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Journal of Research Updates in Polyme r Science, 2016, 5, 149-157 149
E-ISSN: 1929-5995/16 © 2016 Lifescience Global
Optimizing Activators Regenerated by Electron Transfer for Atom
Transfer Radical Polymerization of Methyl Methacrylate Initiated by
Ethyl 2-bromopropionate
Mingsen Chen, Hongwang Zhou, Xiaofang Li, Li Zhou and Faai Zhang*
Guangxi Ministry-Province Jointly-Constructed Cultivation Base for State Key Laboratory of Processing for
Nonferrous Metal and Featured Materials, Key Laboratory of Nonferrous Materials and New Processing
Technology, Ministry of Education, College of Material Science and Engineering, Guilin University of
Technology, Guilin 541004, China
Abstract: In this study, we used ethyl 2-bromopropionate (EBrP) as an initiator of activators regenerated by el ectro n
transfer for atom tr ansfer radical polymerization (ARGE T ATRP) of methyl methacrylate (MMA). We investigated in detail
the effect on polymerization of different kinds of reducing agents and ligands, the amounts of the reducing agent and
catalyst, and reaction temperature. We determined the molecular weight and dispersity of the polymers by gel
permeation chromatography (GPC). The results reveal glucose to be the best reducing agent for this system. The
monomer conversion increased with increases in the reaction temperature and in the feeding amounts of the reducing
agent and catalyst. The optimum amount of the reducing agent and minimal amount of catalyst required depend on the
particular system. For exa mple, we polymerized MMA with 200 ppm of catalyst and 15-fold of glucose/CuCl2 resulting in
a PMMA w ith high Mn (Mn,GP C = 48 700, Mn,theo = 48 500) and low dispersity (1.27). The first-or der kinetics show that the
molecular weights increase d linearly with the monomer conversion and are consistent with the theoretical values, the
chain extension reaction and end group analysis results also demonstrate that the characteristics of polymerization
process belong to a typical “living”/controlled radical polymerization. Moreover, 1H-NMR analysis results indicate the
stereoregularity of the polymer is given priority over syndiotactic architec ture and the effect of the type of ligand on the
stereoregularity is very slight.
Keywords: Ethyl 2-bromopropionate, ARGET ATRP, MMA, reducing agent.
1. INTRODUCTION
In recent years, atom transfer radical polymerization
(ATRP) has been recognized as one of the most
successful “living”/controlled radical polymerization
(CRP) techniques for its simplicity in the preparation of
a polymer with a predetermined structure and a narrow
molecular weight distribution. ATRP can create a
dynamic equilibrium between a small amount of active
species (R•) and a large amount of dormant species
(P-X or P-M-X) [1, 2]. When the concentration of
propagating radicals is sufficiently low, the probability
of bimolecular termination reactions is reduced.
However, ATRP has some limitations, such as the
large dosage of catalyst required, and the sensitivity of
the low-state transition metal to oxygen. To overcome
these drawbacks, Matyjaszewski et al. developed
activators regenerated by electron transfer for ATRP
(ARGET ATRP) [3] and proposed a polymerization
mechanism, as shown in Scheme 1. ARGET ATRP can
be conducted with a significantly lower catalyst
concentration in the presence of an excess of reducing
agent such as ascorbic acid [4-6], tin(II) 2-
ethylhexanoate (Sn(EH)
2) [7, 8], glucose [7], alcohol
*Address corres pondence to th is author at the College of Material Science and
Engineerin g, Guilin University of Technology, No. 12 Jiangan Road, Guilin
541004, P.R. China; Fax: 86-773-5899957; E-mail: zhangfaai@163.com
[9], Triphenylphosphine [10] or others [11, 12]. To date,
ARGET ATRP has been successfully applied in the
synthesis of nanocomposite materials [13-15], hybrid
materials [16, 17], block copolymers [18-20], and
polymers with precisely controlled molecular weights,
relatively low dispersities and controlled molecular
architecture in terms of chain topologies [21, 22].
Recently, researchers have made some important
advances in developing new initiator/catalytic systems
[23-25]. In order to precise design and synthesize well-
defined polymers, it is important to select a suitable
initiator and the appropriate catalyst and reaction
conditions for specific monomers. In previous reports,
the most commonly used initiator for ARGET ATRP
has been ethyl 2-bromoisobutyrate (EBiB) [4, 9, 26-30].
For example, using EBiB as initiator for ARGET ATRP,
Matyjaszewski synthesized polymethyl methacrylate
(PMMA) with Mn,GPC =30 700 (Mn,theo =23 260, Mw/Mn
=1.27) and achieved a monomer conversion of 59%
after a reaction period of 18 h. The author also
synthesized a polymethyl acrylate (PMA) with Mn,GPC =
27 700 (Mn,theo = 30 000, Mw/Mn =1.19) and achieved a
monomer conversion of 87% after reaction period of
only 5.3 h [4].
Researchers have investigated the influence of
different initiator structures on the activation rate
150 Journal of Research Updates in Polymer Science, 2016, Vol. 5, No. 4 Chen et al.
constants (Kact) in ATRP [31]. A variety of initiators
have been investigated, including EBiB, methyl 2-
bromopropionate (MBrP), and 1-phenylethyl bromide
(PEBr). However, data is scarce regarding ethyl 2-
bromopropionate (EBrP). To the best of our knowledge,
there are no reports on the use of EBrP as an initiator
of ARGET ATRP. Wang found EBrP to be an efficient
initiator for the ATRP of MMA [32] and that CuCl-bpy,
rather than CuBr-bpy, was a better catalyst for the
controlled polymerization of MMA. In this study, we
used EBrP, which has a similar molecular structure to
that of EBiB, as an initiator for the ARGET ATRP of
MMA. First, we compared the effect of initiator types
and reducing agents on the ARGET ATRP of MMA.
Then, we systematically studied the effect of the
dosages of the reducing agent and ligand types, the
levels of catalyst, and the temperature on the ARGET
ATRP of MMA in the optimal reducing agent. In
addition, we investigated the kinetics of the ARGET
ATRP of MMA and the chain extension, and analyzed
the end groups and stereoregularity of the PMMA
obtained using different ligands. In this paper, we focus
on optimizing the experimental conditions of the
ARGET ATRP of MMA initiated by EBrP.
Scheme 1: Mechanism of ARGET ATRP.
2. EXPERIMENTAL
2.1. Materials
Methyl methacrylate (MMA, CP), cyclohexanone
(analytical reagent, AR), methanol (AR), ethylene
glycol (EG, AR), tetrahydrofuran (THF, AR), and
CuCl2·2H2O (AR) were all purchased from the Xilong
Chemical Plant in Shantou, Guangdong Province
(China). Tris(2-(dimethylamino)ethyl)amine (Me6TREN,
99%) was provided by Alfa Aesar (Tianjin) Chemical
Co. Ltd. (China). 2,2'-bipyridine (bpy, AR, 99%), ethyl
2-bromoisobutyrate (EBiB，98%)，ethyl 2-
bromopropionate (EBrP, 98%), ascorbic acid (AsAc,
AR,>99%), N,N,N',N',N''-pentamethyldiethylenetriamine
(PMDETA, 99%), 1,1,4,7,10,10-Hexamethyltriethyl-
enetetramine (HMTETA, 98%), tin(II) 2-ethylhexanoate
(Sn(EH)2, 95%), glucose (AR) were all purchased from
Aladdin Industrial Corporation (Shanghai, China).
Ethanol absolute (AR) was purchased from Guangdong
Guanghua Sci-Tech Co., Ltd. (Shantou China). MMA
was washed with 10% NaOH and deionized water, and
vacuum distilled it before use. CuCl2·2H2O was
dehydrated via dissolution and evaporation in ethanol
before use. All other chemicals were used as received
without further purification.
2.2. Synthesis of PMMA by ARGET ATRP
We used the following typical polymerization
procedure: we added 5 mL of cyclohexanone and 5 mL
of a premixed solution (molar ratio of
MMA/EBrP/CuCl2/PMDETA/glucose = 500/1/0.1/1/2),
to a 100 mL well-dried round-bottomed flask. We then
stirred the mixture, degassed it under vacuum
conditions, and bubbled it with nitrogen for 15 min.
Then, the sealed flask was placed in an oil bath at 80
°C for several hours. After the reaction, THF was
added to dissolve the polymer, and then the mixture
was precipitated into excess methanol, and the solids
were filtered and dried under vacuum at 60 °C for 24 h.
2.3. Extension of PMMA Macroinitiator with MMA by
ARGET ATRP
A PMMA macroinitiator (Mn = 22 600, Mw/Mn = 1.22,
0.0229 g) prepared by ARGET ATRP was dissolved in
a MMA monomer (5 mL, 4.72 g), along with the mixture
solutions (molar ratio of MMA/CuCl2/PMDETA/glucose
= 500/0.01/0.1/1.5) were added to a 100 mL well-dried
round-bottomed flask. The resulting mixture was stirred
and degassed under vacuum and bubbled with
nitrogen for 15 min. Then, the sealed flask was placed
in a thermostatic oil bath at 80 °C for several hours.
After the reaction, THF was added to dissolve the
polymer, and then the mixture was precipitated into
excess methanol, and the solids were filtered and dried
under vacuum at 60 °C for 24 h.
2.4. Analysis
The molecular weights and dispersities (Mw/Mn) of
the resulting polymers were measured by gel
permeation chromatography (GPC) with a Malvern
Model 270 equipped with a refractive index detector, a
viscosity detector and a light scattering detector, and
T6000 microstyragel columns. THF was used as the
Optimizing Activators Regenerated by Electron Transfer Journal of Research Updates in Polymer Science, 2 016, Vol. 5, No. 4 151
eluent at a flow rate of 1.0 mL/min and operated at 35
°C. Hydrogen nuclear magnetic resonance (1H-NMR)
spectra were obtained on an Avance 500 MHz
spectrometer (Bruker, Switzerland) using CDCl3 as the
solvent and tetramethylsilane (TMS) as the internal
standard. The monomer conversions were calculated
gravimetrically. Theoretical molecular weights (Mn,theo)
of the resulting PMMA was calculated by the following
equation:
Mn,theo=([M]0/[I]0)*Conv(%)*M MMA+ M EBrP .
Where [M]0 and [I]0 stand for the initial
concentrations of monomer and initiator, respectively.
Conv(%) stands for the monomer conversion, MMMA
and MEBrP indicate the molecular weights of MMA and
EBrP, respectively.
3. RESULTS AND DISCUSSION
3.1. Comparison of EBiB and EBrP
We carried out the ARGET ATRP of MMA using
EBiB and EBrP as initiators under the same
polymerization conditions. As shown in Figure 1, EBr P
was a high-efficiency initiator in this initiating/catalytic
system. The semi-logarithmic plot of ln([M]0/[M]) versus
the polymerization time was linear when MMA was
initiated by EBrP/CuCl2/PMDETA. Moreover, the
molecular weight of PMMA obtained while using EBrP
was closer to the theoretical value than that of using
EBiB. Both products had a relatively low Mw/Mn value
(< 1.40). These results demonstrate that EBrP is a
better initiator for the ARGET ATRP of MMA in this
system and may be contribute to the effect of the
initiator structure on the selectivity of the
CuCl2/PMDETA system.
3.2. Kinetics of the ARGET ATRP of MMA
In general, the most important features in living
radical polymerization are the pseudo first-order
kinetics of polymerization, a well-controlled molecular
weight, the low Mw/Mn, linear evolution of molecular
weight with monomer conversion, and perfect or near-
perfect chain-end functionalities [32]. The reaction
conditions and experimental results for the ARGET
ATRP of MMA are shown in Table 1 and Figure 2.
As shown in Figure 2a, the semi-logarithmic plot of
ln([M]0/[M]) versus polymerization time was linear, with
a pseudo-first order rate constant (kapp) of 2.55 × 10-4
s-1. Moreover, as shown in Figure 2c, the monomer
conversion displayed a rapid increase within the first 2
h. For example, for the ARGET ATRP of MMA, 85.1%
of the monomer conversion was reached after only 2 h.
Subsequently, the rate of polymerization began to
decrease, and the monomer conversion curve tended
to level off. This is possibly due to the increasing
viscosity of the system. Figures 2b and 2d show that
Mn,GPC increased linearly with the monomer conversion
and maintained a low Mw/Mn value (Mw/Mn ≤ 1.30),
indicating that good control over the molecular weights
and a low Mw/Mn in the EBrP/CuCl2/PMDETA system
were achieved. From the above results, it is clear that
the polymerization exhibited characteristics of living
polymerization. Furthermore, the monomer conversion
reached 97% in 4 h, which represents a great
improvement compared with the aforementioned
literature [9, 32], in which an EBiB/CuCl2/TMEDA
system [9] or an EBr P/CuBr/bpy system [32] had been
used. This finding suggests that when the appropriate
reducing agent and ligand are used, EBrP exhibits a
higher initiation efficiency than EBiB for the ARGET
ATRP of MMA.
Figure 1: ARGET ATRP of MMA Initiated by EB iB and EBrP. Polymerization condition: MMA/Initiato r/CuCl2/PMDETA/Glucose =
500/1/0.1/1/1.5. T = 80 oC, MMA/solvent = 1:1 (v/v).
152 Journal of Research Updates in Polymer Science, 2016, Vol. 5, No. 4 Chen et al.
Table 1: Experimental Conditions and Properties of PMMA Prepared by ARGET ATRP
Entry
Reducing
agent
[Reducing
agent]0/[Cu]0
Time (h)
Conv (%)
Mn,theo
/×104
Mn,GPC
/×104
Mw/Mn
1a
EG
20
4
98.8
4.94
4.24
1.50
2a
Sn(EH)2
20
4
96.8
4.84
3.50
1.48
3a
AsAc
20
16
19.0
0.95
5.04
1.31
4a
glucose
20
4
91.2
4.56
4.51
1.41
5a
glucose
15
4
82.6
4.13
4.95
1.50
6a
glucose
10
4
74.4
3.72
4.60
1.49
7a
glucose
5
4
70.1
3.51
4.17
1.57
8b
glucose
15
0.5
25.0
1.25
1.26
1.15
9b
glucose
15
1
47.5
2.38
2.14
1.26
10b
glucose
15
1.5
65.1
3.26
3.33
1.28
11b
glucose
15
2
85.1
4.26
4.38
1.30
12b
glucose
15
2.5
88.7
4.43
4.56
1.26
13b
glucose
15
3
89.4
4.47
4.15
1.25
14b
glucose
15
4
97.0
4.85
4.87
1.27
abpy as ligand, MM A/EBrP/CuCl2/bpy = 500/1/0.1/1. bPMDETA as ligand, MMA/EBrP/CuCl2/PMDETA = 500/1/0.1/1. T = 80 oC, MMA/solvent = 1:1 (v/v).
Figure 2: Ln([M]0/[M]) as a function of time (a) and average-number molecular weight (Mn) and molecular weight distribution
(Mw/Mn) versus the conversion (b) and conversion versus time (c) and GPC traces of PMMA by different polymerization time (d)
for ARGET ATRP of MMA. Polymerization condition: as show n in Table 1 (Entry 8b~14b).
3.3. Effect of Reducing Agents on the ARGET ATRP
of MMA
We also conducted the ARGET ATRP of MMA
using EG, Sn(EH)2, AsAc, and glucose as reducing
agents. Table 1 (entries 1
a–4a) shows the
corresponding experimental conditions and results. As
shown in Table 1, the reaction rate of polymerization
was very fast when using either EG, Sn(EH)
2 or
Optimizing Activators Regenerated by Electron Transfer Journal of Research Updates in Polymer Science, 2 016, Vol. 5, No. 4 153
glucose as a reducing agent, and in these three cases,
the monomer conversion surpassed 90% after a
reaction period of only 4 h. In contrast, the monomer
conversion reached only 19% even after a reaction
period of 16 h when using AsAc as the reducing agent.
This is possibly because AsAc is a relatively weak
reducing agent in this system and cannot convert
enough Cu(II) species to the Cu(I) state. With glucose
as the reducing agent, we observed good control over
the molecular weights in the ARGET ATRP of MMA,
which produced a PMMA with Mn,GPC = 45 100 (Mn,theo =
45 600) and Mw/Mn = 1.41. However, the Mw/Mn value
is a little high, which was probably caused by the use of
bpy as the ligand. Therefore, further investigation the
effect of ligand types on the ARGET ATRP of MMA is
necessary. In addition, as a reducing agent, glucose is
inexpensive, readily available, non-toxic, and
biocompatible. Thus, we chose glucose as our reaction
reducing agent in subsequent experiments.
3.4. Effect of the Amount of Glucose on the ARGET
ATRP of MMA
The amount of reducing agent plays a crucial role in
ARGET ATRP. In order to determine the optimal
amount of glucose for use in ARGET ATRP, we
performed a series of experiments at 80 oC. The results
are listed in Table 1 (Entry 4a~7a ). As shown in Table 1
(Entry 4a~7a), the monomer conversion decreased from
91.2% to 70.1% with a decrease in the amount of the
reducing agent, which indicates that the polymerization
rate increased with an increase in the amount of
glucose, due to the increased concentration of Cu(I)
species. However, when we used only a tiny amount of
glucose, the Mw/Mn of the polymer broadened (Mw/Mn =
1.57, Entry 7a).
3.5. Effect of Ligand Types on the ARGET ATRP of
MMA
Next, we investigated the effect of ligand types on
MMA polymerization by ARGET ATRP. We maintained
the molar ratio of [MMA]0/[EBrP]0/[CuCl2]0/[Ligand]0/
[glucose]0 at 500/1/0.1/1/2 and fixed the polymerization
temperature at 80 oC. Table 2 shows the monomer
conversion, molecular weight, and Mw/Mn results with
different ligands. As seen in Table 2, the
polymerizations of MMA were well controlled when
using bpy, PMDETA and HMTETA as the ligand.
However, no PMMA formed after polymerization for 4 h
and 22 h when using Me6TREN as the ligand, which
suggests that Me
6TREN maybe not be an efficient
ligand for this system. It is possible that the equilibrium
of Cu(Me6TREN)Cl/Cu(Me6TREN)Cl2 favors
Cu(Me6TREN)Cl2 too much, such that glucose is not
strong enough to reduce Cu(Me6TREN)Cl2 to
Cu(Me6TREN)Cl. In addition, we found PMDETA to be
a better ligand than either HMTETA or bpy, as the
measured molecular weight of the PMMA prepared by
PMDETA was closer to the theoretical values, while
also maintaining a low Mw/Mn value. Compared with
HMTETA and bpy, the polymerization rate was also
fastest when using PMDETA as the ligand. Moreover,
PMDETA is cheap and readily available. Hence, we
chose PMDETA as the ligand in the following
experiments.
3.6. Effect of the Amount of Catalyst on the ARGET
ATRP of MMA
We varied the amount of catalyst from a “high
concentration” of 200 ppm to 20 ppm vs the monomer.
Table 3 shows the reaction conditions and results of
these polymerizations. As shown in Table 3, the
polymerization rate decreased slightly with a reduction
in the concentration of the copper species. In ATRP,
the ratio of Cu (I) to Cu (II) determines the
polymerization rate, while the absolute Cu (II)
concentration influences the Mw/Mn [34]. Therefore, it is
important to determine the minimal amount of Cu
needed to control the polymerization while still
achieving an acceptable reaction rate. As shown in
Table 3, both 100 ppm and 200 ppm of catalyst
provided acceptable reaction rates and low Mw/Mn in
the product, whereas 20 ppm and 50 ppm of the
Table 2: Effects of Ligand Type on ARGET ATRP of MMA
Entry
Ligands
Time(h)
Conv(%)
Mn,theo /×104
Mn,GPC /×104
Mw/Mn
1
Bpy
4
91.2
4.56
4.51
1.41
2
PMDETA
4
93.5
4.67
4.65
1.37
3
HMTETA
4
75.0
3.75
3.80
1.26
4
Me6TREN
4
0
-
-
-
5
Me6TREN
22
0
-
-
-
154 Journal of Research Updates in Polymer Science, 2016, Vol. 5, No. 4 Chen et al.
catalyst were somewhat low for the ARGET ATRP of
MMA in this system.
3.7. Effect of Reaction Temperature on the ARGET
ATRP of MMA
Normally, increasing the temperature in an ATRP
system accelerates the polymerization process due to
the increase of both the radical propagation rate
constant and the atom transfer equilibrium constant.
Next, we investigated the effect of temperature on the
ARGET ATRP of MMA. We maintained the molar ratio
of [MMA]0/[EBrP]0/[CuCl2]0/[PMDETA]0/[glucose]0 at
500/1/0.1/1/1.5, and results are listed in Table 4.
As seen in Table 4, the polymerization rates were
very fast at 70 and 80 oC, and increased with
increasing reaction temperatures from 60 to 80 oC. As
further evidenced by the apparent rate constant (kapp),
the kapp values for polymerizations at 60 o
C, 70 oC and
80 o
C were 8.13×10-6, 2.35×10- 4 and 2.55×10-4 s
-1,
respectively. We calculated kapp by the slope of the
kinetic plot (Figure 3), Rp = －d[M]/dt = kp*[Pn]*[M] =
kp
app*[M]. Obviously, the polymerization temperature
favorably influenced the polymerization rate. As shown
in Figure 3, the first-order kinetic plots are linear for the
three reaction temperatures which imply a constant
number of active species throughout the
polymerizations. We note that the molecular weights
deviated significantly from the theoretical values, while
the Mw/Mn remained low at 60 o
C, which may have
contributed to the very low Cu (I) concentration and
thus the low initiation efficiency. Although the Mw/Mn
changed slightly with an increasing polymerization
temperature, the Mw/Mn still remained low (< 1.40).
Table 3: Effects of the Amount of Catalyst on ARGET ATRP of MMA
Entry
R
Cu (ppm)
Time (h)
Conv (%)
Mn,theo /×104
Mn,GPC /×104
Mw/Mn
1
500/1/0.1/1/1.5
200
4
97.0
4.85
4.87
1.27
2
500/1/0.05/1/1.5
100
4
93.5
4.68
4.35
1.41
3
500/1/0.025/1/1.5
50
4
92.9
4.65
5.55
1.45
4
500/1/0.01/1/1.5
20
4
91.8
4.59
5.59
1.45
R= n(MMA)/n(EBrP)/n(CuCl2)/n(PMDETA)/n(Glucose), T = 80 oC.
Figure 3: Kinetic plot for MMA polymerization at different temperatures.
Table 4: Effects of Temperature on ARGET ATRP of MMA
Entry
Temp (oC)
Time (h)
Cu (ppm)
Conv (%)
Mn,theo /×104
Mn,GPC /×104
Mw/Mn
kapp (s-1 )
1
80
1.5
200
65.1
3.26
3.52
1.23
2.55×10-4
2
70
1.5
200
44.2
2.21
3.19
1.37
2.35×10-4
3
60
1.5
200
-
-
-
-
-
4
60
4
200
-
-
-
-
-
5
60
24
200
51.3
2.57
4.04
1.28
8.13×10-6
Optimizing Activators Regenerated by Electron Transfer Journal of Research Updates in Polymer Science, 2 016, Vol. 5, No. 4 155
Figure 4: GPC traces of PMMA macroinitiator before and
after chain extension. Experimental condition for chain
extension: [MMA]0/[PMMA]0/[CuCl2]0/[PMDETA]0/[Glucose]0 =
500/0.01/0.1/1/1.5 (a), 500/0.005/0.1/1/1.5 (b), at 80 °C,
reaction time = 4 h.
3.8. Chain Extension of PMMA
To verify the living characteristics of the ARGET
ATRP of MMA, we performed further polymerization to
examine the chain extension reaction. We used the
obtained PMMA as a macroinitiator to carry out the
chain extension experiment. Figure 4 shows the GPC
curves of the macroinitiator and the chain-extended
PMMA. Obviously, the GPC curves indicate a shift from
a macroinitiator PMMA (Mn,GPC = 22 600, Mw/Mn =1.22)
to a chain-extended PMMA (Mn,GPC = 72 600, Mw/Mn =
1.36) (Figure 4a). The narrow molecular weight
distribution and the unimodal shape of the GPC trace
of the chain-extended polymer demonstrate the
success of the chain extension and the chain-end
functionality of the macroinitiator PMMA. Nevertheless,
termination occurs in all reversible-deactivation radical
polymerizations, and it is important to know how many
chains lost functionality and could not be further
extended. However, when using the chain-extended
PMMA (Figure 4a) as a macroinitiator to carry out the
chain extension reaction again, the molecular weight of
the PMMA no longer increased (as shown in Figure
4b). This suggests that when the molecular weight
reached to a certain point, the macromolecular chain is
so long that the chain-end functionality is decreased.
3.9. End-Group and Stereoregularity Analysis
We used 1H-NMR spectroscopy to characterize the
obtained PMMA via the ARGET ATRP of MMA with
bpy, HMTETA, and PMDETA as ligands. As shown in
Figure 5, the chemical shift at 7.27 ppm was attributed
to the solvent–deuterated chloroform, in which the peak
Figure 5: 1H-NMR spectra of PMMA obtained with different ligands (bpy, HMTETA and PMDETA).
156 Journal of Research Updates in Polymer Science, 2016, Vol. 5, No. 4 Chen et al.
h at 3.76 ppm corresponds to the methoxy group
adjacent to the bromine atom at the ω-end. This result
obviously deviates from the peak g at 3.62 ppm of the
methoxy groups in the PMMA backbone due to the
electron attraction function of the ω-Br atom. The
chemical shift at around 4.2 ppm was assigned to the
protons of the methylene of EBrP. This result is
consistent with previous literature.[34] The peaks at
0.80–1.30 ppm were assigned to the protons of the
methyl groups of -CH3, the peaks at 1.43 and 1.81 ppm
were attributed to the methylene group of -CH2-. The
areas of the three signals at 0.80–1.30 ppm of -CH3
represented the syndiotactic, atactic, and isotactic
PMMA, respectively, with increasing shift value. If the
peak areas were expressed as α, β, and γ, the ratio of
the isotactic configuration was γ / (α+β+γ). We
calculated the syndiotactic values for PMMA-bpy,
PMMA-HMTETA, and PMMA-PMDETA to be 62.1%,
61.3%, and 62.5%, respectively, which illustrate that
the stereoregularity of the polymer had given priority
over a syndiotactic architecture, and the effec t of ligand
types on the stereoregularity was very slight.
4. CONCLUSIONS
In this study, we successfully initiated copper (II)-
mediated ARGET ATRP of MMA by EBrP, and we
found EBrP to be an efficient initiator of the ARGET
ATRP of MMA. Our results show the monomer
conversion increase with increased of polymerization
temperature, and the amounts of reducing agent and
catalyst. Compared with EG, Sn(EH)2, and AsAc,
glucose proved to be the best reducing agent in this
system. And we found PMDETA to be a better ligand
than either HMTETA or bpy. We confirmed the “living”
characteristics of the polymerization by the resulting
first- order kinetics. The molecular weights increased
linearly with monomer conversion and were consistent
with the theoretical values. We further confirmed the
“living” feature by the chain extension of the obtained
PMMA macroinitiator and end-group analysis results.
Moreover, 1H-NMR analysis results indicate that the
stereoregularity of the polymer has given priority over a
syndiotactic architecture. The effect of ligand types on
the stereoregularity was very slight.
ACKNOWLEDGEMENTS
We gratefully acknowledge the financial supports
from the National Natural Science Foundation of China
(51263004), the Innovation Team of Guangxi
University’s Talent Highland, the Guangxi Funds for
Specially Appointed Experts, and the Key Laboratory of
New Processing Technology for Nonferrous Metal and
Materials, Ministry of Education.
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Received on 13-10-2016 Accepted on 15-12-2016 Published on 23-01-2017
DOI: http://dx.doi.org/10.6000/1929-5995.2016.05.04.3
