copolymerization.
• Utilizing a customized reactor setup for controlled monomer feeding and repressurization.
• Employing density functional theory (DFT) to calculate activation free energy differences.
• Characterizing keto-PEs and comparing their mechanical properties to HDPE via tensile testing.

Main Results:

• Pd-2 catalyst, featuring a specific phosphine motif, demonstrated the highest activity, yielding copolymers with molecular weights of 30-40 kg mol⁻¹.
• The keto group microstructure correlated well with DFT-calculated activation free energy differences.
• Melt-pressed keto-PEs with 0.5 and 1.4 mol % keto groups showed mechanical properties comparable to HDPE.

Conclusions:

• Pd(II) phosphinosulfonate catalysts are effective for nonalternating ethylene/CO copolymerization.
• Catalyst design and reactor engineering are crucial for controlling copolymer microstructure and properties.
• The developed keto-PEs represent a promising alternative to traditional HDPE with tunable properties.