Syntheses and Properties of Soluble Biphenyl-Based Polyimides from Asymmetric Bis(Chlorophthalimide)s

Article abstract of DOI:10.1021/ma0350720

A novel synthesis of asymmetric bis(chlorophthalimide)s (3,4-BCPIs) has been established. The polymerizations of them produced higher molecular weight (0.38-0.51 dL/g) polyimides containing biphenyl units than those of isomeric polymers derived from symmetric bis(chlorophthalimide)s (4,4′-BCPIs) and 3,3'-BCPIs. The distribution of the formed biphenyl units of head to tail, head to head, and tail to tail in the chain of the polymers was about 58.0:21.0:21.0, determined by ¹³C NMR spectra of the polymers. The composition of model compounds, determined by HPLC, was well consistent with the ¹³C NMR spectrum result. Comparing with polymers derived from 4,4?′-BCPIs and 3,3′-BCPIs, the polymers derived from 3,4-BCPIs showed better solubilities in N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methylpyrrolinone (NMP). Flexible films could be cast from the polymer solution with the inherent viscosities of above 0.35 dL/g. The polymer derived from asymmetric bis(chlorophthimide)s gave the highest T_g among the isomeric polymers. The 10% weight loss of these polyimides was above 549°C.

Full text of DOI:10.1021/ma0350720

2754
Macromolecules 2004, 37, 2754-2761
Syntheses and Properties of Soluble Biphenyl-Based Polyimides from
Asymmetric Bis(chlorophthalimide)s
Ch a n glu Ga o, Xu ee Wu , Gu a n gh u a Lv, Men gxia n Din g, a n d Lia n xu n Ga o*
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences; Polymer Chemistry Laboratory, Changchun, 130022, P. R. of China
Received J uly 24, 2003; Revised Manuscript Received J anuary 2, 2004
ABSTRACT: A novel synthesis of asymmetric bis(chlorophthalimide)s (3,4-BCPIs) has been established.
The polymerizations of them produced higher molecular weight (0.38-0.51 dL/g) polyimides containing
biphenyl units than those of isomeric polymers derived from symmetric bis(chlorophthalimide)s (4,4′-
BCPIs) and 3,3′-BCPIs. The distribution of the formed biphenyl units of head to tail, head to head, and
tail to tail in the chain of the polymers was about 58.0:21.0:21.0, determined by 13C NMR spectra of the
polymers. The composition of model compounds, determined by HPLC, was well consistent with the 13C
NMR spectrum result. Comparing with polymers derived from 4,4′-BCPIs and 3,3′-BCPIs, the polymers
derived from 3,4-BCPIs showed better solubilities in N,N-dimethylacetamide (DMAc), N,N-dimethyl-
formamide (DMF), and N-methylpyrrolinone (NMP). Flexible films could be cast from the polymer solution
with the inherent viscosities of above 0.35 dL/g. The polymer derived from asymmetric bis(chloro-
phthimide)s gave the highest Tg among the isomeric polymers. The 10% weight loss of these polyimides
was above 549 °C.
In tr od u ction
Aromatic polyimides (PIs) are a class of advanced
materials known for their high-temperature stability,
excellent electrical and mechanical properties, and good
chemical resistance.1 Most PIs are often insoluble and
intractable in their fully imidized form, thus showing
severe difficulties in processing.2 Therefore, significant
synthetic efforts have been carried out to improve
processability and solubility of PIs with compromising
their attractive properties by the incorporation of flex-
ible bridging links and/or bulky units into the rigid PI
backbone or by attachment of bulky side groups.3 It has
been demonstrated that the polymerization of isomeric
dianhydrides and diamines produced polymers with
broad processing windows and good solubilities without
loss of thermal properties.4 Step polymerizations via Ni-
and Pd-catalyzed carbon-carbon bond formation were
developed to synthesize a series of polymers.5 The
polymerization of 4,4′- or 3,3′-BCPIs (Figure 1), easily
prepared from chlorophthalic anhydrides and stiff di-
amines, via nickel-catalyzed coupling reaction produced
low molecular weight polymers due to the formation of
crystalline polymers and cyclic oligomers, respectively.5b
According to our best knowledge, there have been no
reports on the syntheses and polymerizations of 3,4-
BCPIs, and the properties of the polymers therefrom
prior to this work. In this paper, we would like to report
a novel method for the synthesis of 3,4-BCPIs using 3-
and 4-chlorophthalic anhydrides and diamines in xylene
as well as the properties of the polymers resulted from
the polymerization of 3,4-BCPIs (Scheme 1). The com-
position of the biphenyl units in polymer was also
investigated by the 13C NMR spectrum.
F igu r e 1. Isomers of BCPIs.
N,N-dimethylacetamide (DMAc) were purified as described in
the literature.5b 4,4′-Oxydianiline (a ), 1,3-bis(4-aminophenyl-
oxy)benzene (b), and 4,4′-methylenedianiline (c) were used as
received. 2,3,2′,3′-Biphenyltetracarboxylic dianhydride (iso-
BPDA), 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BP-
DA), and 3,4,3′,4′-biphenyltetracarboxylic dianhydride (s-
BPDA) were prepared as reported in the literature (Figure
2).6a-c
In str u m en ta tion . The 1H and 13C NMR spectra were
measured at 400 MHz on a AV400 spectrometer, and acquisi-
tion parameters of 13C NMR spectra were as follows: pulprog,
zgig; ns, 1000; swh, 25062.0 Hz; d1, 8.0 s; and p1, 5.5 µs. The
HPLC analysis was carried out on a Gilson-117 spectrometer
with a Hypersil CN (5 µm) column, and hexane and 2-propanol
(98/2, v/v) were used as mobile phase. The X-ray diffrction
(WAXD) measurements were undertaken on a Philos X-ray
diffractometer with Cu K radiation (40 kV, 30 mA). The
scanning rate was 2°/min. The FTIR spectra, the elemental
analyses data, the inherent viscosities, the thermogravimetric
analyses (TGA) curves, the differential scanning calorimetry
(DSC) curves, the MALDI-TOF mass spectra, and the dy-
namic mechanical property of PI film were obtained as
described in the literature.5b The X-ray diffraction data of
a-BPDA were collected on a SiemensP4 4-circle diffractometer
at 293 K under monochromatized MoKR radiation (λ )
0.710 73 Å). 2,3,3′4-BPDA crystallized in a triclinic system
with space group P-1, Mr ) 294.20, a ) 7.0366(4) Å, b )
Exp er im en ta l Section
Ma ter ia ls. Anhydrous NiCl2, triphenylphosphine (PPh3),
powdered (100 mesh) zinc, chlorophthalic anhydrides, and
* To whom correspondence should be addressed. E-mail:
lxgao@ciac.jl.cn.
10.1021/ma0350720 CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/20/2004

Macromolecules, Vol. 37, No. 8, 2004
Soluble Biphenyl-Based Polyimides 2755
Sch em e 1. Syn th esis of P Is fr om 3,4-BCP Is
15.1679(8) Å, c ) 18.4629(12) Å, â ) 83.296(2)°, and V )
1859.54(4) Å3 with Z ) 4 for Dcalcd ) 1.576 mg/m3. Least-
squares refinement based on 7954 independent reflections
converged to final R1 ) 0.0397 and Rw ) 0.0806. The structure
of a-BPDA was solved by direct methods using the SHELXTL
revision 5.1 program. The single crystal of a-BPDA was
prepared by sublimation at 200 °C.
Mon om er Syn th esis. 2-[4-(4-Am in op h en oxy)p h en yl]-
5-ch lor o-isoin d ole-1,3-d ion e (2a ). In a 500 mL three-necked
round-bottomed flask, 10.01 g (0.05 mol) of a was dissolved in
200 mL of xylene at ca. 100 °C under a nitrogen atmosphere,
9.13 g (0.05 mol) of 4-chlorophthalic anhydride was added in
portion into the system and stirred for 2 h at 95 °C, and then
the resulted suspension was refluxed until the generated water
was removed via a Dean-Stark trap. The resulted soluble
mixture was cooled to 100 °C, and dry hydrochloride was
sparged into the system until 2a was not detected by TLC
(hexane:ethyl acetate ) 2:1, v/v). The resulting suspensions
(hydrochloric salts of 2a and the unreacted a ) were filtered
while hot, washed with hot xylene, and dried under vacuum
at 100 °C for 10 h. Then the mixture of hydrochloric salts was
stirred in boiling water for 1 h, then filtered, and washed with
water. The resulting hydrochloric salt of 2a was dissolved in
20 mL of DMAc, poured slowly into 100 mL of 15% Na2CO3
solution, stirred, filtered, and washed with ethanol until pH
) 7. The product was recrystallized from DMAC and ethanol
(1:1, v/v) to afford 2a in a yield of 56.5% (10.30 g, based on a );
mp 172-174 °C. 1H NMR (CDCl3): 7.92 (1H, s), 7.90-7.77 (2H,
d d), 7.34-7.03 (4H, d d), 6.95-6.70 (4H, d d), 3.53 (2H, s)
ppm. IR (paraffin): 3453 and 3370 cm-1 (NH2 of aryl), 1778
and 1706 cm-1 (CdO of imide), 1388 cm-1(C-N stretching),
742 cm-1 (CdO bending). Anal. Calcd for C20H13O3N2Cl: C,
65.85%; H, 3.59%; N, 7.68%. Found: C, 65.68%; H, 3.50%; N,
7.50%. Meanwhile, the filtrate containing hydrochloric salts
of a was poured slowly into another 50 mL of 15% Na2CO3
solution, stirred, and filtered, and then the unreacted a was
recovered, sublimated in vacuo at 200 °C (1.80 g); mp 189-
191 °C. On the other hand, when the xylene solution was
cooled, symmetric 4,4′-bis(4-chlorophthalimido)diphenyl ether
(s-3a ), was collected, recrystallized from xylene, and obtained
in the yield of 17.1% (4.52 g, based on a ); mp 238-240 °C (lit.5b
mp 238-240 °C).
