Optimization of simultaneous thermal analysis for fast screening of polycondensation catalysts

Dynamic simultaneous thermal analysis was optimized to screen activity of different catalysts for polycondensation of bis-hydroxy ethylene terephthalate (BHET) to polyethylene terephthalate. Reactions were performed by heating BHET to 300 °C at a linear heating rate in 50 μl thermal analysis crucibles under inert gas purging. A sensitive and reproducible screening method was obtained after overcoming of critical problems such as monomer evaporation, catalytic activity of crucible material, and optimization of gas purging, monomer amount in the crucible and heating rate. Under the applied conditions mass transport limitations were absent and the reaction was controlled solely by chemistry. The temperature at which maximum reaction rate occurs was used as an index of catalytic activity. It was obtained from maximum differential scanning calorimetry signal together with the maximum derivative of thermogravimetry signal. Temperature at which the reaction starts was also applied as an activity index. It was obtained from the onset of mass loss. The value of these three indices was smaller for more active catalysts.The optimized method was applied to study the activity of a new polycondensation heterogeneous catalyst based on hydrotalcite. This new catalyst was shown to be much more active than the conventional antimony catalyst under the applied conditions.     

Trace characterization of high-purity molybdenum and tungsten by electrothermal atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry and total reflection X-ray fluorescence spectrometry involving analyte—matrix separation

A technique for the separation of 42 trace elements from up to 5 g of molybdenum and tungsten matrices was developed by means of the radiotracer technique. It is based on adsorption of the analyses on the cation exchanger Dowex 50 W x 9 from a 4% H₂O₂/0.01 mol 1⁻¹ HNO₃ solution followed by their elution with 15 ml of 4 mol I⁻¹ HNO₃ in the opposite flow direction. Both matrices were removed with a separation factor > 10⁴. The separation technique was applied to the analysis of these materials by electrothermal atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry and total reflection X-ray fluorescence spetrometry. For all the determination methods used, the limits of detection are given and compared with those of other methods. With inductively coupled plasma mass spectrometry, for 22 of the 30 assayed elements, limits of detection at the sub-ng g⁻¹ level were achieved. The results are compared with those obtained by radiochemical neutron activation analysis in this work and by glow discharge mass spectrometry, secondary ion mass spectrometry, isotope dilution mass spectrometry and by solution spectrometric methods in other laboratories.     

Dimethylaluminum and gallium amino alkoxides

An S,S′-thioether—thioester chelating ligand [7,8-μ-SCH₂C(O)S-7,8-C₂B₉H₁₀]⁻ (L₁), incorporating the unit [—(C)₂B₉H₁₀]⁻ has been synthesized. Reactions have been conducted with RhCl(PPh₃)₃ and PdCl₂(PPh₃)₂ complexes in ethanol. With Rh, L₁ maintains its original cyclic nature and most probably chelation via thioether—thioester takes place. The carborane negative charge may stabilize this original thioether—thioester complex. The other two Rh positions are occupied by two PPh₃ ancillary ligands forming [Rh(L₁)(PPh₃)₂]. The reaction of L₁ with Pd induces ligand modifications and the cyclic nature of L₁ is lost. A transesterification process leading to a dianionic ligand L₂, [7-S-8-SCH₂C(O)OCH₂CH₃−7,8-C₂B₉H₁₀]²⁻ has taken place. In this way L₂ is capable of compensating the dipositive Pd charge. The other two Pd positions are occupied by two PPh₃. This reaction has been extended to methanol and isopropanol solvents. The crystal structure of [Pd(L₂)(PPh₃)₂] has been determined.     

Investigations on wine bouquet components by solid-phase microextration -capillary gas chromatography (SMPE-CGC) using different fibers

The extraction of wine bouquet components with solid-phase microextraction (SPME) using different fibers was studied. Polyacrylate fibers (PA-85) achieve the most complete bouquet profiles. About ninety substances were identified by capillary gas chromatography-MS and their retention factors were calculated to allow peak identification in capillary-GC-FID chromatograms. The terpene profiles of different wines were recorded by SPME (PA-85)-CGC-FID.     

Surface tension of polystyrene blends: Theory and experiment

Surface tension of linear–linear and star/linear polystyrene blends were measured using a modified Wilhelmy method. Our results show that for both polystyrene blend systems, the surface tension‐composition profile is convex, indicating a strong surface excess of the component with lower surface energy. Star/linear blends display more convex surface tension profiles than their linear–linear counterparts, indicative of stronger surface segregation of the branched‐component relative to linear chains. As a first step toward understanding the physical origin of enhanced‐surface segregation of star polymers, self‐consistent field (SCF) lattice simulations (both incompressible and compressible models) and Cahn‐Hilliard theory were used to predict surface tension‐composition profiles. Results from the lattice simulations indicate that the highly convex surface tension profiles observed in the star/linear blend systems are only possible if an architecture‐dependent, Flory interaction parameter (χ = 0.004) is assumed. This conclusion is inconsistent with results from bulk differential scanning calorimetry (DSC) measurements, which indicate sharp glass transitions in both the star/linear and linear/linear homopolymer blends and a simple linear relationship between the bulk glass transition temperature and blend composition. To implement the Cahn‐Hilliard theory, pressure‐volume‐temperature (PVT) data for each of the pure components in the blends were first measured and the data used as input for the theory. Consistent with the experimental data, Cahn‐Hilliard theory predicts a larger surface excess of star molecules in linear hosts over a wide composition range. Significantly, this result is obtained assuming a nearly neutral interaction parameter between the linear and star components, indicating that the surface enrichment of the stars is not a consequence of complex phase behavior in the bulk. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1666–1685, 2009     

Matrix-assisted laser desorption/ionization mass spectrometry of synthetic polymers. 7. analysis of fatty alcohol ethoxylates by coupled liquid chromatography at the critical point of adsorption and MALDI-TOF mass spectrometry

Fatty alcohol ethoxylates can be analyzed efficiently with respect to functionality and molar mass by coupled liquid chromatography and MALDI-TOF mass spectrometry. Both techniques are coupled via a robotic interface, where the matrix is coaxially added to the eluate and spotted dropwise onto the MALDI target. It is shown that liquid chromatography at critical conditions of adsorption coupled to MALDI-TOF yield useful structural information on oligomer masses and chemical composition. In particular, the analysis of technical fatty alcohol ethoxylates by LC-CC/MALDI-TOF reveals the presence of different functionality fractions in one sample. The oligomer distributions of all functionality fractions are determined.