Chain-growth polymerization. See

For an excellent description of the mechanism of chain-growth polymerization, see Odian, G. In Principles of Polymerization, 3rd edn., Wiley-Interscience New York 1991, Ch. 3. 

To better understand the fundamental and practical differences between step-growth polymerization and chain-growth polymerization (see Table 1.4), consider the industrial chain-growth polymerization of ethylene (by either coordination polymerization or high-pressure free-radical polymerization) to produce polyethylene. 

Typical acrylic resins are high MW polymers or copolymers of acrylate and/or methacrylate monomers prepared by radical-initiated chain-growth polymerization (see Figure 2.28). In addition to the (meth) acrylate monomers, other functional (meth)acrylate monomers as well as non-acrylate monomers (typically vinyl monomers) are frequently used in preparation of commercial acrylic copolymer resins to impart reactive functionality or special properties or for lower cost. Some examples of these monomers are shown in Figure 2.29. 

Elsewhere in this chapter we shall see that other reactions-notably, chain transfer and chain inhibition-also need to be considered to give a more fully developed picture of chain-growth polymerization, but we shall omit these for the time being. Much of the argumentation of this chapter is based on the kinetics of these three mechanistic steps. We shall describe the rates of the three general kinds of reactions by the notation Rj, Rp, and R for initiation, propagation, and termination, respectively. 

Cements, polyester, 30 CFCs. See Chlorofluorocarbons (CFCs) Chain conformation, 54 Chain extenders, 213-214 structure of, 219 Chain extension, 216 Chain-growth polymerizations, 4 Char formation, 421, 423 Chelated phosphine ligands, 488 Chemical recycling, 208 Chemical structure... 

Long-chain approximation. In most chain reactions, a short sequence of steps, once initiated, repeats itself many times until it is terminated. The initiation and termination reactions then contribute very much less to product formation than do the self-repeating steps. The long-chain approximation neglects these minor contributions. It will be taken up in the context of chain reactions (see Section 9.3) and also used in chain-growth polymerization (Sections 10.3 and 10.4). 

The most common type of chain-growth polymerization is free-radical polymerization. An initiator or a photochemical reaction produces a free radical that attaches itself to a monomer molecule, creating a group with odd-electron configuration (reactive center) at which monomer molecules are added until two such centers react with one another or, more rarely, a center is deactivated by some other process. This is a mechanism much like that of ordinary chain reactions (see Chapter 9 the term "chain" in chain growth refers to that kind of mechanisms, not to the growing molecular chain of repeating units in the polymer.)... 

Chain growth differs from step growth in that it involves initiation and usually also termination reactions in addition to actual growth. This makes its kinetic behavior similar to that of chain reactions (see Chapter 9). However, the chain carriers in chain-growth polymerization need not be free radicals, as they are in ordinary chain reactions. Instead, they could be anions, cations, or metal-complex adducts. While the general structure of kinetics is similar in all types of chain-growth polymerizations, the details differ depending on the nature of the chain carriers. 

Chain-growth polymerization proceeds by one of three mechanisms radical polymerization, cationic polymerization, or anionic polymerization. Each mechanism has three distinct phases an initiation step that starts the polymerization, propagation steps that allow the chain to grow, and termination steps that stop the growth of the chain. We will see that the choice of mechanism depends on the structure of the monomer and the initiator used to activate the monomer. 

Note that an apparent chain-growth polymerization method was reported using Pdboronic acids, see (a) Yokoyama, A.,... 

Alcaligenes eutrophus has been used for industrial production of poly(hydroxyaIkanoate)s (PHAs). PHA is prepared from acetyl CoA in three steps and the last step is the chain growth polymerization of hydroxyalkanoate CoA esters catalyzed by PHA polymerase, yielding PHA of high molecular weight, which has heen in vitro examined, leading to synthesis of PHAs with well-defined structure. This synthetic process obeys the biosynthetic pathways (see Poly(3-H DROXYALKANOATES)). 

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