Controlled/living radical polymerizations styrene

The use of several diorganyl tellurides as initiators for controlled living radical polymerization of styrenes has been investigated. " ... 

Controlled living radical polymerization of CD-complexed styrene in water can be conducted via the RAFT process, especially at low conversion (<20%). The molecular weight of PS can be controlled by variation of the RAFT agent concentration and the number-average molecular weight increases linearly with conversion (Fig. 29). 

Initiators for the controlled living radical polymerization could also be introduced to silica particles. Nitroxide-mediated polymerization (NMP) conducted with styrene in miniemulsion led to the generation of core-shell particles, with styrene grafted to the central silica particle [131]. PBA could be polymerized from 20 nm silica beads by attaching an ATRP agent to the silica surface and subsequent miniemulsion polymerization [132]. Confining the polymerization to miniemulsion droplets could avoid gel formation, which was observed in the bulk reaction. Due to the limited monomer diffusion, only 25-35% of conversion could be obtained in bulk. 

In a similar manner, Yoshida and Osagawa [436] synthesized poly(s-caprolactone) with 2,2,6,6-tetramethylpiperdine-l-oxyl (TEMPO) at one end by anionic polymerization of caprolactone using an aluminum tri(4-oxy-TEMPO) initiator. The TEMPO-supported polycaprolactone behaved as a polymeric counter radical for a controlled/ living radical polymerization of styrene to form block copolymers [436]. 

Matyjaszewski, K. Wei, M. Xia, J. McDermott, N. E. Controlled/ living radical polymerization of styrene and methyl methacrylate catalyzed by iron complexes. Macromolecules 1997, 30, 8161-8164. 

Matyjaszewski, K., Patten, T. E., and Xia, J. (1997). Controlled/ living radical polymerization. Kinetics of the homogeneous atom transfer radical pol5merization of styrene. J. Am. Chem. Soc., 119(A) 674-680. 

Greszta, D., and Matyjaszewski, K. (1996). Mechanism of controlled/ living radical polymerization of styrene in the presence of nitroxyl radicals. Kinetics and simulations. Macromolecules, 29(24) 7661-7670. 

Burguiere, C., et al. (2001). Block copol5miers of poly(styrene) and poly(acrylic acid) of various molar masses, topologies, and compositions prepared via controlled/living radical polymerization. Application as stabilizers in emulsion polymerization. Macromolecules, 54(13) 4439 450. 

However, while controlled/living radical polymerizations (C/LRPs) have lately undergone remarkable developments [2-6], and atom transfer, nitroxide or addition-fragmentation methods [2] have proven quite successful for acrylates or styrenes. 

KOU 08] Koumura K., Satoh K., Kamigaito M., Manganese-Based controlled/living radical polymerization of vinyl acetate, methyl aciylate, and styrene Highly active, versatile, and photoiesponsive systems , Macromolecules, vol. 41, pp. 7359-7367, 2008. 

Radical 12 is rather stable under polymerization conditions, but radical 11 decays into a triazole and the phenyl radical, which initiates new chains. Hence, the rate of polymerization is higher with 11 than with 12, because the decay prevents retarding of the buildup of large persistent radical concentrations such as an additional radical generation. This effect of the radical decay is equivalent to the rate enhancement by partial removal of nitroxides by appropriate additives, which was first applied by Georges et al.31 Interestingly, at 95 °C and in toluene solution, the lifetime of 11 is only about 15 min, whereas a reasonable control was found in polymerizations of styrene that lasted many hours at 120— 140 °C.120 Obviously, the radical moiety 11 is stable while it is coupled to the polymer chain. However, the different time scales raise the question of the upper limit of the conversion rate of the persistent radical to a transient one that can be tolerated in living radical polymerization processes (see section IV. C). 

In this reaction, one polymer chain forms per molecule of the organic halide (initiator), while the metal complex serves as a catalyst or as an activator, which catalytically activates, or homolytically cleaves, the carbon—halogen terminal. Therefore, the initiating systems for the metal-catalyzed living radical polymerization consist of an initiator and a metal catalyst. The effective metal complexes include various late transition metals such as ruthenium, copper, iron, nickel, etc., while the initiators are haloesters, (haloalkyl)benzenes, sulfonyl halides, etc. (see below). They can control the polymerizations of various monomers including methacrylates, acrylates, styrenes, etc., most of which are radically polymerizable conjugated monomers. More detailed discussion will be found in the following sections of this paper for the scope and criteria of these components (initiators, metal catalysts, monomers, etc.). 

A series of so-called Grubbs ruthenium—carbene complexes (Ru-12) can mediate living radical polymerization of MMA and styrene to afford controlled polymers with narrow MWDs (MJMn 1.2).63 66 The polymerization apparently proceeds via a radical mechanism, as suggested by the inhibition with galvinoxyl. For example, a novel ruthenium—carbene complex (Ru-13) carries a bromoisobutyrate group and can thus not only initiate but also catalyze living radical polymerization of MMA without an initiator.67... 

The use of Cp or Cp -based ligands is also beneficial for the iron-based systems in controlling radical polymerization. For instance, FeCpI(CO)2 (Fe-3, X = I) induced a living radical polymerization of styrene in conjunction with an iodide initiator [(CH.s C-(C02C2H5)I] in the presence of Ti(Oi-Pr)4 to give very narrow MWDs (MJMn =1.1) and controlled molecular weights.72 The rate was increased with the use of the corresponding bromide, while the MWD was narrowed by replacement of Cp with Cp. 73 A faster and controlled polymerization was possible with dinuclear Fe(I) complexes (Fe-5 and Fe-6) in the absence of metal alkoxides. 

Diamine compounds such as L-15 coordinate to copper species, but their use for MA, MMA, and styrene results in slower polymerizations and broader MWDs (MJMn = 1.3—2.5) than those with bipyridine-based bidentate ligands.81108 An increase of the number of amine linkages and bulkier substituents further broadened the MWDs.81 Sparteine (L-16), a bicyclic diamine, was found to be an efficient ligand for homogeneous living radical polymerization of styrene and MMA with CuBr and CuCl, respectively, to give better-controlled polymers (MJMn = 1.1 —... 

The rapid progress and proliferation of metal-catalyzed living radical polymerization has allowed a variety of vinyl monomers to be polymerized into well-defined polymers of controlled molecular weights and narrow MWDs. Most of them are conjugated monomers such as methacrylates, acrylates, styrenes, acrylonitrile, acrylamides, etc., except dienes, which possess not only alkyl substituents but also aprotic and protic functional groups. This fact attests to the versatility and flexibility of metal catalysis for precision polymerization. 

A wider range of acrylate/styrene block copolymers have been prepared by copper catalysts, partially because the homopolymerizations of both monomers can be controlled with common initiating systems. Both AB- (B-15 to B-17)202,230,254,366,367 and BA-type (B-18 to B-21)28,112,169,230,366,368,369 block copolymers were obtained from macroinitiators prepared by the copper-based systems. The block copolymerizations can also be conducted under air230 and under emulsion conditions with water.254 Combination of the Re-and Ru-mediated living radical polymerizations in... 

A mixture of two monomers that can be homopo-lymerized by a metal catalyst can be copolymerized as in conventional radical systems. In fact, various pairs of methacrylates, acrylates, and styrenes have been copolymerized by the metal catalysts in random or statistical fashion, and the copolymerizations appear to also have the characteristics of a living process. The monomer reactivity ratio and sequence distributions of the comonomer units, as discussed already, seem very similar to those in the conventional free radical systems, although the detailed analysis should be awaited as described above. Apart from the mechanistic study (section II.F.3), the metal-catalyzed systems afford random or statistical copolymers of controlled molecular weights and sharp MWDs, where, because of the living nature, there are almost no differences in composition distribution in each copolymer chain in a single sample, in sharp contrast to conventional random copolymers, in which there is a considerable compositional distribution from chain to chain. Figure 26 shows the random copolymers thus prepared by the metal-catalyzed living radical polymerizations. 

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