Synthesis of new fluorinated polyimides

Article abstract of DOI:10.1016/S0022-1139(01)00462-6

Two monomers 1,2-bis(meta-aminophenyl)hexafluorocyclobutane (1), and 1,2-bis(para-aminophenyl)hexafluorocyclobutene (2), were prepared from meta- or para-nitroiodobenzenes. Palladium-catalyzed coupling reaction of trifluorovinylzinc reagents with nitroiod

Full text of DOI:10.1016/S0022-1139(01)00462-6

Journal of Fluorine Chemistry 111 '2001) 247±251
Synthesis of new ¯uorinated polyimides
Zhen-Yu Yang*
DuPont Central Research and Development, Experimental Station, Wilmington, DE 19880-0328, USA
Received 25 April 2001; accepted 26 June 2001
Abstract
Two monomers 1,2-bis'meta-aminophenyl)hexa¯uorocyclobutane '1), and 1,2-bis'para-aminophenyl)hexa¯uorocyclobutene '2), were
prepared from meta- or para-nitroiodobenzenes. Palladium-catalyzed coupling reaction of tri¯uorovinylzinc reagents with nitroiodo-
benzenes gave the corresponding nitrotri¯uorovinylbenzenes, which dimerized at 130±1508C to give hexa¯uorocyclobutane derivatives.
Reduction of 1,2-di'meta-nitrophenyl)hexa¯uorocyclobutane with NaBH4 and SnCl2 afforded the diamine 1 in high yield. Upon treatment
of 1,2-di'para-nitrophenyl)hexa¯uorocyclobutane with NaBH4 and SnCl2, reduction±de¯uorination occurred to give 2. Diamines, 1 or 2,
polymerized with pyromellitic anhydride 'A), 3,3,4,4-biphenyltetracarboxylic dianhydride 'B), and 4,40-'hexa¯uoroisopropylidene)-
diphthalic anhydride 'C), to give the corresponding poly'amic acids), which were imidized at above 2508C to give thermally stable and
amorphous polyimide ®lms. # 2001Elsevier Science B.V. All rights reserved.
Keywords: 1,2-Bis'meta-aminophenyl)hexa¯uorocyclobutane; 1,2-Bis'para-aminophenyl)hexa¯uorocyclobutene; Poly'amic acids); Polyimides
1. Introduction
2. Synthesis of diamines
Polyimides are well known for their excellent mechanical
properties and thermal and chemical stability [1]. They have
diverse applications in the electronics industry as ¯exible
circuitry substrates, stress buffers, interlayer dielectrics and
passivation layers. Improvements in polyimide properties
have been achieved by introducing tri¯uoromethyl or other
¯uorinated groups leading to lower moisture uptake, lower
dielectrics and better solubility [2,3]. The most common
¯uorinated monomers for these engineering polymers
are 2,20-bis'tri¯uoromethyl-4,40-diaminobiphenyl and 2,20-
diaminobiphenylhexa¯uoro-propane [4,5]. Recently, it has
been recognized that an even better combination of mechan-
ical and electrical properties might be achieved by introduc-
tion of per¯uoroalkyl groups and per¯uoroalkoxyl groups
into more rigid, non-planar monomers for low coef®cient of
thermal expansion [6,7]. However, there are no polyimides
with backbones containing per¯uorocycloalkenyl or per-
¯uorocycloalkyl groups in the literature. We wish to report
new cyclo-per¯uoro-butenyl or -butyl containing aromatic
diamines and their polyimides.
Diamines 1 and 2 were prepared from para- and meta-
nitroiodobenzene, respectively, according Burton's method
[8]. Reaction of tri¯uorovinyl iodide with zinc powder in
DMF gave tri¯uorovinylzinc reagents in high yields. Palla-
dium-catalyzed coupling reaction of nitroiodobenzenes with
tri¯uorovinylzinc reagent afforded para- or meta-nitrotri-
¯uorovinyl benzenes in 80±90% yields. Dimerization of the
tri¯uorostyrene derivatives formed ¯uorinated cyclobutane
derivatives as a cis- and trans-mixture in high yield upon
heating at 140±1508C either neat or in a solvent, such as
tetraglyme and DMF. The three-step reaction can be further
simpli®ed by carrying it out in one pot without prior iso-
lation of tri¯uorovinylnitrobenzene. For example, 1,2-bis'-
meta-nitrophenyl)hexa¯uorocyclobutane was prepared
directly in 82% yield from meta-nitroiodobenzene.
* Fax: ‡1-302-695-9799.
Nitroaromatics can be readily reduced to aminoaromatics
with NaBH4 and SnCl2. Treatment of a cis- and trans-mixture
E-mail address: zhenyu.yang-1@usa.dupont.com 'Z.-Y. Yang).
0022-1139/01/$ ± see front matter # 2001Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ' 0 1 ) 0 0 4 6 2 - 6

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Z.-Y. Yang / Journal of Fluorine Chemistry 111 22001) 247±251
of 1,2-bis'meta-nitrophenyl)hexa¯uorocyclobutane with
SnCl2 and NaBH4 in ethanol at room temperature afforded
diamine 1 as a viscous oil in 93% yield.
the electron-withdrawing character of the ¯uorinated
groups. The poly'amic acid) intermediate can be isolated
by quenching with water. According to GPC data, reason-
ably good molecular weights were attainable. Reaction of
monomer 1 with B gave poly'amic acid) with Mw ˆ 24;800
and Mn ˆ 15;100. The polydispersity value was lower than
that of commercial materials or non-¯uorinated materials,
which is probably due to somewhat lower reactivity of
monomer 1. 1H NMR showed the acidic proton at
12.24 ppm and aromatic protons at 6.88±8.27 ppm. IR spec-
tra showed the acid group at around 3400±3500 cmÀ1. All
poly'amic acid) solutions from 1 or 2 and dianhydrides in
NMP gave brittle ®lms when they were spread on a glass
plate and the solvent was removed. However, transparent,
strong and tough ®lms were obtained upon heating at 230±
2808C for 30±60 min. IR analysis indicated that the heat
treatment converted the poly'amic acid) to the correspond-
ing polyimide, as shown by the appearance of imide absorp-
tion peaks at 1740 and 1780 cmÀ1, and the disappearance of
Interestingly, upon reduction of 1,2-bis'para-nitrophenyl)-
hexa¯uorocyclobutane with NaBH4 and SnCl2 in ethanol
under similar conditions, 19F NMR analysis of the reaction
mixture revealed only a single peak at À114.0 ppm, indicat-
ing a highly symmetrical molecule. After further puri®ca-
tion, a red solid was obtained, which exhibited strong UV
absorption bands 'Zmax ˆ 363, 301and 239 nm, e ˆ 27,465,
14,013 and 14,013, respectively.), which is consistent
with aromatic rings further conjugated with a double bond.
Elemental analysis was also consistent with reduction±
de¯uorination product diamine 2. Although the mechanism
of the new de¯uorination reaction has not been investigated
in detail, we propose that nitro groups were ®rst reduced to
give 3 and then de¯uorination to a quinone-like intermediate
4 occurred, which could be further reduced to 2.
acid peaks at 3400±3500 cmÀ1
.
Thermal stability of polyimide ®lms as measured by
TGA was high. A loss of 10% weight of polymer ®lms
occurred above 5208C, indicating high thermal stability of
the polymers. DSC indicated that all these polyimides were
amorphous polymers. The glass transition temperature of
polyimide ®lms were above 3008C except 6A, whose Tg was
2428C. The high Tg may be due to the very stiff backbones,
which is also supported by lower elongation. Films of 6B
and 6C had 7.8 and 8.3% elongation, respectively.
3. Synthesis of polyimides
Polyimides were prepared from the diamines 1 or 2
and aromatic dianhydrides, such as pyromellitic anhydride
'A), 3,3,4,4-biphenyltetracarboxylic dianhydride 'B), and
4,40-'hexa¯uoroisopropylidene)-diphthalic anhydride 'C)
through the poly'amic acid) route by standard techniques
[7]. The diamines reacted with dianhydrides in N-methyl-
pyrrolidone 'NMP) either at 08C to room temperature or at
room temperature to form viscous poly'amic acid) solutions.
