Impact of PolymerTopology on Physical Aging of ThinFilm Composite Membranes Based on PIM-1, cPIM-1, and Associated Blends

An overview is provided of the influence of polymer topology on the physical aging of PIM-1 thin film composite (TFC) membranes measured in gas permeation studies. Topologically distinct PIM-1 samples are compared first with each other, then in polymeric blends, and then with other literature. Both initial permeability (1 day) and long-term aging rates (up to 1 year) can be attributed to structural components present within the overall microstructure of the polymer. The rigidity and structural regularity of a predominantly disubstituted PIM-1 polymer proved to facilitate high initial CO₂ permeability in TFCs followed by a rapid aging rate (β_P = 1.0) to produce an increasingly nonselective membrane over 28 days. By contrast, TFCs prepared from branched PIM-1 polymers, which have lower glass transition temperature, exhibit lower initial permeabilities followed by much slower aging rates, remaining highly selective for up to one year. Branched PIM-1 polymers which contain a greater proportion of small loop structures show a very slow aging rate (β_P = 0.22−0.25), whereas those with more open branched structure tend to exhibit a faster aging rate (β_P = 0.67−0.69). Thin film nanocomposite (TFN) membranes cast from blends of a disubstituted PIM-1 with colloidal network (CN)-rich PIM-1 fillers can completely halt permeability aging for up to one month but then subsequently resume aging at a faster rate (β_P = 1.8−2.8) to more than compensate. TFNs prepared from blending a branched PIM-1 polymer with a CN-rich Cardo-PIM-1 filler can produce better long-term aging performance (up to 1 year).