Polyimides Of Intrinsic Microporosity Research Articles

Hydroxyl-Functionalized Polymers of Intrinsic Microporosity and Dual-Functionalized Blends for High-Performance Membrane-Based Gas Separations.

Membrane technology has shown significant growth during the past two decades in the gas separation industry due to its energy-savings, compact and modular design, continuous operation, and environmentally benign nature. Robust materials with higher permeability and selectivity are key to reduce capital and operational cost, pushing it forward to replace or debottleneck conventional energy-intensive unit operations such as distillation. Recently designed ladder polymers of intrinsic microporosity (PIM) and polyimides of intrinsic microporosity (PIM-PI) with pores <20 Å have demonstrated excellent gas permeation performance. Here, a series of plasticization-resistant PIM-based membrane materials is reported, including the first example of a hydroxyl-functionalized triptycene- and Tröger's base-derived ladder PIM and two PIM-PI homopolymers and a series of dual-functionalized polyimide blends containing hydroxyl- and carboxyl-functionalized groups. Specifically, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA)-based PIM-PI blends demonstrated extremely high selectivity for a variety of industrially important applications. An optimized polyimide blend containing ─OH and ─COOH groups showed permselectivity values of 136 for CO2/CH4, 11.4 for O2/N2 and 636 for H2/CH4. Such extreme size-sieving capabilities are attributed to physical crosslinking induced by strong hydrogen bonding forming tightly structured polymer networks. The study provides a new general strategy for developing plasticization resistant, robust, and highly-selective PIM-based membrane materials.

Exploring physical aging in PIM-1 using molecular dynamics

This comprehensive study explored the aging process of PIM-1, a ladder polymer of intrinsic microporosity (PIM), by applying molecular dynamics simulations for the first time. Through detailed analysis, our work illustrates the evolution of the polymer structure from a loosely packed, less dense state of the pristine polymer to a more tightly packed configuration due to physical aging. For this purpose, a novel molecular dynamics (MD) methodology was employed in the process toward equilibration of PIM-1. This structural transition was quantitatively captured by measuring key parameters such as density, fractional free volume (FFV), cohesive energy density (CED), d-spacing, surface area, and gas permeabilities. The simulations demonstrate a noticeable increase in density by approximately 7 % in aged PIM-1 compared to a fresh sample. This increase in density is accompanied by a corresponding decrease in FFV, suggesting a more compact molecular arrangement. The impact of these structural changes is evident in the gas transport properties. Permeabilities of all gases tested, He, H2, O2, N2, CO2 and CH4, decreased by 33 %–80 %. Moreover, the selectivity of gas pairs like CO2/CH4 and O2/N2 exhibited increasing trends due to aging, as previously reported in experimental work. Structural analysis performed on the fresh and aged structures indicated collapse of free volume over aging, by disappearance of pores larger than ∼6.5 Å. Furthermore, no intrachain rearrangement was observed during physical aging in the ladder PIM-1 structure; rather, the aging resulted in increased interchain packing efficiency. Our methodology can be employed to other PIM architectures, such as polyimides of intrinsic microporosity (PIM-PIs) as well as low-free volume glassy polymers.

Synthesis and gas separation performance of Tröger's base-containing polyimides derived from 9,9-Bis(trifluoromethyl)-2,3,6,7-xanthenetetracarboxylic dianhydride

Two imide-containing diamine monomers were prepared using 9,9-bis(trifluoromethyl)-2,3,6,7-xanthenetetracarboxylic dianhydride (6FcDA) and 2,6-dimethylaniline or 2,6-diisopropylaniline as the starting materials. Two polyimides of intrinsic microporosity (PIM-PIs), i.e., 6FcDA-Me2NH2-TB and 6FcDA-iPr2NH2-TB, were then synthesized via TB polymerization of imide-containing diamines and dimethoxymethane in trifluoroacetic acid. The surface areas, fractional free volumes, and interchain distances of the PIM-PIs were in the range of 555–569 m2 g−1, 0.16–0.20, and 0.60–0.67 nm, respectively. These values followed the order of 6FcDA-Me2NH2-TB < 6FcDA-iPr2NH2-TB owing to the larger size of isopropyl substituents relative to methyl groups. Furthermore, 6FcDA-Me2NH2-TB exhibited obvious π-π stacking interactions as evidenced by the diffraction peaks at ∼ 26 ° in wide angle X-ray diffraction patterns. Consequently, 6FcDA-Me2NH2-TB showed higher perm-selectivity but lower gas permeability as compared to 6FcDA-iPr2NH2-TB. Particularly, both polymers had a CO2 permeability of > 2900 Barrer and a CO2/CH4 selectivity of > 10, located between the 1991 and 2008 Robeson’s upper bound for CO2/CH4 separation.

