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Living anionic polymerization is a living polymerization technique involving an anionic propagating species. Living anionic polymerization was demonstrated by Szwarc and co workers in 1956. Their initial work was based on the polymerization of styrene and dienes. One of the remarkable features of living anionic polymerization is that the mechanism involves no formal termination step. In the absence of impurities, the carbanion would still be active and capable of adding another monomer. The chains will remain active indefinitely unless there is inadvertent or deliberate termination or chain transfer. This gave rise to two important consequences: # The number average molecular weight, Mn, of the polymer resulting from such a system could be calculated by the amount of consumed monomer and the initiator used for the polymerization, as the degree of polymerization would be the ratio of the moles of the monomer consumed to the moles of the initiator added. #: , where Mo = formula weight of the repeating unit, ()o = initial concentration of the monomer, and () = concentration of the initiator. # All the chains are initiated at roughly the same time. The final result is that the polymer synthesis can be done in a much more controlled manner in terms of the molecular weight and molecular weight distribution (Poisson distribution). The following experimental criteria have been proposed as a tool for identifying a system as living polymerization system. * Polymerization until the monomer is completely consumed and until further monomer is added. * Constant number of active centers or propagating species. * Poisson distribution of molecular weight * Chain end functionalization can be carried out quantitatively. However, in practice, even in the absence of terminating agents, the concentration of the living anions will reduce with time due to a decay mechanism termed as spontaneous termination.〔Odian, G. Ionic Chain Polymerization;In '' Principles of Polymerization''; Wiley-Interscience: Staten Island, New York, 2004, pp. 372-463.〕 ==Synthesis of complex architectures== Polymerization reactions excluding a termination and transfer step are particularly useful for the synthesis of functionalized polymers with well defined architectures.〔Cowie, J.; Arrighi,V. ''Polymers: Chemistry and Physics of Modern Materials''; CRC Press: Boca Raton, FL, 2008.〕 The consumption of the monomer results in stable, anionic polymer chain ends, allowing reactions with a variety of electrophilic functional groups post polymerization. : However the efficacy of these reactions depends on a number of variables such as chain-end structure, solvent, temperature, and concentration. Alternatively, by controlling the functionality of the initiator, one can prepare polymers having different geometries such as symmetric and asymmetric stars, comb shaped, etc. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Living anionic polymerization」の詳細全文を読む スポンサード リンク
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