Porous Polymer Monoliths Research Articles

Emulsion-templated porous polymers prepared by thiol-ene and thiol-yne photopolymerisation using multifunctional acrylate and non-acrylate monomers

The chemical and mechanical properties of macroporous polymer substrates play a crucial role in the determination of their end-application. The preparation of highly (macro)porous monolithic polymers (polyHIPEs) by emulsion templating and thiol-ene/yne photopolymerisation, using multifunctional acrylate, allyl ether and alkyne-based monomers with trimethylolpropane tris (3-mercaptopropionate) (TMPTMP), is described in this work. Issues associated with monomer solubility and/or stability of the produced high internal phase emulsions (HIPEs) are tackled. Scanning electron microscopy (SEM) is used to study the morphology and porosity (average void diameters) of the obtained materials. Due to the nature of the photoinitiated thiol-ene reactions, materials obtained from acrylate monomers display residual thiols that are quantified by a colourimetric (Ellman's) assay. Raman spectroscopy is also shown to be a complementary technique to evaluate the residual thiol content. The influence of the monomer functionality on the mechanical properties of the material is explored using compression tests. Significant differences in the surface functionality and mechanical behavior between materials prepared with comonomers able to homopolymerise (acrylates) and those unable to homopolymerise (allyl ethers; alkynes) are demonstrated.

Wulff-type boronic acids suspended hierarchical porous polymeric monolith for the specific capture of cis-diol-containing flavone under neutral condition

An apparent disadvantage of boronate affinity is that it has to be performed in alkaline media and can lead to the oxidation of cis-diols in compounds. A new strategy named as post functionalization with B-N coordination complex was present to prepare boronic acid suspended macroporous polymeric monolith for the selective capture of cis-diol-containing luteolin (LTL) under neutral condition. In this work, a water-in-oil (W/O) Pickering (high internal phase emulsions) HIPE template stabilized by boronic acid suspended mesoporous silica nanoparticles (BA-MSNs) was applied to prepare macroporous poly(glycidyl methacrylate) monolith (PGM-Pickering-0.10), and then B-N coordination complex resulted from the reaction of 3-aminophenylboronic acid (APBA) and 1,6-hexamethylenediamine was integrated to the PGM-Pickering-0.10. As-prepared hierarchical porous PGM-Pickering-0.10-BN with “Wulff-type boronic acids” possessed special mesopore-in-macropore structure. In static adsorption, pH-dependent adsorption experiments demonstrated that PGM-Pickering-0.10-BN was able to capture LTL with expected high adsorption amount (158.5µmolg−1 at 298K) and fast binding kinetics (equilibrium in 2.0h) under neutral condition, while macroporous polymers without post functionalization or functionalized only with APBA display poor adsorption performance at pH=7.0. In addition, BA-MSNs as the stabilizers enhanced the mechanical property and specific adsorption ability of PGM-Pickering-0.10-BN simultaneously, and the integrated B-N coordination complex did play vital roles in the specific adsorption of LTL. By optimizing dynamic adsorption factors with response surface methodology (RSM), the maximum adsorption amount of 177.8µmolg−1 was also achieved under neutral condition.

Development of an online solid-phase extraction with liquid chromatography method based on polymer monoliths for the determination of dopamine.

Porous polymer monoliths have been used to develop an online solid-phase extraction with liquid chromatography method for determination of dopamine in urine as well as for a continuous monitoring of dopamine in flowing system. A polymerization mixture containing 4-vinylphenylboronic acid monomer has been used to prepare a trapping column based on specific ring formation reaction with dopamine cis-diol functionality. Additionally, a monolithic stationary phase with zwitterion functionality has been used to prepare capillary column for the separation of dopamine. Experimental conditions including molarity, pH, and flow rate of the loading buffer together with a valve switching time have been optimized to provide the highest recovery for dopamine. Experimental setup has been used to determine dopamine in a urine. By using both calibration curve and standard addition method, the dopamine level was determined to be 1.19 and 1.28 mg/L, respectively. Further, we have used experimental design to optimize coupling of two extraction monolithic loops to separation capillary column with monolithic phase for a comprehensive monitoring of dopamine. After multivariate analysis, sample loading flow-rate and a flow-rate of flushing buffer were selected as the most significant variables. Optimized experimental setup was applied to continuously monitor dopamine degradation.

