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Microporous polyimides (MPIs) have been acted a significant role in porous organic polymers (POPs) for gas capture and separation. However, the MPIs are mostly constructed from monomers with rigid 3D or twisted structures or hyperbranched precursors, and their porous structure is mainly tuned by changing the length of the constructed units. Herein, the cross-linkable linear PIs with flexible skeletons are selected as precursors to construct the cross-linked microporous polyimides (C-MPIs). The method has significant comparative advantages including abundant monomers, the convenience of synthesis, cost-effectiveness, structural diversity and designability. Moreover, the micropore size of the C-MPIs (6FA-PE-CL, 6FA-PEPH-CL) can be tuned from 0.64 nm to 0.57 nm through the side-chain engineering of the cross-linkable linear PI precursors. The BET surface area of the C-MPIs are ranging from 635 to 698 m2g-1 and is among the best results for the reported linear MPIs. The smaller pore size (0.57 nm), higher micropore surface area (378 m2g-1) and micropore volume (0.17 cm3g-1) endow 6FA-PE-CL with better CO 2 selective uptake capacity (8.9 wt% and 58) than those of 6FA-PEPH-CL (7.3 wt% and 38). This work provides a side-chain engineering method to tune the pore structure of MPIs, which has tremendous potential for constructing high-performance polymer networks with abundant ultramicroporous structure (<0.7 nm) based on flexible linear polymers. Microporous polymer networks with tunable micropore sizes have been constructed through the side-chain engineering of cross-linkable linear polyimide precursors. [Display omitted] • The microporous polymer networks with abundant ultramicropores were constructed from flexible linear polyimides. • The pore size can be finely tuned through the side-chain engineering method. • The microporous polyimide with a smaller pore size exhibits better CO 2 selective uptake capacity. [ABSTRACT FROM AUTHOR]

In recent years, building microporous polyimides (MPIs) via choosing simple commercial aromatic monomers or concise experimental methods is still an issue worthy to explore. Herein, two cross-linkable aromatic alkynyl monomers (TAPM-PEPA and TAPA-PEPA) were prepared from a commercial alkynyl anhydride PEPA and two aromatic multi-amine TAPM (3D-tetrahedron) and TAPA (near 2D-planar) monomers with different topological structures. The crosslinked polyimides were prepared and endowed microporous features via one-pot thermal crosslinking polymerization in the diphenyl sulfone. The TAPM-PEPA-CL has higher BET surface area and total pore volume (736 m2 g-1 and 0.497 cm3 g-1) than those of the TAPA-PEPA-CL (351 m2 g-1 and 0.358 cm3 g-1). As the topological structure becomes more stereoscopic, CO2 adsorption capacity has been significantly improved from 9.6 wt% to 13.5 wt%. Furthermore, the TAPM-PEPA-CL and TAPA-PEPA-CL have excellent selectivity for CO 2 /CH 4 (12.0–23.6) and CO 2 /N 2 selectivity (54.4–57.6) at 273 K and 1 bar. These results reveal that the introduction of crosslinked structures and control of topological structures have potential application significance for preparing microporous polyimides based on cross-linkable aromatic alkynyl monomers, which is beneficial for the development of the field of gas adsorption and selectivity. [Display omitted] • The crosslinked microporous polyimides were successfully prepared via commercial one-pot thermal crosslinking polymerization. • The porous performance can be tuned by changing topological structures of the precursors. • The crosslinked polyimides show favorable CO 2 adsorption (9.6–13.5 wt%) as well as excellent selectivity for CO 2 /CH 4 (12.0–23.6) and CO 2 /N 2 selectivities (54.4–57.6) at 273 K and 1 bar. [ABSTRACT FROM AUTHOR]

In recent years, linear polyimides of intrinsic microporosity have been widely used in the field of gas adsorption and separation because of their high BET surface area and microporous structures. Most of the microporous structures come from the twisted main-chain structures in the linear polyimides of intrinsic microporosity. Therefore, most linear polyimides (PI) without twisted structure have no porosity. Herein, to construct the linear polyimide with microporous structure, a sequence of microporous polyimides (PIs-CL) were constructed from the flexible linear polyimide precursors through the thermal crosslinking reaction. The polyimide precursors without twisted structure were synthesized from a well-designed diamine TFVBPA with cross-linkable ethynyl groups and several commercial dianhydrides (ODPA, BPDA, PMDA and 6FDA) by polycondensation to research the influence of the main-chain structure on the porous characters. The introduction of crosslinked structures gives the linear crosslinked polyimides (PIs-CL) with porous structures. The PIs-CL show obviously improved porosity (0.52–1.71 nm) and higher BET surface area (337–618 m2 g−1) than those of the uncrosslinked polyimides (PIs). Moreover, PIs-CL have favorable CO 2 adsorption (5.7–9.3 wt%) as well as good CO 2 /N 2 selectivity (34.4–58.5) at 273 K, which are better than other polyimides materials. The introduction of crosslinked structures is an effective way to improve microporous porosity and gas sorption performance. Image 1 • The PIs-CL were successfully prepared via polycondensation and thermal crosslinking reaction. • The porous performance can be tuned by inducting crosslinked structure and changing main-chain structures. • The PIs-CL show excellent pore size (0.52–1.71 nm) and favorable CO 2 adsorption (5.7–9.3 wt%) at 273 K. [ABSTRACT FROM AUTHOR]

