ИСТИНА

The electrostatic interaction between oppositely charged macromolecules leads to the formation of interpolyelectrolyte complexes (IPECs) that are of considerable interest because of the promising potential applications as new intelligent polymeric reagents and materials for industry, ecology, biotechnology, and medicine. In this work, the effect of low-molecular-weight salts on properties and stability of IPECs formed as a result of the electrostatic interactions between poly(dimethyldiallylammonium chloride) and poly(sodium maleate-co-propene) that were taken in a non-equivalent ratio (with respect to concentrations of charged groups) to provide excess of the cationic polyelectrolyte over the anionic polyelectrolyte has been studied. In dependence on the salt concentration, such mixtures were found to be (A) relatively stable colloidal dispersions of IPEC (low salt concentrations), (B) unstable colloidal dispersions of IPEC (moderate salt concentrations), and (C) transparent solutions (high salt concentrations), the salt concentrations that correspond to transitions between these regions being dependent on nature of a low-molecular-weight salt. The turbid dispersions of IPEC prepared at low salt concentrations were shown to contain large aggregates bearing net cationic charge. Hydrodynamic radius of such aggregates was demonstrated to increase whereas their electrophoretic mobility was found to decrease with increasing salt concentration. The formation of macroscopically heterogeneous systems because of pronounced precipitation of IPEC was observed at moderate salt concentrations. The contacts between the oppositely charged macromolecules were detected in a relatively broad interval of salt concentrations that correspond to the transparent solutions. The number of such contacts was found to decrease drastically with increasing salt concentration and to virtually reach zero in concentrated salt solutions. These results indicate that the formation of soluble IPEC whose solubility has been thought to result from partial dissociation of the system of interpolymer salt bonds can take place at high salt concentrations. Finally, an increase in the salt concentration causes interpolyelectrolyte complexation to be unfavorable process because of effective screening of polyionic charges by small counterions and non-interacting macromolecules were shown to coexist with each other in concentrated salt solutions.