Amidine-Mediated Zwitterionic Polymerization of Lactide.

Area of Science:

• Polymer Chemistry
• Organic Synthesis
• Computational Chemistry

Background:

• Ring-opening polymerization (ROP) is a key method for synthesizing polyesters.
• Lactide polymerization typically requires initiators and/or metal catalysts.
• Exploring neutral organic catalysts offers a greener alternative.

Purpose of the Study:

• To investigate the efficacy of 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU) as a neutral catalyst for lactide ROP.
• To characterize the resulting polymers and elucidate the polymerization mechanism.
• To achieve controlled polymerization at room temperature without additional initiators.

Main Methods:

• Ring-opening polymerization of lactide using DBU at room temperature.
• Polymer characterization using techniques such as GPC and NMR spectroscopy.
• Density Functional Theory (DFT) calculations to model the reaction mechanism.

Main Results:

• DBU effectively catalyzes lactide ROP at room temperature without co-initiators.
• The polymerization proceeds with narrow polydispersities and a linear increase in molecular weight with conversion.
• Characterization confirmed the formation of cyclic polymers.
• DFT calculations supported a mechanism involving a zwitterionic acyl amidinium intermediate.

Conclusions:

• DBU is a highly effective neutral catalyst for the controlled ROP of lactide.
• The reaction produces cyclic polymers under mild conditions.
• The proposed mechanism provides insight into the catalytic activity of DBU in lactide polymerization.