TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen T1 - About the crystallization of cyclic and linear poly(L-lactide)s in alcohol-initiated and Sn(II)2-ethylhexanoate- catalyzed ROPs of L-lactide conducted in solution JF - Polymer N2 - 1-Hydroxymethylnaphtalene (HMN) or 11-bromoundecanol (BUND) were used as initiators and Sn(II) 2-ethylhexanoate (SnOct2) as catalyst for ROPs of L-Lactide (LA) at 115 °C in bulk or in 4 M and 2M solutions in toluene. The LA/In ratio, the LA/Cat ratio and the time were varied. The matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectra exclusively displayed peaks of linear chains, when the ROPs were conducted in bulk. But in contrast to reports in the literature, mixtures of linear and cyclic poly(L-lactide) (PLA), were obtained, when the ROPs were performed in solution. The intensity distribution of the mass peaks of cyclic PLAs displayed a “saw-tooth pattern” after annealing in contrast to the mass peak distribution of the liner chains. This new phenomenon indicated that cyclic PLAs and linear PLAs crystallized in separate crystals from the same reaction mixture. This conclusion was confirmed by fractionated crystallization from 2 M solution, which confirmed that the cyclic PLAs nucleate and crystallize faster than the linear chains. KW - Polylactide KW - MALDI-TOF MS KW - Ring opening polymerization KW - Crystallization PY - 2023 DO - https://doi.org/10.1016/j.polymer.2023.125946 SN - 0032-3861 VL - 276 SP - 1 EP - 11 PB - Elsevier Ltd. AN - OPUS4-57308 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen A1 - Meyer, A. T1 - About the Influence of (Non-)Solvents on the Ring Expansion Polymerization of l-Lactide and the Formation of Extended Ring Crystals JF - Macromolecular Chemistry and Physics N2 - Ring-expansion polymerizations (REPs) catalyzed by two cyclic tin catalysts(2-stanna-1.3-dioxa-4,5,6,7-dibenzazepine [SnBiph] and 2,2-dibutyl-2-stanna-1,3-dithiolane [DSTL) are performed at 140 °C in bulk. Small amounts (4 vol%) of chlorobenzene or other solvents are added to facilitate transesterification reactions (ring–ring equilibration) in the solid poly(l-lactide)s. In the mass range up to m/z 13 000 crystalline PLAs displaying a so-called saw-tooth pattern in the MALDI-TOF mass spectra are obtained indicating the formation of extended-ring crystals. The characteristics of extended-ring crystallites and folded-ring crystallites are discussed. Furthermore, extremely high melting temperatures (Tm’s up to 201.2 °C) and melting enthalpies (𝚫Hm’s up to 106 J g−1)) are found confirming that 𝚫Hmmax, the 𝚫Hm of a perfect crystal, is around or above 115 J g−1 in contrast to literature data. KW - Polylactide KW - MALDI-TOF MS KW - Ring-expansion polymerization KW - Crystals PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-565038 DO - https://doi.org/10.1002/macp.202200385 SN - 1022-1352 SP - 1 EP - 8 PB - Wiley VHC-Verlag AN - OPUS4-56503 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen A1 - Meyer, A. T1 - About the Influence of (Non-)Solvents on the Ring Expansion Polymerization of l-Lactide and the Formation of Extended Ring Crystals JF - Macromolecular Chemistry and Physics N2 - Ring-expansion polymerizations (REPs) catalyzed by two cyclic tin catalysts (2-stanna-1.3-dioxa-4,5,6,7-dibenzazepine [SnBiph] and 2,2-dibutyl-2-stanna-1,3-dithiolane [DSTL]) are performed at 140 °C in bulk. Small amounts (4 vol%) of chlorobenzene or other solvents are added to facilitate transesterification reactions (ring–ring equilibration) in the solid poly(l-lactide)s. In the mass range up to m/z 13 000 crystalline PLAs displaying a so-called saw-tooth pattern in the MALDI-TOF mass spectra are obtained indicating the formation of extended-ring crystals. The characteristics of extended-ring crystallites and folded-ring crystallites are discussed. Furthermore, extremely high melting temperatures (Tm’s up to 201.2 °C) and melting enthalpies (𝚫Hm’s up to 106 J g−1)) are found confirming that 𝚫Hm max, the 𝚫Hm of a perfect crystal, is around or above 115 J g−1 in contrast to literature data. KW - Polylactide KW - MALDI-TOF MS KW - Ring-expansion polymerization KW - Biobased PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-573063 DO - https://doi.org/10.1002/macp.202200385 VL - 224 IS - 5 SP - 1 EP - 8 PB - Wiley VHC-Verlag AN - OPUS4-57306 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, Hans A1 - Weidner, Steffen T1 - About the influence of salicylic acid on tin(II)octanoate-catalyzed ring opening polymerizationof L-lactide JF - European Polymer Journal N2 - L-Lactide was polymerized in bulk with tin(II)2-ethylhexanoate SnOct2) as catalyst and salicylic acid as cocatalyst. The Lac/Cat ratio, Cocat/Cat ratio, temperature and time were varied. Increasing Cocat/Cat ratios reduced both,polymerization rate and molecular weight. However,under optimized conditions high molar mass (Mw up to 178,000), colorless, cyclic polylactides were formed in a short time. A few polymerizations performed at 160 and 180°C with the combination of SnOct2 and silylated salicylic acid gave similar results. Neat tin II) salicylate was prepared from SnOct2 and used for REPs of L-lactide in bulk, but the results were not better than those obtained from combinations of SnOct2 and salicylic acid. Furthermore, dibutyltin salicylate was synthesized and used as catalyst for polymerizations of L-lactide in bulk at temperatures varying from 102 to 160°C. Cyclic polylactides with Mw’s up to 40,000 were the main reaction products. At 100–102°C a predominance of odd-numbered cycles was found proving a REP mechanism. KW - Polylactide KW - MALDI-TOF MS KW - Cyclization KW - Catalyst KW - Ring-opening polymerization PY - 2019 DO - https://doi.org/10.1016/j.eurpolymj.2019.07.003 VL - 119 SP - 37 EP - 44 PB - Elsevier Ltd. AN - OPUS4-49211 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weidner, Steffen A1 - Meyer, A. A1 - Chatti, S. A1 - Kricheldorf, H. R. T1 - About the transformation of low Tm into high Tm poly(L-lactide)s by annealing under the influence of transesterification catalysts JF - RSC Advances N2 - Cyclic polylactides were prepared in bulk at 170 °C, crystallized at 120 °C and then annealed at temperatures between 130 and 170 C with variation of catalyst, catalyst concentration and annealing time. The transformation of the initially formed low melting (LTm) crystallites, having melting temperatures (Tm) <180 °C into high melting (HTm) crystallites having Tm values > 189 °C was monitored by means of DSC measurements and characterized in selected cases by SAXS measurements. It was confirmed that the formation of HTm crystallites involves a significant growth of the thickness of the lamellar crystallites along with smoothing of their surface. Annealing at 170 °C for 1 d or longer causes thermal degradation with lowering of the molecular weights, a gradual transition of cyclic into linear chains and a moderate decrease of lamellar thickness. An unexpected result revealed by MALDI TOF mass spectrometry is a partial reorganization of the molecular weight distribution driven by a gain of crystallization enthalpy. KW - Polylactide KW - MALDI-TOF MS KW - Crystallization KW - Annealing PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-521062 DO - https://doi.org/10.1039/d0ra10012a VL - 11 IS - 5 SP - 2872 EP - 2883 PB - Royal Society of Chemistry AN - OPUS4-52106 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen T1 - Alcohol-Initiated and SnOct2-Catalyzed Ring-Opening Polymerization (ROP) of L-Lactide in Solution: A Re-investigation JF - European Polymer Journal N2 - Alcohol-initiated ring-opening polymerizations (ROP) of L-lactide (LA) were studied in solution at 70 °C, whereupon the nature of the alcohol, the LA/initiator ratio, the LA/SnOct2 ratio and the time were varied. In contrast to literature, neat SnOct2 is catalytically active in THF and several aromatic but donor solvents, such as 1,3-dioxolane, dimethylformamide (DMF) or N-methyl pyrrolidone (NMP), strongly reduce the activity of SnOct2. In agreement with literature, no cycles were formed by neat SnOct2 at 70 °C in toluene, whereas almost complete cyclization occurs at 115 °C. This finding is attributed to strongly reduced mobility of the initially formed linear chains having one Sn-O-CH and one anhydride end group. Due to better solvation and enhanced mobility cyclization occurs in THF at 70 °C. KW - Polylactide KW - Ring-opening polymerization KW - MALDI-TOF MS KW - Transesterification PY - 2023 DO - https://doi.org/10.1016/j.eurpolymj.2023.111822 SN - 0014-3057 SP - 1 EP - 18 PB - Elsevier CY - New York, NY [u.a.] AN - OPUS4-56818 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weidner, Steffen A1 - Meyer, A. A1 - Kricheldorf, H. R. T1 - Alcohol-initiated and Tin(II) 2-ethylhexanoate-catalyzed polymerization of L-lactide in bulk – About separate crystallization of cyclic and linear Poly (L-lactide)s JF - Polymer N2 - Alcohol-initiated ROPs of L-Lactide were performed at 140 ◦C in bulk with variation of the initiator/catalyst ratio and time. Lower ratios favor the formation of cycles which upon annealing display a change of the MALDI mass peak distribution towards a new maximum with a “saw-tooth pattern” of the mass peaks representing the cycles. Such a pattern was not observed for the mass peak of the linear chains. The coexistence of these patterns indicate that linear and cyclic poly (L-lactide)s (PLA) crystallize in separate crystals, and that the crystallites of the cycles are made up by extended rings. High Tm and ΔHm values confirm that these extended-ring crystallites represent a thermodynamically optimized form of PLA. Experiments with preformed cyclic and linear PLAs support this interpretation. KW - Polylactide KW - MALDI-TOF MS KW - Crystalinity KW - Polymerization PY - 2023 DO - https://doi.org/10.1016/j.polymer.2023.126355 VL - 285 IS - 126355 SP - 1 EP - 9 PB - Elsevier Ltd. AN - OPUS4-58355 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. A1 - Weidner, Steffen T1 - Cyclic and linear poly(L-lactide)s by ring-expansion polymerization with Bu2SnO, Oct2SnO, and Bu2SnS JF - Journal of Polymer Science N2 - To elucidate the usefulness of commercial Bu2SnO as catalyst for syntheses of linear and/or cyclic polylactides L-Lactide was polymerized in bulk with variation of the LA/Cat ratio, temperature and time. Based on a ring-expansion polymerization (REP) mechanism cyclic polylactides (PLAs) with weight average molecular weights in the range of 200,000–300,000 are obtained at the highest temperature (180 °C). Polymerizations at 150 °C yielded crystalline, mainly cyclic polylactides which, after annealing, showed high melting temperatures (up to 197.5 °C) and high crystallinities (>80%). Polymerization at 120 °C confirmed the trend towards more linear chains with lower temperatures but yielded extended-ring crystals showing a “saw-tooth pattern” in the mass spectra. Oct2SnO gave similar results as Bu2SnO. Bu2SnS proved a sluggish polymerization catalyst, but a good transesterification catalyst in solid PLA. KW - MALDI TOF MS KW - Biobased polymers KW - Polylactide KW - Ring-expansion polymerization PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-584121 DO - https://doi.org/10.1002/pol.20230515 SN - 2642-4169 SP - 1 EP - 10 PB - Wiley CY - Hoboken, NJ AN - OPUS4-58412 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen T1 - Cyclic poly(L-lactide)s via simultaneous ROP and polycondensation (ROPPOC) catalyzed by dibutyltin phenoxides JF - European Polymer Journal N2 - Starting from dibutyltin oxide, four catalysts were synthesized, namely the dibutyltin bisphenoxides of Phenol (SnPh), 4-chlorophenol (SnCP), 4-hydroxybenzonitrile (SnCN) and pentafluorophenol (SnOPF). With the first three catalysts polymerizations of L-lactide at 160 °C in bulk yielded large fraction of linear chains having phenylester end groups at short reaction times. At longer times the fraction of cycles considerably increased at the expense of the linear chains, when SnCN was used as catalyst. With SnOPF only cyclic polylactides were obtained at low Lac/Cat ratios (< 400) with weight average molecular weights (Mw) up to 90 000 Da, whereas for high Lac/Cat ratios mixtures of cyclic and linear chains were found. Polymerizations in solution enabled variation of the molecular weight. Polymerizations of meso-lactide at temperatures down to 60 °C mainly yielded even-numbered linear chains supporting the postulated ROPPOC mechanism. KW - Cyclization KW - MALDI-TOF MS KW - Polycondensation KW - Ring-opening Polymerization KW - Polylactide PY - 2018 DO - https://doi.org/10.1016/j.eurpolymj.2018.10.005 SN - 0014-3057 IS - 109 SP - 360 EP - 366 PB - Elsevier AN - OPUS4-46263 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. A1 - Weidner, Steffen A1 - Scheliga, F. T1 - Cyclic poly(lactide)s via the ROPPOC method catalyzed by alkyl- or aryltin chlorides JF - Journal of Polymer Science, Polymer Chemistry N2 - A comparison of tributyltin chloride, dibutyltin dichloride,and butyltin trichloride as catalysts of ring-opening polymerizations(ROPs) of l-lactides at 160°C in bulk reveals increasing reactivity in the above order, but only the least reactive catalysts, Bu3SnCl, yield a uniform reaction product, namely cyclic poly(L-lactide)s with weight average molecular weights (Mw ́s) in the range of 40,000–80,000. A comparison of dimethyltin , dibutyltin , and diphenyltin dichlorides resulted in the following order of reactivity: Me2SnCl21-2h) depending on catalyst concentration) caused thermal degradation. In polymerization experiments with various commercial Bi(III) salts a better alternative to BiSub was not found. By means of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry a couple of unusual and unexpected transesterification reactions were discovered. Finally, the effectiveness of several antioxidants and potential catalyst poisons was explored, and triphenylphosphine was found to be an effective catalyst poison. KW - Polylactide KW - MALDI-TOF MS KW - Ring-opening polymerization KW - Bismuth PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-519513 DO - https://doi.org/10.1002/app.50394 SN - 0021-8995 VL - 138 IS - 19 SP - 50394 PB - Wiley AN - OPUS4-51951 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen A1 - Meyer, A. T1 - High Tm linear poly(L-lactide)s prepared via alcohol-initiated ROPs of L-lactide JF - RSC Advances N2 - Alcohol-initiated ROPs of L-lactide were performed in bulk at 160 °C for 72 h with variation of the catalyst or with variation of the initiator (aliphatic alcohols). Spontaneous crystallization was only observed when cyclic Sn(II) compounds were used as a catalyst. Regardless of initiator, high melting crystallites with melting temperatures (Tm) of 189–193 °C were obtained in almost all experiments with Sn(II) 2,2′-dioxybiphenyl (SnBiph) as catalyst, even when the time was shortened to 24 h. These HTm poly(lactide)s represent the thermodynamically most stable form of poly(L-lactide). Regardless of the reaction conditions, such high melting crystallites were never obtained when Sn(II) 2-ethylhexanoate (SnOct2) was used as catalyst. SAXS measurements evidenced that formation of HTm poly(L-lactide) involves growth of the crystallite thickness, but chemical modification of the crystallite surface (smoothing) seems to be of greater importance. A hypothesis, why the “surface smoothing” is more effective for crystallites of linear chains than for crystallites composed of cycles is discussed. KW - Polylactide KW - MALDI-TOF MS KW - Ring-opening polymerization PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-524330 DO - https://doi.org/10.1039/d1ra01990b VL - 11 IS - 23 SP - 14093 EP - 14102 PB - Royal Society of Chemistry AN - OPUS4-52433 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Meyer, A. A1 - Weidner, Steffen T1 - High Tm Poly(l-lactide)s by Means of Bismuth Catalysts? JF - Macromolecular