Radical atom transfer

The facile and reversible reaction of propagating species with transition metal halide complexes to form a polymeric halo-compound is one of the key steps in atom transfer radical polymerization (ATRP, see Section 9.4). 

The addition of halocarbons (RX) across alkene double bonds in a radical chain process, the Kharasch reaction (Scheme 9.29),261 has been known to organic chemistry since 1932. The overall process can be catalyzed by transition metal complexes (Mt"-X) it is then called Atom Transfer Radical Addition (ATRA) (Scheme 9.30).262... 

Scheme 9.30 Atom Transfer Radical Addition (ATRA)...

The first reports of ATRP (Atom Transfer Radical Polymerization), which clearly displayed the characteristics of living polymerization, appeared in 1995 from the Laboratories of Sawamoto,2 Matyjaszewski266 and Percec.267 The literature on ATRP is now so vast that a comprehensive review cannot be... 

Atom transfer radical copolymerization can be described by a scheme similar to that shown in Scheme 9.48 except that bimolecular activation steps must be added ( Section 9.4). Copolymerization by ATRP through 2001 has been reviewed by Kelly and Matyjaszewski.554 A summary of ATRP copolymerizalions appears in Table 9.21. 

ORl OX w di-Miutyl peroxyoxalalc deactivation by reversible chain transfer and bioinolecular aclivaiion 456 atom transfer radical polymerization 7, 250, 456,457, 458,461.486-98 deactivation by reversible coupling and untmolecular activation 455-6, 457-86 carbon-centered radical-mediated poly nierizaiion 467-70 initiators, inferlers and iriiters 457-8 metal complex-mediated radical polymerization 484... 

Polystyrene-Woc -polysulfone-/ /oc -polystyrene and poly(butyl acrylate)-Woc -polysulfone-/ /oc -poly(butyl acrylate) triblock copolymers were prepared using a macroinitiator.214 The hydroxyl-terminated polysulfone was allowed to react with 2-bromopropionyl bromide, an atomic transfer radical polymerization (ATRP) initiator, in the presence of pyridine. The modified macroinitiator could initiate die styrene polymerization under controlled conditions. 

Brzezinska KR, Deming TJ (2004) Synthesis of AB diblock copolymers by atom-transfer radical polymerization (ATRP) and living polymerization of alpha-amino acid-N-carboxyan-hydrides. Macromol Biosci 4 566—569... 

In 2003, the van Hest group produced elastin-based side-chain polymers [123]. This research was motivated by the demonstration of the occurrence of an inverse temperature transition in a single repeat of VPGVG [124]. A methacrylate-functionalized VPGVG was synthesized and used as a monomer to perform atom transfer radical polymerization (ATRP) to produce homopolymers (Fig. 16b) or... 

Star polymers are a class of polymers with interesting rheological and physical properties. The tetra-functionalized adamantane cores (adamantyls) have been employed as initiators in the atom transfer radical polymerization (ATRP) method applied to styrene and various acrylate monomers (see Fig. 21). 

Figure 21. Atom transfer radical polymerization (ATRP) synthetic route to tetrafunctional initiators of a star polymer with adamantyl (adamantane core). Taken from Ref. [91] with permission.

For SCVP of styrenic inimers, the mechanism includes cationic (14 [18], 19 [29]), atom transfer radical (15 [22, 27]), nitroxide-mediated radical (16 [21]), anionic (20 [19]), photo-initiated radical (17 [2], 18 [52-55]), and ruthenium-catalyzed coordinative (21 [56]) polymerization systems. Another example in-... 

Block copolymers were synthesized by a combination of fipase-catalyzed polymerization and atom transfer radical polymerization (ATRE). " " At first, the polymerization of 10-hydroxydecanoic acid was carried out by using lipase CA as catalyst. The terminal hydroxy group was modified by the reaction with a-bromopropionyl bromide, followed by ATRP of styrene using CuCE2,2 -bipyridine as catalyst system to give the polyester-polystyrene block copolymer. Trichloromethyl-terminated poly(e-CL), which was synthesized by lipase CA-catalyzed polymerization with 2,2,2-trichloroethanol initiator, was used as initiator for ATRP of styrene. 

Abstract Over the past decade significant advances have been made in the fields of polymerisation, oligomerisation and telomerisation with metal-NHC catalysts. Complexes from across the transition series, as well as lanthanide examples, have been employed as catalysts for these reactions. Recent developments in the use of metal-NHC complexes in a-olefin polymerisation and oligomerisation, CO/olefm copolymerisation, atom-transfer radical polymerisation (ATRP) and diene telomerisation are discnssed in subsequent sections. 

There are a number of reports of NHC complexes of mid-late transition metals being used as catalysts for atom transfer radical polymerisation (ATRP) of acrylates and styrene. Grubbs reported Fe(II) complexes of a simple monodentate carbene. 

Pyun, J., Kowalewski, T. and Matyjaszewski, K. (2003) Synthesis of polymer brushes using atom transfer radical polymerization. Macromol. Rapid Commun., 24, 1043-1059. 

Ejaz, M., Yamamoto, S., Ohno, K., Tsujii, Y. and Fukuda, T. (1998) Controlled graft polymerization of methyl methacrylate on silicon substrate by the combined use of the Langmuir-Blodgett and atom transfer radical polymerization techniques. Macromolecules, 31, 5934-5936. 

Radical addition to alkenes has been used in cyclizations in aqueous media. Oshima and co-worker studied triethylborane-induced atom-transfer radical cyclization of iodoacetals and iodoacetates in water.121 Radical cyclization of the iodoacetal proceeded smoothly both in aqueous methanol and in water. Atom-transfer radical cyclization of allyl iodoacetate is much more efficient in water than in benzene or hexane. For instance, treatment of allyl iodoacetate with triethylborane in benzene or hexane at room temperature did not yield the desired lactone. In contrast, the compound cyclized much more smoothly in water and yielded the corresponding y-lactone in high yield (Eq. 3.31). 

Scheme 3.32. Products and mechanism of an iodine atom transfer radical domino reaction.

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