Advances in Living Anionic Polymerization: From Functional

Perspective pubs.acs.org/Macromolecules

Advances in Living Anionic Polymerization: From Functional Monomers, Polymerization Systems, to Macromolecular Architectures Akira Hirao,*,†,‡,§ Raita Goseki,† and Takashi Ishizone† †

Department of Organic and Polymeric Materials, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1-S1-13, Ohokayama, Meguro-ku, Tokyo 152-8552, Japan ‡ Institute of Polymer Science and Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan § College of Chemistry, Chemical Engineering and Materials Science, Soochow University, 199 Ren Ai Road, Suzhou Industrial Park, Suzhou 215123, China

ABSTRACT: This Perspective presents the development in living anionic polymerization since 1990. The main subjects involve the following concerns of living anionic polymerization: functional styrene derivatives, new monomers and promising additives, the regio- and stereoselective polymerization, special polymers having rigid-rod-like or helical conformations, the synthesis of complex branched polymers composed of comblike segments via living anionic poly(macromonomer)s, and the precise synthesis of macromolecular architectures including multiblock polymers, exact graft polymers, multicomponent μ-star polymers, dendrimer-like star-branched polymers, and hyperbranched polymers by the recently developed methodologies and a new allaround iterative methodology. Throughout the Perspective, attention has focused on recent advances both in the precisely controlled functional polymer syntheses and in various structurally elaborate complex macromolecular architectures. Such advances have significantly expanded the range of available well-defined specialty functional polymers, which have been difficult to synthesize until recently. The future perspectives based on the present situation will also be described.

1. INTRODUCTION

Mn values being 1.05 or even lower. Finally, the resulting living anionic polymers have chain-end anions, which are highly reactive but stable under appropriate conditions. Such characteristics are ideally suited for the tailor-made synthesis of various linear and branched macromolecular architectures. Since the discovery of living anionic polymerization, this polymerization system has significantly contributed to the precise polymer synthesis from both academic and industrial viewpoints.1 For instance, the kinetic and thermodynamic studies of polymerization systems involving various ion pairs and free ions, the achievements in living anionic polymerization of functional monomers, the finding of effective additives to realize the regio- and stereoselective living anionic polymer-

In the past 25 years, remarkable advances in various living/ controlled polymerization systems via different mechanisms, such as not only anionic, but also cationic, radical, transition metal-mediated, and other mechanisms, have been achieved. In particular, the living/controlled radical polymerization has recently received much attention because it embodies attractive features such as the simple experimental operation, tolerance of many functional groups, and applicability of many kinds of monomers in the structure. Among these living polymerization systems, however, living anionic polymerization of certain monomers, such as styrene, 1,3-butadiene, isoprene, 2-vinylpyridine (2VP), and alkyl methacrylate monomers, is still the best system from the viewpoint of the following features: first, the molecular weights can be precisely controlled over a wide range from 103 to even 106 g/mol. Second, extremely narrow molecular weight distributions (MWDs) are attained, with Mw/ © XXXX American Chemical Society

Received: June 7, 2013 Revised: February 4, 2014

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dx.doi.org/10.1021/ma401175m | Macromolecules XXXX, XXX, XXX−XXX

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Figure 1. Functional styrene derivatives capable of living anionic polymerization.

2. LIVING ANIONIC POLYMERZATION OF FUNCTIONAL STYRENE DERIVATIVES Living anionic polymerization of styrene is the most ideal living system and allows ready access to a variety of well-defined macromolecular architectures. However, it has long been believed that the major drawback is the intolerance to most of the useful functional groups. Accordingly, styrene derivatives substituted with such functionalities were considered not to be subjected to living anionic polymerization because they readily react with highly reactive initiators and propagating chain-end anions. Nevertheless, some functional styrene derivatives were previously known to undergo living anionic polymerization.4−6 They involve styrenes para-substituted with alkenes,7,8a,b alkynes,9 aromatics,10 ethers,11a−c thioethers,12 tert-amines,13 and fluorine.14 Recently, living anionic polymerization of interesting styrenes substituted with cyclobutane (cross-linking ability at high temperatures),15 adamantanes (high thermal stability, Tg > 230 °C),16a,b π-conjugated oligo(fluorene)s (electronic/optoelectronic properties),17 and diphenylamine (chromophore, hole-transporting character)18 have been reported. Their successful living anionic polymerization are not very surprising, since these functionalities are proved to be stable toward the highly reactive anionic initiators like RLi reagents under selected conditions. Furthermore, C−Si,19 C− Ge,20 C−Sn,21 C−Bi,22 and C−P23 are reported to be stable under similar conditions. Moreover, we observed that C−Si− Si,24 C−Si−Si−Si,24 Si−OR,25a,b Si−NR2,26 and Si−H bonds27 were also stable under similar conditions. In fact, living anionic polymerization of all styrenes containing such bonds was successfully achieved (see Figure 1).

ization, and the synthesis of living anionic polymers having rigid-rod-like and helical conformations are typical examples. Such advances also provide the most versatile state-of-the-art tools to synthesize a wide variety of macromolecular architectures with a high compositional and molecular homogeneity. Among them, block polymers and multiphase macromolecular architectures synthesized by living anionic polymerization are undoubtedly the most promising high quality nanostructured materials via a morphological approach to fabricate molecular devices in the field of nanoscience. From an industrial viewpoint, living anionic polymerization plays an important role in producing several industrial materials, such as a solution styrene−butadiene rubber (S-SBR), and thermoplastic elastomers having both the elasticity and the processability, such as polystyrene (PS)-b-poly(1,3-butadiene) (PB)-b-PS (SBS), PS-b-polyisoprene (PI)-b-PS (SIS), and the corresponding hydrogenated triblock polymers. Very recently, new block polymers composed of all poly(meth)acrylate segments have been developed as the next generation of thermoplastic elastomers. This Perspective presents the comprehensive development since 1990 of various living anionic polymerization systems and the synthesis of elaborate and complex macromolecular architectures, which has been synthetically difficult until recently, and view the future perspectives based on the present situation. Morphological and nanostructural studies are, although they are interesting, beyond the scope of this Perspective and may be found elsewhere.2,3 B


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Scheme 1. Protection and Living Anionic Polymerization of Functional Styrenes

Figure 2. Styrene derivatives substituted with protected functionalities.

Figure 3. Styrene derivatives para-substituted with electron-withdrawing groups.

Functional groups having active hydrogen(s) and carbonyl groups, such as OH, SH, SiOH, NH2, CCH, CHO, COR, and COOH, are not compatible with anionic initiators and chain-end anions, thus rendering living anionic polymerization of substituted styrenes with such functionalities difficult or probably impossible. To overcome this long-standing problem, Nakahama and Hirao introduced a protective strategy into living anionic polymerization of functional styrenes.4−6,28−30 It involved the following three reaction steps (Scheme 1): (1) the functional group, such as OH,31a−e SH,32 SiOH,25a,b NH2,33a,b CCH,34 CHO,35a,b COR,36 or COOH,37 is suitably masked by an appropriate protective group to convert it to a stable form under the conditions of anionic polymerization, (2) the resulting styrene with the protected functionality is subjected to living anionic polymerization, and (3) the protective group is removed to regenerate the original functional group after the polymerization. With this protective strategy, a wide variety of styrene derivatives substituted with the readily reactive functionalities successfully underwent living anionic polymerization for the first time. These functional styrenes and the corresponding protected functionalities are shown in Figure 2. All the styrenes substituted with protected functionalities are almost the same as styrene regarding their living anionic polymerization behavior. Living anionic polymerization of styrene is generally carried out under the following two different conditions: In a polar solvent, like THF, at low temperature (typically −78 °C) and in nonpolar solvents, such as benzene and cyclohexane, at room or higher temperature. It should be noted that most of the monomers, listed in Figures 1 and 2, underwent living anionic polymerization under the former conditions. Since the latter conditions are used for the industrial production of polystyrene, it is important to further examine the anionic polymerization of these functional styrenes under the latter conditions.

As another effective strategy, Ishizone et al. introduced a series of electron-withdrawing groups (EWGs) into styrene monomers to significantly change the reactivities of the monomers and chain-end anions.4−6,38,39 Such EWGs involve N-alkyl- and N-arylimines,40a−c N,N-dialkylamides,41 2-oxazoline,42a−c alkyl43 and aryl esters,44 N,N-dialkylsulfonamides,45 and nitrile.46a−d Although they were susceptible to react with anionic initiators and living polystyrene, very surprisingly, all of the styrenes para-substituted with these EWGs successfully underwent the anionic polymerization in a living manner. It was observed that the anionic polymerizabilities of the EWGfunctionalized styrenes were remarkably enhanced by the strong electron-withdrawing effects of the EWGs to reduce the electron densities on vinyl groups, as evidenced by the lower 13 C NMR chemical shifts of the vinyl β-carbons of these monomers, while the nucleophilicities of the chain-end anions were significantly lowered by reducing the electron densities on the anions through the EWGs, as confirmed by the crossover polymerization of other monomers. Thus, a well-balanced combination between the enhanced monomer reactivity and the reduced chain-end reactivity makes living anionic polymerization of the EWG-functionalized styrenes possible (Figure 3). Such reduced reactivities of the chain-end anions may be attributed to the tolerance of these electron-withdrawing functional groups. Moreover, the hydrolysis of polystyrenes para-substituted with tert-butyl ester, 2-oxazoline, and Ncyclohexylimine yielded well-defined poly(4-carboxystyrene)s and poly(4-formylstyrene). The successful development of this strategy further broadened the range of functional groups applicable for living anionic polymerization. Thus, overall, styrene derivatives carrying almost all of the useful functionalities now acquire the ability to undergo living anionic polymerization. It should be noted that most of such functionalities were believed to be incompatible with living C


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anionic polymerization until the 1980s. Most importantly, the anion-stable functionalities and two strategies successful in living anionic polymerization may be applied to living anionic polymerization of other monomers, such as 1,3-butadiene, 2vinylpyridine (2VP), alkyl methacrylates, N,N-dialkylacrylamides, and cyclic monomers, since their living chain-end anions have similar or lower reactivities for the living polystyrene. This will enable the synthetic range of available living anionic polymers with functional groups to be significantly broadened.

The suppression of the unwanted addition reaction to the pendant vinyl group, which essentially occurred during the polymerization of p-DVB, may possibly be explained as follows: the countercation of the chain-end anion is considered to be completely replaced by K+ with an excess K+ and significantly shifted to ion pairs via the equilibrium in a high concentration of KOBut. The coordination of some KOBut molecules to the chain-end anion by the ionic interaction may provide the steric hindrance around the chain-end anion. Although the vinyl group of p-DVB is activated by the long π-conjugation system from the vinyl group to the other one, the pendant vinyl group attached to the main chain becomes less reactive due to the disappearance of the long conjugation system by the polymerization and the electron-donating effect of the main chain alkyl (−CH2−CH−). Thus, the resulting less reactive and sterically bulkier chain-end anion may add much more slowly to the less reactive pendant vinyl group on the polymer chain than p-DVB, while one of the activated vinyl groups of p-DVB preferentially undergoes the anionic polymerization. 3.2. N,N-Dialkylmethacrylamides. N,N-Dialkylacrylamides show a high anionic polymerizability due to the electron-withdrawing effect of the amide carbonyl groups, affording stable living polymers.49 In contrast, the corresponding N,N-dialkylmethacrylamides could not be polymerized at all under similar conditions50a−c and even with radical initiators. From several studies using 1H and 13C NMR analyses and modified neglect of diatomic overlap (MNDO) calculations, a twisted conformation is estimated between the CC and C O groups due to the intramolecular steric repulsion between the α-CH3 or CH2= group and N-alkyl substituents and the planarity of the OC−NR2 moiety.49,50a−c Accordingly, the observed nonpolymerizability can be explained by the twisted conformation where the CO function is not well conjugated with the CC group. In addition, the N,N-dialkylmethacrylamides might have a very low ceiling temperature, which hinders their polymerization. In order to clarify the above hypothesis, Ishizone et al.51,52 introduced small membered ring structures in the N-alkyl substituents to achieve an effective resonance between the C C and CO groups by breaking the planarity of the OC− NR2 moiety. A series of newly synthesized N,N-dialkylmethacrylamides carrying cyclic substituents, such as aziridine (MAz), azetidine (MAzt), pyrrolidine (MPy), and piperidine (MPi) rings, were subjected to the anionic polymerization. As expected, the anionic polymerization of MAz and MAzt with three- and four-membered rings quantitatively proceeded in a living manner (Mn ∼ 50 000 g/mol and Mw/Mn < 1.1). In contrast, the anionic polymerization of MPy having a fivemembered ring afforded polymers in 30−77% yields under the same conditions. MPi, having a six-membered ring, could not be polymerized at all even under drastic conditions. Thus, the

3. NEW MONOMERS AND ADDITIVES FEASIBLE FOR LIVING ANIONIC POLYMERIZATION 3.1. 1,4-Divinylbenzene. As is well-known, the radical or anionic polymerization of 1,4-divinylbenzene (p-DVB) usually produces highly cross-linked polymers insoluble in organic solvents. Very recently, Hirao et al. successfully demonstrated for the first time that one of the two vinyl groups of p-DVB exclusively undergoes selective polymerization in a living manner in THF at −78 °C with a specially designed initiator system prepared from oligo(α-methylstyryl)lithium and a 10fold excess of KOBut.47 Indeed, soluble linear poly(p-DVB)s with well-controlled Mn values and nearly monodisperse distributions were quantitatively obtained, as shown in the SEC profiles of the poly(p-DVB)s (Figure 4). The resulting

Figure 4. SEC profiles of poly(p-DVB): (a) without KOBut, Mn = 22 200 g/mol, Mw/Mn = 3.53; (b) in the presence of 15 equiv of KOBut, Mn = 24 900 g/mol, Mw/Mn = 1.04.

living polymers were stable only for a few minutes at −78 °C, but stable even after 30 min at −95 °C.48 Under such conditions, the undesired addition reaction of the chain-end anion to the pendant vinyl group was almost suppressed, and soluble polymers with controlled Mns of up to 60 500 g/mol and narrow MWDs (Mw/Mn < 1.05) were obtained. The living nature of the polymerization was also supported by the successful synthesis of the well-defined diblock polymers, poly(p-DVB)-b-P2VP and poly(p-DVB)-b-PtBMA. They also found that effective additives include several potassium alkoxides and phenoxides derived from 1-methylpropanol, 2,4-dimethyl-3-pentanol, 1-methylcyclohexanol, 1,2:5,6-di-Oisopropylidene-α-D-glucofuranose, phenol, 1-naphthol, 2,6-di(tert-butyl)-4-methylphenol, and even the potassium salt of pivalic acid.48

Figure 5. Exo-methylene type and the corresponding acyclic monomers. D


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anionic polymerizability of the N,N-dialkylmethacrylamides with cyclic substituents dramatically decreases by increasing the ring number from three to six. The polymerizability of MAz and MAzt can be explained by the effective π-conjugation between the CC and CO double bonds. In these monomers, the planar amide conjugation between the CO and NR2 groups might be strongly prohibited and the pyramidal structures of the highly strained small rings in MAz and MAzt were maintained. On the other hand, the CC and CO double bonds of MPi may not be on the same plane, since the amide conjugation between the CO and NR2 group is predominant.52 3.3. Exo-methylene-Type Monomers. α-Methylene-Nmethylpyrrolidone (MMP), a cyclic analogue of N,Ndimethylmethacrylamide (DMMA) (Figure 5), was reported to undergo radical polymerization to give a unique polymer possessing a ring structure perpendicular to the main chain via the vinyl polymerization.53 Recently, Ishizone et al. succeeded in living anionic polymerization of MMP in THF at −78−0 °C with Ph2CHK or Ph2CHLi by the addition of the weak Lewis acidic Et2Zn.54 The resulting polymers possessed predicted molecular weights (Mn ∼ 26 000 g/mol) and narrow MWDs (Mw/Mn < 1.1). The CC bond and the adjacent CO bond in MMP should be almost flat and may effectively conjugate with each other because of the restricted conformation derived from the cyclic structure. Thus, the introduction of an exomethylene group can allow the nonpolymerizable N,Ndialkylmethacrylamide to be polymerized. A similar relationship between structure and polymerizability is observed between DPE and dibenzofulvene (DBF). DPE is known not to undergo homopolymerization due to its very low ceiling temperature. On the other hand, DBF exclusively undergoes radical, cationic, and anionic polymerization to form a vinyl polymer possessing a ring structure vertical to the main chain.55 Thus, the exo-methylene monomer again shows a higher polymerizability compared to the acyclic counterpart. The connection of two phenyl groups converts DPE into a planar molecule to induce the homopolymerizability. Very recently, Ishizone et al. have succeeded in polymerizing a new exo-methylene monomer, benzofulvene (BF, αmethyleneindene).56 BF, a cyclic analogue of 2-phenyl-1,3butadiene (2PhBd), possesses a planar fixed transoid 1,3-diene framework including an exo-methylene group. The anionic polymerization of BF quantitatively proceeded with sBuLi or Ph2CHK in THF at −78 °C for 1 h to give polymers with predicted molecular weights (Mn ∼ 28 000 g/mol) and narrow MWDs (Mw/Mn < 1.1). NMR analyses indicated that the repeating units of the resulting PBF consisted of a 1,2-addition unit (41%) and a 1,4-addition unit (59%). This suggested that BF acts as a polymerizable transoid 1,3-diene and the exomethylene group always participates in the propagation (Scheme 2). Interestingly, BF exhibited an unexpectedly high anionic polymerizability. A low nucleophilic living PMMA quantitatively initiated the polymerization of BF to afford a

well-defined diblock polymer, PMMA-b-PBF, while 2PhBd cannot be polymerized with the living PMMA. Thus, the higher polymerizability of BF is substantiated by changing to the corresponding exo-methylene type structure. 3.4. Ferrocenyldialkylsilanes. Inorganic polymers with backbones containing transition metal atoms are of significant interest because of their unique properties, behavior, and ability to prepare inorganic−organic hybrid materials. Although they are usually synthesized by polycondensation routes, a series of poly(ferrocenylsilane)s can be produced via the thermal ringopening polymerization of strained, ring-tilted, and siliconbridged [1]ferrocenophanes like ferrocenyldimethylsilane (FDS). Very interestingly, they underwent the living anionic ring-opening polymerization with BuLi, PhLi, or ferrocenyllithium in THF at 25 °C to afford well-defined polymers containing Fe and Si atoms in their main chains (Mn ∼ 83 000 g/mol, Mw/Mn < 1.10),57a−c as shown in Scheme 3. The resulting polymers exhibited high refractive indices, a redox activity, and potentials as precursors for semiconductors under oxidative doping. They also showed an excellent thermal stability to weight loss (up to 350−400 °C) and yielded ferromagnetic Fe/Si/C ceramic composites at elevated temperatures (500−1000 °C). Various well-defined block polymers containing PFDS segments, such as PFDS-b-poly(dimethylsiloxane), PS-bPFDS, PI-b-PFDS, P2VP-b-PFDS, and PFDS-b-PMMA,58,59 were synthesized by the sequential anionic polymerization. These block polymers containing PFDS segments often formed fiber-like micelles with a semicrystalline PFDS core in selective solvents.60a,b Very interestingly, micelles with a narrow length distribution were formed, and the length increased in proportion to the amount of added polymer. The living anionic ring-opening polymerization of a novel phosphorus-bridged [1] ferrocenophane, a phosphorus analogue of FDS, was also achieved.61 It is possible to incorporate ferrocene and a phosphorus atom into the main chain, showing the unique property, behavior, and coordination ability to transition-metal catalysts. 3.5. Living Anionic Polymerization of Cyclic Monomers Using Phosphazene Bases as Metal-Free Organocatalyst Systems. Seebach et al. first reported that 1-tertbutyl-4,4,4-tris(dimethylamino)-2,2-bis(tris(dimethylamino)phosphoranylidenamino)-2Λ5,4Λ4-catenadi(phosphazene), the so-called P4-t-Bu phosphazene base, effectively functioned as a metal-free organocatalyst for the polymerization of MMA.62 A polymer with an Mn value of 15 200 g/mol and an Mw/Mn value of 1.11 was obtained in THF at the surprisingly high temperature of 60 °C. Soon after, Möller et al. reported that ethylene oxide (EO) and D3 were anionically polymerized in a controlled manner with 1-ethyl-2,2,4,4,4-pentakis(dimethylamino)-2Λ5,4Λ4-catenadi(phosphazene) (P2-Et) and P4-t-Bu.63a−c They also demonstrated the one-step synthesis of the diblock polymer, PS-b-PEO, by the sequential polymerization of styrene with sBuLi, followed by EO, in the presence of P4-t-Bu. In general, the PS-CH2CH2OLi cannot further polymerize EO due to the strong association. However, the extremely strong base, P4-t-Bu, can complex Li+ to suppress the association and facilitate the polymerization of EO. Similarly, PB-b-PEO, PI-b-PEO, PB-b-PI-b-PEO, and PS-b-PEO-b-poly(glycidol) were synthesized by the addition of P4-t-Bu to the polymerization systems.64a−e A diblock polymer of PEO-bpoly(2-(dimethylamino)ethyl methacrylate) was obtained in

Scheme 2. Microstructure of Poly(benzofulbene) (PBF) Obtained by the Anionic Polymerization

E


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Scheme 3. Anionic Ring-Opening Polymerization of Ferrocenyldimethylsilane (FDS)

the presence of P4-t-Bu, enabling the facile changeover from an oxyanion to a carbanion.65 Recently, Hedrick and Wade et al. reported that P2-t-Bu satisfactorily functions during the polymerization of lactide (LA) using 1-pyrenebutanol as the initiator.66 The polymerization proceeded in a controlled manner to afford the corresponding polyesters (Mn ∼ 27 200 g/mol and Mw/Mn ∼ 1.1). The same group also demonstrated that both 2-tertbutylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphrine and N′-tert-butyl-N,N,N′,N′,N″,N″-hexamethylphosphorimidic triamide (P1-t-Bu) are effective for the living polymerization of LA, ε-caprolactone, and δ-valerolactone. Well-defined PEO-b-PLA, PS-b-PLA, and PMMA-b-PLA were successfully synthesized using the corresponding ω-OHfunctionalized polymers as the macroinitiators for the polymerization of LA.67 It was recently found that the anionic polymerization of dipropylcyclopropane-1,1-dicarboxylate68a,b and [R,S]-4-benzyloxycarbonyl-3,3-dimethyl-2-oxetanone69 are effectively controlled by the addition of P4-t-Bu and other phosphazene bases. Very recently, Hadjichristidis et al. reported the synthesis of high-molecular-weight comb polymers with a single- or double-graft homopolymer, block polymer, and statistical copolymer by the P4-t-Bu-promoted metal-free graft polymerization utilizing the CONH2 moieties as the initiating site in the poly(N,N-dimethylacrylamide-co-acrylamide).70 Thus, the addition of phosphazene bases to the anionic polymerization of cyclic monomers can effectively control the polymerization, rendering the synthesis of a variety of precisely controlled polymers, block polymers, and other macromolecular architectures possible. In the past 15 years, living anionic polymerization systems of LA, alkylene oxides, lactones, and other cyclic monomers have been significantly advanced by using not only phosphazene bases and several other amines but also the combination of other reagents with these bases. Although such polymerization systems are interesting in terms of a precision polymer synthesis, these systems are not herein described due to the limited space and have already been covered in an comprehensive review71 and recent papers.72a−e 3.6. Living Anionic Polymerization of Polar Vinyl Monomers. One of the most important challenges in this field is controlling the anionic polymerization of polar vinyl monomers like alkyl (meth)acrylates and N,N-dialkylacrylamides.73,74 They generally show high polymerization abilities due to the electron-withdrawing effects of the substituents. However, their anionic polymerization are accompanied by serious side reactions such as a carbonyl attack and/or α-proton abstraction with the anionic initiators and chain-end anions. Moreover, the intramolecular Claisen-type condensation of the propagating chain-end enolate anions with the ester group at the antepenultimate unit, the so-called backbiting reaction, often occurs during the polymerization. Therefore, the careful choice of initiator, counterion, solvent, and temperature is

crucial to achieve living anionic polymerization of such polar monomers.73,74,75a−c Several new systems successfully achieving the living polymerization of (meth)acrylate monomers have been so far developed in order to overcome the above-mentioned drawbacks. Typically, the following two systems were developed: first, common salts, such as LiCl, LiClO4, LiOBut, KOBut, lithium 2-(2-methoxyethoxy)ethoxide, and MgBr2,76a−e are added to the polymerization system, by which the propagating chain-end anions are converted to a less reactive ion-pair to suppress the undesired side reactions. As a representative example, Teyssié et al.77 previously reported that the addition of LiCl to a bulky 1,1-diphenylhexyllithium could remarkably control the anionic polymerization of tert-butyl acrylate (tBA) in THF resulting in a well-defined PtBA (Mn = 60 000 g/mol, Mw/Mn = 1.20). Thus, the serious side reactions of the carbonyl attack and α-proton abstraction were almost suppressed in the presence of LiCl. The addition of LiCl to the polymerization of methacrylate monomers is also effective to narrow the MWD of the resulting polymers and their Mw/Mn values being less than 1.05. A kinetic study indicated that LiCl effectively dissociates their aggregated propagating enolate anions, followed by producing simple active species, resulting in the formation of polymers with low polydispersities. The second system involves the addition of weak Lewis acids, such as R3Al, R3−n(R′O)nAl, Et2Zn, and Et3B, to stabilize the propagating chain-end anions.78a−h Nakahama et al.78f,g first reported that the addition of Et2Zn to Ph2CHK in THF induces living anionic polymerization of tBA, alkyl methacrylates, and N,N-dialkylacrylamides. Slower propagations were apparently observed in those systems, where Et2Zn might predominantly coordinate with the propagating chain-end enolate anions to stabilize the anions. Some binary initiator systems, including RLi/LiCl, RLi/Et2Zn, and RK/Et2Zn in THF, were often utilized for the synthesis of block polymers of (meth)acrylates and other comonomers such as styrene, 1,3dienes, and 2VP. A more drastic effect was observed in the polymerization of methacrylonitrile (MAN), tBA, and N,N-dialkylacrylamides by the addition of R3B, such as Et3B and Ph3B.79a,b In these systems, R3B may strongly coordinate to the initiator and/or the propagating chain-end anion at −78 °C and no appreciable polymerization occurs. At a higher temperature, the coordinated species barely dissociates to afford the active chain-ends to initiate the polymerization. Ishizone et al. successfully demonstrated that MAN underwent living anionic polymerization by the addition of Et3B to the conventional system.80 As mentioned above, no apparent polymerization of MAN occurred with the binary initiator system of Ph2CHK/Et3B at −78 °C even after 28 h. However, the polymerization immediately took place and was completed within 1 min by raising the temperature to 0 °C, resulting in the formation of PMANs possessing predicted molecular weights (Mn ∼ 32 000 g/mol) and narrow MWDs (Mw/Mn < 1.1). The side reactions F


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Scheme 4. Estimated Mechanism of Living Anionic Polymerization of Methacrylonitrile (MAN) in the Presence of Et3B

Scheme 5. Stereospecific Living Anionic Polymerization of MMA

narrow MWDs (Mw/Mn ∼ 1.1) were produced even at room temperature.

may be effectively suppressed by the coordination of Et3B to the initiator and/or the propagating enolate anion to stabilize the anionic species (Scheme 4). Based on the polymerization behavior at different temperatures, the dormant species between the propagating polymer anion and Et3B might form in the polymerization system. Unfortunately, the same binary initiator system could not achieve any degree of molecular weight control during the polymerization of acrylonitrile. Several effective polymerization systems of acrylate and methacrylate monomers by the addition of the bulky R3Al and R3−n(R′O)nAl were reported by Kitayama et al.,78e Müller et al.,81 and Kuraray Co., Ltd.82 More details are discussed in the next section. Interestingly, the acceleration of polymerization was often observed in these systems in a nonpolar solvent like toluene, probably due to the coordination of the Lewis acids to the (meth)acrylate monomers. Another interesting example was living anionic polymerization of MMA at ambient temperatures in the presence of the tetraphenylphosphonium cation reported by Hogen-Esch et al.83 The in situ formed Ph3C−Ph4P+ from Ph3CK and Ph4P+Cl− initiated the polymerization of MMA at temperatures between 0 and 20 °C to quantitatively afford (PMMA)s with predictable molecular weights (Mn ∼ 29 100 g/mol) and narrow MWDs (Mw/Mn ∼ 1.1). The bulky Ph4P+ cation probably facilitates the formation of the narrowly distributed PMMA by reducing the rate of the side reactions. Very recently, Kakuchi et al. reported a significant improvement in the group transfer polymerization (GTP) system using 1-triisopropylsiloxy-1-methoxy-2-methyl-1-propene in the presence of pentafluorophenylbis(triflyl)methane as the organocatalyst. With this system, the polymerization of methyl acrylate (MA) rapidly and quantitatively proceeded to afford a welldefined PMA (Mn = 108 000 g/mol, Mw/Mn = 1.07) at room temperature in toluene.84 The use of the bulky triisopropylsilyl group in the silyl enolate initiator may play a key role in controlling the polymerization of the acrylate monomer. The same group also succeeded in the GTP of MMA using either trifluoromethanesulfonimide as a strong Brønsted acid85 or P4t-Bu as an organic superbase catalyst.86 In both systems, the PMMAs with predicted Mn values (∼50 000 g/mol) and very

4. REGIO- AND STEREOSELECTIVE POLYMERIZATION The stereoregularity of vinyl polymers and/or microstructure of the poly(1,3-diene)s that determine the thermal and/or mechanical properties are known to be significantly affected by the polymerization variables, since they can change the coordination states of the propagating species. As the most important example, a series of stereoregulated PMMAs with highly isotactic, syndiotactic, and heterotactic configurations were successfully synthesized by carefully choosing the initiator systems and solvents (Scheme 5).76e,78a−c,e In particular, the combination of RLi or RMgX with appropriate Lewis acids in hydrocarbon media were effective in optimizing the stereoregularity. Kitayama et al. recently succeeded in synthesizing almost perfect isotactic PMMAs with the mm content of up to 99.5% using the binary initiator system (α-lithioisobutyrate/ Me3SiOLi) in toluene.87 Since such highly stereoregular PMMAs are ideal model polymers for various basic properties, the differences in the Tgs and hydrodynamic volume are discussed.78c,88,89 Very interestingly, a mixture of isotactic and syndiotactic PMMAs forms an intermolecular stereocomplex, in which a double-stranded isotactic PMMA helix is included in a single syndiotactic PMMA helix.90a−c Kitayama et al. also reported that various highly stereoregular poly(alkyl methacrylate)s were successfully prepared using specific initiator systems and/or solvents.78e Kuraray Co., Ltd., in Japan, successfully developed living anionic polymerization of (meth)acrylate monomers at ambient temperature by designing the initiator system containing the bulky Lewis acidic diphenoxyalkylaluminum compound.82a,b This is the first example of poly((meth)acrylate)s industrially produced by living anionic polymerization. All (meth)acrylic ABA type triblock polymers, for instance, PMMA-b-poly(nbutyl acrylate)-b-PMMA, were synthesized as a next-generation thermoplastic elastomer. The stereospecific living anionic polymerization of N,Ndiethylacrylamide (DEA) was also developed in THF.79b,91a−c G


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selectivities were perfectly controlled in the polymerization of 2-triisopropoxysilyl-1,3-butadiene (iPOSBd) among such monomers.97a,b In practice, the polymerization of iPOSBd exclusively proceeded in the 1,4-addition mode even in THF with the various initiators carrying a Li+, Na+, or K+. The stereoselectivity was completely regulated as the E configuration (cis configuration in terms of the main chain, Scheme 6). Thus, the anionic polymerization of iPOSBd occurred in

For example, the syndiotactic-rich (rr = 78%) PDEA was prepared using Ph2CHLi/Et2Zn, while isotactic-rich (mm = 80−90%) (PDEA)s were produced using the initiator systems like RLi/LiCl and tBuMgBr/Et2Zn. The addition of Et2Zn to Ph2CHK in THF at 0 °C induced the heterotactic-specific polymerization of DEA (mr = 92%). It should be noted that the stereoregularity of PDEA strongly affects the water solubility and the cloud point (Tc) of the aqueous solution. Although it is believed that PDEA is a water-soluble polymer, highly syndiotactic polymers were observed to be insoluble in water at any temperature. Both isotactic and heterotactic (PDEA)s showed water solubilities, but their aqueous solutions had Tc values of 38 and 28 °C, respectively. Thus, the stereospecific anionic polymerization of DEA evidently contributes to the polymer solution property and behavior. A similar relationship between the stereoregularity and solution property was recently found in poly(Nisopropylacrylamide)s (PNIPAM)s. Since the direct anionic polymerization of NIPAM is difficult due to the presence of the acidic amide proton, the amide proton must be protected prior to the anionic polymerization. Kitayama et al. succeeded in synthesizing a highly isotactic PNIPAM (m = 97%) by the anionic polymerization of a trimethylsilyl-protected NIPAM with t-BuLi/AlR3 in toluene.92 Surprisingly, the polymer was insoluble in water. Ishizone et al. synthesized an acetalprotected NIPAM, N-methoxymethyl-N-isopropylacrylamide, and carried out the anionic polymerization.93a−c This protected monomer readily underwent living anionic polymerization in THF at −78 °C with Ph2CHM (M = Li, K, and Cs) in the presence of either LiCl or Et2Zn (Mn ∼ 48 000 g/mol and Mw/ Mn < 1.1). The initiator system of Ph2CHK/Et2Zn afforded an atactic PNIPAM (r = 50%) showing a Tc value of 32 °C. On the other hand, the Tc value of 37 °C was observed for a syndiotactic-rich polymer (r = 83%) produced by the Ph2CHLi/Et2Zn initiator system. A water-insoluble isotacticrich PNIPAM (m = 69%) was obtained with the Ph2CHLi/LiCl system. Hogen-Esch et al. demonstrated the synthesis of isotacticrich PS (mm = 55−72%) by the anionic polymerization with 3,3-dimethyl-1,1-diphenyl-1-lithiobutane in hexane at −30 °C in the presence of lithium hydroxide.94 On the other hand, the triad (mm) and pentad (mmmm) contents of the PS segment reached 95 and 90%, respectively, when the polymerization of styrene was carried out with polyisopropenyllithium at −60 °C. The control of the regio- and stereoselectivities of PB and PI is an industrially important subject, since their elastic properties strongly depend on the microstructures of the repeating units.95 During the polymerization in hydrocarbon media with RLi, the microstructures of the resulting poly(diene)s are regulated to be 1,4-, especially the cis-1,4-mode, showing the desired elastic properties.1 The significance of high 1,4-mode for poly(diene)s is that such polymers exhibit low Tg (e.g., −64 to −70 °C for PI and −94 °C for PB). The Tg rises linearly as the concentration of 1,2-mode increases. Although numerous studies have been so far dedicated to control the microstructures, perfect control of both the regioselectivity and stereoselectivity has not yet been realized and is still challenging subjects. The highest cis-1,4 microstructures were obtained so far in the absence of solvent at low concentrations of RLi (∼10−6 M): 98% cis-1,4-PI and 86% cis-1,4-PB.95,96 Takenaka et al. reported that a seires of 2-trialkoxysilyl-1,3butadienes underwent living anionic polymerization in THF at −78 °C. It was observed that both the regio- and stereo-

Scheme 6. Stereoselective and Regioselective Living Anionic Polymerization of 2-Triisopropoxysilyl-1,3-butadiene (iPOSBd)

regioselective and stereoselective fashions in addition to the living mechanism. The resulting polymers not only show elastomers in character but also have the advantage to have alkoxysilyl functions capable of linking with metal and inorganic materials. Another interesting example is living anionic polymerization of 1,3-butadiene carrying a bulky and rigid adamantyl substituent, i.e., 2-(1-adamantyl)-1,3-butadiene (AdBd).98a,b The PAdBd with a high cis 1,4-repeating unit (96%, cis/trans = 93/7) was obtained using sBuLi in cyclohexane. Interestingly, even in THF, the microstructure was predominantly regulated in the cis 1,4-addition mode (88%, cis/trans = 82/18). These results suggest that the introduction of a bulky function at the 2-position can potentially control the regio- and stereoselectivity to the cis 1,4-addition mode. Several research groups have focused on living anionic polymerization of 1,3-cyclohexadiene (CHD), a cyclic monomer with a fixed cisoid 1,3-diene structure.99a−d The polymerization of CHD with BuLi in the presence of N,N,N′,N′tetramethylethylenediamine in cyclohexane at 40 °C afforded a polymer containing 52% 1,2- and 48% 1,4-repeating units. Since the cyclohexene moiety in the resulting PCHD can be converted into either a saturated cyclohexane ring or a phenylene ring via hydrogenation or oxidation, the resulting PCHD is considered to be an attractive precursor for rigid poly(cyclohexane)s with a high Tg value and conductive πconjugated poly(phenylene)s.

5. LIVING ANIONIC POLYMERS WITH UNIQUE CONFORMATIONS Polyacetylene (PA) has been extensively studied as a conductive and nonlinear optically active specialty polymer. PA adopts a rodlike conformation due to the conjugated resonance structure, exhibiting a rigid and mechanically tough chain structure. Accordingly, the PA−vinyl polymer molecular conjugates are expected to be new functional materials, which combine advantageous features of PA with the characteristics of vinyl polymers such as solubility, flexibility, elasticity, and processability. Unfortunately, acetylene cannot be directly polymerized under the conditions of anionic polymerization. Hogen-Esch et al. developed an efficient two-step methodology for the synthesis of a well-defined PA via living anionic polymerization of phenyl vinyl sulfoxide (PVS), followed by conversion to the PA segment simply by thermal treatment, as shown in Scheme 7.100 By using this methodology, PAs with H


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Scheme 7. Synthesis of Polyacetylene (PA) by Living Anionic Polymerization of Phenyl Vinyl Sulfoxide (PVS), Followed by Thermal Degradation of the Resulting PPVS

Scheme 8. Complex Branched Polymers by Using Living Poly(macromonomer)s

CBABC pentablock terpolymer, PHI-b-PI-b-PS-b-PI-b-PHI, could be synthesized.104 Interesting and unique morphologies and the formation of supramolecular assemblies have recently been observed from these block polymers.105a−e α-Amino acid N-carboxy anhydrides (NCAs) are anionically polymerized to afford poly(α-amino acid)s, some of which adopt ordered conformations of the α-helices or β-strands. Although the anionic polymerization of NCA was not satisfactorily controlled for a long time, it has recently been much improved to proceed in a living manner.106a−d The molecular weights could be controlled up to a 100 000 g/mol order, and narrow MWDs (Mw/Mn < 1.2) were attained. Various block polymers and even μ-star polymers containing poly(α-amino acid)s were successfully synthesized using chainNH2-functionalized polymers as macroinitiators.107a−f,108 The incorporation of poly(α-amino acid) sequences into block polymers are particularly interesting for the generation of unusual nanostructures and enhanced control over nanoscale structures through intermolecular hydrogen bonding.108 It is also interesting that the resulting biomimetic hybrid polymers behave as potentially biocompatible materials and new smart materials, whose conformation and association properties can reversibly respond by changing pH and temperature.108,109 Thus, living anionic polymers possessing rigid-rod-like or ordered α-helical and β-strand conformations are now available. Accordingly, the molecular design and synthesis of macromolecular architectures containing such characteristic segments become possible. Furthermore, since they possess intriguing properties including conductivity, nonlinear optical activity, liquid crystallinity, biocompatibility, etc., combining such polymer segments with synthetic polymers offers many

controllable molecular weights and narrow MWDs (Mw/Mn < 1.2) could be successfully synthesized for the first time in the field of living anionic polymerization. The success of this methodology provides a new route to the incorporation of the PA segment into elaborate polymer structures accessible through anionic polymerization. The same group synthesized new PA-containing block polymers, PS-b-PA and PA-b-PS-bPA, by the sequential polymerization of styrene and PVS, followed by thermal treatment.100 Soon after, several PAcontaining block polymers101a−e as well as asymmetric starbranched polymers containing one or two PA arms102a,b were synthesized using the two-step synthesis. The resulting polymers are of special interest in that the PA segments are phase-separated at the molecular level, followed by selforganizing, to arrange the conductive PA assemblies inside the microdomains. Moreover, their rigid rod−coil structures are interesting in terms of their physical, mechanical, and solution properties. Poly(alkyl isocyanate)s (PRI)s are interesting polymers that adopt an extended rodlike helical conformation and possess a unique optical activity and liquid crystallinity. Lee et al. first succeeded in achieving living anionic polymerization of RIs under the conditions at −98 °C with the initiators having Na+ in the presence of 15-crown-5 or NaBPh4.103a−c The addition of such additives to the polymerization system is essential to prevent any undesired trimer formation by backbiting from the living polymer chain-end anion. With this living polymerization system, not only well-defined PRIs (Mn ∼ 50 000 g/mol and Mw/Mn < 1.1) but also various well-defined AB diblock polymers, ABA and BAB triblock polymers (A: PS and P2VP; B: poly(hexyl isocyanate) (PHI)), and even a particular I


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Scheme 9. Complex Branched Polymers by Using Living Double, Triple, and Star-Tailed Comb Polymers

monomers and the resulting living anionic poly(macromonomer)s can be utilized for all molecular designs and architectural polymer syntheses developed by living anionic polymerization. The complex branched polymers thus synthesized are very difficult in synthesis by any other methods. Various macromonomers herein synthesized should be added to the list of new monomers capable of living anionic polymerization.

opportunities for the development of new functional specialty polymers for both academic and industrial interests and the next-generation nanomaterials.110a,b,111

6. LIVING ANIONIC POLY(MACROMONOMER)S Poly(macromonomer)s are extremely high-density graft polymers with a polymer chain in each repeating unit. Hadjichristidis et al.112a−i were the first to successfully prepare a series of living anionic poly(macromonomer)s by the direct anionic polymerization of in situ prepared macromonomers without isolation and further rendered them capable of synthesis of complex branched polymers. A living poly(ω-styryl macromonomer) was prepared as follows:112a PSLi was first reacted with 4-(chlorodimethylsilyl)styrene (CDMSS), followed by anionic polymerization of the resulting ω-styryl macromonomer with sBuLi. Thus, the macromonomer is not isolated and directly in situ polymerized to prepare the living anionic poly(macromonomer). The key for the preparation of the macromonomer is the faster reaction of the PSLi with the silyl chloride function than with the vinyl group of CDMSS. The anionic polymerization of the prepared macromonomers (Mn = (1.3−15.0) × 103 g/mol, Mw/Mn = 1.03−1.10) was achieved by the addition of sBuLi to the vinyl double bond of styrene monomer produce a series of welldefined living anionic poly(macromonomer)s (Mw = (30.8− 125.5) × 103 g/mol and Mw/Mn = 1.02−1.11). As shown in Scheme 8, the in situ prepared different macromonomers were sequentially polymerized to afford ABC triblock terpolymers composed of all comblike segments. The in situ linking reaction of the living poly(macromonomer)s with either MeSiCl3 or SiCl4 gave completely new 3- and 4-arm star-comb polymers. A series of comb-b-linear and linear-bcomb-b-linear block polymers were also synthesized by the sequential addition of another monomer or the in situ prepared macromonomer(s) to the living poly(macromonomer).112b−f The same group successfully synthesized new double- and triple-tailed ω-styryl macromonomers by the reaction of PSLi with 4-(dichloromethylsilyl)styrene and 4-(2(dichloromethylsilyl)ethylchloromethylsilyl)styrene.112g,h Furthermore, single and double star-tailed ω-styryl macromonomers were prepared by modifying the procedure using an off-center living polymer composed of three polymer chains. By converting these new macromonomers to the corresponding living poly(macromonomer)s, more complex macromolecular architectures can be synthesized (Scheme 9).112i The key factor in this study is that all of the macromonomers, without isolation, can be handled as conventional

7. PRECISE SYNTHESIS OF MACROMOLECULAR ARCHITECTURES One of the most advantageous features of living anionic polymerization is the synthetic ability of various well-defined macromolecular architectures according to their molecular designs. Since many macromolecular architectures have been reviewed in several articles and books, only recent synthetic advances have been briefly described, and a new conceptual allaround iterative methodology developed by us will be introduced as a future perspective approach for architectural polymer synthesis. We involve block polymers, although they are not macromolecular architectures in the strict sense, graft polymers, star-branched polymers, dendrimer-like starbranched polymers, and hyperbranched polymers in the category of macromolecular architectures because they are all composed of several polymer chains connected with linking point(s) at appropriate position(s). 7.1. Recent Synthetic Advances of Macromolecular Architectures. A huge number of di- and triblock polymers have been synthesized by living anionic polymerization in which two different monomers are sequentially added, the socalled “sequential polymerization”, and widely studied regarding their morphologies, properties, and behavior. The synthesis of alternate multiblock polymers of the (AB)n type is also possible by the sequential addition of both monomers several times. With three monomers having similar reactivities, the ABC, ACB, and BAC triblock terpolymers with different sequential order can be synthesized by the sequential polymerization. The successful synthesis of a particular tetrablock quarterpolymer, PS-b-PB-b-PI-b-poly(1,3-cyclohexadiene), was reported.113 On the other hand, the block polymer synthesis by sequential polymerization using monomers with different reactivities is problematic. Since more reactive monomers usually produce less reactive chain-end anions and vice versa, less reactive chainend anions often cannot polymerize other less reactive monomers. Accordingly, block polymers can be synthesized only by the sequential addition of monomers in the order of J


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methodology using multifunctional chlorosilanes seems attractive because certain μ-star polymers are synthesized in one-pot, while a multiple-pot synthesis is required by other methodologies. The synthetic limitation is undoubtedly attributed to the fact that a multiple number of reaction sites disappear after the introduction of the arm, and thereby the arm can no longer be introduced. In the next section, we will introduce a new methodology by which the above synthetic limitation is overcome to synthesize a series of multicomponent μ-star polymers. A dendrimer-like star-branched polymer (DSP) has emerged as a novel class of well-defined hyperbranched polymers since 1995.126 To understand the structures of the DSPs, the fifthgeneration (5G) DSP and its generation-based block terpolymer composed of three different segments are shown in Figure 7. As it can see, they are similar in branched

decreasing chain-end anion reactivity. Thus, special care is needed for the monomer addition order. Nevertheless, several interesting block polymers has been reported. Stadler et al. and then Müller et al. were successful in synthesizing the triblock terpolymers, PS-b-P2VP-b-P t BMA and PB-b-P2VP-bPtBMA.114a−c Hydrolysis of the PtBMA block with HCl produced a new ABC triblock terpolymer of PS-b-P2VP-bpoly(methacrylic acid), which exhibited pH-dependent solution properties. The following triblock terpolymers were also synthesized by using monomers with similar and/or different reactivities: PS-b-PB-b-PMMA,115 poly(tert-butoxystyrene)-bPB-b-PtBMA,116 poly((5-N,N-dimethylamino)isoprene)-b-PSb-PtBMA,117 PB-b-PtBMA-b-poly(2-dimethylaminoethyl methacrylate),118 and PS-b-poly(2-trimethylsilyloxyethyl methacrylate)-b-PMMA.119 Hadjichristidis et al. reported the successful synthesis of multiblock polymers, i.e., PI-b-P2VP-b-PEO, PS-bPI-b-P2VP-b-PEO, PS-b-PI-b-P2VP-b-PtBMA-b-PEO, PS-b-PIb-PHI, and PHI-b-PI-b-PS-b-PI-b-PHI.120a−c Multiblock polymers with unusual sequences will be described in the next section. Like block polymers, graft polymers have long been studied and reviewed as representative branched polymers and reviewed.121−123 The structure of a graft polymer is defined by the following three factors: (1) the molecular weight of the main chain, (2) the molecular weight of the graft chain, and (3) the distance between the graft chains, as shown in Figure 6. A

Figure 7. 5G dendrimer-like star branched polymer and its block terpolymer.

architecture to the dendrimers but composed of many polymer chains linked to each other between the junctions. Therefore, DSPs are much higher in molecular weight and much larger in molecular size than the dendrimers. DSPs, believed to be globular macromolecules in shape, have many characteristic and potentially applicable features such as specific topological hyperbranched architectures, hierarchic generation-based structures, different branched densities between the core and outermost layer, and many junctions and terminal groups.127−131 Similar to the dendrimers, stepwise iterative methodologies based on two complementary approaches,132 the divergent and the convergent, were employed for the synthesis of the DSPs. Since DSPs are composed of polymer segments, one more reaction step to introduce the polymer chain is required, and the living polymers are usually used to make the synthesized DSPs well-defined in structure. Various DSPs and their block polymers have been synthesized by stepwise iterative methodologies based on either a “core-first divergent” or an “arm-first convergent” approach, which combines the appropriate linking reactions with living polymerization systems. Since they have been introduced in some recent reviews,127−131 the detailed synthetic procedures are omitted due to lack of space, To date, most DSPs synthesized by such methodologies were limited to 2G−4G polymers with molecular weights on the order of 100 000 g/mol because of the required use of high-molecularweight polymers in all the steps. The following examples appear to be noteworthy, involving those by Hedrick et al.,133 Gnanou et al.,134a,b Percec et al.,135 Hadjichristidis et al.,136a,b Hutchings et al.,137 and Monteiro et al.138 For the synthesis of high-generation (≥5G) and highmolecular-weight (>106 g/mol) DSPs, only one example has recently been reported, except for our examples described later. Gnanou et al.139 reported the synthesis of a 7G DSP consisting of 508 PS segments by the stepwise iterative methodology

Figure 6. Three structural factors of graft polymer.

graft polymer, in which all three factors are perfectly controlled, is called an “exact graft polymer” by Hadjichristidis, but almost all the graft polymers so far synthesized are not categorized as an exact graft polymer due to their imperfect structural control. In 2000, Hadjichristidis et al. were the first to successfully synthesize an exact graft copolymer of styrene and isoprene having two graft units by multireaction steps including living anionic polymerization.124 The synthesis of exact graft polymers with more graft units will be shown in the next section. Among the star-branched polymers, the asymmetric starbranched polymers having chemically different arms, the socalled miktoarm star polymers, or μ-star polymers, have recently received much attention because of their unique and unusual morphologies. However, it is far more difficult to synthesize μ-star polymers than regular stars because the synthesis always requires selective multistep reactions that correspond to the number of different arms, and isolation of the intermediate polymers is often needed to obtain pure products. For these reasons, the methodologies developed so far by living anionic polymerization can allow the synthesis of a twocomponent AxBy type, several 3-arm three-component ABC and 4-arm four-component ABCD μ-star polymers.125a−u In addition, structural variation of such μ-stars is quite limited. Among the methodologies, it is worth noting that the K


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Scheme 10. Synthesis of Dendrimer-like Star-Branched PSs up to 7G by Stepwise Iterative Methodology Based on “Core-First Divergent” Approach

Scheme 11. Synthesis of Dendritic Polystyrenes by Convergent Living Anionic Polymerization

based on the “core-first divergent” approach (Scheme 10). By repeating the reaction sequence, the 7G polymer (Mn = 1.92 × 106 g/mol, Mw/Mn = 1.04) was successfully synthesized. In the next section, the iterative methodology developed by our group will be introduced, which is also effective for the synthesis of high-generation and high-molecular-weight DSPs. In addition to DSPs, other types of hyperbranched polymers consisting entirely of branched polymers have recently been reported. The first example was “dendrigraft (or arborescent)” polymers reported by Gauthier et al.140 These polymers were synthesized by repeating the reaction sequence involving living anionic polymerization of styrene and the subsequent functionalization (chloromethylation or acetylation), followed by a grafting reaction of the resulting functionalized PS with the living PS. Since a large number of reaction sites were introduced in each reaction sequence, a very rapid molecular weight growth was observed by repeating the reaction sequence. Even after repeating the same reaction sequence four times, highly branched PSs with Mn values up to 107 g/mol were obtained, and their molecular weight distributions still remained narrow (Mw/Mn < 1.1).141a,b The resulting polymers were found to possess generation-based architectures analogous to the DSPs. Hirao et al. reported the synthesis of highly branched PSs with more controlled architectures by a similar methodology.142 A living anionic block polymer of PS-bpoly(3-(tert-butyldimethylsilyloxy)methylstyrene) was first prepared and in situ coupled with the tetrafunctional core agent, resulting in a 4-arm star-branched polymer. The silyl ether function was then transformed to the bromide, followed by a

coupling reaction of the resulting brominated block polymer with the same living block polymer. The reaction sequence was repeated one more time to afford a generation-based hyperbranched PS, 4-branched at the core and average 12branched in the second or third layer. The final PS had a Mn of 1.4 × 107 g/mol (Mw/Mn = 1.08) and very close to DSP in architecture. Very recently, He et al. reported the synthesis of the same hyperbranched polymers by repeating the reaction sequence involving the preparation of a living anionic PS-b-PI, followed by epoxidation of the PI side chain, and a coupling reaction of the epoxide-functionalized block polymer with the living PS-b-PI (Mn ∼ 4 × 107 g/mol, Mw/Mn ∼ 1.3).143 Dendrimer-like PEOs were synthesized by repeating the anionic ring-opening polymerization of EO, followed by the same polymerization of a mixture of glycidol and propylene oxide using a 3-arm PEO star as the starting precursor (Mn ∼ 105 g/mol and Mw/Mn ∼ 1.3).144 Kunaus et al. synthesized a series of dendritc PSs in a one-pot reaction by a method that combines living anionic polymerization with a convergent process.145 As illustrated in Scheme 11, the synthesis is achieved by reacting PSLi with CDMSS, which contains a polymerizable vinyl group and a moiety capable of undergoing the linking reaction. Adding styrene along with CDMSS allowed for the synthesis of high-molecularweight dendritic PSs (Mn > 600 000 g/mol) with rather narrow polydispersities (Mw/Mn ∼ 1.3) and generational growth approaching an average of 6G. The other type of hyperbranched polymers is prepared by the self-condensing vinyl polymerization (SCVP) of inimers, L


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Scheme 12. Synthesis of Hyperbranched Polystyrenes Using an Anionic Inimer

methodologies via different mechanisms will not be discussed, since an previous review by Frey et al. has recently been published.150 7.2. Syntheses of Macromolecular Architectures by New Conceptual All-Around Iterative Methodologies. Macromolecular architectures are composed of several polymer chains connected at the linking point(s) via suitable reaction sites. However, a serious synthetic limitation is present for such polymer syntheses because the reaction site always disappears after the introduction of a polymer segment, and the polymer segment can no longer be introduced. Because of this limitation, it is long believed that the synthesis of complex macromolecular architectures, such as multiblock polymers, exactly defined graft polymers, multicomponent μ-star polymers, and high-generation and high-molecular-weight DSPs, is very difficult or even impossible. In order to overcome this difficulty, an all-around methodology has been developed based on a new conceptual stepwise iterative approach in conjunction with a living anionic polymerization system. In this methodology, the system is designed in such a way that the reaction site is always regenerated after the introduction of the polymer segment in each reaction sequence, and this “polymer segment introduction and regeneration of the reaction site” sequence is repeatable. If this methodology satisfactorily works, the polymer segment can be successively and, in principle, limitlessly introduced to construct all of the above-mentioned macromolecular architectures. This methodology was first proposed for the synthesis of multicomponent μ-star polymers. After its successful development, the methodology has been extended to the synthesis of high-generation and highmolecular-weight DSPs, multiblock polymers, and exactly defined graft polymers in the same synthetic sense. The iterative methodology was first proposed for the synthesis of μ-star polymers, as it is shown in Scheme 14.151 At first, the chain-end-B-functionalized living polymer is prepared, and the B function is transformed to the “A” function capable of reacting with a living polymer. The second B-functionalized living polymer then reacts with the Afunctionalized polymer to link the two polymer chains. After

which are monomers with latent initiating moieties. Although this methodology has been successfully used for the synthesis of various hyperbranched polymers via different mechanisms, there are only a few reports by Baskaran et al. and He et al. about the synthesis of hyperbranched polymers from anionic inimers (Scheme 12).146,147a,b Frey et al. reported the synthesis of a variety of hyperbranched poly(ether)s with many hydroxyl groups via the anionic ring-opening polymerization of glycidol, representing a latent AB2 monomer (Scheme 13).148a,b Glycidol was slowly Scheme 13. Synthesis of Hyperbranched Polyethers by the Anionic Ring-Opening Polymerization of Glycidol

added to a trifunctional initiator core for the polymerization. Because of the fast proton exchange during the polymerization, different chain ends are able to simultaneously grow into a branched structure. This approach was extended to the synthesis of linear-b-hyperbranched diblock and hyperbranched-b-linear-b-hyperbranched triblock polymers.149a,b The above-mentioned procedures were facile and more conveniently accessible to synthesize hyperbranched polymers on a large scale, but all the resulting polymers exhibited an imperfect structure. Although only a few examples via the (living) anionic polymerization have now been introduced, the synthesis of many other hyperbranched polymers by similar

Scheme 14. Synthesis of μ-Star Polymers by Iterative Methodology Using A and B Functions: (a) Arm Introduction and (b) Regeneration of Reaction Site

M


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Scheme 15. Synthesis of DSPs by Iterative Methodology: (a) Arm Introduction and (b) Regeneration of Reaction Site

Figure 8. Synthesis of DSPs up to 7G by iterative methodology.

respectively. The reaction sequence involving two steps is repeated. Finally, the 7G DSP is successfully synthesized (Figure 8). Herein, both the A and B functions are exactly the same as those used in Scheme 14 . In general, the A and B functions are the BnBr or α-phenylacrylate (PA) moiety and the 3-tert-butyldimethylsilyloxymethylphenyl (SiOMP) moiety, respectively. For this iterative methodology, an α-terminal-B2-functionalized living PMMA was used as the starting polymer, obtained by living anionic polymerization of MMA with the initiator prepared from sBuLi and 1,1-bis(3-tertbutyldimethylsilyloxymethylphenyl)ethylene and after transformation of the silyl group to the BnBr or PA functions as A reaction sites by treatment with Me3SiCl/LiBr or with Bu4NF, followed by esterification with α-phenylacrylic acid. The final DSP is a huge macromolecule with a precisely controlled Mn value of 1.94 × 106 g/mol and a narrowly distributed Mw/Mn value of 1.02. It consists of 508 PMMA segments and possessed 512 BnBr reactive termini capable of continuing the DSP synthesis. The success of this methodology made it possible to synthesize various DSPs composed of not only PMMA but also PtBMA, PS, and a mixture of these segments by slightly modifying the methodology.156,157 As already mentioned, DSPs are well-defined huge macromolecules with regulated hyperbranched architectures. Furthermore, a variety of functional groups can be appropriately introduced into any generation, at any internal and/or external position, and/or at the periphery, resulting in functionalized hyperbranched and nanosize globular macromolecules. However, interesting properties and behavior have not yet been sufficiently characterized; morphological and rheological studies have just started. Very recently, Hutchings has reviewed that temperature gradient interaction chromatography (TGIC), first developed by Chang et al.,158 is an indispensable analytical technique to reveal the structural dispersity in complex branched polymers, like DSPs, and other branched polymers.159 TGIC is an interaction chromatography technique. The resolution power of TGIC is far superior to SEC, and especially for branched polymers, the reliability of SEC is low. Actually, it has been demonstrated that several side products and structural

the transformation to A, the third B-functionalized living polymer reacts with the in-chain-A-functionalized block polymer, resulting in a 3-arm ABC μ-star core-functionalized with B. As can be seen, the B function is stable toward the anion and transformable into the A function. Both the (a) and (b) steps correspond to the “polymer segment (or arm) introduction” and “regeneration of the reaction site”, respectively. Since both steps quantitatively proceed, the reaction sequence involving both steps can be repeated. By repeating the same reaction sequence one more time, a 4-arm ABCD μ-star is synthesized. Since the B function is introduced at the core, it may be possible to continue the synthesis to afford a 5-arm or more armed μ-star polymers. The Bfunctionalized living polymer is obtained by the 1:1 addition reaction of the living polymer with 1-phenyl-1-(3-tertbutyldimethylsilyloxymethylphenyl)ethylene. After the reaction, the silyl group is quantitatively transformed into benzyl bromide (BnBr) reaction site (A) by treatment with Me3SiCl/LiBr. Very recently, basically a similar iterative methodology using an α-phenylacrylate (PA) function as a new reaction site for the synthesis of the μ-star polymers has been developed.152,153 Since the PA reaction site is capable of reacting with less reactive living poly(alkyl methacrylate)s (PRMAs) and P2VP, the connection of PRMAs as well as P2VP is possible. Thus, several 3-arm ABC, 4-arm ABCD, 5arm ABCDE, 6-arm ABCDEF, and even 7-arm ABCDEFG μstars composed of PRMA and/or P2VP arm segments were successfully synthesized.154a−c A more efficient iterative methodology will be introduced later. The methodology was further developed for synthetically difficult high-generation and high-molecular-weight DSPs.155a−c As shown in Scheme 15, a chain-end-B2-functionalized living polymer is prepared and reacts with a core compound having four A functions to afford a 4-arm star polymer. The B function is then transformed into the A function, followed by reacting with the starting B2-functionalized living polymer, resulting in a 2G DSP. The B functions are again transformed to the A functions, and the same reaction sequence is continued. As can be seen, both the (a) and (b) steps correspond to the “arm introduction” and “regeneration of the reaction site”, N


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Scheme 16. Synthesis of Multiblock polymers by Iterative Methodology Using A and B Functionalities: (a) Arm Introduction and (b) Regeneration of Reaction Site

Table 1. Synthesis of a Series of Alternate (AB)n Multiblock Polymers Mn × 10−3 (g/mol)

polymer

a

composition (%wb/wc)

A

B

type

calcd

RALLSa

Mw/Mna

calcd

PS

PMMA

AB (AB)2 (AB)3 (AB)4 (AB)5

10.5 26.4 37.0 51.0 64.5

11.4 28.2 40.5 53.6 66.4

1.03 1.03 1.03 1.04 1.06

50/50 48/52 45/55 45/55 45/55

1

H NMR 48/52 47/53 43/57 43/57 45/55

Determined by SEC equipped with triple detectors. bPS. cPMMA.

Scheme 17. Synthesis of PDMS-b-PtBMA by Reacting ω-Chain-End-BnCl-Functionalized PDMS with Living PtBMA

of these multiblock polymers and triblock terpolymers were not synthesized by the sequential polymerization because of the mismatch in reactivity between the chain-end anion and the monomer. The resulting multiblock polymers possessed predicted Mn values and compositions, as well as narrow MWDs, as summarized in Table 1. Since a variety of functional MMA derivatives applicable to the living polymerization are now available, the following functional triblock terpolymers could also be synthesized: P2VP-b-PS-b-poly(2-tert-butyldimethylsilyloxethyl methacrylate), P2VP-b-PS-b-poly(2,3-dimethyl-1,3-dioxolan-4-yl)methyl methacrylate), P2VP-b-PS-b-PtBMA, and P2VP-b-PS-b-poly(ferrocenylmethyl methacrylate).162 The first three block terpolymers could be converted by hydrolysis to afford the following three new functional block terpolymers: P2VP-b-PSb-poly(2-hydroxyethyl methacrylate), P2VP-b-PS-b-poly(2,3dihydroxypropyl methacrylate), and P2VP-b-PS-b-poly(methacrylic acid). Hadjichristidis et al. previously reported the successful synthesis of PDMS containing block polymers by developing an efficient linking methodology using 2-(4chloromethylphenyl)ethyldimethylchlorosilane (CMPDMS) as a heterofunctional linking agent on the basis of the greater reactivity of the silyl chloride than the benzyl chloride (BnCl) function toward the silanolate anion.163 As illustrated in Scheme 17, the living PDMS was first prepared by the anionic polymerization of D3 and then reacted with CMPDMS. The reaction of the silanolate anion with the silyl chloride function was quite selective, resulting in an ω-terminal-BnCl-function-

defects can be detected by TGIC in such branched polymers, whose SEC profiles suggest an essentially pure product. Next, the further extension of the iterative methodology for the synthesis of multiblock polymers as well as exact graft polymers is demonstrated. The synthetic outline of multiblock polymers ((AB)n) by the iterative methodology is illustrated in Scheme 16. At first, an α-terminal-B-functionalized living AB diblock polymer is prepared by the sequential polymerization of two monomers with the B-functionalized initiator. The B is transformed to the A, followed by the subsequent reaction of the resulting A-functionalized block polymer with the above αterminal-B-functionalized living block polymer to link the two block polymer chains, resulting in an α-terminal-B-functionalized (AB)4 tetrablock polymer. By repeating the same reaction sequence three more times, the (AB)6, (AB)8, and (AB)10 multiblock polymers were successively synthesized.160 The α-terminal-B-functionalized AB block polymer was readily prepared by the sequential polymerization of styrene and MMA (or 2-VP, tBMA) with 3-(tert-butyldimethylsilyloxy)-1-propyllithium. The resulting block polymer was treated with Bu4NF and the subsequent esterification with α-phenylacrylic acid was performed to convert the PA function (A reaction site). This procedure could be applied to the synthesis of triblock terpolymers with an unusual block sequence. For example, synthetically difficult PS-b-PMMA-b-P2VP and P2VP-b-PS-bPMMA triblock terpolymers could be synthesized by the linking reactions of the living PS-b-PMMA with the α-terminalPA-functionalized P2VP and of the living P2VP with the αterminal-PA-functionalized PS-b-PMMA, respectively.161,162 All O


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Scheme 18. Synthesis of Exact Graft Copolymers by Iterative Methodology

alized PDMS. The living PtBMA was then reacted with the BnCl-functionalized PDMS to afford a well-defined PDMS-bPtBMA, difficult to be linked by sequential polymerization. By extending this methodology, a new tetrablock quarter polymer, PS-b-PI-b-PDMS-b-P2VP, was synthesized by the linking reaction of the living P2VP with an ω-terminal-BnCl-functionalized PS-b-PI-b-PDMS, prepared by the reaction of the living PS-b-PI-b-PDMS with CMPDMS.164 Moreover, a particular pentablock quintopolymer of PS-b-PI-b-PDMS-b-PtBMA-bP2VP was successfully synthesized by reacting the living P2VP-b-PtBMA with the same BnCl-functionalized PS-b-PI-bPDMS.164 Finally, the synthesis of exact graft polymers by the iterative methodology is introduced. As mentioned above, a successful example of exact graft polymers has not yet been reported, except for one example having a minimum of two graft units.125 Scheme 18 shows the synthetic outline of exact graft polymers by the iterative methodology, which is basically same as those developed above.166a,b At first, an in-chain-B-functionalized AB living diblock polymer is prepared. After transformation to the A, the resulting in-chain-A-functionalized AB diblock polymer is reacted with the above in-chain-B-functionalized AB living diblock polymer to connect the two block polymers. Thus, one graft unit is prepared. The B function is transformed to the A, followed by reacting with the B-functionalized AB living diblock polymer to prepare two graft units. The linking and transformation reactions correspond to the “arm introduction” (a) and “regeneration of reaction site” (b) steps. By repeating the reaction sequence involving the two steps three more times, a graft copolymer having five graft units was successively synthesized. As the in-chain-B-functionalized living diblock polymer, a living in-chain-(3-tert-butyldimethylsilyloxymethylphenyl)-functionalized PS-b-PMMA was prepared by the sequential addition of styrene, 1-(3-tert-butyldimethylsilyloxymethylphenyl)-1-phenylethylene, and MMA to sBuLi.166a,b The silyl group was deprotected with Bu4NF to generate the hydroxyl function, which was subsequently esterified with αphenylacrylic acid into the PA function (A reaction site). In all the resulting graft copolymers, the molecular weights and compositions agreed with the calculated values (Table 2). For the resulting graft copolymers, the molecular weight of the main chain was exactly equal to the total molecular weight of PMMA blocks, the molecular weight of PS corresponds to that of the graft chain, and the distance between the PS graft chains was the same as the molecular weight of each PMMA block. Thus, obviously, the resulting polymers were all exact graft copolymers where the above-mentioned three variables are perfectly controlled. The living in-chain-functionalized PS-bPtBMA and PS-b-P2VP diblock polymers were also used in the

Table 2. Synthesis of a Series of Exact Graft Copolymers up to Five PS Grafts Mn × 10−3 (g/mol)

a

type

calcd

RALLS

block 2 grafts 3 grafts 4 grafts 5 grafts

12.5 22.2 33.8 43.5 56.2

12.6 23.6 34.6 45.6 55.0

a

composition (%wb/wc) Mw/Mn

calcd

1.03 1.03 1.02 1.04 1.04

50/50 51/49 50/50 49/51 50/50

1

H NMR 48/52 50/50 49/51 50/50 50/50

Determined by SEC equipped with triple detectors. bPS. cPMMA.

same methodology to successfully synthesize the corresponding exact graft copolymers.166b A basically similar iterative methodology was also developed to successfully synthesize two exact graft copolymers and a super H-shaped exact graft PS (Figure 9).167a,b Thus, the success of the iterative methodology allows the synthesis of various complex macromolecular architectures including μ-star polymers, DSPs, multiblock, and exact graft polymers. Concerning the μ-star synthesis, a more effective design of the iterative methodology is possible (Scheme 19).168a−d In this methodology, the A is reacted with the living polymer to change the B, capable of transforming into the A. Another living polymer then reacts with the chain-end-A-functionalized polymer to connect the polymer chain, resulting in the inchain-B-functionalized block polymer. By transformation to the A, followed by reacting with another living polymer, a 3-arm μstar polymer core-B-functionalized polymer is obtained. The repletion of the same reaction sequence one more time produces a 4-arm μ-star. Since the 4-arm μ-star possesses the B function at the core, it may be possible to continue the reaction sequence to afford a 5-arm or more armed μ-stars. Herein, DPE and its anion were utilized as the A and B functions. The transformation was carried out by the reaction of the B with 1(4-(3-bromopropyl)phenyl)-1-phenylethylene (1) to regenerate the DPE of A. The DPE function not only is used to react with a living anionic polymer to link the polymer chain (arm introduction step) but also offers a reaction point for the introduction of the same DPE function (regeneration of the reaction site). With the use of 1,3-bis(1-phenylethyenyl)benzene represented as the AA and 1, the 4-arm A2B2 and 6arm A2B2C2 μ-stars were successively synthesized (Scheme 20).168c,d In order to further increase the number of arms in each sequence, we designed a new agent, 3,5-bis(3-(4-(1phenylethenyl)phenyl)propoxy)benzyl bromide (2), with which two DPE reaction sites can be introduced via one DPE anion produced by the addition reaction.169a,b As illustrated in P


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Figure 9. Synthesis of exact graft (co)polymers and super H-shaped exact graft PS.

Scheme 19. Synthesis of μ-Star Polymers up to 4-Arm ABCD by Iterative Methodology: (a) Arm Introduction and (b) Regeneration of Reaction Site

Scheme 20. Synthesis of μ-Stars by Iterative Methodology Using AA

Scheme 21. Synthesis of μ-Star Polymers up to 31-Arm AB2C4D8E16 Type by Iterative Methodology Using 2

enables the synthetic range of multicomponent μ-star polymers to be significantly broadened. Although the synthesized μ-star polymers are expected to create quite novel morphologies, the morphological studies of μ-star polymers even with three different arms are complicated because of the difficulty in obtaining clear phase-separated structures in their equilibrium states.170 It has been demonstrated that the developed iterative methodology is actually very effective not only for the synthesis of multicomponent μ-star polymers but also for the abovementioned complex macromolecular architectures such as highgeneration high-molecular-weight DSPs, multiblock polymers, and even exact graft polymers. The success of the methodology

Scheme 21, the methodology using 2 is basically similar to those mentioned above. Compound 2 first functions as the core agent and then the agent to introduce two DPE reaction sites. The number of regenerated DPE reaction sites and hence the number of arm segments to be connected exponentially increase in each reaction sequence. By repeating the same reaction sequence with the use of living polymers (B), (C), (D), and (E), the 3-arm AB2, 7-arm AB2C4, 15-arm AB2C4D8, and 31-arm AB2C4D8E16 μ-star polymer having 32 DPE reaction sites at the core were successively synthesized. The iterative methodology using 2 also operates very effectively for the synthesis of multiarmed multicomponent μ-star polymers. Thus, the appearance of the aforementioned methodology Q


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anionic poly(macromonomer)s was described. In section 7, we introduced the recent synthetic advances of complex macromolecular architectures as well as the new conceptual iterative methodology adaptable to the synthesis of almost all macromolecular architectures. With these methodologies, the synthesis of various as-designed macromolecular architectures has now become possible. The future perspectives are as follows: Two main subjects related to the future perspectives remain as unsolved problems. The first one is to achieve the perfect control of the regio- and stereoselectivities. Ideas and proposals based on coordination chemistry successful for the transition-metal-mediated polymerization are needed for this objective. The likeliest candidates are specially designed Lewis acids and phosphazene bases, which might be strongly coordinated to anions or cations to make suitable circumstances for highly selective monomer insertion. Multidentate ligands, such as polyamines, polyethers, crown ethers, and their designed derivatives, may also be utilized. Since the polymer properties and behavior are significantly influenced even by a small difference in the selectivity, these investigations should be continued for the development of new materials. The second one is the achievement of the living polymerization of highly reactive polar monomers, such as acrylonitrile, nitroethylene, vinylidene cyanide, and α-cyanoacrylate. Since the anionic polymerization of acrylate, methacrylates, N,Ndialkylacrylamides, and methacrylonitrile have been significantly improved in livingness by the addition of weak Lewis acids and/or several ligands, these additives are also expected to control the anionic polymerization of such reactive polar monomers. Their growing chain-end anions seem stable even in the presence of oxygen and water, thus rendering the (living) anionic polymerization of aqueous media in air possible. The resulting polymers are highly functionalized living anionic polymers and can be directly used in water in the presence of oxygen. The final perspective is the precise synthesis of complex architectural f unctional polymers. Throughout this Perspective, the synthesis of various new-type living anionic polymers having functionalities, specific structures, regio- and stereoselectivites, although not perfectly controlled, and comblike segments, as well as adopting rigid-rod-like and α-helix and βstrand conformations, were introduced along with the effectiveness. We demonstrated the effectiveness of a newly developed all-around iterative methodology, which is adaptable to almost all complex architectural polymer synthesis. Thus, versatile state-of-the-art synthetic tools with many functions and the know-how for the synthesis of macromolecular architectures are available. The combination of such tools and the know-how offers exciting possibilities for the development of high performance specialty polymers and high-quality nanostructural materials. Unfortunately, morphological and other related studies of supramolecular nanostructures and molecular assemblies, one of the key factors in nanoscience, have not sufficiently progressed. The development of new analytical methodologies and even more improved analytical techniques are now matters of urgency. It is time to truly fulfill the collaborations among the polymer chemists and physicists to make real advances in polymer chemistry. As an insightful proposal, a few practical examples (μ-star polymers and their novel morphologies) about the constructive partnership and mutual understanding among

strongly indicates that various macromolecular architectures can be readily synthesized by developing only one methodology based on the same concept. This means that a methodology developed for μ-star polymer synthesis may also be applied to other architectural polymer synthesis by modifying the methodology to change the numbers and/or positions of the polymer chains and linking points. Since many efficient methodologies individually designed for each of the macromolecular architectures have already been reported, they should be reconsidered from this applicable point. For this reason, we consider the all-around iterative methodology and possible synthesis of various macromolecular architectures introduced in 7.2 to be an effective promising strategy from the viewpoint of future perspectives.

8. CONCLUSIONS AND FUTURE OUTLOOK The recent advances in living anionic polymerization systems and the synthesis of structurally complex macromolecular architectures, which were synthetically difficult until recently, in addition to the principal strengths of this field, have been reviewed. In all the reports, reviews, and books until the mid1980s, it had been recognized that the major drawback in living anionic polymerization was its intolerance to most of the functionalities, thus rendering it difficult or even impossible for functional monomers. In section 2, it was demonstrated that almost all essentially useful functionalities are compatible with living anionic polystyrene, although some of them need to be protected. All these functionalities may possibly be used in other living anionic polymerization systems because their living chain-end anions are comparable to or less reactive than living polystyrene. Accordingly, no special care is now needed when using the many useful functional groups in living anionic polymerization. In section 3, new types of living anionic polymers that appeared by employing specially designed initiator systems and by changing the monomer structures to be feasible for the polymerization were introduced. Living anionic polymerization of cyclic monomers, (meth)acrylates, N,N-dialkylacrylamides, and even methacrylonitrile was practically achieved by adding several promising additives such as phosphazene bases and weak Lewis acids. Among these systems, the high-temperature living anionic polymerization of alkyl (meth)acrylates by the addition of the modified Lewis acid(s) made it possible to use the system in industry. As described in section 4, the stereoselective control was much improved for the living polymerization of (meth)acrylates and N,N-dialkylacrylamides in the presence of several modified Lewis acids. Although living anionic polymerization of 2triisopropoxysilyl-1,3-butadiene was found to completely occur in both regio- and stereoselective manners, as the only exceptional case, the regio- and stereoselectivities have not yet been perfectly controlled for the polymerization of 1,3butadiene and isoprene. In section 5, we introduced the synthesis of special living anionic polymers adopting rigid-rodlike conformations and ordered conformations of α-helices or β-strands. They could be synthesized by living anionic polymerization of phenyl vinyl sulfoxide (followed by thermal treatment), alkyl isocyanates, and NCAs. Moreover, several block polymers and even star-branched polymers consisting of such unique and characteristic segments were synthesized and examined as potentially useful specialty polymers in the fields of nano- and biocompatible materials. In section 6, the successful synthesis of various complex branched polymers composed of comblike polymers by directly using in situ prepared living R


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them have been demonstrated in the review article recently reported by Hadjichristidis.171

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is an assistant professor of Department of Organic and Polymeric Materials at Tokyo Institute of Technology. His research interests are the precise synthesis and phase-selective chemistry in block copolymer system and the synthesis of star-branched polymers and block copolymers for applications in nanomaterials.

AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected] (A.H.). Notes

The authors declare no competing financial interest. Biographies

Takashi Ishizone was born in Saitama, Japan, in 1963. He received a master’s degree in polymer chemistry from Tokyo Institute of Technology in 1988 under the supervision of Professors Seiichi Nakahama and Akira Hirao and started his academic career as an assistant professor in the same institution from 1989. After receiving a doctorate degree in 1994, he studied organic chemistry as a visiting scientist at The University of Chicago in the group of Professor P. E. Eaton from 1995 to 1996. Since 2000, he is an Associate Professor of Department of Organic and Polymeric Materials at Tokyo Institute of Technology. His main research areas center on the synthesis of novel thermally stable polymers possessing adamantane skeletons and the synthesis of novel functional polymers showing water solubility and thermoresponsive property by means of living anionic polymerization.

Professor Akira Hirao graduated with his doctorate degree in 1975 from Tokyo Institute of Technology (Titech), Japan, in chemical engineering. After one and half years as a postdoctoral fellow at the University of Alabama in the USA, he was appointed as an Assistant Professor at Titech and promoted to Full Professor in 1996, via an Associate Professor, and retired from Titech in 2013 to be an Emeritus Professor. He is currently a Distinguished Chair Professor of National Taiwan University (Taiwan), a Chair Professor of Soochow University (China), and Visiting Professors in Pohang University of Science and Technology (Korea) and Fudan University (China) to deliver lectures for a few years. He has published over 300 papers in peer reviewed journals, 20 book chapters including coeditors, and given 80 keynote, plenary, and invited lectures at International Conferences and over 300 invited lectures including Polymer Societies, Chemical Societies, Universities, and companies in Japan (>200) as well as overseas (>100). He was awarded the Japan Polymer Society Award (2010) and the Publication Award for the year 2011, Society of Rheology (USA). His research interests lie at the molecular design and precise synthesis of macromolecular architectures by living anionic polymerization and nano surface structural control using well-defined perfloroalkylated polymers.

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REFERENCES

(1) Anionic Polymerization: Principles and Practical Applications; Hsieh, H. L., Quirk, R. P., Eds.; Marcel Dekker Inc.: New York, 1996. (2) Park, C.; Yoon, J.; Thomas, E. L. Polymer 2003, 44, 6725. (3) Characterization and Self-Assembly. In Complex Macromolecular Architectures: Synthesis, Characterization, and Self-Assembly; Hadjichristidis, N., Hirao, A., Tezuka, Y., Du Prez, F., Eds.; John Wiley & Sons: Singapore, 2011; pp 491−814. (4) Hirao, A.; Loykulnant, S.; Ishizone, T. Prog. Polym. Sci. 2002, 27, 1399. (5) Ishizone, T.; Sugiyama, K.; Hirao, A. Anionic Polymerization of Protected Functional Monomers. In Polymer Science: A Comprehensive Reference; Matyjaszewski, K., Mö ller, M., Eds.; Elsevier BV: Amsterdam, 2012; Vol. 3, pp 591−621. (6) Ishizone, T.; Hirao, A. Anionic Polymerization: Recent Advances. In Synthesis of Polymers: New Structures and Methods; Schlüter, D., Hawker, C. J., Sakamoto, J., Eds.; Wiley-VCH: Singapore, 2012; Vol. 1, pp 81−133. (7) Zhang, H.; Ruckenstein, E. Macromolecules 1999, 32, 5495. (8) (a) Hirao, A.; Kitamura, M.; Loykulnant, S. Macromolecules 2004, 37, 4770. (b) Sugiyama, K.; Hirao, A.; Hayashi, M. Macromolecules 2008, 41, 4235. (9) Ishizone, T.; Uehara, G.; Hirao, A.; Nakahama, S.; Tsuda, K. Macromolecules 1998, 31, 3764. (10) Nossarev, G. G.; Hogen-Esch, T. E. Macromolecules 2001, 34, 5373. (11) (a) Geerts, J.; Van Beylen, M.; Smets, G. J. Polym. Sci., Part A-1 1969, 7, 2859. (b) Se, K.; Watanabe, O.; Isono, Y.; Fujimoto, T. Makromol. Chem., Macromol. Symp. 1989, 25, 249. (c) Kopolow, S.; Hogen-Esch, T. E.; Smid, J. Macromolecules 1973, 6, 133.

Raita Goseki was born in Chiba, Japan, in 1982. He received his M.S. in polymer chemistry from the Tokyo Institute of Technology in 2005 under the supervision of Professor Masa-aki Kakimoto. Since 2010, he S


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(12) Hirao, A.; Shione, H.; Ishizone, T.; Nakahama, S. Macromolecules 1997, 30, 3728. (13) Se, K.; Kijima, M.; Fujimoto, T. Polym. J. 1988, 20, 791. (14) Sugiyama, K.; Ishizone, T.; Hirao, A.; Nakahama, S. Acta Polym. 1995, 46, 424. (15) Sakellariou, G.; Baskaran, D.; Hadjichristidis, N.; Mays, W. J. Macromolecules 2006, 39, 3525. (16) (a) Kobayashi, S.; Matsuzawa, T.; Matsuoka, S.; Tajima, H.; Ishizone, T. Macromolecules 2006, 39, 5979. (b) Kobayashi, S.; Kataoka, H.; Ishizone, T.; Kato, T.; Ono, T.; Kobukata, S.; Ogi, H. Macromolecules 2008, 41, 5502. (17) Sugiyama, K.; Hirao, A.; Hsu, J. C.; Tung, Y. C.; Chen, W. C. Macromolecules 2009, 42, 4053. (18) Higashihara, T.; Ueda, M. Macromolecules 2009, 42, 8794. (19) Chaumont, P.; Bernert, G.; Herz, J. E.; Remp, P. Makromol. Chem. 1982, 183, 1181. (20) Yamazaki, N.; Nakahama, S.; Hirao, A.; Goto, J.; Shiraishi, Y.; Martinez, F.; Phung, H. M. J. Macromol. Sci. Chem., A 1981, 16, 1129. (21) Hirao, A.; Shiraishi, Y.; Martinez, F.; Phung, H. M.; Nakahama, S.; Yamazaki, N. Makromol. Chem. 1983, 184, 961. (22) Ignatious, F.; Sein, A.; Delaviz, Y.; Cabasso, I.; Smid, J. Polymer 1992, 33, 1724. (23) Börner, H. G.; Heitz, W. Macromol. Chem. Phys. 2000, 201, 740. (24) Hirao, A.; Ando, Y.; Ishizone, T.; Nakahama, S. Macromolecules 2003, 36, 5081. (25) (a) Hirao, A.; Nagawa, T.; Hatayama, T.; Yamaguchi, K.; Nakahama, S. Macromolecules 1985, 18, 2101. (b) Hirao, A.; Hatayama, T.; Nagawa, T.; Yamaguchi, M.; Yamaguchi, K.; Nakahama, S. Macromolecules 1987, 20, 242. (26) Taki, T.; Hirao, A.; Nakahama, S. Macromolecules 1991, 24, 1455. (27) Hirao, A.; Hatayama, T.; Nakahama, S. Macromolecules 1987, 20, 1505. (28) Nakahama, S.; Hirao, A. Prog. Polym. Sci. 1990, 15, 299. (29) Hirao, A.; Nakahama, S. Acta Polym. 1998, 49, 133. (30) Hirao, A.; Nakahama, S. Prog. Polym. Sci. 1992, 17, 283. (31) (a) Hirao, A.; Yamaguchi, K.; Takenaka, K.; Suzuki, K.; Nakahama, S.; Yamazaki, N. Makromol. Chem., Rapid Commun. 1982, 3, 941. (b) Hirao, A.; Kitamura, K.; Takenaka, K.; Nakahama, S. Macromolecules 1993, 26, 4995. (c) Ishizone, T.; Mochizuki, A.; Hirao, A.; Nakahama, S. Macromolecules 1995, 28, 3787. (d) Ishizone, T.; Tominaga, T.; Kitamura, K.; Hirao, A.; Nakahama, S. Macromolecules 1995, 28, 4829. (e) Loykulnant, S.; Hayashi, M.; Hirao, A. Macromolecules 1998, 31, 9121. (32) Hirao, A.; Shione, H.; Wakabayashi, S.; Nakahama, S.; Yamaguchi, K. Macromolecules 1994, 27, 1835. (33) (a) Suzuki, K.; Hirao, A.; Nakahama, S. Macromolecules 1989, 22, 2607. (b) Suzuki, K.; Hirao, A.; Nakahama, S. Makromol. Chem. 1989, 190, 2893. (34) Tsuda, K.; Ishizone, T.; Hirao, A.; Nakahama, S.; Kakuchi, T.; Yokota, K. Macromolecules 1993, 26, 6985. (35) (a) Hirao, A.; Ishino, Y.; Nakahama, S. Makromol. Chem. 1986, 187, 141. (b) Ishizone, T.; Kato, R.; Ishino, Y.; Hirao, A.; Nakahama, S. Macromolecules 1991, 26, 1449. (36) Hirao, A.; Kato, K.; Nakahama, S. Macromolecules 1992, 25, 535. (37) Ishizone, T.; Okamoto, K.; Hirao, A.; Nakahama, S. Macromolecules 1999, 32, 1453. (38) Nakahama, S.; Ishizone, T.; Hirao, A. Macromol. Symp. 1993, 67, 223. (39) Ishizone, T.; Hirao, A.; Nakahama, S. Macromolecules 1993, 26, 6964. (40) (a) Hirao, A.; Nakahama, S. Macromolecules 1987, 20, 2968. (b) Ishizone, T.; Sueyasu, N.; Hirao, A.; Nakahama, S. Macromolecules 1993, 26, 6976. (c) Ishizone, T.; Utaka, T.; Hirao, A.; Nakahama, S. Macromolecules 1997, 30, 6458. (41) Hirao, A.; Nakahama, S. Polymer 1986, 27, 309. (42) (a) Ishizone, T.; Wakabayashi, S.; Hirao, A.; Nakahama, S. Macromolecules 1991, 24, 5015. (b) Hirao, A.; Ishino, Y.; Nakahama, S.

Macromolecules 1988, 21, 561. (c) Ishizone, T.; Tsuchiya, J.; Hirao, A.; Nakahama, S. Macromolecules 1998, 31, 5598. (43) Ishizone, T.; Hirao, A.; Nakahama, S. Macromolecules 1989, 22, 2895. (44) Ishizone, T.; Kato, H.; Yamazaki, D.; Hirao, A.; Nakahama, S. Macromol. Chem. Phys. 2000, 201, 1077. (45) Ishizone, T.; Tsuchiya, J.; Hirao, A.; Nakahama, S. Macromolecules 1992, 25, 4840. (46) (a) Ishizone, T.; Hirao, A.; Nakahama, S. Macromolecules 1991, 24, 625. (b) Ishizone, T.; Sugiyama, K.; Hirao, A.; Nakahama, S. Macromolecules 1993, 26, 3009. (c) Ishizone, T.; Okazawa, Y.; Ohnuma, K.; Hirao, A.; Nakahama, S. Macromolecules 1997, 30, 757. (d) Ishizone, T.; Ohnuma, K.; Okazawa, Y.; Hirao, A.; Nakahama, S. Macromolecules 1998, 31, 2797. (47) Hirao, A.; Tanaka, S.; Goseki, R.; Ishizone, T. Macromolecules 2011, 44, 4579. (48) Tanaka, S.; Matsumoto, M.; Goseki, R.; Ishizone, T.; Hirao, A. Macromolecules 2013, 46, 146. (49) Xie, X.; Hogen-Esch, T. E. Macromolecules 1996, 29, 1746. (50) (a) Butler, G. B.; Myers, G. R. J. Macromol. Sci., Chem. 1971, A5, 135. (b) Kodaira, T.; Aoyama, F. J. Polym. Sci., Polym. Chem. Ed. 1974, 12, 897. (c) Kodaira, T.; Tanahashi, H.; Hara, K. Polym. J. 1990, 22, 649. (51) Suzuki, T.; Kusakabe, J.; Ishizone, T. Macromolecules 2008, 41, 1929. (52) Suzuki, T.; Kusakabe, J.; Kitazawa, K.; Nakagawa, T.; Kawauchi, S.; Ishizone, T. Macromolecules 2010, 43, 107. (53) Ueda, M.; Mano, M.; Mori, H.; Ito, H. J. Polym. Sci., Part A: Polym. Chem. 1991, 29, 1779. (54) Ishizone, T.; Kitazawa, K.; Suzuki, T.; Kawauchi, S. Macromol. Symp. 2013, 323, 86. (55) Nakano, T.; Takewaki, K.; Yade, T.; Okamoto, Y. J. Am. Chem. Soc. 2001, 123, 9182. (56) Kosaka, Y.; Kitazawa, K.; Inomata, S.; Ishizone, T. ACS Macro Lett. 2013, 2, 164. (57) (a) Rulkens, R.; Ni, Y.; Manners, I. J. Am. Chem. Soc. 1994, 116, 12121. (b) Ni, Y.; Rulkens, R.; Manners, I. J. Am. Chem. Soc. 1996, 118, 4102. (c) Manners, I. Angew. Chem., Int. Ed. Engl. 1996, 35, 1602. (58) Sheikh, Md. R. K.; Tharanikkarasu, K.; Imae, I.; Kawakami, Y. Macromolecules 2001, 34, 4384. (59) Kloninger, C.; Rehahn, M. Macromolecules 2004, 37, 1720. (60) (a) Qi, F.; Guerin, G.; Cambridge, G.; Xu, W.; Manners, I.; Winnik, M. A. Macromolecules 2011, 44, 6136. (b) Gädt, T.; Schacher, F. H.; McGrath, N.; Winnik, M. A.; Manners, I. Macromolecules 2011, 44, 3777. (61) Peckham, T. J.; Massey, J. A.; Honeyman, C. H.; Manners, I. Macromolecules 1999, 32, 2830. (62) Pietzonka, T.; Seebach, D. Angew. Chem., Int. Ed. Engl. 1993, 32, 716. (63) (a) Ebwein, B.; Molenberg, A.; Möller, M. Macromol. Rapid Commun. 1996, 17, 143. (b) Ebwein, B.; Möller, M. Angew. Chem., Int. Ed. Engl. 1996, 35, 623. (c) Molenberg, A.; Möller, M. Macromol. Chem. Phys. 1997, 198, 717. (64) (a) Förster, S.; Krämer, E. Macromolecules 1999, 32, 2783. (b) Floudas, G.; Vazaiou, B.; Schipper, F.; Ulrich, R.; Wiesner, U.; Iatrou, H.; Hadjichristidis, N. Macromolecules 2001, 34, 2947. (c) Pispas, S.; Hadjichristidis, N. Langmuir 2003, 19, 48. (d) Schmalz, H.; Knoll, A.; Müller, A. J.; Abetz, V. Macromolecules 2002, 35, 10004. (e) Toy, A. A.; Reinicke, S.; Müller, A. H. E.; Schmalz, H. Macromolecules 2007, 40, 5241. (65) Schacher, F.; Müller, M.; Schmalz, H.; Müller, A. H. E. Macromol. Chem. Phys. 2009, 210, 256. (66) Zhang, L.; Nederberg, F.; Messman, J. M.; Pratt, R. C.; Hedrick, J. L.; Wade, C. G. J. Am. Chem. Soc. 2007, 129, 12610. (67) Zhang, L.; Nederberg, F.; Pratt, R. C.; Waymouth, R. M.; Hedrick, J. L.; Wade, C. G. Macromolecules 2007, 40, 4154. (68) (a) Illy, N.; Boileau, S.; Penelle, J.; Barbier, V. Macromol. Rapid Commun. 2009, 30, 1731. (b) Illy, N.; Boileau, S.; Buchmann, W.; Penelle, J.; Barbier, V. Macromolecules 2010, 43, 8782. T


