Role of Intrachain Rigidity in the Plasticization of Intrinsically Microporous Triptycene-Based Polyimide Membranes in Mixed-Gas CO2/CH4 Separations

• Published in: Macromolecules Vol. 47; no. 21; pp. 7453 - 7462
• Main Authors: Swaidan, Raja, Ghanem, Bader, Al-Saeedi, Majed, Litwiller, Eric, Pinnau, Ingo
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 11.11.2014
• Subjects: Applied sciences; carbon dioxide; cellulose acetate; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; methane; Polymer industry, paints, wood; porous media; sorption; superoxide anion; Technology of polymers; Gas absorption; Molecular rigidity; Polyimide; Transport properties; Porous membrane; Fluorine containing polymer; Head to head polymer; Experimental study; Dimension spectrum; Gas permeability; Pore size; Selective permeability; Property structure relationship; Semiladder polymer
• ISSN: 0024-9297; 1520-5835; 1520-5835
• DOI: 10.1021/ma501798v

Based on high-pressure pure- and mixed-gas (50:50) CO2/CH4 separation properties of two intrinsically microporous triptycene-based polyimides (TPDA–TMPD and TPDA–6FpDA), the intrachain rigidity central to “conventional PIM” design principles is not a singular solution to intrinsic plasticization resistance. Despite the significant intrachain rigidity in TPDA–TMPD, a 300% increase in P MIX(CH4), 50% decrease in α(CO2/CH4) from 24 to 12, and continuous increase in P MIX(CO2) occurred from 4 to 30 bar. On the other hand, the more flexible and densely packed TPDA–6FpDA exhibited a slight upturn in P MIX(CO2) at 20 bar similar to a dense cellulose acetate (CA) film, also reported here, despite a 4-fold higher CO2 sorption capacity. Microstructural investigations suggest that the interconnected O2- and H2-sieving ultramicroporosity of TPDA–TMPD is more sensitive to slight CO2-induced dilations and is the physical basis for a more extensive and accelerated plasticization. Interchain rigidity, potentially by interchain interactions, is emphasized and may be facilitated by intrachain mobility.