Fast and selective ring-opening polymerizations by alkoxides and thioureas

Area of Science:

• Polymer Chemistry
• Organic Synthesis
• Catalysis

Background:

• Ring-opening polymerization (ROP) of lactones is crucial for synthesizing functional polyesters.
• Existing catalysts often face challenges balancing polymerization rate and selectivity.

Purpose of the Study:

• To develop a new catalytic system for ROP of lactones that overcomes the rate-selectivity trade-off.
• To achieve rapid and highly selective polymerization of lactones, specifically L-lactide.

Main Methods:

• Development of a catalytic system combining alkoxides with thioureas.
• Generation of alcohol-bonded thioimidate species through deprotonation.
• Investigation of the ROP of L-lactide using the developed catalyst.
• Characterization of polymer properties including molecular weight distribution and tacticity.
• Computational studies to elucidate the catalytic mechanism.

Main Results:

• The alkoxide-thiourea system demonstrated rapid and selective ROP of L-lactide.
• Produced highly isotactic polylactide with narrow molecular weight distributions (M_w/M_n < 1.1).
• Exhibited living polymerization behavior with minimal transesterification, confirmed by chain extension experiments.
• Computational studies revealed a bifunctional catalytic mechanism involving selective activation of monomer and initiator/chain end.

Conclusions:

• The developed catalytic system effectively addresses the limitations of traditional ROP catalysts.
• This approach enables efficient synthesis of well-defined polyesters with high stereocontrol.
• The bifunctional mechanism provides insights into achieving high selectivity in lactone polymerization.