Polyelectrolytes solution properties

This chapter describes the synthesis, kinetics, and solution properties for copolymers ofN-vinylpyrrolidone (NVP) with sulfonate ionic and zwitterionic monomers. Examples of the sulfonate ionic monomers are sodium styrenesulfonate (NaSS) and sodium acrylamido-2-meth-ylpropanesulfonate (NaAMPS) an example of the zwitterionic sulfonate monomer is 2-hydroxyethyt)dimethyl(3-sulfopropyt)-ammonium inner salt, methacrylate (SPE). The NVP-NaAMPS monomer pair was exceptional, showing evidence for donor-acceptor character and an alternating tendency in copolymerization. The NVP copolymers containing simple sulfonate ionic monomers e.g., NaAMPS) showed polyelectrolyte solution properties. On the other hand, the NVP copolymers with zwitterionic sulfonate monomers showed antipoly electrolyte solution behavior. 

Usually the acid-base properties of poly electrolyte are studied by potentiometric titrations. However it is well known, that understanding of polyelectrolyte properties in solution is based on the knowledge of the thermodynamic properties. Up to now, there is only a small number of microcalorimetry titrations of polyelectrolyte solutions published. Therefore we carried out potentiometric and microcalorimetric titrations of hydrochloric form of the linear and branched polyamines at 25°C and 65°C, to study the influence of the stmcture on the acid-base properties. 

Manning, G. S. (1969). Limiting laws and counterion condensation in polyelectrolyte solutions. 1. Colligative properties. Journal of Chemical Physics, 51, 924-33. 

Nagasawa, M. Kagawa, I. (1957). Colligative properties of polyelectrolyte solutions. IV. Activity coeflScient of sodium ion. Journal of Polymer Science, 25, 61-76. 

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). 

Garcia, R., Porcar, I., Campos, A., Soria, V. and Figueruelo, J. E., Solution properties of polyelectrolytes. X. Influence of ionic strength on the electrostatic secondary effects in aqueous size-exclusion chromatography, /. Chromatogr. A, 662, 61, 1994. 

G.S. Manning, The molecular theory of polyelectrolyte solution with applications to the properties of polynucleotides. Quart. Rev. Biophys. II, 179—246 (1978). 

Coulombic, van der Waals, entropic and osmotic forces are coupled in a nontrivial way and give rise to important charge regulation in polyelectrolyte systems. The salt concentration is also an important factor to define the structure and thermodynamic properties of polyelectrolyte solutions. In weak polyelectrolytes the ionization equilibrium is also coupled to these interactions and thus the pKof ionizable groups depends on the organization of the interface and differs from that for the isolated molecule. 

In the mucosal environment, effects of salt, pH, temperature, and lipids need to be taken into consideration for possible effects on viscosity and solubility. A pH range of 4-7 and a relatively constant temperature of 37°C can generally be expected. Observed solution properties as a function of salt and polymer concentration can be referred to as saline compatibility. Polyelectrolyte solution behavior [27] is generally dominated by ionic interactions, such as with other materials of like charge (repulsive), opposite charge (attractive), solvent ionic character (dielectric), and dissolved ions (i.e., salt). In general, at a constant polymer concentration, an increase in the salt concentration decreases the viscosity, due to decreasing the hydrodynamic volume of the polymer at a critical salt concentration precipitation may occur. 

It is the unique properties exhibited by polyelectrolytes that have led to their use in a variety of biomedical applications. Therefore, any discussion of polyelectrolytes as biomaterials should provide some insight into the properties of polyelectrolyte systems. In this section, an overview of polyelectrolyte properties will be presented, including polyelectrolyte solutions, gels, and complexes. The purpose of this section is not to provide an exhaustive review of polyelectrolyte thermodynamics but to provide background information for the ensuing discussion of biomedical applications of polyelectrolytes. 

The thermodynamics of weakly charged polyelectrolyte solutions have been the subjects of several recent investigations [110-112]. In these systems, the properties are intermediate between nonionic polymers and fully charged polyelectrolytes and both electrostatic and nonionic interactions can be important in determining the polymer characteristics. 

The word cross-linked implies that polymer molecules are chemically bridged by a cross-linking agent. Thus cross-linking provides the polyelectrolyte material with properties of a solid, whereas a noncross-linked concentrated polyelectrolyte solution is mechanically a loose, jelly-like object. 

G. S. Manning, Limiting laws for equilibrium and transport properties of polyelectrolyte solutions, in Polyelectrolytes, E. S61dgny, M. Mandel, and U.P. Strauss, eds., D. Riedel, Dordrecht, the Netherlands, 1974, p. 9. 

Matsuoka, H. and he, N. Small-Angle and Ultra-Small Angle Scattering Study of the Ordered Structure in Polyelectrolyte Solutions and Colloidal Dispersions. Vol. 114, pp. 187-232. Miyasaka, K PVA-Iodine Complexes Formation, Structure and Properties. Vol. 108, pp. 91-130. 

Dilute polyelectrolyte solutions, such as solutions of tobacco mosaic virus (TMV) in water and other solvents, are known to exhibit interesting dynamic properties, such as a plateau in viscosity against concentration curve at very low concentration [196]. It also shows a shear thinning at a shear strain rate which is inverse of the relaxation time obtained from the Cole-Cole plot of frequency dependence of the shear modulus, G(co). 

The viscosity of a linear polyelectrolyte solution depends on the conformation of the molecules, which in turn is affected by intramolecular electrostatic interactions between charged segments located along the polymer backbone, but the interactions in systems of charged polyelectrolytes are still far from being understood. The study on the solution property of cyclic polyelectrolyte is of interest, since the chain expansion of a cyclic... 

This latter aspect is of special importance here because it is difficult and less secure to determine molar masses or molar mass distributions of polyelectrolytes. The molecular weight and the contour length of the PPP are needed, however, for a profound interpretation of the observed solution properties. The PPP-based systems open up the opportunity to realize a pre-... 

---