Intrinsically microporous polyimides from p-phenylenediamine with fused cyclopentyl substituents for membrane-based gas separation

In this study, a novel diamine, 1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene-9,10-diamine (DMNDA), was synthesized in six-steps using dicyclopentadiene and p-benzoquinone as the starting materials. Next, four polyimides of intrinsic microporosity (PIM-PIs) were prepared by the high-temperature polycondensation of DMNDA with four typical dianhydrides in m-cresol. The fractional free volumes (FFV) of these polymers were in the range of 0.193–0.216, decreasing in order of SBIDA > 6FDA > BTA > CpODA. Furthermore, the introduction of bulky fused cyclopentyl substituents resulted in free volume elements of ∼ 0.5 nm, evidenced by visible shoulders in the WAXD patterns. Consequently, the gas permeability and perm-selectivity of 6FDA-DMNDA were greater than those of the benchmark polymer, 6FDA-Durene. SBIDA-DMNDA and BTA-6FDA-DMNDA exhibited high H2 permeability, but modest H2/CH4 and H2/N2 selectivity, approaching the 2008 Robeson upper bounds. Furthermore, SBIDA-DMNDA showed a CO2 permeability of 1439 barrer and a CO2/CH4 selectivity of ∼ 14 at 10 bar, approaching the 2018 upper bound for CO2/CH4 mixed-gas separation.

Intrinsically Microporous Polyimides from Norbornyl Bis-benzocyclobutene-Containing Diamines and Rigid Dianhydrides for Membrane-Based Gas Separation

A series of polyimides of intrinsic microporosity (PIM-PIs) were prepared from commercially available rigid dianhydrides (pyromellitic dianhydride (PMDA), cyclo-[2.2.2]oct-7-ene-2-exo,3-exo,5-exo,6-exo-2,3:5,6-dianhydride (BTA), and 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA)) and diamines with norbornyl bis-benzocyclobutene (N2BC) segments (CANAL-2, CANAL-3, and CANAL-4). The physical and gas transport properties of these polymers were systematically investigated. The fractional free volumes (FFV), interchain distances, surface areas, and cumulative micropore volumes of these PIM-PIs were in the range of 0.156–0.185, 0.593–0.619 nm, 422–615 m2 g–1, and 0.059–0.072 cm3 g–1, respectively, showing a general trend of BTA > PMDA > CBDA for certain diamines. Thus, BTA-CANAL-2 concomitantly exhibited higher gas permeability and perm-selectivity relative to its analogues, viz., PMDA-CANAL-2, CBDA-CANAL-2, and 6FDA-CANAL-2 (6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic anhydride). Specifically, it showed H2 permeability of 1685 barrer, H2/CH4 selectivity of 14, and H2/N2 selectivity of 15, which surpassed the 2008 Robeson’s upper bounds. The W-shaped, cage-like architecture of BTA residues imparted the resulting PIM-PIs with both high FFV and high cumulative micropore volumes, which was the reason for their excellent gas separation performance.

Recent Progress on Polymers of Intrinsic Microporosity and Thermally Modified Analogue Materials for Membrane‐Based Fluid Separations

Solution‐processable amorphous glassy polymers of intrinsic microporosity (PIMs) are promising microporous organic materials for membrane‐based gas and liquid separations due to their high surface area and internal free volume, thermal and chemical stability, and excellent separation performance. This review provides an overview of the most recent developments in the design and transport properties of novel ladder PIM materials, polyimides of intrinsic microporosity (PIM–PIs), functionalized PIMs and PIM–PIs, PIM‐derived thermally rearranged (TR), and carbon molecular sieve (CMS) membrane materials as well as PIM‐based thin film composite membranes for a wide range of energy‐intensive gas and liquid separations. In less than two decades, PIMs have significantly lifted the performance upper bounds in H2/N2, H2/CH4, O2/N2, CO2/N2, and CO2/CH4separations. However, PIMs are still limited by their insufficient gas‐pair selectivity to be considered as promising materials for challenging industrial separations such as olefin/paraffin separations. An optimum pore size distribution is required to further improve the selectivity of a PIM for a given application. Specific attention is given to the potential use of PIM‐based CMS membranes for energy‐intensive CO2/CH4, N2/CH4, C2H4/C2H6, and C3H6/C3H8separations, and thin film composite membranes containing PIM motifs for liquid separations.

Nanofiber engineering of microporous polyimides through electrospinning: Influence of electrospinning parameters and salt addition

The electrospinning of high-performance polyimides (PI) has recently sparked great interest. In this study, we explore the effect of the electrospinning parameters — namely polymer concentration, voltage, tip-to-collector distance and flow rate — and salt addition on the diameter, morphology, and spinnability of electrospun PI nanofibers. Three different polyimides of intrinsic microporosity (PIM-PIs) with high Brunauer–Emmett–Teller (BET) ranging from 270 to 506 m2 g−1, and two microporous polyimides, were synthesized through the polycondensation of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and aromatic diamines. The addition of tetraethylammonium bromide (TEAB) salt considerably increased the conductivity of all the PI solutions, significantly improved spinability, and resulted in thinner fibers. We also used molecular dynamic simulations to investigate the macromolecular mechanism of improved spinnability and fiber morphology in the presence of an ammonium salt. The small droplets detached from the parent droplet, followed by the rapid evaporation of the ions through the hydration effect, which facilitated the electrospinning. The resulting uniform nanofibers have great potential in environmental applications due to the presence of microporosity and hydrophobic pendant trifluoromethyl groups, which enhance the sorption performance of the fibers for hydrophobic species.

Synthesis of Highly Gas-Permeable Polyimides of Intrinsic Microporosity Derived from 1,3,6,8-Tetramethyl-2,7-diaminotriptycene.

A simple synthetic route to a novel sterically hindered triptycene-based diamine, 1,3,6,8-tetramethyl-2,7-diaminotriptycene (TMDAT), and its use in the preparation of high molecular weight polyimides of intrinsic microporosity (PIM-PIs) are reported. The organosoluble TMDAT-derived polyimides displayed high Brunauer–Emmett–Teller surface areas ranging between 610 and 850 m2 g–1 and demonstrated excellent thermal stability of up to 510 °C. Introduction of the rigid three-dimensional paddlewheel triptycene framework and the tetramethyl-induced restriction of the imide bond rotation resulted in highly permeable polyimides with moderate gas-pair selectivity. The best performing polyimide made from TMDAT and a triptycene-based dianhydride showed gas transport properties located between the 2008 and 2015 polymer permeability/selectivity trade-off curves with H2 and O2 permeabilities of 2858 and 575 barrer combined with H2/N2 and O2/N2 selectivities of 24 and 4.8, respectively, after 200 days of physical aging.

Intrinsically microporous polyimides containing spirobisindane and phenazine units: Synthesis, characterization and gas permeation properties

