Synthesis and properties of polyamides containing high contents of thioether units

Article abstract of DOI:10.1016/j.reactfunctpolym.2011.04.008

Two kinds of monomers containing the thioether units 4,4′- thiodibenzoyl chloride (T-DC) and 4,4′-bis(4-chloroformylphenylthio) benzene (BPB-DC) were synthesized in two steps and were reacted with diamine-containing thioether (-S-) and sulfone units to pr

Full text of DOI:10.1016/j.reactfunctpolym.2011.04.008

Reactive & Functional Polymers 71 (2011) 775–781
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Reactive & Functional Polymers
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Synthesis and properties of polyamides containing high contents of thioether units
Gang Zhang a, Dong-sheng Li a, Guang-shun Huang b, Xiao-jun Wang a, Sheng-ru Long a, Jie Yang a,c,
⇑
a Analytical & Testing Center, Sichuan University, Chengdu 610064, PR China
b College of Polymer Materials Science and Engineering of China, Sichuan University, Chengdu 610065, PR China
c State Key Laboratory of Polymer Materials Engineering of China, Sichuan University, Chengdu 610065, PR China
a r t i c l e i n f o
a b s t r a c t
Two kinds of monomers containing the thioether units 4,40-thiodibenzoyl chloride (T-DC) and 4,40-bis(4-
chloroformylphenylthio)benzene (BPB-DC) were synthesized in two steps and were reacted with dia-
mine-containing thioether (–S–) and sulfone units to prepare a polyamide containing high contents of
thioether groups. The intrinsic viscosities of the polyamides were 0.81–0.93 dl/g. These polymers had
good optical properties, including an optical transmittance of the aromatic polyamide film at 450 nm that
was higher than 90%. Additionally, the high quantity of thioether units provided the polymers with high
refractive indices of 1.710–1.716 and low birefringences of 0.007–0.009. These polyamides also had
excellent thermal properties, with glass transition temperatures (Tg) of 230–246 °C and initial degrada-
tion temperatures (Td) of 477–473 °C. Finally, they showed improved solubility in polar aprotic solvents.
Ó 2011 Elsevier Ltd. All rights reserved.
Article history:
Received 24 January 2011
Received in revised form 25 April 2011
Accepted 28 April 2011
Available online 6 May 2011
Keywords:
Polyamide
Refractive index
Birefringence
Soluble
Thermo-stability
1. Introduction
they have attracted considerable efforts at improving their solubil-
ity because these polymers usually present limited solubility in
In recent years, there has been a strong demand to develop high
refractive index polymers for optical applications, such as encapsu-
lants for organic light-emitting diode devices, components for
charge-coupled devices (CCDs) and complementary metal oxide
semiconductor (CMOS) image sensors (CISs), among others [1–5].
A high refractive index, optical transparency and low birefringence
are the most important factors in optical applications. According to
the Lorentz–Lorenz equation, the introduction of substituents with
high molar refractions and low-molar volumes can efficiently in-
crease the refractive indices of polymers [6–13]. For example, heavy
halogen atoms (Cl, Br, I), sulfur atoms and metal atoms are com-
monly used for this purpose. In particular, the sulfur atom, which
has a high atomic refraction, is one of the most effective candidates.
To improve the refractive indices and transparencies of polymers,
recent attention has been paid to sulfur-containing polymers, such
as epoxies [14], polyurethanes [15], polymethacrylates [16],
polyarylenethioethers [17] and polyimides [18]. Among them,
polyimides (PI) are promising candidates for advanced optical
applications. Aromatic polyamides have good thermal and physical
properties [19]. Due to their exceptional technological importance,
most organic solvents. Furthermore, high melting and glass transi-
tion temperatures decrease their processability and restrict appli-
cations. To overcome these shortcomings, various approaches
have been developed to obtain thermally stable, high molecular
weight and organic-soluble aromatic polyamides. These techniques
include the introduction of bulky pendant groups [20,21], func-
tional groups [22], hydrazide groups [23], non-symmetric groups
[24,25], hexafluoro isopropyl groups[26] and flexible chains such
as ethers (AOA) or ester groups (ACOOA) into the polymer
backbone.
The chemical structure of aromatic polyamides is similar to PI,
but PI has a more rigid structure than polyamide, leading to a
higher birefringence. Thus, we aimed to prepare polyamides with
high refractive indices, but with much lower birefringences than
PI. Usually, the transmittance of a polymer film is decreased
when a high content of thioether units are incorporated into
the polymer chain. Therefore, we introduced a diamine-contain-
ing sulfone group into the polycondensation reaction to improve
the polymer’s transmittance. Herein, we report the synthesis of
two types of dibenzoyl chloride-containing thioether units. Poly-
condensation reactions of these dibenzoyl chlorides and diamine
monomers containing sulfones and a high content of thioether
groups were conducted in the presence Me3SiCl (TMSCl) as a cat-
alyst. The resultant polyamides were found to have high refrac-
tive indices and low birefringences, while maintaining excellent
optical transparencies.
⇑
Corresponding author at: State Key Laboratory of Polymer Materials Engineer-
ing of China, Sichuan University, Chengdu 610065, PR China. Fax: +86 28 8541
2866.
E-mail address: ppsf@scu.edu.cn (J. Yang).
1381-5148/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2011.04.008

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G. Zhang et al. / Reactive & Functional Polymers 71 (2011) 775–781
2.2.2. 4,40-bis(4-carboxyphenylthio)benzene (BPB-DA) (shown in
Scheme 1)
BPB-DA was prepared according to the following procedure:
2. Experimental
2.1. Materials
200 ml of NMP, 30 ml of toluene, 14.3 g (0.11 mol) of sodium sul-
fide, 4 g (0.10 mol) of sodium hydroxide, 1.7 g of sodium benzoate
and 3.6 g of sodium 4-methylbenzenesulfonate were added into a
500 ml three-necked flask equipped with a water segregator, reflux
condenser, mechanical stirrer and thermometer [28,29]. The reac-
tor was heated to 180 °C for 35 min and kept for 2 h; during this
time, 45.8 ml of liquid was removed. When the above reaction ves-
sel was cooled to 130 °C, 100 ml of NMP containing 14 g (0.1 mol) of
4-FBA was added into the reactor dropwise over 3 h and kept at
125 °C for 6 h to prepare 4-mercaptobenzoic acid (the solution col-
or changed from blue to pale-yellow). Then, 14 g (0.095 mol) of DCB
was added into the reaction solution, and the reaction flask was
heated to 200 °C and maintained for 8 h. The reaction solution
was then poured into deionized water and filtered. The filter liquor
was acidified with 1 mol/L HCl to precipitate a cottony crude prod-
uct under stirring. The crude product was then washed several
times with hot water to remove possible residual salts. Next, the
purified product was filtered, dissolved in a solution of NaHCO3, fil-
tered, acidified with hydrochloric acid and then filtered again. This
process was repeated three times. The material was then vacuum-
dried at 110 °C for more than 12 h to yield a pale-yellow powder.
Yield: 27.6 g, 76.2%.
Commercially available 1,4-chlorobenzene (DCB) (AR, Chen-
gdu, Kelong Chemical Industry Company), 4,40-dichlorodiphe-
nylsulfone (DCDPS) (AR, Suzhou Yinsheng Chemical Industry
Company), 4-aminobenzenthiol and 4,40-thiodianiline (AR, Zhe
Jiang Shou Er Fu Chemical Industry Group Co., Ltd.), sodium
hydroxide (NaOH) (AR, SiChuan ChengDu ChangLian Chemical
Reagent Company), sodium sulfide (Na2SꢀxH2O, Na2S% ꢁ 60%)
(Nafine Chemical Industry Group Co., Ltd.), N-methyl-2-pyrrol-
idone (NMP) (JiangSu NanJing JinLong Chemical Industry Com-
pany) and Me3SiCl (TMSCl) (AR, Aladdin Reagent Company)
were used without further purification. 4-Fluorobenzoic acid
(4-FBA) was made in our laboratory, while sodium benzoate,
sodium 4-methylbenzenesulfonate (AR, Aladdin Reagent Com-
pany) and other reagents and solvents were commercially
obtained.
