Accepted Manuscript Title: Synthesis, characterization and non-isothermal decomposition kinetic of a new galactochloralose based polymer Author: G¨okhan K¨ok Kadir Ay Emriye Ay Fatih Do˘gan ˙Ismet Kaya PII: DOI: Reference:
S0144-8617(13)00957-0 http://dx.doi.org/doi:10.1016/j.carbpol.2013.09.065 CARP 8154
To appear in: Received date: Revised date: Accepted date:
27-7-2013 28-8-2013 18-9-2013
Please cite this article as: K¨ok, G., Ay, K., Ay, E., Do˘gan, F., & Kaya, ˙I., Synthesis, characterization and non-isothermal decomposition kinetic of a new galactochloralose based polymer, Carbohydrate Polymers (2013), http://dx.doi.org/10.1016/j.carbpol.2013.09.065 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
Synthesis, characterization and non-isothermal decomposition kinetic of a
2
new galactochloralose based polymer
3 Gökhan Köka, Kadir Ayb, Emriye Ayb, Fatih Doğanc and İsmet Kayad*
4 5
a
6
b
7
Manisa, Turkey.
8
c
ip t
cr
Department of Chemistry, Faculty of Arts and Sciences, Celal Bayar University, 45140,
Secondary Science and Mathematics Education, Faculty of Education, Çanakkale Onsekiz
Mart University, 17100, Çanakkale, Turkey.
us
9
Department of Chemistry, Faculty Sciences, Ege University, 35100, İzmir, Turkey.
10
d
11 12
Çanakkale Onsekiz Mart University, 17020, Çanakkale, Turkey.
13
Abstract
14
A glycopolymer, poly(3-O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-trichloroethylidene-
15
α-D-galactofuranose) (PMIPTEG) was synthesized from the sugar-carrying methacrylate
16
monomer,
17
galactofuranose (MIPTEG) via conventional free radical polymerization with AIBN in 1,4-
18
dioxane. The structures of glycomonomer and their polymers were confirmed by UV-Vis,
19
FT-IR, 1H-NMR, 13C-NMR, GPC, TG/DTG-DTA, DSC, and SEM techniques. SEM images
20
showed that PMIPTEG had a straight-chain length structure. On the other hand, the thermal
21
decomposition kinetics of polymer were investigated by means of thermogravimetric analysis
22
in dynamic nitrogen atmosphere at different heating rates. The apparent activation energies
23
for thermal decomposition of the PMIPTEG were calculated using the Kissinger, Kim-Park,
24
Tang, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Friedman methods
25
and were found to be 100.15, 104.40, 102.0, 102.2, 103.2 and 99.6 kJ/mol, respectively. The
26
most likely process mechanism related to the thermal decomposition stage of PMIPTEG was
27
determined to be a Dn Deceleration type in terms of master plots results.
28
Keywords: Carbohydrate based polymer, chloralose, thermal analysis, decomposition kinetic,
29
methacrylate.
30
To whom all correspondence should be addressed.
31
Phone: +90 286 218 00 18 Fax: +90 286 218 05 33 E-mail: [email protected]
M
an
Polymer Synthesis and Analysis Lab., Department of Chemistry, Faculty of Arts and Sciences,
Ac ce p
te
d
3-O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-trichloroethylidene-α-D-
1
Page 1 of 27
32
1. Introduction In recent times, the basic raw materials used for polymers have expanded by including
34
sugars such as glucose, galactose, fructose, and sucrose. Chemically connecting sugar moieties
35
onto synthetic polymers is an individual method of functionalization of synthetic polymers.
36
Through this method, the polymer is not only functionalized, but other desirable properties
37
such as biodegradability can be achieved. This latter is a hotly-debated and much researched
38
topic nowadays [1]. Sugar-carrying polymers, generally known as poly(vinylsaccharide)s, have
39
been investigated intensively by researchers for a variety of applications, particularly in the
40
biomedical field. Some potential applications for these types of polymers are drug delivery
41
systems, dental medicine, bioimplants, contact lenses and tissue engineering [2]. Furthermore,
42
they
43
poly(vinylsaccharide)s have a synthetic C–C backbone with pendant carbohydrate molecules.
44
Since sugars are a good source of food for micro-organisms, many poly(vinylsaccharide)s have
45
the potential to be utilized as biodegradable polymers. Syntheses of vinyl monomers prepared
46
from isopropylidene and other protected sugars were comprehensively reviewed by Wulff [3]
47
and Varma [2] in their classical reviews. These sugar monomers are usually synthesized via the
48
reaction of corresponding acid chloride [4] or anhydride [5] with sugars in the presence of an
49
organic amine such as pyridine. Sugar-carrying methacrylates such as 3-O-methacroyl-1,2:5,6-
50
di-O-isopropylidene-α-D-glucofuranose [6], 6-O-methacroyl-1,2:3,4-di-O-isopropylidene-α-D-
51
galactofuranose
52
monomethacroyl sucrose [8] have already been reported. Homopolymerization or
53
copolymerization of these sugar methacrylate monomers was performed via both atom transfer
54
radical
55
azobisisobutyronitrile (AIBN) [4]. Poly(methacryoyl glucose) could be dyed by a water-soluble
56
dyestuff [1]. Owing to their low price, sugars such as sucrose and D-galactose play an
the
advantage
of
being
potentially
biodegradable.
Structurally,
the
Ac ce p
te
d
M
have
an
us
cr
ip t
33
[5],
polymerization
1-O-acroyl-2,3:5,6-di-O-isopropylidene-α-D-mannofuranose
(ATRP)
[9]
and
free
radical
methods
such
as
a
[7],
2,2′-
2
Page 2 of 27
57
important role for this purpose. In this context, we decided to prepare a new isopropylidene
58
protected
59
trichloroethylidene-α-D-galactofuranose.
60
trichloroethylidene
61
Monosaccharides mostly react in their furanose forms with chloral to give trichloroethylidene
62
acetals. Thus, 1,2-O-trichloroethylidene acetals of D-glucofuranose [11], D-galactofuranose
63
[10],
64
Trichloroethylidene-α-D-glucofuranose is a commercially available compound, also known as
65
α-chloralose, which is used as an anesthetic for animals [14]. Additionally, trichloroethylidene
66
acetals are suitable protecting groups for the synthesis of some biologically important
67
compounds [15] and antimicrobial chloralose derivatives are also known [16]. On the other
68
hand, thermogravimetric analyses of polymer samples have been extensively utilized for
69
determining decomposition characteristics and also for determining kinetic parameters.
70
However, non-isothermal thermogravimetry has been widely used to investigate the thermal
71
stability characteristic of various substances, including the polymer pyrolyses. Several papers
72
have shown that nonisothermal thermogravimetric analysis is a powerful tool to characterize
73
the thermal decomposition of polymers [17-19]. Doğan et al. investigated the thermal behavior,
74
kinetic and thermodynamic parameters of many polyphenol-based polymeric materials using
75
different thermogravimetric methods [20]. They reported for first time that the thermal
76
decomposition processes of so-called polymeric materials follow a Diffusion model [21, 22].
77
Budrugeac and Segal [23] studied the decomposition mechanism and kinetic parameters of an
78
epoxy system using isoconversional and multivariate non-linear regression methods. Briefly,
79
the thermal decomposition kinetics for many polymer species has been studied in the literature.
80
However, the thermal decomposition kinetics and process mechanisms of a carbohydrate-based
81
polymer are presented for the first time in this study. Accordingly, a new sugar derivative of the
vinyl
saccharide,
of
This
D-galactose,
compound also
known
was
obtained
“galactochloralose”
from [10].
[12]
and
D-mannofuranose
[13]
are
known.
1,2-O-(R)-
Ac ce p
te
d
M
an
us
D-arabinofuranose
cr
ip t
acetal
3-O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-
3
Page 3 of 27
methacrylate polymer was synthesized from 3-O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-
83
trichloroethylidene-α-D-galactofuranose by free radical polymerization with AIBN in 1,4-
84
dioxane. The structures of the resulting compounds were confirmed by UV-vis, FT-IR, 1H-
85
NMR and 13C-NMR. Further characterization processes were performed by thermogravimetry-
86
differential thermal analysis (TG-DTA), gel permeation chromatography (GPC), scanning
87
electron microscope (SEM) and solubility testing. Also, the kinetics of the thermal
88
decomposition of a carbohydrate-based sugar polymer was investigated with the TG technique.
89
The kinetic parameters related to the decomposition kinetics of a carbohydrate-based sugar
90
polymer were calculated using the Kissinger [24], Kim-Park [25], Tang [26], Flynn-Wall-
91
Ozawa [27, 28] (FWO), Kissinger-Akahira-Sunose [29] (KAS) and Friedman [30] (FR)
92
methods under an N2 dynamic atmosphere and at different heating rates of 5, 10, 15 and 20
93
°C/min. The mechanism function and pre-exponential factor were determined by master plots
94
curves.
95
2.Experimental
te
d
M
an
us
cr
ip t
82
TLC and column chromatography were performed on pre-coated aluminium plates
97
(Merck 5554) and silica gel G-60 (Merck 7734), respectively. Methacrylic anhydride and all
98
the solvents were commercially obtained as chemical pure reagents and used without further
99
purification.
100 101
Ac ce p
96
2.1. Synthesis of MIPTEG
5.0 mL of methacrylic anhydride was added to a solution of 5,6-O-isopropylidene-1,2-O-
102
(S)-trichloroethylidene-α-D-galactofuranose (5.0 g, 14.3 mmol) [10] in 30 mL of dry pyridine.
103
The mixture was stirred at room temperature and after 24 h. TLC (Toluen:MeOH, 8:2) showed
104
that no original starting compound remained. The solvent was evaporated under reduced
105
pressure at 35 °C and the residue was extracted with CH2Cl2 (3×50 mL). The combined
106
extracts were dried with anhydrous sodium sulfate and evaporated under reduced pressure. The 4
Page 4 of 27
syrupy residue was purified using column chromatography on silica gel eluted with CH2Cl2:
108
MeOH (50:1) and 5.44 g of a monomeric syrupy compound were obtained, yield: 91%. The
109
resulting monomer was characterized using spectroscopic analyses such as UV-vis, FT-IR, 1H-
110
NMR and 13C-NMR techniques. The synthetic strategy is outlined in Scheme 1.
ip t
107
111
UV-vis (λmax) (DMSO): 278 nm, FTIR (ATR): 2982-2897 ν (C-H), 1711 ν (C=O), 1610 ν
113
(C=C), 1153 ν (COC), 798 cm-1 ν (CH-Cl). 1H-NMR (CDCl3): δ 6.34 (d, 1H, J1,2=4.4 Hz, H-1),
114
6.15 (bs, 1H, CH2=C-CH3), 5.74 (s, 1H, CHCCl3), 5.67 (dt, 1H, CH2=C-CH3, JCH2=1.6 Hz,
115
JCH2,CH3=1.6 Hz), 5.16 (d, 1H, J3,4=1.6 Hz, J2,3=0.0 Hz, H-3), 5.09 (d, 1H, H-2), 4,35 (dd, 1H,
116
H-5), 4.14 (m, 1H, H-4), 4.09 (dd, 1H, J6a,6b=8.4 Hz, J5,6a=6.8 Hz, H-6a), 3.96 (dd, 1H,
117
J5,6b=7.2 Hz, H-6b), 1.96 (bs, 3H, CH2=C-CH3), 1.49 and 1.42 (s, 6H, (CH3)2C).
118
(CDCl3): δ 166.4 (C=O), 135.4 (CH2=C-CH3), 127.6 (CH2=C-CH3), 110.6 and 109.8 (CHCCl3
119
and C-1), 107.8 ((CH3)2C), 99.5 (CHCCl3), 87.4, 87.0, 78.6, 75.8, 72.4, (C-2, C-3, C-4, C-5,
120
C-6), 26.6 and 25.7 ((CH3)2C), 18.3 (CH2=C-CH3). Anal. Calcd. for MIPTEG: C, 57.50; H,
121
6.70. Found: C, 58.07; H, 6.12.
d
O
123
C-NMR
te
Ac ce p O
122
13
M
an
us
cr
112
O OH
+
O
O O
O
O
dry pyridine, 24h
O
O
CCl3
O
O
H
O O
CCl3
O H
Scheme 1. Synthetic method for the preparation of MIPTEG
124 125
2.2. Synthesis of PMIPTEG
126
PMIPTEG was obtained through a conventional free radical polymerization using 2,2′-
127
azobisisobutyronitrile (AIBN) (2%, based on the total weight of the monomer) as initiator in 5 5
Page 5 of 27
128
mL of 1,4-dioxane at 70 °C for 24 h with 92% conversion in an all glass Schlenk flask. The
129
resulting polymer was precipitated in ethanol and dried under vacuum at 40 °C for 24 h and
130
characterized using various spectroscopic methods (yield: 95%).
131
presented in Scheme 2.
ip t
The synthetic route is
UV-vis (λmax) (DMSO): 253, 375 nm, FTIR (ATR): 2986 ν (C-H), 1730 ν (C=O), 1153
133
ν (COC), 809 cm-1 ν (CH-Cl); 1H-NMR (DMSO-d6): δ 6.43 (H-1), 5.52 (CH-CCl3), 4.82 (H-
134
3), 4.52 (H-2), 4.01 (H-5 ), 3.81 (H-4 and H-6a ), 3.67 (H-6b), 1.28-0.60 (H-8, H-9, H-10 and
135
H-11); 13C-NMR (DMSO-d6): δ 179.7 (C=O), 111.7 (CHCCl3), 109.2 (C-1), 107.0 (C-9), 99.3
136
(CHCCl3), 86.2, 78.8, 74.1, 65.3 (C-2, C-3, C-4, C-5 and C-6), 47.8, 30.4, 26.4 , 20.1, 19.3 (C-
137
10, C-11, C-13, C-14 and C15). Calcd. for PMIPTEG: C, 57.26; H, 7.00. Found: C, 57.97; H,
138
7.32.
M
an
us
cr
132
O
139 140 141 142 143
70 o C, 24h
O
O
CCl3
O
O
Ac ce p
O
O
AIBN, dioxane
O
n O
te
O
CH2 C
d
O
CH3
O
O
CCl3
O
H
H
Scheme 2. Synthetic route for PMIPTEG
2.3. Characterization Techniques Ultraviolet-visible (UV-vis) spectra were measured with the Perkin-Elmer Lambda 25.
144
The spectral analyses of MIPTEG and PMIPTEG were recorded using a Mattson FT-IR-1000
145
spectrometer with KBr discs (4000-400 cm-1). 1H- (400 MHz) and
146
spectra of PMIPTEG were recorded on a Varian AS 400 instrument, and NMR spectra of
147
MIPTEG were recorded on the Varian XL200. TMS was used as an internal standard.
