Rational Design of Intrinsically Ultramicroporous Polyimides Containing Bridgehead-Substituted Triptycene for Highly Selective and Permeable Gas Separation Membranes

• Published in: Macromolecules Vol. 47; no. 15; pp. 5104 - 5114
• Main Authors: Swaidan, Raja, Al-Saeedi, Majed, Ghanem, Bader, Litwiller, Eric, Pinnau, Ingo
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 12.08.2014
• Subjects: air; Applied sciences; diamines; Exact sciences and technology; geometry; hydrogen; methane; modulus of elasticity; Organic polymers; permeability; Physicochemistry of polymers; Polymers with particular structures; Preparation, kinetics, thermodynamics, mechanism and catalysts; sieving; surface area; tensile strength; Polyimide; Transport properties; Fluorine containing polymer; Aromatic polymer; Mechanical properties; Polycyclic compound; Long term variation; Experimental study; Oxygen heterocycle; Dimension spectrum; Porous material; Modeling; Polyaddition; Geometrical structure; Gas permeability; Pore size; Microporosity; Preparation; Selective permeability; Property structure relationship; Surface area; Semiladder polymer
• ISSN: 0024-9297; 1520-5835; 1520-5835
• DOI: 10.1021/ma5009226

Highly ultramicroporous, solution-processable polyimides bearing 9,10-bridgehead-substituted triptycene demonstrated the highest BET surface area reported for polyimides (840 m2 g–1) and several new highs in gas selectivity and permeability for hydrogen (1630–3980 barrers, H2/CH4 ∼ 38) and air (230–630 barrers, O2/N2 = 5.5–5.9) separations. Two new dianhydrides bearing 9,10-diethyl- and 9,10-dipropyltriptycenes indicate that the ultramicroporosity is optimized for fast polymeric sieving with the use of short, bulky isopropyl bridgeheads and methyl-substituted diamines (TrMPD, TMPD, and TMBZ) that increase intrachain rigidity. Mechanically, the triptycene-based analogue of a spirobisindane-based polyimide exhibited 50% increases in both tensile strength at break (94 MPa) and elastic modulus (2460 MPa) with corresponding 90% lower elongations at break (6%) likely due to the ability of highly entangled spiro-based chains to unwind. To guide future polyimide design, structure/property relationships are suggested between the geometry of the contortion center, the diamine and bridgehead substituent, and the mechanical, microstructural, and gas transport properties.