Effect of Film Thickness and Physical Aging on “Intrinsic” Gas Permeation Properties of Microporous Ethanoanthracene-Based Polyimides

Artificial Lithium Channels Built from Polymers with Intrinsic Microporosity

In sharp contrast to numerous artificial potassium channels developed over the past decade, the study of artificial lithium-transporting channels has remained limited. We demonstrate here the use of an interesting class of polymers with intrinsic microporosity (PIM) for constructing artificial lithium channels. These PIM-derived lithium channels show exceptionally efficient (γLi +>40 pS) and highly selective transport of Li+ ions, with selectivity factors of>10 against both Na+ and K+. By simply adjusting the initial reaction temperature, we can tune the transport property in a way that PIMs synthesized at initial reaction temperatures of 60 °C and 80 °C exhibit improved transport efficiency and selectivity, respectively, in the dioleoyl phosphatidylcholine membrane.

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.

Advancements in Gas Separation for Energy Applications: Exploring the Potential of Polymer Membranes with Intrinsic Microporosity (PIM)

Membrane-based Polymers of Intrinsic Microporosity (PIMs) are promising candidates for energy-efficient industrial gas separations, especially for the separation of carbon dioxide over methane (CO2/CH4) and carbon dioxide over nitrogen (CO2/N2) for natural gas/biogas upgrading and carbon capture from flue gases, respectively. Compared to other separation techniques, membrane separations offer potential energy and cost savings. Ultra-permeable PIM-based polymers are currently leading the trade-off between permeability and selectivity for gas separations, particularly in CO2/CH4 and CO2/N2. These membranes show a significant improvement in performance and fall within a linear correlation on benchmark Robeson plots, which are parallel to, but significantly above, the CO2/CH4 and CO2/N2 Robeson upper bounds. This improvement is expected to enhance the credibility of polymer membranes for CO2 separations and stimulate further research in polymer science and applied engineering to develop membrane systems for these CO2 separations, which are critical to energy and environmental sustainability. This review aims to highlight the state-of-the-art strategies employed to enhance gas separation performances in PIM-based membranes while also mitigating aging effects. These strategies include chemical post-modification, crosslinking, UV and thermal treatment of PIM, as well as the incorporation of nanofillers in the polymeric matrix.

Dibenzomethanopentacene-Based Polymers of Intrinsic Microporosity for Use in Gas-Separation Membranes

Dibenzomethanopentacene (DBMP) is shown to be a useful structural component for making Polymers of Intrinsic Microporosity (PIMs) with promise for making efficient membranes for gas separations. DBMP-based monomers for PIMs are readily prepared using a Diels-Alder reaction between 2,3-dimethoxyanthracene and norbornadiene as the key synthetic step. Compared to date for the archetypal PIM-1, the incorporation of DBMP simultaneously enhances both gas permeability and the ideal selectivity for one gas over another. Hence, both ideal and mixed gas permeability data for DBMP-rich co-polymers and an amidoxime modified PIM are close to the current Robeson upper bounds, which define the state-of-the-art for the trade-off between permeability and selectivity, for several important gas pairs. Furthermore, long-term studies (over ≈3 years) reveal that the reduction in gas permeabilities on ageing is less for DBMP-containing PIMs relative to that for other high performing PIMs, which is an attractive property for the fabrication of membranes for efficient gas separations.

Synthesis, microstructures, and gas separation performance of norbornyl bis-benzocyclobutene-Tröger’s base polymers derived from pure regioisomers

Chain configuration significantly influences the microstructures and gas separation performance of polymers of intrinsic microporosity. Herein, pure regioisomers of norbornyl bis-benzocyclobutene-containing (N2BC) diamines, i.e. anti-CANAL-4-MeNH2, syn-CANAL-4-MeNH2, anti-CANAL-2-Me2NH2, and syn-CANAL-2-Me2NH2, were...

Microporous polyimides with high surface area and CO2 selectivity fabricated from cross-linkable linear polyimides

Linear polyimides of intrinsic microporosity have been intensively investigated for gas separation due to their microporous structure and high surface area. The microporous structure in the linear polyimides of intrinsic microporosity comes from their contorted structure. Therefore, most linear polyimides without contorted structure do not have micropores. In this work, the microporous polyimides are constructed through the condensation of a cross-linkable dianhydride monomer with two novel nitrogen-rich diamine monomers and post crosslinking reaction. The linear polyimide precursors without contorted structure have the same main-chain structure. The introduction of crosslinked structure endow the crosslinked polyimides (PI-CLs) with microporous structure. The microporous structure in PI-CLs can be tuned by changing the substituents of the linear polyimide precursors. The PI-CLs have competitive CO₂ uptake capacity (7.3-9.4 wt%) at 273 K and 1 bar. Particularly, the crosslinked polyimide containing trifluoromethyl groups (CF₃-PI-CL) shows high CO₂/N₂ and CO₂/CH₄ selectivity (72 and 22) at 273 K, which are among the best results for reported porous materials. This work reveals that the introduction of crosslinked structure and changing substituents is an efficient method for constructing microporous polyimides with abundant micropores and excellent CO₂ selective adsorption capacity. This method also has great potential for fabricating high-performance microporous polymers based on other linear polymers without rigid contorted structure.

