Benzodioxinone Photochemistry in Macromolecular Science: Progress

Nov 30, 2017 - This paper reviews the photoinduced reactions of benzodioxinones and how they function in polymer synthesis and UV curing applications...
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Benzodioxinone Photochemistry in Macromolecular Science: Progress, Challenges, and Opportunities Mehmet Atilla Tasdelen*,† and Yusuf Yagci*,‡,§ †

Department of Polymer Engineering, Faculty of Engineering, Yalova University, 77200 Yalova, Turkey Department of Chemistry, Istanbul Technical University, Maslak, TR-34469 Istanbul, Turkey § Center of Excellence for Advanced Materials Research (CEAMR) and Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia ‡

ABSTRACT: This paper reviews the photoinduced reactions of benzodioxinones and how they function in polymer synthesis and UV curing applications. The mechanistic characteristics of the ketene and benzophenone production from the photolysis of benzodioxinone indicate that, under certain conditions, each intermediate may undergo further reactions expedient for the formation of various polymeric structures. While ketenes are efficient contributors to stepgrowth polymerization when subjected to reaction with the compounds possessing hydroxyl or amine groups, the released benzophenone can be utilized as a photoinitiator in both the free radical and cationic polymerizations. It has been shown that the photolysis of heterobifunctional monomers equipped with benzodioxinone and aliphatic hydroxyl groups leads to the formation of oligoesters with a narrow molecular weight distribution. We also validated the photochemical ability of benzodioxinone to induce the synthesis of block and graft copolymers, hybrid and branched polymers, and cross-linked monofunctional vinyl monomers or hydroxyl group-containing linear polymers.

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Thermally generated ketenes from Meldrum’s acid derivatives are stable, robust, and modular and can be used for the synthesis of a wide range of macromolecular architectures;6 thermally generated (220 °C) reactive bisketenes were used as building blocks in the presence of alcohols or phenols for the synthesis of various high molecular weight polyesters.7 The combination of orthogonal Meldrum’s acid with nitrile N-oxide chemistry allowed for the successful functionalization of polymer or glass surfaces under catalyst-free conditions.8 A recent review9 highlighted the utility of ketene chemistry employing classical methods with fascinating synthetic potential in polymer science. However, this article will primarily focus on benzodioxinone chemistry generating ketenes by photochemical means. In organic synthesis, α-oxoketenes are very reactive species that achieve high synthetic utility.10 They rearrange and react remarkably in concerted additions involving the α-oxo and ketenyl groups. Quino-ketenes generated from benzodioxinones are an important class of α-oxoketenes.11 The two notably reactive compounds, namely, quino-ketene and benzophenone, were simply generated by mild UV irradiation at room temperature. The formation of a quino-ketene

he scientific literature already lists numerous favorable and technologically valuable precursors for organic reaction applications in macromolecular science. For over a century, ketenes have been utilized as excellent precursors in various organic reactions, such as [2 + 2] and [4 + 2] cyclo, electrophilic, and nucleophilic additions and nucleophilic SN2 substitutions. The [2 + 2] cycloadditions of ketene with imine that led to the formation of a β-lactam derivative corroborate their influence in organic chemistry since their discovery in 1905 by Hermann Staudinger,1 as this emerged as the first synthetic antibiotic compound (penicillin).3 Ketenes have a middle sp carbon atom with a CC double and an extra carbonyl CO bond with right angles. Due to their instability (susceptible to homopolymerization and oxidation reactions), ketenes are typically generated in situ via various chemical processes, e.g., oxygenation, carbonylation, dioxinone thermolysis, ultrasonication of β-lactams, ring opening of cyclobutenones, decomposition of carboxylic acids and their derivatives, and photolysis of diazo-ketones and benzodioxinones.2 Upon their discovery, several forms of ketenes, such as bisketenes, haloketenes and α-oxoketenes, have been used in various organic reactions.4 One example is the esterification of long-lived bisketene with a poly(ethylene glycol) monomethyl ether as a nucleophilic polymer, which led to the formation of a monotelechelic ketene polymer.5 © XXXX American Chemical Society

Received: October 5, 2017 Accepted: November 29, 2017

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photochemical means, has been scarcely investigated.14 In this context, it is worth mentioning that the isocyanates, which contain a cumulated system of double bonds (NCO) similar to ketenes, have been used abundantly in step-growth polymerization.15 While bisketenes can be quantitatively obtained in a stable and isolable form, there are a few studies using bisketenes with diols or diamines as starting materials for the synthesis of polyesters and polyamides. In a recent report,16 bifunctional benzodioxinone derivatives containing both a masked ketene and a sterically hindered alcohol group in their structures were utilized in photoinitiated step-growth polymerization. This way, a true polyester synthesis was achieved for the first time by a photochemical means. Upon UV irradiation, the 5-(3-hydroxypropoxy)-2,2-diphenyl-4Hbenzo[d][1,3]dioxin-4-one (HDPD) liberated a highly reactive ketene intermediate that readily reacted with an active alcohol group to produce an ester bond. Mild light irradiation at the near-UV region was already applied to the process using the 7(3-hydroxypropoxy)-2,2-diphenyl-4H-naphtho[2,3-d][1,3]dioxin-4-one compound, which has extended optical properties from the introduced naphthalene ring. Studies under different experimental conditions revealed that, in all cases, the oligoesters containing 3−8 repeating units with relatively low molecular weight distributions were formed (Scheme 2). The

intermediate was identified by using time-resolved infrared spectroscopy, and its possible reactions with diethylamine, methanol, and water were comprehensively investigated in the literature. Apparently, their products are salicylic amide, ester, and acid (Scheme 1). On the other hand, the released benzophenone compound can be utilized as a photoinitiator in free radical and free radical-promoted cationic polymerizations. Scheme 1. Photogeneration of Quino-ketene and Benzophenone from Benzodioxinone and Their Possible Reactions

Scheme 2. Photoinitiated Step-Growth Polymerization of 5(3-Hydroxypropoxy)-2,2-diphenyl-4H-benzo[d][1,3]dioxin4-one

Compared to conventional methods, the generation of ketenes by the photochemical process has the advantage of being possible at low temperatures, especially at room temperature, and provides spatiotemporally controlled, ecofriendly, and economic conditions with low-energy consumption.12 A mild photochemical activation of benzodioxinones in the presence of anilines, phenols, and alcohols enables the synthesis of a number of salicylic amide and ester derivatives. In the case of benzodioxinone with 1-adamantanol or 2,6diisopropylaniline, the corresponding ester and amide were obtained with 77 and 79% yields, respectively.13 The desired quino-ketene compounds were directly formed via either a photochemical [4 + 2] cycloreversion process or a homolytic C−O bond cleavage reaction that generates a biradical intermediate followed by a thermal decomposition process. A model study using 2,2-dialkyl-substituted benzodioxinones was undertaken to elucidate the underlying mechanisms. Due to their weak optical properties, the reactions likely proceed through the formation of a biradical intermediate, which provides more stable phenyl substitution compared to alkyl substitution.13 The purpose of this article is to survey the newly developed benzodioxinone photochemistry reaction and its use in photoinduced step-growth, free radical, and cationic chain polymerization processes. Special emphasis will be devoted to the curing applications and polymer modifications such as functionalization, blocking, grafting, and cross-linking. Typically, two major polymerization reactions will be discussed: step-growth and chain polymerization processes that simply link small molecules and monomers, respectively. Although photoinitiated polymerization is well established and the mechanistic details have been evaluated, the corresponding step-growth process, in which a macromolecule is obtained by

limited molecular weight observed in this step-growth reaction may be because for the release of each ketene molecule, which can react with the hydroxyl groups, one photon is required. Prolonged irradiation times and the use of certain catalysts, such as metal oxides and metal−organic salts and strong acids,17 may favor further chain growth. The monomer concentration was a direct influence on the degree of polymerization, and although the monomer concentration was higher than [M] = 1 mol L−1, only dimeric and trimeric products were obtained. This process was quite chemoselective and produced polymers with narrow polydispersity because of its limited photochemical activation of the growing chain. The approach was not limited to polyester formation, and at least in principle, polyamides can also be prepared by using bifunctional amines as nucleophiles to react with the photochemically generated bisketenes in a similar manner. The characteristic structural feature of the benzodioxinone compounds is the liberation of two reactive intermediates, namely, a ketene and a benzophenone, upon UV or visible-light irradiation. These intermediates can also be utilized as a photoinitiator in free radical polymerization and a cross-linker in UV curing applications.18 Benzophenone is a widely used Type II photoinitiator because of its high quantum yield 1393

