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 H-1 NMR and differential scanning calorimetry (DSC). The H-1 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 degreesC. 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. H-1 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).