topological "interfacial polymer chemistry: … journal of polymer science, part b: polymer...

Topological "Interfacial“ Polymer Chemistry: Dependency of Polymer

“Shape” on Surface Morphology and Stability of Layer Structures When

Heating Organized Molecular Films of Cyclic and Linear Block Copolymers

of n-Butyl Acrylate-Ethylene Oxide

Qi Meng,1 Satoshi Honda,2* Yasuyuki Tezuka,2 Takuya Yamamoto,2 Atsuhiro Fujimori1

1Graduate School of Science and Engineering, Faculty of Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku,

Saitama 338-8570, Japan2Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan

Correspondence to: A. Fujimori (E-mail: [email protected])

Received 15 July 2015; accepted 16 September 2015; published online 22 October 2015

DOI: 10.1002/polb.23936

ABSTRACT: The “topological polymer chemistry” of amphiphilic

linear and cyclic block copolymers at an air/water interface was

investigated. A cyclic copolymer and two linear copolymers

(AB-type diblock and ABA-type triblock copolymers) synthe-

sized from the same monomers were used in this study. Rela-

tively stable monolayers of these three copolymers were

observed to form at an air/water interface. Similar condensed-

phase temperature-dependent behaviors were observed in sur-

face pressure–area isotherms for these three monolayers.

Molecular orientations at the air/water interface for the two lin-

ear block copolymers were similar to that of the cyclic block

copolymer. Atomic force microscopic observations of trans-

ferred films for the three polymer types revealed the formation

of monolayers with very similar morphologies at the meso-

scopic scale at room temperature and constant compression

speed. ABA-type triblock linear copolymers adopted a fiber-like

surface morphology via two-dimensional crystallization at low

compression speeds. In contrast, the cyclic block copolymer

formed a shapeless domain. Temperature-controlled out-of-

plane X-ray diffraction (XRD) analysis of Langmuir–Blodgett

(LB) films fabricated from both amphiphilic linear and cyclic

block copolymers was performed to estimate the layer regular-

ity at higher temperatures. Excellent heat-resistant properties

of organized molecular films created from the cyclic copolymer

were confirmed. Both copolymer types showed clear diffraction

peaks at room temperature, indicating the formation of highly

ordered layer structures. However, the layer structures of the

linear copolymers gradually disordered when heated. Con-

versely, the regularity of cyclic copolymer LB multilayers did

not change with heating up to 50 8C. Higher-order reflections

(d002, d003) in the XRD patterns were also unchanged, indicative

of a highly ordered structure. VC 2015 Wiley Periodicals, Inc. J.

Polym. Sci., Part B: Polym. Phys. 2016, 54, 486–498

KEYWORDS: amphiphiles; block copolymer; cyclic polymer; LB

films; molecular orientation; monolayers; monolayer at air/water

interface; thermal properties; topological polymer chemistry

INTRODUCTION A large amount of research in the field of poly-mer science is currently focused on effecting changes in theproperties of polymers that have different shapes. Polymers

having linear, branched, cyclic, and polycyclic forms are allbeing investigated.1,2 The effect of differently shaped amphi-philic polymers applied as monomolecular layers to air/water

This article was published online on 22 October 2015. An error was subsequently identified in the article title. This notice is

included in the online and print versions to indicate that both have been corrected on 5 November 2015.

*Present address: Satoshi Honda, Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-

8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan

Additional Supporting Information may be found in the online version of this article.

Abbreviations: XRD, X-ray diffraction; LB, Langmuir–Blodgett; l-BAEO, linear poly[(butyl acrylate)-block-(ethylene oxide)]; l-

BAEOBA, linear poly[(butyl acrylate)-block-(ethylene oxide)-block-(butyl acrylate); c-BAEO, cyclic poly[(butyl acrylate)-block-

(ethylene oxide)]; p–A, pressure–area; AFM, Atomic force microscopy

VC 2015 Wiley Periodicals, Inc.

486 JOURNAL OF POLYMER SCIENCE, PART B: POLYMER PHYSICS 2016, 54, 486–498

FULL PAPER WWW.POLYMERPHYSICS.ORGJOURNAL OF

POLYMER SCIENCE

FIGURE 1 Conceptual diagram of topological polymer interfacial chemistry. [Color figure can be viewed in the online issue, which

is available at wileyonlinelibrary.com.]

JOURNAL OFPOLYMER SCIENCE WWW.POLYMERPHYSICS.ORG FULL PAPER

WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE, PART B: POLYMER PHYSICS 2016, 54, 486–498 487

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interfaces on the formation and behavior of interfacial molecu-lar films has received considerable attention.3,4 In addition,polymers having different shapes that exist in biological sys-tems are of particular interest from a materials properties per-spective. For example, the primary components of cellmembranes (including those of humans) consist of linear lipidmolecules, and the membrane5,6 of the single-celled microor-ganism archaea (a thermophile7) consists of cyclic lipids thathave excellent heat resistance.8,9

The relationship of structure and function for these polymershas been hard to understand based on traditional structuralclassifications. The concept of primary, secondary, and terti-ary structures is a firmly established and well-used conceptin almost every area of polymer research.10,11 In this context,primary structure refers to the polymer’s chemical structure,including molecular weight; secondary structure refers to

the conformation adopted by the polymer through intermo-lecular interactions such as cis-trans, trans-gauche, and heli-cal conformations; and the tertiary structure refers to apolymer’s three-dimensional structure, including crystalline,amorphous, and liquid crystal forms. A “higher-orderstructure” can exist, corresponding to the fusion of second-ary and tertiary structures, such as occurs in spherulites andphase separations (Fig. 1).

A new polymer classification based on higher order polymershapes has been termed as topological polymer chemis-try.12,13 Of interest in this paper is the application of topo-logical polymer chemistry to the field of polymersynthesis.14,15 Although topological polymers are findingtheir place in polymer science, understanding the relation-ship between the chemistry and resulting physical propertiesis still incomplete. One nice step in this direction is the

FIGURE 2 Chemical structures of (a) l-BAEO, (b) l-BAEOBA, and (c) c-BAEO. [Color figure can be viewed in the online issue, which

is available at wileyonlinelibrary.com.]


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chemistry of the very thin polymer structures limited by thedimensions of a single molecule. Elucidation of the behaviorof polymers built from the same monomers, but having dif-ferent shapes within a single molecular dimension wouldgreatly facilitate the development of topological polymerchemistry of the work discussed in this paper.

In this study, three types of amphiphilic block copolymerscomposed of n-butyl acrylate/ethylene oxide were used.16,17

These three copolymers, all synthesized from the same set ofmonomers, consisted of one ring-shaped and two linearblock copolymers. The molecular structure and packing ofthese polymers at an air/water interface and on solid sub-strates are of interest to the field of basic polymer science.In this paper, topological polymer chemistry at the air/waterinterface has been investigated using amphiphilic linear (AB-type diblock and ABA-type triblock) and cyclic block copoly-mers.18 In addition, the ability of these three topologicalpolymers to maintain the characteristics of layer regularityunder heating were examined (Fig. 1). This knowledge couldthen be applied to the study of the function of thermophilicarchaea. Layer structures exist all around us, as biologicalcell membranes,19 proteins organized into b-sheets,20 ingraphite,21 natural clay minerals,22 surfactants,23 and liquidcrystals.24 Of course, Langmuir–Blodgett (LB) films25–27

which include polymer LB film,28,29 are also layer structuresincluding polymer LB film. Long-chain compounds constitut-ing LB films show a similarity to a layer structure30 alongthe c axis and subcell structure31 in the ab-plane at the stateof “molecules with low molecular weight”, “polymerizedmacromolecules”, “three-dimensional crystal”, and “a two-

dimensional molecular film”. Maintained force of the subcellcorresponds van der Waals interaction between alkyl chains.Comparison with this lateral interaction, there are tendencyof easily disordering by the external effects, such as the heat-ing since layer structure is only supported by the interactionbetween the terminal groups.32 However, regularity of layerstructure in LB film is generally high, studies on polymernanosheet33,34 and clay nanosheets35–37 dealing with thisordering are very famous. Work has also been reported onstudies of novel polymer nanosheets supported by p–p inter-actions between carbazole groups,38 polymer nanosphere-layer structures,39,40 and layered organizations of organo-modified-inorganic nanoparticles.41,42 In addition, changes inhydrophobic chain lengths caused by heating have also beeninvestigated as a disordering process effect.

