Retention behavior of polystyrene oligomers in reversed-phase liquid chromatography

Reversed-phase liquid chromatography (RPLC) was employed to investigate the behaviour of low-molecular-mass polystyrene oligomers with three different end groups, n-butyl, sec-butyl, and tert.-butyl polystyrenes. Exothermodynamic retention studies on the polystyrene oligomers were carried out using a C18 stationary phase column and 100% methanol mobile phase over the temperature range 15 to 60 °C. The resulting van't Hoff plots were linear over the entire temperature range for all three end group polystyrenes. Enthalpy-entropy compensation (EEC) showed a linear compensation for the higher-order oligomers, but was non-linear for the lower-order oligomers, indicating a change in the mechanism of retention. Differences in the extent of retention for each of the three end groups were also apparent. The ramifications of these differences are discussed.