Synthesis and characterization of polyimides based on novel isomeric perfluorinated naphthylenediamines

Article abstract of DOI:10.1016/j.jfluchem.2009.05.019

Novel highly fluorinated polyimides containing hexafluoronaphthylene fragment in the main chain were prepared by the two-stage polymerization of 2,7- and 2,6-diaminohexafluoronaphthalenes with 4,4′-oxydiphthalic anhydride: polycondensation in a solution a

Full text of DOI:10.1016/j.jfluchem.2009.05.019

Journal of Fluorine Chemistry 130 (2009) 733–741
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis and characterization of polyimides based on novel isomeric
perfluorinated naphthylenediamines
Inna K. Shundrina a, Tamara A. Vaganova a, Soltan Z. Kusov a, Vladimir I. Rodionov a, Elena V. Karpova a,
Vladimir V. Koval b, Yulia V. Gerasimova b, Evgenij V. Malykhin a,
*
a N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, Lavrentiev Avenue 9, 630090 Novosibirsk, Russian Federation
b Institute of Chemical Biology and Fundamental Medicine, Siberian Branch of the Russian Academy of Sciences, Lavrentiev Avenue 8, 630090 Novosibirsk, Russian Federation
A R T I C L E I N F O
A B S T R A C T
Article history:
Novel highly fluorinated polyimides containing hexafluoronaphthylene fragment in the main chain were
prepared by the two-stage polymerization of 2,7- and 2,6-diaminohexafluoronaphthalenes with 4,40-
oxydiphthalic anhydride: polycondensation in a solution at 80 8C followed by high-temperature solid-
state chain extension. The influence of hexafluoronaphthylene fragment isomerism on the key polyimide
features – molecular weight, thermal stability, solubility, optical properties – was characterized.
Polyimides based on 2,7-diaminohexafluoronaphthalene or easily accessible mixture of isomeric
diamines formed the flexible, transparent, and thermostable films.
Received 14 April 2009
Received in revised form 26 May 2009
Accepted 28 May 2009
Available online 6 June 2009
Keywords:
Fluorinated polyimides
Polyimide properties
Diaminohexafluoronaphthalenes
MALDI-TOF MS
ß 2009 Elsevier B.V. All rights reserved.
1. Introduction
direct amination of commercially available octafluoronaphthalene
by liquid ammonia used as a reagent/medium system (see also
Incorporation of fluorine into the framework of aromatic
polyimides (PIs) is intensively explored with the purpose of
improving the polymer properties that are of particular interest for
optical and electronic applications [1–5]. Increase of fluorine
content has been found to generally lower optical loss, dielectric
constant and moisture absorption, to enhance solubility in organic
solvents and thermal stability.
[18]).
The aims of the present work are: (i) to synthesize PIs from 4,40-
oxydiphthalic anhydride (ODPA) and isomeric hexafluoronaphthy-
lene diamines or their mixture (Scheme 1) for investigating the
diamines relative reactivity, and (ii) to study the influence of
structural isomerism of hexafluoronaphthylene fragment in the
main chain on the properties of the highly fluorinated PIs.