Chemistry and Physics N2 - One series of BiSub-catalyzed ring-opening polymerizations (ROPs) is per-formed at 160 °C for 3 days with addition of difunctional cocatalysts to find out, if poly(l-lactide) crystallizes directly from the reaction mixture. An analogous series is performed with monofunctional cocatalysts. High Tm crystal-lites (Tm > 190 °C) are obtained from all bifunctional cocatalysts, but not from all monofunctional ones. It is shown by means of SAXS measurements that the high Tm values are mainly a consequence of a transesterification–homogenization process across the lamellar surfaces resulting in thickness and smoothing of the surfaces. An unusual enthalpy-driven modification of the molecular weight distribution is found for samples that have crystallized during the polymerization. A third series of ROPs is performed at 170 °C for 2 h followed by annealing at 120 °C (2 h) to induce crystallization. Complete transformation of the resulting low Tm crystallites (Tm < 180 °C) into the high Tm crystallites by annealing at 170 °C for 1 d is not achieved, despite variation of the cocatalyst. KW - Polylactide KW - MALDI-TOF MS KW - Crystallization PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-522777 DO - https://doi.org/10.1002/macp.202100019 SN - 1022-1352 VL - 222 IS - 8 SP - 19 PB - Wiley AN - OPUS4-52277 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen A1 - Meyer, A. T1 - High Tm poly(L-lactide)s via REP or ROPPOC of L-lactide JF - Polymer Chemistry N2 - A new kind of high melting (HTm) pol(L-lactide) was discovered when cyclic poly(L-lactide)s were prepared by ring-expansion polymerization with cyclic tin catalysts at 130–160 °C in bulk. By DSC measurements with 10 K min−1 melting temperatures (Tm) in the range of 190–196 °C were found. The WAXS and SAXS measurements evidenced that not a new crystal lattice but a well-ordered morphology and a higher perfection of the crystallites are responsible for the high Tm values and high crystallinities. Under identical reaction conditions SnOct2-catalyzed and alcohol-initiated ROPs do not yield these crystallites. Furthermore, it was found that the standard crystallites are kinetically favored upon rapid crystallization, whereas the high melting form of poly(L-lactide) is thermodynamically more stable. KW - Polylactide KW - MALDI-TOF MS KW - ROPPOC PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-507477 DO - https://doi.org/10.1039/c9py01908a VL - 11 IS - 12 SP - 2182 EP - 2193 PB - Royal Society of Chemistry AN - OPUS4-50747 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weidner, Steffen A1 - Kricheldorf, H. R. T1 - Matrix-assisted laser desorption/ionization behavior of neat linear and cyclic poly(L-lactide)s and their blends JF - Rapid Communications in Mass Spectrometry N2 - Numerous new tin catalysts that enable the synthesis of cyclic polylactides with broad variation in their molecular mass were recently developed. The abundance of cyclics in matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra is, however, frequently reported to greatly exceed that of linears. Thus, the MALDI ionization behavior of various end-capped linear poly(L-lactide)s and one cyclic poly(L-lactide) was investigated and compared. Neat compounds and various blends of cyclic and linear species were prepared and studied under identical conditions with regard to sample preparation and instrumental condition, except for the laser power. For this purpose, two different MALDI-TOF mass spectrometers were applied. Our results reveal that cyclics indeed show a slightly better ionization in MALDI, although their ionization as a neat compound seems to be less effective than that of linear polylactides. The ionization of most linear polylactides investigated does not depend on the end group structure. However, linear polylactides containing 12-bromododecyl end groups reveal an unexpected saturation effect that is not caused by fragmentation of the polymer or the end