Multidetector Size Exclusion Chromatography

Abstract

Size exclusion chromatography (SEC) is the premier polymer characterization method for determining molar masses. As a polymer fractionation method it provides not only average molar masses (like viscometry or light scattering) but also molar mass distributions (MMD). In SEC, the separation mechanism is based on molecular hydrodynamic volume. For linear homopolymers, condensation polymers and strictly alternating copolymers, there is a direct correspondence between elution volume and molar mass. Thus, chemically similar polymer standards of known molar mass can be used for calibration. However, for SEC of random and block copolymers and branched polymers, no simple correspondence exists between elution volume and molar mass because of possible compositional heterogeneity of these materials. As a result, molar mass calibration with polymer standards can introduce a considerable amount of error. To address this problem, selective detection techniques in addition to universal concentration detectors were introduced to be combined with SEC separation. In this chapter the focus is on using these powerful detectors for the SEC analysis of complex polymers.