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Reversible-deactivation Polymerization
Reversible-deactivation polymerization (RDP) is a form of polymerization propagated by chain carriers the some of which at any instant are held in a state of dormancy through an equilibrium process involving other species. An example of reversible deactivation anionic polymerization (RDAP) is group transfer polymerization of alkyl methacrylates, where the initiator and the dormant state is a silyl ketene acetal. In the case of reversible deactivation radical polymerization (RDRP), a majority of chain must be held in a dormant state to ensure that the concentration of active carriers is sufficiently low as to render chain termination reactions negligible. Despite having some common features, RDP is distinct from living polymerization 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
International Union Of Pure And Applied Chemistry
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is a member of the International Science Council (ISC). 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 IUPAC's 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, or other bodies representing chemists. There are fifty-four National Adhering Organizations and three Associate National Adhering Organizations. IUPAC's Inter-divisional Committee on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reversible-deactivation Radical Polymerization
Reversible deactivation radical polymerizations (RDRPs) are members of the class of reversible deactivation polymerizations which exhibit much of the character of living polymerizations, but cannot be categorized as such as they are not without chain transfer or chain termination reactions. Several different names have been used in literature, which are: *Living radical polymerization *Living free radical polymerization *Controlled/"living" radical polymerization *Controlled radical polymerization *Reversible deactivation radical polymerization Though the term "living" radical polymerization was used in early days, it has been discouraged by IUPAC, because radical polymerization cannot be a truly living process due to unavoidable termination reactions between two radicals. The commonly used term controlled radical polymerization is permitted, but reversible-deactivation radical polymerization or controlled reversible-deactivation radical polymerization (RDRP) is recommended. Histor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reversible Addition−fragmentation Chain-transfer Polymerization
Reversible addition−fragmentation chain-transfer or RAFT polymerization is one of several kinds of reversible-deactivation radical polymerization. It makes use of a chain-transfer agent in the form of a thiocarbonylthio compound (or similar, from here on referred to as a RAFT agent, see Figure 1) to afford control over the generated molecular weight and polydispersity during a free-radical polymerization. Discovered at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) of Australia in 1998, RAFT polymerization is one of several living or controlled radical polymerization techniques, others being atom transfer radical polymerization (ATRP) and nitroxide-mediated polymerization (NMP), etc. RAFT polymerization uses thiocarbonylthio compounds, such as dithioesters, thiocarbamates, and xanthates, to mediate the polymerization via a reversible chain-transfer process. As with other controlled radical polymerization techniques, RAFT polymerizations can be performed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymerization
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer, monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many forms of polymerization and different systems exist to categorize them. In chemical compounds, polymerization can occur via a variety of reaction mechanisms that vary in complexity due to the functional groups present in the reactants and their inherent steric effects. In more straightforward polymerizations, alkenes form polymers through relatively simple free-radical reaction, radical reactions; in contrast, reactions involving substitution at a carbonyl group require more complex synthesis due to the way in which reactants polymerize. Alkanes can also be polymerized, but only with the help of strong acids. As alkenes can polymerize in somewhat straightforward radical reactions, they form useful compounds such as polyethylene and p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Equilibrium
In a chemical reaction, chemical equilibrium is the state in which both the reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system. This state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but they are equal. Thus, there are no net changes in the concentrations of the reactants and products. Such a state is known as dynamic equilibrium. Historical introduction The concept of chemical equilibrium was developed in 1803, after Berthollet found that some chemical reactions are reversible. For any reaction mixture to exist at equilibrium, the rates of the forward and backward (reverse) reactions must be equal. In the following chemical equation, arrows point both ways to indicate equilibrium. A and B are reactant chemical species, S and T are p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silyl Ketene Acetal
Silyl enol ethers in organic chemistry are a class of organic compounds that share a common functional group composed of an enolate bonded through its oxygen end to an organosilicon group. They are important intermediates in organic synthesis. Synthesis Silyl enol ethers are generally prepared by reacting an enolizable carbonyl compound with a silyl electrophile and a base, or just reacting an enolate with a silyl electrophile.Clayden, J., Greeves, N., & Warren, S. (2012). Silyl enol ethers. In ''Organic chemistry'' (Second ed., pp. 466-467). Oxford University Press. Since silyl electrophiles are hard and silicon-oxygen bonds are very strong, the oxygen (of the carbonyl compound or enolate) acts as the nucleophile to form a Si-O single bond. The most commonly used silyl electrophile is trimethylsilyl chloride. To increase the rate of reaction, trimethylsilyl triflate may also be used in the place of trimethylsilyl chloride as a more electrophilic substrate. When using an unsy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reversible-deactivation Radical Polymerization
Reversible deactivation radical polymerizations (RDRPs) are members of the class of reversible deactivation polymerizations which exhibit much of the character of living polymerizations, but cannot be categorized as such as they are not without chain transfer or chain termination reactions. Several different names have been used in literature, which are: *Living radical polymerization *Living free radical polymerization *Controlled/"living" radical polymerization *Controlled radical polymerization *Reversible deactivation radical polymerization Though the term "living" radical polymerization was used in early days, it has been discouraged by IUPAC, because radical polymerization cannot be a truly living process due to unavoidable termination reactions between two radicals. The commonly used term controlled radical polymerization is permitted, but reversible-deactivation radical polymerization or controlled reversible-deactivation radical polymerization (RDRP) is recommended. Histor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chain Termination
Chain termination is any chemical reaction that ceases the formation of reactive intermediates in a chain propagation step in the course of a polymerization, effectively bringing it to a halt. Mechanisms of termination In polymer chemistry, there are several mechanisms by which a polymerization reaction can terminate depending on the mechanism and circumstances of the reaction. A method of termination that applies to all polymer reactions is the depletion of monomer. In chain growth polymerization, two growing chains can collide head to head causing the growth of both of the chains to stop. In the case of radical or anionic polymerization, chain transfer can occur where the radical at the end of the growing chain can be transferred from the chain to an individual monomer unit causing a new chain to start growing and the previous chain to stop growing. With step-growth polymerization, the reaction can be terminated by adding a monofunctional species containing the same funct ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Living Polymerization
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 polymer chains grow at a more constant rate than seen in traditional chain polymerization and their lengths remain very similar (i.e. they have a very low polydispersity index). Living polymerization is a popular method for synthesizing block copolymers since the polymer can be synthesized in stages, each stage containing a different monomer. 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 novel/useful properties of polymers result from t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
