Polyallene-block-polythiophene-block-polyallene Copolymers: One

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Polyallene-block-polythiophene-block-polyallene Copolymers: OnePot Synthesis, Helical Assembly, and Multiresponsiveness Zhi-Peng Yu, Cui-Hong Ma, Qian Wang, Na Liu,* Jun Yin, and Zong-Quan Wu* Department of Polymer Science and Engineering, School of Chemistry and Chemical Engineering, and Anhui Key Laboratory of Advanced Functional Materials and Devices, Hefei University of Technology, Hefei 230009, China S Supporting Information *

ABSTRACT: A family of coil−rod−coil ABA triblock copolymers containing poly(3-hexylthiophene) (P3HT) and poly(hexadecyloxyallene) (PHA) were facilely synthesized in one-pot via three sequential living polymerizations of hexadecyloxyallene, 2-bromo-3-hexyl-5-chloromagnesiothiophene, and hexadecyloxyallene using the π-allylnickel complex as a single catalyst. Although the different monomers were polymerized under distinct polymerization mechanisms, the one-pot block copolymerization were revealed to proceed in a living/controlled chain-growth manner, affording welldefined PHA-b-P3HT-b-PHA triblock copolymers in high yields with controlled molecular weights and tunable compositions. The isolated triblock copolymers were found to self-assemble into well-defined supramolecular helical polymers with equivalent of right- and left-handedness. The helicity of the assemblies can be facilely tuned through the induction of chiral cholesteryl pendants introduced on the polyallene segments. Moreover, by using this synthetic method, amphiphilic P3HT triblock copolymers containing hydrophobic P3HT and hydrophilic poly(triethylene glycol allene) (PTA) were readily prepared. Such water-soluble PTA-b-P3HT-b-PTA triblock copolymer exhibited multiresponsiveness including solvent, pH, and temperature.

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INTRODUCTION Conjugated polymers have attracted considerable research attention in the past few years owing to their potential applications in organic photovoltaics,1 light-emitting devices,2 and field-effect transistors.3 Among the reported conjugated polymers, poly(3-hexylthiophene) (P3HT) has attracted considerable research attention in recent years due to their excellent electronic properties and environmental stability.4 P3HT is commonly prepared by Grignard metathesis polymerization (GRIM) via the quasi-living catalyst-transfer polycondensation mechanism.5 Taking advantage of the living nature of GRIM, various end-functionalized P3HTs have been developed, some of which were further fabricated into block copolymers to control the patterning and optimize the optoelectronic properties.6 Compared to the vast reports on P3HT diblock copolymers, research on P3HT triblock copolymers is relatively rare, although they allow for incorporation of additional functionalities as well as a greater variety of tunable morphologies in thin films and in solution.7 The typical methods for synthesis of hybrid P3HT triblock copolymers including either the coupling preformed homopolymers with complementary end-functionalities8 or elaborating an end-functionalized polythiophene into an appropriate macroinitiator for the chain extension of two second blocks via a polymerization process that are mechanistically distinct from that of P3HT.9 However, these methodologies usually © XXXX American Chemical Society

require mass synthesis manipulation and can be inefficient and complex and frequently result in materials containing impurities that difficult to separate. Actually, hybrid block copolymers containing two or more distinct segments that cannot by polymerize under the same polymerization mechanism still remain a great challenge in the field of polymer synthesis. Therefore, development of novel synthetic strategy for facilely synthesis of P3HT triblock block copolymers is of great desire. Owing to π−π interaction and immiscibility of the distinct segments, P3HT block copolymers have been revealed to selfassemble into various supramolecular structures including nanofibers, nanosheets, spherical particles, and others.10 However, supramolecular helical polymers based on the selfassembly of P3HT block copolymers have rarely been reported. Emrick and co-workers reported an exquisite hierarchical helical assembly of conjugated P3HT-b-poly(3-triethylene glycol thiophene) diblock copolymers assisted by the interaction of alkali metal ion with the triethylene glycol side chains.11 Koeckelberghs et al. have performed extensive research on the chiroptical properties of chiral polythiophenes, although the helical structures of the self-assemblies have not been revealed.12 As we know, helicity is one of the essential Received: December 22, 2015 Revised: January 20, 2016

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DOI: 10.1021/acs.macromol.5b02759 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Scheme 1. One-Pot Synthesis of P3HT Triblock Copolymers

Figure 1. (a) Size exclusion chromatograms of PHA homopolymer poly-120, and the resulting PHA-b-P3HT diblock copolymer poly(120-b-240), and the PHA-b-P3HT-b-PHA triblock copolymer poly(120-b-240-b-120). (b) Plots of Mn and Mw/Mn values of PHA-b-P3HT block copolymers measured as a function of the feed ratio of 2 to the macroinitiator, Ni(II)-terminated poly-115 (Mn = 4.2 kDa, Mw/Mn = 1.15). SEC conditions: eluent = THF, temperature = 40 °C.

triblock copolymers.20 However, exploration on the synthesis of coil−rod−coil P3HT triblock copolymers by one-pot living block copolymerization method has never been reported. In this contribution, we report one-pot synthesis of a novel coil− rod−coil ABA triblock polymer, poly(hexadecyloxyallene)-bP3HT-b-poly(hexadecyloxyallene) (PHA-b-P3HT-b-PHA) with different sequence using π-allylnickel complex as a single catalyst. Such triblock copolymers were found to self-assembly into well-defined supramolecular helical structures. The helicity of the assemblies can be controlled through the communication of the chiral pendants of polyallene to P3HT segment. Moreover, amphiphilic P3HT triblock copolymer poly(triethyl glycol allene)-b-P3HT-b-poly(triethyl glycol allene) (PTA-bP3HT-b-PTA) was facilely synthesized, which showed good solubility in water and exhibit multiresponsiveness including solvent, pH, and temperature.

structural elements in biological systems, and there is a longstanding question whether it correlates with the origin of homochirality in nature.13 Thus, development of novel supramolecular helical polymers with controlled helicity is of great interesting. On the other hand, incorporation of hydrophilic polymer onto P3HT homopolymer to form P3HT block copolymers not only provides controllability on the self-assembly morphology but also improves the water solubility.14 Water-soluble P3HT block copolymers have attracted considerable research attention, particularly for applications that can benefit from environmental-friendly processing steps or applications that focus on the use of conducting polymers in biological environments.15 Moreover, the nanostructure and photophysical properties of such conjugated block copolymer can be readily tuned by external stimuli, such as light, temperature, pH, etc.16 Therefore, development of novel P3HT block copolymers that can selfassemble into well-defined supramolecular helical polymers with controlled helical sense and with tunable properties is of great interest. Recently, we developed a novel synthetic strategy for facile preparation of P3HT-b-polyisocyanide diblock copolymers in one-pot under living/controlled manner.17 Inspired by this finding, various P3HT diblock copolymers can be facilely prepared using the Ni(II)-terminated P3HT as macroinitiator such as P3HT-b-poly(6,7-dimethylquinoxaline-2,3-diyl),18 P3HT-b-poly(hexadecyloxyallene) (P3HT-b-PHA),19 and also P3HT triblock copolymer such as rod−coil−rod P3HT-bpoly(hexadecyloxyallene)-b-P3HT (P3HT-b-PHA-b-P3HT)

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RESULTS AND DISCUSSION Synthesis of PHA-b-P3HT-b-PHA Copolymers. The PHA-b-P3HT-b-PHA coil−rod−coil triblock copolymers were synthesized in one-pot via three sequential living polymerizations of hexadecyloxyallene (1), 2-bromo-3-hexyl-5-chloromagnesiothiophene (2), and 1 using the Ni(II) complex as a single catalyst (Scheme 1). First, a THF solution of Ni(II) catalyst was prepared according to the procedure reported by us previously,19 which was treated with 1 in THF at room temperature ([1]0 = 0.2 M, [1]0/[Ni]0 = 20). The polymerization process was monitored by size exclusion chromatography (SEC) analysis of small aliquots taken out from the B

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Table 1. Results for One-Pot Synthesis of Triblock Copolymers through Sequential Living Block Copolymerization Using the Ni(II) Complex as a Single Catalysta homopolymerb run

polymers

Mnc

1 2 3 4 5 6 7

poly(1m-b-2n-b-1o) poly(1m-b-2n-b-1o) poly(1m-b-2n-b-1o) poly(3m-b-2n-b-3o) poly(4m-b-2n-b-4o) poly(4m-b-2n-b-4o) poly(4m-b-2n-b-4o)

5.6 11.5 5.8 4.2 3.3 4.1 4.8

diblock copolymerb

triblock copolymer

Mw/Mnc

Mnc

Mw/Mnc

Mnc

Mw/Mnc

yieldd (%)

block ratioe (m:n:o)

1.18 1.22 1.15 1.14 1.18 1.19 1.19

12.4 24.8 9.5 7.8 6.7 6.4 8.1

1.22 1.13 1.28 1.19 1.21 1.33 1.28

16.2 33.1 44.1 12.2 10.7 9.8 28.1

1.25 1.22 1.19 1.22 1.25 1.22 1.29

83 78 86 84 68 65 61

20:40:20 40:80:40 20:20:120 10:20:10 15:20:20 20:15:20 20:20:100

a

All of the polymers were synthesized according to Scheme 1. bThe Mn and Mw/Mn of the polymers were determined by analysis via SEC of aliquots removed from the respective reaction mixtures prior to the addition of a new monomer. cMn and Mw/Mn were measured by SEC and are reported as their polystyrene equivalents. dIsolated yield over the three steps. eBlock ratios deduced from the 1H NMR analysis.

more detail, SEC analysis of the afforded block copolymers were performed using a UV−vis detector. As expected, single model and symmetric elution peaks were also observed on the SEC traces of poly(120-b-240) diblock copolymer and poly(120b-240-b-120) triblock copolymer (Figure S1, Supporting Information). To further confirm the living nature of the one-pot block copolymerization, a series of block copolymerizations of monomer 2 with a common macroinitiator Ni(II)-terminated poly-115 (Mn = 4.2 kDa, Mw/Mn = 1.15) were performed with different initial feed ratios of monomer to the initiator in THF at room temperature. It was found that all the isolated poly(115b-2n) block copolymers showed symmetric and single mode elution peaks on the size exclusion chromatograms (Figure S2). As shown in Figure 1b, the Mns of the isolated block copolymers were linearly correlated to the initial feed ratios of monomer to the macroinitiator, and all the block copolymers have narrow Mw/Mn values. These studies support the established living/controlled nature of the polymerization of monomer 1 using the Ni(II) complex as initiator and that the block copolymerization of 2, as initiated by Ni(II)-terminated poly-1m, also proceed in a similar living/controlled manner. Taking advantage of the living nature of the one-pot block copolymerization, a variety of well-defined poly(1m-b-2n) and poly(1m-b-2n-b-1o) block copolymers with different Mns and narrow Mw/Mns were facilely prepared in high yields just through the variation on the initial feed ratios of monomer to catalyst (Figure S3). The results of the one-pot block copolymerization are summarized in Table 1. The structures of the isolated PHA-b-P3HT-b-PHA triblock copolymer as well as the PHA-b-P3HT diblock copolymer were further verified by 1 H NMR, FT-IR, and UV−vis absorption spectra. The 1H NMR spectra of the PHA homopolymer, poly-120 and the corresponding poly(120-b-220) diblock copolymer and poly(120b-220-b-1120) triblock copolymer are shown in Figure 2. For comparison, P3HT homopolymer poly-240 (Mn = 6.1 kDa, Mw/ Mn = 1.21) was prepared, and the 1H NMR spectrum is shown in Figure 2d. It was found that both the di- and triblock copolymers showed characteristic resonances assignable to PHA and P3HT segments. For example, resonances at range of 5.6−6.2 ppm attributable to the characteristic signals of the double bond protons of PHA segment, and the signal at 6.98 ppm assigned to the aromatic proton of P3HT is clearly observed in Figure 2b,c, suggesting formation of the expected block copolymers containing PHA and P3HT blocks. It should note that no signals appeared around 5.1 ppm on the 1H NMR spectra of poly(120-b-220) and poly(120-b-220-b-1120), assignable

reaction solution at appropriate time intervals. When the molecular weight of the afforded poly-120 (the footnote indicates the initial feed ratio of monomer to initiator, the same below) ceased to increase, a small aliquot was taken out and quenched by methanol for further analysis. The numberaverage molecular weight (Mn) and its distribution (Mw/Mn) of the generated poly-120 were estimated to be 5.6 kDa and 1.18, respectively, by SEC analysis with equivalent to polystyrene standard (Figure 1a). The rest polymerization solution was treated with monomer 2, which was freshly generated from the reaction of 2,5-dibromo-3-hexylthiophene with iPrMgCl in THF at room temperature ([2]0 = 0.4 M, [2]0/[Ni]0 = 40). After the resulting mixed solution was stirred at room temperature for a further 2 h, an aliquot was then taken out for analysis. The success of the one-pot diblock copolymerization was first confirmed by SEC analysis. SEC traces of the macroinitiator Ni(II)-terminated poly-120 and the resulting PHA-b-P3HT block copolymer poly(120-b-240) are shown in Figure 1a. Both the macroinitiator and the resulting block copolymer exhibited single modal and symmetric elution peaks. Compared with the poly-120 precursor, the elution peak of the isolated block copolymer poly(120-b-240) was located at shorter retention-time region, suggesting chain extension occurred. The Mn and Mw/Mn of poly(120-b-240) were estimated to be 12.4 kDa and 1.22, respectively. The Mn of the block copolymer is larger than that of the poly-120 precursor (Mn = 5.6 kDa, Mw/ Mn = 1.18), while Mw/Mn remains narrow. The rest solution of Ni(II)-terminated PHA-b-P3HT block copolymer was then explored to reinitiate a new block copolymerization of monomer 1 through a change of mechanism. A THF solution of 1 was added to the reaction solution of Ni(II)-terminated poly(120-b-240) at room temperature ([1]0 = 0.2 M, [1]0/[Ni]0 = 20). The polymerization reaction was followed by SEC analysis. When monomer 1 was completely consumed, that is, no molecular weight increase was observed by SEC, the polymerization solution was quenched by methanol, and the precipitated solid was isolated by filtration. The isolated PHAb-P3HT-b-PHA triblock copolymer poly(120-b-240-b-120) still showed a symmetric and single modal elution peak on SEC trace and shifted to the shortest retention time region as compared with its precursors poly(120-b-240) and poly-120 (Figure 1a). The Mn of the obtained triblock copolymer as determined by SEC is 16.2 kDa, which is larger than that of the poly(120-b-240) and poly-120, while the Mw/Mn kept narrow (Mw/Mn = 1.25). These results confirmed the living nature of the one-pot block copolymerization and the formation of the expected PHA-b-P3HT-b-PHA triblock copolymer. To get C

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of P3HT) on the 1H NMR spectra, the block ratios of the PHA to P3HT were estimated to be ca. 1:1 for poly(120-b-220) and ca. 7:1 for poly(120-b-220-b-1120). The increased block ratio of PHA to P3HT in the triblock copolymer compared to that of the diblock copolymer confirms the chain extension of the third block. Moreover, the block ratios of the di- and triblock copolymers deduced from 1H NMR spectra agree well with the molar ratios of the monomers used in the one-pot block copolymerization. These results confirm not only the structure of the block copolymers but also the living nature of the onepot triblock copolymerization. The 1H NMR profiles of the diand triblock copolymers are similar to each other, which indicated that the two PHA segments on the P3HT triblock copolymers possessing almost the same chemical structures even they were polymerized in different sequence. FT-IR spectra of the one-pot synthetic PHA-b-P3HT diblock copolymer and the corresponding PHA-b-P3HT-b-PHA triblock copolymer also support the formation of the expected polymers because the vibrational absorptions attributable to each block can be clearly observed (Figure S4). The structures of the one-pot synthetic block copolymers were further verified by UV−vis absorption spectroscopy. Both poly(140-b-280) and poly(140-b-280-b-140) exhibited two major absorbance bands corresponding to PHA block with the maximum located at the range of 230−300 nm and the π−π* transform of P3HT segment around 370−640 nm (Figure 3 and Figure S5). Compared with poly(140-b-280), the absorption of poly(140-b-280-b-140) at the PHA segment region (230−300 nm) was pronouncedly increased because of the incorporation of additional PHA segment on the other P3HT chain end. The optical property of the block copolymers in thin film state was also investigated. As shown in Figure 3a, the absorption spectra of thin films casted from poly(140-b-280-b-140) were significantly red-shifted about 40 nm relative to the solution absorption spectra, suggesting intermolecular π−π stacking of the P3HT segment in thin films. For comparison, UV−vis absorption spectra of the one-pot synthetic poly(140-b-280) diblock copolymer in thin film state were also investigated. It was found that about 70 nm red-shift was observed relative to that in solution. This result indicates the different intermolecular interactions between the P3HT di- and triblock copolymers. The incorporation of additional coil PHA block on the P3HT segment may reduce the intermolecular π−π interaction. Thermal stability of the block copolymers and their corresponding homopolymers was studied by thermogravimetric analysis (TGA) under N2 with 10 °C min−1 heating rate

Figure 2. 1H NMR spectra of PHA homopolymer poly-120 (a), PHAb-P3HT diblock copolymer poly(120-b-220) (b), PHA-b-P3HT-b-PHA triblock copolymer poly(120-b-220-b-1120) (c), and P3HT homopolymer poly-240 (d) measured in CDCl3 at 25 °C.

to the exo-methylene moiety in the 1,2-polymerized unit of monomer 1, indicated the polymerizations were highly region selective took place on the 2,3-position of the allene unit. Based on the integral analysis of the signals at 5.6−6.2 ppm (resonance of PHA) and the signal at 6.98 ppm (resonance

Figure 3. (a) UV−vis absorption spectra of PHA-b-P3HT diblock copolymer poly(140-b-280) and PHA-b-P3HT-b-PHA triblock copolymer poly(140b-280-b-140) in THF (solid line) and in thin film (dashed line). (b) DSC curves of poly(140-b-280) and poly(140-b-280-b-140) block copolymers, and poly-140 and poly-280 (Mn = 12.2 kDa, Mw/Mn = 1.21) homopolymers, recorded under an inter-N2 atmosphere at a heating rate of 10 °C min−1. D

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Macromolecules (Figure S6). For poly(140-b-280), an initial 26% weight loss was observed from 247 to 419 °C, followed by an 56% weight loss from 419 to 569 °C. While for the triblock poly(140-b-280-b140), the weight loss was 66% from 254 to 452 °C and 23% from 452 to 561 °C. As a comparison, the TGA of P3HT and PHA homopolymers was tested. It was found that the weights losses for PHA was 93% from 255 to 505 °C and 70% for P3HT from 468 to 560 °C. These results support both the PHA segment and P3HT segment are existed in the di- and triblock copolymers. The thermal properties of both PHA-bP3HT diblock copolymer poly(140-b-280) and PHA-b-P3HT-bPHA triblock copolymer poly(140-b-280-b-140) were analyzed by differential scanning calorimetry (DSC). The DSC curves of the two block copolymers as well as the two homopolymers of poly-140 and poly-280 are shown in Figure 3b. It was found that both the di- and triblock copolymers exhibit two glass transition temperatures (Tg), respectively corresponding to the PHA and P3HT blocks. This result supports the phase segregation of the PHA-b-P3HT and PHA-b-P3HT-b-PHA block copolymers in solid state. To gain insight into the surface morphologies, the thin films of poly(140-b-280) and poly(140-b-280-b-140) were visualized by atomic force microscopy (AFM) at room temperature. The films were prepared on silicon wafers by spin-coating from THF solutions of the block copolymers at room temperature, followed by exposure the samples to the vapor of the same solvent at room temperature for 12 h. The AFM image of the thin film of poly(140-b-280) diblock copolymer is shown in Figure 4a. Well-defined spherical nanoparticles with ca. 60 nm in diameters were clearly observed, probably due to the intermolecular π−π interaction of P3HT and immiscibility of the two blocks of the PHA-b-P3HT copolymer.19 In contrast to the PHA-b-P3HT diblock copolymer, the thin film of the corresponding coil−rod−coil PHA-b-P3HT-b-PHA triblock copolymer casted from the THF solution exhibited welldefined nanofibrils morphology with clear microphase separation (Figure 4b). The aggregated nanofibrils were estimated to have a diameter of ca. 50 nm with the persist length up to several micrometers. However, the morphology of the triblock copolymer poly(140-b-280-b-140) was dependent on the solvents used. Spin-coating from toluene solution, the triblock copolymer self-assembled into supramolecular helical structures as revealed by AFM phase image (Figure 4c). Such helical structures were determined to have a diameter of ca. 30 nm with the persistent up to several micrometers. The different morphology between the PHA-b-P3HT diblock copolymer and the PHA-b-P3HT-b-PHA triblock copolymer suggests the incorporation of another PHA segment on the P3HT chain end make an important influence on the self-assembly behavior. The formation of the supramolecular helical structures of the triblock copolymer was further confirmed by transmission electron microscopy (TEM) observations (Figure 4d). The contrast variations along each single helix gave rise to a banded appearance that allowed left- and right-handed helices to be distinguished. Based on the achiral nature of the structure of the triblock copolymer and the process of the self-assembly, a roughly equal mixture of left- and right-handed helices was observed on AFM and TEM images. Circular dichroism (CD) measurements of the films casted from the THF solution of the poly(140-b-280-b-140) triblock copolymer also did not revealed any preference for a particular chirality (Figure S7). The mechanism of the self-assembly of such supramolecular helical polymers of the coil−rod−coil triblock copolymer may be

