A UNIFIED ANALYTICAL TREATMENT OF THE ACID-DISSOCIATION EQUILIBRIA OFWEAKLY ACIDIC LINEAR POLYELECTROLYTES AND THE CONJUGATE ACIDS OF WEAKLY BASIC LINEAR POLYELECTROLYTES

The influence of added sodium chloride concentration levels on the aci d-dissociation equilibria of a weakly acidic linear polyelectrolyte an d a conjugate acid of weakly basic linear polyelectrolyte has been inv estigated potentiometrically by use of polyacrylic acid (PAA) and poly (N-vinylimidazole) (PVIm) as examples of polyelectrolytes, Both equili bria are strongly influenced by the degree of dissociation of the poly acids as well as the concentration levels of sodium chloride due to an electrostatic effect originating from the negatively or positively ch arged polymer surfaces. These have been analyzed in a unified manner b y taking accounts of two-phase properties of the charged linear polyio ns. Distribution of counterions and colons between a polyelectrolyte p hase formed around the polymer skeleton and a bulk solution phase has been rationalized by a Donnan's relation. Introduction of a volume ter m for the polyelectrolyte phase permits definition of averaged concent rations of mobile ions in the vicinity of the polyion molecules, which enables us to define hypothetical intrinsic acid-dissociation constan ts in the polyion domain, The intrinsic constants estimated by extrapo lation of apparent acid: dissociation constants at zero-charge state a re in good agreement with the acid-dissociation constants of the monom er analogs of the polymers, i.e., acetic acid for PAA and Imidazole fo r PVIm, respectively. The difference between the apparent and intrinsi c acid-dissociation constants for PVIm was much higher than that for P AA at defined degree of dissociation of the polyacids, even though the separations of the functionalities fixed on the linear polymers are a pproximately equal to each other.