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Perspective pubs.acs.org/Macromolecules
50th Anniversary Perspective: Metal-Catalyzed Living Radical Polymerization: Discovery and Perspective Makoto Ouchi* and Mitsuo Sawamoto* Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan ABSTRACT: Development of living polymerizations via reversible activation of dormant species opened the door to discovery of metal-catalyzed living radical polymerization that is now very useful for precise construction of tailor-made polymeric architectures. In this commemorative Perspective, the historical aspects as well as the prospects as a new polymerization tool are described toward advanced structural control or technological materials innovation in various fields.
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difficult, albeit not impossible, because, in contrast to ionic intermediates, the bimolecular radical termination (i.e., coupling and disproportionation) of carbon radicals is a builtin side reaction that is inherently unavoidable. Nevertheless, hints for living radical polymerization began to emerge.9 For example, as early as in 1982, concurrently with the new family of living ionic polymerizations as mentioned above, Otsu reported the radical polymerization with an “iniferter” (initiator, chain-transfer agent, and terminator),10 although reaction control was not fully satisfactory for living polymerization with regard to polymer molecular weight and other aspects. In the iniferter system, the propagating radical is proposed to be temporarily capped with a dithiocarbamate or related thioesters into a covalent precursor that regenerates the radical upon heating, photoirradiation, and/or chain transfer to another growing radical (Figure 1d), thus heralding the concepts of reversible termination and dormant species.11 In the early 1990s, living radical polymerizations were eventually reported, with a stable radical [e.g., (2,2,6,6tetramethylpiperidin-1-yl)oxyl or TEMPO: Figure 1e]12 and a cobalt complex (Figure 1f)13 as the capping moieties for dormant species for styrene and acrylate, respectively. These pioneering discoveries further stimulated interest in, and perhaps hope for, living radical polymerizations based on the dormant species and their reversible activation into radicals. Such controlled radical polymerization with dormant species is now referred as “reversible deactivation radical polymerization”.14 Also in the early 1990s, following our lead in the Lewis-acid mediated living cationic polymerization in 1984,6 where a
n the recent history of polymer science, the year 1956 is remembered as the dawn of the extensive and dramatic development, or literally a mushrooming, of a series of living polymerizations in the 1980s and 1990s covering virtually all the conceivable mechanisms of chain-growth polymerization.1 In that year, where the present authors were either just a toddler or even not yet born, the first living polymerization, a controlled anionic polymerization of styrene, was reported by Szwarc, which opened the door to the precision synthesis of polymers of controlled molecular weight and architecture, including block and end-functionalized polymers.2,3 Its concept and definition, along with the term “living”, were also established. Though effective and efficient, however, the “classical” living anionic polymerization requires highly pure reagents and stringent reaction conditions free from oxygen, water, and other impurities, rendering high-vacuum systems almost mandatory. Also, the monomers are primarily confined to nonpolar hydrocarbon alkenes and dienes. The development of a new generation of living polymerizations has apparently begun in the 1980s, such as anionic polymerization with a lithium salt additive (Figure 1a),4 group transfer polymerization (Figure 1b),5 and the Lewis-acidcatalyzed cationic living polymerization of vinyl ethers (Figure 1c)6 and isobutylene,7 among others, and in parallel with the deepened understanding of their mechanisms and implications, a general concept of precision polymerization, namely, the dormant-active species equilibrium, has been recognized and then established.8 As the 1990s approached, with nearly all conceivable ionic living polymerizations now explored, polymer scientists turned attention to living radical polymerization (LRP), a significant but challenging frontier in polymer chemistry at that time, given the prevailing importance of this process in industry and long-standing basic research. Obviously, the precision control of radical polymerization had been considered fundamentally © XXXX American Chemical Society
Received: December 16, 2016 Revised: March 2, 2017
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methacrylate (MMA) for carbon tetrachloride with ruthenium catalyst [RuCl2(PPh3)3] to ensure the radical addition reaction is repeated from the resultant carbon−halogen bond leading to PMMA generation. At that time, we considered an addition of aluminum compound could be helpful for acceleration of polymerization through interaction of pendant ester group in MMA as in anionic polymerization,18 and indeed the addition was essential to induce the polymerization. Later, it was revealed that such an aluminum compound can stabilize Ru(III) species moderately or accelerate the halogen exchange reaction via an internal nucleophilic substitution.19,20 Thus, we submitted the first manuscript on metal-catalyzed living radical polymerization (LRP) to Macromolecules in 1994 (accepted in 1995).21
Figure 2. (a) Radical addition of haloalkane to alkene with RuII catalyst. (b) First example of metal-catalyzed LRP of MMA.
