Article Cite This: Macromolecules XXXX, XXX, XXX−XXX
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Library of Fluorescent Polysulfonamides and Polyamide Synthesized by Iridium-Catalyzed Direct C−H Amidation Polymerization Yoon-Jung Jang, Soon-Hyeok Hwang, Jinkyung Noh, and Tae-Lim Choi* Department of Chemistry, Seoul National University, Seoul 08826, Korea
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S Supporting Information *
ABSTRACT: Step-growth polymerization via C−H activation is an attractive technique due to its advantages such as atom- and stepeconomy, derived from the reduced the number of synthetic steps required for the overall process and elimination of organometallic byproducts. To expand the utility of C−H activation polymerization beyond C−C bond coupling, we recently developed a highly efficient direct C−H amidation polymerization (DCAP) involving C−N bond formation, as a green polymerization process for synthesizing polysulfonamides. Here, we present a full account of the use of DCAP in the preparation of a library of polysulfonamides and polyamide from various diamides and diazides. From extensive model studies, several directing groups were screened, and it was found that subtle design of the directing groups by altering the steric hindrance and chelating bond angle greatly affected the efficiency of C−H amidation. Five directing groups were selected and seven AA-type monomers and seven BB-type monomers of azides were designed. After optimizing the polymerization process, 25 examples of well-defined high-molecular-weight (up to 171.4 kDa) polysulfonamides and polyamide were prepared. Notably, even diamide monomers containing four reactive ortho-C−H bonds produced defect-free polysulfonamides without cross-linking, supported by 1H NMR spectroscopy and size exclusion chromatography (SEC) traces. Furthermore, many of these polysulfonamides emitted light via an excited-state intramolecular proton transfer (ESIPT) process as a result of tautomerization upon photoexcitation.
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developed to synthesize nonconjugated polymers.30−38 In 2014, Xia and co-workers achieved the synthesis of rigid ladder polymers via palladium-catalyzed annulation between norbornadiene and aryl dibromides.33 In 2016, Hou and associates utilized half-sandwich rare earth metal catalysts to give alternating copolymers of dimethoxyarenes and unconjugated dienes.34 Interestingly, although many polymerization methods employing C−H activation have been reported, the previous examples are limited to C−C bond formation, resulting in a narrow scope of polymers. Thus, a polymerization process involving C−H activation to generate C−N bonds would be desirable for expanding the utility of C−H activation chemistry. Inspired by the highly efficient C−H amidation chemistry reported by Chang and associates,39−42 we recently reported direct C−H amidation polymerization (DCAP) for the synthesis of polysulfonamides using bis-sulfonyl azides, diamides, and [{IrCp*Cl2}2].43 This DCAP is not only an efficient polymerization technique for producing defect-free high-molecular-weight polysulfonamides (up to 149 kDa), but also a green polymerization process with low catalyst loading that generates N2 as a single byproduct. In addition, the polysulfonamides containing unique hydrogen-bonds emitted
INTRODUCTION Over the last two decades, C−H activation chemistry has received great attention because it serves as an atom- and stepeconomical route for preparing complex molecules.1−6 C−H activation has been introduced into the field of polymer synthesis for preparing both conjugated and nonconjugated polymers. For example, direct (hetero) arylation polymerization (DHAP) utilizing C−H bond activation instead of organometallic functional groups can replace cross-coupling polycondensations such as Heck, Suzuki-Miyaura, and Stille couplings that are frequently used in the synthesis of conjugated polymers.7−19 The first DHAP process was reported by Lemaire and co-workers in 1999, who reported the polymerization of 2-halo-3-alkylthiophenes to obtain poly(3-alkylthiophene) (P3AT).20 Ten years later, Ozawa and co-workers improved the polymerization by using the Herrmann-Beller catalyst (aryl phosphine-ligated Pd) to prepare poly(3-hexylthiophene) (P3HT) with high molecular weight (31 kDa) and excellent regioregularity (up to 98%).21 Subsequently, many attempts have been made to utilize DHAP for the synthesis of various conjugated polymers.22−29 For instance, Kanbara and co-workers demonstrated the synthesis of alternating copolymers of 2,2′-bithiophene and 2,7dibromo-9,9-dioctylfluorene, and brominated fluorene and 1,2,4,5-tetrafluorobenzene instead of thiophenes.22,23 In addition to DHAP, polyadditions to olefins instead of aryl bromides as coupling partners via C−H activation were © XXXX American Chemical Society
Received: July 2, 2018 Revised: August 24, 2018
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DOI: 10.1021/acs.macromol.8b01405 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Scheme 1. Model Reaction of C−H Amidation using Various Directing Groups
to 99% at 50 °C (Scheme 1). To further expand the scope of the directing groups, the ring size was modified from a 6membered lactam (D2) to 5- and 7-membered lactams, D5 and D6, respectively. Even though both D5 and D6 showed very low reactivity at 25 °C, D6 yielded 83% and 99% of the desired product at 50 °C and 70 °C, respectively (Scheme 1). In addition to directing groups (D1−D6) with which catalysis proceeded via intermediates of stable 5-membered iridacycles, directing groups (D7−D12) generating key intermediates of relatively less stable 6-membered iridacycles were also investigated (Scheme 1).46,47 As expected, the yield obtained with the tertiary amide, D7, was very low, and D8 containing a 6-membered heterocycle also produced only 57% and 68% of the desired product at 25 and 50 °C, respectively (Scheme 1). Unexpectedly, changing to D9 containing a 5-membered heterocycle to produce the intermediate of 6-membered iridacycle, greatly improved the yield to 99% contrarily to the earlier reports (Scheme 1).46,47 Furthermore, pyrrolidinone was another excellent directing group (D10) to give the product in quantitative yield at 25 °C, whereas larger lactams, piperidone (D11) and caprolactam (D12), showed much lower reactivity at 25 °C (Scheme 1). In short, these results suggest that even small changes in the structures of the directing groups could lead to huge changes in the efficiency of C−H amidation, regardless of whether the intermediates are 5or 6-membered iridacycles. After identifying several excellent directing groups from the previous screening, we designed a variety of diamides as AAtype monomers and bis-sulfonyl azides as BB-type monomers for the polymerization. First, by utilizing the much simpler D6moiety having just one ortho-C−H bond, we designed 1a having a rigid linker to suppress cyclization and attempted DCAP with bis-sulfonyl azide (2a) under the optimized conditions with low catalyst loading (1.5 mol % of [{IrCp*Cl2}2], 70 °C, 0.5 M, and 48 h, see Table S1 in the Supporting Information, SI). P1 was thus obtained with a Mn of 35.2 kDa and an absolute Mn of 171.4 kDa, measured by multiangle laser light scattering (MALLS, Table 1, entry 1). Various bis-sulfonyl azides were also explored under the same
blue light with high quantum yields and large Stokes’ shifts due to excited-state intramolecular proton transfer (ESIPT). In this process, a proton migrates from a hydrogen-bond donor to an acceptor, dissipating excited-state energy to induce a large Stokes’ shift.44,45 Even though the DCAP expanded the scope of polymerization via C−H activation to C−N bond formation and produced fluorescent polysulfonamides, the scope of amides in the previous report was rather narrow.43 Hence, broadening the monomer scope would be valuable for expanding the utility of DCAP. Herein, we present a full account of successful attempts to greatly broaden the monomer scope to synthesize a library of polysulfonamides and polyamide. In this regard, model reactions are designed to systematically investigate how the structures of the amides as directing groups affect the efficiency of iridium catalysis. On the basis of these results, we design new monomers containing these effective directing groups and prepare a library of highmolecular-weight polysulfonamides and polyamide. Lastly, we evaluate the effects of structural variation of these amides on the fluorescent properties of the resulting polymers.
