EVALUATION OF UNPERTURBED POLYMER DIMENSIONS FROM INTRINSIC-VISCOSITYIN NONIDEAL SOLVENTS

For solutions of polystyrene (PS) samples of different relative molecu lar mass (molecular weight) M and intrinsic viscosities [eta] have bee n measured at 298,15 K in pure toluene (T) and toluene/methanol (MeOH) mixtures. Upon mixing toluene (good solvent (1)) and methanol (nonsol vent (2)), a systematic decrease in the solvation power was obtained. A critical examination of the Stockmayer-Fixman method for obtaining u nperturbed dimensions from intrinsic viscosity measurements has been m ade. It was found that the unperturbed dimensions were not constant an d different from those measured in a theta solvent (T/MeOH mixture hav ing volume fraction of methanol (phi(MeOH)) = 0,23). The derived value s of unperturbed dimensions were found to increase with increasing Kuh n-Mark-Houwink-Sakurada exponent a. A modified form of the Stockmayer- Fixman equation is presented. It is suggested that the volume effect b e taken into account in a complementary fashion to obtain accurate est imates of unperturbed dimensions from data in active solvents where th e mean-square end-to-end distance [r2] increases at these conditions m ore rapidly than M. Different viscosity measurements of polystyrene (P S) and poly-(N-vinyl-2-pyrrolidone) solutions containing non-ideal sol vents were taken from the literature and found that the newly proposed , though purely empirical equation is valid.