Polyampholyte solution properties

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). 

Polyammonium-containing ligands, 24 44 Polyammonium macropolycycles, 76 780 Polyampholytes, 20 475 479 solution properties of, 20 479 synthesis of, 20 477- 478 Poly(anhydrides), bioresorbable polymers, 3 740... 

Solution prepregging, 20 284-285 Solution processing, 14 80 Solution process, of ethylene-propylene polymer manufacture, 10 708-710 Solution properties of lignin, 15 13 of polyampholytes, 20 479 ofVDC copolymers, 25 703-706 Solution spectrophotometry, 9 232 Solution spinning... 

Keywords Polyampholytes, Theory of Polyampholytes, Acid-Base Equilibrium, Solution Properties, Associates and Complexes, Zwitterions, Amphoteric Gels, Application... 

Our fietailed investigation of the aqueous solution properties of a poly(vinylimidazolium sulfobetaine) has demonstrated viscosity enhancement in the presence of increased salt concentration (6). This polyampholyte, though insoluble in water, became soluble in certain aqueous salt solutions. The solution properties of this polymer were found to be related to the type and concentration of salt employed. 

Block Synthesis. Water-soluble block copolymers are formed from the copolymerization of macromonomers of methacrylates with acrylic and methacrylic acid monomers and their solution properties compared with random copolymers of similar composition (224). Diblock and triblock copolymers may be prepared by a number of techniques and are also used on ink-jet inks (225) and scale inhibition in water boilers (226), respectively. Associative properties of block polymers to form micellar structures are well established (227,228). Triblock polyampholyte polymers are also known (229). 

Synthesis. Polyampholytes are most readily prepared by the direct statistical copolymerization of anionic and cationic monomers typically in aqueous media, via conventional free radical pol3unerization. Examples of such materials were first reported in the 1950s (240-244). Using this approach a wide range of copolymers and terpolymers, often with a neutral hydrophilic monomer such as acrylamide, have been reported. For example, early reports of statistical polyampholytes include the methacrylic acid-stat-2-(dimethylamino)ethyl methacrylate copolymers (245), from IZ and 2Z with 6Z and the iV,A(-diethylallylamine-stat-acrylic acid copolymers from IZ and 6Z (246). More recently, synthesis and properties of novel polyampholytic terpol5uners have been described (247-250). For example, the aqueous solution properties of novel ampholytic terpolymers of acrylamide, sodium 3-acrylamido-3-methylbutanoate 5Z and 3-(acrylamidopropyl)trimethylammonium chloride 8Z have been studied in detail (187). 

Solution Properties. The aqueous solution behavior of polyampholytes is dictated by coulombic interactions between the basic and acidic residues. Polyampholytes have the ability to exhibit both polyelectrolyte and antipolylelectrolyte behavior in aqueous media. Which type of behavior is exhibited depends on factors such as solution pH, copolymer composition, the relative strengths of the acidic and basic residues, and the presence/absence of low molecular weight electrolyte (239). A feature of polyampholytes—in particular those comprised of weak acidic and basic residues—is the so-called isoelectric point, or lEP. This is simply defined as the solution pH at which the polyampholyte is electrically neutral. Statistical polyampholytes often remain soluble at and around the lEP whereas block polyampholytes tend to be soluble above and below but insoluble at this critical pH. The lEP may be determined either by titration or by measuring the reduced viscosity as a function of pH—the lEP also represents the point at which the polyampholyte chain is in its most compact conformation and thus corresponds to the minimum in reduced viscosity (239,266). With a knowledge of the respective piiLa s and copolymer composition it is also possible to predict the lEP (267). 

Solution Properties. Zwitterionic polymers show interesting aqueous solution behavior. As a general rule, they are insoluble in pure water due to the formation on intra- and interchain ion contacts resulting in an ionically cross-linked network-type structure. Polyampholytes and polybetaines which are not soluble become soluble upon the addition of low molecular weight electrolytes, such as NaCl (Fig. 51). This dissolution process can best be understood in terms of the low molecular weight electrolyte penetrating the ionically cross-linked network whereupon the ions screen the net attractive interactions between the polymer chains and hence promote solubility. The addition of the salt also results in an-tipolylelectrolyte behavior, ie chain expansion upon the addition of the salt. 

In this chapter, we have presented an overview of the properties of solutions of charged polymers. Electrostatic interactions between charges lead to the rich behavior of polyelectrolyte and polyampholyte solutions qualitatively different from those of neutral polymers. " For example ... 

The theory of solutions of flexible uncharged polymers with excluded volume is at present well developed, but the properties of polyelectrolytes and especially polyampholytes have been considered much less from the theoretical point of view. It is well known that polyampholytes exhibit a change in phase from the extended random flight configuration to a condensed microphase. The polyampholyte theory of Edwards et al. [6] considers the isoelectric state of polyampholytes as a microelectrolyte satisfying a Debye-Huckel-type of structure. The criterion of transition from the collapsed conformation to the extended one is described as follows ... 

The modification of water soluble polymers for tailored solution behavior has been of interest to many research groups seeking different end uses. Enhanced oil recovery, fracturing fluids, flocculation, associative thickeners, personal care products and many other applications exist for polymers of unique solution behavior. Although the ultimate applications may differ, a common goal of researchers in the water soluble polymer field is a solution viscosity enhanced through polymer-polymer intermolecular associations, often with the stipulation that associations must remain intact in the presence of mono- and divalent salts. To this end our research group has extensively studied the properties of several classes of water soluble polymers. While the majority of our studies have involved ampholytic systems ampholytic ionomers [1], polyampholytes [2,3], polysulfobetaines [4,5] and liquid crystalline ionomers [6], we recently have been... 

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