Solubility of polyelectrolytes

Fig. 17 a, b. Solubility of polyelectrolyte complexes in ternary solvent systems at 30 °C. 

These results show that the solubility of polyelectrolytes in the presence of multivalent salt, especially at high salt concentration, depends on the relative affinity between charged groups of the polyelectrolyte and counterions. With organic multivalent cations, as spermidine and spermine, where... 

Ionic polymers (polyelectrolytes and polyampholytes) constitute an important class of water-soluble maaomole-cules. ° Their monomer units are capable of ionization in polar solvents, for example, in water. The ionization occurs via either dissociation of hydrogen ions H from the acidic groups or dissociation of water molecules and protonation of the basic groups on the polymer chain. The solubility of polyelectrolytes in polar solvents is determined first of all by a huge gain in translational entropy of the counterions. The majority of bio-maaomolecules (proteins, nucleic acids, and polysaccharides) operating in aqueous environment carry ionizable groups (carboxyl, sulfate, amine, etc.) and are included in this class of polymers. 

B02 Bokias, G., Vasilevskaya, V.V., Iliopoulos, L, Homdet, D., and Khokhlov, A.R., Influence of migrating ionic groups on the solubility of polyelectrolytes phase behavior of ionic poly(V-isopropylaciylaniide) copolymers in water. Macromolecules, 33, 9757, 2000. 

As shown above, it has been known for some time that the solubility of polyelectrolytes in aqueous media can be influenced by the electrochemical switching of the counterions. However, this principle has only recently been applied to trigger electrochemically built-up micellar aggregates from unimolecular solutions by adjusting the solubility of one part of a binary block-like copolymer [235]. Hereby, the electrolysis of ferrocyanide to ferricyanide led to the formation of vesicles (polymersomes). In contrast to real film formation, the solubilizing part, poly (ethylene oxide) (PEO), prevented film deposition on the electrode. Instead, bilayer film formation in bulk solution was favored under vesicle build-up with an insoluble polyelectrolyte complex as the vesicle wall, sandwiched between a well-hydrated PEO brush. 

The binding of cationic surfactant to DNA reduces its charge density, ultimately to a very low value. This has many consequences and manifestations. One effect is that the conformational state is affected to the extent that the stiffness is related to electrostatic repulsions - a polyelectrolyte is extended because of an osmotic swelling effect associated with the counterion entropy. A second effect is that the solubility is decreased since the solubility of polyelectrolytes is often determined by the counterion entropy. Below, we deal with phase separation in DNA solutions induced by the addition of cationic surfactant. 

Because of the aqueous solubiUty of polyelectrolyte precursor polymers, another method of polymer blend formation is possible. The precursor polymer is co-dissolved with a water-soluble matrix polymer, and films of the blend are cast. With heating, the fully conjugated conducting polymer is generated to form the composite film. This technique has been used for poly(arylene vinylenes) with a variety of water-soluble matrix polymers, including polyacrjiamide, poly(ethylene oxide), polyvinylpyrroHdinone, methylceUulose, and hydroxypropylceUulose (139—141). These blends generally exhibit phase-separated morphologies. 

Interest in the chemistry of water-soluble polymers (polyelectrolytes) has been continually increasing during the past 45 years. The tremendous scope of utility for water-soluble polymers has led to a vigorous search for new materials and the rapid development of polyelectrolytes into a dynamic field of industrial research. Growth in this field has been especially rapid since 1960 and today, many companies are engaged in synthesis and applications research on polyelectrolytes that are primarily used in four main marketing areas water treatment, paper, textiles, and oil recovery [1]. Polyacrylamide gel was also used as soil conditioner [2-4]. 

The extensive industrial and commercial utilization of water-soluble polymers (polyelectrolytes) in water treatment has been developed based on the charge along the polymer chains and the resultant water solubility. The use of water-soluble polymers in water treatment has been investigated by several authors [5-26] in the recovery of metals radioactive isotopes, heavy metals, and harmful inorganic residues. This allows recycling water in the industrial processes and so greatly saves... 

The precipitation of polyelectrolytes by the addition of multivalent counterions may be explained in these terms. When there are no multivalent ions in solution there is a strong repulsive force between polyions and the osmotic pressure is large. The solubility of polyions is a result of these repulsive forces. 

Solutions of polyelectrolytes contain polyions and the free (individual) counterions. The dissociation of a polyacid or its salt yields polyanions, and that of a polybase or its salt yields polycations, in addition to the simple counterions. The polyampholytes are amphoteric their dissociation yields polyions that have anionic and cationic functions in the same ion and often are called zwitterions (as in the case of amino acids having HjN and COO groups in the same molecule). Such an amphoter will behave as a base toward a stronger acid and as an acid toward a stronger base its solution properties (particularly its effective charge) will be pH dependent, and an isoelectric point (pH value) exists where anionic and cationic dissociation is balanced so that the polyion s charges add up to zero net charge (and solubility is minimal). 

In solutions, the counterions of poly electrolytes are HjO (for the polyacids) and OH (for the polybases), cations such as K+ and Na, or anions such as Cl (for the polysalts). The addition of polyvalent counterions (such as Ca, Mg, Cu, AT ) produces ionic cross-linking interfering with solubility The polyelectrolyte precipitates and may be redissolved upon addition of a strong acid (such as HCl). This can be regarded as a special case of ion exchange. 

Barone, G., Crescenzi, V., Pispisa, B., Quadrifoglio, B. (1966) Hydrophobic interactions in polyelectrolytes solutions. II. Solubility of some C3-C6 alkanes in poly(methacrylie acid) aqueous solutions. J. Macromol. Chem. 1, 761-771. 

AB block copolymers containing two water-soluble blocks are often referred to as double-hydrophilic block copolymers. These copolymers have spurred much interest in recent years because they can generally be transformed into amphiphilic copolymers once an adequate stimulus is applied. In other words, one of the hydrophilic water-soluble blocks can be transformed into a hydrophobic block whenever a given property of the aqueous medium is changed. Since these copolymers may contain one or two polyelectrolytic blocks, the typical features of polyelectrolytes described in Sect. 4.2 should also be considered for some double-hydrophilic block copolymers. 

Figure 45 should be compared with the distorted plots shown previously137, 1411 (Fig. 43) for a strongly cationic polyelectrolyte. Normal plots yielding the correct molecular weight are obtained when salt is included KC1 for aqueous solutions and LiCl for methanolic ones in view of the insufficiently great solubility of KC1 in... 

The release kinetics of polyelectrolyte-containing controlled release compositions were modeled by Ozturk et al. [331]. According to this analysis the drug release rate depends on intrinsic solubilities as well as pKa values of the drug and polymer. Explicit relationships between release rates and these factors were derived, resulting in successful predictions of experimental data. 

Other investigators have considered polyamines as polymeric drugs. Panarin and coworkers [467] studied the immunogenic and antibacterical activity of water-soluble cationic polyelectrolytes based on vinylamine amino-alkyl methacrylate quaternary ammonium salts. Macrophages were successfully activated in vivo to become cytotoxic to tumor cells in vitro, and cytotoxic or... 

Significant research has been directed toward the use of polyelectrolyte complexes as blood compatible materials. Several investigators found that water-insoluble polyelectrolyte complexes can suppress blood coagulation [487-490]. Davison and coworkers reviewed and studied the biological properties of water-soluble polyelectrolyte complexes [491] between quatemized poly(vinyl imidazole) or polyvinyl pyridine) and excess sulfonated dextran or poly(methacrylic acid). By forming complexes with a stoichiometric excess of anionic charge, a more compact conformation with anionic character was obtained. 

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