Complex formation between polyelectrolytes in dilute aqueous solution

Abstract

Polyelectrolyte complexes (PEC) have been formed from mixing dilute aqueous solutions of the polyanion poly[sodium (2-acrylamido-2-methyl propane sulfonate)] (PAMPSNa) with the polycations poly(4-vinylpyridinium chloride) (P4VPHCl) and poly(2-vinylpyridinium chloride) (P2VPHCl). Simultaneous conductometric and potentiometric titrations indicated the electrochemical endpoint of each titration. In all cases, the endpoint occurred at a unit molar ratio (UMR) of polyanionic to polycationic groups between 0.9 and 1.1 which means that titrations exhibit approximate 1/1 stoichiometry. Moreover, the position of the titrimetric endpoint was in good accord with the UMR at which PEC particles were observed to flocculate rapidly. It was found that endpoints were not affected by: (1) changing from P4VPHCl to P2VPHCl; (2) using P2VPHCl samples of different molecular weights; (3) the addition of salt to the titrant or (4) by raising the reaction temperature from 298 K to 323 K. Elemental analysis of precipitates revealed, however, that PEC were deficient in polyanionic units. Potentiometric titrations performed at different pH values yielded strong evidence that complex composition is dependent primarily upon the degree of ionization of polycationic groups in the system and to the conclusion that elemental analysis data emphasize deviations in complex composition which are not apparent from titrimetric results. Turbidimetric measurements showed that the PEC particles were large (compared to the wavelength range scanned) and did not change size significantly in the range of UMR measured.