DOI: 10.1021/acsmacrolett.7b00788 ACS Macro Lett. 2017, 6, 1392−1397

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ACS Macro Letters efficiency for radical generation through hydrogen abstraction from a suitable hydrogen donor.19 Photodissociation of the benzodioxinone as well as the in situ generation of benzophenone were monitored by means of UV/vis spectroscopy and gas chromatography−mass spectrometry analysis. As shown in Figure 1a, the characteristic sets of UV/vis spectra

Figure 1. (a) Typical UV spectral change of benzodioxinone irradiation at λ = 350 nm under nitrogen and (b) plots concentration of benzodioxinone (■) and benzophenone (▲) irradiation time.18 Reprinted with permission. Copyright © 2006 Elsevier.

Scheme 3. Photoinitiated Free Radical and Cationic Polymerizations by Using Benzodioxinone in a Stepwise Two-Photon Absorption Process

the addition of the photoinitiator and the actual photoinitiation process. In another study, a novel benzodioxinone compound, 2(benzo[d][1,3]dioxol-5-yl)-9-hydroxy-2-phenyl-4H-naphtho[2,3-d][1,3]dioxin-4-one possessing naphthodioxinone and 1,3benzodioxole moieties was designed for photoinitiated free radical polymerization.21 This compound provides a variety of advantages over traditional benzodioxinones. The 1,3-benzodioxole group enables the polymerization to proceed without an additional hydrogen donor and in the presence or absence of air. The naphthodioxinone group shows a more favorable absorption characteristic (376 nm) compared to the 1,3benzodioxole (316 nm), such that this photoinitiating system can be utilized in a two-photon polymerization reaction to fabricate a wide variety of micro- and nanodevices. There was also an effort to make use of all the products (ketene and benzophenone) formed from the photolysis of benzodioxinone.22 For this purpose, the bisbenzodioxinone compound was structurally designed to generate both bisketene as cross-linker and corresponding benzophenone as Type II photoinitiator. Upon UV light irradiation of this compound, a polymer network was successfully prepared from monofunctional vinyl monomers containing pendant hydroxyl groups, such as 2-hydroxyethyl methacrylate (HEMA), without the use of a conventional initiator and cross-linker. While benzophenone was able to initiate free radical polymerization for HEMA in the presence of a tertiary amine, the simultaneous interchain esterification of bisketene with HEMA’s hydroxyl groups led to the transformation of linear polymer chains into a network. The photo-cross-linking process following the change of the O−H band at 3600−3200 cm−1 was also investigated with FTIR spectroscopy. According to the FT-IR analysis, the monomer conversion reached over 80% after 80 min irradiation, whereas approximately 30% of the hydroxyl groups was consumed. This photoinitiating system was also applied to cross-link the linear polymer containing pendant hydroxyl groups and poly(methyl methacrylate)-co-poly(2-hydroxyethyl methacrylate) (PMMA-co-PHEMA) upon UV light irradiation in the presence of bisbenzodioxinone.23 A very simple experimental setup was designed to demonstrate the value of this system in coatings and photoresist applications. A mixture of copolymer and bisbenzodioxinone in tetrahydrofuran was prepared and cast as film to be used in a photoresist coating through a mask. While the UV-light-exposed parts became insoluble from the

on of vs by

were measured during UV irradiation (nominally at λ = 350 nm) of the benzodioxinone in methylene chloride solution under nitrogen. The absorption bands for benzodioxinone at 325 nm rapidly diminished, whereas the absorption bands at approximately 360 nm, corresponding to benzophenone, gradually increased. Furthermore, photolysis products were also analyzed by GC-MS analysis; plots of the benzodioxinone to benzophenone concentrations versus irradiation time are shown in Figure 1b. According to the GC-MS analysis, it can be concluded that the photodecomposition of benzodioxinone followed first-order kinetics under the experimental conditions applied. The subsequent step was the classical radical formation via the Norrish Type II reaction; the excited benzophenone abstracted a hydrogen from the tertiary amines to generate two radicals (ketyl and amino alkyl radicals). The free radical polymerization of methyl methacrylate (MMA) was initiated by an amino alkyl radical, while the ketyl radical was not reactive toward the monomer due to its steric hindrance and delocalization of unpaired electrons (Scheme 3). Amino alkyl radicals are particularly suitable for the polymerization of acrylates and methacrylates.20 In this initiating system, benzophenone was concomitantly formed only after UV irradiation of benzodioxinone, whereupon it could serve as a Type II photoinitiator. This circumstance not only increases the shelf life of the photoinitiator but also adjusts the time between 1394

DOI: 10.1021/acsmacrolett.7b00788 ACS Macro Lett. 2017, 6, 1392−1397

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ACS Macro Letters interchain esterification reaction between photochemically generated bisketenes and pendant hydroxyl groups, the unexposed regions were easily removed with a suitable solvent after the process. To gain more insight into the photo-crosslinking process, a model study was performed using a monofunctional benzodioxinone in order to obtain a soluble side-chain-functionalized polymer, which could then be analyzed with spectral thermal analysis. The appearance of peaks belonging to the aromatic protons of benzodioxinone and change of the glass transition temperature of the copolymers confirmed the successful photochemical modification. As a result, this photo-cross-linking process is a versatile method for modifying both natural and synthetic polymers containing hydroxyl groups in order to enable sufficient solubility of the components. Self-condensing vinyl polymerization (SCVP) is one of the most versatile methods for the synthesis of dendrimers and branched polymers due to its operational simplicity, suitability for various monomer types, better branching density and distribution, and lower gelation risk. This method relies on the polymerization of inimers, a special kind of vinyl monomer, possessing both a polymerizable group and an initiating site in one molecule. In a recent study, benzodioxinone photochemistry was also facilitated in the SCVP of MMA with two different inimers, HEMA and 2-(dimethylamino)ethyl methacrylate (DMAEMA).24 In the case of HEMA, initiating radicals were formed via the hydrogen abstraction reaction of excited benzophenone released from bisbenzodioxinone with carbon atoms located next to the hydroxyl groups. However, HEMA’s hydroxyl group simultaneously reacted with concomitantly generated bisketene to create additional branching sites. Because of the contribution of the two processes, both hydrogen abstraction and ketene chemistry, higher branching was attained, and rapid gelation occurred in a short period. To reduce the branching density, the second inimer, DMAEMA, was used by inhibiting the ketene chemistry reaction. Thus, only the hydrogen abstraction process was operative, and branched polymers with relatively lower branching densities were achieved (Scheme 4). The influence of inimer concentration and irradiation time on the branching density was also investigated. As expected, higher DMAEMA concentration and longer irradiation time resulted in the formation of polymers with relatively higher molecular weights and branching densities. It should also be noted that the longer irradiation time (greater than 225 min) also caused gel formation due to radical coupling reactions in viscous media. Apart from its synthetic capacity in photoinduced free-radical polymerization, benzodioxinone chemistry has also been utilized to initiate the cationic polymerization of epoxy monomers.25 It is well-known that excited benzophenone is extensively used to reduce an onium salt through electron transfer reactions forming cationic species that are capable of initiating cationic polymerization. Benzodioxinone and naphthodioxinone can facilitate the initiation of another mode of photopolymerization, namely, cationic polymerization in a stepwise two-photon absorption process. In the case of our reaction, the first photon absorption was used to release the desired benzophenone from benzodioxinone or naphthodioxinone, while the second photon was absorbed by the liberated benzophenone to generate radicals through successive electron transfer and proton abstraction reactions. These radicals were then oxidized to form a carbocation in the presence of an

Scheme 4. Synthesis of Branched Polymers Using a Combination of Self-Condensing Vinyl Polymerization and Benzodioxinone Photochemistry

iodonium salt to initiate the cationic polymerization of cyclohexene oxide (Scheme 3). The polymerization kinetics of this system were compared with the polymerization initiated by neat benzophenone under identical conditions. Remarkably, a short induction period was detected in the case of benzodioxinone, providing clear evidence for the two-photon nature of the process. The coupling ability of benzodioxinone photochemistry was also tested for the synthesis of graft copolymers.26 First, a benzodioxinone end-functional polystyrene and a PMMA-coPHEMA copolymer containing 20 mol % hydroxyl groups were independently prepared by atom transfer radical polymerization (ATRP); these polymers were then coupled through a photoinduced esterification reaction via the “grafting” method. Although a moderate grafting efficiency (58%) was reported, this method provides several advantages such as being orthogonal, requiring no additional catalyst, and simplifying the reaction conditions. These advantages make this method particularly beneficial for the modification of many commercially available natural and synthetic polymers possessing hydroxyl functionality. By taking advantage of benzodioxinone photochemistry, a versatile and user-friendly route was demonstrated for the grafting of benzodioxinone end-functional polystyrene onto the silanol groups of neat silica particles.27 Compared to existing photografting methods, which require multistep reactions, this system is more useful and provides processing advantages including mild conditions starting with unmodified silicate particles. Lastly, benzodioxinone photochemistry combined with photoinduced copper(I)-catalyzed alkyne−azide cycloaddition (CuAAC) proved useful for the synthesis of block copolymers from commercially available one-pot procedures (Scheme 5).28 This combination brings with it several benefits of photo1395

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Scheme 5. Synthesis of Block Copolymer by Combining Photoinduced CuAAC and Benzodioxinone Chemistries in Simultaneous and Sequential Modes

The authors declare no competing financial interest.

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(1) Staudinger, H. Keteneine neue körperklasse. Ber. Dtsch. Chem. Ges. 1905, 38 (2), 1735−1739. (2) (a) Staudinger, H.; Mitteilung, L. Ü ber additions- und polymerisationsreaktionen des dimethylketens. 1. Ü ber neue verbindungen des dimethylketens mit kohlendioxyd. Helv. Chim. Acta 1925, 8 (1), 306−332. (b) Staudinger, H. Ü ber ketene. 4. Mitteilung: Reaktionen des diphenylketens. Ber. Dtsch. Chem. Ges. 1907, 40 (1), 1145−1148. (c) Staudinger, H.; Klever, H. W. Ü ber ketene. 5. Mitteilung. Reaktionen des dimethylketens. Ber. Dtsch. Chem. Ges. 1907, 40 (1), 1149−1153. (3) (a) Staudinger, H. Zur kenntniss der ketene. Diphenylketen. Justus Liebigs Ann. Chem. 1907, 356 (1−2), 51−123. (b) Tidwell, T. T. Hugo (ugo) schiff, schiff bases, and a century of β-lactam synthesis. Angew. Chem., Int. Ed. 2008, 47 (6), 1016−1020. (4) (a) Sung, K.; Tidwell, T. T. Theoretical study of the reactivity of ketene with free radicals. J. Org. Chem. 1998, 63 (26), 9690−9697. (b) Agarwal, S. Chemistry, chances and limitations of the radical ringopening polymerization of cyclic ketene acetals for the synthesis of degradable polyesters. Polym. Chem. 2010, 1 (7), 953−964. (c) Allen, A. D.; Tidwell, T. T. Ketenes and other cumulenes as reactive intermediates. Chem. Rev. 2013, 113 (9), 7287−7342. (d) Paull, D. H.; Weatherwax, A.; Lectka, T. Catalytic, asymmetric reactions of ketenes and ketene enolates. Tetrahedron 2009, 65 (34), 6771−6803. (e) Tidwell, T. T. Ketene chemistry after 100 years: Ready for a new century. Eur. J. Org. Chem. 2006, 3, 563−576. (f) Seikaly, H. R.; Tidwell, T. T. Addition-reactions of ketenes. Tetrahedron 1986, 42 (10), 2587−2613. (g) Moore, H. W.; Decker, O. H. W. Conjugated ketenes - new aspects of their synthesis and selected utility for the synthesis of phenols, hydroquinones, and quinones. Chem. Rev. 1986, 86 (5), 821−830. (h) Tidwell, T. T. Ketene chemistry - the 2nd golden-age. Acc. Chem. Res. 1990, 23 (9), 273−279. (i) Tidwell, T. T. The first century of ketenes (1905−2005): The birth of a versatile family of reactive intermediates. Angew. Chem., Int. Ed. 2005, 44 (36), 5778−5785. (5) (a) Rafai Far, A. Ketenes in polymer-assisted synthesis. Angew. Chem., Int. Ed. 2003, 42 (21), 2340−2348. (b) Rafai Far, A.; Tidwell, T. T. Soluble polymer-bound allenecarboxylates: Useful beta-ketoester equivalents. J. Comb. Chem. 1999, 1 (6), 458−460. (6) (a) Burke, D. J.; Kawauchi, T.; Kade, M. J.; Leibfarth, F. A.; McDearmon, B.; Wolffs, M.; Kierstead, P. H.; Moon, B.; Hawker, C. J. Ketene-based route to rigid cyclobutanediol monomers for the replacement of bpa in high performance polyesters. ACS Macro Lett. 2012, 1 (11), 1228−1232. (b) Jung, H.; Leibfarth, F. A.; Woo, S.; Lee, S.; Kang, M.; Moon, B.; Hawker, C. J.; Bang, J. Efficient surface neutralization and enhanced substrate adhesion through ketene mediated crosslinking and functionalization. Adv. Funct. Mater. 2013, 23 (12), 1597−1602. (c) Leibfarth, F. A.; Wolffs, M.; Campos, L. M.; Delany, K.; Treat, N.; Kade, M. J.; Moon, B.; Hawker, C. J. Lowtemperature ketene formation in materials chemistry through molecular engineering. Chem. Sci. 2012, 3 (3), 766−771. (d) Diaz, Y. J.; Page, Z. A.; Knight, A. S.; Treat, N. J.; Hemmer, J. R.; Hawker, C. J.; de Alaniz, J. R. A versatile and highly selective colorimetric sensor for the detection of amines. Chem. - Eur. J. 2017, 23 (15), 3562−3566. (e) Hemmer, J. R.; Poelma, S. O.; Treat, N.; Page, Z. A.; Dolinski, N. D.; Diaz, Y. J.; Tomlinson, W.; Clark, K. D.; Hooper, J. P.; Hawker, C. J.; de Alaniz, J. R. Tunable visible and near infrared photoswitches. J. Am. Chem. Soc. 2016, 138 (42), 13960−13966. (f) Leibfarth, F. A.; Schneider, Y.; Lynd, N. A.; Schultz, A.; Moon, B.; Kramer, E. J.; Bazan, G. C.; Hawker, C. J. Ketene functionalized polyethylene: Control of cross-link density and material properties. J. Am. Chem. Soc. 2010, 132 (42), 14706−14709. (g) Leibfarth, F. A.; Kang, M.; Ham, M.; Kim, J.; Campos, L. M.; Gupta, N.; Moon, B.; Hawker, C. J. A facile route to ketene-functionalized polymers for general materials applications. Nat. Chem. 2010, 2 (3), 207−212.

