Monofunctional polylactones were prepared by Bu2Sn(OMe)(2)-initiated ring-opening polymerization Of E-caprolactone (ECL) followed by acylation with bromoacetyl-bromide. Telechelic polylactones and polylactides were prepared via ring-expansion polymerization with 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP) or 2,2-dibutyl-2-stanna-pentaoxacyclotridecane (Bu(2)SnTEG) as cyclic initiator. In situ combination of the polymerization with condensation by means of bromoacetylbromide yielded polylactones having bromoacetate endgroups. These endgroups were subjected to nucleophilic substitution with 3-mercaptopropyl trimethoxysilane (3-MPTMS). Analogous experiments were conducted with DL-lactide. The telechelic trimethoxysilyl-endcapped polylactones were characterized by viscosity, H-1 and C-13 NMR-spectroscopy, and MALDI-TOF mass spectrometry. The mass spectra revealed small amounts of cyclic oligolactones as byproducts in all samples. (c) 2005 Wiley Periodicals, Inc.