Polylactones, 19. Anionic polymerization of L‐lactide in solution

The anionic polymerization of L‐lactide was studied with four potential initiators of different basicity: potassium benzoate, potassium phenoxide, potassium tert ‐butoxide and butyllithium. Regardless of the solvent, only the two most basic initiators proved to be reactive enough to initiate and maintain the polymerization. This result and the formation of benzyloxy end‐groups upon addition of benzyl bromide prove that the polymerizations proceed via alkoxide chain ends. Absence of initiator fragments in the isolated polylactide chains suggests that initiation mainly involves deprotonation of L‐lactide, whereas nucleophilic substitution only occurs to a minor extent. Furthermore, optical rotation measurements indicate that both the initiator and the alkoxide chain end cause partial racemization regardless of solvent and temperature. Furthermore, it was found that reagents such as triethylamine, pyridine or potassium benzoate which are not reactive enough to initiate polymerization, are basic enough to cause partial racemization of L ‐lactide by deprotonation.