Ralph-Peter Krüger

Bundesanstalt für Materialforschung und -prüfung, Berlín, Berlin, Germany

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Publications (15)36.94 Total impact

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    Steffen Weidner · Jana Falkenhagen · Ralph-Peter Krueger · Ulrich Just
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    ABSTRACT: Two-dimensional polymer characterization is used for a simultaneous analysis of molar masses and chemical heterogeneities (e.g., end groups, copolymer composition, etc.). This principle is based on coupling of two different chromatographic modes. Liquid adsorption chromatography at critical conditions (LACCC) is applied for a separation according to the chemical heterogeneity, whereas in the second-dimension fractions are analyzed with regard to their molar mass distribution by means of size exclusion chromatography (SEC). Because appropriate standards for a calibration of the SEC are seldom available, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) was used to substitute the SEC. The LACCC-MALDI MS coupling enables acquiring additional structural information on copolymer composition, which can considerably enhance the performance of this coupled method.
    Full-text · Article · Aug 2007 · Analytical Chemistry
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    ABSTRACT: Das cyclische, arylsubstituierte Chlorphosphonit 3 reagiert mit Chlor zum Trichlor-oxyphosphoran 4 (6, 6, 6-Trichlor-6H-dibenzo[c, e]1, 2-oxaphosphorin). Die Stabilität des Phosphorans ist lösungsmittelabhängig.A stable Trichloro-oxyphosphorane with an Oxaphosphorine RingThe cyclic, aryl-substituted chlorophosphonite 3 reacts with chlorine to give the trichloro-oxyphosphorane 4 (6, 6, 6-trichloro-6H-dibenzo[c, e]1, 2-oxaphosphorine). The stability of the phosphorane is solvent-dependent.
    No preview · Article · Jun 2003 · Zeitschrift für anorganische Chemie
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    ABSTRACT: Liquid chromatography in combination with spectroscopic methods like matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) or nuclear magnetic resonance (NMR) spectroscopy is a powerful method to characterize silsesquioxanes and silsesquioxane mixtures. As new examples, the formation of silsesquioxyl-substituted silsesquioxanes [(n-octyl)(7)(SiO(1.5))(8)](2)O and [(n-octyl)(7)(SiO(1.5))(8)O](2)[(n-octyl)(6)(SiO(1.5))(8)] as well as the cage rearrangement of octa-[(n-heptyl)silsesquioxane] to larger structures [(n-heptyl)SiO(1.5))](n) up to n=28 are shown.
    No preview · Article · Feb 2003 · Rapid Communications in Mass Spectrometry
  • Hildegard Kukula · Helmut Schlaad · Jana Falkenhagen · Ralph-Peter Krüger
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    ABSTRACT: The synthesis of chlorosilane and styrene derivatives bearing a silazane functional group was facilitated. As a result, the availability of well-defined primary amino-functional polymers was improved.
    No preview · Article · Aug 2002 · Macromolecules
  • Hans R. Kricheldorf · Sigrid Böhme · Ralph-Peter Krüger
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    ABSTRACT: Various dibutyltin derivatives were polycondensed with aliphatic α,ω-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 (M̄n ⪇ 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.
    No preview · Article · Jan 2002 · Macromolecular Chemistry and Physics
  • Bernd Grimm · Ralph-Peter Krüger · Sigurd Schrader · Dietrich Prescher
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    ABSTRACT: Three new aromatic polyazomethines have been synthesized by solution polycondensation reactions of terephthalic dialdehyde with fluorine containing aromatic diamines. The polymers were obtained in high yields. The investigation of these polymers by means of matrix-assisted laser desorption ionization–time-of-flight–mass spectrometry (MALDI–TOF–MS) proved the initial members of the four theoretical possible series of the corresponding oligomers with 2–10 repeating units per molecule.
    No preview · Article · Jan 2002 · Journal of Fluorine Chemistry
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    ABSTRACT: 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”.
    No preview · Article · Nov 2001 · Macromolecules
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    ABSTRACT: We prepared 2,2-dibutyl-2-stanna-1,3-dithiacycloalkanes from dibutyltin oxide and α,ω-dimercaptoalkanes. Heterocycles with five-, six-, seven-, or nine-ring members were used as bifunctional monomers for polycondensations with aliphatic dicarboxylic acid chlorides. These polycondensations conducted in bulk were highly exothermic and yielded poly(thio ester)s with number average molecular weights (Mn's) in the range of 5000–30,000 Da. These poly(thio ester)s proved to be rapidly crystallizing materials with melting temperatures in the range of 90–150 °C. In addition to the success of the new synthetic approach, two interesting and unpredictable results were obtained. All volatile species detectable by matrix assisted laser desorption induced-time of flight (MALDI-TOF) mass spectrometry were cyclic oligo- and poly(thio ester)s. Second, several polyesters showed a reversible first-order change of the crystal modification as identified by differential scanning calorimetry measurements and X-ray scattering with variation of the temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3656–3664, 2000
    No preview · Article · Oct 2000 · Journal of Polymer Science Part A Polymer Chemistry
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    ABSTRACT: Synthesis and structure of novolaks continue to be investigated due to their significant influence on the performance of photoresists. Previously a two-step procedure was reported which enables the manufacturer to vary the monomer composition and order in novolak molecules in a wide range which then allows for the tailoring of the resin properties. Recent reinvestigation of the molecular structure of these novolaks applying gel permeation chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry has given very interesting new insight into the molecular structure of the two-step synthesis novolaks. Coupling of the two analytical methods provides a new powerful tool to get detailed information on the molecular architecture which cannot be deduced by other methods. Three species of novolak chains have been found. This analytical approach can generally be applied to explore the structure of novolaks made of monomers differing in their molar masses. Using the two- step novolaks high resolution positive and negative tone photoresists for MEMS applications and lift-off processes, respectively, with high alkaline and etch resistance can be produced.