13
C-NMR (100 MHz)
6
Page 6 of 27
Elemental analysis was carried out with a Carlo Erba 1106. The number-average molecular
149
weight (Mn), weight-average molecular weight (Mw) and polydispersity index (PDI) of
150
PMIPTEG were determined by using a Huwlett Packard GPC-SEC system calibrated with
151
polystyrene standards at 30 °C using THF as an eluent at a flow rate of 1.0 mL/min. The
152
TG/DTA and DSC curves were obtained using a Shimadzu TGA-50 thermobalance and a
153
Shimadzu differential scanning calorimeter (DSC) DSC-50 model, respectively. The TG
154
measurements were performed by using a dynamic nitrogen furnace atmosphere at a flow rate
155
of 60 ml/min up to 1273 K. The heating rates were 5, 10, 15 and 20 K/min and sample sizes
156
ranged in mass from 8 mg to 10 mg. Platinum was used for the sample container. DSC
157
experiments were performed using aluminium pans with 5 mg samples in the temperature range
158
of 20-450 °C at a heating rate of 10 K/min. All experiments were performed twice for
159
repeatability, and the results showed good reproducibility with small variations in the kinetic
160
parameters. α-Al2O3 was used as a reference material. The surface morphology of PMIPTEG
161
was evaluated via scanning electron microscopy (SEM), using a Philips XL 30S FEG
162
apparatus.
164 165
cr
us
an
M
d
te
1. Results and Discussion
Ac ce p
163
ip t
148
3.1. Characterization studies As shown in Scheme 1, 5,6-O-isopropylidene-1,2-O-(S)-trichloroethylidene-α-D-
166
galactofuranose reacted with methacrylic anhydride in pyridine at room temperature to give 3-
167
O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-trichloroethylidene-α-D-galactofuranose
168
(MIPTEG). Then PMIPTEG was obtained through the homopolymerization of MIPTEG with
169
2,2’-azobisisobutyronitrile (AIBN) as a radicalic initiator in a 1,4-dioxane solution at 70 °C.
170
PMIPTEG was isolated as a white powder in high yield (95%). MIPTEG and PMIPTEG were
171
structurally characterized by using different spectral techniques: FT-IR, 1H- and
172
Further characterization of PMIPTEG was carried out by GPC, SEM, TG/DTG-DTA and DSC 7
13
C-NMR.
Page 7 of 27
analyses. PMIPTEG was soluble in common organic solvents, such as dimethylsulfoxide
174
(DMSO), dimethylformamide (DMF), dimethylacetamide (DMA), N-methyl-2-pyrrolidone
175
(NMP). However, it was insoluble in chloroform, dichloromethane, hexane, toluene, and
176
methanol. Infrared spectroscopy is widely used for analysis of poly(vinyl saccharide)s. In
177
almost all cases, the disappearance of C=C bond is a means for deciding the completion of
178
polymerization of the vinyl sugars.
cr
ip t
173
Representative FT-IR spectra of MIPTEG and PMIPTEG are provided in Figure 1. In the
180
FT-IR spectrum of the glycomonomer and glycopolymer, the bands observed at approximately
181
1711 and 1730 cm-1 for both MIPTEG and PMIPTEG, respectively, are due to the
182
characteristic carbonyl vibrations of the methacrylate groups. The intensity of the vinyl
183
linkage observed at 1630 cm-1 for PMIPTEG drastically decreased and shifted to a longer wave
184
number after polymerization, which was attributed to the absence of conjugation between
185
C=O and C=CH2 linkages. On the other hand, the extended spectrum of polymers compared
186
to monomers is also common for sugar-based polymers bearing vinyl groups and suggests the
187
presence of the polymerized structure of MIPTEG with broad chain dispersity. The band at
188
1630 cm-1 which is the most important and characteristic absorption for vinyl structure is also
189
observed for monomer. However in the case of polymers, this band disappeared.
191
an
M
d
te
Ac ce p
190
us
179
Insert Figure 1 here
The 1H-NMR peak performance of the glycomonomer (MIPTEG) is presented in Figure
192
2, and shows the specific double bond protons at 5.67-6.15 ppm (H-10) and the methyl group at
193
1.96 ppm (H-11) from the methacroyl moiety. The protons of the sugar moiety of MIPTEG
194
were observed at 6.34 (H-1), 5.74 (H-7), 5.16 (H-3), 5.09 (H-2), 4.35 (H-5), 4.14 (H-4), 4.09
195
and 3.96 (H-6), 1.49 and 1.42 ppm (H-8 and H-9) in the spectrum (in Figure 2a). However,
196
disappearance of characteristic vinyl peaks (H-10) for the methacroyl moiety of the monomer
197
can be observed in the 1H-NMR spectrum of PMIPTEG (Figure 2b) 8
Page 8 of 27
198 199
Insert Figure 2 here Also, the
13
C-NMR peak performance of MIPTEG and PMIPTEG were described in 13
Figure 3 and similarly, the expected indications were observed. In the
C-NMR spectrum of
201
MIPTEG (Figure 3a), the peaks at 127.7 and 135.4 ppm (C-13 and C-14) were assigned the
202
vinyl carbon and a carbonyl peak was observed at 166.4 ppm. In the case of the polymer, it
203
was observed that vinyl protons disappeared after the polymerization process and alkyl group
204
peaks (C-13, C-14) of glycopolymer appeared in the range from 47.6 to 22.1 ppm. Also, vinyl
205
carbons of PMIPTEG shifted to a higher field as a result of increased electron intensity.
206
NMR peaks of the sugar moiety for both the polymer and the monomer were observed as
207
predicted from C-1 to C-11 in Figure 3.
208
13
C
an
us
cr
ip t
200
M
Insert Figure 3 here
The uncleavage of the isopropylidene groups MIPTEG and PMIPTEG are understood
210
from NMR spectra. IR and NMR analyses clearly indicated that MIPTEG was successfully
211
obtained and that PMIPTEG was polymerized by free radical reaction. The number average
212
molecular weight (Mn), mass average molecular weight (Mw) and polydispersity index (PDI)
213
of PMIPTEG were found to be 9300 g/mol, 13400 g/mol and 1.44, respectively. The thermal
214
properties of MIPTEG and PMIPTEG were studied using the TG/DTG and DTA techniques
215
from ambient temperature to 1000o C under nitrogen atmosphere. Typical TG/DTG and DTA
216
curves for MIPTEG and PMIPTEG in N2 were presented in Figure 4. The initial and final
217
temperatures and total mass losses in the thermal decomposition of compounds were
218
determined, together with temperatures of the highest rate of decomposition (DTGmax).
