TY - JOUR A1 - Kricheldorf, H. A1 - Weidner, Steffen A1 - Meyer, A. T1 - Syntheses of high molecular mass polyglycolides via ring-opening polymerization with simultaneous polycondensation (ROPPOC) by means of tin and zinc catalysts N2 - Glycolide was polymerized in bulk by means of four different ROPPOC catalysts: tin(II) 2-ethylhexanoate (SnOct2), dibutyltin bis(pentafluoro-phenoxide) (BuSnOPF),zinc biscaproate (ZnCap), and zinc bis(pentafluoro-phenyl sulfide) (ZnSPF). The temperature was varied between 110 and 180°C and the time between 3 h and 7 days. For the few polyglycolides (PGAs) that were soluble extremely high molecular masses were obtained. The MALDI TOF mass spectra had all a low signal-to-noise ration and displayed the peaks of cyclic PGAs with a“saw-tooth pattern ”indicating formation of extended-ring crystallites in the mass range below m/z 2500. The shape of DSC curves varied considerably with catalyst and reaction conditions, whereas the long-distance values measured by SAXS were small and varied little with the polymeriza-tion conditions. KW - MALDI TOF MS KW - Polyglycolide KW - Crystalinity PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-598221 DO - https://doi.org/10.1002/pat.6365 VL - 35 IS - 4 SP - 1 EP - 10 PB - John Wiley & Sons Ltd. AN - OPUS4-59822 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. A1 - Weidner, Steffen T1 - Low Molar Mass Cyclic Poly(L-lactide)s: Separate Transesterification Reactions of Cycles and Linear Chains in the Solid State N2 - L-Lactide (LA) was polymerized with neat tin(II) 2-ethylhexanoate (SnOct2) in toluene at 115 °C at low concentration with variation of the LA/Cat ratio. Cyclic polylactides (cPLAs) with number average molecular weights (Mn) between 7 000 and 17 000 were obtained. MALDI-TOF mass spectrometry also revealed the formation of a few percent of linear chains. Crystalline cPLAs with Mn around 9 000 and 14 000 were annealed at 140 °C in the presence of ScOct2 or dibutyl-2-stanna-1,3-dithiolane (DSTL). Simultaneously, crystallites of extended linear chains and crystallites of extended cycles were formed regardless of the catalyst, indicating that transesterification reaction proceeded different for linear chains and for cycles, governed by thermodynamic control. The formation of extended chain crystallites with low dispersity indicates the existence of symproportionation of short and long chains. A complementary experiment was carried out with a PLA ethyl ester composed mainly of linear chains with a small fraction of cycles KW - Polylactide KW - MALDI-TOF MS KW - Annealing PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-606228 DO - https://doi.org/10.1039/D4SM00567H SN - 1744-6848 SP - 1 EP - 12 PB - Royal Society of Chemistry (RSC) AN - OPUS4-60622 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weidner, Steffen A1 - Meyer, A. A1 - Kricheldorf, H. T1 - Transformation of poly(L-lactide) crystals composed of linear chains into crystals composed of cycles N2 - A poly(L-lactide) with a trifluoroethyl ester end group and an average degree of polymerization (DP) of 50 was synthesized by ROP of L-lactide initiated with trifluoroethanol. Small-angle X-ray scattering (SAXS) in combination with differential scanning calorimetry (DSC) measurements revealed an average crystal thickness of 13 nm, corresponding to 45 repeat units. This suggests that most crystallites were formed by extended PLA chains, and both flat surfaces were covered by CF3 groups. The crystalline PLAs were annealed at 140 or 160 °C in the presence of two catalysts: tin(II) 2-ethylhexanoate, (SnOct2) or dibutyltin bis(pentafluorophenoxide) (BuSnPhF). The chemical reactions, such as polycondensation and cyclization, proceeded in the solid state and were monitored by matrix-assisted laser desorption/ionization time-offlight (MALDI TOF) mass spectrometry and gel permeation chromatography (GPC) measurements. Under optimal conditions a large fraction of linear chains was transformed into crystallites composed of extended cycles. Additionally, MALDI TOF MS analysis of GPC fractions from samples annealed for 28 or 42 days detected chain elongation of the linear species up to a factor of 20. KW - Polylactide KW - MALDI-TOF MS KW - Crystalinity KW - Transesterification PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-597250 DO - https://doi.org/10.1039/D3PY01370G SN - 1759-9954 VL - 15 IS - 12 SP - 1173 EP - 1181 PB - Royal Society for Chemistry AN - OPUS4-59725 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. A1 - Weidner, Steffen A1 - Meyer, A. T1 - About alcohol-initiated polymerization of glycolide and separate crystallization of cyclic and linear polyglycolides N2 - Alcohol-initiated polymerizations of glycolide (GL) catalyzed by tin(II) 2-ethylhexanoate (SnOct2) were carried out in bulk with variation of GA/In ratio, temperature and time. Due to a rather strong competition of cyclization polyglycolide (PGA) free of cycles were never obtained. When the cyclic catalysts 2,2-dibutal-2-stanna − 1,3-dithiolane (DSTL) or 2-stanna 1,3-dioxo-4,5,6,7 bibenzepane (SnBiph) were used in combination with 1,4-butanediol the influence of cyclization was even stronger. Furthermore, the degrees of polymerization were higher than the GA/alcohol ratio due to rapid polycondensation in the solid state. At 160 °C or below, the matrixassisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra indicated separate crystallization of low molar mass cyclic and linear PGAs from the same reaction mixture (also observed for poly(L-lactide)s). KW - MALDI TOF MS KW - Polyglycolide KW - Ring opening polymerization KW - Cyclization KW - Crystallization PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-607282 DO - https://doi.org/10.1016/j.polymer.2024.127440 SN - 0032-3861 VL - 309 SP - 1 EP - 9 PB - Elsevier Ltd. AN - OPUS4-60728 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. A1 - Weidner, Steffen A1 - Meyer, A. T1 - Syntheses of Polyglycolide via Polycondensation: A Reinvestigation N2 - The Na salt of chloroacetic acid is condensed in suspension. Furthermore,glycolic acid is condensed in bulk or in concentrated solution by means of SnCl2 or 4-toluene sulfonic acid (TSA) as catalysts. The temperatures are varied from 160 to 200°C and the time from 1 to 5 days. Low molar mass cyclic poly(glycolic acid) (PGA) is detected by means of matrix-assisted laser desorption ionization time-of-flight (MALDI TOF) mass spectrometry in most PGAs. A predominance of certain cycles having an even number of repeat units is observed suggesting a thermodynamically favored formation of extended-ring crystals. Extremely high melting temperatures (up to 237.5°C)and high melting enthalpies are found for polycondensations with TSA in 1,2-dichlorobenzene. KW - MALDI TOF MS KW - Polycondensation KW - Polyglycolide KW - Cyclization PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-596856 DO - https://doi.org/10.1002/macp.202300397 IS - 2300397 SP - 1 EP - 7 PB - Wiley VHC-Verlag AN - OPUS4-59685 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, Hans R. A1 - Weidner, Steffen A1 - Meyer, A. T1 - About Polycondensation, Disproportionation, and Cyclization of Acetylated Poly(L-Lactide) Esters N2 - L-lactide (LA) is polymerized with ethyl L-lactate or trifluoroethanol as initiators (LA/In = 30/1), and the resulting poly(L-lactide) esters are acetylated with acetic anhydride. The acetylated PLA esters are mixed with SnOct2, dibutyltin bis(4-chlorophenoxide), or dibutyltin bis(pentafluorophenoxide) in solution and crystallized at 120 °C. The doped crystals are annealed at 140 °C or at 160 °C for 7, 14, and 28 days, and the chemical modifications that occurred in the solid state are monitored by matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometry, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) measurements. All catalysts promoted polycondensation, while no significant formation of cycles is observed. However, in the presence of SnOct2, disproportionation of chains occurred upon annealing at 120 or 140 °C, and crystallites consisting of extended chains with Mn values ≈3500 – 3600 and low dispersities (Ð < 1.5) are formed. KW - MALDI-TOF MS KW - Polycondensation KW - Polylactides KW - Transesterifcation PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-630349 DO - https://doi.org/10.1002/macp.202400175 SN - 1521-3935 VL - 225 IS - 19 PB - Wiley VHC-Verlag AN - OPUS4-63034 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 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 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. 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 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. A1 - Scheliga, F. A1 - Weidner, Steffen T1 - Syntheses of Cyclic Poly(l-lactide)s by Means of Zinc-Based Ring-Opening Polymerization with Simultaneous Polycondensation (ROPPOC) Catalysts N2 - Ring-opening polymerizations of l-lactide are studied in bulk at 140 or 160 °C with zinc n-hexanoate, zinc 4-chlorothiophenolate, and zinc pentafluoro thiophenolate (ZnSPF) as catalysts. The reactivity increases in the given order. With all three catalysts a high fraction of cycles is obtained only at polymerization (annealing) times around 7 d. With ZnSPF weight average molecular weights (Mw) up to 178 000, a Tm around 199 °C and a 𝚫Hm around 99 J g−1 were achieved. The samples annealed for 4 or 7 d also display a saw tooth pattern of the mass peak distribution in the matrix-assisted laser desorption/ionization time of flight spectra indicating transesterification reactions across the surface of extended ring crystals. This process optimizes the thermodynamical properties of the crystalline cyclic polylactides and is responsible for the high Tm and 𝚫Hm values. KW - Polylactide KW - MALDI-TOF MS KW - Ring opening polymerization KW - Polymerization PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-578264 DO - https://doi.org/10.1002/macp.202300070 SN - 1022-1352 SP - 202300070 PB - Wiley VHC-Verlag AN - OPUS4-57826 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 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 - Chabbah, T. A1 - Chatti, S. A1 - Jaffrezic-Renault, N. A1 - Weidner, Steffen A1 - Marestin, C. A1 - Mercier, R. T1 - Impedimetric sensors based on diethylphosphonate-containingpoly(arylene ether nitrile)s films for the detection of lead ions N2 - This article describes the elaboration and characterization of diethylphosphonate-containing polymers coated electrodes as sensors for the detection of heavy metalstraces, by electrochemical impedance spectroscopy. Diethylphosphonate groupswere chosen as heavy metals binding sites. Two different series of polymers bearingthese anchoring groups were synthesized. Whereas the diethylphosphonate groupsare directly incorporated in the aromatic macromolecular chain in some polymers, analiphatic spacer is removing the chelating site from the polymer backbone in others.The influence of the macromolecular structure on the sensing response was studied,especially for the detection of Pb2+,Ni2+,Cd2+and Hg2+. Polymer P6, including thehigher amount of diethylphosphonate groups removed from the polymer chain by ashort alkyl spacer gave the higher sensitivity of detection of lead ions, with a detec-tion limit of 50 pM KW - Heavy metals KW - Phosphonate esters KW - Lead ions KW - MALDI TOF MS PY - 2023 DO - https://doi.org/10.1002/pat.6065 SN - 1042-7147 SP - 1 EP - 11 PB - John Wiley & Sons, Ltd AN - OPUS4-57356 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Becker, Roland A1 - Scholz, Philipp A1 - Jung, Christian A1 - Weidner, Steffen T1 - Thermo-Desorption Gas Chromatography-Mass Spectrometry for investigating the thermal degradation of polyurethanes N2 - Thermo-Desorption Gas Chromatography-Mass Spectrometry (TD-GC-MS) was used to investigate the thermal degradation of two different polyurethanes (PU). PU samples were heated at different heating rates and the desorbed products were collected in a cold injection system and thereafter submitted to GC-MS. Prospects and limitations of the detection and quantification of semi-volatile degradation products were investigated. A temperature dependent PU depolymerization was found at temperatures above 200 °C proved by an increasing release of 1,4-butanediol and methylene diphenyl diisocyanate (MDI) representing the main building blocks of both polymers. Their release was monitored quantitatively based on external calibration with authentic compounds. Size Exclusion Chromatography (SEC) of the residues obtained after thermodesorption confirmed the initial competitive degradation mechanism indicating an equilibrium of crosslinking and depolymerization as previously suggested. Matrix-Assisted Laser Desorption Ionization (MALDI) mass spectrometry of SEC fractions of thermally degraded PUs provided additional hints on degradation mechanism. KW - Thermo-desorption KW - Mass spectrometry KW - Polyurethanes KW - Thermal degradation PY - 2023 DO - https://doi.org/10.1039/D3AY00173C SN - 