Variation of refractive index of polystyrene with molecular weight: Effect on the determination of molecular weight distributions

Sensitive refractive index measurements on solutions have indicated that the narrow molecular weight polystyrene samples prepared by the Mellon Institute method exhibit a small systematic molecular weight–refractive index dependence up to 300,000 and higher. This upper limit is higher than had previously been suggested. Sensible consistency is generally assumed above a few thousand molecular weight. The effect on this molecular weight–refractive index dependence on gel permeation chromatography and light‐scattering molecular weight measurements on polystyrene standards is illustrated.