Synthesis and Postfunctionalization of Rod–Coil Diblock and Coil

Nov 30, 2012 - Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan. Macromolecules , 2012, 45 (24), ...
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Synthesis and Postfunctionalization of Rod−Coil Diblock and Coil− Rod−Coil Triblock Copolymers Composed of Poly(3-hexylthiophene) and Poly(4-(4′‑N,N‑dihexylaminophenylethynyl)styrene) Segments Hiroyuki Fujita,† Tsuyoshi Michinobu,‡,* Masatoshi Tokita,† Mitsuru Ueda,† and Tomoya Higashihara†,§,* †

Department of Organic and Polymeric Materials, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552, Japan ‡ Global Edge Institute, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8550, Japan § Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan S Supporting Information *

ABSTRACT: Poly(3-hexylthiophene) (P3HT) with a bromobutyl functional group at the ω-chain-end (P3HT-C4Br) and P3HT with bromobutyl functional groups at the α,ωchain-ends (BrC4-P3HT-C4Br) were synthesized by selecting the appropriate initiators for the Grignard metathesis (GRIM) polymerization. The high end-functionality was confirmed by matrix assisted laser desorption-ionization time-of-flight (MALDI−TOF) mass spectrometry. These polymers were efficiently reacted with the living anionic polymers of 4-(4′N,N-dihexylaminophenylethynyl)styrene (DHPS) to yield novel rod−coil diblock and coil−rod−coil triblock copolymers composed of rigid P3HT and flexible poly(4-(4′-N,Ndihexylaminophenylethynyl)styrene) (PDHPS) segments. The expected structures of the block copolymers were confirmed by size exclusion chromatography (SEC), proton nuclear magnetic resonance (1H NMR), and Fourier transform infrared (FT-IR) spectroscopies. Furthermore, the side chain alkynes of the PDHPS segments of both P3HT-b-PDHPS and PDHPS-b-P3HT-bPDHPS were quantitatively functionalized by a [2 + 2] cycloaddition followed by a cycloreversion with tetracyanoethylene (TCNE), producing the corresponding block copolymers with donor−acceptor moieties in the flexible polystyrene segments. The formation of the new chromophores was confirmed by UV−vis spectroscopy and cyclic voltammetry (CV), which revealed strong intramolecular charge-transfer bands and redox activities ascribed to the formed donor−acceptor moieties. The thermal properties and surface morphology of the block copolymers were also evaluated by differential scanning calorimetry (DSC), atomic force microscopy (AFM) observations, and small-angle and wide-angle X-ray scattering (SAXS and WAXS). This is the first report about the development of P3HT-based block copolymers with tunable optoelectronic properties, which was achieved by the combined synthetic techniques of the GRIM polymerization, living anionic polymerization, and click postfunctionalization.

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separation of dissimilar segments.9 Since the flexible coil segments tend to effectively assist the microphase separation by preventing the aggregation of the crystalline P3HT domains, the rod−coil types seem to be superior to the rod−rod types in the sense of morphological control. To synthesize well-defined rod−coil block copolymers containing a P3HT segment, multistep and complex site transformation reactions have been required because different polymerization systems must, in general, be used for the synthesis of each P3HT and coil segments. This difficulty has limited the establishment of a general synthetic route to the well-defined rod−coil block copolymers. Nevertheless, some

INTRODUCTION There has been growing attention paid to poly(3alkylthiophene)s (PATs) in the field of polymer electronic devices, such as organic field-effect transistors1 and organic photovoltaic cells,2 because PATs are the best class of balanced high-performance materials as p-type semiconductors in terms of solubility, chemical stability, charge mobility, and commercial availability. The discovery of the quasi-living GRIM polymerization system, independently reported by Yokozawa et al.3 and McCullough et al.,4,5 made it possible to synthesize a wide variety of chain-end-functional polythiophene derivatives,6 their block copolymers5,7 and star-branched polymers.8 Among them, rod−coil block copolymers containing the poly(3hexylthiophene) (P3HT) moiety as a rod segment are of particular interest due to their unique self-assembled structures on a nanometer scale, originating from the microphase © 2012 American Chemical Society

Received: August 9, 2012 Revised: November 19, 2012 Published: November 30, 2012 9643

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polymers including polystyrenes, polyurethanes, polyacetylenes, conjugated polymers, and aromatic polyamines were successfully functionalized by this method.17 In the previous studies of the P3HT-based rod−coil block copolymers, the energy levels of the coil segments were inevitably determined by the vinyl monomer structures, and the number of available vinyl monomers was limited from the synthetic standpoint. However, such a polymer functionalization method based on the new click chemistry would provide the desired (or varied) energy levels of the coil segments, and this will lead to the fast energy transfer from P3HT into the coil segments in organic solar cells. We now report the synthesis and postfunctionalization of rod−coil diblock and coil−rod−coil triblock copolymers composed of P3HT and poly(4-(4′-N,Ndihexylaminophenylethynyl)styrene) (PDHPS) segments, P3HT-b-PDHPS and PDHPS-b-P3HT-b-PDHPS, respectively, by the combination of the GRIM polymerization, living anionic polymerization, and click postfunctionalization. The brominated polythiophene derivatives, P3HT-C4Br and BrC4− P3HT-C4Br, were for the first time synthesized by selecting the appropriate initiators, and the individual polythiophenes were isolated. These polymers were then reacted with the living anionic polymers of DHPS to produce the corresponding block copolymers. Furthermore, the block copolymers were postfunctionalized with TCNE. The thermal, optical, and electrochemical properties as well as the thin film and bulk sample morphology are comprehensively investigated. This study established the general synthetic route to the P3HT-based block copolymers with tunable optoelectronic and selfassembling properties.

rod−coil block copolymers composed of P3HT segments have already been reported.10 We have also succeeded in synthesizing polystyrene-b-P3HT-b-polystyrene and poly(4-N,N-diphenylaminostyrene)-b-P3HT-b-poly(4-N,N-diphenylaminostyrene) by the combination of the GRIM polymerization and living anionic polymerization techniques.11,12 The synthetic methodology requires only two reaction steps, (a) the synthesis of P3HT with 1,1-diphenylethylene (DPE) functional groups at α,ω-chain-ends (DPE-P3HT-DPE) and (b) the linking reaction of DPE-P3HT-DPE with 2 equiv of the living anionic polystyrene or poly(4-N,N-diphenylaminostyrene). Because of the living anionic polymerization system and reduced reaction steps, the polydispersity indices (PDIs) of the final products are relatively low (PDI < 1.2). Although significant purification efforts are required to remove homopolymers used in excess and/or unreacted in the linking reaction, the most advantageous feature of this polymer/polymer linking method is the high accuracy of individual polymer segments in the block copolymers in terms of the molecular weights and molecular weight distributions, as compared to other initiation methods using end-functionalized polymers. In addition to the excellent semiconducting characteristics of P3HT, it is also expected that the coil segments show some specific properties, especially when the applications to organic solar cells are considered. Although the triphenylamine moiety, previously adopted as a side chain of the coil segments, is redox active and possesses p-type semiconducting features, the absorption range is limited in the ultraviolet (UV) region.12 Also, the shallow lowest unoccupied molecular orbital (LUMO) level of the triphenylamine unit generally hinders the efficient energy transfer from P3HT to the coil segments. To expand the absorption range into the visible-near-infrared and lower the LUMO level, intramolecular charge-transfer (CT) interactions are often used. Since aromatic amines are a strong electron-donating group, the direct substitution by electron-accepting moieties would result in a new low-energy CT band due to the elevation of the highest occupied molecular orbital (HOMO) level and reduction of the LUMO level. However, electron-accepting units are usually unstable under anionic polymerization conditions. Thus, the electron-accepting moieties have not been introduced into the P3HT-based rod− coil block copolymers. Recently, another approach to construct donor−acceptor chromophores in polymer side chains was proposed. That is based on the formation of electron-accepting units during the last stage of the polymer functionalization by high-yielding addition reactions between electron-rich alkynes and strong acceptor molecules, such as tetracyanoethylene (TCNE).13 A [2 + 2] cycloaddition of the electron-deficient olefin of TCNE to electron-rich alkynes, followed by a cycloreversion, yields donor-substituted 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) chromophores.14 When alkynes are substituted by aromatic amines, this reaction quickly proceeds under mild conditions without any side reactions and byproducts. Accordingly, this class of reactions is regarded as metal-free click chemistry.15 A significant advantage of this reaction over the conventional click chemistry reactions, such as the azide−alkyne cycloaddition, thiol−ene reactions, and Diels−Alder reactions, is the emergence of new functinonalities based on intramolecular CT interactions. For example, an improved second-order nonlinearity, metal ion sensitivity, and energy level tuning ability were realized.16 This method is highly promising because of its applicability to almost all polymers. Indeed, various

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RESULTS AND DISCUSSION Synthesis of Chain-end Functional P3HT. The chainend functionalization of P3HT is a very important step for obtaining rod−coil block copolymers, because the terminal functional groups are responsible for the introduction of the coil segments. McCullough reported the chain-end functionalization of P3HT by terminating the quasi living P3HTNi(dppp)Br (dppp = diphenylphosphinopropane) with the Grignard reagent (R-MgX).6 However, the R-MgX type significantly affected the final product structures as to whether the monofunctionalization at the ω-terminal or difunctionalization at the α,ω-termini takes place. This fact suggested the difficulty in selectively synthesizing either the mono- or difunctional P3HT derivatives. For instance, during the course of our studies on the synthesis of DPE-P3HT-DPE,11 we could not achieve the monofunctional P3HT with a DPE moiety, probably because of the diffusion of the Ni(0) species to the media after the monofunctionalization of P3HT-Ni(dppp)Br with the Grignard reagent of 1-(4-bromopropylphenyl)-1phenylethylene (DPE-C4-MgBr), resulting in the occurrence of difunctionalization in terms of the oxidative insertion of the Ni(0) species to the α-chain-end. Luscombe and co-workers reported the efficient initiation from an o-halotoluene based on a ligand exchange approach, aimed at the synthesis of a defect-free regioregular P3HT.18 It should be noted that the initiation using Ni(dppp)Cl2 causes tail-to-tail dimer formation at the initiating site.3−5 On the basis of this finding, we first intended to synthesize the monofunctional P3HT, in which only the ω-chain-end was terminated by P3HT-Ni(dppp)Br with R-MgX. The α-chain-end was capped by the tolyl group. As can be seen in Scheme 1a, the ligand of 9644

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Scheme 1. Synthesis of (a) 8, P3HT-C4Br, and (b) 9, BrC4-P3HT-C4Br

the trans-bromo(tolyl)bis(triphenylphosphine)nickel(II) complex (1) was replaced with dppp in tetrahydrofuran (THF) at room temperature to yield the monofunctional initiator, the cisbromo(tolyl)(dppp)nickel(II) complex (2). This was followed by the initiation of 2-bromo-5-chloromagnesio-3-hexylthiophene (4) in THF, which was obtained by the Grignard exchange reaction of 2,5-dibromo-3-hexylthiophene (3) with isopropylmagnesium chloride (iPrMgCl). By terminating the monofunctional living polymer (5) with 2-(4-bromobutyl)-5(chloromagnesio)thiophene (7), which was obtained by the Grignard exchange reaction of 5-bromo-2-(4-bromobutyl)thiophene (6) with iPrMgCl, P3HT with the bromobutyl functional group at the ω-chain-end (8: P3HT-C4Br) was successfully obtained. When Ni(dppp)Cl2 was used as the initiator instead of 2, P3HT with the bromobutyl functional groups at the α,ω-chain-ends (9: BrC4-P3HT-C4Br) was obtained (Scheme 1b). The polymer structures were characterized by SEC, 1H NMR, FT-IR, and MALDI−TOF mass spectrometry. The selected data are summarized in Table 1. In the SEC curves of 8 and 9 (Figure 1a for 8 and Figure 2a for 9), unimodal peaks were observed, indicating the living manner of the GRIM polymerization system. The estimated molecular weights were ca. 10 000 and the polydispersity indices (PDIs) were narrow (1.11). The 1H NMR spectrum of 8 is shown in Figure 3a. There is the characteristic singlet signal d at 2.48 ppm, assignable to the three methyl protons of the tolyl initiating site. Also, the triplet signal b ascribed to the two methylene protons next to the terminal Br group is observed at 3.43 ppm. The peak intensity ratio d:b was determined to be 3.12:2.00, which is close to the theoretical value of 3:2. This result indicates that the efficient initiation and monofunctionalization reactions proceeded without any undesired chaintransfer or termination reactions. The molecular weight of 8, calculated from the ratio of the 1H NMR peak intensities, was close to that determined by SEC. The 1H NMR spectrum of 9

Table 1. Molecular Weights, Polydispersities, and Composition of Polymers P3HT: PSt derivatives

Mn (g/mol) SECa

PDIa

(mol %)

(wt %)

42 400d

11 000 12 500 31 300 42 300 10 700 10 600 40 900

1.11 1.06 1.06 1.15 1.11 1.05 1.05

− − 49:51b 49:51e − − 37:63b

− − 29:71 24:76 − − 20:80

53 400d

56 300

1.07

37:63e

16:84

1

polymer

H NMR

P3HT-C4Br (8) PDHPSc P3HT-b-PDHPS (11) P3HT-b-PTCNE (13) BrC4−P3HT-C4Br (9) PDHPSf PDHPS-b-P3HT-bPDHPS (12) PTCNE-b-P3HT-bPTCNE (14)

b

9 800 − 32 800d 40 400d 8 800b

a

Calculated from the calibration using polystyrene standards. Calculated from the peak intensity ratio between the thiophene ring and alkyl groups. cThe coil segment used for the synthesis of 11 after capped with DPE. dCalculated from the peak intensity ratio and each molecular weight. eThe same composition ratios as the corresponding precursor polymers. fThe coil segment used for the synthesis of 12 after capped with DPE. b

(Figure 3b) also confirmed the progress of the efficient difunctionalization reaction. The peak positions and integration ratios were consistent with the chemical structure and the estimated molecular weight of 9. Furthermore, the MALDI− TOF mass spectra of 8 and 9 (Figure 4, parts a and b, respectively) showed a series of peaks corresponding to the calculated molecular ions or their protonated forms. In the case of the monofunctional P3HT 8, the most intense molecular ion peak was detected at m/z = 5297.4, which agreed well with the theoretical value of the 30-mer ([M]+ = 5297.66, m = 30). The protonated forms were also sometimes detected. A sharp peak ascribed to the protonated 29-mer ([M + H+] = 5132.38, m = 29) was clearly observed. Accordingly, reasonable peak intervals corresponding to the monomer repeat unit (166.28) were 9645

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Figure 1. SEC curves of (a) 8, P3HT-C4Br, (b) PDHPS, (c) crude products after the coupling reaction of 8 with the living PDHPS, (d) 11, P3HT-b-PDHPS, after HPLC fractionation, and (e) 13, P3HT-bPTCNE.

Figure 3. 1H NMR spectra of (a) 8 and (b) 9 in CDCl3 at 25 °C. The residual CHCl3 peak is marked.

Figure 2. SEC curves of (a) 9, BrC4−P3HT-C4Br, (b) PDHPS, (c) crude products after the coupling reaction of 9 with the living PDHPS, (d) 12, PDHPS-b-P3HT-b-PDHPS, after HPLC fractionation, and (e) 14, PTCNE-b-P3HT-b-PTCNE.

The living polymers were quenched with methanol, yielding PDHPS. The time-dependent conversion of DHPS into PDHPS was investigated from the polymerization experiments in benzene at 25 °C. The representative SEC curves are shown in Figure 5a and the results are summarized in Table 2. The SEC curves of the products directly collected from a reaction flask (before precipitation into methanol) at varying times gradually shifted to higher molecular weight ranges, maintaining the narrow PDI of 98% purities) were purchased from Aldrich, Japan, and used as received unless otherwise noted. Benzene (superdehydrated, Wako Pure Chemical Industries, Ltd.) and tetrahydrofuran (THF) (superdehydrated, Wako Pure Chemical Industries, Ltd.) were used as received in a glovebox in a nitrogen atmosphere. 2,5-Dibromo-3-hexylthiophene 3 was purchased from Aldrich, Japan, and distilled under the reduced pressure just before use. trans-Bromo(tolyl)bis(triphenylphosphine)nickel(II) complex, 1,29 and 2-(4-bromobutyl)thiophene30 were synthesized according to the literature methods. 4-(4′-N,N-dihexylaminophenylethynyl)styrene (DHPS) was synthesized by Sonogashira coupling between 4ethynylstyrene and N,N-dihexyl-4-iodoaniline. General Measurements. 1H NMR spectra were recorded on a JEOL model AL300 or ECS400 spectrometer at 25 or 40 °C. Deuterated chloroform was used as a solvent. Chemical shifts are reported in ppm (parts per million) using either tetramethylsilane (TMS) or residual solvent signals as an internal reference. Coupling constants (J) are given in Hz. The resonance multiplicity is described as s (singlet), d (doublet), t (triplet), and m (multiplet). Fourier transform infrared (FT-IR) spectra were recorded on a JASCO FT/IR4100 spectrometer in the range from 4000 to 600 cm−1. MALDI− TOF mass spectra were measured on a Shimadzu/Karatos AXIMACFR mass spectrometer using 2,2′:5,2″-terthiophene as a matrix. Size exclusion chromatography (SEC) was measured on a JASCO GULLIVER 1500 equipped with a pump, an absorbance detector (UV, λ = 254 nm), and three polystyrene gel columns based on a conventional calibration curve using polystyrene standards. THF (35 °C) was used as a carrier solvent at the flow rate of 1.0 mL min−1 after calibration with standard polystyrenes. Elemental analysis was performed on a YANACO CHN corder MT-6. UV−vis spectra were recorded on a JASCO V-670 spectrophotometer. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements were carried out on a Rigaku TG8120 and a Rigaku DSC8230, respectively, under nitrogen flow at the scan rate of 10 °C min−1. Electrochemistry measurements were carried out on a BAS electrochemical analyzer model 612C at 25 °C in a classical threeelectrode cell. The working, reference, and auxiliary electrodes were a glassy carbon electrode, Ag/AgNO3/CH3CN/(nC4H9)4NPF6, and a Pt wire, respectively. All potentials are referenced to the ferrocene/ ferricinium (Fc/Fc+) couple used as an internal standard. Atomic force microscopy (AFM) images were taken by a Seiko Instruments SPA400 with a stiff cantilever of Seiko Instruments DF-20. The SAXS and WAXS patterns were measured using Cu Kα (λ = 1.5418 Å) radiation with a Bruker AXS Nano-STAR-U and a Bruker D8 DISCOVER, respectively. The two-dimensional scattering patterns were measured using two-dimensional PSPC detectors, and the intensity was

The SAXS profiles of the block copolymers 11 and 12 are shown in Figure 12, parts c and d. The diblock copolymer 11 showed a peak at 2θ = 0.320° (d = 27.6 nm), while the peak of the triblock copolymer 12 was detected at 2θ = 0.508° (d = 17.4 nm). These peaks suggested the occurrence of the microphase separation between the rod and coil blocks. Furthermore, 12 displayed the weak shoulder peak centered at 2θ = 1.05° (d = 8.4 nm), which can be assigned as the second order reflection of the main peak. Taking into account the AFM phase image of the thin film of 12, it is reasonable to conclude that this triblock copolymer formed the lamellar structure in the bulk state. In contrast, no higher order peaks were observed for 11, and the d-spacing value was by ca. 10 nm larger than that of 12. Therefore, it is thought that 11 formed a different type of self-assembled structures. Dai and co-workers previously reported the relationship between the P3HT content and the microstructure of a rod−coil diblock copolymer, P3HT-bpoly(2-vinylpyridine).9 They found that the microstructure and d-spacing value of the block copolymer changed from spheres or disorder micelles (30 nm) to hexagonal close-packed cylinders (23.3 nm), lamellae (19.3 nm), and nanofibers (32 nm) with the increasing P3HT content. In our polymers, the diblock copolymer 11 has higher P3HT content (29 wt %) than the triblock copolymer 12 (20 wt %) with the lamellar structure. Thus, 11 most likely formed a nanofiber structure rather than a lamellar one, as also supported by the AFM phase image of the thin films.

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CONCLUSIONS The GRIM polymerization allowed for the synthesis of monoand difunctional P3HTs, i.e., P3HT-C4Br and BrC4-P3HTC4Br, respectively, by selecting the appropriate initiators. The selective and high end-functionality of those polymers was confirmed by MALDI−TOF mass spectrometry. On the other hand, the living anionic polymerization of DHPS with the initiator of sBuLi was demonstrated. By the coupling reaction of PDHPS-Li with P3HT-C4Br or BrC4-P3HT-C4Br, novel rod− coil diblock and coil−rod−coil triblock copolymers composed of the P3HT and PDHPS segments were synthesized, and they were characterized by SEC, 1H NMR, and FT-IR spectroscopies. The obtained block copolymers were then quantitatively 9653

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integrated azimuthally to obtain the scattering profile as a function of the diffraction angle of 2θ. The bulk samples for SAXS and WAXS measurements were prepared from polymer solutions in chloroform. The solvent was evaporated slowly over 24 h, and then annealed at 150 °C for 30 min under vacuum. 5-Bromo-2-(4-bromobutyl)thiophene (6). In a three-neck flask, 2-(4-bromobutyl)thiophene (10.0 g, 45.6 mmol) was placed and dissolved in chloroform (150 mL) and acetic acid (75 mL). After cooling to 0 °C, N-bromosuccinimide (8.43 g, 47.4 mmol) was added at once. The reaction mixture was stirred at room temperature overnight and poured into water (100 mL). After washing the organic phase with water, sodium bicarbonate aq., and water again, it was dried over magnesium sulfate. It was filtered and concentrated under reduced pressure. Finally silica gel flash column chromatography (eluent: hexane) of the crude product afforded analytically pure 6 as colorless oil (10.7 g, 36.0 mmol, 79%). 1H NMR (300 MHz, CDCl3): δ (ppm) 1.72−1.97 (−CH2CH2CH2Br, m, 4H), 2.78 (ArCH2−, t, J = 7.2 Hz, 2H), 3.41 (−CH2Br, t, J = 6.5 Hz, 2H), 6.55 (Ar, d, J = 3.6 Hz, 1H), 6.85 (Ar, d, J = 3.6 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ (ppm) 29.46, 29.88, 31.87, 33.29, 109.10, 124.85, 129.58, 146.38. Anal. Calcd for [C8H10Br2S]: C, 32.24; H, 3.38. Found: C, 32.40; H, 3.45. P3HT-C4Br (8). All the reactions were carried out in a glovebox under purified N2 atmosphere. In a 300 mL flask, 3 (2.00 g, 6.13 mmol) and LiCl (0.580 g, 13.6 mmol) were dissolved in THF (100 mL). A THF solution of iPrMgCl (2 M x 3.40 mL = 6.80 mmol) was then added to the solution and it was stirred at room temperature for 30 min to give the solution 4. In another flask, 1 (0.0770 g, 0.102 mmol) was dissolved in THF (20 mL), and dppp (84.0 mg, 0.204 mmol) was added. The solution was stirred at room temperature for 30 min to give the solution of 2. The solution of 2 was then added to the solution of 4 at once to start the polymerization, and the mixture was stirred for 15 min to give the solution of 5. In another flask, a THF solution of iPrMgCl (2 M x 0.510 mL = 1.02 mmol) was added to a THF solution (10 mL) of 6 (0.304 g, 1.02 mmol) and LiCl (86.0 mg, 2.04 mmol), and the mixture was stirred at room temperature for 30 min to obtain the solution of 7. The solution of 7 was added to the solution of 5 to terminate the polymerization. The solution was then poured into methanol/water (3/1) to precipitate the polymer. After filtration, the polymer was purified by Soxhlet extraction with methanol, hexane, and chloroform. The chloroform solution was passed through silica gel. After removal of the solvent, the polymer was freeze-dried from its absolute benzene solution to afford P3HT-C4Br (8). Yield: 0.705 g (67%). Mn = 11 000, PDI = 1.11. 1H NMR (300 MHz, CDCl3): δ (ppm) 0.91 (−CH3, t, J = 6.9 Hz, 3mH), 1.27−1.46 (Th−CH2CH2CH2CH2−, m, 6mH), 1.66−1.76 (Th−CH2CH2−, m, 2mH), 2.48 (tolyl, s, 3H), 2.80 (ThCH2−, t, J = 7.8 Hz, 2mH), 3.43 (−CH2Br, t, J = 6.4 Hz, 2H), 6.97 (Th, s, 1mH). IR (neat): 3059, 2953, 2923, 2854, 2671, 1635, 1562, 1509, 1455, 1377, 1302, 1259, 1204, 1113, 1092, 1049, 1019, 922, 888, 821, 757, 724, 676, 661, 647, 633, 615 cm−1. Anal. Calcd for [(C10H14S1)57 + C15H17S1Br1]: C, 71.77; H, 8.41. Found: C, 70.47, H, 8.15. Br-C4-P3HT-C4Br (9). The titled compound was synthesized in the same way as 8 in a glovebox under purified N2 atmosphere except for the use of Ni(dppp)Cl2 instead of 2. Yield: 0.167 g (63%). Mn = 10 700, PDI = 1.11. 1H NMR (300 MHz, CDCl3): δ (ppm) 0.92 (−CH3, t, J = 6.6 Hz, 3mH), 1.35−1.44 (Th−CH2CH2CH2CH2CH2−, m, 6mH), 1.69 (Th−CH2CH2−, m, 2mH), 2.81 (ThCH2−, t, J = 7.5 Hz, 2mH), 3.43 (−CH2Br, t, J = 6.3 Hz, 4H), 6.98 (Th, s, 1mH). IR (neat): 3057, 2953, 2923, 2854, 2668, 1650, 1559, 1541, 1509, 1455, 1376, 1340, 1302, 1252, 1203, 1112, 1049, 1014, 920, 888, 821, 793, 761, 724, 660, 616 cm−1. Anal. Calcd for [(C10H14S1)50 + C16H20S2Br2]: C, 70.81, H, 8.31. Found: C, 69.91; H, 8.03. Anionic Polymerization of DHPS. All of the polymerizations of DHPS were carried out in a glovebox under purified N2 atmosphere. In a typical experiment, a benzene solution (10 mL) of DHPS (0.700 g, 1.81 mmol) was titrated with a cyclohexane solution of sBuLi until yellowish color appeared with stirring. A cyclohexane solution of sBuLi (1.05 M × 0.0700 mL = 0.0735 mmol) was added to start the polymerization. After the set polymerization time, ethanol was added to quench the polymerization. SEC analysis was carried out before

precipitation. The benzene solution was then poured into methanol (100 mL) to precipitate the polymer, followed by filtration and drying under vacuum. Finally, PDHPS was obtained as a white solid. Yield: 0.641 g (91%). Mn = 9 710, PDI = 1.15. 1H NMR (300 MHz, CDCl3): δ (ppm) 0.88 (−CH3, br, 6nH), 1.29−1.54 (N− CH2CH2CH2CH2CH2− + −CH2CH−, br, 19nH) 3.23 (N−CH2−, br, 4nH), 6.52 (Ar, br, 4nH), 7.36 (Ar, br, 4nH). IR (neat): 3029, 2952, 2925, 2855, 2208, 1601, 1520, 1464, 1400, 1367, 1294, 1254, 1226, 1195, 1181, 1135, 1107, 1017, 1004, 975, 948, 930, 917, 888, 864, 828, 811, 758, 722, 693, 675, 666, 653, 644, 628, 620, 607 cm−1. Anal. Calcd for [(C28H37N1)25 + C4H9]: C, 86.73; H, 9.68; N, 3.59. Found: C, 86.62; H, 9.55; N, 3.79. Synthesis of P3HT-b-PDHPS (11). All the polymerizations and reactions were carried out in a glovebox under purified N2 atmosphere in THF at −78 °C. To a THF solution (10 mL) of DHPS (0.600 g, 1.55 mmol) was added a THF solution of Bu2Mg (1 M × 0.200 mL = 0.200 mmol), and the mixture was stirred for 10 min. Then, a cyclohexane solution of sBuLi (1 M × 0.060 mL = 0.060 mmol) was added at one time to start the polymerization at −78 °C. After stirring for 10 min, 1,1-diphenylethylene (32 mg, 0.18 mmol) was added and allowed to stand for 5 min for end-capping. To this solution was added a THF solution (20 mL) of 8 (0.300 g, 0.027 mmol) which was completely dehydrated by adding a THF solution of Bu2Mg (1 M × 0.200 mL = 0.200 mmol). After 30 min, the reaction was quenched by adding ethanol. The solution was then poured into methanol/water (200 mL/100 mL) to precipitate the polymer. After filtration, the polymer was again dissolved in THF (20 mL) and poured into ethyl acetate (200 mL) to remove excess homopolymers of PDHPS. The crude polymer was further purified by HPLC fractionation to finally yield the analytically pure P3HT-b-PDHPS (11). Yield: 0.323 g (59%). Mn = 31 300, PDI = 1.06. 1H NMR (400 MHz, CDCl3): δ (ppm) 0.90 (−CH3, m, (3m+6n)H), 1.28−1.67 (Th−CH2CH2CH2CH2CH2− + N−CH2CH2CH2CH2CH2− + −CH2CH−, m, (6m+19n)H), 1.71 (Th−CH2CH2−, m, 2mH), 2.48 (tolyl, s, 3H), 2.80 (ThCH2−, t, J = 7.8 Hz, 2mH), 3.20 (N−CH2−, br, 4nH), 6.49 (Ar, br, 4nH), 6.98 (Th, s, 1mH), 7.34 (Ar, br, 4nH). IR (neat): 3033, 2952, 2925, 2854, 2208, 2167, 1602, 1556, 1520, 1458, 1399, 1367, 1294, 1254, 1227, 1195, 1135, 1108, 1051, 1017, 1004, 976, 931, 889, 811, 759, 723, 699, 671, 643, 632, 619, 607 cm−1. Anal. Calcd for [(C10H14S1)57 + (C28H37N1)59 + C33H38S1]: C, 82.52; H, 9.29; N, 2.52. Found: C, 82.22; H, 9.20; N, 2.53. Synthesis of PDHPS-b-P3HT-b-PDHPS (12). The synthesis of the titled compound was carried out in the same procedure as 11 except for the use of 9 instead of 8. Yield: 0.217 g (49%). Mn = 40 900, PDI = 1.05. 1H NMR (400 MHz, CDCl3): δ (ppm) 0.88 (−CH3, m, (3m+12n)H), 1.29−1.54 (Th−CH2 CH 2 CH 2 CH 2 CH 2 − + N− CH2CH2CH2CH2CH2− + −CH2CH−, m, (6m+38n)H), 1.71 (Th− CH2CH2−, m, 2mH), 2.80 (ThCH2−, t, J = 7.4 Hz, 2mH), 3.21 (N− CH2−, br, 8nH), 6.50 (Ar, br, 8nH), 6.98 (Th, s, 1mH), 7.34 (Ar, br, 8nH). IR (neat): 3039, 2952, 2925, 2854, 2208, 2167, 1602, 1520, 1462, 1399, 1367, 1294, 1254, 1227, 1195, 1135, 1107, 1053, 1017, 1003, 981, 930, 889, 828, 811, 759, 725, 700, 671, 654, 644, 619, 607 cm−1. Anal. Calcd for [(C10H14S1)50 + (C28H37N1)86 + C52H62S2]: C, 83.83; H, 9.39; N, 2.84. Found: C, 83.77; H, 9.35; N, 2.57. Synthesis of P3HT-b-PTCNE (13). To a solution of 11 (82.1 mg, 0.147 mmol alkyne unit−1) in dichloromethane (14.7 mL) was added a TCNE solution in 1,2-dichloroethane (0.149 mmol, 4.0 mL) under air. The mixture was stirred at 20 °C for 1 h. After the solution was evaporated, the crude product was dissolved in a small amount of THF and poured into methanol, yielding 13 as a black solid. Yield: 100.6 mg (99.7%). Mn = 42 300, PDI = 1.15. 1H NMR (400 MHz, CDCl3): δ (ppm) 0.90 (−CH 3 , m, (3m+6n)H), 1.34−1.74 (Th− C H 2 C H 2 C H 2 C H 2 CH 2 − + N −C H 2 CH 2 C H 2 C H 2 C H 2 − + −CH2CH−, m, (8m+19n)H), 2.49 (tolyl, s, 3H), 2.80 (ThCH2−, br, 2mH), 3.39 (N−CH2−, br, 4nH), 6.70 (Ar, br, 4nH), 6.97 (Th, s, 1mH), 7.44 (Ar, br, 2nH), 7.78 (Ar, br, 2nH). IR (neat): 3039, 2952, 2925, 2854, 2208, 2167, 1602, 1520, 1462, 1399, 1367, 1294, 1254, 1227, 1195, 1135, 1107, 1053, 1017, 1003, 981, 930, 889, 828, 811, 759, 725, 700, 671, 655, 644, 619, 607 cm−1. Anal. Calcd for 9654

dx.doi.org/10.1021/ma301692b | Macromolecules 2012, 45, 9643−9656

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[(C10H14S1)57 + (C34H37N5)59 + C33H38S1]: C, 77.61; H, 7.55, N, 10.24. Found: C, 77.02; H, 7.46, N, 10.93. Synthesis of PTCNE-b-P3HT-b-PTCNE (14). To a solution of 12 (80.5 mg, 0.163 mmol alkyne unit−1) in dichloromethane (16.3 mL) was added a TCNE solution in 1,2-dichloroethane (0.166 mmol, 4.0 mL) under air. The mixture was stirred at 20 °C for 1 h. After the solution was evaporated, the crude product was dissolved in a small amount of THF and poured into methanol, yielding 14 as a black solid. Yield: 100.2 mg (98.8%). Mn = 56 300, PDI = 1.07. 1H NMR (400 MHz, CDCl3): δ (ppm) 0.90 (−CH3, m, (3m+12n)H), 1.33− 1.63 (Th−CH2CH2CH2CH2CH2− + N−CH2CH2CH2CH2CH2− + −CH2CH−, m, (8m+38n)H), 2.80 (ThCH2−, br, 2mH), 3.39 (N− CH2−, br, 8nH), 6.70 (Ar, br, 8nH), 6.98 (Th, s, 1mH), 7.45 (Ar, br, 4nH), 7.78 (Ar, br, 4nH). IR (neat): 3052, 2953, 2927, 2856, 2214, 1602, 1538, 1485, 1467, 1445, 1415, 1343, 1295, 1262, 1213, 1182, 1144, 1119, 1078, 1015, 975, 889, 820, 795, 760, 722, 688, 666 cm−1. Anal. Calcd for [(C10H14S1)50 + (C34H37N5)86 + C52H62S2]: C, 78.15; H, 7.46, N, 11.28. Found: C, 77.63; H, 7.42, N, 12.13.

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ASSOCIATED CONTENT

S Supporting Information *

1

H NMR spectra of 12 and 14, UV−vis absorption spectra of 11 and 12 upon TCNE titration, FT-IR spectra and TGA curves of 11−14, and WAXS and SAXS profiles of 13 and 14. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: (T.M.) [email protected]; (T.H.) [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is partially supported by the Japan Science and Technology Agency (JST), PRESTO program (JY 220176), a Grant-in-Aid for Scientific Research from MEXT, Japan, and the Takahashi Industrial and Economic Research Foundation. The authors thank Satoru Genseki, Center for Advanced Materials Analysis, Tokyo Institute of Technology, for the elemental analyses.

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