1759-9660 SP - 1 EP - 6 PB - Royal Society for Chemistry AN - OPUS4-57307 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. A1 - Weidner, Steffen A1 - Meyer, A. T1 - Ring-expansion polymerization (REP) of L-lactide with cyclic tin catalysts – About formation of extended ring crystals and optimization of Tm and ΔHm N2 - L-Lactide was polymerized in bulk at 140 °C with three different cyclic tin catalysts and the time was varied from 1 d up to 14 d. The MALDI TOF spectra confirmed the formation of cyclic polylactides (PLAs) and displayed a characteristic change of peak intensity distribution with formation of a “saw tooth pattern”. This pattern confirms a previous hypothesis that cyclic PLAs tend to form crystallites with extended ring conformation and relatively smooth surface. This type of crystallites is formed under thermodynamic control by transesterification on the surface of the crystallites. In this way PLAs with extraordinarily high melting temperatures (Tm's up to 200.6 °C) and extraordinarily high melting enthalpy were obtained (ΔHm's up to 105 J g−1). These ΔHm values require a revision of the maximum ΔHm value calculated in the literature for ideal PLA crystals. KW - Polylactide KW - MALDI-TOF MS KW - ring-expansion polymerization PY - 2022 DO - https://doi.org/10.1016/j.polymer.2022.125516 SN - 0032-3861 VL - 263 SP - 125516 PB - Elsevier Ltd. AN - OPUS4-56338 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Martins, Ines A1 - Al-Sabbagh, Dominik A1 - Bentrup, U. A1 - Marquardt, Julien A1 - Schmid, Thomas A1 - Scoppola, E. A1 - Kraus, Werner A1 - Stawski, Tomasz A1 - de Oliveira Guilherme Buzanich, Ana A1 - Yusenko, Kirill A1 - Weidner, Steffen A1 - Emmerling, Franziska T1 - Formation Mechanism of a Nano-Ring of Bismuth Cations and Mono-Lacunary Keggin-Type Phosphomolybdate N2 - A new hetero-bimetallic polyoxometalate (POM) nano-ring was synthesized in a one-pot procedure. The structure consists of tetrameric units containing four bismuth-substituted monolacunary Keggin anions including distorted [BiO8] cubes. The nano-ring is formed via self-assembly from metal precursors in aqueous acidic medium. The compound (NH4)16[(BiPMo11O39)4] ⋅ 22 H2O; (P4Bi4Mo44) was characterized by single-crystal X-ray diffraction, extended X-ray absorption fine structure spectroscopy (EXAFS), Raman spectroscopy, matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF), and thermogravimetry/differential scanning calorimetry mass spectrometry (TG-DSC-MS). The formation of the nano-ring in solution was studied by time-resolved in situ small- and wide-angle X-ray scattering (SAXS/WAXS) and in situ EXAFS measurements at the Mo−K and the Bi−L3 edge indicating a two-step process consisting of condensation of Mo-anions and formation of Bi−Mo-units followed by a rapid self-assembly to yield the final tetrameric ring structure. KW - Bismuth KW - In situ EXAFS KW - In situ SAXS/WAXS KW - Lacunary Keggin ion KW - Polyoxometalates KW - Self-assembly PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-546823 DO - https://doi.org/10.1002/chem.202200079 SN - 0947-6539 VL - 28 IS - 27 SP - 1 EP - 7 PB - Wiley-VCH CY - Weinheim AN - OPUS4-54682 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen T1 - Synthesis of polylactides by means of tin catalysts N2 - This article reviews the usefulness of tin(II) and tin(IV) salts and compounds as catalysts for the polymerization of lactides. The text is subdivided into nine parts mainly reflecting different polymerization strategies, such as ring-opening polymerization (ROP), ring-expansion polymerization (REP), ROP combined with simultaneous polycondensation (ROPPOC), various catalysts with unknown polymerization mechanisms, and polycondensation of lactic acid. Since the toxicity of tin salts and compounds is a matter of concern and frequently mentioned in numerous publications, the first section deals with facts instead of myths about the toxicity of tin salts and compounds. KW - Polylactide KW - MALDI-TOF MS KW - Tin catalysts PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-545050 DO - https://doi.org/10.1039/d2py00092j SP - 1 EP - 30 PB - Royal Society for Chemistry AN - OPUS4-54505 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 - Ring-opening polymerizations of L-Lactide catalyzed by zinc caprylate: Syntheses of cyclic and linear poly(L-lactide)s N2 - Alcohol-initiated ring-opening polymerizations (ROPs) of L-Lactide (LA) were conducted in bulk at 130 °C catalyzed by Zn acetate (ZnAc2), lactate (ZnLac2), or caprylate (ZnCap2). 