Stationary Phases Based on PIM-1 Polymer of Intrinsic Microporosity for Gas Chromatography

Polyimide PIM-1, which forms a porous polymer layer on the walls of a capillary column, exhibits high thermal stability. It is studied as a stationary phase for gas chromatography. A column with the PIM-1 stationary phase displays a drastic difference in efficiency, depending on the molecular size of the analyte: 2500–3000 theoretical plates per meter for methane and ethane and fewer than 1000 plates for larger molecules. This behavior of the column is attributed to the poor accessibility of sorption sites, as is apparent from the high loss of entropy during the sorption of light hydrocarbons and the low diffusion coefficients for these sorbates. The effect the physical aging of PIM-1 has on the separating properties of a column is studied in the accelerated thermal aging mode using the example of separation of a model C₁–C₄ hydrocarbon mixture. It is shown that upon heating the stationary phase to 200°C, sorbate retention and column efficiency fall monotonously. When the temperature is raised to 300°C, an unexpected increase in the analyte retention is observed, though the column's efficiency continues to fall with respect to all sorbates except isobutane, for which this parameter increases. The causes of these unexpected effects have yet to be revealed.