Formation of the chain microstructure in the synthesis of adamantane-containing copolyimides in molten benzoic acid

Article abstract of DOI:10.1007/s11172-015-0957-8

High-resolution ¹³C NMR spectroscopy was applied to study the chain microstructure of copolyimides obtained at 140 °C by one-pot high-temperature polycondensation in molten benzoic acid from 2,2-propylidene-bis(4-phenylene-4-oxyphthalic acid) d

Full text of DOI:10.1007/s11172-015-0957-8

Russian Chemical Bulletin, International Edition, Vol. 64, No. 4, pp. 930—935, April, 2015
930
Formation of the chain microstructure in the synthesis
of adamantaneꢀcontaining copolyimides in molten benzoic acid
M. R. Batuashvili,a A. Yu. Tsegel´skaya,a N. S. Perov,a G. K. Semenova,a B. S. Orlinson,b and A. A. Kuznetsova
aN. S. Enikolopov Institute of Synthetic Polymer Materials, Russian Academy of Sciences,
70 ul. Profsoyuznaya, 117393 Moscow, Russian Federation.
Eꢀmail: kuznets24@yandex.ru
bVolgograd State Technical University,
28 prosp. Lenina, 400005 Volgograd, Russian Federation
Highꢀresolution 13C NMR spectroscopy was applied to study the chain microstructure of
copolyimides obtained at 140 C by oneꢀpot highꢀtemperature polycondensation in molten
benzoic acid from 2,2ꢀpropylideneꢀbis(4ꢀphenyleneꢀ4´ꢀoxyphthalic acid) dianhydride (DA,
intermonomer) and two comonomers, 1,3ꢀbis(2ꢀaminoethyl)adamantane (ADA) and 9,9ꢀbis(4ꢀ
aminophenyl)fluorene, varying the order of introduction of components into the system. The
experimentally found value of chain microheterogeneity coefficient determined from the
13C NMR data is in a good agreement with the values theoretically calculated using the matheꢀ
matical model developed earlier by the authors and the kinetic data for the model reactions of
acylation of amino groups and imidization of amido acid fragments. An ADA—DAꢀ2,2ꢀhexaꢀ
fluoropropylideneꢀbis(phthalic acid) dianhydride system provides another example of the prinꢀ
cipal possibility of varying orders of introduction of components to control the chain microꢀ
structure of copolyimides.
Key words: polyimides, highꢀtemperature polycondensation, diamines, tetracarboxylic acid
dianhydrides, benzoic acid, copolymers, chain microstructure, highꢀresolution 13C NMR
spectroscopy, mathematical modeling, kinetics.
The oneꢀpot highꢀtemperature polycondensation
The purpose of this work is to extend the developed
model8 to calculate the parameter Km from the kinetic
data for a new reaction system, 1,3ꢀbis(2ꢀaminoethyl)ꢀ
adamantane (ADA)—9,9ꢀbis(4ꢀaminophenyl)fluorene
(AFL)—2,2ꢀpropylideneꢀbis(4ꢀphenylenꢀ4´ꢀoxyphthalic
acid) dianhydride (DA). It seemed also interesting to comꢀ
pare the obtained data with the experimental values deterꢀ
mined from the 13С NMR spectra for the samples of coꢀ
polyimides synthesized in a BA medium needed for calcuꢀ
lations. An intermediate stage of the study is obtaining the
kinetic data for acylation of ADA comonomer in acidic
medium which are necessary for calculation. The choice
of ADA as an object of the study is due to the fact that
ADA, being highly basic diamine,9 should substantially
differ from AFL in effective reactivity, and this would
favor an increase in the tendency to the block character of
the chain. At the same time, it can be assumed that
a combination of the bulky fragment and dimethylene units
in ADA would enhance the solubility of copolyimides in
organic solvents.
(HTPC) of tetracarboxylic acid diamines and dianhydrides
in highꢀboiling solvents (mꢀcresol, nitrobenzene, etc.) is
widely used for the synthesis of soluble homoꢀ and coꢀ
polyimides.1—4 The use of molten benzoic acid (BA) as
a catalytically active medium5—7 makes it possible to
substantially diminish the temperature and duration of
the HTPC synthesis (140—150 С, 1—2 h) and provides
a number of other advantages over the traditional syntheꢀ
sis.5—7 A series of multiblock copolyimides (CPI) with
fiveꢀmembered imide rings was obtained in molten BA by
the gradual addition of an intermonomer (dianhydride) to
a mixture of two comonomers (diamines).5—7 It was shown
that for the synthesis in BA the behavior of the reaction
system in which several reactions occur simultaneously is
similar to the behavior characteristic of the simple process
of ideal interbipolycondensation. We earlier8 developed
a mathematical model describing the formation of the
chain microstructure of copolyimides in the HTPC synꢀ
thesis. The model makes it possible to calculate the paraꢀ
meter of chain microheterogeneity (Km) on final CPI using
the kinetic data for model reactions. These reactions have
different orders of introduction of intermonomer (tetraꢀ
carboxylic acid dianhydride) into the system.
Another aim of the study was to synthesize multiblock
CPI in the reaction system in which two dianhydrides act
as comonomers and diamine, namely, ADA, acts as an
intermonomer.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 0930—0935, April, 2015.
1066ꢀ5285/15/6404ꢀ0930 © 2015 Springer Science+Business Media, Inc.

Adamantaneꢀcontaining copolyimides
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 4, April, 2015
931
A solution of perchloric acid (0.1 mol L–1) in 100% AcOH was
used as a titrant. The kinetic data were analyzed using the
secondꢀorder reversible reaction and the MapleR mathematical
program.
Experimental
9,9ꢀBis(4ꢀaminophenyl)fluorene (SigmaꢀAldrich) was puriꢀ
fied by sublimation in vacuo (Тm = 237—238 C), and 2,2ꢀproꢀ
pylideneꢀbis[(4ꢀphenyleneꢀ4´ꢀoxyphthalic acid) dianhydride
(Changzhou Wujin Linchuan Chemical Co.) was recrystallized
from acetic anhydride (Тm = 188—189 С).
Results and Discussion
1,3ꢀBis(2ꢀaminoethyl)adamantane (ADA) was synthesized
using a previously described procedure.9 At room temperature
ADA is a viscous liquid (Тb = 160—162 С at 4 Torr). To obtain
dibenzoate salt (ADAB), a solution of BA (5.50 g, 0.045 mol) in
THF was added to a solution of ADA (5.00 g, 0.02 mol) in THF.
A precipitate that formed (ADAB) was filtered, washed with
THF, and dried in vacuo. A white crystalline substance was obꢀ
tained with Тm = 247 С (DSC). The composition of ADAB
(molar ratio ADA : BA = 1 : 2) was confirmed by the data of
potentiometric titration of a weighed sample of ADAB with
a solution of HClO4 in AcOH.
4,4´ꢀ(Hexafluoroisopropylidene)diphthalic anhydride (DAF)
(Sigma Aldrich) was purified by sublimation in vacuo at 200 С
(Тm = 244—247 C).
Homopolymers ADA—DA and ADA—AFL were syntheꢀ
sized in molten BA using the procedure similar to that described
previously,6,7 but diamine was introduced in the form of dibenzoꢀ
ate salt. Copolyimides based on ADA—DA—AFL (CPIꢀI) and
ADA—DA—DAF (CPIꢀII) were obtained using an earlier deꢀ
scribed procedure5—7 varying order of introduction of compoꢀ
nents into the system.
A series of copolyimides were synthesized by the HTCP
method in molten BA (140 C). Two procedures were used
for the synthesis: simultaneous introduction of all compoꢀ
nents into the DA—AFL—ADA system (samples CPIꢀIꢀ1)
and gradual addition of intermonomer DA for 30 min to
a solution of comonomers AFL—ADA in molten BA (samꢀ
ples CPIꢀIꢀ2). The ratio of diamines and intermonomer
was ADA : AFL : DA = 1 : 1 : 2 in both cases.
The copolyimides based on ADAB, AFL, and DA were
synthesized according to Scheme 1.
The details of the 13С NMR spectra of the samples of
the CPIꢀI series are presented in Fig. 1. Microstructure of
the chain polymers was characterized using the simplest
units, triads. The mole ratio of ACA, ACB, and BCB triads
was calculated by signal processing in the structureꢀsensiꢀ
tive regions (determined earlier in Ref. 7). These signals
correspond to the carbon atoms of the anhydride fragment
indicated in the chemical formula of the polymer.
By comparing the 13С NMR spectra of samples CPIꢀI
with the spectra of homopolyimides the characteristic sigꢀ
nals were assigned to triads АСА, ВСВ, and АСВ (Table 1).
The relative content of triads and parameter Km were calꢀ
culated from the 13С NMR spectra. For the simultaꢀ
neous comonomer introduction, Km = 1 (random sample
CPIꢀIꢀ1). For CPIꢀIꢀ2, Km = 0.51 (miltiblock sample).
We have earlier8 analyzed the generalized kinetic
scheme of chain microstructure formation in the synthesis
of CPI in a catalytic medium formed by two symmetrical
bifunctional comonomers specifically, diamines (A, B)
with independent groups (a, b), and symmetrical bifuncꢀ
tional intermonomer (for example, dianhydride C) also
with independent groups (с) were used. The scheme inꢀ
cludes the following main reactions: acylation of amino
13С NMR spectra were recorded in a CDCl3 solution on
a Bruker instrument (300 MHz) at a scan increment of 0.001 ppm
with a high signal accumulation.
The kinetics of the model reaction of acylation of diamine
ADA with phthalic anhydride (PA) was studied in glacial AcOH
(100%). The reaction was carried out in a temperatureꢀconꢀ
trolled cell of an APT 09 Akvilon automated potentiometer usꢀ
ing a known procedure.5 A temperatureꢀcontrolled solution of
PA in AcOH was added to a temperatureꢀmaintained solution of
ADA in AcOH. The initial concentrations of the reagents were
сADA = 0.03 mol L–1 and сPA = 0.031 mol L–1. The measureꢀ
ments were carried out at several temperatures in a range of
50—80 C. Sampling was conducted at specified time intervals to
determine the concentration of residual amino groups. Ttiration
was carried out at a high rate of titrant introducing to ensure that
the duration of sample treatment does not exceed 5—10 s.
Scheme 1
AFL
ADA
DA
R1 =
, R2 =
, R3 =

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Russ.Chem.Bull., Int.Ed., Vol. 64, No. 4, April, 2015
Batuashvili et al.
111 ppm
42 ppm
147ppm
CPIꢀI
groups with anhydride groups to form amido acid fragꢀ
ments, decomposition of these fragments to the initial
groups, and imidization of the amido acid fragments to
form imide cycles. Since the synthesis of CPI by the HTCP
method is carried out in the regime of effective removal of
evolved water from the system with an inert gas flow, the
imidization was considered in the first approximation as
an irreversible reaction. An important distinction of the
a
b
c
1
2
1
1
2
2
3
4
3
4
3
4
147.8 147.6 147.4 147.2 147.0 112.2 112.0 111.8 111.6 111.4 111.2 43.0 42.8 42.6 42.4 42.2 42.0 
Fig. 1. Signals in the structureꢀsensitive regions of the 13С NMR spectra corresponding to atoms C(1) (a), C(2) (b), and C(3) (c) in the
structural formula of CPIꢀI for samples AFL—DA (1), ADA—DA (2), CPIꢀIꢀ1 (3), and CPIꢀIꢀ2 (4).

Adamantaneꢀcontaining copolyimides
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 4, April, 2015
933
Table 1. Assignment of the characteristic 13С NMR
signals () to triads in samples CPIꢀI
Scheme 2
Triad
С(1)
С(2)
С(3)
АСА
АСВ
ВСВ
147.31
147.27, 147.51
147.48
111.57
111.54, 111.82
111.79
42.45
42.47
42.49
CPI synthesis in a BA medium from the synthesis in "inert"
solvents (mꢀcresol, nitrobenzene) is the pronounced cataꢀ
lytic character of the first step (acylation—decomposition
of PAA). The mathematical model8 corresponding to this
kinetic scheme consists of a system of kinetic equations
describing the change in the independent variables: curꢀ
rent concentrations of free amino groups of two types (а, b),
anhydride groups (c), amido acid fragments of two types
(ac1, bc1), and imide cycles (ac2, bc2). The material balꢀ
ance and different characters of introduction of intermonoꢀ
mer into the system were taken into account in the model.
The model also contains equations for the calculation of
the concentrations of triads with difference sequences of
units ACA, ACB, and BCB; the average current length of
blocks ...ACAC... and ...BCBC...; and parameter Km.
To calculate Km for copolyimide CPIꢀIꢀ2 synthesized
by the HPCP method from ADA—DA—AFL in molten
BA, kinetic data for the steps of acylation and imidization
of ADA under the conditions of CPI synthesis are needed
that are unavailable in literature. The expected rate for
ADA acylation at 140 С is very high and, in addition,
acylation and imidization under these conditions are conꢀ
jugated reactions. Therefore, to obtain the necessary
kinetic information, imaginary separation of these steps
was introduced. For this purpose, the model reaction of
ADA acylation with phthalic anhydride in glacial AcOH
was studied at several temperatures below 100 С, i.e.,
under the conditions where the rate of the conjugated reꢀ
action (imidization of the amido acid fragment) is negligiꢀ
ble (Scheme 2). The obtained rate constants were extrapꢀ
olated to the temperature of CPI synthesis equal to 140 С.
The kinetic curves for the acylation of ADA (50—80 С)
with phthalic anhydride in 100% AcOH are presented in
Fig. 2 in the conversion—time coordinates. The retardaꢀ
tion of the reaction rate was observed until equilibrium at
30—40% conversions was achieved.
R =
k2 = 0.5 min–1 for the model bis(amido acid) obtained
from hexamethylenediamine and PA.10 Similar kinetic
data for AFL were presented earlier.8
Using the mathematical model presented in Ref. 8 for
final CPIꢀIꢀ2 and the kinetic data (Table 2), we calculatꢀ
ed the average length of the blocks l ~ 4 and Km = 0.506.
For the regime of simultaneous introduction of comonoꢀ
mers and intermonomer into the system, the calculated
values were l = 2 and Кm = 1, which corresponds to the
formation of random CPI.
Thus, for sample CPIꢀIꢀ2, the calculated and experiꢀ
mental values of Km coincide with a fairly high accuracy.
All earlier considered5—8 CPI were obtained in the sysꢀ
tems in which orthodicarboxylic acid dianhydrides were
used as an intermonomer and diamines with different reꢀ
P (%)
45
1
2
40
35
30
25
20
15
10
5
3
4
P (%)
40
a
3
2
30
20
10
4
The rate constants of the forward (k1) and backward
(kr1) acylation reactions were calculated from the Arrheꢀ
nius dependences extrapolated to the temperature of the
CPI synthesis equal to 140 С (Fig. 3). The values of the
rate constants are presented in Table 2 along with the
values of activation energy of the acylation of amino groups
(Ea1) and the decomposition of amido acid fragments
(Ea10), as well as the equilibrium constants (Кр) and changꢀ
es in the enthalpy of the acylation step (Н1). The value of
k2 was accepted to be equal to the corresponding value
1
4
8
12
16
18 t/min
20 40 60 80 100 120 140 160
t/min
Fig. 2. Kinetic curves for ADA acylation (С0 = 0.03 mol L–1
with phthalic anhydride at temperatures 50 (1), 60 (2), 70 (3),
and 80 (4) C. Inset: the initial region is marked with hatched
rectangular (а).
)

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Russ.Chem.Bull., Int.Ed., Vol. 64, No. 4, April, 2015
Batuashvili et al.
a
b
lnk1
lnKp
4.5
4.0
3.5
3.0
2.5
6
5
4
3
2
1
0
2.62
2.82
3.02
3.22 103/T
2.62
2.82
3.02
103/T
Fig. 3. Temperature dependences of the rate constant (а) and equilibrium constant (b) for the acylation reaction.
activities served as comonomers. Random or multiblock
CPI were obtained depending on the method of interꢀ
monomer introduction into the system (simultaneous or
gradual introduction, respectively). In this work, a similar
approach was also applied to the reaction system in which
diamine ADA was used as an intermonomer and two orthoꢀ
dicarboxylic acid dianhydrides (DA and DAF) served as
comonomers. The choice of DAF was motivated by the
expectation that this dianhydride bearing a strong elecꢀ
tronꢀacceptor bridging substituent should be more reacꢀ
tive in acylation than DA.
A series of CPIꢀII samples based on DA—DAF—ADA
was also synthesized using two methods of introduction of
components. The first method involved simultaneous inꢀ
troduction of a DA—DAF comonomer mixture into a soꢀ
lution of intermonomer ADAB in molten BA (samples
CPIꢀIIꢀ1). The second method included gradual introꢀ
duction for 30 min of intermonomer ADAB into a soluꢀ
tion of a DA—DAF comonomer mixture in molten BA
(samples CPIꢀIIꢀ2).
The microstructure of the synthesized samples was
studied by 13С NMR spectroscopy. A signal in a structureꢀ
sensitive region (46 ppm) was revealed corresponding to
the C atom indicated in the formula of diamine moiety.
Figure 4 shows that in the structureꢀsensitive region of
the spectra of CPI a new signal appears between the sigꢀ
nals of the C(4) atom (in the CPIꢀII structure) assigned to
homotriads (ppm): 46.51 (C(4), АСА), 46.63 (C(4), АСВ),
and 46.71 (С(4), ВСВ). The intensity ratio of these signals
changes depending on the order of introduction.
The values of Km were calculated from the highꢀresoꢀ
lution 13C NMR spectra: 0.91 for CPIꢀIIꢀ1 and 0.76 for
CPIꢀIIꢀ2. The change in the method of introduction of
intermonomer from the simultaneous to gradual one reꢀ
sulted in an increase in the average length of the block
from 2 to 3, indicating a tendency for the formation of
46 ppm
CPIꢀII
Table 2. Calculated parameters for the acylation of diamines ADA and AFL with phthalic anhydride in АсОН
at 140 С
Comꢀ
pound
Kp
/L mol–1
k1
kr1
k2
Ea1
Ear1
–H1
/L (mol min)–1
min–1
kJ mol–1
ADA
AFL8
19
28
1294
4800
32.6
170.0
0.5
0.8
77.4
28.8
97.5
65.7
20.1
36.9

Adamantaneꢀcontaining copolyimides
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 4, April, 2015
935
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 13ꢀ03ꢀ00915).
References
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2
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46.2 
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Fig. 4. Signals in the structureꢀsensitive regions of the 13С NMR
spectra for samples ADA—DAF (1), ADA—DA (2), CPIꢀIIꢀ1 (3),
and CPIꢀIIꢀ2 (4).
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a multiblock microstructure, but the latter is not very proꢀ
nounced. This can be explained by a substantially lower
influence of the nature of the bridging substituent in diꢀ
phthalic anhydrides on their reactivity in acylation comꢀ
pared to a similar effect in a series of diamines.11
Thus, in this work we synthesized two series of samꢀ
ples, CPIꢀI and CPIꢀII, containing the fragment of
1,3ꢀbis(2ꢀaminoethyl)adamantane. In the first series, diꢀ
amine acted as one of the comonomers. In the second
series, diamine served as an intermonomer. In both series,
CPI with the random chain microstructure was obtained
by simultaneous introduction of intermonomer into the
system, whereas multiblock CPI were obtained with gradꢀ
ual introduction. Therefore, the chain microstructure can
be purposefully affected by different introduction of interꢀ
monomer, no matter what compound acts as an interꢀ
monomer, diamine or orthodicarboxylic acid dianhydride.
The parameter Km calculated from the kinetic data for
the model system ADA—DA—AFL is well consistent with
the experimental values obtained from the 13С NMR spectra.
Received December 17, 2014;
in revised form February 5, 2015