Degenerative chain transfer technique

These methods are based on the idea of establishing equilibrium between the active and dormant species in solution phase. In particular, the methods include three major techniques called stable free-radical polymerization (SFRP), atom transfer radical polymerization (ATRP), and the degenerative chain transfer technique (DCTT) [17]. Although such syntheses pose significant technical problems, these difficulties have all been successively overcome in the last few years. Nevertheless, the procedure of preparation of the resulting copolymers remains somewhat complicated. 

Several studies reported the successful application of reversible chain transfer techniques in water-borne systems. All of these studies apply RCTA species with low Qx constants to control the polymerisation. The alkyl iodides (degenerative transfer) used by several groups (Lansalot et aL, 1999 Butte et al., 2000) have a transfer constant only shghtly higher than unity. The ab initio emulsion polymerisation of styrene using CsFbI was carried out at 70°C (Lansalot et aL, 1999). It was found that the rate of polymerisation was not affected by the presence of CeFial. However, the evolution of Mn with conversion was not in accord with the Qx value. The authors postulated that due to the hydrophobic character of CsFbI, its transfer from droplets to particles was slower than the rate of consumption of CeF I within the particles. To overcome slow diffusion of CsFbI to the particles, the authors carried out miniemulsion (essentially Interval III kinetics), in which polymerisation takes... 

This technique for controlling radical polymerizations is based on one of the oldest technique, that of chain transfer, and has often been used in telomeriza-tion [83]. Similar to the concept of degenerative transfer with alkyl iodides [50, 51, 84], reversible addition fragmentation chain transfer with dithio esters (RAFT) [52-55, 85] is successful because the rate constant of chain transfer is faster than the rate constant of propagation. Analogous to both nitroxide-medi-... 

VAc has been successfully polymerized via controlled/ living radical polymerization techniques including nitroxide-mediated polymerization, organometallic-mediated polymerization, iodine-degenerative transfer polymerization, reversible radical addition-fragmentation chain transfer polymerization, and atom transfer radical polymerization. These methods can be used to prepare well-defined various polymer architectures based on PVAc and poly(vinyl alcohol). The copper halide/t is an active ATRP catalyst for VAc, providing a facile synthesis of PVAc and its block copolymers. Further developments of this catalyst will be the improvements of catalytic efficiency and polymerization control. 

Controlled radical polymerization techniques are suitable for synthesizing polymers with a high level of architectural control. Notably, they not only allow a copolymerization with functional monomers (as shown previously for free-radical polymerization), but also a simple functionalization of the chain end by the initiator. Miniemulsion systems were found suitable for conducting controlled radical polymerizations [58-61], including atom transfer radical polymerization (ATRP), RAFT, degenerative iodine transfer [58], and nitroxide-mediated polymerization (NMP). Recently, the details of ATRP in miniemulsion were described in several reviews [62, 63], while the kinetics of RAFT polymerization in miniemulsion was discussed by Tobita [64]. Consequently, no detailed descriptions of the process wiU be provided at this point. 

ATRP), and reversible chain transfer catalyzed polymerizations " and (iii) degenerative transfer-based polymerization (with reversible addition-fragmentation chain transfer (RAFT) polymerization being the most successful technique but also including iodine-mediated polymerizations and polymerizations in the presence of tellurium or antimony compounds ). Most of these techniques are covered in detail in other chapters of this book. 

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