Mechanism of free radical polymerization

Similar to general free radical polymerization, the free radical polymerization of methacrylate and acrylate monomers consists of four kinetic steps radical formation, chain initiation, chain propagation, and chain termination. 

2 Radical Formation and Chain Initiation Generate primary radicals  

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The mechanism of free radical polymerization of ethylene is outlined m Figure 6 17 Dissociation of a peroxide initiates the process m step 1 The resulting per oxy radical adds to the carbon-carbon double bond m step 2 giving a new radical which then adds to a second molecule of ethylene m step 3 The carbon-carbon bond forming process m step 3 can be repeated thousands of times to give long carbon chains... 

Bamford and coworkers [24] also investigated the kinetics and mechanism of free radical polymerization of bulk MMA photoinitiated by Mn2(CO)io or Re2(CO)io in the presence of a series of fluoro-olefms such as ... 

Still another, and chains, long or short, may be built up. This is the mechanism of free-radical polymerization. Short polymeric molecules (called telomers), formed in this manner, are often troublesome side products in free-radical addition reactions. 

Many of the synthetic elastomers now made are still polymerized by a free radical mechanism. Polychloroprene, polybutadiene, polyisoprene, and styrene-butadiene copolymer are made this way. Initiation by peroxides is common. Many propagation steps create high molecular weight products. Review the mechanism of free radical polymerization of dienes given in Chapter 14, Section 2.2. 

At its simplest, the mechanism of free-radical polymerization consists of free-radical production by an initiator (initiation), link-up of the free radical with a monomer molecule (often considered part of initiation), addition of further monomer (propagation), and eventual deactivation (termination) of the growing polymer radicals by coupling, also called combination, that is, by link-up of two radicals with one another. This is much as in ordinary chain reactions (see Section 9.5). Free-radical polymerization of styrene may serve as an example [31,32]. 

The mechanism of free-radical polymerization has been studied extensively. Most monomers that have... 

It was initially thought that the mechanism of free-radical polymerization was comprised of the stages of initiation, propagation, and termination of the chain. In 1937 Flory20 introduced the concept of a chain transfer consisting of two elementary... 

Dr. Bovey was born in Minneapolis in 1918. He received a B.S. degree in chemistry from Harvard in 1940, worked during World War II for the National Synthetic Rubber Corporation, a 3M subsidiary, and entered graduate school at the University of Minnesota as a Rubber Reserve Fellow in 1945. His thesis work, carried out under the direction of 1. M. Kolthoff, dealt with the mechanism of free radical polymerization. During this time he worked out the mechanism of oxygen inhibition and discovered oxygen styrene copolymers. 

In order to explain how inhibitors work, we need to quickly describe the mechanism of free radical polymerization encountered for the ethylenically unsaturated monomers. For more details, several reviews (refs. 1-7) also described free radical polymerization. 

Hagemann H.J. (1989) Photoinitiators and photoionization mechanisms of free-radical polymerization processes. In Allen, N.S. (ed) Photopolymerization and photoimaging science and technology 1 -53. Elsevier, Crown House. 

Whether initiated by radiation or by the thermal decomposition of free radical initiators, and whether in the bulk or in the imbibed state, the mechanisms of free radical polymerizations of monomers in wood should be essentially similar. As with any free radical polymerization, three basic steps must be involved initiation, propagation, and termination also, chain transfer reactions may occur, depending on the monomer, additives, and on the mode of initiation (Chapiro, 1962 Siau et al, 1965a see also Appendix A, Chapter 1). In such cases, the rate of polymerization should depend on the square root of the concentration of initiating radicals, which, in turn, should depend on the dose or on the concentration of free radical initiator ... 

As might be expected, the emulsion polymerization system does not alter the basic mechanism of free radical polymerization as regards the chain unit structure. The latter is, of course, independent of the type of free radical initiator used, in view of the free nature of the growing chain end radical. The temperature of polymerization does exert some influence, as shown by the data in Table Vlll, but not to a very great extent. It can be seen that the 1,2 side-chain vinyl content is rather insensitive to the temperature, whereas the trans-, A content increases with decreasing temperature, at the expense of the m-1,4 content. The latter almost vanishes, in fact, at low temperatures and... 

Obviously, more experimental data for wider ranges of temperatures and monomer concentrations are required to arrive at a better understanding of the mechanism of free-radical polymerization in partially and fully ionized systems. Acryhc acid is no perfect monomer for kinetic studies in wide ranges of experimental conditions. As in the case of PLP-SEC studies into kp of non-ionized monomers, methacrylic acid is a better choice also for investigations into ionized systems within extended temperature and monomer concentration ranges. For MAA, kp values were measured at monomer concentrations, Cmaa, between 5 and 40 wt.-% and at temperatures from 6 to 80 °C over the entire range of MAA ionization, between a = 0 and a = The experimental procedure is similar to the one used in the experiments on aqueous solutions of AA at different degrees of ionic dissodation. ... 

Kinetics and mechanism of free radical polymerization of acrylic and methacrylic acids in aqueous solution [127]. 

When the mechanism of free radical polymerization was established, this structure seemed improbable. So further work was undertaken and it was learned that in our synthetic approach to the two model sulfone sulfinic acids rearrangements had occurred and the two synthesized products were actually the reverse in structure to what we had thought. The olefin sulfiir dioxide polymers then actually have the orthodox head to tail structures. 

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