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The synthesis and characterization of a novel film‐forming organic cage and of its smaller analogue are here described. While the small cage produced single crystals suitable for X‐ray diffraction studies, the large one was isolated as a dense film. Due to its remarkable film‐forming properties, this latter cage could be solution processed into transparent thin‐layer films and mechanically stable dense self‐standing membranes of controllable thickness. Thanks to these peculiar features, the membranes were also successfully tested for gas permeation, reporting a behavior similar to that found with stiff glassy polymers such as polymers of intrinsic microporosity or polyimides. Given the growing interest in the development of molecular‐based membranes, for example for separation technologies and functional coatings, the properties of this organic cage were investigated by thorough analysis of their structural, thermal, mechanical and gas transport properties, and by detailed atomistic simulations. [ABSTRACT FROM AUTHOR]

Cover Feature: Gas Permeation through Mechanically Resistant Self-Standing Membranes of a Neat Amorphous Organic Cage (Chem. Eur. J. 56/2023) Keywords: gas transport; membranes; molecular materials; organic cages; thin films EN gas transport membranes molecular materials organic cages thin films 1 1 1 10/12/23 20231009 NES 231009 B Gas separation b : A novel organic cage with excellent film-forming tendencies was processed into transparent, mechanically robust, self-standing membranes of controllable thickness. Gas transport, membranes, molecular materials, organic cages, thin films. [Extracted from the article]

Global warming by greenhouse gas emissions is one of the main threats of our modern society, and efficient CO2 capture processes are needed to solve this problem. Membrane separation processes have been identified among the most promising technologies for CO2 capture, and these require the development of highly efficient membrane materials which, in turn, requires detailed understanding of their operation mechanism. In the last decades, molecular modeling studies have become an extremely powerful tool to understand and anticipate the gas transport properties of polymeric membranes. This work presents a study on the correlation of the structural features of different membrane materials, analyzed by means of molecular dynamics simulation, and their gas diffusivity/selectivity. We propose a simplified method to determine the void size distribution via an automatic image recognition tool, along with a consolidated Connolly probe sensing of space, without the need of demanding computational procedures. Based on a picture of the void shape and width, automatic image recognition tests the dimensions of the void elements, reducing them to ellipses. Comparison of the minor axis of the obtained ellipses with the diameters of the gases yields a qualitative estimation of non-accessible paths in the geometrical arrangement of polymeric chains. A second tool, the Connolly probe sensing of space, gives more details on the complexity of voids. The combination of the two proposed tools can be used for a qualitative and rapid screening of material models and for an estimation of the trend in their diffusivity selectivity. The main differences in the structural features of three different classes of polymers are investigated in this work (glassy polymers, superglassy perfluoropolymers and high free volume polymers of intrinsic microporosity), and the results show how the proposed computationally less demanding analysis can be linked with their selectivities. [ABSTRACT FROM AUTHOR]

A detailed comparison of the gas permeability of four Polymers of Intrinsic Microporosity containing Tröger's base (TB-PIMs) is reported. In particular, we present the results of a systematic study of the differences between four related polymers, highlighting the importance of the role of methyl groups positioned at the bridgehead of ethanoanthracene (EA) and triptycene (Trip) components. The PIMs show BET surface areas between 845–1028 m2 g−1 and complete solubility in chloroform, which allowed for the casting of robust films that provided excellent permselectivities for O2/N2, CO2/N2, CO2/CH4 and H2/CH4 gas pairs so that some data surpass the 2008 Robeson upper bounds. Their interesting gas transport properties were mostly ascribed to a combination of high permeability and very strong size-selectivity of the polymers. Time lag measurements and determination of the gas diffusion coefficient of all polymers revealed that physical ageing strongly increased the size-selectivity, making them suitable for the preparation of thin film composite membranes. [ABSTRACT FROM AUTHOR]

