Visible-Light-Induced Reversible Complexation Mediated Living

Article pubs.acs.org/Macromolecules

Visible-Light-Induced Reversible Complexation Mediated Living Radical Polymerization of Methacrylates with Organic Catalysts Akimichi Ohtsuki, Atsushi Goto,* and Hironori Kaji* Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan S Supporting Information *

ABSTRACT: Photoinduced reversible complexation mediated polymerization (photo-RCMP) was developed as a new photoinduced living radical polymerization (LRP). It consisted of an alkyl iodide as a dormant species and an amine as a catalyst, using visible light at 350−600 nm. The amine catalysts include such common compounds as tributylamine. Mechanistically, the polymerization is induced by the photolysis of the dormant species and dormant species/catalyst complex, which frequently occurs as the main activation process. The polymer molecular weight and its distribution (Mw/Mn = 1.1−1.4) were well controlled in the polymerizations of methyl methacrylate and some functional methacrylates up to fairly high conversions in many cases. Perfectly no polymerization took place without photoirradiation, meaning that the system is an ideal photo “on”−“off” switchable system. The polymerization rate was also finely tunable by the external irradiation power. Attractive features of photo-RCMP include the uses of inexpensive compounds and visible light, good polydispersity control, good tolerance to functional groups, and fine response to external photoirradiation.

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also be used as external stimuli to switch the reactions “on” and “off” and can trigger the reactions locally at specific positions and spaces. In this regard, photoinduced LRP can expand the scope of LRP. It can widen a range of applicable monomers and open up new applications to photolithography, for example. There have been three approaches to develop photoinduced LRP. One is the direct photolysis of the carbon−X bond of Polymer-X. The earliest attempt was conducted for initiatortransfer-terminator agents (iniferters) (X = SCSNR2).7 However, the photolysis for iniferters was not very efficient. The direct photolysis was also examined in nitroxide-mediated polymerizations (NMP) (X = ONR2),8 reversible addition− fragmentation chain transfer (RAFT) polymerizations (X = SCSR),9 and cobalt-mediated radical polymerizations (CMRP) (X = Co complex).10 While the photolysis was effective in these systems, photodegradation of the dormant species or other side reactions significantly occurred by photoirradiation, broadening the polydispersity particularly at a later stage of polymerization, in many cases. The direct photolysis was the most successfully used in organotellurium-mediated radical polymerizations (TERP) (X = TeR).11 Low-polydispersity polymers were yielded up to high conversions due to both effective photolysis and insignificant side reactions. The second approach focuses on catalysts. Photoredox copper and iridium catalysts were used in atom transfer radical polymerization (ATRP) with an alkyl bromide dormant species (X = Br).12 The catalysts were

INTRODUCTION Living radical polymerization (LRP) has widely been used as an efficient method for preparing well-defined polymers with low polydispersity (narrow distribution of molar mass).1−4 LRP is also called reversible deactivation radical polymerization (RDRP). It is based on the reversible activation of the dormant species (Polymer-X) to the propagating radical (Polymer•) (Scheme 1a). (In Scheme 1a, kact is the pseudo-first-order Scheme 1. Reversible Activation: (a) General Scheme and (b) RCMP

activation rate constant and kdeact is the deactivation rate constant for the general scheme of LRP.) Polymer-X is activated thermally, chemically, or photochemically, depending on the capping agent (X). Photoinduced reactions are widely used in organic synthesis5 and polymer synthesis.6 The reactions do not require heat and thus are applicable to functional groups and materials that decompose at high temperatures. Photochemical stimuli can © XXXX American Chemical Society

Received: October 29, 2012 Revised: December 1, 2012

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dx.doi.org/10.1021/ma302244j | Macromolecules XXXX, XXX, XXX−XXX

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Scheme 2. Possible Mechanisms for the Photolysis of Polymer-I with Amine

mechanisms depend on the dormant species, catalyst, and irradiation wavelength. The latter mechanism is particularly interesting, since a wide range of catalysts with different absorption wavelengths may be used to induce RCMP. This may open up a unique feature of this polymerization. In this paper, we report photo-RCMP at ambient temperature. We present the polymerization performance of methyl methacrylate (MMA) and functional methacrylates. We also show a mechanistic study, use of three different catalysts (Figure 1), systematic studies on the catalyst concentrations and irradiation power, and an attempt toward high molecular weights.

