Films of polyamides with phenylpyridine units in the backbone

Article abstract of DOI:10.1134/S107042721010023X

New polyamides derived from 2-(4-aminophenyl)-5-aminopyridine, 4,4-diaminodiphenyl ether, and 4,4′-terephthaloyloxybis(3-methoxybenzoic) acid dichloride were prepared. These polyamides are of interest as macromolecular ligands. The deformation-strength, t

Full text of DOI:10.1134/S107042721010023X

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 10, pp. 1862−1867. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © I.V. Gofman, M.Ya. Goikhman, I.V. Podeshvo, E.E. Eliseeva, E.E. Bol’bat, I.V. Abalov, A.V. Yakimanskii, 2010, published in Zhurnal
Prikladnoi Khimii, 2010, Vol. 83, No. 10, pp. 1722−1727.
MACROMOLECULAR COMPOUNDS
AND POLYMERIC MATERIALS
Films of Polyamides with Phenylpyridine Units
in the Backbone
I. V. Gofmana, M. Ya. Goikhmana, I. V. Podeshvoa, E. E. Eliseevab, E. E. Bol’batb,
I. V. Abalova, and A. V. Yakimanskiia
a
ꢀInstitute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
b
ꢀSt. Petersburg State University, St. Petersburg, Russia
Received May 5, 2010
Abstract—New polyamides derived from 2-(4-aminophenyl)-5-aminopyridine, 4,4-diaminodiphenyl ether, and
4,4'-terephthaloyloxybis(3-methoxybenzoic) acid dichloride were prepared. These polyamides are of interest
as macromolecular ligands. The deformation–strength, thermomechanical, and thermal properties of films of
polyamides with various content of phenylpyridine fragments were studied.
DOI: 10.1134/S107042721010023X
The design, synthesis, and study of properties of
new polymers containing heterorings are of much
interest for both basic and applied chemistry, because
such systems often exhibit unique properties: high
strength and heat resistance in combination with the
capability to form stable complexes with transition
metals. Among such systems, researchers’attention has
recently been attracted by polymers containing in the
backbone [1] or pendant groups [2] 2-phenylpyridine
(PP) fragments. Such polymers can act as
macromolecular ligands in formation of electrically
neutral metal–polymer complexes with Ir(III). These
compounds exhibit a unique combination of chemical
stability and luminescence and redox properties [3, 4].
Here we report on the synthesis and properties of a new
series of polyamides (PAs) containing PP units in the
backbone.
To 1,1,3,3-tetramethoxypropane (14 ml, 0.085 mol),
we added with stirring 8 ml of 57% perchloric acid and
allowed the mixture to stand for 1 h at room temperature.
Then piperidine (16.8 ml, 0.17 mol) was added dropwise
with stirring and cooling on a water bath. The mixture
was stirred for 20 min, after which 10 ml of 57%
perchloric acid was added. In 20 min, the mixture was
placed for 3 h in a refrigerator for complete precipitation
of the product, after which the yellow precipitate was
filtered off and washed with diethyl ether (2 × 5 ml).
Yield 15.8 g (61%), mp 125–128°С. 1Н NMR spectrum,
δ, ppm (300 MHz, DMSO-d6): 7.67 d (J = 11.7 Hz, 2H,
Н1 and Н3), 5.78 t (J = 11.7 Hz, 1H, Н2), 3.56 m (8H,
2CH2NCH2), 1.60 m (12H, 2CH2CH2CH2).
2-Nitro-1,3-bis(piperidinyl)trimethinium
perchlorate II. To a suspension of I (10.9 g, 0.036 mol)
in acetic anhydride (12.5 ml), cooled to 0°C, we added
dropwise with stirring nitric acid (3.0 ml, ρ = 1.4 g cm–3),
also cooled to 0°С, maintaining the reaction mixture
temperature no higher than 3°С. The mixture was stirred
on an ice bath for 1 h. Then 10 g of ice was added, and
the pale yellow precipitate was filtered off and washed
with ice-cold water (10 ml) and diethyl ether (2 × 5 ml).
EXPERIMENTAL
Commercial solvents and chemicals were used
without additional purification and drying.
2-(4-Aminophenyl)-5-aminopyridine was prepared
in four steps. The first two steps have been implemented
for the first time.
1
Yield 10.5 g (83%), mp 155–157°С (dec.). Н NMR
spectrum, δ, ppm (300 MHz, CDCl3): 8.42 s (2Н, Н1
and Н3), 4.02–3.92 m (4Н, 2CH2N), 3.76–3.66 m (4Н,
1,3-Bis(piperidinyl)trimethinium perchlorate I.
1862

