Review ReviewBlock : Synthesis, Self-Assembly, andBlock Applications Copolymers: Synthesis, Self-Assembly, and Applications Hongbo Feng 1, Xinyi Lu 1, Weiyu Wang 2, Nam-Goo Kang 1 and Jimmy W. Mays 1,3,* Hongbo1 Department Feng 1of, XinyiChemistry, Lu 1, University Weiyu Wang of Tennesse2, Nam-Gooe, Knoxville, Kang TN1 and 37996, Jimmy USA;W. [email protected] Mays 1,3,* (H.F.); [email protected] (X.L.); [email protected] (N.-G.K.) 1 Department of Chemistry, University of Tennessee, Knoxville, TN 37996, USA; [email protected] (H.F.); 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA; [email protected] (X.L.); [email protected] (N.-G.K.) [email protected] 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA; 3 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA [email protected] * Correspondence: [email protected]; Tel.: +1-865-974-0747 3 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA *Received:Correspondence: 19 September; [email protected]; Accepted: 3 October Tel.: 2017; +1-865-974-0747 Published: 9 October 2017

Received: 19 September 2017; Accepted: 3 October 2017; Published: 9 October 2017 Abstract: Research on block copolymers (BCPs) has played a critical role in the development of Abstract: chemistry,Research with on block numerous copolymers pivotal (BCPs) contributions has played that have a critical advanced role in our the ability development to prepare, of polymercharacterize, chemistry, theoretically with numerous model, and pivotal technologically contributions exploit that havethis class advanced of materials our ability in a tomyriad prepare, of wayscharacterize, in the fields theoretically of chemistry, model, physics, and technologicallymaterial sciences, exploit and biological this class and of materials medical sciences. in a myriad The breathtakingof ways in the progress fields of has chemistry, been driven physics, by the material advancement sciences, in experimental and biological techniques and medical enabling sciences. the Thesynthesis breathtaking and characterization progress has been of a driven wide byrange the advancementof block copolymers in experimental with tailored techniques composition, enabling architectures,the synthesis andand characterizationproperties. In this of a review, wide range we ofbriefly block discussed copolymers the with recent tailored progress composition, in BCP synthesis,architectures, followed and properties. by a discussion In this review,of the fundamen we brieflytals discussed of self-assembly the recent progressof BCPs inalong BCP with synthesis, their applications.followed by a discussion of the fundamentals of self-assembly of BCPs along with their applications.

Keywords: block copolymers; synthesis; self-assembly; applications

1. Introduction Block copolymers (BCPs) are a specificspecific class of copolymers, in which the chemically distinct units units are are grouped grouped in in discrete discrete blocks blocks along along the the polymer polymer chain chain [1]. [ 1Figure]. Figure 1 illustrates1 illustrates a few a offew the of many the many architectures architectures of BCPs, of which BCPs, can which be conf canigured be configured into linear, into branched linear, branched (graft and (graft star), and cyclicstar), andmolecular cyclic molecular architectures. architectures. Thanks to Thanks the advancement to the advancement of polymer of polymer synthetic synthetic strategies strategies and techniques,and techniques, e.g., e.g.,controlled controlled polymerization techniques techniques along along with with facile facile post-polymerizationpost-polymerization functionalization, BCPs BCPs with precisely controlled molecular weights and defineddefined macromolecular architectures cancan be be prepared prepared [2 –[2–8].8]. The The extraordinary extraordinary structural structural and and compositional compositional versatility versatility of BCPs of BCPshas facilitated has facilitated an explosion an explosion in the in the discovery discovery and an implementationd implementation of of innovative innovative synthetic synthetic strategiesstrategies capable of generating generating previously previously unattainable unattainable levels levels of of man-made man-made architectural architectural complexity. complexity.

Linear block terpolymers "Comb" graft copolymers "Miktoarm" star terpolymers Cyclic block terpolymers

Figure 1. Representative architectures of linear block terpolymers, “comb” graft polymers, miktoarm star terpolymers, and cyclic block terpolymers.

Polymers 2017, 9, 494; doi:10.3390/polym9100494 www.mdpi.com/journal/polymers

Polymers 2017, 9, 494; doi:10.3390/polym9100494 www.mdpi.com/journal/polymers Polymers 2017, 9, 494 2 of 31 Polymers 2017, 9, 494 2 of 31

One of the ubiquitous features of BCPs is their ability to form a plethora of nanoscale ordered structures.One of By the manipulating ubiquitous features the molecular of BCPs is para theirmeters ability such to form as athe plethora Flory-Huggins of nanoscale interaction ordered structures.parameter By(χ), manipulating the degree of the polymerization molecular parameters (N), and such the volume as the Flory-Huggins fraction (f), various interaction morphologies parameter (includingχ), the degree spherical, of polymerization cylindrical, lamellar, (N), and and the others volume have fraction been ( frevealed), various both morphologies experimentally including and spherical,theoretically cylindrical, [9,10]. lamellar,Furthermore, and others recent have studies been revealed have bothdemonstrated experimentally that andthetheoretically macromolecular [9,10]. Furthermore,architecture is recent another studies key factor have demonstratedin controlling both that thethe macromolecularresulting morphologies architecture and their is another extent key of factorlong range in controlling order [11]. both Due the to resulting these fascinating morphologies features, and theirresearch extent on ofBCPs long has range long order been [11 a]. popular Due to thesetopic worldwide. fascinating features, Figure 2 research shows the on number BCPs has of long publ beenications a popular with the topic topic worldwide. “block ” Figure2 shows over the numberpast five of decades. publications with the topic “block copolymer” over the past five decades.

4500 4000 3500 3000 2500 2000 1500 1000

Number of Publications 500 0 1960 1970 1980 1990 2000 2010 Year

Figure 2. The number of publications with block copolymercopolymer as topic against year. The data were obtained from Web ofof ScienceScience (2017(2017 ClarivateClarivate Analytics).Analytics).

In addition to the academic interest in BCPs, the scope of applications for BCPs has been rapidly expanding toto the the fields fields of advancedof advanced materials materials (e.g., (e.g., thermoplastic elastomers), elasto drugmers), delivery, drug patterning, delivery, porouspatterning, materials, porous and materials, many others and overmany the others last twoover decades the last [12 two]. Thermoplastic decades [12]. elastomers Thermoplastic take advantageelastomers take of the advantage combination of the of combination rubbery segments of rubbery and segments rigid segments and rigid within segments block within copolymers. block Drugcopolymers. encapsulation Drug andencapsulation delivery are and facilitated delivery by theare amphiphilicityfacilitated by of the block amphiphilicity copolymers in of solution. block Thecopolymers application in solution. of block copolymersThe application in both of theblock soft copolymers lithography in and both synthesis the soft of porouslithography materials and issynthesis based on of the porous various materials nanoscale is based morphologies on the various induced nanoscale by self-assembly. morphologies Each of induced the applications by self- mentionedassembly. Each above of willthe applications be elaborated mentioned on in the mainabove text. will be elaborated on in the main text. This reviewreview briefly briefly covers covers the the recent recent breathtaking breathta progressking progress in the synthesis,in the synthesis, self-assembly self-assembly behavior, andbehavior, applications and applications of BCPs. Section of BCPs.2 briefly Section describes 2 briefly the syntheticdescribes strategiesthe synthetic for the strategies preparation for the of BCPs.preparation Section of3 BCPs. discusses Section BCP 3 self-assemblydiscusses BCP in self-assembly bulk and in solution.in bulk and Section in solution.4 presents Section several 4 presents major applicationsseveral major of applications BCPs in thermoplastic of BCPs in elastomer,thermoplastic drug elastomer, delivery, softdrug lithography, delivery, soft and lithography, porous material and applications.porous material The applications. conclusions andThe futureconclusions perspectives and future of BCP perspectives research are of presentedBCP research in the are last presented section. Wein the hope last that section. this reviewWe hope will that attract this review emerging will researchers attract emerging to this fieldresearchers and advance to this thefield understanding and advance andthe understanding utilization of the and fascinating utilization BCP of the systems. fascinating BCP systems.

2. Synthesis of BCPs SignificantSignificant work has been focused on the synthesissynthesis of BCPs withwith structuralstructural andand compositioncomposition variety. The The synthetic synthetic strategies strategies mainly mainly include: (1) (1) the the sequential sequential addition addition of via “living”/controlled“living”/controlled polymerization polymerization techniques; techniques; and and (2) coupling (2) coupling reactions reactions exploiting exploiting the active the chain- active chain-endsends of different of different chain chainsegments segments [13]. [13].

Polymers 2017, 9, 494 3 of 31

Polymers 2017, 9, 494 3 of 31 2.1. Sequential Addtion Polymerization 2.1 Sequential Addtion Polymerization 2.1.1. Controlled Polymerization 2.1.1. Controlled Polymerization Controlled (CRP) techniques represent the most versatile and facile approachControlled for BCP synthesis,radical polymerization mainly due to (CRP) their compatibility techniques represent with a wide the spectrummost versatile of monomers, and facile high toleranceapproach of functionalfor BCP synthesis, groups andmainly impurities, due to their and compatibility ease of experimental with a wide setup spectrum [14–16]. Theof monomers, preparation ofhigh BCPs tolerance using sequential of functional CRP groups relies onand the impuriti fact thates, and the reactiveease of experimental polymer chain setup end [14–16]. is preserved The bypreparation a reversible of reaction BCPs using between sequential the active CRP relies species on andthe fact the dormantthat the reactive species polymer [17–19]. chain Over end the is last preserved by a reversible reaction between the active species and the dormant species [17–19]. Over two decades, numerous literature has described the synthesis of BCPs via controlled polymerization the last two decades, numerous literature has described the synthesis of BCPs via controlled techniques including: atom transfer racial polymerization (ATRP), reversible addition-fragmentation polymerization techniques including: atom transfer racial polymerization (ATRP), reversible chain transfer (RAFT) radical polymerization, nitroxide-mediated polymerization (NMP), and many addition-fragmentation chain transfer (RAFT) radical polymerization, nitroxide-mediated others [20–22]. polymerization (NMP), and many others [20–22]. PolymerPolymer chain chain ends ends equippedequipped with with an an alkyl alkyl halide halide enables enables ATRP ATRP to prepare to prepare BCPs BCPsthrough through the theaddition addition of ofa second a second monomer. monomer. For example, For example, a series a seriesof biocom of biocompatible,patible, thermo-responsive thermo-responsive ABA ABAtriblock triblock copolymers copolymers comprising comprising poly(N poly(-isopropylN-isopropyl acrylamide) acrylamide) (PNIPAM) (PNIPAM) as the A block as the and A block poly(2- and poly(2-methacryloyloxyethylmethacryloyloxyethyl phosphorylcholine) phosphorylcholine) (PMPC) (PMPC) as the as central the central B bloc B blockk was was synthesized synthesized using using ATRPATRP initiated initiated by by aa difunctional initiator, initiator, as asillustrated illustrated in Scheme in Scheme 1 [23].1[ An23 α].,ω An-Br terminatedα,ω-Br terminated PMPC PMPCwas first was synthesized first synthesized in methanol, in methanol, purified, purified, and used and subsequently used subsequently for the polymerization for the polymerization of NIPAM. of NIPAM.This doubly This doubly amphiphilic amphiphilic BCP exhibits BCP exhibits interestin interestingg thermosensitive thermosensitive properties, properties, whereas whereas above abovethe thelower lower critical critical solution solution temperature temperature (LCST) (LCST) of PN ofIPAM, PNIPAM, the BCP the BCPself-assembles self-assembles into a intophysical a physical gel. gel.The The phosphoryl phosphoryl choline choline moiety moiety is isan an important important component component of ofcell cell membranes. membranes. The The cell cell viability viability experimentsexperiments confirmed confirmed that that these these thermo-responsivethermo-responsive gels gels are are sufficiently sufficiently biocompatible biocompatible to toact act as asa a cultureculture medium medium for for hamster hamster lung lung cells. cells.

SchemeScheme 1. Synthesis1. of theSynthesis poly(N-isopropyl of acrylamide-the b-2-methacryloyloxyethylphosphorylcholine-poly(N-isopropyl acrylamide-b-2- b-Nmethacryloyloxyethylphosphorylcholine--isopropyl acrylamide) (PNIPAM-b-PMPC-b-N-isopropylb-PNIPAM) acrylamide) triblock copolymers (PNIPAM- viab-PMPC- atomb transfer-PNIPAM) racial polymerizationtriblock copolymers (ATRP) using via atom a bifunctional transfer ATRPracial initiator.polymerization (ATRP) using a bifunctional ATRP initiator. Matyjaszewski et al. reported the preparation of poly(n-butyl acrylate-b-methyl methacrylate) (PBA-b-PMMA)Matyjaszewski by activators et al. reported regenerated the preparation by electron of transferpoly(n-butyl atom acrylate- transferb-methyl radical methacrylate) polymerization (PBA-b-PMMA) by activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) with ppm levels of Cu catalyst [24]. Controlled polymerization was realized using (ARGET ATRP) with ppm levels of Cu catalyst [24]. Controlled polymerization was realized using tris(2-pyridylmethyl)amine (TPMA) as a ligand because of its strong binding interaction to copper. tris(2-pyridylmethyl)amine (TPMA) as a ligand because of its strong binding interaction to copper. This new ARGET system was also successfully applied to the efficient synthesis of and This new ARGET system was also successfully applied to the efficient synthesis of styrene and n- n-butyl acrylate block copolymers [25]. Later on, miniemulsion ARGET ATRP was developed butyl acrylate block copolymers [25]. Later on, miniemulsion ARGET ATRP was developed by the bysame thesame group group and used and for used the preparation for the preparation of homopo oflymers homopolymers and block copolymers and block copolymers[26,27]. However, [26,27 ]. However,ATRP still ATRP does still not does work not for work some formonomers, some monomers, though it thoughhas many it hasadvantages many advantages compared comparedto other to otherpolymerization polymerization methods methods for block for block copolymeriza copolymerization.tion. For Forexample, example, some some monomers monomers contain contain functionalityfunctionality that that can can form form complexescomplexes with with transition transition metal metal catalyst catalyst and and have have a detrimental a detrimental effect effecton onpolymerization, polymerization, such such as asside side reactions reactions resultin resultingg in ina abroad broad polydispersity polydispersity index index (PDI) (PDI) [15]. [15 ].

Polymers 2017, 9, 494 4 of 31

TremendousPolymers 2017 efforts, 9, 494 have been devoted to developing novel ligands to minimize such side reactions4 of 31 [28]. ATRP-based dispersion have also been developed. Armes and coworkers synthesized Tremendous efforts have been devoted to developing novel ligands to minimize such side reactions zwitterionic PMPC-based block copolymers by a dispersion ATRP process [29]. PEG–Br was used as [28]. ATRP-based dispersion polymerizations have also been developed. Armes and coworkers macroinitiator with CuBr/ 2,20-bipyridine as the catalyst for the dispersion polymerization of PMPC synthesized zwitterionic PMPC-based block copolymers by a dispersion ATRP process [29]. PEG–Br in isopropanol/waterwas used as macroinitiator (9:1, w/w). with Using CuBr/ 2,2′-bipyridine glycol dimethacrylate as the catalyst (EGDMA) for theas dispersion a crosslinker, hydrogelpolymerization particles withof PMPC controllable in isopropanol/water sizes were obtained. (9:1, w/w).The Using particle ethylene size glycol could dimethacrylate be controlled by the block(EGDMA) composition as a crosslinker, and initial MPC particles concentration. with controllable Using sizes a similar were obtained. strategy, The the particle same size group synthesizedcould be well-defined controlled by the PEG- blockb-PDMAEMA- composition andb-PMPC. initial MPC Huang concentration. and coworkers Using a synthesized similar strategy, a series of ABAthe triblocksame group copolymers, synthesized consisting well-defined of double-bond-containing PEG-b-PDMAEMA-b-PMPC. poly(phenoxyallene) Huang and coworkers (PPOA), PMMA,synthesized or PBA segmentsa series usingof ABA sequential triblock free copoly radicalmers, polymerization consisting of and double-bond-containing ATRP [30]. A bifunctional initiatorpoly(phenoxyallene) bearing azo and (PPOA), halogen-containing PMMA, or PBA ATRPsegments initiating using sequential groups free was radical first used polymerization to initiate the and ATRP [30]. A bifunctional initiator bearing azo and halogen-containing ATRP initiating groups conventional free radical homopolymerization of phenoxyallene with a cumulated double bond to give was first used to initiate the conventional free radical homopolymerization of phenoxyallene with a a PPOA-based macroinitiator with ATRP-initiating groups at both ends. PMMA-b-PPOA-b-PMMA cumulated double bond to give a PPOA-based macroinitiator with ATRP-initiating groups at both and PBA-ends.b -PPOA-PMMA-bb-PPOA--PBA triblockb-PMMA copolymers and PBA-b-PPOA- were synthesizedb-PBA triblock by copolymers the ATRP were of methyl synthesized methacrylate by and nthe-butyl ATRP acrylate, of methyl as depictedmethacrylate in Schemeand n-butyl2. acrylate, as depicted in Scheme 2.

Scheme 2. Synthesis of polyallene-based triblock copolymer using conventional free radical and Scheme 2. Synthesis of polyallene-based triblock copolymer using conventional free radical and ATRP. ATRP. Reprinted from Reference [30]. (Copyright (2017) Nature Publishing Group). Reprinted from Reference [30]. (Copyright (2017) Nature Publishing Group). RAFT, on the other hand, has seen rapid growth due to its superior compatibility with a broader RAFT,range of on functionalities the other hand, and hashigh seentolerance rapid ofgrowth impurities. due The to itscreative superior combination compatibility of RAFT with a broaderpolymerization range of functionalities with other andpolymerization high tolerance te ofchniques, impurities. such The as creative ATRP combinationor ring-opening of RAFT polymerizationpolymerization, with has other extended polymerization the array of techniques, available architectures such as ATRP such oras ring-openinggraft, star, hyperbranched, polymerization, has extendedetc. [31,32]. the The array general of availablemethod for architectures the preparation such of BCPs as graft, using star, the hyperbranched,RAFT process is through etc. [31 ,32]. sequential polymerization. For the synthesis of an AB diblock copolymer, the first block was The general method for the preparation of BCPs using the RAFT process is through sequential synthesized via a RAFT process, followed by subsequent purification. The resulting end-reactive polymerization.polymer acts Foras a macro-RAFT the synthesis agent of an for ABa second diblock polymerization copolymer, step. the To first ensure block complete was synthesized end group via a RAFTfunctionalization, process, followed the polymerization by subsequent yield purification. of the first Theblock resulting is usually end-reactive kept rather low polymer (<30%). acts In as a macro-RAFTcontrast agentto this for two-step a second process, polymerization Chaduc et step. al. reported To ensure a completesimple one-pot end group RAFT functionalization, process for the polymerizationamphiphilic block yield copolymers of the first in block water is[33]. usually Using kept 4-cyano-4-thiothiopropylsulfanyl rather low (<30%). In contrast pentanoic to this two-stepacid process,(CTPPA) Chaduc as the et al.RAFT reported agent, poly(acrylic a simple one-pot acid), poly(methacrylic RAFT process acid), for amphiphilic or poly(methacrylic block copolymersacid-co- in waterpoly(ethylene [33]. Using oxide) 4-cyano-4-thiothiopropylsulfanyl methyl ether methacrylate) was first pentanoic formed acidin water. (CTPPA) The resulting as the RAFT macro- agent, poly(), poly(methacrylic acid), or poly(methacrylic acid-co-poly(ethylene oxide) methyl Polymers 2017, 9, 494 5 of 31 ether methacrylate) was first formed in water. The resulting macro-RAFT agents were then directly used without further purification for the RAFT polymerization of styrene in water in the same reactor. This strategy leads to a very good control of the resulting amphiphilic block copolymers. Very recently, short poly(ethylene glycol) (PEG) was employed as the solvent in the macromolecular RAFT agent-mediatedPolymers 2017 dispersion, 9, 494 polymerization of BCPs such as PEG-b-PS, P4VP-b-PS, and PNIPAM-5 of 31 b-PS. A new formulationRAFT agents were of polymerization-induced then directly used without self-assemblyfurther purification of PEG for the named RAFT PEG-PISA polymerization to synthesize of diblockstyrene copolymer in water nanoassemblies in the same reactor. was reported.This strate Ingy PEG-PISA,leads to a very the good viscous control PEG of affordsthe resulting advantages includingamphiphilic fast polymerization block copolymers. rate, Very good recently, control short over poly(ethylene the synthesis glycol) of(PEG) diblock was employed copolymers, as the and in situ synthesissolvent ofin boththe macromolecular amphiphilic andRAFT doubly agent-mediated hydrophobic dispersion diblock polymerizati copolymeron of nanoassembliesBCPs such as at a polymerPEG- concentrationb-PS, P4VP-b of-PS, up and to 50%. PNIPAM- Furthermore,b-PS. A new two formulation new self-assembled of polymerization-induced morphologies of self- ellipsoidal assembly of PEG named PEG-PISA to synthesize diblock copolymer nanoassemblies was reported. vesicles and nanotubes were formed via PEG-PISA. Nevertheless, RAFT dispersion polymerization In PEG-PISA, the viscous PEG affords advantages including fast polymerization rate, good control often suffersover the from synthesis rather of poor diblock colloidal copolymers, stability, and leading in situ synthesis to low polymerization of both amphiphilic rate, and broad doubly molecular weighthydrophobic distribution, diblock and lackcopolymer of control nanoassemblies over molecular at a polymer weight whenconcentration using of a smallup to RAFT50%. agent. The reasonFurthermore, for this is two believed new self-assembled to be the superswelling morphologies effect of ellipsoidal in the early vesicl nucleationes and nanotubes stage [34 were]. Zhu et al. employedformed an amphiphilicvia PEG-PISA. oligomer,Nevertheless, poly(acrylic RAFT dispersion acid- polymerizationb-styrene) trithiocarbonate, often suffers from as rather both poor surfactant colloidal stability, leading to low polymerization rate, broad molecular weight distribution, and lack and RAFT agent to polymerize styrene. This macro-RAFT agent was capable of enhancing the colloidal of control over molecular weight when using a small RAFT agent. The reason for this is believed to stabilitybe and, the assuperswelling a result, the effect polymerization in the early nucleation was successful stage [34]. [34 ,35Zhu]. Well-controlledet al. employed an PS amphiphilic with a molecular weightoligomer, up to 120 poly(acrylic kg/mol and acid- PS-b-styrene)b-PBA weretrithiocarbonate, readily synthesized as both surfactant using this and method. RAFT agent Furthermore, to the samepolymerize group demonstrated styrene. This macro-RAFT that this method agent was could capable be usedof enhancing as a promising the colloidal approach stability and, to synthesize as thermoplastica result, elastomerthe polymerization materials was [ 36successful]. [34,35]. Well-controlled PS with a molecular weight up to NMP120 kg/mol is commonly and PS-b-PBA used were for readily the synthesissynthesized ofusing block this method. copolymers Furthermore, consisting the same of group PS, PMMA, demonstrated that this method could be used as a promising approach to synthesize thermoplastic poly(vinyl acetate) (PVAc) and poly(dimethyl acrylamide) (PDMA). In a typical process, styrene is elastomer materials [36]. polymerizedNMP firstly is usingcommonly a bi-molecular used for the initiator synthesis benzoyl of block peroxide copolymers and 2,2,6,6-tetramethylpiperidinoxyconsisting of PS, PMMA, (TEMPO).poly(vinyl The PS acetate) segment (PVAc) bearing and poly(dimethyl the TEMPO endacrylamide) group is(PDMA). subsequently In a typical used process, as the styrene macroinitiator is for thepolymerized second block. firstly While using the a molecularbi-molecular weight initiator distributions benzoyl areperoxide usually and broad, 2,2,6,6- this may not limittetramethylpiperidinoxy their practical applications. (TEMPO). The The PS segmen monomert bearing conversion the TEMPO is end also group low is when subsequently polymerized at highused temperature. as the macroinitiator The deviation for the second from block. the While target the molecular molecular weight weight distributions became moreare usually significant, broad, this may not limit their practical applications. The monomer conversion is also low when especiallypolymerized when it at became high temperature. higher than The 100,000 deviation g/mol. from the Hawker target molecular et al. reported weight became a modified more NMP systemsignificant, for the controlled especially when polymerization it became higher of than dienes 100,000 in g/mol. the presenceHawker et al. of reported alkoxyamine a modified initiators based onNMP a system 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxy for the controlled polymerization of dienes in skeleton the presence (Scheme of alkoxyamine3). A detailed initiators study revealedbased that on this a 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxy modified system was able to control skeleton the homopolymerization (Scheme 3). A detailed of study isoprene to high conversionrevealed that and this molecularmodified system weights was able from to co 1000ntrol the to homopolymerization 100 000 g/mol with of isoprene polydispersities to high of conversion and molecular weights from 1000 to 100 000 g/mol with polydispersities of 1.06–1.15. 1.06–1.15. Polyisoprene-containing BCPs, PI-b-PtBuA and PS-b-PI, were also prepared with similar Polyisoprene-containing BCPs, PI-b-PtBuA and PS-b-PI, were also prepared with similar control. In control.comparison In comparison with withconventional conventional TEMPO TEMPO system systems,s, these new these systems new systems exhibit exhibita significant a significant improvementimprovement in the in ability the ability to control to control the the polymerization polymerization and and further further demonstrate demonstrate the versatility the versatility of of nitroxide-mediatednitroxide-mediated living living free fr radicalee radical procedures procedures [[37].37].

SchemeScheme 3. Synthetic 3. Synthetic scheme scheme of of PI- PI-b-PbtBuA-PtBuA and PS- andb-PIPS- blockb-PI copolymers block copolymers using a modified using nitroxide- a modified nitroxide-mediatedmediated polymerization polymerization (NMP) (NMP)initiator. initiator.

Polymers 2017, 9, 494 6 of 31 Polymers 2017, 9, 494 6 of 31

2.1.2.2.1.2. Living Living Anionic Anionic Polymerization Polymerization TheThe pioneering pioneering work work on on BCP BCP synthesis synthesis using using living living anionic anionic polymerization polymerization (LAP)(LAP) waswas reportedreported by Szwarcby Szwarc et al. inet 1956al. in [ 381956,39 ].[38,39]. This type This of type polymerization of polymerization proceeds proceeds to quantitative to quantitative conversion conversion without chainwithout transfer chain and/or transfer chain and/or termination. chain termination. Although Although there might there be anmight argument be an argument that the demanding that the experimentaldemanding conditionsexperimental is oneconditions of its limitations, is one of its LAP limitations, has proved LAP itself has toproved be the itself best to polymerization be the best techniquepolymerization for the technique preparation for the of preparation well-defined of BCPswell-defined based BCPs on vinyl based monomers on vinyl monomers such as styrene,such dienes,as styrene, (meth)acrylates, dienes, (meth)acrylates, vinyl pyridines, vinyl , pyridines, acrylonitriles, as well as cyclicas well monomers as cyclic monomers such as lactones, such as lactones, oxiranes, and siloxanes over the last 60 years [2,40,41]. Anionic polymerization is widely oxiranes, and siloxanes over the last 60 years [2,40,41]. Anionic polymerization is widely exploited exploited in industry to create BCPs on a massive scale. Because of its superior control over the in industry to create BCPs on a massive scale. Because of its superior control over the molecular molecular weight, architecture, composition, and functionality as compared to controlled radical weight, architecture, composition, and functionality as compared to controlled radical polymerization, polymerization, almost all well-defined BCPs with complex architectures such as star, comb, graft, almost all well-defined BCPs with complex architectures such as star, comb, graft, dendritic, etc. are dendritic, etc. are achievable via the combination of anionic polymerization and linking chemistry achievable[6,42–47]. via There the combinationare several insightful of anionic reviews polymerization available andthat linkingdescribechemistry the recent [6 ,progress42–47]. Therein the are severalsynthesis insightful of well-defined reviews availableBCPs via thatLAP describe[48,49]. the recent progress in the synthesis of well-defined BCPs viaOne LAP key [ 48condition,49]. that must be satisfied is that the nucleophilicity of the macroanion must be sufficientlyOne key high condition to initiate that the must second be satisfied monomer. is thatThus, the the nucleophilicity monomers must of be the added macroanion in the order must of be sufficientlyincreasing high electron to initiate affinity: the styrene second < monomer. butadiene Thus, ~ isoprene the monomers < vinyl pyridine must be < added methyl in acrylate the order < of increasingethylene electronoxide. affinity:One classic styrene example < butadiene of the ~isoprenesynthesis

SchemeScheme 4. (4.A )(A Synthesis) Synthesis of PS-of bPS--PI-bb-PI--P2VP-b-P2VP-b-PtbBA--PtBA-b-PEOb-PEO pentablock pentablock copolymers copolymers via sequentialvia sequential living anioniclivingpolymerization anionic polymerization (LAP). ((LAP).B) Synthesis (B) Synthesis of PDMS- of PDMS-b-PtBAb-P diblocktBA diblock copolymers. copolymers.

Nevertheless, sequential LAP is restricted especially when the monomers exhibit different Nevertheless, sequential LAP is restricted especially when the monomers exhibit different reactivities. For example, the living polymer of polydimethylsiloxane is not sufficiently nucleophilic reactivities. For example, the living polymer of polydimethylsiloxane is not sufficiently nucleophilic to to initiate the polymerization of t-butyl methacrylate. In order to prepare PDMS-b-PtBA, a linking initiatereagent the bearing polymerization with chlorosilane of t-butyl moiety methacrylate. was used In due order to its to preparehigh reactivity PDMS- (Schemeb-PtBA, a4B) linking [51]. Hirao reagent bearinget al. withprepared chlorosilane a wide variety moiety of was block used copoly duemers to its with high extremely reactivity low (Scheme PDI 4usingB) [ 51 new]. Hirao linking et al. preparedmethodology. a wide Another variety of advantage block copolymers of this linking with extremelychemistry lowis that PDI it usingopens new endless linking possibilities methodology. of Anothervarious advantage molecular ofarchitectures this linking [5,4 chemistry2,52,53], isas that demonstrated it opens endless by the possibilities work of Mays, of variousHadjichristidis, molecular architecturesHirao, Quirk, [5 ,and42,52 many,53], asothers demonstrated through chlorosila by the workne and of 1,1-diphenylethyle Mays, Hadjichristidis,ne (DPE)-based Hirao, Quirk, linking and manychemistry others (Figure through 3). chlorosilane Well-defined and BCPs 1,1-diphenylethylene with structural and (DPE)-based compositional linking homogeneity chemistry prepared (Figure3 ). Well-definedusing LAP BCPshave served with structural as templates and for compositional structure-property homogeneity relationship prepared studies using and LAP have have also served found as templatesmany important for structure-property industrial applications relationship such studiesas and haveand sealants, also found in automotive, many important wire, industrialpaving, applicationsand footwear such applications, as adhesives etc. and [54]. sealants, in automotive, wire, paving, and footwear applications, etc. [54].

Polymers 2017, 9, 494 7 of 31

Polymers 2017, 9, 494 7 of 31 Polymers 2017, 9, 494 7 of 31

Star block copolymer Miktoarm Star Star-b-linear-b-star "Comb"

Star block copolymer Miktoarm Star Star-b-linear-b-star "Comb"

"Centipede" "Barbwire" Comb Star

Figure 3. Illustration of complex architectures using living anionic polymerization and coupling "Centipede" "Barbwire" Comb Star chemistry. Adapted from Reference [55]. (Copyright (2017) WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim). FigureFigure 3. Illustration 3. Illustration of complex of complex architectures architectures using using living living anionic anionic polymerization polymerization and couplingand coupling chemistry. Adaptedchemistry. from ReferenceAdapted from [55 ].Reference (Copyright [55]. (2017)(Copyright WILEY-VCH (2017) WILEY-VCH Verlag GmbH Verlag & GmbH Co. KGaA, & Co. Weinheim).KGaA, 2.2. CombinationWeinheim). of Different Polymerization Techniques 2.2. CombinationIn some cases, of Different sequential Polymerization addition polymeriza Techniquestion techniques are limited when the monomers 2.2. Combination of Different Polymerization Techniques are not suitable to be polymerized using the same polymerization mechanism. A second approach to In some cases, sequential addition polymerization techniques are limited when the monomers are BCPs is theIn somecoupling cases, of sequential two different addition polymerization polymerization techniques techniques or are block limited copolymer when the segments monomers either not suitableare not suitable to be polymerized to be polymerized using using the same the same polymerization polymerization mechanism. mechanism. A secondA second approach approach to to BCPs using a “click” reaction such as Diels–Alder cycloaddition reaction, a thiol-ene reaction, or a copper- is theBCPs coupling is the ofcoupling two different of two different polymerization polymerization techniques techniques or block or block copolymer copolymer segments segments either either using a catalyzed azide–alkyne cycloaddition reaction (CuAAC). With appropriate care, this approach can “click”using reaction a “click” such reaction as Diels–Alder such as Diels–Alder cycloaddition cycloaddition reaction, reaction, a thiol-ene a thiol-ene reaction, reaction, or a copper-catalyzed or a copper- yield BCPs without substantial homopolymers and comparable PDIs as compared with the azide–alkynecatalyzed cycloadditionazide–alkyne cycloaddition reaction (CuAAC). reaction With(CuAAC). appropriate With appropriate care, this care, approach this approach can yield can BCPs sequential addition approach. Yagci et al. reported a one-pot synthetic approach to BCPs using the withoutyield substantial BCPs without homopolymers substantial andhomopolymers comparable and PDIs comparable as compared PDIs with as compared the sequential with additionthe combination of ATRP and ring opening polymerization (ROP) methods simultaneously [56]. Two approach.sequential Yagci addition et al. reported approach. a Yagci one-pot et al. synthetic reported approach a one-pot tosynthetic BCPsusing approach the combinationto BCPs using ofthe ATRP structurallycombination different of ATRP monomers and ring were opening selected polymeri andzation the polymerization (ROP) methods wassimultaneously initiated simultaneously [56]. Two and ring opening polymerization (ROP) methods simultaneously [56]. Two structurally different usingstructurally a difunctional different initiator, monomers as wereshown selected in Scheme and the polymerization5. They found was that initiated the two simultaneously polymerization monomers were selected and the polymerization was initiated simultaneously using a difunctional mechanismsusing a difunctionalproceeded withoutinitiator, affectingas shown eachin Scheme other. 5.The They obtained found thatproducts the two showed polymerization characteristic initiator, as shown in Scheme5. They found that the two polymerization mechanisms proceeded thermalmechanisms transitions proceeded of both without PMMA affecting and polycaprolac each other. Thetone obtained (PCL) blocks, products indicating showed characteristic that BCPs were withoutthermal affecting transitions each other.of both The PMMA obtained and polycaprolac products showedtone (PCL) characteristic blocks, indicating thermal that transitions BCPs were of both synthesized. PMMAsynthesized. and polycaprolactone (PCL) blocks, indicating that BCPs were synthesized.

SchemeSchemeScheme 5. OneOne 5. One pot pot pot polymerization polymerization polymerization of of ofPMMA- PMMA- PMMA-b-PCLb-PCL using using using combination combination combination of metal-freeof metal-free of metal-free ATRP ATRP and ATRP ring and andring opening polymerization (ROP) simultaneously under sunlight. Reprinted from Reference [56]. ringopening opening polymerization polymerization (ROP) (ROP) simultaneously simultaneously un underder sunlight. sunlight. Reprinted Reprinted from from Reference Reference [56]. [56]. (Copyright (2017) Royal Society of Chemisty). (Copyright(Copyright (2017)(2017) RoyalRoyal SocietySociety ofof Chemisty).Chemisty). The synthesis of complex polymeric materials through post-polymerization coupling reactions ThehasThe also synthesissynthesis attracted ofof complexsignificantcomplex polymericpolymeric research in materialsmaterialsterest. Van throughthrough Hest et al.post-polymerizationpost-polymerization synthesized PMMA- couplingcouplingb-PEG diblock reactionsreactions hashas alsoalsocopolymers attractedattracted via significant significantthe combination researchresearch of ATRP interest.interest. and VanVanalkyne-azide HestHest etet al.clickal. synthesizedsynthesized reaction, as PMMA-shownPMMA- inbb -PEG-PEGFigure diblockdiblock4. copolymerscopolymersTerminal via alkyne the combinationand azide moieties of ATRP were and conven alkyne-azideiently introduced click reaction,via protected as shown functionalized in Figure 44.. TerminalTerminalinitiators alkynealkyne [57]. andand azideazide moietiesmoieties werewere convenientlyconveniently introducedintroduced viavia protectedprotected functionalizedfunctionalized initiatorsinitiators Hawker [[57].57]. et al. synthesized a series of cyclic PS-b-PEO BCPs using the ATRP and CuAAC of α,ω- azide-functionalized PS and α,ω-alkyne PEO homopolymers (Figure 5) [11]. The α,ω-azide- HawkerHawker et al. al. synthesized synthesized a aseries series of ofcyclic cyclic PS- PS-b-PEOb-PEO BCPs BCPs using using the theATRP ATRP and andCuAAC CuAAC of α,ω of- functionalized PS was polymerized using a difunctional ATRP initiator, ethylene bis-(2- αazide-functionalized,ω-azide-functionalized PS PSand and α,ωα-alkyne,ω-alkyne PEO PEO homopolymers homopolymers (Figure (Figure 55)) [[11].11]. The The α,ω-azide--azide- functionalizedfunctionalized PS PS was was polymerized polymerized using ausing difunctional a difunctional ATRP initiator, ATRP ethylene initiator, bis-(2-bromoisobutyrate) ethylene bis-(2-. The α,ω-Br-terminated PS was then conveniently converted to the azide moiety. The α,ω-alkyne PEO homopolymer was obtained by treating α,ω-hydroxyl PEO with propargyl bromide. The desired PolymersPolymers 2017 2017, ,9 9, ,494 494 88 of of 31 31

Polymers 2017, 9, 494 8 of 31 bromoisobutyrate).bromoisobutyrate). The The α α,ω,ω-Br-terminated-Br-terminated PS PS was was then then conveniently conveniently converted converted to to the the azide azide moiety. moiety. TheThe αα,ω,ω-alkyne-alkyne PEOPEO homopolymerhomopolymer waswas obtainedobtained byby treatingtreating αα,ω,ω-hydroxyl-hydroxyl PEOPEO withwith propargylpropargyl bromide.bromide.products The wereThe desireddesired isolated productsproducts using preparative werewere isolatedisolated gel permeationususinging preparativepreparative chromatography. gelgel permeationpermeation Tezuka chromatography.chromatography. et al. reviewed TezukaTezukainteresting et et al. al. work reviewed reviewed about interesting interesting topological work work studies about about of BCPstopological topological [58]. studies studies of of BCPs BCPs [58]. [58].

