Dusan Berek
Polymer Institute of the Slovak Academy of Science, Slovakia
Title: Retention mechanisms in liquid chromatography of non-charged synthetic macromolecues
Biography
Biography: Dusan Berek
Abstract
Liquid chromatography (LC) provides information on both average values and distributions of molecular characteristics of synthetic polymers, their molar mass, chemical structure and physical architecture. Gel permeation (size exclusion) chromatography, GPC/SEC, is commonly employed for determination of polymer molar mass. Its basic retention mechanism is steric exclusion controlled by the changes of conformational entropy of coiled macromolecules entering the pores of the column packing. However, GPC/SEC cannot give quantitative information about polymer when two molecular characteristics mutually depend as in copolymers or in polymer blends. In this case, the entropic retention mechanism is to be coupled with the enthalpic retention mechanisms. The ambition is to suppress molar mass effects so that separation depends only on other molecular characteristic. Yet, one should keep in mind that all enthalpy based processes in a LC column are accompanied with large changes of conformational entropy of macromolecules. The most common enthalpic retention mechanism employed in coupled LC methods is adsorption, the distribution of macromolecules between a volume of its solution and a surface of column packing. It is as a rule controlled by eluent polarity. The appropriate stationary phase is bare silica gel. Another LC retention mechanism is absorption (enthapic partition), the distribution of macromolecules between the volumes of mobile and stationary phase. The practically applicable volume of LC stationary phase is formed by the chemically attached appropriate groups, usually C18 alkyls on a carrier, mainly silica gel. Both adsorption and enthalpic partition retention mechanisms are exploited either isocratically or with a mobile phase gradient. Direct practical application of the third enthalpic retention mechanism, polymer phase separation is rather difficult. Sample is precipitated on the column inlet and then gradually dissolved and eluted. However, solubility of polymers strongly depends on their molar mass so that the molar mass effect is difficult to suppress.
Recent Publications
1.Berek D (2017) Separation of parent homopolymers from nonpolar block copolymers by means of liquid chromatography under limiting conditions of enthalpic interactions. Macromolecular Chemistry Physics 218:137-142.
2.Rollet M, Pelletier B, Berek D, Maria S, Phan T N T and Gigmes D (2016) Separation of parent homopolymers from polystyrene and poly(ethylene oxide) based block copolymers by liquid chromatography under limiting conditions. 3. Study of barrier efficiency according to block copolymer chemical composition. Journal of Chromatography A 1462:63-72.
3. Berek D (2016) Critical assessment of “critical” liquid chromatography of block copolymers. Journal of Separation Science 39(1):93–101.
4. Clementi L A, Meira G R, Berek D, Ronco L I and Vega J R (2015) Molar mass distributions in homopolymer blends from multimodal chromatograms obtained by SEC/GPC with a concentration detector. Polymer Testing 43:58-67.
5. Berek D and Macova E (2015) Liquid chromatography under limiting conditions of desorption 6: Separation of a four-component polymer blend. Journal of Separation Science 38(4):543-549.