TY - JOUR A1 - Meyer, Andreas A1 - Weidner, Steffen A1 - Kricheldorf, Hans R. T1 - Star-shaped poly(l-lactide)s based on pentaerythritol: About crystallization and polycondensation plus disproportionation and ring formation in the solid state N2 - Star-shaped poly( L-lactide)s (s-PLAs), were prepared by ring-opening polymerization of with pentaerythritol and catalyzed by tin(II) 2-ethylhyexanoate (SnOct out in bulk at either 120 ◦ C or 160 ◦ L-lactide (LA) initiated 2 ). Two small series of ROPs were carried C with variation of the LA/initiator ratio. Matrix-assisted laser desorption/ ionization time-of-flight (MALDI-TOF) mass spectra revealed traces of cycles in 120 ◦ C samples only at low initiator/catalyst ratios. In contrast, higher fractions of cycles were detected in samples prepared at 160 C, suggesting a "back-biting" origin. The influence of arm length and thermal history on crystallinity was investigated by differential scanning calorimetry (DSC) and wide-angle x-ray scattering (WAXS). It was shown that annealing increased the melting temperature (T ◦ ◦ m ) and crystallinity. However, annealing at 140 ◦ C for 14 d also caused significant solid-state transesterification. In addition, crystallites composed of s-PLAs with extended arms and, simultaneously, crystallites composed exclusively of extended rings were formed, identified by their typical "sawtooth" pattern in the MALDI mass spectra. Small angle x-ray scattering (SAXS) indicated that the crystal thickness was lower than that of linear PLAs annealed under identical conditions, but increased upon annealing at 140 C. KW - MALDI-TOF MS KW - Polylactide KW - Crystallisation KW - AStar-shaped polymers PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-636832 DO - https://doi.org/10.1016/j.polymer.2025.128709 SN - 0032-3861 VL - 334 SP - 1 EP - 11 PB - Elsevier Ltd. AN - OPUS4-63683 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weidner, Steffen A1 - Kricheldorf, Hans R. T1 - Transesterification in the solid state of cyclic and linear poly(l-lactide)s N2 - 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. KW - Equilibration KW - Mass spectrometry KW - Polylactides KW - Ring-opening polymerization KW - Transesterification PY - 2017 DO - https://doi.org/10.1002/macp.201700114 SN - 1521-3935 SN - 1022-1352 VL - 218 IS - 14 SP - 1700114-1 EP - 1700114-10 PB - Wiley-VCH AN - OPUS4-41732 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -