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Polymer Testing 30 (2011) 509–514
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Analysis Method
Analysis of 5-ethylidene-2-norbornene in ethylene-propylene-diene terpolymer using pyrolysis-GC/MS Sung-Seen Choi*, Yun-Ki Kim Department of Chemistry, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 February 2011 Accepted 10 April 2011
Ethylene-propylene-diene terpolymer (EPDM) having 5-ethylidene-2-norbornene (ENB) as a diene unit was pyrolyzed and the pyrolysis products were analyzed using gas chromatography/mass spectrometry (GC/MS) to develop a method for identification and quantitation of ENB. Pyrolysis products formed from ENB units were determined by comparing pyrolysis products of EPDMs with different ENB contents. Principal pyrolysis products generated from ENB units were benzene, toluene and 4-ethylidene-1-cyclopentene. Relative peak intensities of benzene and toluene increased as the pyrolysis temperature increased, whereas that of 4-ethylidene-1-cyclopentene decreased. The differences in peak intensity ratios of the ENB-derived pyrolysis products/propylene between EPDM and EPM (ENB content ¼ 0 wt%) linearly increased as the ENB content of EPDM increased. ENB content in EPDM can be determined using the linear relationship between the difference in the peak intensity ratios and the ENB content. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: EPDM ENB Pyrolysis Benzene Toluene 4-Ethylidene-1-cyclopentene
1. Introduction Ethylene-propylene-diene terpolymer (EPDM) consisting of ethylene, propylene and unsaturated diene is one of the popular synthetic rubbers. In general, 5-ethylidene-2norbornene (ENB), dicyclopentadiene (DCPD) and 1,4hexadiene (HD) are used as the diene, with ENB being the most frequently used. Scheme 1 shows the chemical structure of EPDM having ENB as the diene. Since EPDM has saturated a carbon–carbon backbone, it possesses excellent resistance to oxygen, ozone, heat and UV light, whereas the non-polar structure endows EPDM with excellent electrical resistivity and resistance to polar solvents. Hence, it has broad application in the electrical insulation, building, construction and automotive sectors. Due to its importance, a significant number of studies concerning EPDM in various fields have been performed [1–11].
* Corresponding author. Tel.: þ82 2 3408 3815. E-mail address: [email protected] (S.-S. Choi). 0142-9418/$ – see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2011.04.005
ENB content in EPDM determines the grade of EPDM and cure characteristics of EPDM compounds. Pyrolysisgas chromatography (pyrolysis-GC) has been applied to characterize EPMs and EPDMs [12–15]. Yamada and coworkers [14,15] reported benzene, toluene, C7H8 species (5-ethylidene-1,3-cyclopentadiene) and C7H10 species (4-ethylidene-1-cyclopentene and 3-ethylidene-1-cyclopentene) as pyrolysis products formed from ENB. They estimated their structures by comparing the retention data with the boiling points empirically expected from their structures. In the present work, pyrolysis products formed from ENB units were determined by comparing pyrolysis products of EPDMs with different ENB contents, and the chemical structures of pyrolysis products formed from ENB were identified by interpreting their mass spectra. Formation mechanisms of ENB-derived pyrolysis products are proposed. Variations of the pyrolysis products with pyrolysis temperature were also examined, and a method to determine the ENB content of EPDM is suggested via analysis of the experimental results.
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Scheme 1. General chemical structure of EPDM having ENB as a diene.
2. Experimental Four EPDMs with different ENB contents of 0, 2.3, 5.7, and 8.9 wt%, identified as KEP-070P, KEP-435, KEP-210, and KEP-2490, respectively, were obtained from Kumho Polychem Co. (Korea). Pyrolysis–GC/MS was carried out using a pyroprobe 2000 system with a CDS 1500 interface (Chemical Data System, Oxford, USA) coupled to an Agilent 6890 gas chromatograph equipped with a 5973 mass spectrometer from Agilent Technology Inc. (USA). The sample (about 0.2 mg) was preheated at 250 C for 15 s and pyrolyzed at 700–940 C for 5 s under helium (He) atmosphere. A HP-PLOT/Q capillary column (0.32 mm 15 m, 20 mm film thickness) from Agilent Technology Inc. (USA) was used. The temperatures of the interface and injector were 250 C. The GC oven temperature program was as follows: 100 C (held for 2 min) to 130 C (held for 5 min) at 1 C/min and raised again to 220 C (held for 5 min) at 5 C/ min. The interface temperature of GC to MS was 250 C, electron ionization (70 eV) was used to ionize the pyrolysis products, and the MS source temperature was 230 C. Each experiment was performed at least three times. 3. Results and discussion Fig. 1 shows the pyrolysis-GC/MS TIC chromatograms of EPDMs with different ENB contents, and the major pyrolysis products are listed in Table 1. In order to determine the unique pyrolysis products formed from ENB, the pyrolysisGC/MS TIC chromatograms were compared. Peak intensities of some pyrolysis products increased as the ENB content in EPDM increased, as shown in Fig. 1. Peaks at 36.35, 48.94, 50.20, and 51.10 min notably increased with increases in the ENB content. Therefore, it can be concluded that those pyrolysis products were generated from ENB. The pyrolysis products at 36.35, 48.94, 50.20, and 51.10 min were identified by interpreting their mass spectra as shown in Fig. 3–5, and they were assigned to benzene, toluene, 4ethylidene-1-cyclopentene and 3-ethylidene-1-cyclopentene, respectively. Benzene can be formed from ENB by C–C bond cleavage between the ENB unit and the other unit (ethylene or propylene unit) and following rearrangement, as shown in Scheme 2. However, benzene was detected in EPM (ENB content 0 wt%) in a trace amount, as shown in Fig. 2(a). Toluene can be also formed from the ENB by C–C bond cleavage of the 6-membered ring of the ENB unit to generate biradical intermediate and the following rearrangement, as
Fig. 1. Pyrolysis-GC/MS TIC chromatograms of EPDMs with ENB contents of 0 (a), 2.3 (b), 5.7 (c), and 8.9 wt% (d) at 700 C.
shown in Scheme 3. However, toluene was detected in EPM in trace amount, as shown in Fig. 2(a). 4-Ethylidene-1cyclopentene and 3-ethylidene-1-cyclopentene can also be formed from the ENB by C–C bond cleavage of the 6membered ring of the ENB unit to generate biradical intermediate and the following rearrangement, as shown in Scheme 4. 4-Ethylidene-1-cyclopentene and 3-ethylidene1-cyclopentene were not observed in the pyrolysis-GC/MS TIC chromatogram of EPM, as shown in Fig. 2(a). 4-
Table 1 Major pyrolysis products. Peak No.
Retention time (min)
Product
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
2.04 2.19 6.17 15.78 16.69 17.48 19.73 33.50 34.96 36.35 37.50 45.80 46.40 47.32 47.80 48.47 48.94 50.20 51.10
Propylene Propane Butane Pentenes 2-methyl-1,3-butadiene Pentane 1,4-pentadiene 2-methyl-1-pentene 1-hexene Benzene Hexane 3-methyl-1-hexene 4-methyl-1-hexene 2-methyl-1-hexene 1-heptene Heptane Toluene 4-ethylidene-1-cyclopentene 3-ethylidene-1-cyclopentene
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Fig. 4. Mass spectrum of the peak 17 in Fig. 2.
Fig. 2. Expanded pyrolysis-GC/MS TIC chromatograms of EPDMs with ENB contents of 0 (a), 2.3 (b), 5.7 (c), and 8.9 wt% (d) at 700 C.
Ethylidene-1-cyclopