Third virial coefficient of polystyrene in benzene

Second virial coefficients A2 and third virial coefficients A3 for benzene solutions of ten polystyrene fractions ranging in weight‐average molecular weight Mw from 104 to 2 × 107 at 25°C were determined by light scattering. The third coefficient is represented approximately by A3 = 8.0 × 10−6 M mol g−3 cm6 for Mw above 105. In this molecular weight region, the factor g defined by A3/A Mw/ This trend of g is consistent with predictions of early two‐parameter theories but not with those of renormalization group theories. In particular, quantitative agreement is observed between the present experiments (for Mw ≳ 2 × 105) and the mean‐field two‐parameter theory of Stockmayer and Casassa.