2
G. Koyundereli Çılgı and M. Ak / Journal of Molecular Structure 1221 (2020) 128879
Liu et al. investigated the thermal degradation of four
The activation energy and pre-exponential factor values were cal-
culated from the slope and intercept values respectively. Similar
calculations were repeated according to thirteen different theoretic
model function, g(α) [9, 10]. The most suitable kinetic model was
selected, which showed the lowest standard deviation, and the ac-
tivation energies obtained from the CM I and CM II methods that
are compatible with those obtained from isoconversional proce-
dure KAS and FWO methods with the best regression analysis (r2)
maleimide based polymers which are optically active. TG curves
were taken in both nitrogen and air atmosphere to examine the
surrounding atmosphere. The activation energy values of degrada-
tion reactions were calculated by using the Ozawa and Kissinger
methods [9].
Ke et al. synthesized a novel maleimide-based benzoxazine and
its nearly alternative copolymers with styrene by free radical poly-
merization. It was found that the thermal performance of the
copolymers was directly proportional to polarity of the solvents
used in the copolymerization. The copolymer which were prepared
in DMSO showed the best thermal performance. The curing kinet-
ics of copolymer in DMSO was investigated with using Kissinger
and Flynn-Wall-Ozawa methods [10].
ꢀ
=
ꢀ
=
ꢀ=
value [21-22]. ꢀS , ꢀH and ꢀG values of the activated com-
plexes were calculated according to activated complex (transition
state) theory. Related equations were given below respectively.
ꢀ
S
ꢀ=R
A = (eχkTavg./h).e
ꢀ
ꢀ
H = = Ea − RTavg.
In this work, we investigated thermal degradation stages
of N-(4-(3-Thienyl Methylene)-Oxycarbonylphenyl) Maleimide
monomer, MT and an alternating copolymer of MT with styrene,
P(MT-alt-St). Thermal stabilities of both monomer and copolymer
were investigated. Activation energy values of each degradation
stage were calculated by using isoconversional Kissinger Akahira
Sunose (KAS) and Flynn Wall Ozawa (FWO) methods and degrada-
tion ratio-activation energy were plotted. After these calculations,
KAS and FWO equations were combined with thirteen model
equations, which are known well in academic literature [11, 12].
Thus, suitable reaction models of each degradation stage were
determined. Thermodynamic functions of activated complexes
ꢀ
ꢀ
ꢀ
ꢀ
G = = ꢀH = − Tavg.ꢀS =
where e is the Neper number (2.7183), χ is the transition fac-
tor, which is unity for monomolecular reactions, k is the Boltz-
−
23
−
1), h denotes the Planck’s con-
mann constant (1.381×10
J.K
−
34
stant (6.626×10
J.s), Tavg corresponds to the average reaction
temperature and Ea stands the activation energy which was calcu-
lated from the slope of Composite Methods graphs for the selected
model.
3. Experimental
ꢀ
=
ꢀ
=
ꢀ=
(
ꢀS , ꢀH and ꢀG ) were calculated with using the most proper
model.
3.1. Materials and methods
2. Theory
Acetic
anhydride,
2,2-Dimethoxy-2-phenylacetophenone
(DMPA), triethyl amine, 4-aminobenzoic acid, 3-(2-hydroxyethyl)
In this study, we selected KAS [13] and FWO [14-16] meth-
thiophene were purchased from Sigma-Aldrich and used without
further purification. Styrene monomer (St) and thionyl chloride
(Sigma-Aldrich) were distilled and maleic anhydride (Sigma-
Aldrich) was sublimed before use. Photopolymerization was
performed in merry-go-round-type photoreactor equipped with
16 Philips 8 W/06 lamps (λ=350 nm). Thermal degradation ex-
periments of monomer and polymer were carried out by using
simultaneously Shimadzu DTG-60H apparatus.
ods which are well-known isoconversional and integral technics.
These methods do not require any model or mechanism before-
hand; thus, they are able to predict the most complicated reac-
tion behaviors even at different ranges of temperatures. According
to these methods, degradation ratio (α), temperature (T) and heat-
ing rate (β) do not change with the reaction model. The reaction
model remains the same throughout the reaction. The final equa-
tions of these methods are given below:
ꢀ
ꢁ
3
.2. Synthesis of monomer (MT) and alternating copolymer
β
T2
AR
g(α)E
ꢁ
E 1
P(MT-alt-St)
KAS : ln
=
ln
−
.
R T
ꢀ
In the first step of N-(4-(3-thienylmethylene)-oxycarbonyl
A.E
E 1
. ,
phenyl)maleimide (MT) synthesis, 4-N-maleimidobenzoic acid was
synthesized by condensation and cyclodehydration reaction of
maleic anhydride with 4-aminobenzoic acid using the method
adapted in the literature [23, 24]. Then, 4-N-maleimidobenzoic
acid was converted to its acid chloride in the presence of thionyl
chloride in accordance with the procedure specified in the liter-
ature [24, 25]. Monomer MT was obtained by condensation reac-
tion of synthesized acid chloride and 3-(2-hydroxyethyl)thiophene.
For this purpose, 3-(2-hydroxyethyl)thiophene and triethyl amine
mixture was added dropwise to the stoichiometric ratio of 4-N-
maleimidobenzoic acid chloride in chloroform as in common pro-
cedure in the literature [24, 26]. After the reaction mixture was
refluxed for 24 h, the mixture was washed with hydrochloric acid
solution (1% w, w) and dried over calcium chloride. After removing
the solvent under vacuum, the remaining solid was washed with
hot methyl alcohol and crystallized using THF/hexane mixture fol-
lowingly. The resulting product was dried under vacuum. Melting
FWO : ln β =
− 5.3305 − 1.05178
R.g(α)
R T
where α corresponds to the degradation ratio (α=(w -wt)/(w -w )),
i
i
f
A stands for the pre-exponential factor, E denotes the activation
energy, g(α) represents the differential conversion function, and R
is the gas constant.
In these methods, the plots of lnβ/T2 versus 1/T (for KAS equa-
tion) and lnβ versus 1/T (for FWO equation) are prepared for each
α constant, and activation energy values are calculated by using
these slope values.
We aimed to determine the reaction model and calculate ther-
modynamic parameters. For this purpose, we reorganized KAS and
FWO methods as follows. These equations are called “Composite
Method I” (CM I) and “Composite Method II” (CM II) respectively
in academic literature [17-20].
Modeling KAS equation, CM I: ln g(α) = [ln ] −
Modeling FWO equation, CM II: ln g(α) = [
AR
βE
E
R
A.E
β.R.
.
1
T
T2
] − 5.3305 −
−1
point: 85 °C Yield: 45%, FTIR (cm ): 3020, 3110, 2900, 1767, 1710,
1
.05178 E
.
1
T
1690, 1270, 1210, 1365, 1132, 854, 762, 685; 1H NMR (DMSO-ppm):
8.10–8.05 (d, 2H); 7.71–7.46 (m, 5H); 7.27–7.23 (s, 2H); 5.36 (s, 2H)
For the synthesis of alternating copolymer of MT and St, the
maleimide based monomer was dissolved in dichloromethane and
R
2
The values of ln[g(α)/T ] (in modeling with KAS method) or
ln[g(α)] (in modeling with FWO method) for different α value at
a single β value were calculated and plotted versus 1000/T values.