The significant improvement in the CO2-removal performance of Pebax-1657 when it is embedded with TiO2nanoparticles and chemically modified.
90not give a straight line. Since the anion is not shielded from the solvent as it was in the earlier study, we anticipate that in the hydrogen-bonding solvents the ion pair would be more dissociated than in a nonhydrogen-bonding solvent with similar dielectric constant. As was shown in a previous report from this laboratory,* we would expect specific interaction of the hydrogen-bonding type to occur between chloroform and (C6H&PCo-Br3-. According to the relationship4(where all the terms have the usual meaning4), the hydrogen-bonding solvents could either decrease the fraction of ions paired together or decrease Avp as a result of an increase in interionic distance. Solvent-separated ion pairs would be counted as dissociated by this technique. In ethylene dichloride, another factor would favor a decrease in AvH('). Molecules of this solvent can exist in the gauche and trans forms. This equilibrium is disturbed by the electric field of the ion in favor of the gauche formz4 (polar form) with the resulting increase in the dielectric constant of the solvent medium in the vicinity of an ion in effect causing the bulk dielectric constant to poorly approximate this solvent's dielectric constant.Acknowledgment.Abstract: An elimination of solvation procedure (ESP) is reported which, under appropriate conditions, enables one to study donor-acceptor reactions in polar solvents and predict, from these data, an enthalpy of the adduct formation in the gas phase. The method is tested by predicting enthalpies in poorly solvating media from data in polar solvents. The predicted enthalpies are compared with those directly measured in the nonpolar solvent.n a series of reports from this we have I been concerned with the interpretation and evaluation of the magnitude of donor-acceptor interactions as manifested by the enthalpy of adduct formation. Enthalpies determined in poorly solvating media, or the gas phase, have been correlated by eq 1 where CA, EA -A H = EAEB -+ CACB (1) and C B , EB are empirically determined parameters referring to acceptor and donor, respectively.' Ideally, gas-phase data free from solvation contributions to the enthalpy are desired for evaluation of donor and acceptor strength. However, the difficulty associated with present techniques for gas-phase measurements prevents accumulation of reasonably accurate or extensive amounts of data needed to test the validity of eq 1. Consequently, data obtained in the poorly solvating media (Le., solvents which do not undergo specific interactions greater than 0.2 kcal moland have dielectric constants equal to or lower than 2.3), carbon tetrachloride and cyclohexane, have been employed. It is well established that solution of gaseous materials in cyclohexane or CCI, is accompanied by an interaction between the solvent and solute, e.g., at 21 O the enthalpy of vaporization of diethyl ether is 9.39 kcal mol-', while the apparent molar enthalpy of solution of liquid diethyl ether in CC1, is -0.42 kcal mol-'.
In addition to possessing excellent chemical, mechanical, and thermal stability, polyimides and polyetherimides have excellent solubility in many solvents, which renders them suitable for membrane preparation. Two new monomers [a pentiptycene-based dianhydride (PPDAn) and a pentiptycene imide-containing diamine (PPImDA)] and a pentiptycene-based polyimide [PPImDA-4,4'-hexafluoroisopropylidene diphthalic anhydride (PPImDA-6FDA)] have been synthesized and characterized by FTIR and H NMR spectroscopy, gel-permeation chromatography, mass spectrometry, X-ray photoelectron spectroscopy, thermogravimetric analysis, differential scanning calorimetry, BET surface area, and X-ray diffraction. High-molecular-weight PPImDA-6FDA has remarkable thermal stability and excellent solubility in common organic solvents. It also has an extraordinarily high fractional free volume (0.233) owing to the presence of -C(CF ) - units, the rigid diamine, and the pentiptycene moiety in the polymer structure. It has high CO permeability (812 Barrer) owing to poor chain packing, which is caused by the fact that its rigid groups veil the influence of the ethereal oxygen groups in its backbone. It has the highest CO permeability among all reported pentiptycene-containing polymers (about six times higher than that of the most permeable one) without sacrificing selectivity. The high free volume, good microporosity, high solubility in many solvents, and remarkable thermal stability of PPImDA-6FDA point to the great potential of this polymer for CO removal.
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