Electroactive methacrylate-based triblock copolymer elastomer for actuator application

Article abstract of DOI:10.1002/pola.26563

A series of ABA triblock copolymers of methyl methacrylate (MMA) and dodecyl methacrylate (DMA) [poly(MMA-b-DMA-b-MMA)] (PMDM) were synthesized by Ru-based sequential living radical polymerization. For this, DMA was first polymerized from a difunctional initiator, ethane-1,2-diyl bis(2-chloro-2- phenylacetate) with combination of RuCl₂(PPh₃)₃ catalyst and nBu₃N additive in toluene at 80 °C. As the conversion of DMA reached over about 90%, MMA was directly added into the reaction solution to give PMDM with controlled molecular weight (M _w/M_n ≤ 1.2). These triblock copolymers showed well-organized morphologies such as body centered cubic, hexagonal cylinder, and lamella structures both in bulk and in thin film by self-assembly phenomenon with different poly(methyl methacrylate) (PMMA) weight fractions. Obtained PMDMs with 20-40 wt % of the PMMA segments showed excellent electroactive actuation behaviors at relatively low voltages, which was much superior compared to conventional styrene-ethylene-butylene-styrene triblock copolymer systems due to its higher polarity derived from the methacrylate backbone and lower modulus. 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 A series of well-defined MMA-DMA-MMA triblock copolymers with different molecular weights and compositions were synthesized by in situ sequential block copolymerization of DMA followed by MMA from a difunctional initiator through Ru-based living radical polymerization. Obtained triblock copolymers showed periodically well-organized morphologies both in bulk and in film states, giving excellent actuation performances at relatively lower electric fields due to their polar methacrylate groups (k), lower modulus, and microstructures. Copyright

Full text of DOI:10.1002/pola.26563

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Electroactive Methacrylate-Based Triblock Copolymer Elastomer
for Actuator Application
Kie Yong Cho,1,2 Seung Sang Hwang,1,3 Ho Gyu Yoon,2 Kyung-Youl Baek1,3
1Center for Materials Architecturing, Korea Institute of Science and Technology, Seoul 136-791, Korea
2Department of Material Science, Korea University, Seoul 136-701, Korea
3Nanomaterials Science and Engineering, University of Science and Technology, Daejeon 305-333, Korea
Correspondence to: K.-Y. Baek (E-mail: mailto:baek@kist.re.kr)
Received 10 July 2012; accepted 15 December 2012; published online 19 February 2013
DOI: 10.1002/pola.26563
ABSTRACT: A series of ABA triblock copolymers of methyl
methacrylate (MMA) and dodecyl methacrylate (DMA) [poly
(MMA-b-DMA-b-MMA)] (PMDM) were synthesized by Ru-based
sequential living radical polymerization. For this, DMA was first
polymerized from a difunctional initiator, ethane-1,2-diyl bis
(2-chloro-2-phenylacetate) with combination of RuCl2(PPh3)3
catalyst and nBu3N additive in toluene at 80 ꢀC. As the conver-
sion of DMA reached over about 90%, MMA was directly added
into the reaction solution to give PMDM with controlled molec-
ular weight (Mw/Mn ꢁ 1.2). These triblock copolymers showed
well-organized morphologies such as body centered cubic,
hexagonal cylinder, and lamella structures both in bulk and in
thin film by self-assembly phenomenon with different poly(-
methyl methacrylate) (PMMA) weight fractions. Obtained
PMDMs with 20–40 wt % of the PMMA segments showed
excellent electroactive actuation behaviors at relatively low vol-
tages, which was much superior compared to conventional sty-
rene-ethylene-butylene-styrene triblock copolymer systems due
to its higher polarity derived from the methacrylate backbone
C
V
and lower modulus.
2013 Wiley Periodicals, Inc. J. Polym.
Sci., Part A: Polym. Chem. 2013, 51, 1924–1932
KEYWORDS: atom transfer radical polymerization; block copoly-
mers; elastomers; microstructure; stimuli-sensitive polymers
INTRODUCTION Electroactive polymers (EAPs) have gained
much attention as promising candidates for next generation
compact actuators, sensors, artificial muscles, and micro
robotics, owing to large electromechanical deformation, high
energy density, fast response time, and facile proccessabil-
ity.1–5 Among several EAP materials such as conductive,6 fer-
roelectric,7 and so forth, dielectric elastomers (DE) are espe-
cially interesting because of their large deformation with fast
recovery, making them suitable for artificial muscle
applications.8
dielectric constant and lower modulus for optimal actuation
performance.
However, these previous systems utilizing SEBS triblock
copolymers have had intrinsic limitations on high actuation
performance, because its non-polar hydrocarbon chain pos-
sesses a relatively low dielectric constant (k * 2) as well as
the use of oil additives for softness (elasticity) which may
flow out during operation. To overcome this, more polar and
elastomeric block copolymers such as acrylate or methacry-
late based block copolymers (k * 4) without any oil addi-
tives are considered as interesting alternative materials.10
Various kinds of well-defined acrylate or methacrylate based
di- and triblock copolymers with hard-soft-hard structure,
for example, triblock copolymers consisting of poly(methyl
methacrylate) (PMMA) as a hard block segment in conjunc-
tion with poly(n-butyl acrylate), poly(dodecyl methacrylate)
(PDMA), polyisobutylene, or polybutadiene as a soft block
segment, were already reported using living polymerization
techniques such as living anionic and radical polymeriza-
tions.11–14 However, their elastomeric properties were rela-
tively inferior compared to SEBS or styrene-isoprene-
styrene (SIS) block copolymers, which was probably due to
unclear long ranged ordered phase separations and weak
Actuation with DE materials have been so far carried out
with chemically crosslinked elastic rubbers such as acrylic
and silicon polymers, with a recent report of styrene-ethyl-
ene-butylene-styrene (SEBS) triblock copolymer with mineral
oil additives showing superior electromechanical perform-
ance at relatively low operating voltages.4,8 This electrome-
chanical performance was attributed to the self-assembled
morphology of the block copolymer, which allowed for
enhanced electrostatic Maxwell stress. Critical parameters of
thickness strain (Sz) of DE are dielectric constant (k) and
modulus (Y), described by the equation [Sz ¼ ke0(V/z)2/Y],
where e0 is permittivity at free space, V is applied voltage, z
is the thickness.9 Thus, DE materials generally require higher
C
V
2013 Wiley Periodicals, Inc.
1924
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1924–1932

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
physical crosslinked hard PMMA domains. Fortunately for
this actuation application, such large deformation was not
necessary (thickness strain < 71%),8 the strains from the ac-
rylate or methacrylate based triblock copolymer elastomers
might be enough to cover deformation ranges. Furthermore,
the actuation performance in this system would be enhanced
by increased polarity (k) originated from the acrylate or
methacrylate groups in comparison to the SEBS.
1H NMR analysis: d 4.28 ppm (m, 4H, CH2), 5.27 ppm (d, 2H,
CH), 7.33 ppm (m, 6H, Har), 7.43 ppm (m,4H, Har).
Polymerization PROCEDURE of MMA-DMA-MMA Triblock
Copolymer
The polymerizations were carried out by the syringe tech-
nique under argon using baked flasks with three-way stop-
cocks.
A
typical
procedure
with
DMA/EDBCPA/
RuCl2(PPh3)3/n-Bu3N/MMA follows: In a 100 mL round-bot-
tom flask was placed RuCl2(PPh3)3 (0.1 mmol, 95.9 mg), tol-
uene (10 mL), n-Bu3N (0.4 mmol, 1 mL, 400 mM in toluene),
DMA (20 mmol, 5.86 mL), and a solution of EDBCPA (0.1
mmol, 0.25 mL, 400 mM in toluene) was added sequentially
in this order at 25 ꢀC under argon. The reaction solution
In this study, a series of well-defined hard-soft-hard methyl
methacrylate (MMA)-dodecyl methacrylate (DMA)-MMA tri-
block copolymers (PMDMs) were synthesized by living radi-
cal polymerization, especially atom transfer radical polymer-
ization (ATRP) to examine their actuation property without
oil additive.15,16 Syntheses of these triblock copolymers by
ATRP have already been discussed using Cu-based catalytic
system.12 However, those by Ru-based system have yet to be
examined, especially by in situ direct addition of the second
monomer to the reaction solution of the precursor, which is
a more convenient method because of no cumbersome isola-
tion process of the precursor. Obtained PMDMs with differ-
ent molecular weights and compositions were characterized
their morphologies both in bulk and in thin film states.
Actuation performances with those PMDM were then carried
out at different electric fields and the relationship of the
actuation with their microstructure changes was examined.
ꢀ
was then placed in a oil bath set at 80 C. After the polymer-
ization reached ca. 90% conversion for 24 h, MMA (50
mmol, 5.35 mL) was rapidly added to the unquenched solu-
tion. The reaction terminated by cooling down to ꢃ78 ꢀC.
The conversions at predetermined times were determined by
integration ratio of 1H NMR spectra of the polymer and the
unreacted monomer, which was directly achieved from the
reaction solution. The quenched reddish solution was then
diluted with THF (10 mL) and then vigorously shaken with
neutralized aluminum oxide. After filtering aluminum oxide,
the solution was collected and solvents were removed by
reduced pressure. The concentrated solution was dropped
into methanol. Obtained white rubber-like solid was deca-
ꢀ
nted and then dried at 25 C for 48 h under vacuum.
EXPERIMENTAL
Bulk Sample Preparation for Small Angle X-Ray
Scattering
Materials
All chemicals were purchased from Aldrich and used without
purification process unless mentioned otherwise. Ethane-1,2-
diyl bis(2-chloro-2-phenylacetate (EDBCPA) was prepared by
a modified literature procedure (see below).17 MMA (Aldrich,
99%), tributylamine (n-Bu3N) (Aldrich, ꢂ98.5%) and toluene
(Aldrich, 99.8%) was purified by vacuum distillation with
calcium hydride before use. DMA (Aldrich, 96%) was puri-
fied by passing through an inhibitor remover column
(Aldrich, AL-154) without pressure.
A solution of the PMDM (10 wt % in THF) was filtered by
0.45 lm syringe filter and then poured onto a Teflon petrid-
ꢀ
ish, which was slowly dried in atmosphere at 25 C and fur-
ther dried in the vacuum oven at 25 ꢀC for overnight. After
separating PMDM from the petridish, PMDM casted film was
secured covering the pin-hole of the brass small angle X-ray
scattering (SAXS) holder and subsequently annealed at 170
ꢀC in the vacuum oven for 3 days. After the annealing pro-
ꢀ
cess, the samples were slowly cooled to 25 C.
Synthesis of Ethane-1,2-diyl bis(2-chloro-2-phenylacetate)
Difunctional Initiator
Thin Film Sample Preparation for Atomic Force
Microscope
In a 300 mL round-bottom flask filled with nitrogen, 2-
chloro-2-phenylacetyl chloride (7.5 g, 40 mmol) was added
dropwise to a solution of ethylene glycol (0.993 g, 16 mmol)
and anhydrous triethylamine (3.235 g, 32 mmol) in anhy-
drous THF (150 mL) at 0 ꢀC. ꢀThe solution was stirred at 0
ꢀC for 10 min and then at 25 C for an additional 10 h. The
solution was then evaporated to remove THF and methylene
chloride (200 mL) was added, and then poured into distilled
water (200 mL). The organic solution was then separated
and extracted with saturated sodium hydrogen carbonate
three times, followed by deionized water three times. The or-
ganic layer was then collected and dried over sodium sulfate
for overnight. After filtration and evaporation of the solution
under vacuum, a yellowish crude product was obtained,
which was further purified by chromatography on silica
using ethyl acetate and hexane (1:4) as eluent (3.1 g, yield:
44.4%).
Solutions of the PMDM (ꢄ2.5 wt % in toluene) were filtered
by 0.2-lm syringe filter and spin coated on 2 ꢅ 2 cm2 sili-
con wafer at 1500 rpm for 60 s. Silicon wafers were previ-
ously treated by piranha solution followed by rinsed using
IPA, acetone, and distilled water in order to make a hydro-
ꢀ
philic surface. Obtained thin film sample was dried at 25 C
overnight and annealed at 170 ꢀC in the vacuum oven for 3
days. After the annealing process, the samples were slowly
ꢀ
cooled to 25 C.
Actuation Sample Preparation
A solution of the PMDM (10 wt % in THF) was filtered by
0.45 lm syringe filter and then poured onto a teflon petrid-
ꢀ
ish, which was slowly dried in atmosphere at 25 C and fur-
ther dried in the vacuum oven at 25 ꢀC for overnight. After
separating the PMDM films from the petridish, the films
were pressed using 2 ꢅ 2 cm2 molder at 170 ꢀC. Obtained
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1924–1932
1925

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
PMDM sheets were further annealed at 170 ꢀC in vacuum
oven for 3 days, when conductive carbon grease was sten-
ciled on both sides of the sheet as a compliant electrode.
For this, ethane-1,2-diyl bis(2-chloro-2-phenylacetate)
(EDBCPA) (A) was first synthesized and used as a difunc-
tional alkyl halide initiator to polymerize with DMA (B),
which gave PDMA as the first block segment precursor.
Characterization
Figure 1 shows the number average molecular weight (Mn),
polydispersity (Mw/Mn), and size exclusion chromatography
scans (SEC, PMMA std.) of the obtained PDMA as the conver-
sion increased. The polymerization proceeded smoothly with
increase of the conversion to 90% (24 h) and the Mn corre-
sponded well with the theoretical value. The polydispersity
was relatively broad (PDI < 1.5) at early conversions (ꢄ50%)
but it became narrow on the end of the polymerization (PDI
¼ 1.26). As the conversion of DMA reached over 90%, MMA
as a second monomer was directly added to the reaction solu-
tion. Added MMA was then polymerized from both chloride
end groups of the PDMA chain to give hard-soft-hard MMA-
DMA-MMA triblock copolymer (PMDM) (C). The molecular
weight (Mn) of the PMDM linearly increased with increase of
the conversion to 80% (37 h). SEC curves of the PMDMs also
shifted to higher molecular weight fraction in comparison to
the PDMA precursor with narrow polydispersity (PDI ¼ 1.21)
(Fig. 2). These results indicated that the Ru catalyzed living
radical polymerization was particularly well suited for a one
pot system to synthesize well-defined PMDMs.
The number average molecular weight (Mn) and molecular
weight distributions (Mw/Mn) of the samples were measured
using a JASCO PU-2080 plus SEC system equipped with RI-
2031 and a UV-2075 (254-nm detection wavelength) using
THF as an eluent at 40 ꢀC with 1 mL/min of the flow rate.
The samples were separated through four columns: Shodex-
GPC KF-802, KF-803, KF-804, and KF-805. PMMAs were used
as calibration standards for SEC analysis. 1H NMR spectra
were taken in CDCl3 at 25 ꢀC on a 300 MHz Varian Unity
INOVA. Thermal gravimetric analysis (TGA) was performed
by TA instrument (TGA 2950) under nitrogen. Differential
scanning calorimeter (DSC) was performed by TA instrument
(TA Q20-142653) under nitrogen. Tapping mode atomic
force microscope (AFM) measurement was performed by
Multimode 8 with Nanoscope V controller (Veeco), which
equipped with a E-type vertical engage scanner at RT.
Synchrotron SAXS was performed at 4C1 SAXS beam line in
Pohang Light Source. All conditions for 4C1 beam line
followed literature procedure.18 Dynamic mechanical analysis
was performed by dynamic mechanical analyzer (DMA Q800,
TA instruments) under nitrogen. Tensile modulus was deter-
mined using a universal test machine (H5KT, Tinius Olsen)
with a cross header speed of 10 mm/min. Thickness strain
(Sz) for actuation test was measured by incident laser beam
which were exposed vertically to the sheet surface during a
voltage applied. The sheet was located between two lasers,
of which deviations generated by actuation were detected by
photo-responsive sensor. The measurement system consists
of a high voltage amplifier (Trek 10110B), a function genera-
tor (Agilent 33251A), a laser sensor set (Keyence LK-G80)
and a sample holder.19
Obtained PDMA precursor and PMDM were then analyzed by
1H NMR spectroscopy (Fig. 3). The PDMA precursor obtained
after 24 h (Mn ¼ 43,900; PDI ¼ 1.26) showed the character-
istic peaks originating from the ester dodecyl protons (e–f),
the a-methyl protons (b), and the methylene protons (a) of
the main backbone [Fig. 3(A)]. However, it was difficult to
figure out the peaks from the initiating moieties in the cen-
ter of the PDMA and the x-end moiety adjacent of the chlo-
rine atom, which was probably due to relatively high molec-
ular weight. The product obtained after the block
copolymerization of MMA from the PDMA precursor (Mn
¼
79,000; PDI ¼ 1.21) showed additional peaks from the ester
methyl protons (g), the a-methyl protons (b0), and the meth-
ylene protons (a0) of the PMMA [Fig. 3(B)], which indicated
that the PMDM was successfully synthesized as shown in
Scheme 1. Weight fraction of this block copolymer was
achieved by peak integration ratios of the ester methylene
(c) and methyl (g) of the PDMA and the PMMA block
RESULTS AND DISCUSSION
A series of ABA triblock copolymers of MMA and DMA were
synthesized by sequential living radical polymerization with
RuCl2(PPh3)3 catalyst and n-Bu3N additive in toluene at
17
ꢀ
80 C (Scheme 1).
SCHEME 1 Synthesis of MMA-DMA-MMA triblock copolymer by sequential block copolymerization of DMA and MMA from
difunctional initiator (EDBCPA) by Ru-catalyzed living radical polymerization.
1926
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1924–1932

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 1 Mn and MWD curves of PDMA precursors obtained from EDBCPA/ RuCl2(PPh3)3/n-Bu3N (10/10/40 mM) in toluene
at 80 ꢀC: [DMA]0 ¼ 2 M.
segments, respectively. Table 1 shows series of the PDMAs
and the PMDMs with different molecular weights (Mn) and
weight fractions (15–46 wt %). Run 1–5 and 6–11 were the
PMDMs from the PDMA precursors with lower molecular
weighs (Mn ¼ 43,900–53,500) and higher molecular weights
(Mn ¼ 70,300–74,600), respectively. The number averaged
molecular weights (Mn,NMR) of the PMDMs calculated from
1H NMR analyses were well corresponded with those
(Mn,SEC) from SEC analyses, especially for the lower molecu-
lar weight series (run 1–5), while the higher molecular
weight series (run 6–11) showed relatively higher Mn,NMR
than Mn,SEC, probably due to the significantly larger hydrody-
namic volume changes in comparison to the smaller molecu-
lar weight series. Thus, the forthcoming number averaged
molecular weight (Mn) for the PMDM was used as that based
calorimetry (DSC). Figure 4(A) shows the TGA curve of the
PMDM with 45 wt % of the PMMA (Mn ¼ 88,900, run 4) at
a heating rate of 10 ꢀC/min under nitrogen. Decomposition
ꢀ
started at 180 C and complete decomposition was observed
at 442 ꢀC. These decomposition behaviors were in good
agreement with those of the PDMA and PMMA homopoly-
mers. Figure 4(B), a-c shows the DSC curve of the PDMA (Mn
¼ 72,300), the PMMA (Mn ¼ 16,300), and the PMDM with
30 wt % of the PMMA (Mn ¼ 68,900, run 2). The tempera-
ꢀ
ture scan ranged from ꢃ80 to 170 C at a heating rate of 10
ꢀC/min under nitrogen. The glass transition temperatures
(Tg) of PDMA and PMMA were observed at ꢃ49 and 119.5
ꢀC, while those block segments of the PMDM appeared at
ꢃ51.3 and 98.7 ꢀC, respectively, where the Tg of the PMMA
block segment was a little lower than that from the PMMA
homopolymer, probably due to lower molecular weight of
the PMMA block segment (Mn ¼ 25,000/2) or contamination
of DMA in the PMMA block segment during the block copoly-
merization of MMA. From these thermal analyses results,
1
on H NMR analysis.
Thermal property of the PMDM was characterized by
thermogravimetric analysis (TGA) and differential scanning
FIGURE 2 Mn and MWD curves of MMA-DMA-MMA triblock copolymers obtained by in situ addition of MMA when DMA conver-
sion reached over 90%: [MMA]0 ¼ 5 M.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1924–1932
1927

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
which were more clearly observed in the higher molecular
weight series because segregation of block copolymer was
strongly affected by the parameter vN, where v is Flory–Hug-
gins interaction parameter and N is the degree of polymer-
ization of the copolymer (molecular weight).20,21 The domain
sizes of these triblock copolymers (d ¼ 2p/q*) enlarged as
the PMMA weight fractions increased, which ranged from 22
to 45 nm (Table 1). The PMDM with 15 wt % of the PMMA
weight fraction showed typical body centered cubic (BCC)
structured scattering patterns, 1q:H2q:H3q:H4q:H5q:H6q:
H7q [Fig. 5(B-a)], however that with 18 wt % showed
unclear periodic patterns [Fig. 5(A-a)], which was probably
the phase transition between sphere and cylinder structures.
The PMMA weight fractions ranged from 30 to 39 wt % also
showed long ranged ordered multiple patterns, 1q:H3q:H4q:
H7q:H9q:H13q, indicating the formation of hexagonal
packed cylinder structures (HEX) [Fig. 5(A,b-c, B, b-c)]. The
PMDM with over 40 wt % of the PMMA showed clear
lamella structures with typical ordering patterns of
1q:2q:3q:4q:5q [Fig. 5(A-d, B-d)].
FIGURE 3 1H NMR spectra of (A) PDMA precursor and (B) MMA-
DMA-MMA triblock copolymer at room temperature in CDCl3.
optimized annealing conditions were ascertained to achieve
ordered morphology of the PMDM.
Surface morphologies of the PMDMs were then characterized
by AFM (Fig. 6). Thin film samples were prepared by spin
coating process on silicon wafer followed by thermal anneal-
Morphology of the PMDM triblock copolymers were then
characterized both in bulk and in thin film states by SAXS
and AFM, respectively, because a well-defined morphology of
the triblock copolymer strongly affects actuation perform-
ance. Figure 5 shows the SAXS profiles of the PMDMs with
different molecular weights and weight fractions, where Fig-
ure 5(A) consisted of the lower molecular weight series (run
1–4) and Figure 5(B) consisted of the higher molecular
weight series (run 6–9) as shoꢀwn in Table 1. All samples
were thermally annealed at 170 C for 3 days under vacuum.
Both PMDM series showed long ranged ordered X-ray scat-
tering profiles regardless of the PMMA weight fractions,
ꢀ
ing at 170 C for 3 days under vacuum. The SAXS profile of
the PMDM with 18 wt % of the PMMA showed unclear peri-
odic scattering patterns [Fig. 5(A-a)], however its AFM image
showed clear embossed patterns on the film surface [Fig.
6(A)]. The cylinder structured PMDMs as shown in Figure 5
(30–39 wt % of the PMMA) showed laterally laid domains of
the PMMA on the silicon wafer, of which domain size
increased as the molecular weight increased (Fig. 6, B and C
for the lower molecular weight series and E–G for the higher
molecular weight series).22 In addition, the shapes of the lat-
eral cylinder domains with the higher PMMA weight
TABLE 1 Various PDMA Precursors and MMA-DMA-MMA Triblock Copolymers with Different Molecular Weights and Weight
Fractions
PDMA Precursor
Mn,SEC Mw/Mn
MMA-DMA-MMA Triblock Copolymer (PMDM)
Run
Mn,SEC
MW/MN
Mn,NMR
PMMA (wt %)
Microstructure
d (nm)
1a
2a
3a
4a
5b
6b
7c
8c
9c
10b
11a
a
43,900
43,900
43,900
43,900
54,500
71,700
73,500
73,500
73,500
70,300
74,600
1.26
1.26
1.26
1.26
1.23
1.22
1.36
1.36
1.36
1.21
1.26
52,800
67,600
79,000
85,000
75,800
88,700
93,400
114,000
140,000
86,000
109,000
1.26
1.24
1.21
1.20
1.20
1.21
1.35
1.30
1.29
1.19
1.27
54,000
68,900
81,400
88,900
82,500
91,700
112,500
146,600
163,600
101,300
109,500
c
18
30
39
45
17
15
30
38
46
26
29
BCC/HEX
HEX
21.6
24.5
28.0
28.7
22.2
27.8
34.9
38.5
45.2
25.8
30.5
HEX
LAM
BCC
BCC
HEX
HEX
LAM
HEX
HEX
[DMA]/[MMA]/[RuCl2(PPh3)3]/[Bu3N]/[EDBCPA]
¼
2
M/5 M/10 mM/40
[DMA]/[MMA]/[RuCl2(PPh3)3]/[Bu3N]/[EDBCPA] ¼ 1.75 M/5 M/5 mM/20
mM/10 mM in toluene at 80 ꢀC.
mM/5 mM in toluene at 80 ꢀC.
b
[DMA]/[MMA]/[RuCl2(PPh3)3]/[Bu3N]/[EDBCPA] ¼ 1.5 M/2.5 M/5 mM/20
mM/5 mM in toluene at 80 ꢀC.
1928
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1924–1932

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 4 Thermal properties of MMA-DMA-MMA triblock copolymers: (A) TGA curves of PMDM (Mn ¼ 85,000, PMMA ¼ 45 wt %)
and (B) DSC curves of (a) PDMA (Mn ¼ 72,300), (b) PMMA (Mn ¼ 16,000), (c) PMDM (Mn ¼ 67,600, PMMA ¼ 30 wt %). Heating
and/or cooling rate ¼ 10 ꢀC/min under nitrogen.
fractions [Fig. 6(C, F–G) ]were less extended than those with
the lower PMMA weight fraction series [Fig. 6(B,E)]. The sur-
face morphology of the low molecular weight PMDM with 45
wt % of the PMMA fraction was similar to those with the
cylinder structured series in spite of the lamella structure as
shown in Figure 5(A-d), which indicated that the lamella
domains stood vertically to the surface [Fig. 6(D)]. However,
the high molecular weight PMDM with similar weight frac-
tion (46%) laid horizontally on the surface [Fig. 6(H)], which
was probably due to the susceptibility of the smaller poly-
mer chains to the surface between the silicon wafer and air
in the lamella structures. From these results, we found that
the PMMA and the PDMA of the triblock copolymers were
not miscible to show efficient phase separations both in bulk
and in film states, especially more periodic ordering micro-
structures in bulk states, which was important to show bet-
ter actuation performance.
The elastomeric properties of these well-defined triblock
copolymers were then characterized using dynamic mechani-
cal analyzer (DMA), especially with 26 wt % (run 10) and
45 wt % (run 4) of the PMMA. The scanning range of tem-
perature was from ꢃ80 to 140 ꢀC with a heating rate of 4
ꢀC/min. Figure 7(A) shows the temperature dependence of
storage modulus (G0) and tan d. Both samples showed two
characteristic G0 losses at the points close to the glass transi-
tion temperatures of the PDMA and the PMMA as well as
FIGURE 5 SAXS profiles of MMA-DMA-MMA triblock copolymers in bulk states: (A) low molecular weight series with (a) 18%, (b)
30%, (c) 39%, and (d) 45% of PMMA weight fractions (run 1–4); (B) high molecular weight series with (e) 15%, (f) 30%, (g) 38%,
and (h) 46% of PMMA weight fractions (run 6–9). See Table 1.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1924–1932
1929

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 6 Tapping mode AFM images of MMA-DMA-MMA triblock copolymers in thin film states: (A-D) low molecular weight se-
ries with (A) 18%, (B) 30%, (C) 39%, and (D) 45% of PMMA weight fractions (run 1–4); (E–H) high molecular weight series with (E)
26%, (F) 30%, (G) 38%, and (H) 46% of PMMA weight fractions (run 7–10). See Table 1.
rubbery G0 plateaus between them, indicating microphase
separation of the soft PDMA and the hard PMMA domains,
which is generally observed from conventional block copoly-
mer elastomers.23 The PMDM with the lower PMMA weight
fraction (26%) showed more sharp losses of G0 than that
with the higher PMMA weight fraction (45%), which indi-
cated that softer PMDM showed more elastomeric behavior.
The glass transition temperatures obtained from tan d were
a little underestimated in comparison to those from DSC,
especially the PMDM with the lower PMMA weight fraction,
probably due to low frequency set in DMA measurement, of
which phenomenon was also observed in the previous stud-
ies.12 Tensile properties of the PMDMs with various PMMA
weight fractions were examined by universal testing machine
(UTM). The samples were prepared by hot press molding
method at 170 ꢀC for 10 min and expended with 10 mm/
min with preload 1 g. Figure 7(B, a-c) shows tensile stress–
strain curves of the PMDMs with 17 wt % (run 5), 29 wt %
(run 10), and 45 wt % (run 4) of the PMMAs, respectively.
Although the entire tensile properties of the PMDMs were in-
ferior to conventional SEBS or SIS block copolymer elasto-
mers, the relatively softer PMDMs with 17 and 29 wt % of
the PMMAs, had modulus values of 0.14 and 0.53 MPa,
respectively, showed classical elastic behaviors within 50%
FIGURE 7 Elastic and tensile properties of MMA-DMA-MMA triblock copolymers: (A) DMA analyses for temperature dependence
storage modulus (G0) and tan d with (a) 26% and (b) 45% of PMMA weight fractions (run 10 and 4) and (B) UTM analyses for
stress–strain curves with (a) 17%, (b) 29%, and 45% of PMMA weight fractions (run 4–5 and run 11). See Table 1.
1930
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1924–1932

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 8 Actuation performances of MMA-DMA-MMA triblock copolymers: (A) illustration of actuation operation at voltage on/
off and (B) thickness strain changes (Sz, %) with increasing electric field (V/lm). Open symbols for low molecular weights: (a) 30
wt %, (b) 39 wt %, and (c) 45% of PMMA weight factions (run 2–4) and closed symbols for high molecular weights: (a) 30%, (b)
38%, (c) 46% of PMMA weight factions (run 6–8). (d) Conventional SEBS system (Mn ¼ 100,000, 30 wt % of the polystyrene) for
comparison. See Table 1.
of the strain ranges [Fig. 7(B, inset)],14 which were elongated
to 98 and 200%, respectively. This strain range was suffi-
ciently enough to perform for the actuation applications.
However, the PMDM with the high PMMA weight fraction
(45%) showed high modulus (87.9 MPa) and poor elonga-
tion at break point (40%). From these results, more soft and
elastic PMDMs with the lower weight fractions of PMMAs
were employed for forthcoming actuation tests.
a conductive carbon grease compliant on both sides as an
electrode [Fig. 8(A)]. Figure 8(B) showed thickness strain
changes of the PMDMs with different weight fractions and
molecular weights with increase in electric fields (operating
voltage). As the PMMA weight fractions decreased, the soft-
ness of the PMDM increased, and the thickness strain
changed to a larger degree. For example, the PMDMs with
ca.45 wt % of the PMMA fractions showed merely ꢄ2% of
the strain change at relatively high electric fields (30–35 V/
lm) [Fig. 8(B-c)], while those with 30 wt % of the PMMA
fractions were largely strained (ꢄ16%) at much lower elec-
tric fields (20–25 V/lm) [Fig. 8(B-a)]. Surprisingly, these
strain changes were almost two times larger than conven-
tional SEBS system (SEBS/oil ¼ 40/60 wt %) even at almost
half of the corresponding electric field [Fig. 8(B-d)]. These
Actuation tests with these triblock copolymers were con-
ducted by measuring the change of the thickness strain by
2-laser system with external electric field source.24 For this,
thin sheet samples were prepared by hot press molding
ꢀ
method at 170 C, which were further thermally annealed at
ꢀ
170 C for 3 days under vacuum, followed by stenciling with
FIGURE 9 Microstructure changes of MMA-DMA-MMA triblock copolymers of 29% of PMMA weight fraction (run 11) by applied
voltages. (A) SAXS profiles changes and (B) relative domain size changes.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1924–1932
1931

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
results showed that softness (Y) and high dielectric constant
(k) in DE materials were important factors to increase actua-
tion performance at lower operating voltage because the
thickness strain (Sz) changes by maxwell stress were
strongly dependent on those two factors. However, the
PMDMs with the lower molecular weights [open symbols in
Fig. 8(B)] were more easily shorted out in comparison to
corresponding higher molecular weight PMDMs [closed sym-
bols in Fig. 8(B)] at relatively lower electric field because of
durability problems with smaller molecules.
(10035373). Synchrotron SAXS measurements were per-
formed at the Pohang Light Source (PLS).
REFERENCES AND NOTES
1 P. Brochu, Q. Pei, Macromol. Rapid. Commun. 2010, 31,
10–36.
2 R. Shankar, T. K. Ghosh, R. J. Spontak, Soft Matter 2007, 3,
1116–1129.
3 R. Pelrine, R. Kornbluh, Q. Pei, J. Joseph, Science 2000, 287,
836–839.
These strain changes on the actuation performance were fur-
ther characterized by in situ SAXS under electric field to
examine their microscopic structure changes, discussed in
Figure 5.19 Figure 9(A) shows SAXS profiles of the PMDM
with 29 wt % of the PMMA (run 11) at different applied vol-
tages. Obtained morphology showed well organized hexago-
nal cylinder structure with 29.7 nm of the domain size (d ¼
2p/q*) with voltage off. This ordered SAXS patterns were
gradually shifted to lower scattering vector (q) with increas-
ing the voltage to 7 kV, which indicated that the domain
sizes increased by the applied voltages. For example, the do-
main size was 30.2 nm at 7 kV, which was 0.5 nm larger
than that at 0 kV. The relative domain spacing (d/d0) of the
PMDM proportionally increased as the electric field
increased [Fig. 9(B)], indicating that the microstructure
domains of the PMDM were strongly affected under the
applied electric field. From these results, the actuation
performances with the PMDMs were strongly dependent on
their microstructure as well as polarity (k) and the elasticity
(Y), which indicated that the PMDM was one of the best
candidates as an electroactive material.
4 R. Pelrine, R. Kornbluh, J. Joseph, R. Heydt, Q. Pei, S. Chiba,
Mater. Sci. Eng. C 2000, 11, 89–100.
5 Y. Bar-Cohen, Electroactive Polymer (EAP) Actuators as Arifi-
cial Muscles: Reality, Potential, and Challenges, 2nd ed.; SPIE
Press, 2004.
6 L. Bay, K. West, Sommer-P. Larsen, S. Skaarup, M. Bensli-
mane, Adv. Mater. 2003, 15, 310–313.
7 C. Huang, R. Klein, F. Xia, H. Li, Q. M. Zhang, Ieee T. Dielect.
El. In. 2004, 11, 299–311.
8 R. Shankar, T. K. Ghosh, R. J. Spontak, Adv. Mater. 2007, 19,
2218–2223.
9 R. E. Pelrine, R. D. Kornbluh, J. P. Joseph, Sens. Actuators A
1998, 64, 77–85.
10 E. A. Stefanescu, X. Tan, Z. Lin, N. Bowler, M. R. Kessler,
Polymer 2010, 51, 5823–5832.
11 Y. J. Jang, T. Kato, T. Ueki, T. Hirai, Sens. Actuators A 2011,
168, 300–306.
12 D. P. Chatterjee, B. M. Mandal, Macromolecules 2006, 39,
9192–9200.
13 S. Coca, K. Matyjaszewski, J. Polym. Sci. Part A: Polym.
Chem. 1997, 35, 3595–3601.
14 J. M. Yu, P. Dubois, R. Jerome, Macromolecules 1996, 29,
8362–8370.
CONCLUSION
15 M. Ouchi, T. Terashima, M. Sawamoto, Chem. Rev. 2009,
109, 4963–5050.
Ru-based ATRP system successfully gave well-defined MMA-
DMA-MMA triblock copolymers with controlled molecular
weights and narrow polydispersities by in situ sequential
block copolymerization of DMA followed by MMA from a
difunctional initiator. Obtained triblock copolymers showed
periodically well-organized self-assembled morphologies
from BCC to LAM structures both in bulk and in film states
depending on the PMMA weight factions. Actuation perform-
ance with these triblock copolymers showed relatively large
deformations with relatively lower electric fields, especially
those with lower PMMA weight fractions, which were
strongly relative to their high dielectric constant (k) from
the methacrylate groups, elastomeric properties with lower
modulus, and well-defined microstructures.
16 W. A. Braunecker, K. Matyjaszewski, Prog. Polym. Sci. 2007,
32, 93–146.
17 K. Y. Baek, M. Kamigaito, M. Sawamoto, J. Polym. Sci. Part
A: Polym. Chem. 2002, 40, 1937–1944.
18 J. Bolze, J. Kim, J. Huang, S. Rah, H. Youn, Macromol. Res.
2002, 10, 2–12.
19 B. Kim, Y. D. Park, K. Min, J. H. Lee, S. S. Hwang, S. M.
Hong, B. H. Kim, S. O. Kim, C. M. Koo, Adv. Funct. Mater.
2011, 21, 3242–3249.
20 L. Leibler, Macromolecules 1980, 13, 1602–1617.
21 I. W. Hamley, The Physics of Block Copolymers, 1st ed.;
Oxford Science Publications, 1999.
22 X. Zhang, B. C. Berry, K. G. Yager, S. Kim, R. L. Jones, S.
Satija, D. L. Pickel, J. F. Douglas, A. Karim, ACS Nano 2008, 2,
2331–2341.
ACKNOWLEDGMENTS
23 S. M. Lai, C. M. Chen, Eur. Polym. J 2007, 43, 2254–2264.
This research was supported by a grant from Korea Institute of
Science and Technology (KIST) and partially supported by the
industrial strategic technology development program funded
by the Ministry of Knowledge Economy, Republic of Korea
24 H. L. Kwak, K. Y. Cho, S. G. Yu, K. Y. Baek, J. C. Lee, S. M.
Hong, C. M. Koo. Sens. Actuators A 2012, 174, 547–554.
25 B. Kim, Y. Park, J. Kim, S. M. Hong, C. M. Koo, J. Polym.
Sci. Part A: Polym. Phys. 2010, 48, 2392–2398.
1932
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1924–1932