Abstract
The behavior of polyvinylpyrrolidone in mixed water/methanol solvents was studied by rheoviscosimetry over a temperature range of 20°C-40°C. For the lower temperatures of this range, the intrinsic viscosity variation of the polymer vs. methanol molar fraction shows structural transitions (coil-globule-coil). This transition, which is usually attributed to the cononsolvency phenomenon, agrees with our previously published results obtained by dynamic light scattering. For higher temperatures, near 40°C, the intrinsic viscosity increase shows an expansion of the polymer over the alcohol molar fraction range 0.2 < X
A
< 0.5. This last result can be attributed to the water/alcohol complex destruction under temperature increase. The "excess viscosity" of the polymer-mixed solvents vanishes with increasing temperature and becomes positive at 40°C. So, the polymer chain tends to transit from a globular to an ideal chain in the middle composition range of the mixed solvents.