Most works were focused on the incorporation of trifluor-
omethyl group or hexafluoroisopropylidene moiety into dianhy-
dride and diamine components [2,5–13]. This concentration of
efforts was presumably due to a significant enhancement of PI
properties. Other fluorinated monomers are hard to get because
they are relatively difficult and expensive to synthesize. To our
2. Results and discussion
2.1. Synthesis of polyimides
The replacement of all hydrogens in the aromatic ring by
fluorines is known to decrease the reactivity of phenylenediamines
for acylation by a factor of ꢀ10ꢁ5 [1] because of the high
electronegativity of fluorine. The resultant low nucleophilicity of
polyfluoroaromatic diamines, as reported for benzene and
biphenyl derivatives [1,2,15], impedes their interaction with
dianhydride and the formation of poly(amic)acids. Indeed,
solutions of equivalent amounts of 2,7-DAHFN or 2,6-DAHFN
and ODPA in NMP at ambient temperature have a low viscosity
knowledge, only three perfluorinated aromatic diamines
tetrafluoro-meta- and -para-phenylenediamines and octafluoro-
benzidine were used as monomers for preparing highly
–
–
fluorinated PIs [1,2,14–16]. Recently we have elaborated [17] a
method of selective preparation and high-purity isolation of new
compounds, which can serve as potential monomers—2,7- and 2,6-
diaminohexafluoronaphthalenes (2,7-DAHFN and 2,6-DAHFN), as
well as an inexpensive short route to their 3:1 mixture through
(h
inh 0.06 dL gꢁ1), which remains unchanged for 24 h. Correspond-
ingly, there occur no changes in 19F NMR spectra of these solutions.
Nevertheless, coating the solutions of monomers (method A,
Scheme 1) onto a glass plate, drying them slowly to a constant
* Corresponding author. Fax: +7 383 3309752.
E-mail address: malykhin@nioch.nsc.ru (E.V. Malykhin).
0022-1139/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.05.019

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I.K. Shundrina et al. / Journal of Fluorine Chemistry 130 (2009) 733–741
Scheme 1. Synthesis of PIs.
weight, and curing at 350 8C (rate of heating is 1 8C minꢁ1) provide
the preparation of PI-1(A) and PI-2(A) films (Table 1). It should be
noted that the yields of the samples thus obtained are far from
quantitative (80–85%), which is evidently caused by partial loss of
monomers during the thermal cure. Moreover, there is some
absorption of residual anhydride groups in FTIR spectra of PI-1(A)
and PI-2(A) (Fig. 1), which testifies to a relatively low poly-
condensation degree. Thus, slow high-temperature curing yields
the samples of PIs due to the solid-state chain extension, but it does
not provide a good quality of the films. As it was shown in the
works [2,15], using the high-temperature solution stage for the
process acceleration results in a higher polycondensation degree.
For the synthesis of prepolymers from DAHFNs and ODPA we
carried out the solution stage at 80 8C (method B, Scheme 1).
Thermal cure of the samples provided the preparation of high-
quality films (Table 1).
Table 2). After that the viscosity of the condensation solution
noticeably increased, but did not achieve the values testifying to
the formation of high-molecular weight compounds [2,9–13].
According to 19F NMR data, the prepolymer formed at this stage
consists of low molecular weight derivatives, because in the
spectrum there are no signals of prevailing intensity which would
indicate long, structurally uniform fragments. It is noteworthy that
amic acid and imide fragments are contained in comparable
quantities (determined from signal intensity ratio (j + k)/(a + d),
Fig. 2b). So, the formation of amic acid at 80 8C is accompanied by
its substantial cyclodehydration. Released water can hydrolyze
anhydride groups thereby interrupting the further growth of the
The polycondensation process has been investigated in detail
by using 19F NMR and FTIR spectroscopy, TGA/DSC, and MALDI-TOF
MS (matrix-assisted laser desorption/ionization time-of-flight
mass spectrometry) to control the extent and type of the occurring
transformation and to get information on the molecular weight
and structure of PIs. Table 2 contains quantitative characteristics of
the polycondensation of ODPA with individual 2,7- or 2,6-DAHFN
and their 3:1 mixture. Figs. 2–4 show the changes in 19F NMR
spectra of condensation solutions and PI samples obtained at
different cure temperatures (Tc 150, 250 8C). The ratios of the
different types of hexafluoronaphthylene units given in Table 2
were determined from the intensity ratios of
a-fluorine signals
located in the down-field area of 19F NMR spectra (ꢁ120 to
ꢁ125 ppm).
