Synthesis and thermal, optical, and mechanical properties of sequence-controlled poly(1-adamantyl acrylate)-block-poly(n-butyl acrylate) containing polar side group

Article abstract of DOI:10.1002/pola.27322

We prepared the sequence-controlled block copolymers including poly(1-adamantyl acrylate) (PAdA) and poly(n-butyl acrylate) sequences as the hard and soft segments, respectively, by the organotellurium-mediated living radical polymerization. The thermal,

Full text of DOI:10.1002/pola.27322

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Synthesis and Thermal, Optical, and Mechanical Properties of
Sequence-Controlled Poly(1-adamantyl acrylate)-block-
Poly(n-butyl acrylate) Containing Polar Side Group
Yoshinori Nakano,1 Eriko Sato,1 Akikazu Matsumoto2
1Department of Applied Chemistry and Bioengineering, Graduate School of Engineering, Osaka City University, 3-3-138 Sugi-
moto, Sumiyoshi-ku, Osaka 558-8585, Japan
2Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku,
Sakai, Osaka 599-8531, Japan
Correspondence to: A. Matsumoto (E-mail: matsumoto@chem.osakafu-u.ac.jp)
Received 25 April 2014; accepted 4 July 2014; published online 31 July 2014
DOI: 10.1002/pola.27322
ABSTRACT: We prepared the sequence-controlled block copoly-
mers including poly(1-adamantyl acrylate) (PAdA) and poly(n-
butyl acrylate) sequences as the hard and soft segments,
respectively, by the organotellurium-mediated living radical
polymerization. The thermal, optical, and mechanical proper-
ties of the adamantane-containing block copolymers with
polar 2-hydroxyethyl acrylate (HEA) and acrylic acid (AA)
repeating units were investigated. The microphase-separated
structures of the block copolymers were confirmed by the dif-
ferential scanning calorimetry and atomic force microscopy
observations as well as dynamic mechanical measurements.
The a- and b-dispersions due to the main-chain and side group
molecular motions, respectively, of the hard and soft seg-
ments were observed. Their transition temperatures and acti-
vation energies increased due to the formation of
intermolecular hydrogen bonding by the introduction of the
HEA and AA repeating units. The effects of the hydrogen
bonding on their tensile elasticity, strength, and strain were
C
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also evaluated.
2014 Wiley Periodicals, Inc. J. Polym. Sci.,
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KEYWORDS: block copolymers; controlled polymerization; glass
transition; living polymerization; phase separation; optics; radi-
cal polymerization; thermal properties; transparent polymer
lates have been used as adhesives, paints, sealants, rubbers,
and UV-curable resins, poly(1-adamantyl acrylate) (PAdA)
exhibits a Tg value of 150 ꢀC,3(a),3(b),14 which is high
enough to be used as a thermoplastic material with an
excellent thermal stability. High-temperature and transpar-
ent polymers have become more important for recent infor-
mation and electronic technologies for optical disk, fiber,
lens, display, digital signage, and lighting.15 In this study,
we prepared the sequence-controlled block copolymers con-
sisting of PAdA and poly(n-butyl acrylate) block sequences
as the hard and soft segments, respectively, including polar
repeating units by the organotellurium-mediated living radi-
cal polymerization16–19 (TERP). The TERP technique is one
of the most powerful method for the controlled radical
polymerization syntheses of high-molecular-weight polyacry-
lates containing a polar and functional side group.16,19 We
investigated the thermal, optical, and mechanical properties
of the acrylate block copolymers containing a bulky and
hydrophobic adamantly moiety as well as a polar and func-
tional moiety as new transparent acrylic polymers with a
high Tg.
INTRODUCTION Adamantane (tricyclo[3.3.1.13,7]decane) is a
unique compound that consists of fused cyclohexane rings
with a fixed, highly symmetric, and thermodynamically stable
structure the same as the diamond lattice, leading to charac-
teristics such as a high melting point, reduced intermolecular
interaction, a low friction coefficient, and high hydrophobic-
ity.1 A large variety of adamantane-containing polymers has
been synthesized for use as thermoresistant polymers,2–5
rigid-chain polymers,6 high-performance membranes,7 den-
dritic polymers,8 photoresists,9 photoswitchable supramolec-
ular hydrogels,10 unimolecular polymer micelles,11 and host–
guest materials.12 Poly(methyl methacrylate) (PMMA) is one
of the polymers with an excellent transparency and weather
resistance, but its thermal stability is insufficient for use
which requires a high-temperature resistance. Polymethacry-
lates including PMMA have a relatively rigid main chain and
a low decomposition temperature as the intrinsic features of
the poly(1,1-disubstituted ethylene)s, being in contrast to
flexible polyacrylates as the typical soft materials with a low
glass transition temperature (Tg) and a high decomposition
temperature over 300 ꢀC.13 Although conventional polyacry-
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EXPERIMENTAL
pheric conditions and temperature control. The measure-
ments were performed using the flexural mode at
General Procedures
ꢀ
frequencies of 0.5–10 Hz and the heating rate of 2 C/min in
The NMR spectra were recorded using Bruker AV300N and
JEOL JNM-A400 spectrometers in CDCl3. The number-average
molecular weight (Mn), weight-average molecular weight (Mw),
and polydispersity (Mw/Mn) were determined by size exclusion
chromatography (SEC) in tetrahydrofuran (THF) as the eluent
using a Tosoh CCPD RE-8020 system and calibration with
standard polystyrenes. The atomic force microscopy (AFM)
images were taken using a NanoScope IIIa system (Digital
Instruments/Veeco) and an MMAFM-type Multimode SPM unit
with a cantilever (OMCLAC240TS-C2, Olympus, spring constant
2.1–2.5 N/m, resonant frequency 73.4–77.6 kHz) at the scan
rate of 0.5 Hz in the tapping mode for an area of 5 3 5 lm2.
The 2 wt % chloroform solutions of the polymers (ca. 1 lL)
were spin coated (250 rpm for 10 s and subsequent 2500 rpm
for 40 s) on a glass plate (1.2 3 1.2 cm2), which were cleansed
using acetone, 2-propanol under supersonic irradiation, then
dried using an air duster. The film thickness was determined
by scratching the films and measuring the step height between
the glass and the film surface in the height mode. The watꢀer
absorption property of the polymers was carried out at 23 C
using a test piece (10 3 10 3 1 mm3), according JIS K7209.
The amount of absorbed water was calculated based on a
change in the polymer weight after immersion. The weight loss
of the samples during immersion in water for a long time was
corrected based on the weight of the dried samples.
ꢀ
the temperature range of 2150 to 230 C. The strain ampli-
tude was 10 lm. The apparent activation energy was eval-
uated for the relaxations using the peak tan d temperatures
and the applied frequency. The sample for the measurements
was prepared using a dumbbell-type metal mold, AH-K1 (30
mm sample length, 5 mm width, 1.5 mm thickness for the
narrow part), by compression of the polymer powders at the
applied pressure of 10 MPa in vacuo at a temperature over
each Tg for 2–3 h using an As-One AH2003 press machine.
The tensile mechanical test was performed according to the
standard test method using a universal testing machine, LSC-
1/30 (JT Tone, Tokyo) with a 1 kN (at maximum) load cell
ꢀ
at the rate of 1 mm/min at 20 C. The tensile elasticity value
was determined based on the initial slope of the curves in
the stress–strain relationship (0.05–0.25% strain). The aver-
age value of the measurements for three samples was typi-
cally recorded except for the single datasets of some
measurements. For preparing the cross-linked polymer sam-
ple for the dynamic mechanical measurements, the solution
of tolylene diisocyanate (TDI, 0.169 mg, isocyanate content
0.137 mmol) and 3.5 g of PAdA43.7-b-P(AdA2.6/nBA47.3
/
HEA6.4) (hydroxy content 1.37 mmol) in 3 mL of toluene
was cast on a Teflon plate and dried under atmospheric con-
ditions to obtain polymer films containing TDI. The cut films
were put in a dumbbell-type metal mold, and compressed
ꢀ
under a load of 15 MPa at room temperature, then at 100 C
Thermal Properties
The thermogravimetric and differential thermal analyses (TG/
DTA) were performed using a Seiko TG/DTA 6200 in a nitro-
gen stream (200 mL/min) at the heating rate of 10 C/min in
the temperature range of 30–500 C. The onset temperature
for 1 h. For the preparation of the thermally cross-linked
ꢀ
test plates, the polymer powders were compressed at 200 C
ꢀ
under a load of 10 MPa in a metal mold, then at 240 C for
ꢀ
2 h. The gel fraction was 79%.
ꢀ
of decomposition was evaluated as the 5% weight-loss tem-
perature (Td5) in the TG analysis. The maximum temperature
of decomposition (Tmax) was determined using the derivatives
of the TG curves. Differential scanning calorimetry (DSC) was
performed in a nitrogen stream (50 mL/min) using a Seiko
DSC-6200 at the heating rate of 10 ꢀC/min in the temperature
range of 2100 to 200 ꢀC to determine the Tg values.
Materials
Methyl acrylate (MA), n-butyl acrylate (nBA), tert-butyl acry-
late (tBA), and 2-hydroxyethyl acrylate (HEA) were pur-
chased from Tokyo Chemical Industry, Tokyo or Wako Pure
Chemicals, Osaka, and distilled before use. 2,20-Azobis(isobu-
tyronitrile) (AIBN) and 2,20-azobis(4-methoxy-2,4-dimethyl-
valeronitrile) (AMVN) were purchased from Wako Pure
Chemicals, and recrystallized from methanol. All the solvents
were used after distillation. Acryloyl chloride (Wako Pure
Chemicals), 1-adamantanol (Sigma–Aldrich), triethylamine
(TEA, Wako Pure Chemicals), benzenethiol (PhSH, Tokyo
Chemical Industry, Tokyo), p-toluenesulfonic acid monohy-
drate (TsOH, 99.0%, Wako Pure Chemical Industries, Osaka),
tolylene 2,4-diisocyanate (TDI, Tokyo Chemical Industry),
and poly(methyl methacrylate) (PMMA, Mn 5 6.33 3 104,
Mw/Mn 5 1.84, Wako Pure Chemical Industries, Osaka) were
used as received. Ethyl 2-(n-butyltellanyl)-2-methylpropio-
nate (BTEE, Otsuka Chemical, Tokushima, Japan) was used
as received without further purification.
Optical Properties
The UV–vis spectra were recorded using a JASCO V-550 spec-
trophotometer. The polymer films were prepared by casting
of a 5 wt % chloroform solution and drying at 20 ꢀC over-
night. The refractive indices (nF, nD, and nC) were measured
at the wavelengths of 486, 589, and 656 nm, respectively,20
using an Abbe-type refractometer (Atago DR-M2, aqueous
zinc dichloride saturated solution, halogen lamp). The aver-
age value of five measurements was typically recorded. The
Abbe number (mD) was calculated as follows.
ðnD21Þ
mD5
:
(1)
ðnF2nCÞ
Synthesis of AdA
Mechanical Properties
The dynamic mechanical properties were determined using a
Seiko DMS-6100 dynamic mechanical analyzer under atmos-
AdA was synthesized from acryloyl chloride and 1-
adamantanol. To the solution of 1-adamantanol (25 g, 164
mmol) and triethylamine (20 g, 198 mmol) in
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SCHEME 1 Synthesis of block copolymers I with or without the HEA repeating unit [PAdA-b-P(AdA-co-nBA) and PAdA-b-P(AdA-
co-nBA-co-HEA)] by TERP.
dichloromethane (400 mL), acryꢀloyl chloride (24.7 g, 248
mmol) was dropwise added at 0 C in an argon atmosphere.
After the mixture was stirred at room temperature over-
night, the resulting triethylamine hydrochloride as the pre-
cipitated salt was filtered out and the dichloromethane
solution was washed with a saturated sodium bicarbonate,
water, and a saturated saline solution, then dried over
sodium sulfate. The dichloromethane was evaporated under
reduced pressure, and the products were purified by silica
gel chromatography using n-hexane and ethyl acetate (9:1
volume ratio). The isolated AdA was distilled under reduced
pressure (115 ꢀC/0.4 MPa) in the presence of catechol as
the polymerization inhibitor, followed by passing through an
alumina short column to completely remove the catechol.
without isolating the produced block copolymers for the
transformation of the polymer chain-end structure to the sta-
ble CAH one, then the final conversion was determined by
1H NMR spectroscopy. The molar ratio of [AMVN]/[BTEE]/
[PhSH]/[AIBN] was always fixed at 0.2/1.0/1.5/0.2 in this
study. The deactivated block copolymers were finally isolated
in a large amount of methanol as the precipitant, then dried
in vacuo. The block copolymers were characterized by 1H
NMR spectroscopy, SEC, and DSC measurements. For the syn-
thesis of the block copolymers containing an acrylic acid
repeating unit, the copolymerization was similarly performed
using tBA instead HEA, then the tBA repeating unit included
in the resulting block copolymers was hydrolyzed. To a 200-
mL flask, AdA-b-P(nBA/tBA) (4.2 g, tBA content 4.8–12.7
mol %) and TsOH (104 mg, 5.4 3 1024 mol) in 100 mL of
toluene were added, then refluxed for 5 h. The solution was
poured into a large amount of methanol to precipitate the
block copolymer. The copolymer was separated by filtration,
then dried under reduced pressure overnight. After the rep-
recipitation, the quantitative transformation was confirmed
AdA
ꢀ
Yield 50%; colorless crystals. M.p. 40.1 C.
1H NMR (CDCl3, 300 MHz) d 6.17 (dd, J 5 1.6 and 17.3 Hz,
1H), 5.91 (dd, J 5 10.3 and 17.3 Hz, 1H), 5.61 (dd, J 5 1.6
and 10.3 Hz, 1H), 2.15 (br, 9H), 1.67 (br, 6H).
1
by H NMR spectroscopy and TG/DTA analyses.
Polymerization
RESULTS AND DISCUSSION
To a 15-mL glass tube, AMVN (0.72–1.49 mg) and a mono-
mer (0.50–4.30 g) in 0.50–4.30 g of anisole were added and
the solution was stirred with bubbling argon at 0 ꢀC for 30
min, followed by the addition of BTEE (2.65–5.00 lL) using
a syringe. The polymerization was performed at 50 ꢀC for 2
h. The conversion, Mn, and Mw/Mn values of the produced
polymer were determined based on the NMR and SEC analy-
ses of an aliquot. The block copolymerization was further
performed at 50 ꢀC for 2 h by the addition of the second
monomer (1.00–3.39 g). After the block copolymerization,
PhSH (0.33–3.70 lL) and AIBN (0.38–0.79 mg) in 2.0–3.0 g
of anisole were further added and heated at 80 ꢀC for 5 h
Synthesis of Block Copolymers
The block copolymers consisting of various PAdA and PnBA
sequence structures were synthesized by the TERP method.
After the first-step polymerization of AdA at 89–94% conver-
sion, the block copolymerization of nBA or a nBA/HEA mix-
ture was performed without isolating the precursor polymer
(Scheme 1). Similarly, the AdA polymerization was performed
in the presence or absence of HEA after the preparation of
the precursor PnBA (Scheme 2). The results of the homo, ran-
dom, and block polymerizations in the absence of a polar
comonomer are summarized in Table 1. The results for the
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SCHEME 2 Synthesis of block copolymers II with or without the HEA repeating unit [PnBA-b-P(nBA-co-AdA) and PnBA-b-P(nBA-
co-AdA-co-HEA)] by TERP.
preparation of the block copolymers containing polar HEA
repeating units in either the hard or soft block segment are
shown in Table 2. The produced block copolymers included a
small amount of the AdA and nBA repeating units (0.4–3.6
mol %) in the second PnBA and PAdA sequences for the
series of the block copolymers I-x and II-x, respectively. The
letter x indicates the molar fraction of the AdA repeating units
in the copolymers. In Table 2, the letters x and y indicate the
molar fractions of the AdA and HEA repeating units, respec-
tively, for I-xHy and II-xHy. Similarly, the letter y indicates the
molar fractions of the tBA and AA repeating units for I-xTBy
and I-xAy, respectively. The alkyltellanyl group on the polymer
chain end was converted to the stable CAH bond by the chain
transfer reaction with benzene thiol (PhSH) at 80 C for 5 h
in the presence of AIBN before isolating the resulting poly-
mers by a precipitation method.
ꢀ
The structure of the produced block copolymers was charac-
terized by 1H NMR spectroscopy and SEC measurements.
The SEC peaks of the precursor PAdA and PnBA shifted to
the higher molecular weight region while maintaining their
narrow molecular weight distributions during the block
TABLE 1 Characterization of the Polymers without Polar Repeating Units Synthesized by TERP Method
Conversionb
(%)
Polymer
Sequence Structurea
AdA
nBA
Mwb/105
Mw/Mn
Td5 (ꢀC)
%Td
b
c
Tg (ꢀC)
PAdA
PnBA
P(AdA/nBA)
I-33
AdA homopolymer
96
2
2.31
1.48
358
346
364
359
343
156
92.8
e
nBA homopolymer
–
93
94
92
88
1.61
1.19
253
e
e
P(AdA74.5-co-nBA25.5) [random]
90
2.87
1.85
25
PAdA31.9-b-P(AdA0.9-co-nBA67.2
PAdA50.4-b-P(AdA2.1-co-nBA47.5
PAdA50.4-b-P(AdA2.1-co-nBA47.5
)
96(93)
93(90)
1.44(0.79)
1.86(1.22)
1.29(1.28)
1.44(1.39)
249, 145
250, 151
I-53
I-53g
)
)
92.8(90.9)f
92.3(68.4)f
92.0
I-53M
II-64
PAdA51.3-b-P(AdA1.5-co-MA47.2
PnBA32.1-b-P(nBA3.6-co-AdA64.3
PnBA24.3-b-P(nBA0.4-co-AdA75.3
PnBA18.1-b-P(nBA3.0-co-AdA78.9
)
96(94)
85
91
2.06(1.40)
1.45(0.45)
1.60(0.38)
2.36(0.26)
1.44(1.33)
1.21(1.19)
1.23(1.14)
1.24(1.18)
354
378
360
361
10, 149
)
)
)
95(92)
96(92)
92(89)
250, 127
247, 133
254, 137
92.5
II-75
90
91.1
II-79
93
92.1
a
e
f
The numbers in subscript denote the molar fraction of each monomer
Not determined.
units.
b
Values in parentheses indicate for the polymers after heating at 200 ꢀC
Values in parentheses indicate those for the first-step polymerization.
Determined by DSC.
for 2 h in air.
g
c
Butyltellanyl-terminated polymer without the postpolymerization reac-
d
Transmittance at 380 nm.
tion with PhSH.
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TABLE 2 Characterization of Block Copolymers Containing HEA and AA Units Synthesized by TERP Method
Conversionb (%)
HEA or
Polymer Sequence Structurea
AdA
nBA
tBA
Mwb/105
Mw/Mn
Td5 (ꢀC) Tmax (ꢀC) Tg (ꢀC)
b
c
I-45H5
I-46H6
PAdA43.4-b-P(AdA1.7-co-nBA50.1-co-HEA4.8
)
)
)
)
)
93(89) 87
96(92) 91
90
86
2.04(1.54) 1.50(1.41) 340
2.53(1.67) 1.46(1.38) 342
345
407
238, 152
240, 149
238, 153
240, 154
227, 152
218, 149
10, 152
PAdA43.7-b-P(AdA2.6-co-nBA47.3-co-HEA6.4
411
I-46H6-Xd PAdA43.7-b-P(AdA2.6-co-nBA47.3-co-HEA6.4
I-46H6-Xe PAdA43.7-b-P(AdA2.6-co-nBA47.3-co-HEA6.4
421
344
418
I-48H8
PAdA42.8-b-P(AdA5.3-co-nBA44.2-co-HEA7.7
96(91) 90
95(91) 88
96(91) 86
88
88
84
2.36(1.58) 1.43(1.39) 343
2.34(1.38) 1.37(1.34) 349
2.31(1.84) 1.48(1.44) 343
1.98(0.64) 1.34(1.25) 335
1.79(1.32) 1.26(1.26) 293
2.14(1.39) 1.33(1.20) 264
2.10(1.38) 1.29(1.24) 256
345
406
I-46H14
I-82H6
PAdA42.6-b-P(AdA2.9-co-nBA40.8-co-HEA13.7
PAdA75.3-b-P(AdA6.2-co-nBA13.0-co-HEA5.5
PnBA45.3-b-P(nBA2.5-co-AdA43.4-co-HEA8.8
)
407
)
420
II-43H9
I-45TB5
I-44TB9
)
89
93(89) 87
405
250, 92
PAdA43.7-b-P(AdA1.3-co-nBA50.2-co-tBA4.8
)
92(90) 89
93(91) 86
90(90) 88
83
82
90
269, 414
265, 414
259, 402
403
PAdA42.1-b-P(AdA2.1-co-nBA47.3-co-tBA8.5
)
I-44TB13 PAdA43.4-b-P(AdA0.9-co-nBA43.0-co-tBA12.7
)
I-45A5
I-44A9
I-44A13
PAdA43.7-b-P(AdA1.3-co-nBA50.2-co-AA4.8
PAdA42.1-b-P(AdA2.1-co-nBA47.3-co-AA8.5
)
)
225, 149
4, 153
350
410
PAdA43.4-b-P(AdA0.9-co-nBA43.0-co-AA12.7
)
342
418
36, 154
a
c
The numbers in subscript denote the molar fraction of each monomer
Determined by DSC.
d
e
units.
b
After thermal curing with TDI at 100 ꢀC for 1 h.
Values in parentheses indicate those for the first-step polymerization.
After thermal curing without TDI at 240 ꢀC for 2 h.
copolymerization (Fig. 1). The Mw and Mw/Mn values of the
polymers are shown in Tables 1 and 2, together with the
Td5, Tmax, and Tg values as well as the transmittance of light
at 380 nm. The block copolymers exhibited high Td5 and
Tmax values, which were over 340 and 400 ꢀC, respectively,
independent of the composition and the structure of the
polar repeating units due to the excellent thermal stability of
the polyacrylate main chain and the adamantyl ester group.
The synthetic path shown in Scheme 1 was preferred for the
production of the block copolymers with a constant Tg value
mer is valid to avoid a less-controlled polymerization and pre-
cipitation of the copolymers during the polymerization. The
polymers including tert-butyl acrylate (tBA) as the repeating
unit are readily converted to the polymers containing acrylic
acid (AA) repeating units via postpolymerization reactions.21
In this study, AdA was first polymerized, then nBA and tBA
were copolymerized (Scheme 3). After the polymerization, the
isolated PAdA-b-P(AdA-co-nBA-co-tBA)s (I-xTBy) were trans-
formed to PAdA-b-P(AdA-co-nBA-co-AA)s (I-xAy) by an acid-
catalyzed reaction. The process of transformation was moni-
tored by TG/DTA, IR, and NMR spectroscopies. The TG themo-
gram of the polymers containing a tert-butyl ester in the side
group exhibited the characteristic decomposition behavior,
which included the reaction steps of elimination of the isobu-
tene and the decomposition of the resulting carboxylic acid
polymers at a higher temperature (Fig. 2). The weight loss of
the block copolymers containing the tBA repeating units
started from 250 ꢀC and the magnitude of weight loss
increased according to the content of the tBA units in the
copolymers. No weight loss due to the isobutene elimination
was observed in the TG curve of the PAdA-b-P(AdA-co-nBA-co-
AA), indicating that the chemical transformation totally
occurred. The quantitative transformation was also confirmed
based on the fact that the peak due to the tert-butyl group
ꢀ
for the PAdA segment at about 150 C. In contrast, the reac-
tion process according to Scheme 2 provided the block
copolymers containing the hard segment with lower Tg val-
ꢀ
ues (92–137 C), which depended on the composition of the
repeating units in the hard segment. The films of PAdA and
the block copolymers obtained by casting the polymer solu-
tions exhibited high transparency of visible light with over a
90% transmittance at 380 nm. The copolymers including the
butyltellanyl group at the chain end without a postpolymeri-
zation process to obtain the stable CAH chain end become
colored after heating at 200 ꢀC for 2 h in air and the trans-
mittance value decreased to 68%. In contrast, the postpoly-
merization chain-end transformation by PhSH in the
presence of AIBN for removing the terminal telluride moiety
produced thermally stable transparent copolymers; no
change in the transmittance value occurred before and after
the heating (see Table 1).
1
was not detected in the H NMR spectrum after the side-chain
transformation. The Tg due to the PnBA soft segment including
the AdA and AA repeating units was observed in the range of
225 to 36 ꢀC after the transformation reaction. The Tg value
of the soft segment in the PAdA-b-P(AdA-co-nBA-co-AA)s
increased with an increase in the AA content, while no change
was observed in the Tg value of the PAdA segment.
We also synthesized the block copolymers containing a carbox-
ylic acid as the alternative polar repeating unit. To synthesize
polymers containing a carboxylic acid in the side group during
the living radical polymerization, the use of a protected mono-
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Microphase-Separated Structure
The block copolymers exhibited two Tg values corresponding
to the hard and soft segments, as shown in the DSC thermo-
grams in Figure 3. This was due to the formation of a
microphase-separated structure. The Tg values of the PAdA
segments were as high as 145–151 ꢀC. The PAdA sequences
including a small amount of the nBA repeating unit exhibited
lower Tg values (127–133 ꢀC). The soft segments exhibited
Tg values in a wide range according to the sequence struc-
tures. The Tg values of the PnBA soft segments increased in
the polar repeating units due to the intermolecular interac-
tions between the hydroxy and carboxy groups. Conversely,
the introduction of the HEA units into the hard PAdA seg-
ꢀ
ments decreased the Tg values to 92 C, as seen in the result
for the block copolymer, II-43H9, of which the PAdA hard
segments contained a small amount of nBA and HEA repeat-
ing units (see Table 2).
Figure 4 shows phase images for the AFM observations of the
spin-coated film surfaces of the block copolymer containing
different amounts of the HEA units. The block copolymers of
PAdA and PnBA with the 1:1 composition including no HEA
unit (I-53) exhibited a lamella structure, as shown in Figure
4(a). A similar lamella structure was also observed for I-48H5
including 4.8 mol % of the HEA unit. The island structure was
more clearly observed for I-46H14 including a higher amount
of HEA in the soft segment. This island structure correspond-
ing to the component with a small phase delay was assigned
as the PAdA hard segment. The reverse image consisting of the
soft segment as the island and the PAdA continuous phase was
observed for I-82H6, of which the AdA content was 75.3 mol
% in the hard segment [Fig. 4(d)].
FIGURE 1 SEC curves for precursor polymers (dotted) and
block copolymers (solid); (a) I-48H8, (b) II-43H9, and (c) I-
44TB9. See Table 2 for the detailed structures of the block
copolymers.
Optical Property
The copolymers were soluble in organic solvents, such as
toluene, chloroform, 1,2-dichloroethane, and THF, and the
SCHEME 3 Synthesis of block copolymers with the AA repeating unit [PAdA-b-P(AdA-co-nBA-co-AA)] by TERP.
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no polar substituents, PAdA-b-PnBA, exhibited a low water
absorption property similar to that of the PAdA homopoly-
mer. The introduction of the HEA unit increased the amount
of the absorbed water according to the amount of the intro-
duced HEA unit in the copolymers (Fig. 5). The polymers
containing a hydroxy group in the side chain tended to imply
water in the hydrophilic domain formed by the aggregation
of the hydroxy units, as shown in the poly(2-hydroxyethyl
methacrylate) and the N-(hydroxyalkyl)maleimide-olefin
copolymers.23 Conversely, a carboxylic acid moiety readily
dimerizes to form its robust dimer by strong hydrogen bond-
ing without any participation by the water molecules. As a
result, the water absorption amount for the block copoly-
mers containing AA repeating units was low due to the
excellent hydrophobic property of the adamantyl group com-
pared to that for PMMA.
Dynamic Mechanical Property
The viscoelastic properties of the block copolymers with dif-
ferent repeating structures were investigated by the dynamic
mechanical analysis in the flexural mode at the frequencies
ꢀ
of 0.5–10 Hz in the range of 2150 C to a temperature over
the Tg values at the heating rate of 2 ꢀC/min. The tempera-
ture dependences of the storage modulus (E0) and tan d val-
ues for I-46H14 are shown in Figure 6. The results for the
other block copolymers and PAdA are summarized in Table
4, together with the apparent activation energies (Eact),
which were calculated based on the plots of the tan d values
as a function of the temperature. High tan d peaks were
observed in the temperature range of 172–221 ꢀC, which
corresponded to the glass transition of the hard segment of
FIGURE 2 TG curves for (a) PAdA-b-P(AdA-co-nBA-co-tBA)s (I-
45TB5, I-45TB9, and I-45TB13) and (b) PAdA-b-P(AdA-co-nBA-
co-AA)s (I-45A5, I-45A9, and I-45A13) at the heating rate of 10
ꢀC/min in a nitrogen stream. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
the block copolymers. Weaker tan
d peaks were also
ꢀ
detected in the range of 250 to 24 C, which corresponded
to the glass transition of the soft segment. Broad and weak
b-dispersions were also observed due to the side-chain
dynamics in the temperature range lower than 280 ꢀC.24
The high and constant Eact values (275–294 kJ/mol) were
observed for the glass transition motion of the hard PAdA
transparent films were obtained by casting the solutions.
The block copolymers were highly transparent as well as
PAdA and the other polymethacrylates including PMMA and
poly(1-adamantyl methacrylate).22 The transmittance of visi-
ble light (at 380 nm) was more than 90% for the block
copolymers. The microphase separated structure of the
copolymers did not influence the scattering of light due to a
domain size smaller than the wavelength of the light and
similar reflective index values for the PAdA and PnBA seg-
ments. The nD and mD values were in the ranges of 1.491–
1.492 and 45–47, respectively, for both the PAdA and PAdA-
b-PnBAs. The nD values slightly increased to 1.492–1.494
and the mD values decreased to 42–45 by the introduction of
the HEA units into the block copolymers. The magnitude of
the change in the nD and mD values depended on the HEA
content. The introducton of the AA unit into the copolymers
provided simialr results; a high nD value and a low mD value
were observed for I-45A5. The films of the copolymers con-
taining an amount greater than 8.5 mol % as the repeating
unit (I-44A9 and I-44A13) were brittle and their optical
parameters other than the transmittance values were not
determined in this study.
FIGURE 3 DSC curves for homopolymers (a) PnBA and (b)
PAdA, and block copolymers (c) I-45H5, (d) I-46H14, and (e) I-
53M at the heating rate of 10 ꢀC/min. See Tables 1 and 2 for
the structures of the polymers.
The amount of absorbed water by PAdA was lower than that
of PMMA, as shown in Table 3. The block copolymers with
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FIGURE 4 AFM observations of microphase separated structures of the block copolymers. (a) I-53, (b) I-48H5, (c) I-46H14, and (d) I-
82H6. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
segment for all the block copolymers. This was due to the
repeating unit structure of the hard segment, which exclu-
sively consisted of the AdA repeating unit without incorpo-
rating any other monomer units such as nBA, HEA, and AA.
The Eact value for the block copolymers including the HEA
repeating units in their soft segments were higher than those
of the copolymers including no HEA units and the values
increased in the order of I-45H5 < I-48H8 < I-46H14 due
to the intermolecular hydrogen bonding between the
TABLE 3 Optical and Water Absorption Properties of the Block
Copolymers
Transmittance
at 380 nm
Absorbed
Watera (%)
Polymer
nD
mD
PAdA
92.8
92.8
92.4
91.4
90.7
92.6
91.0
89.7
94.0
1.4913
1.4915
1.4918
1.4923
1.4943
45.3
46.5
45.0
44.1
42.3
0.42
0.41b
0.55
0.65
0.75
0.42
0.46
0.51
0.66
I-53
I-45H5
I-48H8
I-46H14
I-45A5
I-44A9
I-44A13
PMMA
1.5026
c
42.1
c
c
c
1.4916
54.3
FIGURE 5 Water absorption property of the block copolymers
with the (᭺) HEA and (D) AA repeating units. The water absorp-
tion ratio increased with an increase in the content of the polar
repeating units (see Table 3).
a
After at room temperature for 72 h.
After 48 h.
b
c
Not determined.
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ship. All the samples showed nonductile fracture without
necking except for the random copolymer, P(AdA/nBA),
which had a low elasticity and was not broken even after an
elongation over 10%. The block copolymers showed tensile
elasticity values similar to that of PAdA due to the PAdA
domain as the continuous phase for the copolymers I-53 and
II-75 with the PAdA content over 60 wt %. The high elastic-
ity of PAdA as the matrix was reflected in all the mechanical
characteristics of the block copolymers. Conversely, the maxi-
mum tensile strength and strain values of the block copoly-
mers were lower than those of PAdA; for example, the
maximum tensile strength values were 2.8–8.9 MPa and the
maximum tensile strain values were 0.4–0.9% for the block
copolymers, being much lower than those for PAdA; 14.3
MPa and 1.5% (Fig. 7). This is due to the reduced area of
the cross section of the hard segment, resulting in a
decreased mechanical toughness. The block copolymer
including the soft segment with a high Tg, that is, I-53M
ꢀ
with the Tg value of 10 C for the soft segment, showed high
elasticity, tensile strength, and strain values compared to
those of I-53, as shown in Table 5. This supported that the
mechanical failure was induced by the plastic deformation of
the soft domain.
The effect of the introduction of the HEA and AA repeating
units as the polar groups in the side chain on the mechanical
properties was investigated (Fig. 8). The maximum tensile
strength and strain values increased four to five times by the
introduction of the HEA units into the soft segment. The
maximum tensile strain of I-46H14 was 2.4%, which is 1.6
times greater than that of PAdA. No increment in the
mechanical strength was observed when the HEA units were
introduced in the hard segment, as seen in the results for II-
43H9. Similarly, I-44A9 exhibited the highest tensile
strength and strain values when the properties were com-
pared among the block copolymers containing a different
amount of the AA unit. The enhancement effect of the
strength of the AA unit was greater than that of HEA units
due to the robust intermolecular hydrogen bonding between
two carboxylic acid groups. This is due to the high Tg value
of I-44A13. When the content of the AA units in the soft
segment further increased from 8.5 to 12.7 mol %, the maxi-
mum tensile strength and strain values were reduced. This is
due to the change in the Tg of the soft segments; 225, 4,
and 36 ꢀC for the block copolymers containing the AA units
FIGURE 6 Temperature dependence of (a) storage modulus
(E0), and loss modulus (E00), (b) tan d values for I-46H14 deter-
mined by dynamic mechanical measurement at frequencies of
0.5, 1, 2, 5, and 10 Hz. (c) Expansion of the data of tan d in the
low temperature region. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
hydroxy moieties. It is also noted that the Eact value for I-
53M was higher than that for I-53 due to a difference in the
chain flexibility of the soft segment. These results were the
same as the order for the peak temperatures of the tan d by
viscoelastic measurements and agreed well with the Tg
behaviors evaluated by DSC.
Tensile Mechanical Property
The tensile test was performed at 20 C and tensile elasticity
ꢀ
was determined based on an initial stress–strain relation-
TABLE 4 Dynamic Mechanical Property of the Block Copolymers at a Frequency of 1 Hz in the Flexural Mode
tan d Peak Temperature (ꢀC)
tan d Peak Intensity Eact (kJ/mol) (0.5–10 Hz)
Polymer
E0 (20 ꢀC) (GPa)
a1
a2
b
a1
a2
b
a1
a2
b
PAdA
I-53
1.03
0.85
0.79
1.05
0.86
1.01
183
172
196
198
198
221
296
79.1
92.9
97.4
59.6
41.2
44.0
0.039
292
275
294
279
287
287
251
211
27
295
0.057
0.098
0.061
0.091
0.122
0.059
210
236
239
257
272
I-53M
I-45H5
I-48H8
I-46H14
285
0.088
282
0.050
152
26
280
0.045
147
24
289, 2109
0.059, 0.059
130, 113
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FIGURE 7 Stress–strain curves for (a) homopolymer (PAdA), random copolymer [P(AdA/nBA)], and block copolymers (I-53, II-64,
and II-75) and (b) bock copolymer including a polar group before and after cross-linking (I-46H6 and I-46H6-X). [Color figure can be
viewed in the online issue, which is available at wileyonlinelibrary.com.]
with 4.8, 8.5, and 12.7 mol %, respectively. Because the
mechanical strength tests were performed at room tempera-
ture, the I-44A13 sample that included both block sequences
in the glassy state exhibited a more fragile failure behavior
compared to I-43A9. In this study, the higher toughness of
the block copolymers containing the HEA units was further
examined by the introduction of a cross-linking structure.
The cross-linking reaction was performed in the presence of
diisocyanate (TDI) as the cross-linker (see data for I-46H6-X
in Tables 2 and 5). As a result, the maximum tensile strength
and strain values reached 25 MPa and 3.2% which were 1.5–
2 times greater than those before the cross-linking. Similar
enhanced mechanical properties were also observed by the
transmittance of light at 380 nm decreased to about 70%
after the TDI cross-linking.
CONCLUSIONS
Transparent polymers with high Tg values and excellent
mechanical properties are some of key materials for elec-
tronic and photonic applications. Several materials consisting
of components with different physical properties, such as
organic-inorganic composites using nanoparticles, thermo-
plastic elastomers, fiber reinforced composites, and bicontin-
uous
network
structures,
exhibited
an
excellent
transparency, low birefringence, and low water absorption as
well as a high thermal resistance.15 Another simple method
for the fabrication of high Tg and transparent polymers is
the introduction of a bulky substituent in the side group of
ꢀ
thermally cured polymers without any cross-linker at 240 C
for 2 h. No change was observed for the Tg value determined
by DSC during the cross-linking reaction (Table 2), while the
TABLE 5 Tensile Mechanical Property of the Block Copolymers
Polymer
Tensile Elasticity (GPa)
Maximum Tensile Strength (MPa)
Maximum Tensile Strain (%)
PAdA
1.13
14.3
1.47
P(AdA/nBA)
I-53
0.13
No breaking
2.8
No breaking
0.39
0.71
I-53M
1.03
6.8
0.69
II-75
0.99
8.9
0.92
I-45H5
I-46H6
I-46H6-Xa
I-46H6-Xb
I-48H8
I-46H14
II-43H9
I-45A5
I-44A9
I-44A13
0.66 6 0.04
0.69
9.7 6 0.2
10.9
1.55 6 0.1
2.05
0.88
24.8
3.19
1.04
25.7
2.67
0.66 6 0.05
0.70 6 0.05
0.45 6 0.04
0.69 6 0.04
0.70 6 0.01
0.71 6 0.03
11.5 6 1.7
12.7 6 0.3
3.5 6 1.0
11.2 6 0.2
16.3 6 0.5
13.5 6 1.1
2.11 6 0.4
2.37 6 0.2
0.97 6 0.4
1.77 6 0.1
2.62 6 0.1
2.06 6 0.1
a
b
After thermal curing with TDI at 100 ꢀC for 1 h.
After thermal curing without TDI at 240 ꢀC for 2 h.
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reaction of diisocyanate led to the further enhancement of
the maximum mechanical strength and elongation values, as
expected. The living radical polymerization includes several
features superior to the living anionic polymerization, such
as a tolerance to polar and functional groups, the formation
of random and alternating copolymer sequences, the possi-
bility of various polymer sequence designs, and so forth.26
We have demonstrated that the TERP method is valid for the
synthesis of polyacrylate block copolymers with well-
controlled sequence structures including polar side groups,
and that the combination of bulky cycloalkyl substituents in
the side groups with the controlled polymerization technique
provides various kinds of high-performance transparent
polymers, which will be useful for electronic and photonic
technologies in the future.
ACKNOWLEDGMENT
The authors deeply appreciate to Otsuka Chemical, Tokush-
ima, Japan, for the supply of ethyl 2-(n-butyltellanyl)-2-
methylpropionate.
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