Aqueous solutions of poly(maleic acid) (PMA) exhibit a phase separation when neutralized with monovalent bases, prior to the complete neutralization, irrespective of the presence or absence of added salts. The values of the critical degree of neutralization (a,) at which the precipitation develops were measured for the PMA aqueous solutions neutralized with various kinds of monovalent counterions, as a function of polymer (Cp) and added salt concentrations (Cs). It was found that, at constant Cs, a, decreases sharply with increasing Cp and that, at constant o" the critical NaCl concentration (C8) decreases linearly with increasing Cp. This phenomenon is attributable to the strong binding of monovalent counterions to ionized sites of a polyion and can be analyzed in terms of a site-binding model. The phase separation was shown to occur even in a salt-free solution when the amount of strongly bound Na+ became a certain value, Cp7, where = 0.58.Addition of monovalent salts facilitates the phase separation. At a low degree of neutralization, PMA was found to be quite soluble, in accordance with the neutralization dependence of the solubility of its monomer unit, maleic acid, which was also examined together with that of fumaric acid.

ABSTRACT:Conformational properties of polyelectrolyte chain with maleic acid units (MA polyelectrolyte) are investigated by a mean of Monte Carlo simulation. The polyelectrolyte chains are modeled as a self-avoiding walk on tetrahedral lattice with charges fixed. The each charge interacts through Debye-Hiickel potential and attraction energy from hydrogen bonding between un-ionized and ionized carboxyl groups in short-range. Mean-square end-to-end distance, (R 2 ), mean-square radius of gyration, (S 2 ), and mean conformational energy, (£), are simulated as a function of degree of polymerization (N) and dissociation (a), and salt concentration (Cs)-The dependence of (R 2 ) and (S 2 ) on N shows that MA polyelectrolyte chain assumes a rod like conformation at high a and low Cs. The simulation results provide an interpretation for characteristic viscometric behavior of MA polyelectrolytes which show a maximum in an intrinsic viscosity nearly at a= 0.5. The polymer dimensions in the region of a~ 0.5 increases with the energy of the hydrogen bonding assumed. The characteristic viscometric behavior of MA polyelectrolytes is deduced to result from the balance between repulsion from the electrostatic interaction and attraction from the hydrogen bonding in short-range. KEY WORDSMonte Carlo Simulation/ Conformation/ Hydrogen Bond / Polyelectrolyte / Intrinsic Viscosity/ Radius of Gyration/ Dielectric Constant/ Solution properties of macromolecules strongly depend on conformation of a polymer chain. The conformational properties of an un-charged polymer chain have been fairly understood by much theoretical, numerical, and experimental effort. 1 • 2 In contrast, the understanding of the conformation for a polyelectrolyte chain still remains many unanswered subjects. The difficulty in describing behavior of the polyelectrolyte solutions comes from electrostatic interaction among dense charges fixed on the polymer backbone, which depends on density and distribution of the charges of the polyelectrolyte, as well as solvent property. 3 · 4 The conformational properties of uncharged polymer is normally determined in terms of short-and long-range interactions. 1 The former is related to chain stiffness, persistence length of the polymer, Kuhn segment length, and the latter, to the excluded volume. This also holds for the conformational properties of polyelectrolyte chains. The investigation is, however, rather complicated because the electrostatic interaction affects concurrently on both short-and long-range in the polyelectrolyte chain. Two interpretations for the polyelectrolyte conformation have been established. One is the increase of electrostatic persistence length (Le) with increasing the electrostatic interaction for wormlike chain. 5 • 6 The total persistence length (L 1 ) of the polyelectrolyte chain is expressed by the sum of intrinsic persistence length (L 0 ) and Le.

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