Mechanism of dispersion polymerization of L-lactide initiated with 2,2-dibutyl-2-stanna-1,3-dioxepane |
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Authors: | S Sosnowski S Slomkowski A Lorenc H R Kricheldorf |
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Institution: | Center of Molecular and Macromolecular Studies, Polish Academy of Sciences Sienkiewicza 112, 90-363 Lodz, Poland e-mail: stasosno@bilbo.cbmm.lodz.pl Tel: + 48-42-6819815 Fax: + 48-42-6877126, PL Institut für Technische und Makromolekulare Chemie der Universit?t Hamburg, Bundesstrasse 45 20146 Hamburg, Germany, DE
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Abstract: | Biodegradable polyester microspheres were synthesized directly by ring-opening polymerization of l-lactide initiated with 2,2-dibutyl-2-stanna-1,3-dioxepane. The polymerizations were carried out at 95 °C in a mixture of
organic solvents (heptane/1,4–dioxane 4:1 v:v), in the presence of poly(dodecyl acrylate)-g-poly(ɛ-caprolactone) used as a surface-active agent. Under these conditions the poly(L-lactide) synthesized was shaped into microspheres. The absence of new particles in the polymerizations with multistep monomer
addition indicated that after the formation of particle seeds the propagation proceeds exclusively inside the microspheres.
The mean volume of these microspheres was proportional to the monomer conversion. It was found that regardless of the initiator
concentration the average number of poly(L-lactide) macromolecules in one microsphere was 1.84 × 108. Matrix-assisted laser desorption ionization time of flight spectroscopy of poly(L-lactide) in the microspheres indicated that the propagation in the particles was accompanied by intra- and intermolecular
transesterification side reactions, resulting in reshuffling of the polymer segments and the formation of cyclic oligomers.
Received: 20 December 2000 Accepted: 7 June 2001 |
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Keywords: | l-Lactide Dispersion polymerization Formation of microspheres |
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