Impact of Polymer Topology on Physical Aging of Thin Film Composite Membranes Based on PIM-1, cPIM-1, and Associated Blends
Andrew B. Foster, Ming Yu, Mustafa Alshurafa, Peter M. Budd
Abstract
High Resolution Image Download MS PowerPoint Slide 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 CO 2 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).