Search results for "Solvent"
showing 10 items of 1395 documents
On the viscosity of moderately concentrated solutions of poly(ether imide) in a mixed solvent of marginal quality
2000
Abstract Viscosities η were measured for moderately concentrated (15.5 wt%) solutions of poly(ether imide) (PEI) as a function of the composition of the cosolvent tetrahydrofuran (THF) plus γ-butyrolactone (γ-BL). The solutions are almost by a factor of four less viscous when THF predominates than when γ-BL is the major component of the solvent mixture. Furthermore, the viscosity passes a minimum as the composition of the mixed solvent is varied. Both observations can be well understood in terms of the viscosities of the mixed solvents and the hydrodynamic interaction between the polymer molecules. The pronounced dissymmetry of η as a function of the composition of the mixed solvent η resul…
Preferential evaporation of precipitants from polymer solutions in mixed solvents
2000
Partial vapor pressures were measured for the volatiles of solutions of polysulfone or polyethersulfone in mixtures of N,N-dimethylformamide (DMF, solvent) and water or acetone (precipitants) by means of headspace gas chromatography. The results demonstrate that the enrichment of water in the gas phase increases exponentially with rising polymer concentration, in contrast to that of acetone which remains constant. The reinforced expulsion of water resulting from the presence of polymers is theoretically conceivable and should be useful in the field of separation techniques.
Poly(4-vinylbenzoyl azide): A New Isocyanato Group Generating Polymer
2007
4-Vinylbenzoyl azide was synthesized from p-vinylbenzoic acid and polymerized by free radical polymerization. The obtained polymer contained acyl azide groups which were thermally transformed to the corresponding isocyanato groups. Reactions on these polymers with ethanol, hydroxyethyl methacrylate and 1-pyrene-butanol proceeded quantitatively. Time-resolved FT-IR studies of the reactions with ethanol were carried out by varying the concentration and temperature. The effect of the solvent polarity on the Curtius rearrangement was investigated.
An Alternate Interpretation of Polymer/Solvent Jump Size Units for Free-Volume Diffusion Models
1996
Polystyrene/toluene mutual-diffusion coefficients have been measured as a function of temperature in the limit of infinite solvent dilution. The solvent to polymer jump size unit ratio (ξ) was determined from the Vrentas−Duda free-volume diffusion model for polymer self-diffusion and is in excellent agreement with values evaluated from solvent self- and binary mutual-diffusion coefficient data. Comparison of the free-volume model to a version of the Kirkwood−Riseman theory, modified for diffusion at infinite dilution under non-ϑ conditions, suggests that ξ follows the temperature dependence of the root-mean-squared end-to-end distance of the polystyrene and can be estimated without the use …
Evidence of ternary interaction parameters for polymer solutions in mixed solvents from headspace-gas chromatography
2000
Partial vapor pressures of the volatiles have been measured for four solvent/precipitant/polymer systems at different temperatures. The high molecular weight compounds were polysulfone or polyethersulfone and the mixed solvent was either DMF/acetone or DMF/water. Systems containing the very powerful precipitant water exhibit a special phenomenon: Upon the addition of polymer to a mixed solvent of constant composition the partial vapor pressure of water increases by a factor of more than two before it falls to zero as the volume fraction of the polymer approaches unity. This particular situation cannot be modeled using binary interaction parameters only, in contrast to the results obtained w…
Ion pair association in isodielectric mixtures at 25�C
1974
Conductance measurements of potassium perchlorate and iodide have been carried out on the following mixtures: methanol-ethylene carbonate, acetone-ethylene carbonate, acetonitrile-ethylene carbonate, sulfolane-ethylene carbonate, isodielectric with water; and in benzene-sulfolane, benzene-acetonitrile, ethanol-sulfolane, isodielectric with methanol. The extent of ionic association at a given concentration in two solvents of the same dielectric constant is greater in the aprotic solvent.
Influence of solvent structure on ion pair association: The conductance of potassium perchlorate in ethylene carbonate-acetonitrile mixtures at 25�C
1974
The conductance of potassium perchlorate in mixtures of ethylene carbonate and acetonitrile covering the range 82.6 ≥ D ≥ 36.0 in dielectric constant has been measured. The Walden products in these aprotic solvents are approximately one-half as large as the products for the same salt in isodielectric mixtures of water and tetramethylene sulfone. This alters the distribution between electrostatic and hydrodynamic terms in the theoretical conductance function in such a way that the calculated association constants for potassium perchlorate are much smaller in the aprotic mixtures.
7-Amino-2-methylsulfanyl-1,2,4-triazolo[1,5-a]pyrimidine-6-carboxylic acid as the dimethylformamide and water monosolvates at 293 K.
2010
The molecular structure of 7-amino-2-methylsulfanyl-1,2,4-triazolo[1,5-a]pyrimidine-6-carboxylic acid is reported in two crystal environments, viz. as the dimethylformamide (DMF) monosolvate, C(7)H(7)N(5)O(2)S·C(3)H(7)NO, (I), and as the monohydrate, C(7)H(7)N(5)O(2)S·H(2)O, (II), both at 293 (2) K. The triazolo[1,5-a]pyrimidine molecule is of interest with respect to the possible biological activity of its coordination compounds. While the DMF solvate exhibits a layered structural arrangement through N...O hydrogen-bonding interactions, the monohydrate displays a network of intermolecular O...O and N...O hydrogen bonds assisted by cocrystallized water molecules and weak π-π stacking intera…
Energy-stable linear schemes for polymer-solvent phase field models
2017
We present new linear energy-stable numerical schemes for numerical simulation of complex polymer-solvent mixtures. The mathematical model proposed by Zhou, Zhang and E (Physical Review E 73, 2006) consists of the Cahn-Hilliard equation which describes dynamics of the interface that separates polymer and solvent and the Oldroyd-B equations for the hydrodynamics of polymeric mixtures. The model is thermodynamically consistent and dissipates free energy. Our main goal in this paper is to derive numerical schemes for the polymer-solvent mixture model that are energy dissipative and efficient in time. To this end we will propose several problem-suited time discretizations yielding linear scheme…
Solvent-Induced Length Variation of Cylindrical Brushes
2001
Communication: Polymacromonomers with a main chain much larger than the side-chain length adopt the form of cylindrical brush polymers the contour length per mainchain monomer of which depends on the side-chain length. In the present investigation it is demonstrated that the length per monomer also depends on the solvent quality, i.e., the cylinders are shorter in a poor solvent as compared to a good solvent. It is argued that the repulsion of the side chains represents the extension force, which acts against the entropic contraction force of the main chain. Thus, cylindrical brushes may be suitable as responsive materials for sensors, actuators or soft machines.