group, or by electronic saturation of the detector digitizer. Furthermore, polylactides with a 2-bromoethyl end group did not show such a saturation effect. An overestimation of cyclic species in MALDI-TOF mass spectra of poly(L-lactide)s must be considered, but the commonly assumed peak suppression of linear polymers in mixtures of both structures can be excluded. KW - Polylactide KW - MALDI-TOF MS KW - Blends KW - Ionization PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-504216 DO - https://doi.org/10.1002/rcm.8673 VL - 34 SP - e8673 PB - Wiley Online Libary AN - OPUS4-50421 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen A1 - Meyer, A. T1 - Poly(L-lactide): Optimization of Melting Temperature and Melting Enthalpy JF - Materials Advances N2 - Twice recrystallized L-lactide was polymerized with a dozen of different tin or bismuth catalysts in bulk at 160°C for 24 h and was annealed at 150°C afterwards. In two cases Tm values above 197.0°C were obtained. The parameters causing a scattering of the DSC data were studied and discussed. The samples prepared with SnCl2, 2,2-dibutyl-2-stanna-1,3-ditholane (DSTL) or cyclic tin(II) bisphenyldioxide (SnBiph) were subject to annealing programs with variation of time and temperatures, revealing that the Tm´s did not increase. However, an increase of Hm was achieved with maximum values in the range of 93-96 J g-1 corresponding to crystallinities off around 90%. Further studies were performed with once recrystallized L-lactide. Again, those samples directly crystallized from the polymerization process showed the highest Tm values. These data were compared with the equilibrium Tm0 and Hm0 data calculated by several research groups for perfect crystallites. A Tm0 of 213+/-2°C and a Hm0 of 106 J g-1 show the best agreement with the experimental data. The consequences of annealing for the thickness growth of crystallites are discussed on the basis of SAXS measurements. Finally, a comparison of cyclic and linear poly L-lactide)s is discussed. KW - Polylactide KW - MALDI-TOF MS KW - Transesterification PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-538656 DO - https://doi.org/10.1039/D1MA00957E SP - 1 EP - 10 PB - Royal Society for Chemistry AN - OPUS4-53865 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. A1 - Weidner, Steffen A1 - Scheliga, F. T1 - Polycondensation of poly(L-lactide) alkyl esters combined with disproportionation and symproportionation of the chain lengths JF - Journal of Polymer Science A: Polymer Chemistry N2 - Ring-opening polymerizations (ROPs) of l-lactide (LA) were performed with ethyl l-lactate or 11-bromoundecanol as initiators (In) and tin(II) ethyl hexanoate (SnOct2) as catalyst (Cat) using four different LA/In ratios (20/1, 40/1, 60/1, and 100/1). One series of ROPs was conducted in bulk at 120 °C, yielding PLAs with low dispersities (Ð ~ 1.2–1.4), and a second series was conducted in bulk at 160 °C, yielding higher dispersities (Ð ~ 1.3–1.9). Samples from both series were annealed for 1 or 14 days at 140 °C in the presence of SnOct2. Both polycondensation and disproportionation reactions occurred, so that all four samples tended to form the same type of molar mass distribution below 10,000 Da, regardless of their initially different number average molar masses (Mn). Both initiators gave nearly identical results. The thermodynamic control of all reversible transesterification processes favored the formation of crystallites composed of chains with a Mn around 3500–3700, corresponding to a crystal thickness of 10–13 nm. KW - Polylactide KW - MALDI-TOF MS KW - Crystalinity PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-600081 DO - https://doi.org/10.1002/pol.20240118 SN - 2642-4150 SP - 1 EP - 12 PB - Wiley AN - OPUS4-60008 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 - Polycondensations and Cyclization of Poly(L-lactide) Ethyl Esters in the Solid State JF - Polymer Chemistry 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 -