Choline Chloride Based Natural Deep Eutectic Solvents as Extraction Media for Extracting Phenolic Compounds from Chokeberry (Aronia Melanocarpa).

For the isolation of selected phenolic compounds from dried chokeberries, natural deep eutectic solvents (NADESs) were investigated as a green alternative to conventionally used extraction solvents. Four types of NADESs were synthesised, with choline chloride as the hydrogen bond acceptor in combination with different hydrogen bond donors (sugars, organic acid and urea). Ultrasound-assisted extraction was used to improve the extractability of the phenolic compounds and the results were compared to those obtained with 80% methanol as the extraction media. The highest values of total phenols and total flavonoids were found in the extract obtained with choline chloride-fructose NADES (36.15 ± 3.39 mg gallic acid g-1 dry weight (DW) and 4.71 ± 0.33 mg rutin g-1 DW, respectively). The extraction recoveries for the individual phenolic compounds depended strongly on the phenolic compound's structure, with relative mean values between 70% and 97%.

Thiol-Acrylate polyHIPEs via Facile Layer-by-Layer Photopolymerization.

A highly reactive thiol-ene high internal phase emulsion based on the monomers 1,6-hexanediol diacrylate and tris 2-(3-mercaptopropionyloxy)ethyl isocyanurate was developed for the purpose of light-driven additive manufacturing, resulting in highly porous customizable poly(high internal phase emulsion) materials. The formulation was specifically designed to facilitate short irradiation times and low amounts of photoinitiator. Furthermore, the developed emulsion does not rely on employing harmful solvents to make scale-up and industrial applications feasible. The selected thiol was added to the printing formulation as a chain-transfer agent, decreasing the brittleness of the acrylate-based system and potential of oxygen inhibition. The thickness of the printed layers lay <50 µm, and the average pore size of all samples was <5 µm.

Hierarchically porous materials from layer-by-layer photopolymerization of high internal phase emulsions.

A combination of high internal phase emulsion (HIPE) templating and additive manufacturing technology (AMT) is applied for creating hierarchical porosity within an acrylate and acrylate/thiol-based polymer network. The photopolymerizable formulation is optimized to produce emulsions with a volume fraction of droplet phase greater than 80 vol%. Kinetic stability of the emulsions is sufficient enough to withstand in-mold curing or computer-controlled layer-by-layer stereolithography without phase separation. By including macroscale cellular cavities within the build file, a level of controlled porosity is created simultaneous to the formation of the porous microstructure of the polyHIPE. The hybrid HIPE-AMT technique thus provides hierarchically porous materials with mechanical properties tailored by the addition of thiol chain transfer agent.

The use of an emulsion templated microcellular poly(dicyclopentadiene-co-norbornene) membrane as a separator in lithium-ion batteries.

The preparation of open-cell macroporous membranes made by the ring opening metathesis polymerization (ROMP) of a mixture of norbornene and dicyclopentadiene, and their basic applicability as separators in lithium-ion batteries, is discussed. Cyclic voltammetry (CV) measurements of negative electrodes (graphite) and positive electrodes (LiCoO2 ) are performed and the results prove the absence of parasitic decomposition reactions within the membrane at high oxidative or reductive potentials. Furthermore, LiCoO2 /Li half cell cycling studies of 100 charging/discharging cycles reveal that the newly disclosed separator and conventional commercial polyolefin based separators have similar performance. These results demonstrate that a potential weakness in the newly disclosed separator, namely residual double bonds present in the polymer network, does not limit the use of this material as a separator in lithium-ion batteries.

RAFT Polymerisation and Hypercrosslinking Improve Crosslink Homogeneity and Surface Area of Styrene Based PolyHIPEs.

The influence of a polymerisation mechanism (reversible addition-fragmentation chain transfer; RAFT vs. free radical polymerisation; FRP) on the porous structure of highly porous poly(styrene-co-divinylbenzene) polymers was investigated. The highly porous polymers were synthesised via high internal phase emulsion templating (polymerizing the continuous phase of a high internal phase emulsion), utilising either FRP or RAFT processes. Furthermore, residual vinyl groups in the polymer chains were used for the subsequent crosslinking (hypercrosslinking) applying di-tert-butyl peroxide as the source of radicals. A significant difference in the specific surface area of polymers prepared by FRP (between 20 and 35 m2/g) and samples prepared by RAFT polymerisation (between 60 and 150 m2/g) was found. Based on the results from gas adsorption and solid state NMR, it could be concluded that the RAFT polymerisation affects the homogeneous distribution of the crosslinks in the highly crosslinked styrene-co-divinylbenzene polymer network. During the initial crosslinking, RAFT polymerisation leads to the increase in mesopores with diameters between 2 and 20 nm, resulting in good accessibility of polymer chains during the hypercrosslinking reaction, which is reflected in increased microporosity. The fraction of micropores created during the hypercrosslinking of polymers prepared via RAFT is around 10% of the total pore volume, which is up to 10 times more than for polymers prepared by FRP. Specific surface area, mesopore surface area, and total pore volume after hypercrosslinking reach almost the same values, regardless of the initial crosslinking. The degree of hypercrosslinking was confirmed by determination of the remaining double bonds by solid-state NMR analysis.

High internal phase emulsion templating--a path to hierarchically porous functional polymers.

Recently, a series of new monomers and polymerization mechanisms has been applied to the templating of high internal phase emulsions (HIPEs) providing a route to hierarchically porous materials with a range of functionalities and applications. The high degree of control over the pore size is another attractive feature of these materials. Usually, the continuous phase contains monomers, the droplet phase is used to template the large, primary pores, which are interconnected by secondary pores. The addition of nonpolymerizable components to the continuous phase can result in phase separation during polymerization and tertiary pores. Applications include polymer supports for catalysis and synthesis, separation and filtration, cell culture media, enzyme supports, and structural and isolation applications.

Natural Deep Eutectic Solvent-Based Matrix Solid Phase Dispersion (MSPD) Extraction for Determination of Bioactive Compounds from Sandy Everlasting (Helichrysum arenarium L.): A Case of Stability Study.

In the present study, vortex-assisted matrix solid-phase dispersion (VA-MSPD) extraction was used to isolate the major bioactive compounds from H. arenarium. To reduce the negative environmental impact of the conventionally used organic solvents, four different choline chloride-based natural deep eutectic solvents (NADES) were investigated as possible eluents. The most influential VA-MSPD extraction parameters: stationary phase (adsorbent), adsorbent/sample ratio, vortex time, and volume of extraction solvent were systematically optimized. Ultrasound-assisted extraction with 80% MeOH was used as the standard method for the comparison of results. The stability of the obtained extracts was studied over a period of 0 to 60 days at three different temperatures (-18 °C, 4 °C, and 25 °C). All extracts were evaluated both spectrophotometrically (determination of total phenolic content (TPC) and antioxidant activity by ABTS and FRAP assay) and chromatographically (HPLC-UV). NADES based on choline chloride and lactic acid (ChCl-LA) was selected as the most effective extractant, with a determined TPC value of its extract of 38.34 ± 0.09 mg GA/g DW (27% higher than the methanolic VA-MSPD extract) and high antioxidant activity. The content of individual phenolic compounds (chlorogenic acid, dicaffeoylquinic acid isomers, naringenin isomers, and chalcones) in the ChCl-LA extract, determined by HPLC-UV, was comparable to that of the conventionally obtained one. Moreover, the stabilization effect of ChCl-LA was confirmed for the studied compounds: chlorogenic acid, naringenin-4'-O-glucoside, tomoroside A, naringenin-5-O-glucoside, isosalipurposide, and naringenin. The optimum VA-MSPD conditions for the extraction of H. arenarium polyphenols were: florisil/sample ratio of 0.5/1, a vortex time of 2 min, and an elution volume of ChCl-LA of 10 mL.

Emulsion Templated Porous Poly(thiol-enes): Influence of Photopolymerisation, Emulsion Composition, and Phase Behaviour on the Porous Structure and Morphology.

1,6-hexanediol diacrylate (HDDA) or divinyl adipate (DVA) and pentaerythritol tetrakis(3-mercaptopropionate) (TT) were polymerised via a thiol-ene radical initiated photopolymerisation using emulsions with a high volume fraction of internal droplet phase and monomers in the continuous phase as precursors. The porous structure derived from the high internal phase emulsions (HIPEs) followed the precursor emulsion setup resulting in an open porous cellularly structured polymer. Changing the emulsion composition and polymerisation conditions influenced the resulting morphological structure significantly. The investigated factors influencing the polymer monolith morphology were the emulsion phase ratio and surfactant concentration, leading to either interconnected cellular type morphology, bicontinuous porous morphology or a hollow sphere inverted structure of the polymerised monoliths. The samples with interconnected cellular morphology had pore diameters between 4 µm and 10 µm with approx. 1 µm sized interconnecting channels while samples with bicontinuous morphology featured approx. 5 µm wide pores between the polymer domains. The appropriate choice of emulsion composition enabled the preparation of highly porous poly(thiol-enes) with either polyHIPE or bicontinuous morphology. The porosities of the prepared samples followed the emulsion droplet phase share and could reach up to 88%.

Reusable Pd-PolyHIPE for Suzuki-Miyaura Coupling.

Palladium was immobilized on a highly porous copolymer of 4-vinylpyridine and divinylbenzene (polyHIPE-poly(high internal phase emulsion)) using palladium(II) acetate to obtain PolyPy-Pd with 6.1 wt % or 0.57 mmol Pd/g. The immobilized catalyst was able to catalyze the coupling of iodobenzene and phenylboronic acid in ethylene glycol monomethyl ether/water (3:1) within 4 h at rt and complete conversion was observed when 2.5 mol % of Pd per PhI was used. The reaction tolerated a wide range of substituents on the aromatic ring. Iodobenzene derivatives with electron-withdrawing substituents showed higher reactivity, while the opposite was true for the phenylboronic acid series. The polyHIPE-supported Pd catalyst was also used for the direct conversion of phenylboronic acid to biphenyl through an iodination/coupling reaction sequence. The recyclability of the heterogeneous catalyst was also optimized, and by finding a suitable combination of solvents for the loading of Pd, the reaction, and the isolation of the product, the solid-supported catalyst was completely regenerated and used in the next reaction with the same activity.

Hierarchically Porous Microspheres by Thiol-ene Photopolymerization of High Internal Phase Emulsions-in-Water Colloidal Systems.

A facile method for the preparation of hierarchically porous spherical particles using high internal phase water-in-oil-in-water (w/o/w) double emulsions via the photopolymerization of the water-in-oil high internal phase emulsion (w/o HIPE) was developed. Visible-light photopolymerization was used for the synthesis of microspherical particles. The HIP emulsion had an internal phase volume of 80% and an oil phase containing either thiol pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) or trimethylolpropane tris(3-mercaptopropionate) (TMPTMP) and acrylate trimethylolpropane triacrylate (TMPTA). This enabled the preparation of microspheres with an open porous morphology, on both the surface and within the microsphere, with high yields in a batch manner. The effect of the thiol-to-acrylate ratio on the microsphere diameter, pore and window diameter, and degradation was investigated. It is shown that thiol has a minor effect on the microsphere and pore diameter, while the acrylate ratio affects the degradation speed, which decreases with increasing acrylate content. The possibility of free thiol group functionalization was demonstrated by a reaction with allylamine, while the microsphere adsorption capabilities were tested by the adsorption of methylene blue.

Porous Polymers from High Internal Phase Emulsions as Scaffolds for Biological Applications.

High internal phase emulsions (HIPEs), with densely packed droplets of internal phase and monomers dispersed in the continuous phase, are now an established medium for porous polymer preparation (polyHIPEs). The ability to influence the pore size and interconnectivity, together with the process scalability and a wide spectrum of possible chemistries are important advantages of polyHIPEs. In this review, the focus on the biomedical applications of polyHIPEs is emphasised, in particular the applications of polyHIPEs as scaffolds/supports for biological cell growth, proliferation and tissue (re)generation. An overview of the polyHIPE preparation methodology is given and possibilities of morphology tuning are outlined. In the continuation, polyHIPEs with different chemistries and their interaction with biological systems are described. A further focus is given to combined techniques and advanced applications.

Influence of Functional Group Concentration on Hypercrosslinking of Poly(vinylbenzyl chloride) PolyHIPEs: Upgrading Macroporosity with Nanoporosity.

With the aim to study the influence of monomer ratio in poly(high internal phase emulsions) (polyHIPEs) on the polymer network architecture and morphology of poly(vinylbenzyl chloride-co-divinylbenzene-co-styrene) after hypercrosslinking via the internal Friedel-Crafts process, polyHIPEs with 80% overall porosity were prepared at three different initial crosslinking degrees, namely 2, 5, and 10 mol.%. All had typical interconnected cellular morphology, which was not affected by the hypercrosslinking process. Nitrogen adsorption and desorption experiments with BET and t-plot modelling were used for the evaluation of the newly introduced nanoporosity and in combination with elemental analysis for the evaluation of the extent of the hypercrosslinking. It was found that, for all three initial crosslinking degrees, the minimum amount of functional monomer, 4-vinylbenzyl chloride, was approximately 30 mol.%. Hypercrosslinking of polymers with lower concentrations of functional monomer did not result in induction of nanoporosity while the initial crosslinking degree had a much lower impact on the formation of nanoporosity.

Non-invasive determination of ionizable ligand group density on high internal phase emulsion derived polymer.

Stepwise change between low and high salt concentration buffers of the same pH results in pH transition, the length of which was demonstrated to be proportional to the quantity of ion-exchange groups present on the matrix. In this work, we analyzed the effect of the ligand type, density, and buffer concentration on the pH transition shape for typical ion-exchange groups (QA, DEAE, SO3, and COOH) and ligands acting as metal-chelators, such as IDA, TAEA, and EDA. It was demonstrated that pH transition can occur either as a chromatographic or flat-top peak. pH transition peaks were evaluated by their length, height, and peak center parameters. While no parameter can describe the ligand density accurately with a single linear correlation for both peak types, all parameters can be used for the description of one peak type. Peak length and height exhibited the same accuracy, while their sensitivity depended on the pH transition shape: length being more sensitive for the flat-top peaks, while height for the chromatographic peaks. pH height can be obtained faster, at lower elution volume, and seems to be more suitable for the determination of low amounts of ligand, when typically chromatographic peak type pH transitions occur.

Thiol-Ene Cross-linking of Poly(ethylene glycol) within High Internal Phase Emulsions: Degradable Hydrophilic PolyHIPEs for Controlled Drug Release.

Macroporous polymer monoliths prepared from high internal phase emulsions (HIPEs) can be found in various biomedical applications. While typically water-in-oil HIPEs are applied for polyHIPE preparation, they are not suitable for hydrophilic polyHIPE preparation. Herein, direct oil-in-water emulsions based on water-soluble poly(ethylene glycol)diacrylate or poly(ethylene glycol)dimethacrylate were developed. Furthermore, the incorporation of a hydrophilic water-miscible thiol, ethoxylated trimethylolpropane tris(3-mercaptopropionate) (ETTMP) was reported for the first time within thiol-ene polyHIPEs. Due to the transparency of the emulsions, rapid curing via photopolymerization was feasible. The average pore diameters of the resulting polyHIPEs ranged between 1.2 and 3.6 µm, and porosity of up to 90% was achieved. The water uptake of the materials reached up to 1000% by weight. Drug loading and release were demonstrated, employing salicylic acid as a model drug. Porous profile and biodegradability add to the usefulness of the material for biomedical applications.

Post Polymerisation Hypercrosslinking with Emulsion Templating for Hierarchical and Multi-Level Porous Polymers.

Porosity in polymers and polymeric materials adds to their functionality due to achieving the desired tailored characteristics porosity offers, such as improved mass transfer through the material, improved accessibility of reactive sites, reduced overall mass, tunable separation properties, etc. Therefore, applications in many fields, e.g. catalysis, separation, solid phase synthesis, adsorption, sensing, biomedical devices etc., drive the development of polymers with controlled morphology in terms of pore size, shape, interconnectivity and pore size distribution. Of particular interest are polymers with distinct bimodal or hierarchical pore distribution as this enables uses in applications where pore sizes on multiple levels are needed. Emulsion templating can be used for the preparation of polymers with included interconnected spherical pores on the micrometre level while post polymerisation crosslinking adds micro porosity. Combined use of both techniques yields multi-level and hierarchically porous materials with great application potential.

Open cellular reactive porous membranes from high internal phase emulsions.

High internal phase emulsions (HIPEs) incorporating styrene, 4-vinylbenzyl chloride, divinylbenzene and ethylhexyl acrylate were applied to prepare reactive, cross-linked porous membranes with open cellular architecture and thicknesses between 30 and 500 microm.

Characterisation of grafted weak anion-exchange methacrylate monoliths.

