Atom transfer radical polymerization effect

Tang W, Kwak Y, Braunecker W et al. (2008) Understanding atom transfer radical polymerization effect of ligand and initiator structures on the equilibrium constants. J Am Chem Soc 130 10702-10713... 

SCHEME 2.26 Influence of initiators on values for polymerizations using tris(2-pryidyhnethyl)amine (TPMA) as ligand in conjunction with Cu(I)X. Reprinted (adapted) with permission from Tang W, Kwak Y, Braunecker WA, Tsarevsky NV, Coote ML, Matyjaszewski K. Understanding atom transfer radical polymerization effect of ligand and initiator structures on the equilibrium constants. J Am Chem Soc 2008 130 10702-10713. 2008 American Chemical Society. 

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. 

Fig. 2 Effects of metal salts, ligands, and initiators on Cmma (s)> / (b), PDls (c) of the polymers in the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in p-xylene at 90°C. [MMA]o [initiator]o [metal salt]o [ligand]o = 150 1 1 2, MMA/p —xylene = l 2v/v. EBIB, MBP, BEB, and TsCl were used as initiator from right to left in each ligand column, respectively (Reprinted with permission from [34]. Copyright (2004) John Wiley Sons, Inc.)...

The synthesis of mixed peroxides formed from /-butyl hydroperoxide and carbon-centred radicals has been studied. The reactions were strongly effected by solvents as well as catalytic amounts of Cun/Fem. The kinetic data suggest that the conditions for the Ingold-Fischer persistent radical effect are fulfilled in these cases.191 The use of Cu /Cu" redox couples in mediating living radical polymerization continues to be of interest. The kinetics of atom-transfer radical polymerization (ATRP) of styrene with CuBr and bipyridine have been investigated. The polymer reactions were found to be first order with respect to monomer, initiator and CuBr concentration, with the optimum CuBr Bipy ratio found to be 2 1.192 In related work using CuBr-A-pentyl-2-... 

Nguyen JV, Jones CW (2004) Effect of the synthetic method and support porosity on the structure and performance of sihca-supported CuBr/Pyridyhnethanimine atom transfer radical polymerization catalysts. 1. Catalyst preparation and characterization. J Polym Sci. Part A 42 1367... 

ESR spectroscopy was successfully applied to quantify radical concentration in the polymerizations [4, 8-11], However, the direct detection method of ESR did not reveal information on many additional points that ate very significant in radical polymerization chemistry so far. For example, the length of propagating chain is not known, direct observation of the penultimate unit effect is almost impossible, and detailed mechanisms of radical reactions remain extremely difficult to examine. These problems have not yet been fully resolved but the development of controlled radical polymerization techniques, especially atom transfer radical polymerization (ATRP), enables us to resolve some of these problems. 

The Atom Transfer Radical Polymerization Equilibrinm Strnctnral and Medium Effects... 

Atom transfer radical polymerization (ATRP) was selected as an exemplary CRP technique to systematically study the kinetics and gelation behavior during the concurrent copolymerization of monovinyl monomers and divinyl cross-linkers (Scheme 2). The effect of different parameters on the experimental gelation was studied, including the initial molar ratio of cross-linker to initiator, the concentrations of reagents, the reactivity of vinyl groups present in the cross-linker, the efficiency of initiation, and the polydispersity of primary chains. Experimental gel points based on the conversions of monomer and/or cross-linker at the moment of gelation, were determined and compared with each other in order to understand the influence of each parameter on the experimental gel points. 

W. Feng, J.L. Brash, S. Zhu, Non-biofouling materials prepared by atom transfer radical polymerization grafting of 2-methacryloloxy-ethyl phosphorylcholine separate effects of graft density and chain length on protein repulsion. Biomaterials 27 (2006) 847-855. 

Lately, surface-initiated atom transfer radical polymerization (ATRP) has been used to obtain a surface-grafted membrane (Liu et al. 2010). A porous PTFE membrane was treated by the hydrogen plasma and the C-F groups of the modified surface became effective initiators of ATRP. PEG methacrylate or its copolymer with A-isopropylacrylamide was grafted in such a way and the modified membranes showed temperature-responsive and protein repulsion features (Liu et al. 2010). 

XIA Xia, Y., Burke, N.A.D., and Stoever, H.D.H., End group effect on the thermal response of narrow-disperse poly(V-isopropylaciylanude) prepared by atom transfer radical polymerization, A/acro io/ecM/e5, 39, 2275, 2006. 

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