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Synthesis and thermal properties of urethane-containing epoxy resin
G Model
JIEC-2247; No. of Pages 4 Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Short communication
Synthesis and thermal properties of urethane-containing epoxy resin Fan-Long Jin a,*, Heng-Chang Liu a, Baoqing Yang b, Soo-Jin Park c,** a
Department of Polymer Materials, Jilin Institute of Chemical Technology, Jilin City 132022, People’s Republic of China Jilin City Scientific & Technological Information Institute, Jilin City 132013, People’s Republic of China c Department of Chemistry, Inha University, Nam-gu, Incheon 402-751, South Korea b
A R T I C L E I N F O
Article history: Received 8 August 2014 Received in revised form 26 September 2014 Accepted 3 October 2014 Available online xxx Keywords: Urethane Epoxy resin Bisphenol A Initial curing temperature Thermal decomposition temperature
A B S T R A C T
A urethane-containing epoxy resin was successfully synthesized by reacting bisphenol A with 1,6hexamethylene diisocyanate and epichlorohydrin. The chemical structure of urethane-containing epoxy resin was confirmed using FT-IR, 1HNMR, and elemental analysis. DSC results indicated that the initial curing and maximum exothermic peak temperatures of urethane-containing epoxy resin cured with 4,40 -diaminodiphenylmethane were 60 8C and 135 8C, respectively; these values were lower than those of a bisphenol A-based epoxy resin. The thermal stability of epoxy resins was studied using TGA, and it was found that the degradation temperature of urethane-containing epoxy resin was lower than that of bisphenol A-based epoxy resin under the same conditions. ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Introduction Epoxy resins, an important class of thermosetting polymers, are widely used in many fields because of their good engineering performance such as heat resistance, high electrical resistance, and high modulus. However, these materials also suffer from some disadvantages such as large internal stress, brittleness, flammability, low degradability, little impact resistance, and high moisture absorption. In order to improve the toughness of epoxy resins, several techniques are employed, i.e., improvement of the flexibility of the cured epoxy resins [1,2]. Some methods used for increasing the toughness of epoxy resins by improving their flexibility are introduction of a toughening agent into the epoxy network and chemical modification of the epoxy structure. Some commonly used toughening agents include liquid elastomers, thermoplastics, and inorganic particles; however, their use can deteriorate the final properties of the resins [3–5]. Instead, a modification in the chemical structure can improve the overall physical properties. For example, the introduction of a urethane group into the main chain increases the flexibility of the epoxy resins [6–9]. In this study, a urethane-containing epoxy resin was successfully synthesized and fully characterized using FT-IR, 1HNMR, and
* Corresponding author. Tel.: +86 432 63083156; fax: +86 432 63083156. ** Corresponding author. Tel.: +82 32 8767234; fax: +82 32 8675604. E-mail addresses: [email protected] (F.-L. Jin), [email protected], [email protected] (S.-J. Park).
elemental analysis. Differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) were used to study its cure and thermal decomposition behaviors. Experimental Bisphenol A and epichlorohydrin were supplied by National Medicine Group Chemical Reagent Co., Ltd. 1,6-Hexamethylene diisocyanate and NaOH were obtained from Tianjin Guangfu Chem. 4,40 -Diaminodiphenylmethane (DDM) was purchased from National Medicine Group Chemical Reagent Co., Ltd., and used as a curing agent. Methyl sulfoxide-d6 (MSO-d6) was acquired from Aldrich Chem. and used as the solvent for obtaining 1HNMR spectra. Synthesis of Intermediate. Bisphenol A (11.4 g, 0.05 mol) and epichlorohydrin (23.1 ml, 0.21 mol) were charged, under a nitrogen atmosphere, into a 100-mL glass flask equipped with a mechanical stirrer, thermometer sensor, and circumference condenser. The resulting solution was heated to 50 8C and 1,6hexamethylene diisocyanate (20.16 g, 0.12 mol) was added to it. After stirring the reaction mixture at 50 8C for 1 h, epichlorohydrin and unreacted 1,6-hexamethylene diisocyanate were removed by distillation in a vacuum oven, and a light-yellow viscous intermediate was obtained (95.6%). FT-IR (KBr): 3340 cm1 (OH), 3050 cm1 (aromatic ring), 1710 cm1 (C5 5O), 1607 cm1 (aromatic ring), 1514 cm1 (aromatic ring). 1 HNMR (MSO-d6): d = 1.2 ppm (CH3), 6.8–7.1 ppm (CH, aromatic ring), 7.7 ppm (NH), 9.1 ppm (OH).
http://dx.doi.org/10.1016/j.jiec.2014.10.006 1226-086X/ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: F.-L. Jin, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.10.006
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F.-L. Jin et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
DSC 200 F3) at a heating rate of 10 8C/min from 50 to 250 8C under a nitrogen flow of 30 mL/min. Thermal stabilities of the cured samples were studied using a NETZSCH TG 209 F3 analyzer at a heating rate of 10 8C/min, from 30 to 600 8C, under a nitrogen atmosphere.
Elemental analysis: C, 72.37; H, 7.46; N, 3.35; O, 16.82. Calculated for C38H46N2O6: C, 72.84; H, 7.35; N, 4.47; O, 15.34. Synthesis of Urethane-containing Epoxy Resin. Intermediate (12.52 g, 0.02 mol) and epichlorohydrin (9.25 g, 0.1 mol) were mixed into a 100-mL glass flask equipped with a mechanical stirrer, thermometer sensor, and circumference condenser. The resulting solution was heated to 70 8C and an aqueous solution of NaOH (20%; 4 g, 0.02 mol) was added to the solution with stirring. Then, the solution heated to 70 8C for 1 h, was washed with distilled water, and then filtered. Unreacted epichlorohydrin was removed by distillation in a vacuum oven and the epoxy resin was obtained as a light-yellow viscous oil (92.1%). FT-IR (KBr): 3340 cm1 (OH), 3050 cm1 (aromatic ring), 1607 cm1 (aromatic ring), 1514 cm1 (aromatic ring), 1710 cm1 (C5 5O), 912 cm1 (epoxy ring). 1 HNMR (MSO-d6): d = 1.2 ppm (CH3), 5.5 ppm (epoxy ring), 6.8– 7.1 ppm (CH, aromatic ring), 7.7 ppm (NH), 9.1 ppm (OH). Elemental analysis: C, 71.82; H, 7.6; N, 2.22; O, 18.36. Calculated for C64H80N3O12: C, 70.98; H, 7.39; N, 3.88; O, 17.74. Synthesis of Bisphenol A-based Epoxy Resin. Bisphenol A (6.84 g, 0.03 mol) and epichlorohydrin (13.88 g, 0.15 mol) were mixed into a 100-mL glass flask equipped with a mechanical stirrer, thermometer sensor, and circumference condenser. The resulting solution was heated to 70 8C and an aqueous solution of NaOH (20%; 6 g, 0.03 mol) was added with stirring. The solution was then heated to 70 8C for 1 h, washed with distilled water, and then filtered. Unreacted epichlorohydrin was removed by distillation in a vacuum oven, and the epoxy resin was obtained as a lightyellow viscous oil (96.3%). IR spectra were recorded on KBr pellets with a Bio-Rad Co. Digilab FTS-165 spectrometer. 1HNMR spectra were recorded at room temperature on a Bruker Co. DRX300 spectrometer at an operating frequency of 300 MHz using methyl sulfoxide-d6 (MSOd6) as the solvent. Elemental analysis for H, C, N, and O was performed on a Flash 1112 Elemental Analyzer (Thermo Electron Corporation). The cure behavior of epoxy resins cured with DDM was investigated using a differential scanning calorimeter (NETZSCH,
Results and discussion The synthesis of urethane-containing epoxy resin is shown in Fig. 1. The synthetic process involved two steps: in the first, the hydroxyl groups of bisphenol A reacted with the isocyanate groups of 1,6-hexamethylene diisocyanate to form intermediate. In the second step, intermediate reacted with epichlorohydrin to afford urethane-containing epoxy resin as a light-yellow viscous oil in a 92.1% yield. The chemical structure of urethane-containing epoxy resin was confirmed by FT-IR, 1HNMR, and elemental analysis. Fig. 2(a) shows the FT-IR spectrum of intermediate, which exhibits a characteristic absorption peak at 3340 cm1 due to the hydroxyl group. The absorption peaks at 3010, 1607, and 1514 cm1 reveal the presence of the aromatic ring, while the peak at 2925 cm1 indicates the presence of the CH2 group. The absorption peak at 1710 cm1 corresponds to the C5 5O bond. The characteristic absorption peak of an isocyanate group at 2270 cm1 disappears after the first step reaction, which confirms the successful coupling of bisphenol A with 1,6-hexamethylene diisocyanate [10,11]. Fig. 2(b) shows the FT-IR spectrum of urethane-containing epoxy resin. The absorption peak at 3340 cm1 has decreased in intensity, indicating a reduction in the number of hydroxyl groups after the second step reaction. The IR band at 912 cm1 shows the presence of the epoxide functionality [12,13]. The 1HNMR spectrum of intermediate presented peaks at d = 1.2, 7, 7.7, and 9.1 ppm corresponding to unsaturated, aromatic, amide, and phenolic protons, respectively. The 1HNMR spectrum of urethane-containing epoxy resin presented a peak at d = 5.5 ppm, assigned to the protons in the epoxide group, while the peak at d = 9.1 ppm, corresponding to the phenolic proton, was absent [14,15].
(a)
(b) Fig. 1. Schematic outline for the synthesis of urethane-containing epoxy resin: (a) intermediate and (b) urethane-containing epoxy resin.
Please cite this article in press as: F.-L. Jin, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.10.006
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JIEC-2247; No. of Pages 4 F.-L. Jin et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
(a)
3
120
3340 3010
a
2925
Weight (%)
Transmittance
90
1710
60
30
16071514
0
4000
3000
2000
1000
200
400
600
o
Fig. 4. TGA thermograms of DDM-cured (a) urethane-containing epoxy resin and (b) bisphenol A-based epoxy resin.
Transmittance
(b)
912
4000
3000
2000
1000 -1
Wavenumber (cm ) Fig. 2. FT-IR spectra of (a) intermediate and (b) urethane-containing epoxy resin.
The values obtained in the elemental analysis for urethanecontaining epoxy resin [C (71.82%), H (7.6%), N (2.22%), and O (18.36%)] are in accordance with the theoretical values [C (70.98%), H (7.39%), N (3.88%), and O (17.74%)], which together with the FTIR and 1HNMR data provide strong evidence for the proposed product structure. The cure behavior and thermal stability of epoxy resins were investigated using DSC and TGA, respectively. Fig. 3 shows the DSC thermogram of urethane-containing epoxy resin and bisphenol A-based epoxy resin cured with DDM. The initial curing
b
Heat flow (mW/g)
0
Temperature ( C)
Wavenumber (cm-1)
a
50
b
temperatures of urethane-containing epoxy resin and bisphenol A-based epoxy resin were 60 8C and 82 8C, respectively; the maximum exothermic peak temperatures of urethane-containing epoxy resin and bisphenol A-based epoxy resin were 135 8C and 165 8C, respectively. These results indicated that the curing reaction of urethane-containing epoxy resin with DDM occurred at a lower temperature than that of the bisphenol A-based epoxy resin [16–18]. Fig. 4 shows the TGA thermograms of DDM-cured urethanecontaining epoxy resin and bisphenol A-based epoxy resin. Thermal decomposition temperatures of urethane-containing epoxy resin were 199.9 8C and 247.5 8C, corresponding to the weight loss of 5% and 10%, respectively. These temperatures were lower than those of bisphenol A-based epoxy resin (252.5 8C and 302.5 8C, respectively). The char residues at 600 8C for the urethane-containing epoxy resin and bisphenol A-based epoxy resin were 2.1% and 8.3%, respectively. These differences can be attributed to a lower decomposition temperature of the urethane groups in the main chain of urethane-containing epoxy resin than that of the bisphenol A resin [19–21]. Conclusions A urethane-containing epoxy resin was synthesized and characterized. The urethane-containing epoxy resin cured with DDM had initial curing and maximum exothermic peak temperatures of 60 8C and 135 8C, respectively, which indicated that the curing reaction of urethane-containing epoxy resin with DDM occurred at a lower temperature than that of the bisphenol A-based epoxy resin. Its thermal decomposition temperature was lower than that of the bisphenol A-based epoxy resin under the same conditions because of the presence of the urethane groups in the main chain of urethane-containing epoxy resin. References
100
150
200
250
o
Temperature ( C) Fig. 3. DSC thermograms of (a) urethane-containing epoxy resin and (b) bisphenol A-based epoxy resin curd with DDM.
[1] C.A. May, Epoxy Resins: Chemistry and Technology, 2nd ed., Marcel Dekker, New York, 1988. [2] W. Jiang, F.L. Jin, S.J. Park, J. Ind. Eng. Chem. 18 (2012) 594. [3] S. Sprenger, Polymer 54 (2013) 4790. [4] S.J. Park, F.L. Jin, C. Lee, Mater. Sci. Eng. A 402 (2004) 335. [5] A. Demcˇenko, V. Koissin, V.A. Komeev, Ultrasonics 54 (2014) 684. [6] F.L. Jin, S.J. Park, Mater. Sci. Eng. A 475 (2008) 190. [7] Y. Takeshita, E. Becker, S. Sakata, T. Miwa, T. Sawada, Polymer 55 (2014) 2505. [8] S.W. Lee, J.W. Park, C.H. Park, D.H. Lim, H.J. Kim, J.Y. Song, J.H. Lee, Int. J. Adhes. Adhes. 44 (2013) 138. [9] D.M. Dhevi, S.N. Jaisankar, M. Pathak, Eur. Polym. J. 49 (2013) 3561. [10] F.L. Jin, K.Y. Rhee, S.J. Park, J. Solid State Chem. 184 (2011) 3253. [11] C.H. Lin, Polymer 45 (2004) 7911.
Please cite this article in press as: F.-L. Jin, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.10.006
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[12] [13] [14] [15]
W. Jiang, F.L. Jin, S.J. Park, J. Ind. Eng. Chem. 18 (2012) 1577. H. Liu, X. Wang, D. Wu, Polym. Degrad. Stab. 103 (2014) 96. H.J. Xu, F.L. Jin, S.J. Park, Bull. Korean Chem. Soc. 30 (2009) 2643. C. Aouf, H. Nouaihas, M. Fache, S. Caillol, B. Boutevin, H. Fulcrand, Eur. Polym. J. 49 (2013) 1185. [16] F.L. Jin, S.J. Park, Polym. Degrad. Stab. 97 (2012) 2148.
[17] B. Wucher, F. Lani, T. Pardoen, C. Bailly, P. Martiny, Compos. Part A 56 (2014) 27. [18] F.L. Jin, S.J. Park, J. Polym. Sci. Part B Polym. Phys. 44 (2006) 3348. [19] W. Dong, F.L. Jin, S.J. Park, J. Ind. Eng. Chem. 20 (2014) 1220. [20] A. Agrawai, A. Satapathy, Compos. Part A 63 (2014) 51. [21] F.L. Jin, C.J. Ma, S.J. Park, Mater. Sci. Eng. A 528 (2011) 8517.
Please cite this article in press as: F.-L. Jin, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.10.006
JIEC-2247; No. of Pages 4 Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Short communication
Synthesis and thermal properties of urethane-containing epoxy resin Fan-Long Jin a,*, Heng-Chang Liu a, Baoqing Yang b, Soo-Jin Park c,** a
Department of Polymer Materials, Jilin Institute of Chemical Technology, Jilin City 132022, People’s Republic of China Jilin City Scientific & Technological Information Institute, Jilin City 132013, People’s Republic of China c Department of Chemistry, Inha University, Nam-gu, Incheon 402-751, South Korea b
A R T I C L E I N F O
Article history: Received 8 August 2014 Received in revised form 26 September 2014 Accepted 3 October 2014 Available online xxx Keywords: Urethane Epoxy resin Bisphenol A Initial curing temperature Thermal decomposition temperature
A B S T R A C T
A urethane-containing epoxy resin was successfully synthesized by reacting bisphenol A with 1,6hexamethylene diisocyanate and epichlorohydrin. The chemical structure of urethane-containing epoxy resin was confirmed using FT-IR, 1HNMR, and elemental analysis. DSC results indicated that the initial curing and maximum exothermic peak temperatures of urethane-containing epoxy resin cured with 4,40 -diaminodiphenylmethane were 60 8C and 135 8C, respectively; these values were lower than those of a bisphenol A-based epoxy resin. The thermal stability of epoxy resins was studied using TGA, and it was found that the degradation temperature of urethane-containing epoxy resin was lower than that of bisphenol A-based epoxy resin under the same conditions. ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Introduction Epoxy resins, an important class of thermosetting polymers, are widely used in many fields because of their good engineering performance such as heat resistance, high electrical resistance, and high modulus. However, these materials also suffer from some disadvantages such as large internal stress, brittleness, flammability, low degradability, little impact resistance, and high moisture absorption. In order to improve the toughness of epoxy resins, several techniques are employed, i.e., improvement of the flexibility of the cured epoxy resins [1,2]. Some methods used for increasing the toughness of epoxy resins by improving their flexibility are introduction of a toughening agent into the epoxy network and chemical modification of the epoxy structure. Some commonly used toughening agents include liquid elastomers, thermoplastics, and inorganic particles; however, their use can deteriorate the final properties of the resins [3–5]. Instead, a modification in the chemical structure can improve the overall physical properties. For example, the introduction of a urethane group into the main chain increases the flexibility of the epoxy resins [6–9]. In this study, a urethane-containing epoxy resin was successfully synthesized and fully characterized using FT-IR, 1HNMR, and
* Corresponding author. Tel.: +86 432 63083156; fax: +86 432 63083156. ** Corresponding author. Tel.: +82 32 8767234; fax: +82 32 8675604. E-mail addresses: [email protected] (F.-L. Jin), [email protected], [email protected] (S.-J. Park).
elemental analysis. Differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) were used to study its cure and thermal decomposition behaviors. Experimental Bisphenol A and epichlorohydrin were supplied by National Medicine Group Chemical Reagent Co., Ltd. 1,6-Hexamethylene diisocyanate and NaOH were obtained from Tianjin Guangfu Chem. 4,40 -Diaminodiphenylmethane (DDM) was purchased from National Medicine Group Chemical Reagent Co., Ltd., and used as a curing agent. Methyl sulfoxide-d6 (MSO-d6) was acquired from Aldrich Chem. and used as the solvent for obtaining 1HNMR spectra. Synthesis of Intermediate. Bisphenol A (11.4 g, 0.05 mol) and epichlorohydrin (23.1 ml, 0.21 mol) were charged, under a nitrogen atmosphere, into a 100-mL glass flask equipped with a mechanical stirrer, thermometer sensor, and circumference condenser. The resulting solution was heated to 50 8C and 1,6hexamethylene diisocyanate (20.16 g, 0.12 mol) was added to it. After stirring the reaction mixture at 50 8C for 1 h, epichlorohydrin and unreacted 1,6-hexamethylene diisocyanate were removed by distillation in a vacuum oven, and a light-yellow viscous intermediate was obtained (95.6%). FT-IR (KBr): 3340 cm1 (OH), 3050 cm1 (aromatic ring), 1710 cm1 (C5 5O), 1607 cm1 (aromatic ring), 1514 cm1 (aromatic ring). 1 HNMR (MSO-d6): d = 1.2 ppm (CH3), 6.8–7.1 ppm (CH, aromatic ring), 7.7 ppm (NH), 9.1 ppm (OH).
http://dx.doi.org/10.1016/j.jiec.2014.10.006 1226-086X/ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: F.-L. Jin, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.10.006
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JIEC-2247; No. of Pages 4 2
F.-L. Jin et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
DSC 200 F3) at a heating rate of 10 8C/min from 50 to 250 8C under a nitrogen flow of 30 mL/min. Thermal stabilities of the cured samples were studied using a NETZSCH TG 209 F3 analyzer at a heating rate of 10 8C/min, from 30 to 600 8C, under a nitrogen atmosphere.
