Dihydroxy-terminated poly(L-lactide) obtained by controlled ring-opening polymerization : Investigation of the polymerization mechanism

Hydroxy telechelic poly(l-lactide)s of different molecular weight have been synthesized by controlled ring-opening polymerization using cyclic tin alkoxides. NMR analysis showed that the propagation proceeded through an insertion mechanism. No free hydroxyl or carboxyl end groups were detected in the polymerization mixture. Complete reaction of the initiator was observed over the entire range of compositions studied. Both tin−oxygen bonds were reactive and participated in the propagation reaction. Peak assignments were obtained by 1H, 13C, distortionless enhancement polarization transfer (DEPT), and heteronuclear multiple quantum coherence−gradient selected (hmqc-gs) nuclear magnetic resonance spectroscopy. The kinetics of the solution polymerization of l-lactide has been investigated and showed a first order in monomer. The external order in initiator has been determined to be 3/4 for initiator concentrations above 5 mmol/L and to 2 below 2 mmol/L. The molecular weight could easily be adjusted by the mon...