Figure 1. Equilibrium between dormant (left) and active (right) species: (a) anionic polymerization with a lithium salt additive, (b) group transfer polymerization, (c) Lewis-acid-catalyzed cationic living polymerization, (d) radical polymerization with an iniferter, (e) TEMPO-mediated radical polymerization, and (f) cobalt-mediated radical polymerization.
Shortly after our first paper, Matyjaszewski and his group began reporting copper-catalyzed living radical polymerization,22 which has been termed “atom transfer radical polymerization”, now frequently referred to as ATRP (Figure 3a).23 Now over 20 years have passed since the first paper on metalcatalyzed living radical polymerization, but the polymerization is more and more significant to develop advanced polymeric materials as well as to synthesize tailor-made polymers, such as end-functionalized polymers, block copolymers, and multiarmed polymers, in various fields (Figure 3b).23−25 As described later, the polymerization process will be increasingly vital to development of polymeric materials in the future. In this Perspective, some fundamental aspects of metal-catalyzed living radical polymerization (metal-catalyzed LRP) are reviewed and some recent interesting researches leading to future prospects are then discussed.
carbon−halogen bond is included in the dormant terminal, our group initiated exploration of living radical polymerization (a brief account of this development can be found in our previous review paper15). Noting the ambivalent nature of carbon− halogen bonds that dissociate both heterolytically (into a carbocation) and homolytically (into a radical), we directed efforts toward how to activate a carbon−halogen bond into a carbon radical, instead of a carbocation with a Lewis acid catalyst. For this approach, we focused on the Kharasch addition reaction between a halogen compound and an olefin to give the halogen adduct likely via ruthenium-catalyzed radical-mediated reaction,16 as follows: a carbon-centered radical species is generated from the halogen compound via halogen transfer to the ruthenium complex via one-electron oxidation; subsequent reaction with the double bond of the olefin to give radical species on carbon attached to the substituent; and the radical eventually reacts with the oxidized ruthenium complex to give the halogen adduct.17 An excess of halogen compound is required to synthesize the halogen adduct for the double bond in good yield, especially for a conjugated olefin such as styrene: otherwise, polymerization or oligomerization, which is unfavorable for the purpose of addition reaction, could take place (the product may show unimodal SEC curve). We purposely employed a large excess of methyl
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SYSTEM DESIGN FOR METAL-CATALYZED LIVING RADICAL POLYMERIZATION The metal-catalyzed LRP proceeds under a dynamic equilibrium between dormant species consisting of nonpolymerizable halogen-capped initiator (or chain end) with a transition metal complex in a lower oxidation state (Mtn) and active species of polymerizable radical species with the complex in a higher oxidation state (Mtn+1) (Figure 3a). Herein, the process from dormant to active species is often referred to as “activation”, whereas the reverse reaction as “deactivation”. In order to control the polymerization or the equilibrium, the choice of the B
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Figure 3. (a) Equilibrium between dormant and active species in metal-catalyzed living radical polymerization. (b) Well-defined architectures via metal-catalyzed living radical polymerization.
Figure 4. First generation of catalysts for metal-catalyzed LRP.
Design of Catalyst. Followed by the earlier reports with ruthenium(II) and copper(I) complex, some low valent metals in groups VI to XI were reported available for metal complex catalyst of LRP, such as iron(II),30 iron(I),31 nickel(II),32,33 rhenium(V),34 molybdenum(III),35 osmium(II),36 etc. (Figure 4). The function of these metal complexes is control of both activation and deactivation for initiator and growing terminus under suitable equilibrium along with their own one-electron
complex as the catalyst is crucial as well as that of the alkyl halide initiator, according to desired polymeric structures or the applications. Besides, an additive or a cocatalyst is required as a third component in most systems to assist the redox catalysis more efficiently. Herein, how to select or design the three components is briefly described. See other review papers for deeper understanding of the system design, especially for ATRP (copper-catalyzed LRP).23,26−29 C
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Figure 5. Evolution of ruthenium catalysts.
