USE OF HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY FOR THE CHARACTERIZATION OF SYNTHETIC COPOLYMERS

The evaluation of copolymer distribution as a function of molecular weight and chemical composition requires two separations, known as cross-fractionation. This procedure can be substantially improved by using high-performance liquid chromatographic (HPLC) techniques, including size-exclusion chromatography for the separation by molecular size. The separation by chemical composition can be achieved by gradient HPLC. Examples are given for copolymers of styrene and ethyl methacrylate (S-EMA). Gradient HPLC of these and similar copolymers can be performed in both normal-phase and reversed-phase modes with inversion of elution order. In isooctane-tetrahydrofuran (THF) mixtures on polar columns, the elution of S-EMA samples occurs at a higher THF concentration than required by solubility, i.e., with a distinct contribution of adsorption to retention. In contrast, reversed-phase elution with methanol-THF mixtures takes place almost exactly at the solubility borderline of the system. © 1990.