Free radical addition anionic

Cationic Polymerization. For decades cationic polymerization has been used commercially to polymerize isobutylene and alkyl vinyl ethers, which do not respond to free-radical or anionic addition (see Elastomers, synthetic-BUTYLRUBBEr). More recently, development has led to the point where living cationic chains can be made, with many of the advantages described above for anionic polymerization (27,28). 

Proliferous Polymerization. Eady attempts to polymerize VP anionicaHy resulted in proliferous or "popcorn" polymerization (48). This was found to be a special form of free-radical addition polymerization, and not an example of anionic polymerization, as originally thought. VP contains a relatively acidic proton alpha to the pyrroHdinone carbonyl. In the presence of strong base such as sodium hydroxide, VP forms cross-linkers in situ probably by the following mechanism ... 

Chapters 5 through 7 deal with polymers formed from chain-growth polymerization. Chain-growth polymerization is also called addition polymerization and is based on free radical, cationic, anionic, and coordination reactions where a single initiating species causes the growth of a polymer chain. 

The maleimide group can undergo a variety of chemical reactions. The reactivity of the double bond is a consequence of the electron withdrawing nature of the two adjacent carbonyl groups which create a very electron-deficient double bond, and therefore is susceptible to homo- and copolymerizations. Such polymerizations may be induced by free radicals or anions. Nucleophiles such as primary and secondary amines, phenates, thiophenates, carboxylates, etc. may react via the classical Michael addition mechanism. The maleimide group furthermore is a very reactive dienophile and can therefore be employed in a variety of Diels Alder reactions. Bisdienes such as divinylbenzene, bis(vinylbenzyl) compounds, bis(propenylphenoxy) compounds and bis(benzocyclobutenes) are very attractive Diels Alder comonomers and therefore some are used as constituents for BMI resin formulations. An important chemical reaction of the maleimide group is the ENE reaction with allylphenyl compounds. The most attractive comonomer of this family is DABA particularly when tough bismaleimide resins are desired. 

There are some important differences between anionic and free-radical addition. First, unlike free-radical initiators, which decompose and start chains randomly throughout the course of the reaction, anionic initiators ionize readily in fairly polar organic solvents or at low concentrations in hydrocarbons, and chains are started immediately, one for each molecule of initiator. Second, in the absence of impurities, there is no termination,... 

Cationic polymerization has been used commercially to polymerize isobutylene and alkyl vinyl ethers, which do not respond to free-radical or anionic addition. See also Elastomers and Rubber (Synthetic). 

Considerable effort in the 1970s by Pittman, George, Hayes, Korshak, and others was applied to exploring the addition polymerization of vinylferrocene 6.1 to give organic polymers with pendent ferrocenyl side groups (6.2 in reaction (l)).1 6 This type of polymerization reaction has been attempted with the use of free radical, cationic, anionic, and Ziegler-Natta methods. 

Additional information about the electrochemical behaviour of pyrimidone-2 is furnished by studies in non-aqueous medium, (CH3)2SO, with particular attention to the possible role of free radicals and anionic species (radical anions, dianions, dissociated conjugated bases) as reaction intermediates82). 

In contrast to nucleophilic additions of alcohols to fluorinated alkenes, where the reagent is alkoxide anion, in free-radical addition of alcohols the reacting species is a free radical generated by homolysis of the bond between hydrogen and the alkyl group. 

In contrast to the slow step-reaction polymerizations, chain-reaction polymerizations are fairly rapid.14 Chain-reaction polymerizations (often referred to as addition polymerizations) require the presence of an initiator for polymerization to occur. Initiation can occur by a free radical, an anionic, or a cationic species, which open the double bond of a vinyl monomer and the reaction proceeds as shown in Fig. 15.11 where may be a radical,... 

Perflnoroalkenes are significant industrial starting materials, of which the simplest and most important is TFE. This reactive alkene can be reacted, mainly nnder free radical or anionic conditions, to yield a variety of saturated addition products (Scheme 1). TFE displays versatile polymerization and copolymerization applications. ... 

Mechanism and kinetics of cationic poiymerization initiation. Unlike free-radical and anionic polymerization, initiation in cationic polymerization employs a true catalyst that is restored at the end of the polymerization and does not become incorporated into the terminated polymer chain. Initiation of cationic polymerization is brought about by addition of an electrophile to a monomer molecule. TVpical compounds used for cationic polymerization include protonic acids (e.g., H2SO4, H3PO4), Lewis acids (e.g., AICI3, BF3, TiCl4, SnCl4), and stable carbenium-ion salts (e.g., triphenylmethyl halides, tropylium halides) ... 

Most cyanoacrylate adhesives are maintained in a liquid state at room temperature by the addition of free radical and anionic stabilisers at suitable concentrations so as not to interfere with the functionality of the adhesive. These stabilisers/inhibitors are added at... 

A polymer is a giant molecule composed of a repeating structural unit called a monomer. Addition polymers result from the addition of alkene molecules to one another. The polymerization occurs by cationic, free-radical, and anionic reaction mechanisms. Examples of addition polymers include polyethylene, polystyrene, PVC, and Teflon. 

Optically active polymers can be prepared by free-radical additions that give polymers whose chirality is the result of an excess of one single-screw sense. Most polymers will not maintain a helix screw conformation in solution unless the chain backbone is rigid or the polymer side-chains are very large and prevent conformational relaxation. Polymers derived from trityl and related methacrylates have this apparent capacity, i.e. they display excess helical content in solution. Comprehensive reviews of helix-sense-selective anionic polymerizations have appeared [12], and in this section, we highlight some of the recent developments in this field related to radical polymerizations of these highly hindered methacrylates. 

Styrene is one of those monomers that lends itself to polymerization by free-radical, cationic, anionic, and coordination mechanisms. This is due to several reasons. One is resonance stabilization of the reactive polystyryl species in the transition state that lowers the activation energy of the propagation reaction. Another is the low polarity of the monomer. This facilitates attack by free radicals, differently charged ions, and metal complexes. In addition, no side reactions that occur in ionic polymerizations of monomers with functional groups,are possible. Styrene pol erizes in the dark by a free-radical mechanism more slowly than it does in the presence of light. Also, styrene formed in the dark is reported to have a greater amount of syndiotactic placement. The amount of branching in the polymer prepared by a free-radical mechanism increases with temperature. This... 

The free-radical addition of TFE to pentafluoroethyl iodide yields a mixture of perfluoroalkyl iodides with even-numbered fluorinated carbon chains. This is the process used to commercially manufacture the initial raw material for the fluorotelomer -based family of fluorinated substances (Fig. 3) [2, 17]. Telomeri-zation may also be used to make terminal iso- or methyl branched and/or odd number fluorinated carbon perfluoroalkyl iodides as well [2]. The process of TFE telomerization can be manipulated by controlling the process variables, reactant ratios, catalysts, etc. to obtain the desired mixture of perfluoroalkyl iodides, which can be further purified by distillation. While perfluoroalkyl iodides can be directly hydrolyzed to perfluoroalkyl carboxylate salts [29, 30], the addition of ethylene gives a more versatile synthesis intermediate, fluorotelomer iodides. These primary alkyl iodides can be transformed to alcohols, sulfonyl chlorides, olefins, thiols, (meth)acrylates, and from these into many types of fluorinated surfactants [3] (Fig. 3). The fluorotelomer-based fluorinated surfactants range includes noiuonics, anionics, cationics, amphoterics, and polymeric amphophiles. 

Most commercial grades are amorphous, and the lack of crystalline regions provides transparency and no clearly defined melt temperature. Polystyrene can be polymerized via many mechanisms such as free radical, anionic, cationic, and Ziegler reactions. Commercially available polystyrene is generally produced via free radical-addition polymerization. The polymerized resin is a transparent solid having very low specific gravity (1.054-1.070)... 

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