Syntheses of biphenyl polyimides via nickel-catalyzed coupling polymerization of bis(chlorophthalimide)s

Article abstract of DOI:10.1021/ma034036y

A facile method for the synthesis of biphenyl polyamides, which involves the nickel-catalyzed coupling of aromatic dichlorides containing imide structure in the presence of zinc and triphenylphosphine, has been developed. The polymerizations proceeded smoothly under mild conditions and produced biphenyl polyimides with inherent viscosities of 0.13-0.98 dL/g. The polymerizations of bis(4-chlorophthalimide)s with bulky side substituents gave high molecular weight polymers. Low molecular weight polymers from bis(4-chlorophthalimide)s containing rigid diamine moieties and bis(3-chlorophthalimide)s were obtained because of the formations of polymer precipitate and cyclic oligoimides, respectively. The effects of various factors, such as amount of catalyst, solvent volume, ligand, reaction temperature, and time, on the polymerization were studied. The random copolymerization of two bis(chlorophthalimide)s in varying proportions produced medium molecular weight material. The T_gs of prepared polyimides were observed at 245 - 311 °C, and the thermogravimetry of polymers showed 10% weight loss in nitrogen at 470-530 °C.

Full text of DOI:10.1021/ma034036y

Macromolecules 2003, 36, 5559-5565
5559
Syntheses of Biphenyl Polyimides via Nickel-Catalyzed Coupling
Polymerization of Bis(chlorophthalimide)s
Ch a n glu Ga o, Su obo Zh a n g,* Lia n xu n Ga o, a n d Men gxia n Din g
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Polymer Engineering Laboratory, Changchun, 130022, P. R. of China
Received J anuary 10, 2003; Revised Manuscript Received April 29, 2003
ABSTRACT: A facile method for the synthesis of biphenyl polyimides, which involves the nickel-catalyzed
coupling of aromatic dichlorides containing imide structure in the presence of zinc and triphenylphosphine,
has been developed. The polymerizations proceeded smoothly under mild conditions and produced biphenyl
polyimides with inherent viscosities of 0.13-0.98 dL/g. The polymerizations of bis(4-chlorophthalimide)s
with bulky side substituents gave high molecular weight polymers. Low molecular weight polymers from
bis(4-chlorophthalimide)s containing rigid diamine moieties and bis(3-chlorophthalimide)s were obtained
because of the formations of polymer precipitate and cyclic oligoimides, respectively. The effects of various
factors, such as amount of catalyst, solvent volume, ligand, reaction temperature, and time, on the
polymerization were studied. The random copolymerization of two bis(chlorophthalimide)s in varying
proportions produced medium molecular weight material. The Tgs of prepared polyimides were observed
at 245-311 °C, and the thermogravimetry of polymers showed 10% weight loss in nitrogen at 470-530
°C.
In tr od u ction
Exp er im en ta l Section
Ma ter ia ls. Reagent grade anhydrous NiCl2 was dried at
220 °C under vacuum. Triphenylphosphine (PPh3) was recrys-
tallization from hexane. Powdered (100 mesh) zinc was stirred
with acetic acid, filtrated, washed thoroughly with diethyl
ether, and dried under vacuum. 4-Chlorophthalic anhydride
(99.2%) and 3-chlorophthalic anhydride (99.0%) were purified
by distillation. 4,4′-Oxydianiline, 3,3′-dimethyl-4,4′-methyl-
enedianiline, 2,2′,3,3′-tetramethyl-4,4′-methylenedianiline, and
4,4′-(9-fluoroenylidene)dianiline were used as received from
Aldrich. N,N-Dimethylacetamide (DMAc) was stirred over
phosphorus pentoxide for 5 h, then distilled under reduced
pressure, and stored over 4 Å molecular sieves.
Polyimides (PIs) are high-performance polymers which
exhibit several technologically interesting characteris-
tics, such as excellent mechanical properties, electric
insulation, and good chemical resistance and thermal
stability. Incorporation of biphenyl linkages can lead to
improve mechanical properties, low moisture absorp-
tion, and thermal expansion.1 Biphenyl PIs are exclu-
sively prepared by reacting biphenyltetracarboxylic
dianhydrides (BPDAs) with diamines in solution to give
polyamic acids or polyimides.2 BPDAs are synthesized
by nickel-,2a,3 copper-,2b or palladium4,5-catalyzed cou-
pling of phthalic acid derivatives (Scheme 1). Step
polymerization reactions via Ni- or Pd-catalyzed carbon-
carbon bond formation in polymers prompt us to develop
a simple route to synthesizing biphenyl PIs.
1
In str u m en ta tion . The H NMR spectra were measured at
300 MHz on a AV300 spectrometer. The FTIR spectra were
obtained with a Bio-Rad digilab Division FTS-80 spectrometer.
The elemental analyses were performed on an elemental
analysis FLASH-EA-1112 series. The inherent viscosities were
determined at a 0.5% concentration of polymer in m-cresol with
an Ubbelohde capillary viscometer at 30 ( 0.1 °C. The
thermogravimetric analyses (TGA) were obtained in nitrogen
with a Perkin-Elemer TGA-2 thermogravimetric analyzer, and
the experiments were carried out with 10 ( 2 mg samples at
a heating rate of 10 °C/min. The differential scanning calo-
rimetry (DSC) experiments were carried out on a Perkin-
Elemer DSC-7 system at a heating rate of 20 °C/min under a
nitrogen atmosphere. The dynamic mechanical property of PI
film was measured on a dynamic mechanical thermal analyzer
(DMTA). The MALDI-TOF mass spectra were recorded on a
LDI-1700 mass spectrometer with the instrument set in the
positive reflection mode. 1,8,9-Anthracemetriol (dithranol) was
used as the matrix and CHCl3 was used as the solvent. The
X-ray diffraction data were collected on a SiemensP4 4-circle
diffractometer at 293 K. The UV-vis spectra were obtained
on a Varian Cray 50 spectrophotometer.
Mon om er Syn th esis. 2,2′-Bis[4-(4′-a m in op h en yloxy)-
p h en yl]p r op a n e (b). The compound was prepared as re-
ported in the literature;13 mp 126-127 °C (lit.13 mp 127 °C).
1,1′-Bis(3-m eth yl-4-a m in op h en yl)cycloh exa n e (e). In a
three-necked round-bottomed flask, a mixture of 30 mL of H2O,
30 mL of concentrated HCl (0.36 mol), and 9.8 g (0.1 mol) of
cyclohexanone was stirred in an ice bath, and 23.5 g (0.22 mol)
of o-toluidine was dropped within 20 min under nitrogen and
then refluxed for 24 h. The mixture was poured slowly into
The synthesis of biphenyls via the nickel-catalyzed
coupling of chlorobenzene in the presence of zinc and
triphenylphosphine under mild reaction conditions was
first reported by Colon and Kelsey.7 Since 1990, the Ni-
or Pd-catalyzed coupling reactions have been utilized
in the syntheses of poly(ether ether sulfone)s,8 poly-
(arylene ether ketone)s,9 poly(aryl amide)s,10 and poly-
(3-phenyl-2,5-thiophene).11 Moreover, an extensive num-
ber of poly(phenylene)s via metal-catalyzed coupling
reactions were reported.12
To our best knowledge, there have been no reports
on the Ni(0)-catalyzed coupling polymerization for bi-
phenyl PIs based on bis(chlorophthalimide)s, available
fully imidized monomers. In this paper, we report the
syntheses of biphenyl PIs by coupling bis(chlorophthal-
imide)s using nickel catalyst generated in situ from a
nickel salt and an excess reducing agent (Scheme 2).
The properties of the prepared PIs were also character-
ized.
* To whom correspondence should be addressed. E-mail:
sbzhang@ciac.jl.cn.
10.1021/ma034036y CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/24/2003

5560 Gao et al.
Macromolecules, Vol. 36, No. 15, 2003
Sch em e 1. Typ ica lly Con ven tion a l P r ep a r a tion of Bip h en yl P Is
Sch em e 2. Syn th eses of Bip h en yl P Is fr om Ch lor op h th a lic An h yd r id es a n d Dia m in es
300 mL of 15% Na2CO3 solution; the white precipitate formed
2,2′-Bis[4-(4′-(3-ch lor op h th a lim id o)p h en yloxy)p h en yl]-
p r op a n e 2(3b). This compound was prepared from 3-chloro-
phthalic anhydride and b using the same procedure as
described above and recrystallized from toluene and DMAc
(2.5:1, v/v). The product was as a white solid (85%, 31.4 g);
mp 227-229 °C. 1H NMR (CDCl3): 7.89 (2H, m), 7.74 (4H,
m), 7.39 (2H, d d), 7.28 (2H, d d), 7.14 (2H, d d), 7.02 (2H, d
d), 1.73 ppm (6H, s). IR: 1778 and 1722 cm-1 (CdO of imide),
1375 cm-1(C-N stretching), 739 cm-1 (CdO bending). Anal.
Calcd for C43H28O6N2Cl2: C, 69.83%; H, 3.82%; N, 3.79%.
