Chromatography

Biography

Biography: Dusan Berek

Abstract

Many high-performance synthetic polymers contain macromolecular chains with distinct chemical structure (composition) or physical architecture. Typical examples represent multi-component polymers called complex polymer systems. Size exclusion chromatography, SEC is commonly used for determination of molar mass averages and dispersities of synthetic polymers. However, due to its limited both separation selectivity and sample capacity, as well as generally low detector sensitivity, SEC can hardly give quantitative information on molar masses of components of complex polymer systems. For example, SEC usually does not allow identification and molecular characterization of binary polymer blends, in which one (minor) constituent represents less than ten percent - even if the molar masses of constituents differ more than 100%. Moreover, SEC cannot recognize macromolecules of distinct chemical structure or architecture because both latter characteristics affect retention volumes together with molar mass. To characterize complex polymer systems, entropy based exclusion separation mechanism is to be combined with enthalpic retention mechanisms. Of such coupled methods of polymer liquid chromatography, the best known are liquid chromatography under critical conditions, LC CC, eluent gradient liquid chromatography, EG LC and temperature gradient interaction chromatography, TGIC. The common drawbacks of the latter methods are limited both sample recovery and capacity. LC CC allows only separation of two distinct sample constituents. Recently an alternative group of coupled LC methods were developed, namely liquid chromatography under limiting conditions of enthalpic interactions, LC LC. Similar to LC CC and EG LC, also in LC LC the molar mass effect is suppressed so that macro-molecules are separated exclusively according to their composition or architecture. LC LC exhibits remarkable separation selectivity, as well as high sample capacity and reasonable sample recovery. Moreover LC LC is highly robust, experimentally feasible and well repeatable. It was successfully applied to separation of chemically and physically similar macromolecules including low solubility polymers. It was demonstrated that the method allows reliable identification of very low (<1%) amounts of minor macromolecular admixtures in major polymer matrix. The backgrounds of LC LC will be presented in the contribution. For a comprehensive molecular characterization of complex polymer systems, different retention mechanisms are to be applied in two separate chromatographic systems. This is the basis of two-dimensional polymer liquid chromatography, 2D-LC. A flexible approach called sequential two-dimensional polymer liquid chromatography, S2D-LC was recently developed. It includes a combination of LC LC and SEC. The fractions produced by the LC LC column are in their entirety online transferred into the SEC column. The S2D-LC principle will be elucidated in detail and the typical examples of its application will be shown, especially separation and characterization of block copolymers that contain (small) amounts of their parent homopolymers.