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Pyromellitic Dianhydride
Pyromellitic dianhydride (PMDA) is an organic compound with the formula C6H2(C2O3)2. It is the double carboxylic acid anhydride that is used in the preparation of polyimide polymers such as Kapton. It is a white, hygroscopic solid. It forms a hydrate. Preparation It is prepared by gas-phase oxidation of 1,2,4,5-tetramethylbenzene (or related tetrasubstituted benzene derivatives). An idealized equation is: :C6H2(CH3)4 + 6 O2 → C6H2(C2O3)2 + 6 H2O In the laboratory, it can be prepared by dehydration of pyromellitic acid using acetic anhydride. Reactions PMDA is an electron-acceptor, forming a variety of charge-transfer complexes. It reacts with amines to diimides, C6H2 CO)2NRsub>2 which also have acceptor properties. Applications PMDA is used in PET bottle recycling as a chain extender. It increases the molecular weight of the polymer by linking-together alcohol and carboxylic acid groups formed by hydrolysis of the PET. This improves the rheological properties and overall q ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-containing compounds such as alkanes (e.g. methane ) and its derivatives are universally considered organic, but many others are sometimes considered inorganic, such as certain compounds of carbon with nitrogen and oxygen (e.g. cyanide ion , hydrogen cyanide , chloroformic acid , carbon dioxide , and carbonate ion ). Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The study of the properties, reactions, and syntheses of organic compounds comprise the discipline known as organic chemistry. For historical reasons, a few classes of carbon-containing compounds (e.g., carbonate salts and cyanide salts), along with a few other exceptions (e.g., carbon dioxide, and even ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carboxylic Acid Anhydride
An organic acid anhydride is an acid anhydride that is also an organic compound. An acid anhydride is a compound that has two acyl groups chemical bond, bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the parent acid is a carboxylic acid, the formula of the anhydride being (RC(O))2O. Symmetrical acid anhydrides of this type are named by replacing the word ''acid'' in the name of the parent carboxylic acid by the word ''anhydride''. Thus, (CH3CO)2O is called ''acetic anhydride.'' ''Mixed'' (or ''unsymmetrical'') acid anhydrides, such as acetic formic anhydride (see below), are known, whereby reaction occurs between two different carboxylic acids. Nomenclature of unsymmetrical acid anhydrides list the names of both of the reacted carboxylic acids before the word "anhydride" (for example, the dehydration reaction between benzoic acid and propanoic acid would yield "benzoic propanoic anhydride"). One or both acyl groups of an ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyimide
Polyimide (sometimes abbreviated PI) is a monomer containing imide groups belonging to the class of high-performance plastics. With their high heat-resistance, polyimides enjoy diverse applications in roles demanding rugged organic materials, such as high temperature fuel cells, displays, and various military roles. A classic polyimide is Kapton, which is produced by condensation of pyromellitic dianhydride and 4,4'-oxydianiline.Wright, Walter W. and Hallden-Abberton, Michael (2002) "Polyimides" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim. History The first polyimide was discovered in 1908 by Bogart and Renshaw. They found that 4-amino phthalic anhydride does not melt when heated but does release water upon the formation of a high molecular weight polyimide. The first semialiphatic polyimide was prepared by Edward and Robinson by melt fusion of diamines and tetra acids or diamines and diacids/diester. However, the first polyimide of significant co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kapton
file:Kaptonpads.jpg, Kapton insulating pads for mounting electronic parts on a heat sink Kapton is a polyimide film used in flexible printed circuits (flexible electronics) and space blankets, which are used on spacecraft, satellites, and various space instruments. Invented by the DuPont (1802-2017), DuPont Corporation in the 1960s, Kapton remains stable across a wide range of temperatures, from . Kapton is used in electronics manufacturing and space applications, with x-ray equipment, and in 3D printing applications. Its favorable thermal properties and outgassing characteristics result in its regular use in Cryogenics, cryogenic applications and in high vacuum environments. History Kapton was invented by DuPont in the 1960s. Kapton remains manufactured by DuPont to this day. The name ''Kapton'' is a registered trademark of E. I. du Pont de Nemours and Company. Chemistry and variants Kapton synthesis is an example of the use of a wikt:dianhydride, dianhydride in step pol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxidation
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state. The oxidation and reduction processes occur simultaneously in the chemical reaction. There are two classes of redox reactions: * Electron-transfer – Only one (usually) electron flows from the atom, ion, or molecule being oxidized to the atom, ion, or molecule that is reduced. This type of redox reaction is often discussed in terms of redox couples and electrode potentials. * Atom transfer – An atom transfers from one substrate to another. For example, in the rusting of iron, the oxidation state of iron atoms increases as the iron converts to an oxide, and simultaneously, the oxidation state of oxygen decreases as it accepts electrons released by the iron. Although oxidati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Durene
Durene, or 1,2,4,5-tetramethylbenzene, is an organic compound with the formula C6H2(CH3)4. It is a colourless solid with a sweet odor. The compound is classified as an alkylbenzene. It is one of three isomers of tetramethylbenzene, the other two being prehnitene (1,2,3,4-tetramethylbenzene) and isodurene (1,2,3,5-tetramethylbenzene). Durene has an unusually high melting point (79.2 °C), reflecting its high molecular symmetry. Production It is a component of coal tar and was first prepared from pseudocumene in 1870. It is produced by methylation of other methylated benzene compounds such as ''p''-xylene and pseudocumene. :C6H4(CH3)2 + 2 CH3Cl → C6H2(CH3)4 + 2 HCl In industry, a mixture of xylenes and trimethylbenzenes is alkylated with methanol. Durene can be separated from its isomers by selective crystallization, exploiting its high melting point. The original synthesis of durene involved a similar reaction starting from toluene. Durene is a significant byproduct ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acetic Anhydride
Acetic anhydride, or ethanoic anhydride, is the chemical compound with the chemical formula, formula . Commonly abbreviated , it is one the simplest organic acid anhydride, anhydrides of a carboxylic acid and is widely used in the production of cellulose acetate as well as a reagent in organic synthesis. It is a colorless liquid that smells strongly of acetic acid, which is formed by its reaction with moisture in the air. Structure and properties Acetic anhydride, like most organic acid anhydrides, is a flexible molecule with a nonplanar structure. The C=O and C-O distances are 1.19 and 1.39 Å. The Pi bond, pi system linkage through the central oxygen offers very weak resonance stabilization compared to the dipole, dipole-dipole repulsion between the two carbonyl oxygens. The energy barriers to bond rotation between each of the optimal aplanar conformations are quite low. Production Acetic anhydride was first synthesized in 1852 by the French chemist Charles Frédéric Gerhardt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Charge-transfer Complex
In chemistry, charge-transfer (CT) complex, or electron donor-acceptor complex, describes a type of supramolecular assembly of two or more molecules or ions. The assembly consists of two molecules that self-attract through electrostatic forces, i.e., one has at least partial negative charge and the partner has partial positive charge, referred to respectively as the electron acceptor and electron donor. In some cases, the degree of charge transfer is "complete", such that the CT complex can be classified as a salt. In other cases, the charge-transfer association is weak, and the interaction can be disrupted easily by polar solvents. Examples Electron donor-acceptor complexes A number of organic compounds form charge-transfer complex, which are often described as electron-donor-acceptor complexes (EDA complexes). Typical acceptors are nitrobenzenes or tetracyanoethylene (TCNE). The strength of their interaction with electron donors correlates with the ionization potential ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PET Bottle Recycling
Polyethylene Terephthalate (Polyethylene terephthalate, PET) is one of the most common polymers in its polyester family. Its global market size was estimated to be worth 37.25 billion USD in 2021. Polyethylene terephthalate is used in several applications such as; textile fibres, bottles, rigid/flexible packaging, and electronics. However, it accounts for 12% in global solid waste. This is why bottle recycling is highly encourage and has reached its highest level in decades (33% in 2023). In 2023, the US collected 1,962 million pounds of bottles for recycling. Compared to glass bottles, the Polyethylene terephthalate, PET bottle is lightweight and has a lower carbon footprint in production and transportation. Recycling it would only help further the emission reduction. The recycled material can be put back into bottles, fibres, film, thermoformed packaging and strapping. After collecting the bottles from landfills, they are sorted, cleaned and grinded. This grinded material is ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chain Extender
In polymer chemistry, a chain extender is a low molecular weight (MW) reagent that converts polymeric precursors to higher molecular weight derivatives. Often, it is convenient to prepare a polymer at an intermediate MW, which are suitable for solution- or melt-processing. At or near the final stages of production, the material is treated with a chain extender. Typically, chain extenders are bifunctional, i.e., they have two functional groups, which can link together two polymers. Representative classes of chain extenders are diglycidyl ethers, diols, diamines, or dianhydrides. Chain extenders are often applied to polyurethane Polyurethane (; often abbreviated PUR and PU) is a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane term ...s.{{cite book , doi=10.1016/C2012-0-02516-1 , title=Reactive Polymers Fundamentals and Applications , y ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Occupational Asthma
Occupational asthma is new onset asthma or the recurrence of previously quiescent asthma directly caused by exposure to an agent at workplace. It is an occupational lung disease and a type of work-related asthma. Agents that can induce occupational asthma can be grouped into sensitizers and irritants. Sensitizer-induced occupational asthma is an immunologic form of asthma which occurs due to inhalation of specific substances (i.e., high-molecular-weight proteins from plants and animal origins, or low-molecular-weight agents that include chemicals, metals and wood dusts) and occurs after a latency period of several weeks to years. Irritant-induced (occupational) asthma is a non-immunologic form of asthma that results from a single or multiple high dose exposure to irritant products. It is usually develops early after exposure; however, it can also develop insidiously over a few months after a massive exposure to a complex mixture of alkaline dust and combustion products, as shown i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