ABSTRACTA new diamine containing spirobisindane and phenazine units, namely, 3,3,3′,3′‐tetramethyl‐2,2′,3,3′‐tetrahydro‐1,1′‐spirobi[cyclopenta[b]phenazine]‐7,7′‐diamine (TTSBIDA) was synthesized starting from commercially available 5,5′,6,6′‐tetrahydroxy‐3,3,3′,3′‐tetramethyl‐1,1′‐spirobisindane (TTSBI). TTSBI was oxidized to 3,3,3′,3′‐tetramethyl‐2,2′,3,3′‐tetrahydro‐1,1′‐spirobi[indene]‐5,5′,6,6′‐tetraone (TTSBIQ) which was subsequently condensed with 4‐nitro‐1,2‐phenylenediamine to obtain 3,3,3′,3′‐tetramethyl‐7,7′‐dinitro‐2,2′,3,3′‐tetrahydro‐1,1′‐spirobi[cyclopenta[b]phenazine] (TTSBIDN). TTSBIDN was converted into TTSBIDA by reduction of the nitro groups using hydrazine hydrate in the presence of Pd/C as the catalyst. A series of new polyimides of intrinsic microporosity (PIM‐PIs) were synthesized by polycondensation of TTSBIDA with commercially available aromatic dianhydrides. PIM‐PIs exhibited amorphous nature, high thermal stability (T10 &gt; 480 °C) and intrinsic microporosity (BET surface area = 59–289 m2/g). The gas permeation characteristics of films of selected PIM‐PIs were evaluated and they exhibited appreciable gas permeability as well as high selectivity. The CO2 and O2 permeability of PIM‐PIs were in the range 185.4–39.2 and 30.6–6.2 Barrer, respectively. Notably, polyimide derived from TTSBIDA and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (PIM‐PI‐6FDA) exhibited high CO2 and O2 permeability of 185.4 and 30.6 Barrer with CO2/CH4 and O2/N2 selectivity of 43.1 and 5.1, respectively. The data of PIM‐PI‐6FDA for CO2/CH4 and O2/N2 gas pairs were located near Robeson upper bound. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 766–775

Pure- and mixed-gas propylene/propane permeation properties of spiro- and triptycene-based microporous polyimides

Solution-processable polyimides of intrinsic microporosity (PIM-PIs) comprising relatively inflexible and contorted backbones have demonstrated outstanding molecular-sieving behavior in membrane-based separation of gas/gas pairs. In this work, the effects of systematically increasing intra-chain rigidity on the propylene/propane separation properties were compared for PIM-PIs made from 2,3,5,6-tetramethyl-1,4-phenylene diamine (TMPD) and (i) spiro-centered dianhyride (SPDA-TMPD or PIM-PI-1) and (ii) 9,10-diisopropyltriptycene-based dianhydride (TPDA-TMPD or KAUST PI-1). Pure-gas experiments at 2bar and 35°C showed significant increases in C3H6 permeability and C3H6/C3H8 selectivity by transitioning from PIM-PI-1 (P(C3H6)=393 Barrer, α(C3H6/C3H8)=6) to KAUST-PI-1 (P(C3H6)=817Barrer, α(C3H6/C3H8)=16), positioning KAUST-PI-1 considerably above the experimentally observed pure-gas C3H6/C3H8 polymer upper bound. However, 50:50 C3H6/C3H8 mixed-gas feeds induced significant losses in C3H6 permeability and C3H6/C3H8 selectivity relative to the 2bar pure-gas data for PIM-PI-1 and KAUST-PI-1 as the C3H6/C3H8 selectivity dropped from 6 to 3 and 16 to 5, respectively, at 2bar C3H6 partial pressure due to plasticization and competitive sorption.

Microporous Polyimides with Rationally Designed Chain Structure Achieving High Performance for Gas Separation

Polyimides of intrinsic microporosity are important polymers for gas separation. Achieving polyimides with high permeability and high selectivity relies on rationally designing their chain structure. In this work, new ladder-like diamines, Troger’s Base (TB) derived diamines, are designed, and two microporous polyimides are constructed by polymerizing TB-derived diamines and spirobisindane based dianhydride, aiming at enhancing the stiffness of the whole backbone and thus achieving improved performance by taking advantage of the stiffness of both diamines and dianhydride. The two polyimides present excellent separation performance, surpassing the 2008 Robeson upper bound for gas pairs of H2/N2 and O2/N2 and approach the 2008 Robeson upper bound for gas pairs H2/CH4 and CO2/CH4. Our results show that the designed polyimides have great potential for application especially for oxygen (O2/N2) and hydrogen (such as H2/N2 and H2/CH4) related separation.

A highly permeable polyimide with enhanced selectivity for membrane gas separations

Introducing the highly rigid ethanoanthracene unit into polyimides of intrinsic microporosity provides an impressive enhancement of gas selectivity by molecular sieving.