The preparation and reactivity of metal-containing monomers 54.* Thermolysis of the acrylamide monomer [Co(CH2=CHCONH2)4(H2O)2]( NO3)2

Article abstract of DOI:10.1023/A:1011327730299

The kinetics and pathways of thermolysis of the Co(II) complex with acrylamide, [Co(CH₂=CHCONH₂)₄(H₂O)₂]( NO₃)₂ (1) were studied. The rate of gas evolution is satisfactorily appr

Full text of DOI:10.1023/A:1011327730299

Russian Chemical Bulletin, International Edition, Vol. 50, No. 5, pp. 901—906, May, 2001
901
The preparation and reactivity of metal-containing monomers
54.* Thermolysis of the acrylamide monomer
[Co(CH2=CHCONH2)4(H2O)2](NO3)2
A. S. Rozenberg, A. V. Raevskii, E. I. Aleksandrova, O. I. Kolesova, G. I. Dzhardimalieva, and A. D. Pomogailo«
Institute of Problems of Chemical Physics, Russian Academy of Sciences,
142432 Chernogolovka, Moscow Region, Russian Federation.
Fax: +7 (096) 515 3588. E-mail: adpomog@icp.ac.ru
The kinetics and pathways of thermolysis of the Co(II) complex with acrylamide,
[Co(CH2=CHCONH2)4(H2O)2](NO3)2 (1) were studied. The rate of gas evolution is satisfac-
torily approximated by a first-order equation of autocatalysis. The composition of gaseous and
solid products of thermolysis of 1 was studied by IR spectroscopy, mass spectrometry, and
electronic microscopy. Thermal transformations of acrylamide complex 1 include three macro
stages: dehydration, polymerization of the dehydrated monomer, and thermooxidative de-
struction of the resulting polymer.
Key words: acrylamide complexes of cobalt nitrate, thermal transformations, dehydration,
solid-phase polymerization, thermooxidative destruction, cobalt nano-sized particles.
The kinetics of isothermal transformation was studied based on
gas evolution in a static nonisothermic reactor at the tempera-
ture Ttherm = 463—553 Ê. The heated volume with the studied
compound was ∼0.05 V, where V is the reactor volume. The size
of the cylindrical tube was maintained constant (internal diam-
The complexes of acrylamide (AAm) with transition
metal nitrates are of interest as regards the possi-
bility of thermally initiated frontal polymerization
(FP) and the manufacture of metal-containing ma-
terials (including nano-sized materials) by high-
temperature pyrolysis. Previously,2 the AAm com-
plexes [Ì(CH2=CHCONH2)4](NO3)n•õH2O, where
Ì = CrIII, MnII, FeIII, CoII, NiII, CuII, and ZnII;
n = 2, 3; x = 0, 2, were synthesized and characterized
by X-ray diffraction analysis, and the phenomenology3
and characteristic features4 of frontal polymerization of
complexes with MnII, CoII, NiII, and ZnII nitrates were
studied. Polymerization of these metal-containing mono-
mers takes place in the temperature range of 353—373 Ê;
the addition of radical inhibitors retards this process.
In order to extend the views on the transformation
pathways of AAm complexes both in the frontal poly-
merization and in the pyrolysis, in this work, we stud-
ied the kinetic features and possible pathways of
thermal transformation in relation to the monomer
[Co(CH2=CHCONH2)4(H2O)2](NO3)2 (1), which was
characterized by X-ray diffraction analysis.2
–3
eter din ≈ 4 mm), weighed portion 70•10 g (in some cases,
thermolysis was carried out in tubes with din ≈ 6 mm). The
transformation kinetics was monitored using a diaphragm null
pressure gage. The thermal decomposition of monomer 1,
including that during the FP, was carried out in a self-gener-
ated atmosphere. The sample was preliminarily evacuated at
∼20 °C and ∼1 Pa for 30 min. In the case of FP, ignition of the
samples (powder of 1 pressed to form a 30—50 mm-long
cylinders ∼4 mm in diameter) was performed at the ignition
temperature Tig = 438 Ê.
The total amount of gaseous products evolved at ∼20 °C,
the amount of these products in the low-temperature (77 Ê)
fractionation and, the loss of mass by the sample (∆m, g) were
measured. The gaseous and condensed products of transforma-
tion of compound 1 were studied by IR spectroscopy in the
–1
400—4000 cm region (a Specord IR-75 spectrophotometer).
In addition, the gaseous products were analyzed by mass spec-
trometry using an MS-3701 quadrupole mass spectrometer
(EI, 75 eV). The solid products of transformation of complex 1
were examined by optical microscopy (OM) on the hot stage of
an MBI-6 instrument. The electron-microscopy studies were
performed using an HU-125 transmission electron microscope
with an accelerating voltage of 100 kV. The powder X-ray
diffraction patterns were obtained on a DRON UM-2
diffractometer using Cu-Kα-radiation.
Experimental
The acrylamide complex 1 was synthesized by previously
published procedures.5,6 Found (%): C, 29.6; H, 5.0; Co, 11.5.
C12H24CoN6O12. Calculated (%): C, 28.6; H, 4.8; Co, 11.7.
The powder consists of shapeless agglomerates (blocks) of
particles with sizes of <10 µm (ρ = 1.53 g cm–3), colored pink
in the reflected light.
The magnetic properties of powders were studied qualita-
tively using reactions of the solid products on exposure to a
constant magnetic field.
Thermolysis of complex 1 was studied under nonisothermal
conditions in air (C derivatograph (ÌOÌ, Hungary)) in the
temperature range of 273—873 Ê (heating rate 10 Ê min–1).
Results and Discussion
Characteristic features of heat evolution in the ther-
molysis of complex 1. The results of thermoanalytical
* For Part 53, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 862—867, May, 2001.
1066-5285/01/5005-901 $25.00 © 2001 Plenum Publishing Corporation

902
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 5, May, 2001
Rozenberg et al.
–1
∆T/Ê
α∑,t/mol mol
1
3
863 K
80
60
40
20
7
2
6
5
388 K
498 K
453 K
528 K
3
2
1
4
328 K
4
363 K
3
0
10
20
30
40
50
t/min
2
Fig. 1. Derivatogram of complex 1: (1) DTGA
–1
(dm/dt•0.8/g min mm–1); (2) TGA (∆m•2.5•103/g mm–1);
1
(3) DTA (∆T•0.88/Ê min–1 mm–1); (4) TA (T•0.5/Ê mm–1).
Heating rate 10 K min–1, sample mass 45.8•10 g.
–3
0
100
200
t/min
Fig. 2. Kinetics of gas evolution in the thermolysis of complex
1 under different temperature conditions (Ê): (1) 463 (0.46);
(2) 468 (0.81); (3) 473 (0.98); (4) 483 (1.78); (5) 493 (2.22); (6)
503 (2.40); (7) 503 (∼2.48). The α∑,t values are given in
parentheses. Curves 1—5, 7: din = 4 mm, 6: din = 6 mm.
studies point to a complex pattern of transformations
of compound 1 (Fig. 1). The thermograms exhibit
the following thermal effects: a weak endotherm at
328—333 Ê; a weak endotherm at 358—363 Ê passing
into a strong exotherm with a maximum at Tmax ≈ 388 Ê;
a poorly resolved region of thermal effects at 453—495 Ê;
and a complex exotherm (strong) in the region of
498—578 Ê with Tmax ≈ 528 Ê. The major mass loss
(∆m >50% (w/w)) takes place at 453—578 Ê. In the
region of endothermic effects and the exothermic peak
at 388 Ê, ∆m < 10% (w/w). The endothermic ef-
fect (359—363 Ê) related to the formation of the
liquid phase (melting) is immediately followed by
heat evolution (364 Ê) caused by polymerization of
monomer 1.
depends on the process temperature and increases as the
temperature rises:
Òtherm/Ê
α∑,f – α∑,0/mol mol
463 468 473 483 493
0.46 0.81 0.98 1.78 2.22
–1
When Ttherm ≥ 503 Ê and the dimensions of the
sample remain constant, the curve of gas evolution in
the thermolysis of complex 1 passes through an extre-
mum (see Fig. 1, curve 7). Raising the temperature
(Ttherm = 503—553 Ê) shifts the gas evolution maxi-
mum α∑,max toward shorter times of transformation.
When the sample size changes (din ≈ 6 mm), the gas
evolution is again described by a smooth S-shaped curve
α∑,τ (see Fig. 2, curve 6). This peculiar "explosive"
behavior of the temperature dependence of α∑,τ is,
apparently, caused by the pattern of heat and mass
transfer during thermal destruction and might be one of
the reasons for the propagation of FP.
Evolution of the topography of solid products. Ac-
cording to optical microscopy data, the initial complex
1 powder consists of dispersed particles looking as shape-
less blocks colored pink (in the reflected light). The
consistent temperature OM scanning of the samples in
air revealed a complex pattern of transformations. In
the 273—333 Ê temperature range, the situation does
not change. At 333—358 Ê (the region of endothermic
effects in the thermograms), the liquid phase containing
monodisperse solid particles is evolved. The pink color-
ing of the liquid can, apparently, be explained by disso-
lution of the initial material. An increase in the tem-
perature to 361—385 Ê results in the formation of a
virtually continuous solid, colorless, optically active (in
crossed polarization filters) material with a minor ad-
mixture of the liquid phase. At 385 Ê, the optical
Kinetics of gas evolution in the thermolysis of com-
plex 1 under isothermal conditions. When thermolysis
is carried out in the self-generated atmosphere at
Ttherm = 463—553 Ê and the dimensions of the initial
–3
sample are constant (din ≈ 4 mm, m0 = 70•10 g), the
kinetics of evolution of gaseous products at different
temperatures corresponds to two transformation modes
α∑(t) = α∑,t, where α∑,t is the number of gas moles
evolved by the instant t per mole of the initial substance
(Fig. 2). For Ttherm < 493 Ê, at short transformation
times (corresponding approximately to the time of sample
warming-up (t0 ≈ 4—5 min)), a step of gas evolution
takes place, α∑,t = α∑,0 ≈ 0.3; after that, the dependence
α∑,τ = α∑,t – α∑,0, where τ = t – t0, shows an S-shaped
pattern (see Fig. 2, curve 1—6). Up to the degree of gas
evolution η ≤ 0.9, the rate of the process W is approxi-
mated satisfactorily by a first-order equation of autoca-
talysis
W = dη/dt = k(1 – η)(η + ξ0),
–1
–2
where k = 4.2•107exp[–24000/(RT)] s ; ξ0 ≈ 1.9•10 ;
η = (α∑,t – α∑,0)/(α∑,f – α∑,0); α∑,f is gas evolution over
the whole transformation time. The difference α∑,f – α∑,0

Thermolysis of Co-acrylamide
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 5, May, 2001
903
Table 1. Gas evolution (α∑,f) and the loss of mass by the sample
(∆mf) upon the thermolysis of complex 1 in the self-generated
atmosphere
activity vanishes. No structural analysis of compound 1
was carried out in this transformation region. However,
the available data concerning solid-phase processes im-
ply that the loss of optical activity by a solid can be due
either to chemical transformations (this is unlikely un-
der the given conditions) or to the transition of the
sample to an isotropic modification (for example, cubic).
The phase transition is followed (T > 385 Ê) by one
more formation of the liquid phase and dissolution of
the solid. This process is accompanied by gas evolution
and ends by 399 Ê. On further increase in the tempera-
ture to 413 Ê, the relatively thick pink-colored melt is
transformed into a viscous shrunken matrix. At tem-
peratures of >453 Ê, vigorous gas evolution from this
viscous matrix takes place; this gives rise to a new
optically active solid phase. The material transparency
disappears at 483 Ê.
The topographic features of the products formed at
different degrees of thermal transformation of powdered
1 in the self-generated atmosphere as well as the prod-
ucts of transformations of prelimiarily pressed powders
during the FP indicate that the morphological pattern
observed is similar to the evolution of the topography of
powdered 1 during pyrolysis in air.
For comparison, we performed an OM study of the
thermal decomposition of AAm in air; the samples used
were dispersed powders consisting of colorless well-
faceted optically active (in crossed polarization filters)
crystals with a small number of defects. It was found
that in the temperature range of 349—361 Ê, melting
(Tïë = 357.5 Ê)8 and simultaneous sublimation of AAm
take place. The non-melted substance, which is, appar-
ently, the product of polymerization, does not exhibit
optical activity. Further raising the temperature does
not change qualitatively the topography of the solid-
phase products. The monodisperse colorless inclusions
found in the liquid phase upon thermolysis of complex 1
(333—358 Ê) might be due to partial evolution of AAm
upon dissociation of complex 1.
The composition of the gaseous products of ther-
molysis. The overall amount of gaseous products evolved
upon thermolysis in the self-generated atmosphere at
the end of decomposition of complex 1 increases with
an increase in Ttherm (Table 1). As α∑,f increases, the
mass loss becomes more pronounced. However, the
found values for the mass loss are markedly lower than
the values expected for the thermooxidative destructive
polymerization of complex 1, for example, at the maxi-
mum possible degree of conversion by the reaction
–1
Ttherm/K
α∑,f/mol mol
∆mf (% (w/w))
463
468
473
483
503
0.76
1.08
1.29
2.10
2.70
20.6
23.0
24.0
31.0
38.0
C—H-containing products were detected in the gas
phase.
More comprehensive information about the compo-
sition of the gaseous products of thermolysis of 1 was
derived from mass spectrometry. The data of IR absorp-
tion spectra are consistent in kind with the results pro-
vided by mass spectrometry; however, the latter implies
a much more intricate composition of the gaseous prod-
ucts. The most intense peaks in the mass spectra* are
m/z = 28+ (100), in which the major contribution can
come from [N2]+ (100), [CO]+ (100), [C2H4]+ (100),
and [C2H6]+ (100); m/z = 30 (10—50) – [NO]+ (100),
[NO2]+ (100), [CH3NO2]+ (100); m/z = 44 (30—60) –
[CO2]+ (100), [N2O]+ (100), [CH2CHC(O)NH2]+ (89.2).
Analysis of the mass spectra shows that the gaseous
products of transformation comprise mainly CO, N2,
CO2, N2O, and NO. Calculations showed that the rela-
tive yields of these substances at the final stage vary as
functions of Ttherm and amount to (% v/v): CO (30—38),
N2 (20—25), CO2 (16—20), N2O (10—15), and NO
(0—10). As the Ttherm increases, the contents of N2O,
NO, and CO in the product mixture decrease, while
those of N2 and CO2 increase. According to mass spec-
trometry, the qualitative composition of the gas phase
formed in the FP in the self-generated atmosphere is
generally close to the composition of thermolysis prod-
ucts formed at 463—553 Ê, namely, CO, N2, CO2,
N2O, H2O, and NH3, the greatest contribution to the
gas evolution being made by CO, CO2, and N2O. How-
ever, the gas evolution level α∑,f at the end of FP is
0.1—0.2 (for ∆mf = 2—4% (w/w)), which is much lower
than that in the case of thermolysis.
The ratio of the yields of gaseous products varies
during the thermolysis at a constant temperature. The
evolution of mass spectra during the "explosive" decom-
position of complex 1 is most illustrative (Fig. 3). When
α∑,t reaches the maximum, the greatest contribution to
gas evolution is made by NO (see Fig. 3, curve 6); after
the maximum has been passed (αNO,max ≈ 1.4), the
amount of NO drops almost to zero with simultaneous
decrease in α∑,t. Unlike the αNO,t curve, which passes
[Co(CH2=CHCONH2)4(H2O)2](NO3)2
=
= CoOx + (1/n)(8 – y)(—CH2—)n + 4 CO + 3 N2O +
+ 0.5(4 – x – 3y)O2 + (4 + y)H2O,
through an extremum, the yields αCO ,t and αN ,t in-
2
crease slightly and monotonically after 2the α∑,t function
where α∑,f ≥ 7.0 at ∆mf ≤ 58.5% (w/w).
According to the results of analysis of the IR absorp-
tion spectra, the major gaseous products of the ther-
molysis of complex 1 are CO, N2O, and CO2. In
addition, traces of NH3 and H2O vapor are formed. No
* From here on, the values in parentheses are Irel (%) of peaks
in the mass spectrum (at different Ttherm) and peaks of indi-
vidual compounds.

904
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 5, May, 2001
Rozenberg et al.
α∑
place in the case of "smooth" gas evolution but its yield
is low, both during the process and at the end of
decomposition due to the high rate of transformation of
NO into N2O and N2.
4
3
2
1
Solid-phase products of thermolysis. The IR spec-
trum of complex 1 contains the following absorption
bands (cm )*: 3360—3380 (s) ν(H2O), 3190 (s)
–1
1
νs(N—H), 3290 (s) νas(N—H), 2800 (w) ν(C—H), 1665
(vs) ν(C=O), 1630 (m) ν(C=C), 1580 (m) δ(N—H),
1445 (m) δ(CH2), 1385 (vs) νd(NO3), 1355 (vs) ν(C—N),
1288 (m) δ(C—H), 1055 (m) νs(NO3), 831 (m) π(NO3),
650 (ms) δ(NO3). Comparison of the IR absorption
spectra of the solid products of transformation of 1
formed during decomposition with the IR absorption
spectrum of the initial sample revealed the following
features. Even at low degrees of decomposition attained
during warming-up of the sample, the IR absorption
spectrum changes in kind. The ν(H2O) absorption bands
of complex 1 disappear. The absorption bands associ-
ated with the stretching vibrations of the AAm ligand
are converted into two broad bands with maxima at
2
3
4
5
6
0
–1
3360 and 1600 cm . As this transformation takes place,
100
200
t/min
the ν(CH2) and δ(CH2) bands are broadened and shift
to lower frequencies, and the ν(C=C) band disappears.
These data point to polymerization of the AAm ligand,
which is confirmed by comparison of the changes in the
IR spectra of AAm and the spectra of polyacrylamide.
In parallel with the increase in the degree of trans-
formation, the intensity of the absorption bands corre-
sponding to the NO3 anion in the spectra of the
thermolysis products decreases (down to disappearance),
indicating its decomposition.
According to powder X-ray diffraction data, the
solid products formed during the process and at the end
of gas evolution are X-ray amorphous.
Study of the topography of the final product of
thermolysis of complex 1 by electron microscopy (Fig. 4)
demonstrated that this product is a single-phase mate-
rial consisting of shapeless glassy particles with a uni-
form electron density.
Fig. 3. Yield of gaseous products of transformation of complex
1 during the "explosive" decomposition at 513 Ê: (1) α∑,t; (2)
3αCO ,t; (3) 3αN O,t; (4) αCO,t; (5) αN ,t; (6) αNO,t. The arrows
2
mark2the instant2of sampling.
has reached the maximum, and αCO,t and αN O,t virtu-
2
ally do not change.* It is significant that, after the α∑,t
value has reached the maximum (α∑,max ≈ 3.71 at
∆mmax = 42.7% (v/v), see Fig. 3), the loss of mass by
the sample decreases in parallel with gas evolution (to
∆mf = 36.6% (v/v) for α∑,f ≈ 3.0).
–
In other words, the processes occurring during fur-
ther thermolysis after the α∑,t maximum has been
reached, lead to a higher yield of the condensed phase.
Among other reasons, this can be due to the consump-
tion of NO (the intermediate product formed upon
decomposition of complex 1) for the formation of prod-
ucts condensed under the thermolysis conditions, in
addition to other pathways of NO conversion, including
the formation of N2. The attenuation of the loss of mass
by the sample with the extremal pattern of the gas
evolution curve might be also due to the partial destruc-
tion of 1, resulting in the liberation and evaporation of
the AAm ligand followed by its condensation. This is
indicated indirectly by the data on sublimation of free
AAm on cold parts of the reactor during early stages of
gas evolution (intense IR absorption bands of the subli-
mate in the region of stretching (ν), deformation (δ),
and twisting (τ) vibrations, 3180—3350 ν(N—H), 1680
ν(C=O), 1615 ν(C=C), 1435 δ(CH2), 1360 ν(C—N),
Pathways of thermolysis of complex 1. The results
obtained point to a complex multichannel mechanism
of 1 thermolysis.
According to X-ray diffraction data,2 the crystals of
1 consist of octahedral [Co(CH2=CHCONH2)4(H2O)2]2+
cations and NO3 anions. The CoII atom is coordinated
–
through the O atoms of four AAm ligands and two H2O
molecules and the structural framework is formed by a
three-dimensional system of hydrogen bonds between
the NH2 and NO3 groups and between the coordinated
–
H2O molecules and the NO3 anions. In the initial
complex cation of 1, the Co—O distances are substan-
tially dissimilar and range from 0.2965 to 0.2114 nm,
–1
and τ(NH2) at 965, 990 cm , typical of AAm).
One can suggest that the intermediate formation and
* The designations in parentheses are the relative intensities of
IR absorption bands of degenerate (d), symmetric (s) and
asymmetric (as) stretching, deformation, and scissoring (δ)
vibrations: vs is very strong, s is strong, ms is the medium-
strong, m is medium, w is weak.
consumption of NO during thermolysis of 1 also takes
* The αi,t values were calculated with the assumption that
αΣ,t ≈ αCO,t + αN ,t + αCO ,t + αN O,t + αNO,t
.
2
2
2

Thermolysis of Co-acrylamide
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 5, May, 2001
905
The water and acrylamide vapors formed during the
thermolysis can be removed from the reaction area,
being condensed on cold walls of the reaction vessel
(∼20 °C); this was observed experimentally.
An increase in Ttherm (> 360 Ê) induces polymeriza-
tion of the dehydrated complex.
H2N
C
NH2
C
HC
CH
O
H2C
O
CH2
•
I
Co2
+
n
H2C
HC
CH2
CH
O
O
C
50 nm
C
Fig. 4. Photomicrograph of the product of thermolysis of
complex 1 at 523 Ê obtained by electron microscopy (magnifi-
cation 100 000).
H2N
NH2
H2N
C
NH2
C
which points to nonequivalence of ligands and to ener-
getic differences between the Co—O bonds. An increase
in the temperature facilitates cleavage of the weakest
Co—O bonds and promotes changes in the coordination
environment of the cation.
∼HC
CH∼
O
O
H2C
CH2
Co2
+
At relatively low temperatures (328—362 Ê, the
region of endothermic effects in the thermogram, see
Fig. 1), dehydration of the crystal hydrate takes place
even at low stages of transformation*
H2C
CH2
O
O
C
∼HC
C
CH
∼
H2N
NH2
n
[Co(CH2=CHCONH2)4(H2O)2](NO3)2 (s.) →
Polymerization of this monomer is accompanied by
evolution of a fairly large amount of heat; more pre-
cisely, the heat of polymerization per mole of double
bonds, apparently, does not differ significantly from the
→ [Co(CH2=CHCONH2)4](NO3)2 (s.) +
–1
+ 2 H2O (liq.) – 19 kJ mol
.
(1)
In addition, decomposition of the complex cation with
partial elimination of the AAm ligand may also occur,
for example, as follows:
heat of polymerization of free acrylamide, which is
–1
equal to ∼83 kJ mol
for solution polymerization;11
however, it cannot be ruled out that complexation
decreases the heat of polymerization.
[Co(CH2=CHCONH2)4](NO3)2 (s.) →
Nitrogen oxides (N2O, NO), detected experimen-
tally during the solid-phase thermolysis of 1, appear to
→ [Co(CH2=CHCONH2)2](NO3)2 (s.) +
+ 2 CH2CHCONH2 (liq.) – 134.6 kJ mol
–1
.
(2)
12
arise both upon the thermal decomposition of HNO3
and its reaction with NH3 or directly with the AAm
amino group and upon the possible transformation of
the mononuclear complex 1 into a binuclear cluster,
similar to dimeric µ-oxo complexes.13—15 The appear-
ance of NH3 and HNO3 can be due to the reaction of
the H2O vapor formed upon dehydration with the AAm
* The ∆H° [Co(CH2=CHCONH2)4(H2O)2(NO3)2 (s.)]
=
f
= –2362 kJ mol–1, ∆H° [Co(CH2=CHCONH2)4(NO3)2 (s.)] =
f
= –1768 kJ mol–1 and ∆H° [Co(CH2=CHCONH2)2(NO3)2 (s.)] =
f
–1
= –1096 kJ mol
values were calculated on the basis of
thermochemical estimates, by comparison of the heats of for-
mation7,8 in the series CoCl2 (s.) → CoCl2•NH3 (s.)
→ CoCl2•2NH3 (s.) → CoCl2•6NH3 (s.), CoCl2 (s.)
→ CoCl2•2H2O (s.) → CoCl2•6H2O (s.), CoNO3 (s.)
→
→
→
–
ligand and the NO3 anion of 1 in the reaction area.
Nitrogen oxides (N2O5, NO3, NO, NO2)12 are fairly
reactive and can undergo subsequent transformations.
On the one hand, these species can initiate radical
polymerization of the dehydrated monomer4 (NO and
NO2 are known16,17 to initiate polymerization of AAm
in solutions). On the other hand, these species can be
consumed in the extensive oxidation of organic ligands
giving CO and CO2 and accompanied by substantial
heat evolution. However, in the temperature range stud-
ied, the yields of CO, CO2, and N2O at the end of gas
→ CoNO3•2H2O (s.) → CoNO3•4H2O (s.) → CoNO3•6H2O (s.)
and from the change in the increment to ∆H° upon the
f
H2O → NH3 ligand replacement with the heats of formation
–1 9
∆H° [NH3] = –46.0 (gas), –67.2 (l.) kJ mol
, ∆H° [H2O] =
f
f
–1 9
–241.6 (gas), –285.9 (l.) kJ mol
with the assumption that
the replacement of the H2O ligand by CH2CHCONH2
results in a decrease in ∆H° by ∼33.0 kJ mol–1. The
f
∆H° [CH2=CHCONH2 (gas)] value was calculated with the
f
–1 8
assumption that ∆H° [CH2CHCOOH (gas)] = –426.4 kJ mol
f
and that the replacement of the —C(O)OH fragment by
–1 10
—C(O)NH2 results in the gain in ∆H° equal to 159 kJ mol
.
f

906
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evolution (in the self-generated atmosphere) is lower
than that expected upon complete oxidation of the
initial product. The particular mechanism of the
thermooxidative destruction of the resulting polymer is
not entirely clear now and requires further investi-
gations.
Attention is attracted by the following fact. At the
end of gas evolution, solid-phase products are diamag-
netic, i.e., the thermolyzed material contains no Co-
containing para- and/or ferromagnetic phases (Co, CoO,
Co2O3).18 The magnetic properties of the resulting prod-
uct show themselves only in the case of thermolysis of
acrylamide complex 1 in air at Ttherm > 680 Ê. It can be
suggested that the solid-phase products formed at the
end of transformations in a self-generated atmosphere
have resulted from the interaction of the Co atoms with
the polymer matrix, as indicated by the data of electron
microscopy (see Fig. 4). In other words, at relatively
low temperatures of thermolysis, very small particles
stabilized by the polymer matrix are formed, whereas at
higher temperatures, they become larger and the result-
ing domains exhibit magnetic properties. A similar phe-
nomenon has been observed previously in a study of the
pyrolysis of cobalt carbonyls in a polybutadiene matrix.19
Thus, thermolysis of complex 1 is a multistage pro-
cess, which includes the following three macro stages:
dehydration, polymerization of the dehydrated mono-
mer, and thermooxidative destruction of the resulting
polymer. The exothermicity of the last two stages can be
one of the main reasons for the development of the
frontal polymerization process. Substantial heat evolu-
tion in the oxidative destruction of the polymer at the
third stage of transformations under definite heat and
mass transfer conditions can bring about an "extremal"
pattern of gas evolution.
The authors are grateful to N. V. Chukanov for the
assistance in the interpretation of the IR absorption
spectra of the products of transformation of complex 1
and to S. I. Evstratova for providing the initial sample of 1.
14. A. D. Negro, L. Ungaretti, and A. Perrotti, J. Chem. Soc.,
Dalton Trans., 1972, 15, 1639.
15. D. P. Bullivant, M. F. A. Dove, and M. J. Haley, J. Chem.
Soc., Chem. Commun., 1977, 584.
16. (a) M. K. Mishra, Macromol. Chem., Rapid Commun., 1985,
6, 541; (b) M. K. Mishra, J. Appl. Polym. Sci., 1985,
30, 725.
This study was supported by the Russian Foundation
for Basic Research (Project No. 01-03-33257).
17. S. N. Bhadant and T. K. Prasad, Macromol. Chem., 1980,
191, 1085.
18. D. D. Mishin, Magnitnye materialy, Vyssh. shkola, Mos-
cow, 1991, 384 s.
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Received January 3, 2000;
in revised form May 15, 2000