Stereoselectivity Control Interplay in Racemic Lactide Polymerization by Achiral Al-Salen Complexes.

Area of Science:

• Polymer Chemistry
• Catalysis
• Computational Chemistry

Background:

• Ring-opening polymerization (ROP) of lactide is crucial for synthesizing biodegradable polyesters.
• Achiral catalysts achieving stereocontrol in ROP of racemic lactide remains a challenge.
• Understanding stereochemical origins is key to tailoring polymer properties.

Purpose of the Study:

• To elucidate the stereocontrol mechanism in ROP of racemic lactide using achiral aluminum catalysts.
• To investigate the interplay between enantiomorphic site control (ESC) and chain end control (CEC) models.
• To correlate computational findings with experimental data for precise polymer synthesis.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Molecular descriptor analysis (%V_Bur) to quantify steric influences.
• Activation Strain Model - Non-covalent Interaction analysis (ASM-NEDA) for reaction pathways.
• Analysis of ligand dynamics and monomer configuration effects.

Main Results:

• A novel chain end control (CEC) model was proposed, where ligands adopt chiral configurations.
• Ligand wrapping modes around the aluminum center are dependent on monomer configuration (R,R-LA and S,S-LA).
• Accurate correlation with experimental data requires considering ligand dynamics and steric effects (%V_Bur, ASM-NEDA).

Conclusions:

• The study explains stereocontrol in racemic lactide ROP by achiral aluminum catalysts through a combined CEC and ESC mechanism.
• Ligand design and understanding its dynamic and steric properties are critical for stereoselective ROP.
• This research provides insights for synthesizing biodegradable materials with controlled stereochemistry and tailored properties.