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Vinyl Polymer
In polymer chemistry, vinyl polymers are a group of polymers derived from substituted vinyl () monomers. Their backbone is an extended alkane chain . In popular usage, "vinyl" refers only to polyvinyl chloride (PVC). Examples Vinyl polymers are the most common type of plastic. Important examples can be distinguished by the R group in the monomer H2C=CHR: * Polyethylene R = H * polypropylene from propylene, R = CH3 * Polystyrene is made from styrene, R = C6H5 * Polyvinyl chloride (PVC) is made from vinyl chloride, R= Cl * Polyvinyl acetate (PVAc) is made from vinyl acetate, R = O2CCH3 * Polyacrylonitrile is made from acrylonitrile, R = CN : Production Vinyl polymers are produced using catalysts. Ziegler–Natta catalysts are used commercially for production of polyethylene and polypropylene. Many are produced using radical initiators which are produced from organic peroxides. Still others (poystyrene) are produced using anionic initiators such as butyl lithium. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymer Chemistry
Polymer chemistry is a sub-discipline of chemistry that focuses on the structures of chemicals, chemical synthesis, and chemical and physical properties of polymers and macromolecules. The principles and methods used within polymer chemistry are also applicable through a wide range of other chemistry sub-disciplines like organic chemistry, analytical chemistry, and physical chemistry. Many materials have polymeric structures, from fully inorganic metals and ceramics to DNA and other biological molecules. However, polymer chemistry is typically related to synthetic and organic compositions. Synthetic polymers are ubiquitous in commercial materials and products in everyday use, such as plastics, and rubbers, and are major components of composite materials. Polymer chemistry can also be included in the broader fields of polymer science or even nanotechnology, both of which can be described as encompassing polymer physics and polymer engineering.Hans-Heinrich Moretto, Manfred ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vinyl Acetate
Vinyl acetate is an organic compound with the formula CH3CO2CH=CH2. This colorless liquid is the precursor to polyvinyl acetate and ethene-vinyl acetate copolymers, important industrial polymers. Production The worldwide production capacity of vinyl acetate was estimated at 6,969,000 tonnes/year in 2007, with most capacity concentrated in the United States (1,585,000 all in Texas), China (1,261,000), Japan (725,000) and Taiwan (650,000). The average list price for 2008 was US$1600/tonne. Celanese is the largest producer (ca 25% of the worldwide capacity), while other significant producers include China Petrochemical Corporation (7%), Chang Chun Group (6%), and LyondellBasell (5%). It is a key ingredient in furniture glue. Preparation Vinyl acetate is the acetate ester of vinyl alcohol. Since vinyl alcohol is highly unstable (with respect to acetaldehyde), the preparation of vinyl acetate is more complex than the synthesis of other acetate esters. The major industrial route ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acrylate Polymer
An acrylate polymer (also known as acrylic or polyacrylate) is any of a group of polymers prepared from acrylate monomers. These plastics are noted for their transparency, resistance to breakage, and elasticity. Acrylate polymer is commonly used in cosmetics, such as nail polish, as an adhesive. History The first synthesis of acrylic polymer was reported by G.W.A Kahlbaum in 1880. Acrylic elastomers Acrylic elastomer is a general term for a type of synthetic rubber whose primary component is acrylic acid alkylester ( ethyl or butyl ester). Acrylic elastomer possesses characteristics of heat and oil resistance, with the ability to withstand temperatures of 170–180 °C. It is used primarily for producing oil seals and packaging related to automobiles. Acrylic elastomer can generally be characterized as one of two types. "Old" types include ACM (copolymer of acrylic acid ester and 2-chloroethyl vinyl ether) containing chlorine and ANM (copolymer of acrylic acid ester ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comonomer
In polymer chemistry, a comonomer refers to a polymerizable precursor to a copolymer aside from the principal monomer. In some cases, only small amounts of a comonomer are employed, in other cases substantial amounts of comonomers are used. Furthermore, in some cases, the comonomers are statistically incorporated within the polymer chain, whereas in other cases, they aggregate. The distribution of comonomers is referred to as the " blockiness" of a copolymer. 1-Octene, 1-hexene, and 1-butene are used comonomers in the manufacture of polyethylenes. The advantages to such copolymers has led to a focus on catalysts that facilitate the incorporation of these comonomers, e.g., constrained geometry complexes. Comonomers are often employed to improve the plastification of polymeric materials, i.e. the flexibility of the polymer. Unlike traditional plasticizers, comonomers are not leachable. In other cases, comonomers are used to introduce crosslinking. Divinylbenzene, for exampl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tacticity
Tacticity (from el, τακτικός, taktikos, "relating to arrangement or order") is the relative stereochemistry of adjacent chiral centers within a macromolecule. The practical significance of tacticity rests on the effects on the physical properties of the polymer. The regularity of the macromolecular structure influences the degree to which it has rigid, crystalline long range order or flexible, amorphous long range disorder. Precise knowledge of tacticity of a polymer also helps understanding at what temperature a polymer melts, how soluble it is in a solvent and its mechanical properties. A tactic macromolecule in the IUPAC definition is a macromolecule in which essentially all the configurational (repeating) units are identical. Tacticity is particularly significant in vinyl polymers of the type - where each repeating unit with a substituent R on one side of the polymer backbone is followed by the next repeating unit with the substituent on the same side as the prev ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Absolute Configuration
Absolute configuration refers to the spatial arrangement of atoms within a chiral molecular entity (or group) and its resultant stereochemical description. Absolute configuration is typically relevant in organic molecules, where carbon is bonded to four different substituents. This type of construction creates two possible enantiomers. Absolute configuration uses a set of rules to describe the relative positions of each bond around the chiral center atom. The most common labeling method uses the descriptors ''R'' or ''S'' is based on the Cahn–Ingold–Prelog priority rules. R and S refer to Rectus and Sinister, which are Latin for right and left, respectively. Chiral molecules can differ in their chemical properties, but are identical in their physical properties, which can make distinguishing enantiomers challenging. Absolute configurations for a chiral molecule (in pure form) are most often obtained by X-ray crystallography, although with some important limitations. All ena ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stereogenic
In stereochemistry, a stereocenter of a molecule is an atom (center), axis or plane that is the focus of stereoisomerism; that is, when having at least three different groups bound to the stereocenter, interchanging any two different groups creates a new stereoisomer. Stereocenters are also referred to as stereogenic centers. A stereocenter is geometrically defined as a point (location) in a molecule; a stereocenter is usually but not always a specific atom, often carbon. Stereocenters can exist on chiral or achiral molecules; stereocenters can contain single bonds or double bonds. The number of hypothetical stereoisomers can be predicted by using 2''n'', with ''n'' being the number of tetrahedral stereocenters; however, exceptions such as meso compounds can reduce the prediction to below the expected 2''n''. Chirality centers are a type of stereocenter with four different substituent groups; chirality centers are a specific subset of stereocenters because they can only hav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyvinyl Alcohol
Poly(vinyl alcohol) (PVOH, PVA, or PVAl) is a water- soluble synthetic polymer. It has the idealized formula H2CH(OH)sub>''n''. It is used in papermaking, textile warp sizing, as a thickener and emulsion stabilizer in polyvinyl acetate (PVAc) adhesive formulations, in a variety of coatings, and 3D printing. It is colourless (white) and odorless. It is commonly supplied as beads or as solutions in water. Without an externally added crosslinking agent, PVA solution can be gelled through repeated freezing-thawing, yielding highly strong, ultrapure, biocompatible hydrogels which have been used for a variety of applications such as vascular stents, cartilages, contact lenses, etc. Uses PVA is used in a variety of medical applications because of its biocompatibility, low tendency for protein adhesion, and low toxicity. Specific uses include cartilage replacements, contact lenses, and eye drops. Polyvinyl alcohol is used as an aid in suspension polymerizations. Its largest a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Butyl Lithium
Butyllithium may refer to one of 5 isomeric organolithium reagents of which 3 are commonly used in chemical synthesis: * ''n''-Butyllithium, abbreviated BuLi or nBuLi * ''sec''-Butyllithium, abbreviated ''sec''-BuLi or sBuLi, has 2 stereoisomers, but is commonly used as racemate *isobutyllithium * ''tert''-Butyllithium, abbreviated ''tert''-BuLi or tBuLi {{Chemistry index ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Peroxide
In organic chemistry, organic peroxides are organic compounds containing the peroxide functional group (). If the R′ is hydrogen, the compounds are called hydroperoxides, which are discussed in that article. The O−O bond of peroxides easily breaks, producing free radicals of the form (the dot represents an unpaired electron). Thus, organic peroxides are useful as initiators for some types of polymerisation, such as the epoxy resins used in glass-reinforced plastics. MEKP and benzoyl peroxide are commonly used for this purpose. However, the same property also means that organic peroxides can explosively combust. Organic peroxides, like their inorganic counterparts, are often powerful bleaching agents. Types of organic peroxides Tert-Butyl hydroperoxide Structural Formula V2.svg, ''tert''-Butyl hydroperoxide, a hydroperoxide (formula: ROOH) that is used to epoxide alkenes. Dicumyl peroxide.svg, Dicumyl peroxide, a dialkyl peroxide (formula: ROOR) that is used to initia ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ziegler–Natta Catalyst
A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes ( alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility: * Heterogeneous supported catalysts based on titanium compounds are used in polymerization reactions in combination with cocatalysts, organoaluminum compounds such as triethylaluminium, Al(C2H5)3. This class of catalyst dominates the industry. * Homogeneous catalysts usually based on complexes of the group 4 metals titanium, zirconium or hafnium. They are usually used in combination with a different organoaluminum cocatalyst, methylaluminoxane (or methylalumoxane, MAO). These catalysts traditionally contain metallocenes but also feature multidentate oxygen- and nitrogen-based ligands. Ziegler–Natta catalysts are used to polymerize terminal alkenes (ethylene and alkenes with the vinyl double bond): :''n'' CH2=CHR → − H2−CHR ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
