Synthesis,characterization and kinetics of thermal decomposition of various peroxycarbamates and their initiation of methyl methacrylate polymerization

Several dimeric and polymeric peroxycarbamates were synthesized using various aliphatic diisocyanates and hydroperoxides. The products were characterized by IR spectroscopy, molecular weight measurements, isocyanate and peroxide analyses. Thermal decomposition kinetics of these peroxycarbamates were studied in 1,4-dioxane or toluene solutions at 80, 90, and 100°C. All reactions were found to proceed according to a first-order kinetics with activation energies in the range of 126–144 kJ/mol, depending on the structure of the peroxycarbamate. One of the polymeric products was used to initiate methyl methacrylate polymerization at 80°C in bulk. The initiating activity of this peroxycarbamate was found to be better than that of some hydroperoxides.     

离子液体的制备及N-烷基化反应研究

简述了离子液体的制备及在离子液体中进行的N.烷基化反应,比较传统合成方法,有时间短、产率高、污染小、易操作等优点.     

Specialty polymeric membranes

Summary Pervaporation of acetic acid/water mixture was investigated through uncrosslinked and crosslinked polybutadiene membranes. Crosslinked polybutadiene membrane permeated acetic acid in preference to water indicating that polybutadiene must be a candidate for a permselective membrane material for acetic acid separation from its aqueous solution.     

Conductive polymeric compositions

In most low-strength applications, plastics offer cost, maintenance, and density advantages over metals. Major deficiencies of plastics, however, are low thermal and electrical conductivities. Various studies have dealt with these problems, and it has been found that thermal conductivity and electrical conductivity can both be increased by the addition of conductive fillers to the polymer. The two parameters that most significantly affect the increase in conductivity of the resulting composite are volume loading of filler and filler shape. Fibrous conductors improve conductivity much-more significantly than spheres, flakes, or irregular particulates. The effect of fillers on thermal and electrical conductivities is not the same. The maximum increase in thermal conductivity that can reasonably be expected over the base polymer is 100:1. Electrical conductivity, on the other hand, can be increased by a factor of 10¹⁵. One particularly attractive technique for increasing the electrical conductivity of polymers is electroless plating of metals onto glass fibers which are then incorporated into the polymer. Such a composite can he made electrically conductive with as little as 6 volume percent metal.     

Stress Corrosion of Ionic and Mixed Ionic/Covalent Solids

Slow crack growth data, surface reaction studies, and solubility results for sapphire and magnesium fluoride crystals are used to identify stress corrosion mechanisms for each material. Results suggest that stress corrosion in sapphire proceeds by the dissociative chemisorption of environmental species on strained crack tip bonds. Crack growth rates measured in nonaqueous environments and isotopically labeled water suggest that ion solvation rather than dissociative chemisorption dominates the crack tip interaction in magnesium fluoride.     

Janus polymeric cages

Janus polymeric cages are fabricated by Pickering emulsion interfacial polymerization. The modified silica particles are used to stabilize the emulsions. Oil-soluble monomers and water-soluble monomers copolymerized in between the voids among the silica particles at the interface, forming amphiphilic Janus polymer shell in which the silica particles are embedded. After removal of the silica particles and the oil core, the corresponding Janus polymeric cages are achieved with uniform and regularly arrayed holes across the shell. The Janus cages are permeable to both organic molecules and particles.     

Ionic Supramolecular Assemblies

Supramolecular structures assembled via noncovalent interactions have found diverse applications in mechanical, biological, electronic, and manufacturing-related fields. Ionic interactions represent key noncovalent interactions, which can be used, for example, to create highly ordered, responsive, conductive, reversible, and/or viscoelastic supramolecular assemblies. The recent advances in the field of ionic supramolecular assemblies, including those prepared from polymers, small molecules, or a combination of the two are reviewed. The versatility and simplicity of constructing ionic supramolecular assemblies are illustrated through several examples. Finally, the outstanding issues and potential opportunities are discussed to stimulate critical discussions and encourage further discovery.     

Clays for polymeric nanocomposites

We discuss test methods and results for determining individual clay platelets shape, size, size distribution, elemental composition, and impurities. Commercial sodium salt varieties of natural, semisynthetic and synthetic clay (Cloisite®‐Na⁺, Somasif ME‐100, and Topy‐Na⁺, respectively) were analyzed. In this international collaboration, eight laboratories on three continents carried out the work within the VAMAS TWA‐33 activities. There are large differences between the three nanofillers as far as: (1) the platelet orthogonal dimensions, (2) chemical composition, and (3) contaminants (their diversity and quantity) are concerned. Elaborate purification of natural clays leaves behind 2–5 wt% of organic and mineral impurities, whose nature, shape, size, and chemistry depend on the clay origin. These contaminants affect nanocomposite performance, thus controlling their composition and quantity is essential. The article describes the developed methods, summarizes the preliminary results, discusses the encountered difficulties, and proposes methods for solving them. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Some novel polymeric nanocomposites

The nanocomposites described here all involve polymers and were chosen because they are already of commercial importance, show some promise of becoming so, or simply seem interesting. The field is so broad that some topics are mentioned only very briefly, and there is considerable emphasis on the polysiloxane nanocomposites studied by the author's research group. Some are typically prepared using techniques very similar to those used in the new sol-gel approach to ceramics, with either the polymer or the ceramic being the continuous phase. Other dispersed phases include particles responsive to an applied magnetic field, intercalated or exfoliated platelets obtained from clays, mica, or graphite, silsesquioxane nanocages, nanotubes, dual fillers, porous particles, spherical and ellipsoidal polymeric particles, and nanocatalysts. Also described are some typical studies involving theory or simulations on such particle reinforcement. Experiments on ceramics modified by dispersed polymers are equally interesting, but there is less relevant theory. Many of the fields mentioned have become so vast that the approach taken here is simply to describe general approaches and characteristics of the composites, list some specific examples, and provide leading references (with some emphasis on studies that are relatively recent or in the nature of reviews).     

Synthesis of polymeric nanofiber and polymeric nanosphere by living free radical polymerization

Living free radical polymerizations are employed to synthesize the polystyrene copolymer. The applications of those copolymer in nanomaterials are elucidated in this research. It involves the copolymerization of styrene with 2‐hydroxyethyl methacrylate. The copolymers are reacted with cinnamoyl chloride, and then irradiated with UV light. The polymeric nanofibers are formed by solvent splitting. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3550–3558, 2006     

离子液体的应用

离子液体是室温下呈液态的离子化合物,是一类新型的"软"功能材料或介质,具有优良的可设计性,它作为一种绿色溶剂,具有很多独特的物理化学性能。介绍了离子液体在纤维素科学、有机反应、分离过程、电化学中的应用。     

Ionic liquids in separations

Ionic liquids are liquids composed completely of ions. In the past two decades, ionic liquids have been widely used as "green solvents" replacing traditional organic solvents for organic synthesis and catalysis. In addition, ionic liquids are playing an increasingly important role in separation science. In this Account, the application of ionic liquids in all areas of separation science including extractions, gas chromatography, and supported liquid membrane processes are highlighted.     

Creep resistant polymeric nanocomposites

In the present study, one of the unique improvements in polymer nanocomposites has been detected. Only with a very low volume fraction of inorganic nanoparticles, the creep resistance of thermoplastic could be significantly improved. 21 nm-TiO₂/PA6,6 nanocomposites were compounded using a twin-screw-extruder. The final specimens were formed using an injection-moulding machine. Static tension and tensile creep tests were carried out at room and an elevated temperature (50 °C). It was found out that the nanoparticles contributed to a remarkable reduction of the creep rate under various constant loads at both temperature levels. It is assumed that the nanoparticles restrict the slippage, reorientation and motion of polymer chains. In this way, they influence the stress transfer on a nanoscale, which finally results in these improvements.