However, the reaction seems to be slower than one with non-
¯uorinated diamines based on observation of the increase in
viscosity with time. The lower reactivity is probably due to
4. Experimental
1H and 19F NMR spectra were recorded on a QE-300
'General Electric, 200 Hz) or Brucker DRX-400 instrument
using TMS and CFCl3 as internal standard, respectively. IR
spectra were recorded on Perkin-Elmer 1600 FT spectro-
meter. All starting materials except tri¯uorovinyl iodide were
obtained from Aldrich and used as received. Tri¯uorovinyl

Z.-Y. Yang / Journal of Fluorine Chemistry 111 22001) 247±251
249
iodide was prepared from tri¯uorovinyl bromide, which was
obtained from PCR [9].
2F), À165.0 's, 2F); 1H NMR: major isomer: 7.22 't,
J ˆ 7:8 Hz, 2H), 6.96 'd, J ˆ 7:8 Hz, 2H), 6.86 's, 2H),
6.77 'dm, J ˆ 8:1Hz, 2H), 3.76 's, 4H); minor isomer: 7.04
't, J ˆ 7:1Hz, 2H), 6.63 'd, J ˆ 6:6 Hz, 2H), 6.58 'm, 4H),
3.66 's, 4H). Anal: Calcd. for C16H12F6N2: C, 55.50; H,
3.49; F, 32.92; N, 8.09%. Found: C, 55.47; H, 3.71; F, 31.12;
N, 7.90%.
4.1. Preparation of 1,2-bis23-nitrophenyl)-
hexafluorocyclobutane
To a stirred solution of Zn '22.0 g, 0.338 mol) and 200 ml
of tetraglyme was slowly added tri¯uorovinyl iodide '42.0 g,
0.202 mol) at room temperature and the resulting mixture
was stirred at RT overnight. 19F NMR analysis of the
reaction mixture indicated conversion to tri¯uorovinyl zinc.
After excess Zn was removed by ®ltration under nitrogen,
meta-nitroiodobenzene '44.0 g, 0.177 mol) and Pd'PPh3)4
'1.3 g) were added and the resulting mixture was stirred at
708C overnight. TLC analysis indicated no meta-nitroiodo-
benzene. After being heated to 140±1458C for 150 h, the
reaction mixture was triturated with a mixture of hexane and
ethyl acetate '4:1) three times. The combined organic layers
were washed with water, then dried over MgSO4. After
removal of solvents, the residue '35.3 g) was recrystallized
from hexane and ethyl acetate to give 19.8 g of pure product.
The mother liquid was concentrated to give a viscous liquid,
which was puri®ed by chromatography on silica gel 'hexane/
ethyl acetate ˆ 95/5 to 85/15) to give 9.9 g of product. Total
yield was 82.6% based on meta-nitroiodobenzene. 19F NMR
indicated that the product was a mixture of cis- and trans-
isomers. Major isomer: À124.5 'd, J ˆ 222:6 Hz, 2F),
À126.2 'd, J ˆ 222 Hz, 2F), À168.6 's, 2F); minor isomer:
À122.4 'd, J ˆ 228:1Hz, 2F), À127.8 'd, J ˆ 228:2 Hz,
2F), À167.4 's, 2F). 1H NMR: major isomer: 8.43±8.40 'm,
4H), 7.90 'd, J ˆ 7:80 Hz, 2F), 7.74 't, J ˆ 7:9 Hz, 2H);
minor isomer: 8.25 'dm, J ˆ 7:4 Hz, 2H), 8.12 's, 2H), 7.55
'm, 4H). Anal: Calcd. for C16H8F6N2O4: C, 47.31; H,
1.98; F, 28.06; N, 6.90%. Found: C, 47.30; H, 2.06; F,
26.91; N, 6.39%.
4.3. Synthesis of para-nitrotrifluorostyrene
To a stirred solution of acid-washed Zn '15 g, 0.23 mol)
and 200 ml of tetraglyme was added iodotri¯uoroethylene
'25.7 g, 0.124 mol) at room temperature. After the addition
was complete, the resulting mixture was stirred at room
temperature for 4 h. Excess Zn was removed by ®ltration
under nitrogen, followed by addition of tetrakis'triphenyl-
phosphine)palladium '1.2 g) and para-nitroiodobenzene
'26.1g, 0.105 mol). The reaction mixture was heated at
658C overnight, and then poured into hexane '200 ml)
and triturated. The hexane was decanted, and the trituration
was repeated twice with hexane. The combined hexane
layers were washed with water and dried over MgSO4. After
removal of hexane, the residue was puri®ed by chromato-
graphy on silica gel using hexane as an eluent to give
para-nitrotri¯uorovinylstyrene '17.1 g, 80.2%). 19F NMR
'CDCl3): À94.5 'dd, J ˆ 56:7 Hz, J ˆ 33:3 Hz, 1F),
À109.4 'dd, J ˆ 108:2 Hz, J ˆ 56:6 Hz, 1F), À177.8 'dd,
J ˆ 108:8 Hz, J ˆ 33:3 Hz, 1F). 1H NMR 'CDCl3): 7.65 'd,
J ˆ 9:0 Hz, 2H), 8.30 'd, J ˆ 8:8 Hz, 2H). IR'nujol): 1752
's), 1600 's), 1529 's), 1462 's), 1350 's), 1301 's), 1158 's)
cmÀ1. Anal: Calcd. for C8H4F3NO2: C, 47.29; H, 1.97; F,
28.08; N, 6.90%. Found: C, 46.63; H, 2.04; F, 27.55; N,
6.51%.
4.4. Dimerization of para-nitrotrifluorostyrene
4.2. Preparation of 1,2-bis2meta-
aminophenyl)hexafluorocyclobutane 21)
Para-nitrotri¯uorostyrene '12.0 g) was heated at 1478C
under nitrogen for 27.5 h and then puri®ed by chromato-
graphy on silica gel 'hexane:ethyl acetate ˆ 90:5 to 90:10)
to give the desired product '10.6 g) as cis- and trans-isomers.
19F NMR: one isomer: À122.1 'dm, J ˆ 229:2 Hz, 2F),
À127.6 'dm, J ˆ 229:0 Hz, 2F), À167.1 'm, 2F); other
isomer: À124.3 'dm, J ˆ 223:3 Hz, 2F), À126.0 'dm,
To a stirred solution of SnCl2Á2H2O '8.3 g, 0.037 mol)
and 1,2-bis'meta-nitrophenyl)hexa¯uorocyclobutane
'15.0 g, 0.0735 mol) in 300 ml of ethanol was added NaBH4
'1.5 g, 0.04 mol) at room temperature over 20 min. After the
addition was complete, the reaction mixture was stirred at
room temperature for 3 h, at 608C for 1h, and then poured
into a mixture of water and ether '500 ml/500 ml) and
treated with NaOH solution. The ether layer was separated
and the aqueous layer was extracted with ether '2 Â 300 ml).
The combined ether layers were washed with 3% NaOH
solution and dried over MgSO4. After removal of the
solvent, the residue '13.8 g) was puri®ed by bulb-to-bulb
distillation 'ca. 1708C/0.05 mmHg) twice to give 12.0 g
'83.3%) of a viscous product 1. 19F NMR: major isomer:
À125.0'dm, J ˆ 222 Hz, 2F), À125.9'dm, J ˆ 222 Hz, 2F),
À160.3 's, 2F); minor isomer: À122.1 'dd, J ˆ 225:1Hz,
J ˆ 3:4 Hz, 2F), À128.7 'dd, J ˆ 255:1Hz, J ˆ 2:4 Hz,
1
J ˆ 223:0 Hz, 2F), À168.5 'm, 2F). H NMR: one isomer:
8.35 'd, J ˆ 8:7 Hz, 4H), 7.75 'd, J ˆ 8:8 Hz, 4H); other
isomer: 8.25 'd, J ˆ 8:8 Hz, 4H), 7.48 'd, J ˆ 8:8 Hz, 4H).
