Syntheses of biodegradable (multi) block copolymers, star‐shaped polyesters and networks via ring‐expansion polymerization

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Abstract
Numerous cyclic dibutyltin alkoxides were prepared by condensation of Bu2Sn(OMe)2 with various short or long α,ω‐diols. Insertion of lactones or lactide into the SnO bonds resulted in ring‐expansion polymerizations which allowed a control of the ring size (chain length) via the monomer initiator ratio. When the cyclic initiators were derived from a long α,ω‐diol, such as poly(tetrahydrofuran)diols or polysiloxane diols, the resulting cyclic polylactones were necessarily cyclic triblock copolymers. The high nucleophilicity of the Sn‐O bond enabled ring‐opening polycondensations with dicarboxylic acid dichlorides yielding multiblock copolyesters. Condensations with monocarboxylic acids yielded functionalized A‐B‐A triblock copolymers. Polycondensation with trifunctional acid chlorides yielded biodegradable networks. Hydroxyethylated pentaerythritol condensed with Bu2Sn(OMe)2 yielded a spirocyclic initiator. Ring‐expansion polymerization with lactones followed by acylation with carboxylic acid chlorides produces star‐shaped polylactones having functional endgroups. Biodegradable networks were also obtained when bisstannylenated α‐glucose methyl glycoside was used as initiator for ϵ‐caprolactone, and when the resulting spirocyclic polylactone was polycondensed with sebacoyl chloride. Copyright © 2003 John Wiley & Sons, Ltd.

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