High-Performance Liquid Chromatography of Polymers: Retention Mechanisms and Recent Advances

The high-resolution separation of polymer oligomers, their breakdown products and isomers is a significant challenge to modern separation science. The historically most successful methods are based on size exclusion strategies and not mobile phase/stationary phase partition in the conventional sense. In the last decade significant progress has been made in understanding the requirements for achieving elution chromatography of high {> 5 kDa} molecular weight organic polymers ranging from quite hydrophobic to quantitatively water soluble in character. This paper discusses retention mechanisms, the dynamics of the partition chromatographic process, evidence for significant delays in polymer equilibration to mobile phase conditions and the effect of the temperature dependence of polymer solubility. Conventional chromatographic behavior is shown to obtain for the separation of polystyrenes, polymethylmethacrylates, polyethylene oxides and polypeptides if proper steps are taken to carry out the experiment. The use of thermal gradients in spatial terms is shown to have significant value for achieving enhanced separations.