Export 106 results:
Sort by: Author Title Type [ Year  (Desc)]
Nessim, R. I., M. G. Botros, G. R. Saad, and M. M. Shalaby, "Frequency dependence of the complex dielectric constant of sodium carboxymethyl cellulose", Die Angewandte Makromolekulare Chemie, vol. 204, issue 1, pp. 51 - 61, 1993. AbstractWebsite

The dielectric constant, ε′, and dielectric loss, ε″, were determined for three solid carboxymethyl cellulose samples having different levels of substitution and different degrees of polymerization over a frequency range of 0.1 – 10 000 kHz at temperatures from 10–60°C. In contrast to the two relaxation processes, γ and β, previously observed in native cotton cellulose, only one relaxation process within a frequency range of 0.1 – 1 kHz was identified. It was found that the dielectric properties do not only depend on the degree of substitution, but also on the weight‐average degree of polymerization and uniformity of distribution. © 1993 Hüthig & Wepf Verlag, Basel

Saad, G. R., M. G. Botros, and R. I. Nessim, "Dielectric study of acetylated cotton cellulose and saponified cellulose acetate", Die Angewandte Makromolekulare Chemie, vol. 197, issue 1, pp. 23 - 39, 1992. AbstractWebsite

Dielectric relaxation data are reported at frequencies of 0.1 – 10000 kHz over a temperature range of 10–80°C on cellulose acetates of different degrees of substitution, and on saponified cellulose acetate. The acetyl substitution is found to remove the low‐frequency relaxation process, γ, previously observed in medicated cotton cellulose, and to affect the other higher‐frequency process, β, in different ways, depending on the acetyl content. Conversely, saponification of cellulose acetate leads to the reversion of these two processes but with different features. Analysis of the absorption bands is made, and an assessment of the results obtained is given. © 1992 Hüthig & Wepf Verlag, Basel

Abdel Moteleb, M. M., G. R. Saad, and R. I. Nessim, "The effects of preheating on the dielectric relaxation, and of temperature on the 'static' dielectric constant, of cellulose acetate fibers", Polymer Degradation and Stability, vol. 36, issue 3, pp. 217 - 224, 1992. AbstractWebsite

The effect of preheating at 140°C and 180°C on the dielectric relaxation of cellulose acetate of degree of substitution 1·90 has been investigated, together with the dependence on temperature over the range 80-200°C of the 'static' dielectric constant of variously acetylated cellulose samples. The results obtained are discussed in terms of progressive gain of compact structure, together with the initiation of crystallization at a temperature governed by the acetyl content in the fiber. Phase changes involving discontinuity in the first variation of the 'static' dielectric constant on heating, and irreversibility of the temperature dependence path on cooling are thus observed. © 1992.

Mikhael, M. G., S. M. Mokhtar, G. R. Saad, M. M. Naoum, and M. Z. Elsabee, "Copolymerization and interaction of acrylonitrile and indene", Journal of Polymer Science Part A: Polymer Chemistry, vol. 27, issue 1, pp. 185 - 191, 1989. AbstractWebsite

The donor–acceptor interaction of acrylonitrile (AN) with indene (In) has been investigated by means of ultraviolet spectroscopy and dielectric polarization measurements. The latter method yielded a value of 0.5 for the association constant of the charge‐transfer‐complex (CTC) and a 4.02 D for its dipole moment. The copolymerization of the two monomers was characterized by a tendency towards alternation when conducted in the bulk. This might be due to the participation of a weak CTC in the process of copolymerization. However, this tendency disappeared in polar solvents such as DMF. Copyright © 1989 John Wiley & Sons, Inc.

Naoum, M. M., and G. R. Saad, "Solvent effect on tautomeric equilibria and dipole moments of some alpha substituted benzoylacetanilides", Journal of Solution Chemistry, vol. 17, issue 1, pp. 67 - 76, 1988. AbstractWebsite

Based on dipole moment measurements, a study was made of the keto-enol equilibria of five alpha substituted benzoylacetanilide derivatives in two non-polar and one polar solvents at 30°C. The enol mole fractions of the compounds investigated were determined by analysis of their ultraviolet spectra. The same type of study was extended to salicylanilide for its resemblance to the enol tautomer of these compounds. A deduction of the most probable configurations of the keto and enol forms was tentatively made through a comparison between the dipole moments of some suggested configurations for these forms of benzoylacetanilide and those measured in benzene for the alpha methyl benzoylacetanilide and salicylanilide, respectively. These inferred configurations were used to calculate the dipole moments of both tautomers of the other compounds, and consequently, the dipole moment values of their tautomeric mixtures in dioxane and chloroform. A comparison between the dipole moment values of their tautomeric mixtures in dioxane and chloroform. A comparison between the dipole moment values calculated in this way and those measured indicated a solute-solvent interaction with dioxane, which chloroform behaved as a non-interacting solvent. © 1987 Plenum Publishing Corporation.

Naoum, M. M., G. R. Saad, M. M. Abdel-Moteleb, H. G. Shinouda, and H. A. Rizk, "Dielectric polarization and molecular interaction. Part I. Acetoacetanilide and benzoylacetanilide-triethylamine-benzene systems", Canadian Journal of Chemistry, vol. 65, issue 12, pp. 2760 - 2763, 1987. AbstractWebsite

The apparent molecular polarization at infinite dilution of acetoacetanilide, and benzoylacetanilide in five constant-ratio mixtures of triethylamine in benzene leads to the inference that the equilibrium constants of the association process between the anilide and the amine in benzene are 357 and 600, and that the dipole moments of the complexes formed are 4.43 and 5.25 D, respectively.