Sol–Gel Preparation of Initiator Layers for Surface-Initiated ATRP

Article Cite This: Macromolecules XXXX, XXX, XXX−XXX

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Sol−Gel Preparation of Initiator Layers for Surface-Initiated ATRP: Large-Scale Formation of Polymer Brushes Is Not a Dream Tomoya Sato, Gary J. Dunderdale, Chihiro Urata, and Atsushi Hozumi* National Institute of Advanced Industrial Science and Technology (AIST), 2266-98, Anagahora, Shimoshidami, Moriyama, Nagoya 463-8560, Japan

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S Supporting Information *

ABSTRACT: We demonstrated for the first time a facile and reproducible preparation of large-scale (∼40 m2) initiator layers for surface-initiated atom transfer radical polymerization (SI-ATRP) using a simple sol−gel solution of (pchloromethyl)phenyltrimethoxysilane and tetraethoxysilane. Highly smooth and transparent initiator layers could be formed on various inorganic/organic substrates via a spin-, wire-bar-, or roll-to-roll-coating without any marked change in surface morphology or bulk properties at room temperature. Combining the advantages of this sol−gel approach and subsequent “paint on” SI-ATRP using a variety of waterborne monomers, we have succeeded in the formation of polymer brushes on large-scale real-life substrates (i.e., maximum 50 × 50 cm2) under ambient conditions (room temperature and open to the air) without any complicated apparatus or harsh reaction conditions.

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industrial-scale polymer brushes in the open air for real-life applications is rare and still very challenging. Although conducting SI-ATRP in air offers great advantages, there have only been a limited number of papers describing the synthesis methods requiring neither rigorous deoxygenation nor expensive/complex instrumentation. For example, some of the authors have recently developed a unique approach named “paint on” SI-ATRP.9,10 By the introduction of a proper amount of reducing agent (ascorbic acid (AA)) into the SI-ATRP system, they succeeded in the open-air preparation of polymer brushes on the large-scale aluminum (Al) substrates (30 × 10 cm2).9 A similar methodology has also been applied to fabricate well-defined various polymer brushes on 4 in. silicon (Si) wafers under ambient conditions.11 A small amount of the reaction solution (only 4 mL) was spread on the Si wafer and sandwiched by a same-size copper (Cu) plate, which worked as a source of both catalyst and reducing agent. Matyjaszewski’s group has also recently developed a novel SI-ATRP possessing perfect tolerance against oxygen by employing effective reducing cycles inspired by aerobic respiration of living cells.12 Such oxygentolerant ATRP processes8 are expected to be feasible along with the possibility of industrial-scale manufacture of polymer brushes. However, in contrast to the recent progress in oxygen-tolerant polymerization processes, there have been very few reports on improving or on creating surface initiator layers for SI-ATRP. To

urface modification of solid substrates by grafting of “polymer brushes” with a grafting density >0.1 chain/ nm2 1 is an effective method to control surface physical/chemical properties, such as friction, adhesion, wettability, and stimuliresponsiveness. Among the various grafting techniques, surfaceinitiated atom transfer radical polymerization (SI-ATRP)2 is one of the most promising/practical techniques to fabricate welldefined polymer brushes3−6 on various substrates. SI-ATRP has been typically demonstrated through the following two steps, i.e., (1) fixation of surface initiators with radically generating moieties and (2) subsequent polymerization initiated from these reactive sites. While reports have focused on demonstration of the enhanced surface properties of polymer brushes using small scale test pieces (∼1 cm2), if these materials are going to be used in real-life industrially relevant applications, they will need to be fabricated on a much larger scale (∼1−100 m2). However, increasing the size of functionalized area is not trivial, as many of the processes used to functionalize small pieces of substrate under laboratory conditions cannot be replicated at larger scales outside of the laboratory. One of the main barriers to large-scale fabrication of polymer brushes is that to conduct SI-ATRP effectively, removal of oxygen from the reaction systems is of crucial importance, since oxygen, if present in the system, can immediately trap propagating radicals and deactivate catalysts, consequently stopping polymerizations.7,8 In addition, SI-ATRP also requires high concentrations of monomer and metal catalyst, use of organic solvents, and elevated reaction temperatures, which limit the applicability of polymer brushes to basic research only. Despite the number of publications on polymer brushes now increasing, research focused on designing and producing © XXXX American Chemical Society

Received: October 17, 2018 Revised: December 1, 2018

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DOI: 10.1021/acs.macromol.8b02234 Macromolecules XXXX, XXX, XXX−XXX

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Figure 1. (a) Schematic illustration of the preparation for SI-ATRP initiator layer (iCMPTMS). (b) Appearance of iCMPTMS-covered various substrates. Typical (c) OM (viewing area of 150 × 150 μm2) and (d) AFM (scan area of 3 × 3 μm2) images of iCMPTMS-covered Si substrate.

chloromethyl)phenyltrimethoxysilane (CMPTMS, organosilane with ATRP initiator moiety) and tetraethoxysilane (TEOS) (Figure 1a) could be deposited on not only Si and glass substrates but also polymer and metal substrates with a reasonable adhesion strength at room temperature, and the resulting layer appropriately worked as an initiator for SI-ATRP. We reported herein for the first time a facile and reproducible approach that enables practical-size formation of extremely smooth, transparent, and reactive initiator layers possessing a good affinity for the subsequent SI-ATRP. In this study, we applied the acid-catalyzed sol−gel approach to form the initiator layers on various inorganic/organic substrates over an extremely large scale at room temperature. To realize this, spin-, wire-bar-, or roll-to-roll-coating process was demonstrated using a sol−gel precursor solution as mentioned above. In contrast to previous reports, our technique reported here offers several distinguishing practical advantages: first, stringent control of the experimental conditions is not necessary, meaning that functionalization can be performed outside of the laboratory; second, since our sol− gel process can be conducted at room temperature, our technique is applicable to a wide variety of substrates (for example, Si, glass, polymers, or metals); third, the resulting sol− gel initiator layers are stable against various organic solvents and show reasonable adhesion strength to the various substrates; finally, there are no significant limitations for available substrate dimensions or coating method. Our initiator layers for SI-ATRP containing reactive functional groups were prepared using a conventional co-hydrolysis and co-condensation method according to our previous reports.25−27 A precursor solution prepared by mixing CMPTMS and TEOS in an ethanol/0.01 M HCl aqueous solution was spin-cast on Si, Cu, glass, polycarbonate (PC), and poly(ethylene terephthalate) (PET) substrates and then dried in air at room temperature for 24 h (Figure 1a; we hereafter refer to the resulting SI-ATRP initiator layer as iCMPTMS). The resulting initiator layers appeared highly transparent and colorless as shown in Figure 1b, and we did not observe any change or damage to the substrate even on the organic

date, self-assembled monolayers (SAMs) have been most widely employed to immobilize surface initiators.13−15 Such SAMs have been usually prepared either from a liquid phase process, which has the disadvantage of requiring a large amount of solvent for both the monolayer deposition process and the sample rinsing process which follows, or from the vapor phase, which has no need for the use of organic solvents but requires long treatment times and higher temperatures. Several methods to fabricate initiator layers using polymer-based materials have been also proposed16−23 which utilize anchoring groups and ATRPreactive moieties to produce physically/chemically stable and sufficiently thick/homogeneous initiator layers for SI-ATRP on various substrates. However, in most cases, multiple processing and special reaction apparatuses/conditions are still required. Unfortunately, the development of the initiator layers has been essentially ignored so far, meaning that with the development of oxygen-tolerant ATRP, large-scale fabrication of initiator surfaces is now the limiting factor in the widespread application of polymer brushes in real-life applications. To overcome these shortcomings, an alternative coating method for initiator layer applicable to a wide variety of substrates and various dimensions, which does not require expensive apparatuses or severe experimental conditions, has been strongly demanded. Among the various coating techniques so far reported, a sol− gel approach24 is one of the most promising and well-established methods. Highly homogeneous, transparent, and mechanically robust functional thin films can be fabricated on various substrates at ambient temperatures with reasonable adhesive properties, and it can be also very useful in incorporating appropriate terminal functional groups to the solid surfaces.24 By taking advantage of these merits, several of the authors have recently reported the room temperature fabrication of transparent organic/inorganic hybrid films terminated with alkyl and perfluoroalkyl groups showing unusual dynamic dewetting behavior by an acid-catalyzed sol−gel method.25−27 We began to study these sol−gel methods in an attempt to fabricate new initiator layers for SI-ATRP. Upon creation of these initiator layers, we found that sol−gel precursor solution containing (pB

DOI: 10.1021/acs.macromol.8b02234 Macromolecules XXXX, XXX, XXX−XXX

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Figure 2. (a) Survey and (b) single scan XPS spectra of iCMPTMS-covered Si substrate, (c) XPS mapping image of Cl 2p for an identical surface of (a) and (b), and (d) OM image of iCMPTMS-covered Si substrate after a cross-cut tape peel test.

Figure 3. (a) Schematic illustration of roll-to-roll coating process and appearance of iCMPTMS-covered PET roll film, (b) OM (viewing area of 150 × 150 μm2), and (c) AFM (scan area of 3 × 3 μm2) images of the iCMPTMS-covered PET roll film.

substrates. The average thicknesses of our iCMPTMS were measured to be 530 nm by spectroscopic reflectometry, although this thickness can be altered to be larger or smaller by changing the spin-coating conditions. Surface morphologies of the iCMPTMS-covered Si (Figure 1c,d) and other substrates (Figure S1) were observed by both optical microscopy (OM) and atomic force microscopy (AFM). All sample surfaces appeared very smooth and homogeneous with no aggregates, cracks, or defects. The average root-mean-

square roughness (Rrms) of each sample estimated from AFM images (over the scan area of 3 × 3 μm2, Figure 1d and Figure S1) was 85% in the visible light wavelength range (400−800 nm) and remained unchanged after iCMPTMS coating (Figure S2). The chemical compositions of our spin-coated iCMPTMScovered Si substrates were characterized by X-ray photoelectron spectroscopy (XPS). Survey scans of the sample surfaces detected the Cl 2s and Cl 2p signals at 271.3 and 200.0 eV, respectively (Figure 2a; inclination angle of the sample: 0°). In addition, a typical C 1s XPS spectrum consists of at least two chemical components centered at binding energies (BEs) of 285.0 and 287.3 eV, corresponding to C−C/C−H/aromatic and C−Cl groups,28 respectively (Figure 2b). These results highlight that the ATRP initiating group (C−Cl) was successfully deposited onto the surface unchanged and does not participate in the sol−gel reaction. The concentrations of Si:C:O:Cl were about 19.8:31.8:43.5:4.9 at. %, respectively, which were almost same as those of the theoretical atomic ratios of CMPTMS molecule (Si:C:O:Cl = 22.2:31.1:42.2:4.4), indicating that the outermost surface of the iCMPTMS was terminated with (chloromethyl)phenyl groups and that no preferential deposition or partition of either TEOS or CMPTMS occurred on the surface. To investigate the homogeneity of the initiator moieties, XPS analyses of two different inclination angles (40° and 63°) and XPS mapping of Cl 2p were also performed. The estimated atomic percentages of Si:C:O:Cl were 20.5:37.8:36.9:4.8 (for 40°) and 20.7:33.9:40.6:4.8 (for 63°), which were also almost the same ratio given above. As shown in the mapping image (Figure 2c; bright spots with red and yellow colors indicate the Cl-concentrated areas), the Cl 2p signal could be observed on the entire surface, and there were no marked differences in the intensity within the scan area (200 × 200 μm2 ), indicating that the initiator moieties were homogeneously dispersed entirely over the iCMPTMS surface. For the purpose of fabricating polymer brushes over a largescale area, we next demonstrated preparation of iCMPTMS on the PET roll film with polyester-based varnish layer via a roll-toD

DOI: 10.1021/acs.macromol.8b02234 Macromolecules XXXX, XXX, XXX−XXX

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Figure 5. Average dry thicknesses and water drop profiles with water θS values on the 10 types of hydrophilic polymer brushes grafted from the iCMPTMS-covered PET roll film surfaces (typical polymerization time was 6 h). AMPSNa: 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt; SPMK: 3-sulfopropyl methacrylate potassium salt; PEGMA: poly(ethylene glycol) methacrylate with average Mn of 500; AMPS: acrylamido-2methyl-1-propanesulfonic acid; HEA: 2-hydroxyethyl acrylate; HEMA: 2-hydroxyethyl methacrylate; DMAEA: N,N-dimethylaminoethyl acrylate; MEO2A: 2-[2-(2-methoxyethoxy)ethoxy]ethyl acrylate; VIm: 1-vinylimidazole; DEAEMA: 2-(diethylamino)ethyl methacrylate.

pDMAEMA brushes, and no damage to iCMPTMS was observed. This clearly demonstrates that our iCMPTMS worked effectively as an initiator layer for SI-ATRP, giving an identical thickness and thus grafting density to conventional monolayer initiators. Because of the formation of pDMAEMA brushes, surface wettability markedly altered even after only 5 min polymerization. The moderately hydrophobic iCMPTMScovered PET roll film surface became hydrophilic with its water θS/θA/θR values changing from 88°/89°/79° to 65°/70°/ 27° after 60 min SI-ATRP. In addition, using the same protocol, pDMAEMA brushes possessing reasonable surface quality and sufficient thicknesses (about 80 nm) could be successfully prepared on other substrates (glass, PC, and PET substrates, Table S1). Judging from the UV−vis spectra (Figure S2), the transparency of all samples was >83% in the visible light wavelength range, indicating no damage to the iCMPTMS from the reaction solution during SI-ATRP. To realize extremely large-scale formation of polymer brushes, we also demonstrated open-air “paint on” SI-ATRP9 between two facing samples covered with our iCMPTMS (Figure S5). For example, the SI-ATRP precursor solution of pDMAEMA (about 0.02 mL/cm2) was carefully spread on the top of the iCMPTMS-covered PET film (40 × 40 cm2, cut from the roll film shown in Figure 3a), and then another PET roll film was gently placed on the top of the surface upside down, and kept undisturbed at room temperature for 30 min in air (Figure S5). In spite of such small amounts of the precursor solution and insufficient hydrophilicity of iCMPTMS, polymerizations could proceed efficiently evenly over the entire sample surfaces. Despite such large-size samples, the pDMEMA brush surface was highly homogeneous with a low distribution in its thickness (±4.0 nm) and water θS values (±1°) across the entire sample surfaces, as shown in Figure S6. These results clearly indicate that our method consisting of two processes, that is, sol−gel formation of iCMPTMS and subsequent “paint-on” SI-ATRP, enabled the preparation of homogeneous polymer brushes on large-scale substrates without special reaction apparatuses and severe reaction conditions.

submersion in organic liquids for >12 h at room temperature with no delamination. Such chemical/physical stability is crucial for the subsequent SI-ATRP, which requires various organic solvents to dissolve monomers and catalysts. Next, we tested our sol−gel iCMPTMS initiator surfaces in SI-ATRP reactions. A typical waterborne monomer, namely, N,N-dimethylaminoethyl methacrylate (DMAEMA), was grown using our iCMPTMS-covered organic/inorganic substrates at different polymerization times between 5 and 180 min (Table S1). SI-ATRP was conducted under activators regenerated by electron transfer (ARGET) conditions (Figure 4a). The DMAEMA polymer (pDMAEMA) brushes were prepared according to the following procedure. Briefly, DMAEMA, water, Cu(II)Cl2 (catalyst), and N,N,N′,N″,N″pentamethyldiethylenetriamine (PMDETA, ligand) were first mixed in a glass vial. A water solution of AA (reducing agent) was then added, and the solution was stirred for about 2 min. Afterward, a proper amount of the reaction solution was added to other glass vials, placed together with the iCMPTMS-covered organic/inorganic substrates. As a control, Si substrates covered with a CMPTMS monolayer (we hereafter refer to this monolayer as mCMPTMS, thickness was about 1.9 nm) were also prepared by conventional chemical vapor deposition (CVD)31 and tested against iCMPTMS in terms of the growth kinetics of polymer brushes and their final surface properties. As shown in Figure 4b, in the case of iCMPTMS-covered PET roll film, the ARGET-ATRP gave a fast increase in dry thickness of pDMAEMA brushes against polymerization time, which quickly increased to about 56 nm during first 30 min and then continued to gradually increase when the polymerization time was extended up to 2 h. The final thicknesses of the pDMAEMA brushes (about 64 nm for PET roll film) were almost identical to those of the pDMAEMA brushes grafted from the mCMPTMS (66 nm, Figure 4c) and iCMPTMS on other substrates (Table S1), which also showed very similar growth kinetics. As confirmed by OM and AFM, in both cases, surface morphologies remained almost unchanged (Rrms was 80% RH, ∼50 °C) for 15 s. After this, optical images were immediately taken using a digital camera (PowerShot G1 X Mark II. Canon, Japan). Surface morphology and composition of deposited Cu layer were analyzed by a scanning electron microscope (SEM, Phenom Pro Scanning Electron Microscope, Phenom World, Netherland) with energy-dispersive X-ray spectroscopy (EDS) with an accelerating voltage of 15 kV. Preparation of iCMPTMS by Spin-Coating. Our sol−gel derived initiator layer was prepared using a conventional co-hydrolysis and cocondensation method according to our previous reports.24,25 A precursor solution was prepared by mixing CMPTMS (0.67 mL, 3.2 mmol) and TEOS (2.8 mL, 12.8 mmol) in an ethanol (8.0 mL)/0.01 M HClaq (1.0 mL) solution for 24 h at room temperature. Under these acidic conditions, complete hydrolysis of alkoxysilyl groups occurred, followed by the condensation of silanol groups to form polymer, as reported previously.24,25 This precursor solution was then spin-cast (1000 rpm for 5 s and 2000 rpm for 10 s) on UV/ozone-cleaned inorganic substrates, including Si (2 × 2 cm2), Cu (2 × 2 cm2), and glass (4 × 4 cm2), and no-activated organic substrates, including PC (4 × 4 cm2), and PET (4 × 4 cm2). After spin-coating, all samples were then dried in air at room temperature for 24 h. We refer to this sol−gel derived initiator layer as iCMPTMS. Preparation of CMPTMS Monolayer (mCMPTMS) on Si Substrate by CVD. As a control, an ATRP-reactive monolayer was also prepared on Si substrate by chemical vapor deposition (CVD) using CMPTMS.30 UV-ozone-cleaned Si substrates (2 × 2 cm2) were placed in a Teflon container with a glass vessel containing 0.1 mL of CMPTMS. The container was sealed and then heated for >6 h in an oven maintained at 120 °C. The treated samples were then rinsed with n-hexane, ethanol, and Milli-Q water repeatedly and finally blown dry with a stream of N2 gas. Si substrates covered with CMPTMS monolayer were cut into 1 × 1 cm2 and then used for SI-ATRP. We refer to this initiator monolayer as mCMPTMS. Preparation of Large-Scale iCMPTMS Formed on Substrates by Roll-to-Roll Coating Process. The PET roll film used in this study was a commercially available one having easily adhesive layers (polyester-based varnish) on both sides (Toray Co. Ltd., Lumirror U483, 125 μm thickness) in a roll with a width of 40 cm and a length of 100 m. The sol−gel solution used was 5-fold diluted original precursor solution as mentioned above with ethanol. Our roll-to-roll coating process was based on a microgravure coating technique. The system consisted of four components: film feeding station, coating part, drying oven, and winding station. The coating speed was set at 5 m/min, and the film was dried through an oven (80 °C, 4.5 m long), yielding a calculated dry film layer thickness of 110 nm. SI-ATRP of DMAEMA from iCMPTES- or mCMPTES-Covered Si Substrates and iCMPTES-Covered PET Roll Film. pDMAEMA brushes were prepared through an ARGET-ATRP process in both closed and open systems on each iCMPTES and mCMPTES layer by

METHODS

Materials. (p-Chloromethyl)phenyltrimethoxysilane (CMPTMS) was purchased from Gelest Inc. (Morrisville, PA). 0.01 M hydrochloric acid (HCl), ethanol, ascorbic acid (AA), copper (Cu) plates (purity >99.90%), acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and dichloromethane (DCM) were purchased from Wako Pure Chemical Industries Ltd. (Osaka, Japan). Tetraethoxysilane (TEOS), N,Ndimethylaminoethyl methacrylate (DMAEMA), N,N-dimethylaminoethyl acrylate (DMAEA), 2-(diethylamino)ethyl methacrylate (DEAEMA), 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate (HEA), 2-[2-(2-methoxyethoxy)ethoxy]ethyl acrylate (MEO2A), and 1-vinylimidazole (VIm) were purchased from Tokyo Chemical Industry Co. Ltd. (Tokyo, Japan). Copper(II) chloride (CuCl2), N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), 3-sulfopropyl methacrylate potassium salt (SPMK), 2-acrylamido-2methyl-1-propanesulfonic acid sodium salt (AMPSNa), and poly(ethylene glycol) methacrylate (PEGMA, average Mn of 500) were purchased from Sigma-Aldrich (St. Louis, MO). Silicon (Si) wafers (ntype [100]) were purchased from Shin-Etsu Handotai, Ltd. (Gunma, Japan). Glass slides (40 × 40 mm2) were purchased from Matsunami Glass Ind. Ltd. (Osaka, Japan). All inorganic substrates for spin-coating were cleaned by UV/ozone treatment for 30 min before use. Poly(ethylene terephthalate) (PET, 60 × 90 cm2) substrates were purchased from Sumitomo Bakelite Co., Ltd. (Tokyo, Japan). Polycarbonate (PC, 99.5 × 100 cm2) substrates were purchased from AS ONE Corporation (Osaka, Japan). They were cut into 40 × 40 mm2 and used without any surface activation. All other chemicals and solvents were purchased from commercial sources and used as received without further purification. Measurements. The film thicknesses of the samples were measured by spectroscopic mode of a confocal microscope (OPTELICS HYBRID, Lasertec Corporation, Japan). Surface topography of the samples was observed by the same confocal microscope (macroscopic, scan area: 150 × 150 μm2 to 1.5 × 1.5 mm2) and an atomic force microscope (AFM, XE-100, Park Systems, Korea) using a noncontact mode with Si cantilever (Park Systems, 910MNCHR; spring constant = 42 N/m and response frequency of 330 kHz; microscopic, scan area: 3 × 3 μm2). Surface chemical compositions were analyzed by X-ray photoelectron spectroscopy (XPS, KRATOS ULTRA2, Shimadzu Co. Ltd., Japan) using Al Kα radiation. The X-ray source was operated at 300 W for wide scan and 75 W for narrow scan. The optical G