219
Ac ce p
te
d
209
Insert Figure 4 here
220
MIPTEG and PMIPTEG exhibited the stage one decomposition process. From the TG
221
curve for MIPTEG, it appeared that the sample decomposed with a mass loss of 96.3 % in the
222
temperature range 199-435o C. However, endothermic thermal effects at 121 and 311 oC in the 9
Page 9 of 27
DTA profile correspond to the solvent peak (absorbed in syrup) and thermal decomposition
224
of MIPTEG, respectively. PMIPTEG is thermally stable up to 218o C and decomposed in the
225
temperature range from 218o C to 581o C with a 92.30 % weight loss. The temperature related
226
to the maximum decomposition rate for MIPTEG was determined to be 288o C in the DTG
227
curve. This temperature for PMIPTEG is 303o C. As expected, these results showed that
228
PMIPTEG is more stable than MIPTEG. The differential scanning calorimetry (DSC) was used
229
to investigate the thermal properties of PMIPTEG. The DSC curve of PMIPTEG exhibited an
230
endothermic peak at 74o C and an exothermic peak at 317o C. These peaks in the DSC curve
231
were attributed to the glass transition temperature and the thermal decomposition of PMIPTEG,
232
respectively. The morphological properties of the resulting polymer were investigated by
233
means of SEM analysis. SEM photographs of powdered PMIPTEG are given in Figure 5. The
234
sequence bead structures on the main chain in Figure 5 were observed for the powdered
235
PMIPTEG samples. In addition, as shown in the SEM image of the selected area, PMIPTEG
236
had a linear backbone structure. Also, the linear polymer chains were very condensed,
237
unhomogeneous and did not exhibit a well-ordered structure or shape. They consisted of long
238
and thin channels. The average particle diameter of randomly oriented ellipsoids is lower than
239
approximately 1 μm.
241
cr
us
an
M
d
te
Ac ce p
240
ip t
223
Insert Figure 5 here
On the other hand, isoconversional methods such as FWO, Tang, KAS, FR, Kim-Park
242
and Kissinger were used to investigate the kinetic parameters (activation energy, E, frequency
243
factor, A) related to the solid state thermal decomposition of PMIPTEG. Kinetic analysis of
244
PMIPTEG was investigated using the thermogramivetry technique with samples of 8-10 mg at
245
heating rates of 5, 10, 15 and 20 °C/min under a nitrogen atmosphere (60 ml/min). A typical
246
dynamic TG/DTG-DTA curve for PMIPTEG at a heating rate of 10 °C/min in N2 is represented
247
in Figure 4b.
Additionally, the solid state degradation mechanism of PMIPTEG was 10
Page 10 of 27
determined by master plots of TG/DTG curves under N2. All of the TG/DTG-DTA curves
249
which were obtained at several heating rates for PMIPTEG showed that the thermal
250
decomposition took place mainly in one stage. However, TG-curves are characteristically very
251
similar to each other. In this work, the Kissinger and Kim-Park procedures are the primary
252
thermogravimetric methods. TG data of PMIPTEG were initially analyzed with the Kissinger
253
procedures as it is independent of the heating rate and any thermal decomposition mechanisms.
254
This method uses the maximum decomposition temperature (Tmax) at which the rate of mass
255
loss is the highest. This method may briefly be expressed by the following equation.
β
Ea ⎫ ⎧ AR ) = ⎨ln + ln [ n(1 − α max ) n −1 ]⎬ − ⎭ RTmax ⎩ Ea
us
cr
ip t
248
ln(
257
The activation energy can be calculated using Eq (1) without knowing the solid state
258
2 degradation reaction mechanism. The slope of line drawn between ln (β/ Tmax ) versus
259
2 ) versus 1000/Tmax gives the activation energy. The slope of the line drawn between ln (β/ Tmax
260
1000/Tmax gives the activation energy. On the other hand, the Kim-Park method assumes that
261
maximum degradation fraction, αm is independent of the kinetic triplet: the activation energy,
262
the pre-exponential factor and the decomposition mechanisms. The activation energy can be
263
obtained by the slope of the plot of lnβ versus 1/Tm by using Eq (2).
265
(1)
M
d
te
Ac ce p
264
T
2 max
an
256
E n ⎤ E ⎡ ln β = ln A + ( ) + ln ⎢1 − n + − 5.3305 − 1.0516( ) ⎥ R 0.944 ⎦ RTmax ⎣
(2)
The activation energies related to the thermal decomposition stage of PMIPTEG obtained
266
by using Kissinger and Kim-Park methods in N2 were determined to be 100.1 and 104.4
267
kJ/mol, respectively.
268
The other methods used for calculating the kinetic parameter of PMIPTEG were those of
269
Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Tang and Friedman based on multiple heating
270
rates. The conventional integral procedures such as FWO, KAS and Tang were proposed by 11
Page 11 of 27
assuming invariant activation energies and in the case of variable activation energies they
272
might yield incorrect values [31]. In those cases, advanced integral isoconversional [32] or
273
differential methods are preferred over integral isoconversional methods. Thus, in the present
274
case, differential isoconversional methods (Friedman, Kissinger, Kim-Park), in addition to
275
integral isoconversional methods (FWO, KAS and Tang) were used for solid state
276
decomposition kinetic studies. The Flynn-Wall-Ozawa method is a conventional integral
277
method and the activation energy of a solid state decomposition process without knowledge of
278
the reaction order can determined by this method. In the technique the A, f(α) and E are
279
independent of T while A and E are independent of α. So this method provides the following
280
expression in logarithmic form for thermal decomposition kinetic studies based on the basic
281
Arrhenius equation:
M
an
us
cr
ip t
271
log β =log (AE/R)- log g(α)-2.315-0.4567 E/RT
283
According to the Eq (3), constant mass loss lines were determined by measuring the
284
temperature at a given mass percent for each rate. Figure 6 presents the Arrhenius type plots of
285
dynamic TG runs for mass ranging from α=0.05 to 0.95 in N2. The apparent activation energy
286
of PMIPTEG can be obtained from a plot of log β against 1000/T for a constant degree of
287
conversion since the slope of such a line is given by -0.456E/RT.
289
te
Ac ce p
288
(3)
d
282
Insert Figure 6 here
The activation energies and correlation coefficient on the overall mass loss from 5 to 95
290
mass % determined with the FWO method in N2 are summarized in Table 1 and the average
291
value was found to be 103.2 kJ/mol over the range of α given. However, table 1 indicated that
292
the correlation coefficient with the Arrhenius type plots is acceptable and always superior to
293
0.98202
294
Insert Table 1 here
12
Page 12 of 27
On the other hand, the Tang and KAS methods are an integral isoconversional method
296
similar to the FWO. The Tang method allows the activation energy to be determined by
297
plotting ln (β/T2) against 1/T for a fixed degree of conversion at the different heating rates β.
298
The slope of such a line obtained by the KAS method is given by -0.456E/RT (Eq (4)).
299
However, to calculate the values of the activation energy from plots of ln ⎛⎜
300
over a wide range of conversions, Eq (5) proposed by KAS can also be used. The activation
301
energy E can be obtained from the slope -1.001450 E/R of the regression line. The kinetic
302
procedures of the Tang and KAS methods are given below, respectively.
ip t
295
1/T
us
cr
β ⎞ ⎟ against ⎝ T 1.894661 ⎠
⎛ AE ⎞ 1.001450 E ⎛ β ⎞ ⎟⎟ + 3.635041 −1.894661 ln E − ln⎜ 1.894661 ⎟ = ln⎜⎜ RT ⎝T ⎠ ⎝ R g (α ) ⎠
(4)
304
⎡ AR ⎤ E ⎡ β ⎤ ln ⎢ 2 ⎥ = ln ⎢ ⎥− ⎣T ⎦ ⎣ E g (α) ⎦ RT
(5)
305
In this study the equation α = 0.05-0.95 was chosen to determine the E values of
306
PMIPTEG. The activation energy of PMIPTEG obtained with the Tang and KAS methods were
307
found to be 102.0 and 102.2 kJ/mol, respectively, over the range of 0.05
S0144-8617(13)00957-0 http://dx.doi.org/doi:10.1016/j.carbpol.2013.09.065 CARP 8154
To appear in: Received date: Revised date: Accepted date:
27-7-2013 28-8-2013 18-9-2013
Please cite this article as: K¨ok, G., Ay, K., Ay, E., Do˘gan, F., & Kaya, ˙I., Synthesis, characterization and non-isothermal decomposition kinetic of a new galactochloralose based polymer, Carbohydrate Polymers (2013), http://dx.doi.org/10.1016/j.carbpol.2013.09.065 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
Synthesis, characterization and non-isothermal decomposition kinetic of a
2
new galactochloralose based polymer
3 Gökhan Köka, Kadir Ayb, Emriye Ayb, Fatih Doğanc and İsmet Kayad*
4 5
a
6
b
7
Manisa, Turkey.
8
c
ip t
cr
Department of Chemistry, Faculty of Arts and Sciences, Celal Bayar University, 45140,
Secondary Science and Mathematics Education, Faculty of Education, Çanakkale Onsekiz
Mart University, 17100, Çanakkale, Turkey.
us
9
Department of Chemistry, Faculty Sciences, Ege University, 35100, İzmir, Turkey.
10
d
11 12
Çanakkale Onsekiz Mart University, 17020, Çanakkale, Turkey.
13
Abstract
14
A glycopolymer, poly(3-O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-trichloroethylidene-
15
α-D-galactofuranose) (PMIPTEG) was synthesized from the sugar-carrying methacrylate
16
monomer,
17
galactofuranose (MIPTEG) via conventional free radical polymerization with AIBN in 1,4-
18
dioxane. The structures of glycomonomer and their polymers were confirmed by UV-Vis,
19
FT-IR, 1H-NMR, 13C-NMR, GPC, TG/DTG-DTA, DSC, and SEM techniques. SEM images
20
showed that PMIPTEG had a straight-chain length structure. On the other hand, the thermal
21
decomposition kinetics of polymer were investigated by means of thermogravimetric analysis
22
in dynamic nitrogen atmosphere at different heating rates. The apparent activation energies
23
for thermal decomposition of the PMIPTEG were calculated using the Kissinger, Kim-Park,
24
Tang, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Friedman methods
25
and were found to be 100.15, 104.40, 102.0, 102.2, 103.2 and 99.6 kJ/mol, respectively. The
26
most likely process mechanism related to the thermal decomposition stage of PMIPTEG was
27
determined to be a Dn Deceleration type in terms of master plots results.
28
Keywords: Carbohydrate based polymer, chloralose, thermal analysis, decomposition kinetic,
29
methacrylate.
30
To whom all correspondence should be addressed.
31
Phone: +90 286 218 00 18 Fax: +90 286 218 05 33 E-mail: [email protected]
M
an
Polymer Synthesis and Analysis Lab., Department of Chemistry, Faculty of Arts and Sciences,
Ac ce p
te
d
3-O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-trichloroethylidene-α-D-
1
Page 1 of 27
32
1. Introduction In recent times, the basic raw materials used for polymers have expanded by including
34
sugars such as glucose, galactose, fructose, and sucrose. Chemically connecting sugar moieties
35
onto synthetic polymers is an individual method of functionalization of synthetic polymers.
36
Through this method, the polymer is not only functionalized, but other desirable properties
37
such as biodegradability can be achieved. This latter is a hotly-debated and much researched
38
topic nowadays [1]. Sugar-carrying polymers, generally known as poly(vinylsaccharide)s, have
39
been investigated intensively by researchers for a variety of applications, particularly in the
40
biomedical field. Some potential applications for these types of polymers are drug delivery
41
systems, dental medicine, bioimplants, contact lenses and tissue engineering [2]. Furthermore,
42
they
43
poly(vinylsaccharide)s have a synthetic C–C backbone with pendant carbohydrate molecules.
44
Since sugars are a good source of food for micro-organisms, many poly(vinylsaccharide)s have
45
the potential to be utilized as biodegradable polymers. Syntheses of vinyl monomers prepared
46
from isopropylidene and other protected sugars were comprehensively reviewed by Wulff [3]
47
and Varma [2] in their classical reviews. These sugar monomers are usually synthesized via the
48
reaction of corresponding acid chloride [4] or anhydride [5] with sugars in the presence of an
49
organic amine such as pyridine. Sugar-carrying methacrylates such as 3-O-methacroyl-1,2:5,6-
50
di-O-isopropylidene-α-D-glucofuranose [6], 6-O-methacroyl-1,2:3,4-di-O-isopropylidene-α-D-
51
galactofuranose
52
monomethacroyl sucrose [8] have already been reported. Homopolymerization or
53
copolymerization of these sugar methacrylate monomers was performed via both atom transfer
54
radical
55
azobisisobutyronitrile (AIBN) [4]. Poly(methacryoyl glucose) could be dyed by a water-soluble
56
dyestuff [1]. Owing to their low price, sugars such as sucrose and D-galactose play an
the
advantage
of
being
potentially
biodegradable.
Structurally,
the
Ac ce p
te
d
M
have
an
us
cr
ip t
33
[5],
polymerization
1-O-acroyl-2,3:5,6-di-O-isopropylidene-α-D-mannofuranose
(ATRP)
[9]
and
free
radical
methods
such
as
a
[7],
2,2′-
2
Page 2 of 27
57
important role for this purpose. In this context, we decided to prepare a new isopropylidene
58
protected
59
trichloroethylidene-α-D-galactofuranose.
60
trichloroethylidene
61
Monosaccharides mostly react in their furanose forms with chloral to give trichloroethylidene
62
acetals. Thus, 1,2-O-trichloroethylidene acetals of D-glucofuranose [11], D-galactofuranose
63
[10],
64
Trichloroethylidene-α-D-glucofuranose is a commercially available compound, also known as
65
α-chloralose, which is used as an anesthetic for animals [14]. Additionally, trichloroethylidene
66
acetals are suitable protecting groups for the synthesis of some biologically important
67
compounds [15] and antimicrobial chloralose derivatives are also known [16]. On the other
68
hand, thermogravimetric analyses of polymer samples have been extensively utilized for
69
determining decomposition characteristics and also for determining kinetic parameters.
70
However, non-isothermal thermogravimetry has been widely used to investigate the thermal
71
stability characteristic of various substances, including the polymer pyrolyses. Several papers
72
have shown that nonisothermal thermogravimetric analysis is a powerful tool to characterize
73
the thermal decomposition of polymers [17-19]. Doğan et al. investigated the thermal behavior,
74
kinetic and thermodynamic parameters of many polyphenol-based polymeric materials using
75
different thermogravimetric methods [20]. They reported for first time that the thermal
76
decomposition processes of so-called polymeric materials follow a Diffusion model [21, 22].
77
Budrugeac and Segal [23] studied the decomposition mechanism and kinetic parameters of an
78
epoxy system using isoconversional and multivariate non-linear regression methods. Briefly,
79
the thermal decomposition kinetics for many polymer species has been studied in the literature.
80
However, the thermal decomposition kinetics and process mechanisms of a carbohydrate-based
81
polymer are presented for the first time in this study. Accordingly, a new sugar derivative of the
vinyl
saccharide,
of
This
D-galactose,
compound also
known
was
obtained
“galactochloralose”
from [10].
[12]
and
D-mannofuranose
[13]
are
known.
1,2-O-(R)-
Ac ce p
te
d
M
an
us
D-arabinofuranose
cr
ip t
acetal
3-O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-
3
Page 3 of 27
methacrylate polymer was synthesized from 3-O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-
83
trichloroethylidene-α-D-galactofuranose by free radical polymerization with AIBN in 1,4-
84
dioxane. The structures of the resulting compounds were confirmed by UV-vis, FT-IR, 1H-
85
NMR and 13C-NMR. Further characterization processes were performed by thermogravimetry-
86
differential thermal analysis (TG-DTA), gel permeation chromatography (GPC), scanning
87
electron microscope (SEM) and solubility testing. Also, the kinetics of the thermal
88
decomposition of a carbohydrate-based sugar polymer was investigated with the TG technique.
89
The kinetic parameters related to the decomposition kinetics of a carbohydrate-based sugar
90
polymer were calculated using the Kissinger [24], Kim-Park [25], Tang [26], Flynn-Wall-
91
Ozawa [27, 28] (FWO), Kissinger-Akahira-Sunose [29] (KAS) and Friedman [30] (FR)
92
methods under an N2 dynamic atmosphere and at different heating rates of 5, 10, 15 and 20
93
°C/min. The mechanism function and pre-exponential factor were determined by master plots
94
curves.
95
2.Experimental
te
d
M
an
us
cr
ip t
82
TLC and column chromatography were performed on pre-coated aluminium plates
97
(Merck 5554) and silica gel G-60 (Merck 7734), respectively. Methacrylic anhydride and all
98
the solvents were commercially obtained as chemical pure reagents and used without further
99
purification.
100 101
Ac ce p
96
2.1. Synthesis of MIPTEG
5.0 mL of methacrylic anhydride was added to a solution of 5,6-O-isopropylidene-1,2-O-
102
(S)-trichloroethylidene-α-D-galactofuranose (5.0 g, 14.3 mmol) [10] in 30 mL of dry pyridine.
103
The mixture was stirred at room temperature and after 24 h. TLC (Toluen:MeOH, 8:2) showed
104
that no original starting compound remained. The solvent was evaporated under reduced
105
pressure at 35 °C and the residue was extracted with CH2Cl2 (3×50 mL). The combined
106
extracts were dried with anhydrous sodium sulfate and evaporated under reduced pressure. The 4
Page 4 of 27
syrupy residue was purified using column chromatography on silica gel eluted with CH2Cl2:
108
MeOH (50:1) and 5.44 g of a monomeric syrupy compound were obtained, yield: 91%. The
109
resulting monomer was characterized using spectroscopic analyses such as UV-vis, FT-IR, 1H-
110
NMR and 13C-NMR techniques. The synthetic strategy is outlined in Scheme 1.
ip t
107
111
UV-vis (λmax) (DMSO): 278 nm, FTIR (ATR): 2982-2897 ν (C-H), 1711 ν (C=O), 1610 ν
113
(C=C), 1153 ν (COC), 798 cm-1 ν (CH-Cl). 1H-NMR (CDCl3): δ 6.34 (d, 1H, J1,2=4.4 Hz, H-1),
114
6.15 (bs, 1H, CH2=C-CH3), 5.74 (s, 1H, CHCCl3), 5.67 (dt, 1H, CH2=C-CH3, JCH2=1.6 Hz,
115
JCH2,CH3=1.6 Hz), 5.16 (d, 1H, J3,4=1.6 Hz, J2,3=0.0 Hz, H-3), 5.09 (d, 1H, H-2), 4,35 (dd, 1H,
116
H-5), 4.14 (m, 1H, H-4), 4.09 (dd, 1H, J6a,6b=8.4 Hz, J5,6a=6.8 Hz, H-6a), 3.96 (dd, 1H,
117
J5,6b=7.2 Hz, H-6b), 1.96 (bs, 3H, CH2=C-CH3), 1.49 and 1.42 (s, 6H, (CH3)2C).
118
(CDCl3): δ 166.4 (C=O), 135.4 (CH2=C-CH3), 127.6 (CH2=C-CH3), 110.6 and 109.8 (CHCCl3
119
and C-1), 107.8 ((CH3)2C), 99.5 (CHCCl3), 87.4, 87.0, 78.6, 75.8, 72.4, (C-2, C-3, C-4, C-5,
120
C-6), 26.6 and 25.7 ((CH3)2C), 18.3 (CH2=C-CH3). Anal. Calcd. for MIPTEG: C, 57.50; H,
121
6.70. Found: C, 58.07; H, 6.12.
d
O
123
C-NMR
te
Ac ce p O
122
13
M
an
us
cr
112
O OH
+
O
O O
O
O
dry pyridine, 24h
O
O
CCl3
O
O
H
O O
CCl3
O H
Scheme 1. Synthetic method for the preparation of MIPTEG
124 125
2.2. Synthesis of PMIPTEG
126
PMIPTEG was obtained through a conventional free radical polymerization using 2,2′-
127
azobisisobutyronitrile (AIBN) (2%, based on the total weight of the monomer) as initiator in 5 5
Page 5 of 27
128
mL of 1,4-dioxane at 70 °C for 24 h with 92% conversion in an all glass Schlenk flask. The
129
resulting polymer was precipitated in ethanol and dried under vacuum at 40 °C for 24 h and
130
characterized using various spectroscopic methods (yield: 95%).
131
presented in Scheme 2.
ip t
The synthetic route is
UV-vis (λmax) (DMSO): 253, 375 nm, FTIR (ATR): 2986 ν (C-H), 1730 ν (C=O), 1153
133
ν (COC), 809 cm-1 ν (CH-Cl); 1H-NMR (DMSO-d6): δ 6.43 (H-1), 5.52 (CH-CCl3), 4.82 (H-
134
3), 4.52 (H-2), 4.01 (H-5 ), 3.81 (H-4 and H-6a ), 3.67 (H-6b), 1.28-0.60 (H-8, H-9, H-10 and
135
H-11); 13C-NMR (DMSO-d6): δ 179.7 (C=O), 111.7 (CHCCl3), 109.2 (C-1), 107.0 (C-9), 99.3
136
(CHCCl3), 86.2, 78.8, 74.1, 65.3 (C-2, C-3, C-4, C-5 and C-6), 47.8, 30.4, 26.4 , 20.1, 19.3 (C-
137
10, C-11, C-13, C-14 and C15). Calcd. for PMIPTEG: C, 57.26; H, 7.00. Found: C, 57.97; H,
138
7.32.
M
an
us
cr
132
O
139 140 141 142 143
70 o C, 24h
O
O
CCl3
O
O
Ac ce p
O
O
AIBN, dioxane
O
n O
te
O
CH2 C
d
O
CH3
O
O
CCl3
O
H
H
Scheme 2. Synthetic route for PMIPTEG
2.3. Characterization Techniques Ultraviolet-visible (UV-vis) spectra were measured with the Perkin-Elmer Lambda 25.
144
The spectral analyses of MIPTEG and PMIPTEG were recorded using a Mattson FT-IR-1000
145
spectrometer with KBr discs (4000-400 cm-1). 1H- (400 MHz) and
146
spectra of PMIPTEG were recorded on a Varian AS 400 instrument, and NMR spectra of
147
MIPTEG were recorded on the Varian XL200. TMS was used as an internal standard.
13
C-NMR (100 MHz)
6
Page 6 of 27
Elemental analysis was carried out with a Carlo Erba 1106. The number-average molecular
149
weight (Mn), weight-average molecular weight (Mw) and polydispersity index (PDI) of
150
PMIPTEG were determined by using a Huwlett Packard GPC-SEC system calibrated with
151
polystyrene standards at 30 °C using THF as an eluent at a flow rate of 1.0 mL/min. The
152
TG/DTA and DSC curves were obtained using a Shimadzu TGA-50 thermobalance and a
153
Shimadzu differential scanning calorimeter (DSC) DSC-50 model, respectively. The TG
154
measurements were performed by using a dynamic nitrogen furnace atmosphere at a flow rate
155
of 60 ml/min up to 1273 K. The heating rates were 5, 10, 15 and 20 K/min and sample sizes
156
ranged in mass from 8 mg to 10 mg. Platinum was used for the sample container. DSC
157
experiments were performed using aluminium pans with 5 mg samples in the temperature range
158
of 20-450 °C at a heating rate of 10 K/min. All experiments were performed twice for
159
repeatability, and the results showed good reproducibility with small variations in the kinetic
160
parameters. α-Al2O3 was used as a reference material. The surface morphology of PMIPTEG
161
was evaluated via scanning electron microscopy (SEM), using a Philips XL 30S FEG
162
apparatus.
164 165
cr
us
an
M
d
te
1. Results and Discussion
Ac ce p
163
ip t
148
3.1. Characterization studies As shown in Scheme 1, 5,6-O-isopropylidene-1,2-O-(S)-trichloroethylidene-α-D-
166
galactofuranose reacted with methacrylic anhydride in pyridine at room temperature to give 3-
167
O-methacroyl-5,6-O-isopropylidene-1,2-O-(S)-trichloroethylidene-α-D-galactofuranose
168
(MIPTEG). Then PMIPTEG was obtained through the homopolymerization of MIPTEG with
169
2,2’-azobisisobutyronitrile (AIBN) as a radicalic initiator in a 1,4-dioxane solution at 70 °C.
170
PMIPTEG was isolated as a white powder in high yield (95%). MIPTEG and PMIPTEG were
171
structurally characterized by using different spectral techniques: FT-IR, 1H- and
172
Further characterization of PMIPTEG was carried out by GPC, SEM, TG/DTG-DTA and DSC 7
13
C-NMR.
Page 7 of 27
analyses. PMIPTEG was soluble in common organic solvents, such as dimethylsulfoxide
174
(DMSO), dimethylformamide (DMF), dimethylacetamide (DMA), N-methyl-2-pyrrolidone
175
(NMP). However, it was insoluble in chloroform, dichloromethane, hexane, toluene, and
176
methanol. Infrared spectroscopy is widely used for analysis of poly(vinyl saccharide)s. In
177
almost all cases, the disappearance of C=C bond is a means for deciding the completion of
178
polymerization of the vinyl sugars.
cr
ip t
173
Representative FT-IR spectra of MIPTEG and PMIPTEG are provided in Figure 1. In the
180
FT-IR spectrum of the glycomonomer and glycopolymer, the bands observed at approximately
181
1711 and 1730 cm-1 for both MIPTEG and PMIPTEG, respectively, are due to the
182
characteristic carbonyl vibrations of the methacrylate groups. The intensity of the vinyl
183
linkage observed at 1630 cm-1 for PMIPTEG drastically decreased and shifted to a longer wave
184
number after polymerization, which was attributed to the absence of conjugation between
185
C=O and C=CH2 linkages. On the other hand, the extended spectrum of polymers compared
186
to monomers is also common for sugar-based polymers bearing vinyl groups and suggests the
187
presence of the polymerized structure of MIPTEG with broad chain dispersity. The band at
188
1630 cm-1 which is the most important and characteristic absorption for vinyl structure is also
189
observed for monomer. However in the case of polymers, this band disappeared.
191
an
M
d
te
Ac ce p
190
us
179
Insert Figure 1 here
The 1H-NMR peak performance of the glycomonomer (MIPTEG) is presented in Figure
192
2, and shows the specific double bond protons at 5.67-6.15 ppm (H-10) and the methyl group at
193
1.96 ppm (H-11) from the methacroyl moiety. The protons of the sugar moiety of MIPTEG
194
were observed at 6.34 (H-1), 5.74 (H-7), 5.16 (H-3), 5.09 (H-2), 4.35 (H-5), 4.14 (H-4), 4.09
195
and 3.96 (H-6), 1.49 and 1.42 ppm (H-8 and H-9) in the spectrum (in Figure 2a). However,
196
disappearance of characteristic vinyl peaks (H-10) for the methacroyl moiety of the monomer
197
can be observed in the 1H-NMR spectrum of PMIPTEG (Figure 2b) 8
Page 8 of 27
198 199
Insert Figure 2 here Also, the
13
C-NMR peak performance of MIPTEG and PMIPTEG were described in 13
Figure 3 and similarly, the expected indications were observed. In the
C-NMR spectrum of
201
MIPTEG (Figure 3a), the peaks at 127.7 and 135.4 ppm (C-13 and C-14) were assigned the
202
vinyl carbon and a carbonyl peak was observed at 166.4 ppm. In the case of the polymer, it
203
was observed that vinyl protons disappeared after the polymerization process and alkyl group
204
peaks (C-13, C-14) of glycopolymer appeared in the range from 47.6 to 22.1 ppm. Also, vinyl
205
carbons of PMIPTEG shifted to a higher field as a result of increased electron intensity.
206
NMR peaks of the sugar moiety for both the polymer and the monomer were observed as
207
predicted from C-1 to C-11 in Figure 3.
208
13
C
an
us
cr
ip t
200
M
Insert Figure 3 here
The uncleavage of the isopropylidene groups MIPTEG and PMIPTEG are understood
210
from NMR spectra. IR and NMR analyses clearly indicated that MIPTEG was successfully
211
obtained and that PMIPTEG was polymerized by free radical reaction. The number average
212
molecular weight (Mn), mass average molecular weight (Mw) and polydispersity index (PDI)
213
of PMIPTEG were found to be 9300 g/mol, 13400 g/mol and 1.44, respectively. The thermal
214
properties of MIPTEG and PMIPTEG were studied using the TG/DTG and DTA techniques
215
from ambient temperature to 1000o C under nitrogen atmosphere. Typical TG/DTG and DTA
216
curves for MIPTEG and PMIPTEG in N2 were presented in Figure 4. The initial and final
217
temperatures and total mass losses in the thermal decomposition of compounds were
218
determined, together with temperatures of the highest rate of decomposition (DTGmax).
