Biomacromolecules 2002, 3, 684-690
684
Controlled Synthesis of Star-Shaped L-Lactide Polymers Using New Spirocyclic Tin Initiators Anna Finne and Ann-Christine Albertsson* Department of Polymer Technology, Royal Institute of Technology, SE-100 44 Stockholm, Sweden Received January 15, 2002
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 1H NMR and differential scanning calorimetry (DSC). The 1H 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 °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, 93%, and the yields were very high. There was no induction period prior to polymerization. When the molecular weight of the star-shaped polymer was compared to that of the corresponding linear polymers with SEC, it was shown that the star-shaped polymer had a smaller hydrodynamic volume. The different molecular architectures of the polymers were also confirmed through 1H NMR and DSC. All the polyesters possessed a star-shaped structure, and from these results, it is evident that the new spirocyclic tin initiators are a very attractive class of new functionalized tin alkoxides. Acknowledgment. The authors thank The Swedish Research Council, previously The Swedish Research Council for Engineering Sciences (TFR), Grant No 2001-1604 (1999658), and The Royal Institute of Technology for financial support of this work. References and Notes (1) Leenslag, J. W.; Gogolewski, S.; Pennings, A. J. Appl. Polym. Sci. 1984, 29, 2829-2842. (2) Zhu, K. J.; Xiangzhou, L.; Shilin, Y. J. Appl. Polym. Sci. 1990, 39, 1-9. (3) Tunc, D. C. Polym. Prepr. (Am. Chem. Soc., DiV. Polym. Sci.) 1986, 27, 431-434. (4) Chen, X.; McCarthy, S. P.; Gross, R. A. Macromolecules 1997, 30, 4295-4301. (5) Jacob, S.; Majoros, I.; Kennedy, J. P. Macromolecules 1996, 29, 9, 8631-8641. (6) Tian, D.; Dubois, P.; Grandfils, C.; Jerome, R. Macromolecules 1997, 30, 406-409.
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