41732 2017 eng 1700114-1 1700114-10 14 218 article Wiley-VCH 0 -- -- -- Poly(l-lactide)s are synthesized and annealed at 120 °C and changes of the molecular weight distribution (MWD) are monitored by matrix-assited laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. For example, benzyl alcohol+SnOct2 causes equilibration of odd- and even-numbered chains and the final goal of the transesterification is the most probable distribution. The underlying intermolecular transesterification is even observed at 100 and 80 °C in the solid state. However, cyclic tin mercaptide catalysts transform the initial most probable distribution into a MWD with maxima, which display a conspicuous fine structure due to a preferential crystallization of certain ring sizes. The optimum ring sizes for the crystallization are provided by ring-ring equilibration. The gradual formation of a special morphology shifts the melting temperature to values up to 187 °C. Annealing of commercial poly(l-lactide) with a cyclic tin catalyst also yields a distribution of mass peaks with a maximum showing the characteristic fine structure. Macromolecular Chemistry and Physics 10.1002/macp.201700114 1521-3935 1022-1352 Steffen Weidner Hans R. Kricheldorf eng uncontrolled Equilibration eng uncontrolled Mass spectrometry eng uncontrolled Polylactides eng uncontrolled Ring-opening polymerization eng uncontrolled Transesterification Ingenieurwissenschaften und zugeordnete Tätigkeiten Verlagsliteratur Datei im Netzwerk der BAM verfügbar ("Closed Access")