Found: C, 69.63%; H, 3.76%; N, 3.90%.
was filtered and washed with water until a neutral pH was
obtained. The residual crude product was recrystallized from
isopropyl alcohol. The yield of e was 22.0 g (75%); mp 162-
1
163 °C. H NMR (CDCl3): 6.94-7.98 (4H, m), 6.60-6.63 (2H,
d), 3.35 (4H, s), 2.19-2.22 (4H, t), 2.16 (6H, s), 1.49-1.57 ppm
(6H, m). Anal. Calcd for C20H26N2: C, 81.58%; H, 8.90%; N,
9.51%. Found: C, 81.46%; H, 8.81%; N, 9.70%.
4,4′-Bis(3-ch lor op h th a lim id o)d ip h en yl Eth er 2(3a ). In
a 500 mL round-bottomed flask, a mixture of 18.25 g (0.1 mol)
of 3-chlorophthalic anhydride, 10.01 g (0.05 mol) of a , and 200
mL of acetic acid was stirred at ca. 40 °C for 30 min. The
suspension was refluxed for 24 h, and 50 mL of acetic acid
was distilled off. The hot mixture was filtered, washed with
acetic acid, and dried under vacuum at 130 °C for 24 h. The
product was recrystallized from toluene and DMAc (2:1, v/v),
obtained in the yield of 90% (23.8 g); mp 259-260 °C. 1H NMR
(CDCl3): 7.95-7.89 (6H, m), 7.50-7.53 (4H, d d), 7.24-7.27
ppm (4H, d d). IR (KBr): 1774 and 1718 cm-1 (CdO of imide),
1387 cm-1(C-N stretching), 737 cm-1 (CdO bending). Anal.
Calcd for C28H14O5N2Cl2: C, 63.53%; H, 2.66%; N, 5.29%.
Found: C, 63.38%; H, 2.50%; N, 5.33%.
2,2′-Bis[4-(4′-(4-ch lor op h th a lim id o)p h en yloxy)p h en yl]-
p r op a n e 2(4b). This compound was prepared from 4-chloro-
phthalic anhydride and b using the same procedure as
described above and recrystallized from toluene and DMAc
(2.5:1, v/v). The product was as a yellow solid (83%, 30.7 g);
1
mp 218-220 °C. H NMR (CDCl3): 7.95 (2H, d), 7.92 (2H, d),
7.78 (2H, d d), 7.38 (2H, d d), 7.27 (2H, d d), 7.14 (2H, d d),
7.01 (2H, d d), 1.73 ppm (6H, s). IR: 1779 and 1721 cm-1 (Cd
O of imide), 1384 cm-1(C-N stretching), 738 cm-1 (CdO
bending). Anal. Calcd for C43H28O6N2Cl2: C, 69.83%; H, 3.82%;
N, 3.79%. Found: C, 69.77%; H, 3.86%; N, 3.85%.
4,4′-Bis(4-ch lor op h t h a lim id o)d ip h en yl E t h er 2(4a ).14
This compound was prepared from 4-chlorophthalic anhydride
and a using the same procedure as described above and
recrystallized from toluene and DMAc (2:1, v/v). The product
was as a yellow solid (88%, 23.3 g); mp 238-240 °C (lit.14 mp
238-240 °C). 1H NMR (CDCl3): 7.94 (2H, d), 7.91 (2H, d),
7.78-7.76 (2H, d d), 7.43-7.41 (4H, d d), 7.2-7.18 ppm (4H,
d d). IR: 1777 and 1718 cm-1 (CdO of imide), 1393 cm-1(C-
N stretching), 736 cm-1 (CdO bending). Anal. Calcd for
4,4′-Bis(3-ch lor op h t h a lim id o)-3,3′-d im et h yld ip h en yl-
m eth a n e 2(3c). This compound was prepared from 3-chloro-
phthalic anhydride and
c using the same procedure as
described above and recrystallized from toluene and DMAc (4:
1, v/v). The product was as a white solid (80%, 22.2 g); mp
258-260 °C. 1H NMR (CDCl3): 7.91 (2H, m), 7.74 (4H, m),
7.24 (2H, d), 7.21 (2H, d), 7.18-7.15 (2H, d d), 4.06 (2H, s),
2.22 ppm (6H, s). IR: 1780 and 1718 cm-1 (CdO of imide),
1378 cm-1(C-N stretching), 740 cm-1 (CdO bending). Anal.
Calcd for C31H20O4N2Cl2: C, 67.04%; H, 3.63%; N, 5.04%.
Found: C, 66.97%; H, 3.46%; N, 5.22%.
C
28H14O5N2Cl2: C, 63.53%; H, 2.66%; N, 5.29%. Found: C,
63.33%; H, 2.76%; N, 5.13%.

Macromolecules, Vol. 36, No. 15, 2003
Syntheses of Biphenyl Polyimides 5561
4,4′-Bis(4-ch lor op h t h a lim id o)-3,3′-d im et h yld ip h en yl-
m eth a n e 2(4c). This compound was prepared from 4-chloro-
IR: 1776 and 1725 cm-1 (CdO of imide), 1375 cm-1(C-N
stretching), 742 cm-1 (CdO bending). Anal. Calcd for C41H22
-
phthalic anhydride and
c
using the same procedure as
O4N2Cl2: C, 72.68%; H, 3.27%; N, 4.13%. Found: C, 72.46%;
H, 3.21%; N, 4.16%.
described above and recrystallized from toluene and DMAc (4:
1, v/v). The product was as a white solid (82%, 22.7 g); mp
207-209 °C.1H NMR (CDCl3): 7.96 (2H, d), 7.92 (2H, d) 7.8-
7.7 (2H, d d), 7.24 (2H, s), 7.18 (4H, q), 4.05 (2H, s), 2.20 ppm
4,4′-Bis(2-m eth yl-N-p h en ylp h th a lim id e) (A). Compound
A was prepared from 4-chlorophthalic anhydride and o-
toluidine using a similar procedure as reported in the
literature.2a The yield of A was 80%; mp 302-303 °C. 1H NMR
(CDCl3): 8.01-8.04 (2H, d d), 7.84-7.90 (2H, t), 7.75-7.78 (2H,
d d), 7.11-7.34 (8H, m), 2.14 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, 76.40%; H, 4.21%; N, 5.76%.
(6H, s). IR: 1776 and 1717 cm-1 (CdO of imide), 1374 cm-1
-
(C-N stretching), 741 cm-1 (CdO bending). Anal. Calcd for
31H20O4N2Cl2: C, 67.04%; H, 3.63%; N, 5.04%. Found: C,
C
66.90%; H, 3.55%; N, 5.05%.
4,4′-Bis(3-ch lor op h t h a lim id o)-2,2′,3,3′-t et r a m et h yld i-
p h en ylm eth a n e 2(3d ). This compound was prepared from
3-chlorophthalic anhydride and d using the same procedure
as described above and recrystallized from toluene and DMAc
(5:1, v/v). The product was as a white solid (83%, 24.2 g); mp
172-175 °C. 1H NMR (CDCl3): 7.91 (2H, m), 7.75 (4H, m),
7.00 (2H, d), 6.92 (2H, d), 4.07 (2H, s), 2.29 (6H, s), 2.17 ppm
(6H, s). IR: 1777 and 1723 cm-1 (CdO of imide), 1378 cm-1
(C-N stretching), 743 cm-1 (CdO bending). Anal. Calcd for
3,3′-Bis(2-m eth yl-N-p h en ylp h th a lim id e) (B). This com-
pound was prepared from 3-chlorophthalic anhydride and
o-toluidine using the same procedure as A. The yield of B was
71.0%; mp 290-291 °C. 1H NMR (CDCl3): 8.26 (2H, s), 8.08-
8.14 (4H, m), 7.22-7.41 (8H, m), 2.25 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, 76.20%; H, 4.29%; N,
5.98%. The single crystals of A and B for X-ray diffraction
analysis were obtained by the slow sublimation of the pow-
dered samples at 300 °C under vacuum.
C
33H24O4N2Cl2: C, 67.93%; H, 4.15%; N, 4.80%. Found: C,
67.74%; H, 4.13%; N, 4.98%.
4,4′-Bis(4-ch lor op h t h a lim id o)-2,2′,3,3′-t et r a m et h yld i-
p h en ylm eth a n e 2(4d ). This compound was prepared from
4-chlorophthalic anhydride and d using the same procedure
as described above and recrystallized from toluene and DMAc
(6:1, v/v). The product was as a white solid (81%, 23.6 g); mp
236-238 °C. 1H NMR (CDCl3): 7.97 (2H, d), 7.93 (2H, d), 7.78
(2H, d d), 7.01 (2H, d), 4.06 (2H, s), 2.29 (6H, s), 2.15 ppm
X-r a y St r u ct u r e Det er m in a t ion . The X-ray diffraction
data were collected on a SiemensP4 4-circle diffractometer at
293 K under monochromatized Mo KR radiation (λ ) 0.710 73
Å). Compound A crystallized in a triclinic system with space
group P-1, Mr ) 472.48, a ) 8.349(2) Å, b ) 10.0926(17) Å, c
) 13.7891(18) Å, â ) 80.826(15)°, and V ) 1137.5(4) Å3 with
Z ) 2 for Dcalcd ) 1.380 mg/m3. Least-squares refinement based
on 4478 independent reflections converged to final R1 ) 0.0456
and Rw ) 0.0526. Compound B formed in a monoclinic system
with space group C2/c, Mr ) 472.48, a ) 29.010(2) Å, b )
8.5518(19) Å, c ) 24.000(4) Å, â ) 126.520(9)°, and V ) 4785.1-
(14) Å3 with Z ) 8 for Dcalcd ) 1.312 g/cm3. Least-squares
refinement based on 4715 independent reflections converged
to final R1 ) 0.0452 and Rw ) 0.0826. The structures of
compounds A and B were solved by direct methods using
SHELXTL revision 5.1 program.
(6H, s). IR: 1777 and 1726 cm-1 (CdO of imide), 1375 cm-1
(C-N stretching), 742 cm-1 (CdO bending). Anal. Calcd for
33H24O4N2Cl2: C, 67.93%; H, 4.15%; N, 4.80%. Found: C,
-
C
67.75%; H, 4.08%; N, 4.56%.
4,4′-Bis(3-ch lor op h t h a lim id o)-3,3′-d im et h yld ip h en yl-
1,1′-cycloh exa n e 2(3e). This compound was prepared from
3-chlorophthalic anhydride and e using the same procedure
as described above and recrystallized from toluene and DMAc
(6:1, v/v). The product was as a white solid (76%, 23.4 g); mp
275-277 °C. 1H NMR (CDCl3): 7.85-7.89 (2H, m), 7.68-7.72
(4H, m), 7.27 (2H, d), 7.25-7.22 (2H, d d), 7.10 (2H, d), 2.30
(4H, m), 2.18 (6H, s), 1.60-1.52 ppm (6H, m). IR: 1777 and
1726 cm-1 (CdO of imide), 1375 cm-1(C-N stretching), 742
cm-1 (CdO bending). Anal. Calcd for C36H28O4N2Cl2: C,
69.35%; H, 4.53%; N, 4.49%. Found: C, 69.50%; H, 4.48%; N,
4.43%.
P olym er Syn th esis. Representative examples of the nickel-
catalyzed polymerization are given below.
Hom op olyim id es fr om 2(4c). 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),
and 2(4c) (1.11 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 resulting
viscous mixture was diluted with 10 mL of cresol, filtered, and
then poured into 100 mL of methanol. The polymer was
collected by filtration, washed with methanol, and dried in
4,4′-Bis(4-ch lor op h t h a lim id o)-3,3′-d im et h yld ip h en yl-
1,1′-cycloh exa n e 2(4e). This compound was prepared from
4-chlorophthalic anhydride and e using the same procedure
as described above and recrystallized from toluene and DMAc
(6:1, v/v). The product was as a white solid (85%, 26.3 g); mp
1
303-304 °C. H NMR (CDCl3): 7.92 (2H, d), 7.88-7.90 (2H,
d), 7.73-7.76 (2H, d d), 7.26 (2H, d), 7.25-7.23 (2H, d d), 7.10
(2H, d), 2.31 (4H, t), 2.15 (6H, s), 1.59-1.53 ppm (6H, m). IR:
1776 and 1725 cm-1 (CdO of imide), 1375 cm-1(C-N stretch-
ing), 742 cm-1 (CdO bending). Anal. Calcd for C36H22O4N2-
Cl2: C, 69.35%; H, 4.53%; N, 4.49%. Found: C, 69.50%; H,
4.44%; N, 4.60%.
vacuo at 200 °C for 24 h. The yield was 98% (0.95 g). The
-1
inherent viscosity of the polymer in cresol was 0.98 dL g
,
measured at a concentration of 0.5 g dL-1 at 30 °C.
Cop olym er iza tion of 2(3c) a n d 2(4c). The copolyimide
was prepared via the similar procedure as described above
using 2(3c) (0.555 g, 1 mmol) and 2(4c) (0.555 g, 1 mmol).
4,4′-Bis(3-ch lor op h t h a lim id o)d ip h en yl-9-flu or oen yli-
d en e 2(3f). This compound was prepared from 3-chlorophthal-
ic anhydride and f using the same procedure as described
above and recrystallized from toluene and DMAc (5:1, v/v). The
product was as a white solid (82%, 27.78 g); mp 339.5 °C (based
on DSC, 5 °C/ min). 1H NMR (CDCl3): 7.85-7.88 (2H, m), 7.79
(2H, d), 7.66-7.71 (4H, m), 7.30-7.45 ppm (14H, m). IR: 1776
and 1725 cm-1 (CdO of imide), 1375 cm-1(C-N stretching),
742 cm-1 (CdO bending). Anal. Calcd for C41H22O4N2Cl2: C,
72.68%; H, 3.27%; N, 4.13%. Found: C, 72.46%; H, 3.31%; N,
4.06%.
The yield was 97% (0.94 g). The inherent viscosity of the
-1
polymer in cresol was 0.48 dL g
.
P r ep a r a tion of P olym er 3(4c) fr om Dia n h yd r id e a n d
Dia m in e. This polymer was synthesized as reported in the
literature.3 The yield was 99%. The inherent viscosity in cresol
-1
was 0.70 dL g
.
Resu lts a n d Discu ssion
4,4′-Bis(4-ch lor op h t h a lim id o)d ip h en yl-9-flu or oen yli-
d en e 2(4f). This compound was prepared from 4-chlorophthal-
ic anhydride and f using the same procedure as described
above and recrystallized from toluene and DMAc (5:1, v/v). The
product was as a white solid (83%, 28.11 g); mp 328 °C (based
on DSC, 5 °C/ min). H NMR (CDCl3): 7.90 (2H, d), 7.86 (2H,
d), 7.79 (2H, d), 7.71-7.74 (2H, d d), 7.28-7.45 ppm (14H, m).
Mon om er Syn th esis. Twelve aryl dichlorides 2-
(3a )-2(4f) containing bisimide structure were prepared
from 3- or 4-chlorophthalic anhydrides and six diamines
in high yields. The structures of the monomers were
confirmed by elemental analyses, IR, and NMR spec-
troscopies.
1

5562 Gao et al.
Macromolecules, Vol. 36, No. 15, 2003
F igu r e 1. Cycle distribution of oligoimide 3(3c) (molecular weight: 484.51n, n ) 2, 3, 4, etc.).
Ta ble 1. P r ep a r a tion of Bip h en yl P Isa
Syn th esis of P olym er s. The nickel-catalyzed po-
lymerization was performed with 2 mmol of monomer
in DMAc in the presence of zinc and triphenylphosphine.
The effects of temperature, solvent volume, nickel
catalyst, and 2,2-bipyridine on molecular weight were
studied by following the polymerization of monomer 2-
(4c), which gave soluble polymer in DMAc. Figure S1
shows that the optimal amount of solvent for a 1 mmoL
scale reaction was 4-6 mL,15 and the highest inherent
viscosity was observed with a 7 mol % concentration of
nickel catalyst (Figure S2).15 An increase in nickel
catalyst leads to the formation of long-lived nickel
species at polymer ends,7 leading to lower molecular
weight materials.9a
DMAc
(mL)
ηinh
monomer
time (h) polymer
yield (%) (dL g-1
)
2(3a )
2(4a )
2(3b)
2(4b)
2(3c)
2(4c)
2(3d )
2(4d )
2(3e)
2(4e)
2(3f)
2(4f)
3
5
3
5
3
5
3
5
3
5
3
5
8
8
8
8
8
8
8
8
8
8
8
8
3(3a )
3(4a )
3(3b)
3(4b)
3(3c)
3(4c)
3(3d )
3(4d )
3(3e)
3(4e)
3(3f)
3(4f)
3(4c)b
97
97
98
96
96
98
97
98
96
98
96
98
99
0.25
0.20
0.36
0.24
0.21
0.98
0.23
0.77
0.18
0.40
0.13
0.30
0.70
The inherent viscosity of the polymer from 2(4c) is
shown in Figure S3.15 The polycondensation at 95 °C
gave the highest value. Raising the temperature to
above 105 °C gave inferior results because higher
temperature would favor the formation of the highly
coordinated bis complex [Ni(PPh3)2], and then the
oxidative addition of triphenylphosphine can occur.7 The
effect of the ratio of zinc to nickel catalyst on the
polymerization was examined.15 As shown in Figure S4,
a great deal of excess zinc was needed to obtain higher
molecular weight polymer.15 Since 2,2-bipyridine could
force diarylnickel(II) complex into a cis-aryl geometry
which would facilitate reductive elimination due to the
proximity of the phenyl groups,7 the influences of the
amount of bipyridine on the polymerization are also
investigated. Figure S5 shows that the optimal amount
of bipyridine in the polymerization was 25 mol % in
relation to NiCl2.15 Upon further addition of bipyridine,
the inherent viscosity of the polymer decreased because
of the formation of a stable Ni(0)-bipyridine complex,
which retarded the oxidative addition of aryl chlorides.7
Figure S6 shows the progress of the polymerization as
a function of inherent viscosity. Rapid polymerization
proceeded within 60 min, followed by a very slow
a
Monomer (1 mmoL), NiCl2 (0.07 mol), PPh3 (0.49 mmol), Zn
b
(4 mmol), 95 °C. Prepared by the conventional method.
increase in inherent viscosity.15 When polymerization
was carried out for longer than 8 h, some insoluble
gelation was observed.
The main side reactions in the nickel-catalyzed cou-
pling of aryl chlorides were minimized by using thor-
oughly dried solvents in which water content was less
than 30 ppm and by using excess amounts of triph-
enylphosphine with respect to NiCl2.
The inherent viscosities and results of thermal studies
are summarized in Table 1. The polymerizations of 2-
(4a ) and 2(4b) proceeded rapidly with the polymer
precipitation because of crystalline polymers and gave
low molecular weight materials, and those of 2(3a )-2-
(3f) and 2(4c)-2(4f) took place homogeneously. The
polymerizations of monomers 2(4c)-2(4e) with di-
amines moieties containing side pendants gave poly-
mers with high inherent viscosities up to 0.98 dL g
In contrast, the polymerizations of bis(3-chlorophthal-
imide)s gave polymers with lower molecular weights,
though these polymers had good solubilities. Low inher-
-1
.

Macromolecules, Vol. 36, No. 15, 2003
Syntheses of Biphenyl Polyimides 5563
F igu r e 2. Molecular structures of compounds A and B.
ent viscosities of the polymers from bis(3-chloropthal-
imide)s would indicate the peculiarities of molecular
shapes which favor the formation of oligomers. Figure
1 shows the MALDI-TOF mass spectrum of polymer
3(3c). As expected, the polymerization of bis(3-chlo-
ropthalimide)s produced a large amount of cyclic oli-
goimides (MW ) (C31H20O4N2/484.51)n: 969; 1454; 1983;
2423, etc.).
Rozhanskii et al.2a reported the single-crystal struc-
ture of 4,4′-bis(N-phenylphthalimide) (A′). The biphenyl
unit of A′ was confirmed to be coplanar; the stiffness of
its structure directly decreased its solubility in common
solvents. It could be explained that the polymerizations
of 2(4a ) and 2(4b) did not give high molecular weight
polymers because of the formation of crystalline poly-
mers. For comparison, compounds A and B were syn-
thesized from 2-methyl-N-phenylchlorophthalimides by
Ni-catalyzed coupling, and the structures were deter-
mined by X-ray diffraction methods (see Figure 2). As
expected, steric hindrance forced the phthalimide planes
and the 2-methylphenyl rings in compound A to twist
with dihedral angles of 59.3° and 71°, respectively. The
two phenyl rings of the biphenyl unit are also nonco-
planar with a dihedral angle of 24.8°. The phthalimide
planes in compound B formed a 57.1° dihedral angle,
and the dihedral angles between the phthalimides and
the 2-methylphenyl rings were 94.1° and 80.4°, respec-
tively. The ultraviolet-visible absorption spectra of
biphenyl derivatives provide qualitative information on
the phenyl conformation in solution. As shown in Figure
S9, the UV spectra of compounds A and B indicated a
lower degree of conjugation for B, as may be concluded
from the different intensities of their π-π* bands.15 It
has been recognized that the noncoplanar moieties or
flexible links or bulky side substituents in the main
chain of polymers could improve the solubility of the
polymers because of the reduction of their intermolecu-
lar interaction.16 Assuming a similar configuration of
repeating units in polymers, the solubility of the poly-
mers in DMAc, in the order of 3(3d ) > 3(3c) > 3(3b) >
3(3a ) and 3(4d ) > 3(4c) > 3(4b) > 3(4a ), could be
anticipated (see Table S2).15

5564 Gao et al.
Ta ble 2. Th er m a l P r op er ties of Bip h en yl P Is
Macromolecules, Vol. 36, No. 15, 2003
Tg (°C)
(DSC)
T
5% (°C)
T
10% (°C)
polymer
η
inh, dL g-1
(TGA)
(TGA)
3(3a )
3(4a )
3(3b)
3(4b)
3(3c)
3(4c)
3(3d )
3(4d )
3(3e)
3(4e)
3(3f)
3(4f)
3(4c)a
0.25
0.20
0.36
0.24
0.21
0.98
0.23
0.77
0.18
0.40
0.13
0.30
0.70
296
306
260
245
300
299
500
498
450
480
460
458
440
442
445
450
500
480
462
520
530
470
510
470
480
493
471
486
480
550
520
490
297
300
305
315
311
301
a
Prepared by the conventional method.
On the other hand, the trend of bis-imide B to adopt
syn conformations may indicate a facile formation of
undesired cyclic oligomers. The experimental results are
in good agreement with the conformation of B. In
contrast, the structure features of A to adopt anti
conformation predict the formation of linear polymers
instead of cyclic oligomers. In fact, the MALDI-TOF
mass spectrum of polymer 3(4d ) did not show any peak
value of cyclic oligomers. In our study, the high concen-
trated system did not suppress the cyclization of the
polymerization of the bis(3-chlorophthimide)s. It was
presumed that both intramolecular and intermolecular
cyclizations of polymerization might occur. It has been
recognized that incorporation of long chain diamines
(e.g., b) could reduce the formation of cyclic oligomers
in the polymerization.17 As shown in Table 1, the
polymerization of monomer 2(3b), compared with those
of other 2(3)s, gave higher inherent viscosity polymer
(η ) 0.36 dL/g).
Copolymerization was attempted to obtain higher
molecular weight polymers, and aryl dichlorides, 2(4c)
and 2(3c), were copolymerized in varying proportions.
The results are shown in Table S3; it is observed that
slightly higher molecular weight materials are obtained
when monomer 2(4c) is greater than 66 mol %.15
P olym er Ch a r a cter iza tion . Structural character-
ization of polymers was accomplished by elemental
analyses, IR (KBr), and NMR. The elemental analysis
values of polymers in Table S4 were in agreement with
the calculated values for the proposed structure.15
Figure S10 presents a typical FT-IR spectrum of PI 3-
(4c), which exhibited absorptions at 1776, 1717,1373,
1103, and 742 cm-1 associated with the imide structure,
and no amic acid peaks were found, showing that the
imide rings are intact.15 As shown in Figure S11, the
1H NMR (DMSO-d6, 70 °C) spectrum of PI 3(4c) is
consistent with the proposed structure. Peak assign-
ments are given in the figure.15
F igu r e 3. Dynamic modulus as a function of temperature for
PI films of polymer 3(4c) (O: ηinh ) 0.72 dL g -1, 16.7 µm thick;
3: ηinh ) 0.70 dL g -1, 18.5 µm thick).
by the peak temperature in the E′′ curve and consistent
with DSC results. PI films of 3(4c) prepared via two
methods also show a good modulus (E′) preservation
before 280 °C.
Con clu sion s
Our studies indicate that biphenyl PIs can readily be
prepared by the nickel-catalyzed coupling polymeriza-
tion of bis(chlorophthalimide)s. The polymerization of
bis(4-chlorophthalimide)s containing the diamines moi-
eties with bulky side substituents gave polymers with
high inherent viscosities, but the crystalline PIs with
high molecular weights from bis(4-chlorophthalimide)s
cannot be prepared because of the limited solubility of
the polymers. The polymerization of bis(3-chlorophthal-
imide)s produced undesired cyclic oligoimides which
decreased the molecular weights of the polymers. The
cyclization of the polymerization of bis(3-chlorophthal-
imide) was partially suppressed by copolymerization
with bis(4-chlorophthalimide).
Ackn owledgm en t. The authors express their thanks
to the National Science Foundation of China for finan-
cial support (No. 20174040; No. 50033010).
Su p p or tin g In for m a tion Ava ila ble: Tables of solubilities
of PIs, preparation of copolyimides, and elemental analysis of
polymers; figures of effects of amounts of solvent, catalyst,
reaction temperature, ratio of zinc to nickel catalyst, and
amount of bipyridine, course of polymerization, UV-vis ab-
sorption spectra of compounds A and B, FT-IR spectrum of PI
3(4c), 1H NMR spectrum of PI 3(4c), and TG curves of polymer
3(4c). This material is available free of charge via the Internet
at http://pubs.acs.org.
P olym er P r op er ties. The thermal stability of the
polymers was examined by TGA. For comparison,
polymer 3(4c) was prepared via the conventional method.
Typical traces for polymer 3(4c) are shown in Figure
S12.15 The PIs prepared via the two methods almost
have the same TGA trace and show 10% weight loss at
about 480 °C. The Tgs from DSC are summarized in
Table 2. Polymers 3(3b) and 3(4b) give the lower Tgs
because they contained long chain diamine moiety.
Other PIs give the Tgs at about 300 °C. Figure 3 displays
the dynamic storage modulus (E′) and loss modulus (E′′)
as a function of temperature for polymer 3(4c). The Tg
of polymer 3(4c) was observed at 305 °C, as determined
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