EVALUATION OF UNPERTURBED POLYMER DIMENSIONS FROM INTRINSIC-VISCOSITY IN NONIDEAL SOLVENTS

For solutions of polystyrene (PS) samples of different relative molecular mass (molecular weight) M and intrinsic viscosities [eta] have been measured at 298,15 K in pure toluene (T) and toluene/methanol (MeOH) mixtures. Upon mixing toluene (good solvent (1)) and methanol (nonsolvent (2)), a systematic decrease in the solvation power was obtained. A critical examination of the Stockmayer-Fixman method for obtaining unperturbed dimensions from intrinsic viscosity measurements has been made. It was found that the unperturbed dimensions were not constant and different from those measured in a theta solvent (T/MeOH mixture having volume fraction of methanol (phi(MeOH)) = 0,23). The derived values of unperturbed dimensions were found to increase with increasing Kuhn-Mark-Houwink-Sakurada exponent a. A modified form of the Stockmayer-Fixman equation is presented. It is suggested that the volume effect be taken into account in a complementary fashion to obtain accurate estimates of unperturbed dimensions from data in active solvents where the mean-square end-to-end distance [r2] increases at these conditions more rapidly than M. Different viscosity measurements of polystyrene (PS) and poly-(N-vinyl-2-pyrrolidone) solutions containing non-ideal solvents were taken from the literature and found that the newly proposed, though purely empirical equation is valid.