Hypercrosslinked porous polymer materials: design, synthesis, and applications

Constructing polymers towards ultrathin nanosheets with dual mesopores and intrinsic photoactivity

We developed ultrathin dual-mesoporous polymer nanosheets by combining co-assembly of different templates with in situ synthesis of functional polymers, which featured inherent smaller and template-directed larger mesopores (2.6 nm and 15 nm, respectively), ultrathin nanolayers (20 nm), high surface area (268 m2 g-1), intrinsic fluorescent properties and effective detectability for organophosphates.

Covalent organic frameworks for separation applications

Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers with highly tuneable structures and functionalities. COFs have been proposed as ideal materials for applications in the energy-intensive field of molecular separation due to their notable intrinsic features such as low density, exceptional stability, high surface area, and readily adjustable pore size and chemical environment. This review attempts to highlight the key advancements made in the synthesis of COFs for diverse separation applications such as water treatment or the separation of gas mixtures and organic molecules, including chiral and isomeric compounds. Methods proposed for the fabrication of COF-based columns and continuous membranes for practical applications are also discussed in detail. Finally, a perspective regarding the remaining challenges and future directions for COF research in the field of separation has also been presented.

Porous Aromatic Frameworks (PAFs)

Porous aromatic frameworks (PAFs) represent an important category of porous solids. PAFs possess rigid frameworks and exceptionally high surface areas, and, uniquely, they are constructed from carbon-carbon-bond-linked aromatic-based building units. Various functionalities can either originate from the intrinsic chemistry of their building units or are achieved by postmodification of the aromatic motifs using established reactions. Specially, the strong carbon-carbon bonding renders PAFs stable under harsh chemical treatments. Therefore, PAFs exhibit specificity in their chemistry and functionalities compared with conventional porous materials such as zeolites and metal organic frameworks. The unique features of PAFs render them being tolerant of severe environments and readily functionalized by harsh chemical treatments. The research field of PAFs has experienced rapid expansion over the past decade, and it is necessary to provide a comprehensive guide to the essential development of the field at this stage. Regarding research into PAFs, the synthesis, functionalization, and applications are the three most important topics. In this thematic review, the three topics are comprehensively explained and aptly exemplified to shed light on developments in the field. Current questions and a perspective outlook will be summarized.

Advances in Conjugated Microporous Polymers

Conjugated microporous polymers (CMPs) are a unique class of materials that combine extended π-conjugation with a permanently microporous skeleton. Since their discovery in 2007, CMPs have become established as an important subclass of porous materials. A wide range of synthetic building blocks and network-forming reactions offers an enormous variety of CMPs with different properties and structures. This has allowed CMPs to be developed for gas adsorption and separations, chemical adsorption and encapsulation, heterogeneous catalysis, photoredox catalysis, light emittance, sensing, energy storage, biological applications, and solar fuels production. Here we review the progress of CMP research since its beginnings and offer an outlook for where these materials might be headed in the future. We also compare the prospect for CMPs against the growing range of conjugated crystalline covalent organic frameworks (COFs).

Preparation of Ethylene Glycol Dimethacrylate (EGDMA)-Based Terpolymer as Potential Sorbents for Pharmaceuticals Adsorption

Ethylene glycol dimethacrylate (EGDMA) is used as a crosslinker in poly(acrylonitrile (AN)-co-vinylbenzyl chloride (VBC)) to investigate the effect of long-chain crosslinker to the porosity of the terpolymer system. Poly(AN-co-EGDMA-co-VBC) is synthesized by using precipitation polymerization method and further hypercrosslinked by Friedel-Crafts reaction. FT-IR spectra of poly(AN-co-EGDMA-co-VBC) show that the absorption bands at ~1290 cm-1 that are assigned to the C-Cl vibrations are almost disappeared in hypercrosslinked (HXL) poly(AN-co-EGDMA-co-VBC) polymers, confirming that the hypercrosslinking reaction is successful. SEM images show that the morphologies of the polymers are retained through the hypercrosslinking reactions. Brunauer-Emmett-Teller (BET) analysis shows that hypercrosslinked polymers had a specific surface area up to 59 m2·g-1. The preliminary performance of the terpolymer adsorbent to capture polar analyte is evaluated by adsorbing salicylic acid and mefenamic acid from aqueous solution in a batch system. The maximum adsorption capacity of salicylic acid and mefenamic acid were up to 416.7 mg·g-1 and 625 mg·g-1, respectively, and the adsorption kinetic data obeyed pseudo-second-order rate equation.

