Polyglicolides (PGA) and polylactides (PLA) are among the most promising bio-based polymers nowadays. The N-heterocyclic carbene (NHC) catalysts, which are among the most powerful metal-free catalysts, are especially useful in ring-opening polymerization (ROP). Here, the detailed mechanism of the ring-opening polymerization of glycolide, R,R-lactide and R,S-lactide catalyzed by NHC catalyst in the presence of alcohol were investigated using DFT method. Computational results showed that the general base mechanism is more favored compared to the nucleophilic mechanism. The rate-determining step involves a nucleophilic attack of the methanol on the glycolide (or R,R-lactide, R,S-lactide) coupled with a proton transfer to the NHC. The feasibility of general base mechanism was further confirmed by changing the substituents on the NHC catalyst. Calculations also suggests that our model NHC (1,3,4,5-tetramethylimidazol-2-ylidene) can react with alcohol and generate an unstable NHC-alcohol adduct. This result was extended to probe and clarify the photoswitchable ability of recently synthesized NHC 1,3-dimethyl-2,4-bis(5-methyl-2-thienyl)imodazol-2-ylidene at interest.

N-heterocyclic carbene catalyzed ring opening polymerization of glycolide and lactide: A theoretical study

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.