Solution Processing of Cross-Linked Porous Organic Polymers

Abstract

Conspectus Porous organic polymers (POPs), essentially including polymers with intrinsic microporosity (PIMs), conjugated microporous polymers (CMPs), covalent organic frameworks (COFs), hyper-cross-linked polymers (HCPs) and so on, have recently attracted broad interest in many application areas because of their structural diversity and functional tunability. However, except for linear PIMs that can dissolve in organic solvents for solution processing into membranes, most POPs are highly cross-linked (hereafter termed CPOPs) and are synthesized as insoluble and unprocessable powders, which prevent CPOPs in many applications. Developing methodologies for solution processing CPOPs to high-quality membranes, monoliths, and (aero)­gels has been a major challenge in this field because of the following issues. First, the inherently cross-linked structures and the strong framework–framework interactions in CPOPs give rise to very weak solvation of the frameworks, leading to easy aggregation and precipitation in solutions. Next, to date, several methods for preparing CPOP membranes have been proposed, but their conditions vary with different systems, and there lacks a general strategy for membrane formation of most CPOPs (or at least CPOPs of the same category). Additionally, CPOP-based monoliths and (aero)­gels are rarely reported, and it has been considered difficult to control the hierarchical porosity to form the monoliths and (aero)­gels during the CPOP syntheses. Last, the effects of the forms of membranes/(aero)­gels on the transport (electron, ion, and mass) properties have not been intensively investigated for the lack of suitable systems. Therefore, since it was first announced accompanied by the birth of CPOPs, research studies regarding solution-processed CPOPs have been underexplored for a long time without significant advances being achieved. To break the unprocessable shackles of CPOPs, our group started to make contributions to this field in 2018. We developed two general strategies, namely, “charge-induced dispersion (CID)” and “thermal hyper-cross-linking (THC)” strategies, to produce high-quality CPOP membranes and (aero)­gels, respectively. For the CID strategy, we found that the introduction of plenty of charges to the frameworks of CPOPs substantially enhanced their interactions with polar solvents, rendering the transparent, stable, and solution-like CPOP sols which could be further processed into membranes. For the THC strategy, we intensively investigated the gelation mechanism and found that this system was synthetically controllable to produce CPOP (aero)­gels and could serve as a platform for hybridization with many porous materials to achieve a molecular-level entanglement. Moreover, we successfully demonstrated that the transport properties in the CPOP membranes and gels were largely promoted by 1–2 orders of magnitude compared to their powder forms, thereby expanding the use of CPOP membranes and gels in the fields of electronic conduction, proton conduction, iodine adsorption, and molecul...

Linkage Design in Two‐Dimensional Covalent Organic Frameworks for High Iodine Uptake

“…This value is also better than that of the reported 2D‐COFs such as TTA‐TTB‐COF (5 g g −1 ), [ 32 ] TJNU‐201 (5.62 g g −1 ), [ 33 ] TPT‐DHBDX‐COF (5.43 g g −1 ), [ 35 ] TPT‐Azine‐COF (2.19 g g −1 ), [ 39 ] and SCOF (4.41 g g −1 ). [ 40 ] The work was also comparable to those of progressive 2D COFs such as TJNU‐203 (5.89 g g −1 ), [ 30 ] C‐TP‐BPDA‐COF (6.11 g g −1 ), [ 29 ] PB‐TT COF (5.97 g g −1 ), [ 42 ] COF‐AB‐50 (10.2 g g −1 ), [ 43 ] TAPB‐PDA COF (7.7 g g −1 ), [ 44 ] and QTD‐COF (6.3 g g −1 ). [ 45 ] In addition, iodine‐loaded COFs (COFs@I 2 ) kept their weight upon exposure to air under ambient conditions at 25 °C for 6 days.…”

“…Solid adsorbents are a simple way due to their simplicity, effectiveness, and recyclability. [26][27][28][29][30] Recent progress has shown that the COFs with high porosity, stability, and functional skeleton were potential candidates for iodine vapor uptake. [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] Yin and co-authors reported that the hollow microspheres of COF improved iodine vapor capturability via higher effective volume.…”

“…Solid adsorbents are a simple way due to their simplicity, effectiveness, and recyclability. [ 26–30 ]…”

2D Organic Materials: Status and Challenges

“…COF‐based materials will be more widely used in functional solid‐phase matrices in the future. [ 291 ] Similarly, a new 2D ultra‐microporous phosphate‐based COF has great application potential in the selective adsorption of uranium. [ 292 ] Figure a shows a COF‐based micro‐solid phase extraction.…”

Scalable synthesis of soluble crystalline ionic-graphdiyne by controlled ion expansion

“…The essence of the formation of soluble GDY is to weaken the interlayer stacking forces and enhance framework–solvent interactions of nanosheets to allow self-exfoliation via electrostatic repulsion to obtain high solubility in certain solvents with retaining the GDY basic skeleton. 14 Interlayer engineering has been key in preparing expanded interlayer and monolayer nanosheets in expansion–exfoliation, simultaneously tuning properties and improving performances. 15 This method can readily intercalate or trap substantial charge species into the inter-layer skeletons to reduce the two adjacent-layer interactions.…”