2.2. Monomer synthesis
2.2.1. 4,40-bis(4-aminophenylthio)diphenylsulfone (BAPDS) (shown as
Scheme 1) [27]
BAPDS was prepared as shown in Scheme 1 with the following
procedure. A 250 ml round bottom three-necked flask was used,
and 28.7 g (0.1 mol) of dichlorodiphenylsulfone (DCDPS), 8.0 g
(0.2 mol) of NaOH, 25.5 g (0.22 mol) of 4-aminobenzenthiol and
100 ml of DMF were added. The mixture was stirred at 155 °C for
24 h under nitrogen, as shown in Scheme 1. The crude product
was then purified with water and methanol. The resulting material
was recrystallized from a mixture of water and DMF to provide
BAPDS as a pale yellow crystalline powder.
Elemental analysis (%): Found: C, 62.81; H, 3.69; Calculated: C,
62.43; H, 3.63; FT-IR (KBr, cmꢂ1): 3066 (CAH aromatic ring), 1689
(ACOOH), 1592, 1473 (C@C aromatic ring), 1084 (CASAC), 818
(para-substituent of aromatic ring); 1H NMR (600 MHz, DMSO-d6/
TMS, ppm): 7.18–7.20 (d, 4H, Hf), 7.43 (d, 4H, Hg), 7.90–7.92 (d,
4H, Hh), 12.97 (s, 2H, Hi).
2.2.3. 4,40-bis(4-chloroformylphenylthio)benzene (BPB-DC)
Yield: 33.5 g, 72.3%. m/z(M+): 465.27.
A mixture of 9.6 g (0.025 mol) of BPB-DA, 70 ml of thionyl chlo-
ride (SOCl2) and 0.4 ml of dry pyridine were added and stirred in a
round-bottom flask at room temperature under N2 in darkness for
3 h, followed by refluxing for 12 h. The mixture was then distilled
to dryness under reduced pressure. The resulting residue was ex-
tracted repeatedly at 42 °C with dry dichloromethane. Next, the
FT-IR (KBr, cmꢂ1): 3475, 3379 (ANH2), 3046 (CAH aromatic
ring), 1315, 1146 (ASO2A), 1077 (CASAC), 837 (para-substituent
aromatic ring); 1H NMR (600 MHz, DMSO-d6, ppm): 5.66 (s, 4H,
Ha), 6.64–6.65 (d, 4H, Hb), 7.08–7.09 (d, 4H, Hc), 7.17–7.18 (d, 4H,
Hd), 7.71–7.72 (d, 4H, He).
Scheme 1. Synthesis routes of BPB-DC, T-DC and the polyamides.

G. Zhang et al. / Reactive & Functional Polymers 71 (2011) 775–781
777
extraction solution was gradually cooled to precipitate yellow
crystals, which were filtered and dried under vacuum at 56 °C.
Yield: 9.53 g, 91%, m/z (M+): 420.36.
Elemental analysis (%): Found: C, 57.69; H, 2.86; Calculated: C,
57.28; H, 2.88; FT-IR (KBr, cmꢂ1): 3074 (CAH aromatic ring),
1757, 1727 (ACOCl), 1585, 1483 (C@C aromatic ring), 1078
(CASAC), 826 (para-substituent of aromatic ring); 1H NMR
(600 MHz, chloroform-D/TMS, ppm): 7.28–7.30 (d, 4H, Hf), 7.53
(d, 4H, Hg), 8.00–8.02 (d, 4H, Hh).
PA-b: Yield: 96%. Elemental analysis calculated: C: 64.93%; H:
3.73%; N: 3.99%. Found: C: 64.05%; H: 3.86%; N: 4.01%. FT-IR (cast-
ing film, cmꢂ1): 3326, 1658 (ACOANHA), 1586, 1517, 1491 (C@C
aromatic ring), 1314, 1154 (ASO2A), 1077 (CASAC), 824 (para-
substituent of aromatic ring). 1H NMR (600 MHz, DMSO-d6/TMS,
ppm): 7.20–7.21 (d, 4H, Hb), 7.51–7.52 (d, 4H, Hc), 7.54–7.55 (d,
4H, Hg), 7.77–7.78 (d, 4H, Hd), 7.92–7.93 (d, 4H, Hh), 7.97–7.98
(d, 4H, He), 10.54 (s, 2H, Ha).
2.4. Characterization
2.2.4. 4,40-thiodibenzoic acid (T-DA)
This compound was synthesized using a similar procedure to
that of BPB-DA.
The intrinsic viscosity of the polyamides (PA-(a–b) and PA-(A–
B)) was obtained in NMP at 30 0.1 °C with 0.500 g of polymer dis-
solved in 100 ml of NMP. The number-average molecular weights
(Mn) and weight-average molecular weight (Mw) were obtained
via GPC performed with a Waters 1515 performance liquid chro-
Yield: 20.2 g, 73.9%.
Elemental analysis (%): Found: C, 61.62; H, 3.71; Calculated: C,
61.3; H, 3.67; FT-IR (KBr, cmꢂ1): 3057 (CAH aromatic ring), 1693
(ACOOH), 1590, 1471 (C@C aromatic ring), 1086 (CASAC), 823
(para-substituent of aromatic ring); 1H NMR (600 MHz, DMSO-
d6/TMS, ppm): 7.35–7.36 (d, 4H, Hg), 7.95–7.96 (d, 4H, Hh), 12.97
(s, 2H, Hi).
matography pump,
a Waters 2414 differential refractometer
(Waters Co., Milford, MA) and a combination of Styragel HT-3
and HT-4 columns (Waters Co., Milford, MA), the effective molecu-
lar weight ranges of which were 100–10,000, 500–30,000 and
5000–800,000, respectively. N,N-dimethyl formamide (DMF) was
used as an eluent at a flow rate of 1.0 ml/min at 35 °C. Polystyrene
standards were used for calibration. The samples of monomer and
PA-(a–b) were measured with an elemental analyzer (EURO EA-
3000). FT-IR spectroscopic measurements were performed on a
NEXUS670 FT-IR instrument. The mass spectral analysis was per-
formed on a Bruker-Daltonics ESI instrument. Nuclear magnetic
resonance (1H NMR) spectra were determined on a BRUKER-600
NMR spectrometer in deuterated chloroform or deuterated di-
methyl sulfoxide. Differential scanning calorimetry (DSC) was per-
formed on a NETZSCH DSC 200 PC thermal analysis instrument.
The heating rate for the DSC measurements was 10 °C/min. Ther-
mogravimetric analysis (TGA) measurements were performed on
a TGA Q500 V6.4 Build 193 thermal analysis instrument with a
heating rate of 10 °C/min under a nitrogen atmosphere. An Instron
Corporation 4302 was used to study the stress–strain behavior of
the films. Dynamic Mechanical Analysis (DMA) was performed
on TA-Q800 apparatus operating in tensile mode at a frequency
of 1 Hz in the temperature range from 30 to 300 °C, with a heating
rate of 5 °C/min. The transmittance of the films was determined by
UV–Visible spectroscopy (U-200A). The out-of-plane (nTM) and in-
plane (nTE) refractive indices of the PA films were measured with a
SPA-Lite prism coupler (SPA-4000) equipped with a HeANe laser
light source (wavelength: 632.8 nm). The in-plane (nTE)/out-of-
2.2.5. 4,40-thiodibenzoyl chloride (T-DC)
This compound was synthesized using a similar procedure to
that of BPB-DC.
Yield: 91.9%, m/z (M+): 311.24.
Elemental analysis (%): Found: C, 53.90; H, 2.68; Calculated: C,
54.04; H, 2.59; FT-IR (KBr, cmꢂ1): 3081 (CAH aromatic ring),
1585, 1483 (C@C aromatic ring), 1766, 1728 (ACOCl), 1655
(ACOA), 1079 (CASAC), 835 (para-substituent of aromatic ring);
1H NMR (600 MHz, chloroform-D/TMS, ppm): 7.46–7.47 (d, 4H,
Hg), 8.07–8.08 (d, 4H, Hh).
2.3. Polymer synthesis (shown in Scheme 1)
A typical polymerization was performed as shown in Scheme 1.
In a 100 ml three-necked flask equipped with a mechanical stirrer
and thermometer, 4.64 g (0.01 mol) of BAPDS and 0.66 g
(0.006 mol) of Me3SiCl (TMSCl) were dissolved in 50 ml of NMP.
After the BAPDS had completely dissolved, 4.19 g (0.01 mol) of
BPB-DC was added. The mixture was stirred at 0 °C for 2 h, and
then stirred at room temperature for about 12 h to yield a viscous
pale-yellow solution. Next, the reaction solution was poured into
water to obtain a fibrous precipitate, which was washed with
water and ethanol and dried in a vacuum oven. The fibrous precip-
itate was then pulverized to a powder and washed with water and
ethanol. Finally, it was dried in a vacuum oven at 100 °C for 12 h to
give PA-a.
plane (nTM) indices and birefringences (
Dn) were calculated with
the following equation:
D
n = nTE ꢂ nTM. The average refractive in-
dex was calculated according to the following equation:
Â
Ã
1=2
nAV ¼ ð2n2TE þ nT2MÞ=3
[30]. Dielectric constants were estimated
Yield: 7.86 g, 97%.
from the optical data based on an empirical relation:
PA-a: elemental analysis calculated: C: 65.16%; H: 3.73%; N:
3.45%. Found: C: 65.24%; H: 3.73%; N: 3.76%. FT-IR (casting film,
cmꢂ1): 3333, 1654 (ACOANHA), 1589, 1517, 1488 (C@C aromatic
ring), 1314, 1154 (ASO2A), 1076 (CASAC), 818 (para-substituent
of aromatic ring). 1H NMR (600 MHz, DMSO-d6/TMS, ppm): 7.18–
7.19 (d, 4H, Hb), 7.42–7.43 (d, 4H, Hc), 7.44 (s, 4H, Hf), 7.51–7.52
(d, 4H, Hg), 7.75–7.76 (d, 4H, Hd), 7.90–7.91 (d, 4H, Hh), 7.93–
7.94 (d, 4H, He), 10.49 (s, 2H, Ha).
e
calculated = 1.1n2AV [31,32]. The water absorption of the samples
was measured according to GB/T17037.3-2003. Dielectric con-
stants were measured on a TH2819A in a frequency region of
0.1–100 kHz at 25 °C. The solubility of polymers in various solvents
was tested at room temperature and the boiling point of the
solvent.
PA-b was prepared following a similar procedure. We synthe-
sized the polyamide which have no sulfone groups (PA-s: the poly-
amide of BPB-DC and 4,40-thiodianiline) to compare its
transmittance with PA-(a–b). In order to investigate the catalyst
(TMSCl) whether plays a role in the polymerization process, we
also conducted the polymerization without TMSCl (PA-A: the poly-
amide that polymerized from BPB-DC and BAPDS without TMSCl;
PA-B: the polyamide that polymerized from T-DC and BAPDS with-
out TMSCl).
3. Results and discussion
3.1. Monomers
3.1.1. Synthesis of BPB-DC and T-DC
The synthetic routes to BPB-DC are shown in Scheme 1. BPB-DC
was prepared through a three-step procedure with 4-FBA and DCB.
Sodium benzoate and sodium 4-methylbenzenesulfonate were
added into the reaction system to assist with the dissolution of so-

778
G. Zhang et al. / Reactive & Functional Polymers 71 (2011) 775–781
dium sulfide and the product. First, 4-FBA reacted with sodium sul-
fide to provide 4-mercaptobenzoic acid salt [33–35], which reacted
with DCB under nitrogen to give BPB-DA. Then, BPB-DA was con-
verted to BPB-DC through reaction with SOCl2. This procedure
must be anhydrous or the yield is very low. T-DC was prepared
in a similar way to BPB-DC.
near 1080 cmꢂ1. The 1H NMR spectra (see Supplementary data
Fig. 2) of BPB-DC showed three groups of peaks (ranged from
7.28 to 8.02). The ratio of the corresponding integral curves was
about 1:1:1. The 1H NMR spectra (see Supplementary data Fig. 2)
of T-DC showed two groups of peaks. The ratio of the correspond-
ing integral curves was also about 1:1. Combining the results of the
FT-IR and mass spectral analyses suggested that we had prepared
the monomer as depicted in Scheme 1.
3.1.2. Characterization of BPB-DA, BPB-DC, T-DA and T-DC
The chemical structure of the monomers was confirmed by FT-
IR and 1H NMR. The FT-IR spectra of BPB-DA and T-DA showed the
characteristic absorptions of ACOOH near 1700 cmꢂ1, and the
absorption of ASA near 1080 cmꢂ1. The 1H NMR spectra (Fig. 1)
of BPB-DA and T-DA showed four and three groups of peaks. The
proton signals of ACOOH (see Supplementary data Fig. 1) were
present obviously at high frequency area (12.97 ppm). The FT-IR
spectra of BPB-DC and T-DC showed the characteristic absorptions
of ACOCl near 1760 and 1720 cmꢂ1, and the absorption of ASA
3.2. Polymers
3.2.1. Synthesis of polyamides (PA-(a–b))
The polycondensation reaction of the diamine (BAPDS) and
BPB-DC was conducted in the presence of TMSCl as a catalyst in
NMP. Silylation of the diamine is an efficient activation method
to obtain higher molecular weight polymers. According to the liter-
ature, the diamine component can be activated through the in situ
Fig. 1. 1H NMR spectra of monomers (BPB-DA, T-DA and BAPDS) and the polyamides (PA-a and PA-b).

G. Zhang et al. / Reactive & Functional Polymers 71 (2011) 775–781
779
addition of TMSCl to the diamine solution [36–39]. Due to the
strong affinity of Si for oxygen, the carbonyl oxygen of the acid
chloride is attracted to the Si atom in the amine derivatives, which
in turn facilitates nucleophilic attack of the N atom of the N-silylat-
ed amine at the carbonyl carbon. Subsequent elimination of the
chloride ion from the tetrahedral intermediate is enhanced by
the presence of the b-silicon through the r–p effect, which rapidly
leads to the amide product along with TMSCl. Another important
aspect of using TMSCl is that it scavenges adventitious water.
3.2.2. The intrinsic viscosity (
and PA-(A–B)
gint) and molecular weights of PA-(a–b)
The molecular weights of the polyamides were measured by gint
and GPC. In order to investigate the role of the catalyst we also
studied the polyamides (PA-(A–B)) without adding the catalyst
(TMSCl) during the polymerization process. As shown in Table 1,
the gint values of PA-(a–b) and PA-(A–B) were in the range of
0.81–0.93 dL/g and 0.56–0.60 dL/g, respectively. PA-(a–b) showed
Mn values in the range of 8.0–10.5 ꢃ 104 and Mw values in the
range of 1.38–1.78 ꢃ 105, respectively. The polydispersity indices
(PDIs) of PA-(a–b) were 1.72 and 1.70, respectively. While PA-(A–
B) showed Mn values in the range of 3.2–4.1 ꢃ 104 and Mw values
in the range of 6.1–7.4 ꢃ 104, respectively. The polydispersity indi-
ces (PDIs) of PA-(A–B) were 1.91 and 1.80, respectively. The results
indicate that the catalyst plays an important role in the polymeri-
zation reaction although the changes of the molecular weight are
not very large.
Fig. 2. DSC curves of PA-(a–b) and PA-(A–B) at a heating rate of 10 °C/min in N2.
tion temperatures (T5%) of PA-(a–b) and PA-(A–B) in nitrogen were
477–473 °C and 477–472 °C, respectively. PA-(a–b) and PA-(A–B)
provided about 42% char yield at 800 °C (in Table 1). The TGA data
indicated that these polymers had improved thermo-stability.
3.2.5. Tensile properties
The average tensile strengths of the casting films of the polya-
mides (PA-(a–b)) treated at 120–140 °C for 10 h, and then at
180 °C for 10 h, are given in Table 2. As shown, the average tensile
strengths and the Young’s modulus values of the films PA-(a–b)
were 76.3–89.8 MPa and 2.7–2.1 GPa, respectively. The elongation
at break was less than 5%, suggesting that the films undergo brittle
fracture.
3.2.3. The FT-IR and 1H NMR spectra of PA-(a–b)
The FT-IR spectra of PA-(a–b) showed characteristic absorptions
of the amide group (ACONHA) near 3300 and 1650 cmꢂ1, of the
sulfone group (ASO2A) near 1320 cmꢂ1 and 1150 cmꢂ1 and the
ASA group near 1080 cmꢂ1. In comparison with the monomers
(BPB-DC, T-DC), the absorptions of ACOCl (1760 and 1720 cmꢂ1
)
3.2.6. Dynamic mechanical analysis
disappeared. This finding suggests that the polymers were pre-
pared as shown in Scheme 1. Fig. 1 shows the 1H NMR spectra of
PA-a. Eight groups of peaks appeared in the 1H NMR spectra of
PA-a. The signal at 10.49 ppm was assigned to the amide group.
The aromatic protons were observed at about 7.18–7.94 ppm.
The ratio of corresponding integral curves was Hb:Hc:Hf:Hg:Hd:
Hh:He:Ha = 2:2:2:2:2:2:2:1. In combination with the FT-IR results,
these eight groups of peaks were ascribed to Hb, Hc, Hf, Hg, Hd,
Hh, He and Ha, as shown in Fig. 1. The structure of the polymer
was also confirmed by elemental analysis. The structure of PA-b
was confirmed through the same series of experiments.
DMA was used to characterize the obtained polyamides. Fig. 4
shows the storage modulus curves of PA-(a–b). As listed in Table
2, PA-(a–b) showed a high storage module beyond 1 GPa and
0.8 GPa at 220 °C. This finding indicates that these polyamides
had excellent mechanical properties. At the same time, an obvious
transition behavior was observed. It is well known that the glass
transition temperature (Tg) of polymers can be determined by this
relaxation (
movements in the non-crystalline areas [40,41]. The temperatures
of relaxation of these polyamides were 225 and 248 °C (these re-
a relaxation), since it is usually related to the segment
a
sults were nearly to the DSC data). The glass transition tempera-
ture decreased upon increasing the amount of flexible chain
(thioether) in the polymeric backbone.
3.2.4. Thermal properties of the polyamides (PA-(a–b) and PA-(A–B))
The thermal properties of PA-(a–b) and PA-(A–B) were exam-
ined by DSC and TG analysis. As shown in Fig. 2, the Tg values of
PA-(a–b) and PA-(A–B) were 230–246 °C and 228–244 °C, respec-
tively (in Table 1). It may be that lower molecular weight of PA-
(A–B) caused PA-(A–B) had lower glass transition temperature
than PA-(a–b). The DSC curve of PA-(a–b) and PA-(A–B) did not
have an endothermic melting peak, revealing that PA-(a–b) and
PA-(A–B) were amorphous. As shown in Fig. 3, the initial degrada-
3.2.7. Water absorption
The water absorption of PA-(a–b) was measured according to
GB/T17037.3-2003, and the results are summarized in Table 3.
The water absorptions of PA-(a–b) were 0.19% and 0.21%. These re-
sults indicate that these polyamides had low water absorption,
which is good for their dimensional and mechanical stability.
Table 1
Intrinsic viscosity (gint), molecular weights and thermal properties of PA-(a–b) and PA-(A–B).
Sample
gint (dL/g)
Mn (g/mol)
Mw (g/mol)
PDI (Mw/Mn)
Tg (°C)
T5% (°C)
Char yield (%)
PA-a
0.81
0.93
0.56
0.60
8.0 ꢃ 104
10.5 ꢃ 104
3.2 ꢃ 104
4.1 ꢃ 104
1.38 ꢃ 105
1.78 ꢃ 105
6.1 ꢃ 104
7.4 ꢃ 104
1.72
1.70
1.91
1.80
230
246
228
244
477
473
477
472
43.5
42.1
42.0
41.5
PA-b
PA-Aa
PA-Bb
a
The polyamide that polymerized from BPB-DC and BAPDS without adding TMSCl.
The polyamide that polymerized from T-DC and BAPDS without adding TMSCl.
b

780
G. Zhang et al. / Reactive & Functional Polymers 71 (2011) 775–781
Table 3
Water absorption and dielectric constants of PA-(a–b).
Polymers Thickness Water
Thickness Dielectric constant
(mm)
absorption (lM)
(%)
0.1
1
10
100
(kHz) (kHz) (kHz) (kHz)
PA-a
PA-b
1.03
1.04
0.19
0.21
71
73
3.91
3.97
3.64 3.43
3.67 3.45
3.12
3.16
Fig. 3. TGA curves of PA-(a–b) and PA-(A–B) at a heating rate of 10 °C/min in N2.
Table 2
Tensile properties of PA-(a–b).
Polymer Tensile
strength
Young’s
modulus at break
(GPa)
Elongation Storage
modulus at
(%)
Glass
transition
(MPa)
220 °C (GPa) temperaturea
(°C)
PA-a
PA-b
76.3
89.8
2.7
2.1
4.8
3.6
1
0.8
225
248
Fig. 5. UV–Vis spectra of PA-(a–b) and PA-s films.
a
Detected by dynamic mechanical analysis (DMA).
3.2.9. Optical properties
Fig. 5 shows the optical transmission spectra of PA-(a–b). The
cut-off wavelengths (kcutoff) of the PA-a and PA-b films were 364
and 359 nm, respectively. The spectral shapes of PA-(a–b) were
similar to each other, and the transmittances of the films measured
at 450 nm were much higher than 90% (film thicknesses: 11–
12 lm). However, the transmittances (at 450 nm) of the polya-
mides that had no sulfone groups (PA-s: the polymer of BPB-DC
and 4,40-thiodianiline) were about 49.9% (shown in Fig. 5). This
finding indicates that incorporating the sulfone group into the
polymer chain is beneficial for improving the optical transparency
of the polymer film. The optical properties of the PA films, such as
the cut-off wavelengths, in-plane (nTE) and out-of-plane (nTM
refractive indices, average refractive indices (nav) and birefringenc-
es ( n) are listed in Table 4. The in-plane (nTE) and out-of-plane
)
D
(nTM) refractive indices of PA-(a–b) were in the range of 1.718–
1.713 and 1.713–1.704, respectively. The nav values of PA-(a–b)
measured at 632.8 nm were 1.716 and 1.710. The nav depended
on several factors, such as sulfur content, molecular chain flexibil-
ity and molar volume. PA-a exhibited a higher refractive index than
did PA-b. This finding was mainly attributed to its higher sulfur
content compared to PA-b. Although the refractive indices were
not much higher than that of aromatic PI, which has a similar sul-
Fig. 4. The storage modulus and loss modulus curves of PA-(a–b).
3.2.8. Dielectric constants
Table 3 summarizes the dielectric constants of PA-(a–b). They
showed low dielectric constants of 3.12–3.16 at 100 kHz. These
low dielectric constants may be attributed to the presence of low
polarizability in the molecular structure and low water absorption.
fur content [42], PA-(a–b) showed low
0.009. The highly refractive index and low
D
n values of 0.007 and
n value of PA-(a–b)
D
can be attributed to the high content of flexible ASA linkages in
the main chain. The ecalculated values of PA-a and PA-b were 3.24
Table 4
Optical properties of films of PA-(a–b) and PA-s.
Polymers
Sc (%)
kcutoff (nm)
T450 (%)
nTE
nTM
nAV
D
n
ecalculated
PA-a
PA-b
PA-sa
19.77
18.25
17.09
364
359
369
96.3
96.06
49.9
1.718
1.713
–
1.711
1.704
–
1.716
1.710
–
0.007
0.009
–
3.24
3.22
–
a
The polyamide of BPB-DC and 4,40-thiodianiline; Sc: the content of S; T450: the transmittance of films at 450 nm;
e: dielectric constant; nTE: the in-plane refractive index;
nTM: the out-of-plane refractive index; n: birefringence;
D
e
calculated = 1.1n2AV; –: not detected.

G. Zhang et al. / Reactive & Functional Polymers 71 (2011) 775–781
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