redox reaction. An ideal “active” catalyst in living radical polymerization allows syntheses of well-defined polymers with narrow MWDs and high end-functionality throughout polymerization, even with a tiny amount of metal complex. Particularly, lower redox potential and higher halidophilicity of the transition metal complex could provide such controlled structures via the halogen transfer process. These catalytic performances are inherently determined by the central metal but could be tuned by design of ligands that enable withdrawal or donation of the electron, and ligands are also responsible for solubility as well as additional functions such as thermal reversibility of catalyst. Thus, it is no exaggeration to say that catalysts in metal-catalyzed LRP have evolved along with ligand design. However, selection of the central metal is sometimes essential for the production process and/or purpose of the end product, such as iron-based catalysts for bioapplications due to the biocompatibility, as is mentioned subsequently. Among metals, copper has been most frequently used, and various types of multidendate nitrogen ligands have been studied to clarify the correlation between ligand structure and catalyst activity.37 In this Perspective, the evolution of ruthenium catalysts in our group is briefly reviewed (Figure 5). The first-generation dichloride ruthenium complex (Ru-1) with triphenylphosphine showed catalytic activity for controlled polymerizations of monomers including methacrylate,21,38,39 acrylate,40 acrylamide,41 and styrene,42 in conjunction with an additive [e.g., Al(Oi-Pr3) and amine43]. The performance of the ruthenium catalyst was a little far from satisfactory in terms of requisite catalyst amount and MWDs of obtained polymers. On the other hand, the second-generation complexes with indenyl (Ind: Ru-2)44 and pentamethylcyclopentadienyl (Cp*: Ru-3)45 ligand capable of donating the π-electrons to ruthenium in η5type coordination led to a dramatic increase in the catalytic activity: in some cases, well-defined polymers of high MW (Mn > 105) and narrow MWDs (Mw/Mn < 1.10) could be synthesized even with a smaller amount of catalyst. Especially, the Cp* ruthenium complex showed catalytic activity for
polymerizations of the three fundamental monomers (MMA, MA, and St) under almost identical conditions.46 The higher catalytic activity was corroborated by lower redox potential and more rapid halogen exchange reaction with a bromine-based initiator.45 The catalytic activities were further improved by introduction of electron donating groups (Ru-4)47 or hemilabile chelate ligand (Ru-5).48 The Cp*-based tetrameric ruthenium complex (Ru-6) was useful as the precursor to prepare complexes with various phosphine ligands just on heating, which was convenient for ligand screening without isolation of complex.49 For example, bisphosphine monoxide ligands allowed active catalysis independent of cocatalyst likely due to the dynamic chelate coordination on ruthenium.50 An incorporation of polyethylene glycol (PEG)-embedded phosphine ligand allowed efficient removal of ruthenium residue from solution polymerization in organic solvent51 or dispersed miniemulsion polymerization via the thermoresponsive switching of solubility.52 Design of Initiator. The prominent advantage of metalcatalyzed LRP over other LRP systems is the easy handling and design of the alkyl halide initiator. Generally, the carbon adjacent to halogen is connected to ester, amide, or benzene because the radical species can be moderately stabilized due to the resonance effect. These substituents are corresponding to the conjugated monomers, such as acrylates, (meta)acrylamides, and styrenes. Faster generation of initiating radical species is suitable for polymerization control giving narrower molecular weight distributions (MWDs). Tertiary alkyl halides show higher activation rate constants than secondary and primary ones. The type of halogen also affects the activation rate (I > Br > Cl), but the optimum halogen selection depends on the central metal because relative bond strength of the metal halide after the activation (X−Mtn+1, X = halogen) is related to the dormant-active equilibrium. The halide initiator can be installed on molecules via relatively simple reactions, such as esterification or amidation (Figure 6a), and the stable moiety be effectively converted into reactive radical species under suitable D
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Figure 6. (a) Synthesis of initiator via esterification or amidation. (b) Transformation of halogen-based initiator into initiator or chain transfer agent for other living radical polymerization.
catalysis for quantitative initiation. This is the reason why metal-catalyzed LRP has been often employed for surface modification53 and conjugation with biomolecules.54 Importantly, alkyl halide compounds are available even as a precursor for NMP initiators55 or RAFT agents56 via halogen exchange under copper catalysis (Figure 6b). As described later, the high accessibility of the halogen initiator is helpful even for construction of templated systems toward advanced control of polymer structures. Design of Additive. In the living radical polymerization process, a slight proportion of side reactions between radical species is unavoidable due to the neutral feature of growing active species, unlike living anionic polymerization. Once side reactions occur between radical species, the equivalent amount of oxidized metal complex (e.g., RuIII and CuII) accumulates to incur stagnation in radical generation or polymerization due to unbalanced dormant-active equilibrium. Especially, in the case with a very active catalyst workable even with catalytic amount, the issue becomes more serious due to shortage in absolute amount of the activator. For this problem, Matyjaszewski and co-workers came up with a breakthrough ideaa combination of reducing agent, such as stannous octoate and ascorbic acid (Figure 7a).27,57−59 Such additives are helpful to reduce CuII that is accumulated via unavoidable side reactions during polymerization to CuI, and indeed optimized conditions with a reducing agent allows controlled polymerizations up to higher conversion even with a tiny amount of catalyst. The polymerization using a reducing agent was termed “activators regenerated by electron transfer (ARGET) ATRP”, since the activator (i.e., CuI) is regenerated during polymerization. Some other methodologies have been reported for the regeneration of CuI activator, such as addition of free radical initiator [initiators for continuous activator regeneration (ICAR) ATRP]60 and combination of external stimuli, e.g., electrical current [electrochemically mediated
Figure 7. (a) Addition of reducing agent for copper-mediated living radical polymerization (ATRP). (b) Addition of ferrocene for ruthenium-mediated living radical polymerization.
ATRP (eATRP)],61 light (photoATRP),62 and mechanical force.63 For ruthenium-catalyzed systems, aluminum or titanium alkoxides and amine compounds are often required as additives to promote polymerization. There is the potential for these additives to serve as reducing agents, or more specifically some additives dynamically coordinate on ruthenium to change the catalytic feature.43,64 The addition of an azo-based thermal radical initiator was also demonstrated for decreasing in amount of ruthenium catalyst.65 We have recently found ferrocene can be used as a reducing agent for ruthenium-based catalyst (Figure 7b).66 Some model reactions supported the catalytic contribution of the additive: ferrocene (FcII) reduces RuIIIX to give RuII and FcIII+X−, and eventually the resultant ferrocenium ion could be responsible for deactivation of growing radical species to regenerate ferrocene. Both ruthenium catalyst and ferrocene cocatalyst can be supported on PEG-based polymer chains to achieve removal of the metal residues after polymerization.
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RECENT DEVELOPMENT OF METAL-CATALYZED LRP It has been about more than 20 years since metal-catalyzed LRP was discovered. Finally, we describe recent development of metal-catalyzed LRP that are likely more important in near future for materials applications or advanced structural control. SET-LRP. An example of recent progress in metal-catalyzed LRP is single electron transfer (SET)-mediated LRP (SETLRP) proposed by Percec, where Cu0 could activate alkyl halide (R−X) in conjunction with a proper ligand (L): R−X + Cu0/L E
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Figure 8. (a) Catalytic cycle of SET-LRP, (b) iron catalysis in conjunction with decamethylferrocene as a cocatalyst, (c) hemine-based iron catalyst, and (d) direct polymerization of MAA via SARA ATRP or e-ATRP.
→ [R---X]•− + [CuI/L]+, followed by dissociation ([R---X]•− → [Rδ+• X−]) and complexation ([Rδ+• X−] + [CuI/L]+ → R• + CuIX/L).67−69 Herein Cu0/L is active enough to activate nonconjugated dichloroalkane structure derived from vinyl chloride (VC) that is less active than common conjugated counterparts, leading to controlled polymerization of VC.70 Another crucial aspect in this system is that CuI (CuBr) in conjunction with N-containing multidentate ligand, such as tris[2-(dimethylamino)ethyl]amine (Me6-TREN), undergoes disproportionation to generate Cu0 and CuII/L, which was revealed from study with UV−vis spectroscopy67 and visualization71,72 (Figure 8a). The disproportionation rate highly depends on solvent and takes place quickly in polar solvents such as DMSO and water, and SET-LRP in these solvents allows very fast and highly controlled polymerizations giving high end functionality even at 100% monomer conversion. Indeed, the future of SET-LRP has been supported by the following achievements: ultrahigh MW polymers with narrow polydispersity can be synthesized;67 multiblock copolymerization can be controlled via repeating addition of fresh monomer after ∼100% conversion.73 The high controllability of SET-LRP would be helpful even for industrial applications because it allows syntheses of well-defined polymers free from monomer
residue without relying on purification/separation processes. The polymerization in the presence of Cu0 possibly proceeds via not SET but ATRP mechanism. In the ATRP mechanism, the disproportionation of CuI into Cu0 and CuII species is attributed to negligible: herein CuI is the activator for the halide initiator, and Cu0 is the reducing agent for CuII. The polymerization is thereby called “supplemental activator and reducing agent ATRP”, and study on a detailed mechanism is still continuing.74−76 Iron Catalyst. Among metals of potential use for LRP, iron (Fe) has been examined as a practical catalyst because of its sustainability (Earth-abundant) and low toxicity. However, iron-based catalysts have a critical issue of lower tolerance to polar groups, resulting in limitation of applicable monomers and solvents, and indeed there seem to be a few examples on use of iron-based catalyst for polymer syntheses in fundamental research as well as for industrial applications. Our group has developed some iron catalysts, e.g., FeCl2(PPh3) 2,30 or the related iron-based systems for LRP.31,77−84 Various ligands or additives in conjunction with FeX2 or FeX3 (X: halogen) have been also reported by other groups: halide anion (e.g., tetrabutylammonium bromide),85 polar solvent (e.g., N-methylpyrrolidone),86 phosphine−pyrF
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Figure 9. (a) Concurrent tandem living radical polymerization for gradient copolymer. (b) Template initiator in Ru-catalyzed competitive radical addition. (c) Inimer molecule incorporating two cleavable/renewable bonds for iterative radical addition.