The effect on the gas transport properties of Matrimid®5218 of blending with the polymer of intrinsic microporosity PIM-EA(H2)-TB was studied by pure and mixed gas permeation measurements. Membranes of the two neat polymers and their 50/50 wt % blend were prepared by solution casting from a dilute solution in dichloromethane. The pure gas permeability and diffusion coefficients of H2, He, O2, N2, CO2 and CH4 were determined by the time lag method in a traditional fixed volume gas permeation setup. Mixed gas permeability measurements with a 35/65 vol % CO2/CH4 mixture and a 15/85 vol % CO2/N2 mixture were performed on a novel variable volume setup with on-line mass spectrometric analysis of the permeate composition, with the unique feature that it is also able to determine the mixed gas diffusion coefficients. It was found that the permeability of Matrimid increased approximately 20-fold with the addition of 50 wt % PIM-EA(H2)-TB. Mixed gas permeation measurements showed a slightly stronger pressure dependence for selectivity of separation of the CO2/CH4 mixture as compared to the CO2/N2 mixture, particularly for both the blended membrane and the pure PIM. The mixed gas selectivity was slightly higher than for pure gases, and although N2 and CH4 diffusion coefficients strongly increase in the presence of CO2, their solubility is dramatically reduced as a result of competitive sorption. A full analysis is provided of the difference between the pure and mixed gas transport parameters of PIM-EA(H2)-TB, Matrimid®5218 and their 50:50 wt % blend, including unique mixed gas diffusion coefficients. [ABSTRACT FROM AUTHOR]

The gas transport properties of mixed matrix membranes (MMMs), prepared by dispersing nanoparticles of MOFs MIL-101(Cr) or MIL-177(Ti) into highly permeable Polymers of Intrinsic Microporosity PIM-EA-TB or PIM-TMN-Trip, were investigated. The homogeneity of the dispersion was confirmed by means of Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray (EDX) mapping analysis. Single gas time-lag measurements provided the permeability and ideal selectivity of different gas pairs, both after treatment of the MMMs with methanol and after natural aging over an extended period (up to 2000 days). This data demonstrated that the gas size-sieving pores of MIL-101(Cr) and MIL-177(Ti) and their good dispersion into the PIM matrix results in MMMs with enhanced gas separation performance, as compared to films composed solely of the polymer. The comparison of actual permeability with the Maxwell model for PIM-EA-TB with both MOFs confirmed the good dispersion and the absence of anomalies, whereas the inconsistency of permeability with prediction data for PIM-TMN-Trip suggests that the MOFs improved the polymer properties, stiffening or occupying the polymer free volume. In particular, the incorporation of MIL-101(Cr) into PIM-EA-TB significantly enhances the H 2 permeability from ∼6000 to 13,000 Barrer, with a concurrent increase of the H 2 /N 2 selectivity from 14 to 21. MIL-177(Ti) also enhances the H 2 /N 2 selectivity to 20 due to a slight reduction of the N 2 permeability. The addition of MIL-101(Cr) and MIL-177(Ti) into the ultra-permeable PIM-TMN-Trip showed more modest increases in H 2 permeability and H 2 /N 2 selectivity from 4.6 to ∼ 10. Hence the data for some of the MMMs surpass the 2008, and even approach the 2015/2019 Robeson's upper bounds, particularly for gas pairs including H 2. [Display omitted] • The MIL-101(Cr) and MIL-177(Ti) were loaded into PIM-EA-TB or PIM-TMN-Trip for fabrication of MMMs. • Smaller MIL-101 particle-size favour better compatibility with polymers than larger MIL-177. • Mixed gas experiments confirm an excellent separation performance under a long aging. • Data for some MMMs break the 2008 upper approaching the 2015/2019 Robeson's upper bounds. [ABSTRACT FROM AUTHOR]

Abstract An understanding of gas transport in polymers of intrinsic microporosity (PIMs) is limited by a lack of directly determined (experimental) sorption data and by quantitative inaccuracies in solubilities calculated indirectly from permeation time-lag analysis. To address this, we provide a detailed gas sorption analysis for seven different PIMs and assess the influence of the non-linear steady-state CO 2 concentration profiles on the apparent solubilities obtained from permeation experiments. Equilibrium sorption was analyzed with dual-mode sorption (DMS) and Guggenheim, Anderson and De Boer (GAB) models, which provided accurate descriptions of the data. The non-linear steady-state CO 2 concentration profiles were calculated using the thermodynamic Fick's law based on the DMS or GAB model coefficients. Once the thermodynamic term was incorporated into the model for permeation, better agreement between directly (gravimetric sorption) and indirectly (time-lag analysis) determined solubility was observed for most membranes. The monolayer capacities were found to be linearly dependent between the models and could be used for a qualitative comparison of the apparent surface area of PIM materials. Diffusivities determined from time-lag analysis were higher (e.g., PIM-Trip-TB, CO 2 , 111·10−8 m2 s−1) than those from sorption measurements (24·10−8 m2 s−1), probably due to substantially low mass uptake in Henry mode (11% of total sorption capacity). Thus, a careful gas sorption analysis in combination with time lag experiments provides a deeper insight into the transport behavior of gases in PIMs than when only time lag measurements are performed. Graphical abstract fx1 Highlights • Sorption of gases in seven polymers of intrinsic microporosity. • CO 2 solubility from time-lag analysis is overestimated in most of the PIMs. • Thermodynamic Fick's law allows for the correction of the solubility. • Apparent surface areas based on DMS, GAB and BET models are comparable and highly correlated. [ABSTRACT FROM AUTHOR]

