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Highly porous open-cellular monoliths from 2-hydroxyethyl methacrylate based high internal phase emulsions (HIPEs) : preparation and void size tuning
Sebastijan Kovačič, Dejan Štefanec, Peter Krajnc, 2007, original scientific article

Abstract: Preparation of highly porous (up to 80% pore volume) open-cellular monolithic cross-linked polymers from 2-hydroxyethyl methacrylate is reported. Oil-in-water and water-in-oil high internal phase emulsions are applied as porosity templates, resulting in an interconnected porous structure with void diameters between 550 nm and 18 m. Significantly larger voids were obtained inthe case of oil-in-water emulsions (between 5 and 18 m) as opposed to water in oil emulsions (approx 600 nm). Controlled coarsening exploiting limited kinetical stability of emulsions was used to obtain monoliths with larger voids, diameters being enlarged 3-fold.
Keywords: organic chemistry, polymerization, monolithic polymers, HIPE, emulsions, porous materials, methacrylates
Published: 31.05.2012; Views: 1390; Downloads: 46
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Oil-in-water high internal phase emulsions for porous monolithic polymers
Peter Krajnc, Dejan Štefanec, 2005, published scientific conference contribution abstract

Abstract: Porous monolithic polymers are objects of many studies recently due to their wide applicability. Especially in separation methods use of monoliths is growing. Usually, porous monoliths are prepared by bulk polymerisation with the use of porogenic solvents. An alternative way of preparation is to polymerise the continuous phase of an emulsion. When the volume fraction of the internal phase exceeds 74%, the emulsion is called a HIPE (high internal phase emulsion), and a polymer derived from it, a PolyHIPE. PolyHIPEs of styrene, vinylbenzyl chloride and acrylate chemistry have been prepared from awater in oil emulsion system, where monomers are dissolved in the organic phase. We describe the reversed procedure, an oil in water high internal phaseemulsion, where monomers are water soluble. Porous polymers based on acrylic acid and crosslinked with methylenebisacrylamide were prepared by using a high internal phase emulsion with toluene as the oil phase. The influence of initiator and surfactant on the morphology was studied.
Keywords: organic chemistry, porous monolith polymers, polymer supports, preparation, emulsion polymerization, HIPE
Published: 01.06.2012; Views: 2198; Downloads: 59
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Preparation and characterization of poly(high internal phase emulsion) methacrylate monoliths and their application as separation media
Peter Krajnc, Nermina Leber, Dejan Štefanec, Sandra Kontrec, Aleš Podgornik, 2005, original scientific article

Abstract: Poly(glycidyl methacrylate-co-ethyleneglycol dimethacrylate) monolithic supports were prepared by radical polymerisation of the continuous phase of water in oil high internal phase emulsions. Morphology of monolithic materialswas studied by scanning electron microscopy and mercury intrusion porosimetry. The ratio of phase volume and the degree of crosslinking influenced the void size and pore size distribution of resulting polymers. Void sizes between 1 and 10 m were observed and average pore sizes around 100nm. Polymers with 60, 75, 80 and 90% pore volume were prepared and even samples with highest pore volume showed good mechanical stability. They were modified to bear weak-anion exchange groups and tested on the separation of standard protein mixture containing myoglobin, conalbumine and trypsin inhibitor. Good separation was obtained in a very short time similar to the separation obtained by commercial methacrylate monoliths. However, higher dispersion was observed. Bovine serum albumin dynamic binding capacity for monolith with 90% porosity was close to 9 mg/ml.
Keywords: organic chemistry, methacrylate monoliths, preparation, emulsion polymerization, high porosity, high mechanical stability, polymer chromatographic supports, monolithic methacrylate supports, protein separation
Published: 01.06.2012; Views: 1371; Downloads: 27
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UV polymerization of poly (N-isopropylacrylamide) hydrogel
Manja Kurečič, Majda Sfiligoj-Smole, Karin Stana-Kleinschek, 2012, original scientific article

Abstract: This contribution is focused on the determination of polymerization and crosslinking mechanism of poly (N-isopropyl- acralymide) hydrogel and its swelling properties. Hydrogels were synthesized by environmental friendly UV polymerization method, from monomer N-isopropylacrylamide (NIPAM) and crosslinker N,N´-methylenebisacrylamide (BIS) of different concentrations. UV polymerization was performed in an UV chamber using UVA light with the wave length 350 nm. Surface morphology and pore structure analysis was carried out using SEM microscopy. The polymerization and crosslinking mechanism was determined by Fourier Transform Infrared spectroscopy (FT-IR). It was confirmed that crosslinker concentration influences the hydrogel structure and swelling properties. By increasing the crosllinker concentration the hydrogel structure changes from homogen to heterogen and the equilibrium degree of swelling decreases.
Keywords: poly (N-isopropylacrylamide) hydrogel, UV polymerization, FTIR, polymerization mechanism, swelling properties, SEM
Published: 01.06.2012; Views: 1106; Downloads: 56
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Ring opening metathesis polymerisation (ROMP) as a tool for polyhipes with extraordinary mechanical properties
Sebastijan Kovačič, 2013, professional article

Abstract: PolyHIPE materials have been prepared by Ring Opening Metathesis Polymerisation (ROMP) of dicyclopentadiene. Two characteristic features for successful stabilization of high internal phase emulsions (HIPEs) were tuned in order to achieve improvements regarding mechanical properties of polyHIPEs.Mechanical properties of the new materials were related to variations of the surfactant concentration and the volume ratio of the internal phase in HIPEs. Values for Youngʼs moduli were about a hundred times higher than in standard polyHIPE materials with the same level of porosity, which represents a major improvement for highly porous cellular polymeric materials. Moreover, fully interconnected macroporous morphology was found forpolyHIPEs, where respective HIPEs were stabilized with only 0.25 v% of surfactant.
Keywords: emulsion templating, ring opening metathesis polymerization, dicyclopentadiene, ROMP, mechanical characteristics, polyHIPEs
Published: 21.12.2015; Views: 674; Downloads: 35
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Nanocomposite foams from iron oxide stabilized dicyclopentadiene high internal phase emulsions
Sebastijan Kovačič, Christian Slugovc, Gregor Ferk, Nadejda B. Matsko, 2014, professional article

Abstract: Nanocomposite polyHIPE foams with open-cellular morphology were obtained using nanoparticles ($γFe_2O_3/Fe_3O_4$), surfactant (Pluronic L121) or nanoparticle/surfactant stabilized dicyclopentadiene high internal phase emulsions (DCPD HIPEs). Upon curing, cavity sizes were found to vary drastically between 950 ± 360 µm down to 7 ±3 µm de- pending on the HIPE formulations. As-obtained nanocomposite polyHIPE foams were functionalized using elemental bromine in THF. Upon bromination the nanoparticles are moved from the cavities surfaces into the bulk phase of the polymer scaffold, which affects the inductive-heating capability of the magnetic nanocomposite foams decreasing it by the factor of 2.
Keywords: chemical technology, nanocomposites, bromination, microstructure, pickering HIPEs, $γFe_2O_3/Fe_3O_4$ nanoparticles, Ring Opening Metathesis Polymerization (ROMP), dicyclopentadiene, inductive heating
Published: 24.08.2017; Views: 312; Downloads: 53
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Polyester type polyHIPE scaffolds with an interconnected porous structure for cartilage regeneration
Jakob Naranđa, Maja Sušec, Uroš Maver, Lidija Gradišnik, Mario Gorenjak, Andreja Vukasović, Alan Ivković, Marjan Rupnik, Matjaž Vogrin, Peter Krajnc, 2016, original scientific article

Abstract: Development of artificial materials for the facilitation of cartilage regeneration remains an important challenge in orthopedic practice. Our study investigates the potential for neocartilage formation within a synthetic polyester scaffold based on the polymerization of high internal phase emulsions. The fabrication of polyHIPE polymer (PHP) was specifically tailored to produce a highly porous (85%) structure with the primary pore size in the range of 50–170 μm for cartilage tissue engineering. The resulting PHP scaffold was proven biocompatible with human articular chondrocytes and viable cells were observed within the materials as evaluated using the Live/Dead assay and histological analysis. Chondrocytes with round nuclei were organized into multicellular layers on the PHP surface and were observed to grow approximately 300 μm into the scaffold interior. The accumulation of collagen type 2 was detected using immunohistochemistry and chondrogenic specific genes were expressed with favorable collagen type 2 to 1 ratio. In addition, PHP samples are biodegradable and their baseline mechanical properties are similar to those of native cartilage, which enhance chondrocyte cell growth and proliferation.
Keywords: polyester, polymerization, polyHIPE
Published: 23.06.2017; Views: 673; Downloads: 243
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Development of polymeric materials with rutin and polyrutin for healing of chronic leg ulcers
Tanja Pivec, 2018, doctoral dissertation

Abstract: In this work, the development of cellulose wound dressing materials with rutin (RU) and polyrutin (PR) for the healing of chronic leg ulcers is presented as a new approach of local treatment of this wound type. The flavonoid rutin is a known antioxidant substance of plant origin with wound healing promoting properties. Despite the proven beneficial properties of rutin, its potential application in wound healing is limited due to its low water solubility. This limitation can be overcome by polymerization of rutin into polyrutin. In this work an enzymatic polymerization of rutin in water without addition of organic solvents was performed to obtain a water-soluble polymer polyrutin. The chemical structure of rutin and polyrutin were investigated using UV-Vis spectroscopy, nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, size-exclusion chromatography and potentiometric titrations. Biological activity related to a desired positive influence on chronic leg ulcers was investigated through the determination of the antioxidant activity, iron-chelation ability, cell viability, determination of cell proliferation and through use of the so called “scratch assay” to measure in vitro wound healing performance. Results indicate that rutin and polyrutin have a positive influence on the healing of chronic wounds. Rutin and polyrutin water dispersions at different pH and ionic strength were further characterised by means of dynamic light scattering in order to determine the size of particles and their pH dependent ζ-potential. The knowledge gained from these measurements aided the systematic interaction studies of rutin and polyrutin dispersions with cellulose-based surfaces via model and real wound healing systems. The model cellulose surfaces were thin films prepared by dissolution of trimethylsilyl cellulose in tetrahydrofuran, spin-coating of this solution on sensors of a quartz crystal microbalance (QCM-D) and subsequent regeneration of trimethylsilyl cellulose to cellulose with acid vapors. The influence of pH, salt concentration, and rutin/polyrutin concentration on the interaction with cellulose thin films was evaluated by means of a quartz crystal microbalance with dissipation. This knowledge was transferred to the application of the coatings on real wound healing systems i.e. cellulose non-wovens. The surface morphology was further characterised on model and real wound healing systems. The antioxidant activity and release kinetics were investigated for a real wound healing system, similar to the clinically used, cellulose based wound dressing materials. The main results showed that a higher solubility of polyrutin at low ionic strength contributes to the formation of continuous layers of polyrutin on cellulose surface, while the low solubility of rutin and reduced solubility of polyrutin at higher ionic strengths contribute to deposition of particles of rutin and polyrutin on the cellulose surface. The presence of particles on the surface of non-woven cellulose fibres led to a faster initial release of rutin and polyrutin. On the contrary, a continuous layer of the well soluble polyrutin contributes to a prolonged release. Namely, adsorption of the water soluble polyrutin at pH 2 without the addition of salt results in higher masses of attached polyrutin that release slower and over longer time periods. Since wound dressing materials for chronic leg ulcers often require a lower frequency of dressing change, the latter could provide an efficient therapeutic approach to their treatment.
Keywords: Chronic wounds, Wound dressings, Cellulose, Polymerization of flavonoids, Rutin, Polyrutin
Published: 11.06.2018; Views: 461; Downloads: 82
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Functionalized copolymers from macrolactones by enzymatic ring-opening polymerization
Maja Ivanovski, 2018, master's thesis

Abstract: The work reported in the present thesis is focused predominantly to investigate how to synthesize random copolymers from ω-pentadecalatone (ω-PDL) and globalide (Gl) by enzymatic ring-opening polymerization (eROP). The reason for choosing this specific theme, i.e. "Functionalized copolymers from macrolactones by enzymatic ring-opening polymerization", was to explore a relatively new concept, in which two cyclic esters (macrolactones) – ω-PDL and Gl were synthesized by a combination of eROP and thiol-ene click reaction using biocatalyst Novozym 435 (lipase B from Candida antarctica). The aim was to position the newborn copolymer from ω-pentadecalactone and globalide among other biomaterials, identify possible applications and prepare nanoparticles that can be used in drug delivery systems. Random copolymers PPDLx-r-PGly with different feed ratios were successfully synthesized and later modified via thiol-ene click reaction when using BAET as a suitable compound for this polymeric functionalization, due to its thiol functionality. Boc-amino deprotection lasted and at the end, graft-copolymers were obtained (PPDLx-r-(PGly-g-PBLGz). Characterization methods were performed on GPC and NMR. The yield for all obtained random copolymers ranged between 67% and 88% and Mn between 14 000 g/mol and 45 000 g/mol depending on feed ratio of random copolymers. Meanwhile, the calculated yield for obtained grafted-copolymers ranged between 63% and 95%. Mn detected by GPC was around 7 000 g/mol for both grafted-copolymers (PPDL90(PGl10-PBLGz) and PPDL50(PGl50-PBLGz)) and Mw between 14 000 g/mol and 21 000 g/mol. Thermal analyses were performed on TGA and DSC. TGA showed that obtained PPDLx-r-PGly copolymers start to decompose at around 400 °C and grafted PPDLx-r-(PGly-g-PBLGz) copolymers at around 250 °C. DSC showed that PPDL and PGl are semicrystalline polymers with Tm ranging between (95 and 96 °C) for PPDL and (41 and 42 °C) for PGl. AFM technique was used for nanoparticles characterization. The resulting surface and deep resolution of PPDL50(PGl50-PBLGz) nanoparticles was between (2 to 88.8 nm) and PPDL10(PGl90-PBLGz) between (2 nm to 94.4 nm).
Keywords: ring-opening polymerization, macrolactones, ω-pentadecalatone, globalide, nanoparticles, Novozym 435
Published: 04.10.2018; Views: 290; Downloads: 41
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