2-{4-[3-(4-Am in op h en oxy)p h en oxy]p h en yl}-5-ch lor o-
isoin d ole-1,3-d ion e (2b). This compound was prepared from
4-chlorophthalic anhydride and b using the same procedure
as described above and recrystallized from xylene. The product
was obtained as a white solid in the yield of 58.6% (13.4 g,
1
based on b); mp 160-162 °C. H NMR (DMSO-d6): 8.03 (1H,
s), 7.98-7.93 (2H, d d), 7.76-7.44 (2H, d), 7.35-7.30 (1H, t),
7.17-7.15 (2H, d), 6.84-6.82 (2H, d), 6.70-6.63 (4H, m), 6.58
(1H, s) and 5.35 ppm (2H, s). IR (paraffin): 3454 and 3372
cm-1 (NH2 of aryl), 1778 and 1706 cm-1 (CdO of imide), 1387
cm-1 (C-N stretching), 740 cm-1 (CdO bending). Anal. Calcd
for C26H17O4N2Cl: C, 68.35%; H, 3.75%; N, 6.13%. Found: C,
68.47%; H, 3.86%; N, 5.95%. Symmetric 1,3-bis[4-(4-chloro-
phthalimido)phenoxy]benzene (s-3b), as a white solid, recrys-
F igu r e 2. Isomers ofBPDAs.

2756 Gao et al.
Macromolecules, Vol. 37, No. 8, 2004
Ta ble 1. P r ep a r a tion of P Is Con ta in in g Bip h en yl Un its
polymerization via Ni-Cat coupling polymerization of BPDAs and a
monomer
polymer
3a
4a
95
0.51
flexible
3b
4b
96
0.40
flexible
3c
4c
94
0.38
flexible
s-BPDA
s-P I
iso-BPDA
iso-P I
97
0.25
brittle
a-BPDA
a-P I
98
0.41
flexible
m-BPDAa
m-P I
98
0.56
flexible
yield (%)
99
ηinh (dL g-1
)
0.58b
flexible
film appearance
a
b
s-BPDA:a-BPDA:iso-BPDA ) 21:58:21 (mol/mol/mol). (1) s-BPDA:phthalic anhydride:a ) 0.98:0.04:1 (mol/mol/mol); (2) determined
in p-chlorophennol/m-cresol (1:1, w/w).
F igu r e 3. IR spectrum of 2c.
F igu r e 8. 13C NMR spectrum of compound A (a, measured
in DMSO-d6; b, estimated by calculation.)
C, 68.35%; H, 3.75%; N, 6.13%. Found: C, 68.47%; H, 3.86%;
N, 5.95%. 4,4-Bis(4-chlorophthalimido)diphenylmethane, s-3c,
recrystallized from xylene, was obtained in the yield of 18.1%
(4.78 g, based on c); mp 239-241 °C (lit.7 mp 239-241 °C). In
the meantime, 1.9 g of c was recovered.
4-(4-Ch lor op h th a lim id o)p h en yl-4-(3-ch lor op h th a lim i-
F igu r e 4. 1H NMR spectrum of 2c.
d o)p h en yl Eth er (3a ). In a 100 mL three-necked round-
bottomed flask, 3.65 g (0.01 mol) of 2a , 1.83 g (0.01 mol) of
3-chlorophthalic anhydride, and 50 mL of xylene were added
and refluxed for 24 h in nitrogen until the generated water
was removed via a Dean-Stark trap. The system was cooled,
and a yellow participate was collected by filtration. The
product, 3a , recrystallized from xylene, was obtained in a yield
of 90% (4.76 g); mp 230-232 °C. 1H NMR (DMSO-d6): 8.02
(1H, s), 7.84-7.99 (5H, m), 7.50-7.53 (4H, d), 7.24-7.27 ppm
(4H, d). IR: 1776 and 1725 cm-1 (CdO of imide), 1375 cm-1
(C-N stretching), 742 cm-1 (CdO bending). Anal. Calcd for
tallized from xylene, was obtained in the yield of 15.7% (4.87
g, based on b); mp 257-259 °C. 1H NMR (DMSO-d6): 8.03
(2H, s), 7.98-7.93 (4H, d d), 7.48-7.44 (5H, m), 7.23-7.21 (4H,
t), 6.90-6.87 (2H, d d) and 6.80-6.79 ppm (1H, t). IR
(paraffin): 1778 and 1706 cm-1 (CdO of imide), 1387 cm-1
(C-N stretching), 740 cm-1 (CdO bending). Anal. Calcd for
C
34H18O6N2Cl2: C, 65.71%; H, 2.92%; N, 4.51%. Found: C,
65.57%; H, 2.86%; N, 4.53%. In the meantime, 2.4 g of b was
recovered.
2-[4-(4-Am in oben zyl)p h en yl]-5-ch lor oisoin d ole-1,3-d i-
on e (2c). This compound was prepared from 4-chlorophthalic
anhydride and c using the same procedure as described above
and recrystallized from xylene. The product was as a yellow
solid (53.3%, 9.66 g, based on c); mp 182-184 °C. 1H NMR
(DMSO-d6): 7.93 (1H, s), 7.88-7.90 (2H, d d), 7.34-7.39 (4H,
d), 7.01-7.04 (2H, d), 6.65-6.67 (2H, d), 3.95 (2H, s) and 3.58
ppm (2H, s). IR (paraffin): 3454 and 3372 cm-1 (NH2 of aryl),
1778 and 1706 cm-1 (CdO of imide), 1387 cm-1(C-N stretch-
ing), 740 cm-1 (CdO bending). Anal. Calcd for C26H17O4N2Cl:
C
28H14O5N2Cl2: C, 63.53%; H, 2.67%; N, 5.29%. Found A: C,
63.56%; H, 2.72%; N, 5.26%.
1-[4-(3-Ch lor op h t h a lim id o)p h en oxy]-3-[4-(4-ch lor o-
p h th a lim id o)p h en oxy]ben zen e (3b). This compound was
prepared from 2b and 3-chlorophthalic anhydride using the
same procedure as described above. The product, 3b, as a white
solid, recrystallized from xylene, was obtained in the yield of
86% (5.34 g); mp 235-237 °C. 1H NMR (DMSO-d6): 8.02 (1H,

Macromolecules, Vol. 37, No. 8, 2004
Soluble Biphenyl-Based Polyimides 2757
F igu r e 9. 13C NMR spectra of compounds B and C (DMSO-d6).
s), 7.85-7.98 (5H, m), 7.45-7.49 (5H, t), 7.20-7.23 (4H, d d),
6.87-6.90(2H, d d) and 6.80-6.81 ppm (1H, t). IR: 1774 and
1727 cm-1 (CdO of imide), 1375 cm-1 (C-N stretching), 740
cm-1 (CdO bending). Anal. Calcd for C34H18O6N2Cl2: C,
65.71%; H, 2.92%; N, 4.51%. Found: C, 65.67%; H, 2.96%; N,
4.50%.
4-(3-Ch lor oph th alim ido)ph en yl-(4-ch lor oph th alim ido)-
p h en ylm eth a n e (3c). This compound was prepared from 2c
and 3-chlorophthalic anhydride using the same procedure as
described above. The product, 3c, as a yellow solid, recrystal-
lized from xylene, was obtained in the yield of 84% (4.43 g);
mp 254-256 °C. 1H NMR (DMSO-d6): 8.02 (1H, s), 7.84-7.98
(5H, m), 7.38-7.45 (8H, d d) and 4.10 ppm (1H, s). IR: 1778
and 1727 cm-1 (CdO of imide), 1378 cm-1 (C-N stretching),
745 cm-1 (CdO bending). Anal. Calcd for C29H16O4N2Cl2: C,
66.05%; H, 3.06%; N, 5.31%. Found: C, 65.97%; H, 2.96%; N,
5.40%.
