Metathesis polymerization of N-aryl norbornene dicarboximides. I

Metathesis polymerization of N-phenyl-exo-norbornene dicarboximide and ortho/meta/para methyl substituted phenyl nadimides was carried out using WCl₆/tetramethyltin. Structural characterization was done by FTIR, ¹H- and ¹³C-NMR. A mixture of cis and trans double bond structures were introduced in the backbone during polymerization. The cis content was higher (52 to 65%). In the DSC scan of poly(N-o-tolyl nadimide), two exotherms were observed at 240 and 270°C while in other samples only one exothermic transition was observed above 240°C. These exotherms disappeared in the second heating cycle. The T_g of the polymers, as determined in the second heating cycle, was highest in poly(N-o-tolyl nadimide) and lowest in poly(N-m-tolyl nadimide). The polymers were stable up to 443 ± 3°C and decomposed above this temperature in a single step. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2917–2924, 1997     

Thermal properties of bisitaconimide and bisbenzoxazine blends

Blends of cardanol-based bisbenzoxazine (BZc) and 4,4′-bisitaconimidodiphenyl ether (BIM) having nine different mass ratios (i.e. 100:0, 90:10, 75:25, 60:40, 50:50, 40:60, 25:75, 10:90 and 0:100) were prepared and their curing behaviour was studied by differential scanning calorimetry (DSC) and fourier transform infrared spectroscopy. A curing mechanism comprising two-steps: (1) homopolymerization and co-curing reaction of itaconimide with alkyl side chain double bonds of cardanol BZc at lower temperature (~443 K) and (2) ring-opening polymerization of oxazine at higher temperature (~453–483 K) has been proposed. The T _g of the cured resin blends was determined by DSC and the increase in BIM content in the blend resulted in an increase in T _g from 408 K BZc to 474 K BIM. Increase in bisitaconimide content resulted in improvement of char yield at 1,073 K as well as an increase in mass loss temperatures (5 and 10 %). Compared to BZc, the blends showed a higher thermal stability. The lap shear strength of these blends in metal–metal joints was investigated at 323, 523 and 573 K.     

Removal of cadmium(II) and zinc(II) metal ions from binary aqueous solution by rice husk ash

The present study reports the competitive adsorptive removal of cadmium (Cd(II)) and zinc (Zn(II)) ions from binary systems using rice husk ash (RHA), a waste obtained from the rice husk-fired furnaces, as an adsorbent. The initial pH (pH₀) affects significantly the capacity of RHA for adsorbing the metallic ions in the aqueous solution. The pH₀ ≈ 6.0 is found to be the optimum for the removal of Cd(II) and Zn(II) ions by RHA. The single ion equilibrium adsorption from the binary solution is better represented by the non-competitive Redlich–Peterson (R–P) and the Freundlich models than by Langmuir model in the initial metal concentration range of 10–100 mg/l. The adsorption of Zn(II) ion is more than that of Cd(II) ion, and this trend is in agreement with the single-component adsorption data. The equilibrium metal removal decreases with increasing concentrations of the other metal ion and the combined effect of Cd(II) and Zn(II) ions on RHA is generally found to be antagonistic. Non-modified Langmuir, modified Langmuir, extended-Langmuir, extended-Freundlich, Sheindorf–Rebuhn–Sheintuch (SRS), non-modified R–P and modified R–P adsorption models were tested to find the most appropriate competitive adsorption isotherm for the binary adsorption of Cd(II) and Zn(II) ions onto RHA by minimizing the Marquardt's percent standard deviation (MPSD) error function. The extended-Freundlich model satisfactorily represents the adsorption equilibrium data of Cd(II) and Zn(II) ions onto RHA.     

Rapid hydrocarbon type separation of vacuum residues

Summary A simple and fast column chromatographic procedure for the separation of vacuum residues into saturates, mono-, di-, polyaromatics and polars has been standardized using silica-alumina-bauxite adsorbents and gradient elution with n-pentane, benzene, and methanol. The cut points have been monitored employing ultraviolet and infrared spectroscopy. The method is applicable for preparative separation of short residues from processed products.

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Rasche Trennung der Kohlenwasserstofftypen von Vakuum-RückstÄnden

     

Literatur

Analytical and Bioanalytical Chemistry -     

Magnetic Resonance Spectra and Statistical Geometry

Methods of statistical geometry are introduced which allow one to estimate, on the basis of computable criteria, the conditions under which maximally informative data may be collected. We note the important role of constraints which introduce curvature into parameter space and discuss the appropriate mathematical tools for treating curvature effects. Channel capacity, a term from communication theory, is suggested as a useful figure of merit for estimating the information content of spectra in the presence of noise. The tools introduced here are applied to the case of a model nitroxide system as a concrete example, but we stress that the methods described here are of general utility.     

Synthesis and Sensory Evaluation of <em>ent</em>-Kaurane Diterpene Glycosides

Catalytic hydrogenation of the three ent-kaurane diterpene glycosides isolated from Stevia rebaudiana, namely rubusoside, stevioside, and rebaudioside-A has been carried out using Pd(OH)₂ and their corresponding dihydro derivatives have been isolated as the products. Synthesis of reduced steviol glycosides was performed using straightforward chemistry and their structures were characterized on the basis of 1D and 2D NMR spectral data and chemical studies. Also, we report herewith the sensory evaluation of all the reduced compounds against their corresponding original steviol glycosides and sucrose for the sweetness property of these molecules.