Reversible addition-fragmentation chain transfer radical polymerization

Synthesis of Block Copolymers by Reversible Addition-Fragmentation Chain Transfer Radical Polymerization, RAFT... 

Fig. 26 Continuous flow reactor for the reversible addition-fragmentation chain transfer radical polymerization. M micromixer, R microtube reactor...

Reversible Addition-Fragmentation Chain Transfer Radical Polymerization... 

Several LRP methods have been developed to achieve efficient aaivation/deaaivation reactions to control macromo-lecular stmcture of the resulting polymers. LRPs that have been widely used include nitroxide-mediated radical polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer radical polymerization (RAFT). " Organotellurium-,... 

While in most of the reports on SIP free radical polymerization is utihzed, the restricted synthetic possibihties and lack of control of the polymerization in terms of the achievable variation of the polymer brush architecture limited its use. The alternatives for the preparation of weU-defined brush systems were hving ionic polymerizations. Recently, controlled radical polymerization techniques has been developed and almost immediately apphed in SIP to prepare stracturally weU-de-fined brush systems. This includes living radical polymerization using nitroxide species such as 2,2,6,6-tetramethyl-4-piperidin-l-oxyl (TEMPO) [285], reversible addition fragmentation chain transfer (RAFT) polymerization mainly utilizing dithio-carbamates as iniferters (iniferter describes a molecule that functions as an initiator, chain transfer agent and terminator during polymerization) [286], as well as atom transfer radical polymerization (ATRP) were the free radical is formed by a reversible reduction-oxidation process of added metal complexes [287]. All techniques rely on the principle to drastically reduce the number of free radicals by the formation of a dormant species in equilibrium to an active free radical. By this the characteristic side reactions of free radicals are effectively suppressed. 

Reversible addition-fragmentation chain transfer (RAFT) polymerization using 2,2 -azobisisobutyronitrile and either A, A-dimethyl-5-thiobenzoylthiopropionamide or A-dimethyl-5-thiobenzoylthioacetamide as chain transfer agents has been used to prepare low polydispersity poly(A, A-dimethylacrylamide). The chain transfer agents were unusually effective in suppressing free radical termination reaction, thereby mimicking a living polymerization reaction. 

MAYADUNNE R.T.A., RIZZARDO E., CHIEF ARI J., CHONG Y.K., MOAD G., THANG S.H., Living radical polymerization with reversible addition-fragmentation chain transfer (RAFT polymerization) using dithiocarbamates as chain transfer agent. Macromolecules, (1999), 32 (21), 6977-80. 

Chong, Y.K., Krstina, J., Le, T.P.T., et al., 2003. Thiocarbonylthio compounds [Sc(Ph)S-R] in free radical polymerization with reversible addition-fragmentation chain transfer (RAFT polymerization). Role of the free-radical leaving group (R). Macromolecules 36 (7), 2256-2272. 

CRP provides a versatile route for the preparation of (co) polymers with controlled molecular weight, narrow molecular weight distribution (i.e., Mw/Mn, or PDI < 1.5), designed architectures, and useful end-functionalities. Various methods for CRP have been developed however, the most successful techniques include ATRP, stable free radical polymerization, " and reversible addition fragmentation chain transfer (RAFT) polymerization. " " CRP techniques have been explored for the synthesis of gels " " and cross-linked nanoparticles of well-controlled polymers in the presence of cross-linkers. 

Anionic and later cationic pol3Tnerization gave most of examples of living pol3rmerization systems until recently, when more sophisticated methods of manipulation with free-radical polymerization processes become available. These methods are based on the use of the compounds which reversibly react with propagating radical and convert it to the so-called dormant species . When the equilibrium between the active and dormant species is regulated by special catalysts based on a transition metal, this process is called atom transfer radical polymerization (ATRP). If this equilibrium is provided by stable radicals such as nitroxides, the process is called stable free-radical polymerization (SFRP). In the case when dormant species are formed via a chain transfer rather than reversible termination reactions, this process is referred to as reversible addition fragmentation chain transfer (RAFT) polymerization. All these techniques allow to produce macromolecules of desired architecture and molecular masses. 

In this review, the term macromer is used to describe oligomer or polymer precursors that undergo reversible association to form supramolecular polymers or networks. Macromer synthesis, although a crucial aspect of supramolecular science, is also out of the scope of this review. Several comprehensive reviews of the synthesis of H-bonding polymers are available [10, 11,42] and primarily describe the application of controlled radical polymerization techniques, including atom-transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP). For synthesis of telechelic polymers, avoiding monofunctional impurities that can act as chain stoppers is crucially important [43],... 

SCHEME 9.2 Main control equilibria in atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated pol3fmerization (NMP). 

Brouwer, H. De, Schellekens, M. A. Klumperman, B., Monteiro, M. J., and German, A. L. 2000. Controlled radical copolymerization of styrene and maleic anhydride and the synthesis of novel polyolefin-based block copolymers by reversible addition-fragmentation chain-transfer (RAFT) polymerization. Journal of Polymer Science, Part A Polymer Chemistry 38 3596-3603. 

In the presence of Ge and Sn iodides, Rp was somewhat smaller than in their absence (Tables 1 and 2). This is because Ge and Sn radicals (A ) undergo irreversible crosstermination with P (rate constant k/) and irreversible self-termination between A (rate constant k/ ). This mechanism is analogous to the one for the rate retardation in reversible addition-fragmentation chain transfer (RAFT) polymerization. ... 

Reversible addition-fragmentation chain transfer (RAFT) polymerization has been one of the most promising recent advances in the controlled free radical poljmerization (CRP) technique for both the homogeneous and heterogeneous sys-tem.P The mechanism of the RAFT has been established by a dynamic equihbrium between the active and the dormant spedes.f Although RAFT polymerizations were well developed in the heterogeneous media via emulsion,minie-mulsion and ab initio emulsion polymerization, RAFT emulsion polymer-... 

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