Highly stereoelective polymerization of rac-(D,L)-lactide with a chiral Schiff's base/aluminium alkoxide initiator

A chiral Schiff's base/aluminium alkoxide initiator bearing a ligand derived from R-(+)-1,1'-binaphthyl-2,2'-diamine was synthesized and used for the stereoelective polymerization of rac-(D,L)-lactide. Rather high stereoelectivity is observed: a polymer with 88% enantiomeric enrichment in D units is obtained at 19% conversion. At high conversions a stereocomplex between D- and L-enriched stereocopolymers is formed. The polymerization reaction shows living type features, and narrow molecular weight distributions ((M) over bar(w)/(M) over bar(n) = 1,05-1,30) are obtained up to very high conversions. This indicates that transesterification reactions do not occur significantly with this sterically hindered initiator.