Synthesis of phosphorescent iridium-containing acrylic monomers and their room-temperature polymerization by Cu(0)-RDRP

Article abstract of DOI:10.1002/pola.29233

A series of acrylic monomers based on cyclometalated iridium(III) complexes have been synthesized based on common phosphorescent emitters for organic light-emitting diodes. A simple room-temperature polymerization procedure for these materials was developed using Cu(0) reversible deactivation radical polymerization, providing polymers with low dispersities of 1.08–1.14 at conversions from 81 to 93% when the Ir complexes are copolymerized with a carbazole-based acrylic host. These methods were also found to be suitable for the preparation of high-molecular-weight polymers with M_n approaching 40,000 Da, as well as block copolymers formed in one pot from the chain extension of methyl acrylate. This scalable room-temperature synthesis of iridium-containing copolymers and block copolymers provides a useful route to optoelectronic materials, which we anticipate can be readily adapted to a broad range of acrylic metallopolymers.

Full text of DOI:10.1002/pola.29233

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Synthesis of Phosphorescent Iridium-Containing Acrylic Monomers and
Their Room-Temperature Polymerization by Cu(0)-RDRP
Cheyenne J. Christopherson, Zoë S. Hackett, Ethan R. Sauvé , Nathan R. Paisley
Christopher M. Tonge, Don M. Mayder, Zachary M. Hudson
,
Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
Correspondence to: Z. Hudson (E-mail: zhudson@chem.ubc.ca)
Received 16 July 2018; Revised 13 August 2018; Accepted 22 August 2018
DOI: 10.1002/pola.29233
ABSTRACT: A series of acrylic monomers based on cyclometalated
iridium(III) complexes have been synthesized based on common
phosphorescent emitters for organic light-emitting diodes. A sim-
ple room-temperature polymerization procedure for these mate-
rials was developed using Cu(0) reversible deactivation radical
polymerization, providing polymers with low dispersities of
1.08–1.14 at conversions from 81 to 93% when the Ir complexes
are copolymerized with a carbazole-based acrylic host. These
methods were also found to be suitable for the preparation of
high-molecular-weight polymers with Mn approaching 40,000 Da,
as well as block copolymers formed in one pot from the chain
extension of methyl acrylate. This scalable room-temperature
synthesis of iridium-containing copolymers and block copoly-
mers provides a useful route to optoelectronic materials, which
we anticipate can be readily adapted to a broad range of acrylic
metallopolymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci.,
Part A: Polym. Chem. 2018
KEYWORDS: block copolymer; carbazole host; copolymerization; Cu
(0)-RDRP; iridium copolymer; living polymerization; metallopolymer
can be difficult to remove large amounts of residual monomer
from the product by reprecipitation, owing to the similarity in
solubility characteristics between the semiconducting polymer
and its large, π-conjugated building blocks. These methods
were also used to prepare polyacrylates from organic semicon-
ductors with molecular weights approaching 50,000 Da.
INTRODUCTION Cu(0) reversible deactivation radical polymer-
ization (RDRP) has recently attracted considerable attention
as a low-cost and scalable route to polymers prepared from a
diverse array of vinyl monomers.1–7 Now widely explored
for the polymerization of (meth)acrylates,3,8,9 styrenes,5 and
acrylamides10 among others,11,12 this technique affords polymers
with low dispersity while retaining near-quantitative end-group
fidelity at conversions >90%. Though some debate persists
regarding the mechanistic details of Cu(0)-RDRP,13–15 the tech-
nique offers many advantages with respect to scalability and
cost. For example, many Cu(0)-RDRP processes proceed effi-
ciently at room temperature or with only mild heating, and use
simple Cu(0) powder or wire as catalyst. The method is also
suitable for the preparation of multiblock copolymers in one
pot,16 and can be carried out without explicit degassing of the
reaction mixture in some cases.9,17
We then reasoned that Cu(0)-RDRP would be ideal for the poly-
merization of acrylic monomers based on phosphorescent
transition-metal complexes. Such complexes, particularly those
based on Os, Ir, or Pt, have found widespread use as emitters for
organic light-emitting diode (OLED) displays,20–24 light-emitting
electrochemical cells,25–27 and chemosensors,28–31 with quantum
yields often approaching 100%. Due to the high cost of these
materials, a polymerization method that minimizes waste, maxi-
mizes yield, and simplifies purification would be highly desirable.
Though a recent report describes the photopolymerization of
iridium methacrylates,32 the polymerization of such mono-
mers via Cu(0)-RDRP has not yet been explored. Cu(0)-RDRP
offers many advantages, such as the ability to prepare high-
molecular-weight polymers with low dispersity. In addition,
the versatility of this method has been shown recently
through the synthesis of polymers in both aqueous and
organic solvents,33 and through the fact that the catalyst can
be recovered after the polymerization.34 In addition, this
These same advantages also lend themselves well to the poly-
merization of high-value monomers, as low dispersities can be
obtained at high conversions with minimal monomer waste.
We recently demonstrated that Cu(0)-RDRP provided a simple
and low-cost route to polyacrylates based on p-type and n-type
organic semiconductors, giving polymers with dispersities as
low as 1.12 with conversions up to 97%.18,19 The high conver-
sions afforded by these reactions was of additional benefit as it
Additional supporting information may be found in the online version of this article.
© 2018 Wiley Periodicals, Inc.
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otherwise stated. Dry solvents were obtained from Caledon Labo-
ratories, dried using an Innovative Technologies Inc. solvent purifi-
cation system, collected under vacuum, and stored under a
nitrogen atmosphere over 4 Å molecular sieves unless otherwise
stated. Dry CH2Cl2 was obtained from Sigma-Aldrich and freshly
distilled over P2O5 before use. All reagents were obtained from
Sigma-Aldrich or Alfa Aesar and used as received unless otherwise
stated. NEt3 was dried by distillation on CaH2 onto 4 Å molecular
sieves, then degassed by three freeze-pump-thaw cycles, and
stored under N2 atmosphere. All 1H, 13C, and 19F NMR spectra
were obtained on Bruker Avance 300 or 400 MHz spectrometers.
Absorbance measurements were made on a Cary 60 spectrometer
and fluorescence measurements were made on an Edinburgh
Instruments FS5 spectrofluorometer. Absolute photoluminescence
quantum yields were determined using an Edinburgh Instruments
SC-30 Integrating Sphere Module. Toluene was used as solvent for
all photophysical experiments. Mass spectra were recorded on a
Kratos MS-50 instrument using electron impact ionization. Cyclic
voltammograms were recorded using a BASi Epsilon Eclipse poten-
tiostat at room temperature using a standard three-electrode con-
figuration (working electrode: 2 mm diameter Pt disc; reference
electrode: Ag/AgCl electrode in saturated KCl; counter electrode:
Pt wire). 1-Phenylisoquinoline,36 2-(2,4-difluorophenyl)pyridine,37
and M418 were prepared according to literature procedures.
SCHEME 1 Synthesis of iridium monomers M1–M3.
polymerization method can be combined with different
methods including plasma polymerization to create novel
classes of materials.35
Herein we report the preparation of three iridium-based acrylic
monomers with red, green, and sky-blue phosphorescence, and
their copolymerization with a carbazole-based host via Cu(0)-
RDRP. These methods are further shown to be applicable to the
preparation of doped polymers with molecular weights approach-
ing 40,000 Da, as well as iridium-containing block copolymers
prepared using a one-pot protocol. Kinetic data for these polymer-
izations are also described, alongside the optical, electrochemical,
and thermal properties of the iridium-containing products.
Size Exclusion Chromatography (SEC)
SEC experiments were conducted in chromatography-grade THF
at concentrations of 0.5–2 mg mL−1 using a Malvern OMNISEC
GPC instrument equipped with a Viscotek TGuard guard column
(CLM3008), and Viscotek T3000 (CLM3003) and T6000
(CLM3006) GPC columns packed with porous poly(styrene-co-
divinylbenzene) particles regulated at a temperature of 35 ꢀC. Sig-
nal response was measured using differential viscometer, differen-
tial refractive index, photodiode array, and light scattering (90ꢀ
and 7ꢀ) detectors. Interdetector volume was calibrated using a
single polystyrene (PS) standard with Mn = 101,000 and PDI = 1.04.
