TY - JOUR A1 - Weidner, Steffen A1 - Meyer, A. A1 - Kricheldorf, H. R. T1 - Sn(II)2-ethylhexanoate-catalyzed polymerizations of L-lactide in solution – Solution grown crystals of cyclic Poly(L-Lactide)s N2 - L-lactide (LA) was polymerized in toluene by means of neat tin(II) 2-ethylhexanoate (SnOct2). Concentration, time and temperature were varied. The isothermally crystallized polyLAs (PLA) were characterized in the virgin state with regard to topology, molar mass, melting temperature (Tm), crystal modification, high or low Tm morphology, crystallinity and crystal thickness. Even a small amount of solvent favored cyclization relative to polymerization in bulk, so that cyclic polylactides were obtained at 115 ◦C and even at 95 ◦C. At all temperatures the α-modification of PLA was obtained along with crystallinities up to 90%. With 6 M solution the high Tm morphology with Tm’s > 190 ◦C was obtained at 115 ◦C. The crystal thickness of crystallites grown from solution at 115 ◦C was on the average 10–20% higher than that of PLA polymerized in bulk. At a polymerization temperature of 75 ◦C cyclization was incomplete and fewer perfect crystallites were formed. A new hypothesis for the crystal growth of cyclic polyLAs is proposed. KW - Polylactide KW - MALDI-TOF MS KW - Crystalinity KW - Polymerization PY - 2022 DO - https://doi.org/10.1016/j.polymer.2022.125142 SN - 0032-3861 VL - 255 SP - 1 EP - 9 PB - Elsevier CY - Oxford AN - OPUS4-55283 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 A1 - Scheliga, F. T1 - About formation of cycles in Sn(II) octanoate-catalyzed polymerizations of lactides N2 - At first, formation of cycles in commercial poly(Llactide)s is discussed and compared with benzyl alcoholinitiated polymerizations performed in this work. This comparison was extended to polymerizations initiated with 4-cyanophenol and pentafluorothiophenol which yielded cyclic polylactides via end-biting. The initiator/catalyst ratio and the acidity of the initiator were found to be decisive for the extent of cyclization. Further polymerizations of L-lactide were performed with various diphenols as initiators/co-catalysts. With most diphenols, cyclic polylactides were the main reaction products. Yet, only catechols yielded even-numbered cycles as main reaction products, a result which proves that their combination with SnOct2 catalyzed a ring-expansion polymerization (REP). The influence of temperature, time, co-catalyst, and catalyst concentrations was studied. Four different transesterification reactions yielding cycles were identified. For the cyclic poly(L-lactide)s weight average molecular weights (Mw’s) up to 120,000 were obtained, but 1H NMR end group analyses indicated that the extent of cyclization was slightly below 100%. The influence of various parameters like structure of Initiator and catalyst and temperature on the formation of cyclic poly(Llactide)s has been investigated. Depending on the chosen conditions, the course of the polymerization can be varied from a process yielding exclusively linear polylactides to mainly cyclic polylactides. Three different reaction pathways for cyclization reactions have been identified. KW - Cyclization KW - MALDI-TOF MS KW - Polyester KW - Ring-opening polymerization KW - Transesterification PY - 2018 DO - https://doi.org/10.1002/pola.29077 SN - 0887-624X VL - 56 IS - 17 SP - 1915 EP - 1925 PB - Wiley Periodicals Inc. AN - OPUS4-46052 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 - 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 - 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 - Kricheldorf, H. A1 - Weidner, Steffen T1 - SnOct 2-Catalyzed Syntheses of Cyclic Poly (l-lactide) s with Catechol as Low-Toxic Co-catalyst N2 - Polymerizations of l-lactide in bulk at 160 or 180 °C were performed with 1/1 mixtures of catechol (CA) or 4-tert-butylcatechol (BuCA) and