Inclusion Complexation of Organic Micropollutants with β-Cyclodextrin

Recently, β-cyclodextrin (βCD)-based polymers with enhanced adsorption kinetics and high removal capacity of organic micropollutants (OMPs) and uptake rates have been synthesized and tested experimentally. Although the exact physical–chemical mechanisms via which these polymers capture the various types of OMPs are not yet fully understood, it is suggested that the inclusion complex formation of OMPs with βCD is very important. In this study, the inclusion complex formation of OMPs with βCD in an aqueous solution is investigated by using the well-established attach–pull–release method in force field-based molecular dynamics simulations. A representative set of OMPs is selected based on the measured occurrences in surface and ground waters and the directives published by the European Union. To characterize the formation of the inclusion complex, the binding free energies, enthalpies, and entropies are computed and compared to experimental values. It is shown that computations using the q4md-CD/GAFF/Bind3P force field combination yield binding free energies that are in reasonable agreement with the experimental results for all OMPs studied. The binding enthalpies are decomposed into the main contributing interaction types. It is shown that, for all studied OMPs, the van der Waals interactions are favorable for the inclusion complexion and the hydrogen bond formation of the guest with the solvent and βCD plays a crucial role in the binding mechanism. Our findings show that MD simulations can adequately describe the inclusion complex formation of βCD with OMPs, which is the first step toward understanding the underlying mechanisms via which the βCD-based polymers capture OMPs.

Hierarchical Porous Organometallic Polymers Fabricated by Direct Knitting: Recyclable Single-Site Catalysts with Enhanced Activity

Porous organometallic polymers (POMPs) with hierarchical pore structures, high specific surface areas, and atomically dispersed metal (Ir, Pd, Ru) centers are successfully fabricated by a facile one-pot method through direct knitting of diverse N-heterocyclic carbene metal (NHC-M) complexes. These polymers can function as recyclable solid single-site catalysts and exhibit excellent catalytic activity and selectivity in both dehydrogenation and hydrogenation reactions even at ppm-level catalyst loadings. Remarkably, a record turnover number (TON) of 1.01 × 10⁶ is achieved in the hydrogenation of levulinic acid to γ-valerolactone, which is 750 times higher than that attained with corresponding bis-NHC-Ir complex.

Creation of Carbazole-Based Fluorescent Porous Polymers for Recognition and Detection of Various Pesticides in Water

The development of sensitive, fast, and portable methods for detecting the residual toxic pesticides is essentially important because of the increasing concerns for public health and safety. For this purpose, three fluorescent porous organic polymers containing pendant N-benzyl carbazole, N-benzyl dibromo-carbazole, and N-benzyl dimethoxy-carbazole groups were synthesized via a one-step polymerization reaction. The resultant polymers emit bright cyan, blue, and green light under the ultraviolet lamp, respectively, with the Brunauer-Emmett-Teller area up to 858 m² g^-1 and tunable pore sizes in the range of 0.5-36 nm. Six pesticides including trifluralin, isopropalin, glyphosate, fenitrothion, imidacloprid, and cyfluothrin are selected as the analytes to investigate the recognition and detection ability of polymers in terms of the different photo-physical properties of polymers, chemical structure of organic pesticides as well as the pore sizes of polymers, and molecular sizes of pesticides. It is interesting to find that, even though in water medium, the measured fluorescent quenching Stern-Volmer coefficient for trifluralin still reaches 26,040 L mol^-1 and is nearly unchanged under both acidic or basic service conditions. Moreover, the test paper prepared from the polymer exhibits a rapid fluorescent response when contacting the aqueous trifluralin dispersion liquid, and the sensitivity remains stable after recycling use for twelve times.

