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

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 SnO 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.