tin(II)-2-ethylhexanoate (SnOct2) as catalysts and a variation of the Lac/Cat ratio. Weight average molar masses (Mw) up to 170,000 g mol−1 were obtained with CA and up to 120,000 g mol−1 with BuCA. The cyclic structure of the resulting poly(l-lactide)s was proven by MALDI-TOF mass spectrometry and by comparison of their hydrodynamic volumes with those of commercial linear poly(l-lactide)s. The predominance of even-numbered cycles increased with lower temperatures and shorter polymerization times. This fnding indicates that the cyclic architecture is the results of a ring-expansion polymerization mechanism. Addition of silylated BuCA as co-catalyst was less favorable than addition of free BuCA. KW - Polylactide KW - MALDI-TOF MS KW - Cyclization KW - Catalyst KW - Catechol KW - Toxicity PY - 2019 DO - https://doi.org/10.1007/s10924-019-01545-5 SP - 10924 PB - Springer AN - OPUS4-49210 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H.R. A1 - Eggerstedt, S. A1 - Krüger, Ralph-Peter T1 - Macrocycles, 6a / MALDI-TOF mass spectrometry of tin-initiated macrocyclic polylactones in comparison to classical mass-spectroscopic methods PY - 1999 SN - 1022-1352 SN - 1521-3935 VL - 200 IS - 6 SP - 1284 EP - 1291 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-2166 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H.R. A1 - Vakhtangishvili, L. A1 - Schwarz, G. A1 - Krüger, Ralph-Peter T1 - Cyclic Hyperbranched Poly(ether ketone)s Derived from 3,5-Bis(4-fluorobenzoyl)phenol N2 - 3,5-Bis(4-fluorobenzoyl)phenol was polycondensed under various reaction conditions. Low molecular weights were obtained (Mn < 8000 Da), and MALDI-TOF mass spectrometry indicated that the chain growth was limited by cyclization. In the best mass spectra the cyclic, hyperbranched poly(ether ketone)s were detectable up to masses around 14 000 Da. When 4,4'-difluordiphenyl sulfone was added, star-shaped polymers having a diphenyl sulfone star center were formed, but cyclization was not completely suppressed. The results were compared to those obtained from "linear polycondensations" based on 4,4'-difluorobenzophenone (DFBP) and 4-tert-butylcatechol or bisphenol A. The poly(ether ketone)s of DFBP had also low molecular weights and contained high fractions of cycles. It is concluded that also in the case of hyperbranched polymers cyclization competes with propagation at any stage of the polycondensation at any concentration. Therefore, the fundamental trend of any "abn" polycondensation is the formation of star-shaped polymers having a cyclic core and hyperbranched star arms. PY - 2003 DO - https://doi.org/10.1021/ma021799x SN - 0024-9297 SN - 1520-5835 VL - 36 SP - 5551 EP - 5558 PB - American Chemical Society CY - Washington, DC AN - OPUS4-2622 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H.R. A1 - Vakhtangishvili, L. A1 - Schwarz, G. A1 - Schulz, Günter A1 - Krüger, Ralph-Peter T1 - Macrocycles 25. Cyclic poly(ether sulfone)s derived from 4-tert-butylcatechol N2 - Poly(ether sulfone)s were prepared by polycondensation of silylated 4-tert-butylcatechol and 4,4?-difluorodiphenylsulfone in N-methylpyrrolidone. The feed ratio and the reaction time were varied to study the influence of stoichiometry and conversion on molecular weight and extent of cyclization. Molecular weights and molecular weight distributions (MWD)s were characterized by SEC measurements calibrated with polystyrene. Light scattering confirmed that calibration with polystyrene gives reasonable results and revealed a tendency towards a bimodal MWD for the samples rich in cycles. The MALDI-TOF mass spectrometry indicated that the extent of cyclization increased with higher conversion and with optimization of the stoichiometry. This interpretation was confirmed by 1H NMR endgroup analyses. For the samples with the highest molar masses only mass peaks of cycles were found, which were detectable up to 20 