Macromolecules

Perspective

(89) te Nijenhuis, K. Adv. Polym. Sci. 1997, 130, 67. (90) (a) Kawauchi, T.; Kumaki, J.; Okoshi, K.; Yashima, E. Macromolecules 2005, 38, 9155. (b) Kumaki, J.; Kawauchi, T.; Okoshi, K.; Kusanagi, H.; Yashima, E. Angew. Chem., Int. Ed. 2007, 46, 5348. (c) Kumaki, J.; Kawauchi, T.; Ute, K.; Kitayama, T.; Yashima, E. J. Am. Chem. Soc. 2008, 130, 6373. (91) (a) Kobayashi, M.; Okuyama, S.; Ishizone, T.; Nakahama, S. Macromolecules 1999, 32, 6466. (b) Kobayashi, M.; Ishizone, T.; Nakahama, S. J. Polym. Sci., Part A: Polym. Chem. 2000, 38, 4677. (c) Ishizone, T.; Yashiki, D.; Kobayashi, M.; Suzuki, T.; Ito, M.; Nakahama, S. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 1260. (92) Kitayama, T.; Shibuya, W.; Katsukawa, K. Polym. J. 2002, 34, 405. (93) (a) Ishizone, T.; Ito, M. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 4328. (b) Ito, M.; Ishizone, T. Des. Monomers Polym. 2004, 7, 11. (c) Ito, M.; Ishizone, T. J. Polym. Sci., Part A: Polym. Chem. 2006, 44, 4832. (94) Makino, T.; Hogen-Esch, T. E. Macromolecules 1999, 32, 5712. (95) Morton, M. Organolithium Polymerization of Dienes. In Anionic Polymerization: Principles and Practice; Academic Press: London, 1983; pp 147−164. (96) Reference 1; Chapter 9, pp 197−235. (97) (a) Takenaka, K.; Hirao, A.; Hattori, T.; Nakahama, S. Macromolecules 1987, 20, 2034. (b) Takenaka, K.; Hattori, T.; Hirao, A.; Nakahama, S. Macromolecules 1989, 22, 1563. (98) (a) Kobayashi, S.; Kataoka, H.; Ishizone, T. Macromolecules 2009, 42, 5017. (b) Kobayashi, S.; Kataoka, H.; Ishizone, T.; Kato, T.; Ono, T.; Kubotaka, S.; Arimoto, K.; Ogi, H. React. Funct. Polym. 2009, 69, 409. (99) (a) Natori, I. Macromolecules 1997, 30, 3696. (b) Natori, I.; Inoue, S. Macromolecules 1998, 31, 982. (c) Williamson, D. T.; Elman, J. F.; Madison, P. H.; Pasquale, A. J.; Long, T. E. Macromolecules 2001, 34, 2108. (d) Hong, K.; Wan, Y.; Mays, J. W. Macromolecules 2001, 34, 2482. (100) Kanga, R. S.; Hogen-Esch, T. H.; Randrianalimanana, E.; Soum, A.; Fontanille, M. Macromolecules 1990, 23, 4235−4240 and 4241−4246. (101) (a) Reibel, D.; Nuffer, R.; Mathis, C. Macromolecules 1992, 25, 7090. (b) Leung, L. M.; Tan, K. H. Macromolecules 1993, 26, 4426. (c) Bader, A.; Wünsch, J. R. Macromolecules 1995, 28, 3794. (d) Wu, C.; Niu, A.; Leung, L. M.; Lam, T. S. J. Am. Chem. Soc. 1999, 121, 1954. (e) Sugiyama, K.; Karasawa, Y.; Higashihara, T.; Zhao, Y.; Hirao, A. Chem. Monthly 2006, 137, 869. (102) (a) Zhao, Y.; Higashihara, T.; Sugiyama, K.; Hirao, A. J. Am. Chem. Soc. 2005, 127, 14158. (b) Zhao, Y.; Higashihara, T.; Sugiyama, K.; Hirao, A. Macromolecules 2007, 40, 228. (103) (a) Lee, J. S.; Ryu, S. W. Macromolecules 1999, 32, 2085. (b) Shin, Y. D.; Kim, S. Y.; Ahn, J. H.; Lee, J. S. Macromolecules 2001, 34, 2408. (c) Ahn, J. H.; Shin, Y. D.; Nath, G. Y.; Park, S. Y.; Rahman, M. S.; Samal, S. J. Am. Chem. Soc. 2005, 127, 4132. (104) Vazaios, A.; Pitsikalis, M.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 3094. (105) (a) Kim, J. H.; Rahman, M. S.; Lee, J. S.; Park, J. W. J. Am. Chem. Soc. 2007, 129, 7756. (b) Kim, J. H.; Rahman, M. S.; Lee, J. S.; Park, J. W. Macromolecules 2008, 41, 3181. (c) Koh, H. D.; Changez, M.; Rahman, M. S.; Lee, J. S. Langmuir 2009, 25, 7188. (d) Changez, M.; Kang, N. G.; Koh, H. D.; Lee, J. S. Langmuir 2010, 26, 9981. (e) Changez, M.; Koh, H. D.; Kang, N. G.; Kim, J. G.; Kim, Y. J.; Samal, S.; Lee, J. S. Adv. Mater. 2012, 24, 3253. (106) (a) Aliferis, T.; Iatrou, H.; Hadjichristidis, N. Biomacromolecules 2004, 5, 1653. (b) Lu, H.; Cheng, J. J. J. Am. Chem. Soc. 2007, 129, 14114. (c) Hadjichristidis, N.; Iatrou, H.; Pitsikalis, M.; Sakellariou, G. Chem. Rev. 2009, 109, 5528. (d) Iatrou, H.; Pitsikalis, M.; Sakellariou, G.; Hadjichristidis, N. Complex Macromolecular Chimeras. In Complex Macromolecular Architectures: Synthesis, Characterization, and Self-Assembly; Hadjichristidis, N., Hirao, A., Tezuka, Y., Du Prez, F., Eds.; John Wiley & Sons: Singapore, 2011; pp 461−490. (107) (a) Schlaad, H.; Antonietti, M. Eur. Phys. J. E 2003, 10, 17. (b) Aliferis, T.; Iatrou, H.; Hadjichristidis, N. J. Polym. Sci., Part A:

(69) Winter, J. D.; Coulembier, O.; Gerbaux, P.; Dubois, P. Macromolecules 2010, 43, 10291. (70) Zhao, J.; Alamri, H.; Hadjichristidis, N. Chem. Commun. 2013, 49, 7079. (71) Kamber, N. E.; Jeong, W.; Waymouth, R. M.; Pratt, R. C.; Lohmeijer, B. G. G.; Hedrick, J. L. Chem. Rev. 2007, 107, 5813. (72) (a) Pratt, R. C.; Lohnmeijer, B. G. G; Long, D. A.; Lundberg, P. N. P.; Dove, A. P.; Li, H.; Wade, C. G.; Waymouth, R. M.; Hedrick, J. L. Macromolecules 2006, 39, 7863. (b) Pratt, R. C.; Lohnmeijer, B. G. G; Long, D. A.; Lundberg, P. N. P.; Dove, A. P.; Li, H.; Wade, C. G.; Waymouth, R. M.; Hedrick, J. L. J. Am. Chem. Soc. 2006, 128, 4556. (c) Nedergerg, F.; Lohnmeijer, B. G. G; Leibfarth, F.; Pratt, R. C.; Choi, J.; Dove, A. P.; Waymouth, R. M.; Hedrick, J. L. Biomacromolecules 2007, 8, 153. (d) Pounder, R. J.; Dove, A. P. Biomacromolecules 2010, 11, 1930. (e) Coady, D. J.; Engler, A. C.; Horn, H. W.; Bajjuri, K. M.; Fukushima, K.; Jones, G. O.; Nelson, A.; Rice, J. E.; Hedrick, J. L. ACS Macro Lett. 2012, 1, 19. (73) Davis, T. P.; Haddleton, D. M.; Richards, S. N. J. Macromol. Sci., Rev. Macromol. Chem. Phys. 1994, C34 (2), 243. (74) Baskaran, D. Prog. Polym. Sci. 2003, 28, 521. (75) (a) Anderson, B. C.; Andrews, G. D.; Arthur, P., Jr.; Jacobson, H. W.; Melby, L. R.; Playtis, A. J.; Sharkey, W. H. Macromolecules 1981, 14, 1599. (b) Varshney, S. K.; Jérôme, R.; Bayard, Ph.; Jacobs, C.; Fayt, R.; Teyssié, Ph. Macromolecules 1992, 25, 4457. (c) Antoun, S.; Teyssié, Ph.; Jérôme, R. Macromolecules 1997, 30, 1556. (76) (a) Fayt, R.; Forte, R.; Jacobs, C.; Jérôme, R.; Ouhadi, T.; Teyssié, Ph.; Varshney, S. K. Macromolecules 1987, 20, 1442. (b) Varshney, S. K.; Hautekeer, J. P.; Fayt, R.; Jérôme, R.; Teyssié, Ph. Macromolecules 1990, 23, 2618. (c) Wang, J.-S.; Jérôme, R.; Bayard, Ph.; Patin, M.; Teyssié, Ph. Macromolecules 1994, 27, 4635. (d) Baskaran, D.; Sivaram, S. Macromolecules 1997, 30, 1550. (e) Hatada, K.; Ute, K.; Tanaka, K.; Kitayama, T.; Okamoto, Y. Polym. J. 1985, 17, 977. (77) Kunkel, D.; Müller, A. H. E.; Janata, M.; Lochmann, L. Makromol. Chem., Macromol. Symp. 1992, 60, 315. (78) (a) Kitayama, T.; Shinozaki, T.; Masuda, E.; Yamamoto, M.; Hatada, K. Polym. Bull. 1988, 20, 505. (b) Hirano, T.; Yamaguchi, H.; Kitayama, T.; Hatada, K. Polym. J. 1998, 30, 767. (c) Hatada, K.; Kitayama, T. Polym. Int. 2000, 49, 11. (d) Ballard, D. G. H.; Bowles, R. J.; Haddleton, D. M.; Richards, S. N.; Sellens, R.; Twose, D. L. Macromolecules 1992, 25, 5907. (e) Tabuchi, M.; Kawauchi, T.; Kitayama, T.; Hatada, K. Polymer 2002, 43, 7185. (f) Ozaki, H.; Hirao, A.; Nakahama, S. Macromol. Chem. Phys. 1995, 196, 2099. (g) Ishizone, T.; Yoshimura, K.; Hirao, A.; Nakahama, S. Macromolecules 1998, 31, 8706. (h) Schlaad, H.; Müller, A. H. E. Macromolecules 1998, 31, 7127. (79) (a) Ishizone, T.; Yoshimura, K.; Yanase, E.; Nakahama, S. Macromolecules 1999, 32, 955. (b) Kobayashi, M.; Ishizone, T.; Nakahama, S. Macromolecules 2000, 33, 4411. (80) Ishizone, T.; Yanase, E.; Matsushita, T.; Nakahama, S. Macromolecules 2001, 34, 6551. (81) Schmitt, B.; Stauf, W.; Müller, A. H. E. Macromolecules 2001, 34, 1551. (82) (a) Uchiumi, N.; Harada, K.; Kato, M.; Ono, T.; Yaginuma, S.; Ishiura, K. Preparation Process of Acrylic Acid Ester Polymer. U.S. Patent 6,329,480, Dec 11, 2001. (b) Harada, K.; Ishiura, K.; Kato, M.; Yaginuma, S. Anionic Polymerization Process, and Process for Producing a Polymer by the Anionic Polymerization Process. U.S. Patent 6,555,637, Apr 29, 2003. (83) Zagara, A. P.; Hogen-Esch, T. E. Macromolecules 2001, 29, 3038. (84) Takada, K.; Fuchise, K.; Chen, Y.; Satoh, T.; Kakuchi, T. J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 3560. (85) Kakuchi, R.; Chiba, K.; Fuchise, K.; Sakai, R.; Satoh, T.; Kakuchi, T. Macromolecules 2009, 42, 8747. (86) Kakuchi, T.; Chen, Y.; Kitakado, J.; Mori, K.; Fuchise, K.; Satoh, T. Macromolecules 2011, 44, 4641. (87) Kitaura, T.; Kitayama, T. Macromol. Rapid Commun. 2007, 28, 1889. (88) Spevacek, J.; Schneider, B. Adv. Colloid Interface Sci. 1987, 27 (1−2), 81. U


