Photochemically Mediated Atom Transfer Radical Polymerization of

Jul 19, 2012 - Copyright © 2012 American Chemical Society .... When 100 ppm of a CuBr2/PMDETA was added to the methyl ..... Matyjaszewski , K. ; Davi...
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Photochemically Mediated Atom Transfer Radical Polymerization of Methyl Methacrylate Using ppm Amounts of Catalyst Jaroslav Mosnácě k* and Markéta Ilčíková Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 41 Bratislava, Slovakia S Supporting Information *

ABSTRACT: Well-controlled polymerization of methyl methacrylate at 35 °C was achieved by photochemically mediated atom transfer radical polymerization using a copper catalyst concentration as low as 50−100 ppm. Irradiation at λ > 350 nm provided both a reduction of initially added copper(II) catalyst complexed with either PMDETA or TPMA ligand to a copper(I) activator and a sufficient rate of polymerization. Poly(methyl methacrylate) with a narrow dispersity and predictable molar mass was obtained when an initiator, such as 2-bromopropionitrile, was used. Successful chain-extension polymerization confirmed the living character of the photopolymerization system.

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INTRODUCTION Living/controlled polymerizations have a tremendous impact not only on polymer and materials science but also on related technology. These polymerizations open a wide range of possibilities for the preparation of well-defined polymers with precisely designed molecular architectures and nanostructured morphologies.1,2 Such polymers represent new materials with improved or completely new properties. Presently, various reversible-deactivation radical polymerizations (controlled radical polymerizations; CRP) are known.2,3 The range of suitable monomers is larger for radical polymerization (RP) than for other kinds of chain polymerization because the radicals are tolerant to many functionalities, including acidic, hydroxy, and amino groups.3−5 RP is unaffected by water and protic impurities and can be performed in bulk, solution, aqueous suspension, emulsion, dispersion and so forth; thus, the polymerization conditions for RP do not need to be as strict as those needed for living anionic polymerization.3,6,7 Atom transfer radical polymerization (ATRP) is one of the most powerful CRP techniques. In recent years, many variations of ATRP have been developed.8−11 ATRP with activators generated by electron transfer (AGET) enables the use of the air stable forms of catalyst complexes, which are reduced in situ to their respective activators by various reducing agents.8,9 This principle was found to also be applicable for systems with diminished metal catalyst concentrations as low as 10 ppm in activators regenerated by electron transfer (ARGET) or initiators for continuous activator regeneration (ICAR) ATRP.10−12 These systems are conducted in the presence of an excess amount of reducing agent such that metal activators are continuously regenerated from metals in higher oxidation state deactivators. Various methods to activate dormant species in CRP, such as thermal, photochemical, and chemical stimuli, have been © XXXX American Chemical Society

developed. Photochemical stimuli have some particular advantages.13 The most substantial advantage is that the photochemical process is extremely fast; thick polymer films can be formed within one second under UV irradiation.13,14 For polymer coatings, inks, photoresists, and so forth, photopolymerization is considered the most effective and the most advantageous technologically.15 Photopolymerization represents an ecological alternative to the thermal process because no volatile organic compounds are released in this process.13 Low activation energy is another advantage of photochemical initiation; it is possible to perform photopolymerization at or below room temperature.13,16−18 In addition, a more specified course of polymerization is advantage of the lower temperatures. Photoiniferter (photoinitiator-transfer-terminator) polymerization using a dithiocarbamate under UV irradiation is one of the earliest described CRP techniques.19,20 Since then, there have been many papers describing photopolymerization using photosensitive reversible addition−fragmentation chain transfer (RAFT) agents based on dithiocarbamate derivatives.18,21−26 A visible-light-induced CRP, based on degenerative iodine transfer processes, using a dinuclear manganese complex [Mn2(CO)10] in conjunction with alkyl iodides was recently developed by Kamigaito et al.27−29 This system was applicable to vinyl acetate, acrylates, styrene, and vinylidene flouride with the use of appropriate initiators.27−31 Yamago et al. reported a photoinduced organotellurium-mediated CRP of meth(acrylate)s by direct photolysis of the C−Te bond of the dormant species.32,33 Several attempts of photo-CRP were also made using chromophoric nitroxides for nitroxide-mediated radical polymerization (NMP).34−38 Received: April 16, 2012 Revised: June 25, 2012

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Table 1. Results of PhotoATRP LCCa and ARGET ATRP of MMA entry 1 2 3 4 5 6 7 8 9 10 11 12

initiator

EBiB EBiB BPN BPN BPN BPN BPN BPN BPN BPN

ligand PMDETA PMDETA TPMA PMDETA TPMA PMDETA TPMA PMDETA PMDETA TPMA TPMA

CuBr2/L [ppm]

reducing agent

time [h]

convb [%]

Mn,theor [g/mol]

Mn,exp [g/mol]

Mw/Mn

100 100 100 100 100 100a 100a 200 50 50 25

λ > 350 nm λ > 350 nm λ > 350 nm λ > 350 nm λ > 350 nm λ > 350 nm Sn(Oct)2c Sn(Oct)2c λ > 350 nm λ > 350 nm λ > 350 nm λ > 350 nm

5 3 8 12 8 10 10 6 8.5 10 11 8.5

4 350 nm (i.e., irradiation at λ = 366, 405, 408, 436, and 546 nm) was performed using a medium-pressure mercury lamp in a Spectramat apparatus (Ivoclar AG, Liechtenstein, glass filter λ = 350−550 nm; Figure S1). To prevent heating of the sample during irradiation, the Schlenk tube was placed into a double-layer glass tube. In the outer layer of the finger, water thermostated to 25 °C was circulated. With such a cooling system, the temperature of the reaction mixture during the photopolymerization process slightly increased but remained between 30 and 35 °C. The distance of each sample from the arc was ∼10 cm. The power of the light measured at the sample position was ∼20 mW cm−2. Preparation of a Macroinitiator and Chain Extension. A PMMA-Br macroinitiator was prepared using similar procedures to those described above with an MMA/BPN/CuBr2/PMDETA ratio of 200/1/0.02/0.02 in 25 vol % anisole. A PMMA-Br macroinitiator with an Mn of 8200 g/mol and an Mw/Mn of 1.11 (45% conversion at 4.5 h polymerization) was obtained after passing through an activated neutral alumina column, followed by precipitation in n-hexane. A chain extension of the PMMA-Br macroinitiator with MMA was performed using an MMA/PMMA-Br/CuBr2/PMDETA ratio of 600/1/0.06/ 0.06 in 25 vol % anisole. ARGET ATRP. For ARGET ATRP of MMA, a similar procedure to that described above for photoATRP was used, except only 1 mL of anisole was initially added. The rest of the anisole containing Sn(Oct)2 and ligand was added under an argon atmosphere after the freeze− pump−thaw cycles and backfilling with argon to start the polymerization by reducing the copper(II) catalyst. The Schlenk flask was then immediately immersed in a water bath thermostated to 35 °C. Analysis. The molar masses and dispersity of the polymers were analyzed using gel permeation chromatography (GPC); the setup consisted of a Waters 515 pump, two PPS SDV 5-μm columns (d = 8 mm, l = 300 mm; 500 Å + 105 Å), and a Waters 410 differential refractive index detector with THF as an eluent at a flow rate of 1.0 mL/min. Poly(methyl methacrylate) standards were used for calibration. Anisole was used as the internal standard to correct for any fluctuation in the THF flow rate. Monomer conversions were determined by 1H NMR on a 400 MHz VNMRS Varian NMR

Only a few studies have investigated photochemically initiated ATRP. Qin et al. reported a photoATRP initiating system consisting of 2,2-dimethoxy-2-phenylacetophenone (DMPA)/ferric tri(N,N-diethyldithiocarbamate) [Fe(dtc)3] for polymerization of methyl methacrylate (MMA) in toluene at ambient temperature.39 In this system, DMPA, the photoinitiator, produced active radicals under UV irradiation, which were trapped by Fe(dtc)3, while R−S2CNEt2 and the lower oxidation state metal salt, Fe(dtc)2, were formed. Activation then proceeded by UV light irradiation with dtc functioning as a reversible transfer group. A similar approach of using dithiocarbamates, but in combination with a copper catalyst, was used in photoATRP of MMA by Kwak et al.40 Ishizu et al. used a combination of pendant photolabile dithiocarbamate groups with a copper catalyst for the synthesis of nanocylinders consisting of graft copolymers by photoinduced ATRP of tert-butyl methacrylate (BMA) and MMA.41 A photoATRP system without photolabile dithiocarbamates was recently reported by the Yagci group.42,43 An in situ photochemical reduction of an air-stable CuBr2/PMDETA catalyst to a CuBr/PMDETA activator was used, which subsequently activated an R−Br initiator and started the polymerization of MMA at ambient temperature. In addition, the polymerization was found to accelerate under irradiation. 43,44 This group also used the same system in combination with various photoinitiators.45 In all of these studies, however, the copper catalyst and the initiator were used in equimolar amounts. Herein, we report that photochemicaly mediated ATRP of MMA can be performed with CuBr2/L catalyst amounts on the order of ppm while preserving good control over the molar mass and narrow dispersity. Using a photochemically mediated ATRP system with a low concentration of catalyst (photoATRP LCC) has the advantages of reducing the amount of environmentally harmful chemical reducing agents and avoiding problems with the removal of a large amount of catalyst from the polymer product.

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EXPERIMENTAL SECTION

Materials. Methyl methacrylate was purchased from Sigma-Aldrich and purified before use by passing through a basic alumina column to remove the inhibitor. Ethyl 2-bromo-2-methylpropionate (EBiB), 2bromopropionitrile (BPN), N,N,N′,N″,N′′-pentamethyldiethylenetriamine (PMDETA), copper(II) bromide, tin(II) 2-ethylhexanoate (Sn(Oct)2), and anisole (all from Sigma-Aldrich) were used as received. CuBr (Sigma-Aldrich) was purified according to procedures reported in the literature.46 Tris(2-pyridylmethyl)amine (TPMA) was B

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Figure 1. (a) Kinetic plots and (b) evolution of the molar mass and Mw/Mn with the conversion of MMA during photoATRPLCC using EBiB as an initiator and either PMDETA or TPMA as the ligand complexing with the CuBr2 catalyst. Experimental conditions: MMA/EBiB/CuBr2/L = 200/1/ 0.02/0.02; [MMA] = 7.5 M; T = 35 °C, in anisole (25 vol %); irradiated at λ > 350 nm. spectrometer equipped with a 5 mm 1H−19F/15N−31P PFG AutoX DB NB probe at 25 °C in deuterated chloroform as the solvent.

is well-known that dimethyl 2-bromo-2,4,4-trimethylglutarate, which can be considered as a model for dimeric initiator, formed after reaction of EBiB with one molecule of MMA, is activated faster than the EBiB initiator, likely due to the back strain effect; this effect can result in both higher molar masses and a broader dispersity.4,48 As mentioned previously, the ATRP polymerization rate can be accelerated with irradiation;43,44 therefore, the effect of light on the ATRP polymerization rate of MMA with 100 ppm of a CuBr2/L catalytic system was investigated. As shown in Figure 2, the irradiation of the polymerization mixture with the CuBr2/

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RESULTS AND DISCUSSION Polymerization Using Ethyl 2-Bromo-2-methylpropionate as an Initiator. Control polymerizations were performed without an initiator by irradiation of either pure monomer/solvent mixture or a polymerization mixture containing 100 ppm of a CuBr2/PMDETA catalytic system (Table 1, entries 1 and 2, respectively). When only methyl methacrylate/anisole mixture was irradiated, no polymer was observed in GPC after 3 h of irradiation. Just after 5 h, a low signal of polymer with a molar mass of 174 000 and dispersity of 2.54 was observed in GPC, while NMR showed only about 4% monomer conversion. When 100 ppm of a CuBr2/ PMDETA was added to the methyl methacrylate/anisole mixture, a polymer with a molar mass of 12 200 g/mol and dispersity of 1.60 was obtained after 3 h of irradiation; the conversion of MMA, as determined by NMR, was below 1%. Photochemically mediated ATRP of MMA was initially investigated using EBiB as an initiator. Two ligands, PMDETA and TPMA, were studied in conjunction with a copper(II) bromide catalyst in the amount of 100 ppm to monomer (Table 1, entries 3 and 4), and the polymerizations were performed in 25 vol % of anisole. Kinetic plots are depicted in Figure 1a. The photoATRP LCC of MMA proceeded with first-order kinetics, indicating a constant concentration of growing radicals during polymerization. A short induction period was observed when the PMDETA ligand was used, likely as a result of not enough fast photoreduction of Cu(II) to Cu(I) activator. In contrast, no induction period was observed when using TPMA as a ligand. In the case of photoATRP LCC of MMA with the PMDETA ligand, despite the induction period, the rate of polymerization after 3 h was faster than that with the TPMA ligand. This result is in contrast to the higher redox potential and higher KATRP previously described for copper halide/TPMA compared with a copper halide/PMDETA catalytic system.47 Evolution of the molar mass and dispersity (Mw/Mn) (Figure 1b) shows that during photoATRP LCC of MMA with the EBiB initiator, the dispersity in both experiments was slightly broader (1.25−1.35), and the obtained molar masses were higher than those calculated theoretically. This result is likely a cause of the slow initiation when the EBiB initiator was used. It

Figure 2. Kinetic plot of ATRP of MMA during both irradiation at λ > 350 nm and no irradiation. Experimental conditions: MMA/EBiB/ CuBr2/TPMA = 200/1/0.02/0.02; [MMA] = 7.5 M; T = 35 °C, in anisole (25 vol %).

TPMA catalytic system for 5 h resulted in a fast polymerization of MMA with an apparent rate constant of 9.6 × 10−2 h−1; the monomer conversion after 5 h was 38%. After irradiation for 5 h, the polymerization mixture was mixed in the dark for 16 h at 35 °C; the conversion of the monomer increased during this time by only ∼2%. Thus, the rate of polymerization in the dark, with an apparent rate constant of ∼2 × 10−3 h−1, was significantly lower than that in the light. Subsequently, the polymerization mixture was irradiated for an additional 7 h, and the rate of polymerization increased to the same apparent rate constant observed during the first irradiation step (9.6 × 10−2 h−1). Similar behavior was observed when the polymerization C

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Figure 3. (a) Kinetic plots and (b) evolution of the molar mass and Mw/Mn with the conversion of MMA during photoATRP LCC or ARGET ATRP. BPN was used as an initiator, and either PMDETA or TPMA was used as ligands complexing with the CuBr2 catalyst. Experimental conditions: photoATRP LCC: MMA/BPN/CuBr2/L = 200/1/0.02/0.02, irradiation at λ > 350 nm; ARGET ATRP: MMA/I/CuBr2/L/Sn(Oct)2 = 200/1/0.02/0.22/0.2; in all experiments: [MMA] = 7.5 M, T = 35 °C, anisole (25 vol %).

Scheme 1 presents the proposed simplified mechanism of photoATRP. The CuIX/L activator is first formed after the

was performed with the PMDETA ligand except with the short induction period, as described above. This experiment showed that the rate of photoATRP LCC in this system was nearly 2 orders of magnitude higher with irradiation than without irradiation. Thus, irradiation dramatically accelerated the rate of ATRP with low catalyst concentration and without any other reducing agent. Polymerization Using 2-Bromopropionitrile as an Initiator. To improve the control of the photoATRP LCC of MMA, an initiator ensuring faster initiation, such as BPN, was used instead of EBiB (Table 1, entries 5 and 6; Figure 3).49 As is shown in Figure 3a, a linear dependence was again observed in the kinetic plots, indicating a constant concentration of growing radicals during polymerization. Similar to the previous case, the rate of photopolymerization was higher using the PMDETA ligand than when using the TPMA ligand. Evolution of the molar mass and dispersity (Figure 3b), however, shows that in both cases the polymerization was well controlled with a narrow dispersity (below 1.20) and with molar masses of the polymers similar to those of the theoretical values. Dispersity was slightly narrower using the PMDETA ligand than when using the TPMA ligand. Polymerizations of MMA by ARGET ATRP were performed under the same conditions except that instead of the light, Sn(Oct)2 was used as a reducing agent. The results were then compared (Table 1, entries 7 and 8; Figure 3). Evolution of the molar mass and dispersity (Figure 3b) was almost identical with that of photoATRP LCC, which also had a slightly narrower dispersity when PMDETA was used as a ligand. The kinetic plots (Figure 3a) show that the rate of MMA polymerization by ARGET ATRP with the TPMA ligands was similar to the rate of polymerization observed for photoATRP LCC with the same ligand. In contrast, the rate of photoATRP LCC with the PMDETA ligand was significantly higher than the rate of ARGET ATRP with the same ligand, which was comparable to the polymerization rates with TPMA as the ligand. The higher rate of photoATRP LCC with the PMDETA ligand could be from the different redox potentials of Cu(II)/Cu(I) complexed with PMDETA when it is in excited state, as observed for some metal complexes.50−55 Regardless, additional studies are needed to explain the above-mentioned difference in the rate of polymerization.

Scheme 1

photochemical reduction of a deactivator by irradiation in the UV−vis region, while probably also bromide radicals are formed. Subsequently, polymerization is started by the activation of an RX initiator by the CuIX/L activator. In addition to the classical ATRP equilibrium between the activation and deactivation process (represented by activation (ka) and deactivation (kd) rate constants, respectively), two photochemical processes can occur during the subsequent propagation step. Absorption of the light by the CuIX/L activator results in the formation of the activator in its excited state [CuIX/L]*, which subsequently either returns to CuIX/L in the ground state through a radiation process (1/τ°) or proceeds to react with the initiator (ka* activation rate constant). Similarly, absorption of light by the CuIIX2/L deactivator results in the formation of the deactivator in its excited state [CuIIX2/L]*, which subsequently either returns to CuIIX2/L in the ground state through a radiation process (1/ τ°) or proceeds to react with the (macro)radical (kd* deactivation rate constant). Thus, contrary to classical ATRP, the polymerization rate in the photoATRP also depends on the ka* and kd* rate constants. It also is worth to mention that during the initial photochemical reduction of CuIIX2/L, halide radicals are probably generated. These radicals can contribute in formation of new polymer chains. However since the concentration of catalyst is very low, their contribution in initiation of new polymer chains is negligible. This could be D

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Figure 4. (a) Kinetic plots and (b) evolution of the molar mass and Mw/Mn with the conversion of MMA during photoATRP LCC using 50 ppm of copper catalyst. BPN was used as an initiator, and either PMDETA or TPMA was used as ligands complexing with the CuBr2 catalyst. Experimental conditions: photoATRP LCC: MMA/BPN/CuBr2/L = 200/1/0.01/0.01, irradiation at λ > 350 nm; in all experiments: [MMA] = 7.5 M, T = 35 °C, anisole (25 vol %).

extended polymer in the GPC spectra. After 7 h (78% conversion), the chain extended PMMA with Mn = 45 100 g/ mol and Mw/Mn = 1.18 was obtained. As observed from the GPC traces of the PMMA before and after the chain extension polymerization (Figure 5), the molar mass clearly increased with the absence of any appreciable amount of macroinitiator.

seen from the experiment carried out without R−Br initiator (Table 1, entry 2). Effect of Copper Catalyst Concentration. To obtain additional information on the effect of the copper catalyst amount and to determine the minimal catalyst concentration required for a well-controlled polymerization of MMA, experiments with various concentrations of CuBr2/L were performed (Table 1, entries 9−12). When the concentration of the CuBr2/PMDETA catalyst was increased to 200 ppm, polymerization was well controlled, similar to what was observed with 100 ppm of the catalyst except that a slightly longer induction period was observed at the beginning of polymerization. Decreasing the CuBr2/PMDETA amount to 50 ppm resulted in a slower polymerization and a polymer with a higher molar mass than what was theoretically calculated and a dispersity of ∼1.6, thus indicating loss of control (Table 1, entry 10; Figure 4). When polymerization was employed with TPMA as a ligand (Table 1, entry 11; Figure 4), decreasing the CuBr2/TPMA amount to 50 ppm resulted in a well-controlled polymerization with a predictable molar mass and narrow dispersity of the polymer. Further decreasing the CuBr2/TPMA amount to 25 ppm, however, resulted in a loss of control (Table 1, entry 12; Figure S2). The difference in control over the molar mass and dispersity between the experiments with a lower concentration of PMDETA and TPMA is likely caused by the lower stability of the Cu(II) complex of PMDETA compared with the Cu(II) complex of TPMA.12 Dissociation of the Cu(II) complex would result in lower absolute value of the deactivator concentration, decreasing the control of the polymerization system. Chain Extension of the PMMA−Br Macroinitiator. The living character of the photoATRP LCC was demonstrated by chain extending a PMMA−Br macroinitiator. The PMMA−Br macroinitiator (Mn = 8200 g/mol and Mw/Mn = 1.11) was prepared by photoATRP LCC under experimental conditions similar to that mentioned above with an MMA/BPN/CuBr2/ PMDETA ratio of 200/1/0.02/0.02. Polymerization was stopped after 4.5 h at 45% monomer conversion. The chain extension was then performed under identical experimental conditions with an MMA/PMMA−Br/CuBr2/PMDETA ratio of 600/1/0.06/0.06. A higher degree of polymerization was targeted in the chain extension polymerization to provide substantial separation between the macroinitiator and the

Figure 5. GPC traces from chain extension of PMMA-Br with MMA: (- - -) PMMA−Br macroinitiator and () chain extended PMMA after 78% conversion of MMA. Both the preparation of PMMA−Br macroinitiator and the chain extension was performed by photoATRP LCC using CuBr2/PMDETA. Experimental conditions: preparation of PMMA−Br: MMA/BPN/CuBr2/PMDETA = 200/1/0.02/0.02; chain extension: MMA/PMMA−Br/CuBr2/PMDETA = 600/1/0.06/0.06; in both polymerizations: [MMA] = 7.5 M, T = 35 °C, anisole (25 vol %), irradiation at λ > 350 nm.

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CONCLUSIONS In summary, ATRP of MMA employed with ppm amounts of copper catalyst under irradiation was reported. The polymerization started after the photochemical reduction of the copper(II) catalyst complex to a copper(I) activator. Subsequent activation/deactivation processes and thus also rate of polymerization were affected by irradiation. The rate of polymerization employed using low catalyst concentration was significantly higher under irradiation than in the dark without any reducing agent. The polymerization rate of MMA by photoATRP LCC was similar to or, in the PMDETA ligand case, even higher than the rate of ARGET ATRP employed E

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(12) Matyjaszewski, K.; Jakubowski, W.; Min, K.; Tang, W.; Huang, J. Y.; Braunecker, W. A.; Tsarevsky, N. V. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 15309−15314. (13) Yagci, Y.; Jockusch, S.; Turro, N. J. Macromolecules 2010, 43, 6245−6260. (14) Decker, C. Prog. Polym. Sci. 1996, 21, 593−650. (15) Fouassier, J. P. Photochemistry and UV Curing, New Trends; Research Signpost: Trivandrum, India, 2006. (16) Tasdelen, M. A.; Durmaz, Y. Y.; Karagoz, B.; Bicak, N.; Yagci, Y. J. Polym. Sci., Polym. Chem. 2008, 46, 3387−3395. (17) Quinn, J. F.; Barner, L.; Barner-Kowollik, C.; Rizzardo, E.; Davis, T. P. Macromolecules 2002, 35, 7620−7627. (18) Lu, L. C.; Yang, N. F.; Cai, Y. L. Chem. Commun. 2005, 5287− 5288. (19) Otsu, T.; Yoshida, M. Makromol. Chem., Rapid Commun. 1982, 3, 127−132. (20) Otsu, T.; Yoshida, M.; Tazaki, T. Makromol. Chem., Rapid Commun. 1982, 3, 133−140. (21) Otsu, T.; Matsumoto, A. Adv. Polym. Sci. 1998, 136, 75−137. (22) Davis, T. P.; Rizzardo, E.; Barner, L.; Barner-Kowollik, C.; Quinn, J. F. Abstr. Pap. Am. Chem. Soc. 2002, 224, U448−U448. (23) Ishizu, K.; Khan, R. A.; Ohta, Y.; Furo, M. J. Polym. Sci., Polym. Chem. 2004, 42, 76−82. (24) Lu, L.; Zhang, H. J.; Yang, N. F.; Cai, Y. L. Macromolecules 2006, 39, 3770−3776. (25) Jiang, W. D.; Lu, L. C.; Cai, Y. L. Macromol. Rapid Commun. 2007, 28, 725−728. (26) Durmaz, Y. Y.; Karagoz, B.; Bicak, N.; Yagci, Y. Polym. Int. 2008, 57, 1182−1187. (27) Koumura, K.; Satoh, K.; Kamigaito, M. Macromolecules 2008, 41, 7359−7367. (28) Koumura, K.; Satoh, K.; Kamigaito, M. Macromolecules 2009, 42, 2497−2504. (29) Koumura, K.; Satoh, K.; Kamigaito, M. J. Polym. Sci., Polym. Chem. 2009, 47, 1343−1353. (30) Koumura, K.; Satoh, K.; Kamigaito, M. Polym. J. 2009, 41, 595− 603. (31) Asandei, A. D.; Adebolu, O. I.; Simpson, C. P. J. Am. Chem. Soc. 2012, 134, 6080−6083. (32) Yamago, S. Chem. Rev. 2009, 109, 5051−5068. (33) Yamago, S.; Ukai, Y.; Matsumoto, A.; Nakamura, Y. J. Am. Chem. Soc. 2009, 131, 2100−2101. (34) Hu, S.; Malpert, J. H.; Yang, X.; Neckers, D. C. Polymer 2000, 41, 445−452. (35) Guillaneuf, Y.; Bertin, D.; Gigmes, D.; Versace, D. L.; Lalevee, J.; Fouassier, J. P. Macromolecules 2010, 43, 2204−2212. (36) Guillaneuf, Y.; Versace, D. L.; Bertin, D.; Lalevee, J.; Gigmes, D.; Fouassier, J. P. Macromol. Rapid Commun. 2010, 31, 1909−1913. (37) Versace, D. L.; Lalevee, J.; Fouassier, J. P.; Gigmes, D.; Guillaneuf, Y.; Bertin, D. J. Polym. Sci., Polym. Chem. 2010, 48, 2910− 2915. (38) Versace, D. L.; Lalevee, J.; Fouassier, J. P.; Guillaneuf, Y.; Bertin, D.; Gigmes, D. Macromol. Rapid Commun. 2010, 31, 1383−1388. (39) Qin, S. H.; Qin, D. Q.; Qiu, K. Y. New J. Chem. 2001, 25, 893− 895. (40) Kwak, Y.; Matyjaszewski, K. Macromolecules 2010, 43, 5180− 5183. (41) Ishizu, K.; Katsuhara, H. Des. Monomers Polym. 2006, 9, 99−115. (42) Tasdelen, M. A.; Uygun, M.; Yagci, Y. Macromol. Rapid Commun. 2011, 32, 58−62. (43) Tasdelen, M. A.; Uygun, M.; Yagci, Y. Macromol. Chem. Phys. 2010, 211, 2271−2275. (44) Guan, Z. B.; Smart, B. Macromolecules 2000, 33, 6904−6906. (45) Tasdelen, M. A.; Uygun, M.; Yagci, Y. Macromol. Chem. Phys. 2011, 212, 2036−2042. (46) Keller, R. N.; Wycoff, H. D. Inorg. Synth. 1946, 2, 1−4. (47) Tang, W.; Kwak, Y.; Braunecker, W.; Tsarevsky, N. V.; Coote, M. L.; Matyjaszewski, K. J. Am. Chem. Soc. 2008, 130, 10702−10713.

with Sn(Oct)2 as a reducing agent in the CuBr2/Sn(Oct)2/L ratio of 1/10/11. Control of the polymerization depended on the specific initiator used. EBiB resulted in an initiation that was too slow, but when BPN was used as an initiator with either PMDETA or TPMA ligands, PMMA with a predictable molar mass and narrow dispersity was prepared. The control of the photoATRP LCC polymerization system with respect to the dispersity and predictability of the molar mass of the PMMA product was comparable to that of ARGET ATRP. Wellcontrolled photoATRP of MMA could be employed with as little as 50 ppm of the CuBr2/TPMA catalyst without the addition of a reducing (co)agent. A high degree of livingness of the polymer chain ends was found by the chain-extension polymerization experiment.

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ASSOCIATED CONTENT

S Supporting Information *

Figure showing absorption spectra of polymerization mixtures, part of emission spectra of medium-pressure mercury lamp, and transmittance of used filter; figure of kinetic plots, evolution of molecular weight and Mw/Mn with monomer conversion during photoATRP of MMA employed with 25 ppm of CuBr2/ TPMA; figure showing decrease of Cu(II) d−d ligand field transition band in UV−vis absorption spectra during irradiation of polymerization mixture containing CuBr2/PMDETA complex. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the Slovak Research and Development Agency for financial support through the grant APVV-0109-10 as well as the Centre of Excellence SAS for Functionalized Multiphase Materials (FUN-MAT).

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REFERENCES

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