Comparative study on polyimides from isomeric 3,3′-, 3,4′-, and 4,4′-linked bis(thioether anhydride)s

Article abstract of DOI:10.1002/pola.24681

Three isomeric bis(thioether anhydride) monomers, 4,4′-bis(2,3- dicarboxyphenylthio) diphenyl ketone dianhydride (3,3′-PTPKDA), 4,4′-bis(3,4-dicarboxyphenylthio) diphenyl ketone dianhydride (4,4′-PTPKDA), and 4-(2,3-dicarboxyphenylthio)-4′-(3,4- dicarboxy

Full text of DOI:10.1002/pola.24681

Comparative Study on Polyimides from Isomeric 3,30-, 3,40-,
and 4,40-Linked Bis(thioether anhydride)s
HAIBING WEI, XUELIANG PEI, XINGZHONG FANG
Ningbo Key Laboratory of Polymer Materials, Ningbo Institute of Material Technology and Engineering,
Chinese Academy of Sciences, Ningbo, Zhejiang 315201, People’s Republic of China
Received 13 February 2011; accepted 18 March 2011
DOI: 10.1002/pola.24681
Published online 11 April 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Three isomeric bis(thioether anhydride) monomers,
4,40-bis(2,3-dicarboxyphenylthio) diphenyl ketone dianhydride
(3,30-PTPKDA), 4,40-bis(3,4-dicarboxyphenylthio) diphenyl ketone
dianhydride (4,40-PTPKDA), and 4-(2,3-dicarboxyphenylthio)-40-
(3,4-dicarboxyphenylthio) diphenyl ketone dianhydride (3,40-
PTPKDA), were prepared through multistep reactions. Their
structures were determined via Fourier transform infrared,
NMR, and elemental analysis. Three series of polyimides
(PIs) were prepared from the obtained isomeric dianhydrides
and aromatic diamines in N-methyl-2-pyrrolidone (NMP) via
the conventional two-step method. The PIs showed excellent
solubility in common organic solvents such as chloroform,
N,N-dimethylacetamide, and NMP. Their glass-transition tem-
peratures decreased according to the order of PIs on the basis
of 3,30-PTPKDA, 3,40-PTPKDA, and 4,40-PTPKDA. The 5% weight
loss temperatures (T5%) of all PIs in nitrogen were observed
at 504–519 ꢀC. The rheological properties of isomeric PI resins
based on 3,30-PTPKDA/4,40-oxydianiline/phthalic anhydride
showed lower complex viscosity and better melt stability
compared with the corresponding isomers from 4,40- and 3,40-
PTPKDA. In addition, the PI films based on three isomeric
dianhydrides and 2,20-bis(trifluoromethyl)benzidine had
a
C
V
low moisture absorption of 0.27–0.35%.
2011 Wiley Periodi-
cals, Inc. J Polym Sci Part A: Polym Chem 49: 2484–2494,
2011
KEYWORDS: bis(thioether anhydride)s; isomer/isomerization;
polyimides; rheology; structure–property relations
INTRODUCTION Polyimides (PIs) have been attracting con-
siderable attention for over 50 years as well-known high
performance polymers for their excellent thermal stability,
mechanical properties, and low dielectric constants.1–4
Despite their outstanding properties, most PIs are infusible
and insoluble in common organic solvents because of their
rigid backbones and strong interchain interaction. To over-
come these limitations, much effort has been focused on the
improvement of the solubility and the fusibility by means of
structure design and modification of aromatic dianhydride
and diamine monomers.
ing other excellent properties.13 For instance, Li et al.14
reported that the PI derived from 2,3,30,40-oxydiphthalic dia-
nhydride (3,40-ODPA) exhibits higher solubility and lower
melt viscosity than those from 2,20,3,30-ODPA (3,30-ODPA)
and 3,30,4,40-ODPA (4,40-ODPA). Similar rules have also been
found by Ding13 and Japanese researchers15 from other iso-
meric dianhydrides, such as 3,30-BPDA, 3,40-BPDA, and 4,40-
BPDA; 3,30-TDPA, 3,40-TDPA, and 4,40-TDPA; and 3,30-BTDA,
3,40-BTDA, and 4,40-BTDA (Fig. 1).
Generally, there are two isomers with different substitution
positions on the benzenetetracarboxylic acid dianhydrides,
pyromellitic dianhydride, and mellophanic dianhydride
(MPDA; Fig. 1). Moreover, there are three isomers with dif-
ferent substitution positions on the two phthalate rings of
bridged dianhydrides (two phthalic anhydride (PA) moieties
are separated by a simple group, as a single bond or one
atom), as 3,30-dianhydride, 3,40-dianhydride, and 4,40-dianhy-
dride (Fig. 1). Similarly, there are also three isomers for
bis(ether anhydride)s and bis(thioether anhydride)s.
The development of processable (melt and/or soluble proc-
essing) PIs has been bloom into an interesting issue in the
research of aromatic polymers. Generally, there are three
main structural design approaches and they are: the
introduction of flexible and other aliphatic spacers5–7; the
attachment of bulky lateral units8,9; and the involvement of
asymmetric or noncoplanar moieties into the polymer back-
bone.10–12
Interestingly, due to the lower melt viscosity, and compara-
ble thermal and mechanical properties, developing isomeric
PIs have been proven to be an effective approach to attain
the good solubility and melt processability without sacrific-
Systematically research on structure–property relations of
isomeric PIs mainly focused on benzene dianhydrides and
bridged dianhydrides, such as MPDA, ODPA, BPDA, TDPA,
and so on. However, to the best of our knowledge, the
Additional Supporting Information may be found in the online version of this article. Correspondence to: X. Fang (E-mail: fxzhong@nimte.ac.cn)
C
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Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 2484–2494 (2011) 2011 Wiley Periodicals, Inc.
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FIGURE 1 Structures of isomeric
benzene and bridged dianhydrides.
studies of isomeric bis(ether anhydride)s and/or bis(thioether
anhydride)s are limited in 3,30-dianhydride and 4,40-dianhy-
dride,16,17 more in-depth researching is lacking about another
asymmetric isomer, 3,40-dianhydride isomer, and the compre-
hensive comparison of the corresponding PI.
In continuation of our research to investigate the structure–
property relations of isomeric PIs, we successfully synthe-
sized a new series of isomeric bis(thioether anhydride)s,
including 4,40-bis(2,3-dicarboxyphenylthio) diphenyl ketone
dianhydride (3,30-PTPKDA), 4-(2,3-dicarboxyphenylthio)-40-
(3,4-dicarboxyphenylthio) diphenyl ketone dianhydride (3,40-
PTPKDA), and 4,40-bis(3,4-dicarboxyphenylthio) diphenyl
ketone dianhydride (4,40-PTPKDA), as shown in Figure 2. In
addition, the effect of dianhydride isomerism on the proper-
ties of polymer such as solubility, thermal property, dynamic
mechanical property, and rheological property was systemi-
cally investigated as well.
RESULTS AND DISCUSSION
Monomer Synthesis
4,40-Dimercaptobenzophenone18 and 4-chloro-40-mercapto
benzophenone19 (CMBP) were prepared by the reported
FIGURE 2 Structures of three PTPKDA isomers.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthesis of symmetric
PTPKDAs.
methods. To avoid oxidation, 4,40-dimercaptobenzophenone
and CMBP were dried at room temperature under vacuum
and stored under nitrogen atmosphere at low temperature.
Symmetrical dianhydrides 3,30-PTPKDA and 4,40-PTPKDA
were synthesized via aromatic nucleophilic substitution reac-
tion from 4,40-dimercaptobenzophenone with 3-chloroph-
thalic anhydride and 4-chlorophthalic anhydride, as shown
in Scheme 1. Because of the high nucleophilicity of thiophen-
oxides, the reaction can proceed smoothly in the presence of
triethylamine (TEA). The structures of symmetrical dianhy-
drides 3,30-PTPKDA and 4,40-PTPKDA were confirmed by ele-
mental analysis, NMR, and IR spectra. Supporting Informa-
tion Figures S1 and S2 illustrate the 1H NMR and 13C NMR
spectra of 3,30-PTPKDA and 4,40-PTPKDA.
electrophilicity of CMBP and 3-chlorophlic anhydride, the
attacks by the thiophenoxide ions on chlorine of 3-chlor-
ophlic anhydride are dominant and produce compound 1
with a yield of 81%. Then, the PA group of precursor 1 was
protected with methylamine to afford 2. Second, asymmetric
bisimide 3 was synthesized from N-methyl-4-mercaptophtha-
limide and 2 via nucleophilic substitution reaction. Due
to the impairment of nucleophilicity of the thiophenoxide
ions by the phthalimide group and the limited activation of
the chlorine in 2 by the ketone group, the reaction was able
to proceed at higher temperature in the presence of tribu-
tylamine. Hydrolysis of 3 with potassium hydroxide and
subsequent acidification with hydrochloric acid gave tetra
acid, which was cyclodehydrated with acetic anhydride to
generate an 82% yield of asymmetric dianhydride 3,40-
PTPKDA.
Four steps were used to synthesize another asymmetric iso-
mer 3,40-PTPKDA from CMBP and 3-chlorophthalic anhydride
as shown in Scheme 2. First, the intermediate 1 was
obtained from the nucleophilic chloro-displacement of 3-
chlorophthalic anhydride with the thiophenoxide ions of
CMBP in N,N-dimethylacetamide (DMAc) in the presence of
TEA as an acid scavenger. Because chlorine is ortho and
meta to the two carbonyl groups of 3-chlorophthalic anhy-
dride, the chlorine electron deficiency of 3-chlorophlic anhy-
dride is higher than that of CMBP. Given the difference of
Elemental analyses, Fourier transform infrared (FTIR), and
NMR spectroscopic techniques were used to identify the
structures of the intermediate compounds (1, 2, and 3) and
the target anhydride monomer 3,40-PTPKDA. Figure 3 illus-
13
trated the 1H NMR and C NMR spectra of 3,40-PTPKDA.
Assignments of each carbon were assisted by the two-dimen-
sional CAH heteronuclear multiple bond correlation spec-
trum shown in Figure 4. Furthermore, its elemental analysis
SCHEME 2 Synthesis of asymmetric 3,40-
PTPKDA isomer.
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FIGURE 3 1H NMR and 13C NMR
spectra of 3,40-PTPKDA in DMSO-
d6.
was in good agreement with the proposed chemical
compositions.
Complete imidization from PAAs to PIs was confirmed by the
FTIR spectra and are shown in Figure 5. The characteristic
absorption peaks of amide groups around 3200–2900 and
1660 cmꢁ1 disappeared, and those of the imide groups are
clearly observed near 1780 (asym C¼¼O stretching), 1720
(sym C¼¼O stretching), 1380 (CAN stretching), and 725
cmꢁ1 (imide ring deformation). In addition, the special
absorption at 1655 cmꢁ1 corresponding to stretching vibra-
tions of a carbonyl group bonded to two aromatic rings and
the aromatic thioether groups (ArASAAr) at about 1084
cmꢁ1. WAXD measurements for PI films showed that all
these PIs are amorphous, which may be attributed to the in-
hibition of crystallization due to the flexible ether and thio-
ether linkages in the PI chains.
