Bis(8-quinolinolato)aluminum ethyl complexes: Iso-Selective Initiators for <i>rac</i>-Lactide Polymerization

The synthesis and characterization of a series of bis­(8-quinolinato)­aluminum
ethyl complexes, substituted at the 2-, 5-, and 7- positions on the
8-quinolinol ligand, are presented. These complexes are viable initiators
for the ring-opening polymerization of rac-lactide
in the presence of 1 equiv of isopropyl alcohol. The polymerization
control is good, it shows a linear evolution of molecular weight as
the polymerization progresses, the polylactide molecular weights are
in close agreement with those determined on the basis of the reaction
stoichiometry, and the polydispersity indices are narrow. The polymerization
kinetics have been monitored, and the influence of the site of ligand
substitution has been related to the rates. Some of the initiators
show stereocontrol, producing PLA with a good probability of isotactic
enchainment (Pi = 0.76).