Postpolymerization Modification of Block Copolymers - ACS Publications

Perspective pubs.acs.org/Macromolecules

Postpolymerization Modification of Block Copolymers Joy Romulus, John T. Henssler, and Marcus Weck* Department of Chemistry and Molecular Design Institute, New York University, New York, New York 10003, United States ABSTRACT: The postpolymerization modification of block copolymers has seen a growing interest in the past decade ranging from fundamental synthesis and structure−property relationships to potential applications. The resulting side-chain-modified block copolymers can retain the properties inherent to the parent block copolymer core, while introducing side-chain functionality that can allow for a tunable handle on material properties and consequently applications. In this Perspective, we discuss different methods of postpolymerization side-chain modification of block copolymers using either covalent or noncovalent strategies. We also describe potential applications, discuss some of the challenges remaining in this area, and suggest strategies for the advancement of the field.

■

INTRODUCTION The ability of block copolymers to microphase separate1 and form self-assembled nanoscale features in the melt, solid state, and solution has initiated research on block copolymers with an emphasis toward improving structural control, accessing greater chemical diversity, enhancing synthetic efficiency, and exploring new applications.2−4 The development of new synthetic strategies for achieving well-defined and chemically diverse block copolymers continues to expand. The majority of block copolymers are synthesized by either the sequential addition of monomers to an active chain-end using methods such as ringopening metathesis, controlled radical, anionic, or cationic polymerizations, the initiation of a homopolymer with a bisfunctional initiator, or quenching of a homopolymer with a functionalized chain-terminator that is subsequently converted to a macroinitiator and finally used to initiate the polymerization of a second block, or linking together two or more telechelic polymers through functionalized chain-ends.5,6 The latter of these approaches allows for the formation of block copolymers with blocks that cannot be synthesized in the same reaction vessel due to incompatible polymerization methodologies and/ or uncontrolled polymerization methods. This strategy generally requires quantitative termination by a functionalized chainterminator followed by a reaction with a complementary chainend of a second polymer, thus linking the two chemically distinct polymers to form a block copolymer.6 Not only covalent but also noncovalent strategies have been utilized to facilitate the connection between chain-ends to afford block copolymers.7−10 Strategies of block copolymer synthesis, characterization, and applications have previously been reviewed.2,4,11−17 The versatility of block copolymers is enhanced by the incorporation of functional handles, either in the main- or sidechains, that allow for further chemistry to be performed after polymer formation. This postpolymerization modification facilitates the production of multiple polymer architectures derived from a single polymer backbone (Figure 1). The © XXXX American Chemical Society

Figure 1. Postpolymerization modification of one block copolymer segment with different pendent moieties.

combination of block copolymers with postpolymerization modification has emerged as a powerful method of accessing unique and increasingly complex nanostructures with potential applications such as controlled-delivery assemblies,18 stimuliresponsive materials,19−21 and drug delivery.16,22 Postpolymerization modification strategies can be divided into two areas: covalent and noncovalent. The formation of covalent bonds between a polymer backbone and functionalized moieties has been the most commonly used method to modify polymer architectures.23 More recently, noncovalent interactions have emerged in close analogy to covalent systems.24,25 Incorporation of multiple functionalities, covalent or noncovalent, into a polymer introduces the potential for increased structural complexity and versatility. In order to modify a polymer that contains two or more functionalities, the chemistries must be orthogonal, that is, the transformations or binding events must not inhibit each other (Figure 2). Review articles that focus on strategies for postpolymerization modification of homopolymers Received: May 13, 2014 Revised: July 28, 2014

A

dx.doi.org/10.1021/ma5009918 | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules

Perspective

Azide and Alkyne (1,3-Dipolar Cycloaddition) Chemistry. The most commonly employed reaction for postpolymerization modification is the 1,3-dipolar cycloaddition between an azide and an alkyne. The frequent use of the alkyne−azide click reaction can be attributed to its tolerance of a wide range of functional groups and high yields under a wide range of conditions, including aqueous solvents and ambient temperature. Utilization of this approach involves incorporation of either azide or alkyne functionalities into the side-chains of the polymer. Since the azide functionality is not compatible with most common polymerization techniques, a two-step strategy is employed when it is desirable to incorporate the azide moiety into the polymer side-chains. Polymers with primary halides are first synthesized, followed by a postpolymerization modification to convert the halides into azides.52 In an excellent example of utilizing orthogonal chemistries, Tang and Zhang incorporated both azides and allyl functionalities on the side-chains of separate segments of a diblock copoly(α-peptide). A mannose derivative bearing a propargyl group was quantitatively attached to the block containing the azide functionalities, without affecting the allyl groups which were further functionalized in high efficiency via a thiol−ene reaction (Figure 3). The orthogonal strategy used required reaction of the alkyne functionality first, as thiol−yne reactions may also readily occur. This work demonstrates an approach to access helical block copoly(α-peptides) with diverse structures by side-chain conjugation, allowing for control over polymer bioactivity, solubility, and self-assembly.31 Wooley and co-workers took advantage of the self-assembly of amphiphilic diblock copolymers followed by postpolymerization modification via alkyne−azide click chemistry to generate nanoparticles. Specifically, poly(acrylic acid)-b-poly(styrene) copolymers were synthesized. Subsequently, the acrylic acid moieties were partially converted to alkynyl groups. The resulting diblock copolymers were assembled into micelles and reacted with dendrimers bearing terminal azide functionalities to achieve shell click-cross-linking (SCC). Cross-linking the shell in this manner established a robust nanostructure and allowed for the incorporation of excess alkyne functionalities that can undergo further reactions (Figure 4).32

Figure 2. Block copolymer with two segments containing different functional side-chains that allow for orthogonal postpolymerization modification.

and random copolymers using covalent and noncovalent chemistries have previously been published.23,26−28 This Perspective focuses on the fascinating area of block copolymer functionalization by highlighting some key systems that undergo covalent or noncovalent postpolymerization modification of side-chain units.

■

COVALENT POSTPOLYMERIZATION MODIFICATION OF BLOCK COPOLYMERS Selection of appropriate chemistries to form covalent bonds between polymer side-chains and pendent moieties is critical. Ideal chemistries for this purpose are wide in scope and modular, high yielding, without any byproducts or only inoffensive byproducts, stereospecific, based on readily available starting materials and reagents, carried out in no or benign solvents, and generate easily purifiable products. Thiol−ene and thiol−yne chemistries, alkyne−azide cycloadditions, Michael additions, and the Diels−Alder click reactions typically fulfill these requirements and have been applied to postpolymerization modification.6,29 The following discussion and Table 1 focus on the postpolymerization modification of block copolymer side-chains using common functional handles that can undergo selected click chemistries. Further, the incorporation of functional handles on the polymer side-chains that can undergo covalent cross-linking between polymers or act as polymerization initiators will be described. We will discuss advantages and disadvantages of these chemistries as they are applied to block copolymers that have been, or have the potential to be, modified after polymerization. We will also highlight selected examples of macromolecular architectures that arise from the combination of block copolymers and postpolymerization modification.

Table 1. Selected Functional Group Handles That Are Used for Covalent Postpolymerization Modification of Block Copolymers

B


Macromolecules

Perspective

Figure 3. Orthogonal modification of a copoly(α-peptide) by 1,3-dipolar cycloaddition and subsequent thiol−ene reactions.31 Reproduced with permission from ref 31. Copyright 2011 Royal Society of Chemistry.

Figure 4. Shell click-cross-linked (SCC) micelles achieved with alkyne-containing block copolymers and azide-terminated dendritic structures.32

Thiol−Ene Chemistry. Alkene or thiol functionalities have been incorporated into polymer architectures as a synthetic handle for the purpose of postpolymerization modification. The thiol−ene reaction is attractive in part due to its tolerance toward a wide range of functional groups. The alkene and thiol functionalities undergo reaction upon introduction of a radical source or following a Michael addition reaction.54 However, when alkene groups are incorporated into polymer side-chains, creation of a radical can result in the formation of cycles or crosslinks,55 which is exacerbated when the alkene groups are in close proximity.56 As an alternative strategy, Wurm and co-workers have shown that the use of vinyl ethers as the alkene functionality prevents cross-linking, which is attributed to the relatively high stability of the vinyl ether radical. The authors demonstrated this by incorporating vinyl ether side-chains into PEG−poly(ethoxy vinyl glycidyl ether) random and block copolymers (Figure 6).

Dendrimers can be viewed as block copolymers when each branch, that can be considered a block, is chemically distinct. Similar to the functional group localization found in conventional linear block copolymers, dendrimers are constructed with the clustering of functional groups either within or at the periphery of each branch. In comparison to linear polymers, dendrimers typically offer the advantage of a higher degree of control over the number of functional groups in the macromolecular structure. Ornelas and Weck reported a multifunctionalization strategy to access dendrimer scaffolds such as the one shown in Figure 5. The dendrimer contains a fluorescence label and has nine azide groups as well as nine carboxylic acid groups. The azide and carboxylic acid moieties serve as a platform for further modification of the dendrimer, with potential drug deliver applications.53 C


Macromolecules

Perspective

Figure 5. Macromolecular dendritic structure bearing azide and carboxylic acid functionalities that may be orthogonally reacted in a postpolymerization fashion.53 Reproduced with permission from ref 53. Copyright 2009 Royal Society of Chemistry.

Figure 6. Synthesis of PEG−poly(ethoxy vinyl glycidyl ether) and subsequent postpolymerization modification by reaction of thiols or alcohols with the vinyl ether side-chains.45

Huang and Rzayev synthesized bottlebrush copolymers based on triblock terpolymers bearing alkene moieties on the sidechains of the terminal block (Figure 7).59 This material forms highly branched comb-like architectures with a cylindrical shape. In order to create nanoparticles, the alkene groups were crosslinked using Grubbs’ first generation catalyst via a postpolymerization modification step. Upon acid hydrolysis, the core of the nanoparticle was removed, creating porous cylindrical nanoparticles with potential applications for encapsulation, extraction, and separations of nano- and biomaterials.59 The combination of amphiphilic block copolymers with postpolymerization modification allowed for the formation of these fascinating tubular nanostructures. Nanoporous monoliths with aligned cylindrical pores were created from postpolymerization modified polylactide-b-poly(norbornenyl ethylstyrene) (PLA-b-P(N-S)) block copolymers

The vinyl ether side-chains were utilized for postpolymerization modification through both thiol−ene addition reactions and acetal formation with alcohols in rapid and quantitative yields. The PEG-based polymers with acid labile acetyl linkages on the side-chains have potential biomedical applications as controlled release agents of tethered drug molecules.45 Cross-Linkable Moieties and Initiators as Side-Chain Functionalities. Amphiphilic block copolymers are often employed due to their ability to self-assemble into nanostructures and ordered domains.57,58 In order to enhance the structural integrity of the materials, the polymers may be crosslinked via main- or side-chain functionalities in a postpolymerization modification step.59,60 The enhanced structural stability of the resulting cross-linked block(s) often allows for further manipulation or removal of the non-cross-linked block(s) while retaining the order or shape of the material. D


Macromolecules

Perspective

thylsilyl)-4-pentyn-1-ol methacrylate (TPYM).61 Each of the polymer segments contained functional handles that allowed for postpolymerization modification via different covalent chemistries (Figure 8). First, poly(methyl methacrylate) was grafted to the BIEM block by atom transfer radical polymerization (ATRP) followed by dehalogenation of the resulting polymer. Next, alkyne groups were installed on the TPYM block, which were subsequently reacted with the azide-containing RAFT agent 3azidopropyl ester via alkyne−azide “click” chemistry, and ultimately allowed for the grafting of polystyrene by RAFT. Lastly, deprotection of the diol was achieved by acid exposure of the ketal groups on the side-chains of the SM block, which was followed by ring-opening polymerization (ROP) of DL-lactide initiated by the diols resulting in poly(lactide) grafted from the bottlebrush backbone. This remarkable macromolecular architecture is among the most complex structures achieved through block copolymer postpolymerization modification. Conclusions for Covalent Postpolymerization Modification of Block Copolymers. To date, a limited number of examples of the postpolymerization modification of block copolymers using covalent chemistries have been demonstrated, but the precedent has been set for this unique strategy as a means to construct new macromolecules and particles with tunable bulk morphologies. These materials have exciting potential applications ranging from drug delivery to electronic materials and materials in nanotechnology. For example, labile bonds may be incorporated into polymer backbones or side-chains to allow for degradation under particular conditions, which can be useful for drug delivery applications. The block copolymer structure is critical to many applications in order to impart solubility or, more commonly, to direct self-assembly of the amphiphilic regions of the polymer. Upon self-assembly of the polymer chains in solution, an alternative postpolymerization modification can take place by covalently linking polymer strands via side-chain coupling in order to form particles.

Figure 7. Nanoparticle formation from a bottlebrush copolymer with triblock terpolymer side-chains after cross-linking alkene groups with Grubbs’ first generation catalyst and subsequent acid hydrolysis to remove the core.59

as reported by Hillmyer and Chen.60 First, the block copolymers self-assembled into lamellae morphologies and upon mixing with dicyclopentadiene (DCPD) and Grubbs’ first generation catalyst form ordered structures with cylindrical PLA nanodomains. After treating this mixture with pressure to align the cylindrical domains, the material was subjected to heat which induced curing via ring-opening metathesis of DCPD and the norbornenyl functionalities on the side-chains of the poly(styrene) block. Exposure to mild basic conditions removed the PLA portion of the structure, which yielded a nanoporous material with cylindrical channels and similar strength as poly(DCPD). This work is an example of strategic pairing of amphiphilic block copolymers and postpolymerization modification to form materials with nanoscale features. Bolton and Rzayev described the synthesis of a complex bottlebrush triblock copolymer achieved by the sequential reversible addition−fragmentation chain transfer (RAFT) polymerization of solketal methacrylate (SM), 2(bromoisobutyryl)ethyl methacrylate (BIEM), and 5-(trime-

Figure 8. Bottlebrush triblock copolymer derived from sequential postpolymerization modification of a triblock copolymer containing ATRP, RAFT, and ROP initiators on the side-chains.61 E


Macromolecules

Perspective

Table 2. Selected Examples of the Most Commonly Used Noncovalent Motifs That Have Been Incorporated into the Side-Chains of Polymers*

*

The examples illustrated in this table represent noncovalent interactions that have been demonstrated in various polymer architectures and are not limited to block copolymers. **Additional interactions including π−π stacking and electrostatic forces contribute to the strong affinity of this motif.

■

NONCOVALENT POSTPOLYMERIZATION MODIFICATION OF BLOCK COPOLYMERS Noncovalent interactions serve as the primary driving force in Nature to direct the assembly of biomacromolecules into distinct architectures (e.g., helices and sheets).62 These structures give rise to the vast functions within biological systems such as energy storage, catalysis, and replication. Much attention has been focused on the use of noncovalent interactions to direct the selfassembly of synthetic systems on a wide range of length scales; these interactions include hydrogen bonding, metal coordination, electrostatic interactions, hydrophobic interactions, π−π interactions, and inclusion complexes.22 The incorporation of moieties poised for noncovalent chemistry into block copolymers affords a reversible handle for postpolymerization modification. These interactions have the potential to allow for the interchanging of side-chain functionalities, contrary to the analogous covalently linked systems, introducing versatility and tunability. Table 2 provides a list of noncovalent bonding pairs that have been used as sidechains on polymers. The subsequent discussion will focus on examples of block copolymers that exploit heterocomplementary63 (i.e., two different interacting units), herein termed complementary, hydrogen bonding and metal coordination interactions for postpolymerization modification. We will focus on materials with interesting properties resulting from the exploitation of the respective interactions and applications of the

side-chain-functionalized block copolymers. Additional noncovalent interactions including ionic interactions, host−guest systems, and hydrophobic interactions exploited for polymer self-assembly are briefly discussed. Lastly, examples of block copolymer systems containing orthogonal noncovalent sidechain interactions are described. Hydrogen Bonding. Hydrogen bonding interactions are the most used noncovalent interactions for the design of supramolecular polymers due to their reversible, highly directional, and tunable nature.110 Over the past two decades, for example, many research groups have reported variations of the complementary hydrogen bonding pairing between derivatives of pyridine and benzoic acid for the postpolymerization modification of various side-chain-functionalized block copolymers and demonstrated their use in a range of applications such as metal nanofoams,76 liquid crystalline materials,111 and nanomaterials.112 The strength of hydrogen bonding interactions can be readily tuned by varying temperature, solvent, or the number of hydrogen bonds in the interacting motif.7,65,86 Ikkala and ten Brinke exploited the hydrogen bonding selfassembly of poly(styrene)-b-poly(4-vinylpyridine) (PS-b-P4VP) with functionalized phenolic amphiphiles (hydrogen acceptor and hydrogen donor, respectively) to obtain varying morphologies.72−74,113 These polymeric assemblies exhibit reversible liquid-crystalline properties due to supramolecular interactions between the side-chains and end-functionalized mesogens, while also displaying microphase separation imparted by the nature of F


Macromolecules

Perspective

Figure 9. Representation of the preparation of a bicontinuous gyroid nickel nanofoam using poly(styrene)-b-poly(4-vinylpyridine)/3pentadecylphenol.76

Figure 10. (a) Illustration of (top) micelle-like gold nanoparticles coated with thiol-terminated PS-b-PI amphiphilic copolymers and (bottom) hydroxylation of the double bonds on the PI segment of the block copolymers. (b) Illustration of the hydrogen bonding between hydroxylated PS-b-PISH copolymers and pyridine units of PS-b-P2VP copolymer.114

the block copolymer. The morphology of the polymer systems was altered by varying the lengths of the polymer blocks and by changing the alkyl chain length on the phenolic amphiphile, ultimately obtaining a range of “structure-within-structure” morphologies.72−74,113 More recently, Loos and co-workers described the postpolymerization modification of poly(styrene)-b-poly(4-vinylpyridine)/3-pentadecylphenol (PS-b-P4VP/PDP) that served as a template toward obtaining metallic nickel nanofoams (Figure 9). 76 The template for a bicontinuous gyroid morphology was achieved from the PS-b-P4VP/PDP supramolecular complex. The phenolic proton of the 3-pentadecylphenol molecules interacts with the nitrogen atom in the pyridine rings of the poly(4-vinylpyridine) blocks via hydrogen bonding. Removal of the phenol derivative by solvent washings resulted in the formation of an exposed free-standing nanoporous template that was accessible for nickel plating via electroless deposition. After removal of the polymer by pyrolysis, a well-ordered metal nanofoam was obtained. These materials have potential for application as high power density batteries and for hydrogen storage. Postpolymerization modification of block copolymers containing hydrogen bonding interactions have also been exploited to increase the solubility of gold nanoparticles in nonpolar organic solvents. For example, Jang et al. demonstrated the

controlled segregation of core−shell gold nanoparticles driven by hydrogen bonding interactions between poly(styrene)-b-(1,2-/ 3,4-isoprene) (PS-b-PI) and poly(2-vinylpyridine) (P2VP) (Figure 10).114 Gold nanoparticles were chemically functionalized with thiol-terminated PS-b-PI, followed by hydroxylation of the double bonds in the PI inner block. The hydroxyl groups then hydrogen bonded with the P2VP chains of poly(styrene)-bpoly(2-vinylpyridine). These hydrogen bonding interactions increased the solubility of the nanoparticles in a range of nonpolar organic solvents (e.g., dichloromethane and chloroform), resulting in enhanced processability of the nanoparticles. This study demonstrates the cooperative benefits of block copolymer phase separation combined with hydrogen bonding. Metal Coordination. Coordination chemistry typically involves strong interactions and short bond distances (1.8−2.5 Å) depending on the given metal, ligand, and the solvent.115 As a result, there is some debate whether or not coordination chemistry can be classified as a noncovalent interaction. For the purpose of this Perspective, we will view it as a noncovalent interaction. Metal coordination has been exploited extensively due to its highly directional nature and the tunability of the bond strengths and functionalities.8,116 Furthermore, coordination bonds can impart additional functional properties such as conductivity, catalysis, light emission, and gas binding.117 G


Macromolecules

Perspective

analogues. Many applications can be envisioned for such materials including drug delivery, sensor arrays, and catalyst immobilization. Orthogonal Noncovalent Side-Chain-Functionalized Block Copolymers. The examples described above demonstrate the use of a single type of noncovalent interaction along the side-chains of block copolymers. Biomacromolecules, however, exploit the combination of multiple interactions to achieve discrete architectures that enable their vast functions. The combination of multiple highly directional recognition sites on a block copolymer introduces versatility and complexity. This allows for the incorporation of different moieties onto a block copolymer. To demonstrate the orthogonal self-assembly between different pairs of noncovalently interacting complementary units, the Weck group has paired various combinations of noncovalent recognition motifs along the side-chains of block copolymers.64−66,87 Burd et al. incorporated two sets of hydrogen bonding pairs and one metal coordination pair (Hamilton wedge/cyanuric acid, diaminopyridine/thymine, pincer/pyridine, respectively) into the side-chains of poly(norbornene) block copolymers and demonstrated the orthogonality of the different interacting units (Figure 13).65 Adjusting the polarity of the solvent resulted in a switch-type mechanism of the Hamilton wedge/cyanuric acid and pincer/pyridine recognition pairs where one pair was disassembled while the other was assembled. This functionalized block copolymer serves as an example of a stimuli-responsive assembly. Expanding this concept, Ambade et al. combined three directional noncovalent recognition pairs, i.e., pincer/pyridine, cyanuric acid/Hamilton Wedge, and guanine/cytosine (metal coordination and two hydrogen bonding pairs, respectively), into the side- and main-chains of poly(norbornene) block copolymers to obtain functionalized telechelic terpolymers (Figure 14).66 Ikkala and co-workers reported a complex self-assembled supramolecular framework achieved by the hydrogen bonding and aromatic stacking of the diblock copolymer poly(γ-benzyl-Lgultamate)-b-poly(L-lysine) ionically complexed to 2′-deoxy-

Rupar et al. demonstrated the reversible cross-linking of poly(ferrocenyl dimethylsilane)-b-poly(dimethylsiloxane) (PFSb-PDMS)/poly(isoprene)-b-poly(ferrocenyldimethylsilane) (PI-b-PFS) triblock comicelles through the coordination of platinum complexes to the olefins of the isoprene backbone, using Karstedt’s catalyst as the cross-linking agent (Figure 11).118

Figure 11. Representation of the bidirectional cylindrical micelle growth of (PFS-b-PDMS)/(PI-b-PFS) triblock comicelle.118

The metal complexes increased the stability of the micelles via cross-linking and serve as contrast agents for imaging the cylindrical micelles. The metal coordination cross-linking was disrupted upon the addition of the competing ligand 2bis(diphenylphosphino)ethane. This study presents a new strategy to fabricate materials via metal coordination combined with block copolymer self-assembly. The reported system can serve as a reversible micelle cross-linking strategy and potentially provide a method to characterize complex hierarchal structures. MacLachlan et al. reported the postpolymerization modification of diblock copolymers composed of styrene and monoquarternized 4,4′-bipyridinium-functionalized 2-hydroxyethyl methacrylate units for the fabrication of hollow organic nanocapsules.119 Following the self-assembly of the diblock copolymers into spherical morphologies, the [Fe(CN)5]3−containing shells were cross-linked via metal coordination using Zn(NO3)2 to form spherical nanocapsules (Figure 12). The nanocapsules were shown to encapsulate water-soluble molecules in the core of the coordination framework. These nanomaterials demonstrate selectivity in permeability and release capability and are more stable than their non-cross-linked

Figure 12. Synthetic approach to obtain hollow organic nanocapsules via metal coordination of zinc nitrate with block copolymers composed of styrene and monoquarternized 4,4′-bipyridinium-functionalized 2-hydroxyethyl methacrylate units.119 H


Macromolecules

Perspective

Figure 13. Poly(norbornene) side-chain-functionalized triblock copolymers consisting of orthogonal hydrogen bonding (Hamilton wedge/cyanuric acid, diaminopyridine/thymine) and metal coordination (pincer/pyridine) interactions.65 Reproduced with permission from ref 65. Copyright 2008 John Wiley & Sons.

Figure 14. Main- and side-chain-functionalized poly(norbornene) triblock copolymers assembled utilizing orthogonal metal coordination (pincer/ pyridine) and hydrogen bonding (Hamilton wedge/cyanuric acid, guanine/cytosine) interactions.66 Reproduced with permission from ref 66. Copyright 2009 Wiley-VCH.

guanosine 5′-monophosphate (Figure 15).120 The combination of these noncovalent interactions in addition to the inherent structural motifs of the polypeptides, i.e., α-helices and β-sheets that serve as template scaffolds, leads to packing frustration which resulted in the formation of a shape-persistent supramolecular motif. This study opens the door to controlled pore sizes of caged assemblies for the encapsulation of small molecules. Additional Noncovalent Interactions. Other noncovalent interactions such as ionic interactions,121−124 host−guest systems,107,125 and hydrophobic interactions have been reported for the self-assembly of polymers. There are few examples, however, of applying these interactions for the postpolymerization modification of side-chain-functionalized block copolymers.103,104,126 This may be attributed, in part, to a lack of directionality of the interacting components or to complex synthetic procedures to obtain the complementary motifs.63 These noncovalent interactions, however, may allow for the realization of unique materials. Electrostatic and hydrophobic interactions, for instance, are two of the main driving forces in protein folding.127,128 Translating Nature’s self-assembly strategies into synthetic materials may allow for control over synthetic polymer assembly in aqueous medium since these interactions are typically viable in an aqueous environment.128

Conclusions for Noncovalent Postpolymerization Modification of Block Copolymers. The incorporation of noncovalent interactions into the side-chains of block copolymers can introduce an added tunable handle for polymer selfassembly. The diversity in these types of interactions span a broad range of strengths, media in which they can be applied, and stimuli that they respond to, and they can provide access to functionalities that are inaccessible using covalent systems. The combination of phase separation behavior of block copolymers with reversible interactions has been demonstrated to give rise to novel material properties as highlighted above. Expanding the library of complementary noncovalent functional pairs used for the directed self-assembly of block copolymers may open the door to access new advanced materials.

■

CONCLUSIONS AND OUTLOOK Combining the advantages of block copolymers with postpolymerization modification strategies allows new access to the formation of complex, tunable polymer architectures. A wide array of side-chain-functionalized block copolymers may be derived from a single polymeric backbone through a combinatorial approach, thereby ensuring consistency in the polymer chain length. A few examples of highly controlled construction of these materials have been demonstrated. This precision and tunability are desirable for a growing number of I


Macromolecules

Perspective

Figure 15. Supramolecular self-assembly of poly(γ-benzyl-L-glutamate)-b-poly(L-lysine) (PBLG-b-PLL) functionalized with 2′-deoxyguanosine 5′monophosphate (dGMP). (a) Ionic complexation of dGMP with lysine side-chains. (b) Packing arrangement of the diblock copolypeptides. (c) β-Sheet arrangement of guanosines from three dGMPs. (d, e) Hydrogen bonding network that form ribbons. (f) Illustration of cage-like framework of the overall supramolecular assembly. Reproduced with permission from ref 120. Copyright 2011 John Wiley and Sons.

Notes

potential applications that require more stringent control over macromolecular structure, such as drug delivery, polymer−drug conjugates, controlled-release assemblies, biomaterials, stimuliresponsive materials, encapsulation, electronics, and separations. The broad range of potential applications in postpolymerization side-chain-modified block copolymer systems demands further development of materials with unique features such as chemical compositions that allow for water solubility and stimuliresponsive degradation. New materials may be accessed by utilizing covalent, noncovalent, or a combination of both strategies with rationally selected, unexplored building blocks. Several groups have described the incorporation of two orthogonal, noncovalent heterocomplementary motifs into one block copolymer system, but the on−off switching of the competing interactions is often triggered utilizing the same stimuli (e.g., temperature, pH), thereby not allowing for a selectively controlled responsive material. The utility of incorporating both covalent and noncovalent chemistries onto the same functionalized block copolymer may give rise to materials with new properties but to date has been surprisingly underexplored. Furthermore, the determination of structure− property relationships as a function of systematic side-chain manipulation is crucial for the advancement of this field.

■

The authors declare no competing financial interest. Biographies

Joy Romulus received her B.S. degree in Chemistry from Binghamton University in 2006 where she completed her honors thesis under the supervision of Professor Omowunmi A. Sadik. She obtained her Ph.D. in Chemistry in 2013 from New York University with Professor Marcus Weck. Currently she is a postdoctoral research scientist in the group of Professor Stuart J. Rowan at Case Western Reserve University. Her research interests include hierarchal assembly of synthetic polymers, colloidal self-assembly, and stimuli-responsive materials.

AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected] (M.W.). J


Macromolecules

Perspective

(5) Hadjichristidis, N.; Pitsikalis, M.; Iatrou, H. Synthesis of block copolymers. In Block Copolymers I; Abetz, V., Ed.; Springer: Berlin, 2005; Vol. 189, pp 1−124. (6) Iha, R. K.; Wooley, K. L.; Nyström, A. M.; Burke, D. J.; Kade, M. J.; Hawker, C. J. Chem. Rev. 2009, 109, 5620−5686. (7) Yang, S. K.; Ambade, A. V.; Weck, M. J. Am. Chem. Soc. 2010, 132, 1637−1645. (8) Hoogenboom, R.; Schubert, U. S. Chem. Soc. Rev. 2006, 35, 622− 629. (9) Shimizu, L. S. Polym. Int. 2007, 56, 444−452. (10) Weck, M. Polym. Int. 2007, 56, 453−460. (11) Hadjichristidis, N.; Pitsikalis, M.; Iatrou, H. Synthesis of Block Copolymers. Springer: Berlin, 2005; Vol. 189, pp 1−124. (12) Yang, S. K.; Ambade, A. V.; Weck, M. Chem. Soc. Rev. 2011, 40, 129−137. (13) Mai, Y.; Eisenberg, A. Chem. Soc. Rev. 2012, 41, 5969−5985. (14) Lynd, N. A.; Meuler, A. J.; Hillmyer, M. A. Prog. Polym. Sci. 2008, 33, 875−893. (15) Kim, H.-C.; Park, S.-M.; Hinsberg, W. D. Chem. Rev. 2009, 110, 146−177. (16) Ebrahim Attia, A. B.; Ong, Z. Y.; Hedrick, J. L.; Lee, P. P.; Ee, P. L. R.; Hammond, P. T.; Yang, Y.-Y. Curr. Opin. Colloid Interface Sci. 2011, 16, 182−194. (17) Luo, M.; Epps, T. H. Macromolecules 2013, 46, 7567−7579. (18) Fleige, E.; Quadir, M. A.; Haag, R. Adv. Drug Delivery Rev. 2012, 64, 866−884. (19) Madsen, J.; Armes, S. P. Soft Matter 2012, 8, 592−605. (20) Cheng, R.; Meng, F.; Deng, C.; Klok, H.-A.; Zhong, Z. Biomaterials 2013, 34, 3647−3657. (21) Zhang, Q.; Re, K. N.; Kwon, O. J. Chem. Commun. 2012, 48, 7542−7552. (22) Kim, S. H.; Tan, J. P. K.; Nederberg, F.; Fukushima, K.; Colson, J.; Yang, C.; Nelson, A.; Yang, Y.-Y.; Hedrick, J. L. Biomaterials 2010, 31, 8063−8071. (23) Günay, K. A.; Theato, P.; Klok, H.-A. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 1−28. (24) Yan, X.; Wang, F.; Zheng, B.; Huang, F. Chem. Soc. Rev. 2012, 41, 6042−6065. (25) Yu, A.-D.; Liu, C.-L.; Chen, W.-C. Chem. Commun. 2012, 48, 383−385. (26) Gauthier, M. A.; Gibson, M. I.; Klok, H.-A. Angew. Chem., Int. Ed. 2009, 48, 48−58. (27) Pollino, J. M.; Weck, M. Chem. Soc. Rev. 2005, 34, 193−207. (28) Boaen, N. K.; Hillmyer, M. A. Chem. Soc. Rev. 2005, 34, 267−275. (29) Moses, J. E.; Moorhouse, A. D. Chem. Soc. Rev. 2007, 36, 1249− 1262. (30) Fiset, E.; Morin, J.-F. Polymer 2009, 50, 1369−1377. (31) Tang, H.; Zhang, D. Polym. Chem. 2011, 2, 1542−1551. (32) Joralemon, M. J.; O’Reilly, R. K.; Hawker, C. J.; Wooley, K. L. J. Am. Chem. Soc. 2005, 127, 16892−16899. (33) Hu, J.; Qian, Y.; Wang, X.; Liu, T.; Liu, S. Langmuir 2011, 28, 2073−2082. (34) Ledin, P. A.; Kolishetti, N.; Boons, G.-J. Macromolecules 2013, 46, 7759−7768. (35) Parrish, B.; Breitenkamp, R. B.; Emrick, T. J. Am. Chem. Soc. 2005, 127, 7404−7410. (36) Huang, J.; Habraken, G.; Audouin, F.; Heise, A. Macromolecules 2010, 43, 6050−6057. (37) Fleischmann, S.; Komber, H.; Voit, B. Macromolecules 2008, 41, 5255−5264. (38) Stadermann, J.; Erber, M.; Komber, H.; Brandt, J.; Eichhorn, K.-J.; Bönsch, M.; Mertig, M.; Voit, B. Macromolecules 2010, 43, 3136−3140. (39) Huang, J.; Bonduelle, C.; Thévenot, J.; Lecommandoux, S.; Heise, A. J. Am. Chem. Soc. 2011, 134, 119−122. (40) O’Reilly, R. K.; Joralemon, M. J.; Hawker, C. J.; Wooley, K. L. J. Polym. Sci., Part A: Polym. Chem. 2006, 44, 5203−5217. (41) Li, C.; Ge, Z.; Fang, J.; Liu, S. Macromolecules 2009, 42, 2916− 2924.

John T. Henssler received his B.S. in Chemistry from the University of Pittsburgh in 2004 and his Ph.D. in Organic Materials Chemistry from the University of Michigan in 2009 under the supervision of Professor Adam J. Matzger. After two years as a postdoctoral research scientist at NYU in the group of Professor Marcus Weck, in 2012 he joined the Chemistry Department at NYU as a Clinical Associate Professor of Chemistry and Director of Organic Chemistry Teaching Laboratories. His research interests include structure−property relationships in conjugated oligomers and polymers, colloidal self-assembly, and chemical education.

Marcus Weck obtained his Ph.D. degree in 1998 from Caltech with Robert H. Grubbs. After a two-year postdoctoral stay at Harvard University with George M. Whitesides, he joined the faculty at GeorgiaTech. In 2007, he moved to NYU where he is a Professor in the Chemistry Department and the Associate Director of the Molecular Design Institute. His research interests are in organic and polymer chemistry as well as materials science. The main foci of his group are in supported catalysis and the introduction of complexity through the use of orthogonal functionalization methods and to synthesize polymers, organized assemblies, biomaterials, and nanostructures.

■

ACKNOWLEDGMENTS Financial support has been provided by the National Science Foundation (CHE-1213743). This work was supported partially by the MRSEC Program of the National Science Foundation under Award Number DMR-0820341.

■

REFERENCES

(1) Leibler, L. Macromolecules 1980, 13, 1602−1617. (2) Smart, T.; Lomas, H.; Massignani, M.; Flores-Merino, M. V.; Perez, L. R.; Battaglia, G. Nano Today 2008, 3, 38−46. (3) Bates, F. S.; Fredrickson, G. H. Phys. Today 1999, 52, 32−38. (4) Bates, F. S.; Hillmyer, M. A.; Lodge, T. P.; Bates, C. M.; Delaney, K. T.; Fredrickson, G. H. Science 2012, 336, 434−440. K


