Sequence-Selective Terpolymerization from Monomer Mixtures Using

Nov 19, 2018 - Orhan, Tschan, Wirotius, Dove, Coulembier, and Taton. 0 (0), pp 1413–1419. Abstract: Despite significant advances in organocatalysis,...
0 downloads 0 Views 913KB Size
Download PDF
Letter Cite This: ACS Macro Lett. 2018, 7, 1420−1425

pubs.acs.org/macroletters

Sequence-Selective Terpolymerization from Monomer Mixtures Using a Simple Organocatalyst Heng Li, Huitong Luo, Junpeng Zhao,* and Guangzhao Zhang Faculty of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, People’s Republic of China

Downloaded via DURHAM UNIV on November 19, 2018 at 21:43:17 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: One-step synthesis of block copolymer from mixed monomers is of great interest and challenge. Using a simple non-nucleophilic organobase as the catalyst, we have achieved sequence-selective terpolymerization from a mixture of phthalic anhydride (PA), an epoxide, and rac-lactide (LA). Alcohol-initiated alternating copolymerization of PA and epoxide occurs first and exclusively because PA is substantially more active than LA for reacting with base-activated hydroxyl. When PA is fully consumed, LA polymerizes from the termini of the first block while excess epoxide stays intact because of the mild basicity of the catalyst. The two polymerizations thus occur tandemly, both in chemoselective manners, so that an aromatic−aliphatic block copolyester is generated in this one-step synthesis. The effectiveness and versatility of this approach is demonstrated by the use of ethylene oxide and several monosubstituted epoxides as well as mono-, di-, or tetrahydroxy initiators.

B

monomers.5 Particularly, ring-opening alternating copolymerization (ROAP) of epoxides with nonhomopolymerizable compounds, including cyclic anhydrides,6 carbon dioxide (CO2),7 carbonyl sulfide,8 and so on, has become increasingly attractive for the (bio)renewable features of such comonomers as well as the (bio)degradability and largely tunable structures and properties of the copolymers (e.g., polyesters and polycarbonates). For the synthesis of block copolymers constituted by both epoxide and nonepoxide monomers, some specialized one-pot, two-step strategies have been developed using metallic and organic catalysts. Some of the strategies are featured by sequential monomer addition with intermediate chain-end and catalyst switching.9 Others use mixed monomers with intermediate catalyst switching10 or with one monomer (CO2) removed halfway to halt the first polymerization and launch the second.11 In some recent reports, ROAP catalyzed by organometallic complexes has been elegantly metamorphosed into a one-step synthesis of block terpolymers from three-component monomer mixtures comprising an epoxide, a cyclic anhydride, CO2,12 or a lactone.13 In each case, the catalyst is effective for both ROAP of anhydride-epoxide and ROAP of CO2-epoxide or ROP of the lactone. The anhydride reacts with the epoxidederived metal alkoxide species significantly faster than CO2 or the lactone, and the anhydride-derived metal carboxylate species can only react with the epoxide. Therefore, ROAP of anhydride-epoxide occurs first, and CO2 or the lactone is enchained only after the anhydride is fully consumed to finally form, respectively, (AB)n(CB)m12 or (AB)nCm-type13 block

lock copolymers, constituted by structurally distinct and end-tethered polymer chains, are of enormous fundamental interests and practical utilities for the unique properties that cannot be achieved from any of the block components alone or their blends.1 For synthesis of a block copolymer, a two- or multistep route based on, for example, sequential monomer addition, presynthesis of macroinitiator, end-to-end coupling of preformed polymer chains are most frequently followed.2 Although one-step transformation of mixed monomers into block copolymers would be much more time-saving and cost-effective, limitations are usually posed by the reactivity ratios of the monomers and the incompatibility of their polymerization mechanisms. A number of successful attempts have been made by use of bifunctional initiators and optimized conditions to simultaneously actuate polymerizations of two mechanisms that do not destructively interfere with each other.3 As an indispensable alternative, tandem occurrence of two mechanistically similar polymerizations from a single initiating site remains a greater challenge, especially for the synthesis of AnBm-type block copolymers from conventional two-component monomer mixtures. Two copolymerizable monomers usually give rise to the same or analogous active chain ends, which causes great difficulty to engender the perfect reactivity ratios and polymerization controls required to afford a sharp blocky structure rather than a gradient, tapered, or scrambled sequence distribution. Therefore, realization of tandem block copolymerization should depend on more delicate sequencecontrolling strategies. As a major family of building materials for synthetic polymers, epoxides are not only valued for their living/ controlled ring-opening polymerization (ROP) toward a rich diversity of aliphatic polyethers and derivatives4 and also for their great competence to copolymerize with nonepoxide © XXXX American Chemical Society

