Visible-Light-Induced Atom-Transfer-Radical Polymerization with a

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Visible Light Induced Atom Transfer Radical Polymerization with ppm-Level Fe Catalyst Chao Bian, Yin-Ning Zhou, Jun-Kang Guo, and Zheng-Hong Luo Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b00710 • Publication Date (Web): 13 Apr 2017 Downloaded from http://pubs.acs.org on April 17, 2017

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Industrial & Engineering Chemistry Research

Visible Light Induced Atom Transfer Radical Polymerization with ppm-Level Fe Catalyst

Chao Bian, Yin-Ning Zhou, Jun-Kang Guo, Zheng-Hong Luo*

Department of Chemical Engineering, School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, P. R. China

Corresponding Author: Professor Z.H. Luo; E-mail: [email protected]; Tel.: +86-2154745602; Fax: +86-21-54745602

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ACS Paragon Plus Environment


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Abstract A low ppm-level Fe-based photoinduced atom transfer radical polymerization (ATRP) under visible light irradiation was developed. Various ligands tris(4methoxyphenyl) phosphine (TMPP), 4,4’-dinonyl-2,2’-dipyridyl (dNbpy) and tris[2(dimethylamino) ethyl] amine (Me6TREN) were used to enhance the catalytic activity of Fe complexes. Activator Fe(Ⅱ) complexes were formed by reduction Fe(Ⅲ) complexes with monomer under visible light irradiation. Linear semilogarithmic plots and low polydispersities (Mw/Mn dNbpy > Me6TREN. Additionally, this polymerization could be ceased and restarted responding to light off and light on. The retention of chain end functionality was analyzed by 1H NMR and chain extension experiments. Results showed that the partial chain end functionality of resulting polymers was lost. Thus there is still having room for improving the chain-end functionality and initiation efficiency of resulting polymers.

Keywords: Photoinduced ATRP; Visible light irradiation; ppm-Level Fe catalyst; Polymerization kinetics

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Introduction Atom transfer radical polymerization (ATRP) is an attractive controlled radical polymerization technique, which can be widely used to synthesize polymer with precise molecular weight (Mn), low polydispersity and predesigned architectures.1-4 ATRP is conducted by a reversible equilibrium of activation and deactivation with catalyst and alkyl halide.5,6 A controlled polymerization is achieved because side reactions are suppressed by low concentration of radicals.7 However, traditional ATRP techniques require high concentration of catalyst and strict deoxygenation to maintain a reasonable reaction rate.2,6 Therefore, many methodologies by continuous regeneration of active polymerization catalyst have been developed. ATRP can now be conducted at ppm levels of metal catalyst, such as initiators for continuous activator regeneration (ICAR) ATRP8-12, activators regenerated by electron transfer (ARGET) ATRP13-17, supplemental activator and reducing agent (SARA) ATRP18-22, electrochemically mediated ATRP (eATRP)23-27 and photoinduced ATRP (photoATRP)28-42. Each of these ATRP techniques offer an effective and convenient way to decrease catalyst loadings and improve the tolerance to air.7,63 As one of the most promising techniques, photoATRP has attracted much attention due to the simple procedure and the possible of using sunlight.43,44 Until now, many papers have been published in the field of photoATRP under ultraviolet (UV) or visible light.45 For example, Matyjaszewski and co-workers used both experimental and kinetic 3



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modeling techniques to investigate the polymerization mechanism of Cu mediated photoATRP.43 Hawker and coworkers developed a new photoredox catalyst [Ir(ppy)3] for photoATRP, which offered a versatile platform for preparing functional materials.46 Miyake and co-workers introduced a visible light photoredox catalyst diaryl dihydrophenazines, which achieved the activation of initiator under visible light to synthesize polymer with low dispersity and tunable molecule weight.47 The mechanisms of visible light photocatalysis were presented by Yoon and co-workers. The generation of radicals was mild and selective by visible light photoreduction of alkyl halide.48 Compared to UV light used in photoATRP, visible light shows environmentally friendly and less damage to chemicals.49 Therefore, it is worthy to explore photoATRP under visible light. Moreover, with the advent of various photocatalyst systems, such as copper (Cu),43,51 iron (Fe),52-54 iridium (Ir),46 ruthenium (Ru),55 gold (Au)56 and metal-free,38,47 Fe catalyst is one of the most promising candidates because of its abundance, low toxicity and excellent biocompatibility.57,58 To our knowledge, several Fe-based photoATRP systems have been developed. Matyjaszewski and co-workers reported a photoinduced Fe-based catalytic system without radical initiators, reducing agents and additional ligands, in which the solvent acted as ligand.52 However, the amount of catalyst loading used in this photoinduced Fe-mediated ATRP system was relatively high. A disadvantage of Fe catalysts was a poor tolerance to polar groups, which often transformed into less active catalysts in the presence of polar groups.59 Therefore, 4


