Anionic polymerization of d,l-lactide initiated by lithium diisopropylamide

The anionic polymerization of d,l-lactide initiated by lithium diisopropylamide.monoTHF complex was performed in different solvents and at various temperatures. No polymerization took place in THF solution. In dioxane at 25°C the polymerization is fast and goes up to completion in few minutes. In toluene, due to solubility requirements, polymerizations were run at 70°C. At initial stage of polymerization Mw/Mns were quite narrow, but at higher conversion a significant broadening occurred due to transesterification reactions. The latter were identified by 13C NMR analysis, while MALDI-TOF spectra revealed the simultaneous presence of cyclic and linear oligomers substantiating the occurrence of both intra and inter ester exchange processes. At low conversion, polymers exhibited a highly syndiotactic microstructure.