Catalytic kinetics and mechanism transformation of Fe(acac)3 on the urethane reaction of 1,2-propanediol with phenyl isocyanate

Article abstract of DOI:10.1002/kin.20798

The urethane reaction of 1,2-propanediol with phenyl isocyanate was investigated with ferric acetylacetonate (Fe(acac)₃) as a catalyst. In situ Fourier transform infrared spectroscopy was used to monitor the reaction, and catalytic kinetics of Fe(acac)₃ was studied. The reaction rates of both hydroxyl groups were described with a second-order equation, from which the influence of the Fe(acac)₃ concentration and reaction temperature was discussed. It was very surprising that the relationship between 1/C and t became constant when reaction temperature increased, which indicated that there was no reactive distinction between the two hydroxyl groups. Although the phenomenon differed with the variation of temperature, it was unaffected by the Fe(acac)₃ concentration. It was attributed to the transformation of the reaction mechanism with the increase in temperature. Furthermore, activation energy (E_a), enthalpy (ΔH), and entropy (ΔS) for the catalyzed reaction were determined from Arrhenius and Eyring equations, which testified to the transformation of the reaction mechanism.

Full text of DOI:10.1002/kin.20798

Catalytic Kinetics and
Mechanism Transformation
of Fe(acac) on the
3
Urethane Reaction of
1
,2-Propanediol with
Phenyl Isocyanate
PENGFEI YANG, TIANDUO LI, JUNYING LI
Shandong Provincial Key Laboratory of Fine Chemicals, Shandong Polytechnic University, Jinan 250353,
People’s Republic of China
Received 10 September 2012; revised 22 January 2013; accepted 18 April 2013
DOI 10.1002/kin.20798
Published online 26 August 2013 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: The urethane reaction of 1,2-propanediol with phenyl isocyanate was investigated
with ferric acetylacetonate (Fe(acac)3) as a catalyst. In situ Fourier transform infrared spec-
troscopy was used to monitor the reaction, and catalytic kinetics of Fe(acac)3 was studied.
The reaction rates of both hydroxyl groups were described with a second-order equation, from
which the influence of the Fe(acac)3 concentration and reaction temperature was discussed.
It was very surprising that the relationship between 1/C and t became constant when reaction
temperature increased, which indicated that there was no reactive distinction between the
two hydroxyl groups. Although the phenomenon differed with the variation of temperature,
it was unaffected by the Fe(acac)3 concentration. It was attributed to the transformation of
the reaction mechanism with the increase in temperature. Furthermore, activation energy (Ea),
enthalpy (ꢀH*), and entropy (ꢀS*) for the catalyzed reaction were determined from Arrhenius
and Eyring equations, which testified to the transformation of the reaction mechanism. ꢀC 2013
Wiley Periodicals, Inc. Int J Chem Kinet 45: 623–628, 2013
INTRODUCTION
PUs can be tailored to meet various demands of mod-
ern technologies, such as coatings, adhesives, fibers,
foams, and thermoplastic elastomers [1,2]. In addi-
tion to their application, the reaction kinetics of hy-
droxyl compounds with isocyanates has been widely
investigated [3,4]. Many factors affect the reaction,
such as reactant [5–8], catalyst [9–13], and solvent
[14,15].
Polyurethanes (PUs) are unique polymeric materials
with a wide range of physical and chemical properties.
Correspondence to: P. F. Yang; e-mail: ypfyyh@gmail.com.
Contract grant sponsor: General Program of National Natural
Science Foundation of China.
Contract grant number: 21176147.
2013 Wiley Periodicals, Inc.
ꢀ
C

6
24
YANG, LI, AND LI
Concerning the needs of safety and health [16],
an important development of the catalyst is the re-
placement of organotin compounds to environmen-
tally friendly metal-β-diketones (M(acac)n) [17–22].
For example, Ligabue et al. [17,18] described cat-
alytic properties of Fe(acac)3 and Cu(acac)2 for the
monourethane and diurethane reactions of hexamethy-
lene diisocyanate with several monobasic alcohols.
They found that different alcohols had different re-
action mechanisms and underwent different transition
states. Furthermore, Lima et al. [21] compared the cat-
alytic property of metal-β-diketones complexes (Fe,
Cu, Sn, and Cr) and the commercial catalyst dibutyltin
dilaurate in the polyurethane synthesis. They found that
when reacting with isophorone diisocyanate dibutyltin
dilaurate was more effective for the urethane reac-
tion with polyethers, and metal-β-diketones complexes
were more effective for the urethane reaction with
polyesters.
Figure 1 3D FT-IR spectra for the reaction of 1,2-
◦
propanediol with phenyl isocyanate (T = 10 C, [Fe(acac)3]
−3
−1
=
10 mol·L ) (color reproduction on wileyonlinelibrary
.
com).
The in situ FT-IR spectrometer React IR IC10, man-
ufactured by Mettler Toledo (Columbia, MD), was
used for all kinetic studies.
As far as the reaction kinetics is concerned, the
structure of diisocyanates is often considered as the
main factor that influences the urethane reaction. Kr o´ l
and Wojturska [23] reported the kinetics of a model
reaction of 2,4- and 2,6-tolylene diisocyanate with 1-
butanol, which was had in the reaction medium of liq-
uid aliphatic hydrocarbons. Rate constants and acti-
vation energy were determined and presented, which
were very useful in discussing the reaction mecha-
nism. However, much less attention is paid to the re-
activity of different hydroxyl groups in asymmetric
diols. Therefore, reaction kinetics and thermochemi-
cal features could be investigated only with the help
of computer simulation [24]. In this work, phenyl
isocyanate is used as the model compound to react
with 1,2-propanediol with Fe(acac)3 as a catalyst. In
situ Fourier transform infrared spectroscopy (FT-IR) is
used to monitor the reaction to work out the rate con-
stant, activation energy, enthalpy, and entropy, on the
basis of which the catalytic properties of Fe(acac)3 are
investigated.
Kinetic Studies of the Urethane Reaction
Clean and dry air was flowed through the instru-
ment continuously until the absorbance of all im-
purities became constant. The background spectra
were recorded to eliminate interference by air. After
that, 1,2-propanediol (1.38 mmol, 0.105 g), butyl ac-
etate (53.0 mmol, 7.00 mL), and different amounts of
Fe(acac) were poured into the flask. The probe of the
3
in situ FT-IR spectrometer was immersed into the re-
actants to monitor the variation of IR spectra. When
the reaction temperature reached the set point, the sto-
ichiometric amount of phenyl isocyanate (2.76 mmol,
0.329 g) (–NCO/–OH = 1) was added and the reaction
began. Data were collected every half minute until the
reaction was terminated at certain extent of conversion.
−1
The resolution was 8 cm , and the scan region was
−1
4000–650 cm
.
RESULTS AND DISCUSSION
EXPERIMENTAL
Spectral analysis is an important tool for discussing re-
action kinetics and dynamics [25,26]. The isocyanate
peak at the region of 2270 cm was most useful and
reliable to monitor the reaction progress [27]. A water-
fall plot of the in situ FT-IR spectra is depicted in
Fig. 1, which clearly shows the changes in iso-
Materials and Instruments
−1
Phenyl isocyanate was purchased from Sigma-Aldrich
(
St. Louis, MO); 1,2-propanediol and Fe(acac)3 were
purchased from the Sinopharm Chemical Reagent Co.
Shanghai, China); all of these were used without fur-
◦
(
cyanate absorbance versus reaction time (T = 10 C,
−3
−1
ther purification. Butyl acetate was also purchased
from the Sinopharm Chemical Reagent Co. and was
purified with distillation and stored over molecular
[Fe(acac)3] = 10 mol·L ).
It is well known that Beer’s law (Eq. (1)) can
be used only for low-concentration solutions. As far
as high-concentration solutions are concerned, it is
˚
sieves (5 A).
International Journal of Chemical Kinetics DOI 10.1002/kin.20798

CATALYTIC KINETICS AND MECHANISM TRANSFORMATION OF FE(ACAC)3
625
acquired from in situ FT-IR, and the relationship be-
tween absorbance (A) and the concentration (C) can be
acquired from Beer’s law, from which the 1/C versus t
curve is plotted.
Influence of Temperature
The relationship between 1/C and t at different temper-
atures is shown in Fig. 2. Detailed data are summarized
in Table I. The concentration of Fe(acac)3 was set as
−
3
−1
10
mol·L to acquire the appropriate reaction rate.
There were two different hydroxyl groups in 1,2-
propanediol, a primary hydroxyl and a secondary hy-
droxyl. Therefore, it could be concluded that the re-
action should be divided into two stages and the 1/C
versus t curve would behave as two consecutive straight
lines with different slopes. The assumption was testi-
Figure 2 Relationship between 1/C and t for the reaction
of 1,2-propanediol with phenyl isocyanate ([Fe(acac)3] =
−3
−1
10
mol·L ).
◦
fied when reaction temperature was lower than 15 C
◦
(
Fig. 2). At 5, 10, and 15 C, the reaction rate of the
primary hydroxyl (kprim) and the secondary hydroxyl
ksec) was different and increased with rising tempera-
ture. The value of kprim/ksec, namely the selectivity of
different hydroxyl groups in 1,2-propanediol, nearly
remained constant.
necessary to examine the relationship between –NCO
absorbance (A) and concentration (C). In our previ-
ous paper [28], it was reported that Beer’s law holds
true when the –NCO concentration is lower than
(
0.4 mol/L. Because of the linear relationship between
However, after the reaction temperature reached
A and C, the value of k0 is conveniently obtained
from the initial absorbance (A0) and concentration
◦
2
0 C or higher, the second-order rate plots became
quite constant and no significant deviation was found.
That is, the reaction rate of the primary hydroxyl and
secondary hydroxyl became equal. It was quite sur-
prising that reaction temperature greatly affected the
urethane kinetics as well as the reaction mechanism.
Either the deceleration of the reaction rate of the pri-
mary hydroxyl or the acceleration of the reaction rate
of the secondary hydroxyl might have led to that re-
sult, and this will be discussed later on the basis of
thermodynamic parameters.
(
C0):
A = k0 · C
(1)
where k0 = A/C = A0/C0 = 0.495 L · mol−1
:
1/C = 1/C0 + kt
(2)
To work out kinetic constants, it is assumed that
there is no side reaction. When the stoichiometric ratio
is used, the total isocyanate concentration can be given
by the general second-order expression [8] as a rela-
tionship of time dependence (Eq. (2)). The relationship
between absorbance (A) and reaction time (t) can be
Influence of Catalyst Concentration
To check the surprising phenomenon caused by tem-
perature and to get rid of the influence of the catalyst
Table I Rate Constants for the Reaction of 1,2-Propanediol with Phenyl Isocyanate at Different Temperatures
[Fe(acac)3] = 10− mol·L−1
3
)
(
Linear Correlation
Coefficient (R)
Linear Correlation
Coefficient (R)
◦
kprim (L·mol−1·min
−1
ksec (L·mol−1·min
−1
)
T ( C)
)
kprim/ksec
5
1.49 × 10−
2
2
2
2
2
1
0.996
0.999
0.998
0.997
0.997
0.998
9.11 × 10
−3
0.951
0.964
0.952
0.997
0.997
0.998
1.64
1.63
1.50
1.00
1.00
1.00
−
−2
10
15
20
25
30
2.59 × 10
1.59 × 10
−
−2
4.28 × 10
2.85 × 10
−
−2
5.60 × 10
5.60 × 10
−
−2
9.66 × 10
9.66 × 10
1.61 × 10−
1.61 × 10
−2
International Journal of Chemical Kinetics DOI 10.1002/kin.20798

6
26
YANG, LI, AND LI
Table II Rate Constants (kprim and ksec) for the 1,2-Propanediol–Phenyl Isocyanate Reaction of Different Fe(acac)3
Concentrations
kprim (L·mol−1·min−1
)
ksec (L·mol−1·min−1
)
kprim/ksec
Concentration
−1
◦
◦
◦
◦
◦
◦
◦
◦
◦
(
mol·L
)
10 C
15 C
20 C
10 C
15 C
20 C
10 C 15 C 20 C
−
−
−
−
3
−2
−2
−2
−2
−2
−2
−2
−2
−1
−1
−2
−1
−1
−1
−1
−2
−2
−2
−2
−2
−2
−2
−2
−2
−2
−2
−1
−1
−1
−1
2
4
6
8
1
× 10
× 10
× 10
× 10
0 × 10
4.40 × 10
4.85 × 10
5.89 × 10
7.52 × 10
8.42 × 10
6.39 × 10
7.87 × 10
9.50 × 10
1.25 × 10
1.39 × 10
8.91 × 10
1.24 × 10
1.45 × 10
1.58 × 10
1.71 × 10
3.04 × 10
3.33 × 10
3.65 × 10
4.63 × 10
5.45 × 10
4.14 × 10
5.30 × 10
6.24 × 10
7.97 × 10
9.01 × 10
8.91 × 10
1.24 × 10
1.45 × 10
1.58 × 10
1.71 × 10
1.45 1.54 1.00
1.46 1.49 1.00
1.61 1.52 1.00
1.63 1.57 1.00
1.55 1.53 1.00
3
3
3
−
3
concentration, the concentration of Fe(acac)3 was var-
−
3
−3
−1
ied from 2 × 10 to 10 × 10 mol·L and each
series was run at different temperatures (10, 15, and
0 C). Detailed results are presented in Table II.
◦
2
As shown in Table II, the reaction rates of pri-
mary and secondary hydroxyls were enhanced with
the increase in the Fe(acac)3 concentration. Simi-
larly, there were two different reaction rates at 10 and
◦ ◦
5 C but only one reaction rate at 20 C. The value
1
of kprim/ksec also changed very little with the varia-
◦
tion of the concentration at 10 and 15 C. Hence, it
could be concluded that, when reacting with phenyl
isocyanate, the selectivity of the urethane reaction
in 1,2-propanediol was independent of the Fe(acac)3
concentration but strongly dependent on reaction
temperature.
Figure 3 Arrhenius and Eyring plots for the reaction of
−3
1
,2-propanediol with phenyl isocyanate ([Fe(acac)3] = 10
−1
mol·L ).
Thermodynamic Parameters
Thermodynamic studies were based on the rate con-
stant (Table I). Activation energy (Ea), enthalpy (ꢀH*),
and entropy (ꢀS*) were determined using Arrhenius
2
3
the Avogadro’s constant (6.02 × 10 ), and h is the
−34
Planck’s constant (6.62 × 10
J·s). The plots are
(Eq. (3)) and Eyring (Eq. (4)) laws:
shown in Fig. 3, and detailed results are presented in
Table III.
Ea
For the secondary hydroxyl group (ksec), activation
energy or activation enthalpy was invariant (35.1 and
ln k = −
+ ln A
(3)
RT
−1
3
3.6 kJ·mol ) and did not change with the increase
in temperature, which was similar to other normal re-
actions. However, as for the primary hydroxyl group
∗
∗
k
R
ꢀS
R
ꢀH
RT
ln T = ln
+
−
(4)
(
kprim), activation energy or activation enthalpy was
Nh
◦
quite lower at low temperature (T ≤ 15 C; 29.4 and
−1
where k is the reaction rate constant, T is the reac-
tion temperature, A is the preexponential factor, R is
27.8 kJ·mol ) and then became a little higher at high
◦
−1
temperature (T ≥ 20 C; 35.1 and 33.6 kJ·mol ). It
−1
−1
the universal gas constant (8.314 J·mol ·K ), N is
could be concluded that when temperature increased
Table III Thermodynamic Parameters for Different Hydroxyl Groups in 1,2-Propanediol
−1
ꢀH* (kJ·mol−1
ꢀS* (J·mol−1·K−1
Run
Ea (kJ·mol−1)
A (L·mol−1·min
)
)
)
6
kprim
ksec
29.4
35.1
6.07 × 10
27.8
33.6
–61.9
–34.3
8
1.73 × 10
International Journal of Chemical Kinetics DOI 10.1002/kin.20798

CATALYTIC KINETICS AND MECHANISM TRANSFORMATION OF FE(ACAC)3
627
Scheme 1 Two-stage reaction route at low temperature.
Scheme 2 One-stage reaction route at high temperature.
the reaction rate of the primary hydroxyl group slowed,
yet the reaction rate of the secondary hydroxyl group
remained invariable. Furthermore, the large negative
values of the activation entropy indicated an associa-
tive mechanism in the transition states, which was re-
viewed by Jayakumar et al. [29].
the secondary hydroxyl formed the Fe(III)–secondary
OH complex and reacted with another phenyl iso-
cyanate. At high temperature, a one-stage reaction
mechanism was assumed as shown in Scheme 2. The
intramolecular hydrogen bond of 1,2-propanediol be-
came so weak that Fe(acac)3 could coordinate with two
hydroxyls simultaneously, followed by the urethane re-
action with phenyl isocyanate. However, the above ex-
planations for the reaction mechanism were two ideal
situations. As far as the actual urethane reaction was
concerned, both of the mechanisms may have played a
part. The transformation from Scheme 1 to Scheme 2
happened when reaction temperature was increased
Discussion of Reaction Mechanism
It had been reported that 1,2-propanediol could form
a five-centered transition state by its intramolecular
hydrogen bond [17,18], which greatly affected the
mechanism of the urethane reaction. When Fe(acac)3
was used as a catalyst, the hydroxyl group in 1,2-
propanediol interacted with the acetylacetonate lig-
and through the hydrogen bond and then eliminated
an acetylacetone molecule [30]. As a result, a chem-
ical bond formed between the oxygen atom in 1,2-
propanediol and the iron atom that possessed a vacant
site (ꢀ). That transition state is shown in Schemes 1
and 2 along with the proposed reaction mechanism.
At low temperature, a two-stage reaction mecha-
nism was assumed as shown Scheme 1. The Fe(III)–
primary OH complex was generated when Fe(acac)3
was added to the reaction system and then the complex
reacted with phenyl isocyanate. The interaction was
not strong enough to overcome the activation energy
barrier of the intramolecular hydrogen bond. After that,
◦
from 5 to 30 C.
The above-mentioned mechanism could be proved
by the variation of the reaction rate. There were two rate
constants when the temperature was low, which were
called as kprim and ksec. They were, respectively, as-
signed to the urethane reaction of Fe(III)—the primary
OH complex with the intramolecular hydrogen bond
and Fe(III)—the secondary OH complex without the
intramolecular hydrogen bond. When reaction temper-
ature increased, both hydroxyls in 1,2-propanediol co-
ordinated with Fe(acac)3 and there was no intramolec-
ular hydrogen bond. It led to only one reaction rate
constant, equal to ksec.
Another proof was the activation entropy. Accord-
ing to transition state theory [31], the activation entropy
International Journal of Chemical Kinetics DOI 10.1002/kin.20798

6
28
YANG, LI, AND LI
was popularly regarded as the degree of disorder in the
system. Breaking of the ring structure may have led
to the increase in the activation entropy. When tem-
3. Madbouly, S. A.; Otaigbe, J. U. Macromolecules 2006,
39, 4144–4151.
4
5
6
. Lubczak, J.; W e˛ glowska, E. Int J Chem Kinet 2009, 41,
512–522.
. Eceiza, A.; Caba, K.; Gasc o´ n, V.; Corcuera, M. A.;
Mondragon, I. Eur Polym J 2001, 37, 1685–1693.
. Eceiza, A.; Kortaberria, G.; Gabilondo, N.; Marieta, C.;
Corcuera, M. A.; Mondragon, I. Eur Polym J 2005, 41,
◦
perature was low (≤15 C), the five-membered ring
of transition state in 1,2-propanediol was not opened.
That is, the reaction system was relatively ordered,
which led to a relatively lower activation entropy
−
1
−1
(
–61.9 J·mol ·K ). On the contrary, activation en-
3051–3059.
−1
−1
tropy would have increased (–34.3 J·mol ·K ) and
the reaction system would have become out of order if
the intramolecular hydrogen bond in 1,2-propanediol
was broken. The break of the intramolecular bond may
7. Yang, P. F.; Li, T. D.; Li, J. Y.; Zhu, X. W.; Xia, Y. M.
Prog React Kinet Mech 2010, 35, 93–104.
8. Yang, P. F.; Yu, Y. H.; Wang, S. P.; Li, T. D. Int J Polym
Anal Charact 2011, 16, 584–590.
be derived from the increase in reaction temperature
9. Draye, A. C.; Tondeur, J. J. J Mol Catal A: Chem 1999,
◦
1
38, 135–144.
10. Draye, A. C.; Tondeur, J. J. J Mol Catal A: Chem 1999,
40, 31–40.
(
(
≥20 C) or the coordination of secondary hydroxyl
◦
≤15 C). In fact, we are planning to further charac-
1
terize the Fe(III)–OH complex, but it is very difficult
because of its high activity.
1
1
1
1. van Benthem, R. A. T. M.; Hofland, A.; Peerlings, H.
W. I.; Meijer, E. W. Prog Org Coat 2003, 48, 164–176.
2. Petrak, S.; Shadurka, V.; Binder, W. H. Prog Org Coat
SUMMARY
2009, 66, 296–305.
3. Yang, P. F.; Yu, Y. H.; Wang, S. P.; Li, T. D. Chin Chem
Lett 2012, 23, 241–244.
The urethane reaction kinetics of 1,2-propanediol with
phenyl isocyanate was studied using in situ FT-IR spec-
troscopy with Fe(acac)3 as the catalyst. The urethane
formation was well described by the second kinetic
model, which considered not only the reactivity of pri-
mary and secondary hydroxyls (kprim, ksec) but also
the selectivity of those hydroxyls (kprim/ksec) in 1,2-
propanediol. It was demonstrated that the reactivity
of primary and secondary hydroxyl groups increased
with the increase in temperature, and the selectivity was
14. Draye, A. C.; Tarasov, D. N.; Tondeur, J. J. React Kinet
Catal Lett 1999, 66, 199–204.
1
1
1
1
1
5. Yang, P. F.; Han, Y. D.; Li, T. D.; Li, J. Y. J Appl Polym
Sci 2012, 123, 580–584.
6. Gorna, K.; Polowinski, S.; Gogolewski, S. J Polym Sci,
Part A: Polym Chem 2002, 40, 156–170.
7. Ligabue, R. A.; Monteiro, A. L.; de Souza, R. F.; de
Souza, M. O. J Mol Catal A: Chem 1998, 130, 101–105.
8. Ligabue, R. A.; Monteiro, A. L.; de Souza, R. F.; de
Souza, M. O. J Mol Catal A: Chem 2000, 157, 73–78.
◦
nearly unchanged at 5, 10, and 15 C. However, it was
´
´
´
9. Stamenkovic, J. V.; Cakic, S. M.; Nikolic, G. S. Chem
very surprising that the relationship between 1/C and t
became constant at 20, 25, and 30 C, which indicated
that there was no reactive distinction between the two
hydroxyl groups. The phenomenon differed with the
variation of reaction temperature but was unaffected
by the Fe(acac)3 concentration.
Ind 2003, 57, 559–562.
◦
20. Inoue, S.; Nagai, Y. Polym J 2005, 37, 380–383.
21. Lima, V.; Pelissoli, N. S.; Dullius, J.; Ligabue, R.;
Einloft, S. J Appl Polym Sci 2010, 115, 1797–1802.
2
2
2
2
2. Raspoet, G.; Nguyen, M. T. J Org Chem 1998, 63, 6878–
885.
3. Kr o´ l, P.; Wojturska, J. J Appl Polym Sci 2003, 88, 327–
36.
6
Thermodynamic parameters were determined using
Arrhenius and Eyring equations. It was found that ac-
tivation energy and enthalpy for the primary hydroxyl
group was lower than that of the secondary hydroxyl
3
4. Cysewski, P.; Kr o´ l, P.; Shyichuk, A. Macromol Theory
Simul 2007, 16, 541–547.
5. Han, K. L.; He, G. Z. J Photochem Photobiol, C 2007,
8, 55–66.
26. Shi, Y.; Zhan, X. L.; Luo, Z. H.; Zhang, Q. H.; Chen, F.
Q. J Polym Sci, Part A: Polym Chem 2008, 46, 2433–
2444.
7. Yilgor, I.; Mather, B. D.; Unal, S.; Yilgor, E.; Long, T.
E. Polymer 2004, 45, 5829–5836.
8. Han, Y. D.; Yang, P. F.; Li, J. Y.; Qiao, C. D.; Li, T. D.
React Kinet Mech Catal 2010, 101, 41–48.
9. Jayakumar, R.; Nanjundan, S.; Prabaharan, M. React
Funct Polym 2006, 66, 299–314.
0. Wang, Y. X.; Li, H. P.; Wang, J. B.; Zhang, F. Q.; Zhao,
J. P.; Dai, M. Acta Phys-Chim Sin 1998, 14, 514–519.
◦
group at low temperature (≤15 C). However, the ac-
tivation energy or activation enthalpy for primary and
secondary hydroxyl groups became the same at high
◦
temperature (≥20 C). Finally, transition state theory
2
2
2
3
was used to propose an appropriate reaction mecha-
nism, which was based on the data of the reaction rate
and activation entropy.
BIBLIOGRAPHY
1
. Kr o´ l, P. Prog Mater Sci 2007, 52, 915–1015.
2
. Chattopadhyay, D. K.; Raju, K. V. S. N. Prog Polym Sci
31. Truhlar, D. G.; Garrett, B. C.; Klippenstein, S. J. J Phys
Chem 1996, 100, 12771–12800.
2007, 32, 352–418.
International Journal of Chemical Kinetics DOI 10.1002/kin.20798