Phase Behavior of Adenine-Containing Block Copolymer

Macromolecules , Article ASAP. DOI: 10.1021/acs.macromol.8b02278. Publication Date (Web): December 6, 2018. Copyright © 2018 American Chemical ...
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Phase Behavior of Adenine-Containing Block Copolymer Eunseol Kim, Avnish Kumar Mishra, Chungryong Choi, Mooseong Kim, Seungkyoo Park, So Yeong Park, Sunghyun Ahn, and Jin Kon Kim* National Creative Research Center for Block Copolymer Self-Assembly, Department of Chemical Engineering, Pohang University of Science and Technology, Kyungbuk 37673, Korea

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S Supporting Information *

ABSTRACT: Nucleobase-containing polymers have received great attention for their complementary multiple hydrogen bonding between nucleobases. However, their polymerization is difficult due to poor solubility in a solvent. In this study, we successfully synthesized adenine-containing block copolymers, poly(9-(4-vinylbenzyl)adenine)-block-polystyrene (PVBA-bPS), using reversible addition−fragmentation chain transfer (RAFT) polymerization in polar solvents of dimethyl sulfoxide and N,N-dimethylformamide and characterized them by size exclusion chromatography and nuclear magnetic resonance spectroscopy. We measured the temperature dependence of the Flory−Huggins interaction parameter (χ) between PVBA and PS as χ = 0.3847 + 55.763/T. The χ was very large (∼0.5 at 200 °C). The phase behavior of PVBA-b-PS with various volume fractions of PS block (f PS) was investigated via small-angle X-ray scattering and transmission electron microscopy. With increasing f PS from 0.1 to 0.8, body-centered-cubic spheres of PS, hexagonally packed (HEX) cylinders of PS, lamellae, and HEX cylinders of PVBA were observed. Interestingly, PVBA-b-PS with f PS = 0.75 showed asymmetric lamellar microdomains. We also prepared a thin film of PVBA-b-PS on a substrate as a template for spatial arrangement of gold nanoparticles (AuNPs). When the surface of AuNPs was modified with thymine-containing polymer chains, AuNPs were selectively sequestered into PVBA microdomains through the complementary hydrogen bonding between thymine and adenine units.

1. INTRODUCTION Nucleobase-containing polymers have received great attention because of the complementary hydrogen bonding and could be used for biosensors and drug therapies.1−6 Especially, because adenine has versatile coordination ability toward various metal ions, adenine-containing polymers can be used as biochemical catalysis.7 Srivatsan et al. showed that poly(9-(4-vinylbenzyl)adenine) homopolymer (PVBA) capable of coordinating with copper exhibited good catalytic activity for various chemical and biochemical reactions.8 Madhavaiah et al. utilized uranylated PVBA for photoinduced DNA scission.9 Recently, two-dimensional (2-D) gold nanoparticle (AuNPs) arrays were fabricated by utilizing hydrogen bonds between complementary nucleobases.10−12 Nonoyama et al. fabricated stripe pattern of adenine-modified AuNPs by utilizing thymine modified β-sheet peptide template.10 Lin et al.11 prepared 2-D arrays of gold nanocubes via DNA hybridization with the aid of electron beam lithography. Also, Myers et al.12 combined electron beam lithography with the 2-D DNA-mediated assembly to directly write grayscale DNA density patterning. 2-D DNA-mediated nanoparticle assembly could be used for photonics, optics, electronics, and bioanalysis.11−13 However, previously reported methods to fabricate a 2-D nanoparticle array utilizing DNA hybridization need electron beam lithography, which limits preparing the array in a large area. © XXXX American Chemical Society

Block copolymers form various microdomain such as lamellae, cylinders, gyroids, and spheres, depending on the volume fraction of one block, the degree of polymerization (N), and the Flory−Huggins segmental interaction parameter (χ).14−17 Because adenine of PVBA can make complementary hydrogen bonding with thymine, the self-assembled nanostructure of PVBA-containing block copolymers can be used for biosensors, biochemical catalysis, and the fabrication of a high density array of gold nanoparticles through hydrogen bonds between complementary nucleobases. However, only a few research groups synthesized PVBA-containing block copolymers. O’Reilly and co-workers synthesized, via nitroxide-mediated radical polymerization (NMRP) with (2,2,6,6tetramethylpiperidin-1-yl)oxyl (TEMPO), polystyrene (PS)block-PVBA copolymer for templating polymerization of poly(vinyl benzyl thymine) (PVBT).18 Long and co-workers synthesized PVBA-block-poly(n-butyl acrylate)-block-PVBA copolymers (PVBA-b-PnBA-b-PVBA) by NMRP with a difunctional initiator.19,20 PVBA-b-PnBA-b-PVBA with a weight fraction of PVBA block having 0.15 showed PVBA cylindrical microdomains, and these were transformed to lamellar microdomains by blending of uracil-containing phosphonium salt.19 But, they did not study in detail the Received: October 23, 2018 Revised: November 24, 2018

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DOI: 10.1021/acs.macromol.8b02278 Macromolecules XXXX, XXX, XXX−XXX

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investigated by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). With increasing f ps, the microdomains changed from body-centered-cubic spheres of PS, hexagonally packed cylinders of PS, lamellae, and hexagonally packed cylinders of PVBA. Interestingly, PVBA-b-PS with f ps = 0.75 showed asymmetric lamellar microdomains, while a conventional coil−coil linear diblock copolymer with the same volume fraction showed cylindrical microdomains. The asymmetric lamellar structure originated from the molecular architectural asymmetry between PS chains and PVBA chains. In addition, we studied the self-assembly of PVBA-b-PS in thin films to selectively sequester gold nanoparticles into only PVBA microdomains. For this purpose, we used thin film of PVBA-b-PS to show hexagonally perforated lamellae. When this film was soaked in chloroform solution containing gold nanoparticles (AuNPs) modified by thymine-containing polymers, AuNPs were selectively sequestered into PVBA microdomains through the complementary hydrogen bonding between thymine and adenine. Thin film of PVBA-b-PS could be used as a template for spatial arrangement of AuNPs in a large area.

morphology or phase behavior of PVBA-containing block copolymers with various volume fractions of PVBA. In addition, it is important to form a well-ordered nanostructure on a substrate for the fabrication of 2-D AuNPs arrays. In this study, we synthesized, via reversible addition− fragmentation chain transfer (RAFT) polymerization with a chain transfer agent (CTA), PVBA-b-PSs with various volume fractions of PS block (f ps) to observe different microdomain structures. The rationale of choosing PS as a flexible coil block in PVBA-b-PS is as follows. First, because of the hydrophobic nature of PS, it would have a large incompatibility (high Flory interaction parameter (χ)) toward hydrophilic PVBA. When a high-χ block copolymer is used, a high density array of nanostructures is fabricated because of small feature size. Second, PS shows good thermal stability at high temperatures (up to ∼300 °C). Because of high glass transition temperature (∼230 °C) of PVBA block, PVBA-b-PS samples should be annealed at 270 °C for a long time (say, more than 1 day) to obtain equilibrium morphology in bulk or thin film. RAFT is a promising polymerization for nucleobase-containing monomers due to solvent compatibility and functional group tolerance.2,21 Additionally, it has advantages over other controlled radical polymerization such as NMRP and atom transfer radical polymerization (ATRP). For NMRP, the conversion of PVBA is expected to be low due to slow polymerization kinetics.22 Also, for ATRP, there exist remaining metal catalysts (e.g., CuBr) affecting polymerization kinetics of nucleobase-containing monomers.21 PVBA homopolymers with various molecular weights were first synthesized in dimethyl sulfoxide (DMSO) solution by controlling reaction time and VBA monomer amounts. Then, the PS block was polymerized by changing DMSO to DMSO/ N,N-dimethylformamide (DMF) mixed solvent because of large polarity difference between PVBA and PS. We successfully synthesized PVBA-b-PS with f ps from 0.15 to 0.80 and narrow polydispersity index (PDI < 1.3). We estimated temperature dependence of χ between PVBA and PS from the SAXS profiles fitted by the Leibler theory by using a low molecular weight and symmetric PVBA-b-PS showing the disordered state in the entire temperature range. The microdomains of PVBA-b-PS with various f ps were

2. EXPERIMENTAL SECTION Materials. 9-(4-Vinylbenzyl)adenine (VBA) and benzyl 2hydroxyethyl carbonotrithioate as a CTA were prepared according to literature procedures.23,24 Styrene (Aldrich Chem.) was distilled from calcium hydride under vacuum prior to polymerization. 2,2′Azobis(isobutyronitrile) (AIBN, Aldrich Chem.) was purified by recrystallization from methanol prior to use. All solvents were of reagent grade and used as received without further purification. Synthesis of PVBA Homopolymer and PVBA-b-PS. Scheme 1 shows synthesis of PVBA homopolymer and PVBA-b-PS. CTA (0.015 g, 6.3 × 10−5 mol), AIBN (0.0021 g, 1.3 × 10−5 mol), and VBA (2.0 g, 8.0 × 10−3 mol) were added to DMSO (5 mL) and polymerized under an argon environment at 80 °C for 24 h (∼80% conversion of VBA, which was confirmed by 1H NMR spectroscopy in DMSO-d6). Because both VBA and PVBA are soluble in DMSO, PVBA homopolymer was synthesized in DMSO, as shown in Scheme 1a. For the purification, acetone was added to the solution containing PVBA, followed by filtration, yielding a light yellow powder. The molecular weight of PVBA was controlled by the amount of VBA. PVBA-b-PS was synthesized by the addition of styrene monomer to B

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Figure 1. 1H NMR spectra of (a) VBA monomer, (b) PVBA homopolymer, and (c) PVBA25.5k-b-PS11.3k. PVBA macroinitiators (Scheme 1b). Because PS has poor solubility in DMSO, the mixture of DMF and DMSO was used for the synthesis of PVBA-b-PS. PVBA macroinitiator and styrene were dissolved in 7/3 (v/v) DMF/DMSO mixed solvent and then polymerized under argon at 130 °C for 24 h. The synthesized PVBA-b-PS was purified by addition of ether, followed by filtration. Characterization of PVBA Homopolymer and PVBA-b-PS. The number-average molecular weight (Mn) of PVBA homopolymer was calculated by using 1H nuclear magnetic resonance spectra (1H NMR: Bruker Avance III 400) in DMSO-d6. We prepared PVBAs with three different Mn (Mn = 25500, 12500, and 6500 g/mol). Mn of PVBA-b-PS and the volume fraction of PS (f ps) were also measured by 1H NMR in DMF-d7, and the polydispersity index (PDI) was measured by size exclusion chromatography (SEC: Waters 2414 refractive index detector) with two 300 mm (length) × 7.5 mm (inner diameter) columns including a particle size of 5 μm (PLgel 5 μm MIXED-C: Polymer Laboratories) with 7/3 (v/v) DMF/DMSO mixed solvent as the eluent and a flow rate of 1 mL/min at 30 °C. Bulk Morphologies. The samples for both TEM and SAXS experiment were prepared by solution casting on a Teflon sheet and annealed at 270 °C for 1 day under vacuum and quenched to room temperature. To obtain a TEM (Hitachi 7600) image, the sample was ultrasectioned with a Leica Ultracut Microtome (EM UC6 Leica Ltd.) with 40 nm thickness and transferred to Cu grid at room temperature. Then, it was stained by exposure to RuO4 vapor for 10 min to stain PS blocks selectively. SAXS experiments were conducted at room temperature on a 4C beamline at Pohang Accelerator Laboratory (PAL, South Korea), where the X-ray wavelength was 0.1608 nm. The sample-to-detector distance was 1 or 4 m, and the scattered X-rays were collected on a 2D CCD detector (Princeton Instruments, SCXTE/CCD-1242). The thickness of the samples was 1.0 mm, and the exposure time was 10 s. Preparation of Gold Nanoparticles Modified with Poly(1-(4vinylbenzyl)thymine). Poly(1-(4-vinylbenzyl)thymine) (PVBT) with Mn of 3500 g/mol was synthesized by RAFT polymerization of VBT monomer similar to that for PVBA. AuNPs grafted by PVBT chains were synthesized according to the literature.25,26 0.1 mmol (37.9 mg) of HAuCl4·xH2O in 10 mL of anhydrous DMF was added to a solution containing 0.01 mmol of PVBT and 0.03 mmol of 1butanethiol dissolved in 10 mL of anhydrous DMF. The mixture was stirred to ensure homogeneity. Then, 1.2 mL of 1.0 M THF solution of LiB(C2H5)3H was added dropwise and stirred for 4 h. The resulting solution was centrifuged with 40 mL of dry ethanol. The nanoparticles were precipitated, and the supernatant was removed. The resulting aggregate was dispersed in chloroform, and the dispersion was purified by ultrafiltration using a porous membrane

