Amphoteric polyelectrolyte

Note 1 A polymer bearing both anionic and cationic groups in the same molecule is called an amphoteric polyelectrolyte. 

Examples of more complex polyelectrolytes are copolymers where only a fraction of the monomers carry charged groups, and polyampholytes or amphoteric polyelectrolytes which carry both positive and negative charges. In this context proteins may be classified as very complex polyampholytes. In the following we shall mainly survey some aspects of simple (linear) polyelectrolytes. We shall only consider a single polyelectrolyte molecule in its aqueous environment (i.e., we restrict ourselves to dilute solutions, where intermolecular interactions may be neglected compare sec. 5.2a). 

Plausibly there is a correlation of the solubility of the stable oxide, hydroxide, or oxyhydroxide of a cation with the stability of the first hydrolysis product (Figure 6. 7). Many multivalent hydrous oxides are amphoteric because of the acid-base equilibria involved in the hydrolysis reactions of aquo metal ions. Alkalimetric or acidimetric titration curves for hydrous metal oxides provide a quantitative explanation for the manner in which the chaige of the hydrous oxide depends on the pH of the medium. The amphoteric behavior of solid metal hydroxides becomes evident from such titration curves. From an operational point of view, such hydrous oxides can be compared with amphoteric polyelectrolytes and can be considered hydrated solid electrolytes, fn -... 

For type (1), styrene, 2-methyl-5-vinylpyridine and divinylbenzene are copolymerized in the presence of the inert polymer and the obtained membrane is sulfonated and then quartemized 100 amphoteric polyelectrolytes such as a copolymer of jV-diethylamino methacrylate and methacrylic acid are dissolved in a... 

The first chapter of the book deals with enzyme-like eatalysis by synthetic polymers - catalysis by polymeric acids and bases, amphoteric polyelectrolytes and nonionic polymers. Because coordination compounds of metal ions with macromolecular ligands are interesting with regard to bioinorganic chemistry, this book elucidates some problems involving the catalysis by water-soluble polymer-metal complexes. Ester hydrolysis, hydrogen peroxide decomposition, oxidation of disubstituted phenols, hydroquinones, mercaptoalcohols and other types of reaction are chosen as model processes. A section devoted to interfacial catalysis is also included. 

Both the nature of their functional groups and the microstructuxe of the chain determine the electrochemical properties of poiyamphoiytes. The acid-base properties of amphoteric polyelectrolytes are quite different from the behaviour of both polyacid and polybase due to the fact that near the lEP it is difficult to... 

Many naturally occurring random-coil polyelectrolytes of a single charge type, including some carbohydrates, pectins, and keratins, are anionic and exhibit the same general surfactant interactions as their synthetic cousins. Proteins, on the other hand, are amphoteric polyelectrolytes, which possess a net charge character (anionic or cationic) that depends on the pH of the aqueous solution. Unhke most synthetic polyelectrolytes, natural polyelectrolytes such as proteins and starches often have well-defined secondary and tertiary structures in solution that can affect, and be affected by, surfactant... 

Poly(6-amino-2,4-hexadienoic acid), for example, represents an amphoteric polyelectrolyte with unusual properties in solution. It can be used as a complexing agent for transition metal ions with a selectivity for divalent ions, such as Cu , Co , or Ni. ... 

Amphoteric polyelectrolyte emulsifier Romania 73,606 1980 Intr. Chim. Risnov... 

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). 

The process described is referred to as ion-exclusion as discussed by Asher and Simpson 9. The resins used are normal and the non-ionic molecules are assumed to be small enough to enter the pores. When large non-ionic molecules are involved, an alternative process called ion-retardation may be used, as discussed by Hatch et al. W]. This requires a special resin of an amphoteric type known as a snake cage poly electrolyte. The polyelectrolyte consists of a cross-linked polymer physically entrapping a tangle of linear polymers. For example, an anion exchange resin which is soaked in acrylic acid becomes entrapped when the acrylic acid is polymerised. The intricacy of the interweaving is such that counter-ions cannot be easily displaced by other counter-ions. On the other hand, ionic mobility within the resin maintains the electro-neutrality. The ionic molecule as a... 

Studies on the interaction between oppositely charged polyelectrolytes date back to 1896 when Kossel389 precipitated egg albumin with protamine. Since that time extensive studies have been made on pairs of strong polyelectrolytes, pairs of strong and weak polyelectrolytes, pairs of weak polyelectrolytes, as well as on amphoteric complexes. However, the theoretical considerations of intermacromolecular interactions between polyelectrolytes were only based on extremely simplified model systems. However, even in the case of such systems, there are many unsolved problems such as the determination of the local dielectric constant in domains of macromolecular chains, the evaluation of other secondary binding forces, especially hydrophobic interactions, and so on. 

Rather frequently the surface sites of modified silicas can also consist of two and more types of centres of diverse nature. For example, during modification of silica, with 7-aminopropyl- triethoxysilane the surface practically always contains both =SiOH and -CH2CH2CH2NH2 groups. In this case the surface shows amphoteric properties and just as for polyelectrolytes we can write ... 

For the present system, we demonstrate the amphiphilic character of the complexed polyelectrolyte to override its amphoteric characteristics. There-... 

For polysalt amphoteric membranes, a cationic polyelectrolyte solution such as poly(benzyl trimethylammonium salt) and an anionic polyelectrolyte solution such as poly(styrene sulfonate) are mixed and a polymer salt precipitated. The polymer salt is then dissolved in a suitable solvent and is formed into a membrane by a casting method.103... 

Recently, membranes prepared by a layer-by-layer method have been actively studied. For example, a cationic polyelectrolyte can be adsorbed on a fiat plate as a monolayer and then an anionic polyelectrolyte layer added to it. The same procedure can be repeated, thus forming an ultrathin, multi-layer, amphoteric ion exchange membrane.107 The multi-layers have been formed on a porous membrane in studies on separation membranes108 and, further, such membranes have been studied as new functional materials for sensors, devices for photoelectronics,109 etc. 

The viscosity of the cationic polysoap exhibits polyelectrolyte character whereas the viscosity of the zwitterionic polysoaps behaves as an uncharged polymer. The unusually low viscosities of zwitterionic polysoaps are attributed to the intramolecular aggregation of the hydrophobic side chains, keeping the hydrodynamic radius small. The surface activity and solubilization capacity of amphoteric polysoaps have been studied. The sequence to solubilize hydrophobic dyes is mid-tail > head > tail-end geometry. 

Static interaction, in addition to the nonionic factors mentioned previously. The polymers may be positively or negatively charged, or they may be amphoteric. In any case, they are commonly referred to as polyelectrolytes because of the multiple charges carried by each polymer molecule. The presence of charges on a polymer complicates the understanding of the solution properties of the polyelectrolytes. The potential for surfactant-polyelectrolyte interactions does so even more. 

The cationic charge on a polymer affects its behavior considerably when surfactants are included in formulations. Cationic polymers (a member of the broader class of polymers termed polyelectrolytes) usually interact strongly with anionic surfactants, weakly with cationic surfactants, and unpredictably with nonionic and amphoteric surfactants (14,167-169). Anionic surfactant binds to cationic polymers at concentrations well below the critical micelle concentration (cmc). The low surfactant concentration where polymer and surfactant begin to interact is known as the critical aggregation concentration (cag). 

Except for synthetic polyelectrolytes natural ones are also used. For example, the amphoteric nature of protein... 

---