Viscometric behavior of polyvinylpyrrolidone (PVP) was investigated for extremely dilute (0.002-0.010 g dL(-1)), dilute (0.02-0.10 g dL-1), and moderately dilute (0.20-1.00 g dL(-1)) solutions at 288.15, 290.15, 293.15, 295.15, 298.15, 300.15, 303.15, 305.15, 308.15, 311.15, and 313.15 K. The experimental data were plotted according to Jones-Dole, Fuoss, and Fedors equations. Intrinsic viscosity ([eta]) variation with temperature indicated the existence of different hydrodynamic states of PVP in solution at different temperatures. The PVP was found to show polyelectrolyte behavior in extremely dilute solutions, probably attributable to the presence of partially polarizable >C=O groups in the chain. Activation energy (DeltaE), differential enthalpy (partial derivativeDeltaH), entropy (partial derivativeDeltaS), and free energy (partial derivativeDeltaG) changes of viscous flow were derived from flow velocity and taken into account for interpretation of the results to better understand the hydrodynamic and conformational behavior of PVP. (C) 2004 Wiley Periodicals, Inc.