Molded monolithic rod of macroporous poly(styrene-co-divinylbenzene) as a separation medium for HPLC of synthetic polymers: "On-column" precipitation-redissolution chromatography as an alternative to size exclusion chromatography of styrene oligomers and polymers

A process for the separation of styrene oligomers and polymers by size and composition using a novel separation medium has been demonstrated. The process involves precipitation of the macromolecules on the molded macroporous rod columns, followed by progressive elution utilizing a simple gradient of the mobile phase. Molded macroporous rod columns are ideally suited for this technique because convection through the large pores of the rod enhances the mass transport of large analyte molecules and accelerates the separation process. Styrene oligomers and polymers are separated in a 50-mm × 8-mm-i.d. column using a solvent gradient composed of a poor solvent such as water, methanol, or acetonitrile and increasing amounts of a good solvent, tetrahydrofuran. Excellent separations are obtained, demonstrating that precipitation-redissolution can be a suitable alternate to size exclusion chromatography (SEC) of some polymers. Compared to SEC, the gradient elution separation can be achieved at higher flow rates in a much shorter time. Precipitation-redissolution with gradient elution can also be used for the separation of copolymers, for which the process is controlled not only by molecular weight but also by the composition of the copolymers.