(Millipore PLTK) with a molar mass cutoff 30000 g/mol. The prepared AuNPs have uniform particle size of ∼6 nm (Figure S7a). We checked PVBA-grafted AuNPs using 1H NMR in DMSO-d6 (Figure S7c). We also prepared AuNPs without using PVBT (thus, only 1-butanethiol was attached to AuNPs) similar to the above method. Preparation of Thin Film and Gold Nanoparticles Array. PVBA6.5k-b-PS22.5k (f ps = 0.80) in 7/3 (v/v) DMF/DMSO (2.0 wt % in solid) was spin-coated on a UV/O3-treated silicon substrate. The film was placed in vacuum oven at 270 °C for 1 day and quenched to room temperature. Then, it was soaked in a chloroform containing AuNPs. After 1 h it was rinsed with chloroform several times. The surface morphologies of thin film were observed by atomic force microscopy (AFM) (Veeco DI dimension 3100 with Nanoscope V) in the tapping mode. To obtain a TEM image of the thin film with AuNPs, the film was floated onto the surface of 5 wt % hydrofluoric acid solution and transferred onto a Cu grid. Then, it was exposed under RuO4 vapor for 10 min at room temperature to selectively stain the PS chains.

3. RESULTS AND DISCUSSION Synthesis of PVBA and PVBA-b-PS. Figure 1 gives 1H NMR spectra of VBA monomer, pure PVBA homopolymer after complete removal of VBA, and PVBA25.5k-b-PS11.3k. As shown in Figure 1a,b, pure PVBA homopolymer does not show a peak at δ = 5.85 ppm, which is the characteristic peak of vinyl group in VBA monomer. Mn of PVBA homopolymer was determined from 1H NMR spectra (Figure S1) of PVBA homopolymer containing VBA monomer by comparing peak area at δ = 5.85 ppm with that at δ = 8.0−8.5 ppm (a detailed calculation is given in section 1 of the Supporting Information). The mole fraction of styrene units in each [A1 −3A 2 ] / 5 , where A1 and PVBA-b-PS was calculated by [A1 −3A 2 ] / 5 + A 2 /2

A2 are the peak areas at δ = 5.8−7.5 ppm and δ = 5.0−5.4 ppm, respectively, in Figure 1c. The total Mn of PVBA-b-PS was obtained using Mn of PVBA homopolymer and the mole fraction of styrene units. All PVBA-b-PSs synthesized in this study showed unimodal peak in SEC traces (Figure S2). The molecular characteristics of PVBA-b-PSs synthesized in this study are given in Table 1. Phase Behavior of PVBA-b-PS in Bulk State. Before discussing the phase behavior of PVBA-b-PSs with various f PS, C

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microdomains. This is quite expected due to smaller PS volume fraction. TEM images also exhibited spherical PS microdomains stained by RuO4. We also found that PVBA25.5kb-PS3k with f PS = 0.12 showed BCC spherical microdomains (see Figure S4). PVBA25.5k-b-PS11.3k having f PS = 0.35 showed hexagonally packed cylindrical microdomains, confirmed by SAXS peaks at positions 1:2:√7 relative to q*, as well as TEM image, as shown in Figure 3b. The above statements are also consistent with birefringence experiment as shown in Figure S5. Both PVBA25.5k-b-PS3k and PVBA25.5k-b-PS6k did not show any birefringence, while a definite birefringence was observed for PVBA25.5k-b-PS11.3k. Figure 4 gives SAXS profiles and TEM images of PVBA-bPSs with three different f PS (0.41, 0.58, and 0.75). All of three samples show lamellar microdomains confirmed by SAXS profiles with scattering peaks with the positions of 1:2:3:4 relative to q*. Interestingly, PVBA12.5k-b-PS35k with f PS = 0.75 exhibits lamellar microdomains. From the inset TEM image (Figure 4c), the lamellar width corresponding to PS block (dark stripes) is 3 times larger than that of PVBA block (white stripes). Thus, PVBA12.5k-b-PS35k showed asymmetric (not symmetric) lamellar microdomains. We also analyzed the SAXS profile by fitting with the variable lamellar thickness structure model, giving the calculated f PS of 0.73, which is close to the measured f PS (see Figure S6). The formation of the asymmetric lamellar microdomains could be explained by the different molecular architecture between PVBA chains and PS chains. Because of the bulky adenine side group of PVBA chains, PVBA chains have larger cross-sectional area than PS chains.33 In addition, the self-complementary hydrogen bonding of adenine groups of PVBA decreases the flexibility of PVBA chain.34,35 Consequently, even at a smaller volume fraction of PVBA, the interface between the PVBA and PS microdomains prefers to be flat rather than a curvature toward PVBA microdomains to accommodate the increased crosssectional area and the stiffness of PVBA chains. This is consistent with the phase behavior of POSS-containing block copolymers such as poly(methyl methacrylate)-block-poly(polyhedral oligomeric silsesquioxane methacrylate) copolymer (PMMA-b-PMAPOSS), where the lamellar structure was observed even at a volume fraction of flexible PMMA block (f PMMA) with 0.78.36,37 When f PS was further increased (0.80), PVBA6.5k-b-PS22.5k showed hexagonally packed PVBA cylindrical microdomains, as demonstrated by SAXS profile (Figure 5) whose peaks of