FigureFigure 4. 4.4. ( (aa) )Preparation( Preparationa) Preparation of of PMMA- PMMA- of PMMA-bb-PEG-PEGb -PEGblock block copolymer block copolymer copolymer via via ATRP ATRP via and and ATRP azide-alkyne azide-alkyne and azide-alkyne click click reaction. reaction. click ((breaction.b)) Size Size exclusion exclusion (b) Size chromatography chromatography exclusion chromatography (SEC) (SEC) curves curves (SEC) of of PMMA, PMMA, curves polyethylene of PMMA, polyethyleneglycol glycol (PEG), (PEG), and glycoland PMMA- PMMA- (PEG), bband-PEG-PEG PMMA- diblockdiblockb-PEG copolymer.copolymer. diblock copolymer. ReprintedReprinted Reprinted fromfrom RefereRefere fromncence Reference [57].[57]. (Copyright(Copyright [57]. (Copyright (2005)(2005) (2005) RoyalRoyal Royal SocietySociety Society ofof Chemistry).Chemistry).of Chemistry).

Figure 5. Synthesis of cyclic PS-b-PEO copolymer. Reprinted from Reference [11]. (Copyright (2012) American Chemical Society). FigureFigure 5. 5. Synthesis Synthesis of of cyclic cyclic PS- PS-bb-PEO-PEO copolymer. copolymer. Reprinted Reprinted from from Reference Reference [11]. [11]. (Copyright (Copyright (2012) (2012) AmericanAmerican Chemical Chemical Society). Society). RAFT polymers can be conveniently converted to thiols by treating the chain end with aliphatic amines.RAFTRAFT A polymers blockpolymers copolymer can can be be conveniently canconveniently therefore converted beconverted obtained to to throughthiols thiols by byrelated treating treating thiol the the chemistrychain chain end end (Figurewith with aliphatic aliphatic6). amines.amines. A A block block copolymer copolymer can can therefore therefore be be obtain obtaineded through through related related thiol thiol chemistry chemistry (Figure (Figure 6). 6).

Polymers 2017, 9, 494 9 of 31 PolymersPolymers 2017 2017, 9, ,9 494, 494 9 of9 of 31 31

Figure 6. Synthetic strategies to block copolymers (BCPs) using thiol-based coupling reactions. Figure 6. Synthetic strategies to block copolymers (BCPs) using thiol-based coupling reactions. FigureReprinted 6. Synthetic from Reference strategies [59]. to(Copyrig block htcopolymers (2014) Royal (BCPs) Society using of Chemistry). thiol-based coupling reactions. Reprinted from Reference [59]. (Copyright (2014) Royal Society of Chemistry). Reprinted from Reference [59]. (Copyright (2014) Royal Society of Chemistry). Barner-Kowollik and Stenzel et al. first synthesized a series of star polymers by a combination ofBarner-Kowollik RAFTBarner-Kowollik chemistry and and Stenzel Stenzelhetero Diels-Alderetet al.al. firstfirst synthesizedsynthesize reaction [60],d a a series seriesin which of of star starthe polymers polymersreaction byoccurs by a combination a combinationbetween ofof RAFTthiocarbonyl RAFT chemistry chemistry group and and heteroahetero diene Diels-AlderinDiels-Alder a [4 + 2] cycloaddition reactionreaction [60], [60 process], in in which which(Scheme the the 6). reaction reaction occurs occurs between between thiocarbonylthiocarbonyl group group and and a a diene diene in in a a [4 [4 ++ 2]2] cycloaddition process process (Scheme (Scheme 6).6).

Scheme 6. Formation of block copolymers via a reversible addition-fragmentation chain transfer (RAFT) polymerization and a hetero Diels-Alder reaction. Adapted from Reference [60]. (Copyright SchemeScheme(2008) 6. American6.Formation Formation Chemical ofof blockblock Society). copolymerscopolymers via a reversiblereversible addition-fragmentation addition-fragmentation chain chain transfer transfer (RAFT)(RAFT) polymerization polymerization and and a a hetero hetero Diels-AlderDiels-Alder reaction. Adapted Adapted fr fromom Reference Reference [60]. [60 ].(Copyright (Copyright (2008)(2008) American American Chemical Chemical Society). Society).

Polymers 2017, 9, 494 10 of 31

ThePolymers incorporation 2017, 9, 494 of supramolecular chemistry also provides a very interesting pathway10 of to 31 form BCPs. Schubert et al. demonstrated that terpyridine-terminated PS and PEO can form BCPs with The incorporation of supramolecular chemistry also provides a very interesting pathway to form RuCl3 [61]. The coordination junction point was formed in two steps: the terpyridine-terminated BCPs. Schubert et al. demonstrated that terpyridine-terminated PS and PEO can form BCPs with PEO was selectively complexed with RuCl3 yielding monocomplex of Ru(III); terpyridine-terminated RuCl3 [61]. The coordination junction point was formed in two steps: the terpyridine-terminated PEO PS was then reacted with the monocomplex under the reduction of Ru(III) to Ru(II), resulting in was selectively complexed with RuCl3 yielding monocomplex of Ru(III); terpyridine-terminated PS PS-b-PEO.was then One reacted advantage with ofthe this monocomplex approach isunder that the reduction non-covalent of Ru(III) junction to Ru(II), point resulting can be broken in PS-b under- externalPEO. stimuli. One advantage of this approach is that the non-covalent junction point can be broken under external stimuli. 3. Self-Assembly of BCPs 3. Self-Assembly of BCPs 3.1. Self-Assembly in Bulk 3.1. Self-Assembly in Bulk Self-assembly of BCPs with immiscible blocks has been extensively studied via experiments and simulationsSelf-assembly since the 1960s of BCPs [62 ].with Several immiscible reviews blocks are availablehas been extensively on this topic studied [22,63 via,64 experiments]. The self-assembly and processsimulations is driven bysince an the unfavorable 1960s [62]. mixing Several enthalpy reviews coupledare available with aon small this mixingtopic [22,63,64]. entropy. The Composition self- (f ), theassembly number process of repeating is driven by units an unfavorable (N), and themixing Flory-Huggins enthalpy coupled interaction with a small parameter mixing entropy. (χ) are the Composition (f), the number of repeating units (N), and the Flory-Huggins interaction parameter (χ) important parameters that determine the morphologies, which include spheres (S), cylinders (C), are the important parameters that determine the morphologies, which include spheres (S), cylinders gyroids (G), and lamellae (L) [65,66]. The self-assembly behavior may also be influenced by other (C), gyroids (G), and lamellae (L) [65,66]. The self-assembly behavior may also be influenced by other externalexternal parameters parameters such such as as mechanical mechanical or or electricelectric fields fields [67,68]. [67,68 ].However, However, it is it beyond is beyond the scope the scope of of this reviewthis review to cover to cover all theseall these aspects. aspects. Therefore, Therefore, we only address address the the basic basic concepts concepts of microphase of microphase separationseparation and presentand present several several recent recent examples examples of the of morphologicalthe morphological behavior behavior of of BCPs. BCPs. Figure Figure7 shows 7 that theshows different that the morphologies different morphologies of a typical of linear a typi diblockcal linear BCP diblock evolve BCP from evolve spherical from spherical to lamellar to and can undergolamellar disorderand can undergo to order disorder transitions, to order as transitions, a function as of af functionand χN. of f and χN.

FigureFigure 7. 7.( a(a)) Equilibrium Equilibrium morphologies morphologies of AB ofdiblock AB copolymers diblock copolymers in bulk: S and in S’ bulk:= body-centered- S and S’ = body-centered-cubiccubic spheres, C and spheres, C’ = hexagonally C and C’ =packed hexagonally cylinders, packed G and G’ cylinders, = bicontinuous G and gyroids, G’ = bicontinuous and L = gyroids,lamellae. and L ( =b)lamellae. Theoretical (b )phase Theoretical diagram phase of AB diagram diblocks of predicted AB diblocks by the predicted self-consistent by the mean-field self-consistent mean-fieldtheory, theory, depending depending on volume on fraction volume (f fraction) of the blocks (f ) of and the blocksthe segregation and the parameter, segregation χN; parameter, CPS and χN; CPS’ = closely packed spheres. (c) Experimental phase diagram of -b-polyisoprene CPS and CPS’ = closely packed spheres. (c) Experimental phase diagram of polystyrene-b-polyisoprene copolymers, in which fA represents the volume fraction of polyisoprene, PL = perforated lamellae. copolymers, in which f represents the volume fraction of polyisoprene, PL = perforated lamellae. Reproduced from ReferenceA [69]. (Copyright (2012) Royal Society of Chemistry). Reproduced from Reference [69]. (Copyright (2012) Royal Society of Chemistry). Furthermore, the self-assembly of triblock copolymers of poly(styrene-b-isoprene-b-styrene) (PS- Furthermore,b-PI-b-PS) has also the been self-assembly extensively of investigated triblock copolymers using small-angle of poly(styrene- X-ray scatteringb-isoprene- (SAXS)b -styrene)and (PS-b-PI- b-PS) has also been extensively investigated using small-angle X-ray scattering (SAXS) PolymersPolymers 20172017, ,99, ,494 494 1111 of of 31 31 transmission electron microscopy (TEM) by Storey et al. and Elabd et al. [70,71]. Unlike the conventionaland transmission study electronon neutral microscopy BCPs, Mays (TEM) et al. bycompared Storey etthe al. morphologies and Elabd et of al. well-defined [70,71]. Unlike neutral the PS-conventionalb-PI and its studycharged on counterpart, neutral BCPs, sulfonated Mays et al. PS- comparedb-fluorinated the morphologiesPI (sPS-b-fPI). Interestingly, of well-defined Inversed neutral morphologiesPS-b-PI and its were charged observed counterpart, when the sulfonated diblock PS-BCP,b-fluorinated 25sPS-b-75f PI ((50%sPS-b of-f PI). PS Interestingly,block was sulfonated Inversed tomorphologies sulfonic form), were was observed casted from when tetrahydrofuran the diblock BCP, compared 25sPS-b-75 withf PI (50%its neutral of PS blockcounterpart, was sulfonated as shown to insulfonic Figure form),8 [72]. was casted from tetrahydrofuran compared with its neutral counterpart, as shown in Figure8[72].

FigureFigure 8. 8. TEMTEM and and small-angle small-angle X-ray X-ray sca scatteringttering (SAXS) (SAXS) images images of of ssPS-PS-bb--fPI.f PI. (A (A) )ordered ordered hexagonal hexagonal ◦ structuresstructures without without annealing; annealing; (B (B) )less less ordered ordered structures structures of of sample sample annealed annealed at at 120 120 °C;C; (C (C) )SAXS SAXS of of thethe corresponding corresponding samples samples in in (A (A,B,B).). Reprinted Reprinted from from Reference Reference [72]. [72]. (Copyright (Copyright (2010) (2010) Royal Royal Society Society ofof Chemistry). Chemistry).

SegalmanSegalman et al.al. preparedprepared a seriesa series of ionicof ionic conducting conducting BCPs BCPs to investigate to investigate the relationship the relationship between betweenionic conductivity ionic conductivity and domain and spacingdomain [ 73spac]. Aing well-defined [73]. A well-defined BCP precursor, BCP PS-precursor,b-PI, was PS- synthesizedb-PI, was synthesizedfollowed by followed a thiol-ene by a reaction thiol-ene to reaction attach the to atta ionicch moietiesthe ionic tomoieties PI segments. to PI segments. The domain The domain spacing spacingwas controlled was controlled by keeping by keeping the volume the fractionvolume offraction ionic moieties of ionic constantmoieties andconstant varying and the varying BCP chain the BCPlength. chain It waslength. revealed It was that revealed the ionic that conductivity the ionic conductivity was independent was independent of domain spacing. of domain The spacing. insights Thegained insights by this gained work couldby this facilitate work could the development facilitate the of development design rules forof thedesign next rules generation for the of next high generationperformance of high ion-conducting performance membranes. ion-conducting Balsara membra et al. studiednes. Balsara the effect et al. ofstudied salt on the the effect morphology of salt on of theelectron morphology conducting of electron poly(3-(2 conducting0-ethylhexyl)thiophene)- poly(3-(2′-ethylhexyl)thiophene)-b-ethylene oxide) (P3EHT-b-ethyleneb-PEO) oxide) [74]. (P3EHT- PEO was bselected-PEO) [74]. due PEO to itswas good selected salt solvationdue to its capability.good salt solvation Their results capability. showed Their that, results in the showed melt state, that, thein thesalt-free melt state, sample the exhibits salt-free a sample gyroid morphologyexhibits a gyroid while morphology the salt containing while the sample salt containing (r = 0.125) sample exhibits (r a =lamellar 0.125) exhibits morphology. a lamellar Furthermore, morphology. quenching Furthe thermore, salt-free quenching sample to the room salt-free temperature sample results to room in a temperaturelamellar morphology results in a due lamellar to the morphology breakout of thedue P3EHT to the breakout crystals. Inof the contrast, P3EHT there crystals. is little In changecontrast, in therethe morphology is little change of the in salt-containing the morphology sample of the upon salt-containing quenching tosample room temperature.upon quenching This to could room be temperature.attributed to This the increase could be in attributedχN. to the increase in χN. OwingOwing to to its its structural structural versatility versatility and and precise precise tunability tunability of of morphology, morphology, dimensionality, dimensionality, and and featurefeature size, size, BCP BCP is isan an ideal ideal platform platform for for studying studying periodically periodically ordered ordered functional functional materials materials on the on mesoscale.the mesoscale. Wiesner Wiesner et al. etdemonstrated al. demonstrated the utilization the utilization of triblock of triblock copolymer copolymer (PI-b-PS- (PI-bb-PEO)-PS-b-PEO) self- assemblyself-assembly to direct to direct the synthesis the synthesis of a ofmesoporous a mesoporous niobium niobium nitride nitride (NbN) (NbN) superconductor superconductor (Figure (Figure 9).9). TheThe formation ofof a three-dimensionallya three-dimensionally continuous continuous gyroidal gyroidal mesoporous mesoporous NbN superconductorNbN superconductor exhibits exhibitsa critical a temperaturecritical temperature (Tc) of about(Tc) of 7about to 8 K,7 to a flux8 K, a exclusion flux exclusion of about of about 5% compared 5% compared to a dense to a dense NbN NbNsolid solid [75]. [75]. More More examples examples will bewill given be given in Section in Section4. 4. TheThe myriad myriad morphologies morphologies that that are are formed formed by by BCPs BCPs are are usually usually obtained obtained by by slow slow cooling cooling so so that that thethe polymer polymer chains chains have have enough enough time time to to reach reach th thermodynamicallyermodynamically preferred preferred alignments. alignments. Rather Rather than than usingusing slow slow cooling, Kim etet al.al. rapidlyrapidly quenched quenched poly(isoprene- poly(isoprene-b-lactide)b-lactide) diblock diblock copolymers copolymers from from the thedisordered disordered state state and revealedand revealed an extraordinary an extraord thermalinary historythermal dependence history dependence [76]. Whereas [76]. conventional Whereas conventionalcooling results cooling in the results formation in the of formation documented of documented morphologies, morphologies, rapidly cooled rapidly samples cooled that samples are then thatheated are fromthen lowheated temperature from low form temperature the hexagonal form C14the hexagonal and cubic C15C14 Laves and cubic phases C15 commonly Laves phases found commonly found in metal alloys. This unusual discovery reinforces fundamental analogies between

Polymers 2017, 9, 494 12 of 31

Polymers 2017, 9, 494 12 of 31 in metalPolymers alloys. 2017, 9, This 494 unusual discovery reinforces fundamental analogies between the way12 of 31 metals and self-assembledthe way metals softand materialsself-assembled break soft symmetry materials when break subjected symmetry to when changes subjected in thermodynamic to changes in state variablesthethermodynamic way that metals drive state phaseand self-assembledvariables transitions. that drive soft materialphase transitions.s break symmetry when subjected to changes in thermodynamic state variables that drive phase transitions.

FigureFigure 9. Gyroid-forming 9. Gyroid-forming PI- PI-b-PS-b-PS-bb-PEO-PEO block copolymers copolymers and and the the preparation preparation process process of NbN of NbN Figure 9. Gyroid-forming PI-b-PS-b-PEO block copolymers and the preparation process of NbN superconductors.superconductors. Reprinted Reprinted with with permission permission fromfrom Reference [75]. [75 ].(Copyright (Copyright (2016) (2016) the authors). the authors). superconductors. Reprinted with permission from Reference [75]. (Copyright (2016) the authors). 3.2. Self-Assembly in Solution 3.2. Self-Assembly3.2. Self-Assembly in Solutionin Solution The self-assembly of amphiphilic BCPs has been a popular topic in fields such as nano-cargo Thedelivery,The self-assembly self-assemblybiomedical/pharmaceutics, of of amphiphilic amphiphilic and BCPsBCPs nanotechnology has been a a popular popular [77–79]. topic topicAlthough in infields fields the such self-assembly such as nano-cargo as nano-cargo of delivery,delivery,amphiphilic biomedical/pharmaceutics, biomedical/pharmaceutics, BCPs is also driven by the andand minimizatio nanotechnology n of free [77–79]. energy [77–79 Although].in Althoughthe system, the theself-assemblyself-assembly self-assembly ofin of amphiphilicamphiphilicsolution BCPsis more BCPs is complicated alsois also driven driven than byby theBCP minimizatio minimization self-assemblyn of offreein freebulk. energy energy The in morphologiesthe in system, the system, self-assembly are primarily self-assembly in solution is more complicated than BCP self-assembly in bulk. The morphologies are primarily in solutiondetermined is more by the complicated so-called packing than parameter BCP self-assembly (p = v/a0lc), where in bulk. v is the The volume morphologies of the hydrophobic are primarily determinedchain, a0 is the by optimalthe so-called area ofpacking the head parameter group, and (p = l v/ac is 0thelc), wherelength vof is the the hydrophobic volume of the tail hydrophobic (Figure 10) determined by the so-called packing parameter (p = v/a0lc), where v is the volume of the hydrophobic chain,[80]. a0 is the optimal area of the head group, and lc is the length of the hydrophobic tail (Figure 10) chain,[80]. a0 is the optimal area of the head group, and lc is the length of the hydrophobic tail (Figure 10) [80].

Figure 10. The types of formed nanostructures of amphiphilic diblock copolymers due to the inherent Figure 10. The types of formed nanostructures of amphiphilic diblock copolymers due to the inherent Figurecurvature 10. The of types the polymer, of formed as estimated nanostructures by chain of pa amphiphiliccking parameter, diblock p. Reprinted copolymers from dueReference to the [80]. inherent curvature of the polymer, as estimated by chain packing parameter, p. Reprinted from Reference [80]. curvature(Copyright of the (2009) polymer, WILEY-VCH as estimated Verlag by GmbH chain & packing Co. KGaA, parameter, Weinheim). p. Reprinted from Reference [80]. (Copyright (2009) WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim). (Copyright (2009) WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

Polymers 2017, 9, 494 13 of 31 Polymers 2017, 9, 494 13 of 31

ByBy controlling controlling the the factors factors that that are are able able toto changechange the packing packing parameter parameter such such as as BCP BCP composition composition andand concentration, concentration, water water content, content, commoncommon solvent,solvent, and additives, additives, aa wide wide range range of of morphologies morphologies havehave been been reported reported including including spherical spherical ,micelles, cylindrical, bi-continuous, bi-continuous, lamella, lamella, vesicles, vesicles, tubules, tubules, etc.etc. [81 [81]] (Figure (Figure 11 11).).

FigureFigure 11. 11.TEM TEMimages images and corresponding schematic schematic diagrams diagrams of various of various morphologies morphologies formed formed by byamphiphilic amphiphilic PS PSm-mb-PAA-b-PAAn copolymers(n copolymers( m and m andn denote n denote the degrees the degrees of polymerization of polymerization of PS and of PAA, PS and PAA,respectively): respectively): (a) spherical (a) spherical micelles; micelles; (b) (rods;b) rods; (c) (bicontinuousc) bicontinuous rods; rods; (d) (dsmall) small lamellae; lamellae; (e) (elarge) large lamellae;lamellae; (f )(f vesicles;) vesicles; ( g()g) hexagonally hexagonally packedpacked hollowhollow hoops (HHHs); (HHHs); (h (h) )large large compound compound micelles micelles (LCMs).(LCMs). Reprinted Reprinted from from Reference Reference [ 69[69].]. (Copyright(Copyright (2012) Royal Society Society of of Chemistry). Chemistry).

Manners and Winnik reported a series of interesting rod-like micelles using poly(ferrocenyldimethylsilane)Manners and Winnik reported(PFDMS). These a series micelles of are interestingable to grow epitaxially rod-like by micelles the addition using poly(ferrocenyldimethylsilane)of more polymer, leading to extended (PFDMS). micelles These with micelles a very narrow areable size distribution to grow epitaxially (Figure 12) [82]. bythe additionSelf-assembly of more polymer, of BCPs enables leading researchers to extended to cons micellestruct nanoscale with a structures very narrow with sizemolecular distribution level (Figureprecision. 12)[ 82Not]. only the chemical composition has significant effect on the properties of nanostructure; molecularSelf-assembly architecture of BCPs also enables has profound researchers effect, to construct as revealed nanoscale by the structures recent studies. with molecularTezuka and level precision.Yamamoto Not et only al. explored the chemical the effect composition of topology has on significant the thermal effect stability on the of properties self-assembled of nanostructure; structures molecularof BCPs: linear architecture poly(butyl also acrylate- has profoundb-ethylene effect, oxide- asb-butyl revealed acrylate) by the (PBA- recentb-PEO- studies.b-PBA) (1) Tezuka and the and Yamamotocyclic counterpart et al. explored (2) (Figure the effect 13). ofDespite topology no ondistinctive the thermal change stability in the of chemical self-assembled composition structures or ofstructure BCPs: linear of the poly(butyl micelles, they acrylate- foundb-ethylene that the cloud oxide- pointb-butyl (Tc acrylate)) was increased (PBA- bby-PEO- moreb-PBA) than 40 (1) °C and thethrough cyclic counterpart the topological (2) conversion. (Figure 13). Moreover, Despite no the distinctive Tc can be tuned change by the in the changing chemical the compositionratio of 1 and or ◦ structure2 [83]. of the micelles, they found that the cloud point (Tc) was increased by more than 40 C through the topological conversion. Moreover, the Tc can be tuned by the changing the ratio of 1 and 2 [83].

Polymers 2017, 9, 494 14 of 31 PolymersPolymers 20172017,, 99,, 494494 1414 ofof 3131

FigureFigure 12.12. TheThe schematicschematic representationrepresentation ofof thethe micellesmicelles fromfrom polyferrocenylsila polyferrocenylsilanepolyferrocenylsilanene (PFS)—containing(PFS)—containing BCPsBCPs via via epitaxialepitaxial growth.growth.growth. Reprinted ReprintedReprinted from fromfrom Reference RefereReferencence [82 [82].[82].]. (Copyright (Copyright(Copyright (2007) (2007)(2007) American AmericanAmerican Association AssociationAssociation for forforthe thethe Advancement AdvancementAdvancement of Science). ofof Science).Science).

FigureFigure 13.13. 13. TheThe schematicTheschematic schematic illustrationillustration illustration ofof linearlinear of amphiphilicamphiphilic linear amphiphilic PBA-PBA-bb-PEO--PEO- PBA-bb-PBA-PBAb-PEO- andand bcycliccyclic-PBA PBA-PBA- andbb-PEO--PEO- cyclic b-PBA self-assembly in aqueous media. The cyclic BCP shows an increased Tcc. Reprinted from bPBA--PBAb -PEO-self-assemblyb-PBA self-assembly in aqueous in media. aqueous The media. cyclic The BCP cyclic shows BCP an shows increased an increased T . Reprinted Tc. Reprinted from ReferenceReferencefrom Reference [83].[83]. (Copyright(Copyright [83]. (Copyright (2010)(2010) (2010) AmericanAmerican American ChemicalChemical Chemical Society).Society). Society).

UsingUsing poly(1,2-butadiene-poly(1,2-butadiene-bb-ehtylene-ehtylene oxide)oxide) (PB-(PB-bb-PEO)-PEO) inin waterwater media,media, BatesBates etet al.al. observedobserved thethe Using poly(1,2-butadiene-b-ehtylene oxide) (PB-b-PEO) in water media, Bates et al. observed the formationformation ofof “Y-junctions”,“Y-junctions”, whichwhich furtherfurther assembledassembled toto formform aa 3D3D networknetwork (Figure(Figure 14).14). ThisThis formation of “Y-junctions”, which further assembled to form a 3D network (Figure 14). This observation observationobservation isis inin contrastcontrast toto thatthat ofof thethe lowlow molecularmolecular weightweight counterpart,counterpart, wherewhere onlyonly sphericalspherical is in contrast to that of the low molecular weight counterpart, where only spherical micelles, wormlike micelles,micelles, wormlikewormlike micelles,micelles, andand vesiclesvesicles werewere obtainedobtained whenwhen mixedmixed withwith waterwater [84].[84]. micelles, and vesicles were obtained when mixed with water [84].

Polymers 2017, 9, 494 15 of 31 Polymers 2017, 9, 494 15 of 31

Figure 14. Morphology diagram for PB-PEO in water (1 wt %) as a function of molecular size and Figure 14. Morphology diagram for PB-PEO in water (1 wt %) as a function of molecular size and composition, where NPB and WPEO are the and weight fraction of the PB and composition, where N and W are the degree of polymerization and weight fraction of the PB and PEO blocks, respectively.PB ReprintedPEO from Reference [84]. (Copyright (2003) American Association for PEO blocks, respectively. Reprinted from Reference [84]. (Copyright (2003) American Association for the Advancement of Science). the Advancement of Science). 4. Applications 4. Applications 4.1. Applications as Thermoplastic Elastomers 4.1. Applications as Thermoplastic Elastomers One of the most important technical applications of BCPs is as thermoplastic elastomers (TPEs). This Onetype of BCP the mosttypically important contains technical physically applications crosslinked of rigid BCPs glassy is as domains thermoplastic and a continuous elastomers soft (TPEs). This‘typerubbery domain. of BCP typicallyIt offers containsthe elasticity physically of conv crosslinkedentional rubber rigid glassy and, domainssince it is and not a continuouschemically soft rubberycrosslinked, domain. is suitable It offers for the typical elasticity of conventionalprocesses such rubber as injection and, since molding it is not and chemically melt extrusion. crosslinked, isTPEs suitable have forfound typical applications plastic processes in adhesives, such coatings, as injection food molding packaging, and and melt many extrusion. other areas TPEs [85]. have The found applicationsmost commonly in adhesives, studied coatings,TPEs are foodpoly(styrene- packaging,b-isoprene- and manyb-styrene) other areas (SIS) [85 and]. The poly(styrene- most commonlyb- studiedbutadiene- TPEsb-styrene) are poly(styrene- (SBS). Theseb two-isoprene- types ofb -styrene)BCPs were (SIS) firstly and developed poly(styrene- by Holdenb-butadiene- and Milkovichb-styrene) (SBS).through These living twoanionic types polymerization of BCPs were in the firstlyearly 1960s developed [86]. The by remarkable Holden mechanical and Milkovich properties through livingare attributed anionic to polymerization the microphase separation in the early of 1960sthe two [86 chemically]. The remarkable incompatible mechanical blocks, PS propertiesand PI (or are attributedPB). SIS with to high the 3,4-isoprene microphase exhibits separation a broad of gl theass twotransition chemically close to incompatibleroom temperature, blocks, providing PS and PI (ora very PB). good SIS with vibration high 3,4-isoprenedamping material exhibits at a room broad temperature [54]. close Polyethylene to room temperature,(PE) or poly(ethylene-alt-propylene) can be obtained through the hydrogenation of the diene block; such providing a very good vibration damping material at room temperature [54]. Polyethylene (PE) products exhibit superior stability under light and oxygen. Hydrogenated SBS has been used in or poly(ethylene-alt-propylene) can be obtained through the hydrogenation of the diene block; such applications such as electrical wire and cable sheathing due to its cold temperature flexibility and products exhibit superior stability under light and oxygen. Hydrogenated SBS has been used in higher extendibility to incorporate flame retardants over conventional poly(vinyl chloride) (PVC) applications such as electrical wire and cable sheathing due to its cold temperature flexibility and [54]. Star-block copolymers of butadiene and styrene have found applications in adhesives and higher extendibility to incorporate flame retardants over conventional poly(vinyl chloride) (PVC) [54]. sealants [87]. Star-block copolymers of butadiene and styrene have found applications in adhesives and sealants [87].

Polymers 2017, 9, 494 16 of 31 Polymers 2017, 9, 494 16 of 31

Because the precise control over composition andand architecture is possible through LAP, thethe resultingresulting BCPsBCPs cancan bebe tailoredtailored toto aa widewide varietyvariety ofof applications [[88].88]. One research focus is to improve thethe upperupper service service temperature temperature of styrenic of styrenic thermoplastic thermoplastic elastomers elastomers (S-TPEs), (S-TPEs), which is mainlywhich controlledis mainly bycontrolled the Tg of by the the hard Tg domain.of the hard Considerable domain. Considerable research has focused research on has developing focused highon developing Tg glassy domains high Tg ◦ ◦ suchglassy as domains poly(α-methyl such as styrene) poly(α-methyl (Tg ~173 styrene)C) [89], (T poly(g ~ 173α-methyl °C) [89],p-methyl poly(α-methyl styrene) p (T-methylg ~183 styrene)C) [90], ◦ and(Tg ~poly( 183 °C)tert [90],-butyl and styrene) poly(tert (P-butyltBS, T styrene)g ~130 C)(PtBS, [91]. Tg In ~ 130 hydrocarbon °C) [91]. In solvent hydrocarbon at room solvent temperature, at room Maystemperature, et al. prepared Mays et a al. series prepared of BCPs a series consisting of BCPs of poly(benzofulvene consisting of poly(benzofulvene (BF)-b-isoprene- (BF)-b-benzofulvene)b-isoprene- (FIF),b-benzofulvene) in which FIF (FIF), with in 14 which vol % FIF of PBFwith exhibited 14 vol % a of maximum PBF exhibited stress a of maximum 14.3 ± 1.3 stress MPa andof 14.3 strain ± 1.3 at breakMPa and of 1390 strain± at66% break from of tensile 1390 ± tests 66% [from92]. Dynamic tensile tests mechanical [92]. Dynamic analysis mechanical showed that analysis the softening showed ◦ temperaturethat the softening of PBF temperature in FIF was 145 of PBFC, which in FIF is muchwas 145 higher °C, thanwhich that is ofmuch thermoplastic higher than elastomers that of withthermoplastic PS hard blocks elastomers (Figure with 15). PS hard blocks (Figure 15).

Figure 15. The structure of poly(benzofulvene (BF)- b-isoprene-b-benzofulvene) (FIF) block copolymer and mechanicalmechanical analysis. analysis. Reprinted Reprinted from from Reference Refere [92nce]. (Copyright[92]. (Copyright (2016) American(2016) American Chemical Chemical Society). Society). In comparison with diene-based TPEs, all acrylic-based TPEs showed higher oxidation In comparison with diene-based TPEs, all acrylic-based TPEs showed higher oxidation stability stability and UV resistance. The same group synthesized a series of TP all acrylic-based high and UV resistance. The same group synthesized a series of TP all acrylic-based high temperature temperature thermoplastic elastomers containing poly(1-adamatyl acrylate) as a hard domain and thermoplastic elastomers containing poly(1-adamatyl acrylate) as a hard domain and poly(tetrahydrofurfuryl acrylate) as a soft domain by RAFT polymerization [93]. These TPEs exhibited poly(tetrahydrofurfuryl acrylate) as a soft domain by RAFT polymerization [93]. These TPEs superior stress-strain behavior compared to that of conventional all acrylic-based TPEs consisting exhibited superior stress-strain behavior compared to that of conventional all acrylic-based TPEs of PMMA and PBA made by controlled radical processes [94], while the tensile strength was lower consisting of PMMA and PBA made by controlled radical processes [94], while the tensile strength compared to that of similar products prepared via living anionic polymerization [95]. was lower compared to that of similar products prepared via living anionic polymerization [95]. TPEs with non-linear architectures have also been synthesized and investigated over the last three TPEs with non-linear architectures have also been synthesized and investigated over the last decades. Multigraft copolymers of PI-g-PS are found to have high tensile strength, high strain at break, three decades. Multigraft copolymers of PI-g-PS are found to have high tensile strength, high strain and low residue strain. Furthermore, Mays et al. synthesized a series of tetrafunctional multigraft at break, and low residue strain. Furthermore, Mays et al. synthesized a series of tetrafunctional copolymer (“centipede”) with varied branching points (Figure 16)[96]. The tetrafunctional copolymer multigraft copolymer (“centipede”) with varied branching points (Figure 16) [96]. The tetrafunctional with 10 branching points showed an exceptional elongation at break ~2100%, almost double that copolymer with 10 branching points showed an exceptional elongation at break ~2100%, almost of commercial ® (1050% at similar composition), and only 40% residual strain on hysteresis double that of commercial Kraton® (1050% at similar composition), and only 40% residual strain on experiments (elongated at 1400%) [97]. Detailed study revealed that the superelasticity was attributed hysteresis experiments (elongated at 1400%) [97]. Detailed study revealed that the superelasticity was to the distinct molecular architectures. Furthermore, the same group developed a low-cost emulsion attributed to the distinct molecular architectures. Furthermore, the same group developed a low-cost polymerization to prepare comb multigraft copolymers such as PI-g-PS and PBA-g-PS as well as to prepare comb multigraft copolymers such as PI-g-PS and PBA-g-PS as centipede PBA-g-PS for TPE applications [98,99]. well as centipede PBA-g-PS for TPE applications [98,99].

Polymers 2017, 9, 494 17 of 31

Figure 16. (A) Stress–strain behavior of tetrafunctional multigraft copolymers compared to commercial thermoplastic elastomers. Reprinted from Reference [96]. (Copyright (2006) American Chemical Society). (B) Hysteresis curve of a tetrafunctional multigraft copolymer with 14 vol % PS and 5.5 branching points. Reprinted from Reference [97]. (Copyright (2006) WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

4.2. Applications in Drug Delivery and Release Advanced nanoscale systems created by self-assembly of BCPs have seen tremendous progress for drug delivery applications over the last decade [100,101]. The advances in BCP self-assembly offer effective control of morphology, surface chemistry, and the introduction of environmental responsiveness. Among these nanostructures, micelles and vesicles are the most studied morphologies. Block copolymer micelles are of interest for drug delivery applications for a number of reasons. First of all, hydrophobic drugs can be entrapped in the core and transported at concentrations that can exceed their intrinsic water solubility. Secondly, the hydrophilic blocks, which are often composed of PEO, can form hydrogen bonds with the aqueous surroundings and form a tight shell around the micellar core. Moreover, the PEO corona resists protein adsorption and cellular adhesion, protecting the hydrophobic drug against hydrolysis and enzymatic degradation. In addition, the PEO corona prevents recognition by the reticuloendothelial system and therefore increases the blood circulation times [100]. Thermo-responsive micelles are the most widely investigated, such as poly(N-isopropyl acrylamide-b-D,L-lactide), poly(N-isopropyl acrylamide-b-butyl methacrylate), and poly(N-isopropyl acrylamide-co-N,N-dimethylacrylamide)-b-poly(D,L-lactide-co-glycolide) [102,103]. These micelles undergo reversible structural changes that facilitate drug release once the temperature is elevated above the LCST of the polymers [104]. Other stimuli-responsive BCPs have also been extensively studied. Park et al. developed an amphiphilic BCP composed of PEG and poly(ε-(4-nitro)benzyloxycarbonyl-L-lysine) for hypoxia-sensitive drug delivery. The formed micelles encapsulated doxorubicin (DOX) in an aqueous condition and exhibited rapid intracellular release of DOX under the hypoxic condition [105]. BCPs used in drug delivery should have low toxicity or be non-toxic. BCP vesicles containing biocompatible PEO, PLA, and PCL have been evaluated [106,107]. Both PEO-b-PLA and PEO-b-PCL vesicles exhibit the controlled release of active dyes and anti-cancer drugs over periods of up to two weeks [108,109]. Discher et al. employed vesicles made from a mixture of biocompatible PB-b-PEO and PLA-b-PEO to simultaneously deliver two anti-cancer drugs, in which hydrophilic doxorubicin was encapsulated in the cavity and hydrophobic paclitaxel was embedded in the vesicle wall [106,110]. In vivo studies revealed that the vesicle-loaded drugs are more effective and sustainable in tumor shrinkage as compared with the direct injection of free drugs. Rates of encapsulant release from the hydrolyzable vesicles are accelerated with an increased proportion of PEG and the molar ratio of degradable copolymer. In particular, BCP vesicles modified with stimuli-responsive functionalities have been studied for smart drug delivery. Attaching the vesicle with antibodies allows the delivery of vesicles to targeted cells [111]. Other than their academic interest, thermosensitive liposomes (TSLs) Polymers 2017, 9, 494 18 of 31

Polymers 2017, 9, 494 18 of 31 have already been investigated for the treatment of breast cancer and colorectal liver metastasis in severalthermosensitive clinical trials. liposomes (TSLs) have already been investigated for the treatment of breast cancer andIn colorectal spite of the liver advances metastasis in thein several design clinical of peptide trials. drugs and the emergence of gene therapy, there is still aIn need spite to of further the advances improve in the design performance of pepti ofde thesedrugs systemsand the emergence that can precisely of gene therapy, direct the there drug to theis desired still a need site into thefurther body improve and to the accurately performance control of these the ratesystems at which that can the precisely drug is released.direct the drug to the desired site in the body and to accurately control the rate at which the drug is released. 4.3. Applications in Soft Lithography 4.3. Applications in Soft Lithography One of the remarkable candidates for soft lithography is the directed self-assembly (DSA) of BCPs, becauseOne of the they remarkable can form candidates ordered features for soft atlithography a length scaleis the as directed low as self-assembly a few nanometers, (DSA) of which is requiredBCPs, because for many they ofcan the form most ordered demanding features nextat a length generation scale as patterning low as a few applications, nanometers, including which is the required for many of the most demanding next generation patterning applications, including the fabrication of bit patterned media (BPM) for hard disk drives as well as fin field effect transistor fabrication of bit patterned media (BPM) for hard disk drives as well as fin field effect transistor (FinFETs) and contact holes for microelectronics [112–118]. Poly(styrene-b-methyl methacrylate) (FinFETs) and contact holes for microelectronics [112–118]. Poly(styrene-b-methyl methacrylate) (PS- (PS-bb-PMMA)-PMMA) is is the the most most studied studied BCP BCP system system because because it can it can produce produce lamellar lamellar or cylinder or cylinder morphologies, morphologies, whichwhich are are perpendicularly perpendicularly oriented oriented toto the substrate simply simply via via thermal thermal treatment treatment (Figure (Figure 17) [119]. 17)[ 119]. ThisThis phenomenon phenomenon is is attributed attributed to to the the similaritysimilarity of of the the interfacial interfacial energies energies between between each each block block and the and the air interfaceair interface [120 [120].]. Hawker Hawker et et al. al. reported reported thatthat the neutral neutral surface surface (γ (PS-AirγPS-Air ≈ γ≈PMMA-Air)γPMMA-Air) could could be be achievedachieved with with thermally thermally annealed annealedPS- PS-bb-PMMA-PMMA at at 225 225 °C◦C in in air air [121]. [121 ].

Figure 17. Surface force microscopy (SFM) phase image of (A) cylinder-forming PS-b-PMMA and (B) Figure 17. Surface force microscopy (SFM) phase image of (A) cylinder-forming PS-b-PMMA and lamella-forming PS-b-PMMA on the substrate modified by R64 (PS mole fraction of 0.64) and R55 (PS (B) lamella-forming PS-b-PMMA on the substrate modified by R64 (PS mole fraction of 0.64) and R55 mole fraction of 0.55), respectively, at various film thicknesses of block copolymer after thermally (PS mole fraction of 0.55), respectively, at various film thicknesses of block copolymer after thermally annealing thin films at 170 °C for 24 h. Reprinted from Reference [119]. (Copyright (2008) American annealing thin films at 170 ◦C for 24 h. Reprinted from Reference [119]. (Copyright (2008) American Chemical Society). Chemical Society). Unfortunately, the minimum feature size is limited to ~13 nm due to its low χ (~0.039 at 150 °C) [122].Unfortunately, To achieve very the high minimum resolution feature (i.e., small size fe isature limited size), tothe~13 chemical nm duestructure to its of lowthe BCPχ (~0.039 must at 150be◦C) carefully [122]. designed To achieve to maximize very high the resolution chemical incompatibility (i.e., small feature between size), blocks the (i.e., chemical high-χ, structurelow-N). of theImpressive BCP must work be carefully has been designed reported toemploying maximize a variety the chemical of high- incompatibilityχ BCPs. Russell et between al. were blocksable to (i.e., achieve a 3-nm cylindrical domain size using PS-b-PEO on a surface of a sapphire single-crystal high-χ, low-N). Impressive work has been reported employing a variety of high-χ BCPs. Russell et al. (Figure 18) [123]. were able to achieve a 3-nm cylindrical domain size using PS-b-PEO on a surface of a sapphire single-crystal (Figure 18)[123]. Polymers 2017, 9, 494 19 of 31 Polymers 2017, 9, 494 19 of 31

FigureFigure 18. 18.Atomic Atomic force force microscopy microscopy (AFM)(AFM) height images of of sawtooth sawtooth patterns patterns and and phase phase images images of of solvent-annealedsolvent-annealed PS- PS-b-PEOb-PEO thinthin films.films. (A,D) When the the M-plane M-plane sapphire sapphire was was annealed annealed at at1400 1400 °C◦ C andand 1500 1500◦C, °C, a a pitch pitch of of ~48 ~48 and and ~24~24 nmnm andand a peak-to-valleypeak-to-valley depth depth of of ~6 ~6 and and ~3 ~3 nm nm were were obtained, obtained, respectively.respectively. Highly Highly orderedordered PEOPEO cylindricalcylindrical microdomains having having areal areal densities densities of of0.74 0.74 to to10.5 10.5 terabit/inch2 from PS-b-PEO (Mn = 26.5 kg/mol) (B), PS-b-PEO (Mn = 25.4 kg/mol) (C), PS-b-PEO (Mn = terabit/inch2 from PS-b-PEO (Mn = 26.5 kg/mol) (B), PS-b-PEO (Mn = 25.4 kg/mol) (C), PS-b-PEO 21.0 kg/mol) (E), and PS-b-PEO (Mn = 7.0 kg/mol) (F) BCP thin films annealed in o-xylene vapor were (Mn = 21.0 kg/mol) (E), and PS-b-PEO (Mn = 7.0 kg/mol) (F) BCP thin films annealed in o-xylene vaporobtained. were obtained.Scale bars, Scale100 nm. bars, Reprinted 100 nm. from Reprinted Reference from [123]. Reference (Copyright [123 ].(2009) (Copyright American (2009) Association American for the Advancement of Science). Association for the Advancement of Science).

Hillmyer et al. synthesized poly(lactide-b-dimethylsiloxane-lactide) (PLA-PDMS-PLA) to achieveHillmyer a 7-nm et al.pitch synthesized size [124]. poly(lactide- Some other BCPsb-dimethylsiloxane-lactide) that are capable of self-assembling (PLA-PDMS-PLA) into sub-10 to achieve nm a 7-nmdomain pitch sizes size include [124]. SomePS-b-PDMS other [125], BCPs PS- thatb-P2VP are capable [126], ofand self-assembling PS-b-PLA [118]. into On sub-10 the other nm hand, domain sizeshigh- includeχ organic PS- bBCPs-PDMS that [ 125can], form PS-b -P2VPsub-10 [nm126 domains], and PS- sufferb-PLA from [118 low]. Onetch the contrast other hand,when sizes high- χ organicapproach BCPs down that to can 10 formnm. Since sub-10 organic nm domainspolymers sufferthat contain from lowinorganic etch contrast constituents, when such sizes as approachsilicon, downare inherently to 10 nm. etch Since resistant, organic the polymers incorporation that of contain one such inorganic block in constituents,high-χ BCPs affords such asexceptional silicon, are inherentlyetch contrast. etch Cushen resistant, et theal. synthesized incorporation a series of one of high- suchχ block BCPs incomposed high-χ BCPs of oligosaccharides affords exceptional coupled etch contrast.to a silicon-containing Cushen et al. synthesized polystyrene aderivative. series of high- The χBCPsBCPs exhibit composed hexagonally of oligosaccharides packed cylinders coupled with to a silicon-containinga 5-nm feature size polystyrenein thin film [127]. derivative. A polarity-switchable The BCPs exhibit top hexagonallylayer was also packed applied cylinders to the surface with a 5-nmof silicon-containing feature size in thin BCPs film films [127 to]. obtain A polarity-switchable perpendicular orientation top layer of was poly(styrene- also appliedb-trimethyl to the surface silyl ofstyrene- silicon-containingb-styrene) (PS- BCPsb-PTMSS- films tob-PS) obtain and perpendicular poly(trimethyl orientation silyl styrene- of poly(styrene-b-lactide) (PTMSS-b-trimethylb-PLA) silyl styrene-after thermalb-styrene) annealing (PS-b-PTMSS- [128]. b-PS) and poly(trimethyl silyl styrene-b-lactide) (PTMSS-b-PLA) after thermalOn annealing the other [hand,128]. BCP architecture also plays a key role in controlling the feature size. Hawker compared linear PS-b-PEO and cyclic PS-b-PEO and found that the thin film self-assembly of the latter On the other hand, BCP architecture also plays a key role in controlling the feature size. Hawker showed a ~30% decrease in domain spacing (Figure 19), which was attributed to the reduced compared linear PS-b-PEO and cyclic PS-b-PEO and found that the thin film self-assembly of the hydrodynamic radii of the cyclic systems [11]. latter showed a ~30% decrease in domain spacing (Figure 19), which was attributed to the reduced Limited synthetic access has largely restricted the application of cyclic BCPs in soft lithography. hydrodynamic radii of the cyclic systems [11]. Other complex architecture such as star copolymers, etc. remains a largely unexplored regime. Nevertheless,Limited synthetic the advancement access has of largely BCP design, restricted synt thehesis, application processing of strategies, cyclic BCPs and in morphological soft lithography. Othercharacterization complex architecture tools (e.g., atomic such as force star microscopy copolymers, (AFM), etc. remainstomographic a largely TEM, unexploredgrazing-incidence regime. Nevertheless,small-angle scattering the advancement (GISAXS), of BCPetc.) offers design, hope synthesis, that this processing technology strategies, may impact and industry morphological and characterizationsociety in the coming tools (e.g.,years. atomic force microscopy (AFM), tomographic TEM, grazing-incidence small-angle scattering (GISAXS), etc.) offers hope that this technology may impact industry and society in the coming years. Polymers 2017, 9, 494 20 of 31 Polymers 2017, 9, 494 20 of 31

Figure 19. 19. AtomicAtomic force forcemicroscopy microscopy height images height for images (a) cyclic for PS13K- (a) cyclicb-PEO5K PS13K- andb-PEO5K (b) PS13K- andb- PEO5K(b) PS13K- diblockb-PEO5K copolymers diblock (inlet: copolymers 2D fast Fourier (inlet: 2Dtransform fast Fourier (FFT) of transform AFM images). (FFT) Scale of AFM bars images). are 250 nm.Scale Reprinted bars are 250 from nm. Reference Reprinted [11]. from (Copyr Referenceight (2012) [11]. (CopyrightAmerican Chemical (2012) American Society). Chemical Society).

4.4. Applications Applications in Mesoporous Materials Research interest in ordered porous materials or originatediginated from the successful synthesis of porous silicates in the 1990s 1990s and and soon soon spread spread to to a a variet varietyy of of framework framework compositions compositions including including metal metal oxides, oxides, non-oxide inorganics,inorganics, and and carbon carbon [129 [129].]. This This group group of materials of materials exhibits exhibits periodically periodically aligned structures aligned structuresand uniform and cavities uniform with cavities sizes rangingwith sizes from rangin micro-g from (<2 nm),micro- to (<2 meso- nm), (2–50 to meso- nm), to(2–50 macropores nm), to 2 macropores(>50 nm) [130 (>50], which nm) lead[130], to which very high lead surface to very areas high (up surface to 1500 areas m2/g) (up [131 to 1500]. With m these/g) [131]. unique With features, these uniqueporous materialsfeatures, porous present materials great value present for applications great value infor energy applications conversion in energy and storage conversion [132– 135and], storagecatalysis [132–135], [136], drug catalysis delivery [136], [137 ],drug gas capturedelivery [ 138[137],,139 gas], and capture water [138,139], purification and [140 water,141 purification]. [140,141].As mentioned in the previous section, the self-assembly of BCPs may induce a series of interesting 2D orAs 3D mentioned morphologies, in the which previous make section, them very the usefulself-assembly as structure-directing of BCPs may “templates”induce a series for theof interestingfabrication 2D of or porous 3D morphologies, materials. Generally, which make the them formation very useful of porous as structure-directing materials through “templates” polymer fortemplating the fabrication involves of porous the following materials. steps: Generally, (1) Cooperative the formation self-assembly of porous ofmaterials amphiphilic through BCPs polymer in the templatingpresence of ainvolves precursor the for following the framework steps: (1) (such Coop as hydrolyzederative self-assembly silicate, metal of amphiphilic oxides, or carbon BCPs source)in the presencewhere the of precursor a precursor is directed for the to framework the hydrophilic (such domain as hydrolyzed through hydrogensilicate, metal bonding, oxides, ion or pairing carbon or source)hydrophilic where interactions; the precursor (2) solidification/condensation/crosslinking/curing is directed to the hydrophilic domain through hydrogen of the precursor bonding, to form ion pairingthe framework or hydrophilic of the porous interactions; material; and(2) (3)solidification/condensation/crosslinking/curing removal of the BCP template by solvent washing of the or precursorthermal decomposition to form the framework leaving spaces of the for porous pores. However,material; and the specific(3) removal procedures of the varyBCP basedtemplate on theby solventfinal shape washing of the porousor thermal material, decomposition namely membranes, leaving spheres,spaces orfor monoliths, pores. However, and detailed the examples specific procedureswill be given vary below. based on the final shape of the porous material, namely membranes, spheres, or monoliths,The most and commonly detailed examples used copolymer will be given template below. are the commercial Pluronic surfactants, a group of poly(ethyleneThe most commonly glycol-b-propylene used copolymer glycol- btemplate-ethylene are glycol) the commercial (PEG-b-PPG- Pluronicb-PEG) surfactants, with limited a options group offor poly(ethylene lengths of polymer glycol- blocks.b-propylene Alternatively, glycol- amphiphilicb-ethylene glycol) BCPs with(PEG- widerb-PPG- choicesb-PEG) for with composition limited optionsand molecular for lengths weight of of polymer the polymer blocks. segments Alternativ are readilyely, amphiphilic designed and BCPs synthesized with wider in the choices laboratory for compositionthrough controlled/“living” and molecular weight polymerization of the polymer techniques segments [142]. are These readily synthesized designed BCPs and usuallysynthesized contain in thepoly(2-vinylpyridine) laboratory through (P2VP),controlled/“living” poly(4-vinylpyridine) polymerization (P4VP), techniques or poly(ethylene [142]. These oxide) synthesized (PEO) asBCPs the usuallyhydrophilic contain block, poly(2-vinylpyridine) and PS, PMMA, PI, (P2VP), polyisobutylene poly(4-vinylpyridine) (PIB), and (P4VP), or poly(ethylene (PAN) oxide) as the (PEO)hydrophobic as the blockhydrophilic [143,144 block,]. In addition and PS, to PMMA, high versatility, PI, polyisobutylene BCPs synthesized (PIB), inand the polyacrylonitrile laboratory show (PAN)other merits as the as hydrophobic compared to block commercial [143,144]. Pluronic In additi copolymers.on to high The versatility, contrast inBCPs hydrophilicity synthesized between in the laboratorythe two selected show blocksother merits are usually as compared higher than to co formmercial the PEG Pluronic and PPG copolymers. pair in the Pluronics,The contrast which in hydrophilicity between the two selected blocks are usually higher than for the PEG and PPG pair in the Pluronics, which is beneficial for the self-assembly of polymer micelles in aqueous solution. Moreover, hydrophobic blocks such as PS and PMMA exhibit much higher glass transition

Polymers 2017, 9, 494 21 of 31 is beneficial for the self-assembly of polymer micelles in aqueous solution. Moreover, hydrophobic blocks such as PS and PMMA exhibit much higher glass transition temperatures than PPG, resulting Polymers 2017, 9, 494 21 of 31 in better stability of the self-assembled structures. In the case of copolymers containing PS and PAN, the hydrophobictemperatures segmentsthan PPG,can resulting be converted in better tostabilit carbony of residue the self-assembled in high yield structures. in the carbonization In the case of step, whichcopolymers provides additionalcontaining PS mechanical and PAN, supportthe hydrophobi to thec mesoporous segments can framework be converted [145 to carbon]. residue Evaporation-inducedin high yield in the carbonization self-assembly step, (EISA) which isprovides widely additional used in mechanical the preparation support ofto orderedthe mesoporousmesoporous films framework and particles, [145]. which is especially important for oxides. In a typical EISA process, the cooperativeEvaporation-induced self-assembly of aself-assembly precursor with (EISA) an amphiphilic is widely used template in the is inducedpreparation by aof concentration ordered mesoporous films and particles, which is especially important for oxides. In a typical EISA process, gradient of an organic solvent such as tetrahydrofuran (THF), chloroform, or dioxane. Different from the cooperative self-assembly of a precursor with an amphiphilic template is induced by a a generalconcentration solvent-annealing gradient of an process, organic solvent precursor such molecules as tetrahydrofuran are crosslinked (THF), chloroform, in EISA or as dioxane. the solvent evaporates,Different leaving from a general no chance solvent-annealing for structure process, refinement precursor after molecules it is formed are crosslinked [146,147]. in Wiesner EISA as et al. synthesizedthe solvent mesostructured evaporates, leaving silicate/copolymer no chance for structure composite refinement film through after EISAit is formed with PS-[146,147].b-PEO as a structure-directingWiesner et al. synthesized agent in a mesost mixtureructured of THF silicate/copolymer and water [148 composite]. A large film variety through of mesoporous EISA with PS- metal oxidesb-PEO in the as forma structure-directing of powder were agent synthesized in a mixture through of THF EISA and water using [148]. commercial A large Pluronicsvariety of as a templatemesoporous [149]. In metal addition, oxides mesoporous in the form of carbon powder films were weresynthesized prepared through via EISA EISA fromusing acommercial thermosetting precursorPluronics (phenol-formaldehyde as a template [149]. In system,addition, resol,mesoporous resorcinol, carbon etc.) films using were prepared a variety via of EISA BCP from templates a thermosetting precursor (phenol-formaldehyde system, resol, resorcinol, etc.) using a variety of BCP such as PS-b-P4VP, PEO-b-PS, PEO-b-PMMA, and PEO-b-PMMA-b-PS [143]. Recently, Wei and templates such as PS-b-P4VP, PEO-b-PS, PEO-b-PMMA, and PEO-b-PMMA-b-PS [143]. Recently, Wei coworkers reported the synthesis of nitrogen-doped mesoporous carbon in the form of powder and coworkers reported the synthesis of nitrogen-doped mesoporous carbon in the form of powder throughthrough EISA, EISA, using using Pluoric Pluoric copolymer copolymer as as the the templa template,te, with with resol resol and dicyandiamide and dicyandiamide as sources as sourcesfor for CC and and N, respectively respectively [147]. [147 For]. clarification, For clarification, some research some researchgroups do groupsnot consider do notsystems consider involving systems involvingformaldehyde formaldehyde as an asactual an actual EISA EISAprocess, process, since sincethe crosslinking the crosslinking of precursors of precursors occurs occurs after afterthe the cooperativecooperative self-assembly, self-assembly, instead instead of of simultaneously, simultaneously, asas in many EISA EISA processes processes [146]. [146 ]. FollowingFollowing the the traditional traditional EISA EISA method, method, anan evaporation-inducedevaporation-induced aggregation aggregation assembly assembly (EIAA) (EIAA) mechanism,mechanism, was proposedwas proposed [150 ].[150]. This solutionThis solution precipitation precipitation method method can producecan produce mesoporous mesoporous materials with variousmaterials shapes with various including shapes spheres, including fibers, spheres, and fi polyhedronsbers, and polyhedrons in the form in the of form powder of powder [151]. [151]. Moreover, Moreover, the EIAA method tolerates a greater portion of water compared to EISA, which makes it the EIAA method tolerates a greater portion of water compared to EISA, which makes it more suitable more suitable for scaling up. In detail, the water-insoluble template PEO-b-PMMA and silica for scaling up. In detail, the water-insoluble template PEO-b-PMMA and silica precursor were first precursor were first dissolved in a mixture of THF and water. As THF evaporated, the BCP and dissolvedsilicate in oligomers a mixture were of THF driven and to water.form composite As THF evaporated,micelles with thesilicates BCP located and silicate at the oligomersshell. With were drivenfurther to form removal composite of the micelles solvent, withthe micelles silicates assembled located at into the shell.mesostructured With further particles removal at the of liquid- the solvent, the micellesliquid interface assembled and intoprecipitated mesostructured from the particles solution. atSubsequent the liquid-liquid calcination interface of the andprecipitants precipitated fromcompletely the solution. removed Subsequent the PMMA calcination block to of form the precipitantspores. A schematic completely illustration removed of EIAA the PMMAis shown block in to formFigure pores. 20. A schematic illustration of EIAA is shown in Figure 20.

FigureFigure 20. ( A20.) Formation(A) Formation mechanism mechanism of of orderedordered mesoporous mesoporous silica silica through through the solvent the solvent evaporation evaporation - -inducedinduced aggregating aggregating assembly assembly (EIAA) (EIAA) process process by using by using diblock diblock copolymer copolymer PEO- PEO-b-PMMAb-PMMA as a template,as a tetraethylorthosilicatetemplate, tetraethylorthosilicate (TEOS) as the (TEOS) silica source, as the si andlica acidic source, tetrahydrofuran and acidic tetrahydrofuran (THF)/H2O (THF)/H mixture2O as the solvent;mixture (B) Typical as the solvent; field-emission (B) Typical scanning field-emission electron scanning microscopy electron (FESEM) microscopy image (FESEM) of mesoporous image of silica calcinatedmesoporous in air at silica 550 ◦ calcinatedC. Reprinted in fromair at Reference550 °C. Reprinted [150]. (Copyright from Reference (2011) American[150]. (Copyright Chemical (2011) Society). American Chemical Society).

Polymers 2017, 9, 494 22 of 31 Polymers 2017, 9, 494 22 of 31 More recently, Tang et al. proposed a facile method to synthesize N-doped mesoporous carbonMore spheres recently, without Tang the et al.EISA proposed process a (Figure facile micelle 21). The method key difference to synthesize of this N-doped research mesoporous from EISA liescarbon in the spheres formation without of thestable EISA micelles process of (Figure dopamine 21). The(both key C differenceand N sources) of this using research a high from molecular EISA lies weightin the formation PS-b-PEO of as stable a template. micelles After of dopamine the micelle (both was C and formed, N sources) dopamine using was a high polymerized molecular weight using ammoniaPS-b-PEO as aan template. initiator. AfterThese the “frozen” micelle micelles was formed, joined dopamine together wasforming polymerized into larger using spheres ammonia with sizesas an initiator.around 200 These nm. “frozen” These composite micelles joined spheres together were formingeasily separated into larger from spheres the withsolution sizes through around centrifugation200 nm. These compositeand allowed spheres for werefurther easily carboni separatedzation from to theremove solution the through template centrifugation and fabricate and mesoporousallowed for further spheres carbonization [152]. to remove the template and fabricate mesoporous spheres [152].

Figure 21. Synthesis of nitrogen-doped mesoporous carbon spheres (NMCS) with extra-large pores through the assemblyassembly ofof diblockdiblock copolymercopolymer micelles.micelles. Reprinted from ReferenceReference [[152].152]. (Copyright (2015) WILEY-VCH VerlagVerlag GmbHGmbH && Co.Co. KGaA,KGaA, Weinheim).Weinheim).

Many studies demonstrated the advantage of mesopores over micropores in the mass transport process in a variety of applications [[135,153].135,153]. Larger pore size facilitates a more efficient efficient diffusion of guest moleculesmolecules within within the the pores pores [136 [136],], and and also allowsalso allows the loading the loading of metal of catalyst metal particlescatalyst [particles154,155]. Thick[154,155]. pore Thick walls pore are alsowalls favorable are also favorable because of because the possibility of the possibility for further for modification further modification on the pore on thesurface pore [ 151surface,155]. [151,155]. Since the pores are produced from the calcinatio calcinationn of the hydrophobic segment of of the the BCP, BCP, high molecular weight of the sacrificial sacrificial block is highly desired. Unfortunately, the mesoporous materials templated fromfrom commercial commercial Pluronic Pluronic copolymers copolymers show sh aow pore a pore size limited size limited to 12 nm to and12 nm a wall and thickness a wall thicknessno more thanno more 6 nm than [151 6]. nm BCPs [151]. with BCPs higher with molecular higher molecular weight inweight the sacrificial in the sacrificial segment segment (higher (higherhydrophobic hydrophobic volume involume the copolymer) in the copolymer) have been have extensively been extensively utilized forutilized larger for pores larger in thepores resulting in the w porousresulting material. porous material. Using PEO- Usingb-PS PEO- (Mwb=-PS 29,700 (M = g/mol) 29,700 asg/mol) the copolymer as the copolymer template, template, adding adding a special a specialhydrothermal hydrothermal treatment treatment step, Deng step, et Deng al. achieved et al. ac mesoporoushieved mesoporous silica with silica pore with diameters pore diameters as large as large30.8 nm as 30.8 [156 ].nm By [156]. varying By varying the lengths the oflengths each segmentof each segment of BCP templates, of BCP templates, Tang et al.Tang observed et al. observed a strong a strong correlation of the resulting pore size with the length of BCP, where PS37-b-PEO114, PS178-b- correlation of the resulting pore size with the length of BCP, where PS37-b-PEO114, PS178-b-PEO886, PEO886, and PS173-b-PEO170 resulted in pore sizes of 5.4 nm, 16 nm and 16 nm, respectively [152]. In and PS173-b-PEO170 resulted in pore sizes of 5.4 nm, 16 nm and 16 nm, respectively [152]. In another anothercase, aluminum-organophosphonate case, aluminum-organophosphonate films with films tunable with macropores tunable macropores (30–200 nm) (30–200 were synthesized nm) were viasynthesized ultra-high via molecular ultra-high weight molecular PEO-b -PSweight (250,000 PEO- g/mol)b-PS (250,000 templates, g/mol) though templates, the resulting though material the resultingexhibited material a relatively exhibited disordered a relatively mesostructure disordered [157 mesostructure]. In addition to[157]. utilizing In addition high molecular to utilizing weight high molecularBCPs as templates weight BCPs to target as templates material withto target larger materi pores,al anwith additional larger pores, hydrophobic an additional component hydrophobic can be componentadded to the can mixture be added as a pore to the swelling mixture agent. as a For pore example, swelling with agent. the aidFor of example, trimethylbenzene with the (TMB),aid of trimethylbenzene (TMB), the pore size of silica can be expanded to 30 nm [158]. Moreover, Deng et

Polymers 2017, 9, 494 23 of 31

Polymers 2017, 9, 494 23 of 31 the pore size of silica can be expanded to 30 nm [158]. Moreover, Deng et al. reported the use of PS al.homopolymer reported the asuse the of pore PS homopolymer expanding agent as the in thepore synthesis expanding of mesoporous agent in the carbon,synthesis when of mesoporous PS-b-PEO is carbon,selected when as the PS- templateb-PEO [is159 selected]. However, as the care template must be[159]. taken However, when using care themust pore be expandingtaken when agent using to thethe pore composite expanding in order agent to to avoid the composite the risk of in unstable order to mesostructures avoid the risk of [160 unstable]. mesostructures [160]. TheThe arrangement arrangement of of a amesostructured mesostructured material material is isclosely closely related related to tothe the microphase microphase separation separation of theof theBCP BCP template. template. Interestingly, Interestingly, simply simply varying varying the the amount amount of of the the precursor precursor with with respect respect to to the the copolymercopolymer would would also also lead lead to to morphological morphological chan changesges in in the composite system [148]. [148]. Garcia Garcia and and coworkerscoworkers fully exploredexplored thethe phase phase diagram diagram of of a polymer/alumina/silanea polymer/alumina/silane composite composite system system aimed aimed for forthe the synthesis synthesis of porous of porous aluminosilicate aluminosilicate using using PEO- PEO-b-PIb as-PI a as template. a template. As illustrated As illustrated in Figure in Figure 22, eight 22, eightmorphologies morphologies of the of composite the composite system system were obtained were obtained by adding by differentadding different amounts amounts of the inorganic of the inorganicprecursor precursor into BCP templatesinto BCP templates [161]. Many [161]. interesting Many interesting crystal symmetries crystal symmetries could be could achieved be achieved through throughfine tuning fine the tuning template the template compositions, compositions, and examples and examples are substantially are substantially reviewed reviewed [151]. [151].

FigureFigure 22. 22. TernaryTernary diagram diagram mapping mapping out out the the morphologies morphologies found found forfor various various composites composites directed directed by PI-byb PI--PEOb-PEO using using (3-glycidyloxypropy (3-glycidyloxypropyl)trimethoxysilanel)trimethoxysilane (GLYMO) (GLYMO) and and aluminum aluminum sec-butoxide sec-butoxide as as inorganicinorganic precursors. AtAt thethe bottom bottom of of the the diagram, diagram, schematics schematics of theof the morphologies morphologies found found for thefor purethe purePI-b-PEO PI-b-PEO are shown. are shown. Hatched Hatched areas alongareas thealong PI- bthe-PEO PI- axisb-PEO indicate axis indicate areas where areas no where data wasno data available was availablefrom the diblockfrom the copolymer diblock copolymer diagram. Eachdiagram. white Each region white within region the within diagram the is diagram labeled with is labeled a schematic with arepresenting schematic representing the morphology the morphology of the composites of the formed. composites The yellow formed. (light) The regionsyellow in(light) these regions schematic in thesemorphologies schematic on morphologies the right and on left the are right a representation and left are a representation of the PEO/inorganic of the PEO/inorganic domains. Closed domains. dark Closedpoints ondark a graypoints background on a gray indicate background areas whereindicate biphasic areas where behavior biphasic is observed. behavior Reprinted is observed. from ReprintedReference from [161]. Reference (Copyright [161]. (2009) (Copyrig Americanht (2009) Chemical American Society). Chemical Society).

5.5. Conclusions Conclusions and and Perspectives Perspectives InIn this this review, review, we we have have discussed discussed the the robust robust synthetic synthetic approaches approaches to to well-defined well-defined block block copolymerscopolymers with with controlled controlled compositions compositions and and archit architectures,ectures, in in which which the the sequential sequential addition addition of of controlled/livingcontrolled/ polymerization techniques techniques and and the the combination combination of of controlled controlled polymerization polymerization techniquestechniques with with facile facile coupling coupling chemistry chemistry have have ex expandedpanded the the spectrum spectrum of of available available BCPs. BCPs. One One of of the the mostmost fascinating fascinating features features of of BCPs BCPs is is their their abilit abilityy to to self-assemble self-assemble into into nanoscale nanoscale ordered ordered structures structures withwith various various morphologies morphologies such such as as spheres, spheres, cylinders, cylinders, bicontinuous bicontinuous structures, structures, lamellae, lamellae, etc. etc. Detailed Detailed studystudy both both from from experiments experiments and and theoretical theoretical modeli modelingng has has revealed revealed that that the the nature nature of of morphologies morphologies isis determined determined by by factors factors including including interaction interaction parameter parameter ( (χχ),), degree degree of of polymerization polymerization (N), (N), and and the the volume fraction (f), as well as molecular architecture. Due to these unique features, BCPs have attracted massive attention as thermoplastic elastomers, as drug delivery systems, in soft lithography, as mesoporous materials, and in many other areas.

Polymers 2017, 9, 494 24 of 31 volume fraction (f ), as well as molecular architecture. Due to these unique features, BCPs have attracted massive attention as thermoplastic elastomers, as drug delivery systems, in soft lithography, as mesoporous materials, and in many other areas. These fascinating BCPs with chemical and topological diversity bring new challenges for the establishment of structure-property relationships and novel applications. For instance, BCP materials including rod–coil diblocks and bottlebrush materials should be investigated to create more elaborate nanostructures. Recent advancements in BCP patterning have pushed the limits of feature sizes to both smaller (<5 nm) and larger scales (>50 nm). We expect that these new challenges can be coped with by precisely tunable interactions between blocks in terms of range and strength, which further relies on their precise synthesis and guidance from theory and simulation. Strategical placement of ionic moieties might offer a promising approach. Although significant work has been reported, more interdisciplinary collaborations are still needed in order to advance the synthesis, structural and dynamic characterization, theory and simulation, and to gain a clear picture of BCP structure-property relationships.

Acknowledgments: This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences, and Engineering Division. No funds were provided to cover the costs to publish in open access. Author Contributions: Jimmy W. Mays conceived the topic of this review. Hongbo Feng, Xinyi Lu, and Weiyu Wang designed the structure of this manuscript and reviewed the literature. Hongbo Feng, Xinyi Lu, Weiyu Wang, Nam-Goo Kang and Jimmy W. Mays edited the manuscript. Conflicts of Interest: The authors declare no conflict of interest.

References

1. Hamley, I.W. The Physics of Block Copolymers; Oxford University Press: New York, NY, USA, 1998; Volume 19. 2. Hadjichristidis, N.; Iatrou, H.; Pitsikalis, M.; Mays, J. Macromolecular architectures by living and controlled/living polymerizations. Prog. Polym. Sci. 2006, 31, 1068–1132. [CrossRef] 3. Uhrig, D.; Mays, J.W. Experimental techniques in high-vacuum anionic polymerization. J. Polym. Sci. Part A Polym. Chem. 2005, 43, 6179–6222. [CrossRef] 4. Zhang, H.; Hong, K.; Mays, J.W. Synthesis of block copolymers of styrene and methyl methacrylate by conventional free radical polymerization in room temperature ionic liquids. Macromolecules 2002, 35, 5738–5741. [CrossRef] 5. Uhrig, D.; Mays, J.W. Synthesis of combs, centipedes, and barbwires: Poly (isoprene-graft-styrene) regular multigraft copolymers with trifunctional, tetrafunctional, and hexafunctional branch points. Macromolecules 2002, 35, 7182–7190. [CrossRef] 6. Hong, K.; Uhrig, D.; Mays, J.W. Living anionic polymerization. Curr. Opin. Solid State Mater. Sci. 1999, 4, 531–538. [CrossRef] 7. Pochan, D.J.; Gido, S.P.; Pispas, S.; Mays, J.W.; Ryan, A.J.; Fairclough, J.P.A.; Hamley, I.W.; Terrill, N.J. Morphologies of microphase-separated A2B simple graft copolymers. Macromolecules 1996, 29, 5091–5098. [CrossRef] 8. Bates, F.S.; Fredrickson, G.H. Block copolymers—Designer soft materials. Phys. Today 1999, 52, 32–38. [CrossRef] 9. Lennon, E.M.; Katsov, K.; Fredrickson, G.H. Free energy evaluation in field-theoretic polymer simulations. Phys. Rev. Lett. 2008, 101, 138302. [CrossRef][PubMed] 10. Matsen, M.W.; Bates, F.S. Origins of complex self-assembly in block copolymers. Macromolecules 1996, 29, 7641–7644. [CrossRef] 11. Poelma, J.E.; Ono, K.; Miyajima, D.; Aida, T.; Satoh, K.; Hawker, C.J. Cyclic block copolymers for controlling feature sizes in block copolymer lithography. ACS Nano 2012, 6, 10845–10854. [CrossRef][PubMed] 12. Kim, H.-C.; Park, S.-M.; Hinsberg, W.D. Block copolymer based nanostructures: Materials, processes, and applications to electronics. Chem. Rev. 2009, 110, 146–177. [CrossRef][PubMed] 13. Hawker, C.J.; Wooley, K.L. The convergence of synthetic organic and polymer chemistries. Science 2005, 309, 1200–1205. [CrossRef][PubMed] Polymers 2017, 9, 494 25 of 31

14. Fan, F.; Wang, W.Y.; Holt, A.P.; Feng, H.B.; Uhrig, D.; Lu, X.Y.; Hong, T.; Wang, Y.Y.; Kang, N.G.; Mays, J.; et al. Effect of molecular weight on the ion transport mechanism in polymerized ionic liquids. Macromolecules 2016, 49, 4557–4570. [CrossRef] 15. Matyjaszewski, K.; Spanswick, J. Controlled/living radical polymerization. Mater. Today 2005, 8, 26–33. [CrossRef] 16. Matyjaszewski, K.; Sumerlin, B.S.; Tsarevsky, N.V. Progress in Controlled Radical Polymerization: Mechanisms and Techniques; ACS Symposium Series; American Chemical Society: Washington, DC, USA, 2012. 17. Braunecker, W.A.; Matyjaszewski, K. Controlled/living radical polymerization: Features, developments, and perspectives. Prog. Polym. Sci. 2007, 32, 93–146. [CrossRef] 18. Gody, G.; Zetterlund, P.B.; Perrier, S.; Harrisson, S. The limits of precision monomer placement in chain growth polymerization. Nat. Commun. 2016, 7, 10514. [CrossRef][PubMed] 19. Cao, P.-F.; Wojnarowska, Z.; Hong, T.; Carroll, B.; Li, B.; Feng, H.; Parsons, L.; Wang, W.; Lokitz, B.S.; Cheng, S.; et al. A star-shaped single lithium-ion conducting copolymer by grafting a poss nanoparticle. Polymer 2017, 124, 117–127. [CrossRef] 20. Wang, J.-S.; Matyjaszewski, K. “Living”/controlled radical polymerization. Transition-metal-catalyzed atom transfer radical polymerization in the presence of a conventional radical initiator. Macromolecules 1995, 28, 7572–7573. [CrossRef] 21. Nicolas, J.; Guillaneuf, Y.; Lefay, C.; Bertin, D.; Gigmes, D.; Charleux, B. Nitroxide-mediated polymerization. Prog. Polym. Sci. 2013, 38, 63–235. [CrossRef] 22. Orilall, M.C.; Wiesner, U. Block copolymer based composition and morphology control in nanostructured hybrid materials for energy conversion and storage: Solar cells, batteries, and fuel cells. Chem. Soc. Rev. 2011, 40, 520–535. [CrossRef][PubMed] 23. Li, C.; Tang, Y.; Armes, S.P.; Morris, C.J.; Rose, S.F.; Lloyd, A.W.; Lewis, A.L. Synthesis and characterization of biocompatible thermo-responsive gelators based on aba triblock copolymers. Biomacromolecules 2005, 6, 994–999. [CrossRef][PubMed] 24. Ding, H.J.; Park, S.; Zhong, M.J.; Pan, X.C.; Pietrasik, J.; Bettinger, C.J.; Matyjaszewski, K. Facile arm-first synthesis of star block copolymers via arget atrp with ppm amounts of catalyst. Macromolecules 2016, 49, 6752–6760. [CrossRef] 25. Min, K.; Gao, H.; Matyjaszewski, K. Preparation of homopolymers and block copolymers in miniemulsion by atrp using activators generated by electron transfer (aget). J. Am. Chem. Soc. 2005, 127, 3825–3830. [CrossRef] [PubMed] 26. Min, K.; Gao, H.; Matyjaszewski, K. Use of ascorbic acid as reducing agent for synthesis of well-defined polymers by arget atrp. Macromolecules 2007, 40, 1789–1791. [CrossRef] 27. Kwak, Y.; Matyjaszewski, K. Arget atrp of methyl methacrylate in the presence of nitrogen-based ligands as reducing agents. Polym. Int. 2009, 58, 242–247. [CrossRef] 28. Siegwart, D.J.; Oh, J.K.; Matyjaszewski, K. Atrp in the design of functional materials for biomedical applications. Prog. Polym. Sci. 2012, 37, 18–37. [CrossRef][PubMed] 29. Sugihara, S.; Sugihara, K.; Armes, S.P.; Ahmad, H.; Lewis, A.L. Synthesis of biomimetic poly (2-(methacryloyloxy) ethyl phosphorylcholine) nanolatexes via atom transfer radical dispersion polymerization in alcohol/water mixtures. Macromolecules 2010, 43, 6321–6329. [CrossRef] 30. Ding, A.; Lu, G.; Guo, H.; Huang, X. Double-bond-containing polyallene-based triblock copolymers via phenoxyallene and (meth)acrylate. Sci. Rep. 2017, 7, 43706. [CrossRef][PubMed] 31. Chong, Y.; Le, T.P.; Moad, G.; Rizzardo, E.; Thang, S.H. A more versatile route to block copolymers and other polymers of complex architecture by living radical polymerization: The raft process. Macromolecules 1999, 32, 2071–2074. [CrossRef] 32. You, Y.; Hong, C.; Wang, W.; Lu, W.; Pan, C. Preparation and characterization of thermally responsive and biodegradable block copolymer comprised of pnipaam and pla by combination of rop and raft methods. Macromolecules 2004, 37, 9761–9767. [CrossRef] 33. Chaduc, I.; Zhang, W.; Rieger, J.; Lansalot, M.; D’Agosto, F.; Charleux, B. Amphiphilic block copolymers from a direct and one-pot raft synthesis in water. Macromol. Rapid Commun. 2011, 32, 1270–1276. [CrossRef] [PubMed] 34. Wang, X.; Luo, Y.; Li, B.; Zhu, S. Ab initio batch emulsion raft polymerization of styrene mediated by poly(acrylic acid-b-styrene) trithiocarbonate. Macromolecules 2009, 42, 6414–6421. [CrossRef] Polymers 2017, 9, 494 26 of 31

35. Luo, Y.; Wang, X.; Li, B.-G.; Zhu, S. Toward well-controlled ab initio raft emulsion polymerization of styrene mediated by 2-(((dodecylsulfanyl)carbonothioyl)sulfanyl)propanoic acid. Macromolecules 2011, 44, 221–229. [CrossRef] 36. Luo, Y.; Wang, X.; Zhu, Y.; Li, B.-G.; Zhu, S. Polystyrene-block-poly (n-butyl acrylate)-block-polystyrene triblock copolymer synthesized via raft emulsion polymerization. Macromolecules 2010, 43, 7472–7481. [CrossRef] 37. Benoit, D.; Harth, E.; Fox, P.; Waymouth, R.M.; Hawker, C.J. Accurate structural control and block formation in the living polymerization of 1, 3-dienes by nitroxide-mediated procedures. Macromolecules 2000, 33, 363–370. [CrossRef] 38. Szwarc, M.; Levy, M.; Milkovich, R. Polymerization initiated by electron transfer to monomer. A new method of formation of block polymers1. J. Am. Chem. Soc. 1956, 78, 2656–2657. [CrossRef] 39. Szwarc, M. ‘Living’ polymers. Nature 1956, 178, 1168–1169. [CrossRef] 40. Pitsikalis, M.; Pispas, S.; Mays, J.W.; Hadjichristidis, N. Nonlinear block copolymer architectures. In Blockcopolymers-Polyelectrolytes-Biodegradation; Springer: Berlin, Germany, 1998; 137p. 41. Hirao, A.; Loykulnant, S.; Ishizone, T. Recent advance in living anionic polymerization of functionalized styrene derivatives. Prog. Polym. Sci. 2002, 27, 1399–1471. [CrossRef] 42. Matsuo, A.; Watanabe, T.; Hirao, A. Synthesis of well-defined dendrimer-like branched polymers and block copolymer by the iterative approach involving coupling reaction of living anionic polymer and functionalization. Macromolecules 2004, 37, 6283–6290. [CrossRef] 43. Advincula, R.; Zhou, Q.; Park, M.; Wang, S.; Mays, J.; Sakellariou, G.; Pispas, S.; Hadjichristidis, N. Polymer brushes by living anionic surface initiated polymerization on flat silicon (sio x) and gold surfaces: Homopolymers and block copolymers. Langmuir 2002, 18, 8672–8684. [CrossRef] 44. Hirao, A.; Hayashi, M.; Haraguchi, N. Synthesis of well-defined functionalized polymers and star branched polymers by means of living anionic polymerization using specially designed 1,1-diphenylethylene derivatives. Macromol. Rapid Commun. 2000, 21, 1171–1184. [CrossRef] 45. Zhou, Q.; Fan, X.; Xia, C.; Mays, J.; Advincula, R. Living anionic surface initiated polymerization (sip) of styrene from clay surfaces. Chem. Mater. 2001, 13, 2465–2467. [CrossRef] 46. Wojnarowska, Z.; Feng, H.; Fu, Y.; Cheng, S.; Carroll, B.; Kumar, R.; Novikov, V.N.; Kisliuk, A.M.; Saito, T.; Kang, N.-G.; et al. Effect of chain rigidity on the decoupling of ion motion from segmental relaxation in polymerized ionic liquids: Ambient and elevated pressure studies. Macromolecules 2017, 50, 6710–6721. [CrossRef] 47. Wojnarowska, Z.; Feng, H.; Diaz, M.; Ortiz, A.; Ortiz, I.; Knapik-Kowalczuk, J.; Vilas, M.; Verdía, P.; Tojo, E.; Saito, T. Revealing the charge transport mechanism in polymerized ionic liquids: Insight from high pressure conductivity studies. Chem. Mater. 2017.[CrossRef] 48. Matsuo, Y.; Konno, R.; Ishizone, T.; Goseki, R.; Hirao, A. Precise synthesis of block polymers composed of three or more blocks by specially designed linking methodologies in conjunction with living anionic polymerization system. Polymers 2013, 5, 1012–1040. [CrossRef] 49. Hadjichristidis, N.; Pitsikalis, M.; Pispas, S.; Iatrou, H. Polymers with complex architecture by living anionic polymerization. Chem. Rev. 2001, 101, 3747–3792. [CrossRef][PubMed] 50. Ekizoglou, N.; Hadjichristidis, N. Synthesis of model linear tetrablock quaterpolymers and pentablock quintopolymers of ethylene oxide. J. Polym. Sci. Part A Polym. Chem. 2002, 40, 2166–2170. [CrossRef] 51. Bellas, V.; Iatrou, H.; Pitsinos, E.N.; Hadjichristidis, N. Heterofunctional linking agents for the synthesis of well-defined block copolymers of dimethylsiloxane and tert-butyl methacrylate or 2-vinylpyridine. Macromolecules 2001, 34, 5376–5378. [CrossRef] 52. Iatrou, H.; Mays, J.W.; Hadjichristidis, N. Regular comb and graft polyisoprene/polystyrene copolymers with double branches (“centipedes”). Quality of (1,3-phenylene) bis (3-methyl-1-phenylpentylidene) dilithium initiator in the presence of polar additives. Macromolecules 1998, 31, 6697–6701. [CrossRef] 53. Quirk, R.P.; Yoo, T.; Lee, Y.; Kim, J.; Lee, B. Applications of 1,1-diphenylethylene chemistry in anionic synthesis of polymers with controlled structures. In Biopolymers PVA , Anionic Polymerisation ; Springer: Berlin, Germany, 2000; pp. 67–162. 54. Handlin, D.L.; Hansen, D.R.; Wright, K.J.; Trenor, S.R. Industrial applications. In Controlled and Living Polymerizations: From Mechanisms to Applications; John Wiley & Sons: Weinheim, Germany, 2010; pp. 555–603. Polymers 2017, 9, 494 27 of 31

55. Wang, H.; Lu, W.; Wang, W.; Shah, P.N.; Misichronis, K.; Kang, N.-G.; Mays, J.W. Design and synthesis of multigraft copolymer thermoplastic elastomers: Superelastomers. Macromol. Chem. Phys. 2017.[CrossRef] 56. Aydogan, C.; Kutahya, C.; Allushi, A.; Yilmaz, G.; Yagci, Y. Block copolymer synthesis in one shot: Concurrent metal-free atrp and rop processes under sunlight. Polym. Chem. 2017, 8, 2899–2903. [CrossRef] 57. Opsteen, J.A.; van Hest, J.C. Modular synthesis of block copolymers via cycloaddition of terminal azide and alkyne functionalized polymers. Chem. Commun. (Camb.) 2005, 57–59. [CrossRef][PubMed] 58. Yamamoto, T.; Tezuka, Y. Topological : A cyclic approach toward novel polymer properties and functions. Polym. Chem. 2011, 2, 1930–1941. [CrossRef] 59. Keddie, D.J. A guide to the synthesis of block copolymers using reversible-addition fragmentation chain transfer (raft) polymerization. Chem. Soc. Rev. 2014, 43, 496–505. [CrossRef][PubMed] 60. Inglis, A.J.; Sinnwell, S.; Davis, T.P.; Barner-Kowollik, C.; Stenzel, M.H. Reversible addition fragmentation chain transfer (raft) and hetero-diels–alder chemistry as a convenient conjugation tool for access to complex macromolecular designs. Macromolecules 2008, 41, 4120–4126. [CrossRef] 61. Lohmeijer, B.G.; Schubert, U.S. Supramolecular engineering with macromolecules: An alternative concept for block copolymers. Angew. Chem. Int. Ed. 2002, 41, 3825–3829. [CrossRef] 62. Guo, Z.; Zhang, G.; Qiu, F.; Zhang, H.; Yang, Y.; Shi, A.-C. Discovering ordered phases of block copolymers: New results from a generic fourier-space approach. Phys. Rev. Lett. 2008, 101, 028301. [CrossRef][PubMed] 63. Förster, S.; Plantenberg, T. From self-organizing polymers to nanohybrid and . Angew. Chem. Int. Ed. 2002, 41, 688–714. [CrossRef] 64. Kim, J.K.; Yang, S.Y.; Lee, Y.; Kim, Y. Functional nanomaterials based on block copolymer self-assembly. Prog. Polym. Sci. 2010, 35, 1325–1349. [CrossRef] 65. Bates, F.S. Polymer-polymer phase behavior. Science 1991, 251, 898–905. [CrossRef][PubMed] 66. Matsen, M.W.; Schick, M. Stable and unstable phases of a diblock copolymer melt. Phys. Rev. Lett. 1994, 72, 2660–2663. [CrossRef][PubMed] 67. Honeker, C.C.; Thomas, E.L. Impact of morphological orientation in determining mechanical properties in triblock copolymer systems. Chem. Mater. 1996, 8, 1702–1714. [CrossRef] 68. DeRouchey, J.; Thurn-Albrecht, T.; Russell, T.; Kolb, R. Block copolymer domain reorientation in an electric field: An in-situ small-angle x-ray scattering study. Macromolecules 2004, 37, 2538–2543. [CrossRef] 69. Mai, Y.; Eisenberg, A. Self-assembly of block copolymers. Chem. Soc. Rev. 2012, 41, 5969–5985. [CrossRef] [PubMed] 70. Storey, R.F.; Baugh, D. Poly (styrene-b-isobutylene-b-styrene) block copolymers and therefrom: Morphology as determined by small-angle x-ray scattering and transmission electron microscopy. Polymer 2000, 41, 3205–3211. [CrossRef] 71. Elabd, Y.A.; Napadensky, E.; Walker, C.W.; Winey, K.I. Transport properties of sulfonated poly (styrene-b-isobutylene-b-styrene) triblock copolymers at high ion-exchange capacities. Macromolecules 2006, 39, 399–407. [CrossRef] 72. Goswami, M.; Sumpter, B.G.; Huang, T.; Messman, J.M.; Gido, S.P.; Isaacs-Sodeye, A.; Mays, J.W. Tunable morphologies from charged block copolymers. Soft Matter 2010, 6, 6146–6154. [CrossRef] 73. Sanoja, G.E.; Popere, B.C.; Beckingham, B.S.; Evans, C.M.; Lynd, N.A.; Segalman, R.A. Structure–conductivity relationships of block copolymer membranes based on hydrated protic polymerized ionic liquids: Effect of domain spacing. Macromolecules 2016, 49, 2216–2223. [CrossRef] 74. Patel, S.N.; Javier, A.E.; Beers, K.M.; Pople, J.A.; Ho, V.; Segalman, R.A.; Balsara, N.P. Morphology and thermodynamic properties of a copolymer with an electronically conducting block: Poly(3-ethylhexylthiophene)-block-poly (ethylene oxide). Nano Lett. 2012, 12, 4901–4906. [CrossRef] [PubMed] 75. Robbins, S.W.; Beaucage, P.A.; Sai, H.; Tan, K.W.; Werner, J.G.; Sethna, J.P.; DiSalvo, F.J.; Gruner, S.M.; Van Dover, R.B.; Wiesner, U. Block copolymer self-assembly-directed synthesis of mesoporous gyroidal superconductors. Sci. Adv. 2016, 2, e1501119. [CrossRef][PubMed] 76. Kim, K.; Schulze, M.W.; Arora, A.; Lewis, R.M.; Hillmyer, M.A.; Dorfman, K.D.; Bates, F.S. Thermal processing of diblock copolymer melts mimics metallurgy. Science 2017, 356, 520–523. [CrossRef][PubMed] 77. Feng, H.; Changez, M.; Hong, K.; Mays, J.W.; Kang, N.-G. 2-isopropenyl-2-oxazoline: Well-defined homopolymers and block copolymers via living anionic polymerization. Macromolecules 2017, 50, 54–62. [CrossRef] Polymers 2017, 9, 494 28 of 31

78. Hamley, I.W. Nanostructure fabrication using block copolymers. Nanotechnology 2003, 14, R39–R54. [CrossRef] 79. Alexandridis, P.; Lindman, B. Amphiphilic Block Copolymers: Self-Assembly and Applications; Elsevier: Amsterdam, The Netherlands, 2000. 80. Blanazs, A.; Armes, S.P.; Ryan, A.J. Self-assembled block copolymer aggregates: From micelles to vesicles and their biological applications. Macromol. Rapid Commun. 2009, 30, 267–277. [CrossRef][PubMed] 81. Zhang, L.; Eisenberg, A. Multiple morphologies and characteristics of “crew-cut” micelle-like aggregates of polystyrene-b-poly (acrylic acid) diblock copolymers in aqueous solutions. J. Am. Chem. Soc. 1996, 118, 3168–3181. [CrossRef] 82. Wang, X.; Guerin, G.; Wang, H.; Wang, Y.; Manners, I.; Winnik, M.A. Cylindrical block copolymer micelles and co-micelles of controlled length and architecture. Science 2007, 317, 644–647. [CrossRef][PubMed] 83. Honda, S.; Yamamoto, T.; Tezuka, Y. Topology-directed control on thermal stability: Micelles formed from linear and cyclized amphiphilic block copolymers. J. Am. Chem. Soc. 2010, 132, 10251–10253. [CrossRef] [PubMed] 84. Jain, S.; Bates, F.S. On the origins of morphological complexity in block copolymer surfactants. Science 2003, 300, 460–464. [CrossRef][PubMed] 85. Wang, W. Novel Thermoplastic Elastomers Based on Benzofulvene: Synthesis and Mechanical Properties. Ph.D. Thesis, University of Tennessee, Knoxville, TN, USA, 2015. 86. Bhowmick, A.K.; Stephens, H. Handbook of Elastomers; CRC Press: New York, NY, USA, 2000. 87. Hadjichristidis, N.; Pispas, S.; Floudas, G. Block Copolymers: Synthetic Strategies, Physical Properties, and Applications; John Wiley & Sons: Hoboken, NJ, USA, 2003. 88. Xenidou, M.; Hadjichristidis, N. Synthesis of model multigraft copolymers of butadiene with randomly placed single and double polystyrene branches. Macromolecules 1998, 31, 5690–5694. [CrossRef] 89. Fetters, L.J.; Morton, M. Synthesis and properties of block polymers. I. Poly-α-methylstyrene- polyisoprene-poly-α-methylstyrene. Macromolecules 1969, 2, 453–458. [CrossRef] 90. Bolton, J.M.; Hillmyer, M.A.; Hoye, T.R. Sustainable thermoplastic elastomers from terpene-derived monomers. ACS Macro Lett. 2014, 3, 717–720. [CrossRef] 91. Fetters, L.; Firer, E.; Dafauti, M. Synthesis and properties of block copolymers. 4. Poly(p-tert- butylstyrene-diene-p-tert-butylstyrene) and poly (p-tert-butylstyrene-isoprene-styrene). Macromolecules 1977, 10, 1200–1207. [CrossRef] 92. Wang, W.Y.; Schlegel, R.; White, B.T.; Williams, K.; Voyloy, D.; Steren, C.A.; Goodwin, A.; Coughlin, E.B.; Gido, S.; Beiner, M.; et al. High temperature thermoplastic elastomers synthesized by living anionic polymerization in hydrocarbon solvent at room temperatuie. Macromolecules 2016, 49, 2646–2655. [CrossRef] 93. Lu, W.; Wang, Y.; Wang, W.; Cheng, S.; Zhu, J.; Xu, Y.; Hong, K.; Kang, N.-G.; Mays, J. All acrylic-based thermoplastic elastomers with high upper service temperature and superior mechanical properties. Polym. Chem. 2017, 8, 5741–5748. [CrossRef] 94. Martín-Gomis, L.; Fernández-García, M.; de la Fuente, J.L.; Madruga, E.L.; Cerrada, M.L. Physical properties of PBMA-b-PBA-b-PBMA triblock copolymers synthesized by atom transfer radical polymerization. Macromol. Chem. Phys. 2003, 204, 2007–2016. [CrossRef] 95. Tong, J.; Leclère, P.; Doneux, C.; Brédas, J.-L.; Lazzaroni, R.; Jérôme, R. Morphology and mechanical properties of poly (methylmethacrylate)-b-poly (alkylacrylate)-b-poly (methylmethacrylate). Polymer 2001, 42, 3503–3514. [CrossRef] 96. Zhu, Y.Q.; Burgaz, E.; Gido, S.P.; Staudinger, U.; Weidisch, R.; Uhrig, D.; Mays, J.W. Morphology and tensile properties of multigraft copolymers with regularly spaced tri-, tetra-, and hexafunctional junction points. Macromolecules 2006, 39, 4428–4436. [CrossRef] 97. Staudinger, U.; Weidisch, R.; Zhu, Y.; Gido, S.; Uhrig, D.; Mays, J.; Iatrou, H.; Hadjichristidis, N. Mechanical properties and hysteresis behaviour of multigraft copolymers. Macromol. Symp. 2006, 233, 42–50. [CrossRef] 98. Wang, W.; Wang, W.; Lu, X.; Bobade, S.; Chen, J.; Kang, N.-G.; Zhang, Q.; Mays, J. Synthesis and characterization of comb and centipede multigraft copolymers PnBA-g-PS with high molecular weight using miniemulsion polymerization. Macromolecules 2014, 47, 7284–7295. [CrossRef] 99. Wang, W.; Wang, W.; Li, H.; Lu, X.; Chen, J.; Kang, N.-G.; Zhang, Q.; Mays, J. Synthesis and characterization of graft copolymers poly (isoprene-g-styrene) of high molecular weight by a combination of anionic polymerization and emulsion polymerization. Ind. Eng. Chem. Res. 2015, 54, 1292–1300. [CrossRef] Polymers 2017, 9, 494 29 of 31

100. Rösler, A.; Vandermeulen, G.W.; Klok, H.-A. Advanced drug delivery devices via self-assembly of amphiphilic block copolymers. Adv. Drug Deliv. Rev. 2012, 64, 270–279. [CrossRef] 101. O’Reilly, R.K.; Hawker, C.J.; Wooley, K.L. Cross-linked block copolymer micelles: Functional nanostructures of great potential and versatility. Chem. Soc. Rev. 2006, 35, 1068–1083. [CrossRef][PubMed] 102. Wei, H.; Cheng, S.-X.; Zhang, X.-Z.; Zhuo, R.-X. Thermo-sensitive polymeric micelles based on poly (n-isopropylacrylamide) as drug carriers. Prog. Polym. Sci. 2009, 34, 893–910. [CrossRef] 103. Lee, H.-N.; Bai, Z.; Newell, N.; Lodge, T.P. Micelle/inverse micelle self-assembly of a peo-pnipam block copolymer in ionic liquids with double thermoresponsivity. Macromolecules 2010, 43, 9522–9528. [CrossRef] 104. Roy, D.; Brooks, W.L.; Sumerlin, B.S. New directions in thermoresponsive polymers. Chem. Soc. Rev. 2013, 42, 7214–7243. [CrossRef][PubMed] 105. Thambi, T.; Son, S.; Lee, D.S.; Park, J.H. Poly(ethylene glycol)-b-poly (lysine) copolymer bearing nitroaromatics for hypoxia-sensitive drug delivery. Acta Biomater. 2016, 29, 261–270. [CrossRef][PubMed] 106. Ahmed, F.; Discher, D.E. Self-porating polymersomes of peg–pla and peg–pcl: Hydrolysis-triggered controlled release vesicles. J. Control. Release 2004, 96, 37–53. [CrossRef][PubMed] 107. Zupancich, J.A.; Bates, F.S.; Hillmyer, M.A. Aqueous dispersions of poly (ethylene oxide)-b-poly (γ-methyl-ε-caprolactone) block copolymers. Macromolecules 2006, 39, 4286–4288. [CrossRef] 108. Meng, F.; Engbers, G.H.; Feijen, J. Biodegradable polymersomes as a basis for artificial cells: Encapsulation, release and targeting. J. Control. Release 2005, 101, 187–198. [CrossRef][PubMed] 109. Ghoroghchian, P.P.; Li, G.; Levine, D.H.; Davis, K.P.; Bates, F.S.; Hammer, D.A.; Therien, M.J. Bioresorbable vesicles formed through spontaneous self-assembly of amphiphilic poly(ethylene oxide)-block-polycaprolactone. Macromolecules 2006, 39, 1673–1675. [CrossRef][PubMed] 110. Discher, B.M.; Bermudez, H.; Hammer, D.A.; Discher, D.E.; Won, Y.-Y.; Bates, F.S. Cross-linked polymersome membranes: Vesicles with broadly adjustable properties. J. Phys. Chem. B 2002, 106, 2848–2854. [CrossRef] 111. Pang, Z.; Lu, W.; Gao, H.; Hu, K.; Chen, J.; Zhang, C.; Gao, X.; Jiang, X.; Zhu, C. Preparation and brain delivery property of biodegradable polymersomes conjugated with ox26. J. Control. Release 2008, 128, 120–127. [CrossRef][PubMed] 112. Bates, C.M.; Maher, M.J.; Janes, D.W.; Ellison, C.J.; Willson, C.G. Block copolymer lithography. Macromolecules 2013, 47, 2–12. [CrossRef] 113. Li, W.; Muller, M. Defects in the self-assembly of block copolymers and their relevance for directed self-assembly. Annu. Rev. Chem Biomol. 2015, 6, 187–216. [CrossRef][PubMed] 114. Seshimo, T.; Maeda, R.; Odashima, R.; Takenaka, Y.; Kawana, D.; Ohmori, K.; Hayakawa, T. Perpendicularly oriented sub-10-nm block copolymer lamellae by atmospheric thermal annealing for one minute. Sci. Rep. 2016, 6, 19481. [CrossRef][PubMed] 115. Maher, M.J.; Rettner, C.T.; Bates, C.M.; Blachut, G.; Carlson, M.C.; Durand, W.J.; Ellison, C.J.; Sanders, D.P.; Cheng, J.Y.; Willson, C.G. Directed self-assembly of silicon-containing block copolymer thin films. ACS Appl. Mater. Interfaces 2015, 7, 3323–3328. [CrossRef][PubMed] 116. Schulze, M.W.; McIntosh, L.D.; Hillmyer, M.A.; Lodge, T.P. High-modulus, high-conductivity nanostructured polymer electrolyte membranes via polymerization-induced phase separation. Nano Lett. 2013, 14, 122–126. [CrossRef][PubMed] 117. Kennemur, J.G.; Hillmyer, M.A.; Bates, F.S. Synthesis, thermodynamics, and dynamics of poly (4-tert-butylstyrene-b-methyl methacrylate). Macromolecules 2012, 45, 7228–7236. [CrossRef] 118. Keen, I.; Yu, A.; Cheng, H.-H.; Jack, K.S.; Nicholson, T.M.; Whittaker, A.K.; Blakey, I. Control of the orientation of symmetric poly (styrene)-block-poly (D,L-lactide) block copolymers using statistical copolymers of dissimilar composition. Langmuir 2012, 28, 15876–15888. [CrossRef][PubMed] 119. Ham, S.; Shin, C.; Kim, E.; Ryu, D.Y.; Jeong, U.; Russell, T.P.; Hawker, C.J. Microdomain orientation of ps-b-pmma by controlled interfacial interactions. Macromolecules 2008, 41, 6431–6437. [CrossRef] 120. Mansky, P.; Liu, Y.; Huang, E.; Russell, T.; Hawker, C. Controlling polymer-surface interactions with random copolymer brushes. Science 1997, 275, 1458–1460. [CrossRef] 121. Mansky, P.; Russell, T.; Hawker, C.; Mays, J.; Cook, D.; Satija, S. Interfacial segregation in disordered block copolymers: Effect of tunable surface potentials. Phys. Rev. Lett. 1997, 79, 237. [CrossRef] 122. Zhao, Y.; Sivaniah, E.; Hashimoto, T. Saxs analysis of the order-disorder transition and the interaction parameter of polystyrene-block-poly (methyl methacrylate). Macromolecules 2008, 41, 9948–9951. [CrossRef] Polymers 2017, 9, 494 30 of 31

123. Park, S.; Lee, D.H.; Xu, J.; Kim, B.; Hong, S.W.; Jeong, U.; Xu, T.; Russell, T.P. Macroscopic 10-terabit–per–square-inch arrays from block copolymers with lateral order. Science 2009, 323, 1030–1033. [CrossRef][PubMed] 124. Rodwogin, M.D.; Spanjers, C.S.; Leighton, C.; Hillmyer, M.A. Polylactide-poly(dimethylsiloxane)-polylactide triblock copolymers as multifunctional materials for nanolithographic applications. ACS Nano 2010, 4, 725–732. [CrossRef][PubMed] 125. Almdal, K.; Hillmyer, M.A.; Bates, F.S. Influence of conformational asymmetry on polymer-polymer interactions: An entropic or enthalpic effect? Macromolecules 2002, 35, 7685–7691. [CrossRef] 126. Yoshida, H.; Suh, H.S.; Ramirez-Herunandez, A.; Lee, J.I.; Aida, K.; Wan, L.; Ishida, Y.; Tada, Y.; Ruiz, R.; de Pablo, J. Topcoat approaches for directed self-assembly of strongly segregating block copolymer thin films. J. Photopolym. Sci. Technol. 2013, 26, 55–58. [CrossRef] 127. Cushen, J.D.; Otsuka, I.; Bates, C.M.; Halila, S.; Fort, S.; Rochas, C.; Easley, J.A.; Rausch, E.L.; Thio, A.; Borsali, R.; et al. Oligosaccharide/silicon-containing block copolymers with 5 nm features for lithographic applications. ACS Nano 2012, 6, 3424–3433. [CrossRef][PubMed] 128. Bates, C.M.; Seshimo, T.; Maher, M.J.; Durand, W.J.; Cushen, J.D.; Dean, L.M.; Blachut, G.; Ellison, C.J.; Willson, C.G. Polarity-switching top coats enable orientation of sub-10-nm block copolymer domains. Science 2012, 338, 775–779. [CrossRef][PubMed] 129. Ma, T.-Y.; Liu, L.; Yuan, Z.-Y. Direct synthesis of ordered mesoporous carbons. Chem. Soc. Rev. 2013, 42, 3977–4003. [CrossRef][PubMed] 130. Liu, J.; Wickramaratne, N.P.; Qiao, S.Z.; Jaroniec, M. Molecular-based design and emerging applications of nanoporous carbon spheres. Nat. Mater. 2015, 14, 763. [CrossRef][PubMed] 131. Wan, Y.; Zhao, D. On the controllable soft-templating approach to mesoporous silicates. Chem. Rev. 2007, 107, 2821–2860. [CrossRef][PubMed] 132. Zhai, Y.; Dou, Y.; Zhao, D.; Fulvio, P.F.; Mayes, R.T.; Dai, S. Carbon materials for chemical capacitive energy storage. Adv. Mater. 2011, 23, 4828–4850. [CrossRef][PubMed] 133. Nishihara, H.; Kyotani, T. Templated nanocarbons for energy storage. Adv. Mater. 2012, 24, 4473–4498. [CrossRef][PubMed] 134. Vu, A.; Qian, Y.; Stein, A. Porous electrode materials for lithium-ion batteries–how to prepare them and what makes them special. Adv. Energy Mater. 2012, 2, 1056–1085. [CrossRef] 135. Tang, J.; Liu, J.; Torad, N.L.; Kimura, T.; Yamauchi, Y. Tailored design of functional nanoporous carbon materials toward fuel cell applications. Nano Today 2014, 9, 305–323. [CrossRef] 136. Rolison, D.R. Catalytic nanoarchitectures—The importance of nothing and the unimportance of periodicity. Science 2003, 299, 1698–1701. [CrossRef][PubMed] 137. Slowing, I.I.; Trewyn, B.G.; Giri, S.; Lin, V.Y. Mesoporous silica nanoparticles for drug delivery and biosensing applications. Adv. Funct. Mater. 2007, 17, 1225–1236. [CrossRef] 138. Patiño, J.; Gutiérrez, M.; Carriazo, D.; Ania, C.; Fierro, J.; Ferrer, M.; Del Monte, F. Des assisted synthesis

of hierarchical nitrogen-doped carbon molecular sieves for selective CO2 versus N2 adsorption. J. Mater. Chem. A 2014, 2, 8719–8729. [CrossRef] 139. Feng, H.B.; Hong, T.; Mahurin, S.M.; Vogiatzis, K.D.; Gmernicki, K.R.; Long, B.K.; Mays, J.W.; Sokolov, A.P.; Kang, N.G.; Saito, T. Gas separation mechanism of co2 selective amidoxime-poly(1-trimethylsilyl-1-propyne) membranes. Polym. Chem. 2017, 8, 3341–3350. [CrossRef] 140. Kamegawa, T.; Ishiguro, Y.; Seto, H.; Yamashita, H. Enhanced photocatalytic properties of tio 2-loaded porous silica with hierarchical macroporous and mesoporous architectures in water purification. J. Mater. Chem. A 2015, 3, 2323–2330. [CrossRef] 141. Cao, Y.; Huang, J.; Peng, X.; Cao, D.; Galaska, A.; Qiu, S.; Liu, J.; Khan, M.A.; Young, D.P.; Ryu, J.E.; et al. Poly(vinylidene fluoride) derived fluorine-doped magnetic carbon nanoadsorbents for enhanced chromium removal. Carbon 2017, 115, 503–514. [CrossRef] 142. Zhang, J.; Deng, Y.; Wei, J.; Sun, Z.; Gu, D.; Bongard, H.; Liu, C.; Wu, H.; Tu, B.; Schüth, F. Design of amphiphilic abc triblock copolymer for templating synthesis of large-pore ordered mesoporous carbons with tunable pore wall thickness. Chem. Mater. 2009, 21, 3996–4005. [CrossRef] 143. Deng, Y.; Liu, C.; Gu, D.; Yu, T.; Tu, B.; Zhao, D. Thick wall mesoporous carbons with a large pore structure templated from a weakly hydrophobic PEO-PMMA diblock copolymer. J. Mater. Chem. 2008, 18, 91–97. [CrossRef] Polymers 2017, 9, 494 31 of 31

144. Liang, C.; Hong, K.; Guiochon, G.A.; Mays, J.W.; Dai, S. Synthesis of a large-scale highly ordered porous carbon film by self-assembly of block copolymers. Angew. Chem. Int. Ed. 2004, 43, 5785–5789. [CrossRef] [PubMed] 145. Wei, J.; Sun, Z.; Luo, W.; Li, Y.; Elzatahry, A.A.; Al-Enizi, A.M.; Deng, Y.; Zhao, D. New insight into the synthesis of large-pore ordered mesoporous materials. J. Am. Chem. Soc. 2017, 139, 1706–1713. [CrossRef] [PubMed] 146. Liang, C.; Li, Z.; Dai, S. Mesoporous carbon materials: Synthesis and modification. Angew. Chem. Int. Ed. 2008, 47, 3696–3717. [CrossRef][PubMed] 147. Yang, P.; Zhao, D.; Margolese, D.I.; Chmelka, B.F.; Stucky, G.D. Generalized syntheses of large-pore mesoporous metal oxides with semicrystalline frameworks. Nature 1998, 396, 152. 148. Templin, M.; Franck, A.; Du Chesne, A.; Leist, H.; Zhang, Y.; Ulrich, R.; Schädler, V.; Wiesner, U. Organically modified aluminosilicate mesostructures from block copolymer phases. Science 1997, 278, 1795–1798. [CrossRef][PubMed] 149. Wei, J.; Zhou, D.; Sun, Z.; Deng, Y.; Xia, Y.; Zhao, D. A controllable synthesis of rich nitrogen-doped ordered

mesoporous carbon for CO2 capture and supercapacitors. Adv. Funct. Mater. 2013, 23, 2322–2328. [CrossRef] 150. Wei, J.; Wang, H.; Deng, Y.; Sun, Z.; Shi, L.; Tu, B.; Luqman, M.; Zhao, D. Solvent evaporation induced aggregating assembly approach to three-dimensional ordered mesoporous silica with ultralarge accessible mesopores. J. Am. Chem. Soc. 2011, 133, 20369–20377. [CrossRef][PubMed] 151. Deng, Y.; Wei, J.; Sun, Z.; Zhao, D. Large-pore ordered mesoporous materials templated from non-pluronic amphiphilic block copolymers. Chem. Soc. Rev. 2013, 42, 4054–4070. [CrossRef][PubMed] 152. Tang, J.; Liu, J.; Li, C.; Li, Y.; Tade, M.O.; Dai, S.; Yamauchi, Y. Synthesis of nitrogen-doped mesoporous carbon spheres with extra-large pores through assembly of diblock copolymer micelles. Angew. Chem. Int. Ed. 2015, 54, 588–593. [CrossRef] 153. Du, H.; Gan, L.; Li, B.; Wu, P.; Qiu, Y.; Kang, F.; Fu, R.; Zeng, Y. Influences of mesopore size on oxygen reduction reaction catalysis of pt/carbon aerogels. J. Phys. Chem. C 2007, 111, 2040–2043. [CrossRef] 154. Ma, G.; Yan, X.; Li, Y.; Xiao, L.; Huang, Z.; Lu, Y.; Fan, J. Ordered nanoporous silica with periodic 30–60 nm pores as an effective support for gold nanoparticle catalysts with enhanced lifetime. J. Am. Chem. Soc. 2010, 132, 9596–9597. [CrossRef][PubMed] 155. Deng, Y.; Cai, Y.; Sun, Z.; Gu, D.; Wei, J.; Li, W.; Guo, X.; Yang, J.; Zhao, D. Controlled synthesis and functionalization of ordered large-pore mesoporous carbons. Adv. Funct. Mater. 2010, 20, 3658–3665. [CrossRef] 156. Deng, Y.; Yu, T.; Wan, Y.; Shi, Y.; Meng, Y.; Gu, D.; Zhang, L.; Huang, Y.; Liu, C.; Wu, X. Ordered mesoporous silicas and carbons with large accessible pores templated from amphiphilic diblock copolymer poly (ethylene oxide)-b-polystyrene. J. Am. Chem. Soc. 2007, 129, 1690–1697. [CrossRef][PubMed] 157. Kimura, T. Colloidal templating fabrication of aluminum-organophosphonate films using high molecular weight PS-b-PEO. Chem. Asian J. 2011, 6, 3236–3242. [CrossRef][PubMed] 158. Kruk, M.; Jaroniec, M.; Ko, C.H.; Ryoo, R. Characterization of the porous structure of sba-15. Chem. Mater. 2000, 12, 1961–1968. [CrossRef] 159. Deng, Y.; Liu, J.; Liu, C.; Gu, D.; Sun, Z.; Wei, J.; Zhang, J.; Zhang, L.; Tu, B.; Zhao, D. Ultra-large-pore mesoporous carbons templated from poly (ethylene oxide)-b-polystyrene diblock copolymer by adding polystyrene homopolymer as a pore expander. Chem. Mater. 2008, 20, 7281–7286. [CrossRef] 160. Yu, K.; Hurd, A.J.; Eisenberg, A.; Brinker, C.J. Syntheses of silica/polystyrene-block-poly (ethylene oxide) films with regular and reverse mesostructures of large characteristic length scales by solvent evaporation-induced self-assembly. Langmuir 2001, 17, 7961–7965. [CrossRef] 161. Garcia, B.C.; Kamperman, M.; Ulrich, R.; Jain, A.; Gruner, S.M.; Wiesner, U. Morphology diagram of a diblock copolymer–aluminosilicate nanoparticle system. Chem. Mater. 2009, 21, 5397–5405. [CrossRef]

© 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).