Hierarchical Porous Polystyrene Monoliths from PolyHIPE

Processable Conjugated Microporous Polymer Gels and Monoliths: Fundamentals and Versatile Applications

Conjugated microporous polymers (CMPs) as a new type of conjugated polymers have attracted extensive attention in academia and industry because of the combination of microporous structure and π-electron conjugated structure. The construction and application of gels and monoliths based on CMPs constitute a fertile area of research, promising to provide solutions to complex environmental and energy issues. This review summarizes and objectively analyzes the latest advances in the construction and application of processable CMP gels and monoliths, linking the basic and enhanced properties to widespread applications. In this review, we open with a summary of the construction methods used to build CMP gels and monoliths and assess the feasibility of different preparation techniques and the advantages of the products. The CMP gels and monoliths with enhanced properties involving various special applications are then deliberated by highlighting relevant scientific literature and discussions. Finally, we present the issues and future of openness in the field, as well as come up with the major challenges hindering further development, to guide researchers in this field.

Emulsion-Templated Porous Polymers for Efficient Dye Removal

A high internal phase emulsion (HIPE) method was used to produce adsorbents with an interconnected porous structure. HIPE was prepared using vinyl benzyl chloride (VBC), divinylbenzene (DVB), tert-butyl acrylate, and Span80 as the organic phase and water with K₂S₂O₈ and CaCl₂ as the water phase. The polymerization of the organic phase produced highly porous polymers called polyHIPE, carrying two functional groups. As a result of the template method, polyHIPEs have a low surface area. To overcome this drawback, polyHIPE was hyper-cross-linked through VBC to create meso- and micropores, resulting in a higher surface area. Then the polymer surface was tailored with carboxylic acid groups by simple hydrolysis of tert-butyl acrylate. The adsorption performances of the acidic functional hyper-cross-linked polyHIPEs prepared for the various reaction times of 0, 15, and 60 min were compared for methylene blue. The hyper-cross-linked polyHIPEs showed an enhanced adsorption kinetics for methylene blue, and the 15 min hyper-cross-linking reaction increased the rate of methylene blue adsorption significantly. It was proven that the polyHIPE adsorbent can be reused by treating it with an aqueous acidic solution in ethanol.

Hypercrosslinked Polymer Gels as a Synthetic Hybridization Platform for Designing Versatile Molecular Separators

Hypercrosslinked polymers (HCPs), amorphous microporous three-dimensional networks based on covalent linkage of organic building blocks, are a promising class of materials due to their high surface area and easy functionalization; however, this type of material lacks processability due to its network rigidity based on covalent crosslinking. Indeed, the development of strategies to improve its solution processability for broader applications remains challenging. Although HCPs have similar three-dimensionally crosslinked networks to polymer gels, HCPs usually do not form gels but insoluble powders. Herein, we report the synthesis of HCP gels from a thermally induced polymerization of a tetrahedral monomer, which undergoes consecutive solubilization, covalent bond formation, colloidal formation, followed by their aggregation and percolation to yield a hierarchically porous network. The resulting gels feature concentration-dependent hierarchical porosities and mechanical stiffness. Furthermore, these HCP gels can be used as a platform to achieve molecular-level hybridization with a two-dimensional polymer during the HCP gel formation. This method provides functional gels and corresponding aerogels with the enhancement of porosities and mechanical stiffness. Used in column- and membrane-based molecular separation systems, the hybrid gels exhibited a separation of water contaminants with the efficiency of 97.9 and 98.6% for methylene blue and KMnO₄, respectively. This result demonstrated the potentials of the HCP gels and their hybrid derivatives in separation systems requiring macroscopic scaffolds with hierarchical porosity.

Unprecedented processable hypercrosslinked polymers with controlled knitting

Processable microporous organic polymers (MOPs) attract incomparable research interests becuase their vairous types such as monoliths and membranes are for practical application. Most of processable MOPs usually need the harsh conditions such as the use of expensive metal catalysts, specialized stereospecific monomers etc., which restrict the sustainable and real applications of processable MOPs. Therefore, the economical mass production of processable MOPs remains a formidable challenge. Herein, we report that a novel strategy for constructing processable hypercrosslinked polymers (HCPs) need two steps synthesis of pre-crosslinking and deep-crosslinking using divinylbenzene (DVB) as self-crosslinking monomer under the catalysis of a small amount of FeCl₃ . The resulting HCPs monoliths possess high BET surface area of 1033-1056 m² g^-1 with hierarchical porosity, and show excellent mechanical strength up to 65 MPa. It is, to the best of our knowledge, the first report of using aromatic vinyl monomers as self-crosslinking monomers to generate HCPs monoliths with high surface area, yielding no by-products and high mechanical strength. This article is protected by copyright. All rights reserved.