Macromolecules

Perspective

(42) Cajot, S.; Lecomte, P.; Jerome, C.; Riva, R. Polym. Chem. 2013, 4, 1025−1037. (43) Zhang, S.; Zou, J.; Zhang, F.; Elsabahy, M.; Felder, S. E.; Zhu, J.; Pochan, D. J.; Wooley, K. L. J. Am. Chem. Soc. 2012, 134, 18467−18474. (44) Zhang, S.; Li, A.; Lin, L. Y.; Wooley, K. L. ACS Macro Lett. 2012, 1, 328−333. (45) Mangold, C.; Dingels, C.; Obermeier, B.; Frey, H.; Wurm, F. Macromolecules 2011, 44, 6326−6334. (46) Dimitriou, M. D.; Zhou, Z.; Yoo, H.-S.; Killops, K. L.; Finlay, J. A.; Cone, G.; Sundaram, H. S.; Lynd, N. A.; Barteau, K. P.; Campos, L. M.; Fischer, D. A.; Callow, M. E.; Callow, J. A.; Ober, C. K.; Hawker, C. J.; Kramer, E. J. Langmuir 2011, 27, 13762−13772. (47) Barriau, E.; García Marcos, A.; Kautz, H.; Frey, H. Macromol. Rapid Commun. 2005, 26, 862−867. (48) Kwon, W.; Rho, Y.; Kamoshida, K.; Kwon, K. H.; Jeong, Y. C.; Kim, J.; Misaka, H.; Shin, T. J.; Kim, J.; Kim, K.-W.; Jin, K. S.; Chang, T.; Kim, H.; Satoh, T.; Kakuchi, T.; Ree, M. Adv. Funct. Mater. 2012, 22, 5194−5208. (49) Sun, G.; Cui, H.; Lin, L. Y.; Lee, N. S.; Yang, C.; Neumann, W. L.; Freskos, J. N.; Shieh, J. J.; Dorshow, R. B.; Wooley, K. L. J. Am. Chem. Soc. 2011, 133, 8534−8543. (50) McLaughlin, C. K.; Hamblin, G. D.; Hänni, K. D.; Conway, J. W.; Nayak, M. K.; Carneiro, K. M. M.; Bazzi, H. S.; Sleiman, H. F. J. Am. Chem. Soc. 2012, 134, 4280−4286. (51) Kolonko, E. M.; Pontrello, J. K.; Mangold, S. L.; Kiessling, L. L. J. Am. Chem. Soc. 2009, 131, 7327−7333. (52) Yang, S. K.; Weck, M. Macromolecules 2007, 41, 346−351. (53) Ornelas, C.; Weck, M. Chem. Commun. 2009, 5710−5712. (54) Li, G.-Z.; Randev, R. K.; Soeriyadi, A. H.; Rees, G.; Boyer, C.; Tong, Z.; Davis, T. P.; Becer, C. R.; Haddleton, D. M. Polym. Chem. 2010, 1, 1196−1204. (55) Justynska, J.; Schlaad, H. Macromol. Rapid Commun. 2004, 25, 1478−1481. (56) Justynska, J.; Hordyjewicz, Z.; Schlaad, H. Polymer 2005, 46, 12057−12064. (57) Discher, B. M.; Won, Y.-Y.; Ege, D. S.; Lee, J. C.-M.; Bates, F. S.; Discher, D. E.; Hammer, D. A. Science 1999, 284, 1143−1146. (58) Zhao, D.; Feng, J.; Huo, Q.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Science 1998, 279, 548−552. (59) Huang, K.; Rzayev, J. J. Am. Chem. Soc. 2011, 133, 16726−16729. (60) Chen, L.; Hillmyer, M. A. Macromolecules 2009, 42, 4237−4243. (61) Bolton, J.; Rzayev, J. Macromolecules 2014, 47, 2864−2874. (62) Nelson, D. L.; Cox, M. M. Principles of Biochemistry; W.H. Freeman and Company: New York, 2005. (63) Noro, A.; Hayashi, M.; Matsushita, Y. Soft Matter 2012, 8, 6416− 6429. (64) Burd, C.; Weck, M. Macromolecules 2005, 38, 7225−7230. (65) Burd, C.; Weck, M. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 1936−1944. (66) Ambade, A. V.; Burd, C.; Higley, M. N.; Nair, K. P.; Weck, M. Chem.Eur. J. 2009, 15, 11904−11911. (67) Altintas, O.; Gerstel, P.; Dingenouts, N.; Barner-Kowollik, C. Chem. Commun. 2010, 46, 6291−6293. (68) Chen, S.; Rocher, M.; Ladaviere, C.; Gerard, J.-F.; Lortie, F.; Bernard, J. Polym. Chem. 2012, 3, 3157−3165. (69) Lo, P. K.; Sleiman, H. F. J. Am. Chem. Soc. 2009, 131, 4182−4183. (70) Ishihara, Y.; Bazzi, H. S.; Toader, V.; Godin, F.; Sleiman, H. F. Chem.Eur. J. 2007, 13, 4560−4570. (71) Pollino, J. M.; Stubbs, L. P.; Weck, M. Macromolecules 2003, 36, 2230−2234. (72) Ruokolainen, J.; ten Brinke, G.; Ikkala, O. Adv. Mater. 1999, 11, 777−780. (73) Alberda van Ekenstein, G.; Polushkin, E.; Nijland, H.; Ikkala, O.; ten Brinke, G. Macromolecules 2003, 36, 3684−3688. (74) Ruokolainen, J.; Saariaho, M.; Ikkala, O.; ten Brinke, G.; Thomas, E. L.; Torkkeli, M.; Serimaa, R. Macromolecules 1999, 32, 1152−1158. (75) Huang, W.-H.; Chen, P.-Y.; Tung, S.-H. Macromolecules 2012, 45, 1562−1569.

