Multiple detectors for molecular weight and composition analysis of copolymers by gel permeation chromatography

Abstract

The use of a single detector in gel permeation chromatography (GPC) for samples of varying composition leads to erroneous conclusions. With certain simplifying assumptions, a gel permeation chromatograph equipped with properly selected dual detectors yields composition and molecular weight distribution information that is meaningful. Examples discussed are a mixture of homopolymers and a sample supposed to have been a styrene–butadiene block copolymer. The ultraviolet absorption is used in conjunction with the refractive index trace to give qualitative information that is much more informative than could be obtained with one detector. Calibration of the relative responses of the detectors to each of the components of the mixture is described, and these calibrations are used to calculate point‐by‐point composition, molecular weights, and molecular weight averages.