Kyuhyun Im

Two-dimensional liquid chromatography analysis of synthetic polymers using fast size exclusion chromatography at high column temperature.

In recent years, two-dimensional liquid chromatography (2D-LC) has been used increasingly for the analysis of synthetic polymers. A 2D-LC analysis provides richer information than a single chromatography analysis at the cost of longer analysis time. The time required for a comprehensive 2D-LC analysis is essentially proportional to the analysis time of the second dimension separation. Many of 2D-LC analyses of synthetic polymers have employed size exclusion chromatography (SEC) for the second-dimension analysis due to the relatively short analysis time in addition to the wide use in the polymer analysis. Nonetheless, short SEC columns are often used for 2D-LC analyses to reduce the separation time, which inevitably deteriorates the resolution. In this study, we demonstrated that high temperature SEC can be employed as an efficient second-LC in the 2D-LC separation of synthetic polymers. By virtue of high temperature operation (low solvent viscosity and high diffusivity of the polymer molecules), a normal length SEC column can be used at high flow rate with little loss in resolution.

2D-LC characterization of comb-shaped polymers using isotope effect.

A rigorous molecular characterization of comb-shaped polystyrene (PS) was carried out taking advantage of its molecular structure, a normal hydrogenous backbone, and deuterated side chains. Normal phase LC (NPLC) can separate the comb PS species well according to their molecular weight. Nonetheless, it cannot distinguish the backbone from the side chains and the differently structured polymers having a similar molecular weight, e.g, a single backbone comb and a coupled backbone comb with fewer side chains. In contrast to NPLC, the hydrogenous polymer is retained longer than the deuterated counterpart in reversed phase LC (RPLC). When the isotope sensitivity of RPLC is taken advantage of, the comb PS is cross fractionated by NPLC and RPLC, and a two-dimensional mapping with respect to the backbone chain length and the number of branches is fully established.

Fractionation of poly(dimethyl siloxane) by interaction chromatography

AbstractPoly(dimethyl siloxane) (PDMS) was characterized by interaction chromatography using C4-bonded silica and a mixture of THF/CH3OH as the stationary phase and the mobile phase, respectively. Under the separation condition, a commercial PDMS with broad molecular weight distribution was successfully fractionated according to molecular weight into fractions with a very narrow molecular weight distribution. The IC separation could be applied to more rigorous characterization of PDMS, modified PDMS, and block copolymer-containing PDMS.