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 is an element of-caprolactone or beta-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.