Inverse Gas Chromatography in Analysis of Polymers

Abstract

Abstract This article describes the application of inverse gas chromatography (IGC) to the study of synthetic and natural polymers. The word “inverse” is used to indicate that the component of interest is the stationary phase, either as a finely divided powder or coating, dispersed on a suitable inert support and packed into a chromatographic column. The time required for a probe molecule to pass through the column gives a measure of the molecular interactions between the probe and the polymer which can be quantified with the help of chromatographic theory. Historically, most thermodynamic studies on polymers were carried out in dilute solution, but IGC provides information on condensed phases under conditions much more similar to those under which polymers are actually used. Using this technique, melting, glass and other solid‐phase transitions can be studied and quantified. Degrees of crystallinity can be determined in an unambiguous procedure without calibration by other methods. Solubility, permeability and diffusion constants can be determined for probe molecules. IGC is also used extensively in determining the permeability of additives such as antioxidants in polymers, as well as thermodynamic quantities such as activity coefficients, heats of solution, Flory–Huggins interaction parameters (χ), and solubility parameters. Surface areas can be measured at any desired temperature by the determination of the adsorption isotherms of suitable probes. Measurements on polymer blends can yield important information on polymer–polymer interactions and can be used to predict the compatibility of the components over a wide range of temperatures. The use of finite concentration IGC provides a rapid method of determining the density of crosslinks in rubber‐like polymers. Almost any commercial gas chromatograph can be easily modified to carry out IGC experiments by procedures described in this report. The method provides a wealth of information of both fundamental and practical importance in the study of polymeric materials.