On the evaluation of unperturbed dimensions from intrinsic viscosity data of binary and ternary polymer solutions

Abstract

Several investigations show that the unperturbed dimensions of a given polymer in any solvent do not depend on the nature of the solvent, as far as the solvent has no influence on the rotation of the chain segments. In this case K θ is a constant. The evaluation of K θ from [ η]− M data by application of the classical Burchard-Stockmayer-Fixman (BSF) theory often results in different values, with dependence on solvent power and, with mixed solvents, on solvent composition. This is mainly due to the non-linearity of the relationship, especially with high molar mass polymers in good solvents. Better results are obtained by non-linear graphical treatment of the BSF plot, or by application of a modified equation proposed by Tanaka, which takes into account the general α 5 ∼ z relationship between molecular expansion factors and the excluded volume parameter z. Plots of ( [η] M 0.5 ) 5 3 versus M 0.5 show linearity over nearly the entire range of molar mass studied and evaluation of unperturbed dimensions results in a quasi unique value of K θ for a given polymer.