Polyelectrolyte behavior

The viscosities were measured with an Ubbelohde Cannon 75-L, 655 viscometer. Formic acid was chosen as the solvent for the viscosity measurement because the polymer (VII) showed very low or no solubility in other common solvents. In a salt free solution, a plot of the reduced viscosity against the concentration of the polymer showed polyelectrolytic behavior, that is, the reduced viscosity ri sp/c increased with dilution (Figure 4). This plot passed through a maximum at 0.25 g/dL indicating that the expansion of the polyions reached an upper limit, and the effects observed on further dilution merely reflected the decreasing interference between the expanded polyions. 

Typical examples of polyelectrolyte micelles have been reported for cationic PS-P4VPQ and for other quaternized P2VP- or P4VP-containing block copolymers by Selb and Gallot [142,143]. Eisenberg et al. [144-147] and Tuzar and coworkers [41,148] have studied the PS-PAA and PS-MAA systems in their acidic or neutralized anionic form. Typical polyelectrolyte behavior was detected for these types of micelles. 

Extensive work has appeared in the Russian literature concerning the piperidinol monomers (97), primarily concerned with polyelectrolyte behavior of the polymers obtained via free radical polymerization through the double bond (80MI11109). 

Figure 2. Viscosity data showing the polyelectrolyte behavior of resoles...

This article will summarize results and information derived from basic and applied research on DADMAC and its polymers. Contrarily to other specific publications, this review will include discussions of the synthesis, chemical structure, molecular characterization, polyelectrolyte behavior, complex formation, and applications. It will be shown that the real solution behavior of polyelectrolytes cannot be investigated separately from their chemical structure and that it is essential to study synthesis and characterization of polyelectrolytes along with their physico-chemical properties. 

This review demonstrated that research on diallyldimethylammoium chloride and its polymers have contributed to the general understanding of the polymerization of ionic monomers, the development of methods for the molecular characterization possibilities of cationic polyelectrolytes, and the understanding regarding polyelectrolyte behavior. However, in comparison to the industrial importance of diallyldimethylammonium chloride polymers, the level of fundamental knowledge is far from adequate. In particular, copolymerization processes with monomers other than acrylamide, the characterization of copolymers related to their chain architecture and charge distribution, the dependence of... 

Addition of polymers can both stabilize and destabilize a solution. If the polymer contains ionizable units it is usually referred to as a polyelectrolyte. In this report we will focus on the effect from polyelectrolytes on the colloidal stability. In high dielectric media like water, where the monomers are ionized, the behavior of a polyelectrolyte is mainly governed by electrostatics and the connectivity of the monomers. Therefore, in theoretical studies, many important features of the polyelectrolyte behavior in water solution can be studied by a schematic description of the polyelectrolyte as a linear chain of charged monomers connected with springs. The bonding interaction between two monomers is Ub=K(r —a)2, where K is the spring constant, a is the equilibrium value and r is the distance between the two monomers (see Fig. 11). 

The properties of ionomer solutions are sensitive to not only the degree of the ionic functionality and the polymer concentration, hut perhaps even to a greater extent, the ability of the solvent to ionize the ion-pairs (64). Thus, non-ionizing solvents, usually those with relatively low dielectric constant, favor association of the ionic groups even in dilute solutions. In contrast, ionomer solutions may exhibit polyelectrolyte behavior in polar solvents due to solvation of the ion-pair that leaves the hound ions unshielded. 

Polyelectrolyte behavior is exhibited by solutions of SPS in DMF, Fig. 12. At low polymer concentrations, the viscosity Increases as a result of repulsion between the unshielded anions, which Increases the hydrodynamic volume of the polymer. The structure of SPS in DMF solutions as determined by static and dynamic light scattering is also discussed in the chapter by Hara and Wu. 

Polyelectrolyte Behavior. Figure 1 shows the characteristic Kc/R vs. c plot of lonomers in polar solvents the reciprocal reduced scattered intensity rises steeply from the intercept at zero polymer concentration, bends over, and becomes nearly horizontal at higher concentration. This type of behavior was reported for some salt-free polyelectrolytes in aqueous solution (23.26), although the reliability of these early measurements is rather poor because of very small scattered intensity from polyelectrolyte/aqueous solution systems. For example, the excess scattered intensity from salt-free sodium poly(methacrylate) in aqueous solution over that of water was only 10 to 100% (2i) - (0.1-1) x 10 °. in ionomer solutions,... 