Received: November 9, 2018 Accepted: November 14, 2018

1420

DOI: 10.1021/acsmacrolett.8b00865 ACS Macro Lett. 2018, 7, 1420−1425

Letter

ACS Macro Letters

Scheme 1. Sequence-Selective Terpolymerization of Mixed Phthalic Anhydride, Epoxide, and rac-Lactide with t-BuP1 as the Catalyst and Alcohols as the Initiators

Table 1. Conditions and Results of Co- or Terpolymerization from Monomer Mixturesa conv.c (%) entry

initiator

[OH]/[t-BuP1]/[PA]0 /[epoxide]0/[LA]0b

temp (°C)

time (h)

PA

LA

Mn,thd (kg mol−1)

Mn,SECe (kg mol−1)

ĐMe

PAEOLA1 PAEOLA2

BDM BDM

1/0.5/25/50/50 1/0.5/15/30/30

60 60

1.09 1.11 1.09 1.10 1.15 1.13

1/0.5/1.5/0/50 1/0.5/0/50/50 1/0.5/25/50/50 1/0.5/15/30/30 1/0.5/25/125/50 1/0.5/25/125/50 1/0.5/25/125/50

60 60 60 60 80 100 100

78 0 0 0 76 95 0 >99 88 95 97 84 94

20.5 2.9 5.8 7.4 12.6 14.1

BA BDM BA PT BDM BDM BDM

>99 32 70 93 >99 >99 67

21.0 2.0 4.2 5.5 12.5 14.1

PALA EOLA PAEOLA3 PAEOLA4 PABOLA PAAGELA PASOLA

72 6 18 28 48 72 1 24 72 72 16 5 6

14.5 11.2 28.1 25.1 25.3 27.1

14.9 10.9 18.0 27.5 21.2 10.7

1.14 1.12 1.13 1.24 1.17 1.19

>99 >99 >99 >99 >99

a Performed in THF for EO and bulk for other epoxides with [PA]0 ranging from 0.9 to 2.3 M. Monomers are indicated in the entry name. bMolar feed ratio of hydroxyl, t-BuP1, PA, epoxide, and LA. cConversion of PA and LA calculated by 1H NMR analysis of the crude product. dTheoretical number-average molar mass calculated from the feed and conversion of PA and LA. eObtained from SEC analysis (THF, 35 °C, PS standards).

terpolymerization in the presence of t-BuP1 and an hydroxy compound. The terpolymerization of mixed PA, ethylene oxide (EO), and LA is conducted with tetrahydrofuran (THF) as a solvent, 1,4-benzenedimethanol (BDM) as a dihydroxy initiator, and EO added in one-fold excess of PA (PAEOLA1 in Table 1). After heating at 60 °C for 72 h, 1H NMR analysis of the crude product shows that complete conversion of PA and high conversion of LA are reached. A large quantity of unreacted EO is also observed, though precise determination of its conversion is difficult because of the possible loss of volatile EO during NMR measurement. Signals presented in the 1H and 13C NMR spectra (Figures S1 and S2) of the isolated product are well assigned to BDM-derived central group, poly(rac-lactide) (PLA), and alternating copolymer of PA and EO, that is, P(PA-alt-EO). The absence of proton signals at 3.3−3.9 ppm (aliphatic ethers) and 5.3−5.5 ppm (−OCOCH(CH3)OCOC6H4−) indicates, respectively, that EO-EO/LA-EO and LA-PA diads are not formed. Therefore, it can be deduced that ROAP of PA-EO and ROP of LA have

terpolymers. The selectivity of the catalyst guarantees that selfpropagation of the epoxide, though used in excess, is avoided or minimized in the whole process. This sequence-controlling strategy derived from ROAP is appealing for further exploration toward other effective and simpler systems. Organocatalytic ROAP has been reported several times recently.14 In addition to the simplicity of the catalysts and the desirable metal-free polyesters/polycarbonates, competitive catalytic efficiency, molar mass control, and chemo-/ regioselectivity are also exhibited by the organocatalysts. We have demonstrated the potency of a mild organobase for the ROAP of phthalic anhydride (PA) and epoxides.15 The nonnulceophilic nature and proper basicity of the catalyst ensures that the copolymerization occurs only from the added protic initiator and proceeds in a perfectly alternating and transesterification-free manner. The organobase (t-BuP1; Scheme 1) used for this ROAP reaction was shown earlier to be effective for catalyzing hydroxyl-initiated ROP of lactides.16 In this study, we have combined PA, epoxide, and rac-lactide (LA) into a three-component monomer mixture and performed their 1421

DOI: 10.1021/acsmacrolett.8b00865 ACS Macro Lett. 2018, 7, 1420−1425

Letter

ACS Macro Letters

Figure 1. (a) SEC traces (left) and 1H NMR spectra (right) of the aliquots withdrawn from the terpolymerization of mixed PA, EO, and LA with tBuP1 as the catalyst and BMD as the initiator (PAEOLA2 in Table 1). (b) 1H DOSY-NMR spectra of the PLA-b-P(PA-alt-EO)-b-PLA triblock terpolymer obtained from the one-step synthesis (upper) and a blend of P(PA-alt-EO) and PLA synthesized separately (lower) with comparable molar masses as the corresponding blocks of the triblock terpolymer.

both occurred and proceeded independently without sharing monomers. Identical refractive index (RI) and UV responses together with unimodal and narrow molar mass distribution (ĐM = 1.09) are shown by size exclusion chromatography (SEC; Table 1 and Figure S1). The apparent number-average molar mass (Mn,SEC) is close to the combined theoretical molar mass (Mn,th) of P(PA-alt-EO) and PLA. The SEC results hence suggest that the two polymers are actually linked together. PAEOLA2 is performed with aliquots withdrawn at different reaction times to monitor the evolution of monomer conversion and molar mass of the polymer formed (Table 1, Figures 1 and S3). It shows that PA and EO consumes first generating P(PA-alt-EO), and LA stays intact without any trace of PLA formation even when the conversion of PA reaches 93% (28 h). A small portion of the product is isolated (precipitated and dried to remove monomers, catalyst, and solvent) at this point and analyzed by 1H NMR to support this judgment (Figure S4). The sole methylene signal from BDMderived central group (−C6H4CH2OCO− at 5.26 ppm) serves as the first proof that the t-BuP1-activated hydroxyl reacts with PA significantly faster than with LA. At 48 h, there is no more PA left, as indicated by the 1H NMR spectrum, and the transformation of LA into PLA is also revealed. A near complete LA conversion is observed at 72 h, and the proton signals of P(PA-alt-EO) remain unchanged during the formation PLA. SEC peaks exhibit identical RI and UV responses, unimodal and narrow distribution, and a steady shift to the low retention volume (high molar mass) side in the entire process (Figure 1). Mn,SEC of the finally isolated product agrees well with Mn,th. 1H and 13C NMR data are similar to those of PAEOLA1 (Figures S5 and S6). These results strongly support the deductions made from PAEOLA1 and depict a general terpolymerization procedure in which BDM-initiated ROAP of PA-EO occurs first, followed by ROP of LA from both termini of P(PA-alt-EO) to finally form a triblock

terpolymer featuring the structure of PLA-b-P(PA-alt-EO)-bPLA (Scheme 1). DOSY-NMR (Figure 1) taken from the product of PAEOLA2 exhibits a single peak with characteristic proton signals from P(PA-alt-EO) and PLA showing the same diffusion coefficient (D = 1.41 × 10−10 m2 s−1). In contrast, DOSY-NMR taken from a blend of P(PA-alt-EO) and PLA, synthesized separately with comparable molar masses as the corresponding blocks of PAEOLA2, shows two distinct diffusion coefficients of 1.86 × 10−10 m2 s−1 and 1.37 × 10−10 m2 s−1 correlated to signals from P(PA-alt-EO) and PLA, respectively. Therefore, these DOSY-NMR results also support the formation of a block terpolymer from the one-step synthesis rather than unconnected P(PA-alt-EO) and PLA. Benzyl alcohol (BA), t-BuP1, PA, and LA are dissolved in THF at a molar ratio of 1/0.5/1.5/50 and heated at 60 °C (PALA in Table 1). After 2 min, 1H NMR spectrum of the product shows that BA is fully consumed by formation of a 1/1 adduct with PA, while LA and the rest of PA are unreacted. It is thus evident that PA is so much more active than LA that the t-BuP1-activated hydroxyl reacts exclusively with PA, even with a low ratio of [PA]/[LA], simulating the situation of the terpolymerization at near-complete PA conversion. The same 1 H NMR spectrum is shown after the mixture is heated for 1 h (Figure S7), which rules out the reaction between t-BuP1activated carboxyl and LA. This experiment hence confirms that LA is not enchained in the ROAP stage. In another experiment, BDM, t-BuP1, EO, and LA are dissolved in THF at a molar ratio of 1/1/100/100 (EOLA in Table 1), simulating the situation of the terpolymerization at complete PA conversion. After the mixture is heated at 60 °C for 24 h, full consumption of LA is evidenced by 1H NMR analysis of the crude product. SEC shows the formation of a narrowly dispersed polymer with Mn,SEC well agrees with the molar mass calculated from the feed ratio of [LA]/[BDM]. 1H NMR 1422

DOI: 10.1021/acsmacrolett.8b00865 ACS Macro Lett. 2018, 7, 1420−1425

Letter

ACS Macro Letters

The terpolymerization of PA, BO, and LA is monitored by in situ ATR-IR spectroscopy as a nonstop tracking technique (Figures 2 and S24). Feed ratio and reaction conditions are the

spectrum of the isolated product presents only the characteristic signals of a BDM-initiated PLA (Figure S8). It is hence confirmed that ROP of LA in the second stage occurs in a chemoselective and controlled manner without enchaining the excess EO. These two control experiments well illustrate and explain the sequence selectivity of the one-step terpolymerization (Scheme 1). Namely, in the presence of PA, t-BuP1-activated hydroxyl reacts solely with PA owing to its exceedingly high electrophilicity. Meanwhile, PA-derived carboxylate can only react with EO,6 allowing the formation of a strictly alternating copolymer, P(PA-alt-EO), in this stage. When PA is fully consumed, terminal hydroxyls of the aromatic polyester persist,15 so the ROP of LA can be launched. The mild basicity of the catalyst guarantees that the excess EO is not enchained in this stage,14d so that flawless PLA (aliphatic polyester) blocks are generated to finally afford the aromatic− aliphatic block copolyester. One major merit of t-BuP1-catalyzed ROAP is that the in situ initiator activation and chain growth mode allows facile and flexible construction of topological alternating polyester structures by use of initiators with varied numbers of functionality.15 In addition to dihydroxy BDM, we have used BA and pentaerythritol (PT) in this study as representative mono- and multifunctional initiators, respectively, for one-step synthesis of a P(PA-alt-EO)-b-PLA diblock terpolymer (PAEOLA3 in Table 1) and a [P(PA-alt-EO)-b-PLA]4 fourarm star-shaped block terpolymer (PAEOLA4 in Table 1). 1H NMR and SEC characterization verifies that full conversion of PA, high conversion of LA, and expected block terpolymer structures with controlled molar masses are achieved in both cases (Table 1 and Figures S9 and S10). To further demonstrate the versatility of this approach, we have used 1,2-butylene oxide (BO), allyl glycidyl ether (AGE), and styrene oxide (SO) as representative substituted epoxides in the one-step block terpolymer synthesis with BDM as the initiator (Scheme 1). Because of their much higher boiling points, solvent-free conditions, and higher temperatures (80 °C for BO and 100 °C for AGE and SO) can be used so that the polymerization rates are considerably enhanced. 1H/13C/ DOSY NMR and SEC characterization of crude and isolated products presents analogous results as those obtained for EO, confirming the successful sequence-selective terpolymerization and one-step synthesis of PLA-b-P(PA-alt-BO)-b-PLA, PLA-bP(PA-alt-AGE)-b-PLA, and PLA-b-P(PA-alt-SO)-b-PLA triblock terpolymers (PABOLA, PAAGELA, and PASOLA in Table 1 and Figures S11−S22). Mn,SEC of the triblock terpolymer agrees well with Mn,th in most cases except PASOLA, which shows a bimodal molar mass distribution and a distinctly lower Mn,SEC. This is probably due to an extra (monofunctional) initiator introduced/generated by SO monomer in the ROAP stage. The allyl groups of PLA-bP(PA-alt-AGE)-b-PLA can be utilized to introduce other functionalities suspended on the aromatic polyester block by radical thiol−ene reaction (e.g., carboxy groups, Figure S23), which further enriches the structural diversity of the one-step synthesized block copolyesters.17 Mn,SEC of the triblock terpolymer stays nearly the same after the thio-ene modification, and 1H NMR analysis clearly evidences the successful functionalization. A slight shoulder to the highmolar-mass side is present on the SEC peak, which is likely due to the association of polymer chains carrying multiple carboxyls.

Figure 2. Evolution of the intensities of characteristic IR absorption bands acquired by in situ ATR-IR spectroscopy during the terpolymerization of mixed PA, BO, and LA with t-BuP1 as the catalyst and BMD as the initiator. The evolution of absorption at wavenumbers of 906, 1186, 1246, and 1294 cm−1 correspond to, respectively, PA consumption, PLA formation, LA consumption, and P(PA-alt-BO) formation. Feed ratio and reaction conditions are the same as PABOLA in Table 1.

same as PABOLA in Table 1. The evolution of the characteristic IR absorption bands clearly shows the two stages of the terpolymerization. In the first stage, the absorption at 906 cm−1 (PA aromatic C−H) gradually decreases in company with an increase at 1294 cm−1 (benzoic ester C−O) at a similar rate, which are ascribed to the consumption of PA and formation of P(PA-alt-BO), respectively. In the second stage, the variation of these two bands ceases and the absorption of bands at 1246 and 1186 cm−1 (aliphatic ester C−O) start to decrease and increase, respectively, in similar rates attributed to the transformation of LA into PLA. An intermediate period is observed between the consumption of PA and LA, which can be ascribed to the transformation of the end group of P(PA-altBO) from carboxyl to hydroxyl. It is somewhat surprising to notice that the enchainment of the last epoxide seems to be much slower than the rest of the ROAP stage. It then implies that the existence of anhydride is helpful for the base-catalyzed reaction between carboxyl and epoxide. This experiment provides additional strong evidence that the enchainment of LA starts only after PA is fully consumed, so that the generated terpolymer has a sharp blocky structure. In summary, one-step synthesis of (AB)nCm-type block terpolymer from the monomer mixture comprising PA, an epoxide, and LA has been realized by the use of a simple but highly selective organocatalyst. Our results have clearly verified the tandem occurrence of ROAP of PA-epoxide and ROP of LA from hydroxy initiators without any monomer involved in both stages. The sequence selectivity stems from perfectly matching activities of the monomers, chain ends, and catalyst. Structural diversity of the block terpolymer can be readily enriched by use of epoxides carrying different substituents and initiators with different numbers of functionality. A new perspective is thus provided on the potency of organocatalysis for facile synthesis of polymers with controlled sequences.18 It is expected that the insights gained here can be translated into other organocatalytic/metal-free strategies for sequence1423

DOI: 10.1021/acsmacrolett.8b00865 ACS Macro Lett. 2018, 7, 1420−1425

Letter

ACS Macro Letters

Polymerization and Copolymerization. Chem. Rev. 2014, 114, 8129− 8152. (d) Klein, R.; Wurm, F. R. Aliphatic Polyethers: Classical Polymers for the 21st Century. Macromol. Rapid Commun. 2015, 36, 1147−1165. (e) Herzberger, J.; Niederer, K.; Pohlit, H.; Seiwert, J.; Worm, M.; Wurm, F. R.; Frey, H. Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation. Chem. Rev. 2016, 116, 2170−2243. (5) (a) Brule, E.; Guo, J.; Coates, G. W.; Thomas, C. M. MetalCatalyzed Synthesis of Alternating Copolymers. Macromol. Rapid Commun. 2011, 32, 169−185. (b) Paul, S.; Zhu, Y.; Romain, C.; Brooks, R.; Saini, P. K.; Williams, C. K. Ring-Opening Copolymerization (ROCOP): Synthesis and Properties of Polyesters and Polycarbonates. Chem. Commun. 2015, 51, 6459−6479. (c) Song, Q.; Hu, S.; Zhao, J.; Zhang, G. Organocatalytic Copolymerization of Mixed Type Monomers. Chin. J. Polym. Sci. 2017, 35, 581−601. (d) Xia, Y.; Zhao, J. Macromolecular Architectures Based on Organocatalytic Ring-Opening (co)Polymerization of Epoxides. Polymer 2018, 143, 343−361. (6) Longo, J. M.; Sanford, M. J.; Coates, G. W. Ring-Opening Copolymerization of Epoxides and Cyclic Anhydrides with Discrete Metal Complexes: Structure-Property Relationships. Chem. Rev. 2016, 116, 15167−15197. (7) (a) Darensbourg, D. J. Making Plastics from Carbon Dioxide: Salen Metal Complexes as Catalysts for the Production of Polycarbonates from Epoxides and CO2. Chem. Rev. 2007, 107, 2388−2410. (b) Lu, X. B.; Darensbourg, D. J. Cobalt Catalysts for the Coupling of CO2 and Epoxides to Provide Polycarbonates and Cyclic Carbonates. Chem. Soc. Rev. 2012, 41, 1462−1484. (c) Li, Y.; Zhang, Y.-Y.; Hu, L.-F.; Zhang, X.-H.; Du, B.-Y.; Xu, J.-T. Carbon DioxideBased Copolymers with Various Architectures. Prog. Polym. Sci. 2018, 82, 120−157. (8) Luo, M.; Zhang, X.-H.; Darensbourg, D. J. Poly(Monothiocarbonate)s from the Alternating and Regioselective Copolymerization of Carbonyl Sulfide with Epoxides. Acc. Chem. Res. 2016, 49, 2209−2219. (9) (a) Wu, G.-P.; Darensbourg, D. J.; Lu, X.-B. Tandem MetalCoordination Copolymerization and Organocatalytic Ring-Opening Polymerization via Water to Synthesize Diblock Copolymers of Styrene Oxide/CO2 and Lactide. J. Am. Chem. Soc. 2012, 134, 17739−17745. (b) Darensbourg, D. J.; Wu, G.-P. A One-Pot Synthesis of a Triblock Copolymer from Propylene Oxide/Carbon Dioxide and Lactide: Intermediacy of Polyol Initiators. Angew. Chem., Int. Ed. 2013, 52, 10602−10606. (c) Zhao, J.; Pahovnik, D.; Gnanou, Y.; Hadjichristidis, N. A ″Catalyst Switch″ Strategy for the Sequential Metal-Free Polymerization of Epoxides and Cyclic Esters/Carbonate. Macromolecules 2014, 47, 3814−3822. (d) Xia, Y.; Chen, Y.; Song, Q.; Hu, S.; Zhao, J.; Zhang, G. Base-to-Base Organocatalytic Approach for One-Pot Construction of Poly(ethylene oxide)-Based Macromolecular Structures. Macromolecules 2016, 49, 6817−6825. (10) (a) Biernesser, A. B.; Delle Chiaie, K. R.; Curley, J. B.; Byers, J. A. Block Copolymerization of Lactide and an Epoxide Facilitated by a Redox Switchable Iron-Based Catalyst. Angew. Chem., Int. Ed. 2016, 55, 5251−5254. (b) Quan, S. M.; Wang, X.; Zhang, R.; Diaconescu, P. L. Redox Switchable Copolymerization of Cyclic Esters and Epoxides by a Zirconium Complex. Macromolecules 2016, 49, 6768− 6778. (c) Qi, M.; Dong, Q.; Wang, D.; Byers, J. A. Electrochemically Switchable Ring-Opening Polymerization of Lactide and Cyclohexene Oxide. J. Am. Chem. Soc. 2018, 140, 5686−5690. (11) (a) Paul, S.; Romain, C.; Shaw, J.; Williams, C. K. Sequence Selective Polymerization Catalysis: A New Route to ABA Block Copoly(Ester-b-Carbonate-b-Ester). Macromolecules 2015, 48, 6047− 6056. (b) Kernbichl, S.; Reiter, M.; Adams, F.; Vagin, S.; Rieger, B. CO2-Controlled One-Pot Synthesis of AB, ABA Block, and Statistical Terpolymers from β-Butyrolactone, Epoxides, and CO2. J. Am. Chem. Soc. 2017, 139, 6787−6790. (c) Hu, C.; Duan, R.; Yang, S.; Pang, X.; Chen, X. CO2 Controlled Catalysis: Switchable Homopolymerization and Copolymerization. Macromolecules 2018, 51, 4699−4704.

selective/controlled polymerization and simplified preparation of materials with tailed properties.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmacrolett.8b00865. Experimental details, additional SEC traces and 1H/13C/ DOSY NMR spectra, and three-dimensional stacked in situ ATR-IR spectra (PDF).

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Junpeng Zhao: 0000-0002-2590-0027 Guangzhao Zhang: 0000-0002-0219-3729 Notes

The authors declare no competing financial interest.

■ ■

ACKNOWLEDGMENTS The financial support of National Natural Science Foundation of China (21734004, 21674038) is acknowledged. REFERENCES

(1) (a) Rösler, A.; Vandermeulen, G. W. M.; Klok, H.-A. Advanced Drug Delivery Devices via Self-Assembly of Amphiphilic block Copolymers. Adv. Drug Delivery Rev. 2001, 53, 95−108. (b) Lohmeijer, B. G. G.; Schubert, U. S. Supramolecular Engineering with Macromolecules: An Alternative Concept for Block Copolymers. Angew. Chem., Int. Ed. 2002, 41, 3825−3829. (c) Bates, C. M.; Bates, F. S. 50th Anniversary Perspective: Block PolymersPure Potential. Macromolecules 2017, 50, 3−22. (2) Hadjichristidis, N.; Pispas, S.; Floudas, G. Block Copolymers; John Wiley & Sons: Hoboken, NJ, 2003. (3) (a) Bernaerts, K. V.; Du Prez, F. E. Dual/Heterofunctional Initiators for the Combination of Mechanistically Distinct Polymerization Techniques. Prog. Polym. Sci. 2006, 31, 671−722. (b) Li, Y.; Themistou, E.; Zou, J.; Das, B. P.; Tsianou, M.; Cheng, C. Facile Synthesis and Visualization of Janus Double-Brush Copolymers. ACS Macro Lett. 2012, 1, 52−56. (c) Kang, H. U.; Yu, Y. C.; Shin, S. J.; Youk, J. H. One-Step Synthesis of block Copolymers Using a Hydroxyl-Functionalized Trithiocarbonate Raft Agent as a Dual Initiator for Raft Polymerization and ROP. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 774−779. (d) Themistou, E.; Battaglia, G.; Armes, S. P. Facile Synthesis of Thiol-Functionalized Amphiphilic Polylactide-Methacrylic Diblock Copolymers. Polym. Chem. 2014, 5, 1405−1417. (e) Freudensprung, I.; Klapper, M.; Müllen, K. Triblock Terpolymers by Simultaneous Tandem Block Polymerization (STBP). Macromol. Rapid Commun. 2016, 37, 209−214. (f) Aydogan, C.; Kutahya, C.; Allushi, A.; Yilmaz, G.; Yagci, Y. Block Copolymer Synthesis in One Shot: Concurrent Metal-Free Atrp and ROP Processes under Sunlight. Polym. Chem. 2017, 8, 2899−2903. (g) Wang, Y.; Zhao, Y.; Ye, Y.; Peng, H.; Zhou, X.; Xie, X.; Wang, X.; Wang, F. A One-Step Route to CO2-Based Block Copolymers by Simultaneous ROCOP of CO2/Epoxides and Raft Polymerization of Vinyl Monomers. Angew. Chem., Int. Ed. 2018, 57, 3593−3597. (4) (a) Obermeier, B.; Wurm, F.; Mangold, C.; Frey, H. Multifunctional Poly(ethylene glycol)s. Angew. Chem., Int. Ed. 2011, 50, 7988−7997. (b) Brocas, A.-L.; Mantzaridis, C.; Tunc, D.; Carlotti, S. Polyether Synthesis: From Activated or Metal-Free Anionic RingOpening Polymerization of Epoxides to Functionalization. Prog. Polym. Sci. 2013, 38, 845−873. (c) Childers, M. I.; Longo, J. M.; Van Zee, N. J.; LaPointe, A. M.; Coates, G. W. Stereoselective Epoxide 1424