Elemental analysis: C, 72.37; H, 7.46; N, 3.35; O, 16.82. Calculated for C38H46N2O6: C, 72.84; H, 7.35; N, 4.47; O, 15.34. Synthesis of Urethane-containing Epoxy Resin. Intermediate (12.52 g, 0.02 mol) and epichlorohydrin (9.25 g, 0.1 mol) were mixed into a 100-mL glass flask equipped with a mechanical stirrer, thermometer sensor, and circumference condenser. The resulting solution was heated to 70 8C and an aqueous solution of NaOH (20%; 4 g, 0.02 mol) was added to the solution with stirring. Then, the solution heated to 70 8C for 1 h, was washed with distilled water, and then filtered. Unreacted epichlorohydrin was removed by distillation in a vacuum oven and the epoxy resin was obtained as a light-yellow viscous oil (92.1%). FT-IR (KBr): 3340 cm1 (OH), 3050 cm1 (aromatic ring), 1607 cm1 (aromatic ring), 1514 cm1 (aromatic ring), 1710 cm1 (C5 5O), 912 cm1 (epoxy ring). 1 HNMR (MSO-d6): d = 1.2 ppm (CH3), 5.5 ppm (epoxy ring), 6.8– 7.1 ppm (CH, aromatic ring), 7.7 ppm (NH), 9.1 ppm (OH). Elemental analysis: C, 71.82; H, 7.6; N, 2.22; O, 18.36. Calculated for C64H80N3O12: C, 70.98; H, 7.39; N, 3.88; O, 17.74. Synthesis of Bisphenol A-based Epoxy Resin. Bisphenol A (6.84 g, 0.03 mol) and epichlorohydrin (13.88 g, 0.15 mol) were mixed into a 100-mL glass flask equipped with a mechanical stirrer, thermometer sensor, and circumference condenser. The resulting solution was heated to 70 8C and an aqueous solution of NaOH (20%; 6 g, 0.03 mol) was added with stirring. The solution was then heated to 70 8C for 1 h, washed with distilled water, and then filtered. Unreacted epichlorohydrin was removed by distillation in a vacuum oven, and the epoxy resin was obtained as a lightyellow viscous oil (96.3%). IR spectra were recorded on KBr pellets with a Bio-Rad Co. Digilab FTS-165 spectrometer. 1HNMR spectra were recorded at room temperature on a Bruker Co. DRX300 spectrometer at an operating frequency of 300 MHz using methyl sulfoxide-d6 (MSOd6) as the solvent. Elemental analysis for H, C, N, and O was performed on a Flash 1112 Elemental Analyzer (Thermo Electron Corporation). The cure behavior of epoxy resins cured with DDM was investigated using a differential scanning calorimeter (NETZSCH,
Results and discussion The synthesis of urethane-containing epoxy resin is shown in Fig. 1. The synthetic process involved two steps: in the first, the hydroxyl groups of bisphenol A reacted with the isocyanate groups of 1,6-hexamethylene diisocyanate to form intermediate. In the second step, intermediate reacted with epichlorohydrin to afford urethane-containing epoxy resin as a light-yellow viscous oil in a 92.1% yield. The chemical structure of urethane-containing epoxy resin was confirmed by FT-IR, 1HNMR, and elemental analysis. Fig. 2(a) shows the FT-IR spectrum of intermediate, which exhibits a characteristic absorption peak at 3340 cm1 due to the hydroxyl group. The absorption peaks at 3010, 1607, and 1514 cm1 reveal the presence of the aromatic ring, while the peak at 2925 cm1 indicates the presence of the CH2 group. The absorption peak at 1710 cm1 corresponds to the C5 5O bond. The characteristic absorption peak of an isocyanate group at 2270 cm1 disappears after the first step reaction, which confirms the successful coupling of bisphenol A with 1,6-hexamethylene diisocyanate [10,11]. Fig. 2(b) shows the FT-IR spectrum of urethane-containing epoxy resin. The absorption peak at 3340 cm1 has decreased in intensity, indicating a reduction in the number of hydroxyl groups after the second step reaction. The IR band at 912 cm1 shows the presence of the epoxide functionality [12,13]. The 1HNMR spectrum of intermediate presented peaks at d = 1.2, 7, 7.7, and 9.1 ppm corresponding to unsaturated, aromatic, amide, and phenolic protons, respectively. The 1HNMR spectrum of urethane-containing epoxy resin presented a peak at d = 5.5 ppm, assigned to the protons in the epoxide group, while the peak at d = 9.1 ppm, corresponding to the phenolic proton, was absent [14,15].
(a)
(b) Fig. 1. Schematic outline for the synthesis of urethane-containing epoxy resin: (a) intermediate and (b) urethane-containing epoxy resin.
Please cite this article in press as: F.-L. Jin, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.10.006
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JIEC-2247; No. of Pages 4 F.-L. Jin et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
(a)
3
120
3340 3010
a
2925
Weight (%)
Transmittance
90
1710
60
30
16071514
0
4000
3000
2000
1000
200
400
600
o
Fig. 4. TGA thermograms of DDM-cured (a) urethane-containing epoxy resin and (b) bisphenol A-based epoxy resin.
Transmittance
(b)
912
4000
3000
2000
1000 -1
Wavenumber (cm ) Fig. 2. FT-IR spectra of (a) intermediate and (b) urethane-containing epoxy resin.
The values obtained in the elemental analysis for urethanecontaining epoxy resin [C (71.82%), H (7.6%), N (2.22%), and O (18.36%)] are in accordance with the theoretical values [C (70.98%), H (7.39%), N (3.88%), and O (17.74%)], which together with the FTIR and 1HNMR data provide strong evidence for the proposed product structure. The cure behavior and thermal stability of epoxy resins were investigated using DSC and TGA, respectively. Fig. 3 shows the DSC thermogram of urethane-containing epoxy resin and bisphenol A-based epoxy resin cured with DDM. The initial curing
b
Heat flow (mW/g)
0
Temperature ( C)
Wavenumber (cm-1)
a
50
b
temperatures of urethane-containing epoxy resin and bisphenol A-based epoxy resin were 60 8C and 82 8C, respectively; the maximum exothermic peak temperatures of urethane-containing epoxy resin and bisphenol A-based epoxy resin were 135 8C and 165 8C, respectively. These results indicated that the curing reaction of urethane-containing epoxy resin with DDM occurred at a lower temperature than that of the bisphenol A-based epoxy resin [16–18]. Fig. 4 shows the TGA thermograms of DDM-cured urethanecontaining epoxy resin and bisphenol A-based epoxy resin. Thermal decomposition temperatures of urethane-containing epoxy resin were 199.9 8C and 247.5 8C, corresponding to the weight loss of 5% and 10%, respectively. These temperatures were lower than those of bisphenol A-based epoxy resin (252.5 8C and 302.5 8C, respectively). The char residues at 600 8C for the urethane-containing epoxy resin and bisphenol A-based epoxy resin were 2.1% and 8.3%, respectively. These differences can be attributed to a lower decomposition temperature of the urethane groups in the main chain of urethane-containing epoxy resin than that of the bisphenol A resin [19–21]. Conclusions A urethane-containing epoxy resin was synthesized and characterized. The urethane-containing epoxy resin cured with DDM had initial curing and maximum exothermic peak temperatures of 60 8C and 135 8C, respectively, which indicated that the curing reaction of urethane-containing epoxy resin with DDM occurred at a lower temperature than that of the bisphenol A-based epoxy resin. Its thermal decomposition temperature was lower than that of the bisphenol A-based epoxy resin under the same conditions because of the presence of the urethane groups in the main chain of urethane-containing epoxy resin. References
100
150
200
250
o
Temperature ( C) Fig. 3. DSC thermograms of (a) urethane-containing epoxy resin and (b) bisphenol A-based epoxy resin curd with DDM.
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