The precise control of porous structure has always been a key factor for porous materials. We tuned the porous structures by enhancing alkynyl-groups contents and introducing metal into porphyrin ring. We used simple polymerization and alkynyl crosslinking reactions to construct crosslinked porous porphyrin-based polyimides (CR-PPBPIs) from 2,5-bis(3,4-dicarboxyphenoxy)-4'-phenylethynyl-biphenyl dianhydride (PEPHQDA) and 5,10,15,20-tetra[4-[(3-aminophenyl)ethynyl]phenyl] porphyrin (TAPEPP). CR-PPBPIs revealed BET surface areas (212, 578 and 593 m2 g−1), dominated pore width (1 and 1.9 nm) and abundant CO 2 -philic substances. Thus, considerable CO 2 uptakes (1.92, 2.43 and 2.52 mmol g−1), CO 2 -adsorption isosteric enthalpies (31.9, 26.0 and 27.9 kJ mol−1) and superior CO 2 /N 2 selectivities (45.77, 38.72 and 46.26) were achieved. This work sheds some light on the precise regulation of porosity parameters in the crosslinked metalloporphyrin-based polyimides for carbon dioxide adsorption and separation. [Display omitted] • We tuned the porous structures by changing alkynyl-groups contents and metals. • CR-PPBPIs revealed dominated micropores and abundant CO 2 -philic substances. • CR-PPBPIs exhibited considerable CO 2 uptakes and CO 2 /N 2 selectivities. [ABSTRACT FROM AUTHOR]

Microporous polyimide networks for highly selective CO 2 capture have been constructed based on linear polyimides through crosslinking reaction. • The microporous polyimides with different substituent group were prepared. • The CO 2 adsorption performance can be tuned by changing the substituents. • The CF 3 -PI-CL shows highly CO 2 selective adsorption performance. 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 CO 2 uptake capacity (7.3–9.4 wt%) at 273 K and 1 bar. Particularly, the crosslinked polyimide containing trifluoromethyl groups (CF 3 -PI-CL) shows high CO 2 /N 2 and CO 2 /CH 4 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 CO 2 selective adsorption capacity. This method also has great potential for fabricating high-performance microporous polymers based on other linear polymers without rigid contorted structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crosslinked porous porphyrin-based polyimides (CR-PPBPIs) were prepared from TAPP, PEPHQDA and terminal monoamines. • With increasing molecular and conjugate sizes effect in different terminal monoamines, the BET surface areas of CR-PPBPIs increased and subsequently declined. • CR-PPBPIs possessed considerable CO 2 uptakes (1.63–2.17 mmol g−1 at 273 K) and high CO 2 /N 2 (85.64–40.34) selectivities. Crosslinked porous porphyrin-based polyimides (CR-PPBPIs) were constructed from 5,10,15,20-tetra(4-aminophenyl)porphyrin (TAPP), 2,5-bis(3,4-dicarboxyphenoxy)-4′- phenylethynyl biphenyl (PEPHQDA) and terminal monoamines (AP, APE, APEP and APEN) via polymerization and alkynyl crosslinking reactions. CR-PPBPIs had permanent porosities and revealed outstanding thermal stabilities. With increasing spatial configuration (molecular sizes and conjugate effect) in terminal monoamines, the BET surface areas of PPBPIs decreased first and then increased (158–42 m2 g−1), whereas, the BET surface areas of CR-PPBPIs increased (505–37 m2 g−1) and subsequently declined. The variation trend of BET surface areas in CR-PPBPIs with increasing spatial configuration in terminal monoamines was derived from molecular sizes and π-stacking effect. The reasonable distribution of terminal alkynyl group was critical key to regulating the porosity parameters of crosslinked terminal-modified polyimides. CR-PPBPIs possessed CO 2 uptakes (1.63–2.17 mmol g−1 at 273 K) and Q st values (31.3–29.7 kJ mol−1). In addition, CR-PPBPIs had high CO 2 /N 2 (85.64–40.34) selectivities. This work provides a strategy to tune the porosity parameters of crosslinked materials towards CO 2 adsorption and separation. [ABSTRACT FROM AUTHOR]