    No preview · Article · Jun 2000 · Proceedings of SPIE - The International Society for Optical Engineering
  • Hans R. Kricheldorf · Karsten Hauser · Ralph-Peter Krüger · Günter Schulz
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    ABSTRACT: 2,2-Dibutyl-2-stanna-1,3-dioxepane (DSDOP) was polycondensed with bis(4-chlorothiophenyl) suberat under various reaction conditions, but only moderate molecular weights (Mn ≈ 10000) were obtained. The MALDI-TOF mass spectrosmetry revealed the formation of cyclic oligo- and polyesters in addition to linear species having OH, CO2H, and unreacted 4-chlorothiophenyl ester endgroups.Furthermore, ϵ-Caprolactone (ϵ-CL) was polymerized with DSDOP as the initiator at monomer/initiator (M/I) ratios of 20 and 50. The resulting tin-containing macrocyclic polylactones were reacted with sebacic acid bis(4-thiocresyl)ester at three different temperatures and with different reaction times. Analogous polycondensations were conducted with suberic acid bis(4-chlorothiophenyl) ester. The presence of thioarylester endgroups in the isolated polyesters was checked by H NMR spectroscopy. The highest conversions were found at long reaction times (24 or 72 hours), or after the addition of pyridine and N,N-dimethylaminopyridine as catalysts. Despite high conversions, the number average molecular weights (Mn's) did not exceed values around 20000. Even in the samples having the highest molecular weights, unreacted 4-chlorothiophenylester endgroups were detected by GPC measurements evaluated with a UV-detector. It is concluded that both factors, cyclization and incomplete conversion, contribute to the limitation of the chain growth.
    No preview · Article · Mar 2000 · Journal of Macromolecular Science Part A
  • Ralph-Peter Krüger · Helmut Much · Günter Schulz · Eckhard Rikowski
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    ABSTRACT: The coupling of the three liquid chromatographic modes with MALDI-TOF mass spectrometry is suitable for the determination of the molecular, functional, and chemical heterogeneities of Si polymers. Silsesquioxanes and siloxanes serve as examples for this method of structure identification. The substance specific construction of the SEC calibration curve by means of MALDI-MS is shown.
    No preview · Article · Jan 1999 · Monatshefte fuer Chemie/Chemical Monthly
  • Ralph-Peter Krüger · Helmut Much · Günter Schulz · Olaf Wachsen
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    ABSTRACT: Liquid Adsorption Chromatography at Critical Conditions (LACCC) of polymers in combination with Matrix-Assisted Laser Desorption / Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF-MS) and different types of detectors is a very convenient method for the characterization of polymer heterogeneities. A pathway for working out these methods is given. Additionally to the coupling of different chromatographic modes a device for post-column reaction detection is described and applied. Examples of applications are given for aliphatic and aromatic polyesters. MALDI-TOF-MS, reaction detection and relations between “critical” solvent composition and structure of polyesters are discussed. Conclusions concerning the mechanism of thermal degradation of polylactides are shown.
    No preview · Article · Jun 1996 · Macromolecular Symposia
  • Bernd Trathnigg · Bernhard Maier · Günther Schulz · Ralph-Peter Krüger · Ulrich Just
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    ABSTRACT: Polyethylene glycol 300 (PEG 300) and polypropylene glycol 425 (PPG 425) were analyzed using size exclusion chromatography (SEC) in different solvents, normal and reversed phase liquid chromatography (NPLC and RPLC), supercritical fluid chromatography (SFC), and matrix-assisted laserdesorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS). In liquid chromatography, different detectors were used: density, refractive index (RI) and evaporative light scattering detector (ELSD).
    No preview · Article · Jun 1996 · Macromolecular Symposia
  • Jörg Leukel · Walther Burchard · Ralph-Peter Krüger · Helmut Much · Günter Schulz
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    ABSTRACT: The mechanism of the strictly alternating anionic copolymerization of phenyl glycidyl ether (PGE) and phthalic anhydride (PA) was initiated by various imidazoles. Because of the strictly alternating copolymerization polyesters with a repeating unit of PGE-PA were obtained. The mechanism of the reaction was analyzed by means of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). With this technique the molar masses of the oligomers, the molar mass of the repeating unit, the weight-average molar mass M̄w and the number-average molar mass M̄n, their ratio M̄w/M̄n and the residual molar mass could be calculated. The strictly alternating copolymerization was easy to prove because the molar masses of PGE and PA are slightly different. The question whether the initiator remains chemically bound during the whole reaction could be solved. To this end polyesters obtained by initiation with various imidazoles with different molar masses were synthesized. The calculated residual molar masses correspond exactly to the molar masses of the imidazoles.
    No preview · Article · May 1996 · Macromolecular Rapid Communications
  • Helmut Schlaad · Axel H. E. Müller · Heinz Kolshorn · Ralph-Peter Krüger
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    ABSTRACT: Methyl methacrylate was polymerized with tert-butyl lithium in the presence of triethylaluminium or triisobutylaluminium at 78C in toluene. As indicated by GPC and MALDI-TOF mass spectrometry, the polymerization is accompanied by side reactions. The lower oligomers were fractionated by distillation and characterised by NMR, FT-IR, UV and electron impact (EI) mass spectrometry. All these data show that part of the polymer chains are carrying exactly one tert-butyl isoprenyl ketone unit. In order to avoid the formation of tert-butyl isoprenyl ketone a molar ratio of Al/Li>2 is necessary.
    No preview · Article · Dec 1994 · Polymer Bulletin