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Poly(methacrylic Acid)
Poly(methacrylic acid) (PMAA) is a polymer made from methacrylic acid (preferred IUPAC name, 2-methylprop-2-enoic acid), which is a carboxylic acid. It is often available as its sodium salt, poly(methacrylic acid) sodium salt. The monomer is a viscous liquid with a pungent odour. The first polymeric form of methacrylic acid was described in 1880 by Engelhorn and Fittig. The use of high purity monomers is required for proper polymerization conditions and therefore it is necessary to remove any inhibitors by extraction (phenolic inhibitors) or via distillation. To prevent inhibition by dissolved oxygen, monomers should be carefully degassed prior to the start of the polymerization. Polymerization PMAA has a pKa of ~4.8, meaning that at neutral pH the MAA groups in the network are almost entirely deprotonated making it an anionic polymer. PMAA can act as a polyelectrolyte and has the ability to absorb and retain water. These properties are strongly affected by the pH and therefore man ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass, relative to small molecule compounds, produces unique physical properties including toughness, high elasticity, viscoelasticity, and a tendency to form amorphous and semicrystalline structures rather than crystals. The term "polymer" derives from the Greek word πολύς (''polus'', meaning "many, much") and μέρος (''meros'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RAFT
A raft is any flat structure for support or transportation over water. It is usually of basic design, characterized by the absence of a hull. Rafts are usually kept afloat by using any combination of buoyant materials such as wood, sealed barrels, or inflated air chambers (such as pontoons), and are typically not propelled by an engine. Rafts are an ancient mode of transport; naturally-occurring rafts such as entwined vegetation and pieces of wood have been used to traverse water since the dawn of humanity. Human-made rafts Traditional or primitive rafts were constructed of wood or reeds. Modern rafts may also use pontoons, drums, or extruded polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a ... blocks. Inflatable rafts up to the 20th century used flotation chambers ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Poly(methyl Methacrylate)
Poly(methyl methacrylate) (PMMA) belongs to a group of materials called engineering plastics. It is a transparent thermoplastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and brands Crylux, Plexiglas, Acrylite, Astariglas, Lucite, Perclax, and Perspex, among several others ( see below). This plastic is often used in sheet form as a lightweight or shatter-resistant alternative to glass. It can also be used as a casting resin, in inks and coatings, and for many other purposes. Although not a type of familiar silica-based glass, the substance, like many thermoplastics, is often technically classified as a type of glass, in that it is a non-crystalline vitreous substance—hence its occasional historic designation as ''acrylic glass''. Chemically, it is the synthetic polymer of methyl methacrylate. It was developed in 1928 in several different laboratories by many chemists, such as William Chalmers, Otto Röhm, and Walter Bauer, and first brought ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophile
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases. ''Nucleophilic'' describes the affinity of a nucleophile to bond with positively charged atomic nuclei. Nucleophilicity, sometimes referred to as nucleophile strength, refers to a substance's nucleophilic character and is often used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis. Nucleophiles may take part in nucleophilic substitution, whereby a nucleophile becomes attracted to a full or partial positive charge, and nucleophilic addition. Nucleophilicity is closely related to basicity. History The terms ''nucleophile'' and ''electrophile'' were introduced by Christopher Kelk Ingold in 1933, replacing the terms ''anionoid'' and ''cationoid' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halide
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluoride, chloride, bromide, iodide, astatide, or theoretically tennesside compound. The alkali metals combine directly with halogens under appropriate conditions forming halides of the general formula, MX (X = F, Cl, Br or I). Many salts are halides; the ''hal-'' syllable in ''halide'' and ''halite'' reflects this correlation. All Group 1 metals form halides that are white solids at room temperature. A halide ion is a halogen atom bearing a negative charge. The halide anions are fluoride (), chloride (), bromide (), iodide () and astatide (). Such ions are present in all ionic halide salts. Halide minerals contain halides. All these halides are colourless, high melting crystalline solids having high negative enthalpies of formation. Test ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atom Transfer Radical Polymerization
Atom transfer radical polymerization (ATRP) is an example of a reversible-deactivation radical polymerization. Like its counterpart, ATRA, or atom transfer radical addition, ATRP is a means of forming a carbon-carbon bond with a transition metal catalyst. Polymerization from this method is called atom transfer radical addition polymerization (ATRAP). As the name implies, the atom transfer step is crucial in the reaction responsible for uniform polymer chain growth. ATRP (or transition metal-mediated living radical polymerization) was independently discovered by Mitsuo Sawamoto and by Krzysztof Matyjaszewski and Jin-Shan Wang in 1995. ::The following scheme presents a typical ATRP reaction: Overview of ATRP ATRP usually employs a transition metal complex as the catalyst with an alkyl halide as the initiator (R-X). Various transition metal complexes, namely those of Cu, Fe, Ru, Ni, and Os, have been employed as catalysts for ATRP. In an ATRP process, the dormant species is activated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Living Polymerization
In polymer chemistry, living polymerization is a form of chain growth polymerization where the ability of a growing polymer chain to terminate has been removed. This can be accomplished in a variety of ways. Chain termination and chain transfer reactions are absent and the rate of chain initiation is also much larger than the rate of chain propagation. The result is that the polymer chains grow at a more constant rate than seen in traditional chain polymerization and their lengths remain very similar (i.e. they have a very low polydispersity index). Living polymerization is a popular method for synthesizing block copolymers since the polymer can be synthesized in stages, each stage containing a different monomer. Additional advantages are predetermined molar mass and control over end-groups. Living polymerization is desirable because it offers precision and control in macromolecular synthesis. This is important since many of the novel/useful properties of polymers result from t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anionic Polymerization
In polymer chemistry, anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of monomers initiated with anions. The type of reaction has many manifestations, but traditionally vinyl monomers are used.Hsieh, H.;Quirk, R. ''Anionic Polymerization: Principles and practical applications''; Marcel Dekker, Inc.: New York, 1996.Quirk, R. Anionic Polymerization. In ''Encyclopedia of Polymer Science and Technology''; John Wiley and Sons: New York, 2003. Often anionic polymerization involves living polymerizations, which allows control of structure and composition. History As early as 1936, Karl Ziegler proposed that anionic polymerization of styrene and butadiene by consecutive addition of monomer to an alkyl lithium initiator occurred without chain transfer or termination. Twenty years later, living polymerization was demonstrated by Michael Szwarc and coworkers. In one of the breakthrough events in the fiel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nitroxide-mediated Radical Polymerization
Nitroxide-mediated radical polymerization is a method of radical polymerization that makes use of an nitroxide initiator to generate polymers with well controlled stereochemistry and a very low dispersity. It is a type of reversible-deactivation radical polymerization. Alkoxyamine Initiators The initiating materials for nitroxide-mediated radical polymerization (NMP) are a family of compounds referred to as alkoxyamines. An alkoxyamine can essentially be viewed as an alcohol bound to a secondary amine by an N-O single bond. The utility of this functional group is that under certain conditions, homolysis of the C-O bond can occur, yielding a stable radical in the form of a 2-center 3-electron N-O system and a carbon radical which serves as an initiator for radical polymerization. For the purposes of NMP, the R groups attached to the nitrogen are always bulky, sterically hindering groups and the R group in the O- position forms a stable radical, generally is benzylic for polymeriz ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Controlled Polymerization
Control may refer to: Basic meanings Economics and business * Control (management), an element of management * Control, an element of management accounting * Comptroller (or controller), a senior financial officer in an organization * Controlling interest, a percentage of voting stock shares sufficient to prevent opposition * Foreign exchange controls, regulations on trade * Internal control, a process to help achieve specific goals typically related to managing risk Mathematics and science * Control (optimal control theory), a variable for steering a controllable system of state variables toward a desired goal * Controlling for a variable in statistics * Scientific control, an experiment in which "confounding variables" are minimised to reduce error * Control variables, variables which are kept constant during an experiment * Biological pest control, a natural method of controlling pests * Control network in geodesy and surveying, a set of reference points of known geospatial coo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methacrylic Acid
Methacrylic acid, abbreviated MAA, is an organic compound. This colorless, viscous liquid is a carboxylic acid with an acrid unpleasant odor. It is soluble in warm water and miscible with most organic solvents. Methacrylic acid is produced industrially on a large scale as a precursor to its esters, especially methyl methacrylate (MMA), and to poly(methyl methacrylate) (PMMA). MAA occurs naturally in small amounts in the oil of Roman chamomile. Production In the most common route, methacrylic acid is prepared from acetone cyanohydrin, which is converted to methacrylamide sulfate using sulfuric acid. This derivative in turn is hydrolyzed to methacrylic acid, or esterified to methyl methacrylate in one step. Another route to methacrylic acid starts with isobutylene, which obtainable by dehydration of ''tert''-butanol. Isobutylene is oxidized sequentially to methacrolein and then methacrylic acid. Methacrolein for this purpose can also be obtained from formaldehyde and ethylene. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chain Propagation
Chain propagation (sometimes referred to as propagation) is a process in which a reactive intermediate is continuously regenerated during the course of a chemical chain reaction. For example, in the chlorination of methane, there is a two-step propagation cycle involving as chain carriers a chlorine atom and a methyl radical IUPAC Gold Book which are regenerated alternately: :•Cl + CH4 → HCl + •CH3 :•CH3 + Cl2 → CH3Cl + •Cl The two steps add to give the equation for the overall chain reaction: :CH4 + Cl2 → CH3Cl + HCl. Polymerization In a chain-growth polymerization ...[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