Polymers of intrinsic microporosity (PIMs) are among the most promising candidates for the development of novel polymeric gas separation membranes for processes such as carbon capture and storage, natural gas treatment and biogas upgrading. As one of the approaches to optimize their performance, PIMs are functionalized by CO 2 -philic groups to improve the CO 2 separation by the enhancement of specific noncovalent interactions. In this work, we show the preparation of amine-PIM from the archetypal PIM-1, using borane dimethyl sulphide complexes in order to control the degree of conversion. The PIM-1 to amine-PIM-1 conversion was characterized by ATR-IR and NMR analysis. The influence of the amine moiety on the gas transport behaviour was investigated by two complementary techniques: gas permeation measurements by the time lag method and analysis of the sorption kinetics and the equilibrium sorption isotherms by the gravimetric method. Both techniques show that permeability decreases with increasing degree of conversion. The trends in the indirectly calculated solubility confirm those of direct analysis, although quantitative comparison of the two shows fundamental differences. A pressure and temperature study on a fully converted sample indicates that the solution-diffusion model should be expressed in concentration dependent transport parameters to be correct. The experimental work was supported by quantum mechanics studies and by molecular dynamics simulations to confirm the selective non-covalent interaction of CO 2 with the amino groups. [ABSTRACT FROM AUTHOR]

This work presents a study of the gas transport properties for a novel class of mixed matrix membranes (MMMs) based on the polymer of intrinsic microporosity PIM-1 loaded with UiO-66 [Zr 6 O 4 (OH) 4 (O 2 CC 6 H 4 CO 2 ) 6 ] based metal-organic frameworks (MOFs). Three isoreticular MOFs were dispersed in the polymer matrix, standard UiO-66, UiO-66-NH 2 (functionalized with an amino group) and UiO-66-(COOH) 2 (functionalized with two carboxylic groups), in order to investigate the effect of the functionalization of the linker on the gas transport. The pure gas permeabilities of He, H 2 , O 2 , N 2 , CH 4 , CO 2 were studied, for the as prepared membranes and after methanol treatment, focusing attention on the potential use of these membranes for CO 2 /CH 4 separation. The pure gas transport of the MMMs was described on the basis of the Maxwell model. The predictions of the model are discussed and compared with the experimental permeability and selectivity of the MMMs and neat PIM-1. Mixed gas permeation tests were performed on a representative sample to investigate the actual separation performance with industrially relevant gas mixtures. These confirmed the good perspectives of these MMMs in applications like CO 2 removal from biogas or from flue gas. [ABSTRACT FROM AUTHOR]

A series of four novel Tröger's base (TB) derived polyimides of intrinsic microporosity (PIM-TB-PI) is reported. The TB diamine monomer (4MTBDA) possesses four methyl groups in order to restrict rotation about the C-N imide bonds in the resulting polymers. The polymers possess apparent BET (Brunauer, Emmett, and Teller) surface areas between 584 and 739 m² g-1, complete solubility in chloroform, excellent molecular mass, high inherent viscosity and good film-forming properties. Gas permeability measurements demonstrate enhanced performance over previously reported polyimide-based Tröger's base (TB) polymers confirming the benefit of the additional methyl groups within the TB diamine monomer. Notably, a polyimide derived from 4MTBDA and pyromellitic anhydride (PMDA) demonstrates gas permeability data above the 2008 upper bounds for important gas pairs such as O2/N2, H2/N2, and H2/CH4. [ABSTRACT FROM AUTHOR]

