Atom-transfer Radical Polymerization ATRP

Among all LRP methods, ATRP is the most studied and since 1995, when it was rst reported, a very large number of articles have appeared on this topic. An excellent review written by the pioneer in the eld, Matyjaszewski (Matyjaszewski and Xia, 2001) covers the development in ATRP from 1995 till the end of 2000. ATRP can provide extraordinary control over topologies, compositions, microstructures, and functionahties. This has led to the production of a vast array of polymeric materials with application in nanocomposites, thermoplastic elastomers, bioconjugates, drug dehvery systems, etc. 

ATRP is an extension of atom transfer radical addition (ATRA), which is a well-known method of carbon-carbon bond formation (catalyzed by transition metal complexes) in organic synthesis. ATRP also has roots in the transition metal catalyzed telomerization reactions (Boutevin, 

2000) and connections to the transition metal iiutiated redox processes as well as inhibition with transition metal compoimds (Qin and Matyjaszewski, 1997). ATRP was developed by designing an appropriate catalyst (transition metal compound and ligands), using an initiator with the suitable structure, and adjusting the polymerization conditions such that the molecular weights increased linearly with conversion and the polydispersities were typical of a living process (Matyjaszewski andXia, 2001). 

2001) and irreversible termination of propagating free radicals is statistically suppressed to give polymer synthesized via ATRP its living nature (Chan et al., 2010). (Typically, no more than 5% of the total growing polymer ehains imdergo irreversible termination during the initial, short. 

Problem 11,6 Styrene (St) was polymerized by ATRP using a copper(I) bromide (CuBr) catalyst, com-plexed with A, A, A, A, iV -pentamethyldiethylenetriamine (PMDETA) ligand, and methyl 2-bromopropion-ate (MBrP) as initiator. Experiments were performed in 1 E mixed vessel at 110°C with excellent temperature control using a monomer to solvent (toluene) ratio of 70 30 wt% and molar ratios of 50 1 1 1 for St/MBrP/CuBr/PMDETA. Under these reaction conditions, only a portion of the catalyst species was soluble and 90% monomer conversion was obtained in 6 h. Calculate a theoretical molecular weight (MW) of the polymer obtained. How would you explain if the experimental MW is found to be higher than the theoretical 

Atom transfer radical polymerization (ATRP) is based on the well-established method of carbon-carbon bond formation by atom transfer radical addition used in organic synthesis. 

A successful ATRP reaction depends on the reversible activation of a dormant species, such as an alkyl halide (R—X), by a transition metal halide catalyst (MpY/L). The metal halide catalyst abstracts the halogen atom (X) from the dormant species to 

the catalyst is a complex of Cu(I)Cl and the ligand 2,2 bipyridyl. This abstracts chlorine from an alkyl halide such as 1-phenyl ethyl chloride, and a reversible redox process is established where the Cu(II)Cl2/(2bipy) spedes acts as the persistent or mediating radical shown in Equation 3.32. 

ATRP reactions are very versatile with a high tolerance toward the presence of functional groups, such as the allyl, amino, epoxy, hydroxy, and vinyl groups, on both monomer and initiator. The reactions can be carried out either in bulk or in solution and also in heterogeneous systems. If solvents are used, chain transfer to solvent should be low, but the effect on the catalyst must be considraed. 

A l RP methods are successful when monomers such as styimes, (meth)acrylates, (meth)acrylamides, and acrylonitrile are used but arc less useful for monomers containing add groups. 

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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). 

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.

Novel catalytic systems, initially used for atom transfer radical additions in organic chemistry, have been employed in polymer science and referred to as atom transfer radical polymerization, ATRP [62-65]. Among the different systems developed, two have been widely used. The first involves the use of ruthenium catalysts [e.g. RuCl2(PPh3)2] in the presence of CC14 as the initiator and aluminum alkoxides as the activators. The second employs the catalytic system CuX/bpy (X = halogen) in the presence of alkyl halides as the initiators. Bpy is a 4,4/-dialkyl-substituted bipyridine, which acts as the catalyst s ligand. 

Synthesis of Block Copolymers by Atom Transfer Radical Polymerization, ATRP... 

Atom transfer radical polymerization, ATRP, is a controlled radical process which affords polymers of narrow molecular weight distributions. Strictly this is not a coordinative polymerization, but its dependency upon suitable coordination complexes warrants a brief discussion here. 

Acrylate monomers may also be polymerized by atom transfer radical polymerization (ATRP). The reader is referred to Section 9.1.3.3 for an overview of catalyst systems. 

Abstract During the past decade, atom transfer radical polymerization (ATRP) has had a tremendous impact on the synthesis of macromolecules with well-defined compositions, architectures, and functionalities. Structural features of copper and copper(II) complexes with bidentate, tridentate, tetradentate, and multidentate nitrogen-based ligands commonly utilized in ATRP are reviewed and discussed. Additionally, recent advances in mechanistic understanding of copper-mediated ATRP are outlined. 

In 1995, a new class of controlled/ living radical polymerization methods was reported by the groups of Matyjaszewski [34] and Sawamoto [35], This new process, named atom transfer radical polymerization (ATRP) [34], has had a tremendous... 

Over the past decade, copper-catalyzed atom transfer radical polymerization (ATRP) has had a tremendous impact on the synthesis of macromolecules with well-defined architectures, functionalities, and compositions. Structural and mechanistic... 

Matyjaszewski et al. [281-285] succeeded in the synthesis of poly(St) with a narrow molecular weight distribution, comparable to the living anionic polymerization, in the atom transfer radical polymerization (ATRP) using Cu complex and alkyl halides (Eq. 74) ... 

P. Zhou, G. Q. Chen, C. Z. Li, F. S. Du, Z. C. Li, F. M. Li, Synthesis of hammerlike macromolecules of C60 with well-defined polystyrene chains via atom transfer radical polymerization (ATRP) using a C60-monoadduct initiator, Chemical Communications, pp. 797-798, 2000. 

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. 

In this review, synthesis of block copolymer brushes will be Hmited to the grafting-from method. Hussemann and coworkers [35] were one of the first groups to report copolymer brushes. They prepared the brushes on siUcate substrates using surface-initiated TEMPO-mediated radical polymerization. However, the copolymer brushes were not diblock copolymer brushes in a strict definition. The first block was PS, while the second block was a 1 1 random copolymer of styrene/MMA. Another early report was that of Maty-jaszewski and coworkers [36] who reported the synthesis of poly(styrene-h-ferf-butyl acrylate) brushes by atom transfer radical polymerization (ATRP). 

Ruthenium(II)-NHC systems ean be used for atom transfer radical polymerization (ATRP). Generally, similar results as for the analogous phosphine complexes are obtained. For the ATRP of styrene and methyl methacrylate (MMA) [(NHC)2peBr2] was found to rival copper(I)-based systems and to yield poly (MMA) with low polydispersities. Polymerizations based on olefin metathesis that are catalyzed by ruthenium-NHC complexes are discussed separately vide supra). 

Dynamic formation of graft polymers was synthesized by means of the radical crossover reaction of alkoxyamines by using the complementarity between nitroxide radical and styryl radical (Fig. 8.13) [40]. Copolymer 48 having alkoxyamine units on its side chain was synthesized via atom transfer radical polymerization (ATRP) of TEMPO-based alkoxyamine monomer 47 and MMA at 50°C (Scheme 8.9). The TEMPO-based alkoxyamine-terminated polystyrene 49 was prepared through the conventional nitroxide-mediated free radical polymerization (NMP) procedure [5,41], The mixture of copolymers 48 and 49 was heated in anisole... 

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