Well-Defined Selenium-Containing Aliphatic Polycarbonates via

Feb 22, 2018 - Well-Defined Selenium-Containing Aliphatic Polycarbonates via Lipase-Catalyzed Ring-Opening Polymerization of Selenic Macrocyclic Carbo...
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Letter Cite This: ACS Macro Lett. 2018, 7, 336−340

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Well-Defined Selenium-Containing Aliphatic Polycarbonates via Lipase-Catalyzed Ring-Opening Polymerization of Selenic Macrocyclic Carbonate Monomer Chao Wei, Yue Xu, Bingkun Yan, Jiaqian Hou, Zhengzhen Du, and Meidong Lang* Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials and Science and Engineering, East China University of Science and Technology, Shanghai, 200237, China S Supporting Information *

ABSTRACT: The synthesis of well-defined, biodegradable selenium-containing polymers remains a formidable challenge in polymer chemistry. Herein, a selenic cyclic carbonate dimer monomer (MSe) was developed to generate well-defined, biodegradable aliphatic polycarbonates with selenide functionality on the backbone. The monomer was synthesized via the intermolecular cyclization of di(1-hydroxyethylene) selenide and diphenyl carbonate with lipase CA as catalysts in a mass of anhydrous toluene with very dilute monomer concentration. Then living ring-opening polymerization (ROP) was executed by solution method using the same lipase CA as catalysts. Similarly, the copolymerizations with commercial trimethylene carbonate (TMC) generated random copolymers demonstrated by 13C NMR, regulating the density of selenium functional groups. The resulting polymers exhibited a living polymerization characteristic, as evidenced by polymerization kinetics, predictable molecular weights, narrow molecular-weight distribution, and controlled copolymer compositions. Using hydrophilic macroinitiators (PEG), amphiphilic di/triblock copolymers could be obtained, suggesting their potential as controlled drug delivery system (DDS) and hydrogel scaffolds for tissue engineering. with di(1-hydroxylundecyl) diselenide diols and finally terminated by poly(ethylene glycol).1 The copolymers have good solubility in regular solvents and are capable of selfassembling into nanoparticles that could decompose and release the drug when triggered by redox stimuli. Later, monoselenide-containing polymers were reported by means of the similar synthetic routes.11 This team’s remarkable work inspired the design of various selenium-containing polymers with different topologies, providing promising platforms in many systems, including controlled drug release,12 photodynamic therapy (PDT),13,14 synergistic therapy,15 self-healing materials,16,17 and so on. Note that the polymerization mechanism is step-growth, which is often accompanied by uncontrollable molecular weight characteristics and broad molecular weight distributions. Recently, Zhu and co-workers

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n the past decade, selenium-containing polymers have garnered significant interest in nanotechnology and biomedical applications due to their unique stimuli-responsive behaviors under oxidation, reduction, irradiation, and light.1−6 As is well-known, selenium (Se) is the essential trace element in the human body and plays an indispensable role in antioxidation and preventing cellular damage, which was recognized in the 1970s by Rotruck.7 The anticancer activity of Se has been supported by epidemiological studies, preclinical investigations and clinical intervention trials and numerous selenium-containing small molecules have been exploited as anticancer reagents.8,9 However, selenium-containing polymers have been overlooked for a long time, especially in biomedical applications, because of the lack of effective synthetic approach to overcome inherent low solubility and stability, although a few polymers are reported as optoelectronic or semiconducting materials.10 Until 2010, Xu’s group pioneered diselenide-containing copolymers via polymerization of toluene diisocyanate (TDI) © XXXX American Chemical Society

Received: January 14, 2018 Accepted: February 13, 2018

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DOI: 10.1021/acsmacrolett.8b00039 ACS Macro Lett. 2018, 7, 336−340

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ACS Macro Letters

macrocyclic dimer by intermolecular cyclization and the synthetic routes were divided into two main strategies.33,34 The first one was the synthesis of oligomers by the reaction of diols and carbonate ester, followed by depolymerization at high temperature (∼200 °C or higher) in vacuo.33,35 Owing to the lower thermal stability of selenium-containing diols, selenic cyclic carbonates (synthesized using the second strategy) and selenium-containing polymer (Figure S8, the three initial decomposition temperature Tonset ≈ 175 °C), thermaldepolymerization method is infeasible. Second, we found that using mild enzyme catalytic strategy could realize cyclization of diols and diphenyl carbonate to yield polymerizable cyclic dimers,34 and we also disclosed the synthesis of chalcogenbased macrocyclic carbonate monomers very recently through the enzyme catalysis method.36 We hypothesized that this synthetic approach might provide a facile platform to prepare new classes of selenic cyclic carbonate monomers. Herein, we describe the synthesis of selenium-containing macrocyclic carbonate monomers, cyclic diethylene selenide carbonate dimer (MSe) by an efficient two-step procedure, and its enzymatic ring opening polymerization (eROP) (Scheme 1).

presented controlled polymerization strategies, for instance, reversible-deactivation radical polymerization (RDRP, such as atom-transfer radical polymerization (ATRP), selenium-mediated living radical polymerization (SeRP)) and selenium borohydride reaction, to prepare well-defined structures.18−20 While the robustness of these approaches has successfully access to various selenium-containing polymers, such as poly(methyl acrylate) (PMA), poly(vinyl acetate) (PVAc) and polystyrene (PS), and so on, the resulting polymers are nonbiodegradable, which is unfavorable for clinical applications. Although postfunctionalization of reactive polymers is practicable, protection, and deprotection are usually inevitable; the controllability of postfunctionalization is also a great challenge.21 Administrative regulations require well-defined structures and biodegradability to be used in patients,22 therefore, new routes to well-defined biodegradable seleniumcontaining polymers are needed. Aliphatic polycarbonates (APCs), together with APCs-based hybrid polymers, are an important class of biomaterials due to their biocompatibility, promising biodegradability, low toxicity, and wide biomedical applications.23−25 Well-defined APCs are often synthesized by ring opening polymerization (ROP) of cyclic monomers, which mechanistically offers precise control over polymer structure, molecular weights (MW), molecular weight distributions, and compositions.26,27 However, traditional APCs often do not fulfill some practical requirements, due to the lack of functionality to further modification. To satisfy the increasing demand in biomedical and pharmaceutical science, many desired functional groups such as amidogen,28 carboxyl,29 hydroxy,30 and disulfide31 are introduced at the monomer level, vastly expanding the scope of accessible aliphatic polycarbonates. To date, however, there are no reports describing the synthesis of selenium functionalized polycarbonates (SePC), because the design and synthesis of polymerizable selenic carbonate monomers is a challenging topic in polymer chemistry. Along this line, as a first step, the key to SePC is to generate a polymerizable selenic cyclic carbonate from activated seleniumcontaining small molecules. The common synthetic and commercial selenic small molecules are inert and more often impossible to be cyclized. Recently, selenium-containing diols including di(1-hydroxyethylene) selenide and di(1-hydroxypropyl) selenide have been developed, which provide a possible choice to fabricate selenic carbonate monomers according to streamlined synthetic routes of cyclic carbonates.32 As shown in Figure 1, we initially designed to use the most reported intramolecular cyclization to synthesize selenic carbonate monomers. However, the objective product is 8- or 10membered cyclic monomers, which are unstable and difficult to be obtained. Then we shifted our focus to the more stable

Scheme 1. Synthesis of Selenium-Containing Cyclic Carbonate Dimer (MSe) and Selenium-Containing Polycarbonate (PSe)

Polymerization kinetics was investigated in detail. Copolymerization with trimethylene carbonates (TMC) generated hybrid polycarbonates; especially, this method could adjust the density and content of selenium. Subsequently, polyethylene glycol (PEG) was used as macroinitiators to obtain di/triblock amphipathic copolymers. Considering the ever-increasing attention for selenium-containing polymers, we believe that this material platform will impact the biomedical field in the future. Selenic macrocyclic carbonate (MSe) was prepared in two steps, starting from selenium powder, sodium borohydride, and bromoethanol to give di(1-hydroxyethylene) selenide, followed by the intermolecular cyclization with diphenyl carbonate using lipase CA as catalysts (Scheme 1). The cyclization reaction was carried out at 70 °C in a mass of anhydrous toluene with very dilute monomer concentration so as to reduce the amount of byproducts oligomers, because lipase CA could also catalyze ring opening of MSe to yield oligomers (Figure S1), which was also consistent with the Jacobson−Stockmayer theory that ring structures were obtained predominantly under dilute conditions.37 Generally, 1/(500−600) g mL−1 concentration was appropriate to high yields and continuously increasing solvent did not improve the yields observably, but led to the high cost and multistep treatment. The monomer was purified by column chromatography as white crystals with the overall yield to 35− 45%, and was easy to store at room temperature for several months. As the preparation of selenium functional monomer is known to be synthetically challenging, the yield is remarkable,