Facile Synthesis and Study of Microporous Catalytic Arene-Norbornene Annulation-Tröger's Base Ladder Polymers for Membrane Air Separation

We report the facile synthesis and study of two soluble microporous ladder polymers, CANAL-TBs, by combining catalytic arene-norbornene annulation (CANAL) and Tröger's base (TB) formation. The polymers were synthesized in two steps from commercially available chemicals in high yields. CANAL-TBs easily formed mechanically robust films, were thermally stable up to 440 °C, and exhibited very high Brunauer-Teller-Emmett surface areas of 900-1000 m² g^-1. The gas separation performance of the CANAL-TBs for the O₂/N₂ pair is located between the 2008 and 2015 permeability/selectivity upper bounds. After 300 days of aging, CANAL-TBs still exhibited O₂ permeability of 200-500 barrer with O₂/N₂ selectivity of about 5. The polymer with more methyl substituents exhibited higher permeability and slightly larger intersegmental spacing as revealed by WAXS, presumably due to more frustrated chain packing. The facile synthesis, excellent mechanical properties, and promising air separation performance of the CANAL-TB polymers make them attractive membrane materials for various air separation applications, such as aircraft on-board nitrogen generation and oxygen enrichment for combustion.

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.

Thin Composite Carbon Molecular Sieve Membranes from a Polymer of Intrinsic Microporosity Precursor

Ultra-thin composite carbon molecular sieve (CMS) membranes were fabricated on well-defined inorganic alumina substrates using a polymer of intrinsic microporosity (PIM) as a precursor. Details of the pyrolysis-related structural development were elucidated using focused-beam, interference-enhanced spectroscopic ellipsometry (both in the UV-vis and IR range), which allowed accurate determination of the film thickness, optical properties as well as following the chemical transformations. The pyrolysis-induced collapse of thin and bulk PIM-derived CMS membranes was compared with CMS made from a well-known non-PIM precursor 6FDA-DABA. Significant differences between the PIM and non-PIM precursors were discovered and explained by a much larger possible volume contraction in the PIM. In spite of the differences, surprisingly, the gas separation properties did not fundamentally differ. The high-temperature collapse of the initially amorphous and isotropic precursor structure was accompanied by a significant molecular orientation within the formed turbostratic carbon network guided by the laterally constraining presence of the substrate. This manifested itself in the development of uniaxial optical anisotropy, which was shown to correlate with increases in gas separation selectivity for multiple technologically important gas pairs. Reduction of CMS skin thickness significantly below ∼1 μm induced large losses in permeability coefficients with only small to moderate effects on selectivity. Remarkably, skin thickness reduction and physical aging seemed to superimpose onto the same trend, which explains and strengthens some of the earlier fundamental insights.

Accelerated Aging of PS Blocks in PS- b-PMMA Diblock Copolymer under Hard Confinement

This letter presents an accelerated physical aging of polystyrene (PS) blocks in polystyrene- block-poly(methyl methacrylate) (PS- b-PMMA) diblock copolymers under hard confinement. The three-dimensional hard nanoconfinement was provided by the PMMA component owing to its high elasticity and was formed via self-assembled microphase separation. Aging was observed by measuring enthalpy recovery of the PS blocks in the copolymers for which the degree of polymerization ( N) of PS blocks is fixed, whereas the N of PMMA blocks varies. Our results demonstrate that the aging speed of the PS blocks can increase by a factor of three to that of the neat PS as the N of PMMA blocks increases. Therefore, the hard confinement accelerates physical aging of the PS blocks, i.e., the relatively soft component in the copolymer.

Construction and carbon dioxide capture of microporous polymer networks with high surface area based on cross-linkable linear polyimides

Microporous polyimide networks with high surface area and excellent CO₂ adsorption performance have been constructed based on cross-linkable linear polyimides through crosslinking reaction.

Temperature Dependence of Gas Permeation and Diffusion in Triptycene-Based Ultrapermeable Polymers of Intrinsic Microporosity

A detailed analysis of the basic transport parameters of two triptycene-based polymers of intrinsic microporosity (PIMs), the ultrapermeable PIM-TMN-Trip and the more selective PIM-BTrip, as a function of temperature from 25 to 55 °C, is reported. For both PIMs, high permeability is based on very high diffusion and solubility coefficients. The contribution of these two factors on the overall permeability is affected by the temperature and depends on the penetrant dimensions. Energetic parameters of permeability, diffusivity, and solubility are calculated using Arrhenius-van't Hoff equations and compared with those of the archetypal PIM-1 and the ultrapermeable, but poorly selective poly(trimethylsilylpropyne). This considers, for the first time, the role of entropic and energetic selectivities in the diffusion process through highly rigid PIMs. This analysis demonstrates that how energetic selectivity dominates the gas-transport properties of the highly rigid triptycene PIMs and enhances the strong size-sieving character of these ultrapermeable polymers.

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).