Nitroxyl-mediated radical polymerization

The last decades have witnessed the emergence of new living Vcontrolled polymerizations based on radical chemistry [81, 82]. Two main approaches have been investigated the first involves mediation of the free radical process by stable nitroxyl radicals, such as TEMPO while the second relies upon a Kharash-type reaction mediated by metal complexes such as copper(I) bromide ligated with 2,2 -bipyridine. In the latter case, the polymerization is initiated by alkyl halides or arenesulfonyl halides. Nitroxide-based initiators are efficient for styrene and styrene derivatives, while the metal-mediated polymerization system, the so called ATRP (Atom Transfer Radical Polymerization) seems the most robust since it can be successfully applied to the living Vcontrolled polymerization of styrenes, acrylates, methacrylates, acrylonitrile, and isobutene. Significantly, both TEMPO and metal-mediated polymerization systems allow molec-... 

The inclusion of stable free radicals such as TEMPO (18, TO ) in free radical polymerizations leads to precise control of chain length by restricting the number of polymerizing chains (equation 96). This process is known as nitroxyl radical mediated polymerization (NRMP). 

Free-radical polymerization mediated by stable nitroxyl radicals like TEMPO (2,2,6,6-tetramethylpiperidinyl-l-oxy) (Fig. 6.23) is a simple and robust method to synthesize homopolymers and random and block copolymers with narrow poly-dispersities and/or controlled chain architectures. A key to the success of this polymerization is believed to be the reversible combination of a polymer radical, P , with a stable nitroxyl radical, N, to form an adduct, P-N, which is a dormant species ... 

Solomon et al. [75] first used nitroxyl radicals and alkoxyamines in a radical polymerization, but their work was limited to production of low-molecular weight polymers. In 1993, Georges et al. [76] used a mixture of benzoyl peroxide (BPO) initiator and 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) to produce low-polydispersity and high molecular weight polystyrene. Since then many papers about SFRP (also known as nitroxide mediated polymerization or NMP), mainly focused on styrene polymerization in the presence of TEMPO, have been published. Other nitroxide mediators are being developed that are better suited to polymerization of more polar monomers such as meth(acrylates) [77]. 

NMP is another controlled free radical polymerization technique that can be used to polymerize styrene [98-100]. Weimer et al. investigated surface-initiated PS-MMT nanocomposites using MMT modified with a nitroxyl-mediated living... 

More recently, refinements and new approaches for controlling radical polymerization have been described (155). Two of the most studied methods feature either stable counter-radicals, eg, nitroxyl-mediated pol5unerization (NMP), or reversible activation of carbon-halogen bonds by transition-metal species in a... 

The example described below refers to nitroxide-mediated free radical polymerizations. Initially, a methacrylic monomer carrying an alkoxyamine group is copolymerized at moderate temperature with a comonomer (H2C=CHA) to form the backbone. In a second step the grafts are grown by thermal activation of alkoxyamine groups, which produce, in addition to stable nitroxyl free radicals, reactive free radicals capable of initiating the polymerization of H2C=CHB (see Section 8.5.11 for the mechanism). 

Nitroxyl radicals, stable, 14 298 Nitroxy-mediated polymerization (NMP), 14 297-298... 

Nitroxide mediated polymerization (NMP) [56, 57]. This consists in a thermally reversible termination reaction by a homolytic cleavage of a C-ON bond of an alkoxyamine, giving rise to an initiating alkyl radical (active species) and a nitroxyl radical, which brings control to the reaction [58]. 

Describe nitroxyl radical mediated polymerizations. Illustrate TEMPO controlled polymerization of styrene. What is meant by in situ NMP ... 

Zarycz N, Botek E, Champagne B, SciannameaV, Jerome C, Detrembleur C. Joint theoretical experimental investigation of the electron spin resonance spectra of nitroxyl radicals application to intermediates in in situ nitroxide mediated polymerization (in situ NMP) of vinyl monomers. J Phys Chem B 2008 112 10432-10442. 

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