Synthesis of PIs
A series of isomeric PIs were synthesized by a conventional
two-step procedure starting from three isomeric dianhy-
drides and aromatic diamine via the soluble poly(amic acid)
(PAA) precursors and subsequent thermal cyclodehydration
at elevated temperatures (Scheme 3). The inherent viscos-
ities of the PAAs are in the range of 0.42–1.16 dL/g, indicat-
ing the high reactivity and high purity of the prepared dia-
nhydrides. The PAA solutions were coated onto a glass plate
and dried at 80 ꢀC for 6 h, 150 ꢀC for 1 h, 200 ꢀC for 1 h,
ꢀ
ꢀ
250 C for 1 h, and 300 C for 1 h to afford PI films. The ele-
mental analysis values of all PI films are listed in Table 1
and were in good agreement with the proposed chemical
compositions.
As shown in Scheme 4, the isomeric PTPKDA/4,40-oxydiani-
line (ODA)/PA PI resins were synthesized by the
FIGURE 4 CAH heteronuclear multiple
bond correlation spectrum of 3,40-
PTPKDA.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 3 Synthesis of polyimides from isomeric PTPKDAs.
polycondensation of mixtures of ODA and isomeric PTPKDA
through a one-step polymerization. PA was used as an end-
capper to terminate the reactive amine end groups of the PI.
PIs, except PI-2c, were soluble in DMAc, N-methyl-2-pyrroli-
done (NMP), TCE, m-cresol, and p-CPhol at room tempera-
ture. Most of them also have considerable solubility in
CHCl3, DMF, and DMSO. The good solubility of these poly-
mers can be attributed to the introduction of the flexible
linkages (AOA, ASA) into the polymer main chain, and the
twisty chain structure caused by twisted and noncoplanar
Solubility of the Isomeric PIs
The solubility of PIs was investigated qualitatively in various
solvents, and the results are summarized in Table 2. These
TABLE 1 Inherent Viscosities of PAA Precursors and Elemental Analysis Data of
Corresponding PI Films
Elemental Analysis
a
Polymer
PI-1a
ginh (dL/g)
Formula (Molecular Weight)
(C43H20F6N2O5S2)n (822.75)n
C
H
N
0.42
calcd.
found
calcd.
found
calcd.
found
calcd.
found
calcd.
found
calcd.
found
calcd.
found
calcd.
found
calcd.
found
62.77
63.02
62.77
62.86
62.77
62.97
70.07
69.89
70.07
69.79
70.07
70.01
71.02
71.25
71.02
71.28
71.02
71.20
2.45
2.36
2.45
2.40
2.45
2.49
3.16
3.01
3.16
3.12
3.16
3.11
3.30
3.35
3.30
3.29
3.30
3.36
3.40
3.30
3.40
3.26
3.40
3.35
3.99
4.03
3.99
4.15
3.99
3.96
3.52
3.48
3.52
3.63
3.52
3.59
PI-2a
PI-3a
PI-1b
PI-2b
PI-3b
PI-1c
PI-2c
PI-3c
a
0.45
0.47
0.57
0.82
1.09
0.82
0.98
1.16
(C43H20F6N2O5S2)n (822.75)n
(C43H20F6N2O5S2)n (822.75)n
(C41H22N2O6S2)n (702.75)n
(C41H22N2O6S2)n (702.75)n
(C41H22N2O6S2)n (702.75)n
(C47H26N2O7S2)n (794.85)n
(C47H26N2O7S2)n (794.85)n
(C47H26N2O7S2)n (794.85)n
Measured at a concentration of 0.5 g/dL in NMP at 30 ꢀC.
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The temperatures of 5% weight loss (T5%) in nitrogen
atmosphere were determined from the original TGA curves
and included in Table 3. As shown in Figure 6, all polymers
exhibited a similar pattern of decomposition with no signifi-
cant weight loss up to temperature ꢂ460 ꢀC, and the T5%
ꢀ
values of these PIs stayed in the range 504–519 C, demon-
strating that the isomeric PIs possess similar thermo-oxida-
tive stability. Furthermore, the excellent oxidative resistance
of isomeric PIs can also be testified by the char yield, which
ꢀ
maintained over 53% at 800 C in nitrogen. As for PIs from
three isomeric dianhydrides with the same diamine, PI based
on 4,40-PTPKDA displayed higher thermal stability than the
other two kinds of dianhydrides. This difference in thermal
stability may be interpreted by the fact that the 3-phthalim-
ide moiety has lower thermal stability than 4-phthalimide
moiety.20 In addition, the inferior thermal stability of the PIs
derived from 3,30- and 3,40-PTPKDA may be ascribed to the
structural stress caused by nonplanar configuration of the 3-
substituted phthalimide moiety.21
FIGURE 5 The FTIR spectrum of PI-1b.
structures of dianhydride precursor. It should be noted that
the 2,20-bis(trifluoromethyl)benzidine (TFMB)-based PIs are
soluble in all tested solvents, even in THF. A possible expla-
nation is that the trifluoromethyl groups in the resulted
polymer inhibit dense chain packing and reduce the inter-
chain interactions largely.
The Tg values of the isomeric PIs were in the range of 208–
260 C, depending on the structure of dianhydride and diamine
ꢀ
and increase with increasing stiffness of the polymer back-
bones. As shown in Table 3, the Tg values of the polymers from
TFMB, ODA, or TPEQ, measured by DMTA and DSC, displayed a
same decreasing order on the basis of the carenation pattern of
the dianhydrides (3,30- > 3,40- > 4,40-PTPKDA). Higher Tg val-
ues were caused by more difficult chain rotation of polymers,
so this phenomenon could mainly be attributed to the rota-
tional freedom around the carbon-sulfur bonds of 3-substituted
phthalimide, which is partially restricted by the steric effect of
the ortho-carbonyl substituent, leading to the higher Tg value.
The improved solubility of the PIs from 3,30-PTPKDA and
3,40-isomers may be attributed to the formation of more
bent chain structures by the ortho-substituted phthailimide
unit. However, the symmetric structure and most extended
chain of 4,40-isomers, which leads to the strong interchain
interaction and dense chain packing of the resulted PIs,
should be responsible for its poor solubility (Supporting In-
formation, Fig. S3).
Figure 7 shows the variations in the storage modulus (E0)
and loss factor (tan d) at different temperatures. It can be
seen from Figure 7, the storage modulus retains constant or
decreased slightly before the corresponding Tgs. Regarding
the peak temperature in the tan d curves as the glass transi-
tion temperatures, the isomeric PIs of PI-1a, PI-2a, and PI-3a
exhibited a Tg at 256, 216, and 240 ꢀC, respectively. This
trend is consistent with DSC measurements on the Tgs of
isomeric PI, that is, 3,30- > 3,40- > 4,40-linked. These results
reveal that the heat deflection temperature of the PIs can be
improved by the isomerization of polymer backbone.
Thermal Properties
The thermal decomposition and deformation behavior of the
isomeric PIs were evaluated by thermogravimetric analysis
(TGA), differential scanning calorimetry (DSC), and dynamic
mechanical thermal analysis (DMTA) measurements. All data
were obtained from transparent, flexible, and tough films
cast from corresponding PAA solution undergoing the same
cured process.
SCHEME 4 Synthesis of isomeric polyimide resins with close inherent viscosities based on PTPKDA/ODA/PA.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Solubility of Isomeric Polyimidesa
Solventsb
DMAc DMSO
Polymer
CHCl3
TCE
THF
DMF
NMP
m-cresol
p-CPhol
PI-1a
PI-2a
PI-3a
PI-1b
PI-2b
PI-3b
PI-1c
PI-2c
PI-3c
þþ
þþ
þþ
þþ
þꢁ
þþ
þþ
ꢁ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
ꢁ
þþ
þþ
þþ
ꢁ
þþ
þþ
þþ
þꢁ
ꢁ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
ꢁ
þþ
þþ
þþ
þꢁ
þꢁ
þꢁ
þþ
ꢁ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
ꢁ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þꢁ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
ꢁ
ꢁ
þꢁ
þꢁ
ꢁ
ꢁ
ꢁ
þþ
þþ
ꢁ
þꢁ
þþ
þþ
þþ
Key: þþ, soluble at room temperature; þꢁ, partially soluble or swelling; ꢁ, insoluble.
a
Qualitative solubility was determined at 2% w/v concentration, stirring for 24 h at room temperature or
heating up to the solvents boiling temperature for those samples remained insoluble at room temperature.
b
TCE, 1,1,2,2-tetrachloroethane; p-CPhol, p-chlorophenol.
Mechanical Properties and Water Absorption
unit derived from 4,40-PTPKDA and two ether linkages of dia-
mine TPEQ, making the corresponding PI more flexible and
easily prone to formation of denser aggregation and strong
interchain interaction of the polymer chains.13 On the other
hand, the poorest solubility of PI-2c also corroborated the
view that the aggregation of the polymer chains was dense.
The mechanical properties of isomeric PI films are also sum-
marized in Table 3. All isomeric PIs show tensile strength,
elongation at break, and Young’s modulus in the range of
94.2–119.5 MPa, 5.3–57.4%, and 2.5–3.2 GPa, respectively.
Because of the high rigidity of the molecular structure of
3,30-PTPKDA, its PI derivatives have higher tensile strength
and modulus than the two other isomers. On the contrary,
the PIs derived from 4,40-PTPKDA have higher elongation at
break than 3,30- and 3,40-isomers. These may be interpreted
by the fact that the rotation of 4-substituted imide was liber-
ated by the meta-position of SAC bond to the imide group,
not ortho-position of 3-substituted isomer, so the chain rota-
tions are intensified and the breaking elongation of these PIs
are increased as well. It is noted that PI-2c based on 4,40-
PTPKDA and TPEQ showed a relatively higher elongation to
break (57.4%) than other polymers. This is probably due to
the more extended symmetric structure of 4,40-phthtalimide
The PIs derived from diamine TFMB also have low moisture
absorption of 0.27–0.35%, which were tested in distilled
ꢀ
water at 30 C for 120 h. The low moisture absorption of PI-
a series was attributed to the water proofing effect of the tri-
fluoromethyl group contained in the polymer backbone.
Rheology Properties of PI Resins Based on Isomeric
PTPKDA/ODA/PA
The rheological properties of isomeric PTPKDA/ODA/PA-
based PIs were studied in detail. All the PIs discussed were
obtained from the PI powder prepared by one-step polymer-
ization (Scheme 4), and the inherent viscosities of 3,30-, 4,40-,
TABLE 3 Thermal Properties, Mechanical Properties, and Water Uptake of Polyimides
Tg (ꢀC)
Initial
c
T5%
Char
Yieldd (%)
Strength to
Break (MPa)
Elongation
Modulus
(MPa)
Polymer
DSCa
DMTAb
(ꢀC)
to Break (%)
% H2Oe
PI-1a
PI-2a
PI-3a
PI-1b
PI-2b
PI-3b
PI-1c
PI-2c
PI-3c
a
260
230
248
250
220
240
233
208
225
254
216
240
235
207
227
219
193
211
511
519
517
511
518
515
504
512
506
60.8
61.8
59.4
58.7
58.2
57.1
53.5
55.8
54.0
119.5
106.6
112.2
114.5
98.6
5.3
9.2
3208
3056
2995
2827
2608
2846
2705
2491
2881
0.27
0.33
0.35
0.77
0.75
0.70
0.65
1.00
0.68
8.5
8.2
15.4
8.2
110.0
107.6
94.2
8.3
57.4
8.7
109.1
d
e
Obtained from DSC at a heating rate of 20 ꢀC/min in nitrogen.
Obtained from DMTA at a heating rate of 3 ꢀC/min at 1 Hz in air.
Temperature at 5% weight loss were recorded by TGA at a heating at
Residual weight (%) at 800 ꢀC in nitrogen.
Moisture absorption of polyimide films were measured by immersing
films in distilled water at 30 ꢀC for 120 h.
b
c
10 ꢀC/min in nitrogen.
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FIGURE 8 Complex viscosity of isomeric polyimides as a func-
FIGURE 6 TGA thermograms of PI-a series at a heating rate of
10 ꢀC/min. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
tion of temperature.
temperature and with the features of thermosetting resin.
Interestingly, the PI isomers with same chemical composition,
but they exhibited completely different rheological behaviors.
The sulfur atom attached to the ortho-position of phthalimide
group, which lowers the electron density of the sulfur atom,
may be principally responsible for the melt stability of 3,30-
PTPKDA-based PI; whereas in 4,40-PTPKDA-based PI, the sul-
fur atom with higher electron density is attached to the meta-
position of phthalimide group, so the intermolecular crosslink-
ing reaction may occur correspondingly via disulfide bond for-
mation. As expected, due to the sulfur atom at meta-position
of phthalimide group reduced by half, the 3,40-PTPKDA-based
PI exhibited higher crosslinking temperature (about 365 ꢀC)
than 4,40-PTPKDA-based PIꢀ isomer. This resin demonstrated
good flowability below 360 C, and the minimum complex vis-
and 3,40-PTPKDA-based PI samples were 0.42, 0.41, and 0.42
dL/g, respectively.
Figure 8 displays the rheological behavior of three isomeric
PI resins. Because of the 4,40-PTPKDA-based PI resin with
the lowest Tg (220 ꢀC), the initial temperature for measure-
ment was selected as 250 ꢀC, whereas the others were con-
ducted from 280 ꢀC. The complex viscosities dramatically
decreased above Tgs for all the samples, which agreed with
the phenomena of their films softening rapidly in the DMTA
test. The melt viscosity of the 3,30-PTPKDA-based PI dramati-
cally decreased with an increase in the temperature and
exhibited a melt viscosity as low as 120 Pa s at about 390
ꢀC. This meant that the 3,30-PTPKDA-based PI has some
characteristic of thermoplastic polymer with remarkable fusi-
bility. However, the complex viscosity of 4,40-PTPKDA-based
PI did not decrease where the processing temperature was
ꢀ
cosity was about 400 Pa s at 360 C.
To evaluate the melt processability, the rheological measure-
ments for 3,30-PTPKDA-based PI were also conducted iso-
thermally at 350 ꢀC. As shown in Figure 9, it is noted that
ꢀ
over 350 C, and the minimum complex viscosity was ꢂ900
Pa s at 350 ꢀC. This indicates that the crosslinking and/or
chain extension reaction may occur in the melt around that
FIGURE 9 The time dependence of the storage and loss mod-
uli, and the complex viscosity for 3,30-PTPKDA-based polyimide
in air at 350 ꢀC. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
FIGURE 7 DMTA curves of polyimides from three dianhydride
isomers and TFMB. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
COMPARATIVE STUDY ON ISOMERIC POLYIMIDES, WEI, PEI, AND FANG
2491

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
ꢀ
the loss elastic moduli (G00) has a higher value than the stor-
moduli (G00) data were isothermally collected at 350 C with
a frequency of 1 Hz and a strain of 3%.
ꢀ
age elastic moduli (G0) at 350 C and persists for a relatively
long period of time for about 55 min, which exhibits visco-
elastic liquid-like behavior. Furthermore, the range of the
complex viscosity at 350 C was from 200 Pa s at the begin-
ning to 900 Pa s at 55 min. This complex viscosity range
was appropriate for extrusion and injecting molding.
Monomer Synthesis
4,40-Dimercaptobenzophenone
ꢀ
4,40-Dimercaptobenzophenone was synthesized by the
methods given in the literature.18
Yield: 82%. m.p.: 171–173 ꢀC (lit. 171–174 ꢀC). 1H NMR
(CDCl3): 7.66–7.64 (4H, d, J ¼ 8.0 Hz), 7.34–7.32 (4H, d, J ¼
8.0 Hz), 3.63 (2H, s).
EXPERIMENTAL
Materials
4-Chloro-40-mercapto Benzophenone (CMBP)
3-Chlorophthalic anhydride and 4-chlorophthalic anhydride
were kindly supplied by Harbin Shidai Science and Technol-
ogy. 4,40-Difluorobenzophenone and sodium hydrosulfide
hydrate were purchased from Sigma–Aldrich. 4,40-Dichloro-
benzophenone was purchased from Acros. Unless otherwise
noted, the other chemicals were purchased from Sinopharm
Chemical Reagent. DMAc and NMP were purified by distilla-
tion under reduced pressure over phosphorus pentoxide and
stored over 4-Å molecular sieves. N-methyl-4-mercaptoph-
thalimide22 was synthesized in our laboratory.
