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 OPUS4-49210 Zeitschriftenartikel Kricheldorf, H.; Weidner, Steffen SnOct 2-Catalyzed Syntheses of Cyclic Poly (l-lactide) s with Catechol as Low-Toxic Co-catalyst 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. Springer 2019 Journal of Polymers and the Environment 10924 10.1007/s10924-019-01545-5 2019-10-07 OPUS4-49211 Zeitschriftenartikel Kricheldorf, Hans; Weidner, Steffen About the influence of salicylic acid on tin(II)octanoate-catalyzed ring opening polymerizationof L-lactide 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. Elsevier Ltd. 2019 European Polymer Journal 119 37 44 10.1016/j.eurpolymj.2019.07.003 2019-10-07 OPUS4-48862 Zeitschriftenartikel Kricheldorf, H. R.; Weidner, Steffen; Scheliga, F. Synthesis of cyclic poly(l-lactide) catalyzed by Bismuth salicylates-A combination of two drugs l-lactide was polymerized in bulk at 160 or 180°C with mixtures of bismuth subsalicylate (BiSub) and salicylic (SA) as catalysts. The SA/Bi ratio and the monomer/Bi ratio were varied. The highest molecular weights (weight average, Mw) were achieved at a SA/Bi ratio of 1/1 (Mw up to 92 000 g mol−1). l-Lactide was also polymerized with combinations of BiSub and silylated SA, and Mw values up to 120 000 g mol−1 were achieved at 180°C. MALDI-TOF mass spectrometry and Mark-Houwink-Sakurada measurements proved that under optimized reaction conditions the resulting polylactides consist of cycles. Wiley 2019 Journal of Polymer Science A-Polymer Chemistry 29473 urn:nbn:de:kobv:b43-488622 10.1002/pola.29473 https://creativecommons.org/licenses/by/4.0/deed.de 2019-09-05 OPUS4-48619 Zeitschriftenartikel Scholz, Philipp; Wachtendorf, Volker; Panne, Ulrich; Weidner, Steffen Scholz, Philipp Degradation of MDI-based polyether and polyester-polyurethanes in various environments - Effects on molecular mass and crosslinking Size-exclusion chromatography (SEC) was used to monitor changes of the molecular masses of thermoplastic polyether - and polyester urethane (TPU) exposed to thermal, hydrolytic, and photo-oxidative (UV) Degradation conditions for several days. The thermal treatment was performed at elevated temperatures (100-200 °C) under oxidative (air) as well as non-oxidative (nitrogen) conditions to evaluate the specific influence of oxygen on the degradation. At higher temperatures (≥175 °C) a fast decrease of the molecular masses of both PU accompanied by a high degree of crosslinking was found. At lower temperatures (≤150 °C) the polymers remained widely unaffected by thermal degradation within the investigated degradation interval of up to two weeks. Surprisingly, the influence of oxygen (air) was found to be less distinct. In contrast to that, UV treatment at 25 °C at less than 10% rel. humidity (RH) resulted in a fast crosslinking, whereas the molecular masses of both PU decreased slower than for thermal treatments. The depth of penetration of the UV radiation was estimated using 3D printed PU samples with different thicknesses. Hydrolysis based degradation effects were less significant. Only slight molecular mass changes were detected at temperatures ≤80 °C within a time span of 14 days, while no crosslinking could be measured. Considering the degradation results at the investigated exposure parameters, it could be shown that esterbased PU in general exhibits a significant higher stability compared to ether-based materials. Amsterdam Elsevier 2019 Polymer Testing 77 105881, 1 12 10.1016/j.polymertesting.2019.04.028 2019-08-05 OPUS4-48625 Zeitschriftenartikel Scholz, Philipp; Wachtendorf, Volker; Elert, Anna Maria; Falkenhagen, Jana; Becker, Roland; Hoffmann, Katrin; Resch-Genger, Ute; Tschiche, Harald; Reinsch, Stefan; Weidner, Steffen Scholz, Philipp Analytical toolset to characterize polyurethanes after exposure to artificial weathering under systematically varied moisture conditions Polyether and -ester urethanes (PU) were exposed to artificial weathering at 40 °C and artificial UV radiation in a weathering chamber. In 3 parallel exposures, humidity was varied between dry, humid, and wet conditions. Material alteration was investigated by various analytical techniques like size