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RESULTS AND DISCUSSION To test the reactivity of various amides as directing groups, we began our investigations with model studies using AA- and Btype reagents. In our previous report, the reaction between bissulfonyl azide (A) and N,N′-dimethylamide (D1) produced 54% of the dimer under the optimal conditions reported by Chang’s group (Scheme 1). Since efficient formation of the iridium complex via C−H activation was the most important factor, we previously used D2 containing a lactam to reduce the steric repulsion during formation of the iridium intermediate, which improved the yield to 94% at 25 °C (Scheme 1).43 In this report, we tested other directing groups in attempts to lower the steric hindrance. First, we introduced a smaller secondary amide (D3) as a directing group, thus obtaining 95% of the desired product at 25 °C (Scheme 1). Subsequent introduction of pyrrolidine as a cyclic amine (D4), instead of N,N′-dimethyl amine in D1, yielded only 55% of the desired product at 25 °C, but gratifyingly, the yield increased B
DOI: 10.1021/acs.macromol.8b01405 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Table 1. Monomer Scope of Direct C−H Amidation Polymerization (DCAP)
entry
polymer
diamide
bis-sulfonyl azide
[{IrCp*Cl2}2]
temp. (°C)
conc. (M)
time (h)
conv (%)a
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24
1a 1a 1a 1a 1b 1b 1b 1b 1b 1b 1c 1c 1c 1d 1d 1d 1d 1e 1e 1e 1f 1f 1f′ 1f′
2a 2c 2e 2f 2a 2b 2c 2d 2e 2f 2d 2e 2f 2a 2b 2d 2e 2a 2b 2e 2a 2b 2d 2f
1.5 1.5 1.5 1.5 1 1.5 1 1 1 1 1 1 1 1 1 1 1 1 1.5 1.5 1 1 1 1
70 70 70 70 60 60 60 60 60 50 60 60 50 80 80 80 80 50 50 50 60 60 60 50
0.5 0.5 0.5 0.5 1.0 0.5 2.0 1.0 2.0 1.0 0.1 0.15 0.5 0.25 0.25 0.1 0.25 1.0 1.0 1.0 0.25 0.25 0.5 1.0
48 48 48 48 0.5 2 1 1 1 6 5 6 18 6 6 6 6 24 24 24 3 3 1 12
93 97 99 99 99 97 99 99 99 99 99 96 97 99 99 99 99 96 92 96 97 92 96 97
Mnb (MALLS, kDa)c 35.2 11.5 24.0 13.2 60.0 16.7 45.0 30.8 21.4 50.3 34.4 32.4 27.2 29.5 18.8 29.7 33.1 23.4 9.1 11.0 18.7 11.2 19.0 12.7
(171.4) (29.5) (147.6) (27.6) (69.5) (21.7) (55.2) (30.3) (18.6) (61.8) (47.4) (77.6) (56.1) (70.1) (26.9) (40.1) (92.6) (45.7) (13.9) (74.4) (34.0) (17.3) (39.1) (24.2)
Đb
DPd
yield (%)e
3.14 1.51 2.56 1.90 1.65 1.47 1.58 1.60 1.49 1.62 2.59 3.07 3.12 3.08 2.01 1.49 2.78 2.07 1.52 2.56 3.06 2.20 3.20 2.17
170 32 134 30 95 30 87 33 22 96 35 61 51 66 26 32 79 43 13 64 28 14 37 30
81 76 90 83 97 84 96 93 92 99 76 87 82 96 94 69 90 97 90 80 79 73 95 76
a
Determined by 1H NMR analysis of the crude reaction mixture. bDetermined by THF SEC and chloroform SEC for P1−P20 and P21−P24, respectively, calibrated by using polystyrene standards. cAbsolute molecular weights determined by THF SEC and chloroform SEC for P1−P20 and P21−P24, respectively, by using a multiangle laser light scattering (MALLS) detector. dDegree of polymerization was determined by absolute molecular weight (MALLS) divided by the molecular weight of the repeat unit. eIsolated yields after purification from MeOH.
even at 80 °C (Table S2). On the basis of the hypothesis that reducing the steric bulkiness near the directing group would increase the conversion, one of the hexyl groups (1b′) was substituted with a methyl group (1b). Fortunately, repeating the polymerization of 1b and 2a at 80 °C gave higher conversion (99%) to produce P5 with a Mn = 39.6 kDa and after optimization, conditions of 60 °C, 1.0 M, and 30 min yielded an even higher Mn of P5 (60.0 kDa and absolute Mn of 69.5 kDa) (Table 1, entry 5 and Table S3). DCAP of 1b and rigid bis-sulfonyl azides (2b and 2c) produced P6 with a Mn = 16.7 kDa (absolute Mn of 21.7 kDa) and P7 with a Mn = 45.0 kDa (absolute Mn of 55.2 kDa), respectively (Table 1, entries 6 and 7). Flexible bis-sulfonyl azides (2d and 2e) were also shown to be great monomers for DCAP with 1b, resulting in P8 with a Mn = 30.8 kDa (absolute Mn of 30.3 kDa) and P9 with a Mn = 21.4 kDa (absolute Mn of 18.6 kDa), respectively
conditions, and using arylsulfonyl azides (2c and 2e), P2 with a Mn = 11.5 kDa (absolute Mn of 29.5 kDa) and P3 with a Mn = 24.0 kDa (absolute Mn of 147.6 kDa) were respectively produced (Table 1, entries 2 and 3). Furthermore, even alkylsulfonyl azide (2f) led to successful DCAP to give P4 with a Mn = 13.2 kDa (absolute Mn of 27.6 kDa) (Table 1, entry 4). Notably, 1H NMR and 13C NMR spectra showing well-defined peaks demonstrate that this polymerization is indeed selective to give defect-free polysulfonamides. This implies that in this polymerization, the sulfonamide groups did not compete for additional C−H activation even though the sulfonamide groups can be directing groups.48,49 Next, we incorporated D9-moiety, which also has only one ortho-C−H bond, into the monomer (1b and 1b′) for DCAP. Initially, the polymerization of 1b′ with the dihexyl group and 2a was examined, but the conversion was relatively low (85%) C
DOI: 10.1021/acs.macromol.8b01405 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules
Figure 1. Proposed Models for Suppression of Cross-Linking.
