Living ring-opening polymerization of L,L-lactide initiated with potassium t-butoxide and its 18-crown-6 complex

Living polymerization of L,L-lactide initiated by potasium t-butoxide and its 18-crown-6 complex was investigated in THF solution at room temperature. The results support a reversible polymerization mechanism consisting of first order in monomer propagation and of unimolecular depropagation. The presence of 18-crown-6 has a strong MWD narrowing effect (Mw/Mn<1.2), slows down the overall rate of polymerization and gives rise to slow initiation. The polymerizations yield optically pure polymers both in the presence and absence of 18-crown-6.