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An intrinsically microporous polyimide is synthesized in m-cresol by a one-pot high-temperature condensation reaction of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and newly designed 2,6 (7)-dihydroxy-3,7(6)-diaminotriptycene (DAT1-OH). The 6FDA-DAT1-OH polyimide is thermally stable up to 440 °C, shows excellent solubility in polar solvents, and has moderately high Brunauer-Teller-Emmett (BET) surface area of 160 m2 g−1, as determined by nitrogen adsorption at −196 °C. Hydroxyl functionalization applied to the rigid 3D triptycene-based diamine building block results in a polyimide that exhibits moderate pure-gas CO2 permeability of 70 Barrer combined with high CO2/CH4 selectivity of 50. Mixed-gas permeation studies demonstrate excellent plasticization resistance of 6FDA-DAT1-OH with impressive performance as potential membrane material for natural gas sweetening with a CO2 permeability of 50 Barrer and CO2/CH4 selectivity of 40 at a typical natural gas well partial pressure of 10 atm. [ABSTRACT FROM AUTHOR]

Tröger's base (TB) has been utilized as an important building block in designing ladder polymers of intrinsic microporosity (PIMs) and microporous polyimides (PIM-PIs) for membrane-based gas separations due to its unique V-shaped bicyclic structure and versatile molecular chemistry. Nearly a century after its discovery, Hünlich's base (HB) was recently reintroduced as a valuable diamine derivative of TB made by a single-step reaction of 2,4-diaminotoluene and formaldehyde, spurring use in molecular devices such as molecular tweezers and photo-switches. Unlike TB, HB has not been explored as a building block of PIMs and PIM-PIs for membrane-based gas separations. In this study, we synthesized two soluble PIM-PIs for the first time by reaction of HB as diamine and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) or 9,10-diisopropyltriptycene tetracarboxylic dianhydride (TDA i 3), respectively. 6FDA-HB exhibited high Brunauer-Teller-Emmett (BET) surface area of 415 m2 g−1 and fractional free volume (FFV) of 0.26. The gas separation performance of the 6FDA-HB polymer was similar to other 6FDA-based dimethyl-substituted Tröger's base polyimide analogues, exhibiting O 2 , CO 2 and H 2 permeability of 62, 286, and 391 Barrer with O 2 /N 2 , CO 2 /CH 4 and H 2 /CH 4 selectivity of 4.4, 26 and 36, respectively. Compared to 6FDA-HB, the triptycene-containing Hünlich's base polyimide (TDA i 3-HB) displayed a higher BET surface area (501 m2 g−1) owing to the presence of the rigid bridged tricyclic triptycene contortion site, resulting in about two-fold increase in O 2 permeability to 188 Barrer coupled with slightly compromised O 2 /N 2 selectivity of 4.1. Beside the merit of facile synthesis, the Hünlich's base-derived polyimides experienced relatively modest effects of physical aging on gas permeation properties. Image 1 • Hünlich's base, a diamine analogue of Tröger's base, was synthesized. • Facile synthesis of two new polyimides with 6FDA and a triptycene dianhydride. • Polyimides showed microporous features with high BET surface area. • Polyimides displayed modest effects of aging on gas permeability and selectivity. [ABSTRACT FROM AUTHOR]

Back Cover: Triptycene is a unique building block for high‐performance polymers due to its symmetric D3h structure containing fixed internal free‐volume elements. A novel triptycene diamine (2,6(7)‐dihydroxy‐3,7(6)‐diaminotriptycene) (DAT1‐OH) for the synthesis of an intrinsically microporous polyimide (6FDA‐DAT1‐OH) is described by Ingo Pinnau and co‐workers in article number 1700303. As illustrated in the cover design, it exhibits excellent performance as membrane material for gas separation applications, specifically for the removal of CO2 from natural gas. [ABSTRACT FROM AUTHOR]

A hydroxyl-functionalized triptycene-based polyimide of intrinsic microporosity (TDA1-APAF) was converted to a polybenzoxazole (PBO) by heat treatment at 460 °C under nitrogen atmosphere. TDA1-APAF treated for 15 min (TR 460) resulted in a PBO conversion of 95% based on a theoretical weight loss of 11.7 wt% of the polyimide precursor. The BET surface area of the TR 460 (680 m 2 g −1 ) was significantly higher than that of the TDA1-APAF polyimide (260 m 2 g −1 ) as determined by nitrogen adsorption at −196 °C. Heating TDA1-APAF for 30 min (TRC 460) resulted in a weight loss of 13.5 wt%, indicating full conversion to PBO and partial main-chain degradation. The TR 460 membrane displayed excellent O 2 permeability of 311 Barrer coupled with an O 2 /N 2 selectivity of 5.4 and CO 2 permeability of 1328 Barrer with a CO 2 /CH 4 selectivity of 27. Interestingly, physical aging over 150 days resulted in enhanced O 2 /N 2 selectivity of 6.3 with an O 2 permeability of 185 Barrer. The novel triptycene-based TR 460 PBO outperformed all previously reported APAF-polyimide-based PBOs with gas permeation performance close to recently reported polymers located on the 2015 O 2 /N 2 upper bound. Based on this study, thermally-rearranged membranes from hydroxyl-functionalized triptycene-based polyimides are promising candidate membrane materials for air separation, specifically in applications where space and weight of membrane systems are of utmost importance such as nitrogen production for inert atmospheres in fuel lines and tanks on aircrafts and off-shore oil- or natural gas platforms. Mixed-gas permeation experiments also demonstrated good performance of the TR 460 membrane for natural gas sweetening with a CO 2 permeability of ∼1000 Barrer and CO 2 /CH 4 selectivity of 22 at a typical CO 2 wellhead partial pressure of 10 bar. [ABSTRACT FROM AUTHOR]

An intrinsically microporous hydroxyl-functionalized polyimide (PIM-PI) made from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,6(7)-dihydroxy-3,7(6)-diaminotriptycene (DAT1-OH), was thermally converted to polybenzoxazole (PBO). The thermal rearrangement of the PIM-PI to PBO significantly increased the free volume, which was reflected by a boost in its microporosity as indicated by enhanced Brunauer-Emmett-Teller (BET) surface area from 167 to 405 m2 g−1. The increase in free volume noticeably improved the gas permeability but also resulted in reduced gas-pair selectivity. The fresh PBO membrane made by thermal treatment at 460 °C for 30 min (TRIP-TR-460-30) with a PBO conversion of 98% displayed a 20-fold higher CO 2 permeability of 840 barrer than the initial value of 43 barrer for the 6FDA-DAT1-OH polyimide at the expense of ~ 60% decrease in pure-gas CO 2 /CH 4 selectivity from 52 to 21. The TRIP-TR-460-30 PBO showed good performance for propylene/propane separation with pure-gas C 3 H 6 permeability of 21 barrer and C 3 H 6 /C 3 H 8 selectivity of 16 for a 28-days aged sample. When tested under mixed-gas conditions C 3 H 6 permeability dropped to 12.8 barrer and C 3 H 6 /C 3 H 8 selectivity of 8. TRIP-TR-460-30 PBO displayed mechanical properties comparable some rigid polyimides with tensile strength, Young's modulus and elongation at break of 58 MPa, 1.83 GPa and 4.3%, respectively. Image 1 • TR-derived PBO membranes made from 6FDA/triptycene OH-based diamine polyimide. • Fully converted PBO exhibited improved gas permeability but reduced selectivity. • Physical aging had large effect on gas permeability but small effect on selectivity. • PBO demonstrated performance located on the propylene/propane upper bound. [ABSTRACT FROM AUTHOR]