Controlled synthesis of star-shaped L-lactide polymers using new spirocyclic tin initiators.

The reaction between pentaerythritol ethoxylate compounds and dibutyltin oxide was developed as a route to synthesize two new spirocyclic tin initiators. The initiators were successfully synthesized and they were characterized by (1)H NMR and differential scanning calorimetry (DSC). The (1)H NMR spectra showed the characteristic signals for the methylene protons in the ether chains. Furthermore, the usefulness of the new initiators was examined in ring-opening polymerizations of L-lactide in chloroform at 60 degrees C. L-Lactide was polymerized at monomer-to-initiator ([M]/[I]) ratios between 20 and 500. The results indicated that the initiation was instantaneous and that the molecular weight distribution was very narrow, <1.13. The number average molecular weight could be controlled by the [M]/[I] ratio, and the yield was very high. (1)H NMR, size exclusion chromatography, and DSC were used to clarify the architecture. The expected results were obtained. The star-shaped polymers had a smaller hydrodynamic volume, and the melting point was lower than that obtained for the corresponding linear poly(L-lactide).