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Living and Chemoselective (Co)polymerization of Polar Divinyl Monomers Mediated by Bulky Lewis Pairs Ping Zhang, Hui Zhou, and Xiao-Bing Lu* State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, China
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S Supporting Information *
ABSTRACT: A near 100% initiation efficiency and 100% regioselectivity at the methylacrylic CC bond was realized by bulky Lewis pairs-mediated polymerization of polar divinyl monomers such as 4-vinylbenzyl methacrylate at mild conditions, affording soluble polymers bearing pendant active vinyl groups with narrow dispersities. A delicate combination of Lewis acid and base with suitable steric hindrance is necessary for achieving high initiation efficiency and activity. The livingness and robustness of the bulky Lewis pair polymerization systems provide a simple and convenient route to produce various di- or tri-block copolymers by the stepwise addition of the different monomers, as well as the copolymer in random distribution by the use of the mixed monomers.
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gelation at last.9 Especially, in the radical polymerization system of 4-vinylbenzyl methacrylate (VBMA), the formation of gel was observed even at the beginning of the reaction, due to the similar reactivity of the methacrylate CC double bond (r1 = 1.04) and styrene (r2 = 0.85).13 Inspired by the pioneer study from Chen’s group at Colorado State University, who discovered that the alanebased classical or frustrated Lewis pairs (FLPs) were highly active in polymerizing various polar vinyl monomers such as methyl methacrylate (MMA) and α-methylene-γ-butyrolactone,14 we were the first to explore the regioselective polymerization of VBMA mediated by a FLP consisting of Al(C6F5)3 and N-heterocyclic olefin (NHO) and delightedly found that the polymerization process only concerned the methylacrylic CC bond and selectively remained the pendant allylic CC bond.15 The resulting polymers with high molecular weights and low dispersity (D̵ ) are soluble in various organic solvents. Unfortunately, the polymerization system has a very low initiating efficiency of less than 10%. A similar low initiating efficiency was also observed in organic Nheterocyclic carbene (NHC)-mediated polymerization of multivinyl-functionalized γ-butyrolactones, in which quantitatively chemoselective polymerization proceeded exclusively across the conjugated α-methylene double bond, without the participation of the γ-vinyl double bond.16 Furthermore, an obvious improvement in both initiating efficiency and activity was observed in the Lewis pairs based on NHC/B(C6F5)3 for chemoselective polymerization of AMAs or vinyl-functionalized cyclic methacrylates.17,18 Recently, Xu et al. described the chemoselective polymerization of polar divinyl monomers
INTRODUCTION The postpolymerization modification of polymers bearing reactive side-chain groups is a powerful synthetic strategy for introducing target functionalities into polymeric materials with improved physical and chemical properties.1,2 In this field, the chemoselective polymerization of polar divinyl monomers, such as allyl methacrylate (AMA), represents one of the most attractive methods to prepare such functionalized polymers bearing pendant active vinyl groups on the backbone.3 However, most studies focus on indirect polymerization of polar divinyl monomers by the prior protecting of the pendant vinyl groups. As a result, the preparation of functional polymers bearing reactive vinyl groups on the side chains needs cumbersome protecting/deprotecting processes, which significantly decrease the synthetic efficiency. Obviously, chemoselective polymerization at one type of CC bond of polar divinyl monomers possessing comparably polymerizable reactivity represents a more straightforward method for producing functionalized materials with reactive groups distributed at every repeat unit of the polymeric backbone. The much-studied methods are anion polymerization and radical polymerization at harsh reaction conditions (e.g., extremely low temperature or the use of large quantities of suitable Lewis acid additive), taking full account of the reactivity discrepancy of two types of CC bonds of the divinyl monomers.4−12 Unfortunately, the reactivity difference between two kinds of vinyl groups makes it impossible to ensure that the reaction only occurred in one type of CC bond in the whole polymerization process. Usually, polymerization predominantly occurred in the methacrylic CC bond of AMA at the early stage, due to its relatively higher reactivity. However, as the reaction proceeds, the pendant CC bond also readily took place in the polymerization, thus forming the cross-linking network until the reaction mixture turned to © XXXX American Chemical Society
Received: April 2, 2019 Revised: May 13, 2019
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DOI: 10.1021/acs.macromol.9b00652 Macromolecules XXXX, XXX, XXX−XXX
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such as H2, CO2, and N2O has elicited great interest in chemists.24−26 In 2010, Chen and co-workers first investigated the alane-based classical or FLPs for highly active polymerization of various polar vinyl monomers.14 The mechanistic study suggested that the polymerization proceeded via zwitterionic phosphonium or imidazolium enolaluminate active species. Following the Chen’s pioneer contribution, a variety of FLPs and a number of conjugated polar alkene monomers were examined, achieving a remarkable success in the areas of polymer synthesis with high activity and regioselectivity.27,28 However, the low initiating efficiency is the common disadvantage for various systems. It could be attributed to two reasons: one is the formation of the relatively stable Lewis acid−base adduct during the polymerization, and the other is the complete chain-termination side reaction via intramolecular backbiting cyclization involving nucleophilic attack of the polymeric anion to the carboxyl carbon of the adjacent unit to generate a six-membered lactone-terminated polymer chain.29−31 The significant breakthrough came with the use of interacting Lewis pairs consisting of phosphoruscontaining Lewis bases and the less acidic triphenylaluminum for polymerizing a variety of sterically demanding and functionalized monomers with high initiator efficiencies up to 95%.32 The next significant discovery by Zhang and Chen appeared recently by using a non-interacting sterically hindered Lewis pair for the living polymerization of MMA and benzyl methacrylate with nearly 100% initiation efficiency.33 The key is the fine balance of the Lewis acidity and the sufficient stereohindrance for minimizing the Lewis pair interaction. Inspired with the success of Zhang and Chen, we applied several FLPs based on the sterically hindered but less acidic MeAl(BHT)2 and EtAl(BHT)2 to the polymerization of various polar divinyl monomers (Table 1). The Lewis base has a great effect on the polymerization rate. In the presence of 2 equiv of MeAl(BHT)2, no product was observed in the system of PPh3 (pKa = 2.73) as Lewis base and toluene as solvent, even at a prolonged time of 120 min (Table 1, run 1). On the contrary, the use of stronger bases, such as PMe3 (pKa = 8.65), PEt3 (pKa = 8.69), and PCy3 (pKa = 9.7) led to the complete conversion of VBMA monomer at 25 °C within 20 min (runs 2−4), indicating that the sufficient Lewis basicity is necessary for initiating the polymerization. The initiation efficiencies are in the range of 39−74%. An increased initiation efficiency of 88% was observed in the Lewis pair system consisting of NHO-1/MeAl(BHT)2. Furthermore, with the use of more sterically hindered 1,3-dimethyl-4,5-diphenyl-2(propan-2-ylidene)-2,3-dihydro-1H-imidazole (NHO−Me) or 1,3-diethyl-4,5-diphenyl-2-(propan-2-ylidene)-2,3-dihydro-1Himidazole (NHO−Et) as Lewis base, the initiation efficiencies of ∼100% were achieved (runs 6−9). The 1H NMR spectrum (Supporting Information, Figure S4) shows that the polymerization resulted in the complete disappearance of the peaks at 6.15 and 5.58 ppm, which belong to the CH2 of methacrylic CC bond of VBMA, while no change in the resonance intensity of the peak at 6.65 ppm for methine and those at 5.70 and 5.21 ppm for the CH2 belonging to styrene happened, demonstrating that the CC bond of the pendent styrene was unreacted in the polymerization. Also, the decrease in Lewis pair loadings did not affect the complete conversion and high initiation efficiency, with a prolonged reaction time (runs 6, 10−12). The Mn value of PVBMA produced from NHO−Me/MeAl(BHT)2 system increased linearly with the [VBMA]0/[NHO−Me]0/[MeAl-
with homoleptic rare-earth aryloxide-based Lewis Pairs, in which the initiating efficiencies are more than 20%.19 It is worth noting here, parenthetically, that highly chemoselective and living polymerization of polar divinyl monomers such as AMA was achieved by the coordination−addition polymerization mode using discrete ansa-zirconocene enolates or halfmetallocene yttrium complexes as catalysts.20,21 In the present contribution, we report the completely regioselective and living polymerization of various polar divinyl monomers mediated by bulky Lewis pairs with nearly 100% initiating efficiency (Schemes 1 and 2). Moreover, the bulky Scheme 1. Completely Regioselective and Living Polymerization of Polar Divinyl Monomers Mediated by Bulky Lewis Pairs
Scheme 2. Structures of Polar Divinyl Monomers and Lewis Acids and Bases Used in This Study
Lewis pairs are highly efficient in preparing well-defined diand tri-block copolymers by successive addition of monomers and copolymer in random distribution by the use of mixed monomers.
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RESULTS AND DISCUSSION Since the concept “frustrated Lewis pairs” (FLPs), combination of bulky Lewis acids and Lewis base pairs that are sterically precluded from forming classical donor−acceptor adducts, was first introduced by Stephan,22,23 the application of FLP in cooperatively activating a variety of small molecules B
DOI: 10.1021/acs.macromol.9b00652 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Table 1. Lewis Pairs-Mediated Chemoselective Polymerization of Polar Divinyl Monomersa run
monomer
Lewis pair
Mon./base
time (min)
conv.b (%)
Mnc (kg·mol−1)
D̵ (Mw/Mn)c
I*d (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
VBMA VBMA VBMA VBMA VBMA VBMA VBMA VBMA VBMA VBMA VBMA VBMA VBMA VBMA AMA VMA
MeAl(BHT)2/PPh3 MeAl(BHT)2/PMe3 MeAl(BHT)2/PEt3 MeAl(BHT)2/PCy3 MeAl(BHT)2/NHO-1 MeAl(BHT)2/NHO−Me MeAl(BHT)2/NHO−Et EtAl(BHT)2/NHO−Me EtAl(BHT)2/NHO−Et MeAl(BHT)2/NHO−Me MeAl(BHT)2/NHO−Me MeAl(BHT)2/NHO−Me Al(C6F5)3/NHO−Me Al(C6F5)3/NHO−Et MeAl(BHT)2/NHO−Me MeAl(BHT)2/NHO−Me
200 200 200 200 200 200 200 200 200 400 600 800 200 200 400 200
120 20 20 20 10 10 20 100 30 25 60 180 10 10 20 30
0 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
n.d 59.0 54.0 104 45.7 39.1 39.4 39.5 43.4 69.8 110 150 45.1 41.2 54.2 26.1
n.d 1.27 1.29 1.30 1.21 1.19 1.23 1.23 1.27 1.19 1.17 1.15 1.21 1.19 1.24 1.21
n.d 68 74 39 88 103 102 102 93 86.4 111 109 89 98 94 87
Conditions: all polymerization reactions were conducted at 25 °C and a Lewis acid/base ratio of 2; total reaction volume: 5 mL, using toluene as solvent. bConversion and yields of the isolated polymers were determined by 1H NMR spectroscopy. cDetermined by GPC in THF, calibrated with polystyrene. dInitiation efficiency (I*) % = Mn(calcd.)/Mn(exp.) × 100, where Mn(calcd.) = [Mw(monomer)]([monomer]0/[I]0) (conversion) + Mw of the chain end group (Lewis base). a
Figure 1. Plots of Mn and D̵ for PVBMA vs [VBMA]/[NHO−Me] ratio. Figure 3. MALDI-TOF MS spectrum of the PAMA sample produced from NHO-ME/MeAl(BHT)2-mediated polymerization at a low [AMA]/[NHO-ME] molar ratio of 20.
Figure 2. GPC traces of PVBMA samples produced from [NHO− Me]/[MeAl(BHT)2]-mediated polymerization at various ratios of [VBMA]/[NHO−Me] at ambient temperature.
Figure 4. Plots of Mn and D̵ of PVBMA vs conversion mediated by NHO−Me/MeAl(BHT)2. Conditions: [VBMA]/[NHO−Me]/ [MeAl(BHT)2] = 400:1:2; 25 °C; toluene as solvent.
from 100 to 800 while maintaining a narrow unimodal distribution (Figure 2). For a comparison purpose, NHO−Me in combination with more acidic Al(C6F5)3 was tested for VBMA polymerization in a standard condition. The Lewis pair was also highly active, affording PVBMA with Mn = 45.0 kg· mol−1 and D̵ = 1.21, thus yielding an initiation efficiency of
(BHT)2]0 ratio from 100:1:2 to 800:1:2 (Figure 1), while the initiation efficiency and narrow dispersity (1.15−1.19) remained constant, indicating a living-type polymerization. Gel permeation chromatography (GPC) traces of the resulting polymers show the gradual shift to the higher molecular weight region with the increase in the [VBMA]0/[NHO−Me]0 ratio C
DOI: 10.1021/acs.macromol.9b00652 Macromolecules XXXX, XXX, XXX−XXX
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PVBMA samples obtained from various time points, as well as chain extension experiments for synthesizing block copolymers through the stepwise addition of the different monomers. Figure 4 is the plot of the Mn versus monomer conversion at a fixed [VBMA]/[Lewis pair] ratio of 400. The Mn of the PVBMA increases linearly (R2 = 0.9974) in proportion to conversion in the range of 0−99%, while the dispersities remained narrow (1.15−1.18). In previous contribution, we found that the binary NHO/ Al(C6F5)3 system was highly active in polymerizing both MMA and VBMA, but the attempt to synthesize their block copolymers proved to be unsuccessful, due to the backbiting cyclization side reactions to form the stable six-membered lactone chain-ends.29 For the NHO−Me/MeAl(BHT)2mediated VBMA polymerization system, no backbiting cyclization side reaction occurred even 1 h after 100% monomer conversion. As a consequence, PVBMA chain extension is easily realized, as shown in Figure 5. The first block PVBMA possessing a Mn of 18.5 kg·mol−1 and a narrow dispersity of 1.20 was obtained within 10 min after complete conversion of 100 equiv of VBMA. After the mixture system was laid up for 60 min without quenching, another 100 equiv of VBMA was added into the polymerization system to afford the polymer with a Mn of 38.1 kg·mol−1 and D̵ of 1.25 (Figure 5). Because MeAl(BHT)2/NHO−Me Lewis pair is efficient in polymerizing various polar divinyl monomers, various di- or triblock copolymers, such as VBMA-b-AMA, VBMA-b-VMA, VBMA-b-VMA-b-VBMA, and VBMA-b-AMA-b-VBMA, could be prepared by the stepwise addition of different monomers after the complete conversion of the previously added monomer (Figure 6). Moreover, binary MeAl(BHT)2/NHO−Me Lewis pair was also applied to the copolymerization of VBMA and MMA, because of its high activity for the polymerization of both monomers. From the competition polymerization of VBMA and MMA using various feed ratios at room temperature, monomer reactivity ratios could be obtained (rMMA = 0.86, rVBMA = 0.75) (Table S2 and Figures S8−S10). These data indicate the comparable reactivities for both monomers, affording MMA-co-VBMA copolymer in random distribution.
Figure 5. GPC traces of PVBMA samples obtained from chain extension experiments by MeAl(BHT)2/NHO−Me in toluene at ambient temperature.
89% (run 13). Replacing NHO−Me by more sterically hindered NHO−Et provides PVBMA with D̵ = 1.19 and an initiation efficiency of 98% (run 14). This result indicates that the steric hindrance of Lewis base plays an important role in suppressing the formation of the relatively stable Lewis acid− base adduct. As expected, NHO−Me/MeAl(BHT)2 is efficient for polymerization of other polar divinyl monomers, such as AMA and vinyl methacrylate (VMA), with high initiation efficiencies. The 1H NMR spectra (Supporting Information, Figures S5 and S6) show that the peaks at about 6.2 and 5.6 ppm that belong to the CH2 of methacrylic CC bond of polar divinyl monomers completely disappeared, implying that there was no remaining methacrylic CC bond. Meanwhile, the resonance intensity of the −CHCH2 belonging to the pendant vinyl group in the resultant polymers was nearly the same as that of monomers, demonstrating that the pendant CC bond was unreacted in the polymerization. In order to probe the initiation process, a PAMA sample, produced from a low [AMA]/[NHO−Me] molar ratio of 20 and quenched with hydrous methanol, was analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). A series of molecular ion peaks based on m/z = 290.18 (the molecular weight of NHO−Me) at an interval of 126.10 (the unit of AMA), corresponding to the linear PAMA chains capped with NHO−Me/H chain ends, are clearly observed in the spectrum (Figure 3). The living feature of this polymerization process further demonstrated by comparing the molecular weights of the
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CONCLUSIONS In summary, we have demonstrated that the bulky Lewis pairs were very efficient in polymerizing various polar divinyl monomers in 100% regioselectivity at the methylacrylic C C bond and living polymerization mode with a near
Figure 6. GPC traces of homopolymer (black), diblock copolymer (red), and ABA triblock copolymer (blue) produced from NHO−Me/ MeAl(BHT)2-mediated sequential polymerization in toluene at 25 °C. D
DOI: 10.1021/acs.macromol.9b00652 Macromolecules XXXX, XXX, XXX−XXX
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(7) Mohan, Y. M.; Raghunadh, V.; Sivaram, S.; Baskaran, D. Reactive polymers bearing styrene pendants through selective anionic polymerization of 4-vinylbenzyl methacrylate. Macromolecules 2012, 45, 3387−3393. (8) Nagelsdiek, R.; Mennicken, M.; Maier, B.; Keul, H.; Höcker, H. Synthesis of polymers containing cross-linkable groups by atom transfer radical polymerization: poly (allyl methacrylate) and copolymers of allyl methacrylate and styrene. Macromolecules 2004, 37, 8923−8932. (9) Vardareli, T. K.; Keskin, S.; Usanmaz, A. Synthesis and characterization of poly (allyl methacrylate) obtained by free radical initiator. J. Macromol. Sci., Part A: Pure Appl. Chem. 2008, 45, 302− 311. (10) Sugiyama, F.; Satoh, K.; Kamigaito, M. Regiospecific radical polymerization of vinyl methacrylate in the presence of Lewis acids into soluble polymers with pendent vinyl ester substituents. Macromolecules 2008, 41, 3042−3048. (11) Koh, M. L.; Konkolewicz, D.; Perrier, S. A simple route to functional highly branched structures: RAFT homopolymerization of divinylbenzene. Macromolecules 2011, 44, 2715−2724. (12) Gao, H.; Matyjaszewski, K. Synthesis of functional polymers with controlled architecture by CRP of monomers in the presence of cross-linkers: From stars to gels. Prog. Polym. Sci. 2009, 34, 317−350. (13) Greenley, R. Z. In Polymer Handbook, 3rd ed.; Immergut, E. H., Brandup, J., Eds.; Wiley: New York, 1989; pp 267−274. (14) Zhang, Y.; Miyake, G. M.; Chen, E. Y.-X. Alane-based classical and frustrated Lewis pairs in polymer synthesis: rapid polymerization of MMA and naturally renewable methylene butyrolactones into highmolecular-weight polymers. Angew. Chem., Int. Ed. 2010, 49, 10158− 10162. (15) Jia, Y.-B.; Ren, W.-M.; Liu, S.-J.; Xu, T.; Wang, Y.-B.; Lu, X.-B. Controlled divinyl monomer polymerization mediated by Lewis pairs: A powerful synthetic strategy for functional polymers. ACS Macro Lett. 2014, 3, 896−899. (16) Gowda, R. R.; Chen, E. Y.-X. Organocatalytic and chemoselective polymerization of multivinyl-functionalized γ-butyrolactones. ACS Macro Lett. 2016, 5, 772−776. (17) Chen, J.; Chen, E. Y.-X. Lewis Pair Polymerization of Acrylic Monomers by N-Heterocyclic Carbens and B(C6F5)3. Isr. J. Chem. 2015, 55, 216−225. (18) Gowda, R. R.; Chen, E. Y.-X. Chemoselective Lewis Pair Polymerization of Renewable Multivinyl-functionalized γ-Butyrollactones. Philos. Trans. R. Soc., A 2017, 375, 20170003. (19) Xu, P.; Wu, L.; Dong, L.; Xu, X. Chemoselective Polymerization of Polar Divinyl Monomers with Rare-Earth/Phosphine Lewis Pairs. Molecules 2018, 23, 360. (20) Vidal, F.; Gowda, R. R.; Chen, E. Y.-X. Chemoselective, stereospecific, and living polymerization of polar divinyl monomers by chiral zirconocenium catalysts. J. Am. Chem. Soc. 2015, 137, 9469− 9480. (21) Chen, E.; Vidal, F. Precision polymer synthesis via chemoselective, stereoselective, and living/controlled polymerization of polar divinyl monomers. Synlett 2017, 28, 1028−1039. (22) Welch, G. C.; Juan, R. R. S.; Masuda, J. D.; Stephan, D. W. Reversible, Metal-Free Hydrogen Activation. Science 2006, 314, 1124−1126. (23) Stephan, D. W. Frustrated Lewis pairs: From Concept to Catalysis. Acc. Chem. Res. 2015, 48, 306−316. (24) Stephan, D. W.; Erker, G. Frustrated Lewis pairs: metal-free hydrogen activation and more. Angew. Chem., Int. Ed. 2010, 49, 46− 76. (25) Stephan, D. W.; Erker, G. Frustrated Lewis Pairs Chemistry:Developments and Perspectives. Angew. Chem., Int. Ed. 2015, 54, 6400−6441. (26) Frustrated Lewis Pairs I and II; Stephan, D. W., Erker, G., Eds.; Topics in Current Chemistry; Springer: New York, 2013; Vols. 332, 334.
quantitative initiation efficiency. The resultant polymers with narrow molecular weight distribution are soluble in various organic solvents. With the more sterically hindered NHO−Et as Lewis base, even the use of more acidic Al(C6F5)3 afforded a near 100% initiation efficiency. Because of its robustness and living polymerization feature, MeAl(BHT)2/NHO−Me Lewis pair could be applied to the synthesis of various di- or tri-block copolymers by the stepwise addition of different monomers after the complete conversion of the previously added monomer, as well as the copolymerization of VBMA and MMA to afford MMA-co-VBMA copolymer in random distribution. This study provides a simple and convenient way to produce various functional polymers with pendant active vinyl groups, possessing many applications in polymeric material chemistry.
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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.9b00652. Synthetic procedures of all new compounds; supplementary characterization data including 1H NMR and 13 C NMR spectra, Fineman-Ross plot, and GC traces; and representative (co)polymerization procedures of polar divinyl monomers mediated by Lewis pairs (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Xiao-Bing Lu: 0000-0001-7030-6724 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work is supported by the Program for Changjiang Scholars and Innovative Research Team in University (IRT17R14).
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REFERENCES
(1) Das, A.; Theato, P. Activated Ester Containing Polymers: Opportunities and Challenges for the Design of Functional Macromolecules. Chem. Rev. 2016, 116, 1434−1495. (2) Bermeshev, M. V.; Chapala, P. P. Addition polymerization of functionalized norbornenes as a powerful tool for assembling molecular moieties of new polymers with versatile properties. Prog. Polym. Sci. 2018, 84, 1−46. (3) Wong, C.-H.; Zimmerman, S. C. Orthogonality in organic, polymer, and supramolecular chemistry: from Merrifield to click chemistry. Chem. Commun. 2013, 49, 1679−1695. (4) Ishizone, T.; Uehara, G.; Hirao, A.; Nakahama, S. Anionic Polymerization of Monomers Containing Functional Groups. 13. Anionic Polymerizations of 2-, 3-, and 4-(3,3-Dimethyl-1-butynyl)styrenes,12-, 3-, and 4-(1-Hexynyl)styrenes,2and 4-(Phenylethynyl)styrene. Macromolecules 1998, 31, 3764−3774. (5) Tanaka, S.; Goseki, R.; Ishizone, T.; Hirao, A. Synthesis of welldefined novel reactive block polymers containing a poly (1, 4divinylbenzene) segment by living anionic polymerization. Macromolecules 2014, 47, 2333−2339. (6) Tanaka, S.; Matsumoto, M.; Goseki, R.; Ishizone, T.; Hirao, A. Living anionic polymerization of 1, 4-divinylbenzene and its isomers. Macromolecules 2013, 46, 146−154. E
DOI: 10.1021/acs.macromol.9b00652 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules (27) Hong, M.; Chen, J.; Chen, E. Y.-X. Polymerization of polar monomers mdiated by main-group Lewis acid−base pairs. Chem. Rev. 2018, 118, 10551−10616. (28) Zhang, Y.; Miyake, G. M.; John, M. G.; Falivene, L.; Caporaso, L.; Cavallo, L.; Chen, E. Y.-X. Lewis pair polymerization by classical and frustrated Lewis pairs: Acid, base and monomer scope and polymerization mechanism. Dalton Trans. 2012, 41, 9119−9134. (29) Jia, Y.-B.; Wang, Y.-B.; Ren, W.-M.; Xu, T.; Wang, J.; Lu, X.-B. Mechanistic aspects of initiation and deactivation in N-heterocyclic olefin mediated polymerization of acrylates with alane as activator. Macromolecules 2014, 47, 1966−1972. (30) He, J.; Zhang, Y.; Falivene, L.; Caporaso, L.; Cavallo, L.; Chen, E. Y.-X. Chain propagation and termination mechanisms for polymerization of conjugated polar alkenes by [Al]-based frustrated Lewis pairs. Macromolecules 2014, 47, 7765−7774. (31) Sun, X.-Y.; Ren, W. M.; Liu, S. J.; Jia, Y. B.; Wang, Y. M.; Lu, X.-B. Tandem Lewis Pair Polymerization and Organocatalytic RingOpening Polymerization for Synthesizing Block and Brush Copolymers. Molecules 2018, 23, 468. (32) Knaus, M. G. M.; Giuman, M. M.; Pöthig, A.; Rieger, B. End of frustration: Catalytic precision polymerization with highly interacting Lewis pairs. J. Am. Chem. Soc. 2016, 138, 7776−7781. (33) Wang, Q.; Zhao, W.; Zhang, S.; He, J.; Zhang, Y.; Chen, E. Y.X. Living Polymerization of Conjugated Polar Alkenes Catalyzed by N-Heterocyclic Olefin-Based Frustrated Lewis Pairs. ACS Catal. 2018, 8, 3571−3578.
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