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The epithelial permeation of water-soluble fluorescent PAMAM dendrons based on 7H-benz[de] benzimidazo [2,1-a] isoquinoline-7-one as a fluorescent core across epithelial cell models MDCK I and MDCK II has been quantified. Hydrodynamic radii have been derived from self-diffusion coefficients obtained via pulsed-gradient spin-echo Nuclear Magnetic Resonance (PGSE-NMR). Results indicate that these dendritic molecules are molecularly disperse, non-aggregating, and only slightly larger than their parent homologues. MDCK I permeability studies across epithelial barriers show that these dendritic molecules are biocompatible with the chosen epithelial in-vitro model and can permeate across MDCK cell monolayers. Permeability is demonstrated to be a property of dendritic size and cell barrier restrictiveness indicating that paracellular mechanisms play the predominant role in the transport of these molecules., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Polymers of intrinsic microporosity (PIMs), such as the archetypal spirobisindane‐based PIM‐1, are among the most promising new materials for making gas separation membranes with high permeance for potential use in high‐throughput applications. Here it is shown that ultrapermeable PIMs can be prepared by fusing rigid and bulky triptycene (Trip) to the spirobisindane (SBI) unit. PIM‐SBI‐Trip and its copolymer with PIM‐1 (PIM‐1/SBI‐Trip) are both ultrapermeable after methanol treatment (PCO2 > 20 000 Barrer). Old films, although less permeable, are more selective and therefore provide data that are close to the recently redefined Robeson upper bounds for the important CO2/CH4, CO2/N2, and O2/N2 gas pairs. Temperature‐dependent permeation measurements and analysis of the entropic and energetic contributions of the gas transport parameters show that the enhanced performance of these polymers is governed by strong size‐sieving character, mainly due to the energetic term of the diffusivity, and related to their high rigidity. Both polymers show a relatively weak pressure‐dependence in mixed gas permeability experiments up to 6 bar, suggesting a potential use for CO2 capture from flue gas or for the upgrading of biogas. [ABSTRACT FROM AUTHOR]

Abstract: A detailed study of gas permeation, thermodynamic properties and free volume was performed for a novel polymer of intrinsic microporosity (PIM-1). Gas permeability was measured using both gas chromatographic and barometric methods. Sorption of vapors was studied by means of inverse gas chromatography (IGC). In addition, positron annihilation lifetime spectroscopy (PALS) was employed for investigation of free volume in this polymer. An unusual property of PIM-1 is a very strong sensitivity of gas permeability and free volume to the film casting protocol. Contact with water in the process of film preparation resulted in relatively low gas permeability (P(O2)=120Barrer), while soaking with methanol led to a strong increase in gas permeability (P(O2)=1600Barrer) with virtually no evidence of fast aging (decrease in permeability) that is typical for highly permeable polymers. For various gas pairs (O2/N2, CO2/CH4, CO2/N2) the data points on the Robeson diagrams are located above the upper bound lines. Hence, a very attractive combination of permeability and selectivity is observed. IGC indicated that this polymer is distinguished by the largest solubility coefficients among all the polymers so far studied. Free volume of PIM-1 includes relatively large microcavities (R =5Å), and the results of the PALS and IGC methods are in reasonable agreement. [Copyright &y& Elsevier]

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]

Microporous polymer nanosheets with thicknesses in the range 3–5 nm and with high apparent surface area (Brunauer–Emmett–Teller surface area 940 m2 g−1) are formed when the effectively bifunctional (tetrafluoro) monomer used in the preparation of the prototypical polymer of intrinsic microporosity PIM‐1 is replaced with an effectively tetrafunctional (octafluoro) monomer to give a tightly crosslinked network structure. When employed as a filler in mixed‐matrix membranes based on PIM‐1, a low loading of 0.5 wt% network‐PIM‐1 nanosheets gives rise to enhanced CO2 permeability and CO2/CH4 selectivity, compared to pure PIM‐1. [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]

• PIM-1/6FDA-DAM heterogeneous blends with ZIF-8 as filler. • Enhanced filler distribution located near the interphase between polymers. • Mixed matrix membranes for CO 2 /N 2 and CO 2 /CH 4 separation. • Mathematical models to predict the gas separation performance of the membranes. The preparation of mixed matrix membranes (MMMs) for post-combustion CO 2 capture and biogas upgrading from PIM-1 (10–90 wt%)/6FDA-DAM heterogeneous blends with ZIF-8 as filler (3–20 wt% with regard to the polymer blend) is described. The heterogeneity of the blend, considered here as an advantage for the dispersion of the filler within the MMMs, has been confirmed by the existence of a single glass transition temperature, consistent with that of 6FDA-DAM. The segregation between the two polymeric phases and the filler dispersion has been studied by Raman spectroscopy, SEM microscopy and EDX analysis. Increasing the amount of PIM-1 in the blend makes the d-spacing of the polymer chains higher and increases gas permeability. When embedding filler nanoparticles of ZIF-8, a better compatibility with 6FDA-DAM than with PIM-1 is observed. The filler locates near the interphase between polymers helping its dispersion. The use of small loadings of ZIF-8 enhances the gas separation performance of the MMMs in terms of permeability and selectivity for 50/50 CO 2 /CH 4 and 10/90 CO 2 /N 2 mixtures. The best performing membranes are the blends PIM-1/6FDA-DAM 10/90 (w/w) with 10 wt% of ZIF-8, showing a CO 2 permeability of 2891 Barrer, a CO 2 /CH 4 selectivity of 26.6 and 2802 Barrer of CO 2 with a CO 2 /N 2 selectivity of 18.1. Importantly, the CO 2 , N 2 and CH 4 permeabilities of the pure polymeric blends can be predicted using both the logarithmic and the Maxwell models. A new coupled Maxwell model has also been developed able to calculate the flow through the blends containing ZIF-8 and to predict the gas separation properties of the filler itself. [ABSTRACT FROM AUTHOR]