Table 1. Molecular Characteristics of PVBA-b-PSs Synthesized in This Study symbola

Mn (g/mol)b

f PSc

Mw/Mnd

morphologye

PVBA1.7k-b-PS1.5k PVBA25.5k-b-PS3k PVBA25.5k-b-PS6k PVBA25.5k-b-PS11.3k PVBA25.5k-b-PS14.7k PVBA6.5k-b-PS7.4k PVBA12.5k-b-PS35k PVBA6.5k-b-PS22.5k

3200 28500 31500 36800 40200 13900 47500 29000

0.52 0.12 0.22 0.35 0.41 0.58 0.75 0.80

1.10

fully disorder PS sphere PS sphere PS cylinder lamella lamella lamella PVBA cylinder

1.15 1.12 1.10 1.21 1.22

a

The subscript next to each block represents the number-average molecular weight of each block. bCalculated by 1H NMR. cCalculated from mole fraction and with known density of PS (1.05 g/mL) and PVBA (1.25 g/mL) measured by using a density column. dMeasured by SEC in DMF/DMSO (7/3 v/v) as an eluent with PMMA standards. Blank could not be measured due to poor solubility. e Determined by SAXS profiles and TEM images.

we obtained χ between PVBA and PS. For this purpose, we used a low molecular weight and symmetric PVBA-b-PS (PVBA1.7k-b-PS1.5k and f PS = 0.52). We found that SAXS profiles of PVBA1.7k-b-PS1.5k at various temperatures showed a broad first-order peak without any high ordered peaks, indicating that it becomes fully disordered over the entire experimental temperatures (Figure S3). Figure 2a gives structure factor (S(q)) as a function of q at five temperatures. The solid line at each temperature was curve fitting with the Leibler theory,27−30 from which χ between PVBA and PS was estimated as 0.3847 + 55.763/T, in which T is the absolute temperature, as shown in Figure 2b (details are given in section S2 of the Supporting Information). The obtained χ at 200 °C is 0.5, which is quite large compared with other high-χ block copolymers (0.41 for polytrimethylsilylstyrene-block-poly(DLlactide) (PTMSS-b-PLA),31 0.4 for polystyrene-block-poly(4vinylpyridine) (PS-b-P4VP),28 and 0.11 for polystyrene-blockpolydimethylsiloxane (PS-b-PDMS)32). A high χ is expected because of hydrophobic PS and hydrophilic PVBA. Thus, the molecular weights of all block copolymers employed in this study except PVBA1.7k-b-PS1.5k are sufficiently high enough to form well-ordered microdomains. Figure 3a shows SAXS profile and TEM image for PVBA25.5k-b-PS6k with f PS = 0.22. SAXS peaks appeared at the positions of 1:√2:√3:√5:√7 relative to q*, indicating that this sample has body-centered-cubic (BCC) spherical

Figure 2. (a) Structural factor profiles (S(q)) of PVBA1.7k-b-PS1.5k at various temperatures: 200 (○), 210 (□), 220 (△), 230 (◇), and 240 °C (▷) where the solid lines are obtained from the fitting by the Leibler theory. (b) Temperature dependence of χ between PVBA and PS. D

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Figure 3. SAXS profiles at room temperature and TEM images of (a) PVBA25.5k-b-PS6k and (b) PVBA25.5k-b-PS11.3k. Inset of TEM image (b) represents the sample cut perpendicular to the cylinder axis.

Figure 4. SAXS profiles at room temperature and TEM images of (a) PVBA25.5k-b-PS14.7k, (b) PVBA6.5k-b-PS7.4k, and (c) PVBA12.5k-b-PS35k.

SAXS profiles have positions of 1:√3:√7 relative to q* as well as TEM image where white dots and rods corresponding to PVBA microdomains are clearly seen (inset of Figure 5). Morphology of PVBA-b-PS in Thin Film and AuNPs Arrays. Figure 6 gives AFM phase image of thin films of PVBA6.5k-b-PS22.5k. In contrast to the cylinder morphology of this sample in bulk (see Figure 5), its thin film shows hexagonally perforated lamellar (HPL) morphology where the bright regions represent the PVBA layer perforated by hexagonally packed PS microdomains. This AFM image clearly show that the film does not represent perpendicular oriented hexagonally cylinders. If thin film had exhibited perpendicular HEX cylinders, PVBA should become dots in the matrix of PS

microdomains because of f PS = 0.8. But, in the AFM image, the dots represent the PS microdomains. This argument is also consistent with TEM image, as shown in inset of Figure 6, where PS phases look dark due to electively stained by RuO4. Because PVBA is a minor component, the layers of PVBA block should be perforated by PS microdomains. Even for HEX cylindrical microdomains in bulk, thin film shows HPL morphology when the film thickness (t) of a film was 1L0 < t ≤ 2L0, in which L0 is the domain spacing measured by the first peak of the SAXS profile (2π/q* = 41 nm). The appearance of HPL morphology in thin film could be explained by a large favorable interaction between PVBA chains and silicon oxide, E

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situation, physically adsorbed AuNPs on the film were completely removed. When PVBT chains are not grafted on AuNPs, no AuNP is observed because of no interaction of PVBA and PS with AuNPs (Figure 7a). However, when AuNPs are grafted with PVBT chains, they are observed only inside PVBA microdomains, which look bright in the AFM image (Figure 7b). This is because PVBT chains strongly bind to adenine moiety in PVBA microdomains through strong complementary hydrogen bonding between thymine and adenine groups. The inset of Figure 7b is TEM image of the thin film with AuNPs. Here, the small dots looking dark black represent AuNPs, while large dots looking faint black correspond to PS microdomains stained by RuO4, and unstained PVBA microdomains look light gray. It is clearly shown that AuNPs are only located in the PVBA matrix, not inside PS microdomains. This is consistent with AFM image given in Figure 7a. Figure 5. SAXS profile at room temperature and TEM images of PVBA6.5k-b-PS22.5k. Inset of TEM image represents the sample cut perpendicular to the cylinder axis.

4. CONCLUSIONS Adenine-containing block copolymers (PVBA-b-PSs) with various f PS were successfully synthesized using RAFT polymerization. Using reactive CTA and mixed solvent of DMF/ DMSO, we controlled the molecular weight and f PS. With increasing f PS from 0.1 to 0.8, the morphology of PVBA-b-PSs changed from body-centered-cubic spheres of PS, hexagonally packed cylinders of PS, lamellae, and cylinders of PVBA. Interestingly, PVBA-b-PS with f PS of 0.75 showed asymmetric lamellar microdomains. We also successfully sequestered AuNPs into only PVBA microdomains by using AuNPs grafted by PVBT chains. This AuNPs array could be used as biochemical catalysis, biosensors, and DNA-mediated nanoparticle arrays.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b02278.

Figure 6. AFM phase image of PVBA6.5k-b-PS22.5k thin film with thickness of 81 nm. The inset is TEM image of PVBA6.5k-b-PS22.5k thin film.

1 H NMR and SEC traces of PVBA and PVBA-b-PS, estimation of the χ between PVBA and PS, SAXS and TEM image of PVBA25.5k-b-PS3k, depolarized light intensity of PVBA-b-PSs, SAXS profiles fitted by the variable lamellar thickness and characterization of AuNPs grafted with PVBT chains (PDF)

which could induce the layer structure rather than the cylindrical phase.38 Figure 7 shows AFM phase images of PVBA6.5k-b-PS22.5k thin film with a thickness of 67 nm after immersing the film into chloroform solution containing AuNPs grafted without and with PVBT chains, followed by rinsing with chloroform. In this

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (J.K.K.). ORCID

Jin Kon Kim: 0000-0002-3872-2004 Notes

The authors declare no competing financial interest.

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Figure 7. AFM phase images of PVBA6.5k-b-PS22.5k thin film with a thickness of 67 nm after immersing it into chloroform solution containing AuNPs grafted without (a) and with (b) PVBT chains. The inset of (b) is TEM image of the thin film. Bright white dots in AFM image (marked by blue circle) represent AuNPs. AuNPs (marked by blue color) are only located in PVBA matrix. PS microdomains appears dark gray (marked by the red color).

ACKNOWLEDGMENTS This work was supported by the National Creative Research Initiative Program supported by the National Research Foundation of Korea (2013R1A3A2042196). SAXS experiments were done at 4C beamline of PAL (Korea). F

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DOI: 10.1021/acs.macromol.8b02278 Macromolecules XXXX, XXX, XXX−XXX