Gel permeation chromatography: the behaviour of polystyrenes with long-chain branching

The gel permeation chromatography (g.p.c.) behaviour of a wide range of branched polystyrenes, in which the branching frequency and the branch length are varied, is described. It is found that, qualitatively, the separation of these branched polymers by g.p.c. does depend on size but contrary to other results reported in the literature, the hydrodynamic volumeη]M of the polymer molecules is not the appropriate size parameter to use. That is, a single plot of logη]M against elution volume embracing all the branched polystyrenes prepared and linear polystyrenes is not obtained. Because the mean square radii of gyration of these branched polystyrenes could not be measured directly no positive evidence as to the nature of the correct size-separation parameter was obtained. It is pointed out that, even if the correct size-separation parameter were known, g.p.c. could not be used to characterize branched polymers unambiguously.