LAUSR

Abstract This research considers the features of depolymerization of lactic acid oligomers in the presence of oxide catalysts, including the study of their epimerization and the nature of interactions in the synthesis of cyclic diesters. It was shown by the polarimetric method and under depolymerization conditions that the epimerization of L -lactic acid oligomers (L-LAO) proceeds predominantly on strong basic sites of catalysts, while Lewis acid sites promote further polycondensation of oligomers. The nature of the interactions of oligomers was studied using mixtures of oligomers of different chirality. It was shown by IR spectroscopy and thermal analysis that in the case of the studied mixtures of L -LAO and D -lactic acid oligomers (D-LAO), stereocomplexes are formed. During depolymerization, meso-lactide is formed as a result of intermolecular interactions of oligomers and their epimerization. A small amount of meso-lactide can be associated with the formation of stereocomplexes based on L -LAO and D -LAO with a parallel arrangement of oligomeric molecules complicated intermolecular interactions and its lower thermodynamic stability compared to other lactide isomers.