Hyper-Cross-Linked Polymer-Decorated Surfaces with Ultrahigh Efficiency for Oil/Water Emulsion Separation and Recovery

A novel superhydrophobic/superoleophilic surface has been developed by direct surface condensation of dichloroxylene that results in a controlled coating of hyper-cross-linked polymers. Specifically, the coating was successfully applied to a melamine formaldehyde sponge and optimized by fine-tuning the reaction variables. The resulting hierarchical porous sorbents stabilized by polydimethylsiloxane exhibited an increased surface area, good physiochemical stability, high selectivity, and adsorption capacities for a variety of oils and solvents. The composite can separate oil in water emulsions with ultrahigh separation efficiency >99% over 10 cycles in liter-scale experiments, wherein the highest separation efficiency was as low as 2 ppm even with a short period of filtration, suggesting strong potential for oil/water separation and recovery.

One-Pot Fabrication of Hierarchically Bicontinuous Polystyrene Monoliths with Homogeneous Skeletons and Glycopolymer Surfaces

The hierarchically bicontinuous polystyrene monoliths (HBPMs) with homogeneous skeletons and glycopolymer surfaces are fabricated for the first time based on the medium internal phase emulsion (MIPE) templating method via activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP). The synergistic self-assembly of amphiphilic diblock glycopolymer (ADG) and Pluronic F127 (PF127) at the oil/water interface via hydrogen bonding interaction contributes to the formation of bicontinuous MIPE with deformed neighboring water droplets, resulting in the highly interconnected HBPM after polymerization. There is a bimodal pore size distribution in the HBPM, that is, through pores (150-5000 nm) and mesopores (10-150 nm). The HBPMs as prepared show excellent biocompatibility, homogeneous skeletons, strong mechanical strength, and high bed permeability, overcoming the practical limitations of the second generation of polystyrene (PS) monoliths. Glycoprotein concanavalin A (Con A) can be easily and quickly separated by the HBPM in hydrophilic interaction chromatography (HILIC) mode. These results suggest the HBPMs have great potentials in catalysis, separations, and biomedical applications.

The design of hypercrosslinked polymers from benzyl ether self-condensing compounds and external crosslinkers

Hypercrosslinked polymers were produced via the self-condensation of benzyl ether compounds, providing a one-component route to highly porous networks and significant reductions in catalyst waste compared to conventional routes. These compounds also represent a new class of external crosslinkers, able to impart improved textural properties when compared to standard aliphatic crosslinkers.

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.

Polyacrylate/polyacrylate-PEG biomaterials obtained by high internal phase emulsions (HIPEs) with tailorable drug release and effective mechanical and biological properties

The paper focuses on the preparation of polyacrylate based biomaterials designed as patches for dermal/transdermal drug delivery using materials obtained by the high internal phase emulsion (HIPE) technique. In particular, butyl acrylate and glycidyl methacrylate were selected, respectively, as backbone and functional monomer while two different crosslinkers, bifunctional or trifunctional, were used to form the covalent network. The influence of PEG on the main properties of the materials was also investigated. The obtained materials show a characteristic and interconnected internal structure as confirmed by SEM studies. By an industrial point of view, an interesting feature of this system is that it can be shaped as needed, in any form and thickness. The physiochemically characterized materials showed a tailorable curcumin (model of hydrophobic drugs) drug release, effective mechanical properties and cell viability and resulted neither pro nor anti-angiogenic as demonstrated in vivo by the chick embryo choriallantoic membrane (CAM) assay. Based on these results, the obtained polyHIPEs could be proposed as devices for dermal/transdermal drug delivery and/or for the direct application on wounded skin.

Hierarchically structured TiO2-based composites for Fenton-type oxidation processes

A novel hierarchically structured composite aimed as a stable catalyst for the heterogeneous Fenton-type (HFT) oxidation process was developed by using a cost-effective and versatile technique. Prussian Blue nanoparticles (PBNP) were dispersed onto aligned macroporous TiO₂ (rutile) monoliths prepared via directional freezing of aqueous dispersions of TiO₂ nanoparticles. The catalytic performance was evaluated in the HFT oxidation of an azo dye frequently used as a model contaminant, Orange G (OG). Experiments were carried out in a liquid batch-recycle reactor, in which the liquid flow rate was set to ensure negligible external mass transfer resistance. The catalyst exhibited good activity to form highly oxidative radicals from hydrogen peroxide decomposition, which readily discolored OG. Significant reduction of the time required to attain complete discoloration and improvement in TOC removal were achieved by adjusting operating conditions and oxidant dosage strategies. Almost complete OG conversion at around 90 min and 34.4% of TOC removal after 4 h were achieved by using the best evaluated strategy. The catalyst activity was tested under specific operating conditions and remained unaltered during 42 cycles of 4 h each (total 168 h). The fresh and used PBNP/TiO₂ catalysts and the support were thoroughly characterized by several techniques. Results supported the excellent stability exhibited by the catalyst in the OG HFT oxidation.

