Sterically hindered phosphine and phosphonium-based activators and additives for olefin polymerization

Area of Science:

• Organometallic Chemistry
• Polymer Science
• Catalysis

Background:

• Titanocene catalysts are crucial for olefin polymerization.
• Activator choice significantly impacts catalyst performance and polymer properties.
• Understanding activator-cocatalyst interactions is key to designing efficient polymerization systems.

Purpose of the Study:

• To investigate the efficacy of novel phosphonium borates and phosphine-boranes as activators for CpTiMe2(NPtBu3) in olefin polymerization.
• To elucidate the role of liberated phosphine donors on catalyst activity.
• To explore the influence of phosphine sterics on catalytic performance.

Main Methods:

• Stoichiometric reactions were performed to study activator-ligand interactions.
• Catalytic ethylene polymerization experiments were conducted using various phosphonium borate and phosphine-borane activators.
• Independent experiments involving the addition of different phosphine ligands to the active catalyst systems were carried out.

Main Results:

• The activators generally yielded highly active ethylene polymerization catalysts.
• Liberated phosphine donors were observed, with small phosphines decreasing activity.
• Sterically encumbered phosphines led to a notable increase in catalyst activity.

Conclusions:

• Phosphonium borates and phosphine-boranes are effective activators for titanocene-based olefin polymerization.
• The steric bulk of phosphine ligands plays a critical role in modulating catalyst activity.
• The observed increase in activity with bulky phosphines may be explained by the concept of frustrated Lewis pairs.