A comparative study of the thermal properties of homologous series of crystallisable n-alkyl maleate and itaconate monoesters

Article abstract of DOI:10.1016/j.tca.2015.10.015

Homologous series of crystallisable C₈-C₂₂ even-numbered alkane oligomers with either maleate or itaconate monoesters end-groups were synthesized. Their total phase change enthalpy (ΔH_tpce) and entropy (ΔS_tpce) on melting, determined by DSC, show a linear dependence with the number of carbons of the alkyl chain. A comparison was performed with corresponding succinate derivatives. The influence of the end functions on ΔS_tpce was examined in view of ΔS_tpce values estimated by the group additivity approach. A fair agreement between the experimental and the estimated entropy values could be demonstrated. Thermogravimetric analysis (TGA) has shown that the maleate oligomers are less stable than the corresponding succinate and itaconate derivatives. This behaviour could be confirmed by the activation energies of the degradation process.

Full text of DOI:10.1016/j.tca.2015.10.015

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Thermochimica Acta
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A comparative study of the thermal properties of homologous series
of crystallisable n-alkyl maleate and itaconate monoesters
Jean-Victor Richarda, Christelle Delaitea,∗, Gérard Riessa, Anne-Sophie Schullerb
a Laboratoire de Photochimie et d’Ingénierie Macromoléculaires, Université de Haute Alsace, 3 rue Alfred Werner, 68093 Mulhouse Cedex, France
b Mäder Research, 130 rue de la Mer Rouge, 68200, Mulhouse, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Homologous series of crystallisable C8-C22 even-numbered alkane oligomers with either maleate or ita-
conate monoesters end-groups were synthesized. Their total phase change enthalpy (ꢀHtpce) and entropy
(ꢀStpce) on melting, determined by DSC, show a linear dependence with the number of carbons of the alkyl
chain. A comparison was performed with corresponding succinate derivatives. The influence of the end
functions on ꢀStpce was examined in view of ꢀStpce values estimated by the group additivity approach.
A fair agreement between the experimental and the estimated entropy values could be demonstrated.
Thermogravimetric analysis (TGA) has shown that the maleate oligomers are less stable than the cor-
responding succinate and itaconate derivatives. This behaviour could be confirmed by the activation
energies of the degradation process.
Received 23 March 2015
Received in revised form 14 October 2015
Accepted 27 October 2015
Available online xxx
Keywords:
Monoesters
Maleate
Succinate
© 2015 Elsevier B.V. All rights reserved.
Itaconate
Crystallinity
Thermal degradation
1. Introduction
In addition to the alkyl and aryl–alkyl itaconate esters studied
extensively by the research group of Katime [4–6], the interest of
Alkane monomers are molecules with a carbon chain, termi-
nally substituted with a polymerizable group, such as for instance
vinyl, acrylic or methacrylic functions. These functional monomers,
generally in the molar mass range of a few hundred to tens of
thousands, are of major interest for the synthesis of graft copoly-
mers or brush structured block copolymers.
Maleate, fumarate and itaconate end functionalized n-alkanes,
from C1 to around C22, are a special class of monomers, as by free
radical homo- or co-polymerization, they open, in particular for the
higher n-alkanes, a straight way to the synthesis of crystallisable
brush type polymers.
Over the last few decades, this approach to the synthesis of such
type of alkane monomers and their polymerization has been exam-
ined quite extensively for a wide range of n-alkane diesters [1,2].
The corresponding monoesters of maleic-, succinic-and itaconic
acids were studied to a relative minor extend as these types of com-
pounds and corresponding maleate and itaconate polymers may
have, under certain conditions, a limited hydrolytic and thermal
stability [3].
n-alkyl itaconate monoesters resides mainly in the fact that the
remaining free carboxylic end-group leads to amphiphilic products,
so-called surface active macromers also designated as surfmers [7].
These monomers, with
a hydrophobic n-alkyl chain, a
hydrophilic carboxylic function and a polymerizable end-group,
have found a large range of application possibilities such as
polymerizable surfactants, micellar systems or emulsion polymer-
ization stabilizers [8].
Moreover, alkyl maleate and itaconate monoesters are of com-
mon practice for grafting modifications of polyolefines that are
carried out at high temperatures by reactive extrusion techniques
[9,10]. As under these conditions the thermal characteristics of C8-
C22 n-alkyl maleates and itaconates have not yet been studied, it
was therefore of interest to examine their stability by thermogravi-
metric analysis (TGA).
In this context, the aim of the present investigation was to
synthesize and to implement the characterization of homologous
series of crystallisable maleate, succinate and itaconate monoesters
with even-numbered C8 to C22 n-alkyl moieties.
For these well-defined products, a comparative study of melt-
ing characteristics will be reported. Except some melting points,
data such as total phase change melting enthalpy (ꢀHtpce) and
entropy (ꢀStpce), are, to the best of our knowledge, not available
in the literature. The maleic, itaconic and succinic end-group effect
∗
Corresponding author. Tel.: +33 (0)3 89 33 67 15.
E-mail address: christelle.delaite@uha.fr (C. Delaite).
http://dx.doi.org/10.1016/j.tca.2015.10.015
0040-6031/© 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: J.-V. Richard, et al., A comparative study of the thermal properties of homologous series of crystallisable
n-alkyl maleate and itaconate monoesters, Thermochim. Acta (2015), http://dx.doi.org/10.1016/j.tca.2015.10.015

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Fig. 1. Chemical structures of synthetized monoesters.
dodecyl maleate (53.74 g, 92%) were obtained. 1H NMR (300 MHz,
CDCl3, 20 ◦C) ı(ppm): 0.88 (3H, t, CH3), 1.27 (18H, m, CH2), 1.72 (2H,
q, CH2), 4.29 (2H, t, CH2), 6.38 (1H, d, CH), 6.48 (1H, d, CH).
Octyl maleate (1a), hexadecyl maleate (1b) and docosyl maleate
(1c) were obtained using the same procedure with yields about
90–95%. Their NMR characteristics are as follows:
on ꢀHtpce and ꢀStpce will be investigated by a group additivity
approach, which is classical for pure alkanes as demonstrated by
different authors [11,12]. Furthermore, these melting characteris-
tics of the maleate, itaconate and succinic n-alkyl monoesters will
be completed by the determination of their thermal stability by
TGA.
(1a) 1H NMR (300 MHz, CDCl3, 20 ◦C) ı(ppm): 0.89 (3H, t, CH3),
1.28 (10H, m, CH2), 1.72 (2H, q, CH2), 4.28 (2H, t, CH2), 6.38 (1H, d,
CH), 6.48 (1H, d, CH).
2. Experimental part
(1b) 1H NMR (300 MHz, CDCl3, 20 ◦C) ı(ppm): 0.88 (3H, t, CH3),
1.26 (26H, m, CH2), 1.73 (2H, q, CH2), 4.29 (2H, t, CH2), 6.38 (1H, d,
CH), 6.48 (1H, d, CH).
2.1. Materials
1-octanol (Alfa Aesar, 99%), 1-dodecanol (Alfa Aesar, 98%), 1-
hexadecanol (Sigma-Aldrich, 99%), 1-docosanol (Sigma-Aldrich,
98%), maleic anhydride (Sigma-Aldrich, 99%), itaconic anhydride
(Alfa Aesar, 97%), succinic anhydride (Sigma-Aldrich, 99%), n-
heptane (Carlo Erba, 99%), methanol (Carlo Erba, 99%), dibutyltin
dilaurate (Sigma-Aldrich, 95%) have been used as received.
(1c) 1H NMR (300 MHz, CDCl3, 20 ◦C) ı(ppm): 0.89 (3H, t, CH3),
1.26 (38H, m, CH2), 1.73 (2H, q, CH2), 4.29 (2H, t, CH2), 6.38 (1H, d,
CH), 6.49 (1H, d, CH).
Succinate and itaconate monoesters were obtained with the
same reaction conditions by substituting maleic anhydride by suc-
cinic and itaconic anhydride respectively. The NMR characteristics
of all these compounds are provided in Supporting Information
(S1).
2.2. Measurements
Dodecyl maleate diester, as a reference product for thermo-
gravimetric analysis was synthesized in bulk. 1-dodecanol (26.67 g,
0.14 mole) was introduced in three-necked flask fitted with a con-
denser and heated at 110 ◦C. After melting the alcohol, maleic
anhydride (7.02 g, 0.07 mole) was added. Dibutyltin dilaurate
(100 mg, 0.158 mmol) as a catalyst was added. The reaction mix-
ture temperature was maintained at 110 ◦C and stirred for 60 min.
Low pressure (0.5 bars) was applied for 30 min in order to remove
residual water. Product was recrystallised from methanol. White
crystals of di-dodecyl maleate (30.92 g, 95%) were obtained. 1H
NMR (300 MHz, CDCl3, 20 ◦C) ı(ppm): 0.88 (6H, t, CH3), 1.26 (36H,
m, CH2), 1.67 (4H, m, CH2), 4.17 (4H, t, CH2), 6.26 (2H, s, CH).
Proton NMR analyses were performed in chloroform (CDCl3) at
20 ◦C on a Bruker 300 MHz spectrometer.
Differential scanning calorimetry (DSC) was performed by using
a thermal analysis system model DSC Q200 from TA Instruments
calibrated with indium. The purge gas was a nitrogen flow of
50 mL min−1. Aluminium crucibles were filled with about 8–12 mg
of sample and sealed hermetically. A heating rate of 10 ◦C min−1
was adopted for analyses between −50 ◦C and 130 ◦C. Two heating
ramps were performed between which a cooling step was car-
ried out at 10 ◦C min−1. The second heating ramp was analysed to
determine the melting properties and thanks to the cooling ramp
crystallisation was be observed.
All thermogravimetric analyses were carried out on a TA Instru-
ments analyser TGA Q500 at a heating rate of 10 ◦C min−1 under
nitrogen atmosphere (100 mL min−1) from 25 ◦C to 400 ◦C.
The software TA Universal Analysis 2000 was used to determine
the temperature of all thermal events.
3. Results and discussion
3.1. Compounds purity
Maleate, succinate and itaconate monoesters purity was deter-
mined by 1H NMR. Indeed, the chemical shift of CH2 next to the
hydroxyl function in alcohol at 3.30 ppm moves to 4.10–4.29 ppm
after the esterification. Taking into account the residual amount of
alcohol, the purity of each compound has been determined and the
corresponding results are presented in Table 1.
2.3. Synthesis
The synthesis procedures of maleate, succinate and itaconate
monoesters were extensively described in the literature [2,13,14].
These compounds were prepared by heating molar equivalents of
the requisite anhydride with different n-alkanols. The correspond-
ing chemical structures obtained by this straightforward technique
are presented in Fig. 1.
From Table 1 it appears that all the n-alkyl monoesters have
a purity of at least 96%. Impurities are generally residual alcohol
A typical synthesis example is given herewith for dodecyl
maleate. 1-dodecanol (38.16 g, 0.20 mole) was introduced in a one-
neck flask and heated at 110 ◦C. After melting the alcohol, maleic
anhydride (20.08 g, 0.20 mole) was added. The reaction mixture
temperature was maintained at 110 ◦C and the medium was stirred
for 90 min. The reaction product was poured in heptane (100 mL)
under magnetic stirring and left at room temperature for 4 h. The
formed precipitate was collected by filtration. White crystals of
Table 1
Purity of monoester compounds as determined by 1H NMR.
Compound
Succinates (%)
Maleates (%)
Itaconates (%)
C8
99
98
99
99
97
96
97
96
99
98
99
98
C12
C16
C22
Please cite this article in press as: J.-V. Richard, et al., A comparative study of the thermal properties of homologous series of crystallisable
n-alkyl maleate and itaconate monoesters, Thermochim. Acta (2015), http://dx.doi.org/10.1016/j.tca.2015.10.015

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Table 2
3
Isomeric proportions of the maleate and itaconate monoesters determined by 1H
NMR.
Compound
Maleate monoesters
Itaconatemonoesters
Cis (%)
Trans (%)
␣ (%)
␤ (%)
C8
99
98
98
95
1
2
2
5
6
14
12
15
94
86
88
85
C12
C16
C22
Fig. 2. Itaconate isomers: (1) ␣-itaconate monoester (2) ␤-itaconate monoester.
used in synthesis of monoesters in addition to traces of residual
anhydride and diacid in the range of 0–1%. The opening of cyclic
anhydrides by an alcohol leads to the monoester in the case of
succinic anhydride as no isomerization is possible. However, for
maleic and itaconic anhydride, isomeric products can be obtained.
Indeed, for the maleate monoester synthesis, the isomerization of
the double bond may occur, leading to the fumarate monoester
[15]. Furthermore, it could be shown by Cowie and Haq [14] as well
as by Yang et al. [16] that the reaction of an alcohol with itaconic
anhydride leads to a mixture of the ␣-monoester itaconate and the
␤-itaconate monoester as shown in Fig. 2.
Thanks to the 1H NMR analysis, the proportion of isomers for each
compound has been determined and the corresponding results are
presented in Table 2.
For the previously mentioned synthesis conditions, the trans
isomer proportion of the maleate monoesters remains in the neg-
ligible range of 2%, whereas in the case of itaconate monoesters,
the proportion of ␣ isomer is typically in the range of 6–15% with
an increasing tendency for the longer alkyl chains. At the present
stage of our investigation it is not clear if this effect is inherent in
the synthesis and/or the purification process by recrystallisation.
The presence of these isomeric forms may have an influence on
the crystallisation characteristics. Therefore the isomeric propor-
tions of the maleate and itaconate compounds have been checked
by 1H NMR analysis.
3.2. Melting characteristics
In order to quantify the proportion of isomeric forms, the chemi-
cal shifts of the double bond protons have been used. As an example,
chemical shifts of double bonds protons of dodecyl itaconate are
presented in Fig. 3.
The chemical shifts at 6.47 and 5.84 ppm correspond to the dou-
ble bond protons of the ␣-dodecyl itaconate. For the ␤-dodecyl
itaconate the corresponding chemical shifts are 6.37 and 5.74 ppm.
Fig. 4 shows typical DSC melting and cooling curves of dodecyl
maleate with its endothermic melting peak at Tm = 51.3 ◦C as the
onset value and an exothermic crystallisation peak at Tc = 41.7 ◦C.
Slight undercooling effects are noticed, as Tc is systematically lower
than Tm, especially for the n-octyl derivatives. However, within
the experimental error limits, no major differences are observed
between melting (ꢀHtpce) and crystallisation (ꢀHc) enthalpies.
Fig. 3. Zoom of 1H NMR (CDCl3) spectrum of dodecyl itaconate.
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Table 3
Maleate monoesters melting characteristics.
a
Compound name
Tmelting
(◦C)
Tmelting (◦C)
ꢀHtpce (kJ/mol)
ꢀStpce (J/mol K)
lit.
Octyl maleate
30.0 [17]
58.0 [2]
71.5 [11,18]
82.0 [19]
31.1
51.3
71.8
82.0
33.2
52.0
71.4
87.1
109.2
159.0
207.1
245.4
Dodecyl maleate
Hexadecyl maleate
Docosyl maleate
a
Melting temperatures reported in literature.
Table 4
Itaconate monoesters melting characteristics.
a
Compound name
Tmelting
(◦C)
Tmelting (◦C)
ꢀHtpce (kJ/mol)
ꢀStpce (J/mol K)
lit.
Octyl itaconate
58.0 [20]
77.0 [21]
84.0 [22]
95.0 [23]
58.0
74.6
85.6
86.9
43.7
57.2
74.6
93.3
132.0
164.5
208.1
259.2
Dodecyl itaconate
Hexadecyl itaconate
Docosyl itaconate
a
Melting temperatures reported in literature.
The melting characteristics, including the onset of melting tem-
perature, enthalpy and entropy of the C8, C12, C16 and C22 maleate
and itaconate monoesters are summarized in Tables 3 and 4 respec-
tively. In the present study, the ꢀStpce values were calculated from
the experimental values of ꢀHtpce and the corresponding temper-
ature in Kelvin according to Eq. (1).
␣ and ␤ isomers by an enzymatic approach as suggested by Ferra-
boschi et al. [27] and to blend these isomers in well-defined ratios.
The melting temperatures of these three series of compounds,
increase as expected with the carbon chain lengths. These values
match with those provided in literature. In order to demonstrate
the influence of monoester end-group on melting temperatures, the
results were further compared to the corresponding values of pure
n-alkanes reported by Broadhurst [28]. This comparison is outlined
in Fig. 5.
ꢀStpce = ꢀHtpce/Tmelting
(1)
Furthermore, in Table 5 are provided the melting characteristics
of the corresponding succinate monoesters where no isomers are
present.
Fig. 5 confirms the major influence of the end-group on melting
behaviour, in particular for the lower alkane chain lengths. Accord-
ing to Boudevska et al. [29], this trend could be explained by the
presence of carboxylic end-groups for monoesters, leading to the
formation of intra- and/or inter-molecular hydrogen bonds.
The end-group effect on n-alkane chains is also relevant by tak-
ing into consideration the melting enthalpy ꢀHtpce of the different
series as shown in Fig. 6.
Within the range of even-numbered C8–C22 alkanes and
monoesters, a linear correlation can be noticed in Fig. 6 between
ꢀH and n, the number of carbons of the alkyl chain. As suggested
by Cowie and Haq [1] and Jordan et al. [30], the data can be fitted
by a first degree polynomial given in Eq. (2).
From the DSC curves of the itaconate monoesters given in
Supporting Information (S2), it can be noticed that in each case
only a single monomodal transition peak is obtained. According
to Domanska and Wyrzykowska-Stankiewicz [25] this may be a
direct indication that in the present experimental conditions, such
as a heating rate of 10 ◦C/min, a solid/solid and a solid/liquid tran-
sitions occur for even-numbered paraffins in a short temperature
range. Moreover, it might not be excluded that the ␣ and ␤ ita-
conate isomers could have a tendency to form eutectic or even
co-crystallisable systems. In fact, according to Kelly et al. [26] iso-
mers with identical and even-numbered crystallisable paraffinic
moieties could have the possibility to co-crystallise, in particular if
the compounds have in addition hydrogen bonding end-groups,
such as COOH end-groups of the itaconic monoesters. For the
verification of this alternative of eutectic composition versus co-
crystallisation it would be necessary to prepare separately the pure
ꢀHtpce = B n + A
(2)
where, n is the number of CH2 units, including the terminal CH3
methyl group, A the contribution of the chain ends and B the
enthalpy of fusion per mole of CH2.
At first, the experimental correlations between n, the number of
CH2 units (plus one CH3), and the enthalpy melting values ꢀHtpce
are considered. These correlations are summarized in Table 6.
Concerning the influence of the alkyl carbon chain length n
(including the CH3 group), a reasonable agreement can be noticed
6
41.7°C
4
2
100
80
60
43.2°C
175.1J/g
40
20
0
-20
-40
-60
Itaconates
0
Maleates
Succinates
Alkanes
51.3°C
-2
181.5J/g
57.9°C
-4
0
10
20
30
-100
-50
0
50
100
150
Exo Up
Universal V4.5A TA Instruments
Carbon chain length
Temperature (°C)
Fig. 4. DSC curves of dodecyl maleate monoester.
Fig. 5. Monoesters melting temperature compared to those of n-alkanes.
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Table 5
Succinate monoesters melting characteristics.
a
Compound name
Tmelting
(◦C)
Tmelting (◦C)
ꢀHtpce (kJ/mol)
ꢀStpce (J/mol K)
lit.
Octyl succinate
37.0 [24]
47.5 [24]
64.5 [11]
81.0 [24]
36.5
45.8
64.2
73.6
41.8
53.1
66.1
93.0
135.1
166.7
196.1
268.4
Dodecyl succinate
Hexadecyl succinate
Docosyl succinate
a
Melting temperatures reported in literature.
(Tables 3, 4 and 5) and those estimated by the group additivity
approach according to Chickos et al is shown in Fig. 7.
From Fig. 7, for 12 entries, the equation of the line obtained by
a linear regression analysis is given by ꢀStpce (experimental)= 1.02
ꢀStpce (estimated)+ 3.68 with r2 = 0.98. Within the experimental
limits, a fair agreement appears between the experimental and the
estimated data.
90
80
70
60
50
40
30
20
Itaconates
Maleates
Succinates
Alkanes
3.3. Thermal degradation
The thermal degradation of poly(di-n-alkyl itaconate)
homopolymers and various copolymers, as well as of corre-
sponding maleate polymers, has been studied quite extensively
over the past decades [32–35]. Popovic et al. [34] for instance
demonstrated that the volatiles arising from the thermal degrada-
tion of poly(n-alkylitaconates) with C1 to C8 ester side-groups, are
mainly the corresponding monomers.
0
10
20
30
Carbon chain length
Fig. 6. Total phase change enthalpy as a function of the carbon chain length: com-
parative values of even-numbered n-alkanes and monoester functional alkanes.
Minor attention in literature has been paid to the thermal
degradation of mono-n-alkyl maleate and itaconate polymers.
Some systematic studies were performed by the research groups
of Cowie [14], Velada [36,37] and Inciarte [38]. Cowie and Haq
[1] proved by thermogravimetric analysis (TGA) that poly(di-n-
alkyl itaconates) with C1 to C10 alkyl chains, are more stable than
the corresponding poly(n-alkyl monoesters) which undergo dehy-
dratation/desesterification reactions starting in the temperature
range of 130–140 ◦C.
To the best of our knowledge, the thermal stability of the n-
alkyl maleate and itaconate monoesters as monomers has not been
investigated up to now, although this type of components are
important for grafting applications. It was therefore of interest to
study more in detail the thermal stability of maleate and itaconate
monoesters with alkyl chain lengths in the range of C8 to C22, which
are typical co-monomers for the preparation of graft copolymers.
Fig. 8 shows the weight loss of succinate, itaconate and maleate
dodecyl monoesters in comparison to the corresponding dodecyl
maleate diester.
Table 6
Experimental melting enthalpy correlations in comparison to the corresponding
literature values for n-alkanes.
Enthalpy term
ꢀHtpce (kJ/mol)
Correlation
coefficient (r2)
n-alkanes
Maleates
Succinates
Itaconates
4.0n [12]a
3.9n + 4.5
3.7n + 10.3
3.6n + 15.1
/
0.978
0.987
0.996
a
Literature value.
in Table 6 for the ꢀHtpce values, between the experimental data
and those predicted by Van Krevelen and Chermin [12]. According
to these authors, deviations in the order of 10% are considered as
being quite normal as the end-group effect is not directly included
in this approach.
In order to take directly into account the end-group effect on the
total phase transition thermodynamic characteristics, and in partic-
ular of the entropy term, it was of interest to estimate these values
according to the group additivity approach developed by Chickos
and Acree [31]. The calculated values for the total phase change
entropy the different homologous series of alkyl monoesters are
listed in Table 7. The details of calculations are provided in Sup-
porting Information (S2).
A higher thermal stability can be noticed for the maleate diester
compared to the corresponding monoester. For the C12 monoester
300
250
200
For the itaconate series, it should be mentioned that the esti-
mated group contributions to ꢀStpce are the same for ␣ and ␤
isomers. The correlation between the experimental ꢀStpce values
Maleates
150
100
50
Succinates
Itaconates
Table 7
Estimated total phase transition entropy values for monoesters series according to
Chickos and Acree [31].
Estimated ꢀStpce (J/mol K)
0
Octyl
Dodecyl
Hexadecyl
Docosyl
0
50
100
150
200
250
300
Maleates
Succinates
Itaconates
117.2
120.8
120.3
154.4
158.0
157.5
191.6
195.2
194.7
247.4
251.0
250.5
ΔStpce estimated by group additivity (J/mol.K)
Fig. 7. Correlation of experimental and estimated total phase change entropy values.
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Table 8
Degradation temperatures of the maleate, succinate and itaconate monoesters series.
Compounds
Onset temperature (◦C)
Temperature at 20% wt loss (◦C)
Temperature at 50% wt loss (◦C)
Octyl maleate
158.6
166.2
185.1
207.2
193.5
218.5
238.4
257.9
199.6
216.7
231.8
257.1
176.0
163.1
175.7
197.6
230.1
198.1
225.5
247.3
275.7
204.4
223.9
247.3
277.1
191.6
185.7
197.5
227.5
279.2
220.8
248.7
272.5
306.7
227.1
247.2
272.5
310.8
213.3
Dodecyl maleate
Hexadecyl maleate
Docosyl maleate
Octyl succinate
Dodecyl succinate
Hexadecyl succinate
Docosyl succinate
Octyl itaconate
Dodecyl itaconate
Hexadecyl itaconate
Docosyl itaconate
Didodecyl maleate
100
90
80
70
60
50
40
30
20
10
0
the 20% and 50% weight loss temperatures. It is worth noting, that
at given alkyl chain length these thermal characteristics are quite
similar for the succinate and itaconate monoesters. On the con-
trary, those with maleate end-groups are 30–50 ◦C below these two
previous series.
By performing the TGA experiments at different heating rates,
5, 7.5 and 10 ◦C/min, the apparent activation energy of degradation
can be determined. The dodecyl series of monoesters was selected
for this comparative study and the corresponding results, the onset
degradation temperature and that at 20% and 50% weight loss are
shown in Table 9.
The apparent activation energies Ea of thermal degradation
were calculated according to the Flynn-Wall method from the
weight loss curves at three different heating rates [39]. It might
be recalled that the Flynn-Wall method consists in determining
the temperature at a constant degree of degradation conversion for
three different heating rates. By plotting the logarithm of the heat-
ing rate versus the corresponding reciprocal absolute temperature
previously determined, a straight line is obtained as presented in
Fig. 10 for the dodecyl maleate. According to Flynn-Wall, the slope
of the line corresponds to –E/RT.
––––––– Dodecyl maleate diester
– – – –
Dodecyl maleate monoester
––––– · Dodecyl succinate monoester
––– ––– Dodecyl itaconate monoester
0
100
200
300
400
500
Universal V4.5A TA Instruments
Temperature (°C)
Fig. 8. Weight loss by TGA of dodecyl succinate, itaconate and maleate monoesters
in comparison to the corresponding dodecyl maleate diester.
series the stability is similar for succinate and itaconate monoesters
but higher than the corresponding maleate series.
The influence of the alkyl chain length of monoester series is
illustrated in Fig. 9 for the itaconate monoesters.
A clear stability increase appears with the increasing alkyl chain
length. In Table 8 are collected the detailed thermal characteristics
of all the samples, such as their onset temperature of degradation,
as well as the temperature corresponding to 20% and 50% weight
loss.
For a given end-group, maleate, succinate and itaconate respec-
tively, it is confirmed that an increase in the alkyl chain length leads
to an increase of the onset degradation temperature in parallel to
The activation energy values can be calculated from the slope of
the straight line. The apparent activation energies at 20% and 50%
weight loss are provided in Table 10.
These results show clearly the lower thermal stability of the
n-alkyl maleate monoesters in comparison to the corresponding
itaconate derivative. With an onset degradation temperature in the
range of 150 ◦C, the maleate monoesters might therefore have some
limitations for their application in reactive grafting on polyolefines
which are generally carried out at around 200 ◦C. Even if the analy-
sis of the degradation products was not the prime aim of the present
study, it might be of interest to consider, in view of the existing lit-
erature, the degradation mechanism and the thermal degradation
products. According to the investigation of Cowie and Haq [14] and
100
––––––– Octyl itaconate
– – – –
Dodecyl itaconate
90
80
70
60
50
40
30
20
10
0
––––– · Hexadecyl itaconate
––– ––– Docosyl itaconate
2.4
2.2
y = -12.0x + 29.1
2.0
r² = 0.99
1.8
1.6
1.4
1.2
1.0
2.2
2.2
2.3
2.3
2.3
0
100
200
300
400
500
103 (1/T(K))
Universal V4.5A TA Instruments
Temperature (°C)
Fig. 10. Logarithm of heating rate versus reciprocal absolute temperature for the
dodecyl maleate at 20% of degradation.
Fig. 9. Carbon chain length influence on thermal degradation temperature of ita-
conate monoesters.
Please cite this article in press as: J.-V. Richard, et al., A comparative study of the thermal properties of homologous series of crystallisable
n-alkyl maleate and itaconate monoesters, Thermochim. Acta (2015), http://dx.doi.org/10.1016/j.tca.2015.10.015

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J.-V. Richard et al. / Thermochimica Acta xxx (2015) xxx–xxx
7
Table 9
Degradation temperatures determined at different heating rates.
Compounds
Heating rate (◦C/min)
Onset temperature (◦C)
Temperature at 20% wt loss (◦C)
Temperature at 50% wt loss
5
7.5
10
155.3
162.3
166.2
164.5
171.3
175.7
184.8
192.7
197.5
Dodecyl maleate
5
7.5
10
206.5
213.7
218.5
212.2
219.3
225.5
233.6
241.6
248.7
Dodecyl succinate
Dodecyl itaconate
5
7.5
10
204.3
213.5
216.7
212.7
218.8
223.9
234.6
241.3
247.2
Table 10
Apparent activation energies.
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tca.2015.10.015.
Please cite this article in press as: J.-V. Richard, et al., A comparative study of the thermal properties of homologous series of crystallisable
n-alkyl maleate and itaconate monoesters, Thermochim. Acta (2015), http://dx.doi.org/10.1016/j.tca.2015.10.015

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Please cite this article in press as: J.-V. Richard, et al., A comparative study of the thermal properties of homologous series of crystallisable
n-alkyl maleate and itaconate monoesters, Thermochim. Acta (2015), http://dx.doi.org/10.1016/j.tca.2015.10.015