TY - CONF A1 - Weidner, Steffen T1 - Polymer characterization using sophisticated liquid chromatographic techniques combined with MALDI- and ESI-TOF mass spectrometry T2 - 55th ASMS conference on Mass Spectrometry CY - Indianapolis, IN, USA DA - 2007-06-03 PY - 2007 AN - OPUS4-14745 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Weidner, Steffen T1 - LC-MALDI coupling for the analysis of polymers T2 - National Meeting of the Centre National de la Recherche Scientifique (CNRS) CY - Strasbourg, France DA - 2004-06-03 PY - 2004 AN - OPUS4-11308 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Thünemann, Andreas A1 - Rolf, Simone A1 - Knappe, Patrick A1 - Weidner, Steffen T1 - In Situ Analysis of a Bimodal Size Distribution of Superparamagnetic Nanoparticles N2 - The dispersed iron oxide nanoparticles of ferrofluids in aqueous solution are difficult to characterize due to their protective polymer coatings. We report on the bimodal size distribution of superparamagnetic iron oxide nanoparticles found in the MRI contrast agent Resovist, which is a representative example of commercial nanoparticle-based pharmaceutical formulations. The radii of the majority of the nanoparticles (>99%) range from 4 to 13 nm (less than 1% of the particles display radii up to 21 nm). The maxima of the size distributions are at 5.0 and 9.9 nm. The analysis was performed with in situ characterization of Resovist via online coupling of asymmetrical flow field-flow fractionation (A4F) with small-angle X-ray scattering (SAXS) using a standard copper X-ray tube as a radiation source. The outlet of the A4F was directly coupled to a flow capillary on the SAXS instrument. SAXS curves of nanoparticle fractions were recorded at 1-min time intervals. We recommend using the A4F-SAXS coupling as a routine method for analysis of dispersed nanoparticles with sizes in the range of 1-100 nm. It allows a fast and quantitative comparison of different batches without the need for sample preparation. PY - 2009 DO - https://doi.org/10.1021/ac802009q SN - 0003-2700 SN - 1520-6882 VL - 81 IS - 1 SP - 296 EP - 301 PB - American Chemical Society CY - Washington, DC AN - OPUS4-18658 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Knappe, Patrick A1 - Bienert, Ralf A1 - Weidner, Steffen A1 - Thünemann, Andreas T1 - Poly(acrylic acid): A combined analysis with field-flow fractionation and SAXS N2 - Polyelectrolytes such as PAA and its salts are widely used, but are notoriously difficult to characterize due to their polyelectrolyte properties and broad molecular mass distributions. In this paper, we report on a new PAA analysis by combining asymmetrical flow field-flow fractionation and an advanced SAXS technique using an acoustic levitator to minimize background scattering. The proof-of-principle is demonstrated with a mixture of three standard PAAs with different molecular masses. Detailed information on the PAA fractions is available on radii of gyration, polymer contour lengths, and coil conformation. Our method is expected to be applicable for a wide range of water-soluble synthetic and natural polymers and ideal for molecular masses of 5 × 103–2 × 105 g · mol-1. KW - Fractionation of polymers KW - Molar mass distribution KW - Polyelectrolytes KW - Small-angle X-ray scattering KW - Water-soluble polymers PY - 2010 DO - https://doi.org/10.1002/macp.201000163 SN - 1022-1352 SN - 1521-3935 VL - 211 IS - 19 SP - 2148 EP - 2153 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-22005 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Weidner, Steffen T1 - MALDI Imaging MS von Polymeren T2 - BRUKER-Anwendertreffen CY - Kassel, Germany DA - 2011-03-21 PY - 2011 AN - OPUS4-23603 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Chatti, S. A1 - Weidner, Steffen A1 - Fildier, A. A1 - Kricheldorf, H.R. T1 - Copolyesters of isosorbide, succinic acid, and isophthalic acid: biodegradable, high Tg engineering plastics N2 - 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. KW - Biodegradable KW - Cyclization KW - Cyclopolymerization KW - Isophthalic acid KW - Isosorbide KW - Polycondensation KW - Polyesters KW - Renewable resources KW - Succinic acid PY - 2013 DO - https://doi.org/10.1002/pola.26635 SN - 0360-6376 SN - 0887-624X VL - 51 IS - 11 SP - 2464 EP - 2471 PB - Wiley CY - Hoboken, NJ AN - OPUS4-28577 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 - Lüdecke, Nils A1 - Weidner, Steffen