Titanium ONN-(phenolate) Alkoxide Complexes: Unique Reaction Kinetics for Ring-Opening Polymerization of Cyclic...

Area of Science:

• Organometallic Chemistry
• Polymer Science
• Catalysis

Background:

• Titanium alkoxide complexes are valuable catalysts in polymerization.
• Understanding catalyst behavior and reaction mechanisms is crucial for developing new materials.

Purpose of the Study:

• To synthesize and characterize novel titanium ONN-(phenolate) alkoxide catalysts.
• To investigate the polymerization kinetics of ε-caprolactone (CL) and rac-lactide (LA) using these catalysts.
• To elucidate the mechanistic pathways involved in the ring-opening polymerization of CL and LA.

Main Methods:

• Synthesis and characterization of four new titanium catalysts.
• Ring-opening polymerization experiments with CL and LA.
• Gel Permeation Chromatography (GPC) for molecular weight analysis.
• Kinetic studies to determine reaction orders and analyze mechanistic models.

Main Results:

• All synthesized titanium catalysts demonstrated activity in the ring-opening polymerization of both CL and LA.
• GPC analysis confirmed the coordination-insertion mechanism for both polymerizations.
• While CL polymerization showed first-order kinetics, LA polymerization exhibited an unexpected zeroth-order dependence, indicating catalyst saturation.
• A Michaelis-Menten model was proposed to explain the observed kinetics for LA polymerization, suggesting different coordination intermediates.

Conclusions:

• The new titanium catalysts are effective for polymerizing CL and LA.
• Distinct mechanistic pathways, involving different coordination intermediates (7-coordinate for CL, 6-coordinate for LA), are proposed based on kinetic data.
• Further studies are underway to isolate and characterize catalyst-monomer intermediates.