Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (36)
- Beitrag zu einem Tagungsband (27)
- Posterpräsentation (13)
- Beitrag zu einem Sammelband (11)
- Sonstiges (1)
Sprache
- Englisch (88) (entfernen)
Schlagworte
- Polycondensation (6)
- MALDI (5)
- MALDI-TOF-MS (4)
- Oligomers (4)
- Macrocycles (3)
- Macrocyclics (2)
- Model compounds for melanoidins (2)
- Polyesters (2)
- Thermodynamics (2)
- 1,1-Diphenylethylene (1)
- 29Si NMR (1)
- Alternating sequence (1)
- Antioxidative activity (1)
- Antioxidative activity of oligomeric model compounds (1)
- Beta-dicarbonyl pathway of the Maillard reaction (1)
- Biodegradable polyesters (1)
- Captive bubble (1)
- Chain transfer (1)
- Change of crystal structure (1)
- Chromatographie (1)
- Chromatography (1)
- Coatings (1)
- Copolymer structure (1)
- Coupling methods (1)
- Crystallization (1)
- Cyclization (1)
- Dental (1)
- Emulsion polymerization (1)
- Gel permeation (1)
- Glass transition temperature (1)
- Hard segments (1)
- Hydrophobicity (1)
- Ionization mass spectrometry (1)
- Isosorbide (1)
- Kopplung (1)
- LAC (1)
- Liquid adsorption chromatography (1)
- Liquid adsorption chromatography at critical conditions (1)
- MALDI-TOF MS (1)
- MALDI-TOF mass spectrometry (1)
- MALDI-TOF-MS analysis (1)
- Maillard system 2-deoxy-D-ribose / methylamine (1)
- Main-chain liquid crystalline polyurethanes (1)
- Matrix-assisted laser desorption (1)
- Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (1)
- Mesogenic unit (1)
- Metallocene catalysts (1)
- NP-HPLC (1)
- Nanostructure (1)
- Novolak (1)
- Oligomerization of N-methyl-2-hydroxymethyl(and hydroxyl[13C]methyl)pyrrole (1)
- Orthogonal chromatography (1)
- Perfluoralkylalkoxysilane (1)
- Poly(butylene terephthalate) (1)
- Poly(ether sulfone)s (1)
- Poly(ethylene terephthalate) (1)
- Poly(thio-ester)s (1)
- Polyazomethines (1)
- Polyester (1)
- Polyether (1)
- Polyolefins (1)
- Preparative HPLC (1)
- Primer on steel (1)
- Pull-off test (1)
- Pyrroles from pentoses and hexoses (1)
- Ring-Opening Polycondensations (1)
- Ring-opening polycondensation (1)
- SEC (1)
- SP-B (1)
- SP-C (1)
- Silicon compounds (1)
- Siloxysilsesquioxane (1)
- Silsesquioxanes (1)
- Size exclusion chromatography (1)
- Soft segments (1)
- Sols (1)
- Spherosilicate (1)
- Structure (1)
- Surface pressure (1)
- Surfactant proteins (1)
- Synthesis (1)
- Wet adhesion of alkyd melamine resin (1)
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, -Caprolactone (-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 1H 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.
Chemical heterogeneities and molecular weight distributions of poly(ethylene oxide) (PEO)-co-polymethylene (PM) model oligomers, which are relevant to the synthesis of commonly used tensides, were investigated. For analytical characterization, the well-known principle of liquid adsorption chromatography at 'critical conditions' (LACCC) was modified. Near the critical conditions of adsorption of the PEO unit, e.g., at slight adsorption conditions of PM, the copolymers could be separated according to their PM chain length. The eluates were separated and single fractions of each peak were continuously transferred onto the MALDI target by means of a commercially available device. Simultaneously, the MALDI matrix solution was continuously added with a second pump. This procedure offers the possibility of the formation of homogeneous matrix-polymer textures. By MALDI-MS a complete characterization of the chemical composition (PEO and PM chain length) of each peak could be achieved. The obtained MALDI mass spectra of the eluates at different retention times could be used for the molecular weight calibration of the LAC system. In this way, an additional application of SEC, as in conventional 2D-chromatography, was avoided by using the MALDI method as quasi chromatographic separation
We prepared 2,2-dibutyl-2-stanna-1,3-dithiacycloalkanes from dibutyltin oxide and ,-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
Various dibutyltin derivatives were polycondensed with aliphatic ,-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 (n 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.
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(SiO1.5)8]2O and [(n-octyl)7(SiO1.5)8O]2[(n-octyl)6(SiO1.5)8] as well as the cage rearrangement of octa-[(n-heptyl)silsesquioxane] to larger structur es [(n-heptyl)SiO1.5)]n up to n=28 are shown.