The increase of temperature from ambient up to 80 8C provides
an appreciable increase of the reaction rate: after 16 h no more
than 30% of 2,7-DAHFN remains in the condensation solution
prepared from equivalent amounts of 2,7-DAHFN and ODPA in
NMP. The complete conversion of diamine takes 48 h (Fig. 2b;
Table 1
Yield and characteristics of PIs obtained by A and B methods, Tc 350 8C.
PI
Method
Yield (%)
Film forming
The residual anhydride
groups bond (1855 cmꢁ1
in FTIR spectrum
)
PI-1
PI-2
PI-3
A
B
A
B
B
85
94
81
92
94
Yes
Yes
Yes
Yes
Yes
+
ꢁ
+
Fig. 1. FTIR spectra of PI-1 (2,7-DAHFN/ODPA) during polycondensation by methods
A and B at different Tc (in KBr). The absorption at ꢀ1790 and 1740 cmꢁ1 is assigned
to the stretching vibrations of imide group carbonyl, 1855 cmꢁ1—anhydride group
carbonyl.
ꢁ
ꢁ

I.K. Shundrina et al. / Journal of Fluorine Chemistry 130 (2009) 733–741
735
polymer chain; for this reason prolongation of the solution stage is
inexpedient. At the same time, carrying out the solid stage will not
cause any loss of substance due to the absence of volatile
monomers in the prepolymer.
Removing the solvent and curing at 150 8C give a sample of PI-1
with virtually quantitative yield (Table 2). According to the 19F
NMR data (Fig. 2c vs b), this cure results in a considerable growth of
the polyimide chain due to the regeneration of anhydride groups,
their interaction with amino groups, and full imidization of amic
acid fragments. The averaged length of the polymer chain,
estimated by the internal/terminal fragments ratio, amounts to
6–7 structural units. It corresponds to the value of number-
¯
averaged molecular weight Mn ꢀ 3500. The end-groups content
further decreases with increasing cure temperature. The sample
obtained at 250 8C is characterized by the chain length ꢀ12 units
¯
and Mn ꢀ 6500. In accordance with the growth of polymer
molecular weight the inherent viscosity also increased (Table 2).
The observed value of hinh is comparable to the characteristics of
partially fluorinated film forming polyimides [9,12,13]. Curing at
350 8C yields an insoluble sample which has not been character-
ized by 19F NMR.
MALDI-TOF MS is used for the determination of molecular
and repeated unit weights and the identification of end-groups
in synthetic polymers, in particular, polyimides [19,20]. The
spectra of PI-1 samples irrespective of Tc contain repeated
fragments (groups of signals) with the period m/z 540 Da equal
to the molecular weight of the polymer structural unit
C
26H6F6N2O5 (Fig. 5 shows a representative spectrum). All
fragments have a similar intensity ratio of peaks corresponding
to PI molecules with different charge agent cations. The relative
intensities of the main signals decrease with increase of m/z.
Table
3 presents tentative peak mass assignments in the
representative fragment (n = 5) of the spectrum of PI-1 cured
at 250 8C (Fig. 5b). The fragment contains peaks of molecules
with three different end-group combinations (Scheme 2) labeled
AA (two anhydride groups), AB (one anhydride group and one
amino group) and BB (two amino groups). The AA and AB series
can include one or two hydrolyzed anhydride groups in acid and
salt forms. The above species are cationized in different ways.
The MALDI MS data obtained are well correlated with the
assumed polymer structure and evidence that no fragmentation
or destruction has occurred during polyimidization.
Maximal molecular weights (Mmax) detected in PI-1 samples
by MALDI MS increase with rising cure temperature and achieve
¯
ꢀ8400 Da (Table 2). Calculation of number (Mn) and weight
¯
(Mw) averaged molecular weights of synthetic polymers by
MALDI MS data is known to give understated values, as
compared with those obtained by NMR and SEC methods
[20]. This is caused by the discrimination of high-molecular
¯
masses in samples. For this reason, Mn values obtained by MALDI
¯
MS are lower than Mn derived from NMR (Table 2). However,
MALDI data confirm that PI-1 molecular weight increases with
increasing Tc.
Comparison of polycondensation degree of PI-1 samples
obtained by method B at different Tc values and by method A at
350 8C has been done by means of FTIR spectral data (Table 1;
Fig. 1). During the polycondensation by method B, amine and
anhydride end-group absorptions in PI-1, which remain after
high-temperature solution stage, are still present after 150 8C
solid-state cure, are partially consumed by 250 8C cure, and are
fully consumed by 350 8C cure. On the contrary, much more
anhydride end-groups remain in PI-1(A) cured at 350 8C.
Thus, carrying out the high-temperature solution stage provides
a high-polycondensation degree. It is noteworthy that the
yield of polymer obtained from the condensation solution B is
satisfactory.

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I.K. Shundrina et al. / Journal of Fluorine Chemistry 130 (2009) 733–741
Fig. 2. 19F NMR spectra of PI-1 (2,7-DAHFN/ODPA) during polycondensation by method B (solution in NMP): a and b, solution stage; c and d, solid stage.
Evolution of thermal characteristics of PI-1 samples obtained at
group has not changed; thus, the naphthalene units with two
modified amino groups (signals a and k, cf. PI-1) are practically
absent. It is caused by a considerable decrease of nucleophilicity
of the amino group in 2,6-DAHFN monoacyl derivative under the
action of the electron-withdrawing acylamido or imido group at
the resonance position. The electronic effect of the modified
amino group on the reactivity of monoacyl derivatives controls
the possibility of high-molecular weight polymer synthesis. This
effect has been characterized quantitatively in the works [1,21]
for perfluorinated phenylenediamines. The first acylation of
tetrafluoro-p-phenylenediamine provokes decrease of the sec-
ond acylation rate constant by a factor of >103. On the contrast,
the reactivity of the residual amino group in tetrafluoro-m-
phenylenediamine derivative is shown to be little affected by
the first acylation. Similarly, in the perfluoronaphthalene
framework the pseudo-para-located acylamido or imido group
appreciably decelerates the polymeric chain growth (in the case
different Tc values (Table 4) indicates the growth of polycondensa-
tion degree and agrees with the NMR data. The glass transition
temperature (Tg) as well as the thermal stability (weight loss
temperatures) of PIs increases with rising Tc. A considerable
change of these characteristics occurs in going from Tc 250 to
350 8C, which testifies to the increase of the polymer molecular
weight.
Polycondensation of 2,6-DAHFN, containing pseudo-para-
located amino groups, with ODPA and characteristics of PI-2
samples differ from those of PI-1. In both cases the complete
conversion of diamine-monomer takes 48 h at 80 8C, i.e. the
isomeric 2,7- and 2,6-DAHFN have comparable rates of first
acylation. However, according to the 19F NMR data, at the end of
solution stage only one amino group in 2,6-DAHFN has modified
into acylamido or imido group (Fig. 3b, signals j and d of
a-
fluorines, respectively, cf. PI-1, Fig. 2b), whereas second amino

I.K. Shundrina et al. / Journal of Fluorine Chemistry 130 (2009) 733–741
737
Fig. 3. 19F NMR spectra of PI-2 (2,6-DAHFN/ODPA) during polycondensation by method B (solution in NMP): a and b, solution stage; c, solid stage. Assignment of signals j and k
is similar to that in PI-1 spectra, see structures in Fig. 2b.
of 2,6-DAHFN), as compared with pseudo-meta-located sub-
stituent (in the case 2,7-DAHFN). For this reason, PI-2 samples
obtained at Tc 150 and 250 8C have the chain lengths half as long
comparison with the samples obtained from individual 2,6-
DAHFN, seems to result from asymmetric arrangement of
pseudo-meta-disubstituted hexafluoronaphthalene framework
relative to the polyimide chain, which increases the polymer
backbone flexibility and free volume [10,22].
Data of elemental analysis of PIs 1–3 (Tc 350 8C, Table 5) agree
with the calculated values. Therefore, polycondensation and
imidization reactions are completed without by-products. The
high fluorination degree (fluorine content in PIs is ꢀ20%) provides
a high hydrophobicity of the PIs. Water uptake of PIs 1–3 (not more
than 0.36%, Table 5) is comparable with the known characteristics
of partially fluorinated polyimides [10,11].
PI-1 and PI-3 give flexible and transparent films upon curing at
350 8C (Table 5). Unlike this, the film obtained from PI-2 is cracked,
which agrees with its relatively low molecular weight. Besides, this
film is opaque; it becomes opaque during solid-state chain
extension (at ꢀ180 8C), which can be caused by the formation of
a specific crystalline structure [23,24]. DSC of PI 1–3 films cured at
350 8C detect no obvious melting and crystallization transition up
to the temperature of 10% weight loss (see below). However, the
POM data show differences in the morphology of PI-1 and PI-2
films (Fig. 6). It appears that the grainy texture of PI-2 film is
responsible for its opaqueness [23]. Optical properties of PI-1 and
PI-3 films have been investigated using UV–vis spectroscopy
(Table 5; Fig. 7). PI-1 exhibits a rather low cut-off wavelength (l0
and the Mn values less than those of PI-1 (19F NMR and MALDI
¯
MS data, Table 2). Nevertheless, the absorption of residual
anhydride groups in FTIR spectrum of PI-2 obtained by method B
(Table 1) is practically absent, and its yield is above 90%.
Thermal characteristics of PI-2 are worse only in the case of the
sample obtained at Tc 150 8C (Table 4).
Polycondensation of diamine monomers mixture – 2,7- and 2,6-
DAHFN (3:1) – with ODPA at Tc 80, 150 8C occurs with minor
complications, but after curing at 250 8C the averaged molecular
weight of PI-3 sample achieves the value, which is even higher than
that of PI-1 (Fig. 4; Table 2). Curing at 350 8C gives film forming
polymer PI-3 (Table 1) whose thermal properties are comparable
with the characteristics of the structurally uniform PI-1 (Table 4).
2.2. Polyimide properties
Solubility of PIs in different organic solvents has been
investigated at room temperature (Table 4). All PI samples cured
at 150 8C exhibit solubility in polar organic solvents such as NMP,
DMA, and DMF. PI-1 and PI-3 are also soluble in less polar acetone.
Solubility of PIs decreases with increasing Tc: all the samples
obtained at 350 8C are insoluble, and PI-2 cured at 250 8C is
partially soluble. The better solubility of PIs obtained from
individual 2,7-DAHFN and its mixture with 2,6-isomer, in
362 nm). The
l0 of PI-3 is slightly higher because of the presence of
2,6-isomer, but its influence worsens the optical properties of the

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I.K. Shundrina et al. / Journal of Fluorine Chemistry 130 (2009) 733–741
Fig. 4. 19F NMR spectra of PI-3 (2,7 + 2,6-DAHFN/ODPA) during polycondensation by method B (solution in NMP): a and b, solution stage; c, solid stage.
Fig. 5. MALDI-TOF mass spectrum of PI-1, Tc 250 8C: a, the whole spectrum; b, representative repeated fragment, n = 5 (Scheme 2), peak assignment is given in Table 3.
film to an insignificant degree. The PI-1 and PI-3 films exhibit an
excellent transparency at 450 nm (transmittance is ꢀ85%) that is
an inherent attribute of fluorinated PIs [1,3,10,11,25].
