Synthesis of Hyperbranched Polymers by Photoinduced Metal-Free

Article Cite This: Macromolecules XXXX, XXX, XXX−XXX

Synthesis of Hyperbranched Polymers by Photoinduced Metal-Free ATRP Cansu Aydogan, Gorkem Yilmaz, and Yusuf Yagci* Department of Chemistry, Istanbul Technical University, Maslak, Istanbul, Turkey 34469

ABSTRACT: A novel synthetic strategy for the syntheses of hyperbranched homo and block copolymers was developed. By applying the photoinduced metal-free atom transfer radical polymerization (ATRP) using perylene as photocatalyst, monomer/ inimer pairs were transformed into hyperbranched polymer structures under visible light irradiation. Using the halide functional groups in thus-formed structures as initiating sites, further polymerizations were also performed to construct the secondary segments successfully. The strategy described here enables the synthesis of such complex polymeric structures by a simple procedure, under mild and metal-free conditions. All polymers were characterized by spectroscopic and chromatographic techniques.

■

INTRODUCTION Hyperbranched polymers have received significant interest in comparison to their corresponding linear analogous owing to their intrinsic characteristics such as higher solubility, reduced viscosity,1−3 and higher level of terminal functionality.4−6 Because of these particular characteristics, hyperbranched polymers are commonly utilized in different applications such as drug delivery systems, bioimaging agents, gene carriers, viscosity modifiers, catalyst supports, and hydrophobic surfaces.7−13 There are various synthetic approaches for the syntheses of hyperbranched polymers including (a) step-growth polymerization of ABx monomers, (b) self-condensing vinyl polymerization (SCVP) of AB monomers, and (c) ring-opening polymerization of latent ABx monomers.14−19 By selecting structurally suitable inimer, SCVP can successfully be applied to a wide variety of controlled polymerization systems such as living anionic polymerization,20 atom transfer radical polymerization (ATRP),17 reversible addition−fragmentation chain transfer polymerization,21−23 nitroxide-mediated polymerization,24 and group-transfer and ring-opening polymerization.25,26 Photoinduced processes have been commonly applied for various polymerization and modification processes as they offer excellent advantages in comparison to the conventional approaches such as low temperature conditions, low energy requirement, and temporal and spatial control over the chemical processes.27−35 Light-triggered processes have also © XXXX American Chemical Society

been applied to various organic reactions including click reactions, and their mechanistic details have been evaluated in detail.36−43 Photoinduced ATRP has recently become a central focus in synthetic polymer chemistry, as it permits low catalyst concentrations, mild conditions, and relatively easier experimentation.44−47 More recently, it was demonstrated that photochemical approaches provide option to accomplish ATRP even in the absence of inorganic catalysts.48 Phenothiazine derivatives,49−51 perylene,52,53 pyrene,54 phenoxazines,55 dihydrophenazines,56 and dye/amine systems57−59 were shown to catalyze ATRP under metal-free conditions by photochemical means. We have recently reported several photoinduced processes that can be used for the in situ synthesis of hyperbranched polymers. These approaches are generally based on the hydrogen60−62 or halide abstraction63 from the specially designed inimers by photoexcited Type II photoinitiators or manganese decacarbonyl, respectively (Scheme 1). It was also shown that the remaining functional groups can further be activated with the same process to yield block copolymers. Such complex structures possessing hyperbranched hydrophobic segment in the core and linear hydrophilic block Received: October 19, 2017 Revised: November 20, 2017

A

DOI: 10.1021/acs.macromol.7b02240 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

light exposure enabling to successfully form hyperbranched polymers under mild conditions by photoinduced metal-free ATRP.

Scheme 1. Syntheses of Hyperbranched Polymers by Using Photoinduced Processes

■

EXPERIMENTAL SECTION

Materials. Methyl methacrylate (MMA, 99%, Aldrich) and styrene (S, 99%, Aldrich) were passed through a column of basic alumina prior to use. Dimethylformamide (DMF, ≥99.8%, Aldrich), 2-(2-bromoisobutryloxy)ethyl methacrylate (BIBEM), methanol (MeOH; 99.9%, Merck), and silica gel 60 (0.040−0.063 mm, Merck) were used as received. Perylene (98%, Sigma-Aldrich) was crystallized from methanol prior to use. 4-Vinylbenzyl bromide (VBB) was synthesized according to the described literature procedures.68 Analysis. 1H NMR spectra were recorded on an Agilent NMR system VNMRS 500 spectrometer at room temperature in CDCl3 with Si(CH3)4 as an internal standard. The branching densities of the hyperbranched structures were calculated based on the measured molecular weights. Molecular weights were measured from a Viscotek GPCmax Autosampler system consisting of a pump module (GPCmax, Viscotek Corp., Houston, TX), a combined light scattering (Model 270 Dual Detector, Viscotek Corp.), and a refractive index (RI) detector (VE 3580, Viscotek Corp.). The light scattering detector (λ0 = 670 nm) included two scattering angles: 7° and 90°. The RI detector was calibrated with polystyrene standards. The GPC analyses were performed using tetrahydrofuran as eluent with a flow rate of 1 mL min−1 at 35 °C. Data were analyzed using Viscotek OmniSEC Omni-01 software. Photopolymerization. A general photopolymerization procedure for the syntheses of hyperbranched structures is given: MMA (0.5 mL, 4.69 mmol), inimer (either BIBEM or VBB, 5 mol %), photocatalyst (perylene, 0.5 mol %), and DMF (0.5 mL) were put in a glass tube. The reaction mixture was bubbled with dry nitrogen prior to irradiation at λ = 400−500 nm. The irradiations were performed by a Ker-Vis blue photoreactor equipped with six lamps (Philips TL-D 18 W) with a light intensity of 45 mW cm−2 as measured by a Delta Ohm model HD-9021 radiometer. At the end of polymerization, polymers were precipitated in methanol and dried under reduced pressure.

in the outer sphere were successfully used in drug delivery applications.64,65 An alternative approach concerns a modified version of SCVP involving the use of propargyl acrylate as a monomer in photoinitiated free radical copolymerization.66 The reactivity differences of acrylate and propargyl groups toward photochemically generated radicals resulted in the formation of hyperbranched polymers with clickable alkyne groups. The applied strategy can also be used for the synthesis of clickable hydrogels.67 The above-mentioned photochemical methodologies, however, involve conventional free radical polymerization yielding hyperbranced polymers with uncontrolled structures due to the transfer and termination reactions. In a previous study, we have shown that pyrene in the excited and excimer states reacts with alkyl halides to form initiator radicals leading to the formation of polymers with narrow polydispersities and controlled molecular weights.54 It seemed therefore appropriate to apply such controlled/living radical polymerization process for the preparation of hyperbranched polymers by SCVP. In the process, tertiary and benzylic bromide functional monomers were used as inimers, together with methyl methacrylate (MMA) and styrene (S), respectively. Perylene was used as photocatalyst, and the reactions were carried out under visible

Scheme 2. Photoinitiated Copolymerization of MMA and BIBEM in the Presence of Perylene by Metal-Free ATRP

B


Article

Macromolecules Table 1. Effect of Inimer Concentration on Photoinduced Metal-Free ATRP of MMA and BIBEMa inimer cont in feed [mol %]

conv [%]b

inimer cont in the polymer [mol %]c

Mn,GPC‑RI [g mol−1]d

Mn,GPC‑LS [g mol−1 ]e

RMf

DBg

Mw/Mnd

5 10 20 40

47 58 76 ∼100

9.2 14.3 26.5

28000 35100 41900 ∞

101200 177200 603900 ∞

0.27 0.19 0.07

0.12 0.21 0.39

2.7 4.3 6.2

Perylene (0.5% mol with respect to the total monomer mol), λ = 400−500 nm; t: 6 h at room temperature. bDetermined gravimetrically. Calculated from the 1H NMR. dWith refractive index detector. eWith light scattering detector. fRM = Mn,GPC‑RI/Mn,GPC‑LS. gDB = 2D/(2D + L), DB: degree of branching; D: integral area of the peaks of the branching units ((b + c)/4 as shown in Figure 1); L: integral area of the linear part ((a/3) as shown in Figure 1).69 a c

Table 2. Effect of Irradiation Time on Photoinduced Metal-Free ATRP of MMA and BIBEMa time (h)

conv [%]b


Mn,GPC‑RI [g mol−1]d

Mn,GPC‑LS [g mol−1]e

RMf

DBg

Mw/Mnd

3 6 12

60 76 100

20.4 26.5

27400 42000 ∞

78900 604000 ∞

0.34 0.06

0.33 0.39

3.7 6.2

MMA (79.5% mol), BIBEM (20.0% mol), perylene (0.5% mol), λ = 400−500 nm at room temperature. bDetermined gravimetrically. cCalculated from the 1H NMR. dWith refractive index detector. eWith light scattering detector. fRM = Mn,GPC‑RI/Mn,GPC‑LS. gDB = 2D/(2D + L), DB: degree of branching; D: integral area of the peaks of the branching units ((b + c)/4 as shown in Figure 1); L: integral area of the linear part ((a/3) as shown in Figure 1).69 a

Conversions for all samples were determined gravimetrically. The reaction conditions were identical for all the other polymerizations.

Table 3. Effect of Inimer Concentration on Photoinduced Metal-Free ATRP of S and VBBa

■

RESULTS AND DISCUSSION A novel metal-free photoinduced ATRP technique for the synthesis of poly(methyl methacrylate) (PMMA) and polystyrene (PS) hyperbranched polymers having bromo functionalities using perylene as a photocatalyst is developed. Applying the idea of metal free photoinduced ATRP to the SCVP strategy, syntheses of PMMA and PS hyperbranched polymers were successfully performed. In this approach, BIBEM and VBB were employed as inimer for the polymerization of MMA and S, respectively, in the presence of perylene under visible light. Excited-state perylene is responsible for the direct reduction of alkyl bromides to generate carbon-centered radicals for the polymerization of MMA and S, whereas BIBEM and VBB inimers composed of a vinyl moiety and a bromine functionality played a role to construct branching points. The overall procedure including activation and deactivation processes is depicted in Scheme 2. Typical polymerizations were also performed at different BIBEM and perylene concentrations and irradiation time. The results are summarized in Table 1. As can be seen, higher conversions and branching densities were obtained as the feed ratio of the inimer increases. After certain concentration of the inimer, gelation occurred due to extremely high branching arising from the high number of initiating radicals formed from the side chain alkyl halide. The effect of irradiation time on the process was also investigated (Table 2). As expected, by increasing the irradiation time, conversions, molecular weights, and branching densities are also increased. Prolonged irradiation times resulted in the formation of crosslinked polymers as a consequence of the inherent nature of SCVP. In order to expand the applicability of the process to structurally different monomers and inimers, similar polymerizations were conducted using S monomer and VBB inimer (Table 3). The results revealed that copolymerization of MMA and BIBEM displayed higher conversions and branching densities in comparison to the S/VBB couple, which might

inimer cont in feed [mol %]

conv [%]b

Mn,GPC‑RI [g mol−1]c

Mn,GPC‑LS [g mol−1 ]d

RMe

Mw/Mnc

5 10 20

8.0 8.2 9.1

4100 4700 4800

41000 48200 70100

0.10 0.09 0.07

3.1 3.4 3.3

Perylene (0.5 mol % with respect to the total monomer mol), λ = 400−500 nm; t: 6 h, at room temperature. bDetermined gravimetrically. cWith refractive index detector. dWith light scattering detector. e RM = Mn,GPC‑RI/Mn,GPC‑LS. a

be attributed to the possible quenching of the excited perylene with S. Additionaly, the propagation rate constant of S is lower than that of MMA (kp(MMA)/kp(S): 2.7/1.0). 1 H NMR analyses were performed to confirm the structures of the polymers. As can be seen from Figure 1a, both characteristic peaks of MMA and inimer were clearly detected from the spectra of hyperbranced polymer. The sharp peak appeared at 3.7 ppm corresponds to the main chain OCH3 protons of PMMA, whereas the peaks observed at 4.2 and 4.3 ppm belong to the ester protons of the inimer structure. The 1 H NMR spectrum of the PS based hyperbranched polymer also exhibited specific bands (Figure 1b). In order to prove that polymerization proceeds in a controlled manner and bromide functionalities remained at the chain ends, a control experiment was performed. For this purpose, the obtained hyperbranched polymer described above was used as a macroinitiator and S was used as monomer to form a block copolymer with hyperbranced PMMA core and linear PS block at the outer sphere (Scheme 3). The structure of the block copolymer was confirmed by 1H NMR analysis, which indicated characteristic peaks of both PMMA and PS (Figure 2). The benzylic bromide protons at the chain ends of the polystyrene segments was not detectable due to the possible overlapping with the esteric peaks of the inimer units at around 4.2−4.3 ppm. As can be seen from Figure 3, where GPC traces of the precursor PMMA and block copolymer are presented, the molecular weight of the initial polymer is shifted to higher C


Article

Macromolecules

Figure 1. 1H NMR spectra of the PMMA (a) and PS (b) based hyperbranched polymer.

Scheme 3. Synthesis of PMMAhyp-b-PS by Photoinduced Metal-Free ATRP

Figure 3. GPC chromatograms of hyperbranched PMMA (black) and PMMAhyp-b-PS (red).

Table 4. Effect of Inimer Structure on Photoinduced MetalFree ATRP of MMAa

Figure 2. 1H NMR spectrum of the PMMAhyp-b-PS block polymer.

molecular region and no unreacted hyperbranched polymer remained further confirming the chain-end fidelity of the hybranched polymers. The effect of type of inimer structure on the applied photoATRP process was also investigated under identical experimental conditions. In the case of VBB, comparatively lower conversion and molecular weight were attained due to the less structural similarity of the propagating chain ends and the initiating sites in the alkyl halide.

inimer

conv [%]b


VBB BIBEM

19 47

19.3 9.2

Mn,GPC‑RI Mn,GPC‑LS [g mol−1]d [g mol−1 ]e 12000 28000

74000 101200

RMf

Mw/Mnd

0.16 0.25

2.5 2.7

a

MMA (94.5 mol %) and 4-vinylbenzyl bromide (5.0 mol %), perylene (0.5 mol %), λ = 400−500 nm; t: 6 h at room temperature. b Determined gravimetrically. cCalculated from the 1H NMR. dWith refractive index detector. eWith light scattering detector. fRM = Mn,GPC‑RI/Mn,GPC‑LS.

■

CONCLUSION In conclusion, copolymers with controlled hyperbranched architectures have been prepared by visible-light-induced D


Article

Macromolecules

Polymethacrylates via Electrospraying. J. Polym. Sci., Part A: Polym. Chem. 2017, 55 (8), 1338−1344. (14) Inoue, K. Functional dendrimers, hyperbranched and star polymers. Prog. Polym. Sci. 2000, 25 (4), 453−571. (15) Yates, C. R.; Hayes, W. Synthesis and applications of hyperbranched polymers. Eur. Polym. J. 2004, 40 (7), 1257−1281. (16) Jikei, M.; Kakimoto, M.-A. Hyperbranched polymers: a promising new class of materials. Prog. Polym. Sci. 2001, 26 (8), 1233−1285. (17) Gaynor, S. G.; Edelman, S.; Matyjaszewski, K. Synthesis of Branched and Hyperbranched Polystyrenes. Macromolecules 1996, 29 (3), 1079−1081. (18) Fréchet, J. M. J.; Henmi, M.; Gitsov, I.; Aoshima, S.; Leduc, M. R.; Grubbs, R. B. Self-Condensing Vinyl Polymerization: An Approach to Dendritic Materials. Science 1995, 269 (5227), 1080−1083. (19) Sunder, A.; Hanselmann, R.; Frey, H.; Mulhaupt, R. Controlled synthesis of hyperbranched polyglycerols by ring-opening multibranching polymerization. Macromolecules 1999, 32 (13), 4240−4246. (20) Matsuo, A.; Watanabe, T.; Hirao, A. Synthesis of Well-Defined Dendrimer-like Branched Polymers and Block Copolymer by the Iterative Approach Involving Coupling Reaction of Living Anionic Polymer and Functionalization. Macromolecules 2004, 37 (17), 6283− 6290. (21) Wang, Z.; He, J.; Tao, Y.; Yang, L.; Jiang, H.; Yang, Y. Controlled Chain Branching by RAFT-Based Radical Polymerization. Macromolecules 2003, 36 (20), 7446−7452. (22) Luzon, M.; Boyer, C.; Peinado, C.; Corrales, T.; Whittaker, M.; Tao, L.; Davis, T. P. Water-Soluble, Thermoresponsive, Hyperbranched Copolymers Based on PEG-Methacrylates: Synthesis, Characterization, and LCST Behavior. J. Polym. Sci., Part A: Polym. Chem. 2010, 48 (13), 2783−2792. (23) Boyer, C.; Stenzel, M. H.; Davis, T. P. Building Nanostructures Using RAFT Polymerization. J. Polym. Sci., Part A: Polym. Chem. 2011, 49 (3), 551−595. (24) Hawker, C. J.; Frechet, J. M. J.; Grubbs, R. B.; Dao, J. Preparation of Hyperbranched and Star Polymers by a “Living”, SelfCondensing Free Radical Polymerization. J. Am. Chem. Soc. 1995, 117 (43), 10763−10764. (25) Sunder, A.; Hanselmann, R.; Frey, H.; Mülhaupt, R. Controlled Synthesis of Hyperbranched Polyglycerols by Ring-Opening Multibranching Polymerization. Macromolecules 1999, 32 (13), 4240−4246. (26) Liu, J.; Huang, W.; Zhou, Y.; Yan, D. Synthesis of Hyperbranched Polyphosphates by Self-Condensing Ring-Opening Polymerization of HEEP without Catalyst. Macromolecules 2009, 42 (13), 4394−4399. (27) Yagci, Y.; Jockusch, S.; Turro, N. J. Photoinitiated Polymerization: Advances, Challenges, and Opportunities. Macromolecules 2010, 43 (15), 6245−6260. (28) Fouassier, J.-P. Photoinitiation, Photopolymerization, and Photocuring: Fundamentals and Applications; Hanser: 1995. (29) Dadashi-Silab, S.; Doran, S.; Yagci, Y. Photoinduced Electron Transfer Reactions for Macromolecular Syntheses. Chem. Rev. 2016, 116 (17), 10212−10275. (30) Shanmugam, S.; Xu, J. T.; Boyer, C. Utilizing the electron transfer mechanism of chlorophyll a under light for controlled radical polymerization. Chem. Sci. 2015, 6 (2), 1341−1349. (31) Xu, J. T.; Shanmugam, S.; Duong, H. T.; Boyer, C. Organophotocatalysts for photoinduced electron transfer-reversible additionfragmentation chain transfer (PET-RAFT) polymerization. Polym. Chem. 2015, 6 (31), 5615−5624. (32) Tehfe, M. A.; Lalevee, J.; Gigmes, D.; Fouassier, J. P. Green Chemistry: Sunlight-Induced Cationic Polymerization of Renewable Epoxy Monomers Under Air. Macromolecules 2010, 43 (3), 1364− 1370. (33) Tehfe, M. A.; Lalevee, J.; Morlet-Savary, F.; Graff, B.; Blanchard, N.; Fouassier, J. P. Tunable Organophotocatalysts for Polymerization Reactions Under Visible Lights. Macromolecules 2012, 45 (4), 1746− 1752.

metal-free ATRP using the SCVP strategy. The approach relies on the copolymerization of methacrylic or styrenic monomers with respective structurally antagonist inimer in the presence of perylene as photocatalyst. Depending on the concentration, type of inimers, and irradiation time, lightly branched, hyperbranched, and cross-linked polymers were obtained.. As the chain-end halide groups are preserved, the approach offers possibility to form core−shell type block copolymers possessing hyperbranched and linear structures at core and shell, respectively. By using suitably selected monomers with desired hydrophilicity, the approach may open new pathways for the preparation of designed biomaterials particularly useful for drug-delivery systems.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected]; Fax +90-212-2856386; Tel +90-2122853241 (Y.Y.). ORCID

Yusuf Yagci: 0000-0001-6244-6786 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank Istanbul Technical University for financial support.

■

REFERENCES

(1) Hawker, C. J.; Frechet, J. M. J. Monodispersed dendritic polyesters with removable chain ends: a versatile approach to globular macromolecules with chemically reversible polarities. J. Chem. Soc., Perkin Trans. 1 1992, No. 19, 2459−2469. (2) Wooley, K. L.; Fréchet, J. M. J.; Hawker, C. J. Influence of shape on the reactivity and properties of dendritic, hyperbranched and linear aromatic polyesters. Polymer 1994, 35 (21), 4489−4495. (3) Stiriba, S. E.; Kautz, H.; Frey, H. Hyperbranched molecular nanocapsules: Comparison of the hyperbranched architecture with the perfect linear analogue. J. Am. Chem. Soc. 2002, 124 (33), 9698−9699. (4) Sunder, A.; Mülhaupt, R.; Haag, R.; Frey, H. Hyperbranched Polyether Polyols: A Modular Approach to Complex Polymer Architectures. Adv. Mater. 2000, 12 (3), 235−239. (5) Sunder, A.; Heinemann, J.; Frey, H. Controlling the growth of polymer trees: Concepts and perspectives for hyperbranched polymers. Chem. - Eur. J. 2000, 6 (14), 2499−2506. (6) Holter, D.; Burgath, A.; Frey, H. Degree of branching in hyperbranched polymers. Acta Polym. 1997, 48 (1−2), 30−35. (7) Gao, C.; Yan, D. Hyperbranched polymers: from synthesis to applications. Prog. Polym. Sci. 2004, 29 (3), 183−275. (8) Sendijarevic, I.; McHugh, A. J. Effects of Molecular Variables and Architecture on the Rheological Behavior of Dendritic Polymers. Macromolecules 2000, 33 (2), 590−596. (9) Kim, Y. H. Hyperbranched polymers 10 years after. J. Polym. Sci., Part A: Polym. Chem. 1998, 36 (11), 1685−1698. (10) Romagnoli, B.; Hayes, W. Chiral dendrimers-from architecturally interesting hyperbranched macromolecules to functional materials. J. Mater. Chem. 2002, 12 (4), 767−799. (11) Stiriba, S. E.; Frey, H.; Haag, R. Dendritic polymers in biomedical applications: From potential to clinical use in diagnostics and therapy. Angew. Chem., Int. Ed. 2002, 41 (8), 1329−1334. (12) Wilms, D.; Stiriba, S. E.; Frey, H. Hyperbranched Polyglycerols: From the Controlled Synthesis of Biocompatible Polyether Polyols to Multipurpose Applications. Acc. Chem. Res. 2010, 43 (1), 129−141. (13) Isik, T.; Demir, M. M.; Aydogan, C.; Ciftci, M.; Yagci, Y. Hydrophobic Coatings from Photochemically Prepared Hydrophilic E


Article

Macromolecules (34) Tehfe, M. A.; Lalevee, J.; Telitel, S.; Contal, E.; Dumur, F.; Gigmes, D.; Bertin, D.; Nechab, M.; Graff, B.; Morlet-Savary, F.; Fouassier, J. P. Polyaromatic Structures as Organo-Photoinitiator Catalysts for Efficient Visible Light Induced Dual Radical/Cationic Photopolymerization and Interpenetrated Polymer Networks Synthesis. Macromolecules 2012, 45 (11), 4454−4460. (35) Xiao, P.; Zhang, J.; Dumur, F.; Tehfe, M. A.; Morlet-Savary, F.; Graff, B.; Gigmes, D.; Fouassier, J. P.; Lalevee, J. Visible light sensitive photoinitiating systems: Recent progress in cationic and radical photopolymerization reactions under soft conditions. Prog. Polym. Sci. 2015, 41, 32−66. (36) Yilmaz, G.; Iskin, B.; Yagci, Y. Photoinduced Copper(I)Catalyzed Click Chemistry by the Electron Transfer Process Using Polynuclear Aromatic Compounds. Macromol. Chem. Phys. 2014, 215 (7), 662−668. (37) Tasdelen, M. A.; Yagci, Y. Light-induced copper(I)-catalyzed click chemistry. Tetrahedron Lett. 2010, 51 (52), 6945−6947. (38) Tasdelen, M. A.; Kiskan, B.; Yagci, Y. Externally stimulated click reactions for macromolecular syntheses. Prog. Polym. Sci. 2016, 52, 19−78. (39) Tasdelen, M. A.; Yagci, Y. Photochemical methods for the preparation of complex linear and cross-linked macromolecular structures. Aust. J. Chem. 2011, 64 (8), 982−991. (40) Tasdelen, M. A.; Yagci, Y. Light-Induced Click Reactions. Angew. Chem., Int. Ed. 2013, 52 (23), 5930−5938. (41) Tasdelen, M. A.; Yilmaz, G.; Iskin, B.; Yagci, Y. Photoinduced Free Radical Promoted Copper(I)-Catalyzed Click Chemistry for Macromolecular Syntheses. Macromolecules 2012, 45 (1), 56−61. (42) Taskin, O. S.; Yilmaz, G.; Yagci, Y. Fullerene-Attached Polymeric Homogeneous/Heterogeneous Photoactivators for VisibleLight-Induced CuAAC Click Reactions. ACS Macro Lett. 2016, 5 (1), 103−107. (43) Xu, J. T.; Tao, L.; Boyer, C.; Lowe, A. B.; Davis, T. P. Combining Thio-Bromo “Click” Chemistry and RAFT Polymerization: A Powerful Tool for Preparing Functionalized Multiblock and Hyperbranched Polymers. Macromolecules 2010, 43 (1), 20−24. (44) Guan, Z. B.; Smart, B. A remarkable visible light effect on atomtransfer radical polymerization. Macromolecules 2000, 33 (18), 6904− 6906. (45) Tasdelen, M. A.; Uygun, M.; Yagci, Y. Photoinduced Controlled Radical Polymerization in Methanol. Macromol. Chem. Phys. 2010, 211 (21), 2271−2275. (46) Tasdelen, M. A.; Uygun, M.; Yagci, Y. Photoinduced Controlled Radical Polymerization. Macromol. Rapid Commun. 2011, 32 (1), 58− 62. (47) Tasdelen, M. A.; Ciftci, M.; Yagci, Y. Visible Light-Induced Atom Transfer Radical Polymerization. Macromol. Chem. Phys. 2012, 213 (13), 1391−1396. (48) Shanmugam, S.; Xu, J.; Boyer, C. Photocontrolled Living Polymerization Systems with Reversible Deactivations through Electron and Energy Transfer. Macromol. Rapid Commun. 2017, 38 (13), 1700143. (49) Treat, N. J.; Sprafke, H.; Kramer, J. W.; Clark, P. G.; Barton, B. E.; Read de Alaniz, J.; Fors, B. P.; Hawker, C. J. Metal-Free Atom Transfer Radical Polymerization. J. Am. Chem. Soc. 2014, 136 (45), 16096−16101. (50) Pan, X.; Fang, C.; Fantin, M.; Malhotra, N.; So, W. Y.; Peteanu, L. A.; Isse, A. A.; Gennaro, A.; Liu, P.; Matyjaszewski, K. Mechanism of Photoinduced Metal-Free Atom Transfer Radical Polymerization: Experimental and Computational Studies. J. Am. Chem. Soc. 2016, 138 (7), 2411−2425. (51) Jockusch, S.; Yagci, Y. The active role of excited states of phenothiazines in photoinduced metal free atom transfer radical polymerization: singlet or triplet excited states? Polym. Chem. 2016, 7 (39), 6039−6043. (52) Miyake, G. M.; Theriot, J. C. Perylene as an Organic Photocatalyst for the Radical Polymerization of Functionalized Vinyl Monomers through Oxidative Quenching with Alkyl Bromides and Visible Light. Macromolecules 2014, 47 (23), 8255−8261.

(53) 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 (19), 2899− 2903. (54) Allushi, A.; Jockusch, S.; Yilmaz, G.; Yagci, Y. Photoinitiated Metal-Free Controlled/Living Radical Polymerization Using Polynuclear Aromatic Hydrocarbons. Macromolecules 2016, 49 (20), 7785−7792. (55) Pearson, R. M.; Lim, C.-H.; McCarthy, B. G.; Musgrave, C. B.; Miyake, G. M. Organocatalyzed Atom Transfer Radical Polymerization Using N-Aryl Phenoxazines as Photoredox Catalysts. J. Am. Chem. Soc. 2016, 138 (35), 11399−11407. (56) Lim, C.-H.; Ryan, M. D.; McCarthy, B. G.; Theriot, J. C.; Sartor, S. M.; Damrauer, N. H.; Musgrave, C. B.; Miyake, G. M. Intramolecular Charge Transfer and Ion Pairing in N,N-Diaryl Dihydrophenazine Photoredox Catalysts for Efficient Organocatalyzed Atom Transfer Radical Polymerization. J. Am. Chem. Soc. 2017, 139 (1), 348−355. (57) Liu, X.; Zhang, L.; Cheng, Z.; Zhu, X. Metal-free photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) via a visible light organic photocatalyst. Polym. Chem. 2016, 7 (3), 689−700. (58) Kutahya, C.; Aykac, F. S.; Yilmaz, G.; Yagci, Y. LED and visible light-induced metal free ATRP using reducible dyes in the presence of amines. Polym. Chem. 2016, 7 (39), 6094−6098. (59) Allushi, A.; Kutahya, C.; Aydogan, C.; Kreutzer, J.; Yilmaz, G.; Yagci, Y. Conventional Type II photoinitiators as activators for photoinduced metal-free atom transfer radical polymerization. Polym. Chem. 2017, 8 (12), 1972−1977. (60) Aydogan, C.; Ciftci, M.; Kumbaraci, V.; Talinli, N.; Yagci, Y. Hyperbranced Polymers by Photoinduced Self-Condensing Vinyl Polymerization Using Bisbenzodioxinone. Macromol. Chem. Phys. 2017, 218 (10), 1700045. (61) Aydogan, C.; Ciftci, M.; Yagci, Y. Hyperbranched Polymers by Type II Photoinitiated Self-Condensing Vinyl Polymerization. Macromol. Rapid Commun. 2016, 37 (7), 650−654. (62) Yamamoto, Y.; Nakao, W.; Atago, Y.; Ito, K.; Yagci, Y. A novel macroinimer of polyethylene oxide: synthesis of hyper branched networks by photoinduced H-abstraction process. Eur. Polym. J. 2003, 39 (3), 545−550. (63) Bektas, S.; Ciftci, M.; Yagci, Y. Hyperbranched polymers by visible light induced self-condensing vinyl polymerization and their modifications. Macromolecules 2013, 46 (17), 6751−6757. (64) Geyik, C.; Ciftci, M.; Demir, B.; Guler, B.; Ozkaya, A. B.; Gumus, Z. P.; Barlas, F. B.; Demirkol, D. O.; Coskunol, H.; Timur, S. Controlled release of anticancer drug Paclitaxel using nano-structured amphiphilic star-hyperbranched block copolymers. Polym. Chem. 2015, 6 (30), 5470−5477. (65) Seleci, M.; Seleci, D. A.; Ciftci, M.; Odaci Demirkol, D.; Stahl, F.; Timur, S.; Scheper, T.; Yagci, Y. Nanostructured amphiphilic starhyperbranched block copolymers for drug delivery. Langmuir 2015, 31 (15), 4542−4551. (66) Ciftci, M.; Kahveci, M. U.; Yagci, Y.; Allonas, X.; Ley, C.; Tar, H. A simple route to synthesis of branched and cross-linked polymers with clickable moieties by photopolymerization. Chem. Commun. 2012, 48 (82), 10252−10254. (67) Yilmaz, G.; Kahveci, M. U.; Yagci, Y. A one pot, one step method for the preparation of clickable hydrogels by photoinitiated polymerization. Macromol. Rapid Commun. 2011, 32 (23), 1906−1909. (68) Shimomura, O.; Lee, B. S.; Meth, S.; Suzuki, H.; Mahajan, S.; Nomura, R.; Janda, K. D. Synthesis and application of polytetrahydrofuran-grafted polystyrene (PS−PTHF) resin supports for organic synthesis. Tetrahedron 2005, 61 (51), 12160−12167. (69) Sun, H.; Kabb, C. P.; Sumerlin, B. S. Thermally-labile segmented hyperbranched copolymers: using reversible-covalent chemistry to investigate the mechanism of self-condensing vinyl copolymerization. Chem. Sci. 2014, 5 (12), 4646−4655.

F


Synthesis of Hyperbranched Polymers by Photoinduced Metal-Free

Recommend Documents