Figure 4. AFM image of the thin film casted from toluene solution of poly(140-b-280) (a) and poly(140-b-280-b-140) (b) spin-casted from the solution of THF at 25 °C. AFM phase (c) and TEM (d) images of the thin film casted from the solution of poly(140-b-280-b-140) in toluene (c = 0.2 g/L). (e) A plausible model for poly(140-b-280-b-140) selfassembly into supramolecular helical structures.

ascribed to the π−π interactions of the conjugated P3HT segment, and the immiscibility of the P3HT with the PHA segments, exposing the coil PHA segments at the exterior; a plausible assembly model is outlined in Figure 4e. To control the handedness of the self-assembled supramolecular helical polymers, coil−rod−coil P3HT triblock copolymer bearing chiral cholesterol pendants on the two polyallene segments were designed and synthesized. As shown in Scheme 1, chiral cholesteryloxyallene (3) was first polymerized by the Ni(II) complex and then sequentially chain extended with monomer 2 and 3, followed by the procedure described above to afford the ABA poly(cholesterylallene)-b-P3HT-b-poly(cholesterylallene) (PCA-b-P3HT-bPCA) triblock copolymer poly(310-b-220-b-310) (Table 1 and Figure S8). 1H NMR, FT-IR, and UV−vis spectra of the block copolymer showed characteristic signals attributable to each block, demonstrating the formation of expected block copolymers (Figures S9−S13). The chirality of the one-pot synthetic poly(310-b-220-b-310) was investigated by circular dichroism (CD) and UV−vis absorption spectra. As shown in Figure 5, the absorption spectrum of the triblock copolymer poly(310-b-220-b-310) showed two absorption maxima at 241 and 443 nm, respectively corresponding to the poly-3m and poly-2n block. However, the CD spectra of the triblock copolymer in THF showed only a weak Cotton effect at 244 nm, corresponding to the chiral repeating units of cholesterol pendants; no Cotton effect can be observed around 440 nm attributable to the conjugated P3HT segment. This result is ascribed to that the triblock copolymer was molecularly E

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Figure 5. (a) CD and UV−vis absorption spectra of poly(310-b-220-b-310) block copolymers in THF and the mixture of THF and methanol at 25 °C (c = 2.0 g/L). AFM height image (b) and TEM image (c) of the thin film casted from toluene solution of the poly(310-b-220-b-310) block copolymer at 25 °C (c = 0.2 g/L).

Figure 6. UV−vis (a) and emission (b) spectra of poly(415-b-220-b-420) in mixed THF and methanol with different volume ratios at 25 °C. (c) DLS curves of poly(415-b-220-b-420) measured in mixed THF and methanol with different volume ratios at 25 °C. (d) AFM phase image of poly(415-b-220b-420) casted from methanol at the concentration of 0.2 g/L (inset: schematic illustration of the assembly of poly(415-b-220-b-420)).

a chiral aggregates, probably a supramolecular helical polymer, similar to that of the poly(140-b-280-b-140) block copolymer. The self-assembly morphology of the poly(310-b-220-b-310) was visualized by AFM and TEM. As displayed in Figure 5b, welldefined helical nanofibrils with ca. 20 nm diameter and more than several micrometers length were clearly observed on the AFM height image. Very interestingly, compared to the coexistence of left- and right-handed helices of the achiral poly(1m-b-2n-b-1o) copolymer, only left-handed helical nanofibrils could be observed in Figure 5b, probably due to the asymmetric induction of the chiral cholesterol pendants. The TEM image is shown in Figure 5c, which also revealed the poly(310-b-220-b-310) was self-assembled into supramolecular helical polymer, and the helical pitch was estimated to be ca. 60 nm. Stimuli-Responsiveness of Amphiphilic Triblock Copolymers. Utilizing the similar synthetic method, a series of amphiphilic triblock copolymer containing hydrophobic P3HT block and hydrophilic poly(triethyl glycol allene) (PTA) segment were designed and synthesized (Scheme 1). The structure of the amphiphilic PTA-b-P3HT-b-PTA triblock copolymer poly(4m-b-2n-b-4o) was verified by SEC, 1H NMR, FT-IR, and UV−vis analyses (Figures S15−S20). The results of

dissolved in THF solution at room temperature; no aggregation took place. To gain the self-assembly structure, a poor solvent, methanol, was added to the THF solution of the triblock copolymer at room temperature. As shown in Figure 5a, the UV−vis absorption spectra of the block copolymer revealed that the absorption maximum of P3HT block red-shift to 541 nm upon the addition of methanol, accompanied by new absorptions at 551 and 605 nm due to the intramolecular π−π interaction of the conjugated P3HT block. Interestingly, the CD spectrum of the triblock copolymer showed distinct Cotton effects at 244 and 543 nm upon the addition of methanol. The g-value (Δε/ε) at 543 nm was estimated to be −7.0 × 10−4. For comparison, CD and UV−vis spectra of homopolymer poly-310 were measured in THF and THF/methanol (v/v = 1/1) at room temperature under the same conditions to that of the poly(310-b-220-b-310) copolymers. As shown in Figure S14, the homopolymer also showed a weak Cotton effect in THF, while increased CD at 240 nm was clearly observed upon the addition of methanol. Thus, the Cotton effects of the poly(310b-220-b-310) in THF/methanol around 244 nm were assigned to poly-310 block, while the Cotton effect at 543 nm was assigned to the aggregated P3HT block. These results suggest that the P3HT segment of the block copolymer may self-assembled into F

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Figure 7. (a) Photographs of the CH2Cl2 solution of poly(415-b-220-b-420) upon the alternate additions of TFA and TEA under room light and UV light at 365 nm (c = 0.2 g/L). (b) Emission spectra of poly(415-b-220-b-420) triblock copolymer in CH2Cl2 with the alternate additions of TFA and TEA at 25 °C (c = 0.2 g/L).

increased and eventually increased to 220 nm in pure methanol. Moreover, all the DLS traces were single modal and symmetric due to the narrow molecular weight distributions of the block copolymers. The morphology of the self-assembly of the amphiphilic triblock copolymers was then investigated by tapping modal AFM observation on the samples casted from the methanol solution (c = 0.2 g/L) at room temperature. As shown in Figure 6d, well-defined spherical nanoparticles with good homogeneity were clearly observed. The average diameter was estimated to be ca. 210 nm, which agree well with the DLS analysis. Probably, a micellar supramolecular structure with the hydrophobic P3HT at the interior and the hydrophiphilic at the exterior was formed due to the self-association of the πconjugated P3HT and the immiscibility of the hydrophobic P3HT with the hydrophilic PTA segment (Figure 6d, inset). Interestingly, the coil−rod−coil triblock copolymer poly(4mb-2n-b-4o) exhibited both pH- and thermoresponsiveness. As shown in Figure 7a, the yellow color of the CH2Cl2 solution of poly(415-b-220-b-420) was gradually changed to pink upon the addition of trifluoroacetic acid (TFA) at 25 °C. When neutralized this solution by triethylamine (TEA), the color can be changed back to yellow. Accordingly, the emission of poly(415-b-220-b-420) in CH2Cl2 also showed a reversible changes upon the alternate additions of TFA and TEA. The CH2Cl2 solution of poly(415-b-220-b-420) emitted orange light under irradiation at 365 nm at 25 °C owing to the π-conjugated P3HT segment. Upon the addition of TFA, the emission color of the solution was gradually changed to cyan, which can be facilely changed back to orange color emission by neutralization with TEA. As shown in Figure 7b, the poly(415-b-220-b-420) exhibited two emissions bands at 565 and 450 nm on the emission spectra in CH2Cl2 at 25 °C under the irradiation at 365 nm (c = 0.2 g/L). Upon the addition of TFA, the emission at 565 nm was gradually quenched and became constant when the TFA concentration reached to 0.4 M. The decrease of the emission at 565 nm showed a linear correction to the concentration of TFA until it was saturated (Figure S22). Compared to the changes at 565 nm, the emission at 450 nm was almost maintained upon the addition of TFA and TEA. Thus, the poly(415-b-220-b-420) copolymer exhibited a cyan emission in the acidic CH2Cl2 solution. When the solution was neutralized by TEA, the emission at 565 nm was gradually recovered and showed an orange emission again. It should be noted that the emission at 565 nm could not be completely recovered after the neutralization because of the salt effect formed in the solution during the acidification and neutraliza-

the one-pot block copolymerization are summarized in Table 1. Because of the amphiphilic nature, the one-pot synthetic PTAb-P3HT-b-PTA triblock copolymer showed good solubility in most common organic solvents such as THF, chloroform, toluene, and DMF. Interestingly, the triblock copolymers also have good solubility in water. Although the self-assembly and stimuli-responsiveness of rod−coil diblock copolymers have been investigated widely, similar studies on coil−rod−coil ABA P3HT triblock copolymers are very limited. The novel amphiphilic poly(4m-b-2n-b-4o) triblock copolymers may exhibit interesting self-assembly and multiresponsive behaviors, which have never been explored. The UV−vis absorption spectra of poly(415-b-220-b-420) in THF at 25 °C (c = 0.2 g/L) are shown in Figure 6a. The block copolymer exhibited two major absorption bands located at 240 and 445 nm, respectively corresponding to poly-4m and poly-2n segments. Adding methanol, a selective solvent for hydrophilic poly-4m segment to the THF solution, the absorption maximum at 445 nm of poly(415-b-220-b-420) red-shifted to 507 nm, accompanied by two new absorptions at 546 and 596 nm, due to the formation of intermolecular π−π interactions associated with semicrystalline aggregate of the conjugated P3HT segments. In accordance with the absorption changes, the color of the block copolymer solution was also changed upon the addition of methanol to the THF solution. The THF solution of poly(415-b-220-b-420) showed a yellow color, similar to the P3HT homopolymer in nonselective solvents. However, the color was gradually changed to dark pink, upon the addition of methanol, supporting the aggregation of the block copolymer (Figure S21). The emission spectra of the amphiphilic coil−rod−coil triblock copolymer poly(415-b-220-b-420) measured in THF with the increased content of methanol also support the selfassembly. The triblock copolymer showed orange color emission upon the illumination by UV light at 365 nm (Figure S21). However, it was gradually changed to orange-red emission, upon the addition of methanol, and eventually changed to red color in the methanol solution. The emission spectra excited at 365 nm are shown in Figure 6b. In THF, poly(415-b-220-b-420) exhibits strong emission at 571 nm, while it red-shifted to 720 nm in methanol solution. The aggregation behavior of poly(415-b-220-b-420) was further investigated by the dynamic light scattering (DLS) analysis. The diameter of poly(440-b-280-b-440) was determined to be ca. 4 nm in THF, consistent with the large majority of chains being well molecularly dissolved (Figure 6c). Upon the addition of methanol, the diameter of the aggregates was progressively G

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Macromolecules

Figure 8. (a) Transmittance (800 nm) versus temperature curves and photographs of the phase transition for aqueous solution of poly(415-b-220-b420) at a concentration of 2.0 g/L. (b) Transmittance versus temperature curves for aqueous solution of poly(415-b-220-b-420) at different concentrations.

Figure 9. (a) CLSM of HepG2 cells incubated with the poly(415-b-220-b-420) block copolymer with excitation at 420 nm. (b) Bright-field image of HepG2 cells stained with poly(415-b-220-b-420). (c) Merged images of (a) and (b).

poly(415-b-220-b-420) (c = 2.0 g/L) over the temperature range 26−50 °C. It revealed that the average diameter of the aggregates was ca. 149 nm as the temperature fell below the LCST (38 °C), while it increased to more than 1 μm when the temperature above the LCST (Figure S24). This study further supports the excellent thermoresponsiveness of the coil−rod− coil PTA-b-P3HT-b-PTA triblock copolymers. Considering the high water solubility and the excellent optical properties of the one-pot synthetic amphiphilic triblock copolymers, the triblock copolymer poly(4m-b-2n-b-4n) may find applications in biochemistry such as in live cell imaging. Thus, the self-assembly behavior of poly(4m-b-2n-b-4n) in water was then investigated by DLS and TEM. DLS analysis revealed that the hydrodynamic size of the poly(4m-b-2n-b-4n) in water is about 142 nm (Figure S25). The TEM image of the samples casted from the aqueous solution of poly(4m-b-2n-b-4n) at 25 °C is shown in Figure S26. Well-defined spherical nanoparticles with 140 nm in diameter were clearly observed, which is consistent with the DLS analysis. The cytotoxic behavior of these block copolymers was investigated though the incubations of poly(415-b-220-b-420) with the HepG2 cells with different concentrations in water (1−20 mg/L). The cell viability assays revealed that more than 80% of the incubated cells survived after 24 h, suggesting the poly(415-b-220-b-420) has good biocompatibility and the toxicity is low (Figure S27). Then, poly(415-b-220-b-420) was incubated with the HepG2 cells in water, and their imaging performance was investigated by confocal laser scanning microscopy (CLSM) with excitation 420 nm. As illustrated in Figure 9, upon extending the incubation time from 0 to 12 h, strong emission can be gradually observed within the cytosol of the HepG2 cells; almost no emission could be observed on the cell membrane or

tion. The pH-responsiveness of the triblock copolymer may be ascribed to the interaction of the P3HT with the added acidic proton. In addition to pH-responsiveness, the amphiphilic coil−rod− coil PHA-b-P3HT-b-PHA triblock copolymer also exhibited thermoresponsiveness. Heating the aqueous solution of poly(415-b-220-b-420) at a concentration of 2.0 g/L, the clear transparent solution gradually changed to turbid, suggesting the block copolymer is thermoresponsive (Figure 8a). Cooling the solution to room temperature, the turbid solution turned to clear and transparent again. The transmittance (at 800 nm) versus temperature curves of poly(415-b-220-b-420) in water indicated the lower critical solution temperature (LCST) is 38 °C (c = 2.0 g/L), very close to the physiological temperature (Figure 8a). It should be noted that the optical absorption edge of P3HT is around 680 nm and thus would not affect the observation of LCST by optical transmission at 800 nm (Figure S23). The optical transmittance curve of the block copolymer upon heating and cooling cycle is reversible with very small hysteresis. The excellent thermoresponsive behavior of the poly(415-b-220-b-420) block copolymer may be attributed to the variation on the hydrophilic/hydrophobic balance of the poly4m segments. Further studies revealed that the LCST value of poly(415-b-220-b-420) was dependent on the concentration. Decreasing the concentration of the triblock copolymer in water will decrease the LCST value. For example, the LCST of poly(415-b-220-b-420) is 38 °C at the concentration of 2.0 g/L, while it decreased to 34 and 32 °C when the concentration was diluted to 1.0 and 0.5 g/L, respectively. To get more details on the thermoresponsive behavior of the poly(415-b-220-b-420) block copolymer, the heating-induced phase transition was then investigated by DLS analysis on the aqueous solution of H

DOI: 10.1021/acs.macromol.5b02759 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Scheme 2. Synthesis of Monomer 3

in tapping mode with a Digital Instruments Dimension 3100 scanning probe microscope using standard silicon cantilevers with a nominal spring constant of 50 N m−1 and resonance frequency of ∼300 kHz. TEM observations were conducted on a JEM-2100F electron microscope operating at an acceleration voltage of 200 kV. The samples for TEM observation were prepared by casting the corresponding solutions onto copper mesh grids and drying in air at room temperature. HepG2 cells were fluorescence imaged on a Zeiss LSM 710 META upright confocal laser scanning microscope using 40× and 100× magnification water-dipping lenses for the monolayer cultures. Image data acquisition and processing was performed using Zeiss LSM Image Browser, Zeiss LSM Image Expert, and ImageJ. All solvents were obtained from Sinopharm. Co. Ltd. and were purified by the standard procedures before use. THF was further dried over sodium benzophenone ketyl, distilled onto LiAlH4 under nitrogen, and distilled under high vacuum just before use. All starting materials were obtained commercially and used as received without further purification otherwise denoted. The Ni(II) complex and monomers 1, 2, and 4 and homopolymers poly-1m, poly-2m, and poly4m were prepared according to the procedures reported by us previously.18−20 Monomer 3 was synthesized according to Scheme 2. Synthesis of 3-(Prop-2-yn-1-yloxy)cholester (5). The compound 5 was synthesized according to the literature with slight modifications.21 Cholesterol (5.00 g, 12.4 mmol) was dissolve in THF under dry nitrogen. To this stirring solution, NaH (0.45 g, 18.6 mmol) was added batchwise at room temperature. After the suspension was stirred for half an hour at room temperature, propargyl bromide (1.84 g, 15.5 mmol) was added via a syringe. The reaction mixture was stirred at 50 °C for 24 h and then quenched by methanol (10 mL). The solvent was removed by evaporation under reduced pressure. The residual solid was dissolved in CH2Cl2 (50 mL) and washed with water (20 mL × 2) and brine (20 mL × 1). The organic phase was dried over Na2SO4, filtrated, and evaporated to dryness under reduced pressure. The crude product was further purify by column chromatography with petroleum ether as eluent to afford 5 as a white solid (4.60 g, 68% yield). The structure of 5 was confirmed by 1 H NMR.21 Synthesis of 3. KOBut (2.40 g, 21.4 mmol) was added batchwise to a solution of 5 (7.60 g, 17.9 mmol) in THF (100 mL) within 30 min at room temperature. The suspension solution was stirred at room temperature overnight, then filtered through a Celite pad, and washed with CH2Cl2 (50 mL). The combined solution was concentrated under reduced pressure and purified by flash column chromatography using petroleum ether as eluent. The product was recrystallization with CH2Cl2/MeOH (v/v = 2/1) to afford 3 as a faint yellow crystal (3.73 g, 49%); mp 110.0−111.9 °C. 1H NMR (400 MHz, CDCl3, 25 °C): δ 6.63−6.60 (t, J = 6.0 Hz, 1H), 5.38−5.37 (d, J = 6.0 Hz, 2H), 5.36− 5.34 (m, 1H), 3.59−3.51 (m, 1H), 2.44−2.39 (m, 1H), 2.32−2.24 (m, 1H), 2.03−1.92 (m, 3H), 1.89−1.78 (m, 2H), 1.61−1.43 (m, 8H), 1.40−1.25 (m, 5H), 1.19−1.04 (m, 8H), 1.02 (s, 3H), 0.92−0.91 (d, J = 6.4 Hz, 3H), 0.88−0.87 (d, J = 1.6 Hz, 3H), 0.86−0.85 (d, J = 1.6 Hz, 3H), 0.68 (s, 3H). 13C NMR (150 MHz, CDCl3): δ 204.18, 143.00, 124.73, 122.49, 92.34, 80.76, 59.39, 58.75, 52.72, 44.95, 42.39, 42.16, 41.31, 39.71, 39.40, 38.83, 38.45, 34.58, 34.51, 30.90, 30.71, 30.68, 26.94, 26.48, 25.50, 25.24, 23.71, 22.02, 21.37, 14.51. [α]25D −41.7 (c = 0.1, THF). FT-IR (KBr, 25 °C): 2965, 2962, 2951, 2937,

cell nucleus. These results indicated that the one-pot synthetic, water-soluble PTA-b-P3HT-b-PTA triblock copolymers are biocompatible and possess potential applications in biochemistry.

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CONCLUSION In summary, we developed a novel synthetic strategy for facile synthesis of well-defined P3HT triblock copolymers in one pot via three sequential living polymerizations using the πallylnickel(II) complex as a single catalyst. Although the monomers were polymerized via distinct mechanisms, the one-pot block copolymerization was revealed to proceed in living/controlled chain-extension fashion, affording the expected well-defined triblock copolymers in high yields with controlled Mns, narrow Mw/Mns, and tunable compositions. The triblock block copolymer was found to self-assemble into well-defined supramolecular helical structures. The helicity can be controlled through the induction of chiral pendants on the polyallene segments. Moreover, amphiphilic PTA-b-P3HT-bPTA block copolymers can be readily synthesized, which exhibited interesting pH- and thermoresponsiveness. We believe the present study will provide not only a novel synthetic strategy for facile synthesis of coil−rod−coil hybrid conjugated triblock copolymers but also a series of new smart and semiconducting materials that hold great potentials as sensor, fluorescence thermometer, optoelectronic, and bioelectronics devices.

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EXPERIMENTAL SECTION

General Considerations. 1H and 13C NMR spectra were recorded using a Bruker 400 or 600 MHz spectrometer. Chemical shifts are reported in delta (δ) units and expressed in parts per million (ppm) downfield with tetramethylsilane or chloroform as an internal standard. Size exclusion chromatography (SEC) was performed on a Waters 1515 pump and a Waters 2414 differential refractive index (RI) detector (set at 40 °C) using a series of linear Styragel HR1, HR2, and HR4 columns with THF as eluent (0.3 mL/min). Mns and Mw/Mns are reported relative to the polystyrene standards. FT-IR spectra were recorded on PerkinElmer Spectrum BX FT-IR system using KBr pellets at 25 °C. CD and UV−vis spectra were recorded on JASCO J1500 and UNIC 4802 UV/vis double beam spectrophotometers in a 1.0 cm quartz cell at 25 °C. Emission spectra were recorded on a Hitachi F-4600 fluorescence spectrophotometer. DLS was recorded using a Nano-ZS 90 Zetasizer of Malvern (UK) instrument. The optical rotations were measured in THF at 25 °C using a 10.0 cm quartz cell on a WZZ-2B polarimeter. Melting points were obtained with a Mel-Temp apparatus and are uncorrected. Samples for AFM measurements were prepared by casting THF solutions of the corresponding block copolymers onto freshly cleaved silicon wafers, which were further exposed to the same solvent vapor for 12 h according to the reported procedures.17,20 The AFM measurements were performed using a Nanoscope IV microscope (Veeco Instruments, Santa Barbara, CA) in air at 25 °C. AFM images were acquired I

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Macromolecules 2905, 2895, 2869, 2855, 1954 cm−1. MS m/z calcd for C30H49O [M + H]+: 425.3705. Found: 425.1987. Anal. Calcd (%) for C30H48O: C, 84.84; H, 11.39. Found: C, 84.81; H, 11.35. Typical Polymerization Procedure (Poly(120-b-220-b-1120). Under a N2 atmosphere, a 10 mL oven-dried flask was charged with 1 (56.0 mg, 0.20 mmol), dry THF (1.0 mL), and a stirring bar. After being stirred at room temperature for 10 min, a solution of πallylnickel complex (0.026 M, 0.15 mL, 0.01 mmol) was added to this solution via a microsyringe ([1]0 = 0.2 M, [1]0/[Ni]0 = 20). The mixture solution was stirred for 6 h; SCE analysis of the aliquot removed from the reaction solution indicated the polymerization was completed. An aliquot was taken out from the reaction solution and quenched by methanol for further analysis. The rest of the solution of Ni(II)-terminated poly-120 was then treated with a fresh THF solution of monomer 2, which was generated from the reaction of 2,5-dibromo3-hexylthiophene with iPrMgCl, to afford the PHA-b-P3HT diblock copolymer ([2]0 = 0.2 M, [2]0/[Ni]0 = 20). After the resulting mixture was stirred at room temperature for 2 h, SEC analysis indicated the polymerization was completed. A small aliquot was then taken out and quenched by methanol for further analysis. The polymerization solution of Ni(II)-terminated poly(120-b-220) was then treated with monomer 1 in THF at room temperature to afford the PHA-b-P3HTb-PHA triblock copolymer ([1]0 = 0.2 M, [1]0/[Ni]0 = 120). The resulting solution was stirred at 25 °C for 8 h and then poured into a large amount of methanol. The precipitated dark-purple solid was washed with cold methanol and n-hexane and then dried under vacuum to afford the triblock copolymer poly(120-b-220-b-1120) (370 mg, 86% yield). The characterization data for poly-120, poly(120-b-220), and poly(120-b-220-b-1120) are as follows: Poly-120. SEC: Mn = 5.8 kDa, Mw/Mn = 1.15. 1H NMR (600 MHz, CDCl3, 25 °C): δ 6.10−5.67 (brs, 1H, CH of double bond), 3.81− 3.47 (brs, 2H, OCH2), 2.88−2.15 (brs, 2H, CH2 of the main chain), 1.81−1.09 (brs, 28 H, CH2), 0.92−0.82 (brs, 3H, CH3). FT-IR (KBr, 25 °C): 2923, 2851, 1668, 1469 cm−1. Poly(120-b-220). SEC: Mn = 9.5 kDa, Mw/Mn = 1.28. 1H NMR (600 MHz, CDCl3, 25 °C): δ 6.98 (brs, 1H, ArH, P3HT), 5.95−5.76 (brs, 1H, CH of double bonds, PHA), 3.81−3.43 (brs, 2H, OCH2, PHA), 2.78−2.24 (brs, 4H, PHA main chain and thiophene-CH2 of P3HT), 1.91−1.07 (brs, 36H, CH2, alkyl chains of P3HT and PHA), 1.00− 0.81 (brs, 6H, CH3 of the alkyl chain of both P3HT and PHA blocks). FT-IR (KBr, 25 °C): 2912, 2850, 1631, 1447, 1346 cm−1. Poly(120-b-220-b-1120). SEC: Mn = 44.1 kDa, Mw/Mn = 1.19. 1H NMR (600 MHz, CDCl3, 25 °C): δ 6.97 (brs, 1H, ArH, P3HT), 5.99−5.77 (brs, 7H, CH, PHA), 3.84−3.39 (brs, 14H, OCH2, PHA), 2.84−2.18 (brs, 16H, PHA main chain and thiophene-CH2 of P3HT), 1.99−1.07 (brs, 204H, CH2, alkyl chains of P3HT and PHA), 1.00− 0.75 (brs, 24H, CH3, alkyl chains of both P3HT and PHA blocks). FTIR (KBr, 25 °C): 2929, 2852, 1681, 1469, 1381 cm−1. The triblock copolymer poly(310-b-220-b-310) was synthesized in one-pot followed the same procedure described above. The characterization data for poly-310, poly(310-b-220), and poly(310-b-220-b-310) are as follows: Poly-310. SEC: Mn = 4.2 kDa, Mw/Mn = 1.14. 1H NMR (600 MHz, CDCl3, 25 °C): δ 6.07−5.84 (brs, 1H, CH of the double bonds), 5.27 (brs, 1H, CH of cholesteryl pendants), 3.42−3.34 (m, 1H, OCH), 2.71−2.22 (brs, 2H, CH2 of the main chain), 2.01−0.68 (m, 43H, cholesteryl pendants). FT-IR (KBr, 25 °C): 2939, 2900, 2868, 1658, 1466, 1376, 1256, 1141, 1018 cm−1. Poly(310-b-220). SEC: Mn = 7.8 kDa, Mw/Mn = 1.19. 1H NMR (600 MHz, CDCl3, 25 °C): δ 6.98 (s, 2H, ArH, P3HT), 6.02−5.88 (brs, 1H, CH of double bonds, PCA), 5.19 (brs, 1H, CH of cholesteryl pendants of PCA), 3.34−3.15 (brs, 1H, OCH, PCA), 2.83−2.80 (brs, 6H, PCA main chain and thiophene-CH2, P3HT), 2.01−0.83 (m, 65H, alkyl chains of PCA and P3HT). FT-IR (KBr, 25 °C): 2942, 2908, 2874, 1688, 1648, 1600, 1467, 1386 cm−1. Poly(310-b-220-b-310). SEC: Mn = 12.2 kDa, Mw/Mn = 1.22. 1H NMR (600 MHz, CDCl3, 25 °C): δ 6.97 (s, 1H, ArH, P3HT), 6.02− 5.88 (m, 1 H, CH of double bonds), 5.19 (brs, 1H, CH of cholesteryl pendants of PCA), 3.37−3.31 (brs, 1 H, OCH, PCA), 2.81−2.42 (brs, 4 H, PCA main chain and thiophene-CH2 of P3HT), 2.31−0.83 (m,

54H, alkyl chains of PCA and P3HT). FT-IR (KBr, 25 °C): 2940, 2910, 2871, 1698, 1581, 1444, 1376 cm−1. The amphiphilic PTA-b-P3HT-b-PTA triblock copolymer poly(420b-220-b-4100) was synthesized in one pot following the same procedure described above. The characterization data for poly-420, poly(420-b-220) and poly(420-b-220-b-4100) are as follows: Poly-420. SEC: Mn = 4.8 kDa, Mw/Mn = 1.19. 1H NMR (600 MHz, CDCl3, 25 °C): δ 6.12−5.77 (brs, 1H, CH of double bonds), 3.81− 3.62 (brs, 12H, OCH2), 3.33 (brs, 3H, OCH3), 2.81−2.17 (brs, 2H, CH2 of the main chain). FT-IR (KBr, 25 °C): 2936, 2880, 1664, 1467 cm−1. Poly(420-b-220). SEC: Mn = 8.1 kDa, Mw/Mn = 1.28. 1H NMR (600 MHz, CDCl3, 25 °C): δ 6.97 (brs, 1H, ArH, P3HT), 6.11−5.76 (brs, 1H, CH of double bonds, PTA), 3.79−3.46 (brs, 12H, OCH2, PTA), 3.35 (brs, 3H, OCH3, PTA), 2.78−2.15 (brs, 4H, PTA main chain and thiophene-CH2 of P3HT), 1.73−1.26 (brs, 8H, CH2, alkyl chains of P3HT), 0.92−0.88 (brs, 3H, CH3, P3HT). FT-IR: 2918, 2851, 1662, 1513, 1465 cm−1. Poly(420-b-220-b-4100): SEC: Mn = 28.1 kDa, Mw/Mn = 1.29. 1H NMR (600 MHz, CDCl3, 25 °C): δ 6.98 (s, 1H, ArH, P3HT), 6.08− 5.67 (brs, 6H, CH of double bonds, PTA) 3.81−3.52 (brs, 72H, OCH2, PTA), 3.35 (brs, 18H, OCH3, PTA), 2.81−2.17 (brs, 14H, PTA main chain and thiophene-CH2 of P3HT), 1.78−1.22 (brs, 8H, CH2, alkyl chains of P3HT), 0.98−0.79 (brs, 3H, CH3, P3HT). FT-IR: 2922, 2846, 1662, 1519, 1448 cm−1. Typical Procedure Used To Grow Poly(1m-b-2n) of Various Molecular Weights Using a Common Macroinitiator. Under an atmosphere of nitrogen, 0.063, 0.031, 0.021, and 0.016 mL of a common macroinitiator, Ni(II)-terminated poly-115 in THF (0.2 M) were added via a microsyringe to a series of solutions of 2 in THF at room temperature ([2]0 = 0.2 M). The initial feed ratio of monomer 2 to macroinitiator poly-115 is 20, 40, 60, and 80. The reaction solutions were stirred at room temperature for 2 h and then quenched by methanol. The precipitated solids were collected by centrifugation, washed with methanol and n-hexane, and dried under vacuum to afford poly(115-b-2n) block copolymers. The Mn and Mw/Mn of these polymers were characterized by SEC.

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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.5b02759. Additional spectroscopies of monomers and polymers (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (N.L.). *E-mail [email protected] (Z.-Q.W.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported in part by National Natural Science Foundation of China (21104015, 21172050, 21371043, 51303044, and 21574036). Z.W. thanks the Thousand Young Talents Program for financial support.

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REFERENCES

(1) (a) Kim, J. Y.; Lee, K.; Coates, N. E.; Moses, D.; Nguyen, T. Q.; Dante, M.; Heeger, A. J. Science 2007, 317, 222. (b) Günes, S.; Neugebauer, H.; Sariciftci, N. S. Chem. Rev. 2007, 107, 1324. (c) Thomas, S. W., III; Joly, G. D.; Swager, T. M. Chem. Rev. 2007, 107, 1339. (d) Li, C.; Liu, M.; Pschirer, N. G.; Baumgarten, M.; Müllen, K. Chem. Rev. 2010, 110, 6817.

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DOI: 10.1021/acs.macromol.5b02759 Macromolecules XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/acs.macromol.5b02759 Macromolecules XXXX, XXX, XXX−XXX