Syn th eses of Ca libr a tion Com p ou n d s A, B, C, D, a n d
E for HP LC An a lysis. 4,4′-Bis[N-(2-m eth ylp h en yl)p h th a l-
im id e] (A) a n d 3,3′-Bis[N-(2-m eth ylp h en yl)p h th a lim id e]
(B). Compounds A and B were prepared as reported in the
literature.5b The characteristic data were well consistent with
the results in the literature.5b
3,4-Bis[N-(2-m eth ylp h en yl)p h th a lim id e] (C). The com-
pound C was prepared from 2,3,3′,4-BPDA and toluidine using
the similar procedure as reported in the literature.8 The yield
of product was 85% (3.78 g); mp 224-226 °C. 1H NMR
(CDCl3): 8.15 (1H, s), 8.06-8.07 (1H, d), 8.03 (2H, s), 7.90-

2758 Gao et al.
Macromolecules, Vol. 37, No. 8, 2004
F igu r e 10. 13C NMR spectrum of polymer 4a (DMSO-d6, 100 °C).
7.93 (1H, t), 7.77-7.78 (1H, d), 7.30-7.39 (6H, m), 7.19-7.21
(1H, d d), and 2.22 ppm (6H, s). IR: 1776 and 1725 cm-1
(CdO of imide), 1375 cm-1 (C-N stretching), 742 cm-1 (CdO
bending). Anal. Calcd for C30H20O4N2: C, 76.26%; H, 4.27%;
N, 5.93%. Found: C, 76.15%; H, 4.39%; N, 5.88%.
C15H10O2NCl: C, 66.31%; H, 3.71%; N, 5.16%. Found: C,
66.19%; H, 3.85%; N, 5.20%.
Mod el Rea ction for Deter m in g th e Isom er ic Bip h en yl
Distr ibu tion . In a 50 mL two-necked round-bottomed flask
were placed NiCl2 (0.0182 g, 0.140 mmol), PPh3 (0.2566 g,
0.980 mmol), zinc (0.52 g, 8.0 mmol), N-(2-methylphenyl)-3-
chlorophthalimide (0.54 g, 2 mmol), and N-(2-methylphenyl)-
4-chlorophthalimide (0.54 g, 2 mmol). The flask was evacuated
and filled with nitrogen three times. Then, dry DMAc (10 mL)
was added via syringe through the serum cap. The mixture
became red-brown in 20 min and was stirred at 95 °C for 8 h.
The resulted mixture was poured into 100 mL of 10% hydro-
chloric acid solution, extracted with 30 mL of chloroform. The
chloroform solution was dried with anhydrous magnesium
sulfate and analyzed by HPLC analysis to determine the
composition of products. The model compounds A, B, and C
were used as external standards.
N-(2-Met h ylp h en yl)-4-ch lor op h t h a lim id e (D). Com-
pound D was prepared from 4-chlorophthalic anhydride and
o-toluidine using the similar procedure as reported in the
literature.6a The product was obtained in the yield of 90%; mp
1
156-158 °C. H NMR (CDCl3): 7.96 (1H, d), 7.91-7.93 (1H,
d), 7.77-7.80 (1H, d d), 7.20-7.44 (5H, m), and 2.22 ppm (3H,
s). Anal. Calcd for C15H10O2NCl: C, 66.31%; H, 3.71%; N,
5.16%. Found: C, 66.47%; H, 3.96%; N, 4.98%.
N-(2-Meth ylp h en yl)-3-ch lor op h th a lim id e (E). This com-
pound was prepared as described above from 3-chlorophthalic
anhydride and o-toluidine. The yield was 88%; mp 165.5-167
1
°C. H NMR (CDCl3): 7.87-7.92 (1H, m), 7.71-7.77 (2H, m),
7.28-7.41 (5H, m), and 2.24 ppm (3H, s). Anal. Calcd for

Macromolecules, Vol. 37, No. 8, 2004
Soluble Biphenyl-Based Polyimides 2759
Ta ble 3. Solu bilities of P Isa
solventsb
ηinh
polymer (dL g-1
) DMAc p-CPhol m-cresol NMP DMF DMSO
4a
4b
4c
iso-PI
m-PI
a-PI
s-PI
0.51
0.40
0.38
0.25
0.56
0.41
0.58
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+ -
+ -
-
+
+
+ -
-
-
+
+
+ - + -
+ - + -
-
+
+ -
-
a
b
Solubility: +, soluble; + -, partially soluble; -, insoluble. p-
CPhol ) p-chlorophenol; DMSO ) dimethyl sulfone.
Ta ble 4. Th er m a l P r op er ties of Bip h en yl P Is
Tg (°C)
(DSC) (DMTA)
Tg (°C)
T
5% (°C)
T
10% (°C)
polymer ηinh (dL g-1
)
(TGA)
(TGA)
4a
4b
4c
s-PI
iso-PI
a-PI
m-PI
0.51
0.40
0.38
0.58
0.25
0.41
0.56
313
258
302
270
310
306
289
313
262
303
270
534
532
530
529
520
523
502
585
570
565
576
560
557
549
F igu r e 13. Reflection mode WAXD patterns of polymer 4a
and its isomers.
304
295
P olym er Syn th esis. Representative examples of the po-
lymerizations are given below.
P r ep a r a tion of P olym er 4a via Nick el-Ca ta lyzed Cou -
p lin g P olym er iza tion of 3a . The polymerization of 3a was
carried out as reported in the literature.5b The yield was 95%
(0.87 g). The inherent viscosity of the polymer in cresol was
0.51 dL g -1, measured at a concentration of 0.5 g dL-1 at 30
°C. IR: 1775 and 1725 cm-1 (CdO of imide), 1377 cm-1(C-N
stretching), 743 cm-1 (CdO bending).
P r ep a r a tion of P olym er a -P I fr om a -BP DA a n d a . The
polymer a-P I was prepared from a-BPDA and a using the
similar procedure as reported in the literature.4a The inherent
viscosity of the polymer in cresol was 0.41 dL g -1. IR: 1776
and 1725 cm-1 (CdO of imide), 1376 cm-1 (C-N stretching),
742 cm-1 (CdO bending).
Resu lts a n d Discu ssion
Mon om er Syn th esis. Three asymmetric aryl bis-
(chlorophthalimide)s were prepared from 3- and 4-chlo-
rophthalic anhydrides and three diamines, a , b, and c,
in xylene; other solvents, such as chlorobenzene, anisole,
and dichlorobenzene, were also suitable as the solvents
for the reaction. The diamines reacted with chlo-
rophthalic anhydrides in xylene at low temperature (95
°C) to give insoluble amic acids. The reaction was
completed within 2 h, and upon refluxing, the amic acids
dehydrated to give soluble imides. Upon purging the
reaction with dry hydrochloric acid, monochlorophthal-
imides 2 and unreacted diamines were converted into
insoluble hydrochloric salts in xylene and separated
from s-3 by filtration. The hydrochloric acid salt of
compound 2 was insoluble in water and, therefore, easily
separated from the soluble diamine salt. Neutralization
of the salt of compound 2 using Na2CO3 gave the neutral
monochlorophthalimides 2. Figure 3 shows the repre-
sentative IR spectrum of 2c, which shows strong ab-
sorptions at 3453 and 3370 cm-1 (NH2) and at 1776,
1717,1373, 1103, and 742 cm-1 (consistent with the
imide group). As shown in Figure 4, the 1H NMR
spectrum of 2c is consistent with the proposed structure.
The 3,4-BCPIs were easily synthesized from 2 and
3-chlorophthalic anhydride in good yields, and the
F igu r e 14. TGA curves of polymer 4a and its isomers.
Syn th eses of P olym er s. The Ni-catalyzed coupling
polymerization was performed with 1 mmol of monomer
in DMAc in the presence of zinc and triphenylphosphine
at 95 °C as reported in our previous work.5b In contrast,
PIs from BPDAs and a (iso-PI from iso-BPDA and a ;
s-PI from s-BPDA and a ) were prepared via the con-
ventional method.4 The results are shown in Table 1.
The Ni-catalyzed coupling polymerization of 3a -3c
produced the soluble polymers with inherent viscosities
of 0.38-0.51 dL g-1. Because the syn conformation of
iso-BPDA facilitated the formation of cyclic oligmers,5b,10
the polymerization of iso-BPDA and a gave low molec-
ular weight polymer. In comparison, the conformation
of a-BPDA (Figure 7) was confirmed to be anti, and the
two phenyl rings of a-BPDA are also noncoplanar with
dihedral angles of 44.3° (1), 45.8° (2), and 41.09° (3);9
in the meantime, the conformation of s-BPDA was
confirmed to be anti and coplanar.10 Assuming that the
similar conformations in the chain of polymers from
a-BPDA or s-BPDA were adopted, the formation of cyclic
oligomers would not occur. This presumption was sup-
ported by the MALDI-TOF mass spectra of polymer 4
and a-P I that no peak was associated with cyclic
oligomers. Therefore, the polymerizations of a-BPDA,
s-BPDA with a gave higher molecular weight polymers
1
representative H NMR and IR spectra of monomer 3c
are shown in Figures 5 and 6, respectively.9 The spectra
are consistent with the proposed structures and the
amino structure was not found.

2760 Gao et al.
Macromolecules, Vol. 37, No. 8, 2004
F igu r e 15. Dynamic modulus as a function of temperature for PI Films of polymer 4a and its isomers (s-PI, ηinh ) 0.58 dL g-1
,
35.4 µm thick; m-PI, ηinh ) 0.56 dL g-1, 31.5 µm thick; 4a , ηinh ) 0.51 dL g-1, 33.3 µm thick; a-PI, ηinh ) 0.41 dL g-1, 31.2 µm
thick).
(0.41 and 0.58 dL g-1, respectively). The inherent
viscosity of model polymer m-P I, prepared from the
that of C6-C7 overlaps with those of other carbons. It
has been recognized that the coupling reaction of aryl
chlorides, especially those with electron-withdrawing
substituents, can be carried out quantitatively.11 So it
could be presumed that the amount of C6-C7 is equal
to that of C2-C3. Then the proposition of C2-C3, C4-
C5, and C6-C7 could be estimated as 21.0:58.0:21.0. This
result is in good agreement with that of model reaction.
mixture of BPDAs (a-BPDA:s-BPDA:iso-BPDA
)
58:21:21) and a , was 0.56 dL g-1
.
Deter m in a tion of Isom er ic Bip h en yl Distr ibu -
tion . The Ni-catalyzed coupling reactions of 3,4-BCPIs
may produce three isomeric biphenyl units in the PIs,
such as head to head, head to tail, and tail to tail. The
composition of three isomeric biphenyl units would have
effect on the polymer properties. To determine the ratio
of three isomeric biphenyl arrangements, a model
reaction was carried out by coupling equimolar amounts
of N-(2-methylphenyl)-3-chlorophthalimide and N-(2-
methylphenyl)-4-chlorophthalimide using the procedure
described above. Three bisimides (A, B, C) was obtained
in the ratio of 21.2: 20.8: 57.9, as determined by HPLC.
The elemental analyses of the polymers are reported
in Table 2,9 and these are in agreement with calculated
values for the proposed structure. Figure 11 presents a
typical FT-IR spectrum of polymer 4a , which exhibited
absorptions at 1780, 1720, 1380, and 742 cm-1 associ-
ated with the imide structure.9 As shown in Figure 12,
1
the H NMR (DMSO-d6, 100 °C) spectrum of polymer
4a is consistent with the proposed structure.9
P olym er Ch a r a cter iza tion . The phenyl groups of
polymer 4 could not be resolved by 1H NMR specroscopy.
The 13C NMR spectrum is a useful tool to quantitatively
determine compound structure. Figures 8 and 9 show
the 13C NMR spectra of compounds A, B, and C. The
13C NMR spectrum of compound A shows C8 at 144.5
ppm, as determined by calculation, while those of C10
and C16 of compound B are at 135.6 ppm and C10 and
C30 of compound C are found at 137.8 and 142.3 ppm,
respectively. The resolution of these peaks made it
possible to determine the composition of three biphenyl
units. Figure 10 presents the 13C NMR of polymer 4a ,
and the 13C NMR shows C2-C3 at 144.4 ppm and those
of C4-C5 are at 142.0 and 137.5 ppm, respectively, but
P olym er P r op er ties. The solubilities of the poly-
mers are shown in Table 3. The polymers 4a -4c and
iso-PI are soluble in phenolic and amide solvents,
polymers m-PI and a-PI are partially soluble in amide
solvents, and s-PI is only soluble in p-chlorophenol. This
fact may be explained by the coplanar of the two phenyl
rings in biphenyl units and the crystalline generated
from the stiff diamines for s-PI. In contrast, the biphenyl
unit of iso-BPDA, twisted with a dihedral angle of 62.9°
and adopting a syn conformation, was suitable for the
formation of a large amount of cyclic oligomers.5b As
shown in Figure 7,9 the a-BPDA includes three isomers,
in which the biphenyl groups are nonplanar and adopted
anti conformations. So the solubility of a-PI was better

Macromolecules, Vol. 37, No. 8, 2004
Soluble Biphenyl-Based Polyimides 2761
and IR and and 1H NMR spectra of polymer 4a (Figures 11
and 12).This material is available free of charge via the
Internet at http://pubs.acs.org.
than that of s-PI. On the other hand, the crystallinities
of the PIs were evaluated by wide-angle X-ray diffrac-
tion measurements. As shown in Figure 13, the diffrac-
tion patterns indicate that the order of the crystallinities
is s-PI > a-PI > m-PI > 4a , suggesting that polymer
4a was the most soluble among them. The polymers
with inherent viscosities of above 0.35 dL g-1 from 3,4-
BCPIs were easily made into flexible films (Table 1). In
contrast, the film of s-PI must be made from poly(amide
acid), followed by thermal imidization because of its poor
solubility for the imidized form, and polymer iso-PI was
difficult to be made into the film.6a,10
Refer en ces a n d Notes
(1) (a) Itatani. U.S. Patent 4,568,715, 1986. (b) Itatani. U.S.
Patent 4,247,443, 1981. (c) Sasaki. U.S. Patent 4,290,936,
1981. (d) Sasaki. U.S. Patent 4,473,523 1984. (e) Kaneda, T.;
Katsura, T.; Nakagawa, K.; Makino, H. J . Appl. Polym. Sci..
1986, 32, 3151.
(2) (a) Bower, G. M.; Frost, L. W. J . Polym. Sci., Part A-1 1963,
1, 3135. (b) Sroog, C. E.; Endrey, A. L.; Abramo, S. V.; Berr,
C. E.; Edward, W. M.; Oliver, K. L. J . Polym. Sci., Part A-1
1965, 3, 1373. (c) Alvino, V. M.; Frost, L. W. J . Polym. Sci.,
Part A-1 1971, 9, 2209.
The thermal stability of the polymers was examined
by TGA. As shown in Figure 14 and Table 4, PIs showed
10% weight loss at above 549 °C. The Tg’s from DSC
are summarized in Table 4. Polymers 4 give the Tg’s in
the range of 258-313 °C. Figure 15 displays the
dynamic storage modulus (E′) and loss modulus (E′′) as
a function of temperature for polymer 4a and its
isomers. The Tg’s of s-PI, m-PI, a-PI, and 4a are
observed at 270, 295, 304, and 313 °C, respectively, as
determined by the peak temperature in the E′′ curves.
So the Tg of PI from 3,4-BCPIs was higher than that
from m-PI, a-PI, and s-PI. PI film of 4a shows higher
modulus (E′) preservation than that of PI film from s-PI
and similar to those from a-PI and m-PI before 288 °C.
(3) (a) Yang, C. P.; Lin, J . H. J . Polym. Sci., Part A: Polym.
Chem. 1993, 31, 2153. (b) Yang, C. P.; Lin, J . H. J . Polym.
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Lin, J . H. Polymer 1995, 36, 2607.
(4) (a) Li, Q.; Fang, X.; Wang, Z.; Gao, L.; Ding, M. J . Polym.
Sci., Part A: Polym. Chem., in press. (b) Fang, X.; Wang, Z.;
Gao, L.; Li, Q.; Ding, M. Polymer 2003, 44, 2641. (c) Fang,
X.; Yang, Zh.; Zhang, S.; Gao, L.; Ding, M. Macromolecules
2002, 35, 8708. (d) Hasegawa, M.; Sensui, N.; Ashindo, Y.;
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(5) (a) Percec, V.; Hill, D. H. Step Growth Polymers for High-
Performance Materials, New Synthetic Methods; Labadie, J .
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American Chemical Society: Washington, DC, 1996; p 2. (b)
Gao, C.; Zhang, S.; Gao, L.; Ding, M. Macromolecules 2003,
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Con clu sion s
A facile method for synthesis of 3,4-BCPIs was
established. The nickel-catalyzed coupling polymeriza-
tion of 3,4-BCPIs produced soluble biphenyl PIs with
high molecular weight. The proposition of the biphenyl
units, head to tail, head to head, and tail to tail, in the
polymer chain was 58.0:21.0:21.0, determined by model
reaction and the 13C NMR spectrum. The polymers from
3,4-BCPIs were more soluble and had higher Tg than
the other related polymers.
(6) (a) Rozhanskii, I.; Okuyama, K.; Goto, K. Polymer 2000, 41,
7057. (b) Gao, L.; Wu, X.; Ding, M.; Gao, C.; Zhang, S. ZL
02148860, 2002. (c) Ding, M.; Wang, X.; Yang, Z.; Zhang, J .
U.S. Patent 5,081,281, 1992.
(7) Wirth J . G.; Health D. R. U.S. Patent 3,787,364, 1974.
(8) Williams, F. J .; Donahue, P. E. J . Org. Chem. 1977, 42, 3414.
(9) See Supporting Information.
(10) Tong, Y.; Huang, W.; Luo, J .; Ding, M. J . Polym. Sci., Part
A: Polym. Chem. 1999, 37, 1425.
(11) Colon, I.; Keley, D. R. J . Org. Chem. 1986, 51, 2627.
Ackn owledgm en t. The authors express their thanks
to the National Science Foundation of China for finan-
cial support (No.50033010, 50333030).
Su p p or tin g In for m a tion Ava ila ble: Elemental analyses
of polymers (Table 2), 1H NMR and IR spectra of monomer 3c
(Figures 5 and 6), molecular structure of a-BPDA (Figure 7),
MA0350720