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adding additional active ligand is an effective way to improve the catalyst activity for decreasing the concentration of Fe catalysts. Luo and co-workers investigated a UV light photoinduced ATRP system with FeCl3·6H2O/TMPP catalyst complex in the absence of additional initiators.53 However, the use of a UV light with high-energy UV photons resulted in faster reaction and undesired homolytic photodecomposition processes. Therefore, mild visible light is introduced here. In this situation, the generation of radical by photoreduction of alkyl halides is selective and mild. Based on the above research background, it encouraged us to investigate Fe-based photoinduced ATRP with low catalyst loading using active ligands and visible light irradiation. In this work, low ppm (as low as 100 ppm) Fe-based catalyst complexed with different ligands TMPP, dNbpy and Me6TREN were reported for the first time. The mechanism of this system proposed in Scheme 1 showed that light irradiation was required not only for the formation of Fe(II) by reduction of Fe(Ⅲ) with MMA but also for the activation of Fe(II) at room temperature.52,53 The activity of Fe complexes with various ligands was evaluated. Furthermore, the effects of catalyst concentrations and different degrees of polymerization (DP) on reactions were investigated.

Experimental Sections Materials and Characterizations Methyl methacrylate (MMA, 99+%, SCRC) was rinsed with NaOH solution (5 wt %) to eliminate the inhibitor, and then dried with MgSO4 overnight prior to use. N, N-dimethylformamide (DMF, 99.5%, Shanghai Lingfeng Chemical Reagent Co.), ethyl 5



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2-bromophenylacetate (EBPA, 98%, Alfa), iron(III) chloride hexahydrate (FeCl3·6H2O, 99+%, Acros), tris(4-methoxyphenyl) phosphine (TMPP, 95%, Adamas), 4,4’-dinonyl2,2’-dipyridyl (dNbpy, 98%, Adamas), and tris[2-(dimethylamino) ethyl] amine (Me6TREN, 99%, Alfa) were used as received. Monomer conversions were measured via 1H NMR (Bruker AV400 MHz) spectroscopy in CDCl3. Gel permeation chromatography (Wyatt Technology Corp., DAWN EOS) with a multi-angle laser light scattering instrument was selected to detect molecular weight (Mn) and polydispersity (Mw/Mn), with THF as eluent at flow rate of 1.0 mL/min at 30 °C. The UV/Vis absorption spectra of the catalyst complexes in DMF was recorded in a Perkin-Elmer Lambda 35 spectrometer. General Procedure for Photoinduced Fe(III)-Mediated ATRP 0.04 mmol FeCl3·6H2O (10.81 mg) and 0.08 mmol TMPP (28.18 mg) were dissolved in 1 mL DMF for homogeneous solution with stirring 1 hour. 100 μL solution was firstly added in 25 mL Schlenk flask with magnetic stirrer, and then EBPA (0.08 mmol, 19.4 mg), MMA (40 mmol, 4.2 mL) and DMF (4.2 mL) were transferred to the Schlenk flask. The mixture was degassed by three freeze-thaw-pump cycles. After then, the Schlenk flask was put in the photochemical reactor. The photochemical reactor consisted of a Long-arc xenon lamp equipped with a visible filter and a cooling system. The optical wavelength was ranged from 380 nm to 780 nm, which consistent with the wavelength of visible light. The intensity of the visible light source was 42 ± 0.5 mW/cm2 and the reaction temperature was about 36 °C. After a predetermined time, the 6


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sample was obtained from the solution by syringe for 1H NMR and GPC. The sample for GPC was diluted in CHCl3, then filtered via a basic alumina column to eliminate the Fe catalyst and precipitated in methanol. In addition, other systems involving different ligands were conducted in the same procedure. General Procedure for Chain Extension of PMMA Macroinitiator under Normal ATRP Conditions All of the macroinitiators were purified by filtering via a basic alumina column to eliminate the Fe catalyst and precipitating in methanol. Then the macroinitiators were dried at 50 °C in a vacuum oven until a constant weight. A 150 mg sample of macroinitiator Ⅰ (62160 g/mol) synthesized by 100 ppm-level Fe-based photoinduced ATRP with ligand TMPP was transferred into a 25 mL Schlenk flask with magnetic stirrer. After then, 3 mL of DMF was added. FeBr2 (0.1 mmol, 21.6 mg) and TMPP (0.1 mmol, 35.2 mg) were successive placed into the Schlenk flask. Followed by three freeze-thaw-pump cycles, MMA (20 mmol, 2.1 mL) was injected to the flask. Then the flask was placed in oil bath and heated to 80 °C. After a predetermined time, the reaction was stopped. The product was diluted in CHCl3, then filtered via a basic alumina column to eliminate the Fe catalyst and precipitated in methanol. The chainextension reaction of 150 mg macroinitiator Ⅱ (66380 g/mol) and 150 mg macroinitiator Ⅲ (267600 g/mol) were conducted in the same procedure.

Results and Discussion Kinetic Analysis of Photoinduced Fe (III)-Mediated ATRP with Different 7



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Conditions The ligands play a significant role in Fe-based photoinduced ATRP system, which improve the activity and efficiency of catalyst complexes during reaction. Three typical ligands (TMPP, dNbpy and Me6TREN) have been reported to be used in Fe-based ATRP polymerization systems.59-61 Herein, Fe-based visible light induced ATRPs of MMA using TMPP, dNbpy and Me6TREN as ligand, as well as different catalyst concentrations were carried out. As shown in Figure 1, the polymerization results of 500 ppm, 200 ppm and 100 ppm catalyst loadings with ligand TMPP were studied. Kinetic plots (ln [M] 0/[M] vs time) were depicted in Figure 1A. Linear semilogarithmic plots after an induction period suggested that the concentration of free radical kept constant during polymerization. Therefore, the equilibrium between activation and deactivation was well maintained. However, the polymerization rate decreased with the increased catalyst loadings. When the catalyst loading increased, the amount of deactivator (FeCl3·6H2O/TMPP) in the reaction system was higher. As a consequence, the rate of polymerization decreased. Furthermore, the catalyst loading had a great effect on Mn versus monomer conversion. Higher catalyst loading resulted in lower Mn (Figure 1B). As can be seen from the mechanism in Scheme 1, methyl 2,3-dichloroisobutyrate was generated as a by-product via the reduction Fe(Ⅲ) complex with MMA under light irradiation.53 Methyl 2,3-dichloroisobutyrate participated in the reaction in situ as an additional initiator. Also, slower reaction allowed the initiation to generate more 8


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propagating species. Hence, higher catalyst loading could led to lower Mn. In all cases, the polydispersity was low (Mw/Mn 9



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FeCl3·6H2O/dNbpy > FeCl3·6H2O/Me6TREN. Table 1 (entries 1-9) showed the effect of different targeted DPs for Fe-based photoinduced ATRP of MMA with various ligands at 100-ppm catalyst loadings. When the DP ranged from 500 to 100, the molecule weight of the final product decreased from 99560 to 67400 for FeCl3·6H2O/TMPP system. Similarly, the molecule weight of FeCl3·6H2O/dNbpy system and FeCl3·6H2O/Me6TREN system also showed an obvious decrease. The amount of initiators determined the quantity of growing chains. The larger amount of initiators used, the lower average molecule weight obtained. The values of Mw/Mn were narrow and ranged from 1.25 to 1.37. Furthermore, it was noteworthy that the molecule weights (Mn,GPC) were all higher than theoretical values (Mn,theo). This deviation might attribute to the low initiation efficiency and slow initiation step, as has been reported in previous works.24,43 Significantly, the case with FeCl3·6H2O/Me6TREN showed poor initiation efficiency. UV-vis Absorption Spectra of Reaction Mixture with Different Fe-based Catalyst Complexes The UV-vis spectra of each component of this system in DMF were recorded in Figure 4. As shown in Figure 4A, MMA, EBPA and ligand (TMPP, dNbpy, Me6TREN) had almost no absorption in visible light region, which indicated that the visible light absorbance was due to the component of FeCl3·6H2O in this system. Furthermore, the catalyst

complexes

FeCl3·6H2O/TMPP,

FeCl3·6H2O/dNbpy

and

FeCl3·6H2O/Me6TREN also showed absorption band at wavelength of 380nm~600nm 10


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with different intensity (Figure 4B), indicating different plausible photoexcitations of Fe catalyst complexes would happen upon visible light. Specifically, comparing with these three systems, the mixture of FeCl3·6H2O/TMPP system had the maximum absorption in visible light region, while the mixture of FeCl3·6H2O/Me6TREN system had the minimum absorption in visible light region. Consequently, the visible light absorption efficiency of the three Fe-based catalyst complexes decreased in the following order: FeCl3·6H2O/TMPP > FeCl3·6H2O/dNbpy > FeCl3·6H2O/Me6TREN. Generally, the light absorption efficiency has a significant impact on the activity of photocatalysts in photopolymerization reactions.62 In current study, the light absorption efficiency had a positive correlation with the experimentally observed polymerization rate as discussed above. Temporal Control of Photoinduced Fe(III)-Mediated ATRP with Different Ligands To further confirm the controlled nature of the polymerization, temporal control was conducted by light “on-off” switching cycles. The temporal controlled polymerization of 100 ppm-level Fe-based photoinduced ATRP with ligand TMPP, dNbpy and Me6TREN under visible light were exhibited in Figure 5. Nearly no additional conversion after removal of the light in 4 hours and 8 hours later indicated that the photoredox was suspended in the dark. When re-exposure the mixture to the light in 6 hours and 10 hours later, polymerization was restarted (Figure 5A). In addition,

the

molecule

weights

increased

with

monomer

conversion

in 11



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FeCl3·6H2O/TMPP system (Figure 5B), FeCl3·6H2O/dNbpy system (Figure 5C) and FeCl3·6H2O/Me6TREN system (Figure 5D), which were not affected by the interrupted light irradiation. The molecule weight distributions were narrow and ranged from 1.25 to 1.39. These results demonstrated that 100 ppm-level Fe-based photoinduced ATRP with ligand TMPP, dNbpy and Me6TREN were well controlled and highly sensitive to visible light irradiation. Chain End Analysis of PMMA Prepared via Photoinduced Fe(III)-Mediated ATRP The retention of chain-end functionality was another issue for ATRP, which make it possible for the synthesis of block copolymers. Macroinitiators analyzed here were prepared by 100 ppm-level Fe-based photoinduced ATRP with ligand TMPP, dNbpy and Me6TREN. Figure 6 showed the 1H NMR spectra of macroinitiators Ⅰ, Ⅱ, Ⅲ corresponded to the

different

Fe-based

catalyst

complexes

FeCl3

FeCl3·6H2O/TMPP,

FeCl3·6H2O/dNbpy, FeCl3·6H2O/Me6TREN, respectively. The signals of protons of methoxy group (a, -OCH3), methylene group (b, -CH2-) and methyl group (c, -CH3) in macroinitiators were observed at 3.60 ppm, 1.80-2.00 ppm and 0.8-1.00 ppm. Besides, a micro signal at ~3.80 ppm corresponded to the protons of methoxy group (a’, -OCH3) adjacent to halogen atom in the chain end. The above-observed signals suggested that the resulting PMMA retained chain-end functionality. Moreover, the chain extension experiments were carried out to further confirm the 12


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retention of chain end functionality of the resulting PMMA. As shown in Figure 7, chain extension of macroinitiator Ⅰ (Mn=62160 g/mol, Mw/Mn=1.24) with MMA was conducted under FeBr2-mediated conventional ATRP, giving a well-controlled product of PMMA I (Mn=69760 g/mol, Mw/Mn=1.27). This result indicated that the macroinitiator Ⅰ successful initiated the reaction. However, the initiation efficiency was not good as confirmed by the small increase in molecular weight. Low initiation efficiency of macroinitiator might be caused by steric hindrance effect of long polymer chain and partial loss of chain end functionality. Similarly, chain extension of macroinitiator Ⅱ (Mn=66380 g/mol, Mw/Mn=1.24) and macroinitiator Ⅲ (Mn=267600 g/mol, Mw/Mn=1.29) were also carried out and produced polymers PMMA Ⅱ (Mn=73120 g/mol, Mw/Mn=1.19) and PMMA Ⅲ (Mn=271700 g/mol, Mw/Mn=1.28). Improving the chain-end functionality and initiation efficiency of macroinitiator synthesized by 100 ppm-level Fe-based photoinduced ATRP still needs to be done.

Conclusion In summary, we have successfully achieved Fe-based photoinduced ATRP of MMA at low ppm catalyst loadings with different ligands (TMPP, dNbpy and Me6TREN) under visible light irradiation. Adding active ligand and soft visible light irradiation were effective ways for this photoATRP system. The control of the polymerization was good (Mw/Mn

FeCl3·6H2O/dNbpy

>

FeCl3·6H2O/Me6TREN. Temporal control experiment through switching light on and 13



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off was realized, which made this technique versatile. However, the partial loss of chain end functionality of resulting polymers was found in the chain end analysis experiments. Developing visible light photocatalyst for synthesis of polymers with high chain end functionality and initiation efficiency was highly desired. Even so, low ppm Fe catalyst loading and visible light irradiation made this photoATRP system attractive for preparing polymers in some applications. AUTHOR INFORMATION Corresponding Author Professor Z.H. Luo; E-mail: [email protected]; Tel.: +86-21-54745602; Fax: +8621-54745602 Notes The authors declare no competing financial interests. ACKNOWLEDGMENT The authors thank the National Natural Science Foundation of China (No. 21625603) for supporting this work and Y.-N. Zhou also thanks the Shanghai Jiao Tong University for HaiWai ShiZi ChuBei postdoctoral fellowship support.

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mechanism of copper mediated photoRDRP via high resolution mass spectrometry. J. Am. Chem. Soc. 2015, 137, 6889-6896. (32) Liu, X.; Zhang, L.; Cheng, Z.; Zhu, X. Metal-free photoinduced electron transferatom transfer radical polymerization (PET-ATRP) via a visible light organic photocatalyst. Polym. Chem. 2016, 7, 689-700. (33) 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 atomtransfer radical polymerization. J. Am. Chem. Soc. 2014, 136, 16096-16101. (34) 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, 8255-8261. (35) Ohtsuki, A.; Goto, A.; Kaji, H. Visible-light-induced reversible complexation mediated living radical polymerization of methacrylates with organic catalysts. Macromolecules 2013, 46, 96-102. (36) Ohtsuki, A.; Lei, L.; Tanishima, M.; Goto, A.; Kaji, H. Photocontrolled organocatalyzed living radical polymerization feasible over a wide range of wavelengths. J. Am. Chem. Soc. 2015, 137, 5610-5617. (37) Jones, G. R.; Whitfield, R.; Anastasaki, A.; Haddleton, D. M. Aqueous copper (II) photoinduced polymerization of acrylates: Low copper concentration and the importance of sodium halide salts. J. Am. Chem. Soc. 2016, 138, 7346-7352.

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(38) 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, 2411-2425. (39) Pan, X.; Malhotra, N.; Simakova, A.; Wang, Z.; Konkolewicz, D.; Matyjaszewski, K. Photoinduced atom transfer radical polymerization with ppm-level Cu catalyst by visible light in aqueous media. J. Am. Chem. Soc. 2015, 137, 15430-15433. (40) Yang, Q.; Dumur, F.; Morlet-Savary, F.; Poly, J.; Lalevee, J. Photocatalyzed Cubased ATRP involving an oxidative quenching mechanism under visible light. Macromolecules 2015, 48, 1972-1980. (41) Yan, J.; Li, B.; Zhou. F.; Liu, W. Ultraviolet light-induced surface-initiated atomtransfer radical polymerization. ACS Macro Lett. 2013, 2, 592-596. (42) Ribelli, T.G.; Konkolewicz, D.; Pan, X. C.; Matyjaszewski, K. Contribution of photochemistry to activator regeneration in ATRP. Macromolecules 2014, 47, 63166321. (43) Ribelli, T. G.; Konkolewicz, D.; Bernhard, S.; Matyjaszewski, K. How are radicals (re)generated in photochemical ATRP? J. Am. Chem. Soc. 2014, 136, 13303-13312. (44) Anastasaki, A.; Nikolaou, V.; Zhang, Q.; Burns, J.; Samanta, S. R.; Waldron, C.; Haddleton, A. J.; McHale, R.; Fox, D.; Percec, V.; Wilson, P.; Haddleton, D. M. Copper(II)/tertiary amine synergy in photoinduced living radical polymerization:

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Accelerated synthesis of ω-functional and α, ω-heterofunctional poly(acrylates). J. Am. Chem. Soc. 2014, 136, 1141-1149. (45) Pan, X.; Tasdelen, M. A.; Laun, J.; Junkers, T.; Yagci, Y.; Matyjaszewski, K. Photomediated controlled radical polymerization. Prog. Polym. Sci. 2016, 62, 73125. (46) Fors, B. P.; Hawker, C. J. Control of a living radical polymerization of methacrylates by light. Angew. Chem., Int. Ed. 2012, 51, 8850-8853. (47) Theriot, J. C.; Lim, C. H.; Yang, H.; Ryan, M. D.; Musgrave, C. B.; Miyake, G. M. Organocatalyzed atom transfer radical polymerization driven by visible light. Science 2016, 352, 1082-1086. (48) Yoon, T. P.; Schultz, D. M. Solar synthesis: prospects in visible light photocatalysis. Science 2014, 343, 1239176. (49) 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. (50) Konkolewicz, D.; Schroder, K.; Buback, J.; Bernhard, S.; Matyjaszewski, K. Visible light and sunlight photoinduced ATRP with ppm of Cu catalyst. ACS Macro Lett. 2012, 1, 1219-1223. (51) Ciftci, M.; Tasdelen, M. A.; Li, W.; Matyjaszewski, K.; Yagci, Y. Photoinitiated 21



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ATRP in inverse microemulsion. Macromolecules 2013, 46, 9537-9543. (52) Pan, X.; Malhotra, N.; Zhang, J.; Matyjaszewski, K. Photoinduced Fe-based atom transfer radical polymerization in the absence of additional ligands, reducing agents, and radical initiators. Macromolecules 2015, 48, 6948-6954. (53) Zhou, Y.-N.; Guo, J.-K.; Li, J.-J.; Luo, Z.-H. Photoinduced iron(III)-mediated atom transfer radical polymerization with insitu generated initiator: mechanism and kinetics studies. Ind. Eng. Chem. Res. 2016, 55, 10235-10242. (54) Bansal, A.; Kumar, P.; Sharma, C. D.; Ray, S. S.; Jain, S. L. Lightinduced controlled free radical polymerization of methacrylates using iron-based photocatalyst in visible light. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 27392746. (55) Zhang, G.; Song, I. Y.; Ahn, K. H.; Park, T.; Choi, W. Free radical polymerization initiated and controlled by visible light photocatalysis at ambient temperature. Macromolecules 2011, 44, 7594-7599. (56) Nzulu, F.; Telitel, S.; Stoffelbach, F.; Graff, B.; Morlet-Savary, F.; Lalevee, J.; Fensterbank, L.; Goddard, J.P.; Ollivier, C. A dinuclear gold(I) complex as a novel photoredox catalyst for light-induced atom transfer radical polymerization. Polym. Chem. 2015, 6, 4605-4611. (57) Ouchi, M.; Terashima, T.; Sawamoto, M. Transition metalcatalyzed living radical polymerization: toward perfection in catalysis and precision polymer synthesis.

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Chem. Rev. 2009, 109, 4963-5050. (58) di Lena, F.; Matyjaszewski, K. Transition metal catalysts for controlled radical polymerization. Prog. Polym. Sci. 2010, 35, 959-1021. (59) Nishizawa, K.; Ouchi, M.; Sawamoto, M. Phosphine–ligand decoration toward active and robust iron catalysts in LRP. Macromolecules 2013, 46, 3342-3349. (60) Matyjaszewski, K.; Wei, M.; Xia, J.; McDermott, N.E. Controlled/ “living” radical polymerization of styrene and methyl methacrylate catalyzed by iron complexes. Macromolecules 1997, 30, 8161-8164. (61) Zhang, Y.; Wang, Y.; Matyjaszewski, K. ATRP of methyl acrylate with metallic zinc, magnesium, and iron as reducing agents and supplemental activators. Macromolecules 2011, 44, 683-685. (62) Dietlin, C.; Schweizer, S.; Xiao, P.; Zhang, J.; Morlet-Savary, F.; Graff, B.; Fouassier, J. P.; Lalevee, J. Photopolymerization Upon LEDs: New Photoinitiating Systems and Strategies. Polym. Chem. 2015, 6, 3895-3912. (63) Yang, Q. Lalevee, J. Poly, J. Development of a Robust Photocatalyzed ATRP Mechanism Exhibiting Good Tolerance to Oxygen and Inhibitors. Macromolecules 2016, 49, 7653-7666.

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Figure and table captions Table 1. Results of photoinduced Fe-mediated ATRP with different target DP. Scheme 1. The proposed mechanism of photoinduced Fe-mediated ATRP in the presence of ligand TMPP, dNbpy and Me6TREN. Figure 1. Effect of the catalyst loadings on kinetics of photoinduced Fe-mediated ATRP with ligand TMPP ([MMA]:[EBPA]:[FeCl3·6H2O]:[TMPP]=500:1:0.05: 0.10 / 500:1:0.10:0.20 / 500:1:0.25:0.50): (A) semilogarithmic kinetic plots versus time, (B) Mn and Mw/Mn versus conversion. Figure 2. Effect of the catalyst loadings on kinetics of photoinduced Fe-mediated ATRP with

ligand

dNbpy ([MMA]:[EBPA]:[FeCl3·6H2O]:[dNbpy]=500:1:0.05:0.15

/

500:1:0.10:0.30 / 500:1:0.25:0.75): (A) semilogarithmic kinetic plots versus time, (B) Mn and Mw/Mn versus conversion. Figure 3. Effect of the catalyst loadings on kinetics of photoinduced Fe-mediated ATRP with ligand Me6TREN ([MMA]:[EBPA]:[FeCl3·6H2O]:[Me6TREN]= 500:1:0.05:0.10 / 500:1:0.10:0.20 / 500:1:0.25:0.50): (A) semilogarithmic kinetic plots versus time, (B) Mn and Mw/Mn versus conversion.. Figure 4. UV-vis absorption spectra of each component in the reaction system in DMF, conditions:(A) [MMA]:[EBPA]=500:1, [MMA]:[EBPA]:[FeCl3·6H2O]=500:1:0.05, 24


Page 25 of 36

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[MMA]:[EBPA]:[TMPP]=500:1:0.10,

[MMA]:[EBPA]:[dNbpy]=500:1:0.15,

[MMA]:[EBPA]:[Me6TREN]=500:1:0.10, all with 700 vol% DMF. (B) [MMA]: [EBPA]:[FeCl3·6H2O]:[TMPP]=500:1:0.05:0.10, [dNbpy]=500:1:0.05:0.15,

[MMA]:[EBPA]:[FeCl3·6H2O]:

[MMA]:[EBPA]:[FeCl3·6H2O]:[Me6TREN]=500:1:0.05:

0.10, all with 700 vol% DMF. Figure 5. Photoinduced Fe-mediated ATRP with “on-off” light switch: (A) semilogarithmic kinetic plots versus time with ligands TMPP, dNbpy and Me6TREN. (B)

Mn

and

Mw/Mn

versus

conversion,

condition:

[MMA]:[EBPA]:

[FeCl3·6H2O]:[TMPP] =500:1:0.05:0.10. (C) Mn and Mw/Mn versus conversion, condition: [MMA]:[EBPA]:[FeCl3·6H2O]:[dNbpy]=500:1:0.05:0.15. (D) Mn and Mw/Mn versus conversion, condition:[MMA]:[EBPA]:[FeCl3·6H2O]:[Me6TREN] =500:1:0.05:0.10. Figure 6. 1H NMR spectra of PMMA macroinitiator(Ⅰ, Ⅱ and Ⅲ) prepared by photoinduced Fe-mediated ATRP in the presence of different ligands TMPP (Ⅰ), dNbpy (Ⅱ) and Me6TREN (Ⅲ), condition ：

[MMA]:[EBPA]:[FeCl3·6H2O]:[TMPP]

=500:5:0.05:0.10, [MMA]:[EBPA]:[FeCl3·6H2O]:[dNbpy]=500:5:0.05:0.15, [MMA]: [EBPA]:[FeCl3·6H2O]:[ Me6TREN] =500:5:0.05:0.10. Figure 7. GPC traces of macroinitiators (Ⅰ, Ⅱ and Ⅲ) and the corresponding pseudo block copolymers PMMA-b-PMMA.

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Page 26 of 36

Table 1. Results of photoinduced Fe-mediated ATRP with different target DP Time Conv. Entrya

Ligand

Mn,the

Mn,GPC

[MMA]:[EBPA]

Mw/Mn (h)

(%)

(g/mol) (g/mol)

1b

TMPP

500:1

10

42.9

21719

99560

1.28

2b

TMPP

200:1

10

41.5

8553

74440

1.25

3b

TMPP

100:1

10

37.1

3958

67400

1.28 26


Page 27 of 36

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a

4c

dNbpy

500:1

10

36.1

18315

111100

1.30

5c

dNbpy

200:1

10

34.6

7171

84350

1.37

6c

dNbpy

100:1

10

35.1

3757

51250

1.25

7d

Me6TREN

500:1

10

20.0

10255

310000

1.34

8d

Me6TREN

200:1

10

20.6

4368

300000

1.33

9d

Me6TREN

100:1

10

34.2

3667

227450

1.36

Reaction conditions: in 50% (v/v) DMF; [MMA]=4.2ml; light source: 42±0.5 mW/cm2;

light emitted by xenon lamp with a visible filter; temperature: 36 ℃. b

[MMA]:[FeCl3·6H2O]:[TMPP]=500:0.05:0.10. c[MMA]:[FeCl3·6H2O]:[dNbpy]=500:

0.05:0.15. d[MMA]:[FeCl3·6H2O]:[Me6TREN]=500:0.05:0.10. eMn,th =MEBPA + DP × conversion × Mmonomer.

27



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Page 28 of 36

Scheme 1. The proposed mechanism of photoinduced Fe-mediated ATRP in the presence of ligand TMPP, dNbpy and Me6TREN.

28


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Figure 1. Effect of the catalyst loadings on kinetics of photoinduced Fe-mediated ATRP with ligand TMPP ([MMA]:[EBPA]:[FeCl3·6H2O]:[TMPP]=500:1:0.05: 0.10 / 500:1:0.10:0.20 / 500:1:0.25:0.50): (A) semilogarithmic kinetic plots versus time, (B) Mn and Mw/Mn versus conversion.

29



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Page 30 of 36

Figure 2. Effect of the catalyst loadings on kinetics of photoinduced Fe-mediated ATRP with

ligand

dNbpy ([MMA]:[EBPA]:[FeCl3·6H2O]:[dNbpy]=500:1:0.05:0.15

/

500:1:0.10:0.30 / 500:1:0.25:0.75): (A) semilogarithmic kinetic plots versus time, (B) Mn and Mw/Mn versus conversion.

30


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Figure 3. Effect of the catalyst loadings on kinetics of photoinduced Fe-mediated ATRP with ligand Me6TREN ([MMA]:[EBPA]:[FeCl3·6H2O]:[Me6TREN]= 500:1:0.05:0.10 / 500:1:0.10:0.20 / 500:1:0.25:0.50): (A) semilogarithmic kinetic plots versus time, (B) Mn and Mw/Mn versus conversion.

31



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Figure 4. UV-vis absorption spectra of each component in the reaction system in DMF, conditions:(A) [MMA]:[EBPA]=500:1, [MMA]:[EBPA]:[FeCl3·6H2O]=500:1:0.05, [MMA]:[EBPA]:[TMPP]=500:1:0.10,

[MMA]:[EBPA]:[dNbpy]=500:1:0.15,

[MMA]:[EBPA]:[Me6TREN]=500:1:0.10, all with 700 vol% DMF. (B) [MMA]: [EBPA]:[FeCl3·6H2O]:[TMPP]=500:1:0.05:0.10,

[MMA]:[EBPA]:[FeCl3·6H2O]:

[dNbpy]=500:1:0.05:0.15, [MMA]:[EBPA]: [FeCl3·6H2O]:[Me6TREN] =500:1:0.05: 0.10, all with 700 vol% DMF.

32


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Figure 5. Photoinduced Fe-mediated ATRP with “on-off” light switch: (A) semilogarithmic kinetic plots versus time with ligands TMPP, dNbpy and Me6TREN. (B)

Mn

and

Mw/Mn

versus

conversion,

condition:

[MMA]:[EBPA]:

[FeCl3·6H2O]:[TMPP] =500:1:0.05:0.10. (C) Mn and Mw/Mn versus conversion, condition: [MMA]:[EBPA]:[FeCl3·6H2O]:[dNbpy]=500:1:0.05:0.15. (D) Mn and Mw/Mn versus conversion, condition:[MMA]:[EBPA]:[FeCl3·6H2O]:[Me6TREN] =500:1:0.05:0.10.

33



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Page 34 of 36

Figure 6. 1H NMR spectra of PMMA macroinitiators (Ⅰ, Ⅱ and Ⅲ) prepared by photoinduced Fe-mediated ATRP in the presence of different ligands TMPP (Ⅰ), dNbpy (Ⅱ) and Me6TREN (Ⅲ), condition ：

[MMA]:[EBPA]:[FeCl3·6H2O]:[TMPP]

=500:5:0.05:0.10, [MMA]:[EBPA]:[FeCl3·6H2O]:[dNbpy]=500:5:0.05:0.15, [MMA]: [EBPA]:[FeCl3·6H2O]:[ Me6TREN] =500:5:0.05:0.10.

34


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Figure 7. GPC traces of macroinitiators (Ⅰ, Ⅱ and Ⅲ) and the corresponding pseudo block copolymers PMMA-b-PMMA.

35



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Page 36 of 36

For Table of Contents Only

36


Visible-Light-Induced Atom-Transfer-Radical Polymerization with a

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