Effect of low-molecular-mass salts on the behaviour of water-soluble nonstoichiometric polyelectrolyte complexes

The effect of small ions, which are identical or opposite in charge to polyelectrolyte particles, on the structure and properties of a water-soluble nonstoichiometric polyelectrolyte complex (NPEC) composed of lyophilizing polymethacrylate anions (PMA) and blocking poly(N-ethyl-4-vinylpyridine) (PEP) cations was investigated. The luminescence quenching technique was used to study the behavior of NPEC in water-salt solutions, as pyridinium groups of PEP cations can effectively quench luminescence of pyrenyl groups introduced into PMA anions. With respect to their ability to induce NPEC dissociation, the ions were shown to exhibit the following order: Br->Cl->F- and Li+>K+(CH3)4N+; both the affinity of halide ions to a blocking PEP cation, as well as the affinity of the above cation to a lyophilizing PMA anion, appear to follow the same order. The addition of NaCl to NPEC solution and the specific binding of Na+ cations by carboxyl groups were shown to reduce the lyophilizing ability of PMA anions involved in NPEC and may result in phase separation. The addition of tetramethylammonium halides, on the other hand, is associated with a growth in hydrophilicity of lyophilizing PMA anions. In solutions of these salts, NPEC of any composition are soluble until their complete dissociation, and PEP content in NPEC particles can be substantially increased without any loss in NPEC solubility.