Polymersof intrinsic microporosity (PIMs) are receiving increasing attentionfrom the membrane community because of their high gas and vapor permeability.Recently a novel ethanoanthracene-based PIM synthesized by Tröger’sbase formation (PIM-EA-TB) was reported to have exceptional transportproperties, behaving as a polymer molecular sieve membrane. In thepresent work, an extensive investigation of the structural, mechanical,and transport properties of this polymer, both by experimental analysisand by molecular simulation, offers deep insight into the behaviorof this polymer and gives an explanation for its remarkable performanceas a membrane material. Transport properties were determined by thebarometric time-lag method, by the volumetric method with gas chromatographicor mass spectrometric gas analysis, and by gravimetric sorption measurements,yielding all basic transport parameters, permeability (P), diffusivity (D), and solubility (S). Upon alcohol treatment, PIM-EA-TB exhibited a much stronger permeabilityincrease than archetypal “benchmark” polymer PIM-1,with performance above the Robeson upper bound for several gas pairs.This is in part due to an extremely high gas solubility in PIM-EA-TB,higher than in PIM-1. The experimental data were supported by extensivemodeling studies of the polymer structure and the spatial arrangementof its free volume. Modeling confirms that the high gas permeabilitymust be attributed to the large fractional free volume of the polymer.The simulated free volume size distribution in PIM-EA-TB is in agreementwith the average experimental free volume elements size determinedby PALS and 129Xe NMR analysis. The modeled spatial arrangementof the free volume revealed a slightly lower interconnectivity ofthe FV elements in PIM-EA-TB compared to PIM-1. Along with its higherchain rigidity, determined by analysis of the torsion angles in thepolymer model, this was identified as the main reason for its strongersize sieving behavior and relatively high permselectivity. A numberof peculiarities in the behavior of PIMs will also be discussed here,explaining discrepancies between results published in the literatureby different laboratories, the effect of their thermomechanical history,aging, or conditioning, and the influence of the measurement techniqueand of the experimental conditions on the results. This makes thisstudy of inestimable value for unifying the results of different experimentaltechniques and fully understanding the transport properties. [ABSTRACT FROM AUTHOR]

Nitrile groups in the polymer ofintrinsic microporosity PIM-1were reduced to primary amines using borane complexes. In adsorptionexperiments, the novel amine–PIM-1 showed higher CO2uptake and higher CO2/N2sorption selectivitythan the parent polymer, with very evident dual-mode sorption behavior.In gas permeation with six light gases, the individual contributionsof solubility and diffusion to the overall permeability was determinedvia time-lag analysis. The high CO2affinity drasticallyrestricts diffusion at low pressures and lowers CO2permeabilitycompared to the parent PIM-1. Furthermore, the size-sieving propertiesof the polymer are increased, which can be attributed to a higherstiffness of the system arising from hydrogen bonding of the aminegroups. Thus, for the H2/CO2gas pair, whereasPIM-1 favors CO2, amine–PIM-1 shows permselectivitytoward H2, breaking the Robeson 2008 upper bound. [ABSTRACT FROM AUTHOR]

Abstract: The gravimetric sorption technique was used for the study of equilibrium and transient sorption of various groups of vapours (alcohols, hydrocarbons, water) and gases (methane, nitrogen, oxygen, carbon dioxide) in the polymer of intrinsic microporosity PIM-1 at 25°C. Sorption isotherms of all compounds, except gases and water, exhibited S-shaped character, while the isotherms of gases are linear or concave over the inspected pressure region. Sorption isotherms of vapours were quantitatively parameterized with the Guggenheim, Anderson and de Boer (GAB) layered-adsorption model, which provided a comparable approximation of the data on carbon dioxide as the dual mode sorption model. Abnormally fast kinetics of transient sorption (superdiffusion) was observed in the region of diluted and saturated vapours of all measured compounds, except water, n-butane and carbon dioxide. The anomalous sorption kinetics was well parameterized with the convective–diffusion model. The anomalous nature of the mass transport in PIM-1 is also demonstrated by distinct trends for gases, alkanes and alcohol vapours in the correlations of diffusion coefficients with penetrant molecular volume and solubility coefficients with the square of critical temperature. The results obtained in this work indicate the occurrence of a transport mode that has a different nature than the classically employed solution-diffusion model. [Copyright &y& Elsevier]

