Oxidation polymerization of a charge‐transfer complex of 2,6‐bis(2‐thienyl)‐1,4‐dithiafulvene with 7,7,8,8‐tetracyanoquinodimethane

A π‐conjugated poly(α‐dithienylen‐dithiafulvene) ( 2 ) was obtained by the oxidation polymerization of 2,6‐bis(2‐thienyl)‐1,4‐dithiafulvene ( 1 ) as a dithiafulvene monomer derived from 4‐(2‐thienyl)‐1,2,3‐thiadiazole. When a solution of 1 in CHCl₃ was added to a stirred solution of FeCl₃ in CHCl₃, only the low‐molecular‐weight product 2 was obtained. The mixture was stirred for 15 h with an N₂ flow. The polymerization at higher temperatures resulted in polymers with large insoluble fractions. A higher molecular weight polymer was obtained by the oxidation polymerization of a charge‐transfer complex of 1 with 7,7,8,8‐tetracyanoquinodimethane (compound 3 ). In contrast to 2 , polymer 4 was readily soluble in dimethyl sulfoxide, dimethylformamide, and acetone and partially soluble in tetrahydrofuran and methanol and had a larger molecular weight (peak top molecular weight = 37,000). The conductivity of polymer 4 was 3 orders of magnitude larger than that of polymer 2 . © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6592–6598, 2005     

Comparison of decomposition procedures for analysis of titanium dioxide using inductively coupled plasma optical emission spectrometry

The determination of impurities in titanium dioxide pigments, such as Al, Cd, Cr, Fe, Mn, P, Zn and Zr, is relevant because trace elements affect pigment properties. The critical step in the analysis of this pigment is the conversion of the solid sample to a representative solution. This study compared four acid decomposition procedures for TiO₂ for the determination of Al, P and trace impurities using inductively coupled plasma optical emission spectrometry. The decomposition procedures investigated involved acid digestion with: (i) (NH₄)₂SO₄/H₂SO₄; (ii) HF/H₂SO₄; (iii) H₃PO₄; and (iv) HCl/HNO₃/HF. This latter mixture was tested in a microwave-assisted procedure with closed vessels. Comparing the procedures using conventional conductive heating, the procedure using (NH₄)₂SO₄/H₂SO₄ was the most suitable for complete decomposition of TiO₂ samples, requiring approximately 30 min. Applying a paired t-test, it was shown that all strategies led to results in agreement at a 95% confidence level with those obtained using X-ray fluorescence. The accuracy for Cr, Fe, P and Zr was also checked using a certified reference material, and again all results were in agreement at a 95% confidence level. The performance of two ICP-OESs, one based on a mini-torch using a radial view configuration, and the other based on an axial view configuration, were compared. Both plasmas are intensely affected by matrix constituents. The mini-torch plasma is less able to cope with high amounts of solids; however this parameter also negatively affects the background level when using axial-viewed ICP-OES.     

MS-SCF-Xα calculation of the rotational barriers in ethane-like molecules

MS-X_α calculations are performed for the rotational barriers of C₂H₆, Si₂H₆, Ge₂H₆, C₂F₆, in the rigid rotor approximation with different sets of sphere radii. While the results show a large dependence on the radii employed, good results can be obtained with a particular choice based on previously proposed criteria.     

Effect of Individualized Cellulose Fibrils on Properties of Poly(Methyl Methacrylate) Composites

Cellulose fibrils were manufactured from flax fibers using chemical treatments followed by cryo-crushing and ultrasonication techniques. The fibrils, consisting mainly of cellulose free from lignin, pectin and hemicellulose, were exploited as a biofiller in preparing poly(methyl methacrylate) (PMMA) matrix composites. The effects of incorporating cellulose fibrils on the physical and mechanical properties of the polymer matrix were investigated. In particular, the influence of the fibrils on the thermal stability and degradation of the composites was studied by means of thermogravimetric analysis carried out in both inert and oxidative atmospheres. The runs performed under air flow revealed the efficiency of the cellulose fibrils in delaying the polymer decomposition during thermal oxidation. The weight loss was slowed down in the composites of all compositions and the temperature of degradation increased with increasing the amount of the fibrils. The combustion properties of the fibril-based composites were evaluated by means of pyrolysis combustion flow calorimetry. The addition of cellulose fibrils into the PMMA matrix resulted in a noticeable decrease of the primary combustion parameters.     

Amperometric Detection of 4‐Chlorophenol on Two Types of Expanded Graphite Based Composite Electrodes

The assessment of an expanded graphite‐Ag‐zeolite‐epoxy composite (EG‐Z‐Ag‐Epoxy) electrode for the determination of 4‐chlorophenol (4‐CP) is described and compared to the corresponding expanded graphite‐epoxy composite (EG‐Epoxy) electrode. Cyclic voltammetry was used to characterize the electrochemical behavior and determination of 4‐CP at both electrodes in 0.1 M Na₂SO₄ and 0.1 M NaOH supporting electrolytes. A substantial enhancement of sensitivity for the determination of 4‐CP at the EG‐Z‐Ag‐Epoxy electrode was reached by applying a chemical preconcentration step prior to voltammetric quantification. Also, under these last conditions the lowest limit of detection of 1 μM illustrates the analytical versatility of this electrode in a concentration range where aquatic 4‐chlorophenol pollution is known to occur.     

Thermodynamic and structural features of aqueous Ce(III)

With a single f-electron, Ce(III) is the simplest test case for benchmarking the thermodynamic and structural properties of hydrated Ln(III) against varying density functionals and reaction field models, in addition to determining the importance of multiconfigurational character in their wave functions. Here, the electronic structure of Ce(H2O)x(H 2O)y(3+) (x = 8, 9; y = 0, 12-14) has been examined using DFT and CASSCF calculations. The latter confirmed that the wave function of octa- and nona-aqua Ce(III) is well-described by a single configuration. Benchmarking was performed for density functionals, reaction field cavity types, and solvation reactions against the experimental free energy of hydration, DeltaG(hyd)(Ce(3+)). The UA0, UAKS, Pauling, and UFF polarized continuum model cavities displayed different performance, depending on whether one or two hydration shells were examined, and as a function of the size of the metal basis set. These results were essentially independent of the density functional employed. Using these benchmarks, the free energy for water exchange between CN = 8 and CN = 9, for which no experimental data are available, was estimated to be approximately -4 kcal/mol.     

Simultaneous determination of bisphenol A, triclosan, and tetrabromobisphenol A in human serum using solid-phase extraction and gas chromatography-electron capture negative-ionization mass spectrometry

This study aimed at optimizing and validating a sensitive method for simultaneous determination of bisphenol A (BPA), triclosan (TCS), and tetrabromobisphenol A (TBBPA) in human serum using solid-phase extraction (SPE) and gas chromatography coupled to electron-capture negative-ionization mass spectrometry (GC-ECNI/MS). Sample preparation involved denaturation of serum proteins with formic acid followed by SPE on an Oasis HLB cartridge. Fractionation was performed on Florisil from which the phenolic compounds were eluted with methanol-dichloromethane (DCM) (5:1, v/v). The phenolic fraction was further derivatized with pentafluoropropionic acid anhydride (30 min at 70 degrees C). Further liquid-liquid partitioning using hexane-DCM (4:1, v/v) and K(2)CO(3) 3% aqueous solution was used to eliminate excess reagent and acidic by-products formed during derivatization. The cleaned extract was injected into a GC-ECNI/MS system operated in selected ion monitoring mode. For thorough method validation, each step of the procedure was rigorously optimized. The method limits of quantitation for BPA, TCS, and TBBPA were 0.28 ng mL(-1), 0.09 ng mL(-1) and 0.05 ng mL(-1), respectively. Furthermore, the method was applied to 21 Belgian human serum samples. The median concentrations obtained for BPA (0.71 ng mL(-1)) and TCS (0.52 ng mL(-1)) in Belgian human serum samples were similar to previously reported data for human fluids. Slightly higher levels of TBBPA (0.08 ng mL(-1)) were found in Belgium samples compared to Norwegian serum.     

“Living” Radical Polymerization in Tubular Reactors, 2 – Process Optimization for Tailor‐Made Molecular Weight Distributions

“Living” radical polymerization is a relatively new polymerization process that can be used to prepare resins with controlled structures. In this work, a mathematical model developed previously to describe nitroxide‐mediated “living” radical polymerizations performed in tubular reactors is used for the optimization of the process and obtainment of tailor‐made MWDs. Operating conditions and design variables are determined with the help of optimization procedures in order to produce polymers with specified MWDs. It is shown that bimodal and trimodal MWDs, with given peak locations, can be obtained through proper manipulation of the operating conditions. This indicates that the technique discussed in this work is suitable for detailed design of the MWD of the final polymer.