Dušan BerekSlovakia

Block copolymers, BLC belong to the group of synthetic nonmetallic materials called complex polymers. They have valuable properties and found applications for example as flocculants, carriers of drugs and compatibilizers of polymer blends, etc. BLC are formed with two or several (only rarely with more than three) polymeric chains called blocks. Blocks have different chemical composition or physical architecture and they are mutually connected with a chemical bond. The structure of common diblock and triblock copolymers is schematically displayed as A-B, A-B-A or A-B-C. Most BLC contain their parent homopolymers, the “free blocks”, which may spoil their utility properties. Therefore, it is important to determine their amount and to adjust the synthesis of BLC to reduce their formation. The molecular characterization of BLC and determination of parent homopolymers is an analytical challenge. The limited separation selectivity of the most commonly polymer characterization method, size exclusion (gel permeation) chromatography, SEC/GPC is usually not sufficient to fulfill the task. Other, advanced methods of polymer liquid chromatography must be applied. Three of them will be presented in the contribution.
1. Liquid chromatography under critical conditions, based on unique mutual compensation of entropic partition (exclusion) and enthalpic interactions of macromolecules within column
2. Full adsorption of samples containing distinct macromolecules on a nonporous microparticulate sorbent, followed with their sectional, selective elution into an SEC/GPC column
3. Barrier methods, the emerging techniques, which are based on the action of slowly eluting, narrow liquid zones, barriers, which selectively decelerate fast elution of macromolecules of distinct nature.