DOI: 10.1021/acs.macromol.8b02234 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules following our previous method.9 DMAEMA (8 mL, 47 mmol), CuCl2 (2.8 mg, 0.02 mmol), PMEDTA (10 μL, 0.05 mmol), and water (7 mL) were added to a glass vial and immediately mixed by a Vortex mixer. AA (10 mg, 0.05 mmol) was then added to this solution and stirred for ∼2 min to activate the catalyst. Afterward, 2 mL of the reaction solution was separately added to other glass vials (20 mL) with pieces of iPCMPTMS- and mPCMPTMS-covered (1 × 2 cm2 for PET and 1 × 1 cm2 for Si) substrates at the same time. Polymerizations were conducted at room temperature under ARGET conditions without stirring. After an appropriate reaction time, the samples were removed from the solution. They were then extensively rinsed with ethanol and Mill-Q water repeatedly and were blown dry with a N2 gas stream. “Paint-On” SI-ATRP of Waterborne Monomers Grafted from iCMPTES Formed on Large-Scale Substrates. “Paint-on” SI-ATRP (ARGET-ATRP in air),9 which was recently developed by some of the authors, was demonstrated on large-size PET roll films. The identical precursor solution of SI-ATRP for pDMAEMA or pSPMK (about 0.02 mL/cm2) was carefully spread on the top of the iCMPTMS-covered PET roll film (40 × 40 cm2), and then another roll film was gently placed on the top of the surface upside down and kept undisturbed at room temperature for 30 min in air. After this, each sample was rinsed with Mill-Q water repeatedly and were then blown dry with a N2 gas stream. Besides PET roll films, pDMAEMA brushes were similarly grafted on the wire-bar-coated iCMPTMS-covered glass slides or PC substrates (50 × 50 cm2; see the Supporting Information for details) in the same way. Electroless Cu Plating on pDMAEMA-Covered PET Roll Film. A large PET roll film covered with pDMAEMA (28 × 20 cm2) was first activated for 2 h by immersion in 1.4 mM Pd(II) chloride acid aqueous solution (pH 2.4). The activated sample was then immediately immersed in a commercial electroless Cu plating bath (THRUCUPPEA, C. Uyemura & Co., Ltd.) containing formaldehyde as a reducing agent for 30 min at room temperature with shaking. After plating, the sample was washed with Milli-Q water repeatedly and blowdried with a N2 stream. The sample was studied by OM, SEM, and EDS. Both SEM observation and EDS analysis were performed without a conductive coating on the samples.

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measurements. They also thank Mr. Masato Kimura, Higashiyama Film Co., Ltd., for helping in roll-to-roll coating.

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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.8b02234. Detailed syntheses procedures; summary table for polymer brushes on various substrates; OM images; AFM images; UV−vis spectra; structural representation, OM image and SEM image with EDS analysis of the sample after electroless copper plating (DOCX) Movie S1 (MOV) Movie S2 (MOV)

