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 scatteri ng (DLS) measurements were made to study the effects of temperature, T, on association behaviors of poly(vinyl alcohol) (PVA) with weight-average degr ee of polymerization DPw = 350 in aqueous Borax solution. Intrinsic viscosi ty, [eta], monotonically decreased by 23% with a rise in T from 10 to 65 de grees C. At low T, enhancement in viscosity was observed with increasing po lymer concentration, C, due to formation of viscoelastic network with the d idiol complex as temporal cross-links, and the time-temperature superpositi on principle was found to be applicable for construction of a composite cur ve 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 rais ing the temperature, toward a viscous solution owing to a decrease in the n umber of the didiol complexes as well as the shrinkage of the PVA chains. W e found from analysis of DVE and DLS data that a clear boundary line betwee n viscoelastic and viscous behaviors can be drawn on the T-C diagram using the temperature T-N defined as the inflection point in a eta vs T-1 plot fo r each C.