|
Methylaluminoxane
Methylaluminoxane, commonly called MAO, is a mixture of organoaluminium compounds with the approximate formula (Al(CH3)O)''n''. It is usually encountered as a solution in (aromatic) solvents, commonly toluene but also xylene, cumene, or mesitylene, Used in large excess, it activates precatalysts for alkene polymerization. Preparation and structure MAO is prepared by the incomplete hydrolysis of trimethylaluminium, as indicated by this idealized equation :''n'' Al(CH3)3 + ''n'' H2O → (Al(CH3)O)''n'' + 2''n'' CH4 Diverse mechanisms have been proposed for the formation of MAO. Well defined analogues of MAO can be generated with tert-butyl substituents. Uses MAO is well known as catalyst activator for olefin polymerizations by homogeneous catalysis. In traditional Ziegler–Natta catalysis, supported titanium trichloride is activated by treatment with trimethylaluminium (TMA). TMA only weakly activates homogeneous precatalysts, such as zirconacene dichloride. In the mid- ... [...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. : Catalyst development Prior to Kaminsky, 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 methylaluminoxane (MAO). The MAO serves two roles: (i) alkylation of the metallocene halide and (ii) abstraction of an anionic ligand (chloride or met ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organoaluminium Compound
Organoaluminium chemistry is the study of compounds containing bonds between carbon and aluminium. It is one of the major themes within organometallic chemistry. Illustrative organoaluminium compounds are the dimer trimethylaluminium, the monomer triisobutylaluminium, and the titanium-aluminium compound called Tebbe's reagent. The behavior of organoaluminium compounds can be understood in terms of the polarity of the C−Al bond and the high Lewis acidity of the three-coordinated species. Industrially, these compounds are mainly used for the production of polyolefins. History The first organoaluminium compound (C2H5)3Al2I3 was discovered in 1859. Organoaluminium compounds were, however, little known until the 1950s when Karl Ziegler and colleagues discovered the direct synthesis of trialkylaluminium compounds and applied these compounds to catalytic olefin polymerization. This line of research ultimately resulted in the Nobel Prize to Ziegler. Structure and bonding Aluminium( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trimethylaluminium
Trimethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name it has the formula Al2( CH3)6 (abbreviated as Al2Me6 or TMA), as it exists as a dimer. This colorless liquid is pyrophoric. It is an industrially important compound, closely related to triethylaluminium. Structure and bonding The structure and bonding in Al2R6 and diborane are analogous (R = alkyl). In 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 methyl groups are each surrounded by five neighbors: three hydrogen atoms and two aluminium atoms. The methyl groups interchange readily intramolecularly. At higher temperatures, the dimer cracks into monomeric AlMe3. Synthesis TMA is prepared via a two-step process that can be summarized as follows: :2 Al + 6 CH3Cl + 6 Na → Al2(CH3)6 + 6 NaCl Applications Catalysis Starting with the invention of Ziegler-Natta catalysis, o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Walter Kaminsky
Walter Kaminsky (born 7 May 1941) is a German chemist. His research dwells in olefin polymerization, and also in plastic recycling. He discovered the high activity of Group 4 metallocene/methylaluminoxane (MAO) mixtures as catalysts for olefin polymerization in 1980. He was awarded, among other prizes, the Körber European Science Prize in 1988, the 1999 Benjamin Franklin Medal, and the Hermann Staudinger Prize 2002. Kaminsky was born in Hamburg, Germany and studied Chemistry at the University of Hamburg. He joined their faculty in 1979, and is currently a full professor for Technical and Macromolecular Chemistry A macromolecule is a very large molecule important to biophysical processes, such as a protein or nucleic acid. It is composed of thousands of covalently bonded atoms. Many macromolecules are polymers of smaller molecules called monomers. The .... References External links Homepage 20th-century German chemists Scientists from Hamburg 1941 births Living p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ziegler–Natta Catalyst
A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility: * Heterogeneous supported catalysts based on titanium compounds are used in polymerization reactions in combination with cocatalysts, organoaluminum compounds such as triethylaluminium, Al(C2H5)3. This class of catalyst dominates the industry. * Homogeneous catalysts usually based on complexes of the group 4 metals titanium, zirconium or hafnium. They are usually used in combination with a different organoaluminum cocatalyst, methylaluminoxane (or methylalumoxane, MAO). These catalysts traditionally contain metallocenes but also feature multidentate oxygen- and nitrogen-based ligands. Ziegler–Natta catalysts are used to polymerize terminal alkenes (ethylene and alkenes with the vinyl double bond): :''n'' CH2=CHR → − H2−CHRsub>' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyrophoric
A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolithium compounds and triethylborane. Pyrophoric materials are often water-reactive as well and will ignite when they contact water or humid air. They can be handled safely in atmospheres of argon or (with a few exceptions) nitrogen. Fire Classes#Metal, Class D fire extinguisher#Class D dry powder and other agents for metal fires, fire extinguishers are designated for use in fires involving pyrophoric materials. A related concept is hypergolic propellant, hypergolicity, in which two compounds spontaneously ignite when mixed. Uses The creation of spark (fire), sparks from metals is based on the pyrophoricity of small metal particles, and pyrophoric alloys are made for this purpose. The sparking mechanisms in lighters and various toys, using fe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymer Chemistry
Polymer chemistry is a sub-discipline of chemistry that focuses on the structures of chemicals, chemical synthesis, and chemical and physical properties of polymers and macromolecules. The principles and methods used within polymer chemistry are also applicable through a wide range of other chemistry sub-disciplines like organic chemistry, analytical chemistry, and physical chemistry. Many materials have polymeric structures, from fully inorganic metals and ceramics to DNA and other biological molecules. However, polymer chemistry is typically related to synthetic and organic compositions. Synthetic polymers are ubiquitous in commercial materials and products in everyday use, such as plastics, and rubbers, and are major components of composite materials. Polymer chemistry can also be included in the broader fields of polymer science or even nanotechnology, both of which can be described as encompassing polymer physics and polymer engineering.Hans-Heinrich Moretto, Manfred Sch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Progress In Polymer Science
''Progress in Polymer Science'' is a peer-reviewed scientific journal publishing review articles on topics broadly related to polymer chemistry. The 2021 impact factor of this journal was 31.281, ranking it the highest in the subject category "Polymer Science". The journal is available since 1967. Currently it is edited by Editor-in-Chief Jean-Francois Lutz and Senior Editors Michael Bockstaller and Chuanbing Tang. Honorary Editors-in-Chief include Krzysztof "Kris" Matyjaszewski and Guy C. Berry from Carnegie Mellon University Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania. One of its predecessors was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools; it became the Carnegie Institute of Technology .... References {{reflist Chemistry journals Materials science journals English-language journals Elsevier academic journals ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aluminoxane
Aluminoxanes are organoaluminium compounds with the formula AlOsub>m n o, where R = organic substituent. The following structural rules apply: Al is tetrahedral and O is three-coordinate. Methylaluminoxane is widely used in the polymerization of alkenes. These compounds are typically obtained by the partial hydrolysis of trialkylaluminium compounds. Aluminoxanes serve as activators for catalytic olefin polymerisation, such as the Ziegler–Natta catalyst. They also serve a function as scavenger for impurities (e.g. water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...) in reactions that are sensitive to these impurities. Aluminoxane, appearing as white solids, are encountered as solutions. References Aluminium compounds Organometallic compounds Coordination complexes [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scavenger (chemistry)
A scavenger in chemistry is a chemical substance added to a mixture in order to remove or de-activate impurities and unwanted reaction products, for example oxygen, to make sure that they will not cause any unfavorable reactions. Their use is wide-ranged: * In atmospheric chemistry, the most common scavenger is the hydroxyl radical, a short-lived radical produced photolytically in the atmosphere. It is the most important oxidant for carbon monoxide, methane and other hydrocarbons, sulfur dioxide, hydrogen sulfide, and most of other contaminants, removing them from the atmosphere. * In molecular laser isotope separation, methane is used as a scavenger gas for fluorine atoms. * Hydrazine and ascorbic acid are used as oxygen scavenger corrosion inhibitors. * Tocopherol and naringenin are bioactive free radical scavengers that act as antioxidants; synthetic catalytic scavengers are their synthetic counterparts * Organotin compounds are used in polymer manufacture as hydrochloric acid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Angewandte Chemie International Edition In English
''Angewandte Chemie'' (, meaning "Applied Chemistry") is a weekly peer-reviewed scientific journal that is published by Wiley-VCH on behalf of the German Chemical Society (Gesellschaft Deutscher Chemiker). Publishing formats include feature-length reviews, short highlights, research communications, minireviews, essays, book reviews, meeting reviews, correspondences, corrections, and obituaries. This journal contains review articles covering all aspects of chemistry. According to the ''Journal Citation Reports'', the journal had a 2021 impact factor of 16.823. Editions The journal appears in two editions with separate volume and page numbering: a German edition, ''Angewandte Chemie'' ( (print), (online)), and a fully English-language edition, ''Angewandte Chemie International Edition'' ( (print), (online)). The editions are identical in content with the exception of occasional reviews of German-language books or German translations of IUPAC recommendations. Business model ''A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ion Pair
In chemistry, ion association is a chemical reaction whereby ions of opposite electric charge come together in solution to form a distinct chemical entity. Ion associates are classified, according to the number of ions that associate with each other, as ion pairs, ion triplets, etc. Ion pairs are also classified according to the nature of the interaction as contact, solvent-shared or solvent-separated. The most important factor to determine the extent of ion association is the dielectric constant of the solvent. Ion associates have been characterized by means of vibrational spectroscopy, as introduced by Niels Bjerrum, and dielectric-loss spectroscopy. Classification of ion pairs ''Ion pairs'' are formed when a cation and anion, which are present in a solution of an ionizable substance, come together to form a discrete chemical species. There are three distinct types of ''ion pairs'', depending on the extent of solvation of the two ions. For example, magnesium sulphate exist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
