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Sebastijan Kovačič, 2011, dissertation

Abstract: A new class of polyHIPE materials has been prepared using high internal phase emulsions (HIPEs) with monomers in both phases. Resulting materials, namely hybrid polyHIPE materials, are obtained consisting of hydrophobic matrix (consisted of styrene cross-linked with DVB or dicyclopentadiene) filled with hydrophilic polymer gel (polyacrylic acid or polyNIPAM) and exhibit morphology changes according to pH and temperature of the surrounding medium. Our focus with regards to the production of hybrid polyHIPE materials was the responsiveness of such materials used for flow control. This property is beneficial for controlling the flow of the solution through the monolithic polymers. Furthermore, polyHIPE materials have also been prepared by using ring opening metathesis polymerisation of monomers, such as dicyclopentadiene and norbornene. Obtained materials have Young’s moduli in the range of hundred times higher than standard polyHIPE materials with the same level of porosity which represents a very important improvement in the development of highly porous cellular polymeric materials.
Keywords: emulsions, high internal phase emulsions, polymers, polyHIPEs, hybrid, hybrid polyHIPE materials, ROMP, flow-through, styrene, DVB, acrylic acid, NIPAM
Published: 04.05.2011; Views: 2315; Downloads: 208
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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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Evaluation of thermosensitive microspheres as potential components for sun-protectors
Witold Musiał, Vanja Kokol, Bojana Vončina, 2010, original scientific article

Abstract: In this study thermosensitive polymeric microspheres obtained in former research were evaluated in vitro for their photoprotective activity. The UVA/UVB ratio was assessed at so called shelf temperature i.e. at 25°C, and at elevated temperature of 45°C. The evaluated polymers absorb higher levels of UV radiation, when heated from 25°C to 45°C. The MS1 polymer may be defined as polymer with high efficiency in the terms of gaining protection against UVAradiation, when heated. The MS2 absorbs both UVA and UVB radiation, and maybe considered, as most protective, when heated to 45°C. The equalized and less strong activity has the polymer MS3 when heated, with lipophilic radical implemented during synthesis.
Keywords: thermosensitive polymers, photoprotection, UV radiation, N-isopropylacrylamide
Published: 31.05.2012; Views: 985; Downloads: 17
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Acrylic acid "reversed" polyHIPEs
Peter Krajnc, Dejan Štefanec, Irena Pulko, 2005, original scientific article

Abstract: An oil-in-water high internal phase emulsion consisting of acrylic acid, water, and a crosslinker (N,N-methylene bisacrylamide) as the water phase, and toluene as the oil phase was successfully stabilised to sustain thermal initiation of radical polymerisation resulting in porous open-cellular monolithic material. The type of initiator used influenced the average pore size ranging from approx. 708 nm to approx. 1 087 nm, as determined by mercury porosimetry.
Keywords: hydrophilic polymers, macroporous polymers, poly (acrylic acid), polyHIPE, supports
Published: 01.06.2012; Views: 1432; Downloads: 68
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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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Aryl acrylate based high-internal-phase emulsions as precursors for reactive monolithic polymer supports
Peter Krajnc, Dejan Štefanec, Jane F. Brown, Neil R. Cameron, 2005, original scientific article

Abstract: Water-in-oil high-internal-phase emulsions (HIPEs), containing 4-nitrophenyl acrylate and 2,4,6-trichlorophenyl acrylate as reactive monomers, were prepared and polymerized, and highly porous monolithic materials resulted. The novel materials were studied by combustion analysis, Fourier transform infrared spectroscopy scanning electron microscopy, mercury porosimetry, and N2 adsorption/desorption analysis. With both esters, cellular macroporous monolithic polymers were obtained: the use of 4-nitrophenyl acrylate resulted in a cellular material with void diameters between 3 and 7 m and approximately3-m interconnects, whereas the use of 2,4,6-trichlorophenyl acrylate yielded a foam with void diameters between 2 and 5 m, most interconnects being around 1 m. The resulting monoliths proved to be very reactive toward nucleophiles, and possibilities of functionalizing the novel polymer supports were demonstrated via reactions with amines bearing additional functional groups and via the synthesis of an acid chloride derivative. Tris(hydroxymethyl)aminomethane and tris(2-aminoethyl)amine derivatives were obtained. The hydrolysis of 4-nitrophenylacrylate removed thenitrophenyl group, yielding a monolithic acrylic acid polymer. Furthermore,functionalization to immobilized acid chloride was performed very efficiently, with more than 95% of the acid groups reacting. The measurement of the nitrogen content in 4-nitrophenyl acrylate poly(HIPE)s after various times of hydrolysis showed the influence of the total pore volume of the monolithic polymers on the velocity of the reaction, which was faster with themore porous polymer.
Keywords: organic chemistry, macroporous polymers, monolithic polymer supports, emulsion polymerisation, foams, functionalization of polymers, high-internal-phase emulsions
Published: 01.06.2012; Views: 1234; Downloads: 63
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Pressure drop characteristics of poly(high internal phase emulsion) monoliths
Ita Junkar, Tine Koloini, Peter Krajnc, Damjan Nemec, Aleš Podgornik, Aleš Štrancar, 2007, original scientific article

Abstract: Today, monoliths are well-accepted chromatographic stationary phases due to several advantageous properties in comparison with conventional chromatographic supports. A number of different types of monoliths have already been described, among them recently a poly(high internal phase emulsion) (PolyHIPE) type of chromatographic monoliths. Due to their particular structure, we investigated the possibility of implementing different mathematical models to predict pressure drop on PolyHIPE monoliths. It was found that the experimental results of pressure drop on PolyHIPE monoliths can best be described by employing the representative unit cell (RUC) model, which was originally derived for the prediction of pressure drop on catalytic foams. Models intended for the description of particulate beds and silica monoliths were not as accurate. The results of this study indicate that the PolyHIPE structure under given experimental condition is, from a hydrodynamic point of view, to some extent similar to foam structures, though any extrapolation of these results may not provide useful predictions of pressure versus flow relations and further experiments are required.
Keywords: organic chermistry, polymers, monoliths, PolyHIPE, hydrodynamic properties, pressure drop
Published: 01.06.2012; Views: 1211; Downloads: 74
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Development of a 3D printer for thermoplastic modelling
Bogdan Valentan, Dušan Pogačar, Tomaž Brajlih, Tjaša Zupančič Hartner, Ana Pilipović, Igor Drstvenšek, 2012, original scientific article

Abstract: Additive technologies are entering the market in all price segments and the development of new machines and materials is rapidly growing. Machines under 2000 EUR are more and more interesting for home and educational use. This paper presents the development of a 3D printer that shapes the parts layer by layer by depositing the material on a predefined position. The development is presented from the engineering point of view. The construction steps, the control and the actuator solutions are presented. The ABS plastic was analysed for its material properties. The 3D printer evolved from a prototype to the pre-production phase.
Keywords: polymers, rapid prototyping, additive technologies, 3D print
Published: 10.07.2015; Views: 655; Downloads: 80
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Poly(styrene-co-divinylbenzene-co-2-ethylhexyl)acrilate membranes with interconnected macroporous structure
Urška Sevšek, Silvo Seifried, Črtomir Stropnik, Irena Pulko, Peter Krajnc, 2011, original scientific article

Abstract: A combination of doctor blading and emulsion templating was used to prepare macroporous poly(styrene-co-divinylbenzene-co-2-ethylhexylacrylate) and poly(styrene-co-divinylbenzene) membranes with an interconnected porous structure. Water in oil high internal phase emulsions including monomers in the oil phase were cast onto a glass plate and polymerised at elevated temperature. After purification porous polyHIPE membranes were obtained. The volume ratio of aqueous phase (75 % or 85 %) and the molar ratio of divinylbenzene (2 % or 4 %) were varied, while the addition of chlorobenzene to the oil phase influenced the viscosity of the emulsions. A comonomer, 2-ethylhexylacrylate substantially improved the flexibility of the membranes. All yielding membranes were characterized by measuring their cast thicknesses and flow densities for deionised water. Scanning electron microscopy was used to study the morphological features of the membranes.
Keywords: membrane, porous polymers, polyHIPE, emulsions
Published: 10.07.2015; Views: 1061; Downloads: 86
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