Living radical polymerization. See

Metal-catalyzed living or controlled radical polymerizations can generally be achieved with initiating systems consisting of an organic halide as an initiator and a metal complex as a catalyst or an activator as described above. However, these polymerizations are slow in most cases due to low concentration of the radical species, as required by the general principle, the dormant-active species equilibria, for living radical polymerization (see the Introduction). 

For a recent review of transition-metal catalyzed living radical polymerization, see Ouchi, M. Terashima, T. Sawamoto, M. Chem. Rev. 2009,109, 4963. 

Unsymmetrical azo-compounds find application as initiators of polymerization in special circumstances, for example, as initiators of living radical polymerization [e.g. triphenylmethylazobenzene (30) (see 9.3.4)], as hydroxy radical sources [e.g. a-hydroperoxydiazene (31) (see 3.3.3,1)1, for enhanced solubility in organic solvents [e.g. f-butylazocyclohexanecarbonitrile (32)J, or as high temperature initiators [e.g. t-butylazoformamide (33)]. They have also been used as radical precursors in model studies of cross-termination in copolymerization (Section... 

Similarly, it was also found that radical polymerization was induced in the Ni(CO)3(PPh3)/CBrCl3 redox system [155]. This complex is soluble in the polymerization medium, and the polymerization proceeded in a homogeneous system. This redox iniferter system has been intensively developed to the recent successful living radical polymerization using transition-metal complexes in combination with alkyl halides by several independent research groups (see Sect. 6.2). 

Abstract. Water-soluble polymers of acrylamide and acrylic acid with high extent ( 90%) of Ceo consumption are obtained by technique of low-temperature radiation living radical polymerization. In absorption spectra of these copolymers one can see gradually descended unstructured absorption in the range 240-700 mn, characteristic for fullerene covalent-bound or its klasters. The way of radiation initiation is used to obtain the products of high purity, because it is not necessary to embed into the system any initiators or catalyst. Latter is very important in the case of synthesis of polymers for medical purposes. Also at radiation initiation a rate of initiation reaction does not depend on the temperature and the sterilization of products takes place simultaneously. 

Radical 12 is rather stable under polymerization conditions, but radical 11 decays into a triazole and the phenyl radical, which initiates new chains. Hence, the rate of polymerization is higher with 11 than with 12, because the decay prevents retarding of the buildup of large persistent radical concentrations such as an additional radical generation. This effect of the radical decay is equivalent to the rate enhancement by partial removal of nitroxides by appropriate additives, which was first applied by Georges et al.31 Interestingly, at 95 °C and in toluene solution, the lifetime of 11 is only about 15 min, whereas a reasonable control was found in polymerizations of styrene that lasted many hours at 120— 140 °C.120 Obviously, the radical moiety 11 is stable while it is coupled to the polymer chain. However, the different time scales raise the question of the upper limit of the conversion rate of the persistent radical to a transient one that can be tolerated in living radical polymerization processes (see section IV. C). 

In this reaction, one polymer chain forms per molecule of the organic halide (initiator), while the metal complex serves as a catalyst or as an activator, which catalytically activates, or homolytically cleaves, the carbon—halogen terminal. Therefore, the initiating systems for the metal-catalyzed living radical polymerization consist of an initiator and a metal catalyst. The effective metal complexes include various late transition metals such as ruthenium, copper, iron, nickel, etc., while the initiators are haloesters, (haloalkyl)benzenes, sulfonyl halides, etc. (see below). They can control the polymerizations of various monomers including methacrylates, acrylates, styrenes, etc., most of which are radically polymerizable conjugated monomers. More detailed discussion will be found in the following sections of this paper for the scope and criteria of these components (initiators, metal catalysts, monomers, etc.). 

For a review on the inevitability of termination in these living-radical polymerization systems see K. Matyjaszewski, S. Gaynor, D. Greszta, D. Mardare, T. Shigemoto, J. Phy. Org. Chem. 1996, 8, 306. 

ATOMIC FORCE MICROSCOPY. See Volume 1. ATRP. See Living Radical Polymerization. 

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