exclusion chromatography (SEC), liquid chromatography-infrared spectroscopy (LC-FTIR), thermal-desorption gas chromatography-mass spectrometry (TD-GC-MS), fluorescence mapping and dynamic mechanical analysis (DMA). Our results show that depending on the weathering conditions, different degradation effects can be observed. By means of SEC an initial strong decrease of the molar masses and a broadening of the mass distributions was found. After a material dependent time span this was followed by a plateau where molar mass changes were less significant. A minor moisture-dependent degradation effect was only found for polyester PU. Fluorescence measurements on two materials revealed an increase in the luminescence intensity upon weathering process reaching a saturation level after about 500 h. The changes in the optical properties observed after different exposure conditions and times were very similar. The TD-GC-MS data showed the fate of the stabilizers and antioxidant in the course of weathering. LC-FTIR measurements revealed a change in peak intensities and the ratio of urethane and carbonyl bands. Amsterdam Elsevier 2019 Polymer Testing 78 105996, 1 9 10.1016/j.polymertesting.2019.105996 2019-08-06 OPUS4-48011 Zeitschriftenartikel Trimpin, S.; Inutan, E.; Karki, S.; Elia, E.; Zhang, W.; Weidner, Steffen; Marshall, D.; Hoang, K.; Lee, C.; Davis, E.; Smith, V.; Meher, A.; Cornejo, M.; Auner, G.; McEwen, C. Fundamental studies of new ionization technologies and insights from IMS-MS Exceptional ion mobility spectrometry mass spectrometry (IMS-MS) developments by von Helden, Jarrold, and Clemmer provided technology that gives a view of chemical/biological compositions previously not achievable. The ionization method of choice used with IMS-MS has been electrospray ionization (ESI). In this Special issue contribution, we focus on fundamentals of heretofore unprecedented means for transferring volatile and nonvolatile compounds into gas-phase ions singly and multiply charged. These newer ionization processes frequently lead to different selectivity relative to ESI and, together with IMS-MS, may provide a more comprehensive view of chemical compositions directly from their original Environment such as surfaces, e.g., tissue. Similarities of results using solvent- and matrix-assisted ionization are highlighted, as are differences between ESI and the inlet ionization methods, especially with mixtures such as bacterial extracts. Selectivity using different matrices is discussed, as are results which add to our fundamental knowledge of inlet ionization as well as pose additional avenues for inquiry. IMS-MS provides an opportunity for comparison studies relative to ESI and will prove valuable using the new ionization technologies for direct analyses. Our hypothesis is that some ESI-IMS-MS applications will be replaced by the new ionization processes and by understanding mechanistic aspects to aid enhanced source and method developments this will be hastened. Springer 2019 Journal of the American Society for Mass Spectrometry (JASMS) 30 6 1133 1147 10.1007/s13361-019-02194-7 2019-05-20 OPUS4-49396 Zeitschriftenartikel Lüdecke, Nils; Weidner, Steffen; Schlaad, Helmut Poly(2-oxazoline) s Based on Phenolic Acids A series of phenolic-acid-based 2-oxazoline monomers with methoxysubstituted phenyl and cinnamyl side chains is synthesized and polymerized in a microwave reactor at 140 °C using methyl tosylate as the initiator. The obtained poly(2-oxazoline)s are characterized by NMR spectroscopy, MALDITOF mass spectrometry, and size-exclusion chromatography (SEC). Kinetic studies reveal that the microwave-assisted polymerization is fast and completed within less than ≈10 min for low monomer-to-initiator ratios of ≤25. Polymers with number-average molar masses of up to 6500 g mol−1 and low dispersity (1.2-1.3) are produced. The aryl methyl ethers are successfully cleaved with aluminum triiodide/N,N′ diisopropylcarbodiimide to give a poly(2-oxazoline) with pendent catechol groups. Wiley VCH-Verlag 2019 Macromolecular Rapid Communications 1900404 10.1002/marc.201900404 2019-10-28 OPUS4-49483 Zeitschriftenartikel Scholz, Philipp; Ulbricht, Alexander; Joshi, Y.; Gollwitzer, Christian; Weidner, Steffen Microstructure of polymer-imprinted metal-organic frameworks determined by absorption edge tomography Mechanochemically synthesized metal-organic Framework material HKUST-1 in combination with acrylonitrile butadiene styrene polymer was used to form a polymer metal-organic framework composite material by a simple extruder. This composite filament was used for 3D printing. Xray diffraction measurements were used to prove the homogeneous distribution of the metal-organic framework in the polymer on a centimeter scale, whereas X-ray Absorption Edge Tomography using a synchrotron radiation source was able to evaluate the 3D distribution of the metal-organic framework material both in the filament and the resultant printed sample with a resolution of a few lm. Our very first data indicate that, apart from a few clusters having significantly higher Cu concentration, HKUST-1 is distributed homogeneously down to the 100 lm length scale in both polymer bulk materials in the form of clusters with a size of a few lm. Absorption Edge Tomography in combination with data fusion also allows for the calculation of the metal-organic framework amount located on the external polymer surface. Carl Hanser Verlag 2019 International Journal of Materials Research (IJMR) 1 10 10.3139/146.111817 2019-11-04 OPUS4-49669 Zeitschriftenartikel Meyer, A.; Weidner, Steffen; Kricheldorf, H. Stereocomplexation of cyclic polylactides with each other and with linear poly(L-lactide)s Two kinds of cyclic poly(D- and L-lactide)s were synthesized, namely CI labeled samples mainly consisting of even-numbered cycles with low dispersity and CII, CIII or CIV-labeled ones consisting of equal amounts of even and odd-numbered cycles with high dispersity and igher molecular weights (Mw up to 300 000). Furthermore, linear poly L-lactide)s were prepared by initiation with ethanol and in both series the molecular weight was varied. The formation of stereocomplexes from cyclic poly(D-lactide)s and all kinds of poly L-lactide)s was performed in dichloromethane/toluene mixtures. The stereocomplexes crystallized from the reaction mixture were characterized in the virgin state and after annealing at 205 °C. Stereocomplexes free of stereohomopolymers with crystallinities up to 80% were obtained from all experiments in yields ranging from 60 to 80%. Despite the high annealing temperature (maintained for 1 h), little transesterification was observed and the crystallinity slightly increased. Royal Society for Chemistry 2019 RSC Polymer Chemistry 10 6191 6199 urn:nbn:de:kobv:b43-496693 10.1039/c9py01236b https://creativecommons.org/licenses/by-nc/4.0/deed.de 2019-11-25 OPUS4-47363 Zeitschriftenartikel You, Zengchao; Jakubowski, Norbert; Panne, Ulrich; Weidner, Steffen Separation of polystyrene nanoparticles with different coatings using two-dimensional off-line coupling of asymmetrical flow field flow fractionation and capillary electrophoresis The successful off-line coupling of asymmetrical flow field flow fractionation (AF4) and capillary electrophoresis (CE) for separation of nanoparticles (NPs) with different surface coatings was shown. We could successfully demonstrate that, in a certain NP size range, hyphenation of both techniques significantly improved the separation of differently coated NPs. Three mixtures of polystyrene nanoparticles (PS-NPs) with comparable core sizes but different coatings (no coating/carboxyl-coated) were studied. Separation in either method resulted in non-baseline resolved or non-separated peaks. In contrast, two-dimensional off-line coupling of AF4 and CE resulted in clearly separated regions in their 2 D plots in case of 20 and 50 nm particle mixtures, whereas the 100 nm NP mixture could not be separated at all. Various factors affecting the separation like hydrodynamic diameter or SDS concentration were discussed. Elsevier 2019 Journal of Chromatography A 1593 119 126 10.1016/j.chroma.2019.01.056 2019-02-13 OPUS4-47481 Zeitschriftenartikel Kricheldorf, H.; Weidner, Steffen; Scheliga, F. Cyclic poly(lactide)s via the ROPPOC method catalyzed by alkyl- or aryltin chlorides 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: Me2SnCl2