Studies of Polymer Properties via Inverse Gas Chromatography

Abstract

Abstract Gas Chromatosraphy (GC) using a polymer as the stationary phase to reveal the properties of the polymer — known as Inverse Gas Chromatography (IGC) — is in contrast to conventional GC where gaseous components in the mobile phase are separated and studied. Figure l(a) and l(b) are schematic diagrams showing the arrangement of apparatus in a gas Chromatograph for IGC. The column is filled with packings consisting of thin layer of polymer coated onto an inert support, typically Chromosorb W, Chromosorb G (70 ∼ 80 mesh, acid washed and dimethyldichlorosilane treated), or Teflon. The carrier gas, such as N2, H2, or He, acts as the mobile phase. The solvent, injected as a sharp pulse and vaporized immediately into the carrier gas stream at the entrance of the column, is called the probe. As the probe is carried forward, it is partitioned between the mobile gas phase and the stationary polymer phase. The time required to elute the probe through the column is called the retention time (elution is monitored in the detector and reflected on the recorder or integrator as a peak maximum). The corresponding amount of carrier gas needed is called the retention volume. The detector for the probe may be a thermal conductivity cell (TCD) or flame ionization detector (FID). When an FID is used, the flow of gas is diverted to the flow meter before it reaches the detector as shown in Figure l(b). Some notes on the experimental techniques will be discussed in Section IX. GC has been classified into Gas-Liquid Chromatography (GLC) and Gas-Solid Chromatography (GSC) according to whether the stationary phase is a liquid or a solid, respectively. In IGC, the process is GLC when the temperature of the polymer under investigation is far above its glass transition temperature Tg. The retention is due to absorption of the solvent vapor into the polymer bulk (an amorphous polymer above Tg is viewed as a liquid). When the temperature of the polymer is well below its Tg, the process is GSC and the retention mechanism becomes adsorption of the vapor onto the polymer surface. We shall initially discuss the GLC of polymers and then extend our discussions to GSC. Important applications of IGC to polymer research have been the studies of the thermodynamics of polymer-solvent and polymer-polymer interactions via GLC.