Thermal stability properties of final PIs have been evaluated
by TGA/DSC and the results are summarized in Table 6. In inert
atmosphere there are no considerable differences in the thermal
stability of PIs obtained both from individual isomeric diamines
and their mixture (PI-1, PI-2, and PI-3), as well as from different
condensation solutions (A and B). All PIs exhibit a good thermal
stability: there is no obvious weight loss before the scanning
temperature reaches to 540 8C. The temperatures at 5% and 10%
weight loss in inert atmosphere (T5 and T10) are above 540 and

I.K. Shundrina et al. / Journal of Fluorine Chemistry 130 (2009) 733–741
739
Table 3
570 8C, respectively. The residual weight retention Rw at 700 8C
is not less than 56%, which practically coincides with the carbon
content. Further heating of the samples up to 900 8C in inert
atmosphere is not accompanied by appreciable Rw changes. In
oxidative atmosphere PI-2 is less thermostable, as compared to
PI-1 (Table 6), which can be caused by a greater oxidation
susceptibility of the conjugate imide cycles. The total weight
loss temperatures (T100) in oxidative atmosphere for all PIs are
in the range of 650–700 8C. Note that PIs cured at 250 8C exhibit
high Tg values (Table 4) (cf. [2,11,15]); for the final PI samples Tg
have not been detected.
Mass assignments of the peaks displayed in the fragment (n = 5) of MALDI-TOF mass
spectrum of PI-1, Tc 250 8C (Fig. 5b; Scheme 2).
Peak numbera
M (Da)
Structure
1
2
3
4
5
6
7
8
9
3259.81
3281.87
3299.44
3320.94
3530.24
3551.01
3591.26
3610.00
3630.26
AB + H+
AB + Na+
AB + H2O + Na+
AB + H2O + (Na+–H+) + Na+
BB + Na+
AA + H+
AA + H2O + Na+
AA + 2H2O + Na+
AA + 2H2O + (Na+–H+) + Na+
Thus, thermal stability properties of PIs 1–3 are slightly higher
than those of the known PIs, which contain CF3 groups [2,5–13]
and aromatic fluorines (based on tetrafluoro-meta- and -para-
phenylenediamines, octafluorobenzidine) [1,2,15].
a
Peaks 10, 11 (M 3435.91, 3453.16) and 12, 13, 14 (M 3746.28, 3764.67, 3782.73)
can be assigned to adducts consisting of AB and AA molecules correspondingly with
DHB (used as a matrix, cf. [19]), water and charge agent cations.
Scheme 2. PI structures having the three possible end-group combinations.
Table 4
Influence of cure temperature (Tc) on thermal properties and solubility of PIs (method B).
Solubility in organic solventsc
a
b
PI
Tc (8C)
Tg (8C)
T2 (8C)
R580 (%)
NMP
DMA
DMF
Acetone
PI-1
150
250
350
310
224
396
477
83
88
89
++
++
ꢁ
++
++
ꢁ
++
++
ꢁ
++
ꢁ
352
None detected
ꢁ
PI-2
PI-3
150
250
350
295
168
425
505
80
87
88
++
+ꢁ
ꢁ
++
+ꢁ
ꢁ
++
+ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
324
None detected
150
250
350
315
184
411
501
76
88
91
++
++
ꢁ
++
++
ꢁ
++
++
ꢁ
++
ꢁ
320
None detected
ꢁ
a
b
c
T2—temperature at 2% weight loss.
R580—residual weight retention at 580 8C.
Qualitative solubility was determined visually as: completely soluble (++), partially soluble (+ꢁ), and insoluble (ꢁ). The complete solubility is defined as a visibly
transparent and homogenous solution.
Table 5
Characteristics of PI films cured at 350 8C (method B).
b
PI
Elemental analysis (%)
Film qualitya
Water uptake (%)
l0 (nm)
Transmittance at 450 nm (%)c
C
H
N
F
Calcd.
Found
Found
Found
57.78
58.08
57.41
57.67
1.11
1.19
1.15
1.16
5.19
5.22
5.31
5.44
21.11
20.28
20.20
20.34
PI-1
PI-2
PI-3
T, F
O, C
T, F
0.30
0.35
362
371
88
83
a
b
c
T, Transparent; O, opaque; F, flexible; C, cracked.
0—the cut-off wavelength.
Film thickness ꢀ20 m.
l
m

740
I.K. Shundrina et al. / Journal of Fluorine Chemistry 130 (2009) 733–741
and impedes the synthesis of high-molecular weight polymer. For
this reason PI-2 (2,6-DAHFN/ODPA) has a lower molecular weight
than PI-1 and forms a cracked and opaque film. It is noteworthy
that using inexpensive mixture of isomeric diamines (2,7- + 2,6-
DAHFN, 3:1) provides the preparation of PI-3, which has molecular
weight, thermal and optical characteristics comparable with those
of the structurally uniform PI-1. The new highly fluorinated
aromatic polyimides seem to be promising materials for optic and
optoelectronic applications.
4. Experimental
4.1. Measurements
19F NMR spectra were recorded on Bruker AV-300
(282.36 MHz) spectrometer using C6F6
(
d
= ꢁ163 ppm from
CCl3F) as internal standard; are given in ppm relative to
d
Fig. 6. Optical micrographs of polyimide films, Tc 350 8C, PI-1 (a) and PI-2 (b)
CCl3F, J are given in Hz. Solid PI samples, prepared at the
different cure temperatures, were dissolved to concentration
ꢀ5% in NMP for registration of spectra. Signals in the spectra
were assigned by using substituent shielding parameters
determined from the monomers [17], octafluoronaphthalene
[26], 2-aminoheptafluoronaphthalene [27] and model com-
pounds—N-(1,3,4,5,6,7,8-Heptafluoro-2-naphthyl)-3,4,5,6-tetra-
fluorophthalamic acid (FNPA) and N-(1,3,4,5,6,7,8-heptafluoro-
(bar = 10
mm).
2-naphthyl)-3,4,5,6-tetrafluorophthalimide
(FNPI).
Fourier
transform infrared (FTIR) spectra were measured on Bruker
Vector-22 instrument for KBr disks. Ultraviolet–visible (UV–vis)
spectra of polymer films were recorded on Varian spectro-
photometer Cary 5000. PI films for the transmittance determi-
nation were prepared by spin-coating 10% solution on a glass
plate. Precise molecular weights of ions were determined by
high-resolution mass spectrometry on Finnigan MAT-8200
instrument. Thermogravimetric (TGA) and differential scanning
calorimetry (DSC) analyses were performed on NETZSCH STA
409 instrument. Experiments were carried out at the followed
conditions: (a) Al crucible, heating from 25 to 580 8C with rate
10 8C minꢁ1 under flowing He at 27 mL minꢁ1. (b) Pt/Rh crucible,
heating from 25 to 1000 8C with rate 10 8C minꢁ1 under flowing
He or He/O2 mixture (8:2, v/v) at 27 mL minꢁ1. Mass spectra
were recorded using an AutoFlex MALDI-TOF mass spectrometer
(Bruker Daltonics, Germany) equipped with a pulsed N2 laser
(337 nm) in a positive linear or reflectron mode. Ions formed by
a laser beam were accelerated to 20 or 19 keV kinetic energy in
the case of linear or reflectron mode, respectively. The final
spectra were obtained by accumulating 1000–3000 single laser
shot spectra. The saturated solution of 2,5-dihydroxybenzoic
acid (DHB) in 50% aqueous acetonitrile was used as a matrix. A
sample of polymer solution (10% in DMAA) was mixed with the
Fig. 7. UV–vis spectra of PI-1 (a) and PI-3 (b), Tc 350 8C.
Table 6
Thermal degradation properties of PIs obtained by A and B methods, Tc 350 8C.
PI
Method
In inert atmosphere
In oxidative
atmosphere
a
a
b
b
a
a
a
T5
T10
R700
R900
T5
T10
T100
(8C)
(8C)
(%)
(%)
(8C)
(8C)
(8C)
PI-1
PI-2
PI-3
A
B
546
562
570
581
56
58
48
52
527
554
703
A
B
549
553
571
575
57
56
52
52
504
511
536
544
662
655
B
570
586
59
52
same volume of matrix solution. About 0.7
mL of the resulting
a
solution was deposited on the stainless steel multiprobe and
allowed to dry before being introduced into the mass spectro-
meter. Mass spectra were obtained by averaging 3000 laser
shots. External calibration was provided by [M+H]+ ions of
bradykinin fragments 1–7, human angiotensin II, human ACTH
T5, T10, and T100—temperature at 5%, 10%, and 100% weight loss.
R700 and R900—residual weight retention at 700 and 900 8C.
b
3. Conclusions
fragments 18–39, oxidized bovine insulin
b-chain, bovine
New polyimides containing isomeric hexafluoronaphthylene
fragments in the main chain have been successfully synthesized by
the two-step method. The low reactivity of perfluoroaromatic
diamine monomers has been overcome by carrying out high-
temperature solution stage followed by high-temperature solid-
state chain extension. 2,7-DAHFN exhibits a higher reactivity than
2,6-DAHFN, and PI-1 (2,7-DAHFN/ODPA) forms a film with good
thermal and optical properties. The ability of 2,6-DAHFN to
polymerize is weakened by substituents conjugation, which
reduces the reactivity of the amino group in monoacyl derivatives
insulin and equine cytochrome c m/z 757.4, 1046.54, 2465.2,
3494.65, 5734.51 and 12361.96, respectively. Mass accuracy in
¯
¯
the range 0.1–0.5% was usually achieved. Mw and Mn values
were calculated with software supplied by the manufacturer of
the spectrometer. Elemental analyses were performed by a
Eurovector model EA 3000 CHN analyzer. Fluorine content was
determined by spectrophotometric analysis [28]. The values of
inherent viscosity (hinh) were determined by an Ubbelohde
viscosimeter at concentration 0.5 g dLꢁ1 in NMP at 25 8C.
Polarized optical microscopy (POM) observation was performed

I.K. Shundrina et al. / Journal of Fluorine Chemistry 130 (2009) 733–741
741
Scheme 3.
References
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Solubility was determined as follows: 100 mg of PI was mixed
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polyimide film (3 cm ꢂ 1 cm ꢂ 0.01 cm) in water at 25 8C for 24 h,
which was then dried immediately by blotting with a paper towel
and subsequently weighed.
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d
ꢁ156.3 (m, 1 F, F7
0
), ꢁ154.9 (t, 1 F, J = 18, F6 ), ꢁ152.9 and
0
ꢁ151.5 (both t, both 1 F, J = 20, F3 and F6), ꢁ148.8 (dt, 1 F, J = 58,
J = 17, F
J = 16, F
0
4 ), ꢁ147.0 (dt, 1 F, J = 58, J = 16, F5
8 ), ꢁ138.9 (m, 1 F, F3 ), ꢁ139.4 and ꢁ138.0 (both m, both 1
1 ).
0
), ꢁ145.7 (dt, 1 F, J = 65,
0
0
F, F4 and F5), ꢁ123.9 (dd, 1 F, J = 65, J = 17, F
0
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0
d
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J = 60, J = 17, F ), ꢁ143.9 (dt, 1 F,
0
4 ), ꢁ145.8 (dt, 1 F, J = 60, J = 16, F5
0
0
0
J = 67, J = 16, F8 ), ꢁ140.2 (m, 1 F, F3 ), ꢁ143.0 and ꢁ136.1 (both q, 2
F, J = 10, F3,6 and F4,5), ꢁ120.9 (dd, 1 F, J = 67, J = 17, F
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4.3.2. Solid stage
Condensation solution (A or B) was cast onto a glass plate and
kept in vacuum oven at 80 8C for 12 h to constant weight. Polymer
resin thus obtained was cured at the final temperature (variants
150, 250, 350 8C) for 1 h. The rate of heating to the cure
temperature was 1 8C minꢁ1
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