A copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained by copolymerization of two monomer species are sometimes called bipolymers; those obtained from three and four monomers are called quaterpolymers, respectively. There are many commercially relevant copolymers; some examples include acrylonitrile butadiene styrene, styrene/butadiene co-polymer, nitrile rubber, styrene-acrylonitrile, styrene-isoprene-styrene and ethylene-vinyl acetate, all formed by chain-growth polymerization. Another production mechanism is step-growth polymerization, used to produce the nylon-12/6/66 copolymer of nylon 12, nylon 6 and nylon 66, as well as the copolyester family. Since a copolymer consists of at least two types of constituent units, copolymers can be classified based on how these units are arranged along the chain. Linear copolymers consist of a single main chain, include alternating copolymers, statistical copolymers and block copolymers.
Branched copolymers consist of a single main chain with one or more polymeric side chains, can be grafted, star shaped or have other architectures. The reactivity ratio of a growing copolymer chain terminating in a given monomer is the ratio of the reaction rate constant for addition of the same monomer and the rate constant for addition of the other monomer; that is, r 1 = k 11 k 12 and r 2 = k 22 k 21, where for example k 12 is the rate constant for propagation of a polymer chain ending in monomer 1 by addition of monomer 2. The composition and structural type of the copolymer depend on these reactivity ratios r1 and r2 according to the Mayo–Lewis equation called the copolymerization equation or copolymer equation, for the relative instantaneous rates of incorporation of the two monomers. D d = Block copolymers comprise two or more homopolymer subunits linked by covalent bonds; the union of the homopolymer subunits may require an intermediate non-repeating subunit, known as a junction block.
Block copolymers with two or three distinct blocks are called diblock copolymers and triblock copolymers, respectively. Technically, a block is a portion of a macromolecule, comprising many constitutional units, that has at least one feature, not present in the adjacent portions. A possible sequence of repeat units A and B in a triblock copolymer might be ~A-A-A-A-A-A-A-B-B-B-B-B-B-B-A-A-A-A-A~. Block copolymers are made up of blocks of different polymerized monomers. For example, polystyrene-b-poly or PS-b-PMMA is made by first polymerizing styrene, subsequently polymerizing methyl methacrylate from the reactive end of the polystyrene chains; this polymer is a "diblock copolymer". Triblocks, multiblocks, etc. can be made. Diblock copolymers are made using living polymerization techniques, such as atom transfer free radical polymerization, reversible addition fragmentation chain transfer, ring-opening metathesis polymerization, living cationic or living anionic polymerizations. An emerging technique is chain shuttling polymerization.
The synthesis of block copolymers requires that both reactivity ratios are much larger than unity under the reaction conditions, so that the terminal monomer unit of a growing chain tends to add a similar unit most of the time. The "blockiness" of a copolymer is a measure of the adjacency of comonomers vs their statistical distribution. Many or most synthetic polymers are in fact copolymers, containing about 1-20% of a minority monomer. In such cases, blockiness is undesirable. A block index has been proposed as a quantitative measure of blockiness or deviation from random monomer composition. An alternating copolymer has regular alternating A and B units, is described by the formula: -A-B-A-B-A-B-A-B-A-B-, or -n-; the molar ratio of each monomer in the polymer is close to one, which happens when the reactivity ratios r1 and r2 are close to zero, as can be seen from the Mayo–Lewis equation. For example, in the free-radical copolymerization of
Sodium thiocyanate is the chemical compound with the formula NaSCN. This colorless deliquescent salt is one of the main sources of the thiocyanate anion; as such, it is used as a precursor for the synthesis of pharmaceuticals and other specialty chemicals. Thiocyanate salts are prepared by the reaction of cyanide with elemental sulfur: 8 NaCN + S8 → 8 NaSCNSodium thiocyanate crystallizes in an orthorhombic cell; each Na+ center is surrounded by three sulfur and three nitrogen ligands provided by the triatomic thiocyanate anion. It is used in the laboratory as a test for the presence of Fe3+ ions. Sodium thiocyanate is employed to convert alkyl halides into the corresponding alkylthiocyanates. Related reagents include ammonium thiocyanate and potassium thiocyanate, which has twice the solubility in water. Silver thiocyanate may be used as well. Treatment of isopropyl bromide with sodium thiocyanate in a hot ethanolic solution affords isopropyl thiocyanate. Protonation of sodium thiocyanate affords isothiocyanic acid, S=C=NH.
This species is generated in situ from sodium thiocyanate.
Interessen‐Gemeinschaft Farbenindustrie AG known as IG Farben, was a German chemical and pharmaceutical conglomerate. Formed in 1925 from a merger of six chemical companies—BASF, Hoechst, Chemische Fabrik Griesheim-Elektron, Chemische Fabrik vorm. Weiler Ter Meer—it was seized by the Allies after World War II and divided back into its constituent companies. In its heyday, IG Farben was the largest company in Europe and the largest chemical and pharmaceutical company in the world. IG Farben scientists made fundamental contributions to all areas of chemistry and the pharmaceutical industry. Otto Bayer discovered the polyaddition for the synthesis of polyurethane in 1937, three company scientists became Nobel laureates: Carl Bosch and Friedrich Bergius in 1931 "for their contributions to the invention and development of chemical high pressure methods", Gerhard Domagk in 1939 "for the discovery of the antibacterial effects of prontosil"; the company had ties in the 1920s to the liberal German People's Party and was accused by the Nazis of being an "international capitalist Jewish company".
A decade it was a Nazi Party donor and, after the Nazi takeover of Germany in 1933, a major government contractor, providing significant materiel for the German war effort. Throughout that decade it purged itself of its Jewish employees. Described as "the most notorious German industrial concern during the Third Reich", IG Farben relied in the 1940s on slave labour from concentration camps, including 30,000 from Auschwitz. One of its subsidiaries supplied the poison gas, Zyklon B, that killed over one million people in gas chambers during the Holocaust; the Allies seized the company at the end of the war in 1945 and the US authorities put its directors on trial. Held from 1947 to 1948 as one of the subsequent Nuremberg trials, the IG Farben trial saw 23 IG Farben directors tried for war crimes and 13 convicted. By 1951 all had been released by the American high commissioner for John J. McCloy. What remained of IG Farben in the West was split in 1951 into its six constituent companies again into three: BASF, Bayer and Hoechst.
These companies continued to operate as an informal cartel and played a major role in the West German Wirtschaftswunder. Following several mergers the main successor companies are Agfa, BASF, Bayer and Sanofi. In 2004 the University of Frankfurt, housed in the former IG Farben head office, set up a permanent exhibition on campus, the Norbert Wollheim memorial, for the slave labourers and those killed by Zyklon B. At the beginning of the 20th century, the German chemical industry dominated the world market for synthetic dyes. Three major firms BASF, Bayer and Hoechst, produced several hundred different dyes. Five smaller firms, Cassella, Chemische Fabrik Kalle, Chemische Fabrik Griesheim-Elektron and Chemische Fabrik vorm. Weiler-ter Meer, concentrated on high-quality specialty dyes. In 1913 these eight firms produced 90 percent of the world supply of dyestuffs and sold about 80 percent of their production abroad; the three major firms had integrated upstream into the production of essential raw materials, they began to expand into other areas of chemistry such as pharmaceuticals, photographic film, agricultural chemicals and electrochemicals.
Contrary to other industries, the founders and their families had little influence on the top-level decision-making of the leading German chemical firms, in the hands of professional salaried managers. Because of this unique situation, the economic historian Alfred Chandler called the German dye companies "the world's first managerial industrial enterprises". With the world market for synthetic dyes and other chemical products dominated by the German industry, German firms competed vigorously for market shares. Although cartels were attempted, they lasted at most for a few years. Others argued for the formation of Interessen-Gemeinschaft. In contrast, the chairman of Bayer, Carl Duisberg, argued for a merger. During a trip to the United States in the spring of 1903, he had visited several of the large American trusts such as Standard Oil, U. S. Steel, International Paper and Alcoa. In 1904, after returning to Germany, he proposed a nationwide merger of the producers of dye and pharmaceuticals in a memorandum to Gustav von Brüning, the senior manager at Hoechst.
Hoechst and several pharmaceutical firms refused to join. Instead and Cassella made an alliance based on mutual equity stakes in 1904; this prompted chairman of BASF, to accelerate their negotiations. In October 1904 an Interessen-Gemeinschaft between Bayer, BASF and Agfa was formed known as the Dreibund or little IG. Profits of the three firms were pooled, with BASF and Bayer getting 43 percent and Agfa 14 percent of all profits; the two alliances were loosely connected with each other through an agreement between BASF and Hoechst to jointly exploit the patent on the Heumann-Pfleger indigo synthesis. Within the Dreibund, Bayer and BASF concentrated on dye, while Agfa concentrated on photographic film. Although there was some cooperation between the technical staff in production and accounting, there was little cooperation between the firms in other areas. Neither were production or distribution facilities consolidated nor did the commercial staff cooperate. In 1908 Hoechst and Cassella acquired 88 percent of the shares of Chemische Fabrik Kalle.
As Hoechst and Kalle were connected by mutual equity shares and were located close to each other in the Frankfurt area, this allowed them to cooperate more than the Dreibund, although they did not rationalize or consolidate their production facilitie
An ionic liquid is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below some arbitrary temperature, such as 100 °C. While ordinary liquids such as water and gasoline are predominantly made of electrically neutral molecules, ionic liquids are made of ions and short-lived ion pairs; these substances are variously called liquid electrolytes, ionic melts, ionic fluids, fused salts, liquid salts, or ionic glasses. They are known as "solvents of the future" as well as "designer solvents". Ionic liquids are described as having many potential applications, they are powerful solvents and electrically conducting fluids. Salts that are liquid at near-ambient temperature are important for electric battery applications, have been considered as sealants due to their low vapor pressure. Any salt that melts without decomposing or vaporizing yields an ionic liquid. Sodium chloride, for example, melts at 801 °C into a liquid that consists of sodium cations and chloride anions.
Conversely, when an ionic liquid is cooled, it forms an ionic solid—which may be either crystalline or glassy. The ionic bond is stronger than the Van der Waals forces between the molecules of ordinary liquids. For that reason, common salts tend to melt at higher temperatures than other solid molecules; some salts are liquid below room temperature. Examples include compounds based on the 1-Ethyl-3-methylimidazolium cation and include: EMIM:Cl, EMIM dicyanamide, C3H3N+2·N−2, that melts at −21 °C. Low-temperature ionic liquids can be compared to ionic solutions, liquids that contain both ions and neutral molecules, in particular to the so-called deep eutectic solvents, mixtures of ionic and non-ionic solid substances which have much lower melting points than the pure compounds. Certain mixtures of nitrate salts can have melting points below 100 °C; the term "ionic liquid" in the general sense was used as early as 1943. When Tawny crazy ants combat Fire ants, the latter spray them with a toxic, alkaloid-based venom.
The Tawny crazy ant exudes its own venom, formic acid, self-grooms with it, an action which de-toxifies the Fire ant venom. The mixed venoms chemically react with one another to form an ionic liquid, the first occurring IL to be described; the discovery date of the "first" ionic liquid is disputed, along with the identity of its discoverer. Ethanolammonium nitrate was reported in 1888 by J. Weiner. One of the earliest room temperature ionic liquids was ethylammonium nitrate NH+3·NO−3, reported in 1914 by Paul Walden. In the 1970s and 1980s, ionic liquids based on alkyl-substituted imidazolium and pyridinium cations, with halide or tetrahalogenoaluminate anions, were developed as potential electrolytes in batteries. For the imidazolium halogenoaluminate salts, their physical properties—such as viscosity, melting point, acidity—could be adjusted by changing the alkyl substituents and the imidazolium/pyridinium and halide/halogenoaluminate ratios. Two major drawbacks for some applications were moisture sensitivity and basicity.
In 1992, Wilkes and Zawarotko obtained ionic liquids with'neutral' weakly coordinating anions such as hexafluorophosphate and tetrafluoroborate, allowing a much wider range of applications. Although many classical IL's are hexafluorophosphate and tetrafluoroborate salts, bistriflimide − are popular. Ionic liquids are moderate to poor conductors of electricity, non-ionizing viscous and exhibit low vapor pressure, their other properties are diverse: many have low combustibility, are thermally stable, with wide liquid regions, favorable solvating properties for a range of polar and non-polar compounds. Many classes of chemical reactions, such as Diels-Alder reactions and Friedel-Crafts reactions, can be performed using ionic liquids as solvents. IL's can serve as solvents for biocatalysis; the miscibility of ionic liquids with water or organic solvents varies with side chain lengths on the cation and with choice of anion. They can be functionalized to act as acids, bases, or ligands, are precursors salts in the preparation of stable carbenes.
They have been found to hydrolyse, affording acidic or basic media in the aqueous milieu. Because of their distinctive properties, ionic liquids are attracting increasing attention in many fields, including organic chemistry, catalysis, physical chemistry, engineering. Despite their low vapor pressures, some ionic liquids can be distilled under vacuum conditions at temperatures near 300 °C. In the original work by Martyn Earle, et al. the authors wrongly concluded that the vapor was made up of individual, separated ions, but was proven that the vapors formed consisted of ion-pairs. Some ionic liquids generate flammable gases on thermal decomposition. Thermal stability and melting point depend on the liquid's components; the thermal stability of a task-specific ionic liquid, protonated betaine bisimide is of about 534 K and N-Butyl-N-Methyl pyrrolidinium bisimide was thermally stable up to 640 K. The upper limits of thermal stability of ionic liquids reported in the literature are based upon fast TGA scans, they do not imply long-term thermal stability of ionic liquids, limited to less than 500 K for most ioni
Zinc chloride is the name of chemical compounds with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, are soluble in water. ZnCl2 itself is hygroscopic and deliquescent. Samples should therefore be protected from sources of moisture, including the water vapor present in ambient air. Zinc chloride finds wide application in textile processing, metallurgical fluxes, chemical synthesis. No mineral with this chemical composition is known aside from the rare mineral simonkolleite, Zn58Cl2·H2O. Four crystalline forms of ZnCl2 are known: α, β, γ, δ, in each case the Zn2+ ions are tetrahedrally coordinated to four chloride ions. Here a, b, c are lattice constants, Z is the number of structure units per unit cell, ρ is the density calculated from the structure parameters; the pure anhydrous orthorhombic form changes to one of the other forms on exposure to the atmosphere, a possible explanation is that the OH− ions originating from the absorbed water facilitate the rearrangement.
Rapid cooling of molten ZnCl2 gives a glass. The covalent character of the anhydrous material is indicated by its low melting point of 275 °C. Further evidence for covalency is provided by the high solubility of the dichloride in ethereal solvents, where it forms adducts with the formula ZnCl2L2, where L = ligand such as O2. In the gas phase, ZnCl2 molecules are linear with a bond length of 205 pm. Molten ZnCl2 has a high viscosity at its melting point and a comparatively low electrical conductivity, which increases markedly with temperature. A Raman scattering study of the melt indicated the presence of polymeric structures, a neutron scattering study indicated the presence of tetrahedral complexes. Five hydrates of zinc chloride are known: ZnCl2n with n = 1, 1.5, 2.5, 3 and 4. The tetrahydrate ZnCl24 crystallizes from aqueous solutions of zinc chloride. Anhydrous ZnCl2 can be prepared from zinc and hydrogen chloride: Zn + 2 HCl → ZnCl2 + H2Hydrated forms and aqueous solutions may be prepared by treating Zn metal with hydrochloric acid.
Zinc oxide and zinc sulfide react with HCl: ZnS + 2 HCl → ZnCl2 + H2SUnlike many other elements, zinc exists in only one oxidation state, 2+, which simplifies purification of the chloride. Commercial samples of zinc chloride contain water and products from hydrolysis as impurities; such samples may be purified by recrystallization from hot dioxane. Anhydrous samples can be purified by sublimation in a stream of hydrogen chloride gas, followed by heating the sublimate to 400 °C in a stream of dry nitrogen gas; the simplest method relies on treating the zinc chloride with thionyl chloride. Molten anhydrous ZnCl2 at 500–700 °C dissolves zinc metal, and, on rapid cooling of the melt, a yellow diamagnetic glass is formed, which Raman studies indicate contains the Zn2+2 ion. A number of salts containing the tetrachlorozincate anion, are known. "Caulton's reagent", V2Cl36Zn2Cl6 is an example of a salt containing Zn2Cl2−6. The compound Cs3ZnCl5 contains tetrahedral ZnCl2−4 and Cl− anions. No compounds containing the ZnCl4−6 ion have been characterized.
Whilst zinc chloride is soluble in water, solutions cannot be considered to contain solvated Zn2+ ions and Cl− ions, ZnClxH2O species are present. Aqueous solutions of ZnCl2 are acidic: a 6 M aqueous solution has a pH of 1; the acidity of aqueous ZnCl2 solutions relative to solutions of other Zn2+ salts is due to the formation of the tetrahedral chloro aqua complexes where the reduction in coordination number from 6 to 4 further reduces the strength of the O–H bonds in the solvated water molecules. In alkali solution in the presence of OH− ion various zinc hydroxychloride anions are present in solution, e.g. Zn3Cl2−, Zn2Cl2−2, ZnOHCl2−3, Zn58Cl2·H2O precipitates; when ammonia is bubbled through a solution of zinc chloride, the hydroxide does not precipitate, instead compounds containing complexed ammonia are produced, Zn4Cl2·H2O and on concentration ZnCl22. The former contains the Zn62+ ion, the latter is molecular with a distorted tetrahedral geometry; the species in aqueous solution have been investigated and show that Zn42+ is the main species present with Zn3Cl+ present at lower NH3:Zn ratio.
Aqueous zinc chloride reacts with zinc oxide to form an amorphous cement, first investigated in the 1855 by Stanislas Sorel. Sorel went on to investigate the related magnesium oxychloride cement, which bears his name; when hydrated zinc chloride is heated, one obtains a residue of ZnCl e.g. ZnCl2·2H2O → ZnCl + HCl + H2OThe compound ZnCl2·½HCl·H2O may be prepared by careful precipitation from a solution of ZnCl2 acidified with HCl, it contains a polymeric anion n with balancing monohydrated hydronium ions, H5O2+ ions. The formation of reactive anhydrous HCl gas formed when zinc chloride hydrates are heated is the basis of qualitative inorganic spot tests; the use of zinc chloride as a flux, sometimes in a mixture with ammonium chloride, involves the production of HCl and its subsequent reaction with surface oxides. Zinc chloride forms two salts with ammonium chloride: 2ZnCl4 and 3ClZnCl4, which decompose on heating liberating HCl, just as zinc chloride hydrate does; the action of zinc chloride/ammonium chloride fluxes, for example, in the hot-dip galvanizing process produces H2 gas and ammonia fumes.
Cellulose dissolves in aqueous solutions of ZnCl2, zinc-cellulose complexes have been detected. Cellulose dissolves in molten ZnCl2 hydrate and carboxylation and acetylation performed on the cellulose polymer. Thus, although m
Heat fusion is a welding process used to join two different pieces of a thermoplastic. This process involves heating both pieces and pressing them together; the two pieces cool together and form a permanent bond. When done properly, the two pieces become indistinguishable from each other. Dissimilar plastics can result in improper bonding; this process is used in plastic pressure pipe systems to join a pipe and fitting together, or to join a length of pipe directly to another length of pipe. Polyolefins are used for these applications. Butt welding is performed using one of several methods; the first, most common, is butt welding or butt fusion, a type of hot plate welding. This technique involves heating two planed surfaces of thermoplastic material against a heated surface. After a specified amount of time, the heating plate is removed and the two pieces are pressed together and allowed to cool under pressure, forming the desired bond. Butt welding outside of manufacturing is performed to join pipes.
The other major technique is socket fusion. It is distinguished from butt-welding by using custom-shaped and -sized heating plates rather than a basic flat surface; these heads allow for more surface contact, reducing the time needed to fuse the pipe. Socket fusion joins pipe and fittings together, rather than joining pipe to pipe, it requires less pressure than butt-welding and is more used on smaller sizes of pipe. Socket welding has additional advantages of requiring less machinery and is more portable than the heavier equipment required for butt fusion. A third method of thermoplastic welding is called saddle fusion. Sidewall fusion is, like socket fusion, another process based on hot plate welding. Sidewall fusion differs from either socket, or butt fusion methods by performing fusion into the side of the pipe wall in a transverse orientation to the main pipe, rather than in line with the pipe. Sidewall fusion is employed in conjunction with either socket or butt fusion methods as a complementary process and many fusion machines designed for butt fusion are equipped for sidewall fusion.
Adaptor plates that match the outside diameter of the main pipe are applied to the heating plate to perform this type of fusion. Another method used is referred to as electrofusion. Electrofusion is a method of joining HDPE and other plastic pipes with special fittings that have built-in resistive wire, used to weld the joint together; the pipes to be joined are trimmed, inserted into the electrofusion fitting and a voltage is applied using a device called an electrofusion processor. The processor controls how much voltage is applied, for how long, depending on the fitting in use; as current is applied to the resistive wire, the coils heat up and melt the inside of the fitting and the outside of the pipe wall which weld together producing a strong homogeneous joint. The assembly is left to cool for a specified time; the joints produced. Socket Fusion Video