Liquid chromatography of polyethylene glycol mono- and diesters: functional macromolecules or block copolymers?

The chromatographic behavior of polyoxyethylene-based polymers with adsorbing hydrophobic end-fragments was studied under two types of interaction conditions for the ethylene oxide (EO) component of such heteropolymers (which are either critical or of the size-exclusion type). In a theoretical part we assume a wide-pore situation, where the molecules are smaller than pores, and consider models of two-component diblock and triblock copolymers having quite strongly adsorbing blocks. A new step is made to extend a theory from difunctional macromolecules with point-type end-groups to triblock copolymers. It is shown that A-B-A triblocks with adsorbing A-blocks and with a "critical" B-block behave in chromatography like difunctionals with effective end-group interactions. Another important finding is the existence of a second critical region, which was observed on most of the studied columns. This region can be used to separate di- and triblocks from each other. Additionally, the individual oligomers of triblocks can be separated to the baseline. Complete separations of both diblocks and triblocks in one single chromatogram can be achieved by using a step gradient between two types of studied condtions.