Position Makes the Difference: Electronic Effects in Nickel-Catalyzed Ethylene Polymerizations and Copolymerizations

Area of Science:

• Organometallic Chemistry
• Polymer Chemistry
• Catalysis

Background:

• Development of efficient single-component catalysts for olefin polymerization is crucial.
• Tuning ligand electronic and steric properties is key to controlling catalyst performance.

Purpose of the Study:

• To synthesize and characterize novel phosphine-sulfonate nickel complexes.
• To investigate the impact of systematically varied electronic substituents on catalyst activity and polymer properties.
• To explore the copolymerization capabilities of the most active catalyst.

Main Methods:

• Synthesis and characterization of phosphine-sulfonate ligands and nickel complexes.
• Ethylene polymerization studies using single-component catalysts.
• Analysis of polyethylene molecular weight (M_n) and melting point (T_m).
• Copolymerization of ethylene with various functional monomers.

Main Results:

• Nickel complexes with phosphine-sulfonate ligands were successfully prepared.
• Catalyst activity was influenced by substituent type and position; electron-donating groups at position X and electron-withdrawing groups at position Y were beneficial.
• The catalyst with a NMe₂ substituent at position X showed high activity (3.3 × 10⁶ g mol^-1 h^-1), producing high molecular weight (M_n 405,000) and high melting point (T_m 138.5 °C) polyethylene.
• Efficient copolymerization with methyl 10-undecenoate, 6-chloro-1-hexene, and trimethoxyvinylsilane was achieved.

Conclusions:

• Systematic variation of substituents on phosphine-sulfonate ligands allows fine-tuning of nickel catalyst performance for ethylene polymerization.
• The optimized catalyst demonstrates high activity, stability, and produces high-quality polyethylene.
• The catalyst is versatile, enabling efficient copolymerization with functionalized monomers.