CMBP was prepared by previously reported methods20: 4,40-
dichlorobenzophenone (20.1 g, 80 mmol) and DMSO (60
ꢀ
mL) were heated at 60 C under nitrogen atmosphere. Then,
sodium hydrosulfide (Aldrich 68%; 6.4 g, 78 mmol) and po-
tassium carbonate (10.8 g, 78 mmol) were added into the
flask until 4,40-dichlorobenzophenone was completely dis-
solved in DMSO, and the temperature was maintained at 60
ꢀC for 1 h. The solution was then allowed to cool to room
temperature, and the precipitated salt was filtered. The fil-
trate was diluted with water and acidified with a 1 M HCl
solution. The crude product was collected by filtration, then
dissolved in 10% K2CO3 solution, and reprecipitated by add-
ing 1 M HCl solution. This purification process was repeated
three times and off-white product was dried at room tem-
perature under vacuum. The overall yield of the CMBP was
Characterization
1H and 13C NMR spectra were recorded on a Bruker 400
AVANCE III spectrometer operating at 400.23 and 100.65
MHz, using CDCl3 or dimethyl sulfoxide-d6 (DMSO-d6) as sol-
vents. The FTIR spectra were obtained with a Thermo Nico-
let 6700 FTIR spectrometer, where the sample was prepared
with KBr pellets. Melting points were determined on an
XT4-100B melting point apparatus (Beijing Keyi Elec-opti
instrument) and were uncorrected. Elemental analyses were
carried out on a Perkin-Elemer model 2400 II C, H, N, S ana-
lyzer. The inherent viscosities were measured with an Ubbe-
lodhe Viscometer at 30 6 0.1 ꢀC in NMP at a concentration
of 0.5 g/dL. TGA was recorded on a Perkin–Elmer Diamond
TG/DTA instrument at a heating rate of 10 ꢀC/min under
nitrogen atmosphere (flow rate of 50 mL/min). Glass transi-
tion temperatures (Tgs) were determined by DSC with the
aid of a Mettler Toledo DSC using a heating rate of 20 ꢀC/
min under nitrogen atmosphere with 50 mL/min gas flow;
Tgs were reported as temperature at the middle of the ther-
mal transition from the second heating scan. DMTA was per-
formed on PI film specimens (20-mm long, 4-mm wide, and
about 30-lm thick) on a Mettler Toledo DMAꢀ (Switzerland)
ꢀ
29% with the melting point 156–158 C.
4,40-Bis(2,3-dicarboxyphenylthio) Diphenyl
Ketone Dianhydride (3,30-PTPKDA)
A mixture of 3-chlorophthalic anhydride (8.03 g, 0.044 mol),
4,40-dimercaptobenzophenone (4.93 g, 0.02 mol), TEA (4.45
g, 0.044 mol), and 80-mL DMAc were placed in a 250-mL,
three-necked, round-bottomed flask. The mixture was heated
ꢀ
to 60 C and stirred for 3 h under nitrogen atmosphere. The
yellow mixture was cooled and slowly poured into 800-mL
dilute hydrochloric acid solution. The off-white precipitation
was filtered and washed with water until pH ¼ 7 and dried
under vacuum at 150 ꢀC for 12 h. The crude product was
recrystallized from acetic anhydride and DMSO (2:1, v/v),
and a light yellow solid with the yield of 89% (9.6 g) was
obtained. m.p.: 259–261ꢀC.
FTIR (KBr, cmꢁ1): 1851, 1771 (masym. C¼O, msym. C¼O anhydride);
1654 (mC¼O benzophenone). 1H NMR (DMSO-d6, d, ppm): 7.92–
7.89 (m, 6H), 7.86–7.82 (t, J ¼ 8.0 Hz, 2H), 7.78–7.76 (d, J ¼
8.0 Hz, 4H), 7.41–7.39 (d, J ¼ 7.8 Hz, 2H). 13C NMR (DMSO-
d6, d, ppm): 194.7, 163.2, 162.3, 138.2, 137.7, 137.2, 135.3,
134.3, 134.2, 133.3, 131.7, 127.5, 123.2. Elemental analysis
for C29H14O7S2 (538.55 g/mol): calcd. C, 64.68%; H, 2.62%;
S, 11.91%. Found C, 64.53%; H, 2.60%; S, 11.96%.
ꢀ
at a heating rate of 3 C/min from 30 to 300 C with a load
frequency of 1 Hz in air. The tensile measurements were
tested for six PI film samples by an Instron model 5567 at
room temperature, and the results were averaged. The rheo-
logical measurements of PIs were conducted on a rotational
Physica MCR 301 rheometer in an oscillation model. Sample
discs of 25-mm diameter and 1-mm thickness were prepared
by press-molding of the PIs powder at 80 ꢀC under high
pressure, which were then loaded in the rheometer fixture
equipped with 25-mm diameter parallel plates. Complex
viscosity (g*) was measured on a rotational rheometer over
the range of 250–400 ꢀC; and the data were collected at a
frequency of 1 Hz, a strain of 3%, and a heating rate of
4,40-Bis(3,4-dicarboxyphenylthio) Diphenyl Ketone
Dianhydride (4,40-PTPKDA)
This compound was prepared from 4-chlorophthalic anhy-
dride using the same procedure as described above and
recrystallized from acetic anhydride. The product was
obtained as a light yellow solid. (Yield: 80%, 8.65 g); m.p.:
ꢀ
ꢀ
3 C/min. The storage elastic moduli (G0) and the loss elastic
207–209 C.
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ARTICLE
FTIR (KBr, cmꢁ1): 1848, 1774 (masym. C¼O, msym. C¼O anhydride);
1652 (mC¼O benzophenone). 1H NMR (DMSO-d6, d, ppm): 8.05–
8.03 (d, J ¼ 8.0 Hz, 2H), 7.88–7.85 (m, 6H), 7.84–7.82 (dd,
J1 ¼ 8.0 Hz, J2 ¼ 1.6 Hz, 2H), 7.71–7.69 (d, J ¼ 8.0 Hz, 2H).
13C NMR (DMSO-d6, d, ppm): 194.5, 163.1, 163.0, 146.4,
137.3, 137.2, 135.9, 133.2, 133.0, 131.7, 129.6, 126.7, 124.8.
Elemental analysis for C29H14O7S2 (538.55 g/mol): calcd. C,
64.68%; H, 2.62%; S, 11.91%. Found C, 64.49%; H, 2.58%; S,
12.00%.
heated to 160 ꢀC for 15 h under argon atmosphere. The
reaction mixture was allowed to cool to room temperature
and poured into a large excess of ethanol. The precipitate
was washed thoroughly with ethanol and then recrystallized
from toluene and DMAc (v/v, 20/1), and a yellꢀow solid with
the yield of 90% was obtained (m.p.: 236–239 C).