FILMS OF POLYAMIDES WITH PHENYLPYRIDINE UNITS
1863
2CH2N), 2.00–1.73 m (12Н, 2CH2CH2CH2).
fully dissolved. To the solution cooled to –12°C we
added 4,4'-terephthaloyloxybis(3-methoxybenzoic)
The next two steps were performed by the procedure
described in [1].
acid dichloride (0.258 g). The suspension was stirred at
this temperature for 1 h, allowed to warm up to room
temperature, and stirred at room temperature for an
additional 1 h. Then several drops of propylene oxide
were added, and the mixture was stirred for 3 h more.
The resulting viscous solution of the copolyamide in
N-MP was filtered through a glass frit.
The 1Н NMR spectra of 1% solutions of substances
were recorded with an Аvance-400 spectrometer
(Bruker, Germany) operating at 400 MHz, with Me4Si
as internal reference.
2-(4-Nitrophenyl)-5-nitropyridine III. A 100-
ml three-necked round-bottomed flask equipped with
a magnetic stirrer, an internal thermometer, a reflux
condenser, and a dropping funnel was charged
with a suspension of II (10.5 g, 0.03 mol) and
p-nitroacetophenone (4.1 g, 0.025 mol) in acetonitrile
(15 ml). The contents were cooled to 0°С, and
triethylamine (7.5 ml, 0.054 mol) was added dropwise
with the reaction mixture temperature maintained at
approximately 5°С. The mixture was stirred at room
temperature for 3 h. Then glacial acetic acid (8.6 ml) and
ammonium acetate (11.5 g) were added, and the mixture
was heated to 50°С and stirred for 5 h. After cooling,
the grey-yellow precipitate was filtered off and washed
with water, ethanol, and diethyl ether. Yield 3.7 g (80%),
mp 210–213°С. 1Н NMR spectrum, δ, ppm (300 MHz,
DMSO-d6): 9.51 d (J = 3.0 Hz, 1Н, 6-Py–H), 8.75 dd
(J = 3.0 and 9.0 Hz, 1Н, 4-Py–H), 8.50–8.30 m (5Н,
3-Py–H and 4Н–Ph).
The copolyamide films were prepared by casting
from polymer solutions onto glass supports using
a template. The formed solution layers were vacuum-
dried to constant weight (8 h) at 80°С. The film thickness
was 20–25 μm.
The mechanical characteristics and transition
temperatures were determined using films with the
working area size of 20 × 2 mm.
Mechanical tests of the films were performed with
a UTS 10 universal installation (UTStestsysteme,
Germany) in the uniaxial extension mode. In the course
of tests, we determined the elastic modulus Е, plastic
limit σp, tensile strength σt, and elongation at break εb.
2-(4-Aminophenyl)-5-aminopyridine IV. A 1-l
round-bottomed flask equipped with a magnetic stirrer,
a reflux condenser, and a tube for feeding argon was
charged with a solution of III (3.5 g, 0.019 mol) in
tetrahydrofuran (500 ml) and 1.22 g of 10% Pd/C
as catalyst. The reaction was performed in an argon
atmosphere. The mixture was heated to boil, and 18.4 ml
of hydrazine hydrate (90%) was slowly added dropwise.
Refluxing under argon was continued for an additional
3.5 h. TLC analysis (silica gel, eluent methylene
chloride–methanol, 6 : 1) showed that the reaction was
complete. The catalyst was filtered off through a dense
paper filter. The filtrate was evaporated to dryness at
reduced pressure and vacuum-dried at 61°С for 1 h.
Yellow product, yield 2.33 g (99%), mp 195–196°С.
1Н NMR spectrum, δ, ppm (300 MHz, DMSO-d6):
7.93 d (J = 3.0 Hz, 1Н, Н2), 7.59 d (J = 9.0 Hz, 2Н, 2,6-
Ph–Н), 7.41 d (J = 9.0 Hz, 1Н, 3-Py–Н), 6.93 dd (J =
3.0 and 9.0 Hz, 1Н, 4-Py–Н), 6.57 d (J = 9.0 Hz, 2Н,
3,5-Ph–Н), 5.19 s (2Н, Py–NH2), 5.10 s (2Н, Py–NH2).
The temperatures of transitions occurring in the
course of heating of copolyamide films were determined
by thermomechanical analysis with a UMIV-3 device
(Tochpribor, Ivanovo, Russia) in the course of sample
heating at a rate of 5 deg min–1 under a constant tensile
load σ ≤ 0.5 MPa.
Thermal gravimetric analysis (TGA) of films was
performed with a laboratory thermal balance in the self-
generated atmosphere at a heating rate of 5 deg min–1.
From the TGA data we determined the heat resistance
parameters of the copolyamide films: τ1, τ5, and τ10
(temperatures corresponding to 1, 5, and 10% weight loss
of the polymer in the course of heating, respectively).
As a monomer used in the synthesis of the
polymers with 2-phenylpyridine units we chose
2-(4-aminophenyl)-5-aminopyridine. The scheme of its
synthesis is given in Scheme 1.
To prepare the copolyamide,
a
two-necked
round-bottomed flask was charged with a mixture of
2-(4-aminophenyl)-5-aminopyridine (0.057 g, 3 mmol)
and diaminodiphenyl ether (0.348 g, 17.4 mmol) in
N-methyl-2-pyrrolidone (N-MP) (3.64 ml) in 0.1 : 0.9
molar ratio.The mixture was stirred until the components
Fromthemonomerobtainedand4,4'-diaminodiphenyl
ether, we prepared by low-temperature polycondensation
a series of polyamides with different content of
2-phenylpyridine units. As chloride component we
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 10 2010

1864
GOFMAN et al.
Scheme 1.
Scheme 2.
used 4,4'-terephthaloyloxybis(3-methoxybenzoic) acid
dichloride ensuring formation of highly strong, heat-
resistant polymers exhibiting high intrinsic viscosity [5]
(Scheme 2):
synthesized copolyamides in relation to the content of
phenylpyridine fragments in polymer chains.
With an increase in the concentration of PP rings in
elementary units, quite definite and regular changes in
the mechanical behavior of films are observed (Table 1,
Fig. 1). Firstandforemost, aregularincreaseintheelastic
modulus of films with an increase in the content of these
rings should be noted. This effect reflects enhancement
of intermolecular interactions in the material, which
can be associated both with a certain increase in the
degree of ordering of the supramolecular structure of
The maximal content of 2-phenylpyridine units n in
the copolyamide was 40 mol %. Synthesis of polymers
with n > 40 mol % was accompanied by intense gelation
in solutions.
In our study we evaluated the mechanical properties,
determined the characteristics of physical transitions,
and performed thermal gravimetric tests of films of the
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 10 2010

FILMS OF POLYAMIDES WITH PHENYLPYRIDINE UNITS
1865
σ, MPa
Table 1. Mechanical characteristics of copolyamide
films with various concentrations of phenylpyridine rings
Concentration of units with PP, %
εр, %
E, GPa
σp, MPa
σt, MPa εb, %
0
10
20
30
40
4.31 ± 0.07 132 ± 3 181 ± 8 34 ± 2
4.27 ± 0.06 133 ± 4 179 ± 6 33 ± 3
4.29 ± 0.09 134 ± 2 191 ± 6 38 ± 3
4.56 ± 0.19 132 ± 5 181 ± 5 41 ± 3
4.62 ± 0.11 129 ± 3 162 ± 4 51 ± 3
ε, %
Fig. 1. Extension diagrams of copolyamide films. (σ) Stress
and (ε) strain. Content of units with PP rings in the chains, %:
(1) 0, (2) 10, (3) 20, (4) 30, and (5) 40.
the film (increase in the concentration of bonds without
changes in their type) and with formation of new
intermolecular hydrogen bonds involving nitrogen atoms
of the phenylpyridine ring [6]. Apparently, enhancement
of intermolecular interactions takes place already in the
polymer solution, as judged from the tendency to gelation,
observed in the copolyamide solutions at increased (up to
40%) concentrations of PP in polymer chains.
Finally, a regular increase in the elongation at break
of films with an increase in the content of units with PP
rings in copolyamide chains can be noted: an increase
in the concentration of these units from 0 to 40% leads
to an increase in εb of the film by a factor of 1.5. As
already noted, this increase is mainly due to the fact
that a more and more extended segment in which the
plastic mechanism of material deformation prevails
becomes involved in the deformation process, and this is
followed by transition to the range where deformations
due to conformational transitions in the chains become
prevalent.
In the region of high strains (when the plastic limit is
exceeded), the character of variation of the deformation
behavior of films with an increase in the concentration of
PP rings becomes different: The material demonstrates
moreandmorepronouncedplasticbehavior.Whereasthe
deformation process observed with samples containing
no PP rings (Fig. 1, curve 1) is typical of polymer films
with prevalent induced highly elastic deformation
behavior, with an increase in the concentration of PP
units to 40% (Fig. 1, going to curve 5) a well-defined
maximum, “plasticity tooth,” appears in the extension
diagram at approximately 6% strain, which is followed
by more and more pronounced necking.
In thermomechanical tests, we obtained curves of
the temperature dependence of the sample strain at
a constant extending load (Fig. 2). In all the curves
(characterizing films with different PPcontent), there are
two regions of sharp increase in the ductility: at 200–225
and 300–310°С (Table 2). The first of these transitions
is apparently devitrification, whereas the second, high-
temperature, transition is associated with rearrangements
on the chemical level. Indeed, in attempts of multiple
recording of this transition with sample heating in each
measurement cycle to the temperature exceeding by
10°C the transition temperature, followed by cooling
before the next measurement cycle, we observed
a noticeable decrease in the intensity of the defrosting
of the mobility from cycle to cycle and a gradual shift of
the transition toward higher temperatures. This transition
is observed at essentially the same temperature as the
onset of material degradation in the TGA curves (its
temperature practically coincides with the τ1 point in the
TGA curves, Table 2).
After passing to the section of deformation
strengthening, the current modulus of the material
regularlydecreaseswithanincreaseintheconcentration
of PP rings (regular decrease in the slope of curves in
this deformation range, observed in going from the
homopolyamide to the copolyamide containing 40%
PP units), i.e., with an increase in the PP concentration
the material deformation in this range occurs with
decreasing energy consumption. Because in this portion
of the extension diagram the film deformation occurs
mainly at the expense of conformational rearrangement
of macrochains, it can be concluded that incorporation
of PP rings into the polymer chain leads to a decrease
in the mean energy of transitions from rolled-up to
straightened conformations of macrochains.
Finally, with the films containing PP rings, we
recorded one more transition, a low-temperature
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 10 2010

1866
GOFMAN et al.
Table 2. Transition temperatures and parameters of heat
resistance of copolyamide films with various concentrations
of phenylpyridine rings
temperatures above 460–470°С.
It should be noted that, in the first step of the
polymer degradation, significant release of volatiles is
observed: from 24% (of the polymer weight) for the
homopolyamide to 20% for the copolyamide containing
40% units with PP.
τ1
°С
τ5
τ10
Concentration
of units with
PP, %
Ttransition
0
10
20
40
226, 309
310
310
305
295
351
350
344
336
367
364
359
350
As the concentration of units with PP in copolyamide
chains is increased, all the parameters of the heat
resistance of the film regularly decrease: both steps
of thermal degradation are shifted toward lower
temperatures.
108, 216, 311
117, 211, 306
128, 198, 304
Such character of the thermal behavior of the
synthesized polymers becomes clear if we take into
account that thermal degradation of polyamides derived
from 4,4'-terephthaloyloxybis(3-methoxybenzoic) acid
dichloride and aromatic diamines is accompanied by
partial cross-linking. It was shown previously [7] that the
heat resistance of such systems and their degradation rate
are primarily determined by the structure of the diamine
fragment. Studies of the mechanical properties of the
copolyamides with various contents of 2-phenylpyridine
units showed that, at high strains when the processes are
process (in the interval 110–130°С) of very low intensity
(Table 2). With the film of the homopolyamide containing
no PP rings, this process was not detected. Presumably,
it reflects activation of short-scale mobility associated
specifically with the PP rings in the polymer chains.
As seen from the TGA data (Fig. 3, Table 2), the
release of volatiles from the examined films is multistep.
In the first step, at temperatures of up to 120°С, the
sorbed water is removed. Its content in the films is on
the level of 1–3%. Further heating to 220–230°С is
accompanied by the removal of the residual solvent in
which the synthesis was performed, N-MP, and only
on heating to approximately 300°С the polymer itself
starts to degrade. The degradation, in turn, occurs
in two steps readily discernible in the TGA curves,
especially in the differential curves (Fig. 3b). The first
step with the maximal weight loss intensity in the range
370–385°С is complete at 400–420°С, and the second,
high-temperature, step of the degradation occurs at
(a)
T, °C
(b)
T, °C
T, °C
Fig. 2. Thermomechanical curves of copolyamide films.
(ΔL/L0) Relative elongation and (Т) temperature. Content of
units with PP rings in the chains, %: (1) 0, (2) 20, and (3) 40;
the same for Fig. 3.
Fig. 3. TGA curves of copolyamide films. (Т) Temperature;
(a) integral (Δm/m0) and (b) differential (Δm/ΔT) weight loss
curves.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 10 2010