Imidazolium-Functionalized Ionic Hypercrosslinked Porous Polymers for Efficient Synthesis of Cyclic Carbonates from Simulated Flue Gas

The rapid growth of CO₂ emissions, especially from power plants, has led to the urgent need to directly capture and fix CO₂ in the flue gas after simple purification rather than energy-intensive gas separation. Herein, imidazolium-functionalized ionic hypercrosslinked porous polymers (HCPs) bearing adjustable surface groups were straightforwardly synthesized through co-hypercrosslinking of benzylimidazole salts and crosslinker through Friedel-Crafts alkylation. Abundant microporosity and relatively high ionic moieties were obtainable in the ethyl-group-tethered ionic HCP, giving a remarkably selective CO₂ capture performance with a CO₂ uptake of 3.05 mmol g^-1 and an ideal adsorbed solution theory (IAST) CO₂ /N₂ selectivity as high as 363 (273 K, 1 bar). This ionic polymer demonstrated high efficiency in the synthesis of cyclic carbonates from the coupling of various epoxides with the simulated flue gas (15 % CO₂ and 85 % N₂ ), giving high yields, large turnover numbers (up to 4800), and stable reusability under additive- and solvent-free conditions.

Polymer Networks: From Plastics and Gels to Porous Frameworks

Polymer networks, which are materials composed of many smaller components-referred to as "junctions" and "strands"-connected together via covalent or non-covalent/supramolecular interactions, are arguably the most versatile, widely studied, broadly used, and important materials known. From the first commercial polymers through the plastics revolution of the 20^th century to today, there are almost no aspects of modern life that are not impacted by polymer networks. Nevertheless, there are still many challenges that must be addressed to enable a complete understanding of these materials and facilitate their development for emerging applications ranging from sustainability and energy harvesting/storage to tissue engineering and additive manufacturing. Here, we provide a unifying overview of the fundamentals of polymer network synthesis, structure, and properties, tying together recent trends in the field that are not always associated with classical polymer networks, such as the advent of crystalline "framework" materials. We also highlight recent advances in using molecular design and control of topology to showcase how a deep understanding of structure-property relationships can lead to advanced networks with exceptional properties.

One-step fabrication of bifunctional self-assembled oligopeptides anchored magnetic carbon nanoparticles and their application in copper (II) ions removal from aqueous solutions

Copper ion (Cu (II)) pollution has attracted much attention due to its remarkable toxic domino effect at excess amount. Efficient Cu (II) ions removal is thus a prerequisite for wastewater recycling. Herein, we present a facile and environmentally benign strategy to fabricate thiol (SH)-functionalized Fe₃O₄@C nanoparticles (denoted as Fe₃O₄@C-SH NPs) based on one-step self-assembling of a bifunctional oligopeptide with a sequence of Cys-Lys-Cys-Lys-Cys-Lys (CK-VI) for highly efficient removal of copper ions (Cu (II)) in aqueous solutions. Under the physiological conditions, CK-VI readily self-organized into a robust and tailor-made functional monolayer predominately composed of well-packed β-sheets on the surface of Fe₃O₄@C NPs with their thiol groups standing on the outermost layer. The resulting Fe₃O₄@C-SH NPs containing abundant thiol active sites exhibited excellent adsorption capacity (up to 28.8 mg g^-1) and selectivity for Cu (II) ions over coexisting ions. Compared with other covalent grafting methods with multistep processes and in harsh conditions, the proposed oligopeptides assembly-based coating method makes it possible to rapidly fabricate the Fe₃O₄@C-SH NPs in a simple mild one-step aqueous process with low cost. The current study provides facile and environmentally friendly approaches to rapidly tailor multifunctional surfaces of NPs for various toxic metal ions removal from wastewater.

Recent developments of monolithic and open-tubular capillary electrochromatography (2017-2019)

Capillary electrochromatography, which combined the high selectivity of high-performance liquid chromatography and the high separation efficiency of capillary electrophoresis, is an attractive separation tool. In this review, the developments on monolithic and open tubular capillary electrochromatography during 2017 to August 2019 are summarized. Considering the development of novel stationary phases is the most active research field in capillary electrochromatography, monolithic capillary electrochromatography is classified according to the polymer-based and hybrid monolithic columns, while open-tubular capillary electrochromatography is categorized by cyclodextrin, silica, polymer, nanomaterials, microporous materials, and biomaterials-based open tubular columns.