A1 - Schlaad, Helmut T1 - Poly(2‐oxazoline) s Based on Phenolic Acids N2 - 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. KW - 2-oxazoline KW - Catechol KW - Cationic ring opening polymerization KW - Microwave KW - Phenolic acid PY - 2019 DO - https://doi.org/10.1002/marc.201900404 SP - 1900404 PB - Wiley VCH-Verlag AN - OPUS4-49396 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Weidner, Steffen T1 - MALDI-TOF MS und MALDI-MSI zur Identifikation und Klassifizierung von Pollen N2 - Es werden die letzten Ergebnisse präsentiert, die es ermöglichen, einzelne Pollenkörner unterschiedlicher Arten in Mischungen mittels MALDI-TOF Massenspektrometrie bzw. MALDI-TOF Imaging zu messen und unter Zuhilfenahme multivariater Auswertemethoden zu klassifizieren. T2 - 24. Bruker MALDI Anwendertreffen CY - Leipzig, Germany DA - 18.02.2019 KW - MALDI-TOF Massenspektrometrie KW - Pollenkörner KW - Klassifizierung KW - MALDI Imaging KW - Multivariate Analyse PY - 2019 AN - OPUS4-47441 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zeegers, G. P. A1 - Steinhoff, R. F. A1 - Weidner, Steffen A1 - Zenobi, R. T1 - Evidence for laser-induced redox reactions in matrix-assisted laserdesorption/ionization between cationizing agents and target plate material: a study with polystyrene and trifluoroacetate salts N2 - Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is often applied to assess the dispersity and the end groups of synthetic polymers through the addition of cationizing agents. Here weaddress how these cation adducts are formed using polystyrene (PS) as a model polymer. We analyzed PSby MALDI-MS with a 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile (DCTB) as the matrix and a range of trifluoroacetate (TFA) salts as cationizing agents on a range of different targetplate materials (copper, 1.4301 stainless steel, aluminum, Inconel 625, Ti90/Al6/V4 and chromium-, gold-and silver-plated stainless steel). It was found that on a stainless steel substrate the metal cations Al+,Li+, Na+, Cu+and Ag+formed polystyrene adducts, whereas K+, Cs+, Ba2+, Cr3+, Pd2+, In3+, or their lower oxidation states, did not. For the copper and silver substrates, PS and DCTB adduct formation with cations liberated from these target plate materials was observed upon addition of a cationizing agent, which indicates the occurrence of redox reactions between the added TFA salts and the target plate material. Judging from their standard electrode potentials, these redox reactions would not normally occur, i.e.,they require an additional energy input, strongly suggesting that the observed redox reactions are laser-induced. Furthermore, copper granules were found to successfully sequester PS from a tetrahydrofuran(THF) solution, consistent with the view complex formation with the copper target plate can take place prior to the MALDI-MS measurement. KW - Polymer MALDI KW - Cationization KW - Polystyrene KW - Laser-induced redox reactions KW - Target plate material PY - 2017 DO - https://doi.org/10.1016/j.ijms.2016.10.007 SN - 1387-3806 SN - 1873-2798 VL - 416 SP - 80 EP - 89 PB - Elsevier B.V. AN - OPUS4-41146 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weidner, Steffen A1 - Kricheldorf, H. R. T1 - The Role of Transesterification in SnOct 2 - Catalyzed Polymerizations of Lactides N2 - l-lactide or meso-lactide are polymerized either at 120 °C where the polymerization process of l-lactide is accompanied by crystallization, or at 180 °C where poly(l-lactide) remains in the molten state. Polymerizations at 120 °C initially yield even-numbered chains (with respect to lactic acid units) having relatively low dispersity, but the fraction of odd-numbered chains increases with time and the entire molecular weight distribution changes. Traces of cyclics are only formed after 7 d. Polymerizations at 180 °C yield equilibrium of even and odd-numbered chains from the beginning, but at low monomer/initiator ratios and short reaction times (<4 h) cyclics are again not formed. They appear at longer reaction times and entail higher dispersities. The results are discussed in terms of five different transesterification mechanisms. KW - Polylactides KW - MALDI KW - Transesterification KW - Sn catalysts PY - 2017 DO - https://doi.org/10.1002/macp.201600331 SN - 1022-1352 VL - 218 IS - 3 SP - 1600331 PB - Wiley AN - OPUS4-39753 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -