Polyelectrolyte complexes of polyacrylic acid with oligovalent organic counterions

In contrast to formation of polyelectrolyte-surfactant and interpolyelectrolyte complexes, formation of polyelectrolyte complexes with low molecular weight oligovalent organic counterions is almost not studied. This work investigates the interaction of polyacrylic acid (PAA) of different molecular weights (Mn = 2000 and 26,700) with oligoethylenimines having 2–6 amino groups. Formation of colloid or water-insoluble ionic complexes was found as a result of ionic cross-linking of PAA by oligocationic counterions with not less than three amino groups in the molecule. The formed complexes redissolve at certain pH values and NH/COOH ratios in the solution. Complexes sensitive to certain pH could be obtained by changing the number of amino groups in the cross-linker and PAA molecular weight. The particle size of the complexes under consideration is almost independent of the cross-linker and can be controlled by varying the polymer concentration for PAA-2000 complexes and by NH/COOH ratio for PAA-26700 complexes. According to SEM and AFM, complexes of PAA-2000 with oligoethylenimines form hollow spherical particles in dilute solutions and precipitate to form gel-like films in concentrated solutions.