Dynamic light scattering and dynamic viscoelasticity of poly(vinyl alcohol) in aqueous borax solutions. 5. Temperature effects

Steady viscosity, dynamic viscoelasticity (DVE), and dynamic light scattering (DLS) measurements were made to study the effects of temperature, T, on association behaviors of poly(vinyl alcohol) (PVA) with weight-average degree of polymerization DP_w = 350 in aqueous Borax solution. Intrinsic viscosity, [r/], monotonically decreased by 23% with a rise in T from 10 to 65 °C. At low T, enhancement in viscosity was observed with increasing polymer concentration, C, due to formation of viscoelastic network with the didiol complex as temporal cross-links, and the time-temperature superposition principle was found to be applicable for construction of a composite curve at each C. Those composite curves were further reduced so as to give one master curve. The system tended to lose its viscoelastic nature, when raising the temperature, toward a viscous solution owing to a decrease in the number of the didiol complexes as well as the shrinkage of the PVA chains. We found from analysis of DVE and DLS data that a clear boundary line between viscoelastic and viscous behaviors can be drawn on the T-C diagram using the temperature T_N defined as the inflection point in a η vs T^-1 plot for each C.