000 Da before and up to 27 000 Da after fractionation. Via the pseudo-high dilution method low molar mass poly(ether sulfone) containing more than 95 mol% of cycles were prepared, and even these low molar mass samples had broad MWDs. DSC measurements indicated that the glass transition temperatures depend on the structure of the endgroups and increase with higher fractions of cycles. KW - Poly(ether sulfone)s KW - Polycondensation KW - MALDI-TOF mass spectrometry PY - 2003 DO - https://doi.org/10.1016/S0032-3861(03)00410-5 SN - 0032-3861 SN - 1873-2291 VL - 44 SP - 4471 EP - 4480 PB - Springer CY - Berlin AN - OPUS4-2623 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H.R. A1 - Böhme, S. A1 - Schwarz, G. A1 - Krüger, Ralph-Peter A1 - Schulz, Günter T1 - Macrocycles 18. The Role of Cyclization in Syntheses of Poly(ether-sulfone)s N2 - Poly(ether-sulfone)s having an identical backbone were prepared by four different methods. First, silylated bisphenol A (BSBA) was polycondensed with 4,4'-difluorodiphenyl sulfone (DFDPS) and K2CO3 in N-methylpyrrolidone with variation of the temperature. Second, analogous polycondensation were conducted using CsF as catalyst (and no K2CO3). Third, CsF-catalyzed polycondensations BSBA and DFDPS were conducted in bulk up to 290 C. Fourth, free bisphenol was polycondensed with DFDPS or 4,4'-dichlorodiphenyl sulfone and K2CO3 in DMSO with azeotropic removal of water. MALDI-TOF mass spectroscopy revealed that the first method mainly yielded cyclic poly(ether-sulfone)s which were detected up to masses around 13 000 Da. These and other results suggest that these polycondensations take a kinetically kontrolled course at tempeatures 145 C. This interpretation is also valid for the fourth method where high yields of cycles were obtained with DFDPS. With the less reactive 4,4'-dichlorodiphenyl sulfone lower conversions, lower molecular weights and lower fractions of cycles were found. In contrast to KF (resulting from K2CO3) CsF cleaves the poly(ether sulfone) backbone at temperatures > 145 C. Smaller amounts of smaller cycles were found in these CsF-catalyzed polycondensations which were in this case the result of thermodynamically controlled "back-biting degradation". PY - 2001 DO - https://doi.org/10.1021/ma010218l SN - 0024-9297 SN - 1520-5835 VL - 34 SP - 8886 EP - 8893 PB - American Chemical Society CY - Washington, DC AN - OPUS4-2176 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H.R. A1 - Rabenstein, M. A1 - Langanke, D. A1 - Schwarz, G. A1 - Schmidt, M. A1 - Maskos, M. A1 - Krüger, Ralph-Peter T1 - Ring-closing polycondensations N2 - The role of cyclization in polycondensations is discussed for two different scenarios: thermodynamically-controlled polycondensation (TCPs) on the one hand and kinetically-controlled polycondensations (KCPs) on the other. The classical Carothers–Flory theory of step-growth polymerization does not include cyclization reactions. However, TCPs involve the formation of cycles via ‘back-biting degradation’, and when the ring–chain equilibrium is on the side of the cycles the main reaction products of the TCP will be cyclic oligomers. Two groups of examples are discussed: polycondensations of salicyclic acid derivatives (e.g. aspirin) and polycondensations of dibutyltin derivatives with long {alpha}-, {omega}-diols or dicarboxylic acids. Furthermore, various kinetically-controlled syntheses of polyesters and polyamides were studied and carefully optimized in the direction of high molecular weights. High fractions of cyclic oligomers and polymers were found by MALDI-TOF mass spectrometry, and their fractions increased with optimization of the process for molecular weight. These results disagree with the Carothers–Flory theory but agree with the theoretical background of the Ruggli–Ziegler dilution method (RZDM). When poly(ether-sulfone)s were prepared from 