idine hybrid ligand,87 high electron-donating phosphine ligand,88 etc. One example of recent progress in iron catalysis is using decamethylferrocene as a cocatalyst for iron catalytic system with FeBr2/n-Bu4NBr (Figure 8b),89 which was derived from ferrocene cocatalysis in ruthenium-catalyzed LRP as described above.66 The catalytic performance can be improved by the ferrocene-assisted redox reaction, and the high catalytic activity independent of ligands allows controlled polymerizations of various polar vinyl compounds, such as PEGMA, HEMA, and MAA as (co)monomers. This cooperative concept using two iron complexes is unique, and further development is expected toward more useful catalysis.
An iron complex showing high catalytic activity even in water would be interesting for bioapplications due to the inherent biocompatible feature of iron. Matyjaszewski et al. modified the structure of hemine via hydrogenation of the vinyl group and attachment of PEG chain to achieve LRP of [oligo(ethylene oxide) methyl ether methacrylate] in water with the aid of reducing agent and sodium salt (Figure 8c).90 Using such a naturally occurring complex with some modification could open the door to practical iron catalysts for LRP. LRP of Acidic Monomer. Control over radical polymerization of acidic monomers such as methacrylic acid has been a challenging subject for metal-catalyzed LRP. The difficulty is G
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polymers. Radical polymerization would be appropriate for design of template system due to many applicable monomers and the robust propagating species with respect to functional groups, and indeed some template systems with radical polymerization have been reported.101 However, there were few examples to approach control of sequence before development of LRPs due to the difficulty in controlling initiation as well as propagation. The high accessibility to initiator design of metal-catalyzed LRP should be suitable for construction of the template systems toward sequence control. We thus designed a special initiator for metal-catalyzed LRP to nearby embed another reactive site [herein an initiator for living cationic polymerization (LCP)] for incorporation of recognition sites for specific monomers (Figure 9b).102,103 An amino group and a crown ether moiety can be incorporated to recognize MAA and sodium methacrylate, respectively, and the selective monomer radical additions were demonstrated by using the ruthenium catalyst under competitive reaction conditions in the presence of nonrecognized monomer of identical reactivity. The concept is not fully satisfactory to realize sequence control for polymers but significant in terms of a template effect controlling monomer selectivity in LRP. Quite recently, the same group designed an inimer molecule carrying an initiator for metal-catalyzed LRP and a methacrylate vinyl group that are connected via two cleavable and renewable covalent bonds (Figure 9c).104 Although the addition process was on the basis of chain-growth mechanism, the dilution condition with optimized catalysis for metal-catalyzed LRP allowed control of the cyclization. Furthermore, the special bonds allowed the iterative radical cyclization along with cleavage to form the side chain and regeneration to install the vinyl group. The repeated number was limited, but future progress in molecular design and catalysis with the concept could lead to more cycles for construction of sequencecontrolled polymers.
