Direct ATRP

1 Control of molar mass and molar mass distribution 

Statistical copolymers were prepared via direct ATRP in aqueous dispersed systems, in a similar manner to the synthesis of the corresponding homopolymers (Matyjaszewski et al. 

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So far, the grafting from strategy has proven to be the most successful one for the preparation of cylindrical brushes. Both anionic [30, 31, 142, 143] and cationic [29] polyelectrolyte cylindrical brushes with well-defined backbones and side chains were prepared. We have also prepared core-shell brushes with PAA as the core or shell, which will be discussed later [30, 31], Recently we have been able to prepare strong anionic brushes with sulfonate groups by direct ATRP of ionic monomers in organic solvent [144],... 

The control of the polymerization reaction afforded by ATRP is the result of the formation of dormant alkyl (pseudo)halides. This reduces the instantaneous concentration of the active radicals and thereby suppresses bimolecular termination reactions. The reversible deactivation and activation leads to a slow, but steady growth of the polymer chain with a well defined end group (Scheme 27). Control and properties of the synthesized polymers depend on the stationary concentration of active radicals and the relative rates of propagation and deactivation. When one or less than one monomer unit is incorporated into the polymer chain during one activation step, the polymerization is well controlled. The ATRP equilibrium can be approached from both directions in Scheme 27. Beginning with an alkyl halide and the lower valent metal complex, the process is called direct ATRP. If a conventional thermal initiator like AIBN and the higher valent metal complex are the starting materials, the polymerization process is named reverse ATRP [287]. 

Living polymerization in water also led to polymers with a relatively narrow molecular mass distribution (1.1-1.3) and molecular masses, which showed linear increase with conversion, indicating the living character of this polymerization [320]. Recently, Matyjaszewski et al. reported both reverse and direct ATRP of n-butyl methacrylate in an aqueous dispersed system via the miniemulsion approach, characterized by a linear increase of the molecular mass with conversion and a narrow distribution of molecular masses [321]. The suspension-type process of living polymerization of MMA in water not only led to well controlled and high molecular masses and low PDIs, but also the polymerization proceeded without the addition of Al(0-i-Pr)3 and clearly faster than ATRP in organic solvents [322]. 

Experiments have been described where a combination of direct and reverse ATRP is used.290 In this case eq. 12 should apply. 

A side reaction in NMP is loss of nilroxide functionality by thermal elimination. This may occur by disproportionation of the propagating radical with nitroxide or direct elimination of hydroxy lam ine as discussed in Section 9.3.6.3. In the case of methacrylate polymerization this leaves an unsaturated end group.1" The chemistry has also been used to prepare macromonomers from PMMA prepared by ATRP (Section 9.7.2.1),... 

I he method of polymerization needs to be chosen for compatibility with functionality in the cores and the monomers to be used. Star block copolymers have also been reported. Mulli(bromo-compounds) may be used directly as ATRP initiators or they can be converted to RAFT agents. One of the most common... 

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. 

Grafting from silica particles, silicon wafers, and related surfaces usually involves attaching a chlorosilanc or alkoxysilane derivative. Thus alkoxyamincs (e.g, 361,744,749 3627 0) and a wide variety of ATRP initiators (e.g. 363751) have been attached directly to surfaces and used to initiate grafting from" processes. 

The direct determination of DB for hyperbranched methacrylates obtained by SCVP of 9 and 10 via ATRP was reported to be impossible due to overlapping signals in the NMR spectra [47]. However, DB of some hyperbranched methacry-... 

The direct synthesis of poly(3-sulfopropyl methacrylate)-fr-PMMA, PSP-MA-fr-PMMA (Scheme 27) without the use of protecting chemistry, by sequential monomer addition and ATRP techniques was achieved [77]. A water/DMF 40/60 mixture was used to ensure the homogeneous polymerization of both monomers. CuCl/bipy was the catalytic system used, leading to quantitative conversion and narrow molecular weight distribution. In another approach the PSPMA macroinitiator was isolated by stopping the polymerization at a conversion of 83%. Then using a 40/60 water/DMF mixture MMA was polymerized to give the desired block copolymer. In this case no residual SPMA monomer was present before the polymerization of MMA. The micellar properties of these amphiphilic copolymers were examined. 

Like all controlled radical polymerization processes, ATRP relies on a rapid equilibration between a very small concentration of active radical sites and a much larger concentration of dormant species, in order to reduce the potential for bimolecular termination (Scheme 3). The radicals are generated via a reversible process catalyzed by a transition metal complex with a suitable redox manifold. An organic initiator (many initiators have been used but halides are the most common), homolytically transfers its halogen atom to the metal center, thereby raising its oxidation state. The radical species thus formed may then undergo addition to one or more vinyl monomer units before the halide is transferred back from the metal. The reader is directed to several comprehensive reviews of this field for more detailed information. 

In order to produce block copolymer brushes by ATRP directly from the surface, the ATRP initiator, (ll-(2-bromo-2-methyl)propionyloxy)imdecyltri-... 

Zhang HQ, Marin V, Fijten MWM et al. (2004) High-throughput experimentation in ATRP a general approach toward a directed design and understanding of optimal catalytic systems. J Polym Sci Part A Polym Chem 42 1876-1885... 

In principle, aqueous ATRP offers the tantalising possibility of the direct synthesis of reasonably well-defined zwitterionic block copolymers in water without recourse to protecting group chemistry. However, ATRP in acidic media is generally unprofitable, hence the (co)polymerisation of acidic monomers such as methacrylic acid or 4-vinylbenzoic acid must be carried out in weakly alkaline solution, i.e. the monomer should be in its anionic carboxylate... 

Owing to the simphcity and versatility of surface-initiated ATRP, the above-mentioned AuNP work may be extended to other particles for their two- or three-dimensionally ordered assemblies with a wide controllabiUty of lattice parameters. In fact, a dispersion of monodisperse SiPs coated with high-density PMMA brushes showed an iridescent color, in organic solvents (e.g., toluene), suggesting the formation of a colloidal crystal [108]. To clarify this phenomenon, the direct observation of the concentrated dispersion of a rhodamine-labeled SiP coated with a high-density polymer brush was carried out by confocal laser scanning microscopy. As shown in Fig. 23, the experiment revealed that the hybrid particles formed a wide range of three-dimensional array with a periodic structure. This will open up a new route to the fabrication of colloidal crystals. 

Matyjaszewski [83] and Sawamoto [84] have found that a-halo ester chain ends can be used to generate radical ends reversibly by treatment with copper complexes or RuCl2/MeAl(ODBP)2 (ODBP=ortho-di-terf-butylphenoxy) (Scheme 33a,b). In his early work Sawamoto used carbon tetrachloride as initiator and Matyjaszewski, a-halo esters. Percec [85, 86] discovered that sulfonyl chlorides provided advantages over the other initiators and has used these initiators extensively in his research (Scheme 33c). ATRP has been fine-tuned by the three groups. The reader is directed to reviews by Matyjaszewski [87] and by Sawamoto [88]. 

As mentioned above, in both NMP and ATRP the exchange between the active and the dormant states is based on a reversible (although different) termination mechanism. Therefore, the exchange directly affects the radical concentration. In LRP by degenerative transfer, instead, this exchange is carried out by direct transfer of the w-end group between an active and a dormant chain. When an iodine atom is used as end group, the reaction can be expressed as follows ... 

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