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REFERENCES

(1) Zhao, B.; Brittain, W. J. Polymer Brushes: Surface-immobilized Macromolecules. Prog. Polym. Sci. 2000, 25, 677−710. (2) Matyjaszewski, K. Advanced Materials by Atom Transfer Radical Polymerization. Adv. Mater. 2018, 30, 1706441. (3) Zhou, F. S.; Huck, W. T. Surface grafted polymer brushes as ideal building blocks for “smart” surfaces. Phys. Chem. Chem. Phys. 2006, 8, 3815−3823. (4) Higaki, Y.; Kobayashi, M.; Murakami, D.; Takahara, A. Antifouling Behavior of Polymer Brush Immobilized Surfaces. Polym. J. 2016, 48, 325−331. (5) Zoppe, J. O.; Ataman, N. C.; Mocny, P.; Wang, J.; Moraes, J.; Klok, H. A. Surface-Initiated Controlled Radical Polymerization: State-ofthe-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes. Chem. Rev. 2017, 117, 1105−1318. (6) Chen, W. L.; Cordero, R.; Tran, H.; Ober, C. K. 50th Anniversary Perspective: Polymer Brushes: Novel Surfaces for Future Materials. Macromolecules 2017, 50, 4089−4113. (7) Matyjaszewski, K.; Dong, H.; Jakubowski, W.; Pietrasik, J.; Kusumo, A. Grafting from Surfaces for “Everyone”: ARGET ATRP in the Presence of Air. Langmuir 2007, 23, 4528−4531. (8) Yeow, J.; Chapman, R.; Gormley, A. J.; Boyer. Up in the Air: Oxygen Tolerance in Controlled/living Radical Polymerisation. C. Chem. Soc. Rev. 2018, 47, 4357−4387. (9) Dunderdale, G. J.; Urata, C.; Miranda, D. F.; Hozumi, A. LargeScale and Environmentally Friendly Synthesis of pH Responsive OilRepellent Polymer Brush Surfaces under Ambient Conditions. ACS Appl. Mater. Interfaces 2014, 6, 11864−11868. (10) Dunderdale, G. J.; England, M. W.; Urata, C.; Hozumi, A. Polymer Brush Surfaces Showing Superhydrophobicity and Air-Bubble Repellency in a Variety of Organic Liquids. ACS Appl. Mater. Interfaces 2015, 7, 12220−12229. (11) Zhang, T.; Du, Y.; Kalbacova, J.; Schubel, R.; Rodriguez, R. D.; Chen, T.; Jordan, R. Wafer-Scale Synthesis of Defined Polymer Brushes under Ambient Conditions. Polym. Chem. 2015, 6, 8176−8183. (12) Enciso, A. E.; Fu, L.; Russell, A. J.; Matyjaszewski, K. A Breathing Atom -Transfer Radical Polymerization: Fully Oxygen- Tolerant Polymerization Inspired by Aerobic Respiration of Cells. Angew. Chem., Int. Ed. 2018, 57, 933−936. (13) Murugan, P.; Krishnamurthy, M.; Jaisankar, S. N.; Samanta, D.; Mandal, A. B. Controlled Decoration of the Surface with Macromolecules: Polymerization on a Self-assembled Monolayer (SAM). Chem. Soc. Rev. 2015, 44, 3212−3243. (14) Ejaz, M.; Yamamoto, S.; Ohno, K.; Tsujii, Y.; Fukuda, T. Controlled Graft Polymerization of Methyl Methacrylate on Silicon Substrate by the Combined Use of the Langmuir-Blodgett and Atom Transfer Radical Polymerization Techniques. Macromolecules 1998, 31 (17), 5934−5936. (15) Yan, J.; Pan, X.; Wang, Z.; Lu, Z.; Wang, Y.; Liu, L.; Matyjaszewski, K. A Fatty Acid-Inspired Tetherable Initiator for Surface-Initiated Atom Transfer Radical Polymerization. Chem. Mater. 2017, 29, 4963−4969. (16) Edmondson, S.; Armes, S. P. Synthesis of Surface-initiated Polymer Brushes Using Macro-initiators. Polym. Int. 2009, 58, 307− 316. (17) Matsugi, T.; Saito, J.; Kawahara, N.; Matsuo, S.; Kaneko, H.; Kashiwa, N.; Kobayashi, M.; Takahara, A. Surface Modification of Polypropylene Molded Sheets by Means of Surface-Initiated ATRP of Methacrylates. Polym. J. 2009, 41, 547−554. (18) Kuang, J.; Messersmith, P. B. Universal Surface-Initiated Polymerization of Antifouling Zwitterionic Brushes Using a MusselMimetic Peptide Initiator. Langmuir 2012, 28, 7258−7266. (19) Pranantyo, D.; Xu, L. Q.; Neoh, K. G.; Kang, E. T.; Ng, Y. X.; Teo, S. L. M. Tea Stains-Inspired Initiator Primer for Surface Grafting of Antifouling and Antimicrobial Polymer Brush Coatings. Biomacromolecules 2015, 16, 723−732.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Atsushi Hozumi: 0000-0003-4375-3785 Present Address

G.J.D.: Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, UK. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors express their gratitude to Mr. Mitsuhiko Yoshimi and Mr. Shunsuke Watanabe, Shimadzu Co. Ltd., for the XPS H

DOI: 10.1021/acs.macromol.8b02234 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules (20) Parry, A. V. S.; Straub, A. J.; Villar-Alvarez, E. M.; Phuengphol, T.; Nicoll, J. E. R.; Lim, X.; Jordan, L. M.; Moore, K. L.; Taboada, P.; Yeates, S. G.; Edmondson, S. Sub-Micron Patterning of Polymer Brushes: An Unexpected Discovery from Inkjet Printing of Polyelectrolyte Macroinitiators. J. Am. Chem. Soc. 2016, 138, 9009− 9012. (21) Coad, B. R.; Styan, K. E.; Meagher, L. One step ATRP Initiator Immobilization on Surfaces Leading to Gradient-Grafted Polymer Brushes. ACS Appl. Mater. Interfaces 2014, 6, 7782−7789. (22) Ohno, K.; Kayama, Y.; Ladmiral, V.; Fukuda, T.; Tsujii, Y. A Versatile Method of Initiator Fixation for Surface-Initiated Living Radical Polymerization on Polymeric Substrates. Macromolecules 2010, 43, 5569−5574. (23) Coad, B. R.; Lu, Y.; Glattauer, V.; Meagher, L. SubstrateIndependent Method for Growing and Modulating the Density of Polymer Brushes from Surfaces by ATRP. ACS Appl. Mater. Interfaces 2012, 4, 2811−2823. (24) Shimojima, A.; Kuroda, K. Designed Synthesis of Nanostructured Siloxane−Organic Hybrids from Amphiphilic SiliconBased Precursors. Chem. Rec. 2006, 6, 53−63. (25) Urata, C.; Cheng, D. F.; Masheder, B.; Hozumi, A. Smooth, Transparent and Nonperfluorinated Surfaces Exhibiting Unusual Contact Angle Behavior Toward Organic Liquids. RSC Adv. 2012, 2, 9805−9808. (26) Urata, C.; Masheder, B.; Cheng, D. F.; Hozumi, A. Unusual Dynamic Dewetting Behavior of Smooth Perfluorinated Hybrid Films: Potential Advantages over Conventional Textured and Liquid-Infused Perfluorinated Surfaces. Langmuir 2013, 29, 12472−12482. (27) Urata, C.; Masheder, B.; Cheng, D. F.; Miranda, D. F.; Dunderdale, G. J.; Miyamae, T.; Hozumi, A. Why Can Organic Liquids Move Easily on Smooth Alkyl-Terminated Surfaces? Langmuir 2014, 30, 4049−4055. (28) Brandow, S. L.; Chen, M.-S.; Aggarwal, R.; Dulcey, C. S.; Calvert, J. M.; Dressick, W. J. Fabrication of Patterned Amine Reactivity Templates Using 4-Chloromethylphenylsiloxane Self-Assembled Monolayer Films. Langmuir 1999, 15, 5429−5432. (29) Wu, T.; Efimenko, K.; Vlček, P.; Š ubr, V.; Genzer, J. Formation and Properties of Anchored Polymers with a Gradual Variation of Grafting Densities on Flat Substrates. Macromolecules 2003, 36, 2448− 2453. (30) ISO 2409:1992 & JIS K-5600: 1999 “Paints, and varnishes − Cross-cut test”. (31) Hozumi, A.; Ushiyama, K.; Sugimura, H.; Takai, O. Fluoroalkylsilane Monolayers Formed by Chemical Vapor Surface Modification on Hydroxylated Oxide Surfaces. Langmuir 1999, 15, 7600−7604. (32) Kobayashi, M.; Yamaguchi, H.; Terayama, Y.; Wang, Z.; Ishihara, K.; Hino, M.; Takahara, A. Structure and Surface Properties of Highdensity Polyelectrolyte Brushes at the Interface of Aqueous Solution. Macromol. Symp. 2009, 279, 79−87. (33) Ezzat, M.; Huang, C. Zwitterionic Polymer Brush Coatings with Excellent Anti-fog and Anti-frost Properties. RSC Adv. 2016, 6, 61695− 61702. (34) Kobayashi, M.; Terayama, Y.; Yamaguchi, H.; Terada, M.; Murakami, D.; Ishihara, K.; Takahara, A. Wettability and Antifouling Behavior on the Surfaces of Superhydrophilic Polymer Brushes. Langmuir 2012, 28, 7212−7222. (35) Azzaroni, O.; Zheng, Z.; Yang, Z.; Huck, W. T. S. Polyelectrolyte Brushes as Efficient Ultrathin Platforms for Site-Selective Copper Electroless Deposition. Langmuir 2006, 22, 6730−6733.

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DOI: 10.1021/acs.macromol.8b02234 Macromolecules XXXX, XXX, XXX−XXX