Polyanion Substitution in Polyelectrolyte ComplexDispersions Studied by Spin-Label EPR Spectroscopy

A new method for the study of the substitution of polyelectrolytes in polyelectrolyte complexes is demonstrated. A spin-labeled weak polyanion poly(ethylene-alt-maleic acid) (P(E-alt-MA)) has been used to study the substitution of this polyanion in the polyelectrolyte complex with the strong polycation poly(diallyldimethylammonium chloride) (PDADMAC) by the strong polyanion poly(sodium styrenesulfonate) (PSSNa). The study has shown that the substitution of the polyanion can be closely monitored by spin-label EPR spectroscopy. The substitution proceeded over a period of hours. Increasing the ionic strength, the rate of the substitution reaction has been accelerated. The presented method offers more freedom in the choice of the polymers investigated compared to the method of fluorescence quenching, which has been also applied to monitor exchange and substitution reactions, because the oppositely charged polyelectrolyte does not have to be a fluorescence quencher.