体积排除色谱技术在高分子表征中的应用

Applications of Size Exclusion Chromatography in Polymer Characterization

体积排除色谱(SEC)也称为凝胶渗透色谱(GPC),是利用多孔填料色谱柱将溶液中的高分子按照流体力学体积大小进行分离的一种液相色谱技术,主要用于测定各种天然和合成高分子的平均分子量及分子量分布.多检测SEC技术可同时获得经色谱柱分离后高分子各级分的含量、分子量、均方根回转半径、流体力学半径、特性黏数等参数,进而推断高分子在溶液中的形态和链构象.本文首先介绍了SEC分离的基本原理,即由熵驱动的高分子在多孔填料内外分配达到平衡的体积排除机理,接着总结了SEC的一些实验方法和技巧,并详细阐述了SEC在高分子的分子量及其分布测定、定量分析、链构象与刚柔性、支化结构表征、链构象转变等方面的应用,最后展望了SEC的发展趋势.

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.