IR 'neat): 3090 'w), 1609 's), 1526 's), 1351 's), 258 's),
1197 's). Anal: Calcd. for C16H8F6N2O4: C, 47.29; H, 1.97;
N, 6.90%. Found: C, 46.93; H, 2.10; N, 6.37%.
4.5. Synthesis of 1,2-bis2para-
aminophenyl)hexafluorocyclobutene 22)
To a stirred solution of 1,2-di'4-nitrophenyl)hexa¯uoro-
cyclobutane '15.0 g), SnCl2Á2H2O '83.0 g) and ethanol
'300 ml) was slowly added a mixture of NaBH4 '1.5 g) in

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Z.-Y. Yang / Journal of Fluorine Chemistry 111 22001) 247±251
ethanol '30 ml) at room temperature 'exothermic reaction).
After the addition was complete, the resulting mixture was
stirred at room temperature overnight and then poured into
ether '500 ml) and water '500 ml). A solution of NaOH was
added until the solids disappeared. The ether layer was
separated and the aqueous layer was extracted with ether
'2 Â 200 ml). The combined ether layers were washed with
water and dried over MgSO4. After removal of MgSO4, the
ether layer was treated with HCl gas. The solids '13.4 g,
95%) were obtained after ®ltration.
Above solids '8.5 g) were treated with 20% NaOH solu-
tion in 300 ml of ether at 08C, the ether layer was separated
and the aqueous layer was extracted with ether. The com-
bined ether layers were washed with water, then dried over
MgSO4. After evaporation of the ether, red solids '5.5 g)
were obtained. The decomposition temperature was deter-
mined to be about 1308C by TGA under air when heated
at 208C/min. 19F NMR 'CDCl3): À114.0 's). 1H NMR
'CDCl3): 7.50 'd, J ˆ 8:6 Hz, 4H), 6.60 'd, J ˆ 8:5 Hz,
4H), 3.96 'br, 4H). UV 'ethanol): lmax 363 nm 'e ˆ 27465),
301nm' e ˆ 14013)and 239 nm'e ˆ 14013), c ˆ 0:0550 g/l
ethanol. Anal: Calcd. for C16H12F4N2: C, 62.34; H, 3.90; F,
24.68; N, 9.09%. Found: C, 63.20; H, 3.87; F, 24.01; N,
9.05%.
P/D ˆ 1:64. The poly'amic acid) solution was spread on a
glass plate at 808C under air and then heated to 2808C using
the following schedule: 808C for 40 min; 1008C for 30 min,
warmed up to 2808C at a rate of 108C/min and held at 2808C
for 30 min. This heat treatment converted the poly'amic
acid) to polyimide. The IR absorption peaks of the poly-
imide appeared at 1715 and 1980 cmÀ1. The ®lm was strong
but somewhat brittle.
The polyimide glass transition temperature is at 3518C.
By TGA, the polymer shows 10% weight loss at tempera-
tures of about 5308C under air and 5458C under nitrogen,
respectively, when heated at 208C/min.
4.8. Preparation of polyimide from 1 and 2,20-
bis23,4-dicarboxyphenyl)hexafluoropropane
dianhydride 26FDA)
A 50 ml three-necked ¯ask ®tted with a mechanical stirrer
and a condenser topped with a N2 inlet was charged with
diamine '1.20 g) and 11.5 g of NMP. The mixture was stirred
until a clear solution was obtained and 2,20-bis'3,4-dicar-
boxyphenyl)hexa¯uoropropane dianhydride '1.54 g) was
added in one portion and the resulting mixture was stirred
at room temperature for 20 h. Some poly'amic acid) solution
was slowly poured into water in a blender and white powder
was precipitated, which was washed with water and dried at
1108C under vacuum for 20 h, then dissolved in DMAC-d9.
1H NMR 'DMAC-d9): 12.25 'br, COOH), 8.27±6.88 'm,
ArH). GPC 'DMAc): Mw ˆ 28;100, Mn ˆ 16;800, P/
D ˆ 1:67. The poly'amic acid) solution was spread on a
glass plate at 808C under air and then heated to 2808C using
the following schedule: 808C for 40 min, 1008C for 30 min,
warmed up to 2808C at a rate of 108C/min and held at 2808C
for 30 min. This heat treatment converted the poly'amic
acid) to polyimide. The IR absorption peaks of the poly-
imide appeared at 1725 and 1985 cmÀ1 and the peak of
carboxylic acid '3440 cmÀ1) disappeared. The ®lm was
strong but somewhat brittle.The polymer's glass transition
temperature is at 3148C. By TGA, the polymer shows 10%
weight loss at temperatures of about 5458C under nitrogen
when heated at 208C/min.
4.6. Synthesis of 1,2-bis24-N-
acetylaminophenyl)tetrafluorocyclobutene
To a stirred solution of 0.3 g of 1,2-bis'4-aminophenyl)-
tetra¯uorocyclobutene and 10 ml of DMF was added 0.5 g
of CH3COCl at room temperature and the resulting mixture
was stirred at room temperature for 30 min and then poured
into water, extracted with ether and dried over MgSO4. After
evaporation of the ether, a residue '0.3 g) was obtained,
1
which was further puri®ed by chromatography. H NMR
'DMF-d7): 2.16 's, 6H), 7.75 'd, J ˆ 7:8 Hz, 4H), 7.89 'd,
J ˆ 7:8 Hz, 4H), 10.42 's, 2H). 19F NMR: À122.8 's). Anal:
Calcd. for C20H16F4N2O2: C, 61.23; H, 4.11; F, 19.37; N,
7.14%. Found: C, 61.11; H, 4.18; F, 19.32; N, 6.61%.
4.7. Preparation of polyimide from 1 and 3,4,3040-
diphenyltetracarboxlic dianhydride
4.9. Preparation of polyimide from 2 and pyromellitic
dianhydride 2PMDA)
A 50 ml three-necked ¯ask ®tted with a mechanical stirrer
and a condenser topped with a N2 inlet was charged with
diamine '1.38 g) and 8 g of NMP. The mixture was stirred
until a clear solution was obtained and 3,4,30,40-diphenylte-
tracarboxlic dianhydride '1.173 g) was added in one portion
and the resulting mixture was stirred at room temperature for
1h. After an additional 5 g of NMP was added, the mixture
was stirred at room temperature for 20 h. Some solution was
slowly poured into water in a blender and white powder was
precipitated, which was washed with water and dried at
1108C under vacuum for 6 h. The polymer was dissolved in
DMAC-d9. 1H NMR 'DMAC-d9): 12.24 'br, COOH), 8.27±
6.88 'm, ArH). GPC 'DMAc): Mw ˆ 24;800, Mn ˆ 15;100,
A 25 ml three-necked ¯ask ®tted with a mechanical stirrer
and a condenser topped with a N2 inlet was charged with
diamine '1.0 g) and 8 g of NMP. The mixture was stirred
until a clear solution was obtained, then PMDA '0.71g) was
added in one portion and the resulting mixture was stirred at
room temperature overnight. The poly'amic acid) solution
was spread on a glass plate at 508C and solvent was slowly
evaporated at 808C for 1.5 h. The ®lm was cured by heating
at 808C for 40 min, 1008C for 30 min, warmed up to 2808C
at a rate of 108C/min and held at 2808C for 30 min. This heat
treatment converted the poly'amic acid) to polyimide. The

Z.-Y. Yang / Journal of Fluorine Chemistry 111 22001) 247±251
251
IR absorption peaks of the polyimide appeared at 1740 and
1980 cmÀ1
The polymer glass transition temperature is at 2428C. By
TGA, the polymer shows 10% weight loss at temperatures of
about 5458C under nitrogen and 5208C under air, respec-
tively, when heated at 208C/min.
'1.00 g) and 9 ml of NMP. The mixture was stirred until a
clear solution was obtained and the ¯ask was cooled in an
ice±acetone bath. 2,20-Bis'3,4-dicarboxyphenyl)hexa¯uoro-
propane dianhydride '1.44 g) was added in one portion
and the resulting mixture was stirred at this temperature
to room temperature for 0.5 h then at room temperature 4 h.
The poly'amic acid) solution was spread on a glass plate at
508C and some solvent was slowly evaporated at 808C for
1.5 h. The ®lm was cured by heating at 808C for 40 min,
1008C for 30 min, warmed up to 2808C at a rate of 108C/min
and held at 2808C for 30 min. This heat treatment converted
the poly'amic acid) to polyimide. The IR absorption
peaks of the polyimide appeared at 1720 and 1785 cmÀ1
and the peak for carboxylic acid disappeared. This ®lm
gave a tensile strength 15.18 kpsi, modulus 323.6 kpsi
and 8.4% elongation.
.
4.10. Preparation of polyimide from 2 and 3,4,30,40-
diphenyltetracarboxlic dianhydride
A 50 ml three-necked ¯ask ®tted with a mechanical stirrer
and a condenser topped with a N2 inlet was charged with
diamine '1.54 g) and 14 ml of NMP. The mixture was stirred
until a clear solution was obtained and the ¯ask was cooled
in an ice±acetone bath. The 3,4,30,40-diphenyltetracarboxlic
dianhydride '1.47 g) was added in one portion and the
resulting mixture was stirred at this temperature to room
temperature for 3 h then at room temperature overnight. The
poly'amic acid) solution was spread on a glass plate at 508C
and solvent was slowly evaporated at 808C for 1.5 h. The
®lm was cured by heating at 808C for 40 min, 1008C for
30 min, warmed up to 2808C at a rate of 108C/min and held
at 2808C for 30 min. This heat treatment converted the
poly'amic acid) to polyimide. The IR absorption peaks of
the polyimide appeared at 1715 and 1980 cmÀ1. This ®lm
gave a tensile strength 11.6 kpsi, modulus 299.6 kpsi and
5.3% elongation.
The polymer has a glass transition temperature at 3088C.
By TGA, the polymer shows 10% weight loss temperatures
of about 5408C under air when heated at 208C/min.
References
[1] D. Wilson, H.D. Stengenberger, P.M. Hergenrother, Polyimides,
Chapman & Hall, New York, 1990.
[2] J. Scheirs, Modern Fluoropolymers, Wiley, New York, 1997.
[3] B. Auman, D.P. Higley, K.V. Scherer, US Patent 51,45,999
'1992).
The polymer's glass transition temperature is at 311.48C.
By TGA, the polymer shows 10% weight loss at tempera-
tures of about 5658C under air when heated at 208C/min.
[4] S.Z.D. Cheng, S.K. Lee, J.S. Barley, S.L.C. Hsu, F.W. Harris,
Macromolecules 24 '1991) 1883.
[5] P.E. Cassidy, M.T. Aminabhavi, J.M. Farley, J. Marcromol. Sci., Rev.
Macromol. Chem. Phys. C29 '1989) 365.
4.11. Preparation of polyimide from 2 and 2,20-bis23,4-
dicarboxyphenyl)hexafluoropropane dianhydride 26FDA)
[6] M. Eashoo, D. Shen, Z. Wu, S.K. Lee, F.W. Harris, S.Z.D. Cheng,
Polymer 34 '1993) 3209.
[7] A.E. Feiring, B.C. Auman, E.R. Wonchoba, Macromolecules 26
'1993) 2779.
A 50 ml three-necked ¯ask ®tted with a mechanical stirrer
and a condenser topped with a N2 inlet was charged with 2
[8] P.L. Heinze, D.J. Burton, J. Org. Chem. 53 '1988) 2714.
[9] S.W. Hansen, D.J. Burton, J. Fluor. Chem. 35 '1987) 415.