Metal-free atom transfer radical polymerization

Article abstract of DOI:10.1021/ja510389m

Overcoming the challenge of metal contamination in traditional ATRP systems, a metal-free ATRP process, mediated by light and catalyzed by an organic-based photoredox catalyst, is reported. Polymerization of vinyl monomers are efficiently activated and de

Full text of DOI:10.1021/ja510389m

Subscriber access provided by CARNEGIE MELLON UNIV
Article
Metal-Free, Atom Transfer Radical Polymerization
Nicolas J Treat, Hazel Sprafke, John W. Kramer, Paul G Clark, Bryan
E. Barton, Javier Read de Alaniz, Brett P. Fors, and Craig J. Hawker
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja510389m • Publication Date (Web): 24 Oct 2014
Downloaded from http://pubs.acs.org on October 28, 2014
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical
Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 6
Journal of the American Chemical Society
1
2
3
4
5
6
Metal-Free, Atom Transfer Radical Polymerization
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
†
†
∆
∆
∆
Nicolas J. Treat, Hazel Sprafke, John W. Kramer, Paul G. Clark, Bryan E. Barton, Javier Read de
‡
,§
,†,‡
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Alaniz, Brett P. Fors,* and Craig J. Hawker*
†
Materials Department, Materials Research Laboratory, University of California, Santa Barbara, California, 93106
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853
Department of Chemistry and Biochemistry, University of California, Santa Barbara, California, 93106
The Dow Chemical Company, Midland, Michigan, 48674
§
‡
∆
ABSTRACT: Overcoming the challenge of metal contamination in traditional ATRP systems, a metalꢀfree ATRP process,
mediated by light and catalyzed by an organicꢀbased photoredox catalyst is reported. Polymerization of vinyl monomers are
efficiently activated and deactivated with light leading to excellent control over the molecular weight, polydispersity and chain ends
of the resulting polymers. Significantly, block copolymer formation was facile and could be combined with other controlled radical
processes leading to structural and synthetic versatility. We believe that these new organicꢀbased photoredox catalysts will enable
new applications for controlled radical polymerizations and also be of further value in both small molecule and polymer chemistry.
Controlled free radical polymerizations (CRP) represent one
of the most far reaching developments in polymer synthesis,
allowing nonꢀexperts facile access to functionalized polymers
controlled radical polymerization processes in an analogous
manner to traditional ATRP systems (Scheme 1).
1
-6
with wellꢀdefined structure and architecture. Of the CRP
techniques, Atom Transfer Radical Polymerization (ATRP) is
arguably the most utilized and operates via a redox
equilibrium process mediated by a ligated metal catalyst (i.e.
Traditional ATRP: Metal Catalyst (Previous Work)
CuBr, Ligand
1
R
Br
+
Monomer
R Pn Br
Cu(I), Ru(II), Fe(II)). For a variety of applications, such as
microelectronics, biomaterials, etc., a key limiting factor in
7-9
PTH, Light
Metal-free ATRP: Organic Photocatalyst (This Work)
using ATRP is metal contamination. A significant focus for
10-12
the ATRP field since the initial discovery
has therefore
13-15
been directed towards lowering catalyst loadings
and/or
1
6-18
removal of residual metals.
Although catalyst loadings can
Scheme 1. Previous ATRP systems rely on metal catalysts (i.e.
CuBr) with ligands for control; metalꢀfree ATRP relies on an
organic photoredox catalyst (i.e. PTH) to produce identical
polymers.
be decreased to parts per million (ppm), we envisaged that a
much more viable and ambitious solution to this grand
challenge would be the development of a metalꢀfree catalyst
system for atom transfer radical polymerization.
An immediate challenge in developing a metalꢀfree ATRP
is designing an organic catalyst that is highly reducing in the
excited state. The majority of organic based dyes, currently
used as photoredox catalysts, are oxidizing in the excited state
and would not possess the desired reduction potentials
required to reduce the alkyl bromide initiator or subsequent
polymer chain ends to a propagating radical. We therefore
reasoned that an organic catalyst is needed that has an excited
In recent years our group has disclosed the photomediated
ATRP of methacrylates and acrylates using Irꢀbased
1
9-21
photoredox catalysts.
This system provides for excellent
spatial and temporal control over the chainꢀgrowth process,
enabling the formation of complex 3ꢀdimensional
19,22
nanostructures in a single step.
