| 1. |
- Byström, Emil, 1980-, et al.
(author)
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Differences in porous characteristics of styrenic monoliths prepared by controlled thermal polymerization in molds of varying dimensions
- 2010
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In: Journal of Separation Science. - : Wiley. - 1615-9306 .- 1615-9314. ; 33:2, s. 191-199
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Journal article (peer-reviewed)abstract
- Nitroxide-mediated polymerization was used as a model system for preparing styrenic monolithic materials with significant mesopore contents in different mold formats, with the aim of assessing the validity of pore characterization of capillary monoliths by analysis of parallel bulk polymerized precursor solution. Capillary monoliths were prepared in 250 mm id fused silica tubes (quadruplicate samples, in total 17 m), and the batch polymerizations were carried out in parallel in 100 mL microvials and regular 2mL glass vials, both in quintuplicate. The monoliths recovered from the molds were characterized for their meso- and macroporous properties by nitrogen sorptiometry (three repeated runs on each sample), followed by a single analysis by mercury intrusion porosimetry. A total of 14 monolith samples were thus analyzed. A Grubbs’ test identified one regular vial sample as an outlier in the sorptiometric surface area measurements, and data from this sample were consequently excluded from the pore size calculations, which are based on the same nitrogen sorption data, and also from the mercury intrusion data set. The remaining data were subjected to single factor analyses of variance analyses to test if the porous properties of the capillary monoliths were different from those of the bulk monoliths prepared in parallel. Significant differences were found between all three formats both in their meso and macroporous properties. When the dimension was shrunk from conventional vial to capillary size, the specific surface area decreased from 52.274.7 to 34.671.7m2/g. This decrease in specific surface area was accompanied by a significant shift in median diameter of the through-pores, from 31073.9 to 544713 nm. None of these differences was obvious from the scanning electron micrographs that were acquired for each sample type. The common practice of determining the mesopore characteristics from analysis of samples prepared by parallel bulk polymerization and looking for changes in the macropore structure by visual assessment of SEMs are therefore both rather questionable, at least for monoliths of the kind used in this study.
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| 2. |
- Courtois, Julien, et al.
(author)
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A study of surface modification and anchoring techniques used in the preparation of monolithic microcolumns in fused silica capillaries.
- 2006
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In: Journal of Separation Science. - : Wiley. - 1615-9306 .- 1615-9314. ; 29:1, s. 14-24
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Journal article (peer-reviewed)abstract
- Based on a survey of the literature on pretreatment of fused silica capillaries, 3 etching procedures and 11 silanization protocols based on the vinylic silane 3-((trimethoxysilyl)propyl) methacrylate (gamma-MAPS) were found to be most representative as a means of ensuring attachment of in situ prepared vinylic polymers. These techniques were applied to fused silica capillaries and the success in establishing the intended surface modification was assessed. X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical state of the surface, providing information regarding presence of the reagent bound to the capillary. Wetting angles were measured and correlated with the XPS results. An adherence test was done by photopolymerization of a 2 mm long plug of 1,6-butanediol dimethacrylate in the prepared capillaries and evaluation of its ability to withstand applied hydraulic pressure. SEM was also performed in cases where the plug was released or other irregularities were observed. Finally, the roughness of the etched surface, considered to be of importance, was assessed by atomic force microscopy. Alkaline etching at elevated temperature provided a surface roughness promoting adhesion. The commonly used silanization protocols involving water in the silanization or washing steps gave inadequate surface treatment. The best silanization procedure was based on toluene as a solvent.
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| 3. |
- Elhaj, Ahmed, 1981-, et al.
(author)
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Monolithic space-filling porous materials from engineering plastics by thermally induced phase separation
- 2014
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 6:18, s. 15653-15666
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Journal article (peer-reviewed)abstract
- Six different uncompounded engineering and commodity polymers were evaluated for their ability to produce space-filling monolithic entities by thermally induced phase separation (TIPS) from 22 different solvents. Attempts were first made to dissolve the polymers at elevated temperatures, selected below the boiling point of each solvent. Then the solutions of polymers that were homogeneous dissolved underwent a controlled temperature decrease to induce a phase separation as the upper critical solution temperature was passed. Twelve of the solvents gave monolithic entities by this procedure, materials that were characterized with regard to their specific surface area and pore size distribution. These measured parameters were then correlated with their macroporous morphology, assessed by scanning electron microscopy. Monolithic materials with widely different mesoporous properties were obtained with specific surface areas ranging from 169 m(2)/g to structures with essentially nonporous skeletons and distinct mesopore size distribution modes from 6 to 15 nm. The materials furthermore had a wide variation in their macroporous morphologies-among the same polymer processed in different solvents and between different polymers dissolved in the same solvent. TIPS processing therefore appears to be a viable route to prepare space-filling meso- and macroporous support materials for a wide variety of purposes in separation science and heterogeneous chemistry.
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| 4. |
- Elhaj, Ahmed, 1981-, et al.
(author)
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Porous Melamine-Formaldehyde Monoliths by Step-Growth Polymerization Reactions via an Organic Sol-gel Process
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Other publication (other academic/artistic)abstract
- In this explorative study, twenty hydrophilic melamine-formaldehyde (MF) monolith materials were synthesized by acid-catalyzed polycondensation of systems consisting of an aqueous MF precondensate, a block copolymeric surfactant as main porogen, and short aliphatic polyethers as co-porogens, which were dispersed in three different organic solvents covering a wide span in polarity. The molecular size and type of aliphatic polyether (co-porogen), and of the ratio of solvents to the other components were investigated by an experimental design that resulted in monolithic materials covering a wide range of different meso- and macroporous properties. A multivariate assessment revealed that the strongest contributors to the mesopore size and the inversely related surface area were the co-porogens, whereas the macropore dimension was explained by the solvents and the ratio between solvents and the other components. Surface elemental analysis by XPS showed slight differences in the bridging type between monoliths of opaque glass-like vs. white solid appearance. Measurements ζ-potentials in 10 mM ammonium acetate showed that the MF monoliths had no net charge at neutral pH, and +11 and –13 mV at pH 4 and 9.5, respectively.
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| 5. |
- Elhaj, Ahmed, 1981-, et al.
(author)
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Porous Polyvinylidene Difluoride (PVDF) Monoliths via Thermally Induced Dissolution/Precipitation. Three Strategies to Pore-Tuning : Probing the possibilities of further controlling of the PVDF monolith pore formation process
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Other publication (other academic/artistic)abstract
- The porous properties and morphologies of the PVDF monoliths prepared via thermally induced dissolution/precipitation process were proved to be adjustable, by employing several porogenic additives to the PVDF/n-butyl butyrate matrix. PVDF monoliths have been separately precipitated from; only the main diluent (n-butyl butyrate); mixtures of the main diluent and a co-diluent; binary polymer mixtures (including an additional porogenic polymer such as poly ethylene glycol PEG200, PEG400 and poly propylene glycol PPG425); and the main diluent in the presence of a fluoro-surfactant (FSO, FSN). Their meso- and macro-porous properties were characterized by nitrogen cryoption measurements (3-5 repeated runs per sample), and a subsequent single analysis by mercury intrusion porosimetry. The visual assessment of the monoliths morphology differences were carried out using scanning electron microscopy (SEM).
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| 6. |
- Elhaj, Ahmed, 1981-, et al.
(author)
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Porous Space-filling Monolithic Polyvinylidene Difluoride (PVDF) Materials by Thermally Induced Phase Separation
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Other publication (other academic/artistic)abstract
- Thermally induced phase separation was assessed as a means of producing space-filling monoliths from PVDF of three different molecular weights in twenty-two different solvents spanning a wide polarity range. Monolithic materials were produced in six out of these solvents; n-butyl butyrate, 1,4-dimethoxybenzene, cyclohexanone, 2,5-hexanedione, dimethyl succinate, and e-caprolactone. These monoliths had specific surface areas up to 35 m2/g, with the majority of the measured surface area attributable to pores in the mesoporous region from 5-20 nm, depending on solvent. Scanning electron microscopy images revealed radically different structures at the macropore level. In three of the samples essentially monodisperse particles in the 4-5 µm diameter range were found and verified to be of the same chemical composition as the monolithic part of the precipitate. These particles appeared for PVDF of different molecular weights and seem to have phase separated by a mechanism differing from the bulk monolith, which could hint at a novel way to prepare monodisperse PVDF particles.
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| 7. |
- Limé, Fredrik, 1974-, et al.
(author)
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Hydrobromination of residual vinyl groups on divinylbenzene polymer particles followed by atom transfer radical surface graft polymerization
- 2009
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In: Journal of Polymer Science Part A. - : Wiley Periodicals, Inc., A Wiley Company. - 0887-624X .- 1099-0518. ; 47:5, s. 1259-1265
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Journal article (peer-reviewed)abstract
- Rigid and monodisperse spherical polymer particles with 2.36 ± 0.18 m diameter containing residual surface vinyl groups were prepared by photoinitiated precipitation polymerization of divinylbenzene. Anti-Markovnikov addition of HBr to the surface vinyl groups yielded a 2-bromoethyl functionality that was used as macroinitiator for atom transfer radical polymerization (ATRP), providing the possibility for further functionalization by controlled grafting from processes. This was demonstrated by grafting of glycidyl methacrylate brushes from the particle surface, using an ATRP system based on CuBr and pentamethyl diethylenetriamine. Existence of a methacrylic overlayer was verified by FTIR and XPS measurements, and the grafted particles were easily dispersed in water, confirming conversion of the particle surface from hydrophobic to hydrophilic. Hydrobromination of residual vinyl groups yields a macroinitiator that can be used for grafting of glycidyl methacrylate by ATRP.
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| 8. |
- Nordborg, Anna, 1977-, et al.
(author)
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Gradient polymer elution chromatography of methacrylate Telomers on monolithic capillary columns prepared by nitroxide-mediated polymerization
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Other publication (other academic/artistic)abstract
- Linear methacrylate telomers prepared by isopropylxanthic disulfide photoiniferted polymerization of 2-hydroxyethyl methacrylate, methyl methacrylate, and ethyl methacrylate have been separated from their precursor monomers using gradient polymer elution chromatography (GPEC) on a monolithic capillary column. The capillary monoliths were prepared by thermally initiated radical polymerization of styrene and divinylbenzene controlled by 1-carboxy-PROXYL stable free radicals, and characterized by nitrogen adsorption and mercury intrusion porosimetry. The separations in GPEC mode were performed using a mobile phase gradient from water to methanol, where water is the non-solvent and methanol the good solvent with respect to the telomers. Successful separation of telomers from their monomer was achieved for all tested telomers. In addition, it was observed that the retention times of the intact telomers were different from those of telechelic oligomers produced by hydrolysing the isopropylxanthic terminals. The current set-up is therefore promising both for monitoring of the progress of photoiniferted polymerizations and to monitor the hydrolysis of resulting polymerized oligomers into thiol-terminated telechelics.
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