Design and Synthesis of Polyimides Based on Carbocyclic Pseudo-Tröger’s Base-Derived Dianhydrides for Membrane Gas Separation Applications

A Microporous Poly(Arylene Ether) Platform for Membrane-Based Gas Separation

Membrane-based gas separations are crucial for an energy-efficient future. However, it is difficult to develop membrane materials that are high-performing, scalable, and processable. Microporous organic polymers (MOPs) combine benefits for gas sieving and solution processability. Herein, we report membrane performance for a new family of microporous poly(arylene ether)s (PAEs) synthesized via Pd-catalyzed C-O coupling reactions. The scaffold of these microporous polymers consists of rigid three-dimensional triptycene and stereocontorted spirobifluorene, endowing these polymers with micropore dimensions attractive for gas separations. This robust PAE synthesis method allows for the facile incorporation of functionalities and branched linkers for control of permeation and mechanical properties. A solution-processable branched polymer was formed into a submicron film and characterized for permeance and selectivity, revealing lab data that rivals property sets of commercially available membranes already optimized for much thinner configurations. Moreover, the branching motif endows these materials with outstanding plasticization resistance, and their microporous structure and stability enables benefits from competitive sorption, increasing CO2 /CH4 and (H2 S+CO2 )/CH4 selectivity in mixture tests as predicted by the dual-mode sorption model. The structural tunability, stability, and ease-of-processing suggest that this new platform of microporous polymers provides generalizable design strategies to form MOPs at scale for demanding gas separations in industry.

Membrane Separation Technology in Direct Air Capture

Direct air capture (DAC) is an emerging negative CO2 emission technology that aims to introduce a feasible method for CO2 capture from the atmosphere. Unlike carbon capture from point sources, which deals with flue gas at high CO2 concentrations, carbon capture directly from the atmosphere has proved difficult due to the low CO2 concentration in ambient air. Current DAC technologies mainly consider sorbent-based systems; however, membrane technology can be considered a promising DAC approach since it provides several advantages, e.g., lower energy and operational costs, less environmental footprint, and more potential for small-scale ubiquitous installations. Several recent advancements in validating the feasibility of highly permeable gas separation membrane fabrication and system design show that membrane-based direct air capture (m-DAC) could be a complementary approach to sorbent-based DAC, e.g., as part of a hybrid system design that incorporates other DAC technologies (e.g., solvent or sorbent-based DAC). In this article, the ongoing research and DAC application attempts via membrane separation have been reviewed. The reported membrane materials that could potentially be used for m-DAC are summarized. In addition, the future direction of m-DAC development is discussed, which could provide perspective and encourage new researchers' further work in the field of m-DAC.

Synthesis of polyimides containing Tröger's base and triphenylmethane moieties with a tunable fractional free volume for CO2 separation

CO2 separation from natural gas (CO2/CH4) or flue gas (CO2/N2) has a great significance for the sustainable development of the environment and society as well as industrial production.

Evaluation of physicochemical properties and catalytic activity of poly(PMDAH-co-ODA/PPDA) nanocomposites towards the removal of toxic pollutants

Synthesis of Polyimides (PIs) between pyromellitic dianhydride (PMDAH) and oxydianiline (ODA) or p-phenylenediamine (PPDA) in the presence and absence of V₂O₅ and Ag nanoparticles (NPs) were carried out under N₂ atmosphere at 160 °C for 5 h with vigorous stirring in N-methylpyrrolidone (NMP) solvent. The prepared PI and its nanocomposites were analyzed by FT-IR spectroscopy, ¹H NMR spectroscopy, FE-SEM, SEM, DSC and TGA like analytical instruments. The FE-SEM showed various surface morphologies for different PI nanocomposites. The particle size of the prepared nanoparticles was calculated as less than 60 nm for Ag and 15 nm for V₂O₅ nanoparticles by HR-TEM. The PI nanocomposites embedded with Ag nanoparticles (P2 and P5) showed a higher thermal stability than the pristine PIs (P1 and P4) and PI/V₂O₅ nanocomposites (P3 and P6). Further, the possible application of metal (Ag) and metal oxide (V₂O₅) NPs embedded PI nanocomposites was assessed on the catalytic reduction of highly toxic Cr(VI), Rhodamine 6G (R6G) dye and p-nitrophenol (NiP) pollutants with the help of a reducing agent (NaBH₄). The apparent rate constant (k_app) values were calculated to assess the catalytic efficiency of the prepared PI and its nanocomposites. The PI/Ag nanocomposite (P2) system showed an efficient catalytic reduction than the other systems.

