Dokument-ID Dokumenttyp Autoren/innen Persönliche Herausgeber/innen Haupttitel Abstract Auflage Verlagsort Verlag Herausgeber (Institution) Erscheinungsjahr Titel des übergeordneten Werkes Jahrgang/Band ISBN Veranstaltung Veranstaltungsort Beginndatum der Veranstaltung Enddatum der Veranstaltung Ausgabe/Heft Erste Seite Letzte Seite URN DOI Lizenz Datum der Freischaltung OPUS4-59685 Zeitschriftenartikel Kricheldorf, H.; Weidner, Steffen; Meyer, A. Syntheses of Polyglycolide via Polycondensation: A Reinvestigation 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. Wiley VHC-Verlag 2024 Macromolecular Chemistry and Physics 2300397 1 7 urn:nbn:de:kobv:b43-596856 10.1002/macp.202300397 https://creativecommons.org/licenses/by-nc/4.0/deed.de 2024-03-18 OPUS4-54340 Zeitschriftenartikel Kricheldorf, H. R.; Weidner, Steffen; Falkenhagen, Jana The role of transesterifications in reversible polycondensations and a reinvestigation of the Jacobson-Beckmann-Stockmayer experiments 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. Cambridge RSC Publ. 2022 Polymer chemistry 1 9 urn:nbn:de:kobv:b43-543402 10.1039/d1py01679b https://creativecommons.org/licenses/by/4.0/deed.de 2022-02-14 OPUS4-53083 Zeitschriftenartikel Kricheldorf, H. R.; Weidner, Steffen; Falkenhagen, Jana Reversible Polycondensations outside the Jacobson-Stockmayer Theory and a New Concept of Reversible Polycondensations L-Lactide was polymerized with tin(II)acetate, tin(II)2-ethyl hexanoate, diphenyltin dichloride and dibutyltin bis(pentafluorophenoxide) at 130 °C in bulk. When an alcohol was added as initiator, linear chains free of cycles were formed having a degree of polymerization (DP) according to the lactide/initiator (LA/In) ratio. Analogous polymerizations in the absence of an initiator yielded high molar mass cyclic polylactides. Quite similar results were obtained when ε-caprolactone was polymerized with or without initiator. Several transesterification experiments were conducted at 130 °C, either with polylactide or poly(ε-caprolactone) indicating that several transesterification mechanisms are operating under conditions that do not include formation of cycles by back-biting. Furthermore, reversible polycondensations (revPOCs) with low or moderate conversions were found that did not involve any kind of cyclization. Therefore, These results demonstrate the existence of revPOCs, which do neither obey the theory of irreversible polycondensation as defined by Flory nor the hypothesis of revPOCs as defined by Jacobson and Stockmayer. A new concept encompassing any kind of revPOCs is formulated in the form of a "polycondensation triangle". Royal Society for Chemistry 2021 Polymer Chemistry 12 35 5003 5016 urn:nbn:de:kobv:b43-530831 10.1039/d1py00704a https://creativecommons.org/licenses/by/4.0/deed.de 2021-08-11 OPUS4-52051 Zeitschriftenartikel Kricheldorf, H. R.; Weidner, Steffen Polymerization of L-lactide with SnCl2: A Low Toxic and Eco-friendly Catalyst Polymerizations of L-lactide catalyzed either by neat SnCl2 or by SnCl2 + difunctional cocatalysts were conducted in bulk at 180, 160 and 140 °C with variation of the Lac/Cat ratio and time. With neat SnCl2 poly(L-lactide) having weight average molecular weights (uncorrected Mw's) up to 190 000 g mol−1 were obtained mainly consisting of linear chains. Addition of salicylic acid or 1,1-bisphenol yielded a higher fraction of cyclic polylactides but lower molecular weights. Furthermore, SnCl2 was compared with Bu2SnCl2 and various other metal chlorides and the best results were obtained with SnCl2. With ethyl L-lactate as initiator SnCl2-catalyzed ROPs were performed at 120 °C and the lac/initiator ratio was varied. All these experiments were conducted under conditions allowing for comparison with ROPs catalyzed with neat Sn(II)-2-ethyhexanoate. Such a comparison was also performed with ε-caprolactone as monomer. Springer Nature 2021 Journal of Polymers and the Environment 1 13 urn:nbn:de:kobv:b43-520517 10.1007/s10924-020-02042-w https://creativecommons.org/licenses/by/4.0/deed.de 2021-01-28 OPUS4-52359 Zeitschriftenartikel Kricheldorf, H. R.; Scheliga, F.; Weidner, Steffen What does conversion mean in polymer science? The definition of the term "conversion" is discussed for a variety of polymer syntheses. It is demonstrated that in contrast to organic and inorganic chemistry several different definitions are needed in polymer science. The influence of increasing conversion on structure and topology of homo- and Copolymers is illustrated. Chain-growth polymerizations, such as radical polymerization or living anionic polymerizations of vinyl monomers, condensative chain polymerization, two and three-dimensional step-growth polymerizations, ring-ring or chain-chain equilibration and chemical modification of polymers are considered. Wiley VCH 2021 Macromolecular Chemistry and Physics 222 8 10 urn:nbn:de:kobv:b43-523597 10.1002/macp.202100010 https://creativecommons.org/licenses/by-nc-nd/4.0/deed.de 2021-03-29 OPUS4-46263 Zeitschriftenartikel Kricheldorf, H. R.; Weidner, Steffen Cyclic poly(L-lactide)s via simultaneous ROP and polycondensation (ROPPOC) catalyzed by dibutyltin phenoxides 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. Elsevier 2018 European Polymer Journal 109 360 366 10.1016/j.eurpolymj.2018.10.005 2018-10-16 OPUS4-33731 Zeitschriftenartikel Weidner, Steffen; Kricheldorf, H.R.; Scheliga, F. Cyclization and dispersity of poly(alkylene isophthalate)s Poly(alkylene isophthalate)s were prepared by different methods, either in solution or in bulk. The SEC measurements were evaluated in such a way that all oligomers were included. In solution (monomer conc. 0.1–0.7 mol/L) large fractions of rings were formed and high dispersities (up to 12) were obtained, which disagree with theoretical predictions. Polycondensations in bulk did neither generate cyclics by 'back-biting' nor by end-to-end cyclization, when the maximum temperature was limited to 210 °C. The dispersities of these perfectly linear polyesters were again higher than the theoretical values. Regardless of the synthetic method monomeric cycles were never observed. Furthermore, SEC measurements performed in tetrahydrofuran and in chloroform and SEC measurements performed in three different institutes were compared. Finally, SEC measurements of five samples were performed with universal calibration and a correction factor of 0.71 ± 0.02 was found for normal calibration with polystyrene. Hoboken, NJ Wiley 2016 Journal of polymer science A, polymer chemistry 54 1 197 208 10.1002/pola.27892 2016-02-20 OPUS4-30299 Zeitschriftenartikel Kricheldorf, H.R.; Mix, Renate; Weidner, Steffen Poly(ester urethane)s derived from lactide, isosorbide, terephthalic acidm abd various diisocyanates Isosorbide-initiated oligomerizations of ʟ-lactide were preformed in bulk using SnCl2 as catalyst. The resulting telechelic OH-terminated oligoesters were in situ subjected to simultaneous polycondensation and polyaddition with mixtures of terephthaloyl chloride and diisocyanates. Most polymerizations were conducted with 4,4'-diisocyanatodiphenyl methane and 2,4-diisocyanato toluene. The consequences of excess diisocyanate and four different catalysts were studied. The isosorbide/lactide ratio and the terephthalic acid/diisocyanate ratio were varied. Number average molecular weights up to 15 kDa with polydispersities around 3-5 were obtained. Depending on the chemical structure of the copolyester and on the feed ratio, incorporation of urethane groups may reduce or enhance the glass-transition temperature, but the thermal stability decreases dramatically regardless of composition. Hoboken, NJ Wiley 2014 Journal of polymer science A, polymer chemistry 52 6 867 875 10.1002/pola.27069 2016-02-20 OPUS4-28171 Zeitschriftenartikel Kricheldorf, H.R.; Weidner, Steffen Copolyesters of lactide, isosorbide, and terephthalic acid-biobased, biodegradable, high-Tg engineering plastics Various copolyesters of lactide, isosorbide, and terephthalic acid are prepared by a two-step process performed in a 'one-pot' procedure, beginning with an isosorbide-initiated oligomerization of L-lactide followed by polycondensation with terephthaloyl chloride using SnCl2 as a catalyst for both steps. The SEC data show the formation of random copolyesters with high polydispersities as a consequence of the relatively high fraction of cyclics proved by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). The glass-transition temperatures (89-180 °C) obey an almost linear trend with the molar composition. The thermostability decreases with increasing lactide content. The successful incorporation of phenyl phosphate results in copolyesters of lower inflammability. Weinheim Wiley-VCH Verl. 2013 Macromolecular chemistry and physics 214 6 726 733 10.1002/macp.201200612 2016-02-20 OPUS4-28577 Zeitschriftenartikel Chatti, S.; Weidner, Steffen; Fildier, A.; Kricheldorf, H.R. Copolyesters of isosorbide, succinic acid, and isophthalic acid: biodegradable, high Tg engineering plastics Isosorbide, succinyl chloride and isophthaloyl chloride are polycondensed under various reaction conditions. The heating in bulk with or without catalysts as well in an aromatic solvent without catalyst, and polycondensation with the addition of pyridine only yield low molar mass copolyesters. However, heating in chlorobenzene with addition of SnCl2 or ZnCl2 produces satisfactory molar masses. The number average molecular weights (Mn) of most copolyesters fall into the range of 7000-15,000 Da with polydispersities (PD) in the range of 3-9. The MALDI-TOF mass spectra almost exclusively displayed peaks of cyclics indicating that the chain growth was mainly limited by cyclization and not by side reactions, stoichiometric imbalance or incomplete conversion. The glass-transition temperatures increased with the content of isophthalic acid from 75 to 180 °C and the thermo-stabilities also followed this trend. Hoboken, NJ Wiley 2013 Journal of polymer science A, polymer chemistry 51 11 2464 2471 10.1002/pola.26635 2016-02-20 OPUS4-29014 Zeitschriftenartikel Kricheldorf, H.R.; Weidner, Steffen High Tg copolyesters of lactide, isosorbide and isophthalic acid Using SnCl2, ZnCl2, Zn-lactate or Zr-acetylacetonate as catalysts ʟ-lactide was oligomerized in bulk with isosorbide as initiator. The ratio isosorbide/lactide was varied from 8/2 to 2/8. The resulting oligomers were in situ polycondensed with isophthaloyl chloride in various aromatic solvents. In chlorobenzene homogeneous reaction mixtures were obtained, whereas molten copolyesters precipitated from toluene and xylene. The obtained average molecular weights indicated high polydispersities. According to MALDI-TOF MS the low molar mass reaction products (<4 kDa) almost exclusively consisted of cyclics with a composition depending on the feed ratio. The glass-transition temperatures (Tg) varied between the values of poly(ʟ-lactide (64 °C) and poly(isosorbide isophthalate) (180 °C). Four polyesters prepared from 5-tert-butyl isophthalic acid displayed higher Tg values. Differential thermoanalysis evidenced that the thermostability decreases with higher fractions of lactide, but processing from the melt seems to be feasible up to temperatures of 260 °C without risking degradation. Oxford Elsevier 2013 European polymer journal 49 8 2293 2302 10.1016/j.eurpolymj.2013.05.007 2016-02-20 OPUS4-29219 Zeitschriftenartikel