The initially very promising transport properties of glassy high free volume polymers deteriorate rapidly over time. In this work, we focused on this aging phenomenon in two polymers of intrinsic microporosity (PIMs), namely PIM-1 and PIM-EA-TB. To identify the main mechanisms involved, we studied the time-declines of permeability and diffusivity of methanol vapours in flat membranes with approximately equal thicknesses. The permeation measurements were carried out using a continuous flow permeation method with carrier gas, where the methanol vapours were held at constant activity 0.2 at 25 °C. Two different experimental modes were used: (i) continuous experiments that consisted of one long experiment with a duration of over 650 h for each polymer and (ii) momentary experiments that consisted of a vast number of short ( ca. 6 h) consecutive measurements of transient permeation. The observed decreases of methanol permeability due to aging were more intense in the case of continuous mode for both polymers. In other words, the aging was ca. 1.3 times faster in the continuous mode in comparison with the momentary mode. Using time-aging time superposition, we successfully predicted the continuous experiments from the momentary experiments. [ABSTRACT FROM AUTHOR]

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]

Abstract: Atomistic packing models have been built for PIM-1, a polymer belonging to a recently developed new type of “polymers of intrinsic microporosity” (PIMs). The molecular structure of PIM-1 contains sites of contortion (spiro-centres) within a rigid ladder polymer structure. Nitrogen sorption experiments have shown that the polymer, which traps in the glassy state a large amount of interconnected free volume, behaves in many respects like a microporous material. The models obtained by force field-based molecular mechanics and molecular dynamic methods allow a prediction of permeation properties of small gasses, the calculation of N2-sorption isotherms at 77K, and a determination of free volume distributions. The Gusev–Suter transition state theory (TST) was used to calculate gas solubility and diffusion coefficients for He, H2, Ar, O2, N2, CH4, and Xe. Good agreement with experimental data (factors 1–4) was found. The calculated nitrogen adsorption isotherm at 77K shows properties typical for sorption on microporous materials. The obtained microporous volume is in good agreement with the respective experimental value. The size distribution function of free volume elements derived from the models agrees well in its range of pore width of 5–15Å with results obtained from experimental sorption data and analyzed with the Horvath-Kawazoe method. Dihedral angle distributions in the backbone reveal a certain, unexpected flexibility of plane segments between the spiro-centres which act as connecting links. [Copyright &y& Elsevier]

Abstract: When polymeric membranes are employed to remove selectively one component from a gaseous mixture, there is generally a trade-off between selectivity and permeability. Data are presented for two polymers of intrinsic microporosity, PIM-1 and PIM-7, which show a significant advance across the previous upper bound of performance for commercially important gas pairs, including O2/N2 and CO2/CH4. The exceptional properties of PIMs arise from their rigid but contorted molecular structures, which frustrate packing and so create free volume, coupled with chemical functionality giving strong intermolecular interactions. [Copyright &y& Elsevier]

Polymer-based membranes have the potential for use in energy efficient gas separations. The successful exploitation of new materials requires accurate knowledge of the transport properties of all gases of interest. Open-source databases of gas permeabilities are of significant potential benefit to the research community. The Membrane Society of Australasia (https://membrane-australasia.org/) hosts a database for experimentally measured and reported polymer gas permeabilities. However, the database is incomplete, limiting its potential use as a research tool. Here, missing values in the database were imputed (filled) using machine learning (ML). The ML model was validated against gas permeability measurements that were not recorded in the database. Through imputing the missing data, it is possible to re-analyse historical polymers and look for potential "missed" candidates with promising gas selectivity. In addition, for systems with limited experimental data, ML using sparse features was performed, and we suggest that once the permeability of CO 2 and/or O 2 for a polymer has been measured, most other gas permeabilities and selectivities, including those for CO 2 /CH 4 and CO 2 /N 2 , can be quantitatively estimated. This early insight into the gas permeability of a new system can be used at an initial stage of experimental measurements to rapidly identify polymer membranes worth further investigation. [Display omitted] • The Polymer Gas Separation Membrane Database was imputed with machine learning. • The machine learning model is robust against different experiment conditions. • Gas permeability data not recorded in the database can be accurately predicted. • Data driven insight can be obtained to rapidly identify gas selective polymers. [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]