A sterically expanded "constrained geometry catalyst" for highly active olefin polymerization and copolymerization:...

Area of Science:

• Organometallic Chemistry
• Polymer Science
• Catalysis

Background:

• Constrained geometry catalysts (CGCs) are crucial in olefin polymerization.
• Steric bulk around the metal center influences catalyst activity and polymer properties.
• Incorporating bulky ligands can enhance catalyst performance.

Purpose of the Study:

• To synthesize and characterize a sterically expanded CGC incorporating a 14A octamethyloctahydrodibenzofluorene moiety.
• To evaluate the catalytic activity of the new catalyst (1) in olefin polymerization, particularly towards alpha-olefins.
• To investigate the copolymerization behavior of the catalyst with ethylene and higher alpha-olefins.

Main Methods:

• Synthesis of the constrained geometry catalyst Me2Si(eta1-C29H36)(eta1-N-tBu)ZrCl2.OEt2 (1).
• Solid-state structural analysis of the catalyst.
• Olefin polymerization and copolymerization experiments using the catalyst activated with methylaluminoxane (MAO).
• Kinetic analysis of polymerization activities.

Main Results:

• The solid-state structure of catalyst (1) indicates significant spatial accessibility.
• Catalyst (1)/MAO demonstrates extraordinary reactivity towards alpha-olefins, exceeding reactivity towards ethylene.
• Activities in copolymerization with ethylene are linearly and continuously proportional to the concentration of 4-methyl-1-pentene or 1-octene.

Conclusions:

• The sterically expanded ligand design enhances catalyst accessibility and reactivity.
• The catalyst exhibits selective reactivity towards higher alpha-olefins over ethylene.
• The observed linear relationship between activity and comonomer concentration provides insights into copolymerization kinetics.