However, as in ATRP, the
use of ppm levels of metal catalyst limited the practicality of
this system. Although the emergent field of photoredox
catalysis has primarily utilized transition metals (i.e. Iridium
state reduction potential on par with Ir(ppy) , as well as a
3
stable radical cation species, which is formed after reduction
of the alkyl bromide (Figure 1). After surveying a range of
possible organic dyes, phenothiazine derivatives were chosen
as candidates for our initial studies due to the desired
photophysical properties (vide supra), low cost, ready
2
3
and Ruthenium), organic catalysts have recently attracted
24
significant attention and, in some cases, have been shown to
25
be more efficient than metalꢀbased systems. We saw this as
an opportunity to establish a metalꢀfree ATRP process by
developing an organicꢀbased catalyst that could replace
2
6
availability, and facile modification chemistry.
Ir(ppy) in photomediated, controlled radical polymerizations.
3
The ultimate aim is an organic photoredox system that is
reducing in the excited state and effectively catalyzes
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 6
absence of catalyst [f] irradiated with visible light (50 W
fluorescent bulbs).
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
PTH*
encouragement was the observation of conventional CRP
behavior with the molecular weight being determined by the
initial monomer:initiator ratio and low polydispersities being
obtained in each case (Table 1, entries 2 – 6). These
experiments establish that, for the first time, an atom transfer
radical polymerization (ATRP) process could occur with a
metalꢀfree catalyst system.
N
P
n
R
P
n
Br
Light
PTH Br
S
10-Phenylphenothiazine
PTH
(
PTH)
To further support the controlled nature of this
polymerization, a range of experimental conditions were
examined. When the polymerization was conducted in the
absence of light, initiator, or catalyst, either no or uncontrolled
polymerization was observed (Table 1, entries 7–9),
demonstrating that this is indeed a photomediated process that
is initiated by 1 and catalyzed by PTH. Moreover, when other
organicꢀbased photoredox catalysts were employed (Eosin Y
and Methylene Blue), which are oxidizing in the excited state,
no reaction occurred (Table 1, entries 8 and 9). This further
corroborates that a catalyst that is highly reducing in the
excited state is needed to activate the alkyl bromide chainꢀend.
Figure 1. Proposed mechanism of metalꢀfree photomediated
ATRP with 10ꢀphenylphenothiazine as the catalyst (P = polymer
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
n
chain).
Initially, we examined the use of commercially available
0ꢀmethylphenothiazine (Me-PTH) for the polymerization of
1
methyl methacrylate (MMA) under 380 nm irradiation at room
temperature. Encouragingly, polymerization was observed
with good agreement between theoretical and experimental
molecular weight, albeit with poor control over the molecular
weight distribution (Table 1, entry 1). We postulated that
tuning the nitrogen substituent on the phenothiazine ring
would reduce catalyst decomposition, allowing for greater
control over the polymerization process. To this end, we
10ꢀphenylphenothiazine,
commercially available phenothiazine and chlorobenzene
using CꢀN crossꢀcoupling chemistry followed by repeated
purification to obtain highly pure PTH
E (PTH /PTH*) = ꢀ2.1 V vs. SCE ). Significantly, we
synthesized
PTH,
from
2
7
(see SI,
+
.
28
red
found that the controlled polymerization of MMA could be
achieved in the presence of a traditional ATRP initiator, 1, and
PTH. Of even greater
Table 1. Optimization of a lightꢀmediated polymerization of
methyl methacrylate using organic photoredox catalysts.
[
a]
O
Br
1
EtO
Me
Ph
O
Me
Br
0
.1 mol % photocatalyst
O
EtO
n
MeO
380 nm light
DMA, rt
Ph
MeO
O
Entry Catalyst
M (exp)
g/mol]
M (theo) Mw / Mn
n
n
[
[g/mol]
1
Me-PTH
PTH
8,300
15,400
12,000
6,200
2,400
1,300
--
7,400
14,000
11,000
7,200
2,600
1,800
--
1.74
1.32
1.25
1.30
1.18
1.20
--
2[b]
3[b]
4
PTH
PTH
5
PTH
6
PTH
7[c]
8[d]
9[e]
0[f]
1[f]
PTH
PTH
42,300
--
--
2.00
--
--
--
1
Eosin Y
Methylene Blue
--
--
--
1
--
--
--
[
a] Reaction conditions: MMA (1 equiv.), photocatalyst (0.001
equiv.), 1 (0.008ꢀ0.01 equiv), DMA (2.7 M of MMA) at room
temperature with irradiation from 380 nm LEDs for 4 h (M =
number average molecular weight; Mw
molecular weight). Mn and Mw / M determined using size
exclusion chromatography (SEC) or H NMR; [b] reaction run
with benzyl methacrylate (1 equiv.) for 7 h [c] reaction run in the
dark [d] reaction run in the absence of 1 [e] reaction run in the
n
=
weight average
Figure 2. Polymerization of BnMA using PTH with repeated
‘onꢀoff’ cycling of the reaction to light.
n
1
The lack of reaction in the dark suggested that the
polymerization could be activated/deactivated by light leading
to controlled regulation of the polymerization process. To
ACS Paragon Plus Environment

Page 3 of 6
Journal of the American Chemical Society
A fundamental key to the success of any controlled radical
investigate this responsive nature, PTH was combined with
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
the initiator, 1, and benzyl methacrylate (BnMA). Upon
observing no conversion after 1 hour in the dark, the reaction
was exposed to 380 nm light, reaching 18% conversion in 1
hour (Figure 2a). After removal of the light source, no further
conversion was observed during the course of 1 hour;
however, reꢀexposure to 380 nm light led to further reaction
progress. This cycle could be repeated several times up to high
conversions (~ 90%) indicating very efficient activation and
deactivation of the polymerization process. Significantly, a
linear increase in molecular weight vs. conversion is obtained
even with multiple ‘onꢀoff’ light switching cycles (Figure 2b),
and the observation of first order kinetics through the course
of the reaction demonstrated a controlled polymerization
process (Figure 2c). In analogy with traditional ATRP
processes, this data indicates that when light is removed from
the system the chainꢀends are oxidized to the stable and
dormant alkyl bromides and upon reꢀexposure to light in the
presence of PTH, the chainꢀends are efficiently and reversibly
converting to propagating radicals.
process, such as ATRP, is chainꢀend fidelity. Achieving high
chainꢀend fidelity allows for effective block copolymer
formation, chain end functionalization, and the successful
synthesis of a wide variety of wellꢀdefined macromolecules. It
was therefore critical to determine chainꢀend fidelity in these
reactions. Initially, a low molecular weight PMMA (M =
n
1,400 g/mol, M /Mn = 1.08) was synthesized by PTHꢀ
w
mediated, metalꢀfree ATRP under the optimized conditions
described above and analyzed using electrospray ionization
mass spectrometry (ESIꢀMS) (Figure 3a). Of particular note is
the correlation of observed molecular weight with the
expected values for the individual PMMA oligomers based on
the presence of the initiating unit at one chain end and a
bromine atom at the propagating chain end with each peak
separated by the mass of one monomer unit (100 amu).
Further evidence for chainꢀend fidelity is supplied by the
isotopic splitting for the respective molecular ions, clearly
indicating the presence of a single Br atom at one chain end
(Figure S4).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
In contrast to Ir(ppy) and traditional metalꢀcatalyzed ATRP
3
processes, a unique feature of PTH is its highly reducing
excited state, which may allow a wider selection of functional
groups to be tolerated during the polymerization. We sought to
take advantage of this feature by polymerizing monomerꢀtypes
that were inaccessible with the Irꢀbased system. The test
vehicle chosen was 2ꢀ(dimethylamino)ethyl methacrylate
(
DMAEMA); a monomer utilized ubiquitously for its stimuliꢀ
29-32
responsive properties.
In the presence of Ir(ppy) under the
3
previously optimized conditions, very broad polydispersities
were observed (Table S1, M /M > 3). We surmised that the
w
n
uncontrolled polymerization was a result of radical formation
through oxidation of the amine; this is a wellꢀknown reaction
33
pathway for photoredox catalysts. In direct contrast, for the
ox
less oxidizing PTH (E1/2 = 0.68 V vs. SCE, see SI),
irradiation resulted in a wellꢀdefined polymerization process
with accurate control over molecular weight and low
polydispersities (~1.1) (Scheme 2). Moreover, this system
allows precise control over the Mn of these polymers by
varying the initiator to monomer ratio, as well as enabling the
synthesis of functional materials (block copolymers) – both of
which could not be achieved using the Irꢀbased catalyst system
(see SI). Therefore, this system not only avoids metal
contamination, but extends the scope of the photomediated
ATRP in general.
0
.005 mol % Ir(ppy)3
Mn = 9,400 g/mol Mw/M = 3.69
n
O
Me
Br
O
1
Me
EtO
Br
n
O
Ph
EtO
O
380 nm light
Ph
O
O
DMA, rt
NMe
2
NMe
2
0.1 mol % PTH
Mn = 8,800 g/mol M /M = 1.11
w
n
Scheme 2. Dimethylaminoethyl methacrylate (DMAEMA) gives
uncontrolled polymerization with Irꢀbased system and controlled
polymerization with PTH, demonstrating the broad scope of
photomediated ATRP
Figure 3. (a) ESIꢀMS of PMMA produced under optimized
metalꢀfree ATRP conditions with major peaks separated by
molecular weight of the monomer; (b) ESIꢀMS of PMMA
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 6
produced using reported conditions of traditional ATRP; (c) potential orthogonality for combining metalꢀfree ATRP with
1
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
H NMR of PMMA sample showing initiatorꢀderived protons.
To illustrate the similarity of polymers obtained from this
other controlled radical processes, increasing the range of
block copolymers that can be prepared. To demonstrate the
ability of metalꢀfree ATRP to be combined with other catalyst
new process and traditional ATRP procedures, a low
molecular weight PMMA derivative was prepared using CuBr
as catalyst and 4,4’ꢀdinonylꢀ2,2’ꢀdipyridyl as ligand at 90 °C
(M = 1,100 g/mol, M /M = 1.20). Analysis by ESIꢀMS again
systems, the starting PMMA homopolymer (M = 3,600 g/mol,
n
M /M = 1.19) was used to polymerize methyl acrylate under
w
n
2
0
Ir(ppy) catalyst conditions.
Significantly, a wellꢀdefined
3
n
w
n
block copolymer (Figure 4, M = 20,200 g/mol, M /M = 1.24)
showed the expected oligomer distribution and chain ends
with a very similar peak distribution and profile (Figure 3b).
n
w
n
with virtually no tailing in the homopolymer regime of the
SEC trace was obtained. Taking this concept even further, the
same PTHꢀderived PMMA macroinitiator could be used for
the polymerization of styrene under traditional ATRP
conditions employing CuBr as the catalyst. The resulting
block copolymer (Figure 4, M = 11,100 g/mol, M /M = 1.06)
1
H NMR was used to further confirm the level of
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
incorporation and fidelity of the chain ends with resonances
for the initiating ethyl 2ꢀphenylacetate group being observed
at ~ 4.0 and 7.2 ppm. Integration of these resonances and
comparison with resonances for the backbone allowed
molecular weights to be calculated that were in full agreement
with values obtained by both MS and GPC analysis (Figure
n
w
n
again revealed a monomodal shift in retention time of the
chromatogram. Finally, the reverse CRP order ꢀ Cuꢀbased
ATRP to produce a PMMA macroinitiator followed by chain
extension with BnMA using PTH as catalyst was also shown
to be a facile process leading to wellꢀdefined diblock
copolymers (Figure S6). Under our standard conditions
several random copolymers were also synthesized with
varying incorporations of styrene, as well as methyl acrylate,
while maintaining good agreement between theoretical and
experimental molecular weights (Tables S2 and S3).
3
c). This data firmly establishes that PTHꢀmediated, metalꢀ
free ATRP procedures give a similar degree of control over
chain ends as that observed for traditional ATRP systems with
the polymers obtained from both process being analogous.
Although ESIꢀMS and NMR give evidence for α and ω
chain ends, successful block copolymerization provides
definitive proof that a controlled polymerization system has
been achieved. To examine the utility of this metalꢀfree
process, the polymerization of 1 and MMA with 0.1 mol %
PTH, was conducted to give a starting PMMA homopolymer
In conclusion, we have demonstrated a successful metalꢀ
free, atom transfer radical polymerization. Use of an
affordable, easily prepared organic catalyst, PTH, leads to a
controlled, photomediated process that bears many
characteristics of traditional ATRP procedures including
accurate control over molecular weight, low polydispersity,
and high retention of chain end groups. This allows a variety
of block copolymers to be prepared in a sequential manner as
well as in combination with other ATRP processes (traditional
Cuꢀcatalyzed and photomediated Irꢀbased systems). This
organicꢀbased catalyst system circumvents issues of metal
contamination in polymers made using ATRP and allows for
the production of a variety of functional materials, pushing the
field of CRP into new areas and applications. We further
anticipate that the unique properties of this new class of
organicꢀbased photoredox catalysts, specifically their highly
reducing nature, will find applications in both small molecule
and polymer functionalization chemistry.
(
M = 5,100 g/mol, M /M = 1.12). After standard purification
n w n
and storage, the stable homopolymer was examined as a
macroinitiator for the polymerization of benzyl methacrylate
under metalꢀfree ATRP conditions (0.1 mol % PTH, 380 nm
irradiation for 4 h) leading to a wellꢀdefined PMMAꢀbꢀ
PBnMA block copolymer (Figure 4, Mn = 25,900 g/mol,
M /M = 1.31). The size exclusion chromatogram (SEC)
w
n
clearly shows a shift to higher molecular weight species with
little tailing in the homopolymer regime, indicating excellent
alkyl bromide chainꢀend fidelity in the PMMA macroinitiator
and a high reꢀinitiation efficiency. To further explore the
scope of this process, a PMMAꢀbꢀPBnMA copolymer could
also be prepared (Figure S5, M = 27,900 g/mol, M /M =
n
w
n
1
.28) starting from ethyl 2ꢀbromoisobutyrate as initiator,
illustrating the versatility of this process.
Block and random copolymerizations with other monomer
families were then conducted to demonstrate the broad scope
of this system. The presence of bromo chain ends suggest
ACS Paragon Plus Environment

Page 5 of 6
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. Synthesis of block copolymers starting from a PMMA macroinitiator prepared by metalꢀfree ATRP conditions and
accompanying SEC traces of various blocks produced using different combinations of catalyst systems (red trace = starting PMMA
macroinitiator, blue trace = block copolymer)
the California NanoSystems Institute for an Elings Fellowship
in Experimental Science and Cornell University for support.
ASSOCIATED CONTENT
Supporting Information.
Experimental procedures for preparation of all compounds;
characterization data for all compounds. This materials is
available free of charge via the Internet at http://pubs.acs.org.
REFERENCES
(1)
Ouchi, M.; Terashima, T.; Sawamoto, M. Chem.
Rev. 2009, 109, 4963.
AUTHOR INFORMATION
Corresponding Author
(2)
Moad, G.; Rizzardo, E.; Thang, S. H. Polymer
2008, 49, 1079.
(3)
Nicolas, J.; Guillaneuf, Y.; Lefay, C.; Bertin, D.;
*
hawker@mrl.ucsb.edu and brettfors@cornell.edu
Gigmes, D.; Charleux, B. Progress in Polymer Science 2013,
3
8, 63.
Notes
(4) Hawker, C. J.; Bosman, A. W.; Harth, E. Chem. Rev.
001, 101, 3661.
The authors declare no competing financial interest.
2
(
(
5)
6)
Grubbs, R.B. Polym. Rev. 2011, 51, 104.
Allaoua, I.; Goi, B.E.; Obadia, M.M.; Debuigne,
ACKNOWLEDGMENT
A.; Detrembleur, C.; Drockenmuller, E. Polym. Chem., 2014,
5, 2973.
We thank the MRSEC program of the National Science
Foundation (DMR 1121053, C.J.H.) and The Dow Chemical
Company through the Dow Materials Institute at UCSB (N.J.T.,
B.P.F., H.S., C.J.H.) for financial support. N.J.T. thanks the
NSF Graduate Research Fellowship for funding. B.P.F thanks
(7)
Cheng, C.; Khoshdel, E.; Wooley, K.L. NanoLett.
2
006, 6, 1741ꢀ1746.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 6
(
8)
Vogt, A.P.; Sumerlin, B.S. Soft Matter, 2009, 5,
Matyjaszewski, K.; Tsarevsky, N. V. J. Am. Chem.
Boyer, C. Macromolecules 2014, 47, 4930. (d) Xu, J.; Jung, K.;
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2347.
(9)
Soc. 2014, 136, 6513.
(10) Matyjaszewski, K.; Jakubowski, W.; Min, K.; Tang,
W.; Huang, J.; Braunecker, W. A.; Tsarevsky, N. V. Proc.
Natl. Acad. Sci. 2006, 103, 15309.
Corrigan, N. A.; Boyer, C. Chem. Sci. 2014, 5, 3568.
(22) Poelma, J. E.; Fors, B. P.; Meyers, G. F.; Kramer, J.
W.; Hawker, C. J. Angew. Chem. Int. Ed. 2013, 52, 6844.
(23) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C.
Chem. Rev. 2013, 113, 5322.
(24) Nicewicz, D. A.; Nguyen, T. M. ACS Catal. 2014, 4,
355.
(25) Pitre, S. P.; McTiernan, C. D.; Ismaili, H.; Scaiano,
J. C. J. Am. Chem. Soc. 2013, 135, 13286.
(26) Phenothiazineꢀbased molecules are known to have
stable radical cations. For examples, see (a) Odom, S. A.;
Ergun, S.; Poudel, P. P.; Parkin, S. R. Energy Environ. Sci.
2014, 7, 760. (b) Sun, D.; Rosokha, S. V.; Kochi, J. K. J. Am.
Chem. Soc. 2004, 126, 1388.
(
11) Haddleton, D.M.; Jasieczek, C.B.; Hannon, M.J.;
Shooter, A.J. Macromolecules, 1997, 30, 2190.
12) Fleischmann, S.; Rosen, B. M.; Percec, V. J. Polym.
Sci. A Polym. Chem. 2010, 48, 1190.
13) Kwak, Y.; Magenau, A. J. D.; Matyjaszewski, K.
Macromolecules 2011, 44, 811.
14) Magenau, A. J. D.; Strandwitz, N. C.; Gennaro, A.;
Matyjaszewski, K. Science 2011, 332, 81.
15) Gnanou, Y.; Hizal, G. J. Polym. Sci. A Polym.
(
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
(
(
(27) Maiti, D.; Fors, B. P.; Henderson, J. L.; Nakamura,
Y.; Buchwald, S. L. Chem. Sci. 2010, 2, 57.
Chem. 2004, 42, 351.
(16) Matyjaszewski, K.; Pintauer, T.; Gaynor, S.
Macromolecules 2000, 33, 1476.
(17) Munirasu, S.; Aggarwal, R.; Baskaran, D. Chem.
Commun. 2009, 4518.
(28) Excited state reduction potential estimated using
oxidation potential of ground state catalyst and
photoluminescence emission maximum (see SI).
(29) Plamper, F. A.; Schmalz, A.; Müller, A. H. E. J. Am.
Chem. Soc. 2007, 129, 14538.
(30) You, Y.ꢀZ.; Manickam, D. S.; Zhou, Q.ꢀH.;
Oupický, D. J. Controlled 2007, 122, 217.
(31) Wang, X.ꢀS.; Dykstra, T. E.; Salvador, M. R.;
Manners, I.; Scholes, G. D.; Winnik, M. A. J. Am. Chem. Soc.
2004, 126, 7784.
(
(
18) Shen, Y.; Zhu, S. Macromolecules 2001, 34, 8603.
19) Fors, B. P.; Hawker, C. J. Angew. Chem. Int. Ed.
2
012, 51, 8850.
20) Treat, N. J.; Fors, B. P.; Kramer, J. W.; Christianson,
(
M.; Chiu, C.ꢀY.; Alaniz, J. R. de; Hawker, C. J. ACS Macro
Lett. 2014, 3, 580.
(21) Boyer and coworkers have elegantly extended the use
(32) Liu, F.; Urban, M.W. Macromolecules, 2008, 41,
6531.
(33) Nguyen, J. D.; D'Amato, E. M.; Narayanam, J. M.
R.; Stephenson, C. R. J. Nature Chem. 2012, 4, 854.
of photoredox catalysts for photomediated RAFT. (a) Xu, J.;
Jung, K.; Atme, A.; Shanmugam, S.; Boyer, C. J. Am. Chem.
Soc. 2014, 136, 5508. (b) Xu, J.; Jung, K.; Boyer, C.
Macromolecules 2014, 47, 4217. (c) Shanmugam, S.; Xu, J.;
For Table of Contents:
ACS Paragon Plus Environment