induced reactions, including orthogonality of the two reactions at specific wavelengths and the simplicity of being able to switch a light source on and off. Synthesis of the desired poly(ethylene glycol)-b-polystyrene copolymer was simple, using commercially available poly(ethylene glycol) methyl ether (mPEG) and easily accessible azide-functionalized polystyrene (PSt-N3) using alkyne functional benzodioxinone as a click linker.29 Upon UV irradiation of alkyne-functional benzodioxinone, the released alkyne-functional ketene intermediate directly reacted with the terminal hydroxyl of mPEG to form mPEG-Alkyne, whereas the corresponding benzophenone was also capable of reducing Cu(II) into Cu(I) enabling the activation of the CuAAC reaction between mPEG-Alkyne and PSt-N3. Both simultaneous and sequential modes allowed the synthesis of corresponding block copolymers with excellent coupling efficiencies higher than 90%. Various photoreactions of benzodioxinones useful for the synthesis of oligoesters, linear, branched, and cross-linked polymers, block and graft copolymers, and polymer/silica composites were demonstrated. Polyester formation was achieved through photolysis of benzodioxinones structurally equipped with aliphatic hydroxyl groups. Ester formation was achieved through the reaction of ketenes with hydroxyl groups. The other photolysis product, benzophenone, is also useful for initiating polymerization, either free radical polymerization and cross-linking reactions in the presence of hydrogen donors or cationic polymerization in the presence of oxidizing agents, such as iodonium salts. By taking advantage of concomitantly generated ketene and benzophenone compounds, the crosslinking of hydroxyl functional vinyl monomers or polymers was successfully achieved in the absence of a conventional photoinitiator and cross-linker. Furthermore, the benzodioxinone-end-functional linear polymer is easily grafted onto bare silica particles to generate corresponding hybrid composites in a manageable fashion. Overall, benzodioxinone chemistry is a simple, versatile, and efficient tool for the synthesis and modification of complex macromolecular architectures under ambient conditions.

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Mehmet Atilla Tasdelen: 0000-0002-7012-7029 Yusuf Yagci: 0000-0001-6244-6786 Author Contributions

Both authors contributed equally. 1396

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ACS Macro Letters

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DOI: 10.1021/acsmacrolett.7b00788 ACS Macro Lett. 2017, 6, 1392−1397