Polymerization Of Organic Monomers Research Articles

Study on the Gel Casting Process of Silicon Carbide

Silicon carbide possess high performances such as high hardness and strength, oxidation and high temperature resistance, high thermal conductivity and low thermal expansion coefficient. Widely used methods of molding green body for sintered pressureless bonded silicon carbide comprise dry pressing molding and casting molding. The former fails in preparation of complex shapes, while those prepared by casting molding are prone to have defects such as nonuniformity of density and easy cracking. Gel-casting is a net-shape modeling technology caused by the polymerization of organic monomer (acrylamide). The green bodies molded by gel-casting have uniform structure, high density, high strength and machinability. In this study, gel casting molding and pressureless sintering were used to prepare silicon carbide. The effect of the parameters of gel casting and sintering on the microstructure of the obtained silicon carbide was examined

Polymerization of Building Blocks of Life on Europa and Other Icy Moons.

The outer Solar System may provide a potential habitat for extraterrestrial life. Remote sensing data from the Galileo spacecraft suggest that the jovian icy moons--Europa, Ganymede, and possibly Callisto--may harbor liquid water oceans underneath their icy crusts. Although compositional information required for the discussion of habitability is limited because of significantly restricted observation data, organic molecules are ubiquitous in the Universe. Recently, in situ spacecraft measurements and experiments suggest that amino acids can be formed abiotically on interstellar ices and comets. These amino acids could be continuously delivered by meteorite or comet impacts to icy moons. Here, we show that polymerization of organic monomers, in particular amino acids and nucleotides, could proceed spontaneously in the cold environment of icy moons, in particular the jovian icy moon Europa as a typical example, based on thermodynamic calculations, though kinetics of formation are not addressed. Observed surface temperature on Europa is 120 and 80 K in the equatorial region and polar region, respectively. At such low temperatures, Gibbs energies of polymerization become negative, and the estimated thermal structure of the icy crust should contain a shallow region (i.e., at a depth of only a few kilometers) favorable for polymerization. Investigation of the possibility of organic monomer polymerization on icy moons could provide good constraints on the origin and early evolution of extraterrestrial life.

Functional Networks of Organic and Coordination Polymers: Catalysis of Fructose Conversion

The creation of functional porous nanoscale networks with enhanced reactive group accessibility provides rich promise for novel designs of composite materials. We present a straightforward strategy for the preparation of porous polymer/MOF hybrids via polymerization of organic monomers and cross-linkers impregnated within the pores of the MOFs followed by functionalization of the resulting composite. A poly(maleimide-co-dibinylbenzene) network was synthesized in the presence of MOF MIL-101(Cr), resulting in stable hybrid composites, which were then brominated to give porous hybrids of cross-linked poly(N-bromomaleimide), a polymeric analogue of N-bromosuccinimide, interconnected with crystalline nanoparticles of the MOF. Due to the large porosity and surface area, the active bromine (halamine) groups in the polymer network enabled high activity of the composites in heterogeneous catalysis of conversion of d-fructose into 5-hydroxymethylfurfural.

High Porous Alumina Bodies: Production and Properties via Gel-Casting Technique

Porous ceramic materials have found widespread technological and industrial applications from filtration, absorption, catalysts and catalyst supports to lightweight structural components. In the present work, processing is based on the generation of foam from an aqueous suspension of ceramic powder and the subsequent stabilization of the structure by in-situ polymerization of organic monomers. The process offers a number of advantages from other processes. It is shown here, the in-situ polymerization of organic monomers led to a fast solidification and strong, porous bodies. SEM results showed, that the ceramic foams had highly interconnected network of spherical cells with low densities. The cell size distribution was dependent on the density of the samples as well as the polymerization onset time. Good correlations were found between the green microstructure, rheology of the suspensions and the particle interaction forces.

Production of Personalized Thyroid Cartilage Scaffold and Histological Analysis

To meet the bone defect on the personalized needs of implantation, this study presents the manufacture of personalized thyroid cartilage hydroxyapatite (HA) scaffold by the rapid prototyping(RP) technique combined with CT image reconstruction and employs the foaming of suspensions prior to the in situ polymerization of organic monomers contained in the compositions. The organic additives are eliminated at temperatures above 300°C, and sintering is carried out for consolidation of the ceramic matrix. Spherical interconnected cells with sizes ranging from 100μm to 250μm characterize the porous structure, depending on the specimen density. The biological properties of porous personalized scaffolds loaded with bone morphogenetic protein 2 (rhBMP-2) were evaluated, by which a simulated surgical method of thyroid cartilage defects in rabbits and repairing with artificial scaffolds, and compared with rhBMP-2 loaded dense personalized or porous non-personalized scaffolds. The results of the histological analysis and the electronic laryngoscope inspection of airway indicate that rhBMP-2/HA/ porous personalized scaffolds is a promising composite having osteogenic efficient enough for repairing thyroid cartilage defects.

Raspberry-like nanocomposite microsphere via Double In situ miniemulsion polymerization using interfacial redox initiator system

Inorganic/polymer nanocomposites have drawn a lot of attention due to their wide applications in medicine, coating, cosmetics, catalysis, biology, and so on. Many techniques have been adopted to the fabrication and morphology control of nanocomposite particles, such as aqueous dispersion polymerization, surfactant free polymerization, heterophase polymerization, Pickering emulsion polymerization, miniemulsion polymerization, and so forth. Such nanocomposite microspheres have been examined in a wide range of applications, ranging from new synthetic mimics for understanding the behavior of micro-meteorites, to stimulus responsive Pickering emulsifiers to tough, transparent, scratch-resistant coatings for either timber or housing exteriors. However, to control the dispersion of nanoparticles into polymer matrices is a significant challenge and it is often difficult to achieve this goal as inorganic particles are typically immiscible with polymer phase. Among the above methods miniemulsion polymerization has been proved to be a powerful and versatile process in the fabrication of inorganic/polymer microspheres. However, colloidal nanocomposite microspheres are most synthesized by in situ the polymerization of organic monomer in the presence of pre-formed inorganic colloidal particles. In order to obtain high encapsulation efficiencies, the silica particles had to be well dispersed within the monomer phase prior to miniemulsification. The most difficulty in the preparation of nanocomposites is to avoid the aggregation of nanoparticles in the polymer matrix. According to Steven P. Armes’ opinion, raspberry-like nanocomposite microspheres satisfy the basic demands. That is, the nanoparticles not only closely pack on the surface of polymer microspheres, but distribute homogeneously throughout the polymer microspheres. In order to obtain raspberry-like microspheres, auxiliary monomers were required to enhance the interaction between hydroxyl groups (acidic) on silica surfaces and amino groups (basic) during the formation of nanocomposite particles. 4-Vinylpyridine (4-VP), 1-vinylimidazole (1-VID), and 2-(methacryloyl) ethyltrimethylammonium chloride (MTC) have been used to successfully prepare PMMA/SiO2 organic-inorganic microspheres. Following the above synthesis route, Armes prepared a series of conducting polymer-silica nanocomposite microspheres based on either polyaniline, polypyrrole or poly(3,4-ethylenedioxythiophene). Stefan A. F. Bon prepared armored nanocomposite polymer microspheres by soap-free emulsion polymerizations in the presence of silica nanoparticles. Furthermore more complex multilayered nanocomposite polymer colloids were obtained by using a second conventional seeded emulsion polymerization step. Based on our previous works, silica/polymer hybrid particles have been fabricated successfully via double in situ miniemulsion polymerization by taking full advantage of phase separation between inorganic component and the growing polymer. Inspired by these interesting and valuable results, we investigated the feasibility of fabrication of nanocomposite microspheres with nanosilica distributing homogeneously throughout the polymer microspheres. Herein we report a novel and flexible technique to fabricate raspberry-like silica/polystyrene microspheres via interfacial initiated miniemulsion polymerization. The nanocompostite microspheres were fabricated via double in situ miniemulsion polymerization by taking full advantage of phase separation between inorganic component and the growing polymer. Nanosilica particles are formed throughout the polymer microspheres. This method can be expected to produce large quantity of submicrometer sized nanocomposite microspheres with high silica content towards biomimetic nanocomposites.

Heterogeneity of the spatial distribution of the primordial organic substance as an initial stage of biological evolution

An approach to describe the emergence of the primordial evolving system has been developed. The dynamics of polymerization/depolymerization of some spatially distributed prebiological structures has been analyzed, and two phases of the development of the system have been identified. In the first phase, the polymerization of organic monomers occurs by the influence of external factors, and in the second one depolymerization takes place. Both processes are accompanied by "diffuse mixing" of reaction products. The dynamic equations of the system are presented. The numerical examination of the space nonuniform solution of model equations has shown that, in conditions of low stability of uniform space distribution, these solutions resolve into a number of discrete peaks of non-zero density, which are isolated from each other by free space. Such nonuniform distributions are stable when being close to the bifurcation point; yet in other conditions, they can lose their stability, which entails a more pronounced nonuniformity of space dynamics. Thus, interaction of polymerization/depolymerization processes results in the chaotic self-organization and leads to the origination of complex and nomhomogeneous (putchy) spatial structures. These structures can reflect the emergency of the spatial nonuniformity in primordial associations, in physical space, in the distributive space of characters can correspond to the initial steps of individualization of the first discrete domains fixed in the biological evolution.

Preparation and characterization of polymer/silica nanocomposites via double in situ miniemulsion polymerization

Polymer/SiO2 nanocomposite microspheres were prepared by double in situ miniemulsion polymerization in the presence of methyl methacrylate, butyl acrylate, γ-methacryloxy(propyl) trimethoxysilane, and tetraethoxysilane (TEOS). By taking full advantage of phase separation between the growing polymer particles and TEOS, inorganic/polymer microspheres were fabricated successfully in a one-step process with the formation of SiO2 particles and the polymerization of organic monomers taking place simultaneously. The morphology of nanocomposite microspheres and the microstructure, mechanical properties, thermal properties, and optical properties of the nanocomposite films were characterized and discussed. The results showed that hybrid microspheres had a raspberry-like structure with silica nanoparticles on the shells of polymer. The silica particles of about 20 nm were highly dispersed within the nanocomposite films without aggregations. The transmittance of nanocomposite film was comparable to that of the copolymer film at around 70–80% from 400 to 800 nm. The mechanical properties and the fire-retardant behavior of the polymer matrix were improved by the incorporation of silica nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3128–3134, 2010

Comparison of monolithic approaches for enantioselective capillary electrochromatography involving cyclodextrins

The access to CD-modified monoliths for enantiomeric separation by CEC can be divided into two main approaches. (i) Silica-based monoliths, prepared by either a sol-gel process or by sintering of silica particles, are modified after fabrication by coating with a CD selector. Alternatively the fusion of CD functionalized silica particle via gluing is feasible. (ii) Rigid or homogeneous organic polymer-based monoliths, prepared by polymerization of organic monomers in the presence of a porogen, are modified with the CD selector either by copolymerization or by physical incorporation into the continuous bed.

Acid and Base Effects on the Morphology of Composites Formed from Microemulsion Polymerization and Sol--gel Processing

Phase behaviour studies were performed for microemulsions, containing organic monomers (methyl methacrylate and acrylic acid), inorganic monomer (tetraethoxy silane (TEOS)), a cross linking agent (ethylene glycol dimethacrylate) and water, stabilized by a cationic surfactant, cetyltrimethylammonium bromide. Single phase transparent microemulsions were formed over a considerable portion of the composition domain. The effects of an acid, hydrochloric acid (HCl), and a base (NH4OH) on the gel times were studied and the catalytic action of acid and base on the overall sol–gel reaction was analysed. Organic/inorganic polymer composites were obtained from the hydrolysis and polycondensation reactions of TEOS (sol–gel process) and polymerization of organic monomers and inorganic monomer containing microemulsions. Scanning electron microscopy was used to examine the surface morphology of the composites. For the acid and base studies a precursor microemulsion with pH 7.0 exhibiting closed-cell microstructure upon polymerization was selected. The morphology was examined for polymerized microemulsions with the same base composition but with varying HCl to TEOS ratios or NH4OH to TEOS ratios. Pore continuity and morphology are strongly influenced by the presence of acid or base. Both the HCl and NH4OH containing precursor microemulsions led to open celled porous composites.

Microemulsions — phase equilibria characterization, structures, applications and chemical reactions

The progress in understanding microemulsion structure on a molecular level as well as from extensive experimental studies of phase diagrams is reviewed. In this respect the studies involve both ionic and nonionic surfactants. Structures discussed involve the hard sphere model, the bicontinuous model, sponge phases and the flexible surface model. The progress in spectroscopic techniques (like NMR and TDS) together with scattering techniques, when applied to microemulsion systems, is also briefly discussed. Technical applications of microemulsions involve general applications as cleaning systems, fuels and in the field of crude oil exploitation. The last topic summarizes the use of the systems in EOR, acidizing and transport. The major emphasis of the review is in the utilization of microemulsions as systems in chemical reactions. These reactions involve preparation of inorganic particles, polymerization of organic monomers together with preparation of both organic and inorganic complexes and clusters. Enzyme catalyzed reactions involving the enzymes lipase, trypsin, α-chymotrypsin and alcohol dehydrogenase in different microemulsions are also summarized.

Plasma Deposition of Inorganic Thin Films

The possible use of electrical discharges for the preparation of exotic materials has intrigued chemists for nearly as long as the properties of the discharges themselves have been studied by physicists and engineers (1). The use of discharges in chemical reactions now falls under the general subject heading of plasma chemistry. Applications range from extractive metallurgy (2) to investigations of the origins of life itself (3). Polymerization of organic monomers with electric discharges has had periodic popular appeal (4) but has failed to mature into any widespread application. Free radical reactions, which are readily prepared in glow discharges, have been extensively investigated, and their properties are reviewed elsewhere (5). A widespread application of plasma methods for the deposition of dielectrics was developed with the discovery of RF sputtering (6). With the possible exception of reactive RF sputtering, however, this is considered a physical deposition process and is nbt covered in this article. The subject of this review is plasma-enhanced deposition, sometimes referred to as reactive plasma deposition (RPD), of primarily inorganic nonconducting thin films. In this process, gases that normally do not react or decompose at the applied temperature are introduced at moderate pressure (0.1-10.0 torr) into a reaction chamber, and an electric discharge is initiated. The energy coupled into the gas is chosen, along with the other parameters of the system, to produce deposition on exposed surfaces. The development of this process is primarily motivated by the electronics industry, where thin dielectric films are widely used in the manufacture of semiconductor devices. Reactors capable of handling production quantities of material with well-controlled and reproducible results have been developed.