FTIR (KBr, cmꢁ1): 1768, 1717 (masym. C¼¼O, msym. C¼¼O imide); 1654
(mC¼¼O benzophenone); 1380 (mCAN). 1H NMR (DMSO-d6, d, ppm):
7.88–7.83 (m, 5H), 7.78–7.76 (dd, J1 ¼ 8.0 Hz, J2 ¼ 1.6 Hz
1H), 7.73–7.71 (m,3H), 7.67–7.65 (d, J ¼ 8.0 Hz, 2H), 7.62–
7.60 (d, J ¼ 8.0 Hz, 2H), 7.22–7.20 (dd, J1 ¼ 6.8 Hz, J2 ¼ 2.0
Hz 1H), 3.03 (s, 3H), 3.02 (s, 3H). 13C NMR (DMSO-d6, d,
ppm): 194.6, 167.8, 167.7(2C), 167.6, 142.4, 139.2, 137.5,
136.6, 136.2, 135.6, 135.4, 134.0, 133.8, 133.0, 131.6, 131.5,
131.4, 131.0, 129.4, 128.7, 127.7, 124.5, 124.2, 121.0, 24.3,
24.2. Elemental analysis for C31H20N2O5S2 (564.63 g/mol):
calcd. C, 65.94%; H, 3.57%; N, 4.96%, S, 11.36%. Found C,
66.02%; H, 3.59%; N, 4.91%, S, 11.16%.
3-(4-(4-Chlorobenzoyl)thio) Phthalic Anhydride (1)
A flask was charged with CMBP (2.49 g, 10 mmol), 3-chlor-
ophthalic anhydride (2.01 g, 11 mmol), Et3N (1.11 g, 1.52
mL), and dry DMAc (40 mL). The reaction mixture was
heated at 50 ꢀC for 2 h with stirring under N2. Then the
reaction mixture was allowed to cool to room temperature
and poured into dilute hydrochloric acid solution. The pre-
cipitate was collected by filtration, and the product was
washed with water until pH ¼ 7 and dried to afford 3.20 g
ꢀ
(81%) of yellow powder. m.p.: 178–179 C.
4-(2,3-Dicarboxyphenylthio)-40-(3,4-dicarboxyphenylthio)
Diphenyl Ketone Dianhydride (3,40-PTPKDA)
FTIR (KBr, cmꢁ1): 1842, 1771 (masym. C¼O, msym. C¼O anhydride);
1652 (mC¼O benzophenone); 668 (mCACl). 1H NMR (DMSO-d6, d,
ppm): 7.88–7.79 (m, 6H), 7.75–7.73 (d, J ¼ 8.0 Hz, 2H),
7.66–7.64 (d, J ¼ 8.0 Hz, 2H), 7.36–7.34 (d, J ¼ 8.0 Hz, 1H).
13C NMR (DMSO-d6, d, ppm): 194.4, 163.2, 162.4, 138.4,
138.3, 137.8, 137.2, 135.7, 135.0, 134.2, 133.3, 132.1, 131.6,
129.3, 129.2, 127.4, 123.1. Elemental analysis for
In a 50-mL flask, a suspension of 3 (1.00 g, 1.77 mmol) in
deionized water containing dissolved 1.98 g (0.035 mol)
KOH was boiled under refulx. The suspension turned into a
clear solution after about 5 h. After reflux over 48 h and
cooling to room temperature, the clear yellow solution was
filtered to remove any insoluble impurities. The filtrate was
dropped into dilute hydrochloric acid solution slowly to pre-
cipitate a white solid, which was filtered, thoroughly washed
with water. After recrystallization from acetic anhydride, a
light yellow crystal was obtained with the yield of 82%
C21H11ClO4S (394.83 g/mol): calcd. C, 63.88%; H, 2.81%; S,
8.12%. Found C, 63.55%; H, 2.91%; S, 8.22%.
N-Methyl-3-(4-(4-chlorobenzoyl)thio) Phthalimide (2)
In a 250-mL, three-necked, round-bottomed flask, 4.34 g (11
mmol) of 1 was dissolved in 60 mL of HAc at about 80 ꢀC
under a nitrogen atmosphere, and then 2.1 mL (2.05 g, 1.5
eq.) of methylamine solution (25 wt % in H2O) was slowly
added into the system. After methylamine solution was com-
ꢀ
(0.78 g). m.p.: 226–228 C.
FTIR (KBr, cmꢁ1): 1846, 1772 (masym. C¼O, msym. C¼O anhydride);
1653 (mC¼O benzophenone). 1H NMR (DMSO-d6, d, ppm): 8.05–
8.03 (d, J ¼ 8.0 Hz 1H), 7.90–7.88 (m, 6H), 7.86–7.82 (m,
2H), 7.77–7.75 (d, J ¼ 7.8 Hz, 2H), 7.71–7.69 (d, J ¼ 8.0 Hz,
2H), 7.40–7.38 (d, J ¼ 8.0 Hz, 1H). 13C NMR (DMSO-d6, d,
ppm): 194.6, 163.2, 163.0(2C), 162.3, 146.3, 138.2, 137.8,
137.4, 137.3, 137.2, 136.0, 135.2, 134.4, 134.2, 133.3, 133.2,
132.9, 131.7, 131.6, 129.7, 127.5, 126.7, 124.9, 123.2.
Elemental analysis for C29H14O7S2 (538.55 g/mol): calcd. C,
64.68%; H, 2.62%; S, 11.91%. Found C, 64.64%; H, 2.56%; S,
11.88%.
ꢀ
pletely added, the mixture was heated to 145 C and kept in
this temperature for 24 h. After cooling to room tempera-
ture, the white precipitate was collected by filtration, wꢀashed
with acetic acid, and then dried under vacuum at 120 C for
12 hꢀ. Product (3.88 g) was obtained. Yield: 86.6%, m.p.:167–
168 C.
FTIR (KBr, cmꢁ1): 1765, 1712 (masym. C¼¼O, msym. C¼¼O imide); 1656
1
(mC¼¼O benzophenone); 1380 (mCAN); 668 (mCACl). H NMR (DMSO-
General Procedure for Polymer Synthesis
d6, d, ppm): 7.85–7.79 (m, 4H), 7.73–7.64 (m, 6H), 7.23–7.21
(dd, J1 ¼ 6.8 Hz, J2 ¼ 2.0 Hz, 1H), 3.04 (s, 3H). 13C NMR
(DMSO-d6, d, ppm): 194.4, 167.8, 167.6, 138.3, 137.4, 136.2,
135.8, 135.6, 135.3, 134.0, 133.7, 132.9, 132.0, 131.5, 129.3,
127.7, 121.0, 24.2. Elemental analysis for C22H14ClNO3S
(407.87 g/mol): calcd. C, 64.78%; H, 3.46%; N, 3.43%; S,
7.86%. Found C, 64.72%; H, 3.44%; N, 3.43%; S, 7.88%.
A typical procedure for the synthesis of the PI-3b is as
follows: ODA (0.84 g, 4.20 mmol) was dissolved in 25.0 mL
of dried NMP in 50-mL flask. After the diamine was
dissolved completely, 2.26 g (4.20 mmol) of 3,40-PTPKDA
was added in one portion. The mixture was stirred in nitro-
gen atmosphere at room temperature for 24 h to afford a
viscous PAA solution. The inherent viscosity of the resulting
PAA solution was 1.09 dLꢀ/g, measured in NMP at a concen-
tration of 0.5 g/dL at 30 C. An aliquot of PAA solution was
taken out and filtered through a filter to eliminate any par-
ticulates and then coated onto a glassꢀplate and dried at 80
N-Methyl-4-(2,3-dicarboxyphenylthio)-N0-methyl-40-(3,4-
dicarboxyphenylthio) Diphenyl Ketone Diphthalimide (3)
A flask was charged with 1.00 g (2.45 mmol) of 2, 0.47 g
(2.45 mmol) of N-methyl-4-mercaptophthalimide, 0.70 mL
(2.94 mmol) of tributylamine, and 10 mL of NMP. The homo-
geneous darkled mixture was stirred for 0.5 h and then
ꢀ
ꢀC for 8 h, followed by heating at 150 C (1 h), 200 C (1 h),
250 ꢀC (1 h), and 300 ꢀC (1 h) to afford film of PI-3b. By
COMPARATIVE STUDY ON ISOMERIC POLYIMIDES, WEI, PEI, AND FANG
2493

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
REFERENCES AND NOTES
soaking in water, a flexible PI film was lifted off the glass
surface. Then acetic anhydride and TEA were added to the
remaining PAA solution, as the reaction proceed for 24 h
and produced a yellow viscous solution. The solution was
poured slowly into methanol with stirring. The precipitate
was collected by filtration, extracted with methanol in a
Soxhlet extractor for 24 h, and dried in vacuo, to afford pow-
der of the PI.
1 Sroog, C. E. Prog Polym Sci 1991, 16, 561–694.
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5 Hsiao, S. H.; Dai, L. R. J Polym Sci Part A: Polym Chem 1999,
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The reaction scheme for the preparation of isomeric PTPKDA/
ODA/PA end-capped oligomers was accomplished by the
following procedure: ODA, PTPKDA, m-cresol, and several
drops of isoquinoline were added into a three-neck flask fitted
with a Dean-Stark trap topped by a condenser. This solution
was stirred and heated under nitrogen atmosphere for 6 h at
2009, 47, 1673–1684.
7 Wu, S. M.; Hayakawa, T.; Kakimoto, M.; Oikawa, H. Macro-
molecules 2008, 41, 3481–3487.
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ꢀ
200 C. Subsequently, PA was added and reacted for another
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4 h to obtain the PA end-capped PI. After cooling down, the
PI solution was diluted with m-cresol and poured into etha-
nol, washed thoroughly with boiling ethanol three times and
dried.
11 Zheng, H. B.; Wang, Z. Y. Macromolecules 2000, 33, 4310–
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Polym Chem 2009, 47, 2443–2452.
3,30-PTPKDA, 4,40-PTPKDA, and 3,40-PTPKDA were synthe-
sized from 3- or 4-chlorophthalic anhydrides in several
steps. A series of isomeric PIs derived from three PTPKDA
isomers and three diamines were prepared by conventional
two-step method. Because of the presence of the trifluoro-
methyl group in the polymer backbone, the PI-a series PIs
displayed excellent solubility, high Tg, and low moisture
absorption. Isomeric PIs derived from three PTPKDA isomers
exhibited similar thermo-oxidative stability and mechanical
properties, while the solubility and Tgs of polymers displayed
descending order on the basis of the catenation pattern of
dianhydrides, that is, 3,40-PTPKDA > 3,30-PTPKDA > 4,40-
PTPKDA and 3,30-PTPKDA > 3,40-PTPKDA > 4,40-PTPKDA,
respectively. The 3,30-PTPKDA/ODA/PA-based PIs showed
excellent melt stability, and the complex viscosity was
120 Pa s at 390 ꢀC, whereas the crosslinking and/or chain
extension reaction may occur for the two other isomers, 4,40-
13 Ding, M. X. Prog Polym Sci 2007, 32, 623–668.
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20 Wei, H. B.; Wu, X. S.; Hu, B. L.; Fang, X. Z. Polym Adv Tech-
ꢀ
and 3,40-PTPKDA/ODA/PA-based PIs, below 365 C.
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This work was financially supported by International Science
and Technology Cooperation Program of Ningbo City
(2009D10017) and Program of Ningbo Innovative Research
Team (2009B21008).
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