This paper reports a new macromolecular design that incorporates hierarchical triptycene unit into thermally rearranged polybenzoxazole (TR-PBO) structures for highly selective and permeable gas separation membranes with great potential for H 2 purification and CO 2 removal from natural gas. We demonstrate that triptycene moieties not only effectively disrupt chain packing enabling microporous structure for fast mass transport, but also introduce ultrafine microporosity via the unique internal free volume intrinsic to triptycene unit that allows for superior molecular sieving capability in resulting PBO membranes. Consequently, these triptycene-based polybenzoxazole (TPBO) membranes display among the highest gas selectivities for H 2 separations (i.e., α(H 2 /N 2 ) = 96; α(H 2 /CH 4 ) = 203) and CO 2 removal from natural gas (i.e., α(CO 2 /CH 4 ) = 68) among existing glassy polymeric membranes. It is also demonstrated that microporous structure and gas transport properties of TPBO films are highly tailorable by adjusting the triptycene content and the ortho-functionality of the precursors. The highly diverse tunability, along with the excellent resistance toward membrane plasticization and physical aging, render the TPBO membranes with extremely versatile separation capability applicable for a wide range of important industrial processes to get clean or low carbon fuels and reduce carbon footprint.

Poly(ethylene oxide) (PEO)-containing polymer membranes are attractive for CO2-related gas separations due to their high selectivity toward CO2. However, the development of PEO-rich membranes is frequently challenged by weak mechanical properties and a high crystallization tendency of PEO that hinders gas transport. Here we report a new series of highly CO2-selective, amorphous PEO-containing segmented copolymers prepared from commercial Jeffamine polyetheramines and pentiptycene-based polyimide. The copolymers are much more mechanically robust than the nonpentiptycene containing counterparts due to the molecular reinforcement mechanism of supramolecular chain threading and interlocking interactions induced by the pentiptycene structures, which also effectively suppresses PEO crystallization leading to a completely amorphous structure even at 60% PEO weight content. Membrane transport properties are sensitively affected by both PEO weight content and PEO chain length. A nonlinear correlation between CO2 permeability with PEO weight content was observed due to the competition between solubility and diffusivity contributions, whereby the copolymers change from being size-selective to solubility-selective when PEO content reaches 40%. CO2 selectivities over H2 and N2 increase monotonically with both PEO content and chain length, indicating strong CO2-philicity of the copolymers. The copolymer film with the longest PEO sequence (PEO2000) and highest PEO weight content (60%) showed a measured CO2 pure gas permeability of 39 Barrer, and ideal CO2/H2 and CO2/N2 selectivities of 4.1 and 46, respectively, at 35 °C and 3 atm, making them attractive for hydrogen purification and carbon capture.

Pentiptycene-based polyimides with Hierarchically controlled molecular cavity architecture for efficient membrane Gas separation, Journal of Membrane Science, http://dx. ABSTRACT:A series of new pentiptycene-containing diamines with systematically varied substituent groups were designed and synthesized with high purity and high yields. These diamines were used to prepare a series of new polyimides with 4,4'-hexafluoroisopropylidene bisphthalic dianhydride (6FDA) by conventional condensation polymerization. The obtained pentiptycene-containing polyimides possessed high molecule weights, excellent thermal stability, good solubility in a wide range of organic solvents and thus excellent processability for membrane fabrication. Because of the excess amount of internal free volume associated with the molecular cavities in the pentiptycene moieties and the consequently disrupted chain packing, all the polyimides exhibited high fractional free volume (FFV) leading to high gas permeabilities as well as good selectivities that are highly desired for gas separation membranes. In addition, the comparisons between the pentiptycene-containing polyimides bearing various substituent groups indicated that free volume, the vital structural parameter for fast and selective molecular transport, was very sensitive to the size of the substituent groups. Large substituent groups such as CF 3 led to increased FFV, while relatively small substituent groups such as CH 3 resulted in reduced FFV, possibly due to the mechanism of "partial filling" of the molecular cavities of pentiptycene units by the substituent groups. Gas permeability data also supported this unusual trend of the dependence of free volume on the substituent groups. This finding provides a completely new and potentially novel means of molecular-level manipulations to predictably construct preferred free volume architecture that may 2 maximize the separation performance of polymeric membranes. Keywords： ： ： ：pentiptycene, polyimides, free volume, gas separation membrane Highlights • Robust and highly soluble pentiptycene-based polyimides were synthesized • Pentiptycene-based polyimide membranes showed high fractional free volume • Architecture of the molecular cavities was finely tuned by substituent groups• "Partial filling" mechanism was proposed based on free volume studies• Pentiptycene-based polyimides show high permeability and high selectivity

Cellulose triacetate (CTA) is a workhorse polymeric membrane material for industrial CO 2 /CH 4 separation. This study investigates the doping of CTA with ionic liquids (ILs) to reduce the crystallinity of the CTA and enhance its affinity with CO 2 , thus increasing CO 2 permeability and CO 2 /light gas selectivity. CTA films doped with 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF 4 ]) and 1-ethyl-3-methylimidazolium dicyanamide ([emim][dca]) were prepared; and the effect of IL loading on properties of the CTA, such as crystallinity, density, degradation temperature, glass transition temperature, and gas transport properties, were determined. The IL doping reduces the glass transition temperature and degree of crystallinity of CTA, increasing gas diffusivity and permeability. The IL doping also increases CO 2 /CH 4 solubility selectivity and CO 2 /N 2 permeability selectivity, due to the affinity of these ILs with CO 2 , compared to light gases such as CH 4 and N 2. This study demonstrates a promising route in manipulating the morphology and gas transport properties of semi-crystalline polymers by doping with ILs.

Iptycene-based polyimides have attracted extensive attention recently in the membrane gas separation field due to their unique structural hierarchy and chemical characteristics that enable construction of well-defined yet tailorable free volume architecture for fast and selective molecular transport. We report here a new series of iptycene-based polyimides that are exquisitely tuned in the monomer structure to afford preferred microcavity architecture for hydrogen transport. In particular, a triptycene-containing dianhydride (TPDAn) was prepared to react with two iptycene-containing diamines (i.e., TPDAm and PPDAm) or 2,2′-bis­(3-amino-4-hydroxy­phenyl)­hexa­fluoropropane (6FAP) to produce entirely or partially iptycene-based polyimides. The incorporation of iptycene units effectively disrupted chain packing, which resulted in ultrafine microporosity in the membranes with a desired bimodal size distribution with maxima at ∼3 and ∼7 Å, respectively. Depending on the combination of diamine and dianhydride, the microporosity was feasibly tuned and optimized to meet the needs of challenging H2 separations, especially for H2/N2 and H2/CH4 gas pairs. Particularly, a H2 permeability of 27 barrers and H2/N2 and H2/CH4 selectivities of 142 and 300, respectively, were obtained for TPDAn-6FAP.