Abstract: The stepwise addition/elimination and concerted mechanisms for the methanolysis of lactide, as a model for the initiation and propagation of ring-opening polymerization, were investigated computationally using B3LYP/6-31G(d,p) density functional theory calculations, with assistance from one, two and three methanol molecules. The results show that the extra methanol molecules acting as proton shuttles play a significant role in cyclic hydrogen-bonded clusters, and result in considerable energy savings. It is found that increasing the number of the ancillary methanol is accompanied by the reduction of the energy barrier for both stepwise and concerted mechanisms. The calculated results provide a general model that explains the mechanism of the titled reaction.

Key words: Lactide, Ring-opening polymerization, Methanol, Reaction mechanism, Density functional theory