SnOct2-catalyzed ROPs of l-lactide initiated by acidic OH- compounds: Switching from ROP to polycondensation and cyclization

Abstract

Ring-opening polymerizations (ROPs) of l-lactide are performed in bulk at 130°C with tin(II) 2-ethylhexanoate as catalyst and various phenols of different acidity as initiators. Crystalline polylactides having phenyl ester end groups are isolated, which are almost free of cyclics. The dispersities and molecular weights are higher than those obtained from alcohol-initiated ROPs under identical conditions. Polymerizations at 160°C yield higher molecular weights than expected from the monomer/initiator ratio and a considerable fraction of cycles. The fraction of cycles increases with higher reactivity of the ester end group indicating that the cycles are formed by end-to-end cyclization.