SCATTERING FUNCTION OF POLYMER BLENDS

For a system of flexible polymer molecules, the concepts of two concentrations, namely the segmental and the molecular concentrations, have been proposed in this paper. The former is equivalent to the volume fraction. The latter can be defined as the number of the gravity centers of macromolecules in a unit volume. The two concentrations should be correlated with each other by the conformational function of the polymer chain and should be discussed in different thermodynamic equations. On the basis of these concepts it has been proved that the Flory-Huggins entropy of mixing should be the result of the mixing “ideal gases of the gravity centers of macromolecules“. The general correlation between the free energy of mixing and the scattering function (structural factor) of polymer blends has been studied based on the general fluctuation theory. When the Flory-Huggins free energy of mixing is adopted, the de Gennes scattering function of a polymer blend can be derived.     

Syntheses and characterizations of poly[2‐(dimethylamino)ethyl methacrylate]–poly(propylene oxide)–poly[2‐(dimethylamino)ethyl methacrylate] ABA triblock copolymers

A novel, near‐monodisperse, well‐defined ABA triblock copolymer, poly[2‐(dimethylamino)ethyl methacrylate]‐b‐poly(propylene oxide)‐b‐poly[2‐(dimethylamino)ethyl methacrylate], was synthesized via oxyanion‐initiated polymerization. The initiator was a telechelic‐type potassium alcoholate prepared from poly(propylene glycol) and KH in dry tetrahydrofuran. The copolymers produced were characterized by Fourier transform infrared, ¹H NMR, and gel permeation chromatography (GPC). GPC and ¹H NMR analyses showed that the products obtained were the desired copolymers, with narrow molecular weight distributions (ca. 1.09–1.11) very close to that of the original poly(propylene glycol). ¹H NMR, surface tension measurements, and dynamic light scattering all indicated that the triblock copolymer led to interesting aqueous solution behaviors, including temperature‐induced micellization and very high surface activity. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 624–631, 2002; DOI 10.1002/pola.10144     

Transference numbers for ultra concentrated solutions of aqueous hydrochloric acid at 25°C

Transference numbers of HCl(aq) solutions at 25°C, from 0.01 to 13.6 mol-kg^–1(m) have been obtained by measuring the emf of cells with transference using hydrogen gas/platinum electrodes. Good agreement is obtained at concentrations up to 1 m with all previous data, and our results strongly corroborate those of King and Spiro over the 2–8m concentration range. The transference numbers of the hydronium ion fit the empirical equation, _H ^HCl = 0.821 + 0.0457m ^1/2 – 2.476×10^–2m – 1.90×10^–4 m ² – 1.45×10^–5 m ³ the maximum deviation in T _H ^HCl being 0.003.     

Thermodynamics of ionic solid solutions: II. Discontinuous series: A new treatment of existing distribution data

A method of finding the activity coefficients of salts, anhydrous or hydrated, in binary solid solutions, described in an earlier paper as it applies to continuous series, has been applied to discontinuous series. The salts must differ with respect to only one ion. The method requires isothermal distribution data for equilibria between liquid (aqueous) and solid solutions in the ternary system consisting of the two salts and water. The following salt pairs were used for illustration: K(I/Br) at 0, 15, 25, 35, and 50°C., (NH₄/K)SCN at 0, 30, 60, and 90°C., (K/Tl)C10₃ at 10°C., and (NH₄/K)SO₃NH₂, (NH₄/K)Br, (Mg/Co)SO₄-7H₂O, and (Mn/Cu) SO₄.n H₂O-all at 25°C. Two kinds of behavior were noted and treated differently: systems in which the two series have the same, and those in which they have different crystal lattices. For two salts, A and B, which have the same lattice, and whose rational activity coefficients, f _A and f _B , can be described by 2-suffix Margules equations (regular solutions), lnf _A =B_sx _B ² and lnf _B =B_sx _A ² to be partially miscible, B_s>2, but this requirement does not apply if the lattices are different. In each series, distribution constants for the equilibria were also determined. Where possible, the calculated activities of the salts or the Gibbs excess energies of the solid solutions were compared with values reported by others who determined them by other methods. All the salt pairs studied show slight or strong positive deviations from ideality.     

Tetraaryl-methane analogues in group 14—V. Distortion of tetrahedral geometryin terms of through-space π–π and π–σ interactions andNMR sagging in terms of π–σcharge transfer

44 members of thecompound series Ph_4−nMR_n (M=Si, Ge, Sn, Pb; R=o-, m-, p-Tol; n=0–4) were synthesized (15 newcompounds). The crystal structures of Ph₃Sn (o-Tol) and PhSn (o-Tol)₃ were determined and compared to 16 known structures. Subject to the distanced (M–C), an interplay between through-space π–π repulsion and π–σ attraction leads to either elongated or compressed tetrahedral geometry. ²⁹ Si-, ¹¹⁹ Sn- and ²⁰⁷ Pb-NMR chemical shifts were determined in solution and in the solid state. ⁷³ Ge chemical shifts were measured only in solution. Anupfield or downfield sagging of the chemical shifts along each series is rationalized in terms of a π–σcharge transfer which is constrained by torsion of the aromatic groups.     

Selective water sorbents for multiple applications, 3. CaCl2 solution confined in micro- and mesoporous silica gels: Pore size effect on the “solidification-melting” diagram

In this communication we present a low-temperature “solidification-melting” phase diagram for CaCl₂/H₂O solutions confined in KSK and KSM silica gels. At salt concentrations of 0–48 wt. %, the diagram has been found to lie below the diagram reported for the bulk system by 15–30°C. It shows a depression of the solution melting point due to its confinment to the pores. Several other peculiarities of melting and solidification in this system are also reported and discussed. Beside fundamental interest, the data obtained could be of importance in many commercial areas such as refrigeration, accumulation of low temperature heat, frost prevention in building materials,etc.     

Osmotic coefficients of vinylic polyelectrolyte solutions without added salt

 The osmotic pressures of –polyelectrolyte solutions without added salt was measured in the concentration ranges 0.001–0.02 and 0.2–1.9 mol kg^-1. Our results show that the osmotic coefficients φ_p were strongly dependent on the chemical structures of polyelectrolyte through the polyion radius and the interaction between the ionic moiety and counterions. The osmotic pressures in polyelectrolyte solutions without added salt, calculated on the basis of the counterion contribution, are in agreement with the experimental results. We conclude that the counterion contribution is dominant in the osmotic pressures and thus, the polymer contribution is negligible in the examined concentration range 0.2–1.9 mol kg^-1. The P–B approach gave a fair prediction of the absolute values of the osmotic pressures with λ=4.5, where λ is the charge density parameter, except for NaPA. In other words, the concentration dependence of the φ_p values can be explained in terms of the counterion contribution. Received: 11 June 1997 Accepted: 19 August 1997     

On the solution characterization of an all-aromatic liquid-crystalline copolyester

Solution characterization of the thermotropic liquid–crystalline copolyester synthesized from terephthalic acid, phenyl hydroquinone, and (1-phenylethyl) hydroquinone (2 : 1 : 1) has been performed. Viscometry, size exclusion chromatography, and light scattering have been carried out under the optimal conditions found for measurement: 85°C in a 50/50 mixture by weight of phenol/1,2,4-trichlorobenzene. The absolute weight-average molecular weight from light-scattering measurements served for calibration of indirect methods of charac-terization (e.g., the limiting viscosity number [η] is related to the molecular weight by [η] = 5.10 × 10^?4 M_w^0.72), and the molecular weight per unit chain length, $ \bar M_L * $, from light scattering and size exclusion chromatography (SEC) is found to be 28 Å^?1, consistent with theoretical expectations. The calculated persistence length q is 28 Å. Moreover, the meth-odology of SEC characterization enables the kinetics of solid-state postpolymerization of this liquid-crystalline copolyester to be studied. © 1993 John Wiley & Sons, Inc.     

Free release static coating of glass capillary columns; Static coating at elevated pressure — Theoretical considerations and practice

Summary Static coating of glass capillary columns has hitherto solely been carried out by evaporation of the stationary phase solvents under vacuum conditions. However, since a solvent vapour pressure higher than the external pressure is the only requirement for the vapour to flow out of the column, evacuation should not be necessary. Several important factors in the static coating procedure, such as mass (solvent vapour) — and heat transfer, heat of vaporisation of the solvent and viscosity of the stationary phase solution at elevated temperature and outlet pressure are discussed, principally to rationalise an improved static coating procedure. The alternative, so-called free-release static coating procedure, was evaluated practically by coating several columns with OV-101 and SE-30. Coating speed was found to be rapid and relatively constant whereas coating efficiency was between 80 and 100%.     

Surface properties of the binary mixed systems of alkylpyridinium halides and sodium alkylsulfonates

Surface properties of the binary mixed systems of decyl- and dodecylpyridinium chloride or bromide and sodium pentyl- and heptylsulfonate have been investigated. The surface tension of solutions of equimolar mixtures of surfactants and individual surfactants was measured, and the composition of mixed monolayers and surface interaction parameter β were calculated with the regular solution theory. Our results indicate that the properties of mixed films depend on both ionic strength and the kind of added inorganic electrolyte. With the increase of inorganic electrolyte concentration, the content of more surface active ions in the adsorption films enhances and is the highest in the presence of NaI and the smallest when solutions contain NaCl. Mutual interactions in mixed adsorbed films were found to be attractive. However, the strength of interaction weakens with the increase of ionic strength and depends on the kind of inorganic ions in the order: Cl⁻>Br⁻>I⁻.