Synthesis and characterization of poly(amideimide)s from 4-(p-carboxyphenoxy)phthalic anhydride and 4-(p-carboxybenzoyl)phthalic anhydride

Article abstract of DOI:10.1016/j.polymer.2013.08.037

A series of poly(amideimide)s were prepared by the reaction of two new anhydride acidchloride monomers with aromatic diamines. 4-(p-Carboxyphenoxy) phthalic anhydride was synthesized by nucleophilic displacement reaction of N-methyl-4-nitrophthalimide with p-hydroxybenzoic acid, followed by hydrolysis. The tricarboxylic acid was converted to the corresponding anhydride acidchloride. 4-(p-Carboxybenzoyl)phthalic anhydride was synthesized by Friedel-Craft's acylation of toluene with N-phenylphthalimide-4- carbonylchloride, which was then converted to anhydride acidchloride of 4-(p-carboxybenzoyl)phthalic acid. The monomers were characterized by IR and NMR. Several PAI were prepared by the reaction of these anhydride acidchloride monomers with aromatic diamines. The inherent viscosities of the polymers were in the range of 0.42-0.58 dL/g. All polymers were soluble in polar aprotic solvents. The polymers showed good thermal stability and T_g values were in the range of 226-269 C. X-Ray diffractograms of polymers indicate amorphous nature of these polymers.

Full text of DOI:10.1016/j.polymer.2013.08.037

Polymer 54 (2013) 5626e5633
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Polymer
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Synthesis and characterization of poly(amideimide)s from
4-(p-carboxyphenoxy)phthalic anhydride and 4-(p-carboxybenzoyl)
phthalic anhydride
*
S. Rajasekar, D. Venkatesan
Department of Chemistry, School of Chemical and Biotechnology, Sastra University, Thanjavur 613 401, Tamilnadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of poly(amideimide)s were prepared by the reaction of two new anhydride acidchloride
monomers with aromatic diamines. 4-(p-Carboxyphenoxy)phthalic anhydride was synthesized by
nucleophilic displacement reaction of N-methyl-4-nitrophthalimide with p-hydroxybenzoic acid, fol-
lowed by hydrolysis. The tricarboxylic acid was converted to the corresponding anhydride acidchloride.
4-(p-Carboxybenzoyl)phthalic anhydride was synthesized by FriedeleCraft’s acylation of toluene with N-
phenylphthalimide-4-carbonylchloride, which was then converted to anhydride acidchloride of 4-(p-
carboxybenzoyl)phthalic acid. The monomers were characterized by IR and NMR. Several PAI were
prepared by the reaction of these anhydride acidchloride monomers with aromatic diamines. The
inherent viscosities of the polymers were in the range of 0.42e0.58 dL/g. All polymers were soluble in
polar aprotic solvents. The polymers showed good thermal stability and Tg values were in the range of
226e269 ꢀC. X-Ray diffractograms of polymers indicate amorphous nature of these polymers.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 30 May 2013
Received in revised form
7 August 2013
Accepted 16 August 2013
Available online 24 August 2013
Keywords:
Poly(amideimide)s
High performance polymers
Thermal properties
1. Introduction
Among modified polyimides, poly(amideimide)s are the most
successful materials (e.g. TorlonsÒ). The poly(amideimide)s are
Aromatic polyimides are important class of high performance
polymeric materials that has outstanding thermal stability,
excellent mechanical properties and good chemical resistance [1e
4]. These polymers are widely used in aerospace, electronics and
automobile industries [5,6]. However, aromatic polyimides have
close packed polymer chains due to the strong intermolecular
forces and these polymers have very high melting points and
limited solubility in organic solvents [7e11]. In order to improve
the processability of aromatic polyimides, polymers have been
prepared from structurally modified dianhydrides and diamines
[12]. The other structural modifications include incorporation of
flexible groups such as aryl ether, thioether and carbonyl linkages
into the polymer backbone [13,14], incorporation of groups such
as amide, ester, etc. to obtain polyimide derivatives such as pol-
y(amideimide)s, poly(esterimide)s, etc. and introducing sub-
stituents in the aromatic groups present in the polymer backbone
[15e19].
generally prepared by the polycondensation of trimellitic anhy-
dride chloride or aromatic diacids containing preformed imide
rings with aromatic diamines [20e23].
In the present work, two new monomers 4-(p-carboxyphenoxy)
phthalic anhydride and 4-(p-carboxybenzoyl)phthalic anhydride
were synthesized and polymers were prepared by the poly-
condensation of these anhydride acidchloride monomers with
several aromatic diamines. These polymers showed good thermal
stability comparable to aromatic polyimides. The improved pro-
cessability of these polymers compared to polyimides results from
the incorporation of amide groups into polymer backbone.
2. Materials and methods
2.1. Materials
N-Methyl-4-nitrophthalimide, 4-hydroxy benzoic acid and tri-
mellitic anhydride were used as received. Aniline, toluene, thionyl
chloride and pyridine were purified by distillation. The commer-
cially available aromatic diamines such as m-phenylenediamine,
oxydianiline, methylenedianiline and 4,40-diaminodiphenyl sul-
fone were purified by recrystallization. Dimethylsulfoxide (DMSO),
* Corresponding author.
E-mail addresses: dvenkatesan@chem.sastra.edu, dvenkat66@yahoo.co.in
(D. Venkatesan).
0032-3861/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2013.08.037

S. Rajasekar, D. Venkatesan / Polymer 54 (2013) 5626e5633
5627
Scheme 1. Synthesis of 4-(p-chlorocarbonylphenoxy)phthalic anhydride.
dimethylacetamide (DMAc), N,N-dimethylformamide (DMF) and
2.3. Methods
N-methyl-2-pyrrolidone (NMP) were purified by distillation under
ꢀ
reduced pressure and stored over 4 A molecular sieves.
2.3.1. Synthesis of 4-((N-methylphthalimide)-4-oxy) benzoic acid
(III)
To 4-hydroxy benzoic acid (I) (1.38 g, 0.01 mol) and DMSO
(15 mL) in a round-bottom flask was added potassium carbonate
(3.04 g, 0.022 mol) and toluene (20 mL). The reaction mixture was
heated to 140 ꢀC and water was azeotropically removed from the
reaction mixture. The temperature was raised to 160 ꢀC and
remaining toluene was removed. The reaction mixture was cooled
to 40 ꢀC, N-methyl-4-nitrophthalimide (II) (2.06 g, 0.01 mol) was
added and reaction mixture was heated at 120 ꢀC for 6 h. The re-
action mixture was allowed to cool and hydrochloric acid was
added. The precipitated pale yellow compound was isolated by
2.2. Measurements
Infrared spectra were recorded on PerkinElmer spectrum 100
FTIR. 1H and 13C NMR spectra were recorded on Bruker Avance
(300 MHz). The inherent viscosities of the polymers were measured
with an Ostwald viscometer at 0.5 dL/g concentration. Thermog-
ravimetric analysis (TGA) and differential scanning calorimetry
(DSC) were performed on TA Instruments SDT Q600 and DSC Q20.
X-Ray diffraction measurements were recorded on a Bruker XRD D8
FOCUS using Cu Ka radiation.
Scheme 2. Synthesis of 4-(p-chlorocarbonylbenzoyl)phthalic anhydride.

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S. Rajasekar, D. Venkatesan / Polymer 54 (2013) 5626e5633
Fig. 1. 1H NMR spectrum of 4-(p-carboxyphenoxy)phthalic acid (IV) in DMSO-d6.
filtration, washed with wateꢁr1and dried. Yield: 2.62 g (88%); m.p:
217 ꢀC; FTIR (KBr): 3570 cm (OeH stretch, eCOOH), 1680 cmꢁ1
(C]O stretch, eCOOH), 1780 cmꢁ1 (C]O stretch, imide) and
m.p: 234 ꢀC; FTIR (KBr): 3580 cmꢁ1 (OeH stretch, eCOOH),
1690 cmꢁ1 (C]O stretch, eCOOH), 1850 cmꢁ1 (five-membered
cyclic anhydride), 1285 cmꢁ1 (CeO stretch, cyclic anhydride) and
1260 cmꢁ1 (CeO stretch, AreOeAr).
1240 cmꢁ1 (CeO stretch, AreOeAr); 1H NMR (DMSO-d6):
d (ppm)
2.71 (s, 3H), 7.12 (d, J ¼ 8.2 Hz, 2H), 7.27 (d, J ¼ 8.1 Hz, 1H), 7.52 (s,
1H), 7.99 (d, J ¼ 8.7 Hz, 2H), 8.27 (d, J ¼ 7.5 Hz, 1H); 13C NMR
2.3.4. Synthesis of 4-(p-chlorocarbonylphenoxy)phthalic anhydride
(VI)
(DMSO-d6):
d (ppm) 26.2, 119.5, 120.2, 120.8, 127.2, 129.8, 131.4,
135.6, 157.3, 158.6, 166.2, 168.2.
A mixture of compound V (3 g, 0.0105 mol), thionyl chloride
(20 mL) and pyridine (1 mL) was refluxed for 6 h. The excess thionyl
chloride was removed under reduced pressure. The acidchloride
(VI) was recrystallized from toluene. Yield: 3.1 g (100%); m.p:
116 ꢀC; FTIR (KBr): 1770 cmꢁ1 (C]O stretch, acidchloride),
1850 cmꢁ1 (cyclic anhydride) and 1260 cmꢁ1 (CeO stretch, AreOe
Ar).
2.3.2. Synthesis of 4-(p-carboxyphenoxy)phthalic acid (IV)
The tricarboxylic acid IV was prepared by hydrolysis of com-
pound III. The flask was charged with compound III (2.97 g,
0.01 mol) and NaOH solution (40 mL, 10% solution). The reaction
mixture was refluxed for 24 h. The reaction mixture was added to
dilute hydrochloric acid. The precipitated solid was isolated by
filtration, washed with water and dried. Yield: 2.8 g (92%); m.p:
>300 ꢀC; FTIR (KBr): 3700e2500 cmꢁ1 (OeH stretch, eCOOH),
1690 cmꢁ1 (C]O stretch, eCOOH) and 1240 cmꢁ1 (CeO stretch,
2.3.5. Synthesis of N-phenyl phthalimide-4-carboxylic acid (IX)
An RB flask was charged with trimellitic anhydride (VII) (1.92 g,
0.01 mol), aniline (VIII) (0.93 g 0.01 mol) and DMSO (20 mL). The
reaction mixture was stirred for 4 h. Toluene (20 mL) was added
and the reaction mixture was heated at 140 ꢀC for 6 h while
removing water as an azeotrope using DeaneStark trap. Toluene
was completely removed from the reaction mixture, cooled and the
reaction mixture was poured into water. The precipitated yellow
solid was isolated by filtration, washed with water and dried in
vacuum. Yield: 2.6 g (97%); m.p: 248 ꢀC; FTIR (KBr): 3700e
2500 cmꢁ1 (OeH stretch, eCOOH), 1680 cmꢁ1 (C]O stretch, e
COOH), 1785 cmꢁ1 (C]O stretch, imide); 1H NMR (DMSO-d6):
AreOeAr); 1H NMR (DMSO-d6):
d
(ppm) 7.12 (d, J ¼ 8.7 Hz, 2H), 7.21
(d, J ¼ 8.7 Hz, 1H), 7.72 (s, 1H), 7.95 (d, J ¼ 8.7 Hz, 2H), 8.22 (d,
J ¼ 8.7 Hz, 1H); 13C NMR (DMSO-d6):
d (ppm) 167.2, 167.0, 166.7,
159.7, 157.3, 137.7, 135.4, 131.8, 130.3, 126.3, 121.9, 120.7, 118.6.
2.3.3. Synthesis of 4-(p-carboxyphenoxy)phthalic anhydride (V)
A mixture of 4-(p-carboxyphenoxy)phthalic acid (3 g, 0.01 mol)
and acetic anhydride (10 mL) was refluxed for 5 h. The reaction
mixture was cooled and precipitated acid anhydride was filtered,
washed with hexane and dried under vacuum. Yield: 2.8 g (98%);
d
(ppm) 7.11 (d, J ¼ 6.9 Hz, 2H), 7.29e7.34 (m, 3H), 7.62 (d, J ¼ 7.8 Hz,
Fig. 2. 13C NMR spectrum of 4-(p-carboxyphenoxy)phthalic acid (IV) in DMSO-d6.

S. Rajasekar, D. Venkatesan / Polymer 54 (2013) 5626e5633
5629
Fig. 3. 1H NMR spectrum of 4-(p-carboxybenzoyl)phthalic acid (XV) in DMSO-d6.
1H), 7.77 (d, J ¼ 7.8 Hz, 1H), 8.16 (s, 1H) and 10.58 (s, 1H); 13C NMR
were added and the reaction mixture was refluxed for 12 h. The
reaction mixture was cooled and filtered. The filtrate was concen-
trated and the compound XII was refluxed with NaOH solution
(50 mL) for 10 h. The reaction mixture was cooled and the com-
pound was extracted with diethyl ether. The organic layer was
dried with anhydrous sodium sulfate and solvent was evaporated
to give XII. Yield: 2.6 g (73%); m.p: 139 ꢀC; FTIR (KBr): 2780 cmꢁ1
(DMSO-d6):
d (ppm) 123.6, 124.7, 127.9, 128.3, 129.2, 133.8, 134.3,
135.8, 136.5, 165.8 and 192.7.
2.3.6. Synthesis of 4-(N-phenyl phthalimide-4-carbonyl) toluene
(XI)
An RB flask charged with N-phenyl phthalimide-4-carboxylic
acid (IX) (2.67 g, 0.01 mol), thionyl chloride (20 mL) and pyridine
(1 mL). The reaction mixture was refluxed for 12 h. The excess
thionyl chloride was distilled under reduced pressure. N-Phenyl
phthalimide-4-carbonyl chloride (X) was isolated and dried. Yield:
2.85 g (100%).
(CeH stretch, aldehyde); 1H NMR (DMSO-d6):
13C NMR (DMSO-d6):
(ppm) 192.4 (aldehyde carbon).
d (ppm) 10.21 (s, 1H);
d
2.3.8. Synthesis of 4-(N-phenyl phthalimide-4-carbonyl)benzoic
acid (XIV)
A mixture of compound X (2.85 g, 0.01 mol), toluene (30 mL)
and aluminum chloride (3.33 g, 0.025 mol) was refluxed for 12 h.
The excess toluene was removed and the reaction mixture was
poured into dilute HCl (10%). The precipitated yellow solid was
isolated by filtration, washed with NaOH solution and water and
dried in vacuum. Yield: 2.66 g (78%); m.p: 196 ꢀC; FTIR (KBr): 2925
(CeH stretch), 1720 cmꢁ1 (C]O stretch, imide), 1660 cmꢁ1 (C]O
An RB flask was equipped with reflux condenser and magnetic
stirrer and charged with compound XIII (3.55 g, 0.01 mol), pyridine
(1 mL) and water (50 mL). To the reaction mixture KMnO4 solution
(15.8 g, 0.1 mol) was added in small portions and refluxed for 6 h.
After the reaction, MnO2 was removed by filtration and filtrate was
acidified with dilute hydrochloric acid. The pale yellow color
compound was isolated by filtration, washed with water and dried.
Yield: 2.67 g (72%); m.p: 224 ꢀC; FTIR (KBr): 3700e2500 cmꢁ1 (OeH
stretch, eCOOH), 1690 cmꢁ1 (C]O stretch, eCOOH), 1770 cmꢁ1
(C]O stretch, imide), 1670 cmꢁ1 (C]O stretch, diaryl ketone); 1H
stretch, diaryl ketone); 1H NMR (CDCl3):
d (ppm) 2.46 (s, 3H), 7.32
(d, J ¼ 7.5 Hz, 2H), 7.44 (d, J ¼ 6.9 Hz, 2H), 7.46e7.52 (m, 3H), 7.73 (d,
J ¼ 7.2 Hz, 2H), 8.05 (d, J ¼ 7.5 Hz, 1H), 8.18 (d, J ¼ 7.2 Hz 1H), 8.26 (s,
1H); 13C NMR (DMSO-d6):
d
(ppm) 21.8, 123.9, 124.8, 126.6, 128.4,
NMR (DMSO-d6):
d
(ppm) 7.45 (d, J ¼ 6.9 Hz, 2H), 7.52e7.57 (m, 3H),
129.3, 129.5, 130.4, 131.5, 131.7, 133.6, 134.1, 135.7, 143.9, 144.7, 166.5
and 194.4.
7.86 (d, J ¼ 7.8 Hz, 2H), 8.12e8.14 (m, 3H), 8.25 (d, J ¼ 7.8 Hz 2H); 13
C
NMR (DMSO-d6):
d (ppm) 194.2, 166.3, 142.1, 139.3, 135.7, 134.5,
131.8, 131.7, 129.9, 129.6, 128.9, 128.3, 127.4, 123.8.
2.3.7. Synthesis of 4-(N-phenyl phthalimide-4-carbonyl)
benzaldehyde (XIII)
2.3.9. Synthesis of 4-(4-carboxybenzoyl)phthalic acid (XV)
To a solution of XI (3.41 g, 0.01 mol) in CCl4 (50 mL), N-bro-
mosuccinimide (3.91 g, 0.022 mol) and benzoyl peroxide (100 mg)
The compound XIV (3.71 g, 0.01 mol) was refluxed with NaOH
solution (40 mL, 10%). for 48 h. After the reaction, dilute
Fig. 4. 13C NMR spectrum of 4-(p-carboxybenzoyl)phthalic acid (XV) in DMSO-d6.

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S. Rajasekar, D. Venkatesan / Polymer 54 (2013) 5626e5633
Table 1
Preparation of poly(amideimide)s.
Sl. No
Monomer
Diamine
Polymer
Inherent viscosity (
h
)
Yield (%)
1
2
3
4
5
6
7
8
VI
VI
VI
VI
XVII
XVII
XVII
XVII
I
II
III
IV
I
II
III
IV
PAI-1
PAI-2
PAI-3
PAI-4
PAI-5
PAI-6
PAI-7
PAI-8
0.58
0.47
0.53
0.58
0.49
0.42
0.54
0.57
95
97
94
96
93
95
98
96
2.3.10. Synthesis of 4-(4-carboxybenzoyl)phthalic anhydride (XVI)
A mixture of compound XV (3 g, 0.01 mol) and acetic anhydride
(10 mL) was refluxed for 5 h. The reaction mixture was cooled and
the precipitated acid anhydride was isolated by filtration and dried
under vacuum. Yield: 2.8 g (98%); m.p: 242 ꢀC; FTIR (KBr):
3580 cmꢁ1 (OeH stretch, eCOOH), 1680 cmꢁ1 (C]O stretch, e
COOH), 1855 cmꢁ1 (cyclic anhydride) and 1665 cmꢁ1 (C]O stretch,
diaryl ketone).
2.3.11. Synthesis of 4-(4-(chlorocarbonyl)benzoyl)phthalic
anhydride (XVII)
Fig. 5. FTIR spectra of 4-(p-chlorocarbonylphenoxy)phthalic anhydride (VI) and 4-(p-
A mixture of compound XVI (3 g, 0.0101 mol), thionyl chloride
(20 mL) and pyridine (1 mL) was refluxed for 6 h. The excess thionyl
chloride was removed under reduced pressure. The compound XVII
was recrystallized from toluene. Yield: 3.17 g (100%); m.p: 127 ꢀC;
FTIR (KBr): 1805 cmꢁ1 (C]O stretch, acidchloride), 1855 cmꢁ1
(cyclic anhydride) and 1660 cmꢁ1 (C]O stretch, diaryl ketone).
chlorocarbonylbenzoyl)phthalic anhydride (XVII).
hydrochloric acid (1.2 N) was added and precipitated white solid
was isolated by filtration, washed with water and dried. Yield: 2.9 g
(93%); m.p: >300 ꢀC; FTIR (KBr): 3595 cmꢁ1 (OeH stretch, eCOOH),
1685 cmꢁ1 (C]O stretch, eCOOH), 1665 cmꢁ1 (C]O stretch, diaryl
ketone); 1H NMR (DMSO-d6):
d
(ppm) 7.84 (d, J ¼ 8.1 Hz, 2H), 7.9 (d,
J ¼ 8.1 Hz,1H), 7.98 (d, J ¼ 7.8 Hz,1H), 8.09 (d, J ¼ 8.1 Hz, 2H), 8.19 (s,
1H); 13C NMR (DMSO-d6):
(ppm) 194.5, 168, 167.4, 166.6, 139.9,
137.9, 137.8, 134.3, 133.1, 131.8, 131.3, 130.2, 129.8, 129.5.
2.3.12. Synthesis of poly(amideimide)s
A typical procedure followed for the preparation of poly(-
amideimide)s is as follows. Diamine (1.0 mmol) was dissolved in
NMP (10 mL). To this solution anhydride acidchloride (VI or XVII)
d
Scheme 3. Synthesis of poly(amideeimide)s.

S. Rajasekar, D. Venkatesan / Polymer 54 (2013) 5626e5633
5631
NMR and 13C NMR spectra of the compound IV were shown in
Figs. 1 and 2. The carbon atoms of three carboxylic acid groups
showed absorption at 167.2e166.7
at 7.1e8.2 due to aromatic protons.
d
. 1H NMR spectra showed peaks
d
The monomer 4-(p-carboxybenzoyl)phthalic anhydride (XVI)
was synthesized as shown in Scheme 2. Compound XI was pre-
pared by FriedeleCraft’s acylation reaction of N-phenyl phthali-
mide-4-carbonyl chloride with toluene. The structure of the
compound XI was confirmed by 1H NMR and 13C NMR. The peaks at
2.5
respectively. The signals due to methyl, imide and carbonyl carbon
(ketone) were observed at 21.8 , 166.5 and 194.4 respectively.
d and 7.3e8.2 d are due to methyl and aromatic protons
d
d
d
Compound XI was brominated with N-bromosuccinimide and the
product XII was hydrolyzed using dilute sodium hydroxide solution
to give the corresponding aldehyde XIII. The aldehyde XIII was
oxidized to corresponding carboxylic acid XIV using KMnO4. The
hydrolysis of imide group was achieved using 10% NaOH solution to
yield the corresponding tricarboxylic acid. A broad peak at 2400e
3500 cmꢁ1 was observed in IR spectrum of XV, confirming the
presence of eCOOH group. 1H NMR spectrum of compound XV
(Fig. 3) showed peaks at 7.8e8.1
NMR spectrum showed peaks at 166.6
due to carboxylic acid and ketone group (Fig. 4). The spectral data
d
due to aromatic protons. The 13
, 167.4 , 168.0 and 194.5
C
d
d
d
d
Fig. 6. FTIR spectra of poly(amideimide)s.
is in agreement with the proposed structure of the compound XV.
The conversion of carboxylic acid (IV and XV) to anhydride
acidchloride (VI and XVII) was achieved by reaction with acetic
anhydride, followed by reaction with thionyl chloride. The two
anhydride acidchloride monomers were characterized by FTꢁIR1
(Fig. 5). IR spectra of monomers showed absorptions at 1850 cm
(VI) and 1845 cmꢁ1 (XVII) due to cyclic anhydride group, 1170 cmꢁ1
(VI) and 1180 cmꢁ1 (XVII) due to CeO stretch and 1770 cmꢁ1 (VI)
and 1775 cmꢁ1 (XVII) due to acidchloride group. These results
confirm the structure of anhydrideeacidchloride monomers.
(1.0 mmol) and pyridine (0.5 mL) were added. The reaction mixture
was stirred at room temperature for 6 h to yield poly(amide amic-
acid) solution. Chemical imidization was achieved by using a
mixture of acetic anhydride and triethylamine. The polymer solu-
tion was poured into methanol and the precipitated polymer was
collected by filtration, washed with methanol and dried.
3. Results and discussion
3.2. Synthesis of poly(amideimide)s
3.1. Synthesis of monomers
A series of poly(amideimide)s (PAI-1 to PAI-8) were prepared
from the two anhydride acidchloride monomers (Scheme 3).
Poly(amic-acid)s were prepared by the reaction of anhydride
acidchloride monomers with several aromatic diamines in NMP. All
the polymerizations proceeded homogeneously. The chemical
imidization of poly(amic-acid) was achieved using acetic anhydride
and triethylamine. The poly(amideimide)s were obtained in
quantitative yield (>93%) and had inherent viscosity in the range
0.42e0.58 dL/g (Table 1).
The scheme used for the preparation of monomers 4-(p-car-
boxyphenoxy)phthalic anhydride) and 4-(p-carboxybenzoyl)
phthalic anhydride is given in Schemes 1 and 2. The compound III
was synthesized by nucleophilic substitution reaction of N-methyl-
4-nitrophthalimide with p-hydroxybenzoic acid. The compound III
(imide) was hydrolyzed to the corresponding dicarboxylic acid (IV)
and the structure of 4-(p-carboxyphenoxy)phthalic acid (IV) was
confirmed by FTIR and NMR. FTIR spectrum showed absorption
bands at 2500e3500 cmꢁ1 (OeH stretch, eCOOH),1715 cmꢁ1 (C]O
stretch, eCOOH) and 1240 cmꢁ1 (AreOeAr, CeO stretching). The 1H
The structure of these polymers was confirmed by FTIR and 1H
NMR. FTIR spectra of PAI-3 and PAI-7 (Fig. 6) showed characteristic
Fig. 7. 1H NMR spectrum of PAI-3 in DMSO-d6.

5632
S. Rajasekar, D. Venkatesan / Polymer 54 (2013) 5626e5633
Fig. 8. 1H NMR spectrum of PAI-6 in DMSO-d6.
absorptions at 1775, 1770, 1715 and 1720 cmꢁ1 (asymmetric and
symmetric stretching, imide group), 3480 and 3490 cmꢁ1 (NeH
stretching) and 1649, 1657 cmꢁ1 (amide group). 1H NMR spectra of
3.5. X-Ray diffraction
The crystallinity of poly(amideimide)s was studied by powder
X-ray diffraction and the representative diffractograms (PAI-4 and
PAI-8) are shown in Fig. 11. The X-ray diffractograms of these
polymers showed diffused pattern which indicate amorphous na-
ture of these poly(amideimide)s. Aromatic poly(amideimide)s
generally exhibit highly crystallinity. The decrease in crystallinity of
PAIs (Figs. 7 and 8) showed absorptions at 7.1e8.0
d
due to aromatic
protons. The signals observed at 10.2
protons.
d and 10.7 d are due to amide
3.3. Solubility characteristics
The solubility characteristics of these polymers were studied in
various organic solvents (Table 2). All PAIs showed good solubility
in polar aprotic solvents such as DMSO, DMF, DMAc and NMP at
room temperature. PAI-4 and PAI-8 were highly soluble in pyridine
and moderately soluble in THF due to the presence of sulfone group
in the polymer backbone.
3.4. Thermal properties
The thermal properties of the poly(amideimide)s were evalu-
ated by differential scanning calorimetry (DSC) and thermogravi-
metric analysis (TGA). A representative DSC curve is shown in
Fig. 10. The glass transition temperature of these poly(amideimide)
s was in the range 226e269 ꢀC (Table 3). The 10% weight loss
temperature as well as char yield at 800 ꢀC were determined by
TGA (Table 3). The 10% weight loss temperature of these poly(-
amideimide)s was in the range of 425e461 ꢀC. The char yield of
these polymers at 800 ꢀC was in the range 40e61% (Fig. 9). The
polymer backbone essentially contains aromatic rings, imide
groups and amide groups, which is the reason for high thermal
stability of these polymers.
Fig. 9. TGA curves of poly(amideimide)s.
Table 2
Solubility of the poly(amideimide)s in different organic solvents.
Polymer
DMSO
NMP
DMF
DMAc
Pyridine
THF
H2SO4
PAI-1
PAI-2
PAI-3
PAI-4
PAI-5
PAI-6
PAI-7
PAI-8
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þꢁ
þꢁ
þꢁ
þ
ꢁꢁ
ꢁꢁ
ꢁꢁ
þꢁ
ꢁꢁ
ꢁꢁ
ꢁꢁ
ꢁꢁ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
ꢁꢁ
þꢁ
þꢁ
þꢁ
þþ soluble on RT, þ soluble on heating, þꢁ partially soluble on heating, ꢁꢁ
insoluble even on heating.
Fig. 10. DSC curves of poly(amideimide)s.

S. Rajasekar, D. Venkatesan / Polymer 54 (2013) 5626e5633
5633
Table 3
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Decomposition
Char yieldc (%)
temperatureb (ꢀC)
Tg (ꢀC)
Td10
Td15
Td20
PAI-1
PAI-2
PAI-3
PAI-4
PAI-5
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57
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40
49
52
43
57
247
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a
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carbonyl groups in the polymer backbone, which restricts the or-
dered packing of polymer chains.
4. Conclusion
A series of poly(amideimide)s were prepared by the poly-
condensation of two anhydride acidchloride monomers with
several aromatic diamines. All the polymers showed good solubility
in polar aprotic solvents. These polymers had high glass transition
temperature and showed excellent thermal stability comparable to
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