Nitroxide-mediated controlled radical

NMCRP nitroxide-mediated controlled radical polymerization... 

Nitroxide-Mediated Controlled Radical Polymerization (NMCRP) was first discovered by Solomon et al., who patented their discovery in 1985 [205]. This opened up new pathways in the field of free-radical polymerization. Polymer architectures, which were the domain of the anionic polymer chemist, became accessible to the free-radical polymer chemist. However, it was not until the work of Georges et al. [206] was published in 1993, that the world of polymer chemistry became aware of the possibihties of this new class of free-radical polymerization. This was the beginning of what is today one of the leading topics in free-radical polymer chemistry Controlled or Living Free Radical Polymerization. This initiated the search for new Controlled or Living Free Radical Polymerization techniques, and soon afterwards other methods (which will be discussed later) were developed. 

The advent of second-generation alkoxyamines, which are suitable for the polymerization of a range of monomer families, has enabled nitroxide-mediated controlled radical polymerization to synthesize a broad range of block copolymers. 

Stalmach et al. proceeded to the synthesis of a diblock copolymer, comprised of an oligo-PV rod and a poly(n-butyl acrylate) flexible segment, using the macroinitiator procedure. Nitroxide-mediated controlled radical polymerization (NMCRP) using the macroinitiator 11 was performed in order to control the length of the coil blocks. 

C. Earcet, M. Lansalot, B. Charleux, R. Pirri, J. P. Vairon, Mechanistic aspects of nitroxide-mediated controlled radical polymerization of styrene in mini-emulsion, using a water-soluble radical initiator. Macromolecules 2000, 33, 8559-8570. 

By doing so we should also be able to functionalize the pattern generated on the spin-casted block copolymer film. Therefore we synthesized diblock copolymers via nitroxide mediated controlled radical polymerization containing phenolic (1) or hydroxy (2) groups in the hydrophilic segments, whereas the hydrophobic segments remained unfimctionalized. 

Lessard, B. H., Ling, E. J. Y. and Marie, M. (2012) Fluorescent, thermoresponsive oligo(ethylene glycol) methacrylate/9-(4-vinylbenzyl)-9H-carbazole copolymers designed with multiple LCSTs via nitroxide mediated controlled radical polymerization. Macromolecules, 45,1879-1891, doi 10.1021/ma202648k. 

Functionalised PO as block and graft copolymers used as compatibilisers or to increase interactions with other materials are prepared by free radical grafting (the simplest method), metallocene-catalysed copolymerisation of olefins with functional monomers, or anionic polymerisation (silane-containing PO). They are also produced by controlled/living polymerisation techniques such as nitroxide-mediated controlled radical polymerisation, atom transfer radical polymerisation (ATRP), and reversible addition-fragmentation chain transfer (RAFT). 

Natural polymers such as cellulose and natural rubber were also subjected to Sl-NMP. NMP was the first living radical polymerization method to be used in cellulose grafting. Daly et al. [85] reported the first use of nitroxide-mediated, controlled radical grafting from cellulose and cellulose derivatives. Controlled radical grafting from hydroxypropyl cellulose (HPC) was performed using TEMPO monoadducts, formed from the HPC-Barton carbonate derivative... 

Couvreur L, Lefay C, Belleney 1 (2003) First nitroxide-mediated controlled free-radical polymerization of acrylic acid. Macromolecules 36 8260-8267... 

Nitroxide mediated free radical polymerization is a living or controlled polymerization process. It can be used to initiated or terminate polymerization reactions as needed (1). The use of Phosphino, aryloxy, silyl, boryl and seleno mediating agents are described (2). 

While possessing many of the key advantages of controlled/ living polymerization methods, nitroxide-mediated free-radical polymerizations do exhibit several limitations. The range of monomers that have been polymerized using nitroxide-mediated techniques include styrenics. acrylamides and (meth)acrylates but these have predominantly been reported in bulk polymerizations (i.e. without solvent) and are conducted at elevated temperature for long time periods. In addition, synthesis of the unimolecular initiator can prove troublesome (dependent upon the type required) and often requires extensive purification in order to attain sufficient purity levels to allow molecular weight control. 

Atom transfer free-radical polymerization (ATRP) proceeds by a transient/ stable radical mechanism analagous to nitroxide-mediated free-radical polymerizations (see Section 3). This controlled polymerization concept was first described independently by two research groups in 1995, and exhibits a high degree of control over the molecular weight of the desired polymer and more remarkably, the ability to realize very narrow molecular weight distributions < 1.05). ATRP methodologies involve (see... 

During the last ten years, the nitroxide-mediated controlled free-radical polymerization has also been studied in water-based systems (iriimemulsion and macroemulsion polymerizations) as it combines the environmental and technical advantages of polymerization in aqueous dispersed media with the ability to synthesize tailor-made macromolecular structures (Qin et al., 2001 Cunningham, 2002 Charleux, 2003). 

Figure 8 Main mechanistic transformation reactions in living and/or controlled polymerization methods. ATRP, atom transfer radical polymerization RAFT, reversible addition-fragmentation chain transfer NMRP, nitroxide-mediated free radical polymerization CROP, cationic ring-opening polymerization AROP, anionic ring-opening poiymerization.

J. Nicolas, B. Charleux, O. Guerret, S. Magnet, Nitroxide-mediated controlled free-radical emulsion polymerization using difunctional water-soluble alkoxyamine initiator. Toward the control of PS, PSD and the synthesis of triblock copolymers, Macromolecules 2005, 38, 9963-9973. 

B. Charleux, S. R. A. Marque, D. Bertin, S. Magnet, L Couvreur, Living character of polymer chains prepared via nitroxide-mediated controlled free-radical polymerization of methyl methacrylate in the presence of a small amount of styrene at low temperature, Macromolecules 2006,... 

Nitroxide Mediated Living Radical Polymerization. Another controlled radical polymerization developed in recent years is stable free radical mediated polymerization (SFRP), also called as nitroxide mediated radical polymerization (NMP) (78,131). This type polymerization can be reahzed through reversible deactivation of growing radicals by stable radical such as 2,2,6,6-tetramethyl-piperidinyloxy (TEMPO). 

Nicolas, J., Charleux, B., Guerret, O., and Magnet, S. (2004a) Nitroxide-mediated controlled fi ee-radical emulsion polymerization of styrene and n-butyl acrylate with a water-soluble aUcoxyamine as initiator. Angewandte Chemie International Edition, 43,6186-6189. 

Several families of monomers could be polymerized under living/controlled conditions using nitroxide-mediated free radical polymerization, including styrene, alkyl acrylates, acrylamides among others. 

Delaitre, G. and Charleux, B. 2008. Kinetics of in situ formation of polyfacrylic acid)-b-polystyrene amphiphilic block copolymers via nitroxide-mediated controlled free-radical emulsion polymerization. Discussion on the effect of compartmentalization on the polymerization rate. Macromolecules 41 2361-7. 

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