FILMS OF POLYAMIDES WITH PHENYLPYRIDINE UNITS
1867
determined by conformational transitions, introduction
two steps: at 300–400 and above 460–470°С.
of these units leads to a decrease in the rigidity of the
polymer chain. This, in turn, leads to a certain decrease
in the heat resistance of the polymers in the range 350–
400°С, namely, to increased intensity of the release of
volatiles on heating the films in this temperature range.
In the same temperature range, the nitrogen-containing
heterorings start to degrade, which is accompanied by
formation of partially cross-linked structures. Their
degradation corresponds to the high-temperature step
starting at 460–470°С.
(4) An increase in the concentration of units with
phenylpyridine rings leads to an increase in the elastic
modulus and elongation at break of the films, and also
to the shift of the relaxation transition temperatures and
heat resistance parameters toward lower temperatures.
ACKNOWLEDGMENTS
The study was financially supported by the Russian
Foundation for Basic Research (project nos. 09-03-
00408-a and 09-03-12173-ofi_m).
Thus, a study of the behavior of the copolyamidefilms
on heating shows that the upper limit of the admissible
operation temperature of these films is determined by
the glass transition point, which is equal to 200–225°С
and slightly decreases with an increase in the content of
units with PP in the chains.
REFERENCES
1. Aixiang Xia, Guanghua Lu, Xuepeng Qiu, et al., J. Appl.
Polym. Sci., 2006, vol. 102, no. 2, pp. 1844–1851.
2. Jae-Suk Lee, Nam-Goo Kang, Young-Sun Cho, et al.,
Polym. Prepr., 2001, vol. 42, no. 2, pp. 448–449.
CONCLUSIONS
3. Bolletta, F. and Balzani, V., Inorg. Chem. Acta, 1982,
(1) The developed synthesis procedure allowed
preparation of strong elastic films of the copolyamides
containing up to 40% units with phenylpyridine
heterorings in the chains.
vol. 62, pp. 207–213.
4. Peng, Z. and Gharavi, A.R., J. Am. Chem. Soc., 1997,
vol. 119, no. 20, pp. 4622–4632.
5. Goikhman, M.Ya., Podeshvo, I.V., and Mikhailov, G.M.,
(2) A relaxation transition at 200–225°С, associated
with the material devitrification, and a high-temperature
transition at 305–310°С, accompanied by the onset of
thermal degradation, were recorded.
Zh. Prikl. Khim., 1997, vol. 70, no. 2, pp. 312–326.
6. Artem’eva, V.N., Borovik, V.P., Denisov, V.M., et al., Izv.
Akad. Nauk SSSR, Ser. Khim., 1988, no. 2, pp. 405–409.
7. Sazanov, Yu.N., Podeshvo, I.V., Mikhailov, G.M., et al.,
(3) Thermal degradation of the polymers occurs in
Zh. Prikl. Khim., 2002, vol. 75, no. 5, pp. 795–798.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 10 2010