Rational design of intrinsically ultramicroporous polyimides containing bridgehead-substituted triptycene for highly selective and permeable gas separation membranes
KAUST DepartmentAdvanced Membranes and Porous Materials Research Center
Physical Sciences and Engineering (PSE) Division
Chemical and Biological Engineering Program
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AbstractHighly 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, O 2/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. © 2014 American Chemical Society.
SponsorsThis work was supported by KAUST funding for Prof. Ingo Pinnau. The authors thank Prof. N. B. McKeown (University of Edinburgh) and Dr. Caterina Grazia Bezzu for gel permeation chromatography measurements.
PublisherAmerican Chemical Society (ACS)