Synthesis and properties of hyperbranched polyimides derived from novel triamine with prolonged chain segments

Article abstract of DOI:10.1002/pola.26628

Novel pyridine-containing hyperbranched polyimides (HBPIs) were synthesized by using a new triamine 2,4,6-tris[3-(4-aminophenoxy)phenyl]pyridine with prolonged chain segments, ether linkage and meta-linked units as a BB′₂-like monomer, various commercial aromatic dianhydrides as A₂ monomers. Most of the obtained HBPIs were readily soluble in common organic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, m-Cresol, and so forth. Meanwhile, they also had good thermal stability with the glass transition temperatures (T_gs) all above 210 °C, the temperature at 10% weight loss of 537.1-574.4 °C in nitrogen atmosphere. Strong and flexible HBPI films were obtained, which had good mechanical properties with tensile strengths of 83.3-95.8 MPa, tensile modulus of 1.82-2.43 GPa and elongations at break of 4.84-6.98%.

Full text of DOI:10.1002/pola.26628

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
Synthesis and Properties of Hyperbranched Polyimides Derived from
Novel Triamine with Prolonged Chain Segments
Jie Shen,1 Ying Zhang,1 Wenqiu Chen,1 Wenhao Wang,2 Zushun Xu,1,2 Kelvin W. K. Yeung,2
Changfeng Yi1,2
1Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, Faculty of Materials
Science and Engineering, Hubei University, Wuhan 430062, China
2Division of Spine Surgery, Department of Orthopaedics and Traumatology, The University of Hong Kong, Pokfulam, Hong
Kong, China
Correspondence to: C. Yi (E-mail: changfengyi@hubu.edu.cn)
Received 10 December 2012; revised 29 January 2013; accepted 1 February 2013; published online 19 March 2013
DOI: 10.1002/pola.26628
ABSTRACT: Novel pyridine-containing hyperbranched polyi-
mides (HBPIs) were synthesized by using new triamine
2,4,6-tris[3-(4-aminophenoxy)phenyl]pyridine with prolonged
chain segments, ether linkage and meta-linked units as
above 210 ꢀC, the temperature at 10% weight loss of 537.1–
574.4 ꢀC in nitrogen atmosphere. Strong and flexible HBPI
films were obtained, which had good mechanical properties
with tensile strengths of 83.3–95.8 MPa, tensile modulus of
a
a
BB02-like monomer, various commercial aromatic dianhydrides
as A2 monomers. Most of the obtained HBPIs were readily
soluble in common organic solvents such as N,N-dimethylfor-
1.82–2.43 GPa and elongations at break of 4.84–6.98%.
2013
C
V
Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.
2013, 51, 2425–2437
mamide,
N,N-dimethylacetamide,
N-methyl-2-pyrrolidone,
m-Cresol, and so forth. Meanwhile, they also had good ther-
mal stability with the glass transition temperatures (Tgs) all
KEYWORDS: hyperbranched; mechanical properties; polyimide;
prolonged chain segment; pyridine-containing triamine
polyimides can be obtained from ether-containing mono-
mers, as is well known, introduction of flexible groups to the
polyimide backbones will sacrifice their thermal stability and
mechanical properties.16–18 It has been proved that introduc-
tion of rigid heteroaromatic pyridine ring to the polymer
backbone could endow it excellent thermal stability, which
should be useful to decrease the negative effects resulted
from the introduction of flexible ether linkages in the polyi-
mides backbone.19–21 Furthermore, polysubstituted pyridine
derivatives, especially the symmetrical triarylsubstituted pyr-
idine compounds are not only important medicine structural
units, but also key intermediates of the synthesis of complex
organics. They present favorable physiological activity.22
INTRODUCTION Polyimides are high-performance macromo-
lecules with excellent thermal stability, mechanical, electri-
cal and solvent-resistance properties. Therefore, they are
being used in applications such as photoresist, membrane
separation, adhesives, and matrix materials for compo-
sites.1–6 However, many polyimides are insoluble in com-
mon organic solvents and have extremely high glass
transition or melting temperatures due to their rigid
backbones which limited their applications. To overcome
such a difficulty, the current research in this field is fo-
cusing on the development of novel polyimides which not
only maintain the outstanding comprehensive properties
but also exhibit good solubility.7–10
Most of previous experimental studies of structure modifica-
tion, however, have been focused on linear-type polyimides.
Ever since the possibility to synthesize hyperbranched poly-
mers in theory was first announced by Flory in 1952,23 such
kind of polymers had constantly received increasing atten-
tion due to their unique properties when compared to their
linear analogues. The highly branched structure and a large
number of terminal functional groups are two important
structural features of this kind of polymers, which clearly
Much efforts have been directed toward the design and syn-
thesis of new anhydride and amine monomers. It has been
proved that introduction of flexible linkages into the polymer
backbone could improve the solubility of polyimides.11–13
Solubility of polyimides can also be improved by incorpora-
tion of less symmetric meta-linked aromatic units in the
main chain.14,15 The incorporation of meta-linked units into
the polymer backbone may have interrupted the chain pack-
ing, thus leading to improved solubility. Although soluble
C
V
2013 Wiley Periodicals, Inc.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437
2425

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
distinguish them from linear polymers. In recent years, some
hyperbranched polyimides (HBPIs) have been synthesized
and widely examined in many potential applications. These
HBPIs not only inherit the excellent properties of polyimides,
but also exhibit high solubility, low viscosity, and non-crys-
tallinity resulting from hyperbranched structure.24–28
EL III system. The intrinsic viscosity ([g]) was determined at
a 0.8 g dL21 concentration of HBPIs in NMP with an Ubbe-
lohde capillary viscometer at 25 6 0.2 ꢀC. Weight-average
(Mw) and number-average (Mn) molecular weights were
determined by gel permeation chromatography (GPC). Waters
(Ultrastyragel) columns 1515 was used for GPC analysis with
tetrahydrofuran (THF; 1 mL min21) as the eluent. A crystallo-
graphic study of polyimide was performed at room tempera-
ture (about 25 ꢀC) on a D/MAX-IIIC X-ray diffractometer
(Akishima-shi, Tokyo, Japan). The X-ray diffraction (XRD) pat-
As it is known, hyperbranched polymers lack a significant
entanglement in the solid state, indicating that they are very
difficult to prepare tough membranes with good mechanical
strength.29 Because of that, there is almost no data on HBPI
membranes’ mechanical properties. It is reported, increase
distances among branches and afford more flexibility in rela-
tively rigid branched structure could augment a number of
chain physical entanglements, result in a enhanced mechani-
cal properties.30 However, as far as we know, there was no
triamine with relatively long chain used in polyimide
synthesis.
ꢀ
terns were taken from 2 to 80 (2h value) with Cu Ka radia-
tion (k 5 1.5406 Å, operating at 35 kV and 25 mA). Solubility
was determined qualitatively by placing 5 mg of polymer into
ꢀ
1 mL of solvent at room temperature or heating to 60 C. Dif-
ferential scanning calorimetry (DSC) thermograms were
obtained on a Perkin-Elmer DSC-7 differential scanning calo-
rimeter, samples were performed under nitrogen atmosphere
ꢀ
by raising the temperature from 100 to 400 C at a rate of 10
ꢀC min21. Dynamic mechanical analysis (DMA) was per-
formed (TA Instruments DMA Q 800) under the following
conditions: temperature range of 50ꢀ to about 260 ꢀC, fre-
quency of 1 Hz, and heating rate of 3 C min21. Thermogravi-
metric analysis (TGA) of the polyimide was performed under
nitrogen atmosphere from room temperature to 800 ꢀC at a
heating rate of 10 ꢀC min21 using a Perkin-Elmer TGA-7 ther-
mogravimetric analyzer. The tensile tests were performed on
an electronic universal testing machine (Shenzhen Sans test-
Taking all these into account, a novel pyridine-containing tri-
amine 2,4,6-tris[3-(4-aminophenoxy)phenyl]pyridine (TAPP)
with prolonged chain segments, ether linkage and meta-
linked units was synthesized as a BB02-like monomer for the
preparation of HBPIs, aiming to make HBPIs not only inherit
the excellent thermal properties, but also exhibit high solu-
bility and good mechanical properties. We suppose to obtain
a matrix of composite biomaterial with those superior prop-
erties and a large number of terminal functional groups.
ꢀ
ing machine, China) at 25 C with a drawing speed of 5 mm
min21. Water uptake (WU) was measured by immersing com-
pletely dried HBPI film samples into deionized water at room
temperature for 24 h, then the samples were taken out,
wiped with tissue paper, and quickly weighted on a microba-
lance to calculate WU, using the following equation:
EXPERIMENTAL
Materials
3-Hydroxyacetophenone (98%), p-chloronitrobenzene (98%),
3-hydroxybenzaldehyde (AR), palladium on activated carbon
(Pd/C, 5%), N-methyl-2-pyrrolidone (NMP, HPLC grade) and
Isoquinoline (97%) were purchased from Aladdin Reagent
Inc. (Shanghai, China), which were used as received. 4,40-oxy-
diphthalic dianhydride (ODPA) and 2,2-bis[4-(3,4-dicarboxy-
Ws2Wd
WU5
3100%
Wd
phenoxy)phenyl]propane
dianhydride
(BPADA)
were
where Ws and Wd are the weights of swollen and dry mem-
purchased from Shanghai Research Institute of Synthetic Res-
ins (Shanghai, China), 3,30,4,40-benzophenonetetracarboxylic
dianhydride (BTDA) was purchased from Alfa Aesar, these ar-
omatic tetracarboxylic dianhydrides were all recrystallized
brane, respectively.
Monomer Synthesis
Synthesis of 3-(4-Nitrophenoxy)acetophenone (m,p-NPAP)
In a 250-mL three-necked round bottom flask equipped with a
nitrogen inlet, 13.62 g (0.1 mol) of 3-hydroxyacetophenone
and 17.28 g (0.125 mol) of anhydrous potassium carbonate
were suspended in a mixture oꢀf 100 mL of dry DMF. The mix-
ture was then refluxed at 120 C. After it was stirred for 3 h,
15.76 g (0.1 mol) of p-chloronitrobenzene was added when
the mixture waꢀs cooled to 60 ꢀC. The mixture was then
refluxed at 120 C and kept for 12 h. After the reaction mix-
ture was cooled to room temperature, it was poured into 800
mL of ethanol /water (volume ratio 1/9) to give brown precip-
itates. Filtrating and washing with water, the product was
recrystallized from ethanol to afford 23.85 g of brown powder
ꢀ
from acetic anhydride and then dried in vacuo at 100 C for
12 h before use. N,N-dimethylformamide (DMF) was purified
by distillation under reduced pressure over calcium hydride
and was stored over 4-Å molecular sieves. Analytical-grade
potassium carbonate was dried in vacuo at 120 ꢀC for 12 h
before use. All other solvents were obtained from various
commercial sources and used without further purification.
Characterization
Fourier transform infrared (FTIR) spectrometer (Spectrum
One, Perkin-Elmer) was used to identify the structure of the
monomers and polymers. Solid samples were coated on KBr
1
disks. The H NMR and 13C NMR analysis were conducted on
ꢀ
m,p-NPAP. Yield: 92.7%. Melting point: 104.1 C (by DSC at a
scan rate of 10 C/min). FTIR (KBr, cm21): 3108, 3071 (aro-
ꢀ
a Varian INOVA-600 spectrometer at 600 MHz and 150 MHz.
DMSO-d6 was used as solvent and tetramethylsilane as inter-
nal reference. Elemental analysis was carried out on a Vario
matic CAH), 1687 (C@O), 1433 (CAH of ACH3), 1361 (ACH3
of ACOCH3), 1346 (ANO2), 1242 (CAOAC), 850 (CAN).
2426
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
1H NMR (600 MHz, DMSO-d6, d, ppm): 8.23 (d, J 5 9.0 Hz,
2H, H2), 7.85 (d, J 5 7.8 Hz, 1H, H8), 7.66 (s, 1H, H10), 7.62
(t, J 5 7.8 Hz, 1H, H7), 7.45 (d, J 5 7.8 Hz, 1bvH, H6), 7.14 (d,
J 5 9.0 Hz, 2H, H3), 2.56 (s, 3H, ACH3). 13C NMR (150 MHz,
DMSO-d6, d, ppm): 196.94 (C11), 162.21 (C4), 154.62 (C5),
142.53 (C1), 138.99 (C9), 130.83 (C7), 126.05 (C2), 125.04
(C6), 124.86 (C8), 119.32 (C10), 117.65 (C3), 26.68 (C12).
Elemental analysis: calculated for C14H11NO4: C, 65.37; H,
4.31; N, 5.44; Found: C, 65.12; H, 4.38; N, 5.45.
8.19 (s, 2H, H19), 8.08 (s, 2H, H8, H10), 7.63–7.67 (m, 3H,
H7, H16), 7.29–7.33 (m, 3H, H6, H17), 7.17–7.19 (m, 6H, H3,
H21). 13C NMR (150 MHz, DMSO-d6, d, ppm): 163.59 (C4,
C20), 156.03 (C13), 155.34 (C5, C18), 149.22 (C11), 142.84
(C1, C23), 141.70 (C14), 140.41 (C9), 131.80 (C7), 131.55
(C16), 126.86 (C2), 126.90 (C22), 125.43 (C8), 124.83 (C15),
122.24 (C6), 122.10 (C17), 120.62 (C10), 119.73 (C12),
118.04 (C19), 117.90 (C21), 117.79 (C3). Elemental analysis:
calculated for C41H26N4O9: C, 68.52; H, 3.65; N, 7.80; Found:
C, 68.01; H, 3.54; N, 7.67.
Synthesis of 4-[3-hydroxyphenyl]-2,6-bis
[3-(4-nitrophenoxy)phenyl]pyridine (m,p-HNPP)
Synthesis of TAPP
12.86 g (0.05 mol) of m,p-NPAP, 3.05 g (0.025 mol) of 3-
Hydroxybenzaldehyde, 25.05 g (0.325 mol) of ammonium ac-
etate, and 40 mL of glacial acetic acid were placed into a
150-mL three-necked flask equipped with a magnetic force
stirrer and a reflux condenser. The mixture was refluxed
with stirring for 7 h. After the reaction mixture was cooled
to room temperature. Precipitate was collected by filtration,
washed with water, and dried. The light yellow powder m,p-
HNPP was obtained after the precipitate purified by recrys-
tallizatꢀion in ethanol (4.06 g). Yield: 54.3%. Melting point:
To a 250-mL three-necked flask equipped with a dropping
funnel and a reflux condenser, 7.19 g (0.01 mol) of TNPP,
0.6 g of palladium on activated carbon (Pd/C, 5%) and 100
mL of anhydrous ethanol were added. After heating to reflux-
ing temperature with stirring, 20 mL of hydrazine monohy-
drate was added dropwise for 2 h. Then the mixture was
refluxed for an additional 12 h. Afterwards the mixture was
filtered and the filtrate was subsequently poured into 600
mL of water to produce a solid precipitate, which was col-
lected by filtration, washed with water, and dried to get 5.88
g of white powder TAPP. Yieldꢀ: 93.5%. Melting point: 82.4
ꢀC (by DSC at a scan rate of 10 C min21). FTIR (KBr, cm21):
3432, 3359 (NAH), 3214 (ArANH2), 3062, 3039 (aromatic
CAH), 1547 (C@N), 1258 (CAOAC).
205.1 C (by DSC at a scan rate of 10 C min21). FTIR (KBr,
ꢀ
cm21): 3106, 3070 (aromatic CAH), 1548 (C@N), 1346
(ANO2), 1242 (CAOAC), 855 (CAN).
1H NMR (600 MHz, DMSO-d6, d, ppm): 9.68 (s, 1H, AOH),
8.23–8.28 (m, 8H, H8, H11, H18), 8.18 (s, 2H, H15), 7.65 (t,
J 5 7.8 Hz, 2H, H12), 7.47 (d, J 5 7.8 Hz, 1H, H4), 7.41 (s, 1H,
H6), 7.36 (t, J 5 7.8 Hz, 1H, H3), 7.30 (d, J 5 7.8 Hz, 2H,
H13), 7.19 (d, J 5 9.0 Hz, 4H, H17), 6.94 (d, J 5 7.8 Hz, 1H,
H2). 13C NMR (150 MHz, DMSO-d6, d, ppm): 162.75 (C16),
157.84 (C1), 155.12 (C14), 154.68 (C9), 150.01 (C7), 142.16
(C19), 141.08 (C10), 138.67 (C5), 130.70 (C12), 129.87 (C3),
125.98 (C18), 123.87 (C11), 121.07 (C8), 118.79 (C15),
118.03 (C4), 117.22 (C13, C17), 116.22 (C2), 114.12 (C6).
Elemental analysis: calculated for C35H23N3O7: C, 70.35; H,
3.88; N, 7.03; Found: C, 69.72; H, 4.02; N, 6.89.
1H NMR (600 MHz, DMSO-d6, d, ppm): 8.08 (s, 2H, H8),
7.83–7.87 (m, 4H, H10, H11), 7.59–7.63 (m, 2H, H6, H7),
7.41 (s, 3H, H4, H9), 6.80–6.88 (m, 9H, H3, H5, H12, H13),
6.58 (s, 6H, H2, H14), 4.98 (s, 6H, H1, H15). 13C NMR (150
MHz, DMSO-d6, d, ppm): 160.20 (C5), 160.11 (C18), 156.46
(C13), 149.94 (C11), 146.26 (C20), 146.24 (C4), 146.20
(C21), 146.17 (C1), 141.01 (C14), 140.07 (C9), 130.99 (C7),
130.66 (C16), 121.59 (C3, C21), 121.51 (C15), 121.15 (C8),
117.72 (C17), 117.61 (C6), 117.41 (C12), 116.86 (C10),
116.01 (C19), 115.56 (C2, C22). Elemental analysis: calcu-
lated for C41H32N4O3: C, 78.32; H, 5.13; N, 8.91; Found: C,
77.82; H, 5.35; N, 8.91.
Synthesis of 2,4,6-Tris[3-(4-nitrophenoxy)phenyl]pyridine
(TNPP)
Preparation of Model Compounds
Synthesis of Model Compounds 1
TAPP (0.314 g, 0.5 mmol) was dissolved in 5 mL of NMP in
a three-necked flask with stirring and a reflux condenser
In a 100-mL three-necked round bottom flask equipped with a
nitrogen inlet, 5.98 g (0.01 mol) of m,p-HNPP and 1.73 g
(0.0125 mol) of anhydrous potassium carbonate were sus-
pended in a mixture of 25 mL of DMF. The mixture was then
refluxed at 120 ꢀC. After it was stirred for 3 h, 1.58 g (0.01
mol) of p-chloronitrobenzene was added when the mixture
under
a nitrogen atmosphere. A solution of 0.074 g
(0.5 mmol) of phthalic anhydride in 5 mL of NMP was added
dropwise through a dropping funnel over 1 h. After the addi-
tion, the reaction was further conducted for 5 h at room
temperature. Then, the mixture was heated at 180 ꢀC for
10 h. After cooling to room temperature, the solution was
precipitated from water. The precipitate was washed with
ethanol, and dried to give a gray powder.
ꢀ
ꢀ
was cooled to 60 C. The mixture was then refluxed at 120 C
and kept for 12 h. After the reaction mixture was cooled to
room temperature, it was poured into 500 mL of ethanol /
water (volume ratio 1/9) to give light yellow precipitates. Fil-
trating and washing with water, the product was recrystallized
from ethanol to afford 6.74 g of light yellow powder TNPP.
ꢀ
Synthesis of Model Compounds 2
Yield: 93.8%. Melting point: 218.3 C (by DSC at a scan rate of
10 C min21). FTIR (KBr, cm21): 3109, 3074 (aromatic CAH),
ꢀ
To a 100-mL three-necked flask equipped with a dropping
funnel and a reflux condenser, 0.314 g (0.5 mmol) of TAPP
was dissolved and magnetically stirred in 5 mL of NMP
under a nitrogen flow. A solution of 0.148 g (1 mmol) of
phthalic anhydride in 5 mL of NMP was added dropwise
1549 (C@N), 1346 (ANO2), 1242 (CAOAC), 845 (CAN).
1H NMR (600 MHz, DMSO-d6, d, ppm): 8.36 (s, 2H, H12),
8.30 (d, J 5 7.8 Hz, 2H, H3), 8.24–8.27 (m, 6H, H15, H22),
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437
2427

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
through a dropping funnel over 1 h. After the addition, the
reaction was further conducted for 5 h at room temperature.
Then, the mixture was heated at 180 C for 10 h. After cool-
ing to room temperature, the solution was precipitated from
water. The precipitate was washed with ethanol, and dried
to give a light gray powder.
polymer solutions were poured into an excess of ethanol.
The polymers were separated by filtration and washed with
ethanol for several times then dried under vacuum oven at
ꢀ
ꢀ
100 C for 24 h.
Synthesis of Anhydride-terminated HBPIs
The general polymerization procedure is outlined in
Scheme
2 and illustrated as follow. To a solution of
Synthesis of Model Compound 3
2.0 mmol dianhydride in 20 mL of NMP in a 100-mL flask,
1 mmol of TAPP dissolved in 10 mL of NMP was added
dropwise through a dropping funnel over 1 h. The mixture
was stirred at room temperature for 24 h to afford anhy-
dride-terminated hyperbranched poly(amic acid) (HBPAA)
solution. The anhydride-terminated HBPAA was subsequently
converted to HBPI through a chemical imidization process.
The chemical imidization was carried out via the addition of
1 g of pyridine and 3 g of acetic anhydride into the PAA so-
A
mixture of 0.314 g (0.5 mmol) of TAPP, 0.259 g
(1.75 mmol) of phthalic anhydride, and 10 mL of NMP was
magnetically stirred under a nitrogen flow in a 100-mL
three-necked flask at room temperature for 5 h. Subse-
quently, the mixture was heated at 180 ꢀC for 10 h. After
cooling to room temperature, the solution was precipitated
from water. The precipitate was washed with ethanol, and
dried to give a light purple powder.
ꢀ
ꢀ
lution, stirred at 60 C for 6 h and 80 C for 2 h. The result-
ing anhydride-terminated HBPI (AD-HBPI) solution was
poured into acetone to give a precipitate, which was col-
lected by filtration, washed thoroughly with acetone and
Polymer Synthesis
Synthesis of Amino-terminated HBPIs
The general one-step polycondensation procedure for the
preparation of the amino-terminated HBPIs (AM-HBPIs) AM-
1–AM-3 (Scheme 2) is illustrated as follow. TAPP
(2.0 mmol) was first dissolved in 20 mL of NMP in a 100-
mL three-necked round-bottomed flask under nitrogen flow.
To the mixture was added dropwise a solution of dianhy-
dride monomer (2.0 mmol) in NMP (20 mL) through a drop-
ping funnel with a duration of 1 h under magnetic stirring at
room temperature. After the mixture was stirred for 30 min,
isoquinoline (ca., eight drops) was added, and further stirred
for 3 h at 120 ꢀC. Then the mixture was heated at 180 ꢀC
for 24 h. Water formed during the imidization was continu-
ously removed with a stream of nitrogen. The whole poly-
merization proceeded smoothly, and homogeneous,
transparent, viscous polymer solutions were produced. Fi-
brous polymer resins were obtained when the resultant
ꢀ
dried under vacuum at 100 C for 24 h.
Film Preparation
HBPI films were obtained by casting the corresponding
HBPAA solution on glass plate followed by the thermal cur-
ing in foꢀllowing procedure: 100 ꢀC for 8 h, 150, 200, 250,
and 300 C for 1 h at each temperature in air.
RESULT AND DISCUSSION
Monomer Synthesis
As shown in Scheme 1, the novel BB02-like triamine mono-
mer TAPP was obtained through a four-step synthetic route.
First, the nucleophilic substitution reaction of 3-hydroxyace-
tophenone with p-chloronitrobenzene in the presence of
SCHEME 1 Synthesis of the triamine monomer TAPP.
2428
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
NPAP. The m,p-HNPP was subsequently reacted with p-
chloronitrobenzene in the presence of potassium carbonate
gave the trinitro compound TNPP. Finally, the novel triamine
monomer TAPP was obtained in a high yield by the reduc-
tion of TNPP using hydrazine monohydrate catalyzed by
Pd/C. The new aromatic triamine monomer is stable in
atmosphere at room temperature and pure enough for po-
lymerization with commercial aromatic dianhydride mono-
mers to prepare polyimides. The detail characterizations
on the triamine monomer TAPP were done by FTIR
(Fig. 1), 1H NMR techniques (Fig. 2), 13C NMR techniques
(Fig. 3), and elemental analyses, which support unambigu-
ously the structure shown in Scheme 1. The analytical
data of TAPP and the intermediate compounds m,p-NPAP,
m,p-HNPP, and TNPP were given in experimental section.
The results indicate that the design and synthesis of novel
triamine monomer TAPP should be successful and feasible
in this work.
FIGURE 1 FTIR spectra of m,p-NPAP, m,p-HNPP, TNPP and
TAPP.
potassium carbonate gave the intermediate compound
m,p-NPAP. Then, the dinitro compound m,p-HNPP was pre-
pared via a modified Chichibabin reaction, which is one of
the best methods among the several ones for the preparation
of a pyridine ring, from 3-hydroxybenzaldehyde and m,p-
Polymer Synthesis and Characterization
Several commercial aromatic dianhydrides (ODPA, BTDA, and
BPADA) were used as A2-type monomer to react with the
novel BB02-like aromatic triamine (TAPP), as shown in
Scheme 2. The synthesis route was similar to the
FIGURE 2 1H NMR spectrum of TAPP.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437
2429

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 3 13C NMR spectrum of TAPP.
SCHEME 2 Synthesis of novel HBPIs.
2430
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
SCHEME 3 Chemical structure of the HBPI.
conventional polymerization method for the synthesis of lin-
ear polyimides. However, with a different monomer addition
order and monomer molar ratios resulted in different hyper-
branched polymers. The addition of dianhydride into tria-
mine TAPP with a monomer molar ratio of 1:1 (the molar
ratio between the amino and anhydride groups in the mono-
mers was 3:2) yielded the AM-HBPI, while the reverse
monomer addition order with the molar ratio of 2:1 (the
molar ratio between the anhydride and amino groups in the
monomers was 4:3) gave the AD-HBPI. In each case, the
monomer should be added slowly to avoid any high local
concentration.
the band around 1850 cm21 is attributed to the stretching
of C@O of terminal anhydride groups in AD-3. These results
indicated that the HBPIs were obtained and well imidized.
The structural perfection of hyperbranched polymers is gen-
erally characterized by the degree of branching (DB), which
was defined by Frechet as follows:31
DB 5ðD1TÞ=ðD1T1LÞ
where D, T, and L refer to the numbers of dendritic, terminal
and linear units in the polymer, respectively. Experimentally,
DB is usually determined from 1H NMR and 13C NMR spec-
troscopy by comparing the integration of the peaks for the
Different imidization methods were employed for these
HBPAA precursors to protect the terminal functional groups.
The amine-terminated HBPAA s were thermally imidized in
solution at 180 ꢀC for 24 h, while the anhydride-terminated
ones were chemically converted into HBPIs using the mix-
ture of excess acetic anhydride and pyridine. Chemical struc-
tures of the HBPIs were shown in Scheme 3.
The formations of HBPIs were confirmed by FTIR spectros-
copy. Figure 4 shows the representative FTIR spectra of
amino- and anhydride-terminated HBPAA s and HBPIs, which
based on BPADA and TAPP. The complete conversion of amic
acid to imide ring was proved by the disappearance of
absorption bands at 1714 cm21 corresponding to C@O
stretching of carboxylic acid and 1660 cm21 corresponding
to C@O amide stretching, together with the appearance of
absorption bands at about 1778 cm21 (asymmetrical C@O
stretching), 1722 cm21 (symmetrical C@O stretching), 1378
cm21 (CAN stretching), and 744 cm21 (C@O bending) corre-
sponding to the characteristic of imide bands. In addition,
the bands around 3455 and 3373 cm21 are attributed to the
stretching of NAH of terminal amine groups in AM-3, while
FIGURE 4 FTIR spectra of BPADA-based hyperbranched PAAs
and HBPIs: (a) amino-terminated PAA, (b) anhydride-terminated
PAA, (c) amino-terminated AM-3, (d) anhydride-terminated AD-3.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437
2431

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 4 Synthesis of the model compounds.
respective units in the hyperbranched polymers. Therefore,
we tried to synthesize model compounds as stated in experi-
mental section and as shown in Scheme 4. But, the model
compounds of monoimides, diimides, and triimide were not
easy to get separately due to their multiple isomers as
shown in Scheme 5. Furthermore, because of the prolonged
chain segments that the triamine has which weaken the
chemical shifts, we cannot get terminal and linear units’
peaks separated, therefore, cannot determine the branched
structure quantitatively by using traditional method. So, 1H
NMR spectroscopy of model compounds was conducted to
give a qualitative analysis of HBPIs’ DB. Figure 5 shows the
1H NMR spectra of the compounds 1, compounds 2, com-
pound 3, AM-1 and AD-1 in DMSO-d6. The TAPP residues in
2432
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
SCHEME 5 Possible structures of TAPP in the novel HBPIs.
model compounds 1, 2, and 3 are basically same as the
counterparts in terminal, linear and dendritic units of the
HBPI, respectively. For AM-HBPIs, it is impossible to deter-
Some experimental data of the HBPIs have been summar-
ized in Table 1. According to the data from Table 1, all
resulting HBPIs got high yields (95.3–98.2%), the inherent
viscosity ([g]) values of amine- and AD-HBPIs in NMP (0.8
1
mine the DB by H NMR because the peaks of L and T were
always in the same range as shown in Figure 5. For AD-
HBPIs, the representative 1H NMR spectrum of AD-1 which
based on ODPA and TAPP was shown. There were no peaks
in the range of 6.51–6.95 ppm which were assignable to the
terminal and linear units (i.e., TAPP residues were com-
pletely “dendritic”). Furthermore, there was also no free
amine peak appearing around 4.98 ppm confirming that the
amino groups were all reacted with anhydride groups of
ODPA, the AD-1 should have the “completely branched”
structure (DB 5 1). In addition, the spectra of HBPIs showed
no acid protons, confirming full imidization.
g dL21 were in the range of 0.35–0.61 dL g21
) . The
weight-average molecular weight (Mw) of AM-3 and AD-3
based on BPADA and TAPP were 92,000 and 32,000,
respectively. The real molecular weight of the polymer
may be even larger than the value estimated by GPC
because dendritic macromolecules generally have smaller
size than linear polymers with the same molecular weight
and can hardly be expanded in solution. The Mw value of
the AM-3 was larger than the AD-3’s, this is mainly
because of the different imidization methods. One-step
polycondensation which employed for AM-3, could provide
enough energy to promote the polymerization reaction
result in giving high molecular weight polyimides.
Polymer Condensed Structures
Morphological information of the HBPIs were obtained by
XRD studies. In most cases, the degree of crystallinity of the
PI depended on the imidization methods. In general, the
chemical imidization method can yield a material with a
higher degree of crystallinity than that obtained from the
thermal imidization method. This implies that imidization of
the PAA in solution may allow it to obtain a more favorable
conformation for packing.32 The XRD patterns of the HBPIs
prepared in solutions via one-step polycondensation proce-
dure or chemical imidization route were shown in Figure 6.
Two small diffraction peaks around 9ꢀ were observed for
AM-2 and AD-2, which were both derived from dianhydride
BTDA. These two diffraction peaks indicated ordered struc-
tures were formed for synthesized AM-2 and AD-2. No dis-
cernible peaks were observed in the rest of the XRD signals,
which revealed their amorphous character. The polymer
backbones with flexible ether link and meta-linked structure
FIGURE 5 1H NMR spectra of model compounds and ODPA-
based HBPI: (a) model compounds 1, (b) model compounds 2,
(c) model compound 3, (d) AM-1, (e) AD-1.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437
2433

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 1 Yield, Intrinsic Viscosity, Weight-Average Molecular
Weight, PDI, and DB of the HBPIs
Yield
(%)
[g]
b
Polymer
(dL g21 a
)
Mw
PDI
DBd
c
AM-1
AM-2
AM-3
AD-1
AD-2
AD-3
a
95.3
97.5
97.2
96.8
96.1
98.2
0.58
0.61
0.57
0.35
0.40
0.37
–
–
–
–
–
-
–
92,000
1.31
–
–
1
1
1
–
–
32,000
1.62
Intrinsic viscosity.
b
The Weight-average molecular weight (Mw) and polydispersity index
(PDI) were measured by GPC using THF solution.
Not measured for insoluble in THF.
c
d
Degree of branching.
FIGURE 6 XRD patterns of HBPIs.
would increase the disorder of the polymer chains, resulting
in decreasing of the chain to chain interactions and reducing
of chain packaging efficiency to hinder the polymer crystalli-
zation. In general, amorphous polymers have a lower soften-
ing temperature and improved solubility with respect to
their crystalline analogues. Therefore, the amorphous nature
of the resulting HBPIs would endow them a good solubility
and they could be solution-cast into flexible and tough films.
ities. To ODPA-based polymers, AM-1 and AD-1 could easily
dissolve in many high-boiling-point solvents. Polymers AM-3
and AD-3 derived from BPADA dissolved instantly in polar
aprotic solvents such as NMP, N,N-dimethylacetamide, DMF,
dimethyl sulfoxide (DMSO), protic solvents such as m-cresol,
cyclic ethers such as THF or even in chlorinated solvents
such as dichloromethane and chloroform at room tempera-
ture. The improvement in solubility might be resulted from
the flexible ether or ester linkage in the polyimide backbone
combined with the meta-linked unit coming from the tria-
mine monomer. These effects would hinder intermolecular
packing and increase the free volume, solubility is thus
improved accordingly. Also, the incorporation of pyridine
ring and the amorphous character of the polyimides can
increase their solubility.19 Presence of nitrogen atom in the
structure produces a polarized bond which increased dipole-
dipole interactions in the polymer-solvent system.
Polymer Solubility
The solubilities of the resulting HBPIs were investigated in
different organic solvents by dissolving 5 mg of polymers in
ꢀ
1 mL of solvent at room temperature or heating to 60 C, as
shown in Table 2. It is well known that aromatic polyimides,
especially those derived from rigid dianhydride show very
poor solubility in common organic solvents. However, BTDA-
based polymers (AM-2, AD-2) had a keto group in BTDA
segment still showed poorer solubility than those derived
from other dianhydrides. The low solubility of AM-2 and
AD-2 may be due to the partially ordered structure that
exists in the amorphous polyimide as shown by the weak
wide-angle XRD peaks. With the increased ratio of flexible
linkage into the main chain, HBPIs showed improved solubil-
Polymer Thermal Properties
The thermal properties of the PIs were evaluated by means
of DSC, DMA, and TGA. The results are summarized in
Table 3.
TABLE 2 Solubility Behavior of the HBPIsa
Organic Solventsb
NMP
DMF
11
DMAc
Py
DMSO
m-Cresol
THF
CHCl3
CH2Cl2
Polymer
AM-1
11
11
11
11
11
11
11
11
11
11
–
–
–
AM-2
AM-3
AD-1
AD-2
AD-3
a
1(11)
11
1(11)
11
1(1)
11
1(1)
11
1(1)
11
–
–
–
11
–
11
–
11
–
11
11
11
11
1(11)
1(1)
11
1(1)
11
1(1)
11
1(1)
11
1(1)
11
–
–
–
11
11
11
11: soluble at room temperature; 1: partially soluble in room temperature; (): on heating; –: insoluble even on heating.
NMP, N-methyl-2-pyrrolidone; DMF, N,N-dimethylformamide; DMAc, N,N-dimethylacetamide; Py, pyridine; DMSO, dimethyl sulfoxide; THF,
b
tetrahydrofuran.
2434
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
TABLE 3 Thermal Properties of the HBPIs
Tg (ꢀC)a
Polymer
DSC
DMA
T5 (ꢀC)b
T10 (ꢀC)b
Rw (%)b
AM-1
AM-2
AM-3
AD-1
AD-2
AD-3
a
245.3
258.5
231.7
251.8
273.5
219.3
245.6
254.1
222.3
250.2
269.7
213.8
534.9
525.8
511.3
533.8
515.3
516.1
565.8
566.1
532.2
574.7
561.9
537.1
63.8
69.9
58.6
60.4
64.3
53.5
Glass transition temperature.
b
T5 and T10, temperature at 5% or 10% weight loss in nitrogen; Rw
,
residual weight at 800ꢀC in nitrogen.
The heat resistance, glass transition temperatures (Tgs), of the
resulting HBPIs were investigated by DSC at a heating rate of
21
ꢀ
10 C min in N2 atmosphere and DMA at a heating rate of 3
ꢀC min21 frequency of 1 Hz in air. As obtained by DSC, For
AM-HBPIs, AM-2 has relatively higher Tg value of 258.5 ꢀC
than AM-1 (245.3 ꢀC) and AM-3 (231.7 ꢀC). The increasing
order of Tg generally correlated with the structure of the dia-
nhydride component. As expected, the AM-3 derived from dia-
nhydride BPADA showed the lowest Tg value due to the
increase in flexibility of polymer chain determined by the ether
linkage between the phenyl rings, whereas the AM-2 obtained
from dianhydride BTDA had the highest Tg value because of
the ordered structure that confirmed by XRD pattern. Same as
ꢀ
the AM-HBPIs, AD-2 has ꢀthe highest Tg value of 273.5 C, fol-
ꢀ
lowed by AD-1 of 251.8 C and AD-3 of 219.3 C. The Tg val-
FIGURE 7 DMA curves of HBPIs (1 Hz, 3 ꢀC min21): (a) AM-
ues of HBPIs were all above 219 ꢀC which were higher than
HBPIs, (b) AD-HBPIs.
ꢀ
that of commercial polyimide, Ultem 1000 (Tg, 217 C), based
on bisphenol-A diphthalic anhydride and m-phenylene diamine.
and conformation of polymer main chain. Thus, the higher
residual weights of AM-2 and AD-2 can attributed to the ri-
gidity of BTDA moiety and their ordered structure.
The decomposition temperatures at 5 and 10% weight loss
In the DMA profiles of obtained HBPI films (Fig. 7), Tgs were
observed in the range of 213.8 to 269.7 ꢀC (regarding the
peak temperature in the tan d curves as the Tg), which are
nearly the same as those obtained by the DSC method. The
slight differences are mainly attributable to the different
responses of the polymers to these two measurements. All
the HBPI films had high storage modulus (2.28–2.78 GPa) at
50 ꢀC as shown in Figure 7, and the value order corre-
sponded to the tensile modulus: AM-3 < AD-3 < AM-1 < AD-
1 < AM-2 < AD-2. The films also retained high modulus at
very high temperatures.
Thermal stabilities of the HBPIs were evaluated by TGA
21
ꢀ
method at a heating rate of 10 C min from room temper-
ature to 800 ꢀC under N2 atmosphere. Their curves were
shown in Figure 8 and all thermal analysis data were sum-
marized in Table 3. As shown in Figure 8, all the HBPIs
exhibited good thermal stability with insignificant weight
loss up to 500 ꢀC in nitrogen. This is mainly because of the
combination of high temperature resistant imide units. Inter-
estingly, the variation trend of their residual weights at
800 ꢀC (Rw) is similar as that Tg values observed by DSC
measurement. That is, the Rw correlated with the stiffness
FIGURE 8 TG curves of the HBPIs.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437
2435

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 4 Mechanical Properties and Water Uptake of the HBPI
properties but also exhibit high solubility and good mechani-
cal properties. It is favorable for us to conduct further
research with those superior properties.
Films
Tensile
Strength
(MPa)
Tensile
Modulus
(GPa)
Elongation
Water
Polymer
at Break (%)
Uptake (%)
ACKNOWLEDGMENTS
AM-1
AM-2
AM-3
AD-1
AD-2
AD-3
92.1
95.8
83.3
90.8
95.0
84.4
2.04
2.38
1.82
2.09
2.43
1.89
5.91
5.08
6.98
5.60
4.84
6.62
0.68
0.88
0.74
0.91
0.94
0.51
The research was financially supported by the Natural Science
Foundation of Hubei Province (No. 2008CDB276), Hubei,
China. Authors also acknowledge the Ministry-of-Education
Key Laboratory for the Green Preparation and Application of
Functional Materials for providing necessary facilities.
REFERENCES AND NOTES
(T5 and T10), which were usually considered as the criterion
factor in determining the thermal stability of high tempera-
ture polymers. As shown in Table 3, the T5 and T10 of the
1 Y. Xiao, B. T. Low, S. S. Hosseini, T. S. Chung, D. R. Paul,
Prog. Polym. Sci. 2009, 34, 561–580.
2 Z. Song, H. Zhan, Y. Zhou, Angew. Chem. Int. Ed. Engl. 2010,
49, 8444–8448.
ꢀ
HBPIs were in the range of 511.3–534.9 C and 532.2–574.7
ꢀC, respectively. Furthermore, the high percentage of residual
weights of HBPIs at 800 ꢀC indicated the intrinsic fire-re-
tardant properties of the polymers. The good thermal stabil-
ity of the resulting novel HBPIs might be caused by the
presence of the rigid, triphenylpyridine heterocyclic units in
the polymers backbone. In addition, all of the AM-HBPIs
showed slightly higher Rw compared with the corresponding
AD-HBPIs, which can be attributed to the different terminal
functional groups.
3 A. Zhang, X. Li, C. Nah, K. Hwang, M. H. Lee, J. Polym. Sci.
Part A: Polym. Chem. 2003, 41, 22–29.
4 Y. S. Negi, S. R. Damkale, S. Ansari, J. Macromol. Sci. Part C
2001, 41, 119–138.
5 C.-J. Chen, H.-J. Yen, W.-C. Chen, G.-S. Liou, J. Polym. Sci.
Part A: Polym. Chem. 2011, 49, 3709–3718.
6 Y.-S. Ye, Y.-J. Huang, C.-C. Cheng, F.-C. Chang, Chem. Com-
mun. 2010, 46, 7554–7556.
7 W. Chen, W. Yan, S. Wu, Z. Xu, K. W. K. Yeung, C. Yi, Macro-
mol. Chem. Phys. 2010, 211, 1803–1813.
Polymer Mechanical Properties and WU
8 D.-J. Liaw, K.-L. Wang, Y.-C. Huang, K.-R. Lee, J.-Y. Lai, C.-S.
Ha, Prog. Polym. Sci. 2012, 37, 907–974.
As expected, all the synthesized HBPIs displayed pretty good
film forming abilities. Tough and flexible membranes could
be obtained by casting the NMP solutions of HBPAAs onto
glass plates followed by thermal baking to remove the sol-
vent and subsequent thermal curing. The mechanical proper-
ties of the dry HBPI membranes were listed in Table 4.
Depending on their chemical structure, they show variation
in their tensile strength, tensile modulus and elongation at
break. Film AM-2 and AD-2, based on TAPP and BTDA, indi-
cates their high tensile strength and modulus, but they are
less flexible than other films. Containing the maximum ratio
of flexible chain segments, AM-3 and AD-3 were shown
greater breaking elongation. It presumed that the molecular
chains of AM-3 and AD-3 can glide easily when they were
drafted at room temperature. Overall, the HBPI films possess
tensile strength of 83.3–95.8 MPa, tensile modulus of 1.82–
2.43 GPa, and elongation at break of 4.84–6.98%, which indi-
cate that they were strong and tough polymeric materials.
Meanwhile, the HBPI films were also exhibited low WU of
0.51–0.94%.
9 C. H. Lin, S. L. Chang, P. W. Cheng, J. Polym. Sci. Part A:
Polym. Chem. 2011, 49, 1331–1340.
10 Y. Wang, S. Xu, T. Chen, H. Guo, Q. Liu, B. Ye, Z. Zhang, Z.
He, S. Cao, Polym. Chem. 2010, 1, 1048–1055.
11 E. Schab-Balcerzak, D. SeRk, A. Volozhin, T. Chamenko, B.
Jarza˛bek, Eur. Polym. J. 2002, 38, 423–430.
12 C. P. Yang, R. S. Chen, Colloid Polym. Sci. 2001, 279, 736–
744.
13 Y. Liu, Y. Xing, Y. Zhang, S. Guan, H. Zhang, Y. Wang, Y.
Wang, Z. Jiang, J. Polym. Sci. Part A: Polym. Chem. 2010, 48,
3281–3289.
14 W. Jang, H.-S. Lee, S. Lee, S. Choi, D. Shin, H. Han, Mater.
Chem. Phys. 2007, 104, 342–349.
15 J. Shen, Y. Zhang, M. Huang, W. Wang, Z. Xu, K. Yeung, C.
Yi, M. Xu, J. Polym. Res. 2012, 19, 1–9.
16 Y. Seo, S. M. Hong, S. S. Hwang, T. S. Park, K. U. Kim, S.
Lee, J. Lee, Polymer 1995, 36, 515–523.
17 C.-P. Yang, S.-H. Hsiao, H.-W. Yang, Macromol. Chem. Phys.
2000, 201, 409–418.
18 M. Hasegawa, D. Hirano, M. Fujii, M. Haga, E. Takezawa, S.
Yamaguchi, A. Ishikawa, T. Kagayama, J. Polym. Sci. Part A:
Polym. Chem. 2013, 51, 575–592.
CONCLUSIONS
A novel pyridine-containing triamine TAPP with prolonged
chain segments, ether linkage and meta-linked units was
synthesized and employed to prepare a series of amine- and
AD-HBPIs. The structure of the triamine monomer and HBPIs
were verified by FTIR, 1H NMR and 13C NMR spectroscopy.
As expected, the HBPIs not only inherit the excellent thermal
19 S. Mehdipour-Ataei; N. Bahri-Laleh, Iran. Polym. J. 2008, 17,
95–124.
20 D.-J. Liaw, K.-L. Wang, F.-C. Chang, Macromolecules 2007,
40, 3568–3574.
21 K.-L. Wang, W.-T. Liou, D.-J. Liaw, S.-T. Huang, Polymer
2008, 49, 1538–1546.
2436
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
22 R. S. Tewari, N. K. Misra, A. K. Dubey, J. Heterocycl. Chem.
1980, 17, 953–955.
28 A. Scarpaci, E. Blart, V. R. Montembault, L. Fontaine, V.
Rodriguez, F. Odobel, ACS Appl. Mater. Interfaces 2009, 1,
1799–1806.
23 P. J. Flory, J. Am. Chem. Soc. 1952, 74, 2718–2723.
29 T. Itoh, S. Gotoh, T. Uno, M. Kubo, J. Power Sources 2007,
174, 1167–1171.
24 T. Suda, K. Yamazaki, H. Kawakami, J. Power Sources 2010,
195, 4641–4646.
ꢀꢁꢀ
30 J. Peter, A. Khalyavina, J. Krız, M. Bleha, Eur. Polym. J.
25 H. Gao, C. Yan, S. Guan, Z. Jiang, Polymer 2010, 51, 694–
2009, 45, 1716–1727.
701.
31 C. J. Hawker, R. Lee, J. M. J. Frechet, J. Am. Chem. Soc.
1991, 113, 4583–4588.
26 C. Gao, D. Yan, Prog. Polym. Sci. 2004, 29, 183–275.
27 Y. Liu, Y. Zhang, S. Guan, H. Zhang, X. Yue, Z. Jiang, J.
Polym. Sci. Part A: Polym. Chem. 2009, 47, 6269–6279.
32 W.-T. Leu, S.-H. Hsiao, Eur. Polym. J. 2006, 42, 328–335.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 2425–2437
2437