Molecular Sieves: Energy-Efficient Hydrogen Separation by AB-Type Ladder-Polymer Molecular Sieves (Adv. Mater. 39/2014) (original) (raw)

O 2 /N 2 separation. Triptycene, the simplest member of the iptycenes, has three benzene arms bridged about a [2,2,2]-tricyclic ring system in a shape-persistent, 3D paddlewheel confi guration that locks in "internal molecular free volume" (IMFV) between the rings. 9,10-bridgehead substitution can augment the overall rigidity and bulkiness of triptycene. Subsequent incorporation into rigid backbones has produced highly sorbing network polymers and our highly sieving solutionprocessable polyimides. However, polyimides retain an additional degree of fl exibility at the imide bond, which may compromise microporosity and selectivity by sacrifi cing intramolecular rigidity. It is of great interest to evaluate more rigid fused-ring ladder backbones free of the fl exible single bonds of PIM-PIs and the traditional spiro-center employed in PIMs (i.e., single tetrahedral carbon atom shared by two rings). Several soluble triptycene-bearing ladder polymers have beensynthesized before, 19, but none of the investigations addressed the importance of 9,10-bridgehead substituents for gas separation performance. Our recent work on PIM-PIs has established that 9,10-bridgehead substitution of the triptycene can result in signifi cant gains in permeability and selectivity. The integration of 9,10-dialkyl-substituted triptycene into a soluble ladder PIM was successfully demonstrated by self-polycondensation of a novel A-B monomer bearing a 9,10-dibutyl-substituted triptycene and both phenazine-activating o -dichloride and catechol groups. Self-polymerization of such A-B monomers has a signifi cant advantage in stepgrowth polymerization over previously used AA-BB monomers because high molecular weight fi lm-forming products can be achieved without strict control of the stoichiometric balance. Accordingly, this Communication describes the synthesis, microstructures, and exceptional gas transport properties of two new soluble ladder polymers -TPIM-1 and TPIM-2 -containing triptycene moieties substituted with branched isopropyl and linear propyl chains at the 9,10-bridgeheads. The precursor A-B monomers were modifi ed with an o -difl uoride functionality for enhanced activation for nucleophilic aromatic substitution. Technologically attractive selectivity-driven performance signifi cantly transcending the upper bounds is observed for hydrogen and air separations, accounting for about 75% of the membrane-based gas separation business, as well as emerging biogas and natural gas (CO 2 /CH 4 ) applications.