Effect of sporopollenin microparticle incorporation into the hexyl methacrylate-based monolithic columns for capillary liquid chromatography

ABSTRACTSporopollenin microparticles have been prepared form Lycopodium clavatum spores, defatted and incorporated into a porous methacrylate polymer monolith to enhance liquid chromatographic performance of different sets of small neutral molecules. A stable suspension between sporopollenin microparticles and porogenic solvents composed of 1-propanol and 1,4-butandiol has proved before preparation, and seven compositions with increasing sporopollenin microparticles were prepared inside fused silica tubing. After optimizing of the preparation conditions, the structure of the stationary phase was characterized by scanning electron microscopy, surface area analysis, thermodynamic study, short- and long-term precision, and hydrodynamic properties including mechanical stability, porosity, and permeability. The columns were successfully applied to improve the separation efficiency of different mixtures using capillary liquid chromatography. Addition of very small amount of sporopollenin microparticles to the methacrylate mixture enhanced the column efficiency from 3 to 5 times for ketonic and phenolic compounds and reduced the retention with the corresponding better resolution and peak shapes for all studied compounds.

Porous Polymer Microneedles with Interconnecting Microchannels Toward Efficient Sensing of Interstitial Fluid

The microneedle array, the two-dimensional array of small needles of submillimeter length, is a minimally invasive alternative to conventional hypodermic needles. It penetrates skin and bypasses the diffusion barrier of stratum corneum and facilitates drug delivery as well as sampling and electrochemical sensing of biologically relevant molecules in interstitial fluid.1,2 Microneedles for sampling interstitial fluid fall into three types: hollow microneedles, hydrogel microneedles, and porous microneedles. Hollow microneedles have a bore inside the microneedle made by a photolithographic process. Hydrogel microneedles swell by absorption of interstitial fluid, and ex vivo analysis has been achieved. Porous microneedles have random pores in the body of the microneedle, and they have advantages such as a large pore volume ratio, efficient capillary action by many microchannels, large surface area for immobilization of sensor molecules, etc. Making porous microneedles with a polymer material has the advantages such as biocompatibility, easy fabrication by molding, a variety of molecular structures for tuning properties, etc. Despite their apparent advantages, the fabrication of porous polymer microneedles has been a challenge. In this study, we have fabricated microneedle arrays made of a porous polymer with interconnecting micropores.3 A porous polymer monolith is synthesized by polymerizing glycidyl methacrylate (GMA) with bi- and trifunctional crosslinkers by the irradiation of 365 nm UV in the presence of poly(ethylene glycol) in 2-methoxyethanol as a porogen, followed by washing with methanol/water.4 We fabricated a porous polymer monolith of this poly(glycidyl methacrylate) (PGMA) in a soft polydimethylsiloxane mold. The resulting microneedle array was a hard, opaque solid (Figure (a)), whereas a control with no porogen was transparent. Scanning electron microscopy (SEM) observation revealed that microneedles made with a porogen have interconnecting pores with ~1 µm in diameter on the surface and interior (Figure (b)). The porous microneedles with varied porogen ratios were fabricated to investigate its effects on porosity, water absorption speed, and skin penetration efficiency. Porosity was measured by weight increase of the porous microneedles after immersion into water. As an porogen ratio was increased, the porosity increased as well. The pore connectivity parameter, defined as (porosity)/(porogen ratio), versus a porogen ratio showed a sigmoidal profile that converges to unity, which indicated all the pores are interconnecting and accessible from the surface above a certain threshold of the porogen ratio. Water absorption speed of the porous microneedles was evaluated by a piece of water sensor paper that turns blue upon water absorption. The water sensor was attached on the top surface of the microneedle array, and the response time of the water sensor was measured. The response time decreased sharply to less than 20 minutes at the 36% porogen ratio, and this was consistent with the threshold of the porogen ratio for pore connectivity. The microneedle arrays were applied to a pig skin with the force of 1 N/needle, and punctured spots of the pig skin were stained with trypan blue. The microneedle arrays with lower porogen ratios had higher penetration efficiencies, and the porous microneedles with >80% penetration efficiency was achieved for the porogen ratio no more than 49%. With the lower porogen ratios, the porous microneedles become mechanically more robust, and the tips of the microneedles become sharper. In summary, by optimizing the porogen ratio (Figure (c)), we successfully developed porous polymer microneedles that combine fast water absorption speed and high skin penetration efficiency. The fabricated porous microneedles are a potentially versatile tool for sampling and sensing of interstitial fluid.

Preparation of new dioxygen‐active triphenylantimony(V) catecholate‐containing porous polymer

Novel porous polymers with 4‐ethoxy‐3,6‐di‐tert‐butyl‐o‐benzoquinone grafted to the porous surface have been prepared via the secondary functionalization of porous polymer monoliths obtained by the photopolymerization of oligo(carbonate dimethacrylate) and hydroxyethyl methacrylate in methanol solution. These quinone‐functionalized polymers have been applied for the synthesis of triphenylantimony(V) catecholate‐containing polymers by the oxidative addition reaction of quinone moieties with SbPh3. The obtained antimony‐containing porous polymeric material is able to reversibly bind molecular oxygen in nearly quantitative yield. The rate of molecular oxygen sorption is 900 times higher for the porous material than that for the same film material and comparable with the process rate in solution. Copyright © 2016 John Wiley & Sons, Ltd.

Advances in monoliths and related porous materials for microfluidics.

In recent years, the use of monolithic porous polymers has seen significant growth. These materials present a highly useful support for various analytical and biochemical applications. Since their introduction, various approaches have been introduced to produce monoliths in a broad range of materials. Simple preparation has enabled their easy implementation in microchannels, extending the range of applications where microfluidics can be successfully utilized. This review summarizes progress regarding monoliths and related porous materials in the field of microfluidics between 2010 and 2015. Recent developments in monolith preparation, solid-phase extraction, separations, and catalysis are critically discussed. Finally, a brief overview of the use of these porous materials for analysis of subcellular and larger structures is given.

Chip-based electrochromatography coupled to ESI-MS detection.

In this study, we present the coupling of chip-based electrochromatography to MS using a glass chip with a monolithically integrated nanoelectrospray emitter. As separation column, an acrylate-based porous polymer monolith is implemented into the glass chip by photopolymerization. For the establishment and development of this method, we used a test mixture detectable with both fluorescence and ESI-MS. After successful evaluation of the approach with the test solutes, it was applied exemplarily for drug analysis such as high-speed separations of benzodiazepines in pharmaceuticals.

Adjustable Methacrylate Porous Monolith Polymer Layer Open Tubular Silica Capillary Microextraction for the Determination of Polycyclic Aromatic Hydrocarbons

ABSTRACTA novel adjustable porous polymer monolith layer open tubular silica capillary microextraction (PLOT-ME) device was fabricated by thermal polymerization of a poly(glycidylmethacrylate-co-ethylene glycol dimethacrylate) (GMA-co-EDMA) polymer film (∼20 µm) within a 250 µm internal diameter silica capillary initiated with 4,4′-azobis(4-cyanopentanoyl chloride). The polymer film thickness and morphology were controlled by the polymerization time and temperature. The length of the microextraction platform immersed in the sample was adjusted by the sample concentration and sample matrix. Furthermore, since the microextraction platform performance typically degraded with use, the PLOT-ME device affords a new microextraction zone that may be exposed by cleaving off the end. This ability significantly reduces the cost of microextraction for academic and research environments. The performance of the PLOT-ME device was tested for microextraction of polycyclic aromatic hydrocarbons (PAHs): naphthalene, 2,6-dimethylnaphthalene, anthracene, 9-methylanthracene, and phenanthrene in aqueous media. Linear calibration curves for the PAHs were obtained with correlation coefficients near unity and relative standard deviations from 2 to 20% for PAH standards from 100 to 0.1 µg/L. The limits of detection for the PAHs were between 0.02 and 0.06 µg/L, while the recoveries were from 97 to 104% in lake water. The precision between different PLOT-ME devices was 11%.

Thiol-Maleimide Michael Addition Click Reaction: A New Route to Surface Modification of Porous Polymeric Monolith

A new and efficient approach based on the thiol–maleimide Michael addition click reaction is presented for the post-polymerization modification of porous monoliths. To establish the method, a generic matrix containing N-hydroxysuccinimide esters (NHS) as surface reactive units is synthesized inside a capillary column through photoinduced polymerization of N-acryloxysuccininimide and ethylene glycol dimethylacrylate. The as-obtained reactive monolith is further surface-functionalized through nucleophilic substitution of the NHS units with 2-aminoethanethiol. Following such an approach, free thiols are available for reacting with functional maleimides through Michael addition. Success of the successive molecular level surface functionalization steps is ascertained by Raman spectroscopy measurements. Of utmost importance, it is undoubtedly demonstrated that the chemical nature, i.e., hydrophilic versus hydrophobic, of the surface-grafted maleimide governs the surface properties of the corresponding monoliths. More precisely, the electrochromatographic separation mode is found to be intimately correlated to the chemical nature—C8-like versus COOH-like—of the maleimide-functionalized monolith allowing separation upon either reversed-phase or hydrophilic interaction modes, respectively. Furthermore, the strategy is extended to enhancement of surface NHS reactivity enabling the efficient grafting of model biomacromolecule via a spacer arm-driven effect.