Figure 1. Designed possible synthetic routes to cyclic selenic carbonate monomer from selenium-containing small diols. 337

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catalytic ROP22,42 because of a few adverse transesterification occurred via enzyme catalysis. The Mn values obtained by 1H NMR and GPC are discrepant (Table 1), which is mainly a consequence of different hydrodynamic volumes of obtained polymers PSe compared with poly(methyl methacrylate) (PMMA) (standards). Fortunately, Mn values determined by multimeasurement gel permeation chromatography (GPCLSL) are more consistent with MnNMR (Table 1) mainly due to the absence of internal standards. The preliminary results suggest remarkable control of the ROP of MSe with predictable molecular weights and quasi-narrow molecular weight distributions. To further prove the control over polymerization, the ROP kinetics was investigated. The monomer showed fast conversion (above 96%) within 4 h ([Bn−OH]0/[M]0 = 1.0:20; Figure 3a). Besides, ln([M]0/[Mt]) versus reaction time

higher than previously reported N-heterocyclic dimers by thermal-depolymerization method.33 Characterization of MSe was conducted by NMR (1H, 13C, 77Se) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and mass spectrometry (Figures 2a and S2−S5).

Figure 2. 1H NMR spectra of (a) selenium-containing macrocyclic carbonate dimer MSe and (b) main chain selenium-containing aliphatic polycarbonates PSe.

The ROP of MSe was investigated using the same lipase CA as the catalyst with benzyl alcohol as the initiator (Scheme 1) under similar conditions as previously reported by Gross and Zhuo.33,38 Lipase has showed the outstanding capacity for ROP of macrocyclic lactones and carbonates compared to metal and organic catalysts.35,39 Owing to the high melting point of MSe (Tm = 93 °C, Figure S6), the ROP was carried out by solution polymerization in toluene at 70 °C. The obtained PSe structure was verified by 1H NMR and 77Se NMR (Figures 2b and S7). Two typical hydrogen triple peaks at 4.35 and 2.85 ppm corresponding to -CH2OCOCH2- and -CH2SeCH2- were observed. A single resonance in 77Se NMR at 124.3 ppm (Figure S7) further confirmed the successful formation of selenide-containing polymer. The number-average molecular weights (entries 1 and 2, Table 1; calcd by 1H NMR end-group analysis, referring all signals to the resonance of the initiator) are very close to the expected Mn determined by the feed [M]/I ratios. The GPC showed the quasi-narrow molecular-weight distributions, which were similar to the other enzymatic system40 but slightly bigger compared with metal41 or organic

Figure 3. (a) Plot of monomer conversion as a function of reaction time with lipase CA (10 wt % of enzyme to MSe) as the catalyst and BnOH as the initiator ([Bn−OH]0/[M]0 = 1.0:20). (b) Plot of ln([M]0/[Mt]) vs polymerization time for lipase CA catalyzed, BnOHinitiated polymerization. (c) Plot of the number-average molecular weight (Mn) obtained by 1H NMR vs the monomer/initiator (M/I; 10−100). (d) Plot of Mw and ĐM determined by multimeasurement gel permeation chromatography (GPC-LSL) vs the M/I (10−100). The linear dependence of the molecular weight of PSe with M/I is a characteristic of living polymerization.

was found to be linear, indicating that the concentration of growing chains remained constant during the polymerization (kp = 0.69 M−1 min−1, Figure 3b), which was an important characteristic for living polymerization. The plot of Mn versus

Table 1. Lipase-Catalyzed Ring-Opening Polymerization of MSea entry 1 2 3 4 5 6 7

initiator BnOH BnOH BnOH BnOH BnOH mPEG2k−OH HO-PEG2k−OH

monomer MSe MSe MSe/TMC MSe/TMC MSe/TMC MSe MSe

M/Ib 10 100 10/30 20/20 30/10 10 10

expected Mnc (KDa) 4.0 39.2 7.0 9.9 12.8 5.9 5.9

DPd 10 97 10/32 19/21 27/13 9 9

Mnd (KDa) 4.0 38.0 7.2 9.7 12.0 5.5 5.5

Mne (KDa) f

12.4/5.6 22.7/35.9f 16.1 16.3 10.6 9.9 8.7

ĐMe 1.58/1.36f 1.66/1.30f 1.49 1.62 1.48 1.33 1.50

The reactions were conducted in anhydrous toluene at 70 °C, solution/MR (vol/wt, mL/g) = 10:1, weight ratio of catalysts to MSe (g/g) = 10%. The initiator to monomer ratio. cAs calculated by the feed ratios. dAs calculated by 1H NMR spectra. eAs determined by GPC in DMF using PMMA as standards. fAs determined by multimeasurement gel permeation chromatography (GPC-LSL). a b

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ACS Macro Letters monomer conversion was also first-order dependent, further confirming the living polymerization characteristic (Figure S9). We after carried out different [M]/I ratios (10−100) to investigate whether this was a controlled polymerization from low molecular weight (thousands) to high molecular weight (zigtausend). As shown in Figure 3c, the number-average molecular weights (Mn; calcd by 1H NMR) of the polymers were linearly correlated with [M]/I. Furthermore, multimeasurement gel permeation chromatography (GPC-LSL) was used to obtain the weight-average molecular weights (Mw) and found a linear correlation between [M]/I and Mw and the low molecular weight distributions (Figure 3d). These results provide a comprehensive indication that the polymerization process is, indeed, quasi-living. We then explored whether MSe can be copolymerized with other carbonate monomers to generate hybrid polycarbonates. The copolymerizations with trimethylene carbonate (TMC) at various molar fractions (25, 50, 75%) were performed in toluene solution with 10 wt % lipase CA at 70 °C (Scheme S1, Figure S10). Over 97% comonomer conversion was observed and the compositions were approximate to that of the initial feed ratio (entries 3−5, Table 1). This controlled copolymerization process is significant not only to manage the physicochemical properties (thermal properties, degradation, etc.), but also to tune density and content of selenide functionality, further tailoring desired oxidative responsiveness.43 Moreover, 13C NMR analysis revealed that the copolymers were random microstructure (Figures S11−13). For biomedical applications, hydrophilic poly(ethylene glycol) (PEG) is often introduced due to its high aqueous solubility, excellent biocompatible, low toxicity and prolonged circulation time in vivo.44,45 In this work, mPEG (Mn = 2000 g mol−1) and PEG (Mn = 2000 g mol−1) were used to initiate ROP of MSe to afford A−B diblock (entry 6, Figure S14) and A−B−A triblock copolymers (entry 7, Figure S15). The hydrophobic PSe blocks were well-controlled with the targeted molecular weight, while maintaining low molecular weight distribution. Such amphiphilic block copolymers could form stealth micelles to carry hydrophobic drugs or hydrogels for biorelated field. It is worth mentioning that all abtained homopolymers PSe and copolymers are stable at room temperature and can be dissolved easily in the common solvents such as tetrahydrofuran, dichloromethane and N,Ndimethylformamide, which is a tremendous advance to overcome inherent low stability and solubility of seleniumcontaining polymers. In summary, we have reported an enzyme catalytic strategy to generate selenic macrocyclic carbonate dimer monomers via intermolecular cyclization under dilute conditions. Lipasecatalyzed homopolymerization and copolymerization proceeded easily with excellent control, affording a new family of well-defined biodegradable selenide functionalized polycarbonates with predictable molecular weights and low molecular weight distribution, desired copolymer compositions. ROP kinetics was investigated in detail to demonstrate the living polymerization characteristic. This synthetic methodology will not only expand the scope of functional polycarbonates, but also push forward the development of the selenic biomaterials in academic research and practical application. The combination of the outstanding oxidative responsiveness, unique biological effects of selenium and wide biomedical applications of aliphatic polycarbonates makes main chain selenide functionalized polycarbonates (PSe) attractive as a new class

of useful biomaterial for the construction of drug delivery systems (DDS) and hydrogel scaffolds for tissue engineering.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmacrolett.8b00039. Experimental details for the synthesis of monomers and polymers, detailed characterization data, and spectra (PDF).

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Meidong Lang: 0000-0003-2053-9284 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the National Key Research and Development Program (2016YFC1100700) are gratefully acknowledged.

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REFERENCES

(1) Ma, N.; Li, Y.; Xu, H.; Wang, Z.; Zhang, X. Dual Redox Responsive Assemblies Formed from Diselenide Block Copolymers. J. Am. Chem. Soc. 2010, 132, 442−443. (2) Cao, W.; Wang, L.; Xu, H. Selenium/tellurium containing polymer materials in nanobiotechnology. Nano Today 2015, 10, 717− 736. (3) Wei, C.; Zhang, Y.; Xu, H.; Xu, Y.; Xu, Y.; Lang, M. Well-defined labile diselenide-centered poly(ε-caprolactone)-based micelles for activated intracellular drug release. J. Mater. Chem. B 2016, 4, 5059− 5067. (4) Liu, J.; Pang, Y.; Zhu, Z.; Wang, D.; Li, C.; Huang, W.; Zhu, X.; Yan, D. Therapeutic Nanocarriers with Hydrogen Peroxide-Triggered Drug Release for Cancer Treatment. Biomacromolecules 2013, 14, 1627−1636. (5) Cao, W.; Zhang, X.; Miao, X.; Yang, Z.; Xu, H. γ-Ray-Responsive Supramolecular Hydrogel Based on a Diselenide-Containing Polymer and a Peptide. Angew. Chem., Int. Ed. 2013, 52, 6233−6237. (6) Luan, J.; Shen, W.; Chen, C.; Lei, K.; Yu, L.; Ding, J. Seleniumcontaining thermogel for controlled drug delivery by coordination competition. RSC Adv. 2015, 5, 97975−97981. (7) Rotruck, J. T.; Pope, A. L.; Ganther, H. E.; Swanson, A. B.; Hafeman, D. G.; Hoekstra, W. G. Selenium: Biochemical Role as a Component of Glutathione Peroxidase. Science 1973, 179, 588. (8) Misra, S.; Boylan, M.; Selvam, A.; Spallholz, J. E.; Bjornstedt, M. Redox-Active Selenium Compounds-From Toxicity and Cell Death to Cancer Treatment. Nutrients 2015, 7, 3536−3556. (9) Brozmanova, J.; Manikova, D.; Vlckova, V.; Chovanec, M. Selenium: a double-edged sword for defense and offence in cancer. Arch. Toxicol. 2010, 84, 919−938. (10) Hollinger, J.; Jahnke, A. A.; Coombs, N.; Seferos, D. S. Controlling Phase Separation and Optical Properties in Conjugated Polymers through Selenophene−Thiophene Copolymerization. J. Am. Chem. Soc. 2010, 132, 8546−8547. (11) Ma, N.; Li, Y.; Ren, H.; Xu, H.; Li, Z.; Zhang, X. Seleniumcontaining block copolymers and their oxidation-responsive aggregates. Polym. Chem. 2010, 1, 1609−1614. (12) Wei, C.; Zhang, Y.; Song, Z.; Xia, Y.; Xu, H.; Lang, M. Enhanced bioreduction-responsive biodegradable diselenide-containing poly(ester urethane) nanocarriers. Biomater. Sci. 2017, 5, 669−677. 339