DOI: 10.1021/acsmacrolett.8b00865 ACS Macro Lett. 2018, 7, 1420−1425

Letter

ACS Macro Letters (12) (a) Jeske, R. C.; Rowley, J. M.; Coates, G. W. Pre-RateDetermining Selectivity in the Terpolymerization of Epoxides, Cyclic Anhydrides, and CO2: A One-Step Route to Diblock Copolymers. Angew. Chem., Int. Ed. 2008, 47, 6041−6044. (b) Duan, Z.; Wang, X.; Gao, Q.; Zhang, L.; Liu, B.; Kim, I. Highly Active Bifunctional CobaltSalen Complexes for the Synthesis of Poly(Ester-block-Carbonate) Copolymerviaterpolymerization of Carbon Dioxide, Propylene Oxide, and Norbornene Anhydride Isomer: Roles of Anhydride Conformation Consideration. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 789−795. (c) Liu, Y.; Guo, J.-Z.; Lu, H.-W.; Wang, H.-B.; Lu, X.-B. Making Various Degradable Polymers from Epoxides Using a Versatile Dinuclear Chromium Catalyst. Macromolecules 2018, 51, 771−778. (13) (a) Zhu, Y.; Romain, C.; Williams, C. K. Selective Polymerization Catalysis: Controlling the Metal Chain End Group to Prepare Block Copolyesters. J. Am. Chem. Soc. 2015, 137, 12179− 12182. (b) Romain, C.; Zhu, Y.; Dingwall, P.; Paul, S.; Rzepa, H. S.; Buchard, A.; Williams, C. K. Chemoselective Polymerizations from Mixtures of Epoxide, Lactone, Anhydride, and Carbon Dioxide. J. Am. Chem. Soc. 2016, 138, 4120−4131. (c) Stosser, T.; Williams, C. K. Selective Polymerization Catalysis from Monomer Mixtures: Using a Commercial Cr-Salen Catalyst to Access ABA Block Polyesters. Angew. Chem., Int. Ed. 2018, 57, 6337−6341. (14) (a) Han, B.; Zhang, L.; Liu, B.; Dong, X.; Kim, I.; Duan, Z.; Theato, P. Controllable Synthesis of Stereoregular Polyesters by Organocatalytic Alternating Copolymerizations of Cyclohexene Oxide and Norbornene Anhydrides. Macromolecules 2015, 48, 3431−3437. (b) Hu, S.; Dai, G.; Zhao, J.; Zhang, G. Ring-Opening Alternating Copolymerization of Epoxides and Dihydrocoumarin Catalyzed by a Phosphazene Superbase. Macromolecules 2016, 49, 4462−4472. (c) Zhang, D.; Boopathi, S. K.; Hadjichristidis, N.; Gnanou, Y.; Feng, X. Metal-Free Alternating Copolymerization of CO2 with Epoxides: Fulfilling ″Green″ Synthesis and Activity. J. Am. Chem. Soc. 2016, 138, 11117−11120. (d) Zhang, H.; Hu, S.; Zhao, J.; Zhang, G. Phosphazene-Catalyzed Alternating Copolymerization of Dihydrocoumarin and ethylene oxide: Weaker Is Better. Macromolecules 2017, 50, 4198−4205. (e) Yang, J.-L.; Wu, H.-L.; Li, Y.; Zhang, X.-H.; Darensbourg, D. J. Perfectly Alternating and Regioselective Copolymerization of Carbonyl Sulfide and Epoxides by Metal-Free Lewis Pairs. Angew. Chem., Int. Ed. 2017, 56, 1−7. (f) Zhang, C.-J.; Wu, H.-L.; Li, Y.; Yang, J.-L.; Zhang, X.-H. Precise Synthesis of SulfurContaining Polymers via Cooperative Dual Organocatalysts with High Activity. Nat. Commun. 2018, 9, 2137. (15) (a) Li, H.; Zhao, J.; Zhang, G. Self-Buffering Organocatalysis Tailoring Alternating Polyester. ACS Macro Lett. 2017, 6, 1094−1098. (b) Li, H.; Luo, H.; Zhao, J.; Zhang, G. Well-Defined and Structurally Diverse Aromatic Alternating Polyesters Synthesized by Simple Phosphazene Catalysis. Macromolecules 2018, 51, 2247−2257. (16) Zhang, L.; Nederberg, F.; Pratt, R. C.; Waymouth, R. M.; Hedrick, J. L.; Wade, C. G. Phosphazene Bases: A New Category of Organocatalysts for the Living Ring-Opening Polymerization of Cyclic Esters. Macromolecules 2007, 40, 4154−4158. (17) Sanford, M. J.; Van Zee, N. J.; Coates, G. W. ReversibleDeactivation Anionic Alternating Ring-Opening Copolymerization of Epoxides and Cyclic Anhydrides: Access to Orthogonally Functionalizable Multiblock Aliphatic Polyesters. Chem. Sci. 2018, 9, 134−142. (18) (a) Lutz, J.-F.; Ouchi, M.; Liu, D. R.; Sawamoto, M. SequenceControlled Polymers. Science 2013, 341, 628−636. (b) Lutz, J.-F.; Lehn, J.-M.; Meijer, E. W.; Matyjaszewski, K. From Precision Polymers to Complex Materials and Systems. Nat. Rev. Mater. 2016, 1, 16024. (c) Engelis, N. G.; Anastasaki, A.; Nurumbetov, G.; Truong, N. P.; Nikolaou, V.; Shegiwal, A.; Whittaker, M. R.; Davis, T. P.; Haddleton, D. M. Sequence-Controlled Methacrylic Multiblock Copolymers via Sulfur-Free Raft Emulsion Polymerization. Nat. Chem. 2017, 9, 171−178.

1425

DOI: 10.1021/acsmacrolett.8b00865 ACS Macro Lett. 2018, 7, 1420−1425