Weidner, Steffen; Scheliga, F.; Kricheldorf, H.R. Low-temperature polymerization of epsilon-caprolactone catalyzed by cerium triflates Using 22 metal triflates as catalysts, ε-caprolactone is polymerized at 22 °C in bulk. Only five relatively acidic triflates prove active. Three triflates, including the neutral Sm3+, are active using water as initiator. A very low content of cyclics is found in all the experiments. With Ce3+ and Ce4+, polymerizations are performed in CH2Cl2 and in bulk at 2 °C and 22 °C. Low dispersities (down to 1.1) are obtained. At 22 °C, Ce4+ and, even better, Ce3+ also catalyze syntheses of CO2H- and CH2OH-terminated polycaprolactones, whereby higher dispersities and larger fractions of cyclics are obtained. Further polymerizations and polycondensations are catalyzed with protic acids. The results can be explained by a proton-catalyzed activated monomer mechanism. Weinheim Wiley-VCH Verl. 2013 Macromolecular chemistry and physics 214 18 2043 2053 10.1002/macp.201300279 2016-02-20 OPUS4-26500 Zeitschriftenartikel Kricheldorf, H.R.; Weidner, Steffen; Scheliga, F. Poly(Epsilon-caprolactone) by combined ring-opening polymerization and azeotropic polycondensation - the role of cyclization and equilibration Using three different catalysts, water-initiated polymerizations of ε-caprolactone were conducted in bulk with variation of the monomer/water ratio. The resulting CH2OH and CO2H- terminated polylactones were subjected in situ to azeotropic polycondensations. With Bi-triflate and temperatures, the polycondensations were not much successful and involved side reactions. With ZnCl2, and especially SnCl2, considerably higher molar masses were achieved. The substitution of toluene for chlorobenzene for refluxing gave better results. The polycondensations broadened the molar mass distribution of the ROP-based prepolymers, and polydispersities between 1.4-1.8 were obtained. The MALDI–TOF mass spectra revealed that the polycondensations significantly enhanced the fraction of rings due to efficient 'end-biting' reactions. By comparison with copolymerization experiments and Sn methoxide-initiated polymerizations, it was demonstrated that equilibration reactions, such as the formation of rings by 'back-biting,' did not occur. Hoboken, NJ Wiley 2012 Journal of polymer science A, polymer chemistry 50 20 4206 4214 10.1002/pola.26222 2016-02-19 OPUS4-22953 Zeitschriftenartikel Garaleh, M.; Kricheldorf, H.R.; Weidner, Steffen; Yashiro, T. Hafnium chloride catalyzed polycondensation of Alpha, Omega-alkanediol with dicarboxylic acids or succinic anhydride Philadelphia, PA Taylor & Francis 2010 Journal of macromolecular science A 47 4 303 308 10.1080/10601320903539199 2016-02-19 OPUS4-19626 Zeitschriftenartikel Garaleh, M.; Lahcini, M.; Kricheldorf, H.R.; Weidner, Steffen Syntheses of aliphatic polyesters catalyzed by lanthanide triflates Polycondensations of 1,6-hexane diol and sebacic acid were conducted in bulk with addition of a lanthanide triflate as acidic catalyst. With exception of promethium triflate all lanthanide triflates were studied. A particularly low molecular weight was obtained with neodym triflate and the best results with samarium triflate. With Sm(OTf)3 weight average (Mw) values up to 65 kDa (uncorrected SEC data) were achieved after optimization of the reaction conditions. Comparison of these results with those obtained from bismuth, magnesium, and zinc triflates, on the one hand, and comparison with the acidities of all catalysts, on the other, indicates that the esterification mechanism involves complexation of monomer by metal ions. Preparation of multiblock copoly(ether ester)s failed due to insufficient incorporation of poly(tetrahydrofuran) diols. Hoboken, NJ Wiley 2009 Journal of polymer science A, polymer chemistry 47 1 170 177 10.1002/pola.23136 2016-02-19