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 degreesC the polymerization is fast and goes up to completion in few minutes. In toluene, due to solubility requirements, polymerizations were run at 70 degreesC. At initial stage of polymerization M-w/M(n)s were quite narrow, but at higher conversion a significant broadening occurred due to transesterification reactions. The latter were identified by C-13 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. (C) 2001 Elsevier Science Ltd. All rights reserved.