This paper reviews the precise synthesis of architectural polymers by methodologies utilizing either chain-end-or in-chain-functionalized AB diblock copolymers as efficient key building blocks. Architectural polymers herein synthesized are miktoarm star-branched polymers, exact graft copolymers, high-density comblike polymers, and alternative and sequential multiblock copolymers. Chain-end-and in-chain-functionalized AB diblock copolymers and, in some cases, core-functionalized ABC star-branched polymers utilized as building blocks are prepared by living anionic polymerization in conjunction with specially functionalized agents and linked in manners suitably designed for each architectural polymer to successfully synthesize such structurally complex polymers. The resulting polymers are all well-defined in structure and precisely controlled in chain length.

Triblock co-and terpolymers with orders of blocks synthetically difficult to be obtained by means of sequential living anionic polymerization were successfully synthesized by developing a new methodology combining living anionic block copolymers with a specially designed linking reaction. The synthesized polymers involve ACB and BAC triblock terpolymers and ABA 0 , ACA 0 , and BCB 0 triblock copolymers, where A, B, and C are polystyrene, poly(2-vinylpyridine), and poly(methyl methacrylate) segments, respectively. The A 0 , A as well as B, B 0 are identical in polymer structure but different in molecular weight. All of them are new type triblock ter-and copolymers with well-defined structures, i.e., predictable molecular weights, compositions, and narrow molecular weight distributions. Transmission electron microscopic studies were performed on bulk morphologies of ACB and BAC triblock terpolymers to exemplarily investigate the influence of changing block sequence and thus changing interfaces. Although both terpolymers showed the tendency to form a lamellaÀlamella morphology, ACB revealed unusually strongly curved lamellae and BAC even undulated lamellae. ' INTRODUCTIONBlock polymers with a high degree of molecular and compositional homogeneity have attracted increasing interest as model polymers to elucidate interesting properties and behavior in combination with morphologies and molecular assemblies. 1À9 Such welldefined block polymers are usually synthesized by means of living anionic polymerization where two or more monomers are sequentially added to appropriate anionic initiators. 10 In fact, well-defined AB diblock copolymers, ABC triblock terpolymers, and (AB) n multiblock copolymers have been successfully synthesized.In order to achieve further design and synthesis of well-defined block polymers by using living anionic polymerization, it is

This article reviews the successful development of two specially designed linking methodologies in conjunction with a living anionic polymerization system for the synthesis of novel multiblock polymers, composed of three or more blocks, difficult to be synthesized by sequential polymerization. The first methodology with the use of a new heterofunctional linking agent, 2-(4-chloromethylphenyl)ethyldimethylchlorosilane (1), was developed for the synthesis of multiblock polymers containing poly(dimethylsiloxane) (PDMS) blocks. This methodology is based on the selective reaction of the chain-end silanolate anion of living PDMS, with the silyl chloride function of 1, and subsequent linking reaction of the resulting ω-chain-end-benzyl chloride-functionalized polymer with either a living anionic polymer or living anionic block copolymer. With this methodology, various multiblock polymers containing PDMS blocks, up to the pentablock quintopolymer, were successfully synthesized. The second methodology using an α-phenylacrylate (PA) reaction site was developed for the synthesis of multiblock polymers composed of all-vinyl polymer blocks. In this methodology, an α-chain-end-PA-functionalized polymer or block copolymer, via the living anionic polymerization, was first prepared and, then, reacted with appropriate living anionic polymer or block copolymer to link the two polymer chains. As OPEN ACCESSPolymers 2013, 5 1013 a result, ACB (BCA), BAC (CAB), (AB) n , (AC) n , ABA, ACA, BCB, and ABCA multiblock polymers, where A, B, and C were polystyrene, poly(2-vinylpyridine), and poly(methyl methacrylate) segments, could be successfully synthesized. The synthesis of triblock copolymers, BAB, CAC, and CBC, having molecular asymmetry in both side blocks, was also achieved. Furthermore, the use of living anionic polymers, derived from many other monomers, categorized as either of styrene, 2-vinylpyridine, or methyl methacrylate in monomer reactivity, in the linking methodology enabled the number of synthetically possible block polymers to be greatly increased. Once again, all of the block polymers synthesized by these methodologies are new and cannot be synthesized at all by sequential polymerization. They were well-defined in block architecture and precisely controlled in block segment.

This article reviews the development of a novel all-around iterative methodology combining living anionic polymerization with specially designed linking chemistry for macromolecular architecture syntheses. The methodology is designed in such a way that the same reaction site is always regenerated after the polymer chain is introduced in each reaction sequence, and this "polymer chain introduction and regeneration of the same reaction site" sequence is repeatable. Accordingly, the polymer chain can be successively and, in principle, limitlessly introduced to construct macromolecular architectures. With this iterative methodology, a variety of synthetically difficult macromolecular architectures, i.e., multicomponent µ-star polymers, high generation dendrimer-like hyperbranched polymers, exactly defined graft polymers, and multiblock polymers having more than three blocks, were successfully synthesized.

Five A‐B‐A′, A‐C‐A′, B‐A‐B′, C‐A‐C′, and C‐B‐C′ triblock terpolymers with block orders difficult to synthesize by sequential polymerization have been successfully synthesized by a new methodology combining living anionic polymers with a specially designed linking reaction using α‐phenylacrylate as the reaction site. Here, A(A′), B(B′), and C(C′) represent groups of polymers (having chain‐end anions with different nucleophilicities), which are only polymerizable from A(A′) to B(B′) to C(C′) via sequential polymerization. The corresponding polymers are polystyrene (A) and poly(α‐methylstyrene) (A′), poly(2‐vinylpyridine) (B) and poly(4‐vinylpyridine) (B′) and polymers from methacrylate type monomers like poly(methyl methacrylate) (C), poly(tert‐butyl methacrylate) (C′), poly(2‐hydroxyethyl methacrylate) (C′), poly(2,3‐dihydroxypropyl methacrylate) (C′), and poly(ferrocenylmethyl methacrylate) (C′). Furthermore, three synthetically difficult B‐A‐B, C‐A‐C, and C‐B‐C triblock copolymers with molecular asymmetry in both side blocks have also been synthesized by the developed methodology. All of the polymers thus synthesized are quite new triblock terpolymers and copolymers with well‐defined structures, i.e., precisely controlled molecular weights, compositions and narrow molecular weight distributions (Mw/Mn ≤ 1.05).

A methodology combining living anionic polymerization with linking chemistry using 1 : 1 addition reaction has been developed for the syntheses of tetrablock quaterpolymers composed of A, B, C, and D blocks.

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This study demonstrates the versatility and wider applicability of the recently developed methodology combining the living anionic polymerization with a specially designed linking reaction using the α-phenylacrylate (or benzyl bromide) function, allowing the synthesis of triblock co-and terpolymers, which are otherwise diffi cut to be obtained by sequential addition of monomers during a sequential polymerization approach. With this methodology using styrene and four para -substituted styrene derivatives with N -cyclohexylimine, 4-N,N -dimethyl-2-oxazoline, 2,6-di( tert -butyl)-4-methylphenyl ester, and nitrile, 12 polymers among the 16 possible triblock terpolymers and 6 triblock copolymers were successfully synthesized. Furthermore, the synthesis of two tetrablock quarterpolymers was achieved by the same linking methodology. The polymers synthesized in this study are all well-controlled in chain length, composition, which are diffi cult to be obtained by the sequential polymerization. In addition, they possess functional groups usable for the further modifi cation and introduction of other functionalities.