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Polyalphaolefins
A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is an alkyl group. They are usually derived from a small set of simple olefins (alkenes). Dominant in a commercial sense are polyethylene and polypropylene. More specialized polyolefins include polyisobutylene and polymethylpentene. They are all colorless or white oils or solids. Many copolymers are known, such as polybutene, which derives from a mixture of different butene isomers. The name of each polyolefin indicates the olefin from which it is prepared; for example, polyethylene is derived from ethylene, and polymethylpentene is derived from 4-methyl-1-pentene. Polyolefins are not olefins themselves because the double bond of each olefin monomer is opened in order to form the polymer. Monomers having more than one double bond such as butadiene and isoprene yield polymers that contain double bonds (polybutadiene and polyisoprene) and are usually not considered polyolefins. Polyolefins are the foundatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymer
A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. 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 compound (chemistry), compounds, produces unique physical property, physical properties including toughness, high rubber elasticity, elasticity, viscoelasticity, and a tendency to form Amorphous solid, amorphous and crystallization of polymers, semicrystalline structures rath ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Karl Ziegler
Karl Waldemar Ziegler (; 26 November 1898 – 12 August 1973) was a German chemist who won the Nobel Prize in Chemistry in 1963, with Giulio Natta, for work on polymers. The Nobel Committee recognized his "excellent work on organometallic compounds hich..led to new polymerization reactions and ... paved the way for new and highly useful industrial processes". He is also known for his work involving free-radicals, many-membered rings, and organometallic compounds, as well as the development of Ziegler–Natta catalyst. One of many awards Ziegler received was the Werner von Siemens Ring in 1960 jointly with Otto Bayer and Walter Reppe, for expanding the scientific knowledge of and the technical development of new synthetic materials. Biography Early life and education Karl Ziegler was born on 26 November 1898 in Helsa near Kassel, Germany and was the second son of Karl Ziegler, a Lutheran minister, and Luise Rall Ziegler. He attended Kassel-Bettenhausen in elementary scho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Propylene
Propylene, also known as propene, is an unsaturated organic compound with the chemical formula . It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petroleum-like odor. Propylene is a product of combustion from forest fires, cigarette smoke, and motor vehicle and aircraft exhaust. It was discovered in 1850 by A. W. von Hoffmann's student Captain (later Major General) John Williams Reynolds as the only gaseous product of thermal decomposition of amyl alcohol to react with chlorine and bromine. Production Steam cracking The dominant technology for producing propylene is steam cracking, using propane as the feedstock. Cracking propane yields a mixture of ethylene, propylene, methane, hydrogen gas, and other related compounds. The yield of propylene is about 15%. The other principal feedstock is naphtha, especially in the Middle East and Asia. Propylene can be separated by fractional distill ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotactic
Tacticity (from , "relating to arrangement or order") is the relative stereochemistry of adjacent chiral centers within a macromolecule. The practical significance of tacticity rests on the effects on the physical properties of the polymer. The regularity of the macromolecular structure influences the degree to which it has rigid, crystalline long range order or flexible, amorphous long range disorder. Precise knowledge of tacticity of a polymer also helps understanding at what temperature a polymer melts, how soluble it is in a solvent, as well as its mechanical properties. A tactic macromolecule in the IUPAC definition is a macromolecule in which essentially all the configurational (repeating) units are identical. In a hydrocarbon macromolecule with all carbon atoms making up the backbone in a tetrahedral molecular geometry, the zigzag backbone is in the paper plane with the substituents either sticking out of the paper or retreating into the paper;, this projection is called ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comonomer
In polymer chemistry, a comonomer refers to a polymerizable precursor to a copolymer aside from the principal monomer. In some cases, only small amounts of a comonomer are employed, in other cases substantial amounts of comonomers are used. Furthermore, in some cases, the comonomers are statistically incorporated within the polymer chain, whereas in other cases, they aggregate. The distribution of comonomers is referred to as the " blockiness" of a copolymer. Polyolefins 1-Octene, 1-hexene, and 1-butene are used comonomers in the manufacture of polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bott ...s. The advantages to such copolymers has led to a focus on catalysts that facilitate the incorporation of these comonomers, e.g., constrained geometry complexes. Comonome ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymerization
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many forms of polymerization and different systems exist to categorize them. In chemical compounds, polymerization can occur via a variety of reaction mechanisms that vary in complexity due to the functional groups present in the reactants and their inherent steric effects. In more straightforward polymerizations, alkenes form polymers through relatively simple radical reactions; in contrast, reactions involving substitution at a carbonyl group require more complex synthesis due to the way in which reactants polymerize. As alkenes can polymerize in somewhat straightforward radical reactions, they form useful compounds such as polyethylene and polyvinyl chloride (PVC), which are produced in high tonnages each year due to their usefulnes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tacticity
Tacticity (from , "relating to arrangement or order") is the relative stereochemistry of adjacent chiral centers within a macromolecule. The practical significance of tacticity rests on the effects on the physical properties of the polymer. The regularity of the macromolecular structure influences the degree to which it has rigid, crystalline long range order or flexible, amorphous long range disorder. Precise knowledge of tacticity of a polymer also helps understanding at what temperature a polymer melts, how soluble it is in a solvent, as well as its mechanical properties. A tactic macromolecule in the IUPAC definition is a macromolecule in which essentially all the configurational (repeating) units are identical. In a hydrocarbon macromolecule with all carbon atoms making up the backbone in a tetrahedral molecular geometry, the zigzag backbone is in the paper plane with the substituents either sticking out of the paper or retreating into the paper;, this projection is called ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kaminsky Catalyst
A Kaminsky catalyst is a catalytic system for alkene polymerization. Kaminsky catalysts are based on metallocenes of group 4 transition metals (Ti, Zr, Hf) activated with methylaluminoxane (MAO). These and other innovations have inspired development of new classes of catalysts that in turn led to commercialization of novel engineering polyolefins. : __TOC__ Catalyst development The catalyst is named after German chemist Walter Kaminsky, who first described it in 1980 along with Hansjörg Sinn and others. Prior to Kaminsky's work, titanium chlorides supported on various materials were widely used (and still are) as heterogeneous catalysts for alkene polymerization. These halides are typically activated by treatment with trimethylaluminium. Kaminsky discovered that titanocene and related complexes emulated some aspects of these Ziegler–Natta catalysts but with low activity. He subsequently found that high activity could be achieved upon activation of these metallocenes with me ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phillips Catalyst
The Phillips catalyst, or the Phillips supported chromium catalyst, is the catalyst used to produce approximately half of the world's polyethylene. A heterogeneous catalyst, it consists of a chromium oxide supported on silica gel. Polyethylene, the most-produced synthetic polymer, is produced industrially by the polymerization of ethylene: :n C2H4 → (C2H4)n Although exergonic (i.e., thermodynamically favorable), the reaction requires catalysts. Three main catalysts are employed commercially: the Phillips catalyst, Ziegler–Natta catalysts (based on titanium trichloride), and, for specialty polymers, metallocene-based catalysts. Preparation and mechanism of action The Phillips catalyst is prepared by impregnating high surface area silica gel with chromium trioxide or related chromium compounds. The solid precatalyst is then calcined in air to give the active catalyst. Only a fraction of the chromium is catalytically active, a fact that interferes with elucidation of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triethylaluminium
Triethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name the compound has the formula Al2( C2H5)6 (abbreviated as Al2Et6 or TEA). This colorless liquid is pyrophoric. It is an industrially important compound, closely related to trimethylaluminium. Structure and bonding The structure and bonding in Al2R6 and diborane are analogous (R = alkyl). Referring to Al2Me6, the Al-C(terminal) and Al-C(bridging) distances are 1.97 and 2.14 Å, respectively. The Al center is tetrahedral. The carbon atoms of the bridging ethyl groups are each surrounded by five neighbors: carbon, two hydrogen atoms and two aluminium atoms. The ethyl groups interchange readily intramolecularly. At higher temperatures, the dimer cracks into monomeric AlEt3. Synthesis and reactions Triethylaluminium can be formed via several routes. The discovery of an efficient route was a significant technological achievement. The multistep process uses aluminium, hydrogen gas, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