EXPERIMENTAL

MaterialsFigure 2 provides a detailed schematic of the compoundsused in this study. The synthesis of cyclic and ABA-typecopolymers has been described in previously publishedpapers.16,17 AB-type copolymer was synthesized in the samemanner. The cyclic copolymer (abbreviated as c-BAEO), AB-type (l-BAEO) linear block, and ABA-type (l-BAEOBA) linearblock copolymers were synthesized from ethylene oxide andbutyl acrylate. The chemical structure of the cyclic polymercorresponds to an ABA polymer connected at both ends. Themolecular weights of all polymers were less than 10,000,which made these polymers freely soluble in chloroform.Monolayers and single-particle layers prepared from

FIGURE 3 p–A isotherms of monolayers on the water surface for l-BAEO, l-BAEOBA, and c-BAEO at (a) 15, (b) 25, and (c) 35 8C.

(Insert: Schematic illustration of formation mechanism of interfacial conformation.) [Color figure can be viewed in the online issue,

which is available at wileyonlinelibrary.com.]




chloroform solutions (approximately 1024 M) were formedon distilled water (resistivity was approximately 18 MX cm).

MeasurementsThe surface pressure–area (p–A) isotherms were measuredusing a USI-3-22 film balance (USI) at 15, 25, and 35 8C.After evaporation of chloroform from the polymer solutionsfor 5 min, the p–A isotherms were recorded at compressionspeeds of 1.2 and 9.6 cm2/min. Then, monolayer films pre-pared by the LB method at 15 and 20 8C were transferredon to glass for XRD studies, and mica for atomic forcemicroscopy (AFM) studies.

The surface morphologies of the transferred films wereobserved with a scanning probe microscope (Seiko Instru-ment, SPA300 with an SPI-3800 probe station) equipped withmicrofabricated rectangular Si cantilevers with integratedpyramidal tips used under an applied constant force of1.4 Nm21. The spacing between the layers of the polymerstructures along the c axis was estimated using an out-of-plane X-ray diffractometer (Rigaku, Rint-Ultima III, Cu Ka radi-ation, 40 kV, 40 mA) equipped with a graphite monochroma-tor. The inplane spacing of the two-dimensional lattice of thefilms was determined by XRD (Bruker AXS, MXP-BX, CuKaradiation, 40 kV, 40 mA) equipped with a parabolic gradedmultilayer mirror.43,44

RESULTS AND DISCUSSION

Figure 3(a) shows the p–A isotherms describing the mono-layer behaviors of the three block-copolymer shapes exam-ined, in which the compression percentage to the area of LBtrough is expressed on the horizontal axis. A “Mean area perrepeating monomer unit” as the horizontal axis of isothermsare conveniently indicated in Supporting InformationFigure S1. The temperature of the subphase was maintainedat 15 8C. At first glance, all three polymers showed similarisotherms, with limiting condensed phase areas of about20 Å2 and collapsed surface pressures below 30 mNm21.Since the values of the horizontal axis were considerablysmaller than the limiting area per monomer, these valuesseemed unusual. (The horizontal axis values are twice thevalue they should be because two hydrophobic polymerchains cross the air/water interface, as illustrated in the dia-gram at the bottom of Fig. 3.) The reason for this can beseen in the analogs illustrations of the three polymers, whichshow, to some extent, that there is no preference for any ofthe cyclic polymer conformations at the air/water interface,as indicated by the similar results of their individual iso-therms. Linear AB-type, linear ABA-type, and cyclic-typepolymers are expected to have similar interfacial conforma-tions since different topological polymers show similar iso-therms. In other words, it appears that the two types oflinear polymers adopt a conformation similar to that of thecyclic polymer at the interface. At this stage, the expansion

FIGURE 4 AFM images of Z-type monolayers for l-BAEO, l-BAEOBA, and c-BAEO: (a) 15 8C, 15 mNm21, 9.6 cm2/min, and (b) 15 8C,

20 mNm21, 9.6 cm2/min. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]


POLYMER SCIENCE



behavior of the linear polymers having unconnected terminiis more remarkable than that of the cyclic polymers. Theupper part of the illustration of the interfacial model of thelinear AB-type polymer in condensed phase of this figuremight be exaggerated (see Fig. 3). Indeed, the hydrophobicchains exposed to air as shown in the lower part of this fig-ure, seem to be covering the monolayer surface.

The results of p–A isotherm measurements with rising subphasetemperatures are shown in Figure 3(b,c) in which changes in theisotherms at subphase temperatures of 25 and 35 8C can beobserved. All isotherms indicated an expansion tendency con-comitant with an increase in subphase temperature. As a supple-ment to this figure, from which a full understanding of thecharacteristic differences of each polymer might be difficult,actual values of the measurements are summarized in Support-ing Information Table S1. Supporting Information Table S1 sum-marizes the limiting area of condensed and expansion phases asthe surface pressure collapses. This data quantitatively indicates

that the three polymer types also adopted behaviors and surfaceconformations similar to linear polymers, with no significant dis-turbance observed up to 35 8C. Further, the crossing point of theextrapolation lines between the expansion phase and the con-densed phase have defined as the transition point. In SupportingInformation Figure S2, the plots of surface pressure and themolecular area of transition points versus subphase temperatureare shown, respectively. Value of the limiting area of transitionfrom the expanded phase to the condensed phase reasonablyincreases with the rising of subphase temperature. It shows theexpansion trend in high subphase temperature conditions. Valueof the surface pressure of the transition from the expandedphase to the condensed phase decreases with the rising of thesubphase temperature. It finds that the phase transition at rela-tive low surface pressure occurs under the high subphase tem-perature conditions in this system. In this case, thermal behaviorin the bulk is worthy of consideration. DSC thermograms of thesetopological polymers are shown in Supporting InformationFigure S3. PEO units as hydrophilic group in the bulk are

FIGURE 5 AFM images of Z-type monolayers for (a) l-BAEO, (b) l-BAEOBA, and (c) c-BAEO (15 8C, 15 mNm21, 1.2 cm2/min).

(Insert: Conceptual diagram of one-dimensional growth of morphology by slow compression.) [Color figure can be viewed in the

online issue, which is available at wileyonlinelibrary.com.]




crystalline, and hydrophobic n-butyl acrylate corresponds amor-phous state. Here, only the melting peak derived from PEO unitis detected. Since the melting point of monolayer on the watersurface is generally lower than that in the bulk, it is expected toindicate an expansion trend of these polymers with relative lowmelting point in the high subphase temperature conditions.

Surprisingly, amphiphilic polymers having different shapesbut identical polymer components exhibited very similarmonolayer behaviors and a dependence on subphase tem-perature. Such behavior is rare among the recent reviews ofpolymer LB film.28,29 Supporting Information Figure S4 also

shows the p–A isotherms of copolymer monolayers with sys-tematically extended hydrophobic chain lengths for each ofthe three kinds of polymers. In the case of linear AB-typeand cyclic copolymers with long hydrophobic chains, the iso-therms showed almost no change. In contrast, linear ABA-type copolymers with short hydrophilic and long hydropho-bic groups showed a relatively small limiting area. Therefore,it was found that the shortening of hydrophilic groups influ-enced the limiting area of isotherms for these polymers.From the results discussed above, it is expected that the for-mation of this type of interfacial conformation would be rep-resented by the diagram at the top of Figure 3.

FIGURE 6 Schematic illustration of one-dimensional growth of a fiber-like morphology of a monolayer of l-BAEOBA. [Color figure

can be viewed in the online issue, which is available at wileyonlinelibrary.com.]


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The morphological changes at the mesoscopic scale of themonolayers on solid substrates transferred by the upstroke ofthe LB method are shown in Figures 4 and 5. All figures in Fig-ure 4 are shown with a scale of 2 3 2 lm2. Figure 4(a) showsAFM images of Z-type monolayers of the three block copoly-mers that were observed in the liquid expanded phase at15 mNm21, 9.6 cm2/min compression speed, and 15 8C sub-phase temperature. The morphology of the l-BAEO monolayersuggested the presence of a domain structure. Both l-BAEOBAand c-BAEO showed bent line-shaped structures at a 15 8C sub-phase temperature. The aggregation tendencies of the AB-typediblock copolymers appeared quite remarkable at first glance,however, significant differences were not observed in the for-mation processes for any of the monolayers at the mesoscopicscale. The existence of a significant defect part in these AFMimages was expected at a very low transferring ratio. The calcu-lated average transferring ratio for these conditions was 0.35.Therefore, acceleration of the morphological growth at the air/water interface by increasing the transferring surface pressureto 20 mNm21 induced the modification of the transferring ratioto 0.8. Thus, in order to promote the morphological growth atthe air/water interface, spontaneous morphological growth inthe two-dimensional plane was performed by the process ofreducing the compression rate by 1/8.

Figure 5 shows AFM images of Z-type monolayers for each ofthe three block amphiphilic copolymers at slow compressionspeeds, in which obvious differences were confirmed. In all thesystems, it can be seen that the transferring ratio significantlyimproved. The ABA-type triblock copolymer monolayer sponta-neously grew at a slow rate to form a fibrous domain at the air/water surface, yielding nanofibers. For the AB-type diblock lin-ear copolymer, spontaneous structural growth could not be con-firmed, and film quality was rather reduced. Compared with the

analogs linear copolymers, the cyclic polymer initially formedmonolayer precursors in which domains were connected toeach other after formation of individual nuclear domains. Sincethe two terminal hydrophobic chains of the ABA-type triblockcopolymer were oriented to air, it is suggested that a two-dimensional morphology can be easily produced via intertermi-nal van der Waals chain interactions, as illustrated in Figure 6.

It is important to note that the two kinds of linear copoly-mers in this study have a configuration similar to the cyclicpolymer at the air/water interface. However, the formationof nanofibers, as shown for the ABA triblock linear copoly-mer, could not be confirmed in the other polymer films. Thisfact may be attributed to the influence of compression rate-dependent spontaneous structural formation (1st orderspontaneous growth) at the air/water interface. In this study,although much information was gained from preliminaryexperiments, the dependence of polymer shape, as found inarchaea and lipids of other organisms. It becomes a factorinfluenced by the form and functionality in the two-dimensional organization. Indeed, in the case of multilayerformation by stacking of monolayers, it is easy to form peri-odic structures based on their interfacial configurations. Inaddition, the experimental estimation of heat resistance in amultilayer tells us that the layer structure of a cyclic poly-mer is quite stable to heat.

Figure 7 shows inplane XRD profiles of transferred LB multi-layers of amphiphilic block copolymers with different shapes.These polymers were presumed to pack hexagonally in mul-tilayered molecular films. Inplane XRD profiles showed crys-talline peaks that were attributed to the hexagonal close-packing of long alkyl chains [two-dimensional (100) plane,d100 5 4.1–4.2 Å). The upright hydrophobic polymer chainsexposed to air were expected to be packed hexagonally in

FIGURE 7 In-plane XRD profiles of LB multilayers of l-BAEO, l-BAEOBA, and c-BAEO (20 layers, 15 8C, 15 mNm21). [Color figure

can be viewed in the online issue, which is available at wileyonlinelibrary.com.]




multilayers composed of these amphiphilic block copolymers.However, the data are not fully consistent with this expecta-tion, there is a possibility that alkyl groups had aggregatedand packed in a manner similar to what occurs in micro-phase separation.

Figure 8 shows out-of-plane XRD profiles of transferred LBmultilayers of amphiphilic block copolymers with differentshapes. Although these profiles showed similar diffractionprofiles, the peaks in each profile indicated the formation ofa layer structure with a very high degree of order. The layerperiodicity value was calculated to be 5.1 nm from threethird-order reflections (d003 3 3) (since the first-orderreflection was observed at an extremely low angle in the

XRD). The ring diameter of polymers with a cyclic conforma-tion was about 10 nm as determined from the results ofhigh energy X-ray scattering in a photon factory with syn-chrotron radiation17 of block copolymer micellar solutions.These copolymers were not perpendicular, and adopted asubstantial tilt angle to the substrate as shown in the insertsin Figure 8. The sizes of the crystallites in the direction per-pendicular to the layers were also estimated using the Scher-rer equation.45 From the half-width of the first-orderreflection, the sizes of the crystallites were calculated to beabout 15 nm. Figure 8 shows the ex situ out-of-plane XRDprofiles observed with heating of l-BAEO, l-BAEOBA, andc-BAEO LB multilayers. These measurements were carriedout after annealing the LB multilayers in order to study the

FIGURE 8 Ex situ out-of plane XRD profiles at various LB multilayer temperatures for l-BAEO, l-BAEOBA, and c-BAEO. [Color fig-

ure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]


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differences in the heat-resistance properties between the lin-ear and cyclic polymers. In the case of AB-type diblock andABA-type triblock linear copolymers, a reduction and disap-pearance in diffraction intensity was observed with heatingbelow 100 8C. The layer structures of the LB multilayers of l-BAEO and l-BAEOBA were gradually disordered, and the reg-ularity of the layer structures completely disappeared afterannealing at 50 and 95 8C, respectively. However, in the caseof the cyclic polymer, the diffraction intensity was notreduced after annealing up to a temperature of 110 8C. Notonly were first-order reflections observed, but also third-

order reflections, indicating that the regularity of the cyclicpolymer LB multilayers did not change with heating up to110 8C. Therefore, it finds that LB film of the cyclic polymerreceive significantly the effect of the annealing. The heat-resistant properties of micelles of cyclic polymers in aqueoussolution were shown to have excellent heat stability.16

Figure 9 shows the schematic illustration of the disorderingbehavior of polymers in LB multilayers with heating based on theresults of the heated ex site out-of-plane XRD analysis shown inFigure 8. In previous studies, these changes in physical properties

FIGURE 9 Illustration of layer structures of LB multilayers for l-BAEO, l-BAEOBA, and c-BAEO. [Color figure can be viewed in the

online issue, which is available at wileyonlinelibrary.com.]




were attributed to the presence of end groups. Changes in molec-ular mobility with heating and in the presence of salts influencedthe heat resistance and salt resistance of the micellar solution. Itwas found that the presence of the terminal group also inducedthe disordering of the layer structures in this study. This behavior

will be a key to solving the mystery of the heat resistance abilityof thermophilic bacteria compared with linear-type lipid systems.

Based on a precise structural and morphological analysis,Figure 10 shows an illustration of the hierarchical structural

FIGURE 10 Schematic illustration of the topological polymer interfacial chemistry proposed in this study. [Color figure can be

viewed in the online issue, which is available at wileyonlinelibrary.com.]


POLYMER SCIENCE



formation reached from “monolayer morphology” to the“built-up layered organization” of topological polymers like l-BAEOBA and c-BAEO. This figure indicates that polymer top-ological interfacial chemistry is derived from molecularshape, and that intermolecular interactions comes from theshape and change in molecular mobility. A quite stable hier-archical structure was formed from the layered organizationand molecular packing for a mesoscopic morphology such asseen in nanofibers. Such sophisticated molecular techniqueswith bottom-up technology could introduce new avenues forresearch and development of new molecular devices. Forexample, development of heat-resistant molecular devicesmight be within view using only the end-caps of macromole-cules, if the chemical structure of a candidate macromoleculeis similar to the polymers discussed in this paper. The out-come of this study might then be recognized as a significantdevelopment toward new molecular devices and an under-standing of new properties of biomolecules.

CONCLUSIONS

The topological properties of polymers at an air/water interfacewere investigated using amphiphilic linear and cyclic blockcopolymers. A cyclic AB-type diblock linear copolymer and twoABA-type triblock copolymers with the same monomer compo-nents were newly synthesized and used in this study. All copoly-mers were observed to form relatively stable monolayers at anair/water interface. Similar tendencies for the condensed phaseas well as temperature-dependent behaviors were observed inthe p–A isotherms of all three monolayers examined. The molecu-lar orientations at the air/water interface of the two linear blockcopolymers were found to be quite similar to that of the cyclicblock copolymer. As determined by AFM observations of mono-layers on solid substrates, the monomolecular films of the threecopolymers adopted a morphology similar to that of the meso-scopic scale under room temperature and constant compressionspeed conditions. The ABA-type triblock linear copolymer wasobserved to form a fibril structure upon two-dimensional crystal-lization at a low compression speed, while the cyclic block copoly-mer formed an aggregated domain. The LB multilayers of theseblock copolymers formed highly ordered layer structures with alayer periodicity of 5.1 nm. In the case of the cyclic polymer, thediffraction intensity was not reduced after annealing up to 110 8C,indicating that the regularity of the cyclic polymer LB multilayerswere unchanged with heating. The excellent heat stability of cyclicpolymers was also demonstrated and discussed.

ACKNOWLEDGMENTS

This research was supported by a grant-in-aid for scientificresearch on innovative areas [Soft Interface No. 23106703(A.F.) and 23106709(T. Y.)] from the Ministry of Education, Cul-ture, Sports, Science, and Technology (MEXT) of Japan. In addi-tion, the authors greatly appreciate MEXT for Grant-in-Aid forScientific Research [C, 25410219 (A.F.)]. Finally, I offer myheartfelt condolence to mymentor Professor Kiyoshige Fukuda,Saitama University, who died on 7 July, 2015.

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