219
Ac ce p
te
d
209
Insert Figure 4 here
220
MIPTEG and PMIPTEG exhibited the stage one decomposition process. From the TG
221
curve for MIPTEG, it appeared that the sample decomposed with a mass loss of 96.3 % in the
222
temperature range 199-435o C. However, endothermic thermal effects at 121 and 311 oC in the 9
Page 9 of 27
DTA profile correspond to the solvent peak (absorbed in syrup) and thermal decomposition
224
of MIPTEG, respectively. PMIPTEG is thermally stable up to 218o C and decomposed in the
225
temperature range from 218o C to 581o C with a 92.30 % weight loss. The temperature related
226
to the maximum decomposition rate for MIPTEG was determined to be 288o C in the DTG
227
curve. This temperature for PMIPTEG is 303o C. As expected, these results showed that
228
PMIPTEG is more stable than MIPTEG. The differential scanning calorimetry (DSC) was used
229
to investigate the thermal properties of PMIPTEG. The DSC curve of PMIPTEG exhibited an
230
endothermic peak at 74o C and an exothermic peak at 317o C. These peaks in the DSC curve
231
were attributed to the glass transition temperature and the thermal decomposition of PMIPTEG,
232
respectively. The morphological properties of the resulting polymer were investigated by
233
means of SEM analysis. SEM photographs of powdered PMIPTEG are given in Figure 5. The
234
sequence bead structures on the main chain in Figure 5 were observed for the powdered
235
PMIPTEG samples. In addition, as shown in the SEM image of the selected area, PMIPTEG
236
had a linear backbone structure. Also, the linear polymer chains were very condensed,
237
unhomogeneous and did not exhibit a well-ordered structure or shape. They consisted of long
238
and thin channels. The average particle diameter of randomly oriented ellipsoids is lower than
239
approximately 1 μm.
241
cr
us
an
M
d
te
Ac ce p
240
ip t
223
Insert Figure 5 here
On the other hand, isoconversional methods such as FWO, Tang, KAS, FR, Kim-Park
242
and Kissinger were used to investigate the kinetic parameters (activation energy, E, frequency
243
factor, A) related to the solid state thermal decomposition of PMIPTEG. Kinetic analysis of
244
PMIPTEG was investigated using the thermogramivetry technique with samples of 8-10 mg at
245
heating rates of 5, 10, 15 and 20 °C/min under a nitrogen atmosphere (60 ml/min). A typical
246
dynamic TG/DTG-DTA curve for PMIPTEG at a heating rate of 10 °C/min in N2 is represented
247
in Figure 4b.
Additionally, the solid state degradation mechanism of PMIPTEG was 10
Page 10 of 27
determined by master plots of TG/DTG curves under N2. All of the TG/DTG-DTA curves
249
which were obtained at several heating rates for PMIPTEG showed that the thermal
250
decomposition took place mainly in one stage. However, TG-curves are characteristically very
251
similar to each other. In this work, the Kissinger and Kim-Park procedures are the primary
252
thermogravimetric methods. TG data of PMIPTEG were initially analyzed with the Kissinger
253
procedures as it is independent of the heating rate and any thermal decomposition mechanisms.
254
This method uses the maximum decomposition temperature (Tmax) at which the rate of mass
255
loss is the highest. This method may briefly be expressed by the following equation.
β
Ea ⎫ ⎧ AR ) = ⎨ln + ln [ n(1 − α max ) n −1 ]⎬ − ⎭ RTmax ⎩ Ea
us
cr
ip t
248
ln(
257
The activation energy can be calculated using Eq (1) without knowing the solid state
258
2 degradation reaction mechanism. The slope of line drawn between ln (β/ Tmax ) versus
259
2 ) versus 1000/Tmax gives the activation energy. The slope of the line drawn between ln (β/ Tmax
260
1000/Tmax gives the activation energy. On the other hand, the Kim-Park method assumes that
261
maximum degradation fraction, αm is independent of the kinetic triplet: the activation energy,
262
the pre-exponential factor and the decomposition mechanisms. The activation energy can be
263
obtained by the slope of the plot of lnβ versus 1/Tm by using Eq (2).
265
(1)
M
d
te
Ac ce p
264
T
2 max
an
256
E n ⎤ E ⎡ ln β = ln A + ( ) + ln ⎢1 − n + − 5.3305 − 1.0516( ) ⎥ R 0.944 ⎦ RTmax ⎣
(2)
The activation energies related to the thermal decomposition stage of PMIPTEG obtained
266
by using Kissinger and Kim-Park methods in N2 were determined to be 100.1 and 104.4
267
kJ/mol, respectively.
268
The other methods used for calculating the kinetic parameter of PMIPTEG were those of
269
Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Tang and Friedman based on multiple heating
270
rates. The conventional integral procedures such as FWO, KAS and Tang were proposed by 11
Page 11 of 27
assuming invariant activation energies and in the case of variable activation energies they
272
might yield incorrect values [31]. In those cases, advanced integral isoconversional [32] or
273
differential methods are preferred over integral isoconversional methods. Thus, in the present
274
case, differential isoconversional methods (Friedman, Kissinger, Kim-Park), in addition to
275
integral isoconversional methods (FWO, KAS and Tang) were used for solid state
276
decomposition kinetic studies. The Flynn-Wall-Ozawa method is a conventional integral
277
method and the activation energy of a solid state decomposition process without knowledge of
278
the reaction order can determined by this method. In the technique the A, f(α) and E are
279
independent of T while A and E are independent of α. So this method provides the following
280
expression in logarithmic form for thermal decomposition kinetic studies based on the basic
281
Arrhenius equation:
M
an
us
cr
ip t
271
log β =log (AE/R)- log g(α)-2.315-0.4567 E/RT
283
According to the Eq (3), constant mass loss lines were determined by measuring the
284
temperature at a given mass percent for each rate. Figure 6 presents the Arrhenius type plots of
285
dynamic TG runs for mass ranging from α=0.05 to 0.95 in N2. The apparent activation energy
286
of PMIPTEG can be obtained from a plot of log β against 1000/T for a constant degree of
287
conversion since the slope of such a line is given by -0.456E/RT.
289
te
Ac ce p
288
(3)
d
282
Insert Figure 6 here
The activation energies and correlation coefficient on the overall mass loss from 5 to 95
290
mass % determined with the FWO method in N2 are summarized in Table 1 and the average
291
value was found to be 103.2 kJ/mol over the range of α given. However, table 1 indicated that
292
the correlation coefficient with the Arrhenius type plots is acceptable and always superior to
293
0.98202
294
Insert Table 1 here
12
Page 12 of 27
On the other hand, the Tang and KAS methods are an integral isoconversional method
296
similar to the FWO. The Tang method allows the activation energy to be determined by
297
plotting ln (β/T2) against 1/T for a fixed degree of conversion at the different heating rates β.
298
The slope of such a line obtained by the KAS method is given by -0.456E/RT (Eq (4)).
299
However, to calculate the values of the activation energy from plots of ln ⎛⎜
300
over a wide range of conversions, Eq (5) proposed by KAS can also be used. The activation
301
energy E can be obtained from the slope -1.001450 E/R of the regression line. The kinetic
302
procedures of the Tang and KAS methods are given below, respectively.
ip t
295
1/T
us
cr
β ⎞ ⎟ against ⎝ T 1.894661 ⎠
⎛ AE ⎞ 1.001450 E ⎛ β ⎞ ⎟⎟ + 3.635041 −1.894661 ln E − ln⎜ 1.894661 ⎟ = ln⎜⎜ RT ⎝T ⎠ ⎝ R g (α ) ⎠
(4)
304
⎡ AR ⎤ E ⎡ β ⎤ ln ⎢ 2 ⎥ = ln ⎢ ⎥− ⎣T ⎦ ⎣ E g (α) ⎦ RT
(5)
305
In this study the equation α = 0.05-0.95 was chosen to determine the E values of
306
PMIPTEG. The activation energy of PMIPTEG obtained with the Tang and KAS methods were
307
found to be 102.0 and 102.2 kJ/mol, respectively, over the range of 0.05
