COMPLEX-FORMATION BETWEEN POLYELECTROLYTES IN DILUTE AQUEOUS-SOLUTION

Polyelectrolyte complexes (PEC) have been formed from mixing dilute aq ueous solutions of the polyanion poly[sodium (2-acrylamido-2-methyl pr opane sulfonate)] (PAMPSNa) with the polycations poly(4-vinylpyridiniu m chloride) (P4VPHCl) and poly(2-vinylpyridinium chloride) (P2VPHCl). Simultaneous conductometric and potentiometric titrations indicated th e electrochemical endpoint of each titration. In all cases, the endpoi nt occurred at a unit molar ratio (UMR) of polyanionic to polycationic groups between 0.9 and 1.1 which means that titrations exhibit approx imate 1/1 stoichiometry. Moreover, the position of the titrimetric end point was in good accord with the UMR at which PEC particles were obse rved to flocculate rapidly. It was found that endpoints were not affec ted by: (1) changing from P4VPHCl to P2VPHCl; (2) using P2VPHCl sample s of different molecular weights; (3) the addition of salt to the titr ant or (4) by raising the reaction temperature from 298 K to 323 K. El emental analysis of precipitates revealed, however, that PEC were defi cient in polyanionic units. Potentiometric titrations performed at dif ferent pH values yielded strong evidence that complex composition is d ependent primarily upon the degree of ionization of polycationic group s in the system and to the conclusion that elemental analysis data emp hasize deviations in complex composition which are not apparent from t itrimetric results. Turbidimetric measurements showed that the PEC par ticles were large (compared to the wavelength range scanned) and did n ot change size significantly in the range of UMR measured. (C) 1997 El sevier Science Ltd.