Enzyme immobilized millimeter-sized polyHIPE beads with easy separability and recyclability

Enzyme immobilized reusable millimeter-sized beads were prepared through covalently immobilizing Candida antarctica lipase B onto emulsion-templated porous beads.

Hypercrosslinked porous polymer materials: design, synthesis, and applications

Hypercrosslinked polymers (HCPs) are a series of permanent microporous polymer materials initially reported by Davankov, and have received an increasing level of research interest. In recent years, HCPs have experienced rapid growth due to their remarkable advantages such as diverse synthetic methods, easy functionalization, high surface area, low cost reagents and mild operating conditions. Judicious selection of monomers, appropriate length crosslinkers and optimized reaction conditions yielded a well-developed polymer framework with an adjusted porous topology. Post fabrication of the as developed network facilitates the incorporation of various chemical functionalities that may lead to interesting properties and enhance the selection toward a specific application. To date, numerous HCPs have been prepared by post-crosslinking polystyrene-based precursors, one-step self-polycondensation or external crosslinking strategies. The advent of these methodologies has prompted researchers to construct well-defined porous polymer networks with customized micromorphology and functionalities. In this review, we describe not only the basic synthetic principles and strategies of HCPs, but also the advancements in the structural and morphological study as well as the frontiers of potential applications in energy and environmental fields such as gas storage, carbon capture, removal of pollutants, molecular separation, catalysis, drug delivery, sensing etc.

Creation of micropores by RAFT copolymerization of conjugated multi-vinyl cross-linkers

Copolymerization of conjugated multi-vinyl cross-linkers with styrene creates a fluorescent and microporous cross-linked network, useful for the synthesis of hierarchically porous polymers.

Hyper-cross-linked polymers with controlled multiscale porosity via polymerization-induced microphase separation within high internal phase emulsion

Porous polymers containing hierarchically organized, interconnected, and controlled micro-, meso- and macropores allow the effective adsorption of dye molecules from solution.

Hierarchically Porous Carbon Derived from PolyHIPE for Supercapacitor and Deionization Applications

Hierarchically porous carbon (HPC) materials with interconnected porous texture are produced from a porous poly(divinylbenzene) precursor, which is synthesized by polymerizing high-internal-phase emulsions. After carbonation, the macroporous structures of the poly(divinylbenzene) precursor are preserved and enormous micro-/mesopores via carbonation with KOH are produced, resulting in an interconnected hierarchically porous network. The prepared HPC has a maximum specific surface area of 2189 m² g^-1. The electrode materials for supercapacitors and capacitive deionization devices employing the formed HPC exhibit a high specific capacity of 88 mA h g^-1 through a voltage range of 1 V (319 F g^-1 at 1 A g^-1) and a superior electrosorption capacity of 21.3 mg g^-1 in 500 mg L^-1 NaCl solution. The excellent capacitive performance could be ascribed to the combination of high specific surface area and favorable hierarchically porous structure.

Porous PDMS structures for the storage and release of aqueous solutions into fluidic environments

Typical microfluidic systems take advantage of multiple storage reservoirs, pumps and valves for the storage, driving and release of buffers and other reagents. However, the fabrication, integration, and operation of such components can be difficult. In particular, the reliance of such components on external off-chip equipment limits their utility for creating self-sufficient, stand-alone microfluidic systems. Here, we demonstrate a porous sponge made of polydimethylsiloxane (PDMS), which is fabricated by templating microscale water droplets using a T-junction microfluidic structure. High-resolution microscopy reveals that this sponge contains a network of pores, interconnected by small holes. This unique structure enables the sponge to passively release stored solutions very slowly. Proof-of-concept experiments demonstrate that the sponge can be used for the passive release of stored solutions into narrow channels and circular well plates, with the latter used for inducing intracellular calcium signalling of immobilised endothelial cells. The release rate of stored solutions can be controlled by varying the size of interconnecting holes, which can be easily achieved by changing the flow rate of the water injected into the T-junction. We also demonstrate the active release of stored liquids into a fluidic channel upon the manual compression of the sponge. The developed PDMS sponge can be easily integrated into complex micro/macro fluidic systems and prepared with a wide array of reagents, representing a new building block for self-sufficient microfluidic systems.

Swellable functional hypercrosslinked polymer networks for the uptake of chemical warfare agents

Porous materials can be used as sorbents for the bulk uptake (and potential deactivation) of chemical warfare agents (CWAs).