AB2 polymerization on hollow microporous organic polymers: engineering of solid acid catalysts for the synthesis of soluble cellulose derivatives

New post-synthetic functionalization of hollow microporous organic polymers was developed based on AB₂ polymerization and thiol–yne click reaction.

Thiophene-embedded conjugated microporous polymers for photocatalysis

“Bottom-up” embedding of thiophene derivatives into CMPs for highly efficient heterogeneous photocatalysis is reported.

Two-dimensional covalent organic frameworks with hierarchical porosity

This review highlights the state-of-the-art progress achieved in two-dimensional covalent organic frameworks (COFs) with hierarchical porosity, an emerging class of COFs constructed by integrating different types of pores into one framework.

Conjugated porous polymers: incredibly versatile materials with far-reaching applications

This review discusses conjugated porous polymers and focuses on relating design principles and synthetic methods to key properties and applications such as (photo)catalysis, gas storage, chemical sensing, energy storage and environmental remediation.

Visible light-driven Suzuki–Miyaura reaction by self-supported Pd nanocatalysts in the formation of Stille coupling-based photoactive microporous organic polymers

Stille coupling results in deposition of Pd NPs on microporous organic polymers, showing excellent photocatalytic performance.

A heterogeneous pore decoration strategy on a hydrophobic microporous polymer for high-coverage capture of metabolites

A heterogeneous pore decoration strategy on a hydrophobic microporous polymer resulted in its hydrophobic–hydrophilic hybrid properties and high-coverage capture ability of microbial metabolites.

Synthesis of surface functionalized hollow microporous organic capsules for doxorubicin delivery to cancer cells

Functionalized hypercrosslinked hollow microporous capsules are demonstrated to have potential applications in targeted delivery of anticancer drugs.

Sulfoxidation inside a hypercrosslinked microporous network nanotube catalyst

In the present work, a kind of efficient heterogeneous catalyst was synthesized from amine-functionalized hypercrosslinked bottlebrush copolymers of microporous network nanotubes (amine-MNNs) and Na₂WO₄.

Self-assembly of block copolymers towards mesoporous materials for energy storage and conversion systems

This paper reviews the progress in the field of block copolymer-templated mesoporous materials, including synthetic methods, morphological and pore size control and their potential applications in energy storage and conversion devices.

Facile synthesis of a porous polynorbornene with an azobenzene subunit: selective adsorption of 4-nitrophenol over 4-aminophenol in water

The azo-linked porous polynorbornene was synthesizedviathe robust reductive azo-coupling and Ring-Opening-Metathesis-Polymerization (ROMP) polymerization, which selectively adsorbed 4-nitrophenol over 4-aminophenol in water.

Irreversible tautomerization as a powerful tool to access unprecedented functional porous organic polymers with a tris(β-keto-hydrazo)cyclohexane subunit (TKH-POPs)

Irreversible tautomerization could lead to fascinating functional porous organic polymers such as TKH-POPs comprising tris(β-keto-hydrazo)-cyclohexane subunit.

Novel amino-functionalized hypercrosslinked polymer nanoparticles constructed from commercial macromolecule polystyrene via a two-step strategy for CO2 adsorption

Commercial polymers have large cost advantage to drive HCPs to industrialize. The AHCPNPs using commercial PS as main block prove that it still has well-defined microporous structure, high specific surface area and extremely CO₂ capture capacity.

Hollow porous organic nanospheres for anchoring Pd(PPh3)4 through a co-hyper-crosslinking mediated self-assembly strategy

A facile synthesis of Pd(PPh₃)₄-functionalized hollow porous organic nanospheres with excellent catalytic activity is reported for the first time.

Emerging trends in porous materials for CO2 capture and conversion

This review highlights the recent progress in porous materials (MOFs, zeolites, POPs, nanoporous carbons, and mesoporous materials) for CO₂ capture and conversion.

Core hyper-cross-linked star polymers from block polymer micelle precursors

Hyper-cross-linking of a core of block polymer micelles produces core cross-linked polymer with a spacious hyper-cross-linked core, which is solution-processible.

Arm-degradable star polymers with crosslinked ladder-motif cores as a route to soluble microporous nanoparticles

Star polymers were synthesized via cores crosslinking of (macro)molecular ladder motifs and converted to microporous polymer particles after arm degradation.

