TY - JOUR A1 - Weidner, Steffen A1 - Meyer, A. A1 - Falkenhagen, Jana A1 - Kricheldorf, H. R. T1 - Polycondensations and Cyclization of Poly(L-lactide) Ethyl Esters in the Solid State N2 - The usefulness of seven different Tin catalysts, Bismuth subsalicylate and Titan tetra(ethoxide) for the polycondensation of ethyl L-lactate (ELA) was examined at 150 °C/6 d. Dibutyltin bis(phenoxides) proved to be particularly effective. Despite the low reactivity of ELA, weight average molecular masses (Mw) up to 12 500 were found along with partial crystallization. Furthermore, polylactides (PLAs) of similar molecular masses were prepared via ELA-initiated ROPs of L-lactide by means of the four most effective polycondensation catalysts. The crystalline linear PLAs were annealed at 140 or 160 °C in the presence of these catalysts. The consequences of the transesterification reactions in the solid PLAs were studied by means of matrix-assisted laser desorption/ionization (MALDI TOF) mass spectrometry, gel permeation chromatography (GPC) and small-angle X-ray scattering (SAXS). The results indicate that polycondensation and formation of cycles proceed in the solid state via formation of loops on the surface of the crystallites. In summary, five different transesterification reactions are required to explain all results. KW - Polylactide KW - MALDI-TOF MS KW - Crystalinity PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-592934 DO - https://doi.org/10.1039/d3py01232h SN - 1759-9962 VL - 15 IS - 2 SP - 71 EP - 82 PB - RSC Publ. CY - Cambridge AN - OPUS4-59293 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen A1 - Scheliga, F. T1 - Synthesis of cyclic polymers and flaws of the Jacobson–Stockmayer theory N2 - Cyclic poly(L-lactide)s were prepared by ring-opening polymerization combined with simultaneous polycondensation (ROPPOC) in bulk at 160 ° with dibutyltin bis(4-cyanophenoxide) as catalyst. It is demonstrated by MALDI TOF mass spectrometry and 1H NMR end group analyses that cycles are formed by endto-end cyclization in addition to “back-biting” transesterification. Formation of high molar mass cyclic poly L-lactide)s by means of several more reactive ROPPOC catalysts presented previously and in new experiments is discussed. These experimental results, together with theoretical arguments, prove that part of the Jacobson–Stockmayer theory is wrong. The critical monomer concentration, above which end-toend cyclization is seemingly impossible, does not exist and reversible like irreversible polycondensations can theoretically proceed up to 100% conversion, so that finally all reaction products will necessarily adopt a cyclic architecture. KW - Polylactide KW - MALDI-TOF MS KW - Cyclization PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-506419 DO - https://doi.org/10.1039/d0py00226g VL - 11 IS - 14 SP - 2595 EP - 2604 PB - Royal Society for Chemistry AN - OPUS4-50641 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kricheldorf, H. R. T1 - Reversible Polycondensations and the Jacobson-Stockmayer Theory N2 - Reversible polycondensations are polycondensations that include equilibration reactions at any stage of the process. Syntheses of Polyesters in bulk involving transesterification reactions and syntheses of polyamides in bulk involving transamidation are typical examples. In 1950, Jacobson and Stockmayer published a first theory of reversible polycondensations based on experimental studies with aliphatic polyesters.[1,2] They explained the reversibility by the reversible formation of cyclic oligomers and low molar mass polymers from an active chain end (so-called “back-biting”). The formation of cycles via end-to-end cyclization was excluded in agreement with Flory´s theory of irreversible polycondensations.[3] The reinvestigation of the Jacobson-Stockmayer experiments by the authors in combination with theoretical considerations shows that the JS theory is wrong. [4,5] It turned out that the experimental scenario is far from the reality. In real polycondensations, intermolecular equilibration is faster than “back-biting”, and end-to-end cyclization is quite normal. The revised theory of step-growth polymerization predicts that in the ideal case of 100% conversion, all reaction products are cycles, regardless, of whether the step-growth polymerization is reversible or not. T2 - Polycondensation 2024 CY - Lyon, France DA - 15.09.2024 KW - Polycondensation KW - Cyclisation KW - MALDI TOF MS PY - 2024 UR - https://polycond-2024.sciencesconf.org/ AN - OPUS4-61070 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen T1 - Syntheses of cyclic polylactides and the problem of catenane formation N2 - Cyclic poly(L-lactide)s (PLAs) were prepared in bulk either by ring-expansion polymerization (REP) or by ring-opening polymerization (ROP) with simultaneous polycondensation (ROPPOC). In contrast to REP the latter method involves formation of linear chains and thus, may involve formation of polydisperse catenanes that affect crystallization. The reprecipitated PLAs were annealed at 120 °C and compared with regard to melting temperature (Tm) and melting enthalpy (ΔHm). For similar molar masses the PLAs prepared by REP and ROPPOC had almost identical Tm's and crystallinities. Furthermore, the influence of REP and ROPPOC catalysts on the morphology of the virgin reaction products was compared. KW - MALDI-TOF MS KW - Catenane KW - Polylactide PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-625061 DO - https://doi.org/10.1039/d4ra08683j VL - 15 IS - 5 SP - 3686 EP - 3692 PB - RSC AN - OPUS4-62506 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weidner, Steffen A1 - Meyer, A. A1 - Falkenhagen, Jana A1 - Kricheldorf, H. R. T1 - SnOct2-catalyzed and alcohol-initiated ROPs of L-lactide – About the influence of initiators on chemical reactions in the melt and the solid state N2 - SnOct2 (Sn(II) 2-ethylhexanoate) catalyzed ROPs of L-lactide were performed in bulk with eight different alcohols as initiators. The time was varied between 1 h and 24 h for all initiators. For two initiators the temperature was also lowered to 115 ◦C. Even-numbered chains were predominantly formed in all polymerizations at short times, but the rate of transesterification (e.g. even/odd equilibration) and the molecular weight distribution were found to depend significantly on the nature of the initiator. Observed transesterification reactions also continued in solid poly (L-lactide), and with the most active initiator, almost total equilibration was achieved even at 130 ◦C. This means that all chains including those of the crystallites were involved in transesterification reactions proceeding across the flat surfaces of the crystallites. The more or less equilibrated crystalline polylactides were characterized by DSC and SAXS measurements with regard to their melting temperature (Tm), crystallinity and crystal thickness. KW - Polylactide KW - MALDI-TOF MS KW - Crystallization KW - Catalysts KW - SAXS PY - 2021 DO - https://doi.org/10.1016/j.eurpolymj.2021.110508 VL - 153 SP - 110508 PB - Elsevier Ltd. AN - OPUS4-52633 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -