Multiple Detection in Size-Exclusion Chromatography of Macromolecules

detectors characterize the distributions of macro-molecular parameters that have a critical effect on the end product. Synthesizing polymers is not as exact a science as wewould like it to be. Natural syntheses and even well-con-trolled laboratory syntheses often yield macromolecules that vary in length, molar mass, branching, chemical compo-sition, and other properties. Characterizing these properties and their distributions is important because of their critical ef-fect on end-use structure–property relations and, hence, on the end product itself. The most commonly studied proper-ties are the molar mass averages (Mn, Mw, Mz, etc.) and the molar mass distribution (MMD). Various processing charac-teristics of macromolecules can be related to the individual av-erages, for example, flow properties and brittleness (related to Mn) and flex life and stiffness (related to Mz). Similarly, prop-erties such as tensile strength and abrasion resistance tend to increase as MMD narrows, and properties such as elongation and yield strength tend to increase as MMD broadens. During the past four decades, size-exclusion chromatogra-phy (SEC) has been established as the premier method for characterizing M averages and the distribution of natural and