Chromatography

High performance liquid chromatographic (HPLC) methods represent the most important tool for molecular

characterization of synthetic polymers. Mean molar masses and molar mass distributions of linear and branched homopolymers

are easily determined by size exclusion/gel permeation chromatography (SEC/GPC). As by-products, several other

useful data can be assessed with SEC/GPC. Recent progress in SEC/GPC comprises improved instrumental hardware and data

processing procedures. High sample throughput of the ultra-fast SEC/GPC allows acceleration of analyses, which is especially

important in combinatorial material chemistry and in production control. Still, further improvements of the SEC/GPC method

are needed, which include its hardware, especially columns and detectors, and also standardization of sample preparation,

measurements, and data processing. SEC/GPC exhibits excellent intra-laboratory repeatability, which evokes a notion of its

high reliability. Recent series of the round robin tests, however, revealed surprisingly poor inter-laboratory reproducibility

of results. Evidently, accuracy of many SEC/GPC results may be rather limited. In most cases, SEC/GPC does not enable

precise molecular characterization of complex polymer systems, which possess more than one distribution in their molecular

characteristics. Typically, polymer mixtures, copolymers and functional polymers exhibit besides molar mass distribution also

distribution in their chemical structure while e.g. stereo-regular polymer species show also molecular architecture distribution.

To assess above distributions, new HPLC procedures are developed. Th ese are based on the controlled combinations of entropic

(exclusion) and enthalpic (interaction) retention mechanisms within the same HPLC column or in a series of independent

separation systems. Th ese approaches are denoted as “coupled polymer HPLC” and “two-, or multi-dimensional polymer

HPLC”, respectively. Enthalpic retention mechanisms in HPLC of synthetic polymers include adsorption, partition, phase

separation and ionic eff ects. We shall review recent progress and also problems in SEC/GPC, as well