Emulsion-cryogelation technique for fabricating a versatile toolbox of hierarchical polymeric monolith and its application in chromatography

A novel poly (glycidyl methacrylate-co-ethylene dimethacrylate) monolith has been fabricated via the environmental friendly cryogelation-emulsion technique. The polymerization process is assisted by self-assembly of typical tri-block copolymer Pluronic F127 at sub-zero temperature using ice crystal as template, which can avoid consumption of organic porogenic solvents and thermal unstability of emulsion system. The developed monolith possesses hierarchical networks, which is confirmed by nitrogen adsorption measurement, mercury intrusion porosimetry, scanning electron microscopy and permeability testing. Further, the effect of the amounts of Pluronic F127 on the microstructure has been investigated. Moreover, the prepared polymer monolith undergoes acidic hydrolysis of epoxy groups into hydroxyl groups on the surface and its liquid chromatographic performance is explored by separating model analytes. The results indicate that the unique porous polymer monolith with hierarchical networks could be prepared via an organic porogen-free approach and used for analysis of polar and nonpolar molecules, extending the application of cryogelation-emulsion technique and methacrylate-based monolith.

Highly Porous Polymer Monolith Immobilized with Aptamer (RNA) Anchored Grafted Tentacles and Its Potential for the Purification of Lysozyme

An aptamer immobilized tentacle-type monolith is prepared for lysozyme purification with excellent selectivity and high adsorbing capacity. In this study, the aptamer immobilized glycidyl methacrylate (GMA) serves as monomer to be grown into long polymer chains on a highly porous monolith by a series of reactions. This tentacle grafting gives rise to a sharp increase of aptamer coverage density and realizes the multilayer adsorption for protein. The dynamic adsorption capacity of the grafted monolith reaches 68.22 and 77.07 mg mL–1 for lysozyme at the breakthrough of 10% and 50%, respectively, up to approximately 10-fold higher than the ungrafted one. Despite the high adsorption capacity, the novel aptamer anchored tentacle grafted monolith separates perfectly lysozyme from the protein mixture, indicating the excellent adsorptive selectivity. By taking the advantages of high capacity and excellent selectivity, the affinity-grafted monolith is applied successfully to purify lysozyme from the diluted chicke...

Preconcentration of bisphenols by using calix[4]arene derivatives modified porous polymer monolith coupled with HPLC

A functionalized calix[4]arene (alkenyl@C[4]A) was introduced into the poly(butyl methacrylate-ethylene dimethacrylate) monolith inside a capillary to prepare a polymer monolith microextraction (PMME) material (poly(BMA-alkenyl@C[4]A-EDMA)).

Polymerizable organo-gelator-stabilized gel-emulsions toward the preparation of compressible porous polymeric monoliths

Compressible porous polymeric monoliths could be used as highly efficient formaldehyde and toluene adsorbents.

Current trends in the development of porous polymer monoliths for the separation of small molecules.

Since their introduction, the main application area of porous polymer monoliths has been in the fast gradient separation of synthetic and natural polymers. On the other hand, it has proven to be difficult to prepare polymer monoliths providing column efficiency comparable with particulate and monolithic silica-based stationary phases. During this decade, several experimental approaches were performed that aimed to improve this property of polymer monoliths. These protocols include variation in a polymerization time and preparation of monolithic stationary phases at limited conversion of the polymerization reaction, application of novel, highly ordered, nanomaterials, and/or hypercross-linking surface modification controlling the cross-link density of prepared monoliths. By using some of these approaches, monolithic stationary phases with column efficiency reaching 200,000 plates/m for low-molecular-weight compounds have been prepared. This review deals with preparation of polymer monoliths for the separation of small molecules and summarizes recent development in this field. At first, it focuses on monolithic columns morphology and repeatability of their preparation. Then, recent results in individual experimental protocols are discussed. Finally, possible future steps leading to the preparation of more efficient monolithic stationary phases are outlined.

Planar monolithic porous polymer layers functionalized with gold nanoparticles as large-area substrates for sensitive surface-enhanced Raman scattering sensing of bacteria

For the first time, large-area surface-enhanced Raman scattering sensing active substrates using porous polymer monolithic layers have been successfully prepared. Our approach includes a simple photoinitiated polymerization process using glycidyl methacrylate and ethylene dimethacrylate in a glass mold, followed by a chemical reaction of the epoxy functionalities leading to thiols, and the attachment of preformed gold nanoparticles. We demonstrated that this very simple process produced uniform and reproducible large area surfaces that significantly enhance sensitivity of Raman spectroscopy. Experiments were also carried out that confirmed preferential adsorption of living bacteria Escherichia coli from a very dilute solution on the surface of the monolithic layer, and immediate detection of the captured microorganisms using the SERS spectrum.

