Applications of Size Exclusion Chromatography in Polymer Characterization

Size exclusion chromatography (SEC), which is also called gel permeation chromatography (GPC), is a liquid chromatography that sorts molecules according to their hydrodynamic volume in solution by using columns packed with porous particles. It is the most frequently used technique to characterize the molecular weight and its distribution of naturally occurring and synthetic macromolecules. Multi-detector SEC combining differential refractive index, ultraviolet/visible, viscosity and multi-angle laser light scattering detectors is a powerful tool to study the shape and conformation of polymer chains in solution. Here we summarize the separation mechanism of SEC and show that the retention of polymer in SEC is an equilibrium, entropy-controlled and size-exclusion process. In order to achieve a pure SEC separation according to the size of polymer chains, enthalpy interaction between polymer chains and the packing particles should be prevented. Then we introduce the know-how to perform successful SEC experiments with a focus on the choice of eluent, column and detector, as well as sample preparation, optimization of experimental conditions and data analysis. Especially, the eluent composition should be properly optimized according to the analysed polymer sample and the column overloading should be avoided, before accurate results can be obtained by SEC. Finally, we show some examples of the recent applications of SEC in polymer characterization such as molecular weight and its distribution of polymers, composition of multicomponent polymer mixtures, conformation and flexibility of polymer chains, and characterization of branched polymers. More dramatically, delayed elution of high molar mass polymers was observed in SEC at high flow rates, which is not due to polymer degradation. This abnormal elution behaviour results from a chromatographic mode transition from SEC to slalom chromatography, which originates from the coil-stretch transition of polymer chains in elongational flow through the SEC columns. It is shown that SEC can provide abundant structure parameters and their distributions of polymer chains in solution, and plays a pivotal role in the analysis of natural and synthetic macromolecules. This review aims to provide a theoretical and experimental guidance for SEC beginners, hoping to inspire more applications of SEC in the field of polymer science.

Automated summary

Size exclusion chromatography (SEC), also known as gel permeation chromatography (GPC), is a liquid chromatography technique used to separate molecules based on their hydrodynamic volume in solution. It is commonly used to characterize molecular weight and distribution of polymers. Proper optimization of eluent composition and avoidance of column overloading are crucial for obtaining accurate results in SEC experiments.