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International Union of Pure and Applied Chemistry
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The International Union of Pure and Applied Chemistry /ˈaɪjuːpæk/ or /ˈjuːpæk/ is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science, IUPAC is registered in Zürich, Switzerland, and the administrative office, known as the IUPAC Secretariat, is in Research Triangle Park, North Carolina, United States. This administrative office is headed by IUPACs executive director, currently Lynn Soby, IUPAC was established in 1919 as the successor of the International Congress of Applied Chemistry for the advancement of chemistry. Its members, the National Adhering Organizations, can be national chemistry societies, national academies of sciences, there are fifty-four National Adhering Organizations and three Associate National Adhering Organizations. IUPACs Inter-divisional Committee on Nomenclature and Symbols is the world authority in developing standards for the naming of the chemical elements. Since its creation, IUPAC has been run by different committees with different responsibilities. These committees run different projects which include standardizing nomenclature, finding ways to bring chemistry to the world, IUPAC is best known for its works standardizing nomenclature in chemistry and other fields of science, but IUPAC has publications in many fields including chemistry, biology and physics. IUPAC is also known for standardizing the atomic weights of the elements through one of its oldest standing committees, the need for an international standard for chemistry was first addressed in 1860 by a committee headed by German scientist Friedrich August Kekulé von Stradonitz. This committee was the first international conference to create an international naming system for organic compounds, the ideas that were formulated in that conference evolved into the official IUPAC nomenclature of organic chemistry. IUPAC stands as a legacy of this meeting, making it one of the most important historical international collaborations of chemistry societies, since this time, IUPAC has been the official organization held with the responsibility of updating and maintaining official organic nomenclature. IUPAC as such was established in 1919, one notable country excluded from this early IUPAC is Germany. Germanys exclusion was a result of prejudice towards Germans by the Allied powers after World War I, Germany was finally admitted into IUPAC during 1929. However, Nazi Germany was removed from IUPAC during World War II, during World War II, IUPAC was affiliated with the Allied powers, but had little involvement during the war effort itself. After the war, East and West Germany were eventually readmitted to IUPAC, since World War II, IUPAC has been focused on standardizing nomenclature and methods in science without interruption. In 2016, IUPAC denounced the use of chlorine as a chemical weapon, the letter stated, Our organizations deplore the use of chlorine in this manner. According to the CWC, the use, stockpiling, distribution, IUPAC is governed by several committees that all have different responsibilities. Each committee is made up of members of different National Adhering Organizations from different countries, the steering committee hierarchy for IUPAC is as follows, All committees have an allotted budget to which they must adhere. Any committee may start a project, if a projects spending becomes too much for a committee to continue funding, it must take the issue to the Project Committee
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Polymer
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A polymer is a large molecule, or macromolecule, composed of many repeated subunits. Because of their range of properties, both synthetic and natural polymers play an essential and ubiquitous role 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, Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. The units composing polymers derive, actually or conceptually, from molecules of low molecular mass. The term was coined in 1833 by Jöns Jacob Berzelius, though with a distinct from the modern IUPAC definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger, Polymers are studied in the fields of biophysics and macromolecular science, and polymer science. Polyisoprene of latex rubber is an example of a polymer. In biological contexts, essentially all biological macromolecules—i. e, proteins, nucleic acids, and polysaccharides—are purely polymeric, or are composed in large part of polymeric components—e. g. Isoprenylated/lipid-modified glycoproteins, where small molecules and oligosaccharide modifications occur on the polyamide backbone of the protein. The simplest theoretical models for polymers are ideal chains, Polymers are of two types, Natural polymeric materials such as shellac, amber, wool, silk and natural rubber have been used for centuries. A variety of natural polymers exist, such as cellulose. Most commonly, the continuously linked backbone of a used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene, whose repeating unit is based on ethylene monomer, however, other structures do exist, for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant. Oxygen is also present in polymer backbones, such as those of polyethylene glycol, polysaccharides. Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network, during the polymerization process, some chemical groups may be lost from each monomer. This is the case, for example, in the polymerization of PET polyester, the distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Laboratory synthetic methods are divided into two categories, step-growth polymerization and chain-growth polymerization. However, some methods such as plasma polymerization do not fit neatly into either category
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Styrene
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Styrene, also known as ethenylbenzene, vinylbenzene, and phenylethene, is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is an oily liquid that evaporates easily and has a sweet smell. Styrene is the precursor to polystyrene and several copolymers, approximately 25 million tonnes of styrene were produced in 2010. Styrene is named for balsam, the resin of Liquidambar trees of the Altingiaceae plant family. Styrene occurs naturally in small quantities in some plants and foods, in 1839, the German apothecary Eduard Simon isolated a volatile oil from the resin of the American sweetgum tree. He also noticed that when Styrol was exposed to air, light, or heat, it transformed into a hard, rubber-like substance. By 1845, the German chemist August Hofmann and his student John Blyth had determined Styrols empirical formula and they had also determined that Simons Styroloxyd — which they renamed Metastyrol — had the same empirical formula as Styrol. Furthermore, they could obtain Styrol by dry distilling Metastyrol, in 1865, the German chemist Emil Erlenmeyer found that Styrol could form a dimer, and in 1866 the French chemist Marcelin Berthelot stated that Metastyrol was a polymer of Styrol. Meanwhile, other chemists had been investigating another component of storax, namely and they had found that cinnamic acid could be decarboxylated to form cinnamène, which appeared to be Styrol. In 1845, French chemist Emil Kopp suggested that the two compounds were identical, and in 1866, Erlenmeyer suggested that both cinnamol and Styrol might be vinyl benzene. However, the Styrol that was obtained from cinnamic acid seemed different from the Styrol that was obtained by distilling storax resin, the latter was optically active. Eventually, in 1876, the Dutch chemist van t Hoff resolved the ambiguity, the modern method for production of styrene by dehydrogenation of ethylbenzene was first achieved in the 1930s. The production of styrene increased dramatically during the 1940s, when it was popularized as a feedstock for synthetic rubber, because it is produced on such a large scale, ethylbenzene in turn prepared on a prodigious scale. Ethylbenzene is mixed in the gas phase with 10–15 times its volume in high-temperature steam, most ethylbenzene dehydrogenation catalysts are based on iron oxide, promoted by several percent potassium oxide or potassium carbonate. Steam serves several roles in this reaction and it is the source of heat for powering the endothermic reaction, and it removes coke that tends to form on the iron oxide catalyst through the water gas shift reaction. The potassium promoter enhances this decoking reaction, the steam also dilutes the reactant and products, shifting the position of chemical equilibrium towards products. A typical styrene plant consists of two or three reactors in series, which operate under vacuum to enhance the conversion and selectivity, typical per-pass conversions are ca. 65% for two reactors and 70-75% for three reactors. The main byproducts are benzene and toluene, because styrene and ethylbenzene have similar boiling points, their separation requires tall distillation towers and high return/reflux ratios
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Polystyrene
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Polystyrene /ˌpɒliˈstaɪriːn/ is a synthetic aromatic polymer made from the monomer styrene. Polystyrene can be solid or foamed, general-purpose polystyrene is clear, hard, and rather brittle. It is an inexpensive resin per unit weight and it is a rather poor barrier to oxygen and water vapor and has a relatively low melting point. Polystyrene is one of the most widely used plastics, the scale of its production being several million tonnes per year, Polystyrene can be naturally transparent, but can be colored with colorants. Uses include protective packaging, containers, lids, bottles, trays, tumblers, as a thermoplastic polymer, polystyrene is in a solid state at room temperature but flows if heated above about 100 °C, its glass transition temperature. It becomes rigid again when cooled and this temperature behavior is exploited for extrusion and also for molding and vacuum forming, since it can be cast into molds with fine detail. Polystyrene is very slow to biodegrade and is therefore a focus of controversy among environmentalists, Polystyrene was discovered in 1839 by Eduard Simon, an apothecary from Berlin. From storax, the resin of the American sweetgum tree Liquidambar styraciflua, he distilled an oily substance, several days later, Simon found that the styrol had thickened into a jelly he dubbed styrol oxide because he presumed an oxidation. By 1845 Jamaican-born chemist John Buddle Blyth and German chemist August Wilhelm von Hofmann showed that the transformation of styrol took place in the absence of oxygen. They called the product metastyrol, analysis showed that it was identical to Simons Styroloxyd. In 1866 Marcelin Berthelot correctly identified the formation of metastyrol/Styroloxyd from styrol as a polymerization process, about 80 years later it was realized that heating of styrol starts a chain reaction that produces macromolecules, following the thesis of German organic chemist Hermann Staudinger. This eventually led to the substance receiving its present name, polystyrene, the company I. G. Farben began manufacturing polystyrene in Ludwigshafen, about 1931, hoping it would be a suitable replacement for die-cast zinc in many applications. Success was achieved when they developed a reactor vessel that extruded polystyrene through a tube and cutter. In 1941, Dow Chemical invented a Styrofoam process, before 1949, the chemical engineer Fritz Stastny developed pre-expanded PS beads by incorporating aliphatic hydrocarbons, such as pentane. These beads are the raw material for moulding parts or extruding sheets, BASF and Stastny applied for a patent that was issued in 1949. The moulding process was demonstrated at the Kunststoff Messe 1952 in Düsseldorf, the crystal structure of isotactic polystyrene was reported by Giulio Natta. In 1954, the Koppers Company in Pittsburgh, Pennsylvania, developed expanded polystyrene foam under the trade name Dylite, in 1960, Dart Container, the largest manufacturer of foam cups, shipped their first order. In 1988, the first U. S. ban of general polystyrene foam was enacted in Berkeley, in chemical terms, polystyrene is a long chain hydrocarbon wherein alternating carbon centers are attached to phenyl groups
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Chemical reaction
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A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Nuclear chemistry is a sub-discipline of chemistry that involves the reactions of unstable. The substance initially involved in a reaction are called reactants or reagents. Chemical reactions are characterized by a chemical change, and they yield one or more products. Reactions often consist of a sequence of individual sub-steps, the elementary reactions. Chemical reactions are described with chemical equations, which present the starting materials, end products. Chemical reactions happen at a characteristic reaction rate at a given temperature, typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms. Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium, Reactions that proceed in the forward direction to approach equilibrium are often described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of energy to go forward. Different chemical reactions are used in combinations during chemical synthesis in order to obtain a desired product, in biochemistry, a consecutive series of chemical reactions form metabolic pathways. These reactions are catalyzed by protein enzymes. Chemical reactions such as combustion in fire, fermentation and the reduction of ores to metals were known since antiquity, in the Middle Ages, chemical transformations were studied by Alchemists. They attempted, in particular, to lead into gold, for which purpose they used reactions of lead. The process involved heating of sulfate and nitrate minerals such as sulfate, alum. In the 17th century, Johann Rudolph Glauber produced hydrochloric acid and sodium sulfate by reacting sulfuric acid, further optimization of sulfuric acid technology resulted in the contact process in the 1880s, and the Haber process was developed in 1909–1910 for ammonia synthesis. From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle, the phlogiston theory was proposed in 1667 by Johann Joachim Becher. It postulated the existence of an element called phlogiston, which was contained within combustible bodies. This proved to be false in 1785 by Antoine Lavoisier who found the explanation of the combustion as reaction with oxygen from the air
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Chemical compound
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A chemical compound is an entity consisting of two or more atoms, at least two from different elements, which associate via chemical bonds. Many chemical compounds have a numerical identifier assigned by the Chemical Abstracts Service. For example, water is composed of two atoms bonded to one oxygen atom, the chemical formula is H2O. A compound can be converted to a different chemical composition by interaction with a chemical compound via a chemical reaction. In this process, bonds between atoms are broken in both of the compounds, and then bonds are reformed so that new associations are made between atoms. Schematically, this reaction could be described as AB + CD → AC + BD, where A, B, C, and D are each unique atoms, and AB, CD, AC, and BD are each unique compounds. A chemical element bonded to a chemical element is not a chemical compound since only one element. Examples are the diatomic hydrogen and the polyatomic molecule sulfur. Chemical compounds have a unique and defined chemical structure held together in a spatial arrangement by chemical bonds. Pure chemical elements are not considered chemical compounds, failing the two or more atom requirement, though they often consist of molecules composed of multiple atoms. There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly. Characteristic properties of compounds include that elements in a compound are present in a definite proportion, for example, the molecule of the compound water is composed of hydrogen and oxygen in a ratio of 2,1. In addition, compounds have a set of properties. The physical and chemical properties of compounds differ from those of their constituent elements, however, mixtures can be created by mechanical means alone, but a compound can be created only by a chemical reaction. Some mixtures are so combined that they have some properties similar to compounds. Other examples of compound-like mixtures include intermetallic compounds and solutions of metals in a liquid form of ammonia. Compounds may be described using formulas in various formats, for compounds that exist as molecules, the formula for the molecular unit is shown. For polymeric materials, such as minerals and many metal oxides, the elements in a chemical formula are normally listed in a specific order, called the Hill system
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Functional group
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In organic chemistry, functional groups are specific groups of atoms or bonds within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of, however, its relative reactivity can be modified by other functional groups nearby. The atoms of functional groups are linked to other and to the rest of the molecule by covalent bonds. Any subgroup of atoms of a compound also may be called a radical, and if a covalent bond is broken homolytically, Functional groups can also be charged, e. g. in carboxylate salts, which turns the molecule into a polyatomic ion or a complex ion. Complexation and solvation is also caused by interactions of functional groups. In the common rule of thumb like dissolves like, it is the shared or mutually well-interacting functional groups give rise to solubility. For example, sugar dissolves in water because both share the functional group and hydroxyls interact strongly with each other. Combining the names of groups with the names of the parent alkanes generates what is termed a systematic nomenclature for naming organic compounds. In traditional nomenclature, the first carbon atom after the carbon that attaches to the group is called the alpha carbon, the second, beta carbon. IUPAC conventions call for numeric labeling of the position, e. g. 4-aminobutanoic acid, in traditional names various qualifiers are used to label isomers, for example isopropanol is an isomer is n-propanol. The following is a list of functional groups. In the formulas, the symbols R and R usually denote an attached hydrogen, or a side chain of any length. Functional groups, called hydrocarbyl, that only carbon and hydrogen. Each one differs in type of reactivity, there are also a large number of branched or ring alkanes that have specific names, e. g. tert-butyl, bornyl, cyclohexyl, etc. Hydrocarbons may form charged structures, positively charged carbocations or negative carbanions, examples are tropylium and triphenylmethyl cations and the cyclopentadienyl anion. Haloalkanes are a class of molecule that is defined by a carbon–halogen bond and this bond can be relatively weak or quite stable. In general, with the exception of fluorinated compounds, haloalkanes readily undergo nucleophilic substitution reactions or elimination reactions, the substitution on the carbon, the acidity of an adjacent proton, the solvent conditions, etc. all can influence the outcome of the reactivity. Compounds that contain nitrogen in this category may contain C-O bonds, compounds that contain sulfur exhibit unique chemistry due to their ability to form more bonds than oxygen, their lighter analogue on the periodic table
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Steric effects
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See also, intramolecular forces Steric effects arise from a fact that each atom within a molecule occupies a certain amount of space. If atoms are too close together, there is an associated cost in energy due to overlapping electron clouds. Steric hindrance occurs when the size of groups within a molecule prevents chemical reactions that are observed in related molecules with smaller groups. Steric hindrance between adjacent groups can also restrict torsional bond angles, however, hyperconjugation has been suggested as an explanation for the preference of the staggered conformation of ethane because the steric hindrance of the small hydrogen atom is far too small. This is the responsible for the observed shape of rotaxanes. When a Lewis acid and Lewis base cannot combine due to steric hindrance, Steric shielding occurs when a charged group on a molecule is seemingly weakened or spatially shielded by less charged atoms, including counterions in solution. Steric attraction occurs when molecules have shapes or geometries that are optimized for interaction with one another, in these cases molecules will react with each other most often in specific arrangements. Chain crossing, A chain, ring, or a set of rings cannot change from one conformation to another if it would require a chain to pass through itself or another chain and this effect, or lack of, is responsible for the shape of catenanes and molecular knots. Steric repulsions between different parts of a system were found to be of key importance in governing the direction of transition-metal-mediated transformations. Steric effects can even induce a switch in the catalytic reaction. Steric inhibition of resonance is present only in benzene rings, the presence of any group at the ortho position in benzoic acid will throw the carboxylic acid group out of the plane, and thus its mesomeric connection with the benzene ring vanishes. This means that ortho-substituted benzoic acids are stronger than meta- and para-substituted benzoic acids, Steric inhibition of protonation Consider 2,2,6, 6-Tetramethylpiperidine and in, in-diphosphine. The structure, properties, and reactivity of a molecule is dependent on straightforward bonding interactions including covalent bonds, ionic bonds, hydrogen bonds and this bonding supplies a basic molecular skeleton that is modified by repulsive forces. These repulsive forces include the interactions described above. Basic bonding and steric are at times insufficient to explain many structures, properties, there are more esoteric electronic effects but these are among the most important when considering structure and chemical reactivity. A special computational procedure was developed to separate electronic and steric effects of an group in the molecule and to reveal their influence on structure. Understanding steric effects is critical to chemistry, biochemistry and pharmacology, in organic chemistry, steric effects are nearly universal and affect the rates and activation energies of most chemical reactions to varying degrees. Steric effects often dictate reaction pathways in organic synthesis because there are configurations in which molecules can collide
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Alkene
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In organic chemistry, an alkene is an unsaturated hydrocarbon that contains at least one carbon–carbon double bond. The words alkene, olefin, and olefine are used often interchangeably, acyclic alkenes, with only one double bond and no other functional groups, known as mono-enes, form a homologous series of hydrocarbons with the general formula CnH2n. Alkenes have two hydrogen atoms less than the corresponding alkane, the simplest alkene, ethylene, with the International Union of Pure and Applied Chemistry name ethene, is the organic compound produced on the largest scale industrially. Aromatic compounds are drawn as cyclic alkenes, but their structure and properties are different. This double bond is stronger than a single covalent bond and also shorter, each carbon of the double bond uses its three sp2 hybrid orbitals to form sigma bonds to three atoms. The unhybridized 2p atomic orbitals, which lie perpendicular to the created by the axes of the three sp² hybrid orbitals, combine to form the pi bond. This bond lies outside the main C–C axis, with half of the bond on one side of the molecule, rotation about the carbon–carbon double bond is restricted because it incurs an energetic cost to break the alignment of the p orbitals on the two carbon atoms. As a consequence, substituted alkenes may exist as one of two isomers, called cis or trans isomers, more complex alkenes may be named with the E–Z notation for molecules with three or four different substituents. For example, of the isomers of butene, the two groups of -but-2-ene appear on the same side of the double bond, and in -but-2-ene the methyl groups appear on opposite sides. These two isomers of butene are slightly different in their chemical and physical properties, a 90° twist of the C=C bond requires less energy than the strength of a pi bond, and the bond still holds. This contradicts a common assertion that the p orbitals would be unable sustain such a bond. In truth, the misalignment of the p orbitals is less than expected because pyramidalization takes place, trans-Cyclooctene is a stable strained alkene and the orbital misalignment is only 19° with a dihedral angle of 137° and a degree of pyramidalization of 18°. The trans isomer of cycloheptene is stable only at low temperatures, as predicted by the VSEPR model of electron pair repulsion, the molecular geometry of alkenes includes bond angles about each carbon in a double bond of about 120°. The angle may vary because of steric strain introduced by nonbonded interactions between groups attached to the carbons of the double bond. For example, the C–C–C bond angle in propylene is 123. 9°, for bridged alkenes, Bredts rule states that a double bond cannot occur at the bridgehead of a bridged ring system unless the rings are large enough. The physical properties of alkenes and alkanes are similar and they are colourless, nonpolar, combustable, and almost odorless. The physical state depends on mass, like the corresponding saturated hydrocarbons, the simplest alkenes, ethene, propene. Linear alkenes of approximately five to sixteen carbons are liquids, Alkenes are relatively stable compounds, but are more reactive than alkanes, either because of the reactivity of the carbon–carbon pi-bond or the presence of allylic CH centers
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Carbonyl group
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In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom, C=O. It is common to several classes of compounds, as part of many larger functional groups. A compound containing a group is often referred to as a carbonyl compound. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex, the remainder of this article concerns itself with the organic chemistry definition of carbonyl, where carbon and oxygen share a double bond. A carbonyl group characterizes the types of compounds, Note that the most specific labels are usually employed. For example, ROR structures are known as acid anhydride rather than the more generic ester, other organic carbonyls are urea and the carbamates, the derivatives of acyl chlorides chloroformates and phosgene, carbonate esters, thioesters, lactones, lactams, hydroxamates, and isocyanates. Examples of inorganic compounds are carbon dioxide and carbonyl sulfide. A special group of compounds are 1, 3-dicarbonyl compounds that have acidic protons in the central methylene unit. Examples are Meldrums acid, diethyl malonate and acetylacetone, because oxygen is more electronegative than carbon, carbonyl compounds often have resonance structures which affect their reactivity. This relative electronegativity draws electron density away from carbon, increasing the bonds polarity, carbon can then be attacked by nucleophiles or a negatively charged part of another molecule. During the reaction, the double bond is broken. This reaction is known as addition-elimination or condensation, the electronegative oxygen also can react with an electrophile, for example a proton in an acidic solution or with Lewis acids to form an oxocarbenium ion. The polarity of oxygen also makes the alpha hydrogens of carbonyl compounds much more acidic than typical sp3 C-H bonds, for example, the pKa values of acetaldehyde and acetone are 16.7 and 19 respectively, while the pKa value of methane is extrapolated to be approximately 50. This is because a carbonyl is in resonance with an enol. The deprotonation of the enol with a base produces an enolate. Amides are the most stable of the carbonyl couplings due to their high resonance stabilization between the nitrogen-carbon and carbon-oxygen bonds, carbonyl groups can be reduced by reaction with hydride reagents such as NaBH4 and LiAlH4, with bakers yeast, or by catalytic hydrogenation. Ketones give secondary alcohols while aldehydes, esters and carboxylic acids give primary alcohols, carbonyls can be alkylated in nucleophilic addition reactions using organometallic compounds such as organolithium reagents, Grignard reagents, or acetylides. Carbonyls also may be alkylated by enolates as in aldol reactions, carbonyls are also the prototypical groups with vinylogous reactivity
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Alkane
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In organic chemistry, an alkane, or paraffin, is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a structure in which all the carbon-carbon bonds are single. Alkanes have the chemical formula CnH2n+2. The alkanes range in complexity from the simplest case of methane, CH4 where n =1, in an alkane, each carbon atom has 4 bonds, and each hydrogen atom is joined to one of the carbon atoms. The longest series of linked carbon atoms in a molecule is known as its skeleton or carbon backbone. The number of atoms may be thought of as the size of the alkane. One group of the alkanes are waxes, solids at standard ambient temperature and pressure. They can be viewed as molecular trees upon which can be hung the more functional groups of biological molecules. The alkanes have two main sources, petroleum and natural gas. Saturated hydrocarbons are hydrocarbons having only single covalent bonds between their carbons, according to the definition by IUPAC, the former two are alkanes, whereas the third group is called cycloalkanes. Saturated hydrocarbons can also combine any of the linear, cyclic and branching structures, the formula is CnH 2n−2k+2. Alkanes are the ones, corresponding to k =0. Alkanes with more than three carbon atoms can be arranged in different ways, forming structural isomers. The simplest isomer of an alkane is the one in which the atoms are arranged in a single chain with no branches. This isomer is called the n-isomer. However the chain of atoms may also be branched at one or more points. The number of possible isomers increases rapidly with the number of carbon atoms, for example, 3-methylhexane and its higher homologues are chiral due to their stereogenic center at carbon atom number 3. In addition to the alkane isomers, the chain of atoms may form one or more loops
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Copolymer
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When two or more different monomers unite together to polymerize, their result is called a copolymer and its process is called copolymerization. Commercially relevant copolymers include acrylonitrile butadiene styrene, styrene/butadiene co-polymer, nitrile rubber, styrene-acrylonitrile, styrene-isoprene-styrene, 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. 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 blocks are called diblock copolymers and triblock copolymers, respectively. Copolymers may also be described in terms of the existence of or arrangement of branches in the polymer structure, linear copolymers consist of a single main chain whereas branched copolymers consist of a single main chain with one or more polymeric side chains. Other special types of branched copolymers include star copolymers, brush copolymers, in gradient copolymers the monomer composition changes gradually along the chain. A terpolymer is a copolymer consisting of three distinct monomers, the term is derived from ter, meaning thrice, and polymer. Stereoblock copolymers A special structure can be formed from one monomer where now the distinguishing feature is the tacticity of each block, statistical copolymers are dictated by the reaction kinetics of the two chemically distinct monomer reactants, and are commonly referred to interchangeably as “random” in the polymer literature. As with other types of copolymers, random copolymers can have interesting, examples of commercially relevant random copolymers include rubbers made from styrene-butadiene copolymers and resins from styrene-acrylic or methacrylic acid derivatives. A number of parameters are relevant in the composition of the product, namely. Reactivity ratios describe whether the monomer reacts preferentially with a segment of the type or of the other type. For example, a reactivity ratio that is less one for component 1 indicates that this component reacts with the other type of monomer more readily. When both reactivity ratios are less than one, there is a point in the Mayo-Lewis plot. At this point, the fraction of monomer equals the composition of the component in the polymer. There are several ways to synthesize random copolymers, free radical polymerization is less expensive than other methods, and produces high-molecular weight polymer quickly. Several methods offer better control over dispersity, additionally, anionic polymerization is expensive and requires very clean reaction conditions, and is therefore difficult to implement on a large scale. These methods are favored over anionic polymerization because they can be performed in similar to free radical polymerization. The reactions require longer periods than free radical polymerization
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Trimer (chemistry)
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In chemistry, a trimer is an oligomer derived from three identical precursors. An example is the procedure of production of polymers, at first, a monomer is made. By combining two monomers, a dimer is produced, with further additions, a trimer and eventually a polymer is made. Chemical compounds that often trimerise are aliphatic isocyanates and cyanic acids, in 1866, Marcellin Berthelot reported the first example of cyclotrimerization leading to aromatic products, the cyclization of acetylene to benzene. In the Reppe synthesis, the trimerization of acetylene gives benzene, Symmetrical 1,3, the conversion commences at approximately 175 °C,3 H2N-CO-NH2 →3 +3 NH3 The endothermic synthesis of melamine can be understood in two steps. 3 HOCN →33 +3 NH3 → C3H6N6 +3 H2O This water then reacts with cyanic acid present, which helps drive the trimerization reaction, generating carbon dioxide and ammonia. 3 HOCN +3 H2O →3 CO2 + 3NH3 In total, cyclotrimerization of formaldehyde affords 1,3, 5-Trioxane,1,3, 5-Trithiane is the cyclic trimer of the otherwise unstable species thioformaldehyde. This heterocycle consists of a ring with alternating methylene bridges. It is prepared by treatment of formaldehyde with hydrogen sulfide, three molecules of acetaldehyde condense to form “paraldehyde, ” a cyclic trimer containing C-O single bonds
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Nucleophile
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A nucleophile is a chemical species that donates an electron pair to an electrophile to form a chemical bond in relation to a reaction. All molecules or ions with a pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases, Nucleophilic describes the affinity of a nucleophile to the nuclei. Nucleophilicity, sometimes referred to as strength, refers to a substances nucleophilic character and is often used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis, nucleophiles may take part in nucleophilic substitution, whereby a nucleophile becomes attracted to a full or partial positive charge. The terms nucleophile and electrophile were introduced by Christopher Kelk Ingold in 1933, the word nucleophile is derived from nucleus and the Greek word φιλος, philos for love. In general, in a row across the table, the more basic the ion the more reactive it is as a nucleophile. g. The iodide ion is more nucleophilic than the fluoride ion, many schemes attempting to quantify relative nucleophilic strength have been devised. The following empirical data have been obtained by measuring reaction rates for a number of reactions involving a large number of nucleophiles and electrophiles. Nucleophiles displaying the so-called alpha effect are usually omitted in this type of treatment. This treatment results in the values for typical nucleophilic anions, acetate 2.7, chloride 3.0, azide 4.0, hydroxide 4.2, aniline 4.5, iodide 5.0. Typical substrate constants are 0.66 for ethyl tosylate,0.77 for β-propiolactone,1.00 for 2, 3-epoxypropanol,0.87 for benzyl chloride, and 1.43 for benzoyl chloride. The equation predicts that, in a nucleophilic displacement on benzyl chloride, the Ritchie equation, derived in 1972, is another free-energy relationship, log 10 = N + where N+ is the nucleophile dependent parameter and k0 the reaction rate constant for water. In this equation, a substrate-dependent parameter like s in the Swain–Scott equation is absent, the equation states that two nucleophiles react with the same relative reactivity regardless of the nature of the electrophile, which is in violation of the Reactivity–selectivity principle. For this reason this equation is called the constant selectivity relationship. Many other reaction types have since been described. Typical Ritchie N+ values are,0.5 for methanol,5.9 for the anion,7.5 for the methoxide anion,8.5 for the azide anion. The values for the relative cation reactivities are -0.4 for the malachite green cation, +2.6 for the benzenediazonium cation, the constant s is defined as 1 with 2-methyl-1-pentene as the nucleophile
15.
Step-growth polymerization
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Many naturally occurring and some synthetic polymers are produced by step-growth polymerization, e. g. polyesters, polyamides, polyurethanes, etc. Due to the nature of the mechanism, a high extent of reaction is required to achieve high molecular weight. The easiest way to visualize the mechanism of a polymerization is a group of people reaching out to hold their hands to form a human chain — each person has two hands. There also is the possibility to have more than two sites on a monomer, In this case branched polymers are produced. Most natural polymers being employed at early stage of society are of condensation type. The synthesis of first truly synthetic polymeric material, Bakelite, was announced by Leo Baekeland in 1907, through a typical step-growth polymerization fashion of phenol and formaldehyde. The pioneer of synthetic science, Wallace H. Carothers. Carothers developed a series of equations to describe the behavior of step-growth polymerization systems which are still known as the Carothers equations today. Collaborating with Paul J. Carothers is also known for his invention of Nylon. Step growth polymerization and condensation polymerization are two different concepts, not always identical, in fact polyurethane polymerizes with addition polymerization, but its reaction mechanism corresponds to a step-growth polymerization. It can exist as fibers and films, the former is used in garments, felts, tire cords, etc. The latter appears in magnetic recording tape and high grade films, polyamide has good balance of properties, high strength, good elasticity and abrasion resistance, good toughness, favorable solvent resistance. The applications of polyamide include, rope, belting, fiber cloths, thread, substitute for metal in bearings, polyurea shows high Tg, fair resistance to greases, oils, and solvents. It can be used in truck bed liners, bridge coating, caulk, polysiloxane are available in a wide range of physical states—from liquids to greases, waxes, resins, and rubbers. Uses of this material are as antifoam and release agents, gaskets, seals, cable and wire insulation, hot liquids and gas conduits and they possess properties like crystalline thermoplasticity, high impact strength, good thermal and oxidative stability. They can be used in machinery, auto-industry, and medical applications, for example, the cockpit canopy of F-22 Raptor is made of high optical quality polycarbonate. Polysulfides have outstanding oil and solvent resistance, good gas impermeability, good resistance to aging, However, it smells bad, and it shows low tensile strength as well as poor heat resistance. It can be used in gasoline hoses, gaskets and places that require solvent resistance, polyether shows good thermoplastic behavior, water solubility, generally good mechanical properties, moderate strength and stiffness
16.
Heteroatom
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In organic chemistry, a heteroatom is any atom that is not carbon or hydrogen. Usually, the term is used to indicate that non-carbon atoms have replaced carbon in the backbone of the molecular structure, typical heteroatoms are nitrogen, oxygen, sulfur, phosphorus, chlorine, bromine, and iodine. In the context of zeolites, the term refers to partial isomorphous substitution of the typical framework atoms by other elements such as beryllium, vanadium. The goal is usually to adjust properties of the material to optimize the material for a certain application
17.
Condensation polymer
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Types of condensation polymers include polyamides, polyacetals and polyesters. Condensation polymerization, a form of step-growth polymerization, is a process by which two molecules join together, resulting in loss of molecules which are often water. The type of end product resulting from a condensation polymerization is dependent on the number of end groups of the monomer which can react. Monomers with only one reactive group terminate a growing chain, linear polymers are created using monomers with two reactive end groups and monomers with more than two end groups give three-dimensional polymers which are crosslinked. Dehydration synthesis often involves joining monomers with an -OH group and a freely ionized -H on either end, normally, two or more different monomers are used in the reaction. The bonds between the group, the hydrogen atom and their respective atoms break forming water from the hydroxyl and hydrogen. Polyester is created through ester linkages between monomers, which involve the functional groups carboxyl and hydroxyl, nylon is another common condensation polymer. It can be manufactured by reacting di-amines with carboxyl derivatives, in this example the derivative is a di-carboxylic acid, but di-acyl chlorides are also used. Proteins are condensation polymers made from amino acid monomers, carbohydrates are also condensation polymers made from sugar monomers such as glucose and galactose. Condensation polymerization is used to form simple hydrocarbons. This method, however, is expensive and inefficient, so the polymer of ethene is generally used. Condensation polymers, unlike addition polymers, may be biodegradable, the peptide or ester bonds between monomers can be hydrolysed by acid catalysts or bacterial enzymes breaking the polymer chain into smaller pieces. The most commonly known condensation polymers are proteins, fabrics such as nylon, silk, biopolymer Polyester Polyamide Polymers - Virtual Text of Organic Chemistry, William Reusch
18.
Polyurethane
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Polyurethane is a polymer composed of organic units joined by carbamate links. While most polyurethanes are thermosetting polymers that do not melt when heated, polyurethane polymers are traditionally and most commonly formed by reacting a di- or polyisocyanate with a polyol. Both the isocyanates and polyols used to make polyurethanes contain, on average, some noteworthy recent efforts have been dedicated to minimizing the use of isocyanates to synthesize polyurethanes, because the isocyanates raise severe toxicity issues. Non-isocyanate based polyurethanes have recently developed as a new class of polyurethane polymers to mitigate health. Polyurethane products often are simply called “urethanes”, but should not be confused with ethyl carbamate, polyurethanes neither contain nor are produced from ethyl carbamate. Otto Bayer and his coworkers at IG Farben in Leverkusen, Germany, the new polymers had some advantages over existing plastics that were made by polymerizing olefins or by polycondensation, and were not covered by patents obtained by Wallace Carothers on polyesters. Early work focused on the production of fibres and flexible foams, polyisocyanates became commercially available in 1952, and production of flexible polyurethane foam began in 1954 using toluene diisocyanate and polyester polyols. These materials were used to produce rigid foams, gum rubber. Linear fibers were produced from hexamethylene diisocyanate and 1, 4-butanediol, in 1956 DuPont introduced polyether polyols, specifically poly glycol, and BASF and Dow Chemical started selling polyalkylene glycols in 1957. Polyether polyols were cheaper, easier to handle and more water-resistant than polyester polyols, union Carbide and Mobay, a U. S. Monsanto/Bayer joint venture, also began making polyurethane chemicals. In 1960 more than 45,000 metric tons of flexible polyurethane foams were produced, in 1967, urethane-modified polyisocyanurate rigid foams were introduced, offering even better thermal stability and flammability resistance. During the 1960s, automotive interior safety components, such as instrument, in 1969, Bayer exhibited an all-plastic car in Düsseldorf, Germany. Further increases in stiffness were obtained by incorporating pre-placed glass mats into the RIM mold cavity, also known broadly as resin injection molding, polyurethane foams are now used in high-temperature oil filter applications. Polyurethane foam is made using small amounts of blowing agents to give less dense foam. In the early 1990s, because of their impact on ozone depletion, polyurethanes are in the class of compounds called reaction polymers, which include epoxies, unsaturated polyesters, and phenolics. The properties of a polyurethane are greatly influenced by the types of isocyanates, long, flexible segments, contributed by the polyol, give soft, elastic polymer. High amounts of crosslinking give tough or rigid polymers, the crosslinking present in polyurethanes means that the polymer consists of a three-dimensional network and molecular weight is very high. In some respects a piece of polyurethane can be regarded as one giant molecule, one consequence of this is that typical polyurethanes do not soften or melt when they are heated, they are thermosetting polymers
19.
Isocyanate
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Isocyanate is the functional group with the formula R–N=C=O. Organic compounds that contain a group are referred to as isocyanates. An isocyanate that has two groups is known as a di-isocyanate. Di-isocyanates are manufactured for reactions with polyols in the production of polyurethanes, isocyanates should not be confused with cyanate esters and isocyanides, whose behaviors are very different. The cyanate functional group is arranged differently from the isocyanate group, isocyanides have the connectivity R-N≡C, lacking the oxygen of the cyanate groups. Isocyanates are produced by treating amines with phosgene, RNH2 + COCl2 → RNCO +2 HCl These reactions proceed via the intermediacy of a carbamoyl chloride, owing to the hazards associated with phosgene, the production of isocyanates requires special precautions. Isocyanates are electrophiles, and as such they are reactive toward a variety of nucleophiles including alcohols, amines, isocyanates react with water to form carbon dioxide, RNCO + H2O → RNH2 + CO2 This reaction is exploited in tandem with the production of polyurethane to give polyurethane foams. The carbon dioxide functions as a blowing agent, isocyanates also can react with themselves. Aliphatic di-isocyanates can form trimers, which are related to cyanuric acid. Isocyanates participate in Diels-Alder reactions, functioning as dienophiles, schmidt reaction, a reaction where a carboxylic acid is treated with ammonia and hydrazoic acid yielding an isocyanate. Curtius rearrangement degradation of an azide to an isocyanate and nitrogen gas. Lossen rearrangement, the conversion of an acid to an isocyanate via the formation of an O-acyl, sulfonyl. A monofunctional isocyanate of industrial significance is methyl isocyanate, which is used in the manufacture of pesticides, lD50s are typically several hundred milligrams per kilogram. Isocyanates are potentially dangerous irritants to the eyes and respiratory tract, methyl isocyanate was the chemical released in the Bhopal disaster causing the death of nearly 4000 people. Polyurethanes have variable curing times, and the presence of free isocyanates in foams vary accordingly, prepared by the Institute of Occupational Medicine for the Health and Safety Executive
20.
Chain-growth polymerization
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Chain-growth polymerization or chain polymerization is a polymerization technique where unsaturated monomer molecules add onto the active site of a growing polymer chain one at a time. Growth of the polymer occurs only at one ends, addition of each monomer unit regenerates the active site. Polyethylene, polypropylene, and polyvinyl chloride are common types of plastics made by chain-growth polymerization and they are the primary component of four of the plastics specifically labeled with recycling codes and are used extensively in packaging. This type of result in high molecular weight polymer being formed at low conversion. This final weight is determined by the rate of compared to the rate of individual chain termination. Above a certain ceiling temperature, no polymerization occurs, chain-growth polymerization usually has the following steps, chain initiation, usually by means of an initiator which starts the chemical process. Typical initiators include any organic compound with a group, e. g. azo, disulfide. Two examples are benzoyl peroxide and AIBN, chain propagation chain transfer, terminates the chain, but the active site is transferred to a new chain. This can occur with the solvent, monomer, or other polymer and this process increases the branching of the resulting polymer. Chain termination, which occurs either by combination or disproportionation, termination, in radical polymerization, is when the free radicals combine and is the end of the polymerization process. Under the necessary conditions, an addition polymerization can be considered a living polymerization. This is most often seen with anionic polymerization as it can be easy to perform without termination steps, chain growth polymerization and addition polymerization are two different concepts. In fact polyurethane polymerizes with addition polymerization, but its mechanism is a step-growth polymerization. The distinction between addition polymerization and condensation polymerization was introduced by Wallace Hume Carothers in 1929, and refers to the type of product produced. Addition polymerization produces only a molecule, while condensation polymerization produces a polymer as well as a molecule with a low molecular weight
21.
Chemical bond
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A chemical bond is a lasting attraction between atoms that enables the formation of chemical compounds. The bond may result from the force of attraction between atoms with opposite charges, or through the sharing of electrons as in the covalent bonds. Since opposite charges attract via an electromagnetic force, the negatively charged electrons that are orbiting the nucleus. An electron positioned between two nuclei will be attracted to both of them, and the nuclei will be attracted toward electrons in this position and this attraction constitutes the chemical bond. This phenomenon limits the distance between nuclei and atoms in a bond, in general, strong chemical bonding is associated with the sharing or transfer of electrons between the participating atoms. All bonds can be explained by quantum theory, but, in practice, simplification rules allow chemists to predict the strength, directionality, the octet rule and VSEPR theory are two examples. Electrostatics are used to describe bond polarities and the effects they have on chemical substances, a chemical bond is an attraction between atoms. This attraction may be seen as the result of different behaviors of the outermost or valence electrons of atoms and these behaviors merge into each other seamlessly in various circumstances, so that there is no clear line to be drawn between them. However it remains useful and customary to differentiate different types of bond, which result in different properties of condensed matter. In the simplest view of a covalent bond, one or more electrons are drawn into the space between the two atomic nuclei, energy is released by bond formation. This is not as a reduction in energy, because the attraction of the two electrons to the two protons is offset by the electron-electron and proton-proton repulsions. In a polar covalent bond, one or more electrons are shared between two nuclei. Such weak intermolecular bonds give organic molecular substances, such as waxes and oils, their soft bulk character, also, the melting points of such covalent polymers and networks increase greatly. In a simplified view of a bond, the bonding electron is not shared at all. In this type of bond, the atomic orbital of one atom has a vacancy which allows the addition of one or more electrons. These newly added electrons potentially occupy a lower energy-state than they experience in a different atom, thus, one nucleus offers a more tightly bound position to an electron than does another nucleus, with the result that one atom may transfer an electron to the other. This transfer causes one atom to assume a net charge. The bond then results from electrostatic attraction between atoms and the atoms become positive or negatively charged ions, ionic bonds may be seen as extreme examples of polarization in covalent bonds
22.
Polypropylene
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An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids. Polypropylene has a relatively low energy surface that means that many common glues will not form adequate joints. Joining of polypropylene is often done using welding processes, in 2013, the global market for polypropylene was about 55 million tonnes. Polypropylene is the worlds second-most widely produced synthetic plastic, after polyethylene, Polypropylene is in many aspects similar to polyethylene, especially in solution behaviour and electrical properties. The additionally present methyl group improves mechanical properties and thermal resistance, the properties of polypropylene depend on the molecular weight and molecular weight distribution, crystallinity, type and proportion of comonomer and the isotacticity. In isotactic polypropylene, for example, the CH3 groups are oriented on one side of the carbon backbone and this creates a greater degree of crystallinity and results in a stiffer material that is more resistant to creep than both atactic polypropylene and polyethylene. The density of PP is between 0.895 and 0.92 g/cm³, therefore, PP is the commodity plastic with the lowest density. With lower density, moldings parts with lower weight and more parts of a mass of plastic can be produced. Unlike polyethylene, crystalline and amorphous regions differ only slightly in their density, however, the density of polyethylene can significantly change with fillers. The Youngs modulus of PP is between 1300 and 1800 N/mm², Polypropylene is normally tough and flexible, especially when copolymerized with ethylene. This allows polypropylene to be used as a plastic, competing with materials such as acrylonitrile butadiene styrene. Polypropylene has good resistance to fatigue, the melting point of polypropylene occurs at a range, so a melting point is determined by finding the highest temperature of a differential scanning calorimetry chart. Perfectly isotactic PP has a point of 171 °C. Commercial isotactic PP has a point that ranges from 160 to 166 °C, depending on atactic material. Syndiotactic PP with a crystallinity of 30% has a point of 130 °C. Below 0 °C, PP becomes brittle, the thermal expansion of polypropylene is very large, but somewhat less than that of polyethylene. Polypropylene is at room temperature resistant to fats and almost all organic solvents, non-oxidizing acids and bases can be stored in containers made of PP. At elevated temperature, PP can be dissolved in nonpolarity solvents such as xylene, due to the tertiary carbon atom PP is chemically less resistant than PE
23.
Living polymerization
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In polymer chemistry, living polymerization is a form of chain growth polymerization where the ability of a growing polymer chain to terminate has been removed. This can be accomplished in a variety of ways, chain termination and chain transfer reactions are absent and the rate of chain initiation is also much larger than the rate of chain propagation. The result is that the chains grow at a more constant rate than seen in traditional chain polymerization. Living polymerization is a method for synthesizing block copolymers since the polymer can be synthesized in stages. Additional advantages are predetermined molar mass and control over end-groups, Living polymerization is desirable because it offers precision and control in macromolecular synthesis. This is important since many of the properties of polymers result from their microstructure. While these polymerization reactions are similar, there is a distinct difference in the definitions of these two reactions. However, this distinction is still up for debate in the literature, after initial addition of monomer to the initiator system, the viscosity would increase, but eventually cease after depletion of monomer concentration. However, he found that addition of more monomer caused an increase in viscosity, indicating growth of the polymer chain and this was a major step in polymer chemistry, since control over when the polymer was quenched, or terminated, was generally not a controlled step. With this discovery, the list of potential applications expanded dramatically, today, living polymerizations are used widely in the development of various types of polymers or plastics. This is because chemists now have control of the chemical makeup of the polymer and, thus. This level of control rarely exists in non-living polymerization reactions, leaving this method as the synthetic route if attainable. The most common types of living polymerization reactions are anionic, cationic, free-radical, or ring-opening in nature, Fast Rate of Initiation Another key characteristic is that the rate of initiation must be much faster than the rate of chain propagation. This would allow all of the species to form before chain propagation begins so all of the chains grow at the same rate. Low Dispersity Dispersity or polydispersity index is an indication of the broadness in the distribution of polymer chains, Living polymers tend to have low Đ due to the absence of chain termination pathways as well as the rate of initiation being much faster than the rate of propagation. If chain termination are present then chains will die or become inactive at various times during the polymerization which leads to polymer chains with varying xn. As stated in the section, if the rate of propagation is much slower than the rate of initiation then all of the initiators will form the active species before the onset of propagation. When both of these characteristics are considered it becomes apparent that the concentration of active chains, that is those undergoing polymerization, predictable Molecular Weight Since termination and chain transfer are absent in living polymerization then each initiator that generates an active species will be responsible for one chain
24.
Radical polymerization
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Free radical polymerization is a method of polymerization by which a polymer forms by the successive addition of free radical building blocks. Free radicals can be formed via a number of different mechanisms usually involving separate initiator molecules, following its generation, the initiating free radical adds monomer units, thereby growing the polymer chain. Free radical polymerization is a key route for obtaining a wide variety of different polymers. In 2001,40 billion of the 110 billion pounds of polymers produced in the United States were produced by radical polymerization. Free radical polymerization is a type of chain growth polymerization, along with anionic, cationic, initiation is the first step of the polymerization process. During initiation, a center is created from which a polymer chain is generated. Not all monomers are susceptible to all types of initiators, Radical initiation works best on the carbon-carbon double bond of vinyl monomers and the carbon-oxygen double bond in aldehydes and ketones. In the first step, one or two radicals are created from the initiating molecules, in the second step, radicals are transferred from the initiator molecules to the monomer units present. Several choices are available for these initiators, thermal decomposition, The initiator is heated until a bond is homolytically cleaved, producing two radicals. This method is used most often with organic peroxides or azo compounds, photolysis, Radiation cleaves a bond homolytically, producing two radicals. This method is used most often with metal iodides, metal alkyls, photoinitiation can also occur by bi-molecular H-abstraction when the radical is in its lowest triplet excited state. An acceptable photoinitiator system should fulfill the requirements, High absorptivity in the 300-400 nm range. Efficient generation of radicals capable of attacking the double bond of vinyl monomers. Adequate solubility in the binder system, should not impart yellowing or unpleasant odors to the cured material. The photoinitiator and any byproducts resulting from its use should be non-toxic, redox reactions, Reduction of hydrogen peroxide or an alkyl hydrogen peroxide by iron. Other reductants such as Cr2+, V2+, Ti3+, Co2+, persulfates, The dissociation of a persulfate in the aqueous phase. This method is useful in emulsion polymerizations in which the radical diffuses into a hydrophobic monomer-containing droplet, ionizing radiation, α-, β-, γ-, or x-rays cause ejection of an electron from the initiating species, followed by dissociation and electron capture to produce a radical. Electrochemical, Electrolysis of a solution containing both monomer and electrolyte, a monomer molecule will receive an electron at the cathode to become a radical anion, and a monomer molecule will give up an electron at the anode to form a radical cation
25.
Ethylene
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Ethylene is a hydrocarbon which has the formula C 2H4 or H2C=CH2. It is a flammable gas with a faint sweet and musky odour when pure. Ethylene is widely used in the industry, and its worldwide production exceeds that of any other organic compound. Much of this production goes toward polyethylene, a used plastic containing polymer chains of ethylene units in various chain lengths. Ethylene is also an important natural plant hormone, used in agriculture to force the ripening of fruits and this hydrocarbon has four hydrogen atoms bound to a pair of carbon atoms that are connected by a double bond. All six atoms that comprise ethylene are coplanar, the H-C-H angle is 117. 4°, close to the 120° for ideal sp² hybridized carbon. The molecule is relatively rigid, rotation about the C-C bond is a high energy process that requires breaking the π-bond. The π-bond in the molecule is responsible for its useful reactivity. The double bond is a region of high density, thus it is susceptible to attack by electrophiles. Many reactions of ethylene are catalyzed by metals, which bind transiently to the ethylene using both the π and π* orbitals. Being a simple molecule, ethylene is spectroscopically simple and its UV-vis spectrum is still used as a test of theoretical methods. In the United States and Europe, approximately 90% of ethylene is used to produce ethylene oxide, ethylene dichloride, most of the reactions with ethylene are electrophilic addition. Polyethylene consumes more than half of the worlds ethylene supply, polyethylene, also called polyethene, is the worlds most widely used plastic. It is primarily used to make films in packaging, carrier bags, linear alpha-olefins, produced by oligomerization are used as precursors, detergents, plasticisers, synthetic lubricants, additives, and also as co-monomers in the production of polyethylenes. Ethylene is oxidized to ethylene oxide, a key raw material in the production of surfactants and detergents by ethoxylation. Ethylene oxide is hydrolyzed to produce ethylene glycol, widely used as an automotive antifreeze as well as higher molecular weight glycols, glycol ethers. Ethylene undergoes oxidation by palladium to give acetaldehyde and this conversion remains a major industrial process. The process proceeds via the initial complexation of ethylene to a Pd center, major intermediates from the halogenation and hydrohalogenation of ethylene include ethylene dichloride, ethyl chloride and ethylene dibromide
26.
Pi bond
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In chemistry, pi bonds are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital. Each of these orbitals is zero at a shared nodal plane. The same plane is also a plane for the molecular orbital of the pi bond. The Greek letter π in their name refers to p orbitals, P orbitals often engage in this sort of bonding. D orbitals also engage in pi bonding, and form part of the basis for metal-metal multiple bonding, Pi bonds are usually weaker than sigma bonds. From the perspective of quantum mechanics, this weakness is explained by significantly less overlap between the component p-orbitals due to their parallel orientation. This is contrasted by sigma bonds which form bonding orbitals directly between the nuclei of the atoms, resulting in greater overlap and a strong sigma bond. Pi bonds result from overlap of atomic orbitals that are in contact through two areas of overlap, pi-bonds are more diffuse bonds than the sigma bonds. Electrons in pi bonds are referred to as pi electrons. Molecular fragments joined by a pi bond cannot rotate about that bond without breaking the pi bond, for homonuclear diatomic molecules, bonding π molecular orbitals have only the one nodal plane passing through the bonded atoms, and no nodal planes between the bonded atoms. The corresponding antibonding, or π* molecular orbital, is defined by the presence of a nodal plane between these two bonded atoms. A typical double bond consists of one bond and one pi bond, for example. A typical triple bond, for example in acetylene, consists of one sigma bond, two pi bonds are the maximum that can exist between a given pair of atoms. Quadruple bonds are rare and can be formed only between transition metal atoms, and consist of one sigma bond, two pi bonds and one delta bond. A pi bond is weaker than a bond, but the combination of pi. The enhanced strength of a multiple bond versus a single is indicated in many ways, for example, in organic chemistry, carbon–carbon bond lengths are about 154 pm in ethane,134 pm in ethylene and 120 pm in acetylene. More bonds make the total bond shorter and stronger, a pi bond can exist between two atoms that do not have a net sigma-bonding effect between them. In certain metal complexes, pi interactions between an atom and alkyne and alkene pi antibonding orbitals form pi-bonds
27.
Radical (chemistry)
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In chemistry, a radical is an atom, molecule, or ion that has an unpaired valence electron. Most radicals are reasonably stable only at low concentrations in inert media or in a vacuum. A notable example of a radical is the hydroxyl radical. Two other examples are triplet oxygen and triplet carbene which have two unpaired electrons, free radicals may be created in a number of ways, including synthesis with very dilute or rarefied reagents, reactions at very low temperatures, or breakup of larger molecules. The latter can be affected by any process that puts energy into the parent molecule, such as ionizing radiation, heat, electrical discharges, electrolysis. Radicals are intermediate stages in many chemical reactions, free radicals play an important role in combustion, atmospheric chemistry, polymerization, plasma chemistry, biochemistry, and many other chemical processes. In living organisms, the free radicals superoxide and nitric oxide and their reaction products regulate many processes, such as control of vascular tone and they also play a key role in the intermediary metabolism of various biological compounds. Such radicals can even be messengers in a process dubbed redox signaling, a radical may be trapped within a solvent cage or be otherwise bound. The qualifier free was then needed to specify the unbound case, following recent nomenclature revisions, a part of a larger molecule is now called a functional group or substituent, and radical now implies free. However, the old nomenclature may still appear in some books, the term radical was already in use when the now obsolete radical theory was developed. Louis-Bernard Guyton de Morveau introduced the phrase radical in 1785 and the phrase was employed by Antoine Lavoisier in 1789 in his Traité Élémentaire de Chimie, a radical was then identified as the root base of certain acids. Historically, the radical in radical theory was also used for bound parts of the molecule. These are now called functional groups, for example, methyl alcohol was described as consisting of a methyl radical and a hydroxyl radical. In a modern context the first organic free radical identified was triphenylmethyl radical and this species was discovered by Moses Gomberg in 1900 at the University of Michigan USA. In 1933 Morris Kharash and Frank Mayo proposed that free radicals were responsible for anti-Markovnikov addition of hydrogen bromide to allyl bromide. It should be noted that the electron of the breaking bond also moves to pair up with the attacking radical electron. Free radicals also take part in addition and radical substitution as reactive intermediates. Chain reactions involving free radicals can usually be divided into three distinct processes and these are initiation, propagation, and termination
28.
Branching (polymer chemistry)
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Branched polymers have more compact and symmetrical molecular conformations, and exhibit intra-heterogeneous dynamical behavior with respect to the unbranched polymers. In crosslinking rubber by vulcanization, short sulfur branches link polyisoprene chains into a multiply branched thermosetting elastomer, rubber can also be so completely vulcanized that it becomes a rigid solid, so hard it can be used as the bit in a smoking pipe. Polycarbonate chains can be crosslinked to form the hardest, most impact-resistant thermosetting plastic, branching may result from the formation of carbon-carbon or various other types of covalent bonds. Branching by ester and amide bonds is typically by a condensation reaction, polymers which are branched but not crosslinked are generally thermoplastic. Branching sometimes occurs spontaneously during synthesis of polymers, e. g. by free-radical polymerization of ethylene to form polyethylene, in fact, preventing branching to produce linear polyethylene requires special methods. Because of the way polyamides are formed, nylon would seem to be limited to unbranched, but star branched nylon can be produced by the condensation of dicarboxylic acids with polyamines having three or more amino groups. Branching also occurs naturally during enzymatically-catalyzed polymerization of glucose to form such as glycogen, and amylopectin. The unbranched form of starch is called amylose, the ultimate in branching is a completely crosslinked network such as found in Bakelite, a phenol-formaldehyde thermoset resin. A graft polymer molecule is a polymer molecule in which one or more of the side chains are different, structurally or configurationally. A star-shaped polymer molecule is a polymer molecule in which a single branch point gives rise to multiple linear chains or arms. If the arms are identical the star polymer molecule is said to be regular, if adjacent arms are composed of different repeating subunits, the star polymer molecule is said to be variegated. A comb polymer molecule consists of a chain with two or more three-way branch points and linear side chains. If the arms are identical the comb polymer molecule is said to be regular, a brush polymer molecule consists of a main chain with linear, unbranched side chains and where one or more of the branch points has four-way functionality or larger. A polymer network is a network in which all polymer chains are interconnected to form a single entity by many crosslinks. See for example thermosets or interpenetrating polymer networks, a dendrimer is a repetitively branched compound. In free radical polymerization, branching occurs when a chain curls back, when this curl breaks, it leaves small chains sprouting from the main carbon backbone. Branched carbon chains cannot line up as close to other as unbranched chains can. This causes less contact between atoms of different chains, and fewer opportunities for induced or permanent dipoles to occur, a low density results from the chains being further apart
29.
Cationic polymerization
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Cationic polymerization is a type of chain growth polymerization in which a cationic initiator transfers charge to a monomer which then becomes reactive. This reactive monomer goes on to react similarly with other monomers to form a polymer, the types of monomers necessary for cationic polymerization are limited to olefins with electron-donating substituents and heterocycles. Similar to anionic polymerization reactions, cationic polymerization reactions are very sensitive to the type of solvent used, specifically, the ability of a solvent to form free ions will dictate the reactivity of the propagating cationic chain. Cationic polymerization is used in the production of polyisobutylene and poly, monomer scope for cationic polymerization is limited to two main types, olefins and heterocyclic monomers. Cationic polymerization of both types of monomers occurs only if the reaction is thermally favorable. In the case of olefins, this is due to isomerization of the double bond, for heterocycles. Monomers for cationic polymerization are nucleophilic and form a stable cation upon polymerization, cationic polymerization of olefin monomers occurs with olefins that contain electron-donating substituents. These electron-donating groups make the olefin nucleophilic enough to attack electrophilic initiators or growing polymer chains, at the same time, these electron-donating groups attached to the monomer must be able to stabilize the resulting cationic charge for further polymerization. Some reactive olefin monomers are shown below in order of decreasing reactivity, note, however, that the reactivity of the carbenium ion formed is the opposite of the monomer reactivity. Heterocyclic monomers that are cationically polymerized are lactones, lactams, upon addition of an initiator, cyclic monomers go on to form linear polymers. The reactivity of heterocyclic monomers depends on their ring strain, monomers with large ring strain, such as oxirane, are more reactive than 1, 3-dioxepane which has considerably less ring strain. Rings that are six-membered and larger are less likely to due to lower ring strain. Initiation is the first step in cationic polymerization, during initiation, a carbenium ion is generated from which the polymer chain is made. The counterion should be non-nucleophilic, otherwise the reaction is terminated instantaneously, there are a variety of initiators available for cationic polymerization, and some of them require a coinitiator to generate the needed cationic species. Strong protic acids can be used to form a cationic initiating species, high concentrations of the acid are needed in order to produce sufficient quantities of the cationic species. The counterion produced must be weakly nucleophilic so as to prevent early termination due to combination with the protonated olefin, common acids used are phosphoric, sulfuric, fluro-, and triflic acids. Only low molecular weight polymers are formed with these initiators, Lewis acids are the most common compounds used for initiation of cationic polymerization. The more popular Lewis acids are SnCl4, AlCl3, BF3, although these Lewis acids alone are able to induce polymerization, the reaction occurs much faster with a suitable cation source
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Anionic addition polymerization
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Anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of vinyl monomers with strong electronegative groups. This polymerization is carried out through an active species. Like all chain-growth polymerizations, it place in three steps, chain initiation, chain propagation, and chain termination. Living polymerizations, which lack a formal termination pathway, occur in many anionic addition polymerizations, the advantage of living anionic addition polymerizations is that they allow for the control of structure and composition. Anionic polymerizations are used in the production of synthetic rubbers, solution styrene/butadiene rubbers. Twenty years later, living polymerization was demonstrated by Szwarc, the early work of Michael Szwarc and co – workers in 1956 was one of the breakthrough events in the field of polymer science. He proved that the electron results in the formation of a dianion which rapidly added styrene to form a two – ended living polymer. Being a physical chemist, Szwarc set forth in understanding the mechanism of such living polymerization in greater detail and his work elucidated the kinetics and the thermodynamics of the process in considerable detail. At the same time, he explored the structure property relationship of the ion pairs. The use of metals to initiate polymerization of 1, 3-dienes led to the discovery by Stavely and co-workers at Firestone Tire and Rubber company of cis-1. This sparked the development of commercial anionic polymerization processes that utilize alkyllithium initiatiors, in order for polymerization to occur with vinyl monomers, the substituents on the double bond must be able to stabilize a negative charge. Stabilization occurs through delocalization of the negative charge, because of the nature of the carbanion propagating center, substituents that react with bases or nucleophiles either must not be present or be protected. Vinyl monomers with substituents that stabilize the charge through charge delocalization. These monomers include styrene, dienes, methacrylate, vinyl pyridine, aldehydes, epoxide, episulfide, cyclic siloxane, polar monomers, using controlled conditions and low temperatures, can undergo anionic polymerization. The effects of counterion, solvent, temperature, Lewis base additives, polar monomers include acrylonitrile, cyanoacrylate, propylene oxide, vinyl ketone, acrolein, vinyl sulfone, vinyl sulfoxide, vinyl silane and isocyanate. The solvent used in anionic addition polymerizations are determined by the reactivity of both the initiator and carbanion of the chain end. Anionic species with low reactivity, such as monomers, can use a wide range of solvents. The reactivity of initiators used in anionic polymerization should be similar to that of the monomer that is the propagating species, the pKa values for the conjugate acids of the carbanions formed from monomers can be used to deduce the reactivity of the monomer
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Ester
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In chemistry, esters are chemical compounds derived from an acid in which at least one –OH group is replaced by an –O–alkyl group. Usually, esters are derived from an acid and an alcohol. Glycerides, which are fatty acid esters of glycerol, are important esters in biology, being one of the classes of lipids. Esters with low weight are commonly used as fragrances and found in essential oils. Phosphoesters form the backbone of DNA molecules, nitrate esters, such as nitroglycerin, are known for their explosive properties, while polyesters are important plastics, with monomers linked by ester moieties. The word ester was coined in 1848 by German chemist Leopold Gmelin, probably as a contraction of the German Essigäther, ester names are derived from the parent alcohol and the parent acid, where the latter may be organic or inorganic. Esters derived from more complex carboxylic acids are, on the hand, more frequently named using the systematic IUPAC name. For example, the ester hexyl octanoate, also known under the trivial name hexyl caprylate, has the formula CH36CO25CH3, the chemical formulas of organic esters usually take the form RCO2R′, where R and R′ are the hydrocarbon parts of the carboxylic acid and the alcohol, respectively. For example, butyl acetate, derived from butanol and acetic acid would be written CH3CO2C4H9, alternative presentations are common including BuOAc and CH3COOC4H9. Cyclic esters are called lactones, regardless of whether they are derived from an organic or an inorganic acid, one example of a lactone is γ-valerolactone. An uncommon class of organic esters are the orthoesters, which have the formula RC3, triethylorthoformate is derived, in terms of its name from orthoformic acid and ethanol. Esters can also be derived from an acid and an alcohol. For example, triphenyl phosphate is the derived from phosphoric acid. Organic carbonates are derived from acid, for example, ethylene carbonate is derived from carbonic acid. So far an alcohol and inorganic acid are linked via oxygen atoms, in corollary, boron features borinic esters, boronic esters, and borates. As oxygen is a group 16 chemical element, sulfur atoms can replace some oxygen atoms in carbon–oxygen–central inorganic atom covalent bonds of an ester, esters contain a carbonyl center, which gives rise to 120 ° C–C–O and O–C–O angles. Unlike amides, esters are structurally flexible functional groups because rotation about the C–O–C bonds has a low barrier and their flexibility and low polarity is manifested in their physical properties, they tend to be less rigid and more volatile than the corresponding amides. The pKa of the alpha-hydrogens on esters is around 25, the preference for the Z conformation is influenced by the nature of the substituents and solvent, if present
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Acrylic acid
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Acrylic acid is an organic compound with the formula CH2=CHCOOH. It is the simplest unsaturated carboxylic acid, consisting of a group connected directly to a carboxylic acid terminus. This colorless liquid has a characteristic acrid or tart smell and it is miscible with water, alcohols, ethers, and chloroform. More than a million tons are produced annually, Acrylic acid is produced from propylene which is a byproduct of ethylene and gasoline production. CH2=CHCH3 + 3⁄2 O2 → CH2=CHCO2H + H2O Ethylene can be carboxylated to acrylic acid under supercritical carbon dioxide condition, because acrylic acid and its esters have long been valued commercially, many other methods have been developed but most have been abandoned for economic or environmental reasons. An early method was the hydrocarboxylation of acetylene, HCCH + CO + H2O → CH2=CHCO2H This method requires nickel carbonyl and it was once manufactured by the hydrolysis of acrylonitrile which is derived from propene by ammoxidation, but was abandoned because the method cogenerates ammonium derivatives. Other now abandoned precursors to acrylic acid include ethenone and ethylene cyanohydrin, dow Chemical Company and a partner, OPX Biotechnologies, are investigating using fermented sugar to produce 3-hydroxypropionic acid, an acrylic acid precursor. The goal is to reduce gas emissions. Acrylic acid undergoes the reactions of a carboxylic acid. When reacted with an alcohol, it forms the corresponding ester, the esters and salts of acrylic acid are collectively known as acrylates. The most common alkyl esters of acrylic acid are methyl, butyl, ethyl, as a substituent acrylic acid can be found as an acyl group or a carboxyalkyl group depending on the removal of the group from the molecule. More specifically these are, The acryloyl group, with the removal of the –OH from carbon-1, the 2-carboxyethenyl group, with the removal of a –H from carbon-3. This substituent group is found in chlorophyll, Acrylic acid is severely irritating and corrosive to the skin and the respiratory tract. Eye contact can result in severe and irreversible injury, low exposure will cause minimal or no health effects, while high exposure could result in pulmonary edema. Methacrylic acid Acryloyl chloride Acrylamide Acrylate polymer Sodium polyacrylate National Pollutant Inventory, Acrylic acid CDC - NIOSH Pocket Guide to Chemical Hazards - Acrylic acid
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Conjugated system
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Lone pairs, radicals or carbenium ions may be part of the system. The compound may be cyclic, acyclic, linear or mixed, conjugation is the overlap of one p-orbital with another across an intervening σ bond. A conjugated system has a region of overlapping p-orbitals, bridging the interjacent single bonds and they allow a delocalization of pi electrons across all the adjacent aligned p-orbitals. The pi electrons do not belong to a bond or atom. The largest conjugated systems are found in graphene, graphite, conductive polymers, conjugation is possible by means of alternating single and double bonds. As long as each contiguous atom in a chain has an available p-orbital, for example, furan is a five-membered ring with two alternating double bonds and an oxygen in position 1. Oxygen has two pairs, one of which occupies a p-orbital on that position, thereby maintaining the conjugation of that five-membered ring. The presence of a nitrogen in the ring or groups α to the ring like a group, an imine group. There are also types of conjugation. Homoconjugation is an overlap of two separated by a non-conjugating group, such as CH2. For example, the molecule CH2=CH–CH2–CH=CH2 is homoconjugated because the two C=C double bonds are separated by one CH2 group, cyclic compounds can be partly or completely conjugated. Annulenes, completely conjugated monocyclic hydrocarbons, may be aromatic, non-aromatic or anti-aromatic, conjugated, planar, cyclic compounds that follow Hückels rule are aromatic and exhibit an unusual stability. The classic example benzene has a system of 6 π-electrons, which forms the ring along the planar σ-ring with its 12 electrons. Not all compounds with alternating double and single bonds are aromatic, cyclooctatetraene, for example, possesses alternating single and double bonds. The molecule typically adopts a tub conformation, because the p-orbitals of the molecule do not align themselves well in this non-planar molecule, the electrons are not as easily shared between the carbon atoms. The molecule can be considered conjugated, but is neither aromatic. Many pigments make use of conjugated electron systems to absorb visible light, for example, the long conjugated hydrocarbon chain in beta-carotene leads to its strong orange color. When an electron in the system absorbs a photon of light of the right wavelength, in this model the lowest possible absorption energy corresponds to the energy difference between the highest occupied molecular orbital and the lowest unoccupied molecular orbital
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Homopolymer
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A polymer is a large molecule, or macromolecule, composed of many repeated subunits. Because of their range of properties, both synthetic and natural polymers play an essential and ubiquitous role 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, Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. The units composing polymers derive, actually or conceptually, from molecules of low molecular mass. The term was coined in 1833 by Jöns Jacob Berzelius, though with a distinct from the modern IUPAC definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger, Polymers are studied in the fields of biophysics and macromolecular science, and polymer science. Polyisoprene of latex rubber is an example of a polymer. In biological contexts, essentially all biological macromolecules—i. e, proteins, nucleic acids, and polysaccharides—are purely polymeric, or are composed in large part of polymeric components—e. g. Isoprenylated/lipid-modified glycoproteins, where small molecules and oligosaccharide modifications occur on the polyamide backbone of the protein. The simplest theoretical models for polymers are ideal chains, Polymers are of two types, Natural polymeric materials such as shellac, amber, wool, silk and natural rubber have been used for centuries. A variety of natural polymers exist, such as cellulose. Most commonly, the continuously linked backbone of a used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene, whose repeating unit is based on ethylene monomer, however, other structures do exist, for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant. Oxygen is also present in polymer backbones, such as those of polyethylene glycol, polysaccharides. Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network, during the polymerization process, some chemical groups may be lost from each monomer. This is the case, for example, in the polymerization of PET polyester, the distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Laboratory synthetic methods are divided into two categories, step-growth polymerization and chain-growth polymerization. However, some methods such as plasma polymerization do not fit neatly into either category
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Poly(methyl methacrylate)
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The same material can be utilised as a casting resin, in inks and coatings, and has many other uses. Chemically, it is the polymer of methyl methacrylate. PMMA is an alternative to polycarbonate when extreme strength is not necessary. Additionally, PMMA does not contain the potentially harmful bisphenol-A subunits found in polycarbonate and it is often preferred because of its moderate properties, easy handling and processing, and low cost. The first acrylic acid was created in 1843, methacrylic acid, derived from acrylic acid, was formulated in 1865. The reaction between acid and methanol results in the ester methyl methacrylate. In 1877 the German chemist Wilhelm Rudolph Fittig discovered the process that turns methyl methacrylate into polymethyl methacrylate. In 1933, the brand name Plexiglas was patented and registered by another German chemist, in 1936 Imperial Chemical Industries began the first commercially viable production of acrylic safety glass. During World War II both Allied and Axis forces used acrylic glass for submarine periscopes and aircraft windshields, canopies, common orthographic stylings include polymethyl methacrylate and polymethylmethacrylate. The full chemical name is poly, although often called simply acrylic, acrylic can also refer to other polymers or copolymers containing polyacrylonitrile. The other notable names include, Acrylite, a trademark of Evonik Cyro since 1976 Lucite, a trademark of DuPont, first registered in 1937 R-Cast. Founded in 1987 after spinning off from Reynolds & Taylor and they specialize in large scale and thick monolithic acrylic. Plexiglas, a trademark of ELF Atochem, now a subsidiary of Arkema in the US, generally, radical initiation is used, but anionic polymerization of PMMA can also be performed. To produce 1 kg of PMMA, about 2 kg of petroleum is needed, PMMA produced by radical polymerization is atactic and completely amorphous. The glass transition temperature of atactic PMMA is 105 °C, PMMA is thus an organic glass at room temperature, i. e. it is below its Tg. The forming temperature starts at the transition temperature and goes up from there. All common molding processes may be used, including molding, compression molding. The highest quality PMMA sheets are produced by casting, but in this case
