Polyelectrolyte complexes. I. Synthesis and characterization of some insoluble polyanion-polycation complexes

The synthesis of some water-insoluble synthetic polyelectrolyte complexes formed between a weak polyanion and a strong polycation was followed. Sodium salts of poly(acrylic acid) and of some copolymers of acrylic acid with itaconic acid or maleic acid were used as anionic polymers. Cationic polyelectrolytes with quaternary ammonium salt groups in the main chain were used as strong polycations. The cationic polymers were different as concerns both the content of quaternary nitrogen atoms and the degree of branching. The complex formation was followed by the variation of the conductivity and of the specific viscosity of the reaction medium as well as by the turbidimetric titration versus the unit molar ratio polyanion/polycation. The deviation of the endpoint from stoichiometry was influenced mainly by the structure of the complementary polymers and by their molecular weights. The greater the structural differences, the higher the endpoint deviation from stoichiometry. Only insoluble polyelectrolyte complexes (PEC) were obtained in all the polyanion/polycation systems taken into account. The PECs were separated and characterized by elemental and spectral analyses as compared with the complementary polymers. © 1996 John Wiley & Sons, Inc.     

Voltametrische Titration von Halogeniden im Spurenbereich mit Quecksilber(II)-nitrat

A rotating palladium electrode is employed for endpoint detection in this method. The solvent is a mixture of 20 parts of water and 80 parts of ethanol. The lower limit of the method is about 10^?4 mMole of chloride, bromide or iodide in 125 ml. The titration is not affected by neutral salts and is therefore especially suitable for the determination of small amounts of halogens in organic compounds after combustion or decomposition by peroxide. The method, described here, is performed automatically.     

Calorimetric Study of the Aggregation of Lithium Perfluorohexanoate on Poly(ethyleneglycol) Oligomers in Water

The interaction of lithium perfluorohexanoate (LiPFHex) with poly(ethylene glycol) (PEG) of different molecular weights (600 Da≤ MW≤20000 Da) was investigated in aqueous solution at 25.00 °C by isothermal titration calorimetry (ITC). The interaction with one of the PEG polymers (MW=8000 Da) was also followed at the same temperature by viscosity and conductivity measurements. The aggregation pattern of this surfactant on the PEG polymeric chain was very similar to that exhibited by the homologous salts of perfluoroheptanoate, perfluorooctanoate and perfluorononanoate ions. The interaction enthalpies with PEG of this class of surfactants are always endothermic and decrease steeply with the decreasing length of the fluorocarbon chain. Experimental data from calorimetry, viscosity and conductivity consistently indicate a very small tendency of PEG polymers to wrap around the small LiPFHex micellar aggregates. The PFHex ion appears to be the shortest member of the series able to interact with a polyoxyethylenic chain. The same CF₂ contribution to the Gibbs energy of micellization or aggregation on the polymers was found within the series, indicating a common hydrophobic driving force for the two processes.     

Polymerization of surface-active monomers. I. Micellization and polymerization of higher alkyl salts of dimethylaminoethyl methacrylate

Micellization of cationic salts of dimethylaminoethyl methacrylate (DMAEMA) quaternized with n-alkyl bromides such as octyl, lauryl, myristyl, and stearyl bromide and their polymerizations were investigated. The critical micelle concentration (cmc) in water at 25°C was determined by electrical conductivity and dye(azobenzene) solubilization methods and the relation log(cmc) = 1.46–0.31N was obtained, where cmc is in mmol L^?1 and N corresponds to carbon number of alkyl bromides used for the monomer preparations. All of these monomeric salts exhibited a high radical polymerizability in water and benzene. The polymerizations in water appeared to proceed with a higher rate with increasing a chain length of the alkyl moiety of the monomers and those in benzene gave the polymers with a remarkably high viscosity. The rate of polymerization of lauryl bromide salt in anisotropic solutions (in water and benzene) was exceedingly fast as compared with that in isotropic solution(in acetonitrile). All of the polymers obtained here were insoluble in water. Solubility characteristics of these monomers and polymers in other solvents were also presented. The reduced viscosity, in dimethylformamide and methanol, of poly(lauryl bromide salt) prepared in water increased with dilution but that for the polymer obtained in benzene exhibited an inverse concentration dependence. Some discussions were made on the peculiarities of the polymerizations of these monomers and the resulting polymers.     

