Effects of Aggregation and Solvent Quality on the Viscosity of Semidilute Poly(vinylbutyral) Solutions

Abstract

The relative viscosities at 25 °C of solutions containing 12% (w/v) poly(vinylbutyral) in pure methanol (MeOH), 1:1 methyl isobutyl ketone (MIBK)/MeOH by volume, and 9:1 MIBK/MeOH were in the ratio 1.0:0.9:43, respectively. The apparent activation energy for flow was 20 kcal/mol in the latter solution and only 8 kcal/mol in the former two. The dramatic influence of the solvent on the solution viscosity is attributed to the separate effects of solvent quality and polymer aggregation. Better solvents tend to reduce the viscosity while polymer aggregation tends to increase it. Aggregation is controlled not by solvent quality but by solvent polarity and manifests itself as a hysteresis in plots of viscosity vs. 1/T. Aggregates disperse and re-form slowly—weeks may be required to reach equilibrium at room temperature. The thermodynamic quality of various solvents and solvent mixtures was determined by light scattering and intrinsic viscosity measurements. These data demonstrated that most mixtures of MIBK and MeOH are better solvents for PVB than either individual solvent. © 1986, American Chemical Society. All rights reserved.