DOI: 10.1021/acsmacrolett.8b00039 ACS Macro Lett. 2018, 7, 336−340

Letter

ACS Macro Letters (13) Tian, Y. F.; Zheng, J.; Tang, X. L.; Ren, Q. G.; Wang, Y. J.; Yang, W. L. Near-Infrared Light-Responsive Nanogels with DiselenideCross-Linkers for On-Demand Degradation and Triggered Drug Release. Part. Part. Syst. Charact. 2015, 32, 547−551. (14) Wang, Y.; Deng, Y.; Luo, H.; Zhu, A.; Ke, H.; Yang, H.; Chen, H. Light-Responsive Nanoparticles for Highly Efficient Cytoplasmic Delivery of Anticancer Agents. ACS Nano 2017, 11, 12134−12144. (15) Liu, J.; Pang, Y.; Chen, J.; Huang, P.; Huang, W.; Zhu, X.; Yan, D. Hyperbranched polydiselenide as a self assembling broad spectrum anticancer agent. Biomaterials 2012, 33, 7765−7774. (16) Ji, S. B.; Cao, W.; Yu, Y.; Xu, H. P. Visible-Light-Induced SelfHealing Diselenide-Containing Polyurethane Elastomer. Adv. Mater. 2015, 27, 7740−7745. (17) Ji, S.; Fan, F.; Sun, C.; Yu, Y.; Xu, H. Visible Light-Induced Plasticity of Shape Memory Polymers. ACS Appl. Mater. Interfaces 2017, 9, 33169−33175. (18) Gao, F.; Pan, X.; Zhu, J.; Zhang, Z.; Zhang, W.; Zhu, X. Facile synthesis of well-defined redox responsive diselenide-labeled polymers via organoselenium-mediated CRP and aminolysis. Polym. Chem. 2015, 6, 1367−1372. (19) Fan, C.; Ding, C.; Pan, X.; Zhang, Z.; Zhu, J.; Zhu, X. A Straightforward Method for Preparing Well-Defined Responsive Diselenide-Containing Polymers Based on ATRP. Macromol. Rapid Commun. 2015, 36, 903−908. (20) Ding, C.; Fan, C.; Pan, X.; Zhang, Z.; Zhu, J.; Zhu, X. Selenium borohydride reaction as a versatile platform for the straightforward preparation of selenide-containing topological polymers. Polym. Chem. 2017, 8, 3958−3964. (21) Ren, H.; Wu, Y.; Ma, N.; Xu, H.; Zhang, X. Side-chain seleniumcontaining amphiphilic block copolymers: redox-controlled selfassembly and disassembly. Soft Matter 2012, 8, 1460−1466. (22) Steinbach, T.; Ritz, S.; Wurm, F. R. Water-Soluble Poly(phosphonate)s via Living Ring-Opening Polymerization. ACS Macro Lett. 2014, 3, 244−248. (23) Lonnecker, A. T.; Lim, Y. H.; Wooley, K. L. Functional Polycarbonate of a d-Glucal-Derived Bicyclic Carbonate via Organocatalytic Ring-Opening Polymerization. ACS Macro Lett. 2017, 6, 748−753. (24) Park, N. H.; Fevre, M.; Voo, Z. X.; Ono, R. J.; Yang, Y. Y.; Hedrick, J. L. Expanding the Cationic Polycarbonate Platform: Attachment of Sulfonium Moieties by Postpolymerization Ring Opening of Epoxides. ACS Macro Lett. 2016, 5, 1247−1252. (25) Feng, J.; Zhuo, R.; Zhang, X. Construction of functional aliphatic polycarbonates for biomedical applications. Prog. Polym. Sci. 2012, 37, 211−236. (26) Mespouille, L.; Coulembier, O.; Kawalec, M.; Dove, A. P.; Dubois, P. Implementation of metal-free ring-opening polymerization in the preparation of aliphatic polycarbonate materials. Prog. Polym. Sci. 2014, 39, 1144−1164. (27) Ma, Q.; Lei, K.; Ding, J.; Yu, L.; Ding, J. Design, synthesis and ring-opening polymerization of a new iodinated carbonate monomer: a universal route towards ultrahigh radiopaque aliphatic polycarbonates. Polym. Chem. 2017, 8, 6665−6674. (28) Venkataraman, S.; Ng, V. W. L.; Coady, D. J.; Horn, H. W.; Jones, G. O.; Fung, T. S.; Sardon, H.; Waymouth, R. M.; Hedrick, J. L.; Yang, Y. Y. A Simple and Facile Approach to Aliphatic N-Substituted Functional Eight-Membered Cyclic Carbonates and Their Organocatalytic Polymerization. J. Am. Chem. Soc. 2015, 137, 13851−13860. (29) Sanders, D. P.; Fukushima, K.; Coady, D. J.; Nelson, A.; Fujiwara, M.; Yasumoto, M.; Hedrick, J. L. A Simple and Efficient Synthesis of Functionalized Cyclic Carbonate Monomers Using a Versatile Pentafluorophenyl Ester Intermediate. J. Am. Chem. Soc. 2010, 132, 14724−14726. (30) Wolinsky, J. B.; Ray, W. C.; Colson, Y. L.; Grinstaff, M. W. Poly(carbonate ester)s Based on Units of 6-Hydroxyhexanoic Acid and Glycerol. Macromolecules 2007, 40, 7065−7068. (31) Barcan, G. A.; Zhang, X.; Waymouth, R. M. Structurally Dynamic Hydrogels Derived from 1,2-Dithiolanes. J. Am. Chem. Soc. 2015, 137, 5650−5653.

