Influence of the molecular structure of H complexes of dialkyl dihydrogen benzophenonetetracarboxylates with aromatic diamines on the viscosity of their melts

Article abstract of DOI:10.1023/A:1020776632355

The possibility of preparing from dialkyl dihydrogen 3,3′,4,4′- benzophenonetetracarboxylates and 4,4′-diaminodiphenylmethane or 4,4′-diaminodiphenyl ether H complexes of both amorphous and crystalline structures was elucidated. Methods were proposed for disordering the supramolecular structure of the H complexes, which is technologically essential for reducing the melt viscosity when preparing polyimide carbon-filled plastics and foamed composites.

Full text of DOI:10.1023/A:1020776632355

Russian Journal of Applied Chemistry, Vol. 75, No. 7, 2002, pp. 1132 1135. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 7,
2002, pp. 1155 1158.
Original Russian Text Copyright
2002 by Artem’eva, Baklagina, Kukarkina, Kostereva, Samarin, Lavrent’ev, Panov, Kudryavtsev.
MACROMOLECULAR CHEMISTRY
AND POLYMERIC MATERIALS
Influence of the Molecular Structure of H Complexes of Dialkyl
Dihydrogen Benzophenonetetracarboxylates with Aromatic
Diamines on the Viscosity of Their Melts
V. N. Artem’eva, Yu. G. Baklagina, N. V. Kukarkina, T. A. Kostereva, V. P. Samarin,
V. K. Lavrent’ev, Yu. N. Panov, and V. V. Kudryavtsev
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Received January 9, 2002
Abstract The possibility of preparing from dialkyl dihydrogen 3,3 ,4,4 -benzophenonetetracarboxylates and
4,4 -diaminodiphenylmethane or 4,4 -diaminodiphenyl ether H complexes of both amorphous and crystalline
structures was elucidated. Methods were proposed for disordering the supramolecular structure of the H com-
plexes, which is technologically essential for reducing the melt viscosity when preparing polyimide carbon-
filled plastics and foamed composites.
When aromatic diamines are dissolved in solution
of dialkyl dihydrogen tetracarboxylates in alcohol
(methanol or ethanol) or in a water alcohol mixture,
complexes with hydrogen bond (H complexes) are
formed spontaneously between the amino group of
diamine and the ester and carboxy groups of dialkyl
dihydrogen carboxylate [1, 2]. Despite high polarity
of the solvents used, hydrogen bonds are formed even
in solutions with a low concentration of the initial
components (0.01% solutions) [1]. In 7 8% solutions,
H complexes occur as di- and trimers (n = 2, 3) [3]:
polyimides [5], carbon-filled plastics [6], and foamed
composites [7] promising for modern aviation and
space technology, as well as for ship-building applica-
tions. Since all the above-listed materials can be pre-
pared from molten H complexes with low viscosity
only, of special importance are data on how the melt
viscosity is influenced by the structure of the initial
H complexes.
In this work, we proved experimentally that H
complexes with amorphous and crystalline supra-
molecular structures can be obtained by slightly modi-
fying the conditions of their preparation. Also, we
studied how the melt viscosity is influenced by the
crystallization of H complexes and suggested a meth-
od for directed modification of the supramolecular
structure of H complexes.
CO
COOH
HOOC
.
.
.
H2 N R
NH2
AlkOOC
COOAlk
n
At higher solution concentrations, the n-size of the H
complexes increases (n > 5, 6), and the solution gets
anisotropic owing to formation of fluctuation domains
[3], i.e., an ordered supramolecular packing of such
supramolecular structures as H complexes. Even in-
significant changes in the concentrations of such
solutions cause fluctuations of the orientation ordering
factor characterizing the ordering of the H complexes
inside the fluctuation domains [4].
EXPERIMENTAL
Dialkyl dihydrogen 3,3 ,4,4 -benzophenonetetracar-
boxylates (BZPMe and BZPEt, respectively) were
prepared by refluxing 0.03 mol of 3,3 ,4,4 -benzophe-
nonetetracarboxylic dianhydride [TU (Technical
Specifications) TSR 2159 69; purified by refluxing
in acetone; mp 225 C] in 50 ml of the appropriate
alcohol or alcohol with addition of 6 vol % water.
The H complexes were prepared by dissolving at
room temperature equimolar (with respect to BZPMe
or BZPEt) amounts of 4,4 -diaminodiphenylmethane
(DADPM) or 4,4 -diaminodiphenyl ether (DADPE)
(purified by distillation at 1 3 mm Hg; mp 90 92
Under virtually identical conditions, it is possible
to obtain H complexes with different supramolecular
structures because of fluctuations of ambient tempera-
ture and humidity, solvent purity, etc.
The above-mentioned supramolecular structures
can yield polyimide materials such as EPPI foamed
1070-4272/02/7507-1132$27.00 2002 MAIK Nauka/Interperiodica

