Thermal stability and thermal degradation reaction kinetics of 4,4'-diphenylmethane diisocyanatetrimer

Article abstract of DOI:10.14233/ajchem.2014.17278

The trimer of 4,4'-diphenylmethane diisocyanate (MDI) is synthesized using 2,4,6-tris(dimethylaminomethyl) phenol (DMP-30) as catalyst. The thermal stability of MDI and its trimer and thermal degradation reaction kinetics for MDI trimer are studied by the

Full text of DOI:10.14233/ajchem.2014.17278

Asian Journal of Chemistry; Vol. 26, No. 5 (2014), 1527-1529
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.17278
Thermal Stability and Thermal Degradation Reaction Kinetics of
4,4'-Diphenylmethane Diisocyanatetrimer†
1
1
1
JING ZHANG , YAN-FEI TANG , JIN LIU1,2,* and YAN CHEN
1School of Materials and Chemical Engineering, Anhui Jianzhu University, Hefei 230022, P.R. China
2Anhui Key Laboratory of Advanced Building Materials, Anhui Jianzhu University, Hefei 230022, P.R. China
*Corresponding author: E-mail: liujin@ahjzu.edu.cn
Published online: 1 March 2014;
AJC-14819
The trimer of 4,4'-diphenylmethane diisocyanate (MDI) is synthesized using 2,4,6-tris(dimethylaminomethyl) phenol (DMP-30) as catalyst.
The thermal stability of MDI and its trimer and thermal degradation reaction kinetics for MDI trimer are studied by thermo gravimetric
analyzer, respectively. The properties and structure of the trimer of MDI are characterized by X-ray diffraction, Fourier transform infrared
spectroscopy and TGA. The activation energy of degradation reaction of the trimer was obtained by Ozawa method. The results show that
there are two stages of the trimer during thermal degradation process and the apparent activation energy of the first and the second stage
are 200.99 and 259.94 kJ/mol, respectively.
Keywords: Trimer of 4,4'-diphenylmethane diisocyanate, Thermal stability, Reaction kinetics, Ozawa method.
recorded by using a WQF-300 spectrometer (Beijing, China)
with 32 scans and 4 cm-1 resolution at the range 4000-400 cm-1.
The DTG andTGA were measured used STA409PC (NETZSCH-
Gerätebau GmbH, Germany) thermal analyzer with the heating
rate at 10, 15, 20, 30 K/min, respectively and high pure N2 as
shelter gas. The range of temperature was controlled from 50-
800 ºC.
INTRODUCTION
Aromatic or aliphatic isocyanate can be self-addition
reaction to get isocyanurate. There is no active hydrogen atom
in isocyanurate ring and the unit structure become more stabile.
The products containing isocyanurate ring possess high protec-
tive properties, good corrosion resistance and yellowing resis-
tance, good heat resistance and flame retardant. Because of
these properties, the isocyanate trimer had been widely used
in many fields such as coatings, adhesives, sealant elastomers,
foamed plastic, etc.
Preparation of the trimer of MDI: 100 mL of dehydrated
toluene and 50 g of MDI are mixed under the protection of
high purity N2, MDI has absolutely dissolved in toluene by
heating with stirring and adding proper amount of 0.05 % of
DMP-30 as catalyst. Stirring is continued at 60 ºC for 6 h. The
excess MDI monomer and catalyst were removed by washing
with toluene.
Now the published literature were reported more about
toluene diisocyanate (TDI) trimer, 1,6-hexamethylenediiso-
cyanatetrimer (HDI), isophoronediisocyanate (IPDI) trimer,
but little about diphenylmethanediisocyanate (MDI) trimer1-8.
In this study, MDI trimer is synthesized by using solution
polymerization. The thermal stability of the trimer is compared
with MDI monomer and their thermal degradation reaction
kinetics has been explored.
RESULTS AND DISCUSSION
Infrared spectroscopic analysis: There is only-NCO
absorption peak at 2274 cm-1 in MDI infared spectroscopy as
shown in Fig. 1 and the absorption peak intensity of MDI after
polymerization at 2274 cm-1 is weaker than MDI monomer.
The absorption peak of isocyanurate ring are obviously found
at 1720 and 1410 cm-1, but the absorption peak of carbodiimide
structureis not be found9. In general, the formation of carbodi-
imide structure cannot be happened unless at high temperature,
EXPERIMENTAL
Characterization: The structure of the products was as-
certained by XRD (D8Advance, BRUKER, Germany) at 40 kV
and 40 mA with a CuKα radiation source. The spectra were
†Presented at The 7th International Conference on Multi-functional Materials and Applications, held on 22-24 November 2013, Anhui
University of Science & Technology, Huainan, Anhui Province, P.R. China

1528 Zhang et al.
Asian J. Chem.
O
C
MDI
MDI trimer
H2
C
NCO
R
R
O
N
C
N
C
R
O
Cat
3
R
NCO
N
C
N
N
R
-CO2
∆
CH2
H2C
O
C
O
A
N
C
N
N
C
N
C
O
C
O
O
O
N
N
∆
1410
1720
H2
C
H2
C
2274
OCN
N
C
N
NCO
3500
3000
2500
Wavenumber (cm–1)
Fig. 1. Infrared spectroscopy of MDI and MDI- trimer
2000
1500
1000
-CO2
∆
H2
C
N
C N
n
so the carbodiimide structure is not existed in the product. So
the product is proved to be MDI trimer.
∆
NH2
CN
CN
NH2
CH3
Thermal stability: Fig. 2 shows the results of TG and DTG
of MDI and MDI trimer. There is only one stage in the thermal
degradation process of MDI monomer that between 150 and
300 ºC, which due to the volatilization of MDI. The weight
loss of it is 91.11 %. While there is not obviously weight loss
of MDI trimer before 300. There are two stages in the thermal
degradation of MDI trimer. In the first stage that between 300
and 420 ºC, the carbodiimide structure is formed because the
remained -NCO group of MDI trimer continue to reaction and
give off CO210,11, as shown in Fig. 3, the weight loss of the first
stage is 10.03 %. The second stage that between 420 and 620 ºC,
the polycarbodiimide is formed after decomposion of isocya-
nurate ring and give off CO2. The polycarbodiimide decom-
posed at 580 ºC and get a complex mixture of volatile products,
leaving behind carbon residue.
etc
CH3
Fig. 3. Thermal degradation process of MDI-trimer
800 °C
2274
1600
550 °C
400 °C
1520
2160
820
1420
1710
2274
MDI Trimer
820
1000
MDI
MDI trimer
3060
100
MDI
10.03%
0
33.2%
80
60
40
20
0
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm–1
)
91.11%
Fig. 4. Infrared spectroscopy of MDI-trimer before and after carbonization
347.5 °C
-2
-4
peak is disappeared at 3060 cm-1 and the disappearance of
absorption peak at 820 cm-1 is the result of para double instead
Ar-C and Ar-N bond fission, remaining carbon residue at last.
X-Ray diffraction analysis: The MDI trimer and the
product after carbonizationare both present typical amorphous
structures are shown in Fig. 5. The relatively narrow peak that
has symmetrical peak shape is found at 18º diffraction angle
in MDI trimer, which reflects the molecular space configu-
ration is regular. The diffraction peak at 18º in the product
after 400 ºC carbonization is wider than it in MDI trimer, which
mainly because the active-NCO groups of the MDI trimer react
with each other and form a crosslinked structure. The diffrac-
tion peak gradually rises to a high angle with the carbonization
temperature rises to 550 ºC, the peak intensity become weaker
and the peak type become wider, which shows that the
molecular chain is broken and the arrangement of the chain
segments are disorder after carbonization.
505.5 °C
-20
237.5 °C
300
100
200
400
500
600
700
Temperature (ºC)
Fig. 2. TG and DTG of MDI and MDI- trimer
The decomposition product of MDI trimer under different
temperatures are tracked by infrared as shown in Fig. 4. The
absorption peak of cabodiimide structure is found at 2160 cm-1
in MDI trimer after 400 ºC carbonization, C-N stretching vibra-
tion peak is found at 1520 cm-1 and C=O stretching vibration
peak is found at 1600 cm-1.There are not big difference between
infrared spectroscopy of MDI trimer after 500 ºC carbonization
and after 800 ºC carbonization. The Ar-H stretching vibration

Vol. 26, No. 5 (2014)
Thermal Stability and Degradation Reaction Kinetics of 4,4'-Diphenylmethane Diisocyanatetrimer 1529
2000
1800
1600
1400
1200
1000
800
1.5
MDI trimer
(a)
400 °C
550 °C
1.0
1.58
1.59
1.60
1.61
600
Tp–1 × 10–3 (K–1)
400
1.5
(b)
200
10
20
30
40
(°)
Fig. 5. XRD of MDI-trimer at different carbonization temperatures
50
60
70
2θ
Thermal degradation reaction kinetics: In this study,
Ozawa method is used to calculate the activation energy. The
activation energy (E) is calculated by using different DTG
curve peak (Tp) under different heating rate β12.
1.0
1.25
1.26
1.27
Tp–1 × 103 (K–1)
1.28
1.29
 AE 
E
logβ = log
− 2.315− 0.4567


RG(α)
RT


Fig. 7. Fitting curve of ozawa of MDI-trimer (a, the first stage; b, the second
stage)
The E can be calculated from the slope of the line that log
β as Y axis and 1/T as X axis. The log β-1/T fitting curve is
got according the Fig. 6 and Table-1.
Conclusion
The product that synthesized by using solution polymeri-
zation is MDI trimer according to the result of Fourier infrared
spectra. The thermal stability of MDI trimer is better than MDI.
There are two stages through MDI trimer degradation process.
The carbodiimide structure is formed in the first stage, the
isocyanurate ring and carbodiimide structure resolved in the
second stage. The activation energy of MDI trimer are calcu-
lated by Ozawa method.
10K/min
100
80
15K/min
20K/min
30K/min
60
ACKNOWLEDGEMENTS
This work was financially supported by the Natural
Science Foundation of China (No. 21171004), the National
Science & Technology Pillar Program of China (No.
2011BAJ03B04, 2013BAJ01B05) and the Natural Science
Foundation of Anhui Province Education Department
(KJ2011A064).
40
200
400
Temperature (°C)
600
800
100
200
300
400
500
600
700
Temperature (°C)
Fig. 6. TGA and DTG MDI-trimer at different heating rate
TABLE-1
Tp IN DTG OF MDI-TRIMER AT DIFFERENT HEATING RATE
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347
Tp2 (ºC)
505
10
15
20
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347.5
357
510
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