(32) Tempelaar, S.; Mespouille, L.; Coulembier, O.; Dubois, P.; Dove, A. P. Synthesis and post-polymerisation modifications of aliphatic poly(carbonate)s prepared by ring-opening polymerisation. Chem. Soc. Rev. 2013, 42, 1312−1336. (33) Wang, H.; Su, W.; Zhang, C.; Luo, X.; Feng, J. Biocatalytic Fabrication of Fast-Degradable, Water-Soluble Polycarbonate Functionalized with Tertiary Amine Groups in Backbone. Biomacromolecules 2010, 11, 2550−2557. (34) Yamamoto, Y.; Kaihara, S.; Toshima, K.; Matsumura, S. HighMolecular-Weight Polycarbonates Synthesized by Enzymatic ROP of a Cyclic Carbonate as a Green Process. Macromol. Biosci. 2009, 9, 968− 978. (35) Feng, J.; Wang, H.; Zhang, X.; Zhuo, R. Investigation on lipasecatalyzed solution polymerization of cyclic carbonate. Eur. Polym. J. 2009, 45, 523−529. (36) Wei, C.; Zhang, Y.; Yan, B.; Du, Z.; Lang, M. A Versatile Strategy to Main Chain Sulfur/Selenium-Functionalized Polycarbonates by Macro-Ring Closure of Diols and Subsequent Ring-Opening Polymerization. Chem. - Eur. J. 2018, 24, 789−792. (37) Kricheldorf, H. R. Macrocycles. 21. Role of Ring−Ring Equilibria in Thermodynamically Controlled Polycondensations. Macromolecules 2003, 36, 2302−2308. (38) Gross, R. A.; Kumar, A.; Kalra, B. Polymer synthesis by in vitro enzyme catalysis. Chem. Rev. 2001, 101, 2097−2124. (39) Luo, X.; Feng, J.; Wang, H.; Su, W.; Zhang, X.; Zhuo, R. Highly efficient enzymatic catalysis for cyclocarbonate polymerization. Polym. J. 2010, 42, 722−727. (40) Kumar, A.; Kalra, B.; Dekhterman, A.; Gross, R. A. Efficient Ring-Opening Polymerization and Copolymerization of ε-Caprolactone and ω-Pentadecalactone Catalyzed by Candida antartica Lipase B. Macromolecules 2000, 33, 6303−6309. (41) Zhang, J.; Xiao, Y.; Xu, H.; Zhou, C.; Lang, M. Synthesis of welldefined carboxyl poly(ε-caprolactone) by fine-tuning the protection group. Polym. Chem. 2016, 7, 4630−4637. (42) Dove, A. P. Organic Catalysis for Ring-Opening Polymerization. ACS Macro Lett. 2012, 1, 1409−1412. (43) Xu, H.; Cao, W.; Zhang, X. Selenium-Containing Polymers: Promising Biomaterials for Controlled Release and Enzyme Mimics. Acc. Chem. Res. 2013, 46, 1647−1658. (44) Park, N. H.; Voo, Z. X.; Yang, Y. Y.; Hedrick, J. L. Convergent Approach to Boronic Acid Functionalized Polycarbonates: Accessing New Dynamic Material Platforms. ACS Macro Lett. 2017, 6, 252−256. (45) Herzberger, J.; Fischer, K.; Leibig, D.; Bros, M.; Thiermann, R.; Frey, H. Oxidation-Responsive and “Clickable” Poly(ethylene glycol) via Copolymerization of 2-(Methylthio)ethyl Glycidyl Ether. J. Am. Chem. Soc. 2016, 138, 9212−9223.

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