caused by chain-end cyclization giving a halogen-free lactone terminus via intramolecular substitution of a −COOH side chain to the carbon−halogen bond at the dormant terminus as well as catalyst poison by the acidic site. Quite recently, the Matyjaszewski group has realized LRP of MAA in water using two types of efficient ATRP-based systems: eATRP61 and SARA ATRP,91 where the CuI activator complex is regenerated via reduction of CuII electrochemically at a working electrode and by comproportionation between Cu0 and CuII, respectively (Figure 8d).92 Furthermore, the system was tuned to decrease the chance of −COOH-mediated side reactions to the extent possible as follows: NaCl was used to give the tighter dormant terminus with Cl leaving group; tris(2-pyridylmethyl)amine (TPMA) was employed as the ligand to stabilize Cu complex for protection from the acidic group, and pH of water solvent was regulated to lower with HCl to reduce the substitution reactivity of COOH. These optimized conditions allowed direct homopolymerization of MAA up to higher conversion (∼90%) in a controlled manner. Sequence Control with Metal-Catalyzed LRP. Development of living polymerization has enabled us to synthesize monodispersed polymers of targeted molecular weights as well as end-functionalized and block copolymers by using various types of monomers. However, the degree of structural control is still inferior to biopolymers such as DNA and proteins. In the past decade, tremendous efforts have been directed to control of advanced structural factors, particularly “sequence” that is the order of repeating units as well as the position of functional units.93−96 Even for this purpose, living polymerization systems permitting controlled initiation/propagation are useful. In metal-catalyzed LRP, initiation takes place from the carbon−halogen bond in the initiator to give a carbon-centered radical species, followed by propagation with monomers without any side reactions. When some monomers are combined, copolymerization takes place statistically on the basis of the same reactivity ratios determined in free radical polymerization. Herein, unless side reactions occur, the composition distribution among resultant copolymer chains is almost uniform, which is different from the case with free radical polymerization process resulting in nonuniform composition. By mechanically changing ratio of existing comonomers (typically with syringe pump) during living radical polymerization, syntheses of gradient copolymers is accessible.97 Our group has demonstrated a novel methodology to synthesize gradient copolymers without relying on the mechanical regulation of monomer feed, which is the tandem control of transformation for monomer pendant group along with the LRP propagation. The concurrent reaction is transesterification of methacrylate (monomer) pendant with alcohol catalyzed by metal alkoxides such as Al(Oi-Pr)3 and Ti(Oi-Pr)4 that were originally used as cocatalysts for LRP (Figure 9a).98−100 Optimized conditions allowed synchronization of the monomer transformation with the propagation to generate copolymer chains having gradient sequence as well as narrow MWD. The tandem approach could open the door to advanced control of copolymer structure that cannot be reached with common polymerization systems. Nature utilizes templates to control the order of propagating comonomers, that is, “sequence”, for biopolymers (i.e., DNA and peptides). Inspired by the accurately controlled production process, chemists have drawn considerable attention to template polymerization toward sequence control of synthetic
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SUMMARY AND OUTLOOK Unlike living ionic polymerizations, reversible deactivation radical polymerization including metal-catalyzed LRP has allowed precise syntheses of tailor-made macromolecules from variety of monomers without any special technique and equipment as well as protection of the polar groups. Particularly, the merit of metal-catalyzed LRP is controlled generation of radical species from the stable site (i.e., carbon− halogen bond) with the help of chemical stimulus (i.e., catalyst), which has been utilized in various material designs. More recently, a combination of external physical stimulus, typically light, on the basis of metal-catalyzed LRP process has attracted attention toward not only advanced material fabrications, such as gradient surface patterning, but also propagation switching or metal-free systems.105−107 These advances will permit practical applications as well as control of unsolved structural factors.
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AUTHOR INFORMATION
Corresponding Authors
*(M.O.) E-mail:
[email protected]. *(M.S.) E-mail:
[email protected]. ORCID
Makoto Ouchi: 0000-0003-4540-7827 Mitsuo Sawamoto: 0000-0003-0352-9666 H
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immediate past President of the Society of Polymer Science, Japan (SPSJ) (2008−2010), and one of the Editors of the Journal of Polymer Science, Part A: Polymer Chemistry (1995−2015). He was also the leader of the Kyoto University Global Center of Excellence (GCOE) Project “Integrated Materials Science” (2007−2011). His research interest includes development of precision cationic and radical polymerizations and catalysts, the synthesis of designed functional polymers, and most recently the sequence regulation in chain-growth polymerization, leading to over 380 original papers, >40 reviews, >20 named and plenary lectures, >175 invited lectures, and >19000 total citations (2016). The first paper on his living radical polymerization has been cited over 2500 times (Macromolecules no. 3 most cited) and a review over 2600 times [Chemical Reviews top