INFLUENCE OF THE MOLECULAR STRUCTURE OF H COMPLEXES
and 190 C, respectively) in solutions of BZPMe or
1133
BZPEt in the appropriate alcohol. Solid H complexes
were recovered by alcohol evaporation at 1 3 mm Hg
and 20 30 C.
X-ray studies of the samples of H complexes were
carried out on a DRON-2 diffractometer (nickel-fil-
tered copper radiation). The viscosity of molten
H complexes was measured on a PIRSP rheometer
(cone plane working unit; angle at the cone vertex 1 ,
cone diameter 40 mm) at 95 and 105 C at a shear rate
1
of 0.02 s [8].
In most cases, mixing dialkyl dihydrogen benzene-
tetracarboxylates with aromatic diamines yields
H complexes with amorphous structure. Preparation of
crystalline H complexes, though practically unpredict-
able, is rather common. Essential for preparing or-
dered structures are, typically, seasonal fluctuations of
ambient temperature and humidity, uncontrollable
changes in the solvent quality, or minor fluctuations
of the stoichiometry or concentration of the initial
components. Virtually any H complex of any chemic-
al composition can be prepared with amorphous or
differently ordered structures.
2 , deg
Fig. 1. X-ray diffraction patterns of H complexes (1, 1 )
BZPEt DADPE prepared in ethanol, (2, 2 ) BZPMe
DADPE prepared in aqueous methanol, (3, 3 ) BZPMe
DADPM prepared in methanol, and (4, 4 ) BZPEt DADPM
prepared in aqueous ethanol with and without benzimida-
zole addition, respectively. (2 ) Bragg s angle; the same for
Figs. 3 and 4.
Figure 1 presents as an example the X-ray diffrac-
tion patterns of selected H complexes of various
chemical compositions formed in alcohols or aqueous
alcohols. It is seen that H complexes with identical
compositions BZPEt DADPE prepared in ethanolic
solution (Fig. 1, curves 1, 1 ) can have both amorph-
ous (curve 1) and low-crystalline structures (curve 1 ).
In the case of BZPMe DADPE H complexes prepared
in aqueous methanol, it is possible to obtain supra-
molecular structures with various degrees of crystal-
linity (curves 2, 2 ). With DADPM as amino compo-
nent, the degree of ordering of the H complexes is
also diverse (curves 3, 3 ).
, Pa s
In this connection, it was of interest to elucidate
how the crystalline structure of the H complexes
affects their viscosity, which governs the preparation
of polyimide materials.
, min
Fig. 2. Variation of the viscosity with time of molten
H complexes (1, 1 ) BZPEt DADPE prepared in ethanol,
(2) BZPMe DADPE prepared in aqueous methanol,
(3, 3 ) BZPEt DADPM prepared in aqueous ethanol with
and without benzimidazole addition, respectively, and
(4, 4 , 4") BZPMe DADPE prepared in methanol. Tem-
perature, C: (1, 1 , 2, 3, 3 , 4") 105 and (4, 4 ) 95.
Figure 2 shows how the viscosity of molten H com-
plexes with different structures varies with time.
Curves 1 and 1 characterize the variation with time of
the viscosity of molten BZPEt DADPE H complexes,
isolated from ethanolic solution, with amorphous
(Fig. 1, curve 1) and low-crystalline (Fig. 1, curve 1 )
structures. It is seen that the viscosity of the more
highly ordered H complex in the melt is two orders of
magnitude higher than that of the amorphous H com-
plex. Curve 2 refers to the BZPMe DADPE H com-
plex with low-crystalline structure (Fig. 1, curve 2)
isolated from aqueous methanol. The BZPMe
DADPE H complex with a high degree of crystallinity
(Fig. 1, curve 2 ) does not melt at all at 105 C. Thus,
the more highly ordered the supramolecular structure
of the initial H complex, the higher the melting point
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 7 2002

1134
ARTEM’EVA et al.
curve 4 ) significantly decreases on adding benzimida-
zole (Fig. 1, curve 4). The viscosity of the molten
complex decreases, as expected, by two orders of
magnitude relative to the crystalline sample (Fig. 2,
curves 3, 3 ).
In the case of BZPMe DADPE H complex isolated
from methanolic solution, we succeeded in preparing
samples with significantly differing viscosities of
melts. Curves 4 and 4 (Fig. 2) show how the viscosi-
ties of melts of these H complexes, as measured at
95 C (sample nos. 1 and 2), vary with time. Curve 4"
refers to sample no. 3 of this H complex at 105 C.
At 95 C sample no. 3 does not melt.
2 , deg
Fig. 3. X-ray diffraction patterns of BZPMe DADPE
H complexes prepared in methanol. Sample nos.: (1) 1,
(2) 2, and (3) 3.
The X-ray diffraction patterns of these samples
(Fig. 3) show that none of them has highly ordered
crystalline structure. Unlike amorphous sample no. 1,
however, the X-ray diffraction pattern of sample no. 2
in the region of 2 = 10 20 exhibits clear reflections
which evidence formation a more ordered structure
in it. Sample no. 3 exhibits in the 2
18 27 region
low-intensity reflections against the background
of an amorphous halo. This suggests formation of
ordered domains, similar to crystalline domains in
the BZPMe DADPE sample prepared from aqueous
methanol (Fig. 1, curve 2 ).
The diffraction patterns (Fig. 3, curves 2 and 3)
suggest that the samples can contain various ordered
domains responsible for formation at a later time
of both low-crystalline (Fig. 1, curve 1 ) and highly
ordered crystalline (Fig. 1, curves 2 4 ) structures.
2 , deg
Fig. 4. X-ray diffraction patterns of the BZPEt DADPM
H complex prepared in aqueous ethanol: (1) initial and
(2) after melting at 105 C.
Figure 4 presents the X-ray diffraction patterns of
the BZPEt DADPM H complex isolated from aque-
ous ethanolic solution (curve 1) and of the sample ob-
tained on melting this H complex at 105 C (curve 2).
It is seen that the initial sample has a crystalline struc-
ture. On melting and subsequent cooling, the sample
gets amorphous. Similar structural changes were also
observed for crystalline H complexes of other com-
positions.
of the H complex and the higher the viscosity of its
melt.
As known, in preparing foamed polyamides EPPIs,
samples of H complexes are foamed at temperatures
above 180 C [5]. Therefore, high viscosities of molten
crystalline H complexes at 100 5 C are of no im-
portance for foam formation. However, prepregs for
carbon-filled plastics and foamed composites are ob-
tained at temperatures close to 100 C [6, 7]. This
makes undesirable the use of crystalline H complexes
for these purposes.
CONCLUSIONS
(1) The H complexes prepared from dialkyl dihy-
drogen 3,3 ,4,4 -benzophenonetetracarboxylates and
4,4 -diaminodiphenylmethane or 4,4 -diaminodiphenyl
ether can have both amorphous and crystalline struc-
tures. With growing degree of ordering of the H com-
plex, the initial viscosity of its melt tends to increase.
The viscosity of molten crystalline H complex ex-
ceeds by two orders of magnitude that of amorphous
or low-crystalline H complexes with identical chemi-
cal compositions.
In this connection, we suggest a method for dis-
ordering the supramolecular structure of H complexes.
It was found that adding minor amounts of benzimi-
dazole (3 wt % with respect to dialkyl dihydrogen
carboxylate) to the initial reaction mixture yields
H complexes with less highly ordered structure, all
other conditions being the same. For example, the
degree of ordering of the crystalline BZPEt DADPM
H complex prepared from aqueous ethanol (Fig. 1,
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 7 2002

INFLUENCE OF THE MOLECULAR STRUCTURE OF H COMPLEXES
1135
(2) To obtain low-viscosity melts required for suc-
cessfully preparing prepregs, it is recommended that
minor amounts of benzimidazole, which exerts a dis-
ordering effect on the supramolecular structure of the
forming H complex, be added to the initial reactant
mixture.
Zh. Prikl. Khim., 2000, vol. 73, no. 7, pp. 1172 1179.
3. Chupans, P.I., Kallistov, O.V., Artem’eva, V.N., et al.,
Izv. Akad. Nauk SSSR, Ser. Khim., 1991, no. 6,
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Izv. Akad. Nauk SSSR, Ser. Khim., 1994, no. 9,
pp. 1596 1599.
5. RF Patent 1824885.
6. Artem’eva, V.N., Yudin, V.E., Kudryavtsev, V.V.,
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 7 2002