Separation of a diblock-triblock copolymer mixture by phase fluctuation chromatography

A crude mixture of an A-B-A triblock copolymer, an A-B diblock copolymer, and B homopolymer was separated by phase fluctuation chromatography, where A is poly(L-lactic acid) and B is poly(ethylene glycol). The preparative separation method utilizes composition fluctuations occurring in a concentrated solution of the mixture. Injection of the viscous solution in a large volume into a column packed with a chemically modified stationary phase separated the mixture by the chemical composition and the number of blocks. The separation performance depended on the surface moieties, the solvent, the pore size, and the concentration. When the surface preferred B blocks and the solvent preferred A blocks, the early eluent was enriched with lactate and a triblock copolymer. The later eluent was low in the lactate content. We could not, however, find an appropriate combination of the surface moieties and the solvent that reverses the trend.