Late Metal Sandwich Catalysts for Olefin Polymerization

Area of Science:

• Polymer Chemistry
• Organometallic Chemistry
• Materials Science

Background:

• Polyolefins are crucial industrial polymers, typically made with early transition metal catalysts.
• Early metal catalysts lack functional group tolerance and produce linear polyethylene, requiring comonomers for branching.
• Developing new catalysts for controlled polyolefin synthesis is essential for advanced materials.

Purpose of the Study:

• To design and implement novel palladium(II) and nickel(II) olefin polymerization catalysts.
• To understand the mechanism of chain growth for improved polymer synthesis.
• To create new polymer architectures with tailored properties.

Main Methods:

• Synthesis of hindered nickel- and palladium-aryl-substituted diimine complexes.
• Mechanistic investigations of chain growth and chain transfer processes.
• Molecular modeling to design novel 'sandwich' catalyst structures with enhanced axial shielding.

Main Results:

• Developed Pd(II) and Ni(II) catalysts with ortho-disubstituted aryl groups and 'sandwich' structures.
• Achieved living polymerization of ethylene, producing ultrahigh molecular weight polyethylenes (Mw > 10^7 Da) with narrow molecular weight distributions.
• Controlled polymer branching (9-100 per 1000 carbons) and thermal properties (Tm 17-132 °C) by varying reaction conditions.
• Synthesized diblock and multiblock copolymers with controlled molecular weights and segment lengths.

Conclusions:

• Late metal catalysts, particularly Ni(II) and Pd(II) diimine complexes, offer significant advantages over early metal catalysts.
• Novel 'sandwich' catalysts provide exceptional control over molecular weight, branching, and polymer architecture.
• These advancements enable the synthesis of advanced polyolefins with tunable mechanical properties and potential applications as compatibilizers.