Controlled radical polymerization RAFT

A synthesis of poly-A -vinylindole derivatives has also been reported using xanthate-mediated controlled radical polymerization (RAFT polymerization)... 

Example 3.15b Controlled Radical Polymerization (RAFT) of Trimethylsilylpropargyl Methacrylate and Subsequent Polymer Analogous Click Reaction... 

A major application is the synthesis of high molecular weight water-soluble polymers (e.g., polymers and copolymers of acrylamide, acrylic acid, and its salts) for flocculants and tertiary oil recovery. Other uses are the synthesis of polyaniline/CdSe quantum dots composites [49], hybrid polyaniline/carbon nanotube nanocomposites [50], polyani-line-montmorillonite nanocomposites [51], or in reversible addition-fragmentation chain-transfer-controlled radical polymerization (RAFT) [52]. 

Use of a monohydroxy PDMA maaoinitiator to initiate the TU-amino-catalyzed ROP of LA allowed the authors to prepare PDMA-b-PLA diblock copolymers (Scheme 17). Double-headed initiators were also used for the purpose of block copolymer synthesis, by combining controlled radical polymerization (RAFT or NMP) and organocatalysis by TUs. 

Does not distinguish forms of controlled radical polymerization. Includes most papers on ATR.P, RAFT and NMP and would also include conventional (non-living) but controlled radical polymerizations. It would not include papers, which do not mention the terms living , controlled or mediated . 

It remains a common misconception that radical-radical termination is suppressed in processes such as NMP or ATRP. Another issue, in many people s minds, is whether processes that involve an irreversible termination step, even as a minor side reaction, should be called living. Living radical polymerization appears to be an oxymoron and the heading to this section a contradiction in terms (Section 9.1.1). In any processes that involve propagating radicals, there will be a finite rate of termination commensurate with the concentration of propagating radicals and the reaction conditions. The processes that fall under the heading of living or controlled radical polymerization (e.g. NMP, ATRP, RAFT) provide no exceptions. 

The preparation of polymer brushes by controlled radical polymerization from appropriately functionalized polymer chains, surfaces or particles by a grafting from approach has recently attracted a lot of attention.742 743 The advantages of growing a polymer brush directly on a surface include well-defined grafts, when the polymerization kinetics exhibit living character, and stability due to covalent attachment of the polymer chains to the surface. Most work has used ATRP or NMP, though papers on the use of RAFT polymerization in this context also have begun to appear. 

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. 

The need to better control surface-initiated polymerization recently led to the development of controlled radical polymerization techniques. The trick is to keep the concentration of free radicals low in order to decrease the number of side reactions. This is achieved by introducing a dormant species in equilibrium with the active free radical. Important reactions are the living radical polymerization with 2,2,4,4-methylpiperidine N-oxide (TEMPO) [439], reversible addition fragment chain transfer (RAFT) which utilizes so-called iniferters (a word formed from initiator, chain transfer and terminator) [440], and atom transfer radical polymerization (ATRP) [441-443]. The latter forms radicals by added metal complexes as copper halogenides which exhibit reversible reduction-oxidation processes. 

Controlled radical polymerization (CRP) is an attractive tool, because of the resultant controllability of polymerization, and because of it being a versatile method to synthesize of well-defined polymer hybrids. The three main radical polymerization techniques, ATRP, NMP, and RAFT polymerization, have thus been employed. Other techniques, such as the oxidation of borane groups, have also been studied. In general, using CRP techniques, block copolymers can be synthesized from terminally functionalized PO as PO macroinitiator, and block copolymers can be prepared from functionalized PO produced by the copolymerization of olefins with functional monomers. 

Matyjaszewski K (ed) (2000) Controlled/Living Radical Polymerization. Progress in ATRP, NMP, and RAFT. Proceedings of a Symposium on Controlled Radical Polymerization 768 484... 

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-... 

The first step for the core-first stars is the synthesis of multifunctional initiators. Since it is difficult to prepare initiators that tolerate the conditions of ionic polymerization, mostly the initiators are designed for controlled radical polymerization. Calixarenes [39, 58-61], sugars (glucose, saccharose, or cyclodextrins) [62-68], and silsesquioxane NPs [28, 69] have been employed as cores for various star polymers. For the growth of the arms, mostly controlled radical polymerizations were used. There are only very rare cases of stars made from nitroxide-mediated radical polymerization (NMRP) [70] or reversible addition-fragmentation chain transfer (RAFT) techniques [71,72], In the RAFT technique one has to differentiate between approaches where the chain transfer agent is attached by its R- or Z-function. ATRP is the most frequently used technique to build various star polymers [27, 28],... 

Controlled Radical Polymerization (CRP) is the most recently developed polymerization technology for the preparation of well defined functional materials. Three recently developed CRP processes are based upon forming a dynamic equilibrium between active and dormant species that provides a slower more controlled chain growth than conventional radical polymerization. Nitroxide Mediated Polymerization (NMP), Atom Transfer Radical Polymerization (ATRP) and Reversible Addition Fragmentation Transfer (RAFT) have been developed, and improved, over the past two decades, to provide control over radical polymerization processes. This chapter discusses the patents issued on ATRP initiation procedures, new functional materials prepared by CRP, and discusses recent improvements in all three CRP processes. However the ultimate measure of success for any CRP system is the preparation of conunercially viable products using acceptable economical manufacturing procedures. 

In any processes that involve propagating radicals, there will be a finite rate of termination commensurate with the concentration of propagating radicals and the reaction conditions. The processes that fall under the heading of living or controlled radical polymerization (e.g. NMP, ATRP, RAFT) provide no exceptions. 

Figure 4.1 Controlled radical polymerization mechanisms via (a) NMRP, (b) ATRP, and (c) RAFT.

Within the field of radical polymerization, special attention was recently drawn to the use of microreactors for controlled radical polymerization techniques, namely, ATRP, NMRP and RAFT. Shen and Zhu [126] have devised a column reactor packed with silica-gel-supported copper bromide-hexamethyltriethylenetetramine (HMTETA) for the continuous ATRP of homo- and block copolymers of MMA. Wu et al. [127] report the use of microfluidic chips made from thiolene polymer for continuous ATRP of... 

Using NMP [114, 115] or reversible addition-fragmentation chain transfer (RAFT) [ 119,120,127], agents with ammonium groups for the ion exchange allowed the attachment of initiators on the clay surface for controlled radical polymerizations (NMP, RAFT). Samakande et al. investigated the kinetics of RAFT-mediated living polymerization of styrene [120] and styrene/BA [119] mixtures in miniemulsion. 

The advent of controlled radical polymerization methods, such as ATRP, RAFT, and NMP, has allowed for a wide variety of new block and graft polymers to be prepared due to the chemical variety of monomers which can be polymerized by these methods (Matyjaszewski and Tsarevsky, 2009 Matyjaszewski and Braunecker, 2007). Block copolymers can be polymerized by sequential monomer addition, but more often the first block is synthesized, isolated, and... 

Besides the ATRP method, other controlled radical polymerization techniques such as reversible addition/fragmentation chain transfer polymerization (RAFT) (Zhang et al., 2007) and nitroxide-mediated polymerization (NMP) (Yoshida and Ohta, 2005), have also been explored to synthesize azo BCs. 

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