Molecular weights for all iridium-containing copolymers were
determined by conventional calibration using (a) PS standards
and (b) a series of poly(M4) standards18 with molecular weights
EXPERIMENTAL
General Experimental Details
All reactions and manipulations were carried out under a nitrogen
atmosphere using standard Schlenk or glovebox techniques unless
FIGURE 1 Crystal structures of (a) M1, (b) M2, (c) M3, and (d) M4 obtained from X-ray diffraction analysis, depicted with 50% thermal
ellipsoids. [Color figure can be viewed at wileyonlinelibrary.com]
2
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FIGURE 2 SEC RI traces (a–c) and kinetic data (d–f ) for poly(M4) doped with 5 mol % of M1 (a,d), M2 (b,e), and M3 (c,f ). Target
molecular weights = 10 kDa (a–c solid lines; d–f ) or 50 kDa (a–c dashed lines). [Color figure can be viewed at wileyonlinelibrary.com]
between 3000 and 50,000 Da. Molecular weights for poly(M4)
standards were determined using triple detection and the refrac-
tive index increment (dn/dc = 0.195 in THF) of the polymer.
a 4 mL vial capped with a Teflon-lined lid equipped with a
magnetic stir bar and brought into a nitrogen atmosphere glo-
vebox. In the glovebox, 75 μL of ethyl α-bromoisobutyrate
(EBiB) solution in DMAc (CEBiB = 50 mg/mL; EBiB: 3.7 mg,
1.9 × 10−2 mmol, 1 eq.), 82 μL of CuBr2/Me6TREN solution in
DMAc (CCu = 3.4 mg/mL; CuBr2: 2.8 mg, 1.2 × 10−3 mmol,
0.065 eq.; Me6TREN: mg, 1.3 × 10−3 mmol, 0.068 eq.), and
1,3,5-trimethoxybenzene (3 eq.) as an internal standard were
added to the vial containing monomers. DMAc was added to
make the total polymerization volume 1.15 mL. The mixture
was stirred at room temperature for several minutes until all
reagents were dissolved. Concurrently, a 0.96 cm piece of
18 gauge copper (0) wire was stirred in concentrated HCl for
15 minutes to remove surface impurities, then washed
sequentially with deionized water and acetone and dried for
Density Functional Theory
Calculations were performed using the Gaussian 09 software
package. Ground state geometries and energies were calculated
using the hybrid functional B3LYP and the 6-31 + G(d) basis set
for all atoms except for iridium, for which the LANL2DZ ECP
basis was used. To simulate electronic properties of our poly-
meric materials, analogous versions of each monomer were
calculated in which the alkene group in the acrylate moiety is
replaced with a sec-butyl group, similar to the structure found in
the corresponding polymer.
ꢀ
General Procedure for Cu(0)-RDRP
10 minutes in an oven at 120 C. The wire was added to the
M4 (0.46 mmol, 24 eq.) and iridium monomer (0.12 mmol,
6 eq., 20 mol % of total monomer content) were weighed into
reaction vial to initiate the polymerization and the reaction
was allowed to stir at room temperature until complete by H
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1
NMR. The polymerization was quenched by the addition of
water, followed by centrifugation to isolate the polymer. The
polymer was dissolved in CH2Cl2, dried over MgSO4, and con-
centrated in vacuo. The residue was purified by size exclusion
chromatography on a reusable Bio-Rad Bio-Beads S-X1 sup-
port in THF, and fractions containing polymer were collected
and dried in vacuo overnight. The polymers may also be puri-
fied by reprecipitation of polymer from CH2Cl2 into hexanes,
providing a more convenient purification method as the reac-
tion scale increases.
temperature until the polymerization was complete by H NMR
spectroscopy.
RESULTS AND DISCUSSION
Three iridium-containing monomers were designed and synthe-
sized based on the N^C chelate ligands 1-phenylisoquinoline
(piq, M1), 2-phenylpyridine (ppy, M2), or 2(2,4-difluorophenyl)
pyridine (dfppy, M3). These ligands are commonly used to give
red, green, or sky-blue emission in complexes of Ir and Pt, gen-
erally exhibiting mixtures of ligand-centered (3LC) or metal-to-
ligand charge-transfer (3MLCT) phosphorescence.23,37–39
A
Chain Extension of Methyl Acrylate with Iridium-
Doped M4
Methyl acrylate (MA, 190.0 mg, 100 eq.) was weighed into a
4 mL vial equipped with magnetic stir bar and capped with a
Teflon-lined lid and brought into a nitrogen atmosphere glove-
polymerizable group was then prepared using an acrylate-
functionalized β-ketoester, structurally analogous to the acety-
lacetonate ligands commonly used in high-performance OLED
emitters.40,41 This ligand is conveniently prepared by heating
commercially available 2-hydroxyethyl acrylate to 120 ꢀC,
which can react with 2,2,6-trimethyl-4H-1,3-dioxin-4-one in the
presence of radical inhibitors to cleanly afford compound 1 with
the elimination of acetone (Scheme 1).
box. In
a glovebox, 17 μL of EBiB solution in DMAc
(CEBiB = 250 mg/mL; EBiB: 4.3 mg, 2.2 × 10−2 mmol, 1 eq.),
41 μL of CuBr2 and Me6TREN solution in DMAc
(CCu = 7.9 mg/mL; CuBr2: 0.32 mg, 1.4 × 10−3 mmol,
0.065 eq.; Me6TREN: 0.44 mg, 1.5 × 10−3 mmol, 0.068 eq.)
and 1,3,5-trimethoxybenzene (1 eq.) were added to the vial
containing MA. DMAc was added to make the total volume
200 μL, and the vial was stirred at room temperature for sev-
eral minutes until all reagents were dissolved. Concurrently, a
1.1 cm piece of 18 gauge copper (0) wire was cleaned as per
the procedure listed above. The wire was added to the reac-
tion vial to initiate polymerization and the reaction was
allowed to stir at room temperature until a conversion of
98% was reached by NMR. Once complete, M4 (0.63 mmol,
28.5 eq.), and M1, M2, or M3 (0.033 mmol, 1.5 eq.), 74 μL of
CuBr2 solution in DMAc (CCu = 4.3 mg/mL; CuBr2: 0.32 mg,
1.4 × 10−3 mmol, 0.065 eq.; Me6TREN: 0.34 mg, 1.5 × 10−3 mmol,
0.068 eq.), and 1.1 cm of freshly cleaned copper (0) wire was
added to the reaction vial. DMAc was added to bring the total
reaction volume up to 1.35 mL. The reaction was stirred at room
μ-dichloro-bridged dimers of Ir(III) and each cyclometalating
ligand was then prepared by Nonoyama reaction of IrCl3ÁH2O,
which were then treated with AgOTf to abstract the chloride
ligands. Addition of 1 to this mixture in the presence of NEt3
then gave complexes M1–M3, which were isolated as analyti-
cally pure compounds following precipitation from CH2Cl2
into hexanes.
Single crystals of M1–M3 suitable for X-ray diffraction analy-
sis were then obtained by slow evaporation from CH2Cl2/hex-
anes. All complexes crystallize with the N atoms from the
cyclometalating ligands in a trans configuration (see Figure 1),
placing the ketoester ancillary ligand trans to both carbon
atoms. Space groups of P21/c, I2/a, and C2/c are observed for
M1–M3, respectively. A crystal structure was also obtained
for carbazole-based monomer M4, which would form the host
TABLE 1 Synthesis of Iridium-Doped Polymers by Cu(0)-RDRP.a
Mn (Da, M4 Calibration)
Mn (Da, PS Calibration)
Ir Dopant mol %
Mn
Đb
Mn
Đb
Mn,theory
Conv. (%)
t (h)
kpapp (×10−5 s−1
)
20% M1
20% M2
20% M3
10% M1
10% M2
10% M3
5% M1
5% M2
5% M3
0%18
10,600
11,100
12,100
12,300
11,300
11,700
10,600
11,100
11,100
10,100c
1.13
1.09
1.11
1.14
1.09
1.10
1.09
1.09
1.09
1.11
4900
5100
5500
5600
5100
5300
4800
5100
5100
4800
1.11
1.08
1.10
1.11
1.08
1.09
1.08
1.08
1.08
1.07
b
9100
72
89
90
84
90
91
81
93
92
96
7.5
4.5
6.5
7
–
10,700
11,200
9500
13.9
10.6
–
9900
5
13.6
13.9
–
10,200
8600
5
6.5
5
9700
15.3
14.4
14.7
9600
5
9600
8
a
Reactionconditions:[Monomer[/][EBiB]/[CuBr2]/[Me6TREN]=30/1/0.065/0.068;
DMAc = 1.15 mL; 18 gauge Cu(0) wire = 0.96 cm. Monomer = M4 + M1, M2
or M3.
Determined after purification by preparative SEC.
c
Determined using triple detection SEC.
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TABLE 2 Molecular Weights for 50 kDa Polymers of M4 Doped with M1–M3.
M4 Calibration
PS Calibration
Ir Dopant %
Mn
Đb
Mn
Đb
Mn,theory
Conv.a (%)
5% M1
5% M2
5% M3
a
37,400
37,900
38,100
1.47
1.40
1.42
15,800
15,900
16,000
b
1.46
1.37
1.40
41,500
43,400
41,900
79
84
71
Reactionconditions:[Monomer]/[EBiB]/[CuBr2]/[Me6TREN]=150/1/0.065/0.068;
DMAc = 1.15 mL; 18 gauge Cu(0) wire = 0.22 cm. Monomer = M4 + M1, M2,
or M3. Reaction time = 24 h.
Determined after purification by preparative SEC.
material in subsequent Cu(0)-RDRP reactions. For all Ir com-
plexes, the Ir-O bond lengths ranged from 2.13 to 2.17 Å, with
little to no difference observed between the ester and ketone-
based carbonyl groups. These distances are consistent with
reported structures of the common OLED emitter Ir(ppy)2(acac),42
indicating similar bond strengths for the acetylacetonate and the
ketoester.
measured molecular weights approximately 50% below the
theoretical expected value (Table 1). All H NMR signals from
the polymer end groups were also obscured by signals from
the iridium dopants, making estimation of molecular weight
by NMR spectroscopy impractical.
1
To circumvent this, we synthesized a series of standards of
M4 alone using previously reported methods,18 with Mn rang-
ing from 3 to 50 kDa. Absolute molecular weights for these
polymers could then be determined using triple detection
and the dn/dc value for poly(M4) (0.195 in THF), giving a
calibration which more accurately reflects the elution times of
poly(M4) doped with iridium phosphors. Using these
methods, agreement of the molecular weights obtained by SEC
and theory are improved substantially (Table 1).
Polymer Synthesis
Polymers of M4 doped with 5, 10, or 20 mol % of either M1,
M2, or M3 were then prepared via Cu(0)-RDRP in DMAc,
which we previously found to provide a balance of catalyst
activity and monomer solubility for common small-molecule
organic semiconductors.18,19 Polymerizations were carried out
in a nitrogen atmosphere glovebox to rigorously exclude oxy-
gen while aliquots were taken throughout the reaction, but
can also be conveniently conducted on a Schlenk line under
N2. Polymerizations were conducted using 0.96 cm of
18-gauge Cu(0) wire, freshly cleaned prior for 15 minutes to
remove impurities and the CuO surface layer. Using EBiB as
initiator and tris[2-(dimethylamino)ethyl]amine (Me6TREN) as
ligand, polymerizations were carried out with [EBiB]/[CuBr2]/
[Me6TREN] = 1/0.065/0.068 targeting molecular weights of
10 and 50 kDa. Doping of the iridium compound into a carba-
zole matrix is designed to give highly phosphorescent polymer
products with minimal quenching from triplet–triplet annihi-
lation upon excitation, which reduces quantum yields of mate-
rials with high concentrations of triplet emitters.
The results of the polymerizations using 5 mol % of M1, M2,
or M3 are shown in Figure 2 and summarized for all doping
concentrations in Table 1. Targeting molecular weights of
10 kDa gave dispersities of 1.09–1.14 in all cases, with very
slight increases observable as the iridium content of the poly-
mers increased. Molecular weights measured by SEC were in
good agreement with theory at 10,600, 11,100, and 11,100 for
the 5 mol % M1, M2, and M3 polymers, respectively.
Special care had to be taken to obtain accurate molecular
weights by SEC for these materials, as the phosphorescence
spectra of M1–M3 were sufficiently broad as to interfere with
detection by light scattering at 640 nm. Molecular weight
determination was first attempted by conventional calibration
against PS standards, but the poor structural analogy between
PS and the large organic semiconductors employed here gave
FIGURE 3 (a) Solid-state emission spectra for poly(M4)10k doped
with 5 mol % M1 (red), M2 (green), or M3 (blue) (λex = 300 nm).
(b) CIE 1931 diagram showing the corresponding emission
colors of these polymers. (c) Photograph of thin films of poly
(M4)10k doped with M1–M3 under UV irradiation (λex = 365 nm).
[Color figure can be viewed at wileyonlinelibrary.com]
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FIGURE 4 SEC traces showing the chain extension of PMA100 (dashed lines) with (a) M4-co-M1, (b) M4-co-M2, (c) M4-co-M3 (solid
lines). Cz and Ir represent the structures of M4 and iridium-containing monomers M1–M3. x = 0.95, y = 0.05. [Color figure can be
viewed at wileyonlinelibrary.com]
Compared to undoped polymers of M4, the relative rates of
the copolymerization reactions described in Table 1 were
largely unchanged, with a small reduction in apparent rate
constant (kpapp) observable as the doping concentration of
iridium monomer increased. In the case of the bulkier red
monomer, the kinetic data showed some deviation from line-
arity at higher conversions, implying that steric effects may be
reducing chain-end livingness. This was particularly apparent
in the case of the polymer doped with 20% of M1, which
reached the lowest conversion of the series at 72% in 7.5 h.
from both M4 and the iridium dopants in dilute toluene solu-
tion. As anticipated, the relative amount of dopant-based
emission increases with doping concentration, with the poly-
mers containing 20 mol % of the iridium complexes showing
the greatest proportion of phosphorescence in all cases. While
the polymers doped with M1 show impressive quantum yields
ranging from 51% (5 mol % M1) to 81% (20 mol % M1), the
quantum yields of the polymers doped with M2 and M3
decrease substantially with increased iridium content, falling
from 42% and 32% with 5 mol % iridium, respectively, to
11% and 2.7% at 20 mol % (Supporting Information Fig. S11).
Interestingly, the emission from M4 vanishes almost entirely
when thin films of these materials are examined in the solid
state, consistent with an improvement in energy transfer from
host to emitter (Figs. 3 and S12). This effect improves the
emission color purity of the samples substantially, giving CIE
1931 coordinates of (0.62, 0.33), (0.30, 0.57), and (0.20, 0.44)
for poly(M4) doped with 5 mol % of M1, M2, and M3, respec-
tively. As selecting an ideal host for phosphorescent materials is
critical for achieving efficient energy transfer,43,44 further study
on the relationship between these dopants and a variety of acrylic
monomer hosts is required to optimize quantum yields further.
In all cases, the conversion of the polymerizations (10 kDa target
MW) was monitored by 1H NMR spectroscopy. Once a change in
conversion with respect to time was no longer observed, each
polymerization was stopped. For this reason, reaction times and
final conversions for each polymerization differ.
High-molecular-weight polymers with molecular weights of
50 kDa were then targeted via polymerization of M4 containing
5 mol % of M1, M2, or M3. Though dispersities broadened sig-
nificantly (1.40–1.47), polymers with Mn = 37,400–38,100 were
successfully obtained with conversions of 71–84% (Table 2).
Finally, we examined the synthesis of iridium-containing block
copolymers by chain-extension of MA prepared by Cu(0)-
RDRP (see Figure 4). Polymerization of MA in DMAc with
[MA]/[EBiB]/[CuBr2]/[Me6TREN] = 100/1/0.065/0.068 gave
Photophysical Characterization
All iridium-doped polymers show strong luminescence under
UV irradiation at 365 nm, with emission bands originating
TABLE 3 Molecular Weight and Dispersities for MA-b-(M4-co-Ir) Polymers.
MA Block
Ir-Doped Block
Block Copolymer
a
b
b
Monomer
Mn
Đ
DPn
Mn
DPn
Mn
Đ
M1
M2
M3
a
9200
8000
8500
1.03
1.05
1.01
104
91
11,200
9300
12,200
b
32
27
35
20,400
17,300
20,800
1.04
1.06
1.04
97
Determined by SEC in THF.
Determined by 1H NMR.
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6 C. Boyer, N. A. Corrigan, K. Jung, D. Nguyen, T.-K. Nguyen,
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well-defined polymers with dispersities of 1.00–1.03 reach-
ing 98% conversion after 8.5 hours. Without workup or
quenching the reaction, a mixture of M4 and one of M1–M3
was then added to this reaction to extend the polymer chain.
Consistent with our earlier results and those of Bates and
Hawker,45 high chain-end livingness is preserved when addi-
tional catalyst is added with the second batch of monomer.
The resulting PMA100-b-poly(M4-co-Ir) block copolymers
showed monomodal molecular weight distributions with dis-
persities of 1.04, 1.07, and 1.04 for the M1, M2, and M3-
containing diblock copolymers, respectively, indicating minimal
termination before the addition of the luminescent block
(Table 3). These results indicate that Cu(0)-RDRP provides a
facile route for the incorporation of phosphorescent metal com-
plexes into block copolymers, which may have applications as
self-assembled materials, luminescent polymer dots, or litho-
graphic resists.
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CONCLUSIONS
Here we have demonstrated a facile method for the synthe-
sis of iridium-containing acrylic polymers using Cu(0)-
RDRP. The β-ketoester acrylate ligand was shown to effec-
tively provide a polymerizable handle to red, green, and
sky-blue iridium complexes, which could be copolymerized
with a carbazole-based host material to give good color
purity in the solid state. Resulting polymers showed disper-
sities as low as 1.08 with conversions reaching 93%, pro-
viding a low-cost route to phosphorescent metallopolymers
with minimal waste. High-molecular-weight polymers with
Mn approaching 40 kDa were also successfully prepared, as
well as block copolymers by chain extension of MA in one
pot. We anticipate that this strategy can be readily applied
to the polymerization of other organometallic acrylates via
Cu(0)-RDRP, providing an inexpensive and scalable route to
well-defined metallopolymers.
15 F. Alsubaie, A. Anastasaki, V. Nikolaou, A. Simula,
G. Nurumbetov, P. Wilson, K. Kempe, D. M. Haddleton, Macro-
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ACKNOWLEDGMENTS
24 Z. A. Page, C.-Y. Chiu, B. Narupai, D. S. Laitar,
S. Mukhopadhyay, A. Sokolov, Z. M. Hudson, R. Bou Zerdan,
A. J. McGrath, J. W. Kramer, B. E. Barton, C. J. Hawker, ACS
Photonics 2017, 4, 631.
This work was supported by the Natural Sciences and Engi-
neering Council of Canada (NSERC). C. J. Christopherson and
D. M. Mayder thank the University of British Columbia for
4-year fellowships, N. R. Paisley and E. R. Sauvé thank
NSERC for Postgraduate Scholarships, and ZMH is grateful for
support from the Canada Research Chairs program.
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