Microporous polyimides have been extensively investigated for CO 2 capture and separation applications. Here, the crosslinked structure and the polar CO 2 -philic trifluoromethyl group are introduced into the hyperbranched polyimides to construct the microporous polyimide networks for efficient CO 2 capture. The HBPI-CL networks exhibit significant increased micropores (pore size less than 1 nm) surface area and volume ranging from 79 to 89 m2g-1 and 0.03–0.05 cm3 g−1. It is intriguingly found that the CF 3 TAPA-HBPI-CL have more abundant ultramicropores and exhibit higher CO 2 uptake capacity and CO 2 /N 2 selectivity (8.56 wt% and 33.3) than those of TAPA-HBPI-CL (7.47 wt% and 20.4) without the polar CO 2 -philic trifluoromethyl group at 273 K/1 bar. This work reveals that the introduction of polar CO 2 -philic trifluoromethyl group into crosslinked polyimides is an effective method to improve the CO 2 adsorption capacity and selectivity of microporous polyimide, which can be also applied to other microporous polymers. Microporous polyimide networks with efficient CO 2 capture performance have been constructed by introducing crosslinked structure and polar trifluoromethyl group into hyperbranched polyimides. Image 1 • The microporous polyimides (HBPI-CLs) with different substituent groups were prepared. • The polar trifluoromethyl group can facilitate the formation of ultramicropores and enhance the affinity for CO 2 molecule. • The CF 3 TAPA-HBPI-CL exhibit higher CO 2 uptake capacity and CO 2 /N 2 selectivity (8.56 wt% and 33.3) than TAPA-HBPI-CL (7.47 wt% and 20.4) at 273 K and 1 bar. [ABSTRACT FROM AUTHOR]

Graphical abstract Preparation of the microporous polyimide networks with tunable pore size and high CO 2 selectivity. Highlights • The microporous hyperbranched polyimide networks (HBPI-CLs) were prepared. • The pore size can be finely tuned by changing the position of crosslinking points. • The HBPI-CLs exhibit high CO 2 /N 2 and CO 2 /CH 4 selectivity at 273 K and 1 bar. Abstract Developing porous organic polymer materials with plenty micropores is of great importance for highly selective CO 2 capture under ambient conditions. Here, to tune the pore size, two novel microporous hyperbranched polyimide networks, in which the distance between the polymer skeleton and crosslinking points is different, are successfully prepared by a two-step pathway combining polymerization and crosslinking reaction. It is intriguingly found that both porosity and CO 2 sorption performance of microporous hyperbranched polyimides can be finely tuned by reducing the distance between the polymer skeleton and crosslinking points from PEPHQDA-HBPI-CL to PEQDA-HBPI-CL. The micropore size decrease from 1.18 nm to 0.86 nm, and CO 2 adsorption capacity increase from 6.38 to 6.51 wt% (298 K and 1 bar). More excitingly, the PEQDA-HBPI-CL demonstrates the high CO 2 /N 2 and CO 2 /CH 4 selectivity up to 109 and 15 (273 K, 1 bar) according to the Henry's law, which are superior to those of many other microporous organic polymers and among the best results for porous inorganic/ organic materials. This work reveals that the shorter-distance between the polymer skeleton and crosslinking points is in favor of fabricating microporous hyperbranched polyimide networks with abundant smaller micropore and high CO 2 selectivity, which are crucial importance for the CO 2 capture and storage. [ABSTRACT FROM AUTHOR]

We fabricated three crosslinked porphyrin-based polyimides (PPBPI-CRs) from PEPHQDA, TAPP and three terminal anhydrides (PA, PEPA and PENA) via alkynyl groups crosslinking reactions. PPBPI-CRs had permanent porosities and revealed outstanding thermal stabilities. Affected by π-stacking and molecular sizes effect, with increasing conjugate and molecular sizes effect in different terminal anhydrides, porphyrin-based polyimides (PPBPIs) revealed decreased specific surface areas (106.8–8.3 m2 g−1), whereas, PPBPI-CRs showed increased BET surface areas (1.8–633 m2 g−1). Meanwhile, PPBPI-CRs had considerable CO 2 uptakes (1.37, 2.01 and 2.37 mmol g−1) and isosteric heats of CO 2 adsorption (34.8, 27.5 and 22.6 kJ mol−1). The PPBPI-CRs had CO 2 /N 2 (39.83, 36.95, 40.08) and CO 2 /CH 4 (14.13, 9.78, 10.87) separation selectivities. Image 1 • Crosslinked porphyrin-based polyimides (PPBPI-CRs) from different terminal alkynyl groups were synthesized via polymerization and crosslinking reactions. • With the increasing molecular and conjugate sizes effect in terminal anhydrides, PPBPIs revealed decreased specific surface areas (106.8–8.3 m2 g−1), whereas, PPBPI-CRs showed increased BET surface areas (1.8–633 m2 g−1). • PPBPI-CRs had CO 2 uptakes (1.37–2.37 mmol g−1 at 273 K and 1 bar) and isosteric heats of CO 2 adsorption (34.8–22.6 kJ mol−1) as well as the separation factors of CO 2 /N 2 (39.83, 36.95, 40.08) and CO 2 /CH 4 (14.13, 9.78, 10.87). [ABSTRACT FROM AUTHOR]