4,4'-difluorodiphenylsulfone and silylated bisphenol-A two different scenarios were found. With CsF as catalyst at a temperature of more than 145°C cyclic oligoethers were formed under thermodynamic control. When the polycondensation was promoted with K2CO3 in N-methylpyrolidone at ?145°C the formation of cyclic oligoethers and polyethers occurred under kinetic control. A new mathematical formula is presented correlating the average degree of polymerization with the conversion and taking into account the competition between cyclization and propagation. PY - 2001 DO - https://doi.org/10.1088/0954-0083/13/2/312 SN - 0954-0083 SN - 1361-6412 VL - 13 SP - S123 EP - S136 PB - Sage Publ. CY - London AN - OPUS4-2178 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H.R. A1 - Böhme, S. A1 - Krüger, Ralph-Peter T1 - Macrocycles, 16a - Macrocyclic Dibutyltin Dicarboxylates via Thermodynamically Controlled Polycondensations N2 - Various dibutyltin derivatives were polycondensed with aliphatic ,-dicarboxylic acids having chain lengths from 4 (succinic acid) to 22 carbon atoms. White crystalline products were obtained from all experiments, and the structure of the products was independent of the synthetic method. Viscosity measurements revealed low molecular weights (n 1 500 Da) in all cases. Vapor pressure osmometry (VPO) measurements and matrix-assisted laser desorption time-of-flight (MALDI-TOF) mass spectrometry proved that cyclic dimers and trimer were formed from dicarboxylic acids having 6 to 16 carbons, but mainly the monomeric cycle from docosane dioic acid. Heating to 250°C did not change the structure. Therefore, the results indicate that the macrocycles are the result of a thermodynamically controlled ring-closing polycondensation. This means that linear high-molecular weight poly(dibutyltin dicarboxylate)s cannot exist above room temperature. KW - Macrocyclics KW - MALDI KW - Oligomers KW - Polycondensation KW - Thermodynamics PY - 2002 SN - 1022-1352 SN - 1521-3935 VL - 203 IS - 2 SP - 313 EP - 318 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-2181 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Ralph-Peter A1 - Kricheldorf, H.R. A1 - Böhme, S. T1 - Macrocyclic Dibutyltin Dicarboxylates via Thermodynamically Controlled Polycondensations KW - Macrocyclics KW - MALDI KW - Oligomers KW - Polycondensation KW - Thermodynamics PY - 2002 SN - 1022-1352 SN - 1521-3935 IS - 203 SP - 313 EP - 318 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-1656 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Ralph-Peter A1 - Kricheldorf, H.R. A1 - Böhme, S. T1 - Macrocycles 16. Macrocyclic Dibutyltin Dicarboxylates by Ring-Closing Polycondensation N2 - Various dibutyltin derivatives were polycondensed with aliphatic ,-dicarboxylic acids having chain lengths from 4 (succinic acid) to 22 carbon atoms. White crystalline products were obtained from all experiments, and the structure of the products was independent of the synthetic method. Viscosity measurements revealed low molecular weights (n 1 500 Da) in all cases. Vapor pressure osmometry (VPO) measurements and matrix-assisted laser desorption time-of-flight (MALDI-TOF) mass spectrometry proved that cyclic dimers and trimer were formed from dicarboxylic acids having 6 to 16 carbons, but mainly the monomeric cycle from docosane dioic acid. Heating to 250°C did not change the structure. Therefore, the results indicate that the macrocycles are the result of a thermodynamically controlled ring-closing polycondensation. This means that linear high-molecular weight poly(dibutyltin dicarboxylate)s cannot exist above room temperature. PY - 2002 DO - https://doi.org/10.1002/1521-3935(20020101)203:2<313::AID-MACP313>3.0.CO;2-V SN - 1022-1352 SN - 1521-3935 VL - 203 IS - 2 SP - 313 EP - 318 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-1796 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -