Polylactones. LVIII. Star‐shaped polylactones with functional end groups via ring‐expansion polymerization with a spiroinitiator

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Abstract
Two more or less ethoxylated pentaerythritols were reacted with dibutyltin dimethoxide and yielded spirocyclic tin alkoxides that were soluble in hot toluene or in chlorobenzene, chloroform, and 1,1,2,2‐tetrachloroethane at room temperature. These solutions were used in situ as initiators for the ring‐expansion polymerization of ϵ‐caprolactone or β‐D,L‐butyrolactone. The spirocyclic polylactones were reacted with various carboxylic acid chlorides and yielded four‐armed stars with the elimination of Bu2SnCl2. By variation of the acid chlorides, star arms with chloroacetate, 4‐bromobenzoate, 4‐nitrobenzoate, cinnamate, stearate, or methacrylate end groups were obtained. With 4‐chlorothiophenyl esters of N‐protected amino acids, N‐protected aminoacyl end groups were introduced. A complete functionalization of all star arms was not achieved in all cases, and structure–property relationships were examined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1047–1057, 2002

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