Living radical polymerization, model

Unsymmetrical azo-compounds find application as initiators of polymerization in special circumstances, for example, as initiators of living radical polymerization [e.g. triphenylmethylazobenzene (30) (see 9.3.4)], as hydroxy radical sources [e.g. a-hydroperoxydiazene (31) (see 3.3.3,1)1, for enhanced solubility in organic solvents [e.g. f-butylazocyclohexanecarbonitrile (32)J, or as high temperature initiators [e.g. t-butylazoformamide (33)]. They have also been used as radical precursors in model studies of cross-termination in copolymerization (Section... 

A Model for Living Radical Polymerization in a Homogeneous System... 

Tetraethylthiuram disulfide (13) induces St polymerization by the photodissociation of its S-S bond to give the polymer with C-S bonds at both chain ends (15). The C-S bond further acts as a polymeric photoiniferter, resulting in living radical polymerization. Eventually, some di- or monosulfides, as well as 13, were also examined as photoiniferters and were found to induce polymerization via a living radical polymerization mechanism close to the model in Eq. (18), e.g., the polymerization of St with 35 and 36 [76,157]. These disulfides were used for block copolymer synthesis [75,157-161] ... 

The dissociation of model compounds for co-chain ends of polymers obtained using iniferters with the DC group was examined by the spin-trapping technique, similar to the disso dation of 7 and 8 previously mentioned [174,175]. From the results of the trapping experiments, it was concluded that 46,47, and 48 as model compounds for poly(MA), poly(MMA), and poly(VAc), respectively, dissociated at the appropriate position to produce a reactive carbon-centered radical and a stable DC radical. In fact, these compounds were found to induce the living radical polymerization of St when they were used as photoiniferters. 

While there have been several studies on the synthesis of block copolymers and on the molecular weight evolution during solution as well as bulk polymerizations (initiated by iniferters), there have been only a few studies of the rate behavior and kinetic parameters of bulk polymerizations initiated by iniferters. In this paper, the kinetics and rate behavior of a two-component initiation system that produces an in situ living radical polymerization are discussed. Also, a model that incorporates the effect of diffusion limitations on the kinetic constants is proposed and used to enhance understanding of the living radical polymerization mechanism. 

Otaigbe,]. U., Barnes, M. D., Fukui, K., Sumpter, B. G. and Noid, D. W. Generation, Characterization, and Modeling of Polymer Micro- and Nano-Particles. Vol. 154, pp. 1-86. Otsu, T. and Matsumoto, A. Controlled Synthesis of Polymers Using the Iniferter Technique Developments in Living Radical Polymerization. Vol. 136, pp. 75-138. 

The core first method starts from multifunctional initiators and simultaneously grows all the polymer arms from the central core. The method is not useful in the preparation of model star polymers by anionic polymerization. This is due to the difficulties in preparing pure multifunctional organometallic compounds and because of their limited solubility. Nevertheless, considerable effort has been expended in the preparation of controlled divinyl- and diisopropenylbenzene living cores for anionic initiation. The core first method has recently been used successfully in both cationic and living radical polymerization reactions. Also, multiple initiation sites can be easily created along linear and branched polymers, where site isolation avoids many problems. 

Four main studies have been published on styrene in which the authors show that thiuram disulfides play the role of both initiator and counter radical. Otsu et al. [235] demonstrated with 51 and 52 (n = 2) compounds and model molecule 55 that the polymerization of styrene led to the formation of mono-and dithiuram telechelic PS with a behavior close to that of living radical polymerization ... 

Klumperman and coworkers [259] observed that while it is lately quite common to treat living radical copolymerization as being completely analogous to its radical counterpart, small deviatiOTis in the copolymerization behavior do occur. They interpret the deviations on the basis of the reactions being specific to controlled/living radical polymerization, such as activation—deactivation equilibrium in ATRP. They observed that reactivity ratios obtained from atom transfer radical copolymerization data, interpreted according to the conventional terminal model deviate from the true reactivity ratios of the propagating radicals. 

T. Otsu, M. Yoshida, T. Tazaki, A model for living radical polymerization, Makromol. Chem. Rapid Commun. 1982, 3, 133-140. 

In this chapter, three examples of the application of ESR to conventional radical polymerizations based on controlled/living radical polymerizations wUl be demonstrated. The first example is estimation of the effect of chain length on propagating radicals. The second example is the detection of chain-transfer reactions on the propagating radicals in polymerization of tert-butyl acrylate (tBA). The third example is investigation of penultimate unit effects using ESR analysis of dimeric model radicals of (meth)acrylates prepared by ATRA. 

Effect of Dimethyl Sulfoxide in the Cu(0)/Tris(2-Dimethylaminoethyl)Amine-Catalyzed Living Radical Polymerization of Methyl Methacrylate at 0-90 °C Initiated with CH3CHCII as a Model Compound for a,co-Di(Iodo)Poly(Vinyl Chloride) Chain Ends. 43 1935-1947. 

Otsu, T., Yoshida, M., Tazaki, T., A Model for Living Radical Polymerization,... 

Wang R, Luo Y, Li B, Sun X, Zhu S. Design and control of copolymer composition distribution in living radical polymerization using semi-batch feeding policies a model simulation. Macromol Theor Simul 2006 15 356-368. 

Ma JW, Cunningham MF, McAuley KB, Keoshkerian B, Georges M. Nitroxide mediated living radical polymerization of styrene in miniemulsion - modelling persulfate-initiated systems. Chem Eng Sci 2003 58 1177-1190. 

The earlier work by Otsu, titled A model for living radical polymerization, should be noted even if it was not sufficiently successful. Another approach to achieve livingness (not realized in practice so far) was proposed by Kabanov, who considered a possibility of achieving living radical... 

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