Influence of the Chain Architecture and the Presence of End-Groups or Branching Units Chemically Different from Repeating Structural Units on the Critical Adsorption Point in Liquid Chromatography

Abstract

The critical adsorption point (CAP) of linear and star-shaped polymers was investigated by normal phase and reversed phase liquid chromatography (NPLC and RPLC) and computer simulation. Three sets of polystyrenes (PS) differing in chain architecture and chemically distinct groups were prepared: linear PS (sec-butyl and hydrogen end group), 2-arm PS (linear, two sec-butyl end groups and one silyl group in the middle of the chain) and 4-arm star-shaped PS (four sec butyl end groups and one silyl group in the center of the star). It was found that the column temperature at CAP, T-CAP (linear PS) = T-CAP (2-arm PS) > T-CAP (4-arm PS) in both RPLC and NPLC which can be attributed to the variation in chain architecture. However, the elution times at CAP of three polymers are all different: In NPLC, t(E,CAP) (linear) > t(E,CAP) (2 -arm PS) > t(E,CAP) (4-arm PS) while in RPLC, t(E,CAP) (4-arm PS) > t(E,CAP) (2-arm PS) > t(E,CAP) (linear). The variation of t(E,CAP) can be explained by the contribution of the chemically distinct groups. The computer simulation results are in good agreement with the chromatography experiments results and support the interpretation of experimental data.