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Nitroxide Mediated Free Radical Polymerization Pdf

 
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MessagePosté le: Jeu 22 Sep - 22:34 (2016)    Sujet du message: Nitroxide Mediated Free Radical Polymerization Pdf Répondre en citant




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Nitroxide Mediated Free Radical Polymerization Pdf


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Because TEMPO, which is commercially available, is a sufficient nitroxide mediator for the synthesis of polystyrene derivatives, the preparation of alkoxyamine initiators for NMP of copolymers is in many cases a matter of attaching a nitroxide group (TEMPO) to a specifically synthesized alkyl fragment. The efficiency of polymerization increases more and more with increased steric bulk of the nitroxide up to a point. As stated above, nitroxide radicals are effective mediators of well-controlled radical polymerization because they are quite stable, allowing them to act as persistent radicals in a reaction mixture. ^ Siegenthaler, K.O., Studer, A. Nitroxide-mediated radical polymerization is a method of radical polymerization that makes use of an alkoxyamine initiator to generate polymers with well controlled stereochemistry and a very low polydispersity index.[1] It is a type of Reversible-deactivation radical polymerization. Please enable JavaScript to access the full features of the site or access our non-JavaScript page. Rev., 2001, 101 (12), 35813610. The initiating materials for nitroxide-mediated radical polymerization (NMP) are a family of compounds referred to as alkoxyamines. ^ Moon, B., Minjyuk, K. The nitroxide nucleophile is then added to an appropriate alkyl bromide, yielding the alkoxyamine by a simple SN2 reaction.

Because of the PRE, it can be assumed that at any given time, almost all of the growing chains are capped by a mediating nitroxide, meaning that they dissociate and grow at very similar rates, creating a largely uniform chain length and structure.[5]. The utility of this functional group is that under certain conditions, homolysis of the C-O bond can occur, yielding a stable radical in the form of a 2-center 3-electron N-O system and a carbon radical which serves as an initiator for radical polymerization.[2] For the purposes of NMP, the R groups attached to the nitrogen are always bulky, sterically hindering groups and the R group in the O- position forms a stable radical, generally is benzylic for polymerization to occur successfully. Because of the high rate of coupling of the nitroxide to the growing chain end, there is little coupling of two active growing chains, which would be an irreversible terminating step limiting the chain length. Soc. NMP allows for excellent control of chain length and structure, as well as a relative lack of true termination that allows polymerization to continue as long as there is available monomer. This technique has the advantage of requiring only the appropriate alkyl bromide to be synthesized without requiring inconvenient reaction conditions and extremely hazardous reagents like Braso et al.s method.[13]. Alkoxyamines[edit].

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