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

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 (<i>sec</i>-butyl and hydrogen end group), 2-arm PS (linear, two <i>sec</i>-butyl end groups and one silyl group in the middle of the chain) and 4-arm star-shaped PS (four <i>sec</i>-butyl end groups and one silyl group in the center of the star). It was found that the column temperature at CAP, <i>T</i>_CAP (linear PS) = <i>T</i>_CAP (2-arm PS) > <i>T</i>_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, <i>t</i>_E,CAP (linear) > <i>t</i>_E,CAP (2-arm PS) > <i>t</i>_E,CAP (4-arm PS) while in RPLC, <i>t</i>_E,CAP (4-arm PS) > <i>t</i>_E,CAP (2-arm PS) > <i>t</i>_E,CAP (linear). The variation of <i>t</i>_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

Comparison of Critical Adsorption Points of Ring Polymers with Linear Polymers

The critical adsorption points (CAP) for ring and linear polymers are determined and compared using Monte Carlo simulations and liquid chromatography experiments. The CAP is defined as the coelution point of ring or linear polymers with different molecular weights (MW). Computational studies show that the temperature at the CAP, <i>T</i>_CAP, for rings is higher than <i>T</i>_CAP for linear polymers regardless of whether the chains are modeled as random walks or self-avoiding walks. The difference in the CAP can be attributed only to the architectural difference. Experimentally, four pairs of linear and ring polystyrenes (PS) of different MW were synthesized and purified. Care was taken to account for the difference between the end-groups in linear polymers and the linkage unit in ring polymers. Elution of these polymers using a C18 bonded silica stationary phase and a CH₂Cl₂/CH₃CN mixed eluent were studied. The temperature at the coelution point, <i>T</i>_CAP, and the coelution time at the CAP, <i>t</i>_E,CAP, were determined for both ring and linear polymers. Experimentally, it was found that <i>T</i>_CAP of linear PS is lower than <i>T</i>_CAP of cyclic PS and <i>t</i>_E,CAP of linear PS is shorter than <i>t</i>_E,CAP of ring PS. Therefore, at the CAP of linear polymers, ring polymers elute later in order of increasing MW while, at the CAP of ring polymers, linear polymers elute earlier in order of decreasing MW. This is in excellent agreement with the Monte Carlo computer simulation results. We also found that the functionality effect can interfere in the LCCC separation of ring polymers from their linear precursors

Topologically Reversible Transformation of Tricyclic Polymer into Polyring Using Disulfide/Thiol Redox Chemistry

A polyring capable of reversible growth and dissociation is synthesized from a tricyclic polystyrene (PS) prepared by combining atom transfer radical polymerization of a 4-arm star-shaped PS and azide–alkyne click reactions. In the preparation of the tricyclic PS, a coupling agent containing a disulfide linkage is used in the click cyclization reaction. The reduction of the disulfide linkage in the tricyclic PS results in an 8-shaped PS with thiol groups which on oxidation leads to a high molecular weight polyring. The topology transformation between the polymers occurs via reversible redox reaction of disulfide/thiol. The high molecular weight of the polyring is realized due to the formation of flexible S–S linkage between the 8-shaped PSs. Their structures are confirmed by FT-IR, ¹H NMR, SEC, and MALDI-TOF MS analyses. In addition, molecular weight control of the polyring according to polymer concentration has been confirmed through SEC analysis