Tröger's base functionalized recyclable porous covalent organic polymer (COP) for dye adsorption from water

Tröger's base incorporated recyclable COP for acid dye removal from effluent.

Synthesis and gas separation performance of intrinsically microporous polyimides derived from sterically hindered binaphthalenetetracarboxylic dianhydride

Intrinsically microporous polyimides with high gas permeability and favorable selectivity were prepared from a bulky, rigid, and sterically hindered dianhydride, 3,3′-di-t-butyl-2,2′-dimethoxy-[1,1′-binaphthalene]-6,6′,7,7′,-tetracarboxylic dianhydride.

Investigation of thermal and fluorescent properties of benzoxazole-linked triphenylamine-based co-polyimides

A series of novel fluorescent co-polyimides are obtained by combining N 1-(4-aminophenyl)- N 1-(4-(benzo[ d]oxazol-2-yl) phenyl) benzene-1,4-diamine and 4,4′-oxydianiline with four aromatic anhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, 4,4′-oxydiphthalic anhydride, and 4,4 ′-(hexafluoroisopropylidene)diphthalic anhydride following conventional polycondensation method. The resultant co-polyimides are characterized by elemental, Fourier transform infrared spectral analysis and gel permeation chromatography. All newly prepared polyimides (PIs) exhibit shallow highest occupied molecular orbital energy levels in the range of −4.47 to −4.98 eV and have reasonable optical bandgaps. The photoluminescence spectral analysis shows blue to green emission in solution form. Thermal and solubility properties reveal that the PIs with pendant 4-(benzo[ d]oxazol-2-yl group linked to triphenylamine unit in polymer backbone impart not only good thermal stability but also appreciable solubility making these new co-polyimides versatile for multipurpose usage.

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.

Synthesis and characterization of new polyimides from diphenylpyrene dianhydride and ortho methyl substituted diamines

Three new polyimides were synthesized via one-step polycondensation from 3,8-diphenylpyrene-1,2,6,7-tetracarboxylic dianhydride (DPPD) with two diamines with ortho methyl substitution (MBDAM and HFI) and one diamine without ortho substituents (BAPHF). The effect of diamine structure in DPPD based polyimides' physical, thermal, mechanical and gas transport properties has been studied. The polyimide structure was confirmed by FTIR and ¹H NMR. All polymers show high thermal stability with decomposition temperatures above 493 °C, and glass transition temperatures above 336 °C. Changes in packing density of polyimide membranes were assessed by wide angle X-ray diffraction and correlated to fractional free volume FFV. Polyimides based on rigid DPPD dianhydride exhibited an improved gas permeability and selectivity when ortho methyl substituents are present in the diamine used for polyimide synthesis. DPPD-MBDAM polyimide showed the best gas productivity values with 565 barrer CO₂ permeability and a selectivity of 16 for CO₂/CH₄.

Three new polyimides were synthesized from 3,8-diphenylpyrene-1,2,6,7-tetracarboxylic dianhydride (DPPD) with two diamines with ortho methyl substitution (MBDAM and HFI) and one diamine without ortho substituents (BAPHF).

Design and synthesis of a multifunctional porous N-rich polymer containing s-triazine and Tröger's base for CO2 adsorption, catalysis and sensing

A multifunctional porous N-rich polymer containing s-triazine and Tröger's base was synthesized. It shows selective adsorption for CO₂, colorimetric performance for HCl and good catalytic activity in the Knoevenagel condensation.