Polylactones, 53 - Formation of cyclic polyesters in the combined ringexpansion polymerization/ring-opening polycondensation of lactones

Full Paper: Ring-expansion polymerizations of beta-D,L- butyrolactone (beta-BL) or epsilon-caprolactone (epsilon-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 beta-BL) or with suberoyl chlorid (for epsilon-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(epsilon-caprolactone)s were detected up to masses around 10600 Da and cyclic poly(beta-butyrolactone)s up to masses around 17000 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 functinoal groups