inactive in the dark and became active under photoirradiation, successfully running ATRP under the irradiation. The third approach is the use of conventional13 and other14,15 photoinitiators to supply Polymer• in NMP, RAFT, CMRP, ATRP, and iodide-transfer polymerization (ITP) systems. In many cases, the photoinitiators worked as good alternatives to thermal initiators, successfully yielding low-polydispersity polymers. However, in principle, the third approach does not directly enhance the reversible activation, contrary to the first and second approaches. Two photoinitiators recently used, i.e., alkyl iodide/Mn2(CO)10 initiator for ITP14 and dithiocarbamate initiator for ATRP,15 do not generate new chains during the polymerization, while conventional photoinitiators13 such as azo compounds generate new chains. In the latter case, the new chains more or less broaden the polydispersity. We recently developed two new families of LRP, both of which use iodine as an X and an organic molecule as a catalyst. We termed them reversible chain transfer catalyzed polymerization (RTCP)16 and reversible complexation mediated polymerization (RCMP)17,18 after their mechanisms. The latter polymerization will be a topic in the present paper. It uses amines as catalysts. The amines include such simple ones as tributylamine (TBA). The low cost, low toxicity, and ease of handling may be attractive features of the catalysts. The mechanism is shown in Scheme 1b. TBA abstracts iodine from the dormant species (Polymer-I) to generate Polymer• and a complex of iodine radical (I•) and TBA (I• complex). Since I• complex is not a stable radical, it recombines with another I• complex to give a complex of iodine molecule (I2) and TBA (I2 complex). Polymer• reacts with both I• and I2 complexes (deactivators) to regenerate Polymer-I and TBA. This process is a reversible complexation of iodine and catalyst. (In Scheme 1b, ka and kda are the activation and deactivation rate constants, respectively, for the reversible complexation.) In our previous studies, the process was induced under heating at 80−90 °C.17,18 In the literature, the formation of an alkyl radical from an alkyl halide with an amine was studied in organic chemistry.19,20 In all cases, the reaction was irreversible. We found a new and reversible reaction to develop RCMP, as mentioned above. Interestingly, the literature reactions proceeded not only under heating19 but also under photoirradiation.20 This fact promoted us to use photoirradiation to our reaction, developing photoinduced RCMP (photo-RCMP) in the present study. Photo-RCMP contains only an alkyl iodide (dormant species) and an amine (catalyst) and uses visible light for irradiation. It is among the most simple, inexpensive, and robust photoinduced LRPs. It is classified to the first approach mentioned above, directly regulating the reversible activation and giving no new chains in principle. Mechanistically (Scheme 2), the C−I bond of a “free” dormant species is photodissociated and the released I• is captured by amine (Scheme 2a), or a complex of dormant species and amine is initially formed and the C−I bond of the complex is subsequently photodissociated (Scheme 2b).19 The contributions of the two

Figure 1. Structures of an alkyl iodide and catalysts used in this work.

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RESULTS AND DISCUSSION UV−vis Measurement. We carried out UV−vis measurement for a representative system containing 2-cyanopropyl iodide (CP-I) (Figure 1) as a low-mass dormant species and TBA as a catalyst. Figure 2 shows the absorption spectra of

Figure 2. UV−vis spectra of TBA (80 mM) only (dotted line), CP-I (80 mM) only (dashed line), and a mixture of CP-I (80 mM) and TBA (80 mM) (solid line) in MMA (ambient temperature).

TBA (80 mM) only (dotted line), CP-I (80 mM) only (dashed line), and a mixture of CP-I (80 mM) and TBA (80 mM) (solid line) in bulk MMA. The spectrum of TBA had a peak at 290 nm and ranged to about 400 nm (dotted line). The spectrum of CP-I had a peak at 280 nm and ranged to about 400 nm (dashed line). A new shoulder peak appeared for the mixture of CP-I and TBA at about 400 nm and ranged from 350 to 500 nm. The new peak would correspond to a complex of CP-I and TBA. Such red-shifted absorption was reported for complexes of alkyl chlorides/bromides with amines.19 In all B


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experiments shown below, we used visible light at a wavelength of 350−600 nm. (In a strict sense, this region slightly includes UV light (under 380 nm).) This wavelength covers the absorption of both free dormant species and dormant species/ catalyst complex. Experimental Proof of Photolysis. To confirm that the photolysis takes place under the visible light irradiation, we carried out a radical trap experiment (Figure 3).21 A toluene-d8

Figure 4. Plot of ln([M]0/[M]) vs t for the MMA/CP-I/catalyst systems (ambient temperature): [MMA]0 = 8 M (in bulk); [CP-I]0 = 80 mM; [catalyst]0 = 0 or 20 mM; xenon lamp power = 60 W; wavelength = 350−600 nm. The symbols are indicated in the figure. The structures of the catalysts are shown in Figure 1.

Figure 3. 1H NMR spectra (in the range 0.5−2.5 ppm) of the toluened8 solution of CP-I (80 mM), TEMPO (160 mM), and TBA (160 mM) under xenon lamp irradiation (at 60 W power at 350−600 nm wavelength) (ambient temperature) for 0 and 1 h.

solution of CP-I (80 mM), TBA (160 mM), and 2,2,6,6tetramethylpiperidinyl-1-oxy (TEMPO) (160 mM) as a radical trap was photoirradiated for 1 h at ambient temperature. The light source was a xenon lamp at a 60 W electric power, equipped with band-pass optical mirror and filter at 350−600 nm. If the photolysis takes place, the released 2-cyanopropyl radical (CP•) from CP-I is trapped by TEMPO to generate CPTEMPO. Figure 3 shows the 1H NMR spectra of the solutions at time zero and 1 h. At 1 h, new signals appeared and agreed with those of CP-TEMPO (Supporting Information). The conversion of CP-I to CP-TEMPO was about 90% in this particular case. This clearly demonstrates effective photolysis of CP-I with TBA under the visible light irradiation. This observation should also be applicable to the polymeric dormant species with TBA, at least in a qualitative sense. (The chemical shifts of TBA in Figure 3 also slightly changed after the irradiation, since a part of TBA formed an I2/TBA complex after the irradiation (Supporting Information).) Polymerization of MMA with TBA. We carried out a bulk polymerization of MMA (8 M (100 equiv)) with CP-I (80 mM (1 equiv)) and TBA (20 mM (0.25 equiv)) under the visible light irradiation (at a lamp power of 60 W and a wavelength of 350−600 nm) at ambient temperature (Figures 4 and 5 (filled circles) and Table 1 (entry 1)). The polymerization was conducted in a test tube (with 1.5 cm diameter) with magnetic stirring. The polymerization proceeded up to a high monomer conversion in a fairly short time, e.g., 80% for 5 h. The firstorder plot of the monomer concentration [M] (Figure 4) was linear until about 50% conversion, and then the polymerization rate Rp gradually increased due to a gel effect. The numberaverage molecular weight Mn well agreed with the theoretical value Mn,theo, and the polydispersity index (PDI = Mw/Mn, where Mw is the weight-average molecular weight) was as small as 1.2−1.3 from an early stage of polymerization, meaning sufficiently effective photolysis (a sufficiently high frequency of

Figure 5. Plots of Mn and Mw/Mn vs conversion for the MMA/CP-I/ catalyst systems shown in Figure 4. The symbols are indicated in the figure.

the activation−deactivation cycle induced by the irradiation). Also importantly, PDI kept relatively small (about 1.4) up to high conversions, demonstrating the success and usefulness of photo-RCMP. Without TBA (catalyst) (but with CP-I), the polymerization did not smoothly proceed, reaching only a low conversion (about 10%) and a large PDI (about 1.6) for 4 h (Figures 4 and 5 (open circles)). This means that the observed successful photo-RCMP was due to the combination of CP-I and TBA. To examine the livingness of the photo-RCMP, we carried out elemental analysis of the obtained polymers (after purification by preparative GPC) (Supporting Information). The elemental analysis of iodine showed that the polymers obtained at 2 h (31% conversion), 3 h (47% conversion), and 4 h (67% conversion) (Figures 4 and 5 (filled circles)) included high fractions, i.e., 92%, 92%, and 90%, respectively (with ±5% experimental error), of active polymer possessing iodine at the chain end. We also carried out 1H NMR analysis for the polymer at 2 h, estimating the fraction of active polymer to be 91−97% (Supporting Information). (For the higher molecular C


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Table 1. Photo-RCMPs of Several Monomers under Xenon Lamp Irradiation at 350−600 nm Wavelength (Ambient Temperature)

a

entry

monomer (equiv to [CP-I]0)

lamp power (W)

catalyst

[CP-I]0/[catalyst]0 (mM)

t (h)

conv (%)

Mn (Mn,theo)

PDI

1 2 3 4 5 6 7 8 9 10

MMA (100) MMA (100) MMA (100) MMA (100) EHMA (100) BzMA (100) GMA (100) HEMA (100) PEGMA (100) DMAEMA (100)

60 60 60 sunlighta 120 60 60 60 60 60

TBA PMDETA TDEAP TBA TBA TBA TBA TBA TBA TBA

80/20 80/20 80/20 80/20 80/80 80/80 80/5 80/20b 80/10 80/80

4 2.5 4 2.5 2 0.5 1 2 1 1.5

67 60 51 51 97 37 53 98 30 78

6300 (6700) 5900 (6000) 4100 (5100) 5700 (5100) 17100 (19200) 9200 (6500) 9500 (7500) 12000 (12800) 12500 (9000) 13400 (12300)

1.20 1.21 1.23 1.17 1.17 1.42 1.35 1.10 1.31 1.31

At around noon in October in Kyoto. bAddition of I2 (10 mM).

weight polymers at 3 and 4 h, quantitative analysis of the polymer chain end by NMR was difficult.) These analyses demonstrate good livingness (insignificant photoinduced side reactions) in this condition. Mechanistically, Polymer-I can also be activated by degenerative chain transfer (DT) with Polymer•.3,4 However, the DT constant (Cex = 1.6)17 for MMA is so small that the DT mechanism only (ITP) cannot achieve PDI < 1.7 in batch. In order to achieve low polydispersity, Polymer-I must be frequently activated by the photolysis of Polymer-I, along with a small contribution by DT. In contrast, in large Cex systems like TERP,22 slow photolysis of Polymer-X to continuously generate Polymer• is sufficient to achieve low polydispersity due to the fast DT.11 Low lamp power may be used in such large Cex systems.11 Triamine and Phosphine Catalysts. Besides TBA (monoamine), we studied pentamethyldiethylenetriamine (PMDETA) (Figure 1) (triamine) and tris(diethylamino)phosphine (TDEAP) (Figure 1) (phosphine) as catalysts. The two catalysts also well worked, yielding low polydispersity polymers (Figures 4 and 5 and Table 1 (entries 2 and 3)). PMDETA exhibited even faster polymerization than TBA (Figure 4), suggesting faster photolysis for PMDETA. Compared with the monoamine TBA, the triamine PMDETA can more effectively coordinate iodine by wrapping iodine with the multiple nitrogens. Thus, the complex of the dormant species and PMDETA can be more formed, which may lead to faster photolysis. TDEAP (phosphine) had blue-shifted absorption (with a peak top of 350 nm) for the CP-I/catalyst complex (Supporting Information), compared with that of the amines (with a peak top at 400 nm). This suggests that we may tune irradiation wavelength with appropriate catalysts, which we will study in the future. Catalyst Concentration and Lamp Power. We used TBA as a catalyst in the experiments shown below. We systematically studied the effect of the catalyst concentration. We studied the polymerizations of MMA with a fixed amount of CP-I (80 mM) and various amounts of TBA (20−80 mM) at a 60 W lamp power (Figures 6 and 7). As expected from the equilibrium of the reversible activation (Scheme 1b), Rp increased with an increase of the TBA concentration (Figure 6). The polydispersity was similarly well controlled in all examined cases (Figure 7). We also systematically studied the effect of the irradiation power. We fixed the concentrations of CP-I (80 mM) and TBA (80 mM) and varied the lamp power (0−300 W) (Figures 8 and 9). Again, as expected from the equilibrium (Scheme 1b),

Figure 6. Plot of ln([M]0/[M]) vs t for the MMA/CP-I/TBA systems (ambient temperature): [MMA]0 = 8 M (in bulk); [CP-I]0 = 80 mM; [TBA]0 = 0, 20, 40, or 80 mM; xenon lamp power = 60 W; wavelength = 350−600 nm. The symbols are indicated in the figure.

Figure 7. Plots of Mn and Mw/Mn vs conversion for the MMA/CP-I/ TBA systems shown in Figure 6. The symbols are indicated in the figure.

Rp increased with an increase of the lamp power (hence the activation rate constant) (Figure 8). PDI became somewhat larger with an increase of the power (Figure 9), indicating side reactions at high powers (such as 300 W). Figure 8 importantly shows perfectly no polymerization occurring without irradiation. Namely, the system is an ideal D


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Figure 8. Plot of ln([M]0/[M]) vs t for the MMA/CP-I/TBA systems (ambient temperature): [CP-I]0 = 80 mM; [TBA]0 = 80 mM; xenon lamp power = 0, 60, 150, or 300 W; wavelength = 350−600 nm. The symbols are indicated in the figure.

Figure 11. Plots of Mn and Mw/Mn vs conversion for the MMA/CP-I/ TBA system shown in Figure 10.

was switched “on” and the polymerization smoothly proceeded (restarted) in all cycles. When the lamp was turned off, the system was immediately switched “off” and perfectly no polymerization occurred in the dark. Also importantly, Rp was finely tuned by the lamp power. At the studied 30, 60, 30, and 120 W lamp powers in the four cycles (Figure 10), the incremental conversion was 5, 12, 5, and 25%, respectively, in each 30 min polymerization. Thus, the system was repeatedly switched “on” and “off” by the irradiation, and Rp was finely tunable according to the lamp power at 30−120 W. The Mn and polydispersity were also well controlled after the very initial stage of polymerization (Figure 11). This system is an excellent photoswitchable and tunable LRP. The light source was not limited to a xenon lamp, as even sunlight (without an optical filter) was also applicable (Table 1 (entry 4)). Toward High Molecular Weights. We preliminarily examined the synthesis of higher molecular weight polymers. Figures 12 and 13 show the results for the target degrees of polymerization (DPs) of 100, 400, and 600 at 100% conversion. Small PDI (= 1.2−1.5) values were achieved up to about 300 DPs (Mn = ∼30 000). This can widen the usefulness of this polymerization. However, PDI became large at DPs > 300 in the studied cases. We are currently studying controlled polymerization at DPs > 300. Functional Methacrylates. Photo-RCMP was compatible with several functional groups. Low polydispersity (PDI = 1.1− 1.4) polymers were successfully obtained for some functional methacrylates with hydrophobic and hydrophilic functionalities such as 2-ethylhexyl (EHMA), benzyl (BzMA), epoxy (GMA), hydroxyl (HEMA), poly(ethylene glycol) (PEGMA), and dimethylamino (DMAEMA) groups (Table 1 (entries 5− 10)). The Rp was larger for the functional monomers than MMA in many cases. A high conversion was achieved in a fairly short time for EHMA and HEMA (97−98% conversion for 2 h). The amount of the catalyst could also be reduced for some monomers. This is partly because the propagation rate constants kp for the functional monomers23 are larger than that for MMA.24


system switched “on” and “off” by external photoirradiation. Figures 10 and 11 demonstrate temporal control of the polymerization. The lamp was turned on and off at every 30 min in four cycles. When the lamp was turned on, the system

Figure 10. Plot of ln([M]0/[M]) vs t for the MMA/CP-I/TBA system (ambient temperature): [CP-I]0 = 80 mM; [TBA]0 = 20 mM; xenon lamp power = 30 W (for 0−0.5 h), 60 W (for 1−1.5 h), 30 W (for 2− 2.5 h), and 120 W (for 3−3.5 h); wavelength = 350−600 nm. E


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tolerance to functional groups, and fine response to external photostimulus. Photo-RCMP will possibly be applicable to a wider variety of monomers, higher molecular weight polymers, and a wider range of irradiation wavelength, by using appropriate catalysts. These issues are currently examined in our laboratory.

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ASSOCIATED CONTENT

S Supporting Information *

Experimental, preparation of CP-TEMPO, 1H NMR spectrum of TBA/I2 complex, chain-end analyses of polymers by elemental analysis and 1H NMR, and UV−vis spectrum of a mixture of CP-I and TDEAP. This material is available free of charge via the Internet at http://pubs.acs.org.

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Figure 12. Plot of ln([M]0/[M]) vs t for the MMA/CP-I/TBA systems (ambient temperature): [MMA]0 = 8 M (in bulk); [CP-I]0 = 80 mM and [TBA]0 = 80 mM (for target DP = 100), [CP-I]0 = 20 mM and [TBA]0 = 40 mM (for target DP = 400); [CP-I]0 = 13.3 mM and [TBA]0 = 27 mM (for target DP = 600); xenon lamp power = 60 W; wavelength = 350−600 nm. The symbols are indicated in the figure.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (A.G.); [email protected] (H.K.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by Grants-in-Aid for Scientific Research from Japan Society of the Promotion of Science (JSPS), Japan Science and Technology Agency (JST), and New Energy and Industrial Technology Development Organization (NEDO) of Japan. A 1H NMR experiment (Figure S3) was carried out with the NMR spectrometer in the Joint Usage/ Research Center (JURC) at Institute for Chemical Research, Kyoto University.

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REFERENCES

(1) For reviews on LRP: (a) Matyjaszewski, K., Sumerlin, B., Tsarevski, N. Eds.; ACS Symp. Ser. 2012, 1100; 2012, 1101. (b) Matyjaszewski, K., Mö ller, M., Eds.; Polymer Sicence: A Comprehensive Reference; Elsevier: Amsterdam, 2012. (c) Braunecker, W. A.; Matyjaszewski, K. Prog. Polym. Sci. 2007, 32, 93−146. (d) Moad, G.; Solomon, D. H. The Chemistry of Radical Polymerization; Elsevier: Amsterdam, 2006. (2) For reviews on several families of LRP: (a) Sciannamea, V.; Jérôme, R.; Detrembleur, C. Chem. Rev. 2008, 108, 1104−1126. (b) Lena, F.; Matyjaszewski, K. Prog. Polym. Sci. 2010, 35, 959−1021. (c) Matyjaszewski, K. Macromolecules 2012, 45, 4015−4039. (d) Ouchi, M.; Terashima, T.; Sawamoto, M. Chem. Rev. 2009, 109, 4963−5050. (e) Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2009, 62, 1402−1472. (f) Keddie, D. J.; Moad, G.; Rizzado, E.; Thang, S. H. Macromolecules 2012, 45, 5321−5342. (g) Yamago, S. Chem. Rev. 2009, 109, 5051−5068. (h) Zetterlund, P. B.; Kagawa, Y.; Okubo, M. Chem. Rev. 2008, 108, 3747−3794. (i) Rosen, B. M.; Percec, V. Chem. Rev. 2009, 109, 5069−5119. (j) Satoh, K.; Kamigaito, M. Chem. Rev. 2009, 109, 5120−5156. (k) Boyer, C.; Bulmus, V.; Davis, T. P.; Ladmiral, V.; Liu, J.; Perrier, S. Chem. Rev. 2009, 109, 5402−5436. (l) Monteiro, M. J.; Cunningham, M. F. Macromolecules 2012, 45, 4939−4957. (3) For a review on ITP: (a) David, G.; Boyer, C.; Tonnar, J.; Ameduri, B.; Lacroix-Desmazes, P.; Boutevin, B. Chem. Rev. 2006, 106, 3936−3962. For reverse ITP (RITP): (b) Lacroix-Desmazes, P.; Severac, R.; Boutevin, B. Macromolecules 2005, 38, 6299−6309. (c) Tonnar, J.; Lacroix-Desmazes, P. Angew. Chem., Int. Ed. 2008, 47, 1294−1297. (4) For reviews on kinetics of LRP: (a) Fukuda, T. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 4743−4755. (b) Fischer, H. Chem. Rev. 2001, 101, 3581−3618. (c) Goto, A.; Fukuda, T. Prog. Polym. Sci. 2004, 29, 329−385.


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CONCLUSION Photo-RCMP was developed as a new photoinduced LRP. It consists of an alkyl iodide (dormant species) and an amine (catalyst) and uses visible light (350−600 nm). It is among the most simple, inexpensive, and robust photoinduced LRPs. Mechanistically, the key reaction is the photolysis of free dormant species and dormant species/catalyst complex, which frequently occurs as the main activation process. The effective photolysis was demonstrated by a radical trap experiment. The molecular weight and its distribution were well controlled for MMA and several functional methacrylates. The PDI kept small up to high conversions in many cases, showing the usefulness of photo-RCMP. Notably, the system was an ideal photo “on”−“off” system. The Rp was also finely tunable according to external irradiation power. Attractive features of photo-RCMP include no use of expensive compounds, metals, and conventional radical initiators. They also include good polydispersity control, good F


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