Unperturbed dimensions and the theta temperature of dextran in aqueous solutions

Intrinsic viscosity measurements were carried out on dextran samples (of di fferent molecular weights) in aqueous solutions at 25, 28, 31, 34, 37, 40, and 43 degrees C. The extrapolation methods were used for the data; they ga ve unperturbed dimensions, K-0, of the chain. The unperturbed root-mean-squ are end-to-end distance [r(2)](0)(1/2) calculated for the polymer samples i n water indicate that the polymer coils are slightly contracted in this sol vent as the temperature is increased. The long-range interaction parameter, B, was also determined. In aqueous dextran solutions, this showed a signif icant decrease in the long-range interactions between 25 and 43 degrees C. The values of Theta = 317.82 and 316.57 K were obtained from the temperatur e dependence of the interaction parameter B in the Kurata-Stockmayer-Fixman and Berry equations. Calculated values were interpreted mainly on the basi s of hydrogen-bond formation between polymer segments and dextran-water mol ecules in solution. (C) 1999 John Wiley & Sons, Inc.