Poly(amide-ether) Thermoplastic Elastomers Based on Monodisperse Aromatic Amide Hard Segments as Shape-Memory and Moisture-Responsive Materials

Article abstract of DOI:10.1021/acs.macromol.8b01817

A series of high-molecular-weight (M_n up to 29000) multiblock poly(N-methylbenzamide)-b-poly(ethylene glycol) polymers [poly(MAB_x-x-b-PEG)], utilizing monodisperse telechelic aromatic N-methylbenzamide-based molecules (MAB_x-x) (molar mass distribution M_w/M_n = 1.02-1.04) with H₂N-PEG-NH₂, were successfully prepared via conventional solution polycondensation; their shape-memory and moisture-responsive properties were thoroughly investigated. The resultant multiblock copolymers showed three thermal transitions: the glass transition (T_g) and melting (T_m) of the PEG segment at -35 and 55 °C, respectively, and T_g of the MAB_x-x segment at 215 °C. Hard opaque pale-yellow films were successfully prepared using the solution-cast method, and several films showed good shape-memory properties, i.e., a shape fixity of 91% and a shape recovery of 97%. These properties were only observed for multiblock copolymer films having both crystalline PEG (degrees of crystallinity from 34.8% to 43.7% were observed) and aggregated monodisperse MAB_x-x phases. The existence of this cocrystalline structure is critical for the retention of temporary shape at ambient temperature and the recovery of original shape above T_m for the PEG phase in the copolymer film. Upon soaking the film in water for 5 days, it swelled by ≈660 vol % (590 wt %) with a density change from 1.15 to 1.02 g/cm³. Furthermore, we demonstrated that the film exhibits moisture-responsive behavior within just 10 s upon exposing only one of its surfaces to humid air.

Full text of DOI:10.1021/acs.macromol.8b01817

Article
pubs.acs.org/Macromolecules
Cite This: Macromolecules XXXX, XXX, XXX−XXX
Poly(amide−ether) Thermoplastic Elastomers Based on
Monodisperse Aromatic Amide Hard Segments as Shape-Memory
and Moisture-Responsive Materials
,
†
†
‡
§
∥
Yuji Shibasaki,* Toshiki Mori, Atsuhiro Fujimori, Mitsutoshi Jikei, Hideo Sawada,
and Yoshiyuki Oishi†
†Department of Chemistry & Biological Sciences, Faculty of Science & Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate
20-8551, Japan
0
‡
§
∥
Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
Department of Applied Chemistry, Akita University, 1-1, Tegatagakuen-machi, Akita-shi, Akita 010-8502, Japan
Department of Frontier Materials Chemistry, Graduate School of Science and Technology, Hirosaki University, Hirosaki 036-8561,
Japan
*
S Supporting Information
ABSTRACT: A series of high-molecular-weight (M up to
n
2
9000) multiblock poly(N-methylbenzamide)-b-poly-
ethylene glycol) polymers [poly(MABx−x-b-PEG)], utilizing
monodisperse telechelic aromatic N-methylbenzamide-based
molecules (MABx−x) (molar mass distribution M /M
(
=
n
w
1
.02−1.04) with H N-PEG-NH , were successfully prepared
2
2
via conventional solution polycondensation; their shape-
memory and moisture-responsive properties were thoroughly
investigated. The resultant multiblock copolymers showed
three thermal transitions: the glass transition (T ) and melting
g
(
T ) of the PEG segment at −35 and 55 °C, respectively, and
m
T of the MAB segment at 215 °C. Hard opaque pale-yellow films were successfully prepared using the solution-cast method,
g
x‑x
and several films showed good shape-memory properties, i.e., a shape fixity of 91% and a shape recovery of 97%. These
properties were only observed for multiblock copolymer films having both crystalline PEG (degrees of crystallinity from 34.8%
to 43.7% were observed) and aggregated monodisperse MABx−x phases. The existence of this cocrystalline structure is critical
for the retention of temporary shape at ambient temperature and the recovery of original shape above T for the PEG phase in
m
the copolymer film. Upon soaking the film in water for 5 days, it swelled by ≈660 vol % (590 wt %) with a density change from
3
1
.15 to 1.02 g/cm . Furthermore, we demonstrated that the film exhibits moisture-responsive behavior within just 10 s upon
exposing only one of its surfaces to humid air.
INTRODUCTION
We have recently reported a rapid and efficient synthetic
strategy for preparing monodisperse (M /M = 1.03−1.05)
non-hydrogen-bonding N-methylaminobenzoic acid (MAB)-
based oligomeric HSs (MABx−x, where x is the repeating
number of the building block across the core molecule
terephthalic acid) using the common condensation reagent
■
1
−7
w
n
Poly(ether-b-amide) multiblock copolymers (PEBAs)
are
an important class of thermoplastic elastomers (TPEs) because
their properties may be tuned using appropriate polyether soft
segments (SSs) and crystalline aliphatic-amide hard segments
(
HSs). They are commonly applied as gas separation
SOCl . These MAB-based HSs were used to fabricate novel
8−20
21,22
2
membranes,
reactive multiphase blends,
thermoelec-
37−39
40
linear
and hyperbranched TPE materials via copoly-
23
24,25
tric generator components, conductive materials,
shape-memory polymers (SMPs). The properties of TPEs
are strongly influenced by the molecular weight distribution
and
merization with amorphous poly(propylene glycol) (PPG).
These copolymers showed higher storage moduli (up to 4.84
GPa) with clearer phase segregation between the HS and SS
phases compared to those of copolymers comprising broad-
M /M HSs. However, thermal transition temperatures of the
26
27−36
(
M /M ) of the HS,
but M /M cannot be usually
w n
w
n
controlled for aliphatic polyamides such as nylon-6,6 and
nylon-6,10. Furthermore, amide-based HSs generally have
hydrogen-bonding sites, making it difficult to prepare
specifically desired (particularly longer) HSs because of their
poor solubility.
w
n
Received: August 22, 2018
Revised: October 26, 2018
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.macromol.8b01817
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
HS domains were observed from 40 to 60 °C, which are much
lower than the expected value of 200 °C observed in the
homopolymer poly(MAB). This is due to the incomplete
phase segregation of the HS and SS domains. Consequently, to
realize clearer phase segregation, we prepared multiblock
copolymers based on MABx−x with PEG as a crystalline SS,
eventually identifying a phase with SMP characteristics.
SMPs have been widely studied, leading to the development
and industrial application of materials with unique memory/
recovery behaviors that can be induced by a wide variety of
Synthesis of Monodisperse HS MABx−x and Broad-M
/M HS
w n
brMAB5−5. These building blocks were prepared according to our
37
previously reported method.
Synthesis of H N-PEG-NH . These were prepared according to a
2
2
49
previously reported procedure. Briefly, into a solution of HO-PEG-
OH (M = 8000, 4.00 g, 0.50 mmol) in CH Cl (45 mL) were added
n
2
2
triethylamine (1.198 g, 11.84 mmol) followed by methane sulfonyl
chloride (0.3448 g, 3.010 mmol) via syringe at 25 °C. After 18 h, the
solution was poured into diethyl ether (200 mL), and the precipitate
was collected. The obtained white powder was placed in an autoclave
and reacted with NH3aq (25 wt %, 25 mL) at 130 °C for 18 h. The
reaction mixture was then transferred to a separation flask, and the
product was extracted three times with CH Cl and washed with
41
42
43
external stimuli, including heat, light, humidity, and
4
4
2
2
magnetic field. Furthermore, the use of hydrophilic PEG
segments has presented the possibility of using such materials
for biomedical applications, such as drug-delivery systems,
contact lenses, catheters, and wound dressings. Because the
PEG domain is hydrophilic, moisture-responsive SMPs that
exploit hydration and dehydration mechanisms can be
water. The organic layer was concentrated and poured into diethyl
ether. The resultant precipitate was collected and dried at 40 °C for
1
2 h to afford the 2.43 g of title compound in 60.7% yield (Figure 3s).
1
PEG3k. White powder, yield: 49%. H NMR (400 MHz, DMSO-d ,
6
ppm): δ 2.68, 2.69, 2.71 (t, 1H, NH−H), 3.50 (s, 308H, CH−H).
1
PEG8k. White powder, yield: 61%. H NMR (400 MHz, DMSO-d ,
6
4
5−47
designed.
ppm): δ 2.86, 2.87, 2.88 (s, 1H, NH−H), 3.50 (s, 744H, CH−H).
1
Accordingly, we herein report the synthesis of monodisperse
MAB-based poly(MABx−x-b-PEG) multiblock copolymers and
their thermal, mechanical, SMP, and moisture-sensitive
properties. The mechanism of their SMP behavior was fully
investigated using differential scanning calorimetry (DSC),
wide-angle X-ray diffraction (WAXD), polarized optical
microscopy (POM), atomic force microscopy (AFM), and
dynamic mechanical analysis (DMA).
PEG10k. White powder, yield: 73%. H NMR (400 MHz, DMSO-
d , ppm): δ 2.81, 2.82, 2.83 (s, 1H, NH−H), 3.50 (s, 903H, CH−H).
Multiblock Copolymerization. Typical procedure for poly-
MAB5−5-b-PEG8k): into a 30 mL two-necked flask equipped with
6
(
a three-way stopcock were added MAB5−5 (0.1498 g, 0.100 mmol),
H N-PEG-NH (0.800 g, 0.100 mmol), NMP (1.00 mL), and
2
2
triethylamine (0.0240 g, 0.240 mmol). The flask was heated to 70 °C,
and DBOP (0.0922 g, 0.240 mmol) was added to initiate the
polymerization. After 6 h, the viscous solution was poured into diethyl
ether, and the precipitate was collected. This was dissolved with
EXPERIMENTAL SECTION
CHCl at 45 °C and reprecipitated in hexane. The product was dried
■
3
at 45 °C for 8 h under reduced pressure to afford the title compound
in 64% yield.
Materials. MAB was purchased from Wako Pure Chemical
Industries Ltd. and purified via sublimation. Poly(MAB) was prepared
via the polycondensation of MAB in the presence of telephthalic acid
in NMP at 100 °C for 1 h according to a previously reported
Poly(AB1−1-b-PEG3k). Brown compound, yield: 66%. 1H NMR
(
400 MHz, DMSO-d , ppm): δ 3.50 (s, CH −H), 7.01−7.51 (m, Ar−
6
2
48
13
H), 7.89−8.48 (m, Ar−H). C NMR (100 MHz, DMSO-d , ppm): δ
0.20, 120.17, 120.42, 120.45, 120.76, 122.87, 125.20, 128.49, 129.53,
30.32, 130.96, 150.42, 151.13, 153.90, 170.11. Elemental analysis
procedure. Triphenyl phosphite (TPP) was purchased from Tokyo
Chemical Industry Co. Ltd. and distilled under reduced pressure for
polycondensation. Telechelic PEGs comprising NH groups (H N-
6
7
1
(
2
2
C173.28H318.56N O )n: calculated C: 55.99, H: 8.64 (%), N: 1.57;
PEG-NH ) with M = 3350 (PEG3k), 8000 (PEG8k), and 10000
4
78.6
2
n
found C: 54.92, H: 8.77, N: 1.34 (%).
(
PEG10k) (M /M ≈ 1.5) were prepared via the reported procedure
w
n
Poly(AB1−1-b-PEG8k). Brown compound, yield: 64%. 1H NMR
for commercially available telechelic PEGs having OH groups at the
terminals (Sigma-Aldrich Co., LLC.). N-Methylpyrrolidone (NMP)
49
(
400 MHz, DMSO-d , ppm): δ 3.50 (s, CH −H), 6.97−7.51 (m, Ar−
6
2
1
3
H), 7.88−8.11 (m, Ar−H). C NMR (100 MHz, DMSO-d , ppm): δ
70.20, 120.25, 120.45, 122.87, 128.49, 129.42, 130.32. Elemental
was purchased from Kanto Chemical Co. Inc. and dried over calcium
6
hydride (CaH ) and distilled under reduced pressure. Triethylamine
2
(
TEA) from Wako Pure Chemical Industries Ltd. was dried over
analysis (C384.4
0.66; found C: 54.55, H: 8.48, N: 0.63 (%).
Poly(MAB1−1-b-PEG3k). Brown compound, yield: 59%. H NMR
(400 MHz, DMSO-d , ppm): δ 3.50 (s, CH −H), 7.00−7.49 (m, Ar−
H), 7.68−7.78 (m, Ar−H). C NMR (100 MHz, DMSO-d , ppm): δ
38.10, 70.20, 120.17, 120.41, 120.45, 120.76, 122.87, 128.49, 129.53,
130.32. Elemental analysis (C175.28 : calculated C:
H N O ) : calculated C: 55.18, H: 8.92 (%), N:
740.8 4 184 n
KOH and distilled under a N atmosphere. Thionyl chloride (Tokyo
2
1
Chemical Industry Co. Ltd.) was distilled prior to use. Diphenyl (2,3-
dihydro-2-thioxo-3-benzoxazolyl)phosphonate (DBOP) was prepared
6
2
50
13
according to the literature. All other reagents and solvents were used
without further purification.
6
Synthesis of 4,4′-Dicarboxylphenylterephthalamide (AB1−1).
H N O )
322.56 4 78.6 n
This building block was prepared directly from terephthaloyl chloride
56.22, H: 8.68 (%), N: 1.49; found C: 55.66, H: 8.65, N: 1.55 (%).
1
(
1
1.016 g, 5.000 mmol) by stirring 4-aminobenzoic acid (1.392 g,
0.15 mmol) in NMP (10 mL) at 25 °C for 1 h. The reaction
Poly(MAB1−1-b-PEG8k). Brown compound, yield: 43%. H NMR
51
(400 MHz, DMSO-d
H), 7.68−7.78 (m, Ar-H). C NMR (100 MHz, DMSO-d
38.10, 70.36, 120.44, 122.83, 127.11, 128.35, 129.63, 136.38, 137.82.
Elemental analysis (C386.4 : calculated C: 55.28, H: 8.94
(%), N: 0.67; found C: 54.87, H: 8.72, N: 0.68 (%).
Poly(MAB5−5-b-PEG3k). Brown compound, yield: 66%. H NMR
(400 MHz, DMSO-d , ppm): δ 3.50 (s, CH −H), 6.83−7.23 (m, Ar−
H), 7.69−7.71 (m, Ar−H). C NMR (100 MHz, DMSO-d , ppm): δ
38.08, 69.18, 70.11, 120.53, 126.48, 128.62, 129.61, 134.08, 145.79,
168.91. Elemental analysis (C239.28 : calculated C:
, ppm): δ 3.50 (s, CH
−H), 6.97−7.39 (m, Ar−
6
2
1
3
mixture was then poured into water, and the precipitate was collected
by filtration. The product was washed with tetrahydrofuran (THF)
and dried at 100 °C for 8 h under reduced pressure to provide the
6
, ppm): δ
H N O )
744.8 4 184 n
1
title compound as a white powder in 79.0% yield. H NMR (400
1
MHz, DMSO-d , ppm): δ 7.96 (s, 8H, Ar−H), 8.13 (s, 4H, Ar−H),
6
1
0.70 (s, 2H, N−H), and 12.78 (s, 2H, COO−H).
6
2
1
3
Synthesis of MAB1 . Terephthaloyl chloride (1.016 g, 5.000
6
−1
mmol) and NMP (5 mL) under nitrogen were added into a 30 mL
three-necked flask equipped with a three-way stopcock; MAB (1.392
g, 10.200 mmol) was then added to the solution, and the reaction was
kept at 25 °C for 2 h. The reaction solution was poured into water,
and the precipitate was collected by filtration. The product was
H
N O )
378.56 12 86.6 n
59.75, H: 7.93 (%), N: 3.49; found C: 58.99, H: 7.53, N: 3.04 (%).
1
Poly(MAB5−5-b-PEG8k). Brown compound, yield: 64%. H NMR
(400 MHz, DMSO-d , ppm): δ 3.49 (s, CH −H), 6.88−7.23 (m, Ar−
6
2
1
3
recrystallized from water/methanol to afford the title compound as a
H), 7.67−7.79 (m, Ar−H). C NMR (100 MHz, DMSO-d , ppm): δ
6
1
white powder in 93.0% yield. H NMR (400 MHz, DMSO-d , ppm):
37.88, 69.35, 70.33, 120.28, 123.07, 126.44, 128.01, 128.46, 129.50,
130.93, 132.01, 134.01, 137.43, 145.83, 147.77, 149.00, 154.08,
165.65, 166.87, 168.79, 169.68. Elemental analysis
6
δ 7.13 (s, 4H, Ar-H), 7.18, 7.20 (d, 4H, Ar−H), 7.76, 7.79 (d, 4H,
Ar−H).
B
DOI: 10.1021/acs.macromol.8b01817
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Macromolecules
Article
Scheme 1. Synthesis of Various HS-Type Molecules
(
C450.4H800.8N O192)n: calculated C: 57.18, H: 8.53 (%), N: 1.77;
the solution was cast on a glass substrate. The cast film was dried at
30, 50, 70, 90, and 110 °C for 2 h each and at 120 °C for 48 h under
reduced pressure.
12
found C: 56.53, H: 8.36, N: 1.58 (%).
1
Poly(MAB5−5-b-PEG10k). Brown compound, yield: 59%. H NMR
(
400 MHz, DMSO-d , ppm): δ 3.49 (s, CH −H), 6.89−7.23 (m, Ar−
Measurements. NMR spectroscopy was performed on a Bruker
6
2
1
3
1
13
H), 7.68 (m, Ar−H). C NMR (100 MHz, DMSO-d , ppm): δ 37.80,
AC-400P spectrometer at 400 MHz for H and 100 MHz for
C
6
6
1
9.32, 70.35, 120.33, 122.00, 126.30, 128.00, 129.34, 134.20, 145.83,
47.51, 162.14, 169.08. Elemental analysis (C541.2H982.4N O ) :
measurements. Deuterated dimethyl sulfoxide (DMSO-d ) was used
6
as the solvent with tetramethylsilane as the internal reference. The Mn,
M , and M /M values were determined using a Tosoh HLC-8220 gel
12
238 n
calculated C: 56.72, H: 8.64 (%), N: 1.46; found C: 56.73, H: 8.48,
N: 1.19 (%).
w
w
n
permeation chromatograph (GPC) equipped with refractive index as
well as UV detectors and a consecutive polystyrene gel column (TSK-
GEL α-M ×2) at 40 °C and eluted with NMP containing 0.01 mol/L
LiBr at a flow rate of 1.0 mL/min. DSC was performed on a
HITACHI X-DSC7000 system at a heating rate of 20 °C/min under
nitrogen. DMA was performed on a HITACHI DMS7100 at a heating
rate of 2 °C/min under nitrogen. Polymer films were cut into pieces
1
Poly(brMAB5−5-b-PEG8k). Brown compound, yield: 43%. H NMR
(
400 MHz, DMSO-d , ppm): δ 3.50 (s, CH −H), 6.83−7.23 (m, Ar−
6
2
13
H), 7.69−7.71 (m, Ar−H). C NMR (100 MHz, DMSO-d , ppm): δ
3
1
6
8.10, 60.71, 70.35, 72.94, 77.80, 119.84, 123.50, 126.71, 128.40,
29.71, 134.42, 145.79, 165.40, 168.92. Elemental analysis
(
C450.4H800.8N O192)n: calculated C: 57.18, H: 8.53 (%), N: 1.77;
12
3
found C: 56.56, H: 8.37, N: 1.55 (%).
with dimensions of 20 × 9 × 0.12 mm , and a load was applied to the
1
Poly(MAB10−10-b-PEG3k). Brown compound, yield: 73%. H NMR
films with a strain amplitude of 5 μm and a frequency of 1 Hz. The
modes of the polymers in the crystalline phase were examined by
WAXD measurements using a Rigaku R-axis Rapid diffractometer
equipped with a graphite monochromator using Cu Kα radiation at
45 kV and 200 mA. Tapping mode AFM measurements were
performed with a NanoNavi S-image SPM system (Hitachi High-
Tech Sci. Co., Tokyo, Japan) using a cantilever with a force constant
(
400 MHz, DMSO-d , ppm): δ 3.46 (s, CH −H), 6.83−7.22 (m, Ar−
6
2
1
3
H), 7.69−7.71 (m, Ar−H). C NMR (100 MHz, DMSO-d , ppm): δ
3
1
6
8.15, 69.14, 70.32, 120.40, 122.43, 126.48, 128.22, 129.42, 129.61,
30.56, 134.08, 145.80, 165.75, 167.14, 168.95. Elemental analysis
(
C319.28H448.56N O96.6)n: calculated C: 62.44, H: 7.36 (%), N: 5.02;
22
found C: 61.28, H: 7.05, N: 4.69 (%).
1
−1
Poly(MAB10−10-b-PEG8k). Brown compound, yield: 70%. H NMR
400 MHz, DMSO-d , ppm): δ 3.50 (s, CH −H), 6.86−7.22 (m, Ar−
of ∼15 N m and a resonance frequency of 120 kHz. The scan size
2
(
and tip velocity of the AFM measurements were 10 μm and 200 nm/
6
2
1
3
H), 7.69−7.71 (m, Ar−H). C NMR (100 MHz, DMSO-d , ppm): δ
s, respectively. Tensile properties of the films were measured on an
AGS-X (SHIMADZU) at an extension rate of 10 mm/min. The
thermoresponsive SMP effect was investigated using a DMS7100 as
6
3
1
8.39, 69.24, 70.12, 120.30, 122.21, 123.94, 126.48, 128.08, 129.37,
29.55, 130.76, 134.27, 145.76, 168.95. Elemental analysis
(
C530.4H870.8N O202)n: calculated C: 59.03, H: 8.13 (%), N: 2.86;
follows: a rectangular film (length L
was heated at 90 °C, followed by cooling to 50 °C, at which point the
film was elongated by 70% (L
0
) was set in the chamber, which
12
found C: 58.59 H: 8.00, N: 2.60 (%).
Poly(MAB10−10-b-PEG10k). Brown compound, yield: 74%. 1H
NMR (400 MHz, DMSO-d , ppm): δ 3.47 (s, CH −H), 6.71−7.36
). The chamber was cooled to −20 °C,
m
and the stress was released. This strain was denoted as LRet. The
chamber was heated to 90 °C again, and the final strain (LRes) was
measured. This tensile test was performed twice to determine the
6
2
1
3
(
m, Ar−H), 7.68 (m, Ar−H). C NMR (100 MHz, DMSO-d , ppm):
6
δ 38.15, 69.24, 70.12, 120.41, 122.67, 126.5, 127.0, 128.10, 129.40,
29.53, 130.66, 134.00. Elemental analysis (C621.2H1052.4N O ) :
1
shape-memory fixity ratio (R ) and recovery ratio (R ) using eqs 1 and
f
r
22
248 n
calculated C: 58.33, H: 8.29 (%), N: 2.41; found C: 57.83, H: 8.26,
N: 2.58 (%).
2 (presented in Table 3).
4
8
−1
Poly(MAB). FT-IR [KBr (cm )]: 3399 (N−H), 3280−3100
RESULTS AND DISCUSSION
■
(
1
amine and guanamine hydrogen bonding), 3052 (aromatic C−H),
Polymer Synthesis. By use of our previously reported
rapid and efficient synthetic method, a series of non-hydrogen-
bonding HSs MABx−x (x = 1, 5, and 10), along with short HSs
579 (aromatic CC), 1477 (triazine CN), 1415, 806 (aromatic
1
C−H), 1194 (aromatic C−N). H NMR (400 MHz, DMSO-d ,
6
ppm): δ 6.67−8.04 (Ar−H), 8.22, 9.24 (−NH−).
Film Fabrication. All films were prepared using the solution casting
method. Polymer samples were dissolved in dry NMP at 25 wt %, and
such as AB1−1 and brMAB5−5 (broad-M /M of 1.6), were
w n
prepared in moderate yields (Scheme 1), and their structures
C
DOI: 10.1021/acs.macromol.8b01817
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Scheme 2. Synthesis of PEBAs via Direct Solution Polycondensation
1
Figure 1. H NMR spectra of (a) H N-PEG-NH (PEG8k) and (b) PEBA poly(MAB5−5-b-PEG8k).
2
2
Table 1. Synthesis of PEBAs
segment
a
b
b
c
run
hard
AB1−1
AB1−1
soft
yield (%)
Mn (Da)
Mn (Da)
M /Mn
composition MAB:PEG
film
w
1
2
3
4
5
6
7
8
9
PEG3k
PEG8k
PEG3k
PEG8k
PEG3k
PEG8k
PEG10k
PEG8k
PEG3k
PEG8k
PEG10k
52
59
69
76
66
64
59
43
73
70
3720n
8370n
3750n
8400n
4810n
9500n
11460n
9500n
6140n
10800n
12800n
8800
15000
19000
29100
22500
29300
27400
22500
11700
22100
29200
1.8
2.0
2.1
2.0
1.8
2.1
1.9
1.9
2.2
1.8
1.9
1.00:1.25
1.00:1.04
1.00:0.84
1.00:1.08
1.00:0.82
1.00:0.92
1.00:0.78
1.00:0.92
1.00:1.00
1.00:0.97
brittle
brittle
brittle
brittle
flexible
flexible
flexible
brittle
brittle
flexible
flexible
MAB1−1
MAB1−1
MAB5−5
MAB5−5
MAB5−5
brMAB5−5
MAB10−10
MAB10−10
MAB10−10
1
1
0
1
74
1.00:0..94
a
b
c
1
Calculated M of the polymer repeating unit. Determined by GPC (NMP containing 0.01 M LiBr, PSt standard). Determined by H NMR.
n
were characterized via 1H NMR analysis (Figure 1s).
Copolymerization of these monomers with H N-PEG-NH
block copolymer is shifted to a higher molecular weight and
1
has the moderate M /M of 2.1. Figure 1 shows the H NMR
2
2
w
n
(
M = 3K, 8K, and 10K, M /M ≈ 1.5) monomers was
spectra of H N-PEG-NH (PEG8k) and the block polymer
n
w
n
2 2
performed using the well-known phosphine-based condensa-
tion reagent DBOP in NMP at 70 °C for 6 h to afford the
corresponding multiblock copolymers (PEBAs) (Scheme 2).
As shown in the GPC traces of MAB5−5 (M = 1100, M /M
poly(MAB5−5-b-PEG8k). The triplet signal labeled a (Figure
1a) observed at 2.65 ppm is assignable to the α protons of the
terminal amino groups of PEG8k and is completely absent
from the spectrum of the block copolymer. A new signal
labeled a (Figure 1b) is observed at 3.30 ppm, which is
assignable to the α protons of the amide groups. When the
integration of signal f (Figure 1b) at 7.70 ppm (corresponding
n
w
n
=
1.03), H N-PEG-NH (PEG8k, M = 8120, M /M = 1.52),
2 2 n w n
and the block copolymer poly(MAB5−5-b-PEG8k) (Mn
=
2
9300, M /M = 2.10) (Figure 2s), the unimodal peak of the
w
n
D
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Figure 2. Digital camera images of PEBA films cast from NMP solutions.
Figure 3. DSC profiles of multiblock copolymers (poly(MAB-b-PEG)).
to the terephthaloyl group) is set to 4.0, the integration of the
aromatic protons at 7.00 ppm is calculated to be ≈40.0. Thus,
the integration of the methylene protons b and c for PEG8k
observed at 3.35 ppm can be calculated to be 801, which is
comparable to the value of 797 observed in Figure 1a. These
results clearly confirm the satisfactory formation of the
multiblock copolymer with the expected structure.
and PEG3k in NMP, the transparent homogeneous solution
becomes turbid with time probably due to the strong
molecular interactions between polymer chains. The lower
molecular weight of the resulting polymer can be explained by
this poor solubility in NMP. The HS to SS ratios calculated
1
from the H NMR results are 1:1.25 to 1:0.78. Except for
poly(AB1−1-b-PEG3k) and poly(AB1−1-b-PEG8k), the other
polymers in Table 1 exhibit good solubility and the precipitates
become too fine to be collected perfectly. Therefore, the
Table 1 summarizes the results of block copolymerization
with PEG. When the polymerization is conducted with AB1−1
E
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Table 2. Thermal Properties of PEBAs
a
b
b
c
d
e
run
PEBA
Mn
Tm(SS)
Tg(HS)
ΔH(PEG) (J/g)
χ
(%)
SMP
1
2
3
4
5
6
7
8
9
poly(AB1−1-b-PEG3k)
poly(AB1−1-b-PEG8k)
8800
15000
19000
29100
22500
29300
27400
22500
11700
22100
29200
45
55
44
57
33
52
55
54
39
53
55
71.2
141
96
36.2
71.6
48.8
66.1
15.4
41.2
43.7
60.0
8.3
n
n
n
n
n
y
202
poly(MAB1−1-b-PEG3k)
poly(MAB1−1-b-PEG8k)
poly(MAB5−5-b-PEG3k)
poly(MAB5−5-b-PEG8k)
poly(MAB5−5-b-PEG10k)
poly(brMAB5−5-b-PEG8k)
poly(MAB10−10-b-PEG3k)
poly(MAB10−10-b-PEG8k)
poly(MAB10−10-b-PEG10k)
130
30.3
82.4
86.0
118
16.3
68.5
78.7
218
232
215
y
n
n
y
213
213
213
1
1
0
1
34.8
40.0
y
a
b
c
d
Determined by GPC (NMP containing 0.01 M LiBr, PSt standard). Determined by DSC. Heat of fusion of T . Degree of crystallization
m
e
determined by ΔH. Shape-memory property.
Figure 4. SMP characteristics of PEBA films. (a) poly(MAB5−5-b-PEG3k), (b) poly(MAB5−5-b-PEG8k), and (c) poly(MAB5−5-b-PEG10k).
isolated yields range from 43% to 74%. The oligomeric fraction
could not be completely collected. Thus, the measured
composition of the block copolymer is not always 1:1, as
expected. The solubilities in ordinal organic solvents and water
were assessed. The polymers (Table 1, runs 3−11) are highly
soluble in DMF, N,N-dimethylacetamide (DMAc), MeOH,
CHCl , and CH Cl and moderately soluble in NMP and
DMSO. We expected that the polymers might be soluble in
water due to the hydrophilic PEG segment and form micelle in
the media. However, they are totally insoluble in water. To
obtain a homogeneous solution, a high concentration of 10 M
HCl is required as the solvent. However, they are insoluble in
THF, acetone, ethanol, ethyl acetate, toluene, and diethyl
ether. Although the PEBA samples are insoluble in distilled
water, they became too swollen to be retrieved.
(brMAB5−5-b-PEG8k), show hard plastic behavior at 20 °C
but are easily destroyed upon folding. Furthermore, these films
are almost melted at 80 °C and do not maintain their shape.
Thermal Properties. Figure 3 shows the DSC profiles
(second scan, 20 °C/min, N ) of the PEBA samples at from
2
between 0−100 °C and 150−250 °C. The endothermic peak
corresponding to the T of the PEG segment is observed
3
2
2
m
around 55 °C. The shorter PEG3k-segment-containing
polymers show lower Tm values with lower heats of fusion
(ΔH) from 33 and 45 °C due to the lower degree of
crystallization (χ). Conversely, the poly(MAB -b-PEG) and
5−5
poly(MAB10−10-b-PEG) samples show thermal transitions
around 220 °C, which are assignable to the T of the HS.
g
These values seem to be independent of the length of PEG
37
segment. Our previously reported block copolymer, poly-
Polymer films were prepared by solvent-casting a 25 wt %
NMP solution onto a glass substrate. As shown in Figure 2, the
films appear light yellow to dark brown. They are opaque,
except for the poly(AB1−1-b-PEG8k) and poly(MAB1−1-b-
(MAB5−5-b-PPG) (amorphous−crystalline PEBA), presents its
HS T between 50 and 90 °C, far lower than the expected
g
value of 170 °C. Furthermore, this lower T was detected only
g
by DMA measurements; thus, the phase segregation is not
sufficient in the poly(MAB5−5-b-PPG) film. Conversely, the
crystalline−crystalline PEBA copolymer exhibits more defini-
tive segregation in the films.
PEG3k) samples. The poly(MAB5−5-b-PEG8k), poly(MAB5−5
-
b-PEG10k), poly(MAB10−10-b-PEG3k), poly(MAB10−10-b-
PEG8k), and poly(MAB10−10-b-PEG10k) films exhibit hard
plastic characteristics at room temperature and soft rubbery
behavior at 80 °C. Poly(MAB5−5-b-PEG3k) shows rubbery
behavior both at room temperature and at 80 °C. The other
films, including the high-M /M -HS-based PEBA poly-
The thermal properties of the prepared PEBA samples are
summarized in Table 2. Because of the hydrogen bonding at
the terminal of the PEG segment, the T s for the HS of
g
poly(MAB5−5-b-PEG) and poly(MAB10−10-b-PEG) are ob-
w
n
F
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Figure 5. Representative example of two sequential shape-memory cycles for poly(MAB5−5-b-PEG8k).
Table 3. Representative Example of Two Sequential Shape Memory Cycles for Poly(MAB -b-PEG8k)
5‑5
a
b
c
d
L0 (%)
Lm (%)
LRet (%)
LRes (%)
Rf (%)
Rr (%)
R (%) = L
− L0
× 100
× 100
Ret
cycle 1
cycle 2
0
73.9
91.0
67.5
2.5
4.1
91
97
f
L
− L0
(1)
(2)
m
Lm − LRes
Lm − L0
R (%) =
0.5
82.9
91
96
r
a
b
c
d
L is the original length. L is the deformed length. L is retained length. L is the length after recovery.
0
m
Ret
Res
Figure 6. POM images (left) and WAXD profiles (right) of PEBA samples.
served around 215 °C, which are higher than the T s observed
whereas the crystalline HS phase memorizes the original shape.
On cooling to room temperature, the film loses its flexibility
and becomes rigid, giving a temporary shape that is subject to
internal stress. The films exhibiting SMP properties have χ
values from 34.8% to 43.7%. The samples having lower χ
values for the PEG segment cannot fix the temporary shape
against the internal stress, so these films relax, even at room
temperature. Conversely, the samples having higher χ values
cannot maintain the film properties above Tm due to the
absence of the crystalline HS domain. Thus, moderate χ values
are required to maintain the temporary shape at room
temperature and the film shape above Tm.
g
for MAB5−5 (170 °C) and MAB10−10 (180 °C). The value of
ΔH for the PEG segment was determined via DSC
measurements, and the χ values were calculated using the
0
52
reported ΔHm of 196.8 J/g. The χ values of the PEG
segments in the PEBA samples are from 8.3% to 71.6%,
depending on the structural combination of HS and SS.
Basically, the PEG3k-based block copolymer samples exhibit
low χ values and no SMP properties. Thermally induced SMP
behavior can be attributed to the coexistence of a rigid HS
crystalline phase and SS domains. Above the T of the PEG
m
segment, the melted PEG phase allows deformation of the film,
G
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Figure 7. AFM images of PEBA films (scale bar is 500 nm).
Figure 8. DMA profiles of the relation between (a) E′ and temperature as well as (c) tan δ and temperature for PEBA films having SMP property
and (b) those of the relation between E′ and temperature as well as (d) tan δ and temperature for PEBA films that do not show SMP character.
SMP Properties. SMP properties were expected for our
block copolymers since they have two segregated crystalline
domains in the films, as confirmed by the DSC results. Figure 4
shows the results of SMP testing for poly(MAB5−5-b-PEG3k),
poly(MAB5−5-b-PEG8k), and poly(MAB5−5-b-PEG10k) films.
The films were wrapped around a glass rod at 80 °C to form
helix-shaped ribbons. They were then cooled to room
temperature, and the rod was removed. Because the poly-
H
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MAB5−5-b-PEG3k) film exhibits rubbery behavior both at
Article
(
dictated by the MAB5−5 segment. Thus, the E′ value of the film
starts to rapidly decrease around −30 °C (Figure 8b). As
shown in Figure 8c, the SMP samples clearly show two peaks
at −35 and 60 °C for T and T of PEG domain, respectively,
whereas the peaks for non-SMP samples shown in Figure 8d
are complicated and dissimilar. Again, it cannot hold its shape
upon heating and cooling due to the lack of the contribution
from the PEG domain in the poly(MAB5−5-b-PEG3k) film. In
our previous study, the poly(MAB5−5-b-PPG4k) films showed
room temperature and at 80 °C, the helical shape is not
maintained, even after cooling to room temperature. However,
the curved film recovers its flat shape when heated to 80 °C.
Conversely, the poly(MAB5−5-b-PEG8k) and poly(MAB5−5-b-
PEG10k) films show excellent SMP properties, with a stable
temporary fixed shape and perfect recovery of the original flat
shape. In tensile testing, the film (1.1 cm × 0.3 cm × 100 μm)
can be elongated by up to 400% at 80 °C, and the temporary
shape is almost perfectly maintained upon cooling (Figure 4s).
The original shape is quickly recovered (within 3 s) when the
film is reheated to 80 °C.
g
m
relaxations at −70 °C for T of the PPG segment and 50 °C for
g
37
that of the MAB segment. The T for poly(MAB) is ≈200
5−5
g
°C; thus, T observed for the poly(MAB5−5-b-PPG4k) film is
g
To study the shape-memory behavior in more detail, stress−
strain−temperature curves were obtained using DMA. A
quantitative demonstration of temperature memory properties
with the deformation temperature at 90 °C and a strain value
of 70% was performed for two cycles (Figure 5). From these
results, the values of R and R were calculated using eqs 1 and
significantly lower than the expected value. In contrast, the
poly(MAB5−5-b-PEG8k), poly(MAB5−5-b-PEG10k), poly-
(MAB10−10-b-PEG8k), and poly(MAB10−10-b-PEG10k) films
in this study exhibit T values of ≈215 °C, which clearly
g
indicates the almost perfectly phased segregated structures in
the films.
f
r
2
9
and are summarized in Table 3. The excellent values of R =
Mechanical Properties. Figure 9 shows the tensile test
results for the block copolymer films. The SMP samples
f
1% and R = 97% demonstrate the potential of the
r
temperature memory functionality of the PEBA films.
WAXD and POM Studies. Several PEBA films prepared
herein show excellent SMP properties. To more fully
understand the criteria required for these properties, we
performed WAXD analysis. Figure 6 shows the POM images of
PEBA samples at 25, 80, and 250 °C along with the
corresponding WAXD profiles. In the profile of poly-
(
MAB5−5-b-PEG3k) (no SMP properties), diffraction peaks
are observed at 18° and 21°, which are assignable to MAB5−5
HS, and at 20° and 24°, which are assignable to PEG SS. This
low diffraction intensity for the PEG segment is also supported
by the DSC measurements, where the χ value was 15.4%
(Table 2, run 5). Under POM observation, an anisotropic
structure is observed at 25 and 80 °C, but the observed
structure at 25 °C is quite different from that of PEG8k. In the
WAXD profile of poly(brMAB5−5-b-PEG8k) (no SMP proper-
ties), only strong PEG peaks are observed (χ = 60%).
Conversely, diffraction peaks corresponding to both HS and SS
domains are observed in the WAXD measurement for SMP
samples, i.e., poly(MAB5−5-b-PEG8k) (χ = 41.2%) and
poly(MAB5−5-b-PEG10k) (χ = 43.7%). In the POM images
observed for these samples, two types of clear anisotropic
structures are assignable to PEG and MAB5−5 segments at 25
and 80 °C. Thus, to realize SMP properties, the two polymer
segments should have crystalline structures with moderate χ
values.
AFM Study. AFM analysis was performed to ascertain the
surface morphologies of the films. Figure 7 depicts the AFM
images of the block copolymer films. For poly(brMAB5−5-b-
PEG8k) (χ = 60%), fibril morphology corresponding to PEG
spherulites is observed. This type of morphology is also clearly
observed for the SMP samples poly(MAB5−5-b-PEG8k) (χ =
Figure 9. Stress−strain curves for PEBA films.
poly(MAB5−5-b-PEG8k) and poly(MAB5−5-b-PEG10k) show
typical plastic sample behavior with clear yield points and
elongations of over 300%, whereas poly(brMAB5−5-b-PEG8k)
shows hard brittle characteristics because there is only a single
PEG crystalline hard domain in the film. For poly(MAB5−5-b-
PEG3k), the film is very soft, even without heating, and it
cannot maintain the film beyond only ≈28% deformation. This
can be explained by the low χ value (15.4%) of this PEG
domain.
Table 4 summarizes the tensile testing results for the PEBA
films. We expected that the SMP films would exhibit high
elongation at high temperatures, such as 80 °C, which is
beyond the melting point of the PEG segment. However, they
break at similar elongation values to those observed at 25 °C.
At this temperature, as expected, the rigidity and the yield
strength of the films decreased. For the SMP films, the tensile
moduli dramatically decrease to 1/7−1/10 of their original
values and present S-type curves typical of TPE materials.
Swelling and Moisture-Responsive Properties. Be-
cause our films contain hydrophilic PEG domains, we expected
that the SMP films would be moisture responsive. However,
before testing the SMP films, we assessed the swelling behavior
of the poly(MAB5−5-b-PEG8k) film. The dried film (ρ = 1.15
4
1.2%) and poly(MAB5−5-b-PEG10k) (χ = 43.7%) but not for
poly(MAB5−5-b-PEG3k) (χ = 15.4%).
DMA Study. The DMA profiles of SMP and non-SMP
films are shown in Figure 8. Most non-SMP samples break at
∼
50 °C probably because of a lack of aggregation in the HS
domain. In other words, the amide sequences AB and
1
−1
MAB1−1 are too short to form a stable phase. The brMAB5−5
segment is also ineffective for endowing SMP properties
probably because of the weaker aggregation due to its broad
M /M . When the PEG segment is too short, such as in
w
n
3
PEG3k, the properties of the block copolymer film are mainly
g/cm ) was placed in a Petri dish at 20 °C with sufficient
I
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Table 4. Stress−Strain Curves of Multiblock Copolymers
the film absorb the sprayed water, and the film expands more
on this side, resulting in its bent shape. The absorbed water is
confined in the separated area by the MAB5−5 phases, and thus
the film maintains its temporary shape under these stress
conditions. When the film is placed in a drying oven, the
absorbed water is quickly eliminated and once again the PEG
domains form a crystalline structure, returning the overall
shape back to its original form. Thus, this simple moisture
responsivity can be explained in terms of the perfectly
segregated hydrophilic PEG and hydrophobic MAB5−5 micro-
domains.
(
MAB -b-PEG)
5‑5
a
b
c
temp
(°C)
σTS
E
E
y
b
polymer
(MPa)
(%)
(MPa)
poly(MAB5−5-b-PEG3k)
poly(brMAB5−5-PEG8k)
poly(MAB5−5-b-PEG8k)
poly(MAB5−5-b-PEG10k)
poly(MAB5−5-b-PEG3k)
poly(brMAB5−5-PEG8k)
poly(MAB5−5-b-PEG8k)
poly(MAB5−5-b-PEG10k)
25
25
25
25
80
80
80
80
8.8
4.2
9.7
9.8
2.2
26.3
2.9
312.0
290.0
21.9
45.0
180.0
218.0
200.0
18.3
2.7
1.7
262.0
174.0
30.0
20.0
a
b
c
CONCLUSIONS
Tensile strength. Elongation at break. Young’s modulus.
■
Monodisperse polyamide HSs based on N-methylbenzamide
were utilized to construct novel PEBA materials with
crystalline PEG as a soft segment. The resulting PEBA
materials showed good thermoplastic elastomeric properties
deionized water to submerge the film. After 5 days, the film
was carefully retrieved and carefully dabbed dry with a
KimWipe. The volume and weight swelling ratios were
calculated to be 659% and 587%, respectively. The ρ value
with σTS, E
and up to 312%, respectively. The MAB5−5-based PEBA
showed good thermal SMP properties with R = 91% and R
, and E values of 1.7−9.8 MPa, 18.3−218 MPa,
y
B
3
of the swollen film was calculated to be 1.02 g/cm . These
results clearly demonstrate the moisture responsivity of the
film. Thus, a 3 cm long rectangular film sample was prepared
and secured with a clip as shown in Figure 10. Only one side,
f
=
r
97% upon heating to 80 °C and cooling to room temperature.
The PEBA material also showed moisture-responsive behavior,
exhibiting stable bending deformation when one of its surfaces
was exposed to water vapor. The material returned to its
original shape within just 5 min in a drying oven at 100 °C.
Thus, our novel films show excellent potential for a wide
range of biomedical and industrial applications.
∼
2 cm from the bottom, of this film was homogeneously
exposed to moisture, and the film quickly started to bend. This
deformation finishes within 1 min, and the film maintains its
shape for a further hour. The polymer film began to bend from
the narrow point near the grasped part although one side of the
film had been homogeneously sprayed with water. This could
explain the swelling of the sprayed part and the stress
concentrated at the boundary between the crystalline upper
part and swollen lower part. The film was placed in a drying
oven at 100 °C for just 5 min, resulting in the film returning to
its original shape. This moisture-responsive behavior can be
explained simply as follows: the PEG domains on one side of
ASSOCIATED CONTENT
■
*
S
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.macro-
mol.8b01817.
Figure 10. Swelling and moisture-responsive behavior of PEBA films.
J
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1
(
13) Sridhar, S.; Suryamurali, R.; Smitha, B.; Aminabhavi, T. M.
SI 1: H NMR spectra of MAB5 (up) and brMAB5−5
−5
Development of crosslinked poly(ether-block-amide) membrane for
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design of ternary mixed matrix membranes containing Pebax 1657/
silver-nanopowder/[BMIM][BF ] for improved CO separation
(
bottom) samples in CDCl ; SI 2: GPC profiles of (a)
3
2
4
MAB5−5, (b) PEG8k, and (c) poly(MAB5−5-b-PEG8k);
1
SI 3: H NMR spectra of HO-PEG-OH and NH -PEG-
2
13
NH ; SI 4: expanded C NMR spectrum of poly-
MAB10−10-b-PEG3k) copolymer in DMSO-d ; SI 5:
shape-memory effect of poly(MAB5−5-b-PEG8k) copoly-
mer films (DOCX)
2
4
2
(
6
performance. ACS Appl. Mater. Interfaces 2017, 9, 10094−10105.
(15) Dong, L.; Zhang, C.; Bai, Y.; Shi, D.; Li, X.; Zhang, H.; Chen,
M. High-performance PEBA2533-functional MMT mixed matrix
membrane containing high-speed facilitated transport channels for
CO /N separation. ACS Sustainable Chem. Eng. 2016, 4, 3486−3496.
2
2
AUTHOR INFORMATION
Corresponding Author
E-mail: yshibasa@iwate-u.ac.jp.
■
(16) Liu, L.; Chakma, A.; Feng, X. CO /N separation by poly(ether
2 2
block amide) thin film hollow fiber composite membranes. Ind. Eng.
*
Chem. Res. 2005, 44, 6874−6882.
(17) Li, Y.; Wang, S.; Wu, H.; Guo, R.; Liu, Y.; Jiang, Z.; Tian, Z.;
ORCID
Zhang, P.; Cao, X.; Wang, B. High-performance composite membrane
with enriched CO -philic groups and improved adhesion at the
interface. ACS Appl. Mater. Interfaces 2014, 6, 6654−6663.
(18) Wang, Y.; Li, H.; Dong, G.; Scholes, C.; Chen, V. Effect of
Yuji Shibasaki: 0000-0002-9176-0667
2
Notes
The authors declare no competing financial interest.
fabrication and operation conditions on CO separation performance
2
ACKNOWLEDGMENTS
of PEO−PA block copolymer membranes. Ind. Eng. Chem. Res. 2015,
■
54, 7273−7283.
This study was financially supported by the Grant Co-funded
by 3NUNT (National Universities of Northern Tohoku) and
CSTI, SIP (Research and development of innovative
manufacture using molecular adhesion technology). The
authors thank Enago (www.enago.jp) for the English language
review.
(19) Barbi, V.; Funari, S. S.; Gehrke, R.; Scharnagl, N.; Stribeck, N.
SAXS and the gas transport in polyether-block-polyamide copolymer
membranes. Macromolecules 2003, 36, 749−758.
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surface modification for the fabrication of PEBA/SiO nanocomposite
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