Chain addition reactions

Chain growth polymers, which are often referred to as addition polymers, form via chain addition reactions. Figure 2.2 presents a generic chain addition mechanism. Chain addition occurs when the active site of a monomer or polymer chain reacts with an adjacent monomer molecule, which is added to the end of the chain and generates a new active site. The active site is the reactive end of a monomer or polymer that participates in the polymerization reaction. 

Similar results were achieved in a free-radical chain addition reaction with free radicals generated from an EtsB-air or EtsB-air/alkyl iodide system (equation 76). ... 

CEJ1358> and the ruthenium mediated isomerization of double bonds (cf. Scheme 89, Section 8.11.7) <2007TL137> are recent examples of transition metal catalyzed manipulations at the side chain carbon atoms of 1,3-heterocycles. A novel side-chain addition reaction of aldehydes to 6-alkylidene-l,3-dioxin-4-ones was used for the construction of intermediates of lophotoxin <2006CJC1226>. An acid-catalyzed intramolecular cycloaddition of a hydroxy group to an alkene has been effected by the presence of an adjacent 1,3-dithiane moiety <2006TL4549>. 

In the presence of a reactive alkene acceptor, the intermediate radical R- can be intercepted by addition to a reactive alkene (step 3) prior to reaction with the starting thiohydroxamate (step 2). If the adduct radical (35) then adds to the thiohydroxamate (step 4) more rapidly than it adds to another molecule of alkene, a successful chain addition reaction results. In practice, a wide variety of addition reactions can be conducted by this method in yields that range from 30-90%. 

Whereas it has been demonstrated that both malonate ions and thiolate ions can catalyze the free radical chain addition reaction of perfluoroalkyl iodides to olefins [289,290], under appropriate conditions one can obtain products deriving from substitution in such processes. Following early work carried out photo-lytically in liquid ammonia, recent reports have indicated that good yields of substitution products can be obtained in polar solvents at room temperature, without irradiation [291-296]. 

The modem concept of linear polymers was introduced in 1920 by Staudinger, who fully recognized the idea of chain addition reaction yielding long molecules composed of monomeric units linked by covalent bonds. He was also the first to understand the anionic character of formaldehyde polymerization initiated by bases such as sodium methoxide4. In fact, studies of this reaction led him to the notion of linear macromolecules. Polymerization of ethylene oxide initiated by alkali metals and reported as early as 18785 could also be interpreted in these terms. 

Alternative radical chain addition reactions that avoid tributyltin hydride include the use of tris(trimethylsilyl)silane [(Me3Si)3SiH] or the use of thiohydroxamic... 

In these chain addition reactions, the active species is cationic in nature, initiated by strong acids, either of the protic or Lewis variety [21,104-111], Since most of these ionic polymerizations are carried out in nonaqueous solvents with low dielectric constants [109], it is unlikely that the active species is a free ion, analogous to a free radical. A multiplicity of active species may be involved as propagating species as shown below by the spectrum of cationic species, one or more of which may be involved as active propagating species, especially in more polar solvents [112], Unfortunately, very little information... 

Radical Chain Addition Reactions of Aldehydes With Perfluoro Ketones and Chloro Perfluoro Ketones," J. Org. Chem., 347 (1967). 

Reactions with Alkenes, Alkynes, and Allenes. Pentafluorosulfanyl chloride has been used in a free radical chain addition process to alkenes and alkynes. These free radical chain addition reactions have been accomplished thermally (eq 4) in an autoclave or via a room-temperature gas-phase or low-temperature solution-phase photochemical process (eq 5). A... 

The first propagation step in a typical radical chain addition reaction... 

Addition polymers, also referred to as chain growth polymers, are normally formed by a chain addition reaction process. When an adjacent monomer molecule reacts with an active site of the monomer, chain addition is said to have occurred. Here, the active site is considered the reactive end of the polymer or monomer, which participates in the polymerization process. A schematic representation of a typical chain addition mechanism is shown in Fig. 1.2. 

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