Synthesis and characterization of novel thermally stable aromatic and semiaromatic polyamides derived from thiourea-based flexible diacid dichlorides

Article abstract of DOI:10.1007/s00706-010-0422-1

New diacid dichlorides bearing phenyl thiourea groups were prepared by a facile synthetic approach and characterized using spectroscopic and elemental analyses. A series of novel aromatic and semiaromatic polyamides were prepared via a condensation route

Full text of DOI:10.1007/s00706-010-0422-1

Monatsh Chem (2011) 142:201–209
DOI 10.1007/s00706-010-0422-1
ORIGINAL PAPER
Synthesis and characterization of novel thermally stable aromatic
and semiaromatic polyamides derived from thiourea-based
flexible diacid dichlorides
•
•
•
Ayesha Kausar Sonia Zulfiqar Liaquat Ali
Muhammad Ilyas Sarwar
Received: 29 January 2010 / Accepted: 8 November 2010 / Published online: 7 December 2010
Ó Springer-Verlag 2010
Abstract New diacid dichlorides bearing phenyl thiourea
groups were prepared by a facile synthetic approach and
characterized using spectroscopic and elemental analyses.
A series of novel aromatic and semiaromatic polyamides
were prepared via a condensation route from the synthe-
sized diacid dichlorides with 4,40-oxydianiline. The
polymers were characterized by FT-IR, 1H NMR, 13C
NMR, and their physical properties, including their solu-
tion viscosities, solubilities and thermal properties, were
studied too. Polyamides with phenyl thiourea moieties in
the backbone showed good solubilities in amide solvents
such as DMAc, DMF, DMSO, and NMP. All of the syn-
thesized polymers had ginh values of 0.042–0.053 dm3/g,
and were obtained in quantitative yield. GPC measure-
ments of the synthesized polyamides indicated Mw values
of 64,759–86,172. The crystallinity of the polymers was
evaluated via their X-ray diffraction patterns. Their glass
transition temperatures were found to be 218–229 °C.
Furthermore, thermogravimetric analysis indicated that the
polymers were thermally stable in the range 300–398 °C in
a N2 atmosphere.
Introduction
Polyamides that are stable at high temperatures and have a
favorable balance of physical and chemical properties are
increasingly in demand as performance materials for
industrial and aerospace applications [1, 2]. However, dif-
ficulties are encountered when processing these polymers
into articles due to their high melting and glass transition
temperatures and their limited solubilities in common
organic solvents. Processable engineering plastics possess-
ing moderately high softening temperatures and solubilities
in some organic solvents are required for practical use.
Aromatic polyamides have generally proven to be difficult
in this respect, since they show a tendency to decompose
during or even before melting, and have limited solubility
[3–6]. Consequently, efforts to chemically modify the
compositions of these materials are being made with the
objective of improving their processability. The major
factors that account for the low solubility of aromatic
polyamides are molecular order and strong interchain
attractive forces—mainly hydrogen bonding, which enhan-
ces the molecular packing. Consequently, it is acknowl-
edged that the incorporation of bulky pendant groups is
beneficial to solubility, because this approach separates the
chains, weakens hydrogen bonding, and lowers chain
packing, while gaining free volume. Accordingly, bulky side
groups restrict molecular mobility, so that the overall
observable effect is a rise in the glass transition temperature
and an improvement in the solubility (processability)
[7–12]. Furthermore, it has been shown that the incorpora-
tion of flexible linkages into the main polymer chain
greatly enhances molecular mobility and provides better
solubility, but it decreases thermal transitions and stability
[13, 14]. For this reason, a number of attempts have been
made to enhance the processability of polyamides without
Keywords Phenyl thiourea groups ꢀ Polyamides ꢀ
Diacid dichloride ꢀ IR spectroscopy ꢀ NMR spectroscopy ꢀ
Condensation
A. Kausar ꢀ S. Zulfiqar ꢀ L. Ali ꢀ M. I. Sarwar (&)
Department of Chemistry, Quaid-i-Azam University,
Islamabad 45320, Pakistan
e-mail: ilyassarwar@hotmail.com
123

202
A. Kausar et al.
incurring any significant reduction in thermal stability
[15–17].
Scheme 2. The basic reaction employed here is the con-
densation [27] of an aromatic acid chloride and an amine,
which is generally known to be fast and quantitative.
The main objective of this study is to produce modified
polyamides with improved solubility and processability
without deteriorating their thermal properties. The poly-
merization technique used in this work is relatively simple,
and produced polymers in satisfactorily high yields and
with fairly good ginh values and molecular weights (Mw).
Generally, these polymers were yellow in color owing to
the presence of phenylthiourea groups in the polymer
backbone. The structures of the synthesized polyamides
were investigated by FT-IR and NMR spectroscopic tech-
niques. The thermal stabilities, Tg values, and crystallinities
of 7a–7d were also studied using the corresponding tech-
niques, as described below.
The introduction of the thiourea group into the poly-
amide backbone as a flexibilizing agent is a relatively
unexplored area. The thiourea group introduces additional
features like biomedical activity [18], corrosion inhibition
[19–22], organic thermal stabilization [23], and semicon-
ductivity [24, 25]. Moreover, thiourea-based coordinating
polymers have been synthesized that can potentially be
used to bind to noble metals [26]. In this study, the
deliberate incorporation of phenyl thiourea groups into the
polymer backbone enhanced the solubility and process-
ability of polyamides without any significant reduction in
thermal stability. It was shown that thiourea moieties
undermine the packing efficiency of polyamides by
forming flexible intermolecular hydrogen-bonding net-
works. This prompted us to synthesize a new series of
polyamides bearing both carbonyl and thiocarbonyl moi-
eties, with the objective of obtaining new multifunctional
polymers. Thus, poly(thiourea amides) possess multiple
hydrogen-bonding interactions because thiocarbonyl is
capable of participating in weaker intermolecular hydro-
gen bonds (C=S_H) than amide carbonyl (C=O_H).
The present work aimed to create processable polyamides
with improved solubility while conserving the thermal
stability of the polyamides at a high level. Aromatic and
semiaromatic (aromatic–aliphatic) polyamides with phenyl
thiourea groups in the backbone were successfully syn-
thesized from two wholly aromatic diacid dichlorides
[isophthaloyl bis(3-(3-chlorocarbonylphenyl)thiourea) and
terephthaloyl bis(3-(3-chlorocarbonylphenyl)thiourea)] and
two semiaromatic [adipoyl bis(3-(3-chlorocarbonylphenyl)
thiourea) and sebacoyl bis(3-(3-chlorocarbonylphenyl)
thiourea)] diacid dichlorides using a solution polyconden-
sation [27] procedure. All monomers and polymers
The main structural modification of 7a–7d was the
introduction of thiourea linkages in polymers backbones to
augment their solubilities while retaining their thermal
stabilities. These thiourea moieties interrupted their inter-
molecular hydrogen bonding, and degraded their stacking
efficiency. Hence, multiple hydrogen-bonding interactions
(C=S_H and C=O_H) were observed in the poly(thio-
urea amides), as depicted in Scheme 3 [28]. Moreover,
previous research suggested that thioureas have improved
O
C
R
C
O
O
C
R
C
O
Cl
Cl
C
C
S
S
N
N
KNCS / dry benzene
110-120 °C, 6 h
1a-1d
2a-2d
NH2
O
CH2Cl2,
RT, 1 h
1
were characterized by FT-IR, H NMR, and 13C NMR.
HO
3
Attention was focused upon polymer properties such as
thermal stability, thermal properties, crystallinity, solubil-
ity behavior, inherent viscosity, as well as molecular
weight.
S
O
O
S
HO
OH
R
N
N
N
H
N
H
H
H
O
O
4a-4d
SOCl2
S
Results and discussion
S
O
O
Monomer and polymer synthesis
Cl
Cl
R
N
N
H
N
H
N
H
H
The new aromatic and semiaromatic polyamides 7a–7d
containing thiourea units were synthesized from new diacid
dichloride monomers (Scheme 1). Initially, the synthesis of
dicarboxylic acids 4a–4d was accomplished using diis-
othiocyanate compounds 2a–2d, which on treatment with
thionyl chloride yielded corresponding diacid dichlorides
5a–5d. The synthetic route leading to 7a–7d is depicted in
O
O
5a-5d
a
d
b
c
(CH2)4
(CH2)8
R=
Scheme 1
123

Synthesis and characterization of aromatic and semiaromatic polyamides
203
Scheme 2
H2N
NH2
S
O
O
S
Cl
+
Cl
R
N
H
N
H
N
N
O
H
H
O
O
O
DMAc
5a-5d
6
S
O
O
S
H
H
N
N
R
N
H
N
H
N
N
H
H
O
O
7a-7d
Scheme 3
S
O
O
N
H
N
O
H
H
H
N
O
H
N
N
N
O
H
S
O
S
O
H
N
N
O
H
N
H
H
N
H
N
O
N
O
H
O
S
O
H
N
H
N
N
O
S
H
H
N
N
N
S
H
H
O
O
Strong H-Bonding due to amide carbonyl
Weak H-Bonding due to thio carbonyl
properties as hydrogen-bond donors, form more flexible
hydrogen-bonding networks, and show a lower tendency to
self-associate than the corresponding urea analogs. Con-
cisely, the introduction of the C=S units into polyamides
7a–7d led to enhanced solubility and a relatively high Tg
owing to the resulting reduction in segmental mobility as
well as the increased steric hindrance. Thus, a vigilant
investigation revealed that the introduction of C=S groups
in order to increase the solubility and processability of
polyamides was successful.
Table 1 Solubility characteristics of the polyamides
Polymer
Solvent
NMP
DMAc
DMF
DMSO
THF
m-Cresol
7a
7b
7c
7d
??
??
??
??
??
??
??
??
??
??
??
??
??
??
??
??
-
-
-
-
?-
?-
?-
?-
Solubility: ?? soluble at room temperature; ?- partially soluble at
room temperature, - insoluble
Organosolubility
All of the investigated polymers were found to be highly
soluble in common organic polar solvents such as DMAc,
DMSO, NMP, and DMF at room temperature (Table 1).
The solubility was evaluated with 15 mg of the polymer in
1 cm3 of the solvents at room temperature. In general, high
solubility is desirable for polymer processing. The good
organosolubility of the polyamides can be attributed to the
presence of the flexible thiourea groups in the polymer
framework. Furthermore, the presence of the flexible ether
group in the diamine moiety also had a beneficial effect on
the solubilities of the polyamides. It was also established
that the semiaromatic polyamide 7d with the longest alkyl
chain dissolved much more quickly at room temperature
than the aromatic polyamides 7a and 7b which have rigid
chain structures. The solubilities of the polymers follow the
order:
123

204
A. Kausar et al.
their polymer chains are more rigid. On the other hand, ginh
decreased with the incorporation of alkyl groups into the
diacid dichlorides 5c and 5d when compared with 7a and
7b. Accordingly, the polyamide 7b with p-linkages yielded
the highest ginh (0.053 dm3/g), whereas 7d, which has the
longest alkyl chain, produced the lowest viscosity of
0.042 dm3/g. Furthermore, the polyamide 7a, which only
has meta linkages, had an intermediate ginh value of
0.050 dm3/g (i.e., in-between these two extreme values).
The higher inherent viscosity value of the p-oriented type
of polymer was attributed to its higher rigidity and its
increased interchain hydrogen bonding, which are associ-
ated with higher chain symmetry and packing efficiency.
Additionally, GPC measurements during the molecular
weight analysis of 7a–7d supported the above arguments.
The weight-average Mw values and the polydispersity
indices determined by GPC are specified in Table 2. The
Mw values of about 86,172–64,759 indicate that 7a–7d,
which bear C=S moieties, have fairly high molecular
weights. Correspondingly, 7b, which has p-oriented rigid
7d [ 7c [ 7a [ 7b:
Regardless of the nature of the solvent used, it was
perceived that 7a—with all m-linkages—appeared to be
rapidly soluble when compared with 7b, which contains
both m- and p-linkages. In addition, 7b formed viscous
solutions, even at low concentrations. This behavior
indicates that the p-oriented type of polymer possesses
increased rigidity, packing efficiency, and hydrogen
bonding. Likewise, it was observed that the incorporation
of flexible thiourea units into the polymer backbone causes
a decrease in crystallinity and enhances the solubility and
processability of aromatic as well as semiaromatic
polyamides.
Viscometry and molecular weight
The ginh values of polyamides measured at a concentration
of 0.5 g/100 cm3 in DMSO at 30 °C were about 0.042–
0.053 dm3/g (Table 2). It was found that the aromatic
polyamides possess higher ginh values, which indicates that
Table 2 ginh and Mw values as well as the yields of 7a–7d
Polymer
ginh (dm3/g)
Mw
Mw/Mn
Yield (%)
94
0.050
82,789
1.42
O
O
H
N
N
H
S
O
HN
O
HN
HN
S
HN
O
7a
0.053
86,172
1.35
96
S
O
O
N
H
N
H
O
H
H
O
N
N
H
N
N
H
O
S
7b
0.044
0.042
71,763
64,759
1.43
1.45
95
95
S
O
O
S
H
N
H
N
N
H
N
N
N
(CH2)4
H
H
H
O
O
O
7c
S
O
O
S
H
N
H
N
N
H
N
N
H
N
H
(CH2)8
H
O
O
O
7d
123

Synthesis and characterization of aromatic and semiaromatic polyamides
205
units in the backbone, exhibited the highest Mw value of
86,172.
PAMD 1
7a
100
80
PAMD 2
7b
P7AcMD 3
P7AdMD 4
Thermal analyses
The DSC and TGA techniques were used to study the
thermal behaviors and thermal properties of 7a–7d
(Table 3). These properties were followed in N2 at a
heating rate of 10 °C/min. The Tg values (where Tg taken
as the midpoint of the change in slope of the baseline) of
7a–7d were between 218 and 229 °C, and the representa-
tive DSC curves are shown in Fig. 1.
60
40
20
100
200
300
400
500
600
700
Temperature / oC
It appeared that the Tg values of 7a–7d were dependent
on the chemical structures of the diacid dichlorides 5a–5d.
In view of this, 7b exhibited the highest Tg value because
of the p-oriented aromatic nature of its rigid polymer
backbone. On the other hand, 7d, which was derived from
the aliphatic diacid dichloride 5d, showed the lowest Tg
value due to its long, flexible alkyl groups. As a general
rule, when the crystallinity of a polymer increases, its heat
resistance also increases. For this reason, these results were
also corroborated by X-ray diffraction patterns of 7a–7d.
Fig. 2 TGA curves of 7a–7d obtained at a heating rate of 10 °C/min
in N2
100
0
90
80
-10
-20
-30
70
60
50
40
30
Table 3 Thermal analysis data of 7a–7d
-40
-50
Polymer Tg (°C) T0 (°C) T10 (°C) Tmax (°C) Yc at 600 °C (%)
-60
7a
7b
7c
7d
222
229
219
218
338
350
282
274
380
398
319
300
552
576
530
528
59
66
49
40
100
500
600
700
200
300
400
Temperature / OC
Fig. 3 TGA and DTG thermograms of 7a
Tg glass transition temperature, T0 initial decomposition temperature,
T10 temperature required for a 10% weight loss, Tmax maximum
decomposition temperature, Yc char yield; weight of polymer
remaining
Polyamide 7b, which has high thermal properties, dis-
played a crystalline pattern, whilst 7c and 7d showed
amorphous behavior (Fig. 4).