of 33.1 kDa (absolute Mn of 92.6 kDa), respectively (Table 1, entries 16 and 17, and Table S5). Further, 1e containing the D10-moiety also promoted successful DCAP under the optimized conditions employing a lower temperature (50 °C) and high concentration (1.0 M) in 24 h (Table S6). Polymerization of 1e and 2a yielded P18 with a Mn = 23.4 kDa and an absolute Mn of 45.7 kDa (Table 1, entry 18). Using 1.5 mol % of [{IrCp*Cl2}2], DCAP of 1e and 2b and 1e and 2e produced P19 with a Mn = 9.1 kDa (absolute Mn of 13.9 kDa) and P20 with a Mn = 11.0 kDa (absolute Mn of 74.4 kDa), respectively (Table 1, entries 19 and 20). Notably, P14−P20 also gave well-defined defect-free 1H NMR spectra and SEC traces with a symmetric Gaussian distribution (Figures S2n−t), implying suppression of cross-linking even at high temperature for P14−P17 and even at high concentration for P18−P20. It was hypothesized that not only hydrogen bonding between the sulfonamide N−H proton and adjacent carbonyl group, but also steric repulsion between the directing group and sulfonamide after bond rotation of the carbonyl group suppressed the second amidation for cross-linking (Figure 1b,c). Thereafter, 1f containing 2-octyldodecyl side chain was designed by introducing the D10-moiety into fluorene. P21 with a Mn = 18.7 kDa (absolute Mn of 34.0 kDa) and P22 with a Mn = 11.2 kDa (absolute Mn of 17.3 kDa) were successfully obtained from 2a and 2b, respectively, at 60 °C at a concentration of 0.25 M in 3 h (Table 1, entries 21 and 22). DCAP using 1f′ containing a relatively smaller side chain of 2ethylhexyl and flexible 2d produced P23 with a Mn = 19.0 kDa (absolute Mn of 39.1 kDa) at higher concentration (0.5 M), and alkylsulfonyl azide (2f) also underwent efficient polymerization to give P24 with a Mn of 12.7 kDa and an absolute Mn of 24.2 kDa at 50 °C using a concentration of 1.0 M (Table 1, entries 23 and 24, and Table S7). Thus, we successfully introduced the fluorene moiety into the polysulfonamide structures using DCAP. Similar to P18−P20, symmetric SEC traces were also observed (Figure S2u−x), suggesting polymerization without cross-linking. Interestingly, the C−H amidation on 1f containing two nonsymmetric ortho-C−H bonds produced P21 and P22 with high regio-selectivity based on the 1H NMR and 13C NMR spectra, whereas that of P23 and P24 produced from 1f′ containing smaller side chain showed low regio-selectivity based on the 1H NMR. This further demonstrates the importance of proper monomer design for successful DCAP. Lastly, we examined the possibility of using an acyl azide (2g) instead of bis-sulfonyl azides (2a−2f) as the nitrogen source for preparing polyamide.40 Although this polymerization is seemingly similar to the previous examples of DCAP,
(Table 1, entries 8 and 9). Lastly, alkylsulfonyl azide (2f) with low thermal stability also afforded P10 with a high Mn of 50.3 kDa (absolute Mn of 61.8 kDa) at 50 °C (Table 1, entry 10). After successful preparation of polysulfonamides using directing groups (D6 and D9) containing just one ortho-C− H bond, we extended this DCAP method to potentially more complicated directing groups (D3, D4, and D10) containing two ortho-C−H bonds. Accordingly, various monomers (1c− 1f) containing these directing groups were prepared. However, because these groups contain four reactive ortho-C−H bonds, making them potentially A4-type cross-linkers instead of AAtype monomers, the possibility of cross-linking also had to be considered. Indeed, DCAP of 1f and 2a at 60 °C using 0.5 M produced polymers with a Mn = 48.8 kDa having a broad polydispersity (Đ) of 3.8, showing trace with tailing and a shoulder in the high-molecular-weight region observed by sizeexclusion chromatography (SEC) trace, thus suggesting some cross-linking (Figure S1). To suppress this cross-linking, DCAP of 1c−1f was explored either at lower temperature or using a lower concentration. With 1c having a secondary amide functionality and a flexible bis-sulfonyl azide (2d), the polymerization yielded P11 with a Mn of 34.4 kDa (absolute Mn of 47.4 kDa) at 60 °C at a concentration of 0.1 M (Table 1, entry 11) and DCAP with 2e gave P12 with a Mn of 32.4 kDa (absolute Mn of 77.6 kDa) at 60 °C at a concentration of 0.15 M (Table 1, entry 12). In addition to arylsulfonyl azides, alkylsulfonyl azide (2f) also underwent efficient polymerization at 50 °C to give P13 with a Mn = 27.2 kDa (absolute Mn of 56.1 kDa) (Table 1, entry 13). In the cases of P11−P13, 1H NMR analysis showed well-defined defect-free spectra and symmetric SEC traces with a Gaussian distribution, demonstrating that DCAP proceeded with excellent selectivity to give linear polymers, not cross-linked gels (Figures S2k−m). It is proposed that intramolecular hydrogen bonding between the sulfonamide N−H and neighboring carbonyl oxygen would preorganize the carbonyl group after C−H amidation and lock its conformation to restrict bond-rotation of the carbonyl group so that the second amidation for cross-linking would have been suppressed under these conditions (Figure 1a).50−52 We then explored 1d containing the D4-moiety and prepared four polysulfonamides at high temperature using a lower concentration. High-molecular-weight P14 (Mn of 29.5 kDa and absolute Mn of 70.1 kDa) was obtained using 2a at 80 °C at a concentration of 0.25 M in 6 h (Table 1, entry 14 and Table S4). Under the same conditions, DCAP using 1d and 2b produced P15 with a Mn of 18.8 kDa and an absolute Mn of 26.9 kDa (Table 1, entry 15). The flexible sulfonyl azide (2d) and electron-rich sulfonyl azide (2e) also afforded P16 with a Mn of 29.7 kDa (absolute Mn of 40.1 kDa) and P17 with a Mn D
DOI: 10.1021/acs.macromol.8b01405 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Scheme 2. Synthesis of Polyamides via DCAP Using Acylazide
nonradiative decay processes related to the flexible secondary amide (fluorescence quantum yields Φ F = 0.04−0.18, see Table S9). Interestingly, we observed dual emissions from P14−P17 in THF solution, with the first λmax,em at 339−358 nm, assigned as normal emission, and another λmax,em at 464−481 nm attributed to the ESIPT process, in spite of only one absorption λmax at 297−301 nm in THF solution.55 In the film state, only one emission appeared at λmax,em = 453−468 nm, presumably because the normal emissions were quenched. Unfortunately, both in the solution and the film state, P14− P17 displayed weak fluorescence with low quantum yields (Φ F < 0.03) due to the relatively weak hydrogen bonding, indicated by the N−H proton signals at 9.53−9.81 ppm in the 1H NMR profiles. Disappointingly, P5−P10 and P18−P20 were nonfluorescent due to the unstable zwitterionic nature of the tautomer form and the very weak hydrogen bonding (Figure S5), indicated by the observed N−H proton signals of P5− P10 and P18−P20 at 7.89−9.53 ppm.56,57 Interestingly, P21− P23, which bear some structural similarity to P18−P20, showed at least very weak fluorescence in the solution and the film states. Unfortunately, P25 showed emission λmax,em = 393 nm despite the strong hydrogen bonding indicated by its N−H proton signal at 13.65 ppm, implying that this polyamide did not promote emission via ESIPT, unlike the polysulfonamides. In short, using DCAP, we prepared several light-emitting polysulfonamides undergoing ESIPT with λmax,em in the range of 434−502 nm depending on the directing groups. Lastly, the thermal properties of P1−P25 were evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The synthesized polymers showed great thermal stability, as supported by the high decomposition temperature (Td). The Td of P5−P24 ranged from 279 to 339 °C, whereas P1−P4 and P25 showed higher thermal stability with Td ranging from 324−403 °C, suggesting that the polymers with conformationally locked structures showed better thermal stability. In addition, all polymers were amorphous without any melting transition and their glass transition temperatures (Tg) ranged from 41−205 °C depending on the rigidity of the polymer backbones (Table S9).