Macromolecules

Perspective

Polym. Chem. 2005, 43, 4670. (c) Hanski, S.; Houbenov, N.; Ruokolainen, J. Biomacromolecules 2006, 7, 3379. (d) Klok, H. A.; Lecommandoux, S. Adv. Polym. Sci. 2006, 202, 75. (e) Karatzas, A.; Iatrou, H.; Hadjichristidis, N.; Inoue, K.; Sugiyama, K.; Hirao, A. Biomacromolecules 2008, 9, 2072. (f) Junila, S.; Houbenov, N.; Karatzas, A.; Hadjichristidis, N.; Hirao, A.; Iatrou, H.; Ikkala, O. Macromolecules 2012, 45, 2850. (108) Lecommandoux, S. Bulk Self-Assembly of Linear Hybrid Polypeptide-Based Diblock and Triblock polymers. In Complex Macromolecular Architectures: Synthesis, Characterization, and SelfAssembly; Hadjichristidis, N., Hirao, A., Tezuka, Y., Du Prez, F., Eds.; John Wiley & Sons: Singapore, 2011; pp 623−645. (109) Rodriguez-Hernandes, J.; Checot, F.; Gnanou, Y.; Lecommandoux, S. Prog. Polym. Sci. 2005, 30, 691. (110) (a) Liu, C.-L.; Lin, C.-H.; Kuo, C.-C.; Lin, S.-T.; Chen, W.-C. Prog. Polym. Sci. 2011, 36, 603. (b) Ho, R.-M.; Chiang, Y.-W.; Lin, S.C.; Chen, C.-K. Prog. Polym. Sci. 2011, 36, 376. (111) Kuo, C.-C.; Liu, C.-L.; Chen, W.-C. Morphologies and Photophysical Properties of Conjugated Rod-Coil Block Copolymers. In Complex Macromolecular Architectures: Synthesis, Characterization, and Self-Assembly; Hadjichristidis, N., Hirao, A., Tezuka, Y.; Du Prez, F., Eds.; John Wiley & Sons: Singapore, 2011; pp 593−622. (112) (a) Pantazis, D.; Chalari, I.; Hadjichristidis, N. Macromolecules 2003, 36, 3783. (b) Koutalas, G.; Iatrou, H.; Lohse, D. J.; Hadjichristidis, N. Macromolecules 2005, 38, 4996. (c) Vazaios, A.; Lohse, D. J.; Hadjichristidis, N. Macromolecules 2005, 38, 5468. (d) Vazaios, A.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 1038. (e) Christodoulou, S.; Iatrou, H.; Lohse, D. I.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 4030. (f) Koutalas, G.; Lohse, D. I.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 4040. (g) Driva, P.; Iatrou, H.; Lohse, D. I.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 4070. (h) Nikopoulou, A.; Iatrou, H.; Lohse, D. I.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 3513. (i) Driva, P.; Lohse, D. I.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 1826. (113) Tsoukatos, T.; Avgeropoulos, A.; Hadjichristidis, N.; Hong, K.; Mays, J. W. Macromolecules 2002, 35, 7928. (114) (a) Giebeler, E.; Stadler, R. Macromol. Chem. Phys. 1997, 198, 3815. (b) Ludwig, S.; Böker, A.; Abetz, V.; Müller, A. H. E. Polymer 2003, 44, 6815. (c) Goldacker, T.; Abetz, V.; Stadler, R.; Erukhimovich, I.; Leibler, L. Nature 1999, 398, 137. (115) Auschra, C.; Stadler, R. Polym. Bull. 1993, 30, 257. (116) Wolf, A.; Walther, A.; Müller, A. H. E. Macromolecules 2011, 44, 9221. (117) Bieringer, R.; Abetz, V.; Müller, A. H. E. Eur. Phys. J. E 2001, 5, 5. (118) Betthausen, E.; Drechsler, M.; Foertsch, M.; Schacher, F. H.; Müller, A. H. E. Soft Matter 2011, 7, 8880. (119) Böker, A.; Müller, A. H. E.; Kraush, G. Macromolecules 2001, 34, 7477. (120) (a) Ekizoglou, N.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 1198. (b) Ekizoglou, N.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2166. (c) Vazaios, A.; Pitsikalis, M.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 3094. (121) Quirk, R. P. Graft Copolymers. In Anionic Polymerization: Principles and Practical Applications; Hsieh, H. L., Quirk, R. P., Eds.; Marcel Dekker Inc.: New York, 1996; Chapter IV, Section 14, pp 369−392. (122) Hadjichristidis, N.; Pitsikakalis, M.; Pispas, M.; Mays, J. W. Prog. Polym. Sci. 2006, 31, 1068. (123) Uhrig, D.; Mays, J. W. Polym. Chem. 2011, 2, 69. (124) Paraskeva, S.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2000, 38, 931. (125) (a) Iatrou, H.; Hadjichristidis, N. Macromolecules 1992, 25, 4649. (b) Fujimoto, T.; Zhang, H.; Kazama, T.; Isono, Y.; Hasegawa, H.; Hashimoto, T. Polymer 1992, 33, 2208. (c) Iatrou, H.; Hadjichristidis, N. Macromolecules 1993, 26, 2479. (d) Quirk, R. P.;

Yoo, T.; Lee, B. J. Macromol. Sci., Pure Appl. Chem. 1994, A31, 911. (e) Hückstädt, H.; Abetz, V.; Stadler, R. Macromol. Rapid Commun. 1996, 17, 599. (f) Lambert, O.; Dumas, P.; Hurtrez, G.; Riess, G. Macromol. Rapid Commun. 1997, 18, 343. (g) Sioula, S.; Hadjichristidis, N.; Thomas, E. L. Macromolecules 1998, 31, 5272. (h) Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 1999, 37, 857. (i) Hadjichristidis, N.; Pitsikalis, M.; Pispas, S.; Iatrou, H. Chem. Rev. 2001, 101, 3747. (j) Li, Z.; Hillmyer, M.; Lodge, T. P. Macromolecules 2004, 37, 8933. (k) Takano, A.; Wada, S.; Sato, S.; Araki, T.; Hirahara, K.; Kazama, T.; Kawahara, S.; Isono, Y.; Ohno, A.; Tanaka, N.; Matsushita, Y. Macromolecules 2004, 37, 9941. (l) Higashihara, T.; Hirao, A. J. Polym. Sci., Part A: Polym. Chem. 2004, 45, 4535. (m) Hadjichristidis, N.; Iatrou, H.; Pitsikalis, M.; Pispas, S.; Avgeropoulos, A. Prog. Polym. Sci. 2005, 30, 725. (n) Mavroudis, A.; Hadjichristidis, H. Macromolecules 2006, 39, 535. (o) Wang, X.; Xia, J.; He, J.; Yu, F.; Li, A.; Xu, J.; Lu, H.; Yang, Y. Macromolecules 2006, 39, 6898. (p) Fragouli, P.; Iatrou, H.; Hadjichristidis, H.; Sakurai, T.; Matsunaga, Y.; Hirao, A. J. Polym. Sci., Part A: Polym. Chem. 2006, 44, 6587. (q) Wang, X.; He, J.; Yang, Y. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 4818. (r) Hirao, A.; Higashihara, T.; Hayashi, M. Polym. J. 2008, 40, 923. (s) Higashihara, T.; Hayashi, M.; Hirao, A. Prog. Polym. Sci. 2011, 36, 323. (t) Hirao, A.; Hayashi, M.; Higashihara, T.; Hadjichristidis, N. Recent developments in miktoarm star polymers with more than three different arms. In Complex Macromolecular Architectures: Synthesis, Characterization, and Self-Assembly; Hadjichristidis, N., Hirao, A., Tezuka, Y., Du Prez, F., Eds.; John Wiley & Sons: Singapore, 2011; pp 97−132. (u) Hanisch, A.; Schmalz, H.; Müller, A. H. E. Macromolecules 2012, 45, 8300−8309. (126) Six, J. L.; Gnanou, Y. Macromol. Symp. 1995, 95, 137. (127) Hirao, A.; Sugiyama, K.; Tsunoda, Y.; Matsuo, A. J. Polym. Sci., Part A: Polym. Chem. 2006, 44, 6659. (128) Taton, D.; Feng, X.; Gnanou, Y. New J. Chem. 2007, 31, 1097. (129) Hutchings, L. R. Soft Matter 2008, 4, 2150. (130) Yoo, H. S.; Hirao, A. Precise synthesis of dendrimer-like starbranched polymers, a new class of well-defined hyperbranched polymers. In Complex Macromolecular Architectures: Synthesis, Characterization, and Self-Assembly; Hadjichristidis, N., Hirao, A., Tezuka, Y., Du Prez, F., Eds.; John Wiley & Sons: Singapore, 2011; pp 133−167. (131) Konkolewicz, D.; Monteiro, M. J.; Perrier, S. Macromolecules 2011, 44, 7067. (132) Grayson, S. M.; Fréchet, J. M. J. Chem. Rev. 2001, 101, 3819. (133) Trollsås, M.; Hedrick, J. L. J. Am. Chem. Soc. 1998, 20, 4644. (134) (a) Feng, X.; Taton, D.; Chaikof, E. L.; Gnanou, Y. J. Am. Chem. Soc. 2005, 127, 10956. (b) Feng, X.; Taton, D.; Chaikof, E. L.; Gnanou, Y. Macromolecules 2009, 42, 7292. (135) Percec, V.; Barboiu, B.; Grigoras, C.; Bera, T. K. J. Am. Chem. Soc. 2003, 125, 6503. (136) (a) Chalari, I.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 1519. (b) Orfanou, K.; Iatrou, H.; Lohse, D. J.; Hadjichristidis, N. Macromolecules 2006, 39, 4361. (137) Hutchings, L. R.; Roberts-Bleming, S. J. Macromolecules 2006, 39, 2144. (138) Urbani, C. N.; Bell, C. A.; Lonsdale, D.; Whittaker, M. R.; Monteiro, M. J. Macromolecules 2008, 41, 76. (139) Matmour, R.; Gnanou, Y. J. Am. Chem. Soc. 2008, 130, 1350. (140) Teertstra, S. J.; Gauthier, M. Prog. Polym. Sci. 2004, 29, 277. (141) (a) Gauthier, M.; Möller, M. Macromolecules 1991, 24, 4548. (b) Li, J.; Gauthier, M. Macromolecules 2001, 34, 8918. (142) Deffieux, A.; Schappacher, M.; Hirao, A.; Watanabe, T. J. Am. Chem. Soc. 2008, 130, 5670. (143) Zhang, H.; He, J.; Zhang, C.; Ju, Z.; Li, J.; Yang, Y. Macromolecules 2012, 45, 828. (144) Feng, X.; Taton, D.; Chaikof, E. L.; Gnanou, Y. Macromolecules 2009, 42, 7292. (145) Knauss, D. M.; Al-Muallem, H. A.; Huang, T.; Wu, D. T. Macromolecules 2000, 33, 3557. (146) Baskaran, D. Macromol. Chem. Phys. 2001, 202, 1569. V


Macromolecules

Perspective

(147) (a) Sun, W.; He, J.; Wang, X.; Zhang, C.; Zhang, H.; Yang, Y. Macromolecules 2009, 42, 7309. (b) Zhang, H.; Zhu, J.; He, J.; Qiu, F.; Zhang, H.; Yang, Y.; Lee, H.; Chang, T. Polym. Chem. 2013, 4, 830. (148) (a) Sunder, A.; Frey, H.; Mülhaupt, R. Macromol. Symp. 2000, 153, 187. (b) Kautz, H.; Sunder, A.; Frey, H. Macromol. Symp. 2001, 163, 67. (149) (a) Wurm, F.; Nieberle, J.; Frey, H. Macromolecules 2008, 41, 1184. (b) Wurm, F.; Kemmer-Jonas, U.; Frey, H. Polym. Int. 2009, 58, 989. (150) Wurm, F.; Frey, H. Prog. Polym. Sci. 2011, 36, 1. (151) Higashihara, H.; Nagura, M.; Inoue, K.; Haraguchi, N.; Hirao, A. Macromolecules 2005, 38, 4577. (152) Higashihara, T.; Sugiyama, K.; Yoo, H. S.; Hayashi, M.; Hirao, A. Macromol. Rapid Commun. 2010, 31, 1031. (153) Hirao, A.; Murano, K.; Oie, T.; Uematsu, M.; Goseki, R.; Matsuo, Y. Polym. Chem. 2011, 2, 1219. (154) (a) Ito, S.; Goseki, R.; Senda, S.; Hirao, A. Macromolecules 2012, 45, 4997. (b) Ito, S.; Goseki, R.; Ishizone, T.; Senda, S.; Hirao, A. Macromolecules 2013, 46, 819. (c) Goseki, R.; Ozama, Y.; Akemine, E.; Ito, S.; Ehara, S.; Hirao, A. Polymer 2013, 54, 2049. (155) (a) Matsuo, A.; Watanabe, T.; Hirao, A. Macromolecules 2004, 37, 6283. (b) Hirao, A.; Matsuo, A.; Watanabe, T. Macromolecules 2005, 38, 8701. (c) Hirao, A.; Watanabe, T.; Ishizu, K.; Ree, M.; Jin, K. S.; Deffieux, A.; Schappacher, M.; Carlotti, S. Macromolecules 2009, 42, 682. (156) Yoo, H. S.; Watanabe, T.; Hirao, A. Macromolecules 2009, 42, 4558. (157) Yoo, H. S.; Watanabe, T.; Matsunaga, Y.; Hirao, A. Macromolecules 2012, 45, 100. (158) Perny, S.; Allgaier, J.; Cho, D. Y.; Lee, W.; Chang, T. Macromolecules 2001, 34, 5408. (159) Hutchings, L. R. Macromolecules 2012, 45, 5621. (160) Sugiyama, K.; Oieö El-Magd, A. A.; Hirao, A. Macromolecules 2010, 43, 1403. (161) Hirao, A.; Matsuo, Y.; Oie, T.; Goseki, R.; Ishizone, T.; Sugiyama, K.; Göschel, A. H.; Müller, A. H. E. Macromolecules 2011, 44, 6345. (162) Matsuo, Y.; Oie, T.; Goseki, R.; Ishizone, T.; Sugiyama, K.; Hirao, A. Macromol. Symp. 2013, 323, 26. (163) Bellas, V.; Iatrou, H.; Pitsinos, E. N.; Hadjichristidis, N. Macromolecules 2001, 34, 5376. (164) Fragouli, P. G.; Iatrou, H.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 514. (165) Fragouli, P. G.; Iatrou, H.; Lohse, D. J.; Hadjichristidis, N. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 3938. (166) (a) Hirao, A.; Murano, K.; Kurokawa, R.; Watanabe, T.; Sugiyama, K. Macromolecules 2009, 42, 7820. (b) Hirao, A.; Murano, K.; El-Magd, A. A.; Uematsu, M.; Ito, S.; Goseki, R.; Ishizone, T. Macromolecules 2011, 44, 3302. (167) (a) Hirao, A.; Watanabe, T.; Kurokawa, R. Macromolecules 2009, 42, 3973. (b) Hirao, A.; Uematsu, M.; Kurokawa, R.; Ishizone, T. Macromolecules 2011, 44, 5638. (168) (a) Higashihara, T.; Inoue, K.; Nagura, M.; Hirao, A. Macromol. Res. 2006, 14, 287. (b) Hirao, A.; Higashihara, T.; Inoue, K. Macromolecules 2008, 41, 3579. (c) Hirao, A.; Higashihara, T.; Hayashi, M. Macromol. Chem. Phys. 2001, 202, 3165. (d) Higashihara, T.; Hayashi, M.; Hirao, A. Macromol. Chem. Phys. 2002, 203, 166. (169) (a) Hirao, A.; Higashihara, T.; Nagura, M.; Sakurai, T. Macromolecules 2006, 39, 6081. (b) Higashihara, T.; Sakurai, T.; Hirao, A. Macromolecules 2009, 42, 6006. (170) Hasegawa, H. In Complex Macromolecular Architectures: Synthesis, Characterization, and Self-Assembly; Hadjichristidis, N., Hirao, A., Tezuka, Y., Du Prez, F. J., Eds.; Wiley & Sons: Singapore, 2011; pp 569−591. (171) Hadjichristidis, N. Eur. Phys. J. E 2003, 10, 83.

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