Finely Tuning the Free Volume Architecture in Iptycene-Containing Polyimides for Highly Selective and Fast Hydrogen Transport

Abstract

Iptycene-based polyimides have attracted extensive attention recently in the membrane gas separation field due to their unique structural hierarchy and chemical characteristics that enable construction of well-defined yet tailorable free volume architecture for fast and selective molecular transport. We report here a new series of iptycene-based polyimides that are exquisitely tuned in the monomer structure to afford preferred microcavity architecture for hydrogen transport. In particular, a triptycene-containing dianhydride (TPDAn) was prepared to react with two iptycene-containing diamines (i.e., TPDAm and PPDAm) or 2,2′-bis­(3-amino-4-hydroxy­phenyl)­hexa­fluoropropane (6FAP) to produce entirely or partially iptycene-based polyimides. The incorporation of iptycene units effectively disrupted chain packing, which resulted in ultrafine microporosity in the membranes with a desired bimodal size distribution with maxima at ∼3 and ∼7 Å, respectively. Depending on the combination of diamine and dianhydride, the microporosity was feasibly tuned and optimized to meet the needs of challenging H2 separations, especially for H2/N2 and H2/CH4 gas pairs. Particularly, a H2 permeability of 27 barrers and H2/N2 and H2/CH4 selectivities of 142 and 300, respectively, were obtained for TPDAn-6FAP.

Synthesis, characterization, and gas permeation properties of adamantane‐containing polymers of intrinsic microporosity

“…PIM-1 is a widely studied candidate in the class of PIMs due to its rigid and contorted structure. 9 Since then, several examples of PIMs containing units such as triptycene, 10,11 spirobisindane, 12,13 Tr€ oger's base, [14][15][16][17] spirobischromane, 18 spirobifluorene, 19 hexaphenylbenzene, 20 naphthalene, 21 tetraphenylethylene, 22 phthalimide, 23 tribenzotriquinacene, 24 cardo PIMs, and so on 25 have been synthesized and evaluated as membrane materials for gas separation.…”

A New Pentiptycene‐Based Dianhydride and Its High‐Free‐Volume Polymer for Carbon Dioxide Removal

“…The high molecular weight of PPDImDA‐6FDA points to good reactivity and high purity of PPImDA. A higher molecular weight can be achieved by further purification of the monomers and optimizing the reaction conditions . Both PPImDA‐6FDA and 6FDA‐durene have relatively small polydispersities.…”

“…Also, this group synthesized a microporous highly permeable polyimide from a SBF‐based dianhydride . Recently, several new iptycene‐based polyimides with unique structural hierarchies were created on the basis of 1,4‐bis[4‐(3,4‐dicarboxylphenoxy)]triptycene dianhydride) TPDAn), 1,4‐bis(aminophenoxy)triptycene, and pentiptycene‐based diamines (PPDA). [37] These polymers showed high solubility in organic solvents, high selectivity, robust structure, and significant thermal stability.…”

“…These advances provide strong motivation for the synthesis of a highly rigid pentiptycene‐based dianhydride to prepare high free‐volume pentiptycene‐based PIs. Before this, SBI‐, SBF‐, EA‐, and Trip‐based dianhydrides were synthesized by using other groups . Herein, for the first time we report the synthesis and characterization of a pentiptycene‐based dianhydride (PPDAn) and a pentiptycene‐imide‐containing diamine (PPImDA) [obtained directly from the reaction of PPDAn with N , N , N ′, N ′‐tetramethylphenyldiamine (durene or TMPD)].…”

“…The high glass transition temperature ( T g ) of 6FDA‐durene (>400 °C) arises from rigid diamine and −C(CF 3 ) 2 − moieties, and the high T g value of PPImDA‐6FDA (>400 °C) is due to the aromatic‐ring‐rich structure of the pentiptycene moiety. The symmetric arene rings of the pentiptycene with a vertical position to the polymer backbone impede segmental mobility even at high temperatures and increase the rigidity of the backbone . No crystallization or melting peaks were observed.…”