Viscosity-temperature relationships for dilute solutions of cellulose derivatives: II. Intrinsic viscosities of ethyl cellulose

Abstract

Temperature variations of intrinsic viscosities and some other viscosity parameters for ethyl cellulose fractions in representative solvents are considered in terms of some current hydrodynamic and thermodynamic treatments of the viscosities of dilute polymer solutions. The value of [η] decreases strongly with increasing temperature, the dependence being approximately linear. The temperature coefficient of [η] appears to be linearly related to the molecular weight of the polymer. Except in the case of chloroform, in which aggregation of polymer may occur, values of the exponent a in the expression [ η] = KM a decrease slightly with increase of temperature suggesting decreasing chain extension. Values of the Porod-Kratky persistence length q, the Kirkwood-Riseman effective bond length b, and the angle between successive bond planes in the polymer chains suggest decreasing chain stiffness as the temperature increases. The Flory treatment is applied to obtain qualitative information regarding the contributions of different factors to the negative temperature coefficients of [η], suggesting that these are primarily due to decreases in the value of ( r 0 2M) , where r 0 2 is the mean-square unperturbed end-to-end distance of the chains and M the molecular weight. The variations of [η] and its temperature coefficient with solvent are briefly discussed.