Stereoselective polymerization of racemic dl-lactide in the presence of butyllithium and butylmagnesium. Structural investigations of the polymers

The use of butyllithium and butylmagnesium in the polymerization of racemic lactide leads to the formation of polylactide with a partially disyndiotactic structure. A coefficient of stereoselectivity p2 which describes the content of disyndiotactic structures appears to be higher for the lithium initiator; however an increase in the concentration of this initiator tends to enhance an intermolecular transesterification process thus leading to the formation of totally random structures in a polylactide chain. In contrast, in the case of butylmagnesium, an increase in the initiator concentration does not induce the intermolecular transesterification processes.