РОССИЙСКАЯ АКАДЕМИЯ НАУК УРАЛЬСКОЕ ОТДЕЛЕНИЕ ИНСТИТУТ ХИМИИ TBEPДОГО ТЕЛА |
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26.06.2008 | Карта сайта Language |
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Similar problems are also encountered with the copper-mediated atom transfer radical polymerisation (ATRP) reaction, which was discovered in 1995. Mechanistically similar to ATRA, the reaction conditions are modified so that the product of the initial addition reaction can be reactivated. The repetitive addition step is what makes ATRP a polymerisation process. It is a powerful, robust, and easy to conduct method that allows polymeric materials to be prepared with well-defined composition, architecture and functionality. "Environmentally friendly reducing agents continuously regenerate the metal complex in the lower oxidation state" In copper-catalysed ATRA and ATRP, the transition metal in its lower oxidation state activates the dormant alkyl halide species, generating radicals which are then deactivated by the metal in its higher oxidation state. Nevertheless, because the radical deactivation - known as termination - reactions cannot be totally suppressed, the higher oxidation state metal complex accumulates as the reaction proceeds. This means larger metal quantities are required as the catalyst is 'used up'. A recently discovered solution to this problem uses environmentally friendly reducing agents to continuously regenerate the metal complex in the lower oxidation state. These reducing agents include radical initiators, amines, glucose, ascorbic acid and tin(II) compounds. These ARGET (activators regenerated by electron transfer) and ICAR (initiators for continuous activator regeneration) ATRP processes allow polymerisation to be conducted using very small amounts of copper catalyst (1-100 ppm). Generally the amount of catalyst required to carry out a reaction is reduced 500-10 000 times. The methodology also reduces catalyst-based side reactions. A procedure developed for catalyst regeneration in copper- and ruthenium-catalysed ATRA reactions has also been successfully used here, achieving one of the highest turnover numbers for any metal mediated ATRA process. These recent developments could have profound implications for the large-scale industrial synthesis of small organic molecules and well-defined polymeric materials. Read Pintauer and Matyjaszewski's tutorial review on 'Atom transfer radical addition and polymerization reactions catalyzed by ppm amounts of copper complexes' in issue 6, 2008 of Chemical Society Reviews Link to journal articleAtom transfer radical addition and polymerization reactions catalyzed by ppm amounts of copper complexes
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