(76) Vukovic, I.; Punzhin, S.; Vukovic, Z.; Onck, P.; De Hosson, J. T. M.; ten Brinke, G.; Loos, K. ACS Nano 2011, 5, 6339−6348. (77) Vukovic, I.; ten Brinke, G.; Loos, K. Macromolecules 2012, 45, 9409−9418. (78) Rancatore, B. J.; Mauldin, C. E.; Fréchet, J. M. J.; Xu, T. Macromolecules 2012, 45, 8292−8299. (79) Jang, S. G.; Khan, A.; Hawker, C. J.; Kramer, E. J. Macromolecules 2012, 45, 1553−1561. (80) Soininen, A. J.; Tanionou, I.; ten Brummelhuis, N.; Schlaad, H.; Hadjichristidis, N.; Ikkala, O.; Raula, J.; Mezzenga, R.; Ruokolainen, J. Macromolecules 2012, 45, 7091−7097. (81) Kato, T.; Kihara, H.; Kumar, U.; Uryu, T.; Fréchet, J. M. J. Angew. Chem., Int. Ed. 1994, 33, 1644−1645. (82) Kumar, U.; Fréchet, J. M. J.; Kato, T.; Ujiie, S.; Timura, K. Angew. Chem., Int. Ed. 1992, 31, 1531−1533. (83) Kumar, U.; Kato, T.; Frechet, J. M. J. J. Am. Chem. Soc. 1992, 114, 6630−6639. (84) Park, T.; Todd, E. M.; Nakashima, S.; Zimmerman, S. C. J. Am. Chem. Soc. 2005, 127, 18133−18142. (85) Park, T.; Zimmerman, S. C. J. Am. Chem. Soc. 2006, 128, 14236− 14237. (86) Romulus, J.; Weck, M. Macromol. Rapid Commun. 2013, 34, 1518−1523. (87) South, C. R.; Higley, M. N.; Leung, K. C. F.; Lanari, D.; Nelson, A.; Grubbs, R. H.; Stoddart, J. F.; Weck, M. Chem.Eur. J. 2006, 12, 3789−3797. (88) Shunmugam, R.; Tew, G. N. Chem.Eur. J. 2008, 14, 5409− 5412. (89) Wang, X.-Y.; Prabhu, R. N.; Schmehl, R. H.; Weck, M. Macromolecules 2006, 39, 3140−3146. (90) Bode, S.; Bose, R. K.; Matthes, S.; Ehrhardt, M.; Seifert, A.; Schacher, F. H.; Paulus, R. M.; Stumpf, S.; Sandmann, B.; Vitz, J.; Winter, A.; Hoeppener, S.; Garcia, S. J.; Spange, S.; van der Zwaag, S.; Hager, M. D.; Schubert, U. S. Polym. Chem. 2013, 4, 4966−4973. (91) Shunmugam, R.; Tew, G. N. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 5831−5843. (92) Tzanetos, N. P.; Andreopoulou, A. K.; Kallitsis, J. K. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 4838−4848. (93) Tew, G. N.; Aamer, K. A.; Shunmugam, R. Polymer 2005, 46, 8440−8447. (94) Chen, B.; Sleiman, H. F. Macromolecules 2004, 37, 5866−5872. (95) Carlise, J. R.; Wang, X.-Y.; Weck, M. Macromolecules 2005, 38, 9000−9008. (96) Lu, X.; Li, X.; Cao, Y.; Schultz, A.; Wang, J.-L.; Moorefield, C. N.; Wesdemiotis, C.; Cheng, S. Z. D.; Newkome, G. R. Angew. Chem., Int. Ed. 2013, 52, 7728−7731. (97) Aamer, K. A.; Tew, G. N. Macromolecules 2007, 40, 2737−2744. (98) Rowan, S. J.; Beck, J. B. Faraday Discuss. 2005, 128, 43−53. (99) Beck, J. B.; Rowan, S. J. J. Am. Chem. Soc. 2003, 125, 13922− 13923. (100) Burnworth, M.; Tang, L.; Kumpfer, J. R.; Duncan, A. J.; Beyer, F. L.; Fiore, G. L.; Rowan, S. J.; Weder, C. Nature 2011, 472, 334−337. (101) Heinzmann, C.; Coulibaly, S.; Roulin, A.; Fiore, G. L.; Weder, C. ACS Appl. Mater. Interfaces 2014, 6, 4713−4719. (102) Welterlich, I.; Tieke, B. Macromolecules 2011, 44, 4194−4203. (103) Ahmed, R.; Patra, S. K.; Hamley, I. W.; Manners, I.; Faul, C. F. J. J. Am. Chem. Soc. 2013, 135, 2455−2458. (104) Haataja, J. S.; Houbenov, N.; Iatrou, H.; Hadjichristidis, N.; Karatzas, A.; Faul, C. F. J.; Rannou, P.; Ikkala, O. Biomacromolecules 2012, 13, 3572−3580. (105) Ahmed, R.; Patra, S. K.; Chabanne, L.; Faul, C. F. J.; Manners, I. Macromolecules 2011, 44, 9324−9334. (106) Chen, G.; Jiang, M. Chem. Soc. Rev. 2011, 40, 2254−2266. (107) Bertrand, A.; Stenzel, M.; Fleury, E.; Bernard, J. Polym. Chem. 2012, 3, 377−383. (108) Ruokolainen, J.; Mäkinen, R.; Torkkeli, M.; Mäkelä, T.; Serimaa, R.; Brinke, G. t.; Ikkala, O. Science 1998, 280, 557−560. (109) Mäki-Ontto, R.; de Moel, K.; Polushkin, E.; Alberda van Ekenstein, G.; ten Brinke, G.; Ikkala, O. Adv. Mater. 2002, 14, 357−361. L


Macromolecules

Perspective

(110) Brunsveld, L.; Folmer, B. J. B.; Meijer, E. W.; Sijbesma, R. P. Chem. Rev. 2001, 101, 4071−4098. (111) Korhonen, J. T.; Verho, T.; Rannou, P.; Ikkala, O. Macromolecules 2010, 43, 1507−1514. (112) Kuila, B. K.; Rama, M. S.; Stamm, M. Adv. Mater. 2011, 23, 1797−1800. (113) Ruokolainen, J.; Torkkeli, M.; Serimaa, R.; Komanschek, E.; ten Brinke, G.; Ikkala, O. Macromolecules 1997, 30, 2002−2007. (114) Jang, S. G.; Kramer, E. J.; Hawker, C. J. J. Am. Chem. Soc. 2011, 133, 16986−16996. (115) Dance, I. New J. Chem. 2003, 27, 1−2. (116) Fustin, C. A.; Guillet, P.; Schubert, U. S.; Gohy, J. F. Adv. Mater. 2007, 19, 1665−1673. (117) Dobrawa, R.; Würthner, F. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 4981−4995. (118) Rupar, P. A.; Cambridge, G.; Winnik, M. A.; Manners, I. J. Am. Chem. Soc. 2011, 133, 16947−16957. (119) Roy, X.; Hui, J. K. H.; Rabnawaz, M.; Liu, G.; MacLachlan, M. J. J. Am. Chem. Soc. 2011, 133, 8420−8423. (120) Houbenov, N.; Haataja, J. S.; Iatrou, H.; Hadjichristidis, N.; Ruokolainen, J.; Faul, C. F. J.; Ikkala, O. Angew. Chem., Int. Ed. 2011, 50, 2516−2520. (121) Houbenov, N.; Nykänen, A.; Iatrou, H.; Hadjichristidis, N.; Ruokolainen, J.; Faul, C. F. J.; Ikkala, O. Adv. Funct. Mater. 2008, 18, 2041−2047. (122) Nair, K. P.; Weck, M. Macromolecules 2007, 40, 211−219. (123) Fang, Z.; Kennedy, J. P. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 3662−3678. (124) Xu, L.; Jiang, L.; Drechsler, M.; Sun, Y.; Liu, Z.; Huang, J.; Tang, B. Z.; Li, Z.; Cohen Stuart, M. A.; Yan, Y. J. Am. Chem. Soc. 2014, 136, 1942−1947. (125) Feng, A.; Yan, Q.; Zhang, H.; Peng, L.; Yuan, J. Chem. Commun. 2014, 50, 4740−4742. (126) Thünemann, A. F.; Kubowicz, S.; Burger, C.; Watson, M. D.; Tchebotareva, N.; Müllen, K. J. Am. Chem. Soc. 2003, 125, 352−356. (127) LeBard, D. N.; Martin, D. R.; Lin, S.; Woodbury, N. W.; Matyushov, D. V. Chem. Sci. 2013, 4, 4127−4136. (128) Egan, T. J.; Ncokazi, K. K. J. Inorg. Biochem. 2004, 98, 144−152.

M


Postpolymerization Modification of Block Copolymers - ACS Publications

Recommend Documents