Abstrait

Potentiometry and conductimetry characterizations of poly (4-vinylpyridine) homopolymer in dilutewater/methanol solutions

A.Mansri, E.Choukchou-Braham

A set of poly(4-vinylpyridine) were synthesized by free radical polymeriza tion and characterized by 1HNMR spectroscopy. The weight average molar mass were determined by light scattering and by viscosimetry. This work describes the effects of the molecular weight and the concentration on the interaction of poly(4-vinylpyridine) [P4VP] with proton H+ at 25°C, until total neutralization range (0-1). Interactions are followed by potentiometry and conductimetry techniques, in water/methanol mixture. We have considered three P4VP samples: P4VP1, P4VP2 and P4VP3 with respective molecular weights: 6ï‚´104, 18.45ï‚´104, 44ï‚´104 g/mol, and for two different concentrations: 1.6ï‚´10-4 to 7.98ï‚´10-3monomol/l. The phase diagrams were established and reveal ranges of concentration of polymer and solvent composition where phase separation occurs. It sorts that the solubility domain of P4VP is limited and critical point is observed: 64%(v/v) forwater/ methanol mixture and 4 mg/ml of polymer concentration. The solubility is independent of the molecular weight.Many experimental studies have been performed at a particular concentration and particularmolecular weight and the variation of pKa with polymer concentration and molecular weight was generally neglected[1-4]. However, we show in this paper the variation of both pKa and pK0 according to the concentration and the P4VP molecular weight. The P4VP-H+ is a lowcharged poly electrolyte where the hydrogen bonds are responsible for the compact conformation. The pK0 depends on both the concentration and the polyelectrolyte conformation. The critical ionization degree is 0.2 in 50/50 v/v water/methanol mixture. For higher neutralization values, no further changes of the structure and the conformation, were observed. It was concluded that an equilibrium exists between N and N+ in P4VP/HCl systemin 50 %water/methanol solution.