Studies on the dilute solution behavior of sulfonated ionomers have shown these polymers to exhibit unusual viscosity behavior in solvents of low polarity. These results have been interpreted as arising from strong ion pair associations in low polarity diluents. Solvents of higher polarity, such as dimethyl sulfoxide and dimethyl formamide induce classic polyelectrolyte behavior in sulfonate ionomers even at very low sulfonate levels. To a first approximation these two behaviors, ion pair interactions or polyelectrolyte behavior, are a consequence of solvent polarity. Intramolecular association of Lightly Sulfonated Polystyrene (S-PS) results in a reduced viscosity for the ionomer less than that of polystyrene precursor at low polymer levels. Inter-association enhances the reduced viscosity of the ionomer at higher polymer concentrations. Isolation of the intra- and inter-associated species of S-PS has been attempted (via freeze drying). A comparison of selected properties reveals significant differences for these two conformations. 

Few studies have been conducted heretofore on sulfonated ionomers in solvents which can be considered relatively polar, as defined by a high dielectric constant. A recent study (13) on acrylonitrile-methallyl sulfonate copolymers in dimethyl-formamide is a notable exception. S-PS is readily soluble in a wide variety of solvents, some of them exhibiting rather high values of dielectric constant, such as dimethylformamide (DMF) or dimethylsulfoxide (DMSO). The reduced viscosity-concentration behavior of sulfonated polystyrene is markedly different in polar solvents from that in nonpolar-solvent systems. Typically there is a marked upsweep in reduced viscosity at low polymer concentrations and clearly a manifestation of classic polyelectrolyte behavior. ( 7)... 

Typical polyelectrolyte behavior has been observed in several solvents of moderate to high polarity as described in Table II. It is clear that in low polarity solvents ion-pair association prevails, while with high polarity solvents polyelectrolyte behavior is observed. With solvents of intermediate polarity either behavior can be observed suggesting specific solvation effects. 

The influence of small amounts of water as a cosolvent for THF solutions is shown in Figure 3. At water contents of 3% or less the reduced viscosity-concentration profiles are similar to Figure 2. However, increasing water levels induces an upsweep in reduced viscosity at low polymer concentrations typical of polyelectrolyte behavior. This behavior has been observed in other mixed solvent systems and is clearly a consequence of specific cation solvation effects. Sodium23-NMR studies have shown that water solvates sodium cations at least ten times more strongly at similar cosolvent levels and the data in Figures 2 and 3 are consistent with those findings. 

Polar solvents such as dimethylformamide, dimethylsulfoxide, and tetrahydrofuran-water mixtures behave differently in that polyelectrolyte behavior is observed at extreme dilution for sulfonate ionomers therefore, the behavior described above does not apply directly to these solvent systems. 

Thus far we have not succeeded in the isolation of an ionomer free of impurities from a solvent favoring polyelectrolyte behavior where its solution behavior can be compared to that in Table II. Currently such studies are in progress. 

Raspaud E, Olvera de la Cruz M, Sikorav JL, Livolant F. Precipitation of DNA by polyamines a polyelectrolyte behavior. Biophys J 1998 74 381-393. 

More recently, in addition to random ionomers, telechelic ionomers in which ionic groups are located only at the chain end(s) became available and were used for the study of polyelectrolyte behavior [26-29]. Discussion was made from the point of view that the behavior of telechelic ionomers in nonaqueous solutions is basically similar to that of polyelectrolytes in aqueous/nonaqueous solutions (including random ionomers in nonaqueous solutions). Also, the study of fundamental aspects of polyelectrolytes was made possible because of the simplicity of the structure of telechelic ionomers. For example, telechelic ionomers with only one ionic group at the chain end can be used to study the role of intermolecular interactions, since there is no intramolecular electrostatic interaction available for this type of ionomer [27]. Due to space limitations, this chapter will only cover polyelectrolyte behavior of random ionomers in polar solvents. Some results on telechelic ionomers can be found elsewhere [26-29]. 

Classical studies on polyelectrolyte behavior, which were conducted by using polyelectrolyte nonaqueous solutions, are briefly described here. These studies include conductance and viscosity behavior. More details on these subjects can be found in a previous review article [23]. 

II. POLYELECTROLYTE BEHAVIOR OF IONOMERS (WEAKLY CHARGED POLYELECTROLYTES) IN POLAR NONAQUEOUS SOLUTIONS... 

Solution behavior of ionomers can be divided into two types, primarily depending on the polarity of the solvent [46,47], One is polyelectrolyte behavior due to the dissociation of counterions in polar solvents (e.g., DMF), and another is association behavior due to the formation of ion pairs and even higher order aggregates in less polar solvents (e.g., THF). Table 2 shows the solvents frequently used for the study of ionomer solutions, as well as their dielectric constants. As the dielectric constant decreases, the degree of counterion binding and also ion pair formation changes (increases) gradually, and so does the solution behavior. In this chapter, only the polyelectrolyte behavior of ionomers in a polar solvent is described. Some brief... 

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