Radical Polymerization in the Presence of a Chain Transfer Agent

Title Method for Radical Polymerization in the Presence of a Chain Transfer Agent 

1 -Benzyl-2,5-cyclohexadiene-1 -carboxylic acid is a new chain transfer agent that was used to modulate the emulsion terpolymerization of styrene, butadiene, and acryhc acid. Its use resulted in 7% less gel formation than in an equivalent terpolymerization lacking this additive. 

Preparation of Poly(Styrene-co-Butadiene-co-Acrylic Acid) by Emulsion Polymerization 

A polymerization vessel was charged with water (300 g), 33% polymer styrene latex (62 g, dso of 30 nm), 10% of the initiator solution, and sodium peroxodisulfate and then heated to 95°C. Using two separate feeds, the monomer emulsion present in 

8 g 1-benzyl-2,5-cyclohexadiene-l-carboxyhe acid [chain transfer agent] 

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Free radical polymerization in the presence of a chain transfer agent (telogen) is often called telomerization reaction. Many different telogens have been reported (57) the most studied and well-documented telogen is CCI4 (Fig. 5). 

Free radical polymerizations were performed in the presence of a chain transfer agent... 

A multistep reaction pathway leads to polymers 43 and 44 with phosphatidylcholine moieties in the main chain and long alkyl groups in the side chain [122]. These polymers exhibit thermotropic liquid-crystalline behavior. Polyamides 45 were obtained by interfacial polycondensation they are insoluble in any normal solvent [123]. Poly-MPC capped with cholesteryl moieties at one or both polymer ends was prepared by the radical polymerization of MFC initiated with 4,4 -azobis[(3-cholesteryl)-4-cyanopentanoate] in the presence of a chain transfer agent [124]. The self-organization of these polymers was analyzed with fluorescence and NMR measurements. 

Values of CP measured in the presence of added PMMA (for example) will depend on how the PMMA was prepared and its molecular weight (i.e. on the concentration of unsaturated ends). PMMA formed by radical polymerization in the presence of a good H-donor transfer agent (or by anionic polymerization) would have only saturated chain ends. These PMMA chains should have a different transfer constant to those formed by normal radical polymerization where termination occurs by a mixture of combination and disproportionation. This could account for some of the variation in the values of CP for this polymer... 

Another kind of macromonomer has gained interest recently polymers having two functions capable of participating in step growth polymerization reactions at one end of their chain. Such species are synthesized by free radical polymerization carried out in the presence of a bifunctional transfer agent, such as thiomalic acid or thioglycerol. Yamashita has prepared a number of... 

We will show in Chapter 5 that using a large amount of initiator gives polymer chains of smaller length and is therefore undesirable. Instead, radical polymerization in the presence of transfer agents can be performed. The best known transfer agent is carbon tetrachloride, which can abstract an electron from growing polymer radicals, P , as follows ... 

If a vinyl monomer is polymerized in the presence of cellulose by a free radical process, a hydrogen atom may be abstracted from the cellulose by a growing chain radical (chain transfer) or by a radical formed by the polymerization catalyst (initiator). This leaves an unshared electron on the cellulose chain that is capable of initiating grafting. As cellulose is a very poor transfer agent [10], very little copolymer results from the abstraction of hydrogen atoms by a growing chain radical. The... 

To avoid these stability problems, it is necessary to minimize the proportion of chains that terminate by radical-radical reaction. One way of achieving this is to conduct the polymerization in the presence of an appropriate chain transfer agent. For example, if polymerization is performed in the presence of a H-donor chain transfer agent, conditions can be chosen such that most chains terminate by hydrogen-atom transfer. Bagby et al.iA examined the thermal stability of PMMA formed with dodecanethiol. These polymer chains will then possess, more... 

A combination of variables controls the outcome of the copolymerization of two or more unsaturated monomers by CCT free-radical polymerization.382 Of course, all of the features that control the outcome of a normal free-radical polymerization come into effect.40 426 429 These include the molar ratio of monomers, their relative reactivity ratios and their normal chain-transfer constants, the polymerization temperature, and the conversion. In the presence of a CCT catalyst, the important variables also include their relative CCT chain-transfer constants and the concentration of the Co chain-transfer agent. The combination of all of these features controls the molecular weight of the polymer and the nature of the vinyl end group. In addition, they can also control the degree of branching of the product. 

These dual UV/thermally curable conformal coatings are based on the ability to rapidly transform a liquid composition into a cross-linked solid by the free-radical polymerization of a polyfunctional acrylate in the presence of a low concentration of a polyfunctional thiol (1). Under these conditions, the polythiol functions partly by adding across the acrylic double bond and partly as a chain transfer agent in the acrylate homopolymeriza-... 

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