Polyion interchange reactions of interpolyelectrolyte complexes in aqueous solutions and gels

Abstract

AbstractCooperative coupling reaction between two opposite charged polyelectrolytes results in formation of polyelectrolyte complexes (IPEC). This reaction is very fast and diffusion controlled.Whether IPECs formed by linear polyions are soluble or limitary swellable in aqueous media is decided by their composition, namely, by a ratio of oppositely charged polyions as well as by a water phase composition (the nature and the concentration of a simple salt, pH, the presence and the concentration of organic additives etc.).The most important intrinsic property of IPECs is their ability to participate in interchange (exchange and substitution) reactions with competing polyions. The kinetics and the position of equilibria in these reactions are controlled by the low molecular salt concentration, the nature of small counterions, DP of interaction polyelectrolytes, as well as by their linear charge density.IPECs can be formed also by interacting linear and opposite charged networks. It is shown that linear polyelectrolytes dissolved in aqueous solution can penetrate unexpectedly fast into oppositely charged cross‐linked polyelectrolyte gels to form “snake‐in‐cage” composites representing IPECs of corresponding polyion segments. It is proved that the mechanism consists in “relay‐race” transfer of linear polyion segments from one segment of the polyelectrolyte network to the other via interpolyelectrolyte exchange reaction. The driving force for the fast transport of linear polyions into the gel is produced by coupling reaction between two polyelectrolytes proceeding on solution/gel interface.