The relationships between the refractive index increment

SEC response area and weight fraction of the monodisperse species of oligomers are analyzed mathematically. The molecular weight dependsncye of the refractive index increments is originated solely from the end group effect. A theoretical formula is proposed for the refractive index increment correction of SEC chromatogram of polymer

which involves the molecular formula weights and the ratio of dn/ dc of the end group and the structural repeating unit. The refractive index increment ratio could be evaluated a priori by Lorenz-Lorentz or Gladstone-Dale equations. The theoretical judgements have been confirmed exprimentally by the HPSEC data of styrene oligomer.