Recent Synthetic Developments in Miktoarm Star Polymers with More than Three Different Arms

This chapter reviews the precise synthesis of multiarmed and multicomponent asymmetric star-branched polymers, the so-called 'miktoarm star polymers'. Most of the miktoarm star polymers introduced herein are those having more than three different arms and have emerged since 2000. For the synthesis of such complex star polymers, we propose a novel and quite versatile stepwise iterative methodology based on living anionic polymerization. In this methodology, the reaction system is designed in such a way that the same reaction site is always regenerated after the introduction of an arm segment in each iterative process and this 'arm introduction-regeneration of the reaction site' synthetic sequence is repeatable. Accordingly, a series of miktoarm star polymers can be successively and, in principle, limitlessly synthesized by repeating the synthetic sequence. This iterative methodology with the regeneration of reaction sites has been widely developed so far, allowing access to a wide variety of miktoarm star polymers that are well defined in architecture and precisely controlled in arm segments. Furthermore, miktoarm star polymers synthesized since 2000 by other methodologies based on living anionic polymerization and living/controlled radical polymerization are also described.