Synthesis and characterization of hyperbranched polyether imides based on 1,3,5-tris[4-(4′-aminophenoxy)phenoxy]benzene

Article abstract of DOI:10.1039/c5ra26679c

A new triamine monomer 1,3,5-tris[4-(4′-aminophenoxy)phenoxy]benzene, was synthesized by a three step process using hydroquinone, 1-chloro-4-nitrobenzene and 1,3,5-trichlorobenzene. It was successfully polymerized with commercially available dianhydrides [3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA)] into hyperbranched polyimides (HBPIs) by the A₂ + B₃ method. Different monomer addition methods and different monomer molar ratios resulted in hyperbranched polyimides with amino and anhydride end groups. The structure of the resulting hyperbranched polyimides were characterized by FT-IR, ¹H-NMR, ¹³C-NMR and mass spectral analysis. All synthesized HBPIs were soluble in most common organic solvents. They also exhibit good thermal stability. The T_g of the HBPIs is in the range of 230-260 °C and T₁₀ values are above 450 °C. The dielectric constant of the synthesized HBPIs is in the range of 3.08-3.29 at 1 MHz and dielectric loss is in the range of 0.65-0.82 at 1 MHz.

Full text of DOI:10.1039/c5ra26679c

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ARTICLE
Synthesis and characterization of hyperbranched polyether imides
based on 1,3,5-tris[4-(4’-aminophenoxy)phenoxy]benzene
Received 00th January 20xx,
Accepted 00th January 20xx
*
M.Fathima Rigana, P. Thirukumaran, K. Shanthi, M. Sarojadevi
DOI: 10.1039/x0xx00000x
www.rsc.org/
A new triamine monomer 1,3,5-tris[4-(4’-aminophenoxy)phenoxy]benzene, was synthesized by a three step process using
hydroquinone, 1-chloro-4- nitrobenzene and 1,3,5-trichlorobenzene. It was successfully polymerized with commercially
available dianhydrides [3,3’,4,4’-benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA)]
2 3
into hyperbranched polyimides (HBPIs) by A +B method. Different monomer addition methods and different monomer
molar ratios resulted in hyperbranched polyimides with amino and anhydride end groups. The structure of the resulting
1
13
hyperbranched polyimides were characterized by FT-IR, H-NMR, C-NMR and mass spectral analysis. All the synthesized
HBPIs were soluble in most of the common organic solvents. They also exhibit good thermal stability. T of the HBPIs are in
the range of 230-260 C and T10 values are above 450 C. The dielectric constant of the synthesized HBPIs is in the range of
.08–3.29 at 1 MHz and dielectric loss is in the range of 0.65–0.82 at 1 MHz.
g
o
o
3
2 3
Keywords: Hyperbranched poly (etherimides), condensation polymerization, A +B , solubility, thermal and electrical
properties.
and as hyperbranched polymers with imperfectly branched
structure which can be simply prepared through one-step
polymerization. Hyperbranched polymers are thought to have
physical properties similar to those of dendrimers and can be
used as an alternative for dendrimers in various industrial
Introduction
Aromatic polyimides are recognized as an important class of
high performance materials which are used in a wide variety of
applications such as membrane separation, photoresist,
adhesives, matrix materials for composites and Langmuir-
Blodgett (L-B) films owing to their excellent thermal stability,
high chemical resistance, high mechanical strength and
[30-41]
applications
Generally hyperbranched polyimides are synthesized by the
self-condensation of AB (A & B represent two kinds of
.
2
[
1-10]
functional groups) type monomers. Monomer containing one
amine and two anhydride groups or vice-versa seems
unavailable because the reactivity between the functional
groups is too high, and they cannot exist in stable form within
excellent electrical properties
.
Though aromatic
polyimides have many merits, they also have some limitations
such as low solubility and poor processability because of their
[11-16]
rigid backbone
. To overcome this, researchers in this
[
21, 29, 42-44]
a
molecule
hyperbranched polyimides can be synthesized using A
polymerization technique whereas A represents a difunctional
monomer (dianhydride) and B represents a trifunctional
.
To overcome this problem,
field are focusing on the synthesis of novel polyimides that
have good solubility. Introducing flexible linkages (O, S, CO,
SO , and CH ) into the backbone of polyimides improves their
2
+ B
3
2
2
2
[
17-20]
3
solubility
.
monomer (triamine). This type of polymerization reactions
leads to soluble hyperbranched polymers.
Dendritic polymers have unique physical and chemical
properties such as low viscosity and high solubility compared
to their linear analogues because of their highly branched
structure that contains large number of terminal functional
Most of the research works are based on A
2
+ B
polymerization. Fang et al first reported the preparation of
HBPIs by the condensation of a triamine (B ), tris(4-
aminophenyl)amine, and conventional dianhydrides (A ).
3
type of
3
0
[
21-29]
3
groups
. These are mainly classified as dendrimers with
2
well-defined branched structures, which are synthesized by
step wise reactions requiring time consuming purifications,
Unfortunately,
except
for
4,4’-
(
hexafluoroisopropylidene)diphthalic anhydride (6FDA)-based
2
1, 22
polymers, the HBPIs were insoluble. Chen et al
the synthesis of HBPIs from TAPOB (B
available dianhydrides (A ). Recently, Shen et al reported
reported
3
) and commercially
Department of Chemistry, Anna University, Chennai-600025, Tamilnadu, India†
Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
2
0
2
HBPIs with prolonged chain segments and ether linkages. The
synthesized polymers were soluble in most of the common
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o
model using 5–10 mg of the sample at a heating rate of 10 C
organic solvents. Still, it exhibits low solubility in THF, CHCl
and methanol.
3
-1
min in nitrogen atmosphere. Thermogravimetric analysis
In the present study,
a new triamine 1,3,5-tris[4-(4- (TGA) was performed using a TA Q 600 thermal analyzer at a
o
-1
aminophenoxy)phenoxy]benzene
(TAPOPOB)
2
containing heating rate of 20 C min in N atmosphere up to a maximum
o
flexible ether linkages was synthesized. This triamine was used temperature of 800 C. Dielectric constant and dielectric loss
for the preparation of hyperbranched polyimides by reacting measurements were carried out with the help of an
with commercially available dianhydrides BTDA (3,3’,4,4’- impedance analyzer (Solatron 1260 Impedance/Gain-phase
benzophenonetetracarboxylic dianhydride) and PMDA Analyzer, UK) at room temperature. The polymer samples
(pyromellitic dianhydride) using
A
2
+
B
3
method. The were made in the form of pellets (1 mm thickness x 12 mm
synthesized polymers were expected to have good solubility in diameter) using a platinum electrode sandwich model in the
most of the organic solvents without lacking its thermal frequency range of 1 kHz–1 MHz at room temperature. The
properties. The structure of the synthesized triamine and dielectric constant and dielectric loss of the samples were
polyimides were characterized by FT-IR and NMR analysis. The determined using ε′ and ε″ as the standard relations. The
thermal and dielectric properties of the polyimides were inherent viscosities of all polyimides were measured using a
-1
analyzed by DSC, TGA and Impedence analyzer.
0.5 g dl Ubbelohde viscometer. Solubility of the polymers was
determined at a concentration of 5% (w/v) in various organic
solvents. The polymer solvent mixture was kept aside for 24 h
with occasional shaking. If the mixture was insoluble at
ambient temperature, then it was heated and cooled.
Experimental
Materials
Synthesis of 4-(4-nitrophenoxy) phenol [NPOP]
In a 500 mL three necked round bottomed flask fitted with a
Hydroquinone was purchased from Fisher Scientific (a part of reflux condenser, p-chloronitrobenzene (22.1 g, 0.14 mol)
Thermo Fisher Scientific, India Pvt. Ltd.); p-Chloronitrobenzene dissolved in 40 mL of DMF was taken. The solution was
(98%) and 10% Pd/C were purchased from Sisco Research magnetically stirred under nitrogen atmosphere. Potassium
Laboratories, Pvt. Ltd., India. 1,3,5-Trichlorobenzene was carbonate (20 g, 0.14 mol) was added subsequently to the
o
purchased from Alfa Aesar (India), N,N-dimethylformamide
solution, while stirring and heated at 70 C for an hour. Then,
(
DMF) and phthalic anhydride were purchased from E-Merck
hydroquinone (15 g, 0.14 mol) dissolved in DMF was added
dropwise to the solution. After complete addition, the
o
temperature of the mixture was raised to 120 C. The reaction
Limited, India. Analytical-grade Potassium carbonate, N, N-
dimethylacetamide (DMAc), triethylamine, methanol and
ethanol were purchased from Spectrochem, India. BTDA and
PMDA were purchased from Sigma Aldrich, U.S.A. Both were
recrystallized from acetic anhydride and dried in a vacuum
oven at 150 oC overnight prior to use. DMF was purified by
mixture was maintained at this temperature for 12 h then
cooled to room temperature and poured into a beaker
containing 1 L of ice cold water. The yellow precipitate of 4-(4-
stirring with sodium hydroxide, followed by distillation from nitrophenoxy) phenol thus obtained was collected by filtration
phosphorus pentoxide under reduced pressure. Potassium and dried in an air oven. The crude product was recrystallized
carbonate was dried in a vaccum oven at 120 oC for 12 h from ethanol/water (1/1 v/v) to give yellow powder. Yield:
before use. Ethanol was purified by stirring with calcium
carbonate for 12 h, followed by distillation under atmospheric
pressure. All the other chemicals were used as received.
9
3.5%.
FT-IR (KBr, cm ): 3441 (stretching vibrations of the –OH
group), 1345 (stretching vibrations of the -NO group), and
234 (stretching vibrations of the C-O-C group).
-1
2
1
Characterization methods
Fourier transform infrared (FT-IR) spectra of the samples were Synthesis of 1,3,5-tris[4-(4-
obtained using an ABB Bomen (Model MB 3000) spectrometer. nitrophenoxy)phenoxy]benzene [TNPOPOB]
The samples were ground with spectroscopy grade KBr and
1
13
In a 100 mL three necked round bottomed flask fitted with a
reflux condenser, NPOP (23 g, 0.09 mol) dissolved in 10 mL of
DMF was taken and the solution was magnetically stirred
under a nitrogen atmosphere. Potassium carbonate (14 g, 0.09
made into pellets. H (500 mHz) and C (125 mHz) nuclear
magnetic resonance (NMR) spectra were recorded on a Jeol
spectrometer with tetramethylsilane (TMS) as the internal
6
standard. Solutions were prepared in DMSO-d . The molecular
mol) was added subsequently and the mixture was heated at
o
0 C for 2 h. After that 1,3,5-trichlorobenzene (6 g, 0.03
weight of the triamine was analyzed using Agilent 6330 Ion
Trap Mass spectrometer (ESI-MS). Molecular weight of the
polymers was determined by gel permeation chromatography
8
mol)dissolved in 10 mL of DMF was added dropwise. After
complete addition, the mixture was refluxed for 12 h, cooled
to room temperature and poured into a beaker containing 1 L
of ice cold water. The brown precipitate of TNPOPOB thus
obtained was collected by filtration and dried in an air oven for
(
GPC) on a Shimadzu, Lab solution, LC solution versin 1.25 spz.
o
Analysis was performed at 30 C using THF as eluent at a flow
rate of 1 mL/min. Differential scanning calorimetry
analysis of the polymers was performed in a TA instrument Q10
2
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o
1
20 C
HO
OH
+
Cl
NO
2
HO
O
NO2
DMF
K
2
CO
3
12h. The crude product was recrystallized from ethanol/water
Hydroquinone
1-Chloro4-nitrobenzene
4-(4-Nitrophenoxy)phenol
(
1/1 v/v) to give brown powder. Yield: 92.8%, Melting Point:
o
68 C.
NO
2
1
-1
FT-IR (KBr, cm ): 1535, 1342 (asymmetric and symmetric
HO
O
NO2
O
2
stretching vibrations of the -NO group), 1234 (stretching
vibrations of the C-O-C group).
150
o
C
4
-(4-Nitrophenoxy)phenol
+
O
DMF
K CO
2 3
Cl
O
O
Synthesis of 1,3,5-tris[4-(4-
O
O
aminophenoxy)phenoxy]benzene [TAPOPOB]
2
O N
NO
2
Cl
Cl
1,3,5-Tris(4-(4-nitrophenoxy)phenoxy)benzene
TRINITRO COMPOUND
1
,3,5- Trichlorobenzene
Pd/C Ethanol
8
0oC
In a 250 mL three necked round bottomed flask fitted with a
reflux condenser, TNPOPOB (15 g, 0.02 mol) dissolved in 25 mL
of ethanol was taken. The mixture was stirred well and to it 1.5
g of Pd/C was added portionwise. Then, hydrazine hydrate (20
mL) was added dropwise over a period of 30 minutes. After
NH
2
O
o
complete addition, the mixture was heated at 80 C for 12 h.
O
The hot solution was then filtered to remove the catalysts,
cooled to room temperature to obtain the white crystals of
O
O
TAPOPOB. The product was filtered and dried in an air oven at
o
0 C for 12 h. The crude product was recrystallized from
O
O
6
H
2
N
NH
2
ethanol to give white powder. Yield: 92.5%, Melting Point:
o
6 C.
1,3,5-Tris(4-(4-aminophenoxy)phenoxy)benzene
TRIAMINE
9
-1
Scheme 1: Synthesis of Triamine (TAPOPOB)
FT-IR (KBr, cm ): 3379, 3301 (asymmetric and symmetric
stretching vibrations of the N-H group), 3062, 3039
(
asymmetric and symmetric stretching vibrations of the
1
Synthesis of Model compound 2 (M2 - Linear)
aromatic C-H group). H NMR (DMSO-d
6
,
δ
, ppm): 3.51 (H
, s, 6H), 6.91 (H
, ppm): 113.1 (C1), taken in a 3-necked round bottomed flask and stirred under
15.3 (C2), 119.1 (C3), 120.1(C4), 144.9 (C5), 148.1 (C6), 151.1 nitrogen atmosphere. While stirring, a solution of phthalic
a
, s,
, s, TAPOPOB (0.34 g, 0.5 mmol) dissolved in 10 mL of DMAc was
e
6
6
1
H), 6.55 (H
b
, s, 3H), 6.8 (H
c
, s, 6H), 6.9 (H
d
1
3
H), 6.93 (H
f
, s, 6H). C-NMR (DMSO-d , δ
6
(
C7), 153.8 (C8) . m/e value: 674.5.
anhydride (0.14 g, 1 mmol) in 5 mL of DMAc was added
dropwise to the mixture through a syringe over 30 minutes.
The molar ratio between triamine and phthalic anhydride was
kept at 1:2.The reaction was further continued for 12 h at 40
Preparation of Model compounds
o
C. Then, 30 mL of m-xylene was added, and the mixture was
heated to reflux with a Dean-Stark apparatus for 5 h. After
cooling to room temperature, the mixture was poured into ice
cold water and the formed brown precipitate was filtered and
Synthesis of Model compound 1 (M1 - Terminal)
TAPOPOB (0.34 g, 0.5 mmol) dissolved in 10 mL of DMAc was
taken in a 3-necked round bottomed flask and stirred under
nitrogen atmosphere. While stirring, a solution of phthalic
anhydride (0.07 g, 0.5 mmol) in 5 mL of DMAc was added
dropwise to the mixture through a syringe over 30 minutes.
The molar ratio between triamine and phthalic anhydride was
o
washed with methanol and dried in an air oven at 70 C for 24
[
21, 45]
h
.
Synthesis of Model compound 3 (M3 - Dendritic)
kept at 1:1.The reaction was further continued for 12 h at 40 TAPOPOB (0.34 g, 0.5 mmol) dissolved in 10 mL of DMAc was
o
C. Then, 30 mL of m-xylene was added, and the mixture was taken in a 3-necked round bottomed flask and stirred under
heated to reflux with a Dean-Stark apparatus for 5 h. After nitrogen atmosphere. While stirring, a solution of phthalic
cooling to room temperature, the mixture was poured into ice anhydride (0.22 g, 1.5 mmol) in 5 mL of DMAc was added
cold water and the formed yellow precipitate was filtered and dropwise to the mixture through a syringe over 30 minutes.
o
washed with methanol and dried in an air oven at 70 C for 24 The molar ratio between triamine and phthalic anhydride was
[
21, 45]
h
.
kept at 1:3.The reaction was further continued for 12 h at 40
o
C. Subsequently, a mixture of 1 g of triethylamine and 3 g of
acetic anhydride into the solution. The solution was kept at 70
o
C for 6 h under stirring. After cooling to room temperature,
the mixture was poured into methanol. The gray precipitate
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formed was collected by filtration and dried in a vaccum oven
[21, 45]
Synthesis of anhydride-terminated HBPIs
o
at 70 C for 24 h.
.
NH
O
2
To a solution of dianhydride (0.64 g, 2.0 mmol) in 20 mL of
DMAc in a 100 mL round bottomed flask, TAPOPOB (0.68 g, 1
mmol) in 10 mL of DMAc was added dropwise over a period of
b
a
O
o
O
O
b
1 h. The mixture was stirred for 24 h at 40 C. The chemical
e
O
b
O
f
O
c
imidization was carried out by adding a mixture of 1 g of
triethylamine and 3 g of acetic anhydride into the polyamic
o
acid solution. The solution was kept at 70 C for 6 h under
H
2
N
N
d
m/n = 1:1
Model Compound 1
Terminal unit
O
stirring. After cooling to room temperature, the mixture was
poured into methanol. The precipitate formed was collected
by filtration and dried in a vaccum oven for 12 h. The
anhydride- terminated HBPIs obtained from BTDA and PMDA
O
N
O
O
O
f
e
b
NH
O
2
a
will be referred to as HBPI-BTDA-AD-1 and HBPI-PMDA-AD-2
[21, 45]
O
m/n = 1:2
O
O
b
+
O
e
respectively
.
O
b
O
O
O
f
O
H
2
N
c
N
O
O
d
Model Compound 2
Linear unit
O
O
O
H
2
N
NH
2
TAPOPOB
m
Phthalic anhydride
n
O
N
O
O
O
b
m/n = 1:3
a
b
b
O
O
c
O
O
O
d
O
N
N
Model Compound 3
Dendritic unit
O
O
Scheme 2: Synthesis of Model Compounds
Synthesis of HBPIs
Synthesis of amino-terminated HBPIs
TAPOPOB (0.68 g, 1 mmol) was dissolved in 10 mL of DMAc in
a 100 mL, three-necked round bottomed flask under nitrogen
atmosphere, and the solution was strirred. A solution of
dianhydride (0.32 g, 1 mmol) in DMAc was added dropwise to
the mixture through a syringe over a period of 1h under
o
stirring at 35 C. The reaction mixture was further stirred for
24 h. Then, 10 mL of m-xylene was added, and the mixture was
heated to reflux with a Dean-Stark apparatus for 5 h. After
cooling to room temperature, the mixture was precipitated
from methanol. The precipitate was collected by filtration and
dried in a vaccum oven for 24 h. The amino-terminated HBPIs
obtained from BTDA and PMDA will be referred to as HBPI-
Scheme 3: Synthesis of HBPIs
[21, 45]
BTDA-AM-1 and HBPI-PMDA-AM-2 respectively
.
4
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RESULTS AND DISCUSSION
Structural characterization of the triamine
TAPOPOB)
(
A new triamine (TAPOPOB) containing flexible ether linkage
was synthesized by a three-step procedure. In the first step,
the nucleophilic substitution reaction of hydroquinone with p-
chloronitrobenzene in the presence of potassium carbonate
yielded the intermediate compound NPOP. In the second step,
synthesized NPOP was reacted with 1,3,5-trichlorobenzene in
the presence of potassium carbonate, to obtain the trinitro
compound (TNPOPOB). Finally, the triamine monomer
TAPOPOB was synthesized by the reduction of TNPOPOB using
hydrazine hydrate catalyzed by Pd/C. The structure of the
triamine monomer was characterized by FT-IR, NMR
spectroscopy and confirmed by mass spectral analysis.
Figures 1a and 1b show the FT-IR spectra of the TNPOPOB and
TAPOPOB. Figure 1a shows the characteristic absorptions at
-
1
1
535 and 1342 cm due to the asymmetric and symmetric
stretching vibrations of the -NO group. The absorptions
2
-1
Scheme 4: Structure of amino-terminated HBPI
observed at 3062 and 1234 cm are due to the stretching
vibrations of the aromatic C-H and C-O-C groups respectively.
Figure 1b shows the characteristic absorptions at 3371 and
O
O
O
C
C
X
O
O
C
-
1
C
X
C
C
C
O
3
301 cm corresponding to the stretching vibrations of the
O
C
N
N
O
O
amino group. Moreover, the absorptions of the nitro group
were not found in figure 1b, thus confirming that all the nitro
groups in TNPOPOB were completely reduced to the amino
O
O
O
O
C
O
C
O
O
O
O
1
group. Figure 2 shows the H-NMR spectrum of the triamine.
O
O
N
X
N
O
O
C
C
The singlet peak at 3.5 ppm corresponds to the –NH protons.
2
O
O
O
The peaks between 6.5 ppm and 6.8 ppm are assigned to the
1
3
aromatic protons. Figure 3 shows the C-NMR spectrum of the
triamine. The peaks between 113.1 ppm and 153.8 ppm are
assigned to characteristic carbon resonances of the aromatic
ring present in the triamine. The mass spectrum of the
triamine is shown in figure 4, which shows the molecular ion
O
O
N
N
C
C
O
O
X
C
C
X
C
C
O
C
C
O
O
O
O
1
13
O
peak at 674.5 for the triamine. The FT-IR, H-NMR, C-NMR
and mass spectral analysis confirm the proposed structure of
the triamine.
C
R
=
BTDA
PMDA
Scheme 5: Structure of anhydride-terminated HBPI
Synthesis of HBPIs
Hyperbranched polyimides were prepared by A
2
+
B
3
polymerization technique, using the commercially available
dianhydrides, BTDA and PMDA as A monomer and the newly
synthesized triamine (TAPOPOB) as B monomer. By varying
2
3
the mole ratio of the triamine and dianhydrides, different
types of hyperbranched polyimides were formed.
The addition of dianhydride into triamine (TAPPOB) with a
monomer molar ratio of 1:1 (the molar ratio between the
Figure 1: FT-IR spectra of (a) TNPOPOB (b) TAPOPOB
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amine and anhydride groups in the monomer was 3:2) yielded To protect the terminal functional groups different imidazation
the amine terminated hyperbranched polyimides. While the procedures were employed. The amino-terminated
addition of triamine into dianhydride with a monomer molar hyperbranched polyamic acid solutions were thermally
ratio of 1:2 (the molar ratio between the amine and anhydride imidized at 160 °C for 24 h. The anhydride-terminated
groups in the monomer was 3:4) yielded the anhydride polyamic acid solutions were chemically converted into HBPIs
terminated hyperbranched polyimides [20]. In both cases, the in the presence of acetic anhydride and triethylamine at 70 °C
[
20- 22, 30]
monomer was added dropwise to avoid any high local
concentration.
.
Characterization of the HBPIs
The formation of HBPIs was confirmed by FT-IR spectroscopy.
Figure 5 shows the FT-IR spectra of the amino- and anhydride-
terminated HBPIs based on BTDA (HBPI-BTDA-AM1 and HBPI-
-1
BTDA-AD1). The bands at 1784 cm (asymmetric stretching
-1
vibrations of the imide >C=O group), 1728 cm (symmetric
-
1
stretching vibrations of the imide >C=O group), 1380 cm
-
(
stretching vibrations of the imide C-N group), and 725 cm
1
(
bending vibrations of the imide C-N group) are the
characteristic absorption bands of the HBPIs. The characteristic
-1
band of the polyamic acid at 1680 cm is not found in the FT-
-1
1
Figure 2: H-NMR spectrum of TAPOPOB
IR spectra. The band between 3384 and 3312 cm represent
the N-H stretching vibrations of the terminal amino groups
present in the amino-terminated HBPIs , while the band
-1
around 1859 cm represents the >C=O stretching vibrations of
the terminal anhydride groups in anhydride-terminated HBPIs.
Similar characteristic bands were observed in the FT-IR spectra
of HBPI-PMDA-AM1 and HBPI-PMDA-AD2 (based on PMDA).
From these results, it can be concluded that the prepared
HBPIs were completely imidized.
The structural perfection of hyperbranched polymers is
generally characterized by the degree of branching (DB), which
[46]
was defined by Hawker and Frenchet
in 1991 as follows,
DB = (D+T) / (D+T+L)
(1)
where D, T, L refer to the number of dendritic, terminal, and
linear units in the hyperbranched polymer, respectively. DB is
1
usually determined from the H-NMR spectra by comparing
1
3
Figure 3: C-NMR spectrum of TAPOPOB
the integration of the peaks for the respective units in the
hyperbranched polymers with the help of model compounds
prepared using synthesized triamine and phthalic anhydride.
To determine the DB of amino-terminated HBPIs, three model
compounds were synthesized.
To determine the DB of the HBPIs three model compounds M-
1
(terminal); M-2 (linear); M-3 (dendritic) were synthesized.
1
Figure 6 shows the H-NMR spectra of the three model
compounds, amino-terminated HBPI and anhydride-
terminated HBPI. The peak at 3.5 ppm due to the amino
proton has the highest intensity for M-1 (terminal) which has 2
unreacted amino groups. The same peak has moderate
intensity for M-2 (linear) as it has only one unreacted amino
group. For M-3 (dendritic) with no unreacted amino groups,
there is no peak at 3.5 ppm. For the hydrogens in the phenyl
rings of TAPOPOB residues, terminal model compound 1 has 6
Figure 4: Mass spectrum of TAPOPOB
6
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peaks at 6.5 (H ), 7.1 (H
a
b
), 6.9 (H
c
), 6.7 (H
d
), 7.6 (H
e
), 7.7 (H
), 7.1 and PMDA. And also there are no peaks in the range of 6.5-7.0
f
) ppm and model ppm confirming that no trace of terminal and linear units were
f
)
groups have reacted with anhydride groups present in BTDA
ppm; linear model compound 2 also has 6 peaks at 6.4 (H
), 6.8 (H ), 6.7(H ), 7.5 (H ), 7.8 (H
), 7.1 (H
a
(H
b
c
d
e
compound 3 has 4 peaks at 6.9 (H
ppm.
a
b
), 7.6 (H
c
), 7.7 (H
d
)
present [i.e., TAPOPOB residues were completely dendritic
(DB=1)]. In addition, the spectra of HBPIs show no acid
protons, confirming that full imidization has occurred.
Solubility of HBPIs
The synthesized HBPIs show excellent solubility in most of the
common organic solvents. The solubility test was done by
dissolving 0.5 g of the HBPIs in 1 mL of the solvent at room
temperature, and the results are shown in table 1. All the
synthesized HBPIs (based on BTDA and PMDA) dissolved
completely in polar aprotic solvents such as NMP, DMF, DMAc,
m-cresol, and DMSO. They also exhibit good solubility in
chloroform, THF, acetone, ethanol and methanol. The
excellent solubility is due to the presence of flexible ether
linkages in the backbone of the HBPIs. These linkages will
hinder intermolecular packing and increase the free
Figure 5: FT-IR spectra of (a) HBPI-BTDA-AD-1 (b) HBPI-BTDA-
AM-1
[20]
volume, hence solubility improved . In all cases, chemically
imidized anhydride–terminated HBPIs show good solubility
when compared with thermally imidized amino-terminated
HBPIs which is due to cross-linking of polyimide during
[
47]
imidization at high temperature
.
Inherent Viscosity
The inherent viscosity of the synthesized HBPIs was
determined using a Ubbelohde viscometer at a concentration
o
5g/dL in NMP at 30 C. The inherent viscosity values were
of 0
.
1
Figure 6: H-NMR spectra of the a)M-1 b)M-2 c) M-3 d)HBPI-
-1
found to be in the range of 0.76 to 1.21 dl g . Synthesized
HBPIs exhibit moderate viscosity and better solubility, which is
due to the branching nature and presence of terminal
BTDA-AM-1 e)HBPI-BTDA-AD-1
[
48]
functional groups
. Inherent viscosity of the anhydride-
For the amino-terminated HBPI (figure 8d), the peaks in the
range of 6.5-7.2 ppm correspond to the linear and terminal
protons present in the phenyl rings of TAPOPOB residues.
From these values, degree of branching was calculated and
explained. The peak at 3.5 ppm is attributed to the free amine
groups present in the linear and terminal units. By comparing
terminated HBPIs is higher than the amine-terminated HBPIs
[30]
.
These results indicate that the anhydride-terminated HBPIs
show high molecular weight when compared to the amine-
terminated HBPIs. PMDA-HBPIs show better viscosity than the
BTDA-HBPIs is due to the presence of rigid backbone. The
results are shown in table 2.
1
the H NMR spectra of M-1 & M-2 we get details about DB of
amino-terminated HBPIs. The peaks around 6.5, 6.8 and 6.9
ppm are attributed to both the terminal and linear units. The
peak at 7.1 ppm is independent of the terminal units but
related to linear ones, and hence attributed to both dendritic
and linear units. The peak at 7.2 ppm is related neither to
terminal unit nor to linear ones, and hence attributed to
dendritic units. From the equation (1), DB for the amino-
terminated HBPI is found to be 0.67.
Molecular weight
Molecular weight of the synthesized HBPIs was determined by
GPC. Weight average molecular weight (M
w
), number average
molecular weight (M ), Polydispersity index (PDI) values are
n
1
In the H-NMR spectrum of anhydride-terminated HBPI (figure
shown in table 2. M
w
, M
n
values of the HBPIs are in the range
8e), there is no peak at 3.5 ppm confirming that all the amino
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Table 1: Solubility of HBPIs
Solvents
Synthesized
HBPIs
DMF
++
NMP
++
DMSO DMAc m-cresol
CHCl
++
3
THF
+-
Methanol Acetone Ethanol
HBPI-BTDA-AM1
HBPI-PMDA-AM2
++
++
++
++
++
++
--
--
--
--
--
--
++
++
++
+-
HBPI-BTDA-AD1
HBPI-PMDA-AD2
++
++
++
++
++
++
++
++
++
++
++
++
++
++
+-
+-
+-
+-
--
--
++ - soluble; +- - partially soluble; -- - insoluble
PMDA based HBPIs (HBPI-PMDA-AM2 and HBPI-PMDA-AD2)
show good thermal stability when compared with BTDA based
of 42,518 - 2,63,289 and 66,120 – 3,29,172 respectively. On HBPIs (HBPI-BTDA-AM1 and HBPI-BTDA-AD1). This is due to
comparison, the anhydride-terminated HBPIs show high the inherent rigidity of pyromellitic unit present in PMDA and
molecular weight (M
of the different imidization methods employed . PDI values The T
are in the range of 1.25 – 2.98. In all cases, PDI values greater heating rate of 10 C min in nitrogen atmosphere. The values
w
) than amine-terminated HBPIs because susceptibility to oxidation of the >C=O group of BTDA.
[21]
g
of the synthesized HBPIs was determined by DSC at a
o
-1
o
than 1 hence the branching in the polymer is successful.
are in the range of 234 – 254 C (Table 3) which is shown in
figure 8. In figure 8, a, b, c, d represents HBPI-BTDA-AM1,
HBPI-BTDA-AD1,
respectively. Amino-terminated HBPIs show better T
values of HBPI-BTDA-AM1 and HBPI-PMDA-AM2 are 234 and
HBPI-PMDA-AM2,
HBPI-PMDA-AD2
Table 2: Inherent viscosity and molecular weight
of HBPIs
g
(T
g
o
2
54 C respectively) than the anhydride-terminated HBPIs (T
g
values of HBPI-BTDA-AD1 and HBPI-PMDA-AD2 are 227 and
o
Synthesized Inherent
HBPIs Viscosity
dl g
M
w
M
n
PDI
(M /M )
2
48
C respectively). This is because of the strong
w
n
-
1
macromolecular interaction resulting from the hydrogen
[30]
bonds between the terminal amino groups . PMDA based
HBPIs exhibit higher T values than the BTDA based HBPIs
because of the presence of rigid moiety. T values of HBPI-
HBPI-BTDA- 0.76
AM1
66120
42518
1.55
g
g
HBPI-
PMDA-AM2
0.87
165194 55382
2.98
BTDA-AM-1 and HBPI-BTDA-AD-1 are low because of the
presence of flexible linkage (-C=O) between the two phenyl
[47]
HBPI-BTDA- 1.01
AD1
246239 170916 1.44
329172 263289 1.25
rings
.
HBPI-
PMDA-AD2
1.21
Flame Retardancy of the Polymers
The limiting oxygen index (LOI) value indicates the flame
retardant property of the polymers which is shown in table 2.
The LOI values were calculated from the char yield obtained
from TGA analysis by using Van Krevelan and Hofytzer
Thermal analysis
Thermal stability of the HBPIs was characterized by TGA at a
[49]
o
-1
o
equation , as shown below,
LOI = 17.5 + (0.4) CY
where, LOI – limiting oxygen index, CY – char yield
heating rate of 20 C min from room temperature to 800 C
under N atmosphere. As shown in figure 7, all the synthesized
HBPIs exhibit good thermal stability with a 10% weight- loss
2
o
temperature (T10) above 450 C (Table 3). In figure 7, a, b, c, d The LOI values of the synthesized HBPIs are in the range of 35-
represents HBPI-PMDA-AM2, HBPI-BTDA-AM1, HBPI-PMDA- 39% indicating high flame retardancy. In general, the LOI value
AD2, HBPI-BTDA-AD1 respectively. Amino-terminated HBPIs of the polymer should be above the threshold value of 26, to
(
HBPI-BTDA-AM1 and HBPI-PMDA-AM2) show better thermal render them self-extinguishing property and to qualify their
stability than anhydride-terminated HBPIs. This is due to the requirement in many applications requiring good flame
[50]
free terminal functional groups present in amino-terminated
resistance . The synthesized HBPIs show LOI values greater
[51]
[
21]
HBPIs
.
than 26, hence exhibit good flame retardant properties
.
8
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Table 3: Thermal and dielectric properties
samples
Tg
T
CY
LOI
ε′
ε″
10
o
o
C) ( C)
(
(%)
(1MHz) (1 MHz)
HBPI-BTDA- 234 498 49.6 37.3 3.08
0.65
0.71
0.76
0.82
AM1
HBPI-PMDA 254 517 51.4 38.1 3.16
AM2
HBPI-BTDA- 227 484 46.7 36.2 3.21
AD1
HBPI-PMDA 248 489 48.3 36.8 3.29
AD2
Figure 8: DSC of a) HBPI-BTDA-AM1 b) HBPI-BTDA-AD1 C)
HBPI-PMDA-AM2 d) HBPI-PMDA-AD2
Figure 7: TGA of a) HBPI-BTDA-AM1 b) HBPI-BTDA-AD1 c)
HBPI-PMDA-AM2 d) HBPI-PMDA-AD2
Figure 9: Dielectric constant of HBPIs
Dielectric Properties
The dielectric constant and dielectric loss were measured, and
the results are summarized in table 2. The dielectric constant
of the synthesized HBPIs is in the range of 3.08–3.29 at 1 MHz
and dielectric loss is in the range of 0.65–0.82 at 1 MHz which
is shown in figures 9 and 10. These values are comparatively
[
4]
.
low when compared with that of the fluorinated polyimides
The dielectric constant and dielectric loss of the materials are
directly related to the polarizability and porosity of the
materials and are strongly dependent on their chemical
[52]
structure . Low dielectric constant of the HBPIs are due to
the introduction of the flexible ether linkages, and increased
free volume due to the highly branched structure of the HBPIs
which loosened polymer packing, leading to reduced dielectric
[
53]
constant
.
Figure 10: Dielectric loss of HBPIs
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Journal Name
1
2. X. Qingming, L. Junpeng, D. Jie, Y. Chaoqing, D.
Yuxuan, X. Qian, Z. Qinghua, J. Appl. Polym. Sci., 2013,
Conclusions
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29, 145-151.
A
series of hyperbranched polyimides (HBPIs) were
13. M. Masahiko, I. Yuichi, O. Toshio, Y. Rikio,
J.react.funct.polym., 2013, 73, 340-345.
successfully synthesized using
a
new triamine and
commercially available dianhydrides. The structure of the
triamine and synthesized HBPIs were characterized by FT-IR
14. C. Lin, C. Yang, F. Tiantian, Y. Wei, W. Jing, Z. Xin, Y.
Fengchun, J.polymdegradstab., 2013, 98, 839-843.
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J. Polym. Sci., Part A: Polym. Chem., 2008, 46, 4227–
4235.
1
and H-NMR techniques. The introduction of flexible ether
linkages in the backbone of the polymers increases its
solubility in most of the common organic solvents. Synthesized
-1
HBPIs exhibit moderate inherent viscosity (0.76-1.21 dl g ) and
high molecular weight (Mw). All the HBPIs show good thermal
16. Z. Yunhe, L. Pan, Y. Hongyan, G. Shaowei,
J.reactfunctpolym., 2012, 72, 621–626.
o
stability (234 – 254 C) and flame retardancy as indicated by
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Boutevin, G. Caporiccio, J. Polym. Sci., Part A: Polym.
Chem., 2000, 38, 2993-3003.
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their T10 values (above 450 C) and LOI values (36-38). The
dielectric constant of the synthesized HBPIs is in the range of
3
.08–3.29 at 1 MHz and dielectric loss is in the range of 0.65–
.82 at 1 MHz. The synthesized HBPIs exhibit good solubility,
18. Z. Heng, L. Feng, Z. Yongsheng, F. Weifeng, L.
Jingfeng, W. Zhen, Z. Tong, J Appl Polym Sci., 2011,
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(Maulana Azad National Fellowship), for funding this project.
The authors also acknowledge DST (FIST) and UGC (SAP) for
the financial support extended to procure instrumental
facilities.
22. C. Huan, Y. Jie, J. Polym. Sci., Part A: Polym. Chem.,
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5x38mm (600 x 600 DPI)