Deep-Eutectic Solvents as MWCNT Delivery Vehicles in the Synthesis of Functional Poly(HIPE) Nanocomposites for Applications as Selective Sorbents

We report an alternative green strategy based on deep-eutectic solvents (DES) to deliver multiwalled carbon nanotubes (MWCNTs) for a bottom-up approach that allows for the selective interfacial functionalization of nonaqueous poly(high internal phase emulsions), poly(HIPEs). The formation and polymerization of methacrylic and styrenic HIPEs were possible through stabilization with nitrogen doped carbon nanotube (CN_X) and surfactant mixtures using a urea-choline chloride DES as a delivering phase. Subtle changes in CN_X concentration (less than 0.2 wt % to the internal phase) produced important changes in the macroporous monolith functionalization, which in turn led to increased monolith hydrophobicity and pore openness. These materials displayed great oleophilicity with water contact angles as high as 140° making them apt for biodiesel, diesel, and gasoline fuel sorption applications. Overall, styrene divinylbenzene (StDvB) based poly(HIPEs) showed hydrophobicity and fuel sorption capacities as high as 4.8 (g/g). Pore hierarchy, namely pore openness, regulated sorption capacity, and sorption times where greater openness resulted in faster sorption and increased sorption capacity. Monoliths were subject to 20 sorption-desorption cycles demonstrating recyclability and stable sorption capacity. Finally, CN_X/surfactant hybrids made it possible to reduce surfactant requirements for successful HIPE formation and stabilization during polymerization. All poly(HIPEs) retained acceptable conversion as a function of CN_X loading nearing 90% or better with thermal stability as high as 283 °C.

Facile Carbonization of Microporous Organic Polymers into Hierarchically Porous Carbons Targeted for Effective CO2 Uptake at Low Pressures

The advent of microporous organic polymers (MOPs) has delivered great potential in gas storage and separation (CCS). However, the presence of only micropores in these polymers often imposes diffusion limitations, which has resulted in the low utilization of MOPs in CCS. Herein, facile chemical activation of the single microporous organic polymers (MOPs) resulted in a series of hierarchically porous carbons with hierarchically meso-microporous structures and high CO2 uptake capacities at low pressures. The MOPs precursors (termed as MOP-7-10) with a simple narrow micropore structure obtained in this work possess moderate apparent BET surface areas ranging from 479 to 819 m(2) g(-1). By comparing different activating agents for the carbonization of these MOPs matrials, we found the optimized carbon matrials MOPs-C activated by KOH show unique hierarchically porous structures with a significant expansion of dominant pore size from micropores to mesopores, whereas their microporosity is also significantly improved, which was evidenced by a significant increase in the micropore volume (from 0.27 to 0.68 cm(3) g(-1)). This maybe related to the collapse and the structural rearrangement of the polymer farmeworks resulted from the activation of the activating agent KOH at high temperature. The as-made hierarchically porous carbons MOPs-C show an obvious increase in the BET surface area (from 819 to 1824 m(2) g(-1)). And the unique hierarchically porous structures of MOPs-C significantly contributed to the enhancement of the CO2 capture capacities, which are up to 214 mg g(-1) (at 273 K and 1 bar) and 52 mg g(-1) (at 273 K and 0.15 bar), superior to those of the most known MOPs and porous carbons. The high physicochemical stabilities and appropriate isosteric adsorption heats as well as high CO2/N2 ideal selectivities endow these hierarchically porous carbon materials great potential in gas sorption and separation.

Development and characteristics of polymer monoliths for advanced LC bioscreening applications: A review

Biomedical research advances over the past two decades in bioseparation science and engineering have led to the development of new adsorbent systems called monoliths, mostly as stationary supports for liquid chromatography (LC) applications. They are acknowledged to offer better mass transfer hydrodynamics than their particulate counterparts. Also, their architectural and morphological traits can be tailored in situ to meet the hydrodynamic size of molecules which include proteins, pDNA, cells and viral targets. This has enabled their development for a plethora of enhanced bioscreening applications including biosensing, biomolecular purification, concentration and separation, achieved through the introduction of specific functional moieties or ligands (such as triethylamine, N,N-dimethyl-N-dodecylamine, antibodies, enzymes and aptamers) into the molecular architecture of monoliths. Notwithstanding, the application of monoliths presents major material and bioprocess challenges. The relationship between in-process polymerisation characteristics and the physicochemical properties of monolith is critical to optimise chromatographic performance. There is also a need to develop theoretical models for non-invasive analyses and predictions. This review article therefore discusses in-process analytical conditions, functionalisation chemistries and ligands relevant to establish the characteristics of monoliths in order to facilitate a wide range of enhanced bioscreening applications. It gives emphasis to the development of functional polymethacrylate monoliths for microfluidic and preparative scale bio-applications.