Ultracentrifugation, viscometry, pH, and dynamic light scattering studies of the complexation of ionene with poly(acrylic acid) and poly(methacrylic acid)

The degree of complexation at saturation, phi(s), and the equivalent electrostatic radius, R-e, were determined for polyanion-polycation complexes composed of poly(acrylic acid)/ionene and poly(methacrylic acid)/ionene dissolved in water and aqueous alcoholic solvent mixtures. It is found that the complex stability depends on the concentration of the added low molecular salt, c(s). At low c(s) we have nonstoichiometric water-soluble complexes, at intermediate c(s) the complexes fall out, and at high c(s) they redissociate into their single strands. Ultracentrifugation is an excellent method to detect these changes, but it is supported also by viscometry and dynamic light scattering. The kinetics of complexation depends on the ionene molar fraction, X-G. It can be followed by pH-measurements as a function of time. Two possible mechanisms are proposed and discussed. The theory of multiple binding equilibrium is applied to derive R-e, the electrostatic equivalent radius. The accord found between R-e and the hydrodynamic radius, R-h, is quite good, but there still remain several unsolved problems. (C) 1999 Elsevier Science Ltd. All rights reserved.