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DMAc
Dimethylacetamide (DMAc or DMA) is the organic compound with the formula CH3C(O)N(CH3)2. This colorless, water-miscible, high-boiling liquid is commonly used as a polar solvent in organic synthesis. DMA is miscible with most other solvents, although it is poorly soluble in aliphatic hydrocarbons. Synthesis and production DMA is prepared commercially by the reaction of dimethylamine with acetic anhydride or acetic acid. Dehydration of the salt of dimethylamine and acetic acid also furnishes this compound: : CH3CO2H·HN(CH3)2 → H2O + CH3CON(CH3)2 Dimethylacetamide can also be produced by the reaction of dimethylamine with methyl acetate. : The separation and purification of the product is carried out by multistage distillation in rectification columns. DMA is obtained with essentially quantitive (99%) yield referred to methyl acetate. Reactions and applications The chemical reactions of dimethylacetamide are typical of ''N'',''N''-disubstituted amides. Hydrolysis of the acyl- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hour
An hour (symbol: h; also abbreviated hr) is a unit of time historically reckoned as of a day and defined contemporarily as exactly 3,600 seconds ( SI). There are 60 minutes in an hour, and 24 hours in a day. The hour was initially established in the ancient Near East as a variable measure of of the night or daytime. Such seasonal hours, also known as temporal hours or unequal hours, varied by season and latitude. Equal hours or equinoctial hours were taken as of the day as measured from noon to noon; the minor seasonal variations of this unit were eventually smoothed by making it of the mean solar day. Since this unit was not constant due to long term variations in the Earth's rotation, the hour was finally separated from the Earth's rotation and defined in terms of the atomic or physical second. It is a non-SI unit that is accepted for use with SI. In the modern metric system, one hour is defined as 3,600 atomic seconds. However, on rare occasions an hour may inc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a chemical compound, compound with the general formula , where R, R', and R″ represent any group, typically organyl functional group, groups or hydrogen atoms. The amide group is called a peptide bond when it is part of the Polymer backbone, main chain of a protein, and an isopeptide bond when it occurs in a side chain, as in asparagine and glutamine. It can be viewed as a Derivative (chemistry), derivative of a carboxylic acid () with the hydroxyl group () replaced by an amino group (); or, equivalently, an acyl group, acyl (alkanoyl) group () joined to an amino group. Common amides are formamide (), acetamide (), benzamide (), and dimethylformamide (). Some uncommon examples of amides are ''N''-chloroacetamide () and chloroformamide (). Amides are qualified as primary (chemistry), primary, secondary (chemistry), secondary, and tertiary (chemistry), tertiary according to the number of acyl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Excipient
An excipient is a substance formulated alongside the active ingredient of a medication. They may be used to enhance the active ingredient’s therapeutic properties; to facilitate drug absorption; to reduce viscosity; to enhance solubility; to improve long-term stabilization (preventing denaturation and aggregation during the expected shelf life); or to add bulk to solid formulations that have small amounts of potent active ingredients (in that context, they are often referred to as "bulking agents", "fillers", or "diluents"). During the manufacturing process, excipients can improve the handling of active substances and facilitate powder flow. The choice of excipients depends on factors such as the intended route of administration, the dosage form, and compatibility with the active ingredient. Virtually all marketed drugs contain excipients, and final drug formulations commonly contain more excipient than active ingredient. Pharmaceutical regulations and standards mandate the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molar Mass Distribution
In polymer chemistry, the molar mass distribution (or molecular weight distribution) describes the relationship between the number of moles of each polymer species () and the molar mass () of that species. In linear polymers, the individual polymer chains rarely have exactly the same degree of polymerization and molar mass, and there is always a distribution around an average value. The molar mass distribution of a polymer may be modified by polymer fractionation. Definitions of molar mass average Different average values can be defined, depending on the statistical method applied. In practice, four averages are used, representing the weighted mean taken with the mole fraction, the weight fraction, and two other functions which can be related to measured quantities: *''Number average molar mass'' (), also loosely referred to as ''number average molecular weight'' (NAMW). *''Mass average molar mass'' (), where stands for weight; also commonly referred to as ''weight avera ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gel Permeation Chromatography
Gel permeation chromatography (GPC) is a type of size-exclusion chromatography (SEC), that separates high molecular weight or colloidal analytes on the basis of size or diameter, typically in organic solvents. The technique is often used for the analysis of polymers. As a technique, SEC was first developed in 1955 by Lathe and Ruthven.Lathe, G.H.; Ruthven, C.R.J. The Separation of Substance and '1956', ''62'', 665–674. The term ''gel permeation chromatography'' can be traced back to J.C. Moore of the Dow Chemical Company who investigated the technique in 1964. The proprietary column technology was licensed to Waters Corporation, who subsequently commercialized this technology in 1964. GPC systems and consumables are now also available from a number of manufacturers. It is often necessary to separate polymers, both to analyze them as well as to purify the desired product. When characterizing polymers, it is important to consider their size distribution and dispersity (''Đ'') as w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cellulose
Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important structural component of the primary cell wall of green plants, many forms of algae and the oomycetes. Some species of bacteria secrete it to form biofilms. Cellulose is the most abundant biopolymer, organic polymer on Earth. The cellulose content of cotton fibre is 90%, that of wood is 40–50%, and that of dried hemp is approximately 57%. Cellulose is mainly used to produce paperboard and paper. Smaller quantities are converted into a wide variety of derivative products such as cellophane and rayon. Conversion of cellulose from energy crops into biofuels such as cellulosic ethanol is under development as a renewable fuel source. Cellulose for industrial use is mainly obtained from wood pulp and cotton. Cellulose is also greatly affected by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lithium Chloride
Lithium chloride is a chemical compound with the formula Li Cl. The salt is a typical ionic compound (with certain covalent characteristics), although the small size of the Li+ ion gives rise to properties not seen for other alkali metal chlorides, such as extraordinary solubility in polar solvents (83.05 g/100 mL of water at 20 °C) and its hygroscopic properties. Chemical properties The salt forms crystalline hydrates, unlike the other alkali metal chlorides. Mono-, tri-, and pentahydrates are known. The anhydrous salt can be regenerated by heating the hydrates. LiCl also absorbs up to four equivalents of ammonia/mol. As with any other ionic chloride, solutions of lithium chloride can serve as a source of chloride ion, e.g., forming a precipitate upon treatment with silver nitrate: : LiCl + AgNO3 → AgCl + LiNO3 Preparation Lithium chloride is produced by treatment of lithium carbonate with hydrochloric acid. Anhydrous LiCl is prepared from the hydrate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plasticizer
A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture. Plasticizers are commonly added to polymers and plastics such as PVC, either to facilitate the handling of the raw material during fabrication, or to meet the demands of the end product's application. Plasticizers are especially key to the usability of polyvinyl chloride (PVC), the third most widely used plastic. In the absence of plasticizers, PVC is hard and brittle; with plasticizers, it is suitable for products such as vinyl siding, roofing, vinyl flooring, rain gutters, plumbing, and electric wire insulation/coating. Plasticizers are also often added to concrete formulations to make them more workable and fluid for pouring, thus allowing the water contents to be reduced. Similarly, they are often added to clays, stucco, solid rocket fuel, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pharmaceuticals
Medication (also called medicament, medicine, pharmaceutical drug, medicinal product, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and relies on the science of pharmacology for continual advancement and on pharmacy for appropriate management. Drugs are classified in many ways. One of the key divisions is by level of control, which distinguishes prescription drugs (those that a pharmacist dispenses only on the medical prescription) from over-the-counter drugs (those that consumers can order for themselves). Medicines may be classified by mode of action, route of administration, biological system affected, or therapeutic effects. The World Health Organization keeps a list of essential medicines. Drug discovery and drug development are complex and expensive endeavors undertaken by pharmaceutical companies, academic scientists, and governments. As a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adhesive
Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advantages over other binding techniques such as sewing, mechanical fastenings, and welding. These include the ability to bind different materials together, the more efficient distribution of stress across a joint, the cost-effectiveness of an easily mechanized process, and greater flexibility in design. Disadvantages of adhesive use include decreased stability at high temperatures, relative weakness in bonding large objects with a small bonding surface area, and greater difficulty in separating objects during testing. Adhesives are typically organized by the method of adhesion followed by ''reactive'' or ''non-reactive'', a term which refers to whether the adhesive chemically reacts in order to harden. Alternatively, they can be organized either ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spandex
Spandex, Lycra, or elastane is a synthetic fiber known for its exceptional elasticity. It is a polyether- polyurea copolymer that was invented in 1958 by chemist Joseph Shivers at DuPont. Name The name ''spandex'', which is an anagram of the word "expands", is the preferred name in North America. In continental Europe, it is referred to by variants of ''elastane''. It is primarily known as ''Lycra'' in the UK, Ireland, Portugal, Spain, Latin America, Australia, and New Zealand. Brand names for spandex include Lycra (made by The Lycra Company, previously a division of DuPont Textiles and Interiors), Elaspan (The Lycra Company), Acepora ( Taekwang Group), Creora (Hyosung), INVIYA ( Indorama Corporation), ROICA and Dorlastan (Asahi Kasei), Linel (Fillattice), and ESPA ( Toyobo). Production Unlike many other synthetic fibers, spandex cannot be melt-processed because the polymer degrades upon melting. Spandex fibers are produced by several spinning technologies. Typically ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyacrylonitrile
Polyacrylonitrile (PAN) is a synthetic, semicrystalline organic polymer resin, with the linear formula (CH2CHCN)n. Almost all PAN resins are copolymers with acrylonitrile as the main monomer. PAN is used to produce large variety of products including ultra filtration membranes, hollow fibers for reverse osmosis, fibers for textiles, and oxidized PAN fibers. PAN fibers are the chemical precursor of very high-quality carbon fiber. PAN is first thermally oxidized in air at 230 °C to form an oxidized PAN fiber and then carbonized above 1000 °C in inert atmosphere to make carbon fibers found in a variety of both high-tech and common daily applications such as civil and military aircraft primary and secondary structures, missiles, solid propellant rocket motors, pressure vessels, fishing rods, tennis rackets and bicycle frames. It is a component repeat unit in several important copolymers, such as styrene-acrylonitrile (SAN) and acrylonitrile butadiene styrene (ABS) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
