Reverse Atom Transfer Radical Polymerization of Methyl
Methacrylate in Room-Temperature Ionic Liquids
HONGYANG MA, XINHUA WAN, XIAOFANG CHEN, QI-FENG ZHOU
Department of Polymer Science and Engineering, College of Chemistry and Molecular Engineering, Peking University,
Beijing 100871, China
Received 14 August 2002; accepted 14 October 2002
ABSTRACT: The reverse atom transfer radical polymerization (ATRP) of methyl
methacrylate (MMA) was successfully carried out in 1-butyl-3-methylimidazolium
hexafluorophosphate with 2,2⬘-azobisisobutyronitrile/CuCl2/bipyridine as the initiating
system, which had been reported as not able to promote a controlled process of MMA in
bulk. The living nature of the polymerization was confirmed by kinetic studies, endgroup analysis, chain extension, and block copolymerization results. The polydispersity
of the polymer obtained was quite narrow, with a weight-average molecular weight/
number-average molecular weight ratio of less than 1.2. In comparison with other
reverse ATRPs in bulk or conventional solvents, a much smaller amount of the catalyst
was used. After a relatively easy removal of the polymer and residue monomer, the ionic
liquid and catalytic system could be reused without further treatment. © 2002 Wiley
Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 143–151, 2003
Keywords: reverse atom transfer radical polymerization; ionic liquid; methyl
methacrylate; 1-butyl-3-methylimidazolium hexafluorophosphate ATRP; block copolymers; living polymerization
INTRODUCTION
It is a great challenge to reduce the amount of
volatile organic compounds used in chemical and
industrial processes. Room-temperature ionic liquids have been considered and used as a new
generation of green solvents for a number of organic reactions,1–9 such as alkylation, hydrogenation, Diels–Alder addition, Suzuki cross-coupling
reaction, and butadiene dimerization, because
they are nonvolatile, nonflammable, and recyclable. However, only in the past several years has
polymerization been carried out in room-temperature ionic liquids. Examples include the coordination polymerization of olefins via Ziegler–Natta
catalysts, the oxidative dehydropolycondensation
Correspondence to: X. Wan (E-mail: xhwan@pku.edu.cn)
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 41, 143–151 (2003)
© 2002 Wiley Periodicals, Inc.
of benzene to polyphenylene, and the enzymatic
synthesis of polyesters.10 –17 Recently, free-radical polymerizations of vinyl monomers were also
reported.18,19
Atom transfer radical polymerization (ATRP)
provides an efficient new technique for preparing
well-defined polymers.20 –22 The presence of transition-metal-catalyzed reversible atom transfer
steps, which is responsible for the overall control
of the process, is the main difference between
ATRP and conventional free-radical polymerization.23 The properties of the catalysts are usually
manipulated by the use of different kinds of organic ligands, such as bipyridine (bipy) and other
polydentate N-containing compounds. Sometimes, high level of catalysts and ligands are required to enable an acceptable polymerization
rate.24,25 As a result, the removal and recycling of
the catalytic materials become important. It is
expected that using ionic liquids as polymeriza143
144
MA ET AL.
tion solvents will make this relatively easy to
achieve.26 –28
Carmichael et al.26 first took advantages of roomtemperature ionic liquids as ATRP media. They
performed the copper(I)-mediated ATRP of methyl
methacrylate (MMA) in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]). The rate
of reaction was increased, as observed in other polar/coordinating solvents, and the polymers obtained had narrow polydispersities and were easily
separated from the catalyst. Sarbu and Matyjaszewski27 studied the ATRP of MMA in ionic liquids
containing different counterions. No organic ligand
was needed for the iron-catalyzed ATRP of MMA in
the ionic liquids used. However, when copper(I)
was used as a catalyst, an organic ligand was
required for the ATRP of MMA in ionic liquids
with a halide or carbonate anion, but not with a
phosphonate anion. In addition, the catalyst was
successfully regenerated after the removal of the
polymer and unreacted monomer. Biedroń and
Kubisa28 reported the influence of substituents
(methyl, butyl, hexyl, and dodecyl) on the ATRP
of acrylates in [bmim][PF6] with CuBr/pentamethyldiethylenetriamine as a catalyst. Methyl acrylate (MA) dissolved in [bmim][PF6] and formed
a homogeneous polymerization medium. The obtained poly(methyl acrylate) had a number-average molecular weight (Mn) close to the calculated
value and a relatively narrow polydispersity. For
higher acrylates, although they did not dissolve in
[bmim][PF6], ATRP was achieved by efficient stirring facilitating the transfer of the initiator,
monomer, and propagation chains between two
phases. However, to the best of our knowledge, no
reverse ATRP has been approached in ionic liquids.
In this article, we report on the reverse ATRP of
MMA in [bmim][PF6] with 2,2⬘-azobisisobutyronitrile (AIBN)/CuCl2/bipy as the initiating system. In
reverse ATRP, transition-metal compounds at their
higher oxidation states are used as catalysts, and
conventional initiators such as AIBN and benzoyl
peroxide are used in place of organic halides.29
Therefore, the easy oxidation of the catalyst (lower
oxidation-state transition-metal compounds) and
the toxicity of halide initiators in conventional
ATRP are avoided. Initiating systems, including
AIBN/FeCl3/PPh3,30 tetraphenyl-1,2-ethanediol/
FeCl3/PPh3,31 AIBN/CuBr2/4,4⬘-di(5-nonyl)-2,2⬘bipyridine, 32 and diethyl 2,3-dicyano-2,3-di(p-toyl)succinate/CuCl2/bipy,33 have been developed to mediate the reverse ATRP of MMA. However, uncontrolled and heterogeneous reverse
ATRP was observed for MMA with CuCl2 as a
catalyst and with bipy as a complexing ligand.29
One possible reason was that the concentration of
CuII species in the reaction mixture was low on
account of the poor solubility of the catalyst. Another was that the deactivation rate of growing
MMA chains was not fast enough in comparison
with poly(methyl methacrylate) (PMMA) propagation. We found that the same initiating system
could promote the reverse ATRP of MMA in a
well-controlled manner if [bmim][PF6] was used
as a solvent. In addition, the solvent and catalytic
system could be relatively easily recycled and reused after polymerization.
EXPERIMENTAL
Materials
1-Methylimidazole (99%; Acros), 1-chlorobutane
[99%, analytical reagent (AR); Beijing Chemical
Co.], hexafluorophosphoric acid (60 wt % solution
in water; Acros), and bipy (AR; Beijing Chemical
Co.) were used as purchased. MMA (AR; Beijing
Chemical Co.) was first purified with a silica column for the removal of the inhibitor and then
vacuum-distilled from CaH2. AIBN (AR; Wuhan
Chemical Co.) was recrystallized from ethanol
and dried in vacuo. Tetrahydrofuran (THF) and
chlorobenzene (AR; both from Beijing Chemical
Co.) were distilled over CaH2. CuCl (AR; Beijing
Chemical Co.) was purified according to a literature method.33 CuCl2 (99%; Beijing Chemical Co.)
was dried in an oven at 80 °C before use. Other
solvents and reagents were used without further
purification, except as noted.
Synthesis of [bmim][PF6]
The ionic liquid [bmim][PF6] was prepared according to a literature procedure.34 To a dry glass
tube, 8.2 g (0.1 mol) of 1-methylimidazole and
11.4 mL (0.13 mol) of 1-chlorobutane were added.
After three freeze–pump–thaw cycles, the tube
was sealed in vacuo and placed in an oil bath
thermostated at 70 °C. The reaction continued for
3 days, and a pale yellow, viscous liquid appeared.
After it cooled to 0 °C, a white solid, 1-butyl-3methylimidazolium chloride, was obtained. The
solid was washed three times with ethyl acetate
and then was dissolved in deionized water. To the
aqueous solution cooled by an ice bath, 19 mL of
hexafluorophosphoric acid (60% water solution,
REVERSE ATRP IN ROOM-TEMPERATURE IONIC LIQUIDS
0.13 mol) was added slowly. After the mixture
was stirred overnight, an orange, viscous liquid
was obtained. The liquid was diluted with dichloromethane and washed with deionized water until it became neutral. The ionic liquid was dried in
vacuo at 70 °C after the evaporation of dichloromethane.
145
HT2, HT3, and HT4 ␮-Styragel columns with
THF as an eluent (1.0 mL/min) at 35 °C. Calibration was made with standard polystyrene (PSt).
The 1H NMR spectrum was taken at 25 °C on a
Bruker ARX400 NMR spectrometer with chloroform-d as a solvent and with tetramethylsilane
(TMS) as an internal reference.
Polymerization
A dry glass tube was charged with CuCl2, MMA,
bipy, AIBN, and [bmim][PF6]. The mixture was
degassed by three freeze–pump–thaw cycles and
sealed in vacuo. The tube was placed in a water
bath at the desired temperature maintained by a
thermostat. After an expected time, the tube was
placed in an ice bath to stop the reaction. The
reaction mixture was diluted with THF and
added dropwise into methanol. After filtration
and washing three times with methanol, followed
by drying under infrared light for 24 h, PMMA
was obtained. The conversion of the monomer was
determined gravimetrically.
Chain Extension
Chain extension was performed with the conventional ATRP technique at 95 °C. To a polymerization tube, 0.050 g (9.62 ⫻ 10⫺3 mmol) of the
PMMA macroinitiator, 0.516 g (5.16 mmol) of
MMA, 0.008 g (8.08 ⫻ 10⫺2 mmol) of CuCl, 0.072
g (0.46 mmol) of bipy, and 1.544 g of chlorobenzene were added. After three freeze–pump–thaw
cycles, the tube was sealed in vacuo and placed in
a water bath at 95 °C for 7.5 h. The chain-extended PMMA was obtained after precipitation in
methanol, filtration, washing, and drying under
infrared light for 24 h.
Block Copolymerization
The block copolymerization was carried out with
a method similar to that used for chain extension
except that styrene was used in place of MMA. In
addition, the reaction temperature, 120 °C, was
higher than that in chain extension.
Measurements
The Mn and molecular weight distribution
[weight-average molecular weight/number-average molecular weight (Mw/Mn)] values of PMMA
were measured on a Waters 2410 gel permeation
chromatography (GPC) instrument with a set of
RESULTS AND DISCUSSION
Reverse ATRP of MMA
The reverse ATRP of MMA initiated by AIBN
combined with CuCl2, complexed by bipy, was
carried out in [bmim][PF6] at 60, 70, and 90 °C.
The [MMA]/[AIBN]/[CuCl2]/[bipy] molar ratio
was 100:1:2:6. Under these conditions, all the reagents, including the initiator, transition metal,
ligand, monomer, and polymer, were soluble in
[bmim][PF6], and the reaction medium remained
homogeneous throughout the polymerization. The
results are summarized in Table 1.
Figure 1 shows the relationship between
ln([M]0/[M]) and the reaction time. The linear
first-order kinetic plots indicate that the radical
concentration was constant during the polymerization. However, the induction period was observed for the polymerizations carried out at 60
and 70 °C but not at 90 °C. The higher the reaction temperature was, the shorter the induction
period was. This might be rationalized by the fact
that AIBN decomposed more slowly at a lower
temperature. During early stages of the polymerizations at 60 and 70 °C, the primary radicals
generated from AIBN reacted with CuCl2 completely to form dormant species. At the same
time, the concentration of the formed dormant
species and CuCl/bipy complex was too low to
produce enough propagating species for PMMA
chain growth at a noticeable rate through a reversible redox process. Therefore, the propagation
of PMMA chains was inhibited or retarded.
The plots of Mn and Mw/Mn of the resulting
PMMA against conversion are depicted in Figure
2. With an increase in the monomer conversion,
the molecular weight increased linearly, and the
polydispersity decreased slightly at first and then
remained almost unchanged. The values of
Mw/Mn were less than 1.2, implying a well-controlled polymerization process. Figure 3 shows
the GPC curves of the obtained polymers. All are
narrow and symmetrical.
146
MA ET AL.
Table 1. Reverse ATRP of MMA in [bmim][PF6] at Different Temperatures
Runa
Temperature
(°C)
Time (h)
Conversion
(%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
60
60
60
60
60
60
70
70
70
70
70
70
90
90
90
90
90
90
11.6
14.3
22.5
24.4
26.3
30.8
6.0
7.5
8.0
9.5
11.7
12.5
0.5
0.8
1.3
1.9
2.3
2.6
12.56
22.66
47.53
56.67
66.67
87.33
26.54
44.9
51.91
64.46
79.49
89.41
20.34
45.73
63.57
74.11
77.08
81.04
Mn;th ⫻ 10⫺3
b
Mn GPC ⫻ 10⫺4 c
Polydispersity
Index
f
0.65
0.86
1.88
2.03
2.23
2.62
1.26
1.53
1.53
1.76
1.77
2.03
0.44
0.81
1.43
1.60
1.62
1.65
1.19
1.19
1.08
1.08
1.08
1.08
1.11
1.09
1.09
1.08
1.09
1.08
1.18
1.17
1.08
1.08
1.08
1.09
9.69
13.14
12.66
13.94
14.93
16.68
10.55
14.71
16.99
18.3
22.43
22.02
23.18
28.27
22.24
23.19
23.77
24.55
0.63
1.13
2.38
2.83
3.33
4.37
1.33
2.25
2.60
3.22
3.97
4.47
1.02
2.29
3.18
3.71
3.85
4.05
MMA ⫽ 0.50 g; [bmim][PF6] ⫽ 1.50 g; [MMA]/[AIBN]/[CuCl2]/[bipy] ⫽ 100:1:2:6.
Calculated based on Mn;th ⫽ 100 ⫻ (⌬[MMA]/2[AIBN]0) ⫻ conversion.
c
By GPC with polystyrene standards.
a
b
It was reported that the heterogeneous AIBN/
CuCl2/bipy-catalyzed ATRP of MA and MMA in
bulk proceeded in an uncontrolled manner.29 The
poor solubility of CuCl2 and the low deactivation
rate of growing radicals by CuCl2 were considered
to be responsible for the gelation, for the much
higher molecular weight than calculated, and
for the broader molecular weight distribution
observed. The controlled radical process in
[bmim][PF6] with the same catalytic system as in
Figure 1. Dependence of ln([M]0/[M]) on the reaction
time at different temperatures. For the polymerization
conditions, see Table 1.
ref. 29 may be ascribed to the good solubility of the
catalyst complex in the ionic liquid. In such a
case, the concentration of CuII was much higher
than that in a heterogeneous system when the
same amount of CuCl2 was added.
As can be seen in Table 1, the molecular
weights measured by GPC, Mn,GPC, were much
higher than the calculated values, Mn,th, according to Mn,th ⫽ 100 ⫻ (⌬[MMA]/2[AIBN]0) ⫻ conversion. This meant the initiator efficiency, f
⫽ Mn,th/Mn,GPC, of AIBN in the ionic liquid was
lower than that in conventional organic solvents.
A similar behavior was observed by Sarbu and
Matyjaszewski,27 who attributed it to the relatively low concentration of the catalyst in the
organic phase and the very high concentration of
the catalyst in the ionic phase. However, the concentration difference of the catalyst in two separate phases could not account for the low initiator
efficiency in our experiments because all the reagents were soluble in [bmim][PF6] and a homogeneous solution was formed. The viscosity of
[bmim][PF6] was higher than that of bulk MMA
or a solution of MMA in conventional organic
solvents. Therefore, the low initiating efficiency
was most likely due to the cage effect of
[bmim][PF6] molecules. Because of the intense
REVERSE ATRP IN ROOM-TEMPERATURE IONIC LIQUIDS
147
End-Group Analysis of the Obtained PMMA
The chemical structure of the obtained PMMA
was characterized by 400-MHz 1H NMR spectroscopy. Figure 4 showed the representative 1H
NMR spectrum of the well-defined PMMA with
an Mn value of 1.23 ⫻ 104 and an Mw/Mn value of
1.08. The signals at 0.84 –1.26, 1.38 –2.08, and
3.42–3.83 ppm were attributed to the protons of
␣-methyl groups (peak a), methylene groups
(peak b), and methoxy groups (peak c), respectively. Moreover, the absorptions at 3.78 [peak
c(␻)], 2.50 [peak b(␻)], and 1.26 ppm [peak a(␻)]
proved the presence of the end group, OCH2CCl(CH3)(COOCH3).
Figure 2. Mn and Mw/Mn versus conversion. For the
polymerization conditions, see Table 1.
confinement of the highly viscous solvent, some
side reactions of the primary radicals might have
occurred, and as a result, the concentration of the
initiator radicals was depleted. This was consistent with our observations that much less catalyst
was needed for reverse ATRP in an ionic liquid
than in bulk or conventional organic solvents.
This is described in detail in the following sections.
Figure 3. GPC traces of PMMA. For the polymerization conditions, see Table 1.
148
MA ET AL.
Figure 5. GPC curves of PMMA before and after
chain extension via ATRP at 95 °C (MMA ⫽ 0.516 g,
chlorobenzene ⫽ 1.544 g, CuCl ⫽ 0.008 g, bipy ⫽ 0.072
g, PMMA macroinitiator ⫽ 0.050 g, time ⫽ 7.5 h).
Figure 4. 1H NMR spectrum (CDCl3, 400 MHz) of
PMMA polymerized in an ionic liquid at 70 °C (Mn
⫽ 1.23 ⫻ 104 g/mol, Mw/Mn ⫽ 1.08).
ment, except that styrene was used in place of
MMA. The GPC curves are shown in Figure 6.
The GPC curve of the copolymer obviously shifted
to a higher molecular weight after copolymerization.
Effects of the CuCl2 Content on the Polymerization
of MMA
The Mn value of PMMA was estimated from the
ratio of the methylene protons (b) and the terminal one [b(␻)]. The Mn,NMR value (1.33 ⫻ 104) was
close to Mn,GPC (1.23 ⫻ 104). Another proof of the
well-defined PMMA with a chlorine end substituent was provided.
Chain Extension with MMA
The catalyst CuCl2 played an important role in
reverse ATRP. If CuCl2 was absent or not enough
was added, the polymerization proceeded in an
uncontrolled manner. However, the excess CuCl2
would not only slow the polymerization rate significantly but also could contaminate the resultant polymer. The activity of CuCl2 depended dramatically on its solubility in the polymerization
medium.29 In the heterogeneous reverse ATRP of
The chain extension was made by the conventional ATRP of MMA in chlorobenzene, with chlorine-ended PMMA as a macroinitiator, with CuCl
as a catalyst, and with bipy as a complexing ligand. The GPC curves of PMMA before and after
chain extension are displayed in Figure 5. The
increase in the molecular weight was clearly demonstrated. In addition, the Mn,th/Mn,GPC value
was 0.98, indicating the expected chemical structure and a high initiating efficiency of the macroinitiator.
Block Copolymerization with Styrene
The block copolymerization with styrene was carried out with a method similar to that employed
in the aforementioned chain-extension experi-
Figure 6. GPC curves of the PMMA macroinitiator
and resulting PMMA-b-PSt via ATRP at 120 °C (styrene ⫽ 0.520 g, PMMA macroinitiator ⫽ 0.100 g, CuCl
⫽ 0.030 g, chlorobenzene ⫽ 1.839 g, bipy ⫽ 0.035 g,
time ⫽ 39 h).
REVERSE ATRP IN ROOM-TEMPERATURE IONIC LIQUIDS
149
Table 2. Reverse ATRP of MMA in [bmim][PF6] at
Different [AIBN]/[CuCl2] Ratios
Entrya
[AIBN]/
[CuCl2]
Mn
(⫻ 10⫺4)
Mw/Mn
Yield
(%)
1
2b
3
4
5
6
7
8
9
1:0
1:0
1:0.125
1:0.25
1:0.5
1:1
1:2
1:4
1:5
18.65
17.98
3.17
2.62
2.46
1.56
1.60
1.51
1.38
1:54
1:55
1:10
1:09
1:09
1:06
1:07
1:07
1:07
99.00
99.00
97.89
92.05
90.67
58.32
53.77
41.81
34.91
MMA ⫽ 0.50 g; [bmim][PF6] ⫽ 1.50 g; [MMA]/[AIBN]
⫽ 100:1; [CuCl2]/[bipy] ⫽ 1:3.
b
The sample was prepared by conventional free-radical
polymerization but with 5% bipy added.
a
styrene, up to 10 equiv of CuCl2 was required to
achieve good control over the polymerization of
styrene. The ill-controlled heterogeneous reverse
ATRP was also observed for both MA and MMA
under the same conditions. However, only 1 equiv
of CuCl2 was needed to make the reverse ATRP of
styrene, MA, and MMA well controlled in anisole.32
To investigate the effect of the CuCl2 content
on the reverse ATRP of MMA in [bmim][PF6], we
employed a variety of initiating systems, AIBN/
CuCl2/bipy, with varied [CuCl2]/[AIBN] ratios of
0 – 8, while keeping constant [MMA]/[AIBN] at
100 and [bipy]/[CuCl2] at 3. The results were sum-
Figure 7. GPC traces of PMMA obtained at different
AIBN/CuCl2 ratios (MMA ⫽ 0.50 g, [bmim][PF6]
⫽ 1.50 g, temperature ⫽ 70 °C, reaction time ⫽ 8 h).
The sample was prepared by conventional free-radical
polymerization but with 5% bipy added.
Figure 8. Dependence of ln([M]0/[M]) on the polymerization time in [bmim][PF6] at 90 °C (MMA ⫽ 0.50 g,
[bmim][PF6] ⫽ 1.50 g, [MMA]/[AIBN]/[CuCl2]/[bipy]
⫽ 100:1:0.6:6).
marized in Table 2. Figure 7 exhibits the GPC
traces of the polymers. In the absence of CuCl2,
the molecular weight distribution of the obtained
PMMA was broad, suggesting an uncontrolled
process. However, the polymerizations became
well controlled when only 0.125 equiv of CuCl2
versus AIBN was added. All the polymers had
Mw/Mn values of less than 1.10. The polymerization rate increased with an decrease in the
[CuCl2]/[AIBN] ratio, as evidenced by the decreased monomer conversion at the same polymerization time. This was the result of more radicals being generated by the decomposition of
AIBN.
Another series of reverse ATRPs were carried
out in [bmim][PF6] with [MMA]/[AIBN]/[CuCl2]/
[bipy] ⫽ 100/1/0.6/6 at 90 °C. The corresponding
semilogarithmic kinetic plots are displayed in
Figure 8. The linear relationship between ln([M]0/
[M]) and time was again observed.
It was interesting to ask why the amount of
CuCl2 needed to gain control over the reverse
ATRP of MMA was less in an ionic liquid than in
bulk or conventional organic solvents. According
to the mechanism of reverse ATRP proposed by
Matyjaszewski and coworkers,20 –22 1 molar
equivalent of CuII species versus growing radicals
should be required to promote a controlled polymerization. However, the [AIBN]/[CuCl2] ratio
here was as large as 8 when a well-controlled
process was observed. The main reason might be
the low efficiency of AIBN in [bmim][PF6], in addition to the good solubility of CuII species in the
ionic liquid.
150
MA ET AL.
Recycling of [bmim][PF6], CuCl2, and bipy
The probability of recycling the [bmim][PF6] and
catalytic system was evaluated in this work.
When the polymerization was stopped, the reaction mixture was diluted with THF and added
dropwise into a large amount of methanol. The
precipitated PMMA was isolated by filtration. After the evaporation of the methanol, THF, and
residue monomer in vacuo, the initiator, AIBN,
and the monomer, MMA, were introduced into recovered [bmim][PF6] containing recycled CuCl2
and bipy. The reverse ATRP was performed
again. Figure 9 shows the GPC traces of the obtained PMMA. The plots of Mn and Mw/Mn versus
the conversion are shown in Figure 10. The Mn
values increased linearly with conversion, and
the polydispersities remained relatively narrow;
this indicated a well-controlled polymerization
process, although no extra catalyst and ligand
were added.
CONCLUSIONS
The well-controlled reverse ATRP of MMA was
achieved in an ionic liquid, [bmim][PF6], with the
AIBN/CuCl2/bipy initiating system. Much less catalyst was needed to effectively mediate the process
in [bmim][PF6] than in other reverse ATRPs. The
resultant PMMA and residue monomer were relatively easily isolated from the reaction mixture. The
ionic liquid and catalyst complex were readily
recovered and reused. The chlorine-atom-ended
PMMA was used as a macroinitiator for chain
extension or copolymerization with styrene by
conventional ATRP in chlorobenzene.
Figure 9. GPC traces of PMMA polymerized in an
ionic liquid at 70 °C with the recovered ionic liquid and
catalytic system (MMA ⫽ 0.50 g, [bmim][PF6] ⫽ 1.50 g,
[MMA]⶿[AIBN]⶿[CuCl2]⶿[bipy] ⫽ 100:1:2:6).
Figure 10. Mn and molecular weight distribution values of PMMA polymerized in the recovered [bmim][PF6]
and catalytic system at 70 °C versus the conversion.
For the polymerization conditions, see Figure 9.
This work was supported by the National Natural Science Foundation of China (20174001) and the Chinese
Ministry of Education through the research fund for
the doctoral program of higher education (99000136)
and through the teaching and research award fund for
outstanding young teachers in higher education institutions.
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