A weak ion-exchange grafted methacrylate monolith was prepared by grafting a methacrylate monolith with glycidyl methacrylate and subsequently modifying the epoxy groups with diethylamine. The thickness of the grafted layer was determined by measuring permeability and found to be approximately 90nm. The effects of different buffer solutions on the pressure drop were examined and indicated the influence of pH on the permeability of the grafted monolith. Protein separation and binding capacity (BC) were found to be flow-unaffected up to a linear velocity of 280cm/h. A comparison of the BC for the non-grafted and grafted monolith was performed using beta-lactoglobulin, bovine serum albumin (BSA), thyroglobulin, and plasmid DNA (pDNA). It was found that the grafted monolith exhibited 2- to 3.5-fold higher capacities (as compared to non-grafted monoliths) in all cases reaching values of 105, 80, 71, and 17mg/ml, respectively. It was determined that the maximum pDNA capacity was reached using 0.1M NaCl in the loading buffer. Recovery was comparable and no degradation of the supercoiled pDNA form was detected. Protein z-factors were equal for the non-grafted and grafted monolith indicating that the same number of binding sites are available although elution from the grafted monolith occurred at higher ionic strengths. The grafted monolith exhibited lower efficiency than the non-grafted ones. However, the baseline separation of pDNA from RNA and other impurities was achieved from a real sample.

Multiple-Level Porous Polymer Monoliths with Interconnected Cellular Topology Prepared by Combining Hard Sphere and Emulsion Templating for Use in Bone Tissue Engineering.

A combination of hard sphere and high internal phase emulsion templating gives a platform for synthesizing hierarchically porous polymers with a unique topology exhibiting interconnected spherical features on multiple levels. Polymeric spheres are fused by thermal sintering to create a 3D monolithic structure while an emulsion with a high proportion of internal phase and monomers in the continuous phase is added to the voids of the previously constructed monolith. Following polymerization of the emulsion and dissolution of the templating structure, a down-replicating topology is created with a primary level of pores as a result of fused spheres of the 3D monolithic structure, a secondary level of pores resulting from the emulsion's internal phase, and a tertiary level of interconnecting channels. Thiol-ene chemistry with divinyladipate and pentaerythritol tetrakis(3-mercaptopropionate) is used to demonstrate the preparation of a crosslinked polyester with overall porosity close to 90%. Due to multilevel porosity, such materials are interesting for applications in bone tissue engineering, possibly simulating the native sponge like bone structure. Their potential to promote ossteointegration is tested using human bone derived osteoblasts. Material-cell interactions are evaluated and they reveal growth and proliferation of osteoblasts both on surface and in the bulk of the scaffold.

Atrazine removal by covalent bonding to piperazine functionalized PolyHIPEs.

The removal of atrazine from water by a solid phase extraction technique using insoluble polymers is described. Porous crosslinked polymers bearing piperazine moieties were prepared in a one step reaction from the precursor 4-nitrophenylacrylate incorporating polymers (PolyHIPE type prepared by the polymerization of the continuous phase of a high internal phase emulsion and polymer beads prepared by suspension polymerization). Polymers were applied to sequester atrazine from aqueous solutions with a concentration of 33 ppb and irreversible covalent bonding to the polymers was achieved. GC/MS/MS was used to monitor the dynamics of atrazine uptake and it was found that almost complete removal of atrazine was accomplished with an excess of polymer after 48 hours at room temperature. For comparison, polymer beads of identical chemistry but lower porosity were also used and showed significantly slower action (near complete removal after 72 hours).

Separation of heavy metals from water by functionalized glycidyl methacrylate poly (high internal phase emulsions).

Removal of silver, lead and cadmium ions from both model solutions and real contaminated water was achieved, in a flow through manner, by using highly porous functionalized poly(glycidyl methacrylate) materials, prepared by the polymerisation of high internal phase emulsions (polyHIPE), with significant sorption differences between metals allowing for selective removal. PolyHIPEs, initially prepared from glycidyl methacrylate as a functional monomer, were functionalized with pentaerythritol tetrakis(3-mercaptopropionate), 1,9-nonanedithiol and 2-aminobenzenethiol via the epoxy ring opening on the polymer supports and applied in a flow-through manner via encasements into dedicated disk holders. Capacity of 21.7mg Ag per gram of polymer was found for 1,9-nonanedithiol functionalized polymers, while the capacity was decreasing with the decreasing ionic radius of the metal; the dynamics of sorption also depended on metal ion size and furthermore on the thiol used for the polymer functionalization.