ON THE EVALUATION OF UNPERTURBED DIMENSIONS FROM INTRINSIC-VISCOSITY DATA OF BINARY AND TERNARY POLYMER-SOLUTIONS

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 segm ents. In this case K(THETA) is a constant. The evaluation of K(THETA) from [eta]-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. Th is is mainly due to the non-linearity of the relationship, especially with high molar mass polymers in good solvents. Better results are obt ained by non-linear graphical treatment of the BSF plot, or by applica tion of a modified equation proposed by Tanaka, which takes into accou nt the general alpha5 is similar to z relationship between molecular e xpansion factors and the excluded volume parameter z. Plots of ([eta]/ M0.5)5/3 versus M0.5 show linearity over nearly the entire range of mo lar mass studied and evaluation of unperturbed dimensions results in a quasi unique value of K(THETA) for a given polymer.