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[Display omitted] • Amidoxime-functionalized TPE ladder polymer AO-TPE was successfully prepared from TPE-PIM. • Extensive hydrogen bonding led to a large fraction of ultramicroposity in AO-TPE. • CO 2 /N 2 and CO 2 /CH 4 selectivity of fresh AO-TPE nearly doubled compared to the pristine TPE-PIM. • Tightened microstructure in AO-TPE resulted in a strong plasticization resistance. • AO-PIM displayed a CO 2 /CH 4 mixed-gas selectivity of 37.7 with a CO 2 permeability of 36.2 Barrer. Recent advances in solution-processible polymers of intrinsic microporosity (PIM) have attracted extensive research efforts in membrane-based gas separations due to their significantly enhanced gas permeability originating from inefficient chain packing. However, PIM-based membrane materials exhibit typically only moderate gas-pair selectivity, which is often insufficient especially for challenging gas separations containing highly sorbing feed components such as CO 2. More importantly, they suffer from CO 2 -induced polymer chain dilation commonly referred as plasticization, which leads to poor separation performance under aggressive CO 2 /CH 4 mixed-gas testing conditions. In this work, we conducted amidoxime (AO)-functionalization on a microporous tetraphenylethylene-based ladder polymer (TPE-PIM) by reacting its nitrile groups with hydroxyl amine under reflux conditions. Because of strong inter-chain hydrogen bonding, AO-functionalized TPE polymer (AO-TPE) exhibited a tightened and rigidified microstructure with 64 % reduction in Brunauer-Emmett-Teller (BET) surface area (175 m2/g) as compared to TPE-PIM (485 m2/g) derived from N 2 adsorption isotherms at 77 K. As a result, fresh AO-TPE showed decreased gas permeability concurrent with a two-fold increase in CO 2 /CH 4 selectivity (from 18 to 40) compared to TPE-PIM. Under aggressive 50:50 CO 2 :CH 4 mixed-gas testing conditions, AO-TPE showed a strong plasticization resistance with decreased CH 4 permeability over total feed pressure ranging from 4 to 30 bar. At 20 bar total pressure, AO-TPE demonstrated a mixed-gas CO 2 /CH 4 selectivity of 37.7 as compared to 14.5 for TPE-PIM. The simple AO functionalization strategy holds promise to be an effective post-modification method to increase gas selectivity and alleviate the detrimental effects from CO 2 -induced plasticization. [ABSTRACT FROM AUTHOR]

Atomistic simulations were performed to investigate pure- and mixed-gas CO 2 /CH 4 separation properties of a ladder polymer of intrinsic microporosity, PIM-Trip-TB. Despite expected intra-chain rigidity of the polymer, previous experimental reports observed significant loss in CO 2 /CH 4 perm-selectivity under high-pressure mixed-gas conditions. In this work, all-atomistic simulations were applied to accurately predict density, gas uptakes and gas diffusion properties of PIM-Trip-TB. Competitive sorption favoring CO 2 over CH 4 was apparent in mixed-gas sorption simulations, as previously demonstrated by experimental studies from our group. This effect resulted in enhanced mixed-gas CO 2 /CH 4 solubility selectivity. However, this increase did not translate to increased mixed-gas perm-selectivity because a significant increase in CH 4 permeability was observed by co-permeation of CO 2 relative to the pure-gas value. Back-calculated diffusion coefficients indicated very low CO 2 /CH 4 diffusion selectivity under mixed-gas conditions, eliminating any gain from competitive sorption. Structural analysis confirmed intact intra-chain rigidity of the polymer; on the other hand, a significant increase in fractional free volume (FFV) and shift to larger pores in the pore size distribution was revealed by our simulations which may be attributed to polymer dilation due a reduction in inter-chain packing. [Display omitted] • Pure- and mixed-gas CO 2 /CH 4 transport properties of PIM-Trip-TB were modeled accurately. • The effects of competitive sorption and co-permeation under mixed-gas conditions were analyzed. • PIM-Trip-TB preserved its initial intra-chain rigidity under mixed-gas conditions. • CO 2 -induced reduction of inter-chain packing led to loss in mixed-gas CO 2 /CH 4 diffusion- and perm-selectivity. [ABSTRACT FROM AUTHOR]

Hydrogen is an emerging energy source with a wide range of applications in transportation, electricity generation, and manufacturing of important chemicals such as ammonia and methanol. Hydrogen is commonly coproduced with CO 2 using steam reforming of methane and its purification is typically achieved using energy-intensive processes such as pressure swing adsorption (PSA) and cryogenic distillation. Membrane technology with potentially lower energy consumption and lower carbon footprint could play an important role in developing a more sustainable hydrogen economy. In this study, we prepared carbon molecular sieve (CMS) membranes by the pyrolysis of a highly aromatic catalytic arene-norbornene annulation (CANAL)-Tröger's base ladder polymer of intrinsic microporosity precursor — CANAL-TB-1. CMS membranes obtained by pyrolysis between 600 and 900 °C displayed excellent gas separation performance for hydrogen/carbon dioxide separation and related applications. The CANAL-CMS-800 °C membrane showed a pure-gas hydrogen permeability of 41 Barrer with H 2 /CO 2 , H 2 /N 2 , and H 2 /CH 4 selectivity values of 39, 1952, and >8200 at 35 °C. Increasing the pyrolysis temperature to 850 and 900 °C further boosted the selectivity. For example, the CANAL-CMS-900 °C exhibited a stable long-term mixed-gas performance over a period of 38 days with an unprecedented H 2 /CO 2 selectivity of 174 and H 2 permeability of 8.2 Barrer at 10 bar total feed pressure and 100 °C, which significantly exceeded the performance of previously reported polymers and related CMS membrane materials. [Display omitted] • A microporous ladder polymer CANAL-TB-1 was employed as a precursor for CMS membranes fabrication. • CMS membranes pyrolized at high temperatures showed excellent H 2 /CO 2 gas separation performance. • CMS membranes pyrolyzed at 900 °C exhibited pure-gas H 2 /CO 2 selectivity of 248. • CMS membranes showed stable long-term mixed-gas H 2 /CO 2 selectivity of 174 at 10 bar and 100 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ladder PIMs define state-of-the-art polymeric membrane materals for air separation, hydrogen recovery and CO 2 removal applications. • Hydroxyl-functionalized and carboxyl-functionalized ladder PIMs and PIM-PIs. • Physical aging and penetrant-induced plasticization need to be minimized for industrial membrane applications. • PIMs are a new class of precursor materials for ultra-selective carbon molecular sieves. • Polymer scale-up and thin-film membrane formation development are required for commercial utilization. Solution-processible polymers of intrinsic microporosity (PIMs) are appealing materials for membrane applications due to their chemical and structural variety available from a wide range of PIM building blocks and significantly improved gas separation performance compared to conventional low-free-volume glassy polymers. This review highlights recent materials design developments in PIMs including: (i) benzotriptycence-based ladder PIMs, (ii) norbornyl-benzocyclobutene-based PIMs made by catalytic arene-norbornene annulation (CANAL), (iii) high-performance functionalized PIMs (iv) PIM-based thin-film composite membranes, and (v) PIM-based carbon molecular sieve (CMS) membranes. Significant advances in gas separation properties of new generation PIMs have set the recent 2015 H 2 /N 2 , H 2 /CH 4 , and O 2 /N 2 upper bounds, 2018 CO 2 /CH 4 mixed-gas upper bound, and 2019 pure-gas CO 2 /N 2 and CO 2 /CH 4 pure-gas upper bounds. Realizing the full potential of PIMs for future commercial use requires further improvements in (i) gas-pair selectivity, especially for challenging separations, (ii) stability against physical aging and plasticization, (iii) polymer scale-up, and (iv) reproducible membrane fabrication. [ABSTRACT FROM AUTHOR]

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, H 2 , O 2 , N 2 , CO 2 and CH 4 , decreased by 33 %–80 %. Moreover, the selectivity of gas pairs like CO 2 /CH 4 and O 2 /N 2 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. [Display omitted] • Physical aging in PIM-1 was successfully simulated by MD. • Simulated fresh and aged pure-gas transport properties matched experimental data. • Effect of aging on density, d-spacing, FFV, PSD was analyzed. • Aging resulted in more efficient interchain packing without significantly affecting intrachain packing. • Our methodology was extended to other high-free-volume glassy polymers. [ABSTRACT FROM AUTHOR]