Article pubs.acs.org/Macromolecules
Syntheses of Sequence-Controlled Polymers via Consecutive Multicomponent Reactions Ze Zhang,† Ye-Zi You,† De-Cheng Wu,‡ and Chun-Yan Hong*,† †
Key Lab of Soft Matter Chemistry, Chinese Academy of Sciences, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei 230026, Anhui, China ‡ Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Polymer Physics & Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China S Supporting Information *
ABSTRACT: Multicomponent reactions have recently attracted a great deal of attention as they are considered as a powerful tool for constructing sequence-controlled polymers. Although new examples are constantly flourishing in the literature, the process that allows two or more consecutive multicomponent-reactions to react in a single operation for the syntheses of sequence-controlled polymers has not been developed until now. Here, we propose a new strategy combining multicomponent reaction of amine, thiol, and alkene conjugating and multicomponent polymerization of diyne, azide, and diamine coupling in one-pot for the synthesis of sequence-controlled polymer.
■
INTRODUCTION
remarkable control at the molecular scale is particularly important for proteins, as it can direct the folding of a single peptide chain into a three-dimensional nanostructure and imbue the protein with highly specific activity.1−3 The major challenge of polymer chemistry is to mimic such sequence regulation in polymer synthesis.4−6 Multicomponent reaction can connect three or more starting materials in a single synthetic operation with high atom economy and bond-forming efficiency, thereby increasing molecular diversity and complexity in a fast and often experimentally simple fashion, which is now a powerful strategy to regulate molecular diversity and complexity from simple and readily available substrates in onepot process.5,7−13 Though the importance of sequence-control events during polymerizations was recently emphasized by Lutz, Liu, and Sawamoto et al.,1−3,5−7,14−16 so far, the application of multicomponent reactions (MCRs) in polymer synthesis is still in its infancy, and there are only a few MCRs,5 such as the Passerini three-component reaction,9,17−19 the Ugi reaction,20−22 and metal-catalyzed multicomponent reaction,12,23,24 that have been successfully employed to afford highly functionalized polymeric materials.11 However, most of the obtained polymers have only a few components5 whereas the proteins have 20 amino acid components. The fewer components limit molecular diversity and complexity for the
Biopolymers, such as proteins, have well-defined sequence of repeat units and/or functionalities along the backbone. This Scheme 1. Outline of the Synthesis of Sequence-Controlled Polymer via Two Consecutive Multicomponent Reactions of Amine−Thiol−Ene Conjugating Andalkyne−Azide−Amine Coupling in One Pot
Received: March 3, 2015 Revised: May 5, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.macromol.5b00463 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
Figure 1. continued
B
DOI: 10.1021/acs.macromol.5b00463 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
Figure 1. 1H NMR spectra (A) and 13C NMR spectra (B) for mixture of the multicomponent reaction of propargyl methacrylate, N(carbobenzyloxy)homocysteine thiolactone, and 4,7,10-trioxa-1,13-tridecanediamine (∗ is triethylamine).
obtained polymers. To ensure sufficient molecular diversity and complexity, more components should be introduced into a single chain, which needs more starting molecules to react in one pot. The strategy that allows two or more consecutive multicomponent reactions to react in one pot would be a very promising method; however, it has not been developed for sequence-controlled polymer synthesis until now. Here, we report a first example of two consecutive multicomponent-reactions in one pot for the preparation of sequence-controlled polymers via using a unique monomer (A) with two orthogonal reactive groups (alkene unit and alkyne unit) to combine the two multicomponent reactions together in one pot as shown in Scheme 1. First, propargyl methacrylate (PM, A), N-(carbobenzyloxy)homocysteinethiolactone (NC, B), and 4,7,10-trioxa-1,13-tridecanediamine (TT, C) were used as three starting molecules in the first three-component reaction of amine−thiol−ene conjugating to build up an ABCBA-sequenced molecule containing two alkyne units. Subsequently, p-toluenesulfonyl azide (PT, D) and 1,4phenylenediamine (1,4-PA, E) were added into the reaction system, and the Cu-catalyzed three-component polymerization
of diyne (ABCBA), azide (D), and diamine (E) coupling occurred immediately, giving a polymer with a DABCBADE sequence and high molecular weight as shown Scheme 1.
■
EXPERIMENTAL SECTION
Materials. All reagents were used as received unless otherwise stated. N,N′-Diisobutyl-1,6-hexanediamine (97%) and propargyl methacrylate (98%) were purchased from Alfa Aesar. DL-Homocysteine thiolactone hydrochloride (99%), acetyl chloride (98%), and 4,7,10-trioxa-1,13-tridecanediamine (97%) were purchased from Sigma-Aldrich. Benzyl chloroformate (96%), 1,4-butanediol (99%), 1,4-phenylenediamine (98%), and 2,2-dimethyl-1,3-propanediamine (97%) were purchased from TCI. Triethylamine (TEA, 99.5%) and dimethylformamide (DMF, 99.9%) were purchased from Aladdin. pToluenesulfonyl azide (98%) and o-phenylenediamine (99%) were purchased from Adamas-beta. Chloroform-d (99.8 atom % D) was purchased from J&K. Cuprous chloride (98.5%), sodium sulfate anhydrous (99%), sodium hydroxide (96%), n-hexane (97%), ethyl acetate (99.5%), methanol (99.7%), dichloromethane (99.5%), and diethyl ether anhydrous (99.7%) were purchased from Sinopharm Chemical Reagent Co. Ltd. Propargyl methacrylate (Alfa Aesar, 98%) was purified by small aluminum oxide (basic) chromatography to remove inhibitor. C
DOI: 10.1021/acs.macromol.5b00463 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules Characterizations. All NMR spectra were recorded on a Bruker AV300 NMR spectrometer (resonance frequency of 300 MHz for 1H and 75 MHz for 13C) operated in the Fourier transform mode. The samples were dissolved in chloroform-d or DMSO-d6 , with tetramethylsilane (TMS) as an internal reference. Molecular weights and molecular weight distributions were measured by using a SEC instrument. The system was equipped with a PL-RI differential refractive index detector (DRI), PL-BV 400RT viscometer (Visc), and a Precision Detectors PD2020 light scattering detector (LS). LiBr/ DMF (0.1%, w/w) solution with a flow rate of 1.0 mL/min was used as eluent. The molecular weights were calibrated against polystyrene standards. Mass spectrum analysis was performed by using a LC-MS instrument (Thermo Scientific, LTQ Orbitrap XL). The system was equipped with an ESI source, and MS data were processed using Xcalibur software (2.1.0 SP1 built 1160). Synthesis of N-Acetohomocysteine Thiolactone. DL-Homocysteine thiolactone hydrochloride (3.07 g, 20 mmol) was mixed with triethylamine (9.70 g, 96 mmol) in 50 mL of dichloromethane to form a suspension in ice bath. Acetyl chloride (2.36 g, 30 mmol) was added dropwise within 30 min. The solution was stirred overnight at room temperature. The reaction mixture was diluted with 20 mL of dichloromethane, filtered, washed with brine (30 mL × 2), and extracted with dichloromethane (40 mL × 2). The organic layer was dried with anhydrous Na2SO4. Further purification can be achieved by silica gel column chromatography using ethyl acetate as eluent to obtain the product as white powder. Yield was 65%. 1H NMR spectrum (300 MHz, CDCl3): δ 1.931 (m, 1H), δ 2.029 (s, 3H), δ 2.895 (m, 1H), δ 3.301 (m, 2H), δ 4.527 (m, 1H), δ 6.171 (s, 1H). Synthesis of N-(Carbobenzyloxy)homocysteine Thiolactone. DL-Homocysteine thiolactone hydrochloride (3.07 g, 20 mmol) was added to a suspension of NaHCO3 (8.4 g, 100 mmol) in H2O/1, 4dioxane (v/v, 1/1, 80 mL) at 0 °C; subsequently, the mixture was stirred for 30 min. Benzyl chloroformate (5.1 g, 30 mmol) was added dropwise within 30 min, and the mixture was stirred overnight at room temperature. The reaction was terminated by diluting with brine (50 mL) and extracted with ethyl acetate (70 mL × 4). The organic layer was dried with anhydrous Na2SO4. Further purification can be achieved by recrystallization in ethyl acetate to obtain the product as white crystal. Yield was 35%. 1H NMR spectrum (300 MHz, CDCl3): δ 1.986 (m, 1H), δ 2.889 (m, 1H), δ 3.274 (m, 2H), δ 4.337 (m, 1H), δ 5.127 (s, 2H), δ 5.215 (s, 1H). Two Consecutive Multicomponent Reactions in One Pot. Propargyl methacrylate (2 mmol), N-(carbobenzyloxy)homocysteine thiolactone (2 mmol), 4,7,10-trioxa-1,13-tridecanediamine (1 mmol), and triethylamine (10 mmol) were dissolved in DMF (3 mL). Then, the mixture was degassed with argon for 2 min, and afterward the reaction was performed under stirring at room temperature for 12 h. Subsequently, CuCl (0.15 mmol), 1,4-phenylenediamine (1 mmol), and p-toluenesulfonyl azide (4 mmol) were added into the reaction mixture under an argon atmosphere. After the polymerization has been carried out at 70 °C for 24 h, the reaction solution was precipitated into methanol. The obtained crude product was washed several times using EDTA-2Na aqueous solution to remove the residual copper. Then the obtained polymer was separated by filtration and dried under vacuum to obtain the corresponding product as a brown solid.
Figure 2. Conversion of thiolactone (A) and methacrylate (B).
double bond of propargyl methacrylate via thiol-based Michael addition reaction while alkyne unit remained unreacted in the absence of radicals. The quantitative conversion of the starting molecules of A, B, and C into a ABCBA-sequenced molecule with two alkyne unit in the three-component reaction of amine−thiol−ene conjugating ensures the stoichiometric balance between the in situ produced ABCBA molecule and diamine in the following three-component polymerization of alkyne−azide−amine coupling, which is very important for obtaining polymer with high molecular weight because diyne and diamine are involved in the chain-growth process of the step-growth polymerization.12 We used NMR spectroscopy to trace the amine−thiol−ene conjugating reaction, and the detailed results are shown in Figure 1. The signal at 4.53 ppm (I, methine proton in N-(carbobenzyloxy)homocysteine thiolactone) decreased with the increase of reaction time and shifted to 4.22 ppm (I′, Figure 1A) which increased with the increase of reaction time as shown in 1H NMR spectra (Figure 1A). Also, as shown in 13C NMR spectra, lactone unit (8, chemical shift at 205 ppm) is transformed into amide (8′, chemical shift at 172 ppm) (Figure 1B). The conversion of thiolactone to thiol is shown in Figure 2A; the conversion reached 42% after only 20 min, 89% after 6 h, 99% after 12 h, indicating almost quantitative conversion of the starting N(carbobenzyloxy)homocysteine thiolactone (B) and 4,7,10trioxa-1,13-tridecanediamine (C) into a BCB molecule with two thiol units after 12 h reaction. Simultaneously, the in situ produced thiol intermediate is very susceptible to reacting with the double bond of methacrylate (A) via Michael addition reaction,28,29 yielding the ABCBA-sequenced molecule with two alkyne units (diyne). 1 H NMR, 13C NMR, and ESI-MS spectra of the obtained diyne
■
RESULTS AND DISCUSSION Du Prez25,26 and Endo27 et al. introduced three-component reaction of amine−thiol−ene conjugating into polymer synthesis. This conjugating reaction has high efficiency under mild reaction conditions. The three-component reaction of propargyl methacrylate (A), N-(carbobenzyloxy)homocysteine thiolactone (B), and 4,7,10-trioxa-1,13-tridecanediamine (C) was carried out at a molar ratio of 1:1:1 in the presence of triethylamine (TEA) as catalyst, which is similar to previous reports.25 4,7,10-Trioxa-1,13-tridecanediamine would cause the ring-opening of N-(carbobenzyloxy)homocysteine thiolactone to give a thiol intermediate, which can further react with the D
DOI: 10.1021/acs.macromol.5b00463 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
Figure 3. continued
E
DOI: 10.1021/acs.macromol.5b00463 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
Figure 3. SEC curve of the sequence-controlled polymer (A), 1H NMR spectrum (B), and 13C NMR spectrum (C) of the obtained sequencecontrolled polymers with via sequential multicomponent reactions (x is methanol).
Table 1. Results of the Obtained Sequence-Controlled Polymers with via Sequential Multicomponent Reactions entry
A
B
C
D
E
Mn
PDI
1 2 3 4 5
PMa PM PM PM PM
NCb NTi NT NT NT
TTc DDf DD TT DD
PTd PT PT PT PT
1,4-PAe 1,4-PA 1,2-PAg DD BDh
72 600 130 700 153 300 36 400 163 200
1.8 1.5 1.9 2.0 1.4
Scheme 2. Outline of the Synthesis of Sequence-Controlled Polymer via Two Consecutive Multicomponent Reactions of Amine−Thiol−Ene Conjugating and Alkyne−Azide−Diol Coupling in One Pot
a
PM is propargyl methacrylate. bNC is N-(carbobenzyloxy)homocysteinethiolactone. cTT is 4,7,10-trioxa-1,13-tridecanediamine. d PT is p-toluenesulfonyl azide. e1,4-PA is 1,4-phenylenediamine. fDD is 2,2-dimethylpropane-1,3-diamine. g1,2-PA is 1,2-phenylenediamine. h BD is butane-1,4-diol. iNT is N-acetohomocysteine thiolactone.
demonstrate the formation of ABCBA with two alkyne units. As is apparent from Figure 1A, the signal of methacrylate double bond protons (δ = 5.75, 6.1 ppm) decreased with the increase of reaction time, which demonstrates the formation of thioether between the electron-deficient carbon−carbon double bond of propargyl methacrylate and the thiol, released from the aminolysis of N-(carbobenzyloxy)homocysteine thiolactone. 13 C NMR results showed that the signals at 126.8 and 136.9 ppm (carbons of double bond) shifted to 34.5 and 36.1 ppm, respectively, after thiol−Michael addition. The conversion of electron-deficient carbon−carbon double bond reached 28% in 20 min, 86% after 6 h, almost 98% in 12 h as shown in Figure 2B. The high-resolution spectrum of the isolated the formed
new intermediate molecule of ABCBA with two alkyne units is shown in Figure S3; the main peak with mass value of 993.3959 corresponds to the sum of the mass of the intermediate molecule (970.41) and the mass of sodium cation (22.99). Subsequently, p-toluenesulfonyl azide (D), 1,4-phenylenediamine (E), and CuCl were directly added into the above reaction mixture; a large number of bubbles were released from the mixture, indicating that the multicomponent polymerization of ABCBA,12,30 1,4-phenylenediamine, and p-toluenesulfonyl azide occurs via azide−alkyne−amine coupling. After reaction for 24 h, the reaction mixture became dark brown. In this F
DOI: 10.1021/acs.macromol.5b00463 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
coming from propargyl methacrylate (A monomer), the peaks at 5.0 ppm (i protons) and 1.75 ppm (h protons) coming from N-(carbobenzyloxy)homocysteine thiolactone (B monomer), the peaks at δ 2.3 ppm (u protons) and 7.0−8.0 ppm (w, v protons) coming from p-toluene sulfonylazide (D monomer), and the signals at δ 7.0−8.0 ppm ascribed to 1,4-phenylenediamine (E monomer) ppm are all present in the obtained polymer. On the other hand, the signals at δ 10.4 ppm for the proton of amidine, formed from the multicomponent polymerization of azide−alkyne−amine, also appeared in the obtained polymer, which demonstrates that all the starting molecules are cooperated into the sequence-controlled polymer. In Figure 3C, the peaks coming from the starting molecules A, B, C, D, and E are all present in the 13C NMR spectrum of the obtained sequence-controlled polymer, demonstrating the obtained polymer having a DABCBADE sequence in the structure. Furthermore, SEC was used to characterize the molecular weight of the formed sequence-controlled polymer, the obtained polymer has a molecular weight of 72.6 kDa and PDI of 1.8 as shown in Figure 3A. Moreover, this strategy is not limited in using above starting molecules; for example, if 2,2-dimethylpropane-1,3-diamine (DD) was used in the ring-opening of thiolactone instead of 4,7,10-trioxa-1,13-tridecanediamine (C), the obtained polymer with a DCBABCDE sequence has molecular weight of 130.7 kDa and PDI of 1.5. The molecular weight is much higher than that of the obtained polymer using 4,7,10-trioxa-1,13tridecanediamine in the ring-opening of thiolactone, which may result from that 2,2-dimethylpropane-1,3-diamine has very short space, making the corresponding polymer chain more rigidity to suppress cyclization.12 On the other hand, in the multicomponent polymerization of azide−alkyne−amine stage, the polymers obtained using phenylenediamines have much higher molecular weight than that of polymer produced using alkyldiamines as shown in Table 1, which is due to that the polymers produced from phenylenediamines are more rigid than the polymer produced from alkyldiamine, which can suppress entanglement and cyclization although phenylenediamine possesses weaker nucleophilicity than alkyldiamines.12 Compared with those sequence-controlled polymers prepared via single multicomponent polymerization, the polymers prepared via two consecutive multicomponent reaction not only have more components but also have much higher molecular weight. Therefore, this strategy is a promising method for the synthesis of sequence-controlled polymer with high molecular weight. On the other hand, diol is also a nucleophile, if diol (butane1,4-diol, BD) is used in the above multicomponent polymerization instead of diamine, poly(imidate) macromolecules will be formed by an analogous Cu-catalyzed multicomponent polymerization.31 Because of the weaker nucleophilicity of diols, they could be competed by even a small amount of H2O which reacts with ketenimine intermediately to terminate the polymerization;24 therefore, anhydrous and highly purified DMF is used as the solvent in the synthesis, and the polymerization is prolonged to 72 h, a high-molecular-weight polymer is obtained as shown in Scheme 2 and Figure 4.
Figure 4. 1H NMR spectrum (A), 13C NMR spectrum (B), and SEC curve (C) for the obtained sequence-controlled polymervia two consecutive multicomponent reactions of amine−thiol−ene conjugating and alkyne−azide−diol coupling in single pot (X is diethyl ether).
multicomponent polymerization of azide−alkyne−amine coupling, Cu-catalyzed cycloaddition of azide−alkyne (CuAAC) first occurred, and subsequently, nucleophilic amine attack to ring-open the cycloaddition product of azide−alkyne, forming poly(amidine) macromolecules. Figure 3 shows the spectra of 1 H NMR and 13C NMR in DMSO-d6. Based on the 1H NMR spectrum, all the starting molecules are present in the targeting sequence-controlled polymer. Particularly, the peaks at δ 3.2− 3.6 ppm (a and b protons) and 1.6 ppm (c protons) originating from 4,7,10-trioxa-1,13-tridecanediamine (C monomer), the peaks at δ 1.1 ppm (p protons) and 4.2 ppm (q protons)
■
CONCLUSIONS In conclusion, the process that allows two consecutive threecomponent reactions toward sequence-controlled polymers in one-pot was reported, in which first, the three-componentreaction of propargyl methacrylate, N-(carbobenzyloxy)G
DOI: 10.1021/acs.macromol.5b00463 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
(17) Lv, A.; Deng, X. X.; Li, L.; Li, Z. L.; Wang, Y. Z.; Du, F. S.; Li, Z. C. Polym. Chem. 2013, 4, 3659. (18) Li, L.; Deng, X. X.; Li, Z. L.; Du, F. S.; Li, Z. C. Macromolecules 2014, 47, 4660. (19) Kreye, O.; Toth, T.; Meier, M. A. R. J. Am. Chem. Soc. 2011, 133, 1790. (20) Yang, B.; Zhao, Y.; Fu, C. K.; Zhu, C. Y.; Zhang, Y. L.; Wang, S. Q.; Wei, Y.; Tao, L. Polym. Chem. 2014, 5, 2704. (21) Brauch, S.; van Berkel, S. S.; Westermann, B. Chem. Soc. Rev. 2013, 42, 4948. (22) Rudick, J. G. J. Polym. Sci., Polym. Chem. 2013, 51, 3985. (23) Liu, Y. J.; Gao, M.; Lam, J. W. Y.; Hu, R. R.; Tang, B. Z. Macromolecules 2014, 47, 4908. (24) Kim, H.; Choi, T. L. ACS Macro Lett. 2014, 3, 791. (25) Espeel, P.; Goethals, F.; Du Prez, F. E. J. Am. Chem. Soc. 2011, 133, 1678. (26) Stamenovic, M. M.; Espeel, P.; Baba, E.; Yamamoto, T.; Tezuka, Y.; Du Prez, F. E. Polym. Chem. 2013, 4, 184. (27) Ochiai, B.; Ogihara, T.; Mashiko, M.; Endo, T. J. Am. Chem. Soc. 2009, 131, 1636. (28) Nair, D. P.; Podgorski, M.; Chatani, S.; Gong, T.; Xi, W. X.; Fenoli, C. R.; Bowman, C. N. Chem. Mater. 2014, 26, 724. (29) Ma, X. P.; Tang, J. B.; Shen, Y. Q.; Fan, M. H.; Tang, H. D.; Radosz, M. J. Am. Chem. Soc. 2009, 131, 14795. (30) Bae, I.; Han, H.; Chang, S. J. Am. Chem. Soc. 2005, 127, 2038. (31) Yoo, E. J.; Bae, I.; Cho, S. H.; Han, H.; Chang, S. Org. Lett. 2006, 8, 1347.
homocysteine thiolactone, and 4,7,10-trioxa-1,13-tridecanediamine give intermediate molecule with ABCBA-sequenced diyne via amine−thiol−ene conjugating. Subsequently, ptoluenesulfonyl azide and 1,4-phenylenediamine were added into the system, immediately Cu-catalyzed azide−alkyne-amine coupling occur, giving DABCBADE sequence-controlled polymer. Two consecutive multicomponent reactions can incorporate more components into the polymer chain, and the high efficacy of both amine−thiol−ene conjugating and Cucatalyzed azide−alkyene−amine coupling ensures the obtained polymers having high molecular weight. Thereby, this strategy is a promising method for rapid access to constructing sequence-controlled polymers with highly diverse structure and complexity.
■
ASSOCIATED CONTENT
S Supporting Information *
NMR spectra of the prepared monomers and the obtained polymers; SEC curves for the obtained polymers. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.5b00463.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail
[email protected] (C.-Y.H.). Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS We acknowledge support from the National Natural Science Foundation of China (51273187, 21374107, and 21474097), the Fundamental Research Funds for the Central Universities (WK2060200012), and the Program for New Century Excellent Talents in Universities (NCET-11-0882).
■
REFERENCES
(1) Lutz, J. F.; Ouchi, M.; Liu, D. R.; Sawamoto, M. Science 2013, 341, 628. (2) Colquhoun, H.; Lutz, J. F. Nat. Chem. 2014, 6, 455. (3) Chen, W.; Schuster, G. B. J. Am. Chem. Soc. 2013, 135, 4438. (4) Nakatani, K.; Ogura, Y.; Koda, Y.; Terashima, T.; Sawamoto, M. J. Am. Chem. Soc. 2012, 134, 4373. (5) Kakuchi, R. Angew. Chem., Int. Ed. 2014, 53, 46. (6) Kleiner, R. E.; Brudno, Y.; Birnbaum, M. E.; Liu, D. R. J. Am. Chem. Soc. 2008, 130, 4646. (7) Pfeifer, S.; Lutz, J. F. J. Am. Chem. Soc. 2007, 129, 9542. (8) Espeel, P.; Carrette, L. L. G.; Bury, K.; Capenberghs, S.; Martins, J. C.; Du Prez, F. E.; Madder, A. Angew. Chem., Int. Ed. 2013, 52, 13261. (9) Solleder, S. C.; Meier, M. A. R. Angew. Chem., Int. Ed. 2014, 53, 711. (10) Yan, J. J.; Wang, D.; Wu, D. C.; You, Y. Z. Chem. Commun. 2013, 49, 6057. (11) Chan, C. Y. K.; Tseng, N. W.; Lam, J. W. Y.; Liu, J. Z.; Kwok, R. T. K.; Tang, B. Z. Macromolecules 2013, 46, 3246. (12) Lee, I. H.; Kim, H.; Choi, T. L. J. Am. Chem. Soc. 2013, 135, 3760. (13) Espeel, P.; Goethals, F.; Driessen, F.; Nguyen, L. T. T.; Du Prez, F. E. Polym. Chem. 2013, 4, 2449. (14) Ouchi, M.; Badi, N.; Lutz, J. F.; Sawamoto, M. Nat. Chem. 2011, 3, 917. (15) Lutz, J. F. Nat. Chem. 2010, 2, 84. (16) Lutz, J. F. ACS Macro Lett. 2014, 3, 1020. H
DOI: 10.1021/acs.macromol.5b00463 Macromolecules XXXX, XXX, XXX−XXX
