Abstract
Ring-expansion polymerizations of β-D,L-butyrolactone (β-BL) or ε-caprolactone (ε-CL) were initiated with 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP) and the monomer-initiator ratio (M/I) was varied. The resulting tin-containing polylactones were polycondensed in situ either with succinyl chloride (in the case of β-BL) or with suberoyl chlorid (for ε-CL). The reaction conditions were optimized towards high molecular weights by the addition of bipyridine. The isolated tin-free polylactones were characterized by MALDI-TOF mass spectrometry. In the best spectra cyclic poly(ε-caprolactone)s were detected up to masses around 10 600 Da and cyclic poly(β-butyrolactone)s up to masses around 17 000 Da. In addition to the cyclic polyesters linear chains having alcoholic OH and/or CO2H group were found. These results suggest that the chain growth is limited by cyclization and by incomplete conversion of the functional groups.
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