it was much more complicated and challenging because of detrimental side reactions of Curtius rearrangement. We observed that this process was thermally driven and proceeded readily at high temperature. Fortunately, after optimization, DCAP of 1g and 2g resulted in defect-free P25 with a Mn of 9.6 kDa and an absolute Mn of 16.7 kDa at relatively low temperature (40 °C) using a concentration of 0.5 M (Scheme 2 and Table S8). Notably, we successfully extended this DCAP method to produce polyamide as well as polysulfonamides. In short, after optimizing the polymerization, the successful DCAP between seven diamides (1a−1g) and diazides (2a− 2g) demonstrates the versatility of the new polymerization. The detailed microstructures of the polysulfonamides (P1− P24) and polyamide (P25) were analyzed by 1H NMR, and notably, sulfonamide and amide N−H proton signals were observed over broad ranges between 7.81 and 13.65 ppm. Compared to the typical N−H proton peaks of N-phenylbenzenesulfonamide and N-phenylbenzamide at 7 and 10 ppm, respectively,53 these downfield-shifted N−H peaks implied a certain degree of intramolecular hydrogen bonding between the N−H protons and neighboring carbonyl groups.54 As previously reported, this hydrogen bonding promoted emission via ESIPT, resulting in large Stokes’ shifts and high quantum yields. Therefore, we evaluated the photophysical properties of the new polysulfonamides and polyamide. First, P1−P4, the N−H proton signals of which appeared at 9.17−9.55 ppm in the 1H NMR spectra, emitted blue light with λmax,em in the range of 490−502 nm, whereas the absorption λmax appeared in the range of 298−305 nm in the UV−vis spectra in THF solution. Similar photophysical properties were observed in the film state with an absorption λmax at 298−301 nm and emission λmax,em at 471−493 nm. Even though P1−P4 showed large Stokes’ shifts (Δλ = 190−200 nm and 171−195 nm in the solution and film states, respectively), the quantum yields were rather low, Φ F = 0.02−0.05 and 0.03−0.08 in the solution and the film states, respectively. These results are attributed to weaker hydrogen bonding on the 7-membered lactam compared to that on the 6-membered lactam, where the latter showed N−H proton peaks at 12.15−12.65 ppm. We then examined the photophysical properties of P11−P13 for which the sulfonamide N−H proton signals appeared at 11.20−11.47 ppm in the 1H NMR spectra, implying strong hydrogen bonding. The UV−vis spectra in THF solution and the film state both showed a maximum absorption at 295−300 nm, and both species emitted blue light with λmax,em at 434−448 nm with large Stokes’ shifts (Δλ = 134−149 nm). However, P11− P13 still showed weak emission, presumably because of
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CONCLUSIONS
In summary, we expanded the polymerization scope of direct C−H amidation polymerization (DCAP) using various diamides and diazides. DCAP is a green polymerization process that requires low catalyst loading with great atom E
DOI: 10.1021/acs.macromol.8b01405 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules
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economy, releasing just N2 gas as a byproduct. Initially, we conducted model studies and discovered various reactive directing groups for C−H amidation. After proper design of the AA-type monomers accordingly and optimizing the polymerization conditions, we prepared a library of 25 examples of polysulfonamides and polyamide, testifying to the versatility of this technique. This polymerization is highly efficient and selective for the production of defect-free polymers with high molecular weights up to an absolute Mn of 171.4 kDa. Moreover, many of the resulting polysulfonamides exhibit emission derived from the ESIPT process. This work not only expands the structural diversity of the polysulfonamides and polyamide prepared by DCAP, but also provides a platform for obtaining fluorogenic polymers.
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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.8b01405. Experimental procedures, characterizations, NMR spectra for new compounds and polymers, SEC traces, photophysical and physical properties of polymers, and other supporting experiments (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Tae-Lim Choi: 0000-0001-9521-6450 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The financial support from the Creative Research Initiative Grant, Creative Material Discovery Program, and the Nano Material Technology Program through NRF. We thank the group of Prof. Dongwhan Lee at SNU for supporting absorption and emission spectra, and the NICEM and the NCIRF at SNU for supporting 13C NMR spectroscopy.
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REFERENCES
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DOI: 10.1021/acs.macromol.8b01405 Macromolecules XXXX, XXX, XXX−XXX