Microporous polymers of extreme rigidity are required for gas-separation membranes that combine high permeability with selectivity. We report a shape-persistent ladder polymer consisting of benzene rings fused together by inflexible bridged bicyclic units. The polymer's contorted shape ensures both microporosity--with an internal surface area greater than 1000 square meters per gram--and solubility so that it is readily cast from solution into robust films. These films demonstrate exceptional performance as molecular sieves with high gas permeabilities and good selectivities for smaller gas molecules, such as hydrogen and oxygen, over larger molecules, such as nitrogen and methane. Hence, this polymer has excellent potential for making membranes suitable for large-scale gas separations of commercial and environmental relevance. [ABSTRACT FROM AUTHOR]

The potential of an ultrapermeable benzotriptycene-based polymer of intrinsic microporosity (PIM-TMN-Trip) for the upgrading of biogas is investigated. Permeation experiments were performed using an in-house bespoke permeation unit for pure gases and gas mixtures, and included tests with model mixtures as well as real biogas from a sewage treatment plant, under dry and humid conditions. Permeability and CO 2 /CH 4 selectivity for either pure gases or for real biogas were high and lie close to or on the recently defined 2019 Robeson upper bound based on ideal permselectivities. In addition, a remarkable increase in CO 2 /CH 4 selectivity was observed after two weeks of continuous exposure to CO 2 due to a significant decrease of CH 4 permeability. The constant CO 2 permeability and increased selectivity upon ageing suggest that ageing in the presence of CO 2 causes a rearrangement, rather than a reduction of the fractional free volume. The mixed gas permeability experiments were performed with high stage-cut in order to mimic a real separation process, and the results confirmed the potential of PIM-TMN-Trip membranes for biogas upgrading. Image 1 • PIM-TMN-Trip membrane can excellently separate biogas at small pressure difference. • Model binary mixture represents very well the behaviour of real biogas. • Increasing upstream pressure causes the decrease of mixed gas selectivity. • Pristine membrane had an ideal CO 2 /CH 4 selectivity of about 15. • CO 2 treatment strongly enhances the ideal CO 2 /CH 4 selectivity up to 39. [ABSTRACT FROM AUTHOR]

This manuscript describes the gas separation performance of PIM-2, a partially fluorinated linear copolymer synthesized from 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethylspirobisindane (TTSBI) and decafluorobiphenyl (DFBP). As one of the early members of the family of polymers of intrinsic microporosity, it had never been tested as a gas separation membrane because of insufficient mechanical resistance. This has been solved only recently, allowing the preparation of robust self-standing films. Molecular modelling studies demonstrated a high fractional free volume (34%) and an elevated surface area (642 m2 g−1), and the latter is in good agreement with experimental BET results. Pure gas permeabilities measured on a fixed-volume time-lag instrument at 1 bar compare well with the results of mixed separation tests on a variable volume setup from 1-6 bar(a). Molecular modelling and independent sorption measurements on a gravimetric sorption balance both show strong dual-mode sorption behaviour, especially for CO 2 and to a lesser extent for CH 4. Temperature-dependent pure gas permeation measurements show typical Arrhenius behaviour, with a clear increase in the activation energy for diffusion with the increasing molecular size of the gas, indicating high size-selectivity. This is in agreement with the highly rigid PIM structure, determined by AFM force spectroscopy measurements. The dual-mode behaviour results in a moderate pressure dependence of the CO 2 permeability and the CO 2 /N 2 and CO 2 /CH 4 selectivity, all slightly decreasing with increasing pressure. The presence of humidity in the gas stream has a remarkable small effect on the membrane performance, which is probably due to the high fluorine content and the consequently low water vapour solubility in the polymer, as confirmed by gravimetric sorption measurements. The manuscript describes an extensive study on the structure-property relationships in PIM-2. Image 1 • Fluorinated PIM-2 forms robust self-standing membranes. • CO 2 /N 2 and CO 2 /CH 4 mixed gas separation data lie close to the 2008 upper bound. • Separation performance is hardly affected by the presence of humidity in the feed gas. • Water sorption is very low due to the hydrophobic nature of the fluoropolymer. • MD simulations show how halogen bond networks enhance the energetic diffusion selectivity. [ABSTRACT FROM AUTHOR]