Organocatalysts in Ring-Opening Polymerization: Revealing Their Effect on Stereochemistry

Organocatalysts derived from thioureas and amines commonly play a part in ring-opening polymerization (ROP) of lactone monomers such as 8-valerolactone and mandelic o-carboxyanydride. Organocatalysts have a dual role in ROP reactions they create a balance between the rate and the selectivity; the fate of the reaction depends on their structure, the presence of the co-initiator and the degree of basicity. These parameters eventually determine the stereochemistry of the final product which is highly associated with the activation mechanism of the monomer. Thereupon, we performed a computational study to understand the course of action of several organocatalysts combined with co-initiators having different basicities and we have thus shed light on the tacticity of the products by using density functional theory (DFT). Calculations have shown that electron withdrawing CF3 groups on the benzene ring significantly ensure the selectivity through hydrogen bonding, while the balance between nucleophilicity and basicity of pyridine determines the reaction pathway. We have also demonstrated that bifunctional organocatalysts can be tuned to increase the isotactic yield in the ROP reaction of mandelic o-carboxyanydride.