Facile Polymerization of Water and Triple-Bond Based Monomers

Oct 18, 2017 - Water is an abundant, natural, and sustainable resource. However, it has not been used as a monomer for the construction of polymers. I...
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Article Cite This: Macromolecules XXXX, XXX, XXX-XXX

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Facile Polymerization of Water and Triple-Bond Based Monomers toward Functional Polyamides Jie Zhang,† Wenjie Wang,† Yong Liu,‡ Jing Zhi Sun,† Anjun Qin,*,†,‡ and Ben Zhong Tang*,†,‡,§ †

MOE Key Laboratory of Macromolecules Synthesis of Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China ‡ Guangdong Innovative Research Team, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China § Department of Chemistry, Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong Kong, China S Supporting Information *

ABSTRACT: Water is an abundant, natural, and sustainable resource. However, it has not been used as a monomer for the construction of polymers. In this paper, we take this challenge and develop a new polymerization of water and triple-bond based monomers of isocyanides and bromoalkynes, and polyamides with high molecular weights (up to 41 700) and stereoregularities (the fraction of Z-isomer generally higher than 80%) are obtained in excellent yields (up to 98.1%) under mild reaction conditions. The polymers possess good solubility and exhibit high thermal stability and refractive index. The tetraphenylethene-containing polymers show the unique aggregation-enhanced emission (AEE) characteristics. Moreover, thanks to their containing bromoacrylamide groups in the main chains, these polyamides could be easily postmodified through different reactions, providing a convenient platform for polymer functionalization. Thus, this work not only established a stereoselective polymerization of water and triple-bond based monomers but also provided a powerful strategy for the preparation of functional polyamides under mild reaction conditions.

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INTRODUCTION

Thus, it is a really huge challenge to prepare polymers using water as a comonomer. Our groups have been working on the development of new polymerization reactions based on triple-bond building blocks for decades.14−17 Recently, we developed a new kind of Cu(I)catalyzed azide−alkyne click polymerization based multicomponent polymerization (MCP).18 During the course of further expanding this MCP, we tried to use water as the comonomer. However, only insoluble products could be obtained, further indicative of the difficulty on incorporation of water into a polymer. Thus, new possible reactions should be surveyed and studied. Recently, Jiang and co-workers reported an elegant CsF-promoted nucleophilic addition reaction of isocyanides to bromoalkynes in the presence of an excess amount of water in DMSO at 90 °C, and functional cisbromoacrylamides were afforded in good to excellent yields after 8−12 h.19 In this stereoselective reaction, the water was used as a reactant. Moreover, the isocyanides and bromoalkynes are triple-bond based starting materials. Attracted by the features of inexpensive additive, simple procedures and high

In nature, organisms can facilely convert inorganic resources to organic biopolymers under ambient conditions. For instance, soybeans could generate nitrogenous biomacromolecules by fixing N2 with the help of rhizobium,1,2 and plants readily convert CO2 and H2O into biopolymers by taking advantage of photosynthetic reaction.3−8 These natural resources of N2, CO2, and H2O are inexpensive and available, which are potentially admirable monomers for polymer preparation. Polymer scientists have devoted tremendous efforts to mimic the nature to utilize these resources for the preparation of polymers. Among these monomers, CO2 has been successfully used to synthesize polycarbonates.9−13 However, to the best of our knowledge, water, which is exceedingly abundant, cheap, and sustainable, has not been used as a monomer to construct polymers. Instead, water always appears during the condensation polymerizations as a byproduct or as a quencher to terminate the reaction. In most cases, the accumulation of water in the reaction system is harmful to the positive movement of reaction equilibrium. Thus, water is always removed from the reaction system as soon as possible. Meanwhile, most of polymerizations need to be carried out under strict water-free conditions because of the fragility of the catalytic systems. © XXXX American Chemical Society

Received: July 25, 2017 Revised: October 1, 2017

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DOI: 10.1021/acs.macromol.7b01592 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules

After confirming the optimal reaction time of 24 h, we screened the reaction solvents. Since the organic reaction was carried out at 90 °C, we thus tested the solvents with boiling points above this temperature. The experimental results showed that the polymerization propagated smoothly in highly polar solvents such as dimethyl sulfoxide (DMSO) and N,Ndimethylformamide (DMF), but the Mw and yield of the polymer produced in the former are much higher than that in the latter (entries 3 and 4, Table 1), while no product could be obtained in the nonpolar solvent of toluene probably because CsF could not be dissolved in it (entry 5, Table 1). We thus used DMSO as solvent. Next, we investigated the effect of additives on the polymerization results, which showed that K2CO3 and Et3N could also promote the reaction, but the yields of the products are lower (entries 6 and 7, Table 1). We thus kept using CsF as the additive. At last, we studied the effect of reaction temperature on the polymerization (entries 8−10, Table 1). A trace amount of product was obtained when the polymerization was performed at 70 °C. Raising the temperature is beneficial to the polymerization, but only partially soluble product could be yielded at 100 °C, which may be due to its extremely high Mw. What is more, the hydrogen binding interactions between the amide groups in the product backbones may play a destructive role for its solubility, which could be concluded from the shift of the vibration peak of amine to higher wavenumber as well as the broadening of the shifted vibration band in the FT-IR spectra (Figure S1).39,40 It is worth noting that our polymerization is insensitive to the reaction atmosphere. As shown in entry 11 of Table 1, the products with high Mw values could be obtained in excellent yields in air or under nitrogen. Moreover, the 1H NMR spectra of resultant polymers indicated that they were almost no difference in terms of the resonance peaks presumably due to the relative stability of the additive and monomers (Figure 1). However, to ensure the resultant polymers with higher Mw, we prefer to carry out the polymerization under nitrogen rather than in air. Generally, stoichiometry is crucially important for the polymerization of comonomers. However, our developed polymerization could produce products without using equivalent molar ratio of monomers. We thus investigated the effect of feeding ratio of monomers on the polymerization. First, we varied the amount of water while keeping the ratio of 1a and 2a unchanged. The precipitates appeared when the polymerization was carried out for 10 h in the system containing 0.2 mL of water probably due to the decrease of the solvating ability of the mixture solvent. The polymerization results showed the product with lower Mw was obtained in lower yield when the molar concentration ratio of water/2a is 2 because water could be volatilized at 90 °C from the reaction solution to the Schlenk tube wall, making the amount of water deficient for the polymerization, whereas the best results could be achieved when the amount of water is 0.1 mL (Table S1). Next, we studied the ratio of 1a/2a in the presence of 0.1 mL of water. As shown in Table 2, when the concentration of 1a is 1.5 times higher than that of 2a, the product with the highest Mw and yield was obtained, indicating that this polymerization performed in a nonstoichiometric fashion probably due to the less activity of isocyanides than that of bromoalkynes.41−43 Finally, with the optimal reaction conditions in hand, we polymerized different diisocyanides 1 and bis(bromoalkyne)s 2 in the presence of water to show its robustness and universality

yields of this reaction, we tried to develop it into a new polymerization reaction, from which we could not only polymerize water but also expand our triple-bond building blocks from alkynes to isocyanides.20−27 Moreover, a new kind of polyamide with broad applications will be generated.28,29 Polyamide, one of the high performance engineering plastics, is typically prepared by the condensation polymerization of diacids/diesters and diamines30,31 or by the ring-opening polymerization of lactam.32,33 However, the former does not perform in an atom economy way because it will generate byproducts, and the latter requires a little specific monomer.34 Thanks to the ready availability of monomers and atom economic fashion, our developed water involved polymerization not only breaks through the traditional limitation but also provides a straightforward and fire-new way to prepare polyamides. What is more, the resultant polyamides could be easily postfunctionalized. The postpolymerization modification (PPM) is well-known as “polymer analogous reaction”,35 which can efficiently consume reactive groups on the prepolymers to enrich the functions of a polymer with the same backbone. Through conventional Sonogashira reaction and substitution reaction, a series of polyamides were derived, and it is worth mentioning that postfunctionalization via substitution reaction could even be immediately carried out in one-pot without purification of the polymers. Therefore, it displayed a convenient platform for polymer functionalization, which would greatly enrich their property and largely broaden their applications.

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RESULTS AND DISCUSSION Polymerization. In order to establish the polymerization using water as one of the monomers, the diisocyanides 1 and bis(bromoalkyne)s 2 were designed and synthesized according to the literature procedures (Scheme 1, Schemes S1 and Scheme 1. Water Involved Polymerization of Diisocyanides and Bis(bromoalkyne)s

S2).36,37 We first followed the reported reaction conditions to try the polymerization except that the ratio of isocyanide and bromoalkyne was adjusted from 2.0 to 1.5 to save the used amount of diisocyanide.19 When 1a (0.15 M), 2a (0.10 M), and water (0.1 mL) were polymerized in the presence of CsF (0.2 M) in DMSO (2 mL) at 90 °C under nitrogen for 12 h, a product with satisfactory weight-average molecular weight (Mw) of 14 900 was obtained in a yield of 64.3% (entry 1, Table 1). Further prolonging the reaction time to 24 h, the Mw and yield of product remarkably increased to 41 700 and 98.1%, respectively. These experiments suggest that it is hard to fully follow the reaction conditions used for the organic reaction.38 Thus, we systematically optimized the polymerization conditions using 1a, 2a, and water as model monomers. B

DOI: 10.1021/acs.macromol.7b01592 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Table 1. Polymerization of Water, Diisocyanide (1a), and Bis(Bromoalkyne) (2a) under Various Conditionsa entry

t (h)

T (°C)

solvent

additive

Mwb

Mn

Đb

yield (%)

1 2 3 4 5 6 7 8 9 10 11d

12 18 24 24 24 24 24 24 24 24 24

90 90 90 90 90 90 90 70 80 100 90

DMSO DMSO DMSO DMF toluene DMSO DMSO DMSO DMSO DMSO DMSO

CsF CsF CsF CsF CsF K2CO3 Et3N CsF CsF CsF CsF

14900 28300 41700 28400

5600 6700 7300 6800

2.64 4.20 5.71 4.19

64.3 77.5 98.1 72.3

22200 5600

7200 3800

3.08 1.47

23900 6900c 20000

6300 4300 6000

3.81 1.60 3.35

57.9 61.1 trace 53.1 59.3 96.2

Carried out in 2 mL of solvent and 0.1 mL of water under nitrogen ([1a]/[2a] = 1.5, [CsF]/[2a] = 2, [2a] = 0.1 M). bMw and Đ (Mw/Mn) of polymers were estimated by GPC in DMF containing 0.05 M LiBr on the basic of a poly(methyl methacrylate) calibration. cSoluble part. dCarried out in air ([1a]/[2a] = 1.5, [CsF]/[2a] = 2, [2a] = 0.1 M, feeding ratio of H2O vs 2a: 27.8). a

Table 3. Polymerization of Water, Diisocyanides 1, and Bis(bromoalkyne)s 2a entry polymer 1 2 3 4 5 6

PI PII PIII PIVc PVc PVIc

monomer

Mwb

Mn

Đb

yield (%)

Z/E

1a + 2a 1a + 2b 1a + 2c 1b + 2a 1b + 2b 1b + 2c

41700 26400 9300 8000 11700 14000

7300 6500 5100 3300 4300 4200

5.71 4.04 1.84 2.45 2.75 3.32

98.1 56.1 36.3 62.1 80.6 73.4

80/20 85/15 82/18 84/16 90/10 76/24

The reaction was carried out at 90 °C in 2 mL of DMSO with 0.1 mL of water under nitrogen for 24 h ([1]/[2] = 1.5, [CsF]/[2] = 2, [2] = 0.1 M, feeding ratio of H2O vs 2a: 27.8). bMw and Đ (Mw/Mn) of polymers were estimated by GPC in DMF containing 0.05 M LiBr on the basic of a poly(methyl methacrylate) calibration. cThe reaction was carried out at 90 °C in DMSO under N2 for 9 h ([1]/[2] = 1.5, [CsF]/[2] = 2, [2] = 0.1 M, feeding ratio of H2O vs 2a: 27.8). a

Different from traditional polyamides, all the resultant polymers PI−PVI possess excellent solubility in commonly used organic solvents, such as DMSO, DMF, chloroform, and tetrohydrofuran (THF). They are also thermally stable. As revealed by the thermogravimetric analysis (TGA) under nitrogen, the temperatures for the 5% loss of their weights are between 243 and 383 °C (Figure S2). Structural Characterization. Thanks to their good solubility, their structures were characterized by spectroscopic methods. For the spectral profile of PI (Figure 2) resembles with those of other five polymers (Figures S3−S7), the FT-IR

Figure 1. 1H NMR spectra of PI prepared in air (A) and under nitrogen (B) in DMSO-d6. The solvent peaks are marked with asterisks.

Table 2. Effect of the Ratio between Diisocyanide (1a) and Bis(bromoalkyne) (2a) on Polymerizationa entry

[1a]/[2a]

Mwb

Mn

Đb

yield (%)

1 2 3

1.5:1 1:1 1:1.5

41700 25500 11100

7300 6700 5000

5.71 3.78 2.24

98.1 74.8 44.0

Carried out in 2.0 mL of DMSO with 0.1 mL of water at 90 °C under nitrogen for 24 h, [2a] = 0.2 M, [CsF]/[2a] = 2, feeding ratio of H2O vs 2a: 27.8. bMw and Đ (Mw/Mn) of polymers were estimated by GPC in DMF containing 0.05 M LiBr on the basic of a poly(methyl methacrylate) calibration. a

(Table 3). The experiments showed that all the polymerizations propagated smoothly, and polymers PI−PVI with Mw up to 41 700 could be obtained in satisfactory yields (up to 98.1%). It is worth noting that both of the aromatic or aliphatic diisocyanides and bis(bromoalkyne)s are also suitable for the polymerization, indicative of its universality and robustness.

Figure 2. FT-IR spectra of 1a (A), 2a (B) and PI (C). C

DOI: 10.1021/acs.macromol.7b01592 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules spectra of PI and its monomers 1a and 2a are shown in Figure 2 as an example. The absorption bands at 2115 and 2194 cm−1 are assignable to the stretching vibration of CN and CC in 1a and 2a, respectively. However, these peaks weakened obviously in the spectrum of PI. Meanwhile, new bands at 3255, 1662, and 1597 cm−1, which are the stretching vibration of N−H, stretching vibration of CO, and deformation vibration of N−H, respectively, appeared in the spectrum of PI. All these results indicated that 1a, 2a, and water had been reacted, and an amide group had been formed accordingly. More detailed structure information on polymers could be obtained from the 1H NMR spectrum. To facilitate the structural characterization, model compound 5 was prepared under the same reaction conditions (Scheme 2). The 1H NMR Scheme 2. Synthetic Route to the Model Compound 5

spectra of PI, monomers 1a and 2a, and the model compound 5 in DMSO-d6 are shown in Figure 3 as an example. The characteristic proton resonant peaks of “i” in amide and “h” in 5 resonated at δ 9.85 and 7.10 are observed in Figure 3C. Correspondingly, amidic proton peaks of “i’” and “h’” of PI are found at δ 9.85 and δ 7.34 in Figure 3D, respectively. Meanwhile, two sets of peaks assigned to E-stereoregular isomer were also observed at δ 10.13 and 7.39 in PI. Since the peaks at δ 9.85 and 10.13 are well-separated, they were used to calculate the ratio of Z/E conformation in PI, which was deduced to be 80/20 (Table 3). The 1H NMR spectra of PII− PVI are similar to that of PI, and the value of Z/E ratio is also very high (Figures S8−S12). In order to further verify the polymerization and polymer structures, D2O was used as the comonomer to replace H2O. As shown in the 1H NMR spectrum of the product (Figure S13), the resonant peaks at δ 10.15 and 9.85 remarkably vanished and the peaks at δ 7.39 and 7.34 also completely disappeared, confirming that the structures of the polymers are correct and water is indeed involved in the polymerization. The 13C NMR spectra were also measured to verify the structures of the polymers (Figure 4 and Figures S14−S18). The peaks representing carbons “1” and “2” in 2a do not appear in the spectrum of PI. Meanwhile, the resonance of the carbonyl carbon “3” in 5 is observed in the spectrum of PI at δ 165. These results suggest that 1a and 2a had been polymerized together with water, and PI was indeed obtained. Light Refractivity. In general, a high fraction of heteroatoms, highly polarized aromatic rings, and other conjugated units may lead to high refractive index of a polymer, which will be applicable in diverse areas such as lenses, prisms, optical waveguides, and holographic image recording systems.44,45 PI−PVI are rich in aromatic rings and heteroatoms and thus are expected to show high refractive index. Indeed, these polymers exhibit higher refractive indices (except PIV due to its poor film-forming ability) than those commodity polymeric materials, such as polystyrene, polycarbonate, poly(methyl methacrylate), and polyacrylate, which exhibit refractive values lying in the region of 1.49−1.58.46,47 Aggregation-Enhanced Emission. PIII and PVI contain the unique moieties of tetraphenylethene (TPE), which is a

Figure 3. 1H NMR spectra of 2a (A), 1a (B), model compound 5 (C), and PI (D) in DMSO-d6. The solvent peaks are marked with asterisks.

typical luminogen exhibiting aggregation-induced emission (AIE) feature.48 In accordance, PIII and PVI show the unique aggregation-enhanced emission (AEE) characteristics. For example, as shown in Figure 6, PIII emits moderate in THF, which could ascribe to the conjugation of the backbone and restriction of intramolecular rotation. With increasing the water content in the THF solution, the emission of PIII is intensified gradually. The emission intensity reaches the highest in the THF/water mixture with water fraction of 80%, which is 3 times higher than that in THF, demonstrating a typical AEE feature (Figure 6b). Postmodification. PI−PVI contain two bromoacrylamide groups in the repeating unit, which provide an ideal platform to further functionalize the polymers via post modification. Postmodification via Sonogashira Reaction. PI with Mw of 34 800 could readily react with trimethylsilylacetylene to produce PI−PM1 with Mw of 32 400 in 97.1% yield (Scheme 3, route 1). Owing to the alkalinity of PI itself and remaining CsF, desilylation was occurred in situ. The slight decrease in Mw of PI−PM1 was due to the lower molecular weight of ethynyl (25) than that of bromo group (80). To facilitate the structural characterization, model compound 5-PM1 was prepared under the same reaction conditions (Scheme S3). The structures of PI−PM1 and 5-PM1 were characterized by 1H NMR spectra D

DOI: 10.1021/acs.macromol.7b01592 Macromolecules XXXX, XXX, XXX−XXX

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The above results suggested the success of postmodification of PI via the Sonogashira reaction. Postmodification via Substitution Reaction. Thanks to the connected electron-withdrawing carbonyl group, the bromo group of PI is activated and can be substituted by a nucleophile. For example, the substitution reaction between PI (Mw = 32 800) and thiophenol can occur under ambient condition, generating PI−PM2 with Mw of 32 400 in 93.4% yield (Scheme 3, route 2). Similar to the postmodification via the Sonogashira reaction, the model compound 5-PM2 was also prepared under the same reaction conditions (Scheme S4). The 1H NMR spectra of 5-PM2 and PI−PM2 confirm their structures, from which the grafting degree of PI was calculated to be as high as 73.6% (Figures S21 and S22). Thus, the second postmodification route via substitution reaction was established successfully. Polymerization and Postmodification in One Pot. Inspired by such an efficient and robust postmodification via substitution reaction, the one-pot method was developed (Scheme 3, route 3). After polymerization, thiophenol was injected into the polymeric tube directly at ambient temperature without extra additive and solvent. Eventually, PI−PM3 with Mw of 25 600 was obtained in 78.5%. The grafting degree of PI−PM3 was calculated as 72.7% from the 1H NMR spectrum (Figure S23), which was very close to that of PI− PM2. This experiment confirms the compatibility of the polymerization and postmodification in one pot and further simplifies the operations.

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CONCLUSION In this work, water was first copolymerized with triple-bond based monomers of diisocyanides 1 and bis(bromoalkyne)s 2 in the presence of CsF under mild reaction conditions. With the optimal polymerization conditions, polyamides PI−PVI with high Mw values were prepared in high yields. This new polymerization is stereoselective, and the fraction of Zstereoregular isomers in the polymers is generally higher than 80% probably because it is more stable than that of E-isomers. The resultant polyamides are soluble in commonly used organic solvents and thermally stable with the temperatures for 5% weight loss higher than 243 °C. Thanks to their containing aromatic units and heteroatoms as well as bromoethylene groups, these polymers possess high refractive index values. Furthermore, the polymers can be postmodified via Sonogashira coupling and substitution reaction. It is worth noting that postmodification via substitution reaction could even be performed in one pot by addition of the nucleophile after polymerization. Thus, we not only established a new stereoselective polymerization of water and triple-bond based monomers but also provided a powerful strategy for the preparation of functional polyamide via postmodification under mild reaction conditions.

Figure 4. 13C NMR spectra of 2a (A), 1a (B), and model product 3 (C), and PI (D) in DMSO-d6. The solvent peaks are marked with asterisks.

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Figure 5. Light refraction spectra of thin solid films of polymers PI, PII, PIII, PV, and PVI.

EXPERIMENTAL SECTION

Polymer Synthesis. All the polymerization reactions, except as specially provided, were carried out under a nitrogen atmosphere using a standard Schlenk technique. A typical procedure for the polymerization of water, 1a, and 2a is given below as an example. 1a (90.6 mg, 0.3 mmol), 2a (56.8 mg, 0.2 mmol), and CsF (60.8 mg, 0.4 mmol) were added into a 10 mL Schlenk tube. After being evacuated and refilled with nitrogen for three times, DMSO (2.0 mL) was injected into the tube to dissolve the monomers, and then H2O (0.1 mL) was injected. The mixture was stirred at 90 °C for 24 h. After

(Figures S19 and S20). The resonant peak ascribed to terminal ethynyl group of PI−PM1was observed at δ 3.10. A new set of amidic protons after modification resonated at δ 8.8−9.5, while the peaks of unmodified amide protons remain unshifted. The grafting degree of PI−PM1 could be calculated to be 63.5%. E

DOI: 10.1021/acs.macromol.7b01592 Macromolecules XXXX, XXX, XXX−XXX

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Figure 6. (a) PL spectra of PI in THF and THF/water mixtures with different water fractions ( f w, vol %). Concentration: 10−5 M; excitation wavelength: 337 nm. (b) Plot of relative PL intensity versus water fraction in THF/water mixtures.

Scheme 3. Postmodification Routes of PI via Different Reactions

Characterization Data of PII. Yellowish-brown solid (89.8 mg); yield 56.1% (Table 3, no. 2); Mw: 26 400. Mw/Mn: 4.04 (GPC, PMMA calibration). FT-IR (KBr), v (cm−1): 3404, 3272, 2956, 2925, 2877, 2112, 1667, 1606, 1507, 1372, 1296, 1219, 1177, 1009, 932, 825, 726, 556. 1H NMR (500 MHz, DMSO-d6) δ (TMS, ppm): 9.63, 9.15, 7.12−6.63, 4.76, 3.81, 2.63, 2.31, 2.16, 1.58, 1.15, 1.04. 13C NMR (125 MHz, DMSO-d6) δ (ppm): 168.32, 164.71, 156.12, 143.55−127.96, 114.45, 108.99, 78.56, 69.31, 55.75, 41.70. Characterization Data of PIII. Yellowish-brown solid (63.6 mg); yield 36.3% (Table 3, no. 3); Mw: 9300. Mw/Mn: 1.84 (GPC, PMMA calibration). FT-IR (KBr), v (cm−1): 3396, 3280, 3060, 2956, 2916, 2860, 2208, 2112, 1660, 1595, 1487, 1446, 1223, 1180, 1028, 847, 737, 699. 1H NMR (500 MHz, DMSO-d6) δ (TMS, ppm): 10.04, 9.72, 7.32, 7.13, 6.96, 3.79, 2.67, 2.28, 2.12, 0.99. 13C NMR (125 MHz, DMSO-d6) δ (ppm): 168.33, 165.59, 151.47, 144.18−126.09, 123.53, 106.77, 92.81, 67.50, 24.91, 18.81, 15.64. Characterization Data of PIV. Yellowish-brown solid (81.2 mg); yield 62.1% (Table 3, no. 4); Mw: 8000. Mw/Mn: 2.45 (GPC, PMMA calibration). FT-IR (KBr), v (cm−1): 3385, 3049, 2964, 2868, 2217, 2112, 1667, 1591, 1487, 1449, 1219, 1143, 1035, 847, 740, 699, 638,

being cooled down to room temperature, the resultant solution was diluted with CHCl3 (20 mL). The solution was washed with brine for three times to remove CsF and DMSO. The combined organic layers were concentrated to about 5 mL under reduced pressure and added dropwise into 300 mL of hexane/CHCl3 (5:1, v/v) through a cotton filter under stirring. The precipitate was allowed to stand overnight and then collected by filtration. The product was washed with hexane and dried to a constant weight, affording a yellowish-brown powder product. The control polymerization for mechanism study was performed with similar procedures except that H2O was placed by D2O. Characterization Data of PI. Yellowish-brown solid (122.0 mg); yield 98.1% (Table 3, no. 1); Mw: 41 700. Mw/Mn: 5.71 [GPC, poly(methyl methacrylate) (PMMA) calibration]. FT-IR (KBr), v (cm−1): 3255, 2964, 2857, 2203, 2107, 1662, 1592, 1484, 1364, 1223, 1033, 959, 844, 736, 527. 1H NMR (500 MHz, DMSO-d6) δ (TMS, ppm): 10.17, 9.85, 7.59, 7.39, 7.32, 7.10, 6.95, 3.86, 2.55, 2.33, 2.19, 1.17, 1.08. 13C NMR (125 MHz, DMSO-d6) δ (ppm): 168.51, 165.54, 160.15, 151.52, 144.00−122.43, 24.92, 19.41, 15.67. F

DOI: 10.1021/acs.macromol.7b01592 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules

filtration. The product was washed with hexane and dried to a constant weight. A yellowish-brown powder product was obtained in 78.5% yield (74.7 mg). 1H NMR (500 MHz, DMSO-d6) δ 10.11, 9.83, 9.57, 9.38, 8.0−6.0, 3.77, 2.20, 2.10, 1.09.

572, 484. 1H NMR (500 MHz, DMSO-d6) δ (TMS, ppm): 9.37, 9.05, 8.07−6.23, 4.84, 4.41. 13C NMR (125 MHz, DMSO-d6) δ (ppm): 166.59, 156.96, 143.24, 140.01−125.83, 122.13, 107.49, 45.15, 41.92. Characterization Data of PV. Yellowish-brown solid (153.1 mg); yield 80.6% (Table 3, no. 5); Mw: 11 700. Mw/Mn: 2.75 (GPC, PMMA calibration). FT-IR (KBr), v (cm−1): 3433, 3300, 3060, 2208, 2141, 1655, 1602, 1510, 1227, 1020, 833, 737, 480. 1H NMR (500 MHz, DMSO-d6) δ (TMS, ppm): 9.17, 8.82, 7.36−6.66, 4.81, 4.69, 4.35, 1.53. 13C NMR (125 MHz, DMSO-d6) δ (ppm): 165.62, 156.09, 143.62−132.41, 127.96, 127.41, 114.62, 108.82, 78.62, 69.09, 55.75, 45.10, 42.22, 41.58, 31.16, 25.62. Characterization Data of PVI. Yellowish-brown solid (107.2 mg); yield 73.4% (Table 3, no. 6); Mw: 14 000. Mw/Mn: 3.32 (GPC, PMMA calibration). FT-IR (KBr), v (cm−1): 3385, 3272, 2964, 2868, 2104, 1671, 1602, 1502, 1441, 1372, 1300, 1223, 1180, 1009, 828, 729, 556. 1 H NMR (500 MHz, DMSO-d6) δ (TMS, ppm): 9.22, 8.96, 8.48, 8.12, 7.36−6.54, 4.82, 4.37, 4.26 13C NMR (125 MHz, DMSO-d6) δ (ppm): 165.85, 161.50, 144.28−125.70, 106.87, 67.53, 44.94, 42.26, 31.21, 25.77. Preparation of Model Compound 5. Into a 10 mL Schlenk tube was placed CsF (1.5 mmol, 228 mg). After being evacuated and refilled with nitrogen for three times, bromoethynylbenzene (1 mmol, 180 mg), 1-isocyano-4-methylbenzene (2 mmol, 234 mg), DMSO (2 mL), and H2O (0.1 mL) were injected into the tube one by one. The mixture was stirred at 90 °C for 24 h. Afterward, the reaction mixture was concentrated under reduced pressure, and the crude product was purified by a silica gel column chromatography using DCM/PE (4:1, v/v) as eluent. A light yellow powder of 5 was obtained in 56.3% yield (177.3 mg). 1H NMR (500 MHz, DMSO-d6) δ 10.45 (s, 1H), 7.58 (d, J = 5.0 Hz, 2H), 7.48 (d, J = 10.0 Hz, 2H), 7.45−7.37 (m, 3H), 7.34 (s, 1H), 7.15 (d, J = 8.2 Hz, 2H), 2.27 (s, 3H). 13C NMR (125 MHz, DMSO-d6) δ (ppm): 165.40 (s), 144.09 (s), 136.59 (s), 135.27 (s), 133.40 (s), 129.63 (s), 129.40 (s), 129.19 (s), 126.30 (s), 120.13 (s), 107.17 (s), 20.97 (s). Preparation of PI−PM1. Into a 10 mL Schlenk tube were placed PI (the product of polymerization for 18 h, 0.1 mmol, 65 mg), Pd(PPh3)Cl2 (0.004 mmol, 1.4 mg), PPh3 (0.01 mmol, 2.6 mg), and CuI (0.01 mmol, 1.9 mg). After being evacuated and refilled with nitrogen for three times, THF (2 mL), TMSA (0.3 mmol, 44 μL), and Et3N (10 μL) were injected into the tube one by one. The mixture was stirred at 70 °C for 20 h. After being cooled down to room temperature, the resultant solution was added dropwise into 300 mL of hexane/CHCl3 (5:1, v/v) through a cotton filter under stirring. The precipitate was allowed to stand overnight and then collected by filtration. The product was washed with hexane and dried to a constant weight. A yellowish-brown powder product was obtained in 97.1% yield (33.2 mg), and the soluble part is in 37.4%. 1H NMR (500 MHz, DMSO-d6) δ 10.12, 9.82, 9.32, 9.08, 7.83−6.26, 3.78, 3.10, 2.32, 2.19, 1.19, 1.07. Preparation of PI−PM2. Into a 10 mL tube were placed PI (the product of polymerization for 18 h, 0.0645 mmol, 40 mg) and K2CO3 (0.0645 mmol, 9 mg). Then N-methylpyrrolidone (NMP, 4 mL) and compound 6 (0.2 mmol, 25 μL) were injected into the tube. The mixture was stirred under ambient condition for 12 h. The resultant solution was added dropwise into 300 mL of hexane/CHCl3 (5:1, v/v) through a cotton filter under stirring. The precipitate was allowed to stand overnight and then collected by filtration. The product was washed with hexane and dried to a constant weight. A yellowish-brown powder product was obtained in 93.4% yield (38.2 mg). 1H NMR (500 MHz, DMSO-d6) δ 10.14, 9.29, 8.0−6.0, 3.77, 2.32, 2.19, 1.09. Preparation of PI−PM3. 1a (68 mg, 0.225 mmol), 2a (42.6 mg, 0.15 mmol), and CsF (45.6 mg, 0.3 mmol) were added into a 10 mL Schlenk tube. After being evacuated and refilled with nitrogen for three times, DMSO (1.5 mL) was injected into the tube to dissolve the monomers, and then H2O (0.075 mL) was injected. The mixture was stirred at 90 °C for 18 h. After being cooled down to room temperature, compound 6 (0.45 mmol, 55 μL) was injected into the tube. After 12 h, the resultant solution was added dropwise into 300 mL of hexane/CHCl3 (5:1, v/v) through a cotton filter under stirring. The precipitate was allowed to stand overnight and then collected by

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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.7b01592. Detailed synthetic routes to monomers; TGA curves, FT-IR spectra, and 1H and 13C NMR spectra of PII−PVI (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected], [email protected] (A.J.Q.). *E-mail [email protected] (B.Z.T). ORCID

Anjun Qin: 0000-0001-7158-1808 Ben Zhong Tang: 0000-0002-0293-964X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (21525417 and 21490571); the key project of the Ministry of Science and Technology of China (2013CB834702); The National Program for Support of TopNotch Young Professionals; and the Innovation and Technology Commission of Hong Kong (ITC-CNERC14S01). A.J.Q. and B.Z.T. thank the support from Guangdong Innovative Research Team Program (201101C0105067115).

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REFERENCES

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DOI: 10.1021/acs.macromol.7b01592 Macromolecules XXXX, XXX, XXX−XXX