11-undecenol (UND), 1-hydroxymethylnaphtalene (HMN), and 4-nitrobenzylalcohol (4NB) were used as alcohols. Whereas variation of the alcohols had little effect, the usefulness of the catalysts increased in the order: acetate < lactate < caprylate. Hence, further alcohol-initiated polymerizations were performed with ZnCap2 alone and with variation of the lactide/catalyst (LA/Cat) ratio. With increasing LA/Cat ratio higher fractions of cyclic poly(L-lactide) (PLA) were found, so that the measured degree of polymerization (DP) is considerably lower than the theoretical value (i.e., 2 x LA/alcohol). With neat ZnCap2 cyclic PLAs were the largely prevailing reaction products. For these cyclic PLAs weight average molar masses (Mw) up to 134,000 were obtained and an optical purity around 99% was indicated by 13C NMR spectroscopy and DSC measurements even after 48 h at 150 or 160 °C. KW - Cyclization KW - Lactide KW - Ring opening polymerization KW - Transesterification KW - Zinc catalyst KW - MALDI PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-557565 DO - https://doi.org/10.1002/pol.20220328 SN - 2642-4150 SP - 1 EP - 10 PB - Wiley AN - OPUS4-55756 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 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 - Falkenhagen, Jana T1 - The role of transesterifications in reversible polycondensations and a reinvestigation of the Jacobson-Beckmann-Stockmayer experiments N2 - The polycondensations of adipic acid and 1,10-decanediol catalyzed by toluene sulfonic acid (TSA) were reinvestigated using MALDI TOF mass spectrometry and NMR spectroscopy. Unexpected reactions of TSA were detected along with incomplete conversion of the monomers. Furthermore, transesterification reactions of end-capped poly(1,10-decanediol adipate) and end-capped poly(ε-caprolactone) catalyzed by TSA were studied. Despite the quite different (ionic) reaction mechanisms, it was found that for polycondensations performed in bulk intermolecular transesterification is more efficient than the intramolecular “back-biting”; this scenario was not considered in the Jacobson–Stockmayer theory of reversible polycondensations. These results also confirm that the Jacobson–Stockmayer explanation of reversible polycondensations solely on the basis of ring chain equilibration is not only devoid of any experimental evidence, but also in contradiction to the results elaborated in this work. KW - Polylactide KW - MALDI-TOF MS KW - Polycondensation PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-543402 DO - https://doi.org/10.1039/d1py01679b SN - 1759-9962 SP - 1 EP - 9 PB - RSC Publ. CY - Cambridge AN - OPUS4-54340 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 - SnOct2-catalyzed and alcohol-initiated ROPS of L-lactide - Control of the molecular weight and the role of cyclization N2 - Ring-opening polymerizations (ROP) of l-lactide (LA) are conducted in bulk at 130, 160, or 180 °C and are initiated with two different alcohols at 160 °C. The lactide/initiator ratio (LA/In) is varied from 50/1 (20/1 at 180 °C) to 900/1 and the lactide/catalyst ratio (LA/Cat) between 2000/1 and 8000/1. At all temperatures a nearly perfect control of number average molecular weight (Mn) via the LA/In ratio is feasible up to LA/In = 200/1, but at higher ratios the Mn value lags behind the theoretical values and the discrepancy increases with higher LA/Cat ratios. Variation of the LA/Cat ratio influences the formation of cycles but does not significantly influence Mn, when the LA/In ratio is kept constant. The formation of cycles is favored by lower In/Cat ratios and is the main reason for the unsatisfactory control of Mn at high LA/In ratios. The results also suggest that the cycles are mainly or exclusively formed by end-to-end cyclization and not, as believed previously, by back-biting. KW - Polylactide KW - MALDI-TOF MS KW - Cyclization KW - Ring-opening polymerization PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-543066 DO - https://doi.org/10.1002/macp.202100464 SN - 1521-3935 SP - 1 EP - 10 PB - Wiley-VCH CY - Weinheim AN - OPUS4-54306 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -