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Step-growth Polymerization
In polymer chemistry, step-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long chain polymers. 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 polymerization mechanism, a high extent of reaction is required to achieve high molecular weight. The easiest way to visualize the mechanism of a step-growth polymerization is a group of people reaching out to hold their hands to form a human chain—each person has two hands (= reactive sites). There also is the possibility to have more than two reactive sites on a monomer: In this case branched polymers production take place. IUPAC has deprecated the term ''step-growth polymerization'', and recommends use of the terms polyaddition (when the propagation steps are addition ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Condensation Reaction
In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a dehydration synthesis. However other molecules can also be lost, such as ammonia, ethanol, acetic acid and hydrogen sulfide. The addition of the two molecules typically proceeds in a step-wise fashion to the addition product, usually in equilibrium, and with loss of a water molecule (hence the name condensation). The reaction may otherwise involve the functional groups of the molecule, and is a versatile class of reactions that can occur in acidic or basic conditions or in the presence of a catalyst. This class of reactions is a vital part of life as it is essential to the formation of peptide bonds between amino acids and to the biosynthesis of fatty acids. Many variations of condensation reactions exist. Common examples include ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glass Transition
The glass–liquid transition, or glass transition, is the gradual and Reversible reaction, reversible transition in amorphous solid, amorphous materials (or in amorphous regions within Crystallinity, semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rubbery state as the temperature is increased. International Organization for Standardization, ISO 11357-2: Plastics – Differential scanning calorimetry – Part 2: Determination of glass transition temperature (1999). An amorphous solid that exhibits a glass transition is called a glass. The reverse transition, achieved by supercooling a viscous liquid into the glass state, is called vitrification. The glass-transition temperature ''T''g of a material characterizes the range of temperatures over which this glass transition occurs (as an experimental definition, typically marked as 100 s of relaxation time). It is always lower than the melting point, melting temperature, ''T''m, of the cr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyester
Polyester is a category of polymers that contain one or two ester linkages in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include some naturally occurring chemicals, such as those found in plants and insects. Natural polyesters and a few synthetic ones are biodegradable, but most synthetic polyesters are not. Synthetic polyesters are used extensively in clothing. Polyester fibers are sometimes spun together with natural fibers to produce a cloth with blended properties. Cotton-polyester blends can be strong, wrinkle- and tear-resistant, and reduce shrinking. Synthetic fibers using polyester have high water, wind, and environmental resistance compared to plant-derived fibers. They are less Fireproofing, fire-resistant and can melt when ignited. Liquid crystalline polyesters are among the first industrially used liquid crystal polymers. They are used for their mechanical propert ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Step Growth
Step(s) or STEP may refer to: Common meanings * Steps, making a staircase * Walking * Dance move * Military step, or march ** Marching Arts Films and television * ''Steps'' (TV series), Hong Kong * ''Step'' (film), US, 2017 Literature * ''Steps'' (novel), by Jerzy Kosinski * Systematic Training for Effective Parenting, a book series Music * Step (music), pitch change * Steps (pop group), UK * ''Step'' (Kara album), 2011, South Korea ** "Step" (Kara song) * ''Step'' (Meg album), 2007, Japan * "Step" (Vampire Weekend song) * "Step" (ClariS song) Organizations * STEP (company), Belgium * Society of Trust and Estate Practitioners, international professional body for advisers who specialise in inheritance and succession planning * Board on Science, Technology, and Economic Policy of the U.S. National Academies * Solving the E-waste Problem, a UN organization Science, technology, and mathematics * Step (software), a physics simulator in KDE * Step function, in mathemat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chain-growth Polymerization
Chain-growth polymerization (American English, AE) or chain-growth polymerisation (British English, BE) is a polymerization technique where monomer molecules add onto the active site on a growing polymer chain one at a time. There are a limited number of these active sites at any moment during the polymerization which gives this method its key characteristics. Chain-growth polymerization involves 3 types of reactions : # Initiation: An active species I* is formed by some decomposition of an initiator molecule I # Propagation: The initiator fragment reacts with a monomer M to begin the conversion to the polymer; the center of activity is retained in the adduct. Monomers continue to add in the same way until polymers Pi* are formed with the degree of polymerization i # Termination: By some reaction generally involving two polymers containing active centers, the growth center is deactivated, resulting in dead polymer Introduction In 1953, Paul Flory first classified polymeriza ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reaction Mechanism