Salt effects on cloud points and viscosities of polymethacrylates with pendant oligo-oxyethylene chains

Comblike polymethacrylates with oligo-oxyethylene side chains were synthesized from the commercially available monomers CH₂ ? C (CH₃) COO (CH₂CH₂O)_nCH ₃, the average n being 4, 8, and 22. The three polymers exhibited lower critical solution temperatures in aqueous media. Cloud points were determined as a function of the nature and concentration of salt. For salts that destabilize the polymer solutions, the cloud points decrease linearly with salt concentration, the extent of the decrease being strongly anion dependent. Salt effects on the viscosity of the polymers were measured in water, methanol, and acetonitrile. In water the viscosity decreases on adding salt, but in methanol and acetonitrile the neutral polymers are converted to polycations as cations form stable adducts with the oligo-oxyethylene side chains. The increase in viscosity is both cation and anion dependent. The general behavior of the comblike polymers resembles that reported for aqueous or methanolic salt solutions of poly (ethylene oxide) and nonionic surfactants.     

Potentiometric titration behavior of poly(ethylene glycol methyl ether)-b-poly(ethylenimine)

Poly(ethylene glycol methyl ether)-b-poly(ethylenimine hydrochloride) was characterized using potentiometric and viscosimetric titration methods. The average chemical compositions of the polyamine hydrochloride salts estimated by the acid-base titration,¹H-NMR, and elemental analysis were compared. The apparent dissociation constant, pK, and the inherent viscosity of the polyamine hydrochloride were found to be highly dependent on the degree of neutralization. Very strong coulombic interactions among the charged sites were observed at low pH's for this polymer.     

Physico-chemical study of ionic equilibria for poly-2 and poly-4-vinylpyridines in alcohol-water solutions

The ionic equilibria for poly-4-vinyl pyridine (P4VP) and poly-2-vinyl pyridine (P2VP) were studied by physico-chemical techniques such as potentiometry, viscosity and NMR-¹H. The mixture of ethanol (45 per cent w.p.) and water was used as solvent to obtain the total range of ionization (0–1). It was found that the dissociation constants of pyridine residue of polymers in the absence of electrostatic interaction (pK₀ = 3·3–3·9) are lower than for the monomer analogues 4-ethylpyridine and 2-ethylpyridine (5·02) and depend on ionic strength (NaCl).A sharp decrease of pK_app at the beginning of titration and increase of specific viscosity for P4VP and P2VP are both explained by electrostatic interactions between positive charges forming during titration of the macromolecules. Most probably, these interactions act through the organic part of the macromolecule. On the other hand, it is shown by NMR-¹H that sharp changes in pK_app and specific viscosity at the beginning of the titration are not associated with changes in the average conformation of the monomer unit in the polymer. This conformation can be destroyed only when the energy of electrostatic interactions is large enough and this occurs when the mean distance between positive charges is relatively short.     

Rheology of a mixture of liquid-crystal polymers in solution

The rheological behavior of a mixture of two liquid-crystal polymers, hydroxypropyl cellulose and ethyl cellulose, in acetone solution is studied. The total polymer concentration in the solvent is held constant (40%) as the ratio of the two polymers is varied. The mixtures are anisotropic, isotropic, or biphasic (isotropic/anisotropic), depending on the concentration. Curves of viscosity vs shear rate for all the mixtures studied show three regions of viscosity, as described by Onogi and Asada for liquid-crystal polymers. The viscosity as a function of the weight ratio of the two polymers at constant shear rate exhibits deviations from additivity of viscosities of the two components at all concentrations. In mixtures of two polymers in the melt, deviations are also observed; the negative ones are attributed to phase separation and the positive ones to homogenous mixing (comparison with the phase diagram). All the mixtures studied (anisotropic, isotropic, or biphasic), show ranges of shear rates where the first normal-stress difference is negative, as is generally observed for anisotropic liquid-crystal polymers. It is concluded that the isotropic solutions become anisotropic under shear, as they are not far from the critical concentration. © 1994 John Wiley & Sons, Inc.     

Thermal decyanation,a new organic reaction. II

When heated in solution at about 160°C, pyridine quaternary salts of bromomalonamides lose 1 mole of cyanic or isocyanic acid almost quantitatively in a manner quite analogous to the decarboxylation of an acid. By DTA and DSC, the crystalline salts are stable up to their melting points (>220°C) at which temperatures concurrent fusion and decyanation processes occur (endotherm); these are immediately followed by an exotherm related to the trimerization of cyanic acid. TGA measurements on the solid salts do not clearly define the loss of 1 mole of cyanic acid because in the solid state, thermal decyanation is accompanied to some extent by other pyrolytic reactions. Preparative methods for quaternizing poly(4-vinylpyridine) with bromomalonamide are described and two polymeric quaternary salts (33 and 100% substituted) were prepared and analyzed. These polyelectrolytes are water soluble and upon the addition of base the yellow polymeric nitrogen ylids are generated. Infrared spectra on the polymeric quaternary salts and visible spectra on the polymeric ylids are included. The ylid chromophore has an ε = 1800 at λ_max = 415 nm. The dilute solution viscosity behavior of these polymers in H₂O and in 0.05N KBr is typical of polyelectrolytes. Both polymers in dilute solution show a maximum in η_sp versus pH plots. In water, the viscosity of these polymers decreases with time, and it is proven that this results from a conformational change which accompanies amide hydrolysis rather than polymer backbone degradation. Glass transitions are not detectable by DTA but both polymers show well-defined trimerization exotherms for cyanic acid starting at 170–175°C. Thus, decyanation of the solid polymeric quaternary salts is more analogous to decyanation of the crystalline quaternarys in solution than as solids. TGA measurements on the polymers show weight losses which are of the correct order of magnitude and in the correct temperature range for monodecyanation. Some data are presented which suggest that perhaps a second mole of cyanic acid is lost at about 250°C. Quaternization of poly(4-vinylpyridine) with bromomalonamide reduces its gross decomposition temperature from 385°C to about 285–317°C. It is demonstrated how thermal decyanation can be used for the in situ generation of cyanic acid for the modification of organic compounds. The preparation of a partial urethane of poly(vinyl alcohol) using this method is described. We have also shown that aliphatic quaternary salts can be prepared and that they too undergo the decyanation reaction.     

Viscometric determination of the two critical concentrations of polymers in solution

A viscometric study is presented using ternary systems polymer-1/polymer-2/solvent. The variation of the reduced viscosity of the polymer mixture with the total concentration shows two crossover points corresponding to the two critical concentrations of polymers C7 and C1. The influences of the temperature and of the hydrodynamic volume of the polymers on the critical concentrations are also presented.     

Impact of ionic liquids on silver thermoplastic polyurethane composite membranes for propane/propylene separation

This work describes newly synthesized composite polymeric membranes and their utilization in propane/propylene separation in a gas mixture. The nonporous composite polymers were successfully synthesized by using thermoplastic polyurethane (TPU) and several silver salts/silver salts with ionic liquids (ILs). Our studies showed that silver bis(trifluoromethanesulfonyl)imide (Ag[Tf₂N]) containing membranes outperformed other silver salt containing membranes in terms of selectivity. In addition, to this finding, ILs, as additives for the membranes, enhanced the selectivity by facilitating improved coordination of the olefin with the silver ions in the dense composite polymers.     

Nanoporous carbons obtained by carbonization of copolymers impregnated by salts

This paper demonstrates the results of research on influence of types of polymer and kinds of salts used for impregnation of the polymer on porous structure formation in the final carbonaceous product. The studies were performed in two stages. In the first stage, the role of polymer structure were mainly studied. To achieve the aim, three different porous copolymers (polyimide and two types of polyester) were impregnated with the same salts (NiSO₄, and the mixture of AgNO₃ and Gd(NO₃)₃). In the second part of the study, only one polymer (polyimide) was impregnated by three mixtures of salts (chlorides, nitrates and sulphates of K, Cu(II) and Fe(III)). This approach allowed to evaluate the impact of the mixture of salts on porosity of the carbons, which were to be prepared. The obtained results revealed that when the impregnation was applied as a method for activation and moulding of porosity of carbonaceous materials prepared from polymers, several factors should be taken into account. First of all, initial decomposition temperatures of the polymers and the salts should be compared to find out if carbonization and activation processes proceed simultaneously or not. If the copolymer was carbonized and gases were released from decomposing salts, they reacted each other and synergic effect of polymer and salts properties were observed. Such conditions favored the development of microporous structure of the obtained carbon. On the contrary, if the processes were separated in time because of high temperature of melting point of the salts more mesopores were retained.     

Mercurimetric determination of chloride with diphenylcarbazide disodium disulfonate as an indicator

A procedure is given for the use of diphenylcarbazide disodium disulfonate as an indicator in the direct titration of chloride with mercuric nitrate. By adding ferric nitrate to form the carbazone and an inert green substance to serve as a color screen, a sharp and reversible endpoint changing from green to grey to purple is obtained. Studies were made on the indicator reaction and other factors, such as mercuric chloride concentration, pH, volume, temperature and the effect of various added salts. The pH must be adjusted to 1.8 to 2.0 for best results. A series of ten determinations on a sample gave a standard deviation of ±0.16 part per thousand.     

A precise direct heterometric determination of traces of copper with diethyldithiocarbamate in excesses of metals

The most favorable conditions for the heterometric titration of copper with sodium diethyldithiocarbamate and the influence of complexing agents on the titration were investigated.Titrations of copper were carried out in the presence of large excesses (? 99. 5%) of most of the common cations. A method is presented for a precise determination of traces of copper in metals and salts.The titration time was 7–10 minutes. In most titrations the amount of copper present was determined with an error close to zero.     

Potentiometric and Coulometric Determination of 5-Phenyl-1,3,4-Oxadiazole-2-Thiol

A method for the determination of 5-phenyl-1,3,4-oxadiazole-2-thiol involving its reaction with iodine in an alkaline medium has been presented. In volumetric titration with potentiometric endpoint detection, the determination range is 25–500 μmol. In coulometric titration using biamperometric endpoint detection, 0.5–5 μmol of 5-phenyl-1,3,4-oxadiazole-2-thiol were successfully determined. The errors and the relative standard deviations were below 1%. The shapes of the obtained potentiometric titration curves of the tested compound are unusual at higher concentrations of sodium hydroxide and depend on the material of the indicator electrode (platinum and gold). Addition of iodine resulted in a significant potential drop. The studied system did not exhibit Nernstian behavior. __________ From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 10, 2005, pp. 1094–1097. Original English Text Copyright ? 2005 by Ciesielski, Krenc. The text was submitted by the authors in English.     

Precise and accurate determination of halogens in organic compounds using an amalgamated gold electrode

Precise and accurate titration of halogens in organic and inorganic materials has been studied. The halogen was titrated with coulometrically generated silver and determined potentiometrically by using an amalgamated gold indicator electrode. An argentometric titration curve using the amalgamated gold indicator electrode showed a large jump in potential at the endpoint as well as in mercurometric determination. Sodium carboxymethyl cellulose (CMC) and aluminum nitrate were added as they are most effective for clarifying the sample solution and eliminating adsorption of the halide ion on the silver halide generated. The electrolytes used were 0.5 M nitric acid containing 0.1% CMC and 0.2 M aluminum nitrate. Approximately 0.2 mmol of chloride, bromide, and iodide ions were titrated with high precision and accuracy. Their standard deviations were 0.03, 0.02, and 0.02%, respectively, with no apparent systematic error. The precise determination of halogens, employing oxygen flask combustion and dissolution of the halide salts in the electrolyte, was carried out with ±0.1% absolute error using samples weighing between 20 and 30 mg.     

Conductivity of nonaqueous solutions of aromatic polymers containing ionizable side groups

The concentration dependence of the equivalent conductivity has been measured for dilute DMAc solutions of K, Na, and Li salts of aromatic polymers with ionizable side groups [poly(diphenylenesulfophthalide) and poly(arylene ether ketone) with side COOH groups]. A correlation between the concentration dependences of the equivalent conductivity and reduced viscosity shows that the first parameter initially sharply decreases with an increase in concentration and then achieves a limiting value at a rather low concentration and that precisely in this concentration range the polyelectrolyte effect manifests itself in the concentration versus reduced viscosity curve. With an increasing amount of metal ions incorporated into the polymer, the equivalent conductivity grows. It was demonstrated that the type of counterion affects the reduced viscosity and equivalent conductivity of salt solutions. This effect depends on the structure of the polymer backbone: for poly(arylene ether ketone) salts, the reduced viscosity and the equivalent conductivity increase in the sequence Li → Na → K, while for poly(diphenylenesulfophthalide) salts, the reduced viscosity increases in the reverse order and the equivalent conductivity remains almost invariable. The limiting values of the equivalent conductivity and the degree of association of polyelectrolytes have been estimated in terms of the Arrhenius-Ostwald theory. It has been shown that, in the case of poly(diphenylenesulfophthalide) salts, the equivalent conductivity and the degree of association are higher than those for poly(arylene ether ketone) salts with side COOH groups. This finding is indicative of a stronger binding of counterions by poly(arylene ether ketone).     

Determination of Diaryliodonium Species by Reverse Iodometric Titration with Ascorbic Acid

Diaryliodonium salts are used in organic chemistry, materials science and pharmaceutical chemistry. For the quantitative analysis of diaryliodonium salts, only instrumentally demanding techniques requiring highly skilled operators are available. Surprisingly, no titration method taking advantage of the oxidising ability of diaryliodonium is available in the literature. In the present work, a titration method for the determination of diaryliodonium salts is presented. It is based on the reaction of diaryliodonium species with ascorbic acid, whose excess is subsequently determined by means of iodometric potentiometric titration. Application of the protocol to various diaryliodonium salts revealed the scope and limitations of the method.     

Acid-base equilibria in ethylene glycol--II: autoprotolysis constants and acid-base properties of ethylene glycol and its mixtures

The acid-base behaviour of ethylene glycol and its mixtures with water (1, 5 and 10%), methanol, ethanol, isopropanol, nitromethane (each 10%) and ethyl methyl ketone-chloroform (5 + 5%) have been investigated by potentiometric titration, in a cell without liquid junction, equipped with a glass and a silver-silver chloride electrode. The autoprotolysis as well the protolysis constants of phthalic acid were determined for each mixture. The added solvents improve the properties of ethylene glycol, decreasing the viscosity without changing the acid-base behaviour of the ethylene glycol itself, which is favourable for the titration of weak bases. Water increases the basic, and nitromethane the acidic, properties of the mixture. Small quantities of water (ca. 1%) do not impair the titration conditions.