Liquid adsorption chromatography of copolymers: Molar mass (In)dependent retention

Liquid adsorption chromatography with a continuous solvent gradient elution has been shown by several authors to often separate random and graft copolymers according to their chemical composition whereas their molar masses do not play an important role. A tentative explanation of this finding is presented. It is assumed that the copolymer species travel along the column with a velocity which exactly corresponds with that of the eluent composition, exhibiting a displacing power just necessary to prevent a fast progress of the macromolecules due to their exclusion. Under specific circumstances, retention of macromolecules at this adsorption promoting "barrier" depends almost exclusively on the copolymer composition and not on its molar mass. This hypothesis is based on the mechanism of the recently proposed and tested liquid chromatographic elution of homopolymers under limiting conditions of desorption and takes into account the simultaneous effect of adsorption and exclusion of macromolecules onto/from the column packing.