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Polyelectrolytes. XII. Conductance of partially quaternized poly‐4‐vinylpyridine in methanol‐butan‐2‐one mixtures

1957; Wiley; Volume: 23; Issue: 103 Linguagem: Inglês

10.1002/pol.1957.1202310334

1542-6238

Robert Macfarlane, Raymond M. Fuoss,

Electrostatics and Colloid Interactions

Abstract By partially quaternizing polyvinylpyridine with n ‐butyl bromide, a series of polyelectrolytes were obtained in which from Q = 3 to Q = 20% of the pyridine nitrogens were converted to butylpyridinium ions. These products thus are copolymers of ionic and nonionic units. Their conductance was measured over the concentration range 10 −4 ≤ c ≤ 3 × 10 −3 equivalent of bromide ion per liter in mixtures of methanol and butan‐2‐one (MEK) ranging from pure methanol to a 20:80 MeOH–MEK mixture. The viscosity of the solvent was thereby varied from 0.00546 to 0.00400 poise and the dielectric constant from 32.6 to 21.6. The phoreograms (Λ− c 1/2 curves) are all sharply concave‐up, indicating a high degree of association of counterions with the polymeric ions in this range of concentration. The product of equivalent conductance and solvent viscosity gives a dependent variable which accounts for the primary hydrodynamic effect of changing solvent, showing that the ionic mobilities are determined by local viscosity rather than by macroscopic solution viscosity. Plots of log Λη are linear in reciprocal dielectric constant, and therefore ionic association for a given salt is controlled by electrostatic forces. As degree of quaternization decreases, the equivalent conductance increases (other variables remaining constant); this change corresponds primarily to decrease in association of counterions as the charge density of the polycation is decreased. The fact that observed conductances extrapolate to values greater than the single bromide ion conductance in the limits c = 0, Q = 0 shows that cationic sites in the chains are capable of contributing to conductance in alternating fields. Therefore a rigid model represents an oversimplification for the a.c. conductance of polyelectrolytes, although it probably will serve well for d.c. conductance.