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 OPUS4-28171 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 OPUS4-26273 Zeitschriftenartikel Kricheldorf, H.R.; Weidner, Steffen; Scheliga, F.; Lahcini, M. Poly(epsilon-caprolactone) by combined ring-opening polymerization and polycondensation Numerous water-initiated polymerizations of εCL are conducted in bulk with variation of catalyst, reaction time, and temperature. The conversions are determined by 1H NMR and the molar masses by SEC measurements. For polymerizations at 100 °C, Bi triflate and Hf triflate are used as catalysts, whereas at 140 °C, Al triflate, Sn(II) triflate, SnCl2, HfCl4, BiCl3, and LaCl3 are used. In addition to a closed reaction vessel, experiments are also performed with stirring in a vacuum. Under these conditions, the best catalyst (SnCl2) yields 2-3 times higher molar masses and mass spectra indicate a significant higher fraction of cyclic polymers. The results prove that a modification of the procedure may stimulate a polycondesation process without change of catalyst, time, and temperature. Weinheim Wiley-VCH Verl. 2012 Macromolecular chemistry and physics 213 14 1482 1488 10.1002/macp.201200061 2016-02-19 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 OPUS4-54306 Zeitschriftenartikel Kricheldorf, H. R.; Weidner, Steffen; Scheliga, F. SnOct2-catalyzed and alcohol-initiated ROPS of L-lactide - Control of the molecular weight and the role of cyclization 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. Weinheim Wiley-VCH 2022 Macromolecular chemistry and physics 1 10 urn:nbn:de:kobv:b43-543066 10.1002/macp.202100464 https://creativecommons.org/licenses/by-nc/4.0/deed.de 2022-02-11 OPUS4-55756 Zeitschriftenartikel Kricheldorf, H. R.; Weidner, Steffen; Scheliga, F. Ring-opening polymerizations of L-Lactide catalyzed by zinc caprylate: Syntheses of cyclic and linear poly(L-lactide)s 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. Wiley 2022 Journal of Polymer Science A: Polymer Chemistry 1 10 urn:nbn:de:kobv:b43-557565 10.1002/pol.20220328 https://creativecommons.org/licenses/by-nc-nd/4.0/deed.de 2022-09-21 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 OPUS4-22953 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