Second and third virial coefficients for binary polystyrene mixtures in benzene

Light‐scattering second and third virial coefficients for benzene solutions (at 25°C) of two binary polystyrene mixtures, in which the molecular weight ratios of component fractions (essentially monodisperse) were 98 and 11.6, were determined as functions of polymer composition. The cross‐term virial coefficients A 12 (for two different solutes 1 and 2), A 112 (for two same solutes 1 and one solute 2), and A 122 were evaluated from such functions. It was found that none of the existing theories for A 12 yield a consistent and quantitative description of our experimental finding. No theory is yet available for A 112 and A 122 , but the numerical values of these coefficients as estimated here are of interest in themselves.