Assessing structural correlations and heterogeneity length scales in functional porous polymers from physical reconstructions.

A general, model-free, quantitative approach to the key morphological properties of a porous polymer monolith is presented. After 3D reconstruction, image-based analysis delivers detailed spatial and spatially correlated information on the structural heterogeneities in the void space and the polymer skeleton. Identified heterogeneities, which limit the monolith's performance in targeted applications, are traced back to the preparation process.

Radical-mediated step-growth: Preparation of hybrid polymer monolithic columns with fine control of nanostructural and chromatographic characteristics

The currently most successful type of porous polymer monoliths utilized in chromatography is prepared by free-radical cross-linking (co)polymerization in porogenic solvents and a single-step molding process. Though such types of materials are well-recognized in the scientific community, they suffer from their multi-scale heterogeneity originating from the nanoscale through to their microscale and ultimately limited performance on their macroscale. This is in particular true when estimating their performance under equilibrium (i.e. isocratic) elution conditions for retained compounds.In this contribution, we study a new concept in the preparation of porous monolithic hybrid materials based on polyhedral oligomeric vinylsilsesquioxanes which undergo radical mediated step-growth cross-linking with thiol-linkers. Fundamental characterization of this new entry of materials is performed via a variety of characterization approaches including infrared and Raman spectroscopies, thermogravimetric analysis, gel fraction, dry-state surface area analysis, and visualization of the capillary-scale porous structure by scanning electron microscopy. This characterization identifies that a rational choice of experimental conditions in monolith preparation leads to destined and desirable materials’ properties, in particular with experimentally accessible near-ideal nanoscale network structures. With the obtained structural informations at hand, we finally evidence the monoliths’ tailored chromatographic performance by isocratic elution experiments of structurally similar small molecules under reversed-phase type of chromatographic conditions. This validates the fundamental origin for an improved performance of these types of monolithic materials under solvated conditions that has its foundation established in the creation of near-ideal nanoscale networks of material. This identified ideality is manifested in an enhanced and almost retention-insensitive performance in liquid chromatographic separations of small molecules across wide ranges of retention factors over at least two orders of magnitude and wide ranges of mobile phase compositions. Such experimental observation is explained by a more homogeneous energetic distribution of partition and adsorption sites. A reference analysis of normalized plate height data at varied retention was performed and set in context with data of state-of-the-art silica- and polymer-based monoliths. This analysis clearly identifies the present materials to display performance behavior clearly located in the domain of derivatized silica-based monoliths.

Hierarchically Porous Polymer Monoliths by Combining Controlled Macro- and Microphase Separation.

The ability to tune polymer monolith porosity on multiple length scales is desirable for applications in liquid separations, catalysis, and bioengineering. To this end, we have developed a facile synthetic route to nanoporous polymer monoliths based on controlled polymerization of styrene and divinylbenzene from a poly(lactide) macro-chain transfer agent in the presence of nonreactive poly(ethylene oxide) (PEO). Simple variations in the volume fraction and/or molar mass of PEO lead to either polymerization-induced microphase separation or simultaneous macro- and microphase separation. These processes dictate the resultant morphology and allow for control of the macro- and microstructure of the monoliths. Subsequent selective etching produces monoliths with morphologies that can be tailored from mesoporous, with control over mesopore size, to hierarchically meso- and macroporous, with percolating macropores. This convenient synthetic route to porous polymer monoliths has the potential to be useful in applications where both rapid mass transport and a high surface area are required.

Incorporation of ionic liquid into porous polymer monoliths to enhance the separation of small molecules in reversed-phase high-performance liquid chromatography.

An ionic liquid was incorporated into the porous polymer monoliths to afford stationary phases with enhanced chromatographic performance for small molecules in reversed-phase high-performance liquid chromatography. The effect of the ionic liquid in the polymerization mixture on the performance of the monoliths was studied in detail. While monoliths without ionic liquid exhibited poor resolution and low efficiency, the addition of ionic liquid to the polymerization mixture provides highly increased resolution and high efficiency. The chromatographic performances of the monoliths were demonstrated by the separations of various small molecules including aromatic hydrocarbons, isomers, and homologues using a binary polar mobile phase. The present column efficiency reached 27 000 plates/m, which showed that the ionic liquid monoliths are alternative stationary phases in the separation of small molecules by high-performance liquid chromatography.