Viscometric titration of a linear polyelectrolyte

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Abstract
Viscosities of dilute solutions of linear poly(2-vinyl pyridine) with molecular weights ranging from 3.0×104 to 1.0×106 have been measured under conditions where the polymer can be charged by protonation. By employing weakly acidic solvents, large reduced viscosities typical of polyelectrolytes in low-salt solutions are observed. They exhibit a pronounced maximum occurring at a concentration which is independent of molecular weight. Separate pH titrations are used to calculate polyion charge density and electrostatic screening lengths. The origin of the viscosity maximum is explained by consideration of changing electrostatic persistence lengths on dilution, resulting in polyion coil expansion and contraction. Investigations of limiting conditions of low charge density and full electrostatic screening with basic and high acid or salt solutions reveal expected normal polymer behavior in concentration extrapolations to the intrinsic viscosity.