Salen-based hypercrosslinked polymer-supported Pd as an efficient and recyclable catalyst for C-H halogenation

In this work, we report the first use of a salen-based hypercrosslinked polymer-supported Pd catalyst to carry out C-H halogenation. This catalyst can effectively catalyze C-H bromination and chlorination even better than its homogeneous counterpart Pd(OAc)2. It also showed excellent reusability without loss of catalytic activity for ten cycles. A broad substrate scope was explored and moderate to excellent yields were obtained.

Synthesis and properties of porous polymers synthesized by Michael addition reactions of multi-functional acrylate, diamine, and dithiol compounds

Porous polymers have been synthesized by Michael addition reactions of multi-functional acrylate and diamine or dithiol compounds. Aza-Michael addition reaction of multi-functional acrylate, trimethylolpropane propoxylate triacrylate (TPT) and hexamethylene diamine (HDA) in dimethyl sulfoxide (DMSO) successfully yielded the porous polymer. The porous structure was characterized by connected globules or co-continuous structure, and could be controlled by the reaction conditions. Mechanical properties of the porous polymers were investigated by compression test. The porous polymers with co-continuous structure showed higher Young's modulus than those with connected globules. The porous polymer absorbed some organic solvents, especially CHCl₃. The porous polymer as prepared in DMSO state showed coloring induced by Christiansen filter effect depending on the reaction time and observation temperature. The thio-Michael addition reaction of TPT and 1,6-hexanedithiol (HDT) in DMSO using different base catalysts also yielded the porous polymer. The porous structure could be controlled by the catalysts amount when the reaction was initiated by a photo-base generator as the base catalyst. The present reaction systems make it possible to synthesize the porous polymers with simple process without phase separator.

A Porous Polymer-Based Solid Acid Catalyst with Excellent Amphiphilicity: An Active and Environmentally Friendly Catalyst for the Hydration of Alkynes

Developing efficient solid acid catalysts for aqueous organic reactions is of great importance for the development of sustainable chemistry. In this work, a porous polymeric acid catalyst was synthesized via a solvothermal copolymerization and a successive ion-exchange method. Physicochemical characterizations suggested that the prepared polymers possessed large Brunauer-Emmett-Teller (BET) surface areas, a hierarchically porous structure, excellent surface amphiphilicity, and nice swelling properties. Notably, an activity test in phenylacetylene hydration indicated that the prepared solid acid exhibited high catalytic activity in water, which outperformed commercial amberlyst-15, sulfuric acid, and benzenesulfonic acid. Moreover, the prepared solid acid can be easily recovered and reused at least four times. Additionally, a variety of aromatic and aliphatic alkynes could be effectively transformed into corresponding ketones under optimal reaction conditions.

Preparation of Chloromethylated Pitch–Based Hyper–Crosslinked Polymers and An Immobilized Acidic Ionic Liquid as A Catalyst for the Synthesis of Biodiesel

Hyper-crosslinking polymers and its immobilized acid ionic liquid catalyst were prepared using cheap pitch, as a monomer, through hyper-crosslinking reactions and allyl chloride, as a chlorine source, for chloromethylation and further grafting with imidazole and functionalizing with sulfonic acid. The polymers were characterized by FE-SEM, FTIR, TG, and nitrogen sorption. The grafting ratios of the chloromethylated pitch-based hyper-crosslinked polymer (HCPpitch–CH2–Cl) and immobilized acid ionic liquid [HCPpitch–Im–Pros][Tos] were 3.5 mmol/g and 3.0 mmol/g, and the BET specific surface areas were 520 m2/g and 380 m2/g, respectively. This strategy provides an easy approach to preparing highly stable and acid functionalized mesoporous catalysts. The immobilized acidic ionic liquid was used as a catalyst for the esterification of oleic acid and methanol to synthesize biodiesel. The results demonstrated that under the optimal conditions of an alcohol to acid molar ratio of 7:1, ionic liquid to oleic acid molar ratio of 0.12, and a reaction time of 3 h at atmospheric pressure, the yield of methyl oleate can reach up to 93%. Moreover, the catalyst was reused five times without the yield decreasing significantly. This study shows that [HCPpitch–Im–Pros][Tos] is a robust catalyst for the synthesis of biodiesel.