Effect of Temperature-Induced\nAging on the Gas Permeation\nBehavior of Thin Film Composite Membranes of PIM‑1 and Carboxylated\nPIM‑1

Polymers of intrinsic microporosity (PIMs) are a class\nof promising\ngas separation materials due to their high membrane permeabilities\nand reasonable selectivities. When processed into thin film composite\n(TFC) membranes, their high gas throughput aligns closely with industrial\nrequirements, but they are prone to physical aging and plasticization\neffects. TFC membranes based on the prototypical PIM-1 and its carboxylated\nderivative cPIM-1 exhibit temperature-dependent gas permeation behavior,\nwhich has not been extensively studied before. In single CO<sub>2</sub> permeation tests, measurable physical aging occurred when the temperature\nwas raised to 55 °C within a period of 90 min, and the aging\nrate accelerated as temperature was raised further. TFC membranes\nprepared from cPIM-1 exhibited a faster aging rate compared to PIM-1\nat the same temperature. The decreased permeance could be at least\npartially recovered through a 5 day methanol vapor treatment. In mixed\ngas experiments, all membranes showed decreased permselectivities\nat elevated temperatures. The plasticization pressure of TFC membranes\noccurred at around 1 bar of CO<sub>2</sub> partial pressure, independent\nof temperature. Significant plasticization was particularly evident\nfor cPIM-1 TFC membranes under CO<sub>2</sub>/CH<sub>4</sub> conditions\nwith increasing temperature, which resulted in increased gas permeance\nfor both components.