The effect of heterogeneity in composition on the determination of molecular weight distribution of block copolymers by gel permeation chromatography

The molecular weight of samples of block copolymers of poly(isoprene : styrene) determined by gel permeation chromatography (g.p.c.) are found to deviate from the values obtained by light scattering and osmometry. The extent of the deviation depends on composition, and comparision of (g.p.c.) values with osmometry (MN) can be interpreted if account is taken of the effect of heterogeneity. The drift in composition with molecular weight calculated from light scattering data can be used to predict the direction of the deviation, at least qualitatively.