According to the TGA data, the initial decomposition
temperatures (T0) were about 274–350 °C, and the tem-
peratures for 10% gravimetric loss (T10, which is an
important indicator of thermal stability) were in the range of
300–398 °C (Fig. 2). Subsequently, the maximum decom-
position temperatures (Tmax) were about 528–576 °C, and
the char yields of 7a–7d (600 °C) were around 40–66%.
Tmax values for 7a–7d were evaluated from DTG thermo-
grams, as illustrated in Fig. 3.
2
1
PAMD 1
7a
PAMD 2
7b
PAMD 3
7c
PAMD 4
7d
0
-1
-2
Moreover, 7a–7d illustrated a double-step decomposi-
tion pattern from 300 to 600 °C, indicating a complex
degradation mechanism. Apparently, the flexible thiourea
group and the electrophilic oxygen atom in 6 allow looser
molecular packing, resulting in improved solubility in
organic solvents without degrading the thermal properties
of 7a–7d.
100
150
200
250
Temperature / oC
Fig. 1 DSC thermograms of 7a–7d obtained at a heating rate of
10 °C/min in N2
123

206
A. Kausar et al.
versus solubility) was observed for these polyamides. The
incorporation of thiourea groups into the polymer back-
bones in order to enhance the solubility and processability
of the polyamides without significantly reducing the ther-
mal stability was achieved. The properties of the polymers
were strongly affected by their structures; the incorporation
of aliphatic units in the place of aromatic ones within the
polymers greatly affected their physical and thermal
properties. In general, it was established that the intro-
duction of p-phenylene rings led to polymers with higher
thermal stabilities, ginh values, and molecular weights.
These properties indicated the regularity of the supermo-
lecular packing occurring within the bulk of polymer in
addition to the collinear arrangement of the p-phenylene
units, which permits the establishment of stronger inter-
chain hydrogen bonding. On the other hand, semiaromatic
polyamides with aliphatic contents exhibited lower thermal
stabilities, ginh values, and molecular weights, indicating an
overall flexibility of the polymer chains. Therefore, 5a–5d
can be considered candidates for the preparation of soluble
and heat-resistant polyamides. Furthermore, this novel
series of multifunctional poly(thiourea amides) can be
exploited as potentially excellent candidates in supramo-
lecular chemistry due to their specific interactions with
biologically important anions [32, 33], in addition to their
potential use as ideal supports for immobilized enzymes
and to bind to noble metals.
7a
7b
7c
7d
20
10
15
25
30
35
40
45
20 / °
Fig. 4 X-ray diffraction patterns of 7a–7d
X-ray diffraction
X-ray diffraction scans with 2h ranging from 5° to 50° for
powder specimens were obtained for the synthesized
polyamides (Fig. 4). Certain sharp peaks were observed in
the X-ray diffractrogram of 7b in the region 2h = 16–30°.
The crystalline morphology of 7b may be related to the
rigidity of the p-phenylene structure, a hypothesis sup-
ported by its higher thermal stability. However, the XRD
pattern for 7a revealed small crystalline peaks at around
20° and 28°, which demonstrated a small degree of crys-
tallinity. Nevertheless, the semiaromatic polyamides 7c
and 7d showed almost amorphous behavior. This is
because the presence of an aliphatic group in addition to
the flexible ether group in 6 reduce intermolecular forces
between the polymer chains, causing a decrease in crys-
tallinity. On the whole, new wholly aromatic polyamides
gave crystalline patterns, whereas semiaromatic polya-
mides showed amorphous behaviour.
Experimental
Materials
3-Aminobenzoic acid (3, 97%), isophthaloyl chloride (1a,
98%), terephthaloyl chloride (1b, 99%), potassium thio-
cyanate (98%), and dimethylformamide (DMF, 99%), all
procured from Fluka, were used. N-Methylpyrrolidone
(NMP, 99%), dimethyl sulfoxide (DMSO, 99%), and
benzene (99%) were purchased from Merck. 4,40-Oxydi-
aniline (6, 97%), adipoyl chloride (1d, 98%), sebacoyl
chloride (1c, 92%), and N,N-dimethylacetamide (DMAc,
99%), all obtained from Aldrich, were used as received.
Conclusions
The design and synthesis of the novel diacid dichlorides
5a–5d that could be used in the preparation of thermally
stable polyamides with improved solubility was our main
aim. Consequently, 5a–5d were successfully prepared in
high yield from dicarboxylic acids 4a–4d in the presence of
SOCl2. In the present study, a series of aromatic and
semiaromatic polyamides 7a–7d were synthesized by
solution polycondensation of diacid dichlorides containing
phenyl thiourea units and commercially available dia-
mines. A nice balance of properties (thermal stability
Measurements
IR spectra of the monomers and polymers were obtained at
room temperature at a resolution of 4 cm-1 using an
Excalibur Series FTIR spectrometer, model No. FTSW 300
MX, manufactured by Bio-Rad. NMR spectra were recor-
ded at room temperature using a Bruker spectrometer
operating at 300.13 MHz for 1H and at 75.47 MHz for 13
C
NMR. The solvent used in the analysis was DMSO-d6.
Elemental analysis was performed using a PerkinElmer
123

Synthesis and characterization of aromatic and semiaromatic polyamides
2400 CHN elemental analyzer; found values agreed
207
recrystallized from methanol. Diacid 4b (1.00 g,
0.002 mol) was dissolved in 20 cm3 of a 1:1 mixture of
acetone:ethanol. The sample was titrated with 0.1 M KOH
solution using phenolphthalein as indicator, so the acid
value was calculated potentiometrically. Diacid 4b was
found to be 95% pure. The other dicarboxylic acids 4a, 4c,
and 4d were prepared by the same procedure but using the
appropriate diisothiocyanate 2a, 2c, and 2d instead.
favorably with calculated ones. Inherent viscosity (ginh
)
was measured in DMSO at 30 °C with an Ubbelohde vis-
cometer for polymer solutions at concentrations of 0.5 g/
100 cm3. Gel permeation chromatography (GPC) analysis
was carried out with Waters Alliance GPCV2000 for
molecular weight determination. Polystyrene was
employed as the standard and THF was used as an eluent.
The eluents were monitored with a refractive index (RI)
detector. Qualitative solubility was determined with 15 mg
of polymer in 1 cm3 of various solvents at room temper-
ature. Thermal stability of the polyamides was determined
by Mettler Toledo TGA/SDTA 851e thermogravimetric
analyzer using 1–5 mg of the sample in an Al2O3 crucible
at a heating rate of 10 °C/min under a nitrogen atmosphere
at a gas flow rate of 30 cm3/min. Differential scanning
calorimetry (DSC) was performed to obtain glass transition
temperatures by a Mettler Toledo DSC 822e differential
scanning calorimeter, using 5–10 mg of samples encapsu-
lated in aluminum pans and heated at a rate of 10 °C/min
under a nitrogen atmosphere. X-ray diffraction patterns
were obtained at room temperature on an X-ray diffrac-
tometer (3040/60 X’pert PRO) using Ni-filtered Cu Ka
radiation (40 kV, 30 mA) at a scanning rate of 0.04°/s.
3,30-[(1,3-Phenylene)bis(carbonyliminocarbonothioyl-
imino)]bis[benzoic acid] (4a, C24H18N4O6S2)
Dirty white solid; yield 94%; FTIR (KBr): vꢀ = 3,399 (O–H),
3,345 (N–H), 3,108, 1,703 (acid C=O), 1,687 (amide C=O),
1,587, 1,413 (C–N), 1,156 (C=S) cm-1
;
1H NMR
(DMSO-d6): d = 6.80 (d, 2H, ArH), 7.22 (t, 2H, ArH),
7.33 (s, 2H, ArH), 7.49 (d, 2H, ArH), 7.62 (t, 1H, ArH), 8.20
(d, 2H, ArH), 8.64 (s, 1H, ArH), 9.40 (s, 2H, ArNH), 10.42
(s, 2H, amide NH), 12.04 (s, 2H, OH) ppm; 13C NMR
(DMSO-d6): d = 126.30, 129.07, 131.69, 137.01, 124.90,
125.10, 129.10, 130.60, 130.91, 134.31, 169.01 (amide
C=O), 169.4 (acid C=O), 181.30 (C=S) ppm.
3,30-[(1,4-Phenylene)bis(carbonyliminocarbonothioyl-
imino)]bis[benzoic acid] (4b, C24H18N4O6S2)
Dirty white solid; yield 95%; FTIR (KBr): vꢀ = 3,404 (O–H),
3,291 (N–H), 3,068, 1,704 (acid C=O), 1,686 (amide C=O),
1,586, 1,413 (C–N), 1,186 (C=S), 804, 878 cm-1; 1H NMR
(DMSO-d6): d = 6.91 (d, 2H, ArH), 7.23 (t, 2H, ArH), 8.01
(d, 2H, ArH), 8.31 (s, 2H, ArH), 8.74 (s, 4H, p-ArH), 9.45 (s,
2H, ArNH), 10.44 (s, 2H, amide NH), 12.06 (s, 2H, OH)
ppm; 13C NMR (DMSO-d6): d = 125.01, 126.30, 129.77,
131.70, 134.50, 139.01, 128.32, 139.60, 169.01 (amide
C=O), 169.4 (acid C=O), 182.90 (C=S) ppm.
Monomer synthesis
General procedure for the preparation of diisothiocyanates
2a–2d
A saturated solution of 40 g potassium thiocyanate
(0.41 mol) in 300 cm3 boiling ethanol was poured into
1.5 dm3 of diethylether, forming a fine white powder. The
solid was collected by filtration and washed with 300 cm3
of diethylether. Finely powdered potassium isothiocyanate
was isolated after drying in vacuum at 110 °C for 10 h.
A mixture of 1 mol diacid dichloride 1a–1d, 194 g of
finely pulverized and thoroughly dried potassium isothio-
cyanate (2 mol), and 500 cm3 of dry benzene was refluxed
for 6 h at 110–120 °C. The mixture was subsequently fil-
tered twice through a Buchner funnel. The salt was
removed by filtration and the excess of benzene was
evaporated in a vacuum oven at 80 °C [29].
3,30-[(Butane-1,4-diyl)bis(carbonyliminocarbonothioyl-
imino)]bis[benzoic acid] (4c, C22H22N4O6S2)
Light brown solid; yield 95%; FTIR (KBr): vꢀ = 3,394
(O–H), 3,335 (N–H), 3,101, 2,916, 1,701 (acid C=O),
1,686 (amide C=O), 1,586, 1,412 (C–N), 1,155
;
(C=S) cm-1 1H NMR (DMSO-d6): d = 2.18 (t, 4H,
CH2), 1.57 (m, 4H, CH2), 6.79 (d, 2H, ArH), 7.20 (t, 2H,
ArH), 7.31 (s, 2H, ArH), 7.47 (d, 2H, ArH), 9.39 (s, 2H,
ArNH), 10.40 (s, 2H, amide NH), 12.00 (s, 2H, OH) ppm;
13C NMR (DMSO-d6): d = 25.10, 35.51, 126.10, 124.81,
129.01, 130.41, 131.59, 136.90, 169.39 (acid C=O), 175.30
(amide C=O), 181.20 (C=S) ppm.
General procedure for the synthesis of diacids 4a–4d;
example 4b
A solution of 2b (2.48 g, 0.01 mol; synthesized as descri-
bed above) in 50 cm3 of dichloromethane was cooled to
0 °C followed by the addition of 2.74 g (0.02 mol) of 3-
aminobenzoic acid (3) with continuous stirring for 1 h
under an inert atmosphere [29, 30]. The solution was then
washed with 1% HCl, distilled water, and brine. The sol-
vent was removed by filtration and dried under vacuum,
yielding the solid product. The crude product was then
3,30-[(Octane-1,8-diyl)bis(carbonyliminocarbonothioyl-
imino)]bis[benzoic acid] (4d, C26H30N4O6S2)
Light brown solid; yield 94%; FTIR (KBr): vꢀ = 3,391 (O–H),
3,329 (N–H), 3,100, 2,911, 1,701 (acid C=O), 1,685 (amide
1
C=O), 1,586, 1,413 (C–N), 1,154 (C=S) cm-1; H NMR
(DMSO-d6): d = 2.18 (t, 4H, CH2), 1.57 (m, 4H, CH2), 1.29
(m, 8H, CH2), 6.78 (d, 2H, ArH), 7.19 (t, 2H, ArH), 7.30 (s,
2H, ArH), 7.45(d, 2H, ArH), 9.39(s, 2H, ArNH), 10.38 (s, 2H,
123

208
A. Kausar et al.
amide NH), 11.98 (s, 2H, OH) ppm; 13C NMR (DMSO-d6):
d = 26.02, 28.72, 29.03, 36.21, 124.71, 126.01, 129.03,
130.36, 131.49, 136.89, 169.36 (acid C=O), 175.29 (amide
C=O), 181.11 (C=S) ppm.
ArNH), 10.13 (s, 2H, amide NH) ppm; 13C NMR (DMSO-
d6): d = 35.51, 25.03, 125.91, 127.31, 129.32, 133.01,
133.42, 137.21, 167.85 (acid chloride C=O), 175.33 (amide
C=O), 181.21 (C=S) ppm.
3,30-[(Octane-1,8-diyl)bis(carbonyliminocarbono-
thioylimino)]bis[benzoic acid chloride]
(5d, C26H28Cl2N4O4S2)
General procedure for the synthesis of diacid dichlorides
5a–5d; example 5b
Diacid dichloride 5b was prepared by reacting an excess of
thionyl chloride and 4b at 35 °C for 7 days [31]. The crude
product was recrystallized from acetone. A sample (1.0 g,
1.7 mmol) was dissolved in 20 cm3 of a 1:1 mixture of
acetone. Then the sample was titrated with 0.1 M KOH
solution using phenolphthalein as indicator, and the acid
value was calculated potentiometrically. Diacid dichloride
5b was found to be 94% pure. The other diacid dichlorides
5a, 5c, and 5d were prepared and analyzed by the same
methods.
Dark brown solid; yield 95%; FTIR (KBr): vꢀ = 3,253 (N–
H), 3,107, 2,896, 1,785 (acid chloride C=O), 1,686 (amide
1
C=O), 1,594, 1,413 (C–N), 1,155 (C=S) cm-1; H NMR
(DMSO-d6): d = 1.29 (m, 8H, CH2), 1.57 (m, 4H, CH2),
2.18 (t, 4H, CH2), 6.65 (d, 2H, ArH), 7.06 (s, 2H, ArH),
7.12 (t, 2H, ArH), 7.22 (d, 2H, ArH), 9.10 (s, 2H, ArNH),
10.11 (s, 2H, amide NH) ppm; 13C NMR (DMSO-d6):
d = 26.03, 28.73, 29.03, 36.22, 123.41, 124.81, 129.02,
130.90, 137.11, 137.13, 171.31 (acid chloride C=O),
175.31 (amide C=O), 181.21 (C=S) ppm.
3,30-[(1,3-Phenylene)bis(carbonyliminocarbono-
thioylimino)]bis[benzoic acid chloride]
(5a, C24H16Cl2N4O4S2)
General procedure for the synthesis of polyamides 7a–7d;
example 7b
Gray solid; yield 94%; FTIR (KBr): vꢀ = 3,285 (N–H),
3,088, 1,782 (acid chloride C=O), 1,686 (amide C=O),
1,590, 1,413 (C–N), 1,154 (C=S) cm-1; 1H NMR (DMSO-
d6): d = 6.73 (d, 2H, ArH), 7.11 (t, 2H, ArH), 7.17 (s, 2H,
ArH), 7.33 (d, 2H, ArH), 7.52 (t, 1H, ArH), 8.19 (d, 2H,
ArH), 8.54 (s, 1H, ArH), 9.19 (s, 2H, ArNH), 10.14 (s, 2H,
amide NH) ppm; 13C NMR (DMSO-d6): d = 125.12,
129.02, 130.90, 134.31, 126.01, 127.41, 129.43, 133.11,
133.60, 137.41, 167.90 (acid chloride C=O), 169.43 (amide
C=O), 181.32 (C=S) ppm.
A 100 cm3 two-necked round-bottom flask equipped with a
dropping funnel and gas inlet tube was charged with a
solution of 0.1 g 6 (0.5 mmol) in 12 cm3 DMAc. Trieth-
ylamine (0.1 g, 1 mmol) was added to the solution and
0.28 g 5b (0.5 mmol) dissolved in 5 cm3 DMAc were
added dropwise to the solution at 0 °C under N2 with
constant stirring for 5 h and then at room temperature
overnight in a N2 atmosphere. The solution was subse-
quently poured into water, and the yellow precipitate of 7b
was filtered off and washed with distilled water. Eventu-
ally, the obtained product was dried in vacuum at 80 °C for
24 h. This method was also used for the preparation of 7a,
7c, and 7d using 5a, 5c, and 5d and 6. Yields of polymers
are given in Table 2.
3,30-[(1,4-Phenylene)bis(carbonyliminocarbono-
thioylimino)]bis[benzoic acid chloride]
(5b, C24H16Cl2N4O4S2)
Gray solid; yield 94%; FTIR (KBr): vꢀ = 3,283 (N–H),
3,076, 1,783 (acid chloride C=O), 1,689 (amide C=O),
1,592, 1,412 (C–N), 1,155 (C=S), 678, 804, 871 cm-1; H
Poly[imino-1,4-phenyleneoxy-1,4-phenyleneiminocarbon-
yl-1,3-phenyleneiminocarbonothioyliminocarbonyl-
1,3-phenylenecarbonyliminocarbonothioylimino-
1,3-phenylenecarbonyl] (7a, (C36H26N6O5S2)n)
1
NMR (DMSO-d6): d = 6.97 (d, 2H, ArH), 7.30 (t, 2H,
ArH), 8.08 (d, 2H, ArH), 8.28 (s, 2H, ArH), 8.78 (s, 4H,
ArH), 9.19 (s, 2H, ArNH), 10.14 (s, 2H, amide NH) ppm;
13C NMR (DMSO-d6): d = 128.32, 139.89, 125.01,
129.93, 131.68, 133.86, 135.07, 137.01, 167.63 (acid
chloride C=O), 169.50 (amide C=O), 181.31 (C=S) ppm.
FTIR (KBr): vꢀ = 3,300 (N–H), 3,100, 1,663 (amide C=O),
1,596, 1,412 cm-1(C–N), 1,262 (C–O), 1,124 (C=S) cm-1
;
1H NMR (DMSO-d6): d = 6.39 (d, ArH ODA unit), 6.64
(d, ArH ODA unit), 7.00 (s, ArH), 7.21(d, ArH), 7.43 (t,
ArH), 7.83 (d, ArH), 8.20 (d, ArH), 8.64 (s, ArH), 9.39 (Ar
NH), 10.36 (amide NH) ppm.
3,30-[(Butane-1,4-diyl)bis(carbonyliminocarbono-
thioylimino)]bis[benzoic acid chloride]
(5c, C22H20Cl2N4O4S2)
Poly[imino-1,4-phenyleneoxy-1,4-phenyleneiminocarbon-
yl-1,3-phenyleneiminocarbonothioyliminocarbonyl-
1,4-phenylenecarbonyliminocarbonothioylimino-
Dark brown solid; yield 94%; FTIR (KBr): vꢀ = 3,323
(N–H), 3,106, 2,899, 1,786 (acid chloride C=O), 1,687
(amide C=O), 1,595, 1,412 (C–N stretch), 1,154 (C=S
1,3-phenylenecarbonyl] (7b, (C36H26N6O5S2)n)
FTIR (KBr): vꢀ = 3,283 (N–H), 3,077, 1,669 (amide C=O),
1,597, 1,417 (C–N), 1,258 (C–O), 1,121 (C=S
;
stretch) cm-1 1H NMR (DMSO-d6): d = 6.38 (d, ArH
stretch) cm-1
;
1H NMR (DMSO-d6): d = 2.18 (t, 4H,
CH2), 1.57 (m, 4H, CH2), 6.71 (d, 2H, ArH), 7.10 (t, 2H,
ArH), 7.15 (s, 2H, ArH), 7.30 (d, 2H, ArH), 9.14 (s, 2H,
123

Synthesis and characterization of aromatic and semiaromatic polyamides
209
`
5. Fomine S, Fomina L, Sanchez C, Ortiz A, Ogawa T (1997) Polym
J 29:49
6. Imai Y (1996) React Funct Polym 30:3
7. Liaw DJ, Liaw BY, Chung CY (1999) Macromol Chem Phys
200:1023
ODA unit), 6.67 (d, ArH ODA unit), 7.01 (s, ArH), 7.12 (d,
ArH), 7.33 (t, ArH), 7.62 (d, ArH), 8.16 (s, p-ArH), 9.39
(Ar NH), 10.42 (amide NH) ppm.
Poly[imino-1,4-phenyleneoxy-1,4-phenyleneiminocarbon-
yl-1,3-phenyleneiminocarbonothioyliminocarbonyl-
1,4-butanediylphenylenecarbonyliminocarbonothioyl-
imino-1,3-phenylenecarbonyl] (7c, (C34H30N6O5S2)n)
FTIR (KBr): vꢀ = 3,337 (N–H), 3,149, 1,666 (amide C=O),
1,588, 1,418 (C–N), 1,258 (C–O), 1,154 (C = S) cm-1; 1H
NMR (DMSO-d6): d = 1.57 (m, CH2), 2.18 (m, CH2), 6.36
(d, ArH ODA unit), 6.70 (d, ArH ODA unit), 6.99 (s, ArH),
7.18 (d, ArH), 7.32 (t, ArH), 7.73 (d, ArH), 9.29 (Ar NH),
10.31 (amide NH) ppm.
8. Tamami B, Yeganeh H (2001) Polymer 42:415
9. Zhang Y, Tebby JC, Wheeler JW (1996) J Polym Sci Part A
Polym Chem 34:1561
10. Liaw DJ, Liaw BY (1998) J Polym Sci Part A Polym Chem
36:1075
11. Zhu X, Jian X (2004) J Polym Sci Part A Polym Chem 42:2026
12. Lious GS, Oishi Y, Kakimoto M, Imai Y (1991) J Polym Sci Part
A Polym Chem 29:995
13. Liaw DJ, Liaw BY, Su KL (1999) J Polym Sci Part A Polym
Chem 37:1997
14. Hsiao SH, Chang CF (1996) J Polym Sci Part A Polym Chem
34:1433
15. Mehdipour-Ataei S, Heidari H (2003) Macromol Symp 193:159
16. Mehdipour-Ataei S, Malekimoghaddam R, Nami M (2004) Eur
Polym J 40:2523
17. Mehdipour-Ataei S, Sarrafi Y, Hatami M, Akbarian-Feizi L
(2005) Eur Polym J 41:491
18. D’Cruz JD, Venkatachalam TK, Uckun FM (2000) Biol Reprod
63:196
19. Wang C, Chen S, Zhao S (2004) J Electrochem Soc 151:B11
20. Shams El Din AM, El Hosary AA, Saleh RM, Abd El Kader JM
(1997) Mater Corros 28:26
Poly[imino-1,4-phenyleneoxy-1,4-phenyleneiminocarbon-
yl-1,3-phenyleneiminocarbonothioyliminocarbonyl-
1,8-octanediylcarbonyliminocarbonothioylimino-
1,3-phenylenecarbonyl] (7d, (C38H38N6O5S2)n)
FTIR (KBr): vꢀ = 3,360 (N–H), 3,043, 1,668 (amide C=O),
1
1,593, 1,417 (C–N), 1,263 (C–O), 1,156 (C=S) cm-1; H
NMR (DMSO-d6): d = 1.29 (m, CH2), 1.82 (m, CH2), 2.34
(m, CH2), 6.32 (d, ArH ODA unit), 6.68 (d, ArH ODA
unit), 7.03 (s, ArH), 7.29 (d, ArH), 7.52 (t, ArH), 7.81 (d,
ArH), 9.23 (Ar NH), 10.29 (amide NH) ppm.
21. Dehri I, Ozcan M (2006) Mater Chem Phys 98:316
22. Ozcan M, Dehri I, Erbil M (2004) Appl Surf Sci 236:155
23. Sabaa MW, Mohamed RR, Yassin AA (2003) Polym Degrad Stab
81:37
´
24. Avalos M, Babiano R, Cintas P, Chavero MM, Higes FJ, Jimenez
Acknowledgments A. Kausar gratefully acknowledges the Higher
Education Commission of Pakistan (HEC) for monetary assistance in
this work under Indigenous 5000 PhD Fellowship Scheme Batch-III
(063-111354-Ps3-068).
JL, Palacios JC, Silvero G (2000) J Org Chem 65:8882
25. Atta A (2003) Int J Polym Mater 52:361
26. Zuo G, Muhammed M (1995) React Polym 24:165
27. Kwolek SL, Morgan PW (2003) J Polym Sci Part A Polym Chem
41:2693
28. Buhlmann P, Nishizawa S, Xiao KP, Umezawa Y (1997) Tetra-
hedron 53:1647
References
29. Linton BR, Carr AJ, Orner BP, Hamilton AD (2000) J Org Chem
65:1566
30. Kumamoto K, Misawa Y, Tokita S, Kubob Y, Kotsukia H (2002)
Tetrahedron Lett 43:1035
31. Caouthar A, Roger P, Tessier M, Chatti S, Blais JC, Bortolussi M
(2007) Eur Polym J 43:220
32. Yen YP, Ho KW (2006) Tetrahedron Lett 47:7357
33. Kondo SI, Sato M (2006) Tetrahedron 62:4844
1. Negi YS, Razdan U, Saran V (1999) Macromol Chem Phys
C39:391
2. Akutsu F, Inoki M, Sawano M, Kasashima Y, Naruchi K, Miura
M (1998) Polym J 30:849
3. Hsiao SH, Chang HY (1996) J Polym Sci Part A Polym Chem
34:1421
4. Hsiao SH, Huang PC (1997) J Polym Sci Part A Polym Chem
35:2421
123