Advances in HPLC & Chromatography Techniques

Biography

Biography: Dusan Berek

Abstract

Most high-performace synthetic polymers exhibit besides dispersity in their molar mass also dispersity in another molecular characteristic, namely in chemical structure (composition) or in physical architecture of macromolecules. They are designated complex polymers. Typical examples of complex polymers are all kinds of copolymers, branched and functional polymers. Blends of macromolecules with distinct chemical structure or physical architecture are called complex polymer systems. Size exclusion chromatography (gel permeation chromatography), SEC/GPC is commonly used for assessment of molar mass averages and dispersities (distributions) of complex polymers and complex polymer systems. However, due to simultaneous dependence of size of macromolecules on all their molecular characteristics, as well as following limited separation selectivity, sample capacity, and low detector sensitivity, SEC/GPC can hardly give quantitative information on molar masses of complex polymers and complex polymer systems. For example, SEC/GPC even does not enable molecular characterization of binary polymer blends of components with fairly different molar masses, in which the content of the minor constituent is less than few percent. To characterize complex polymers and complex polymer systems, enthalpic retention mechanisms are to be coupled with entropy based size-exclusion retention mechanism. Of the presently utilized coupled methods of polymer LC the best known are liquid chromatography under critical conditions of enthalpic interactions, LC CC, eluent gradient liquid chromatography, EG LC and temperature gradient interaction chromatography, TGIC. The common drawbacks of the latter methods are limited to both sample recovery and capacity. LC CC permits only separation of two distinct sample constituents. Recently an alternative group of coupled LC metods was developed, namely liquid chromatography under limiting conditions of enthalpic interactions, LC LC. Similar to LC CC and EG LC, the molar mass effect is supressed also in LC LC. LC LC exhibits remarkable separation selectivity, as well as both high sample capacity and 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. The method enables reliable identification of very low (<1% and even <<1%) amounts of minor macromolecular admixtures in a polymer matrix. The basic principle of LC LC will be discussed in the contribution. For a comprehensive molecular characterization of complex polymer systems, two 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 consists of a combination of LC LC and SEC/GPC. The fractions produced by the LC LC column are in their entirety transferred into the SEC/GPC column for determination of average and disperity of sample. The principle of S2D-LC 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.