Evaluation of unperturbed polymer dimensions from intrinsic viscosity in non‐ideal solvents

For solutions of polystyrene (PS) samples of different relative molecular mass (molecular weight) M and intrinsic viscosities [ n ] 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 (ϕ 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 〈 r 2 〉 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.