In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical reaction occurs. A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction. The detailed steps of a reaction are not observable in most cases. The conjectured mechanism is chosen because it is thermodynamically feasible and has experimental support in isolated intermediates (see next section) or other quantitative and qualitative characteristics of the reaction. It also describes each reactive intermediate, activated complex, and transition state, which bonds are broken (and in what order), and which bonds are formed (and in what order). A complete mechanism must also explain the reason for the reactants and catalyst used, the stereochemistry observed in reactants and products, all products formed and the amount of each. The electron or arrow pushing method is often used in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nylon
Nylon is a family of synthetic polymers characterised by amide linkages, typically connecting aliphatic or Polyamide#Classification, semi-aromatic groups. Nylons are generally brownish in color and can possess a soft texture, with some varieties exhibiting a silk-like appearance. As Thermoplastic, thermoplastics, nylons can be melt-processed into fibres, Thin film, films, and diverse shapes. The properties of nylons are often modified by blending with a variety of additives. Numerous types of nylon are available. One family, designated nylon-XY, is derived from diamines and dicarboxylic acids of carbon chain lengths X and Y, respectively. An important example is nylon-6,6 (). Another family, designated nylon-Z, is derived from amino acid, aminocarboxylic acids with carbon chain length Z. An example is nylon-[6]. Nylon polymers have extensive commercial applications, including uses in textiles and fibres (such as apparel, flooring and rubber reinforcement), molded components fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paul Flory
Paul John Flory (June 19, 1910 – September 9, 1985) was an American chemist and Nobel laureate who was known for his work in the field of polymers, or macromolecules. He was a pioneer in understanding the behavior of polymers in solution, and won the Nobel Prize in Chemistry in 1974 "for his fundamental achievements, both theoretical and experimental, in the physical chemistry of macromolecules". Biography Personal life Flory was born in Sterling, Illinois, on June 19, 1910 to Ezra Flory and Martha Brumbaugh. His father worked as a clergyman-educator, and his mother was a school teacher. His ancestors were German Huguenots, who traced their roots back to Alsace. He first gained an interest in science from Carl W Holl, who was a chemistry professor at Manchester College. In 1936, he married Emily Catherine Tabor. They had three children together: Susan Springer, Melinda Groom and Paul John Flory, Jr. His first position was at DuPont with Wallace Carothers. He was posthumou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DuPont
Dupont, DuPont, Du Pont, duPont, or du Pont may refer to: People * Dupont (surname) Dupont, also spelled as DuPont, duPont, Du Pont, or du Pont is a French surname meaning "of the bridge", historically indicating that the holder of the surname resided near a bridge. , the name was the fourth most popular surname in Belgium, and , i ..., a surname of French origin * Du Pont family, one of the wealthiest families in the United States Companies * DuPont, one of the world's largest chemical companies * Du Pont Motors, a marine engine and automobile manufacturer from 1919 to 1931 * Dupont Brewery, a brewery in Belgium Places in the United States * Dupont, Colorado, an unincorporated community * Du Pont, Georgia, a town * Dupont, Indiana, a town * Dupont, Pointe Coupee Parish, Louisiana, an unincorporated community * Dupont, Ohio, a village * Dupont, Pennsylvania, a borough * Dupont, Tennessee, a community * DuPont, Washington, a city * Dupont, Wisconsin, a town * DuPont ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wallace Carothers
Wallace Hume Carothers (; April 27, 1896 – April 29, 1937) was an American chemist, inventor, and the leader of organic chemistry at DuPont, who was credited with the invention of nylon. Carothers was a group leader at the DuPont Experimental Station laboratory, near Wilmington, Delaware, where most polymer research was done. Carothers was an organic chemist who, in addition to first developing nylon, also helped lay the groundwork for neoprene. After receiving his Ph.D., he taught at several universities before he was hired by DuPont to work on fundamental research. He married Helen Sweetman on February 21, 1936. Carothers had been troubled by periods of depression since his youth. Despite his success with nylon, he felt that he had not accomplished much and had run out of ideas. His unhappiness was exacerbated by the death of his sister, and on April 28, 1937, he committed suicide by drinking potassium cyanide. His daughter, Jane, was born on November 27, 1937. Educati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Formaldehyde
Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as aqueous solutions (formalin), which consists mainly of the hydrate CH2(OH)2. It is the simplest of the aldehydes (). As a precursor to many other materials and chemical compounds, in 2006 the global production of formaldehyde was estimated at 12 million tons per year. It is mainly used in the production of industrial resins, e.g., for particle board and coatings. Formaldehyde also occurs naturally. It is derived from the degradation of serine, dimethylglycine, and lipids. Demethylases act by converting N-methyl groups to formaldehyde. Formaldehyde is classified as a group 1 carcinogen and can cause respiratory and skin irritation upon exposure. Forms Formaldehyde is more complicated than many simple carbon compounds in that i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
