Electronic Activity Tuning of Acyclic Guanidines for Lactide Polymerization

Novel aromatic guanidine-based organocatalysts for the ring-opening of l-lactide were synthesized and applied in comprehensive polymerization experiments and kinetic studies. The introduction of electronically active substituents led to a significant change in activity by 2 orders of magnitude. The formed polylactide is featured with narrow polydispersity and high end-group fidelity, both characteristics that are typical for living polymerizations. Besides that, using linear free-energy relationships and DFT calculations revealed new insights into the polymerization mechanism. The formation of an adduct consisting of the catalyst and initiator/chain end turned out to be the rate-limiting step.