Radicals nitroxide radical, amphiphilic

Experimental studies reported by Lucarini et al.216 are in agreement with the hypothesis of the existence of an increasingly available space between thiols upon reduction of the diameter of the NPs. In this investigation, ESR spectroscopy has been used to study the interaction of an amphiphilic nitroxide radical with the mono-layer of water-soluble protected gold clusters having a core diameter between 1.6 and... 

The presence of the nitroxide radical was confirmed through EPR and XH NMR spectroscopic methods. The copolymer GPC trace (Mn=33,100, Mw/Mn=1.37) was symmetrical with no evidence of unreacted macroinitiator or homopolymer of St resulting from either thermal initiation or from disproportionation of the pSt from the TEMPO chain end [231]. The kinetic results showed a first-order relationship between monomer conversion and time and the molecular weights increased linearly with conversion, indicating the polymerization proceeded with minimal termination or chain transfer reactions. The presence of the pEAD block produces an amphiphilic copolymer with a biodegradable block that may be useful for biomedical applications. 

Well-defined amphiphilic block copolymers can be prepared by various controlled polymerization reactions, such as atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT), and nitroxide mediated polymerization (NMP). The amphiphilic copolymers most frequently used in bio-inspired strategies consist of hydrophilic blocks, such as poly(aciylic acid) (PAA), poly(ethylene oxide) (PEO), or poly(2-methyl oxazoline) (PMOXA), and a hydrophobic block, such as... 

Gotz H, Harth E, Schiller SM, Frank CW, Knoll W, Hawker CJ (2002) Synthesis of lipo-glycopolymer amphiphiles by nitroxide-mediated living free-radical polymerization. J Polym Sci A Polym Chem 40(20) 3379-3391... 

Li X, Ni X, Liang Z, Shen Z (2012) Preparation of main-chain imidazolium-functionalized amphiphilic block copolymers through combination of condensation polymerization and nitroxide-mediated free radical polymerization and their micelle study. J Polym Sci A Polym Chem 50 2037-2044... 

Since the number of monomers, and thus the resulting polymer structures, are limited by any of the specific living polymerization techniques, appropriate combination of different polymerization mechanisms can lead to a variety of new and useful polymeric materials. Therefore combinations of controlled radical polymerizations and other polymerizations applied to synthesize block copolymers have been developed. Generally, polymers with active sites, such as carbon-halogen or nitroxide or dithioester terminal groups, are synthesized by other living polymerizations, and the product is further used to initiate the controlled radical polymerization. In many cases, this method is essentially a variant of the macroinitiator method discussed above. However, in some cases, these kinds of macromolecules do not act as initiators, and may act as transfer agents. For example, an AB-type amphiphilic block copolymer, CLB-2 was prepared by RAFT polymerization of 2-(N-dimethylamino)ethyl methacrylate... 

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. 

Since the self-assembly phenomena requires well-defined block copolymers with narrow molecular weight distribution, only living/controlled polymerization techniques have been exploited for the preparation of polymeric nanoparticles via PISA. In particular, in aqueous media, the controlled radical polymerizations have been the methods of choice, taking the advantage of the compatibility of the reactions with water and the ability to create a wide variety of amphiphilic polymers. Atom transfer radical polymerization (ATRP), nitroxide-mediated polymerization (NMP), and reversible addition-fragmentation chain transfer (RAFT) polymerization have been the most studied techniques. The three methods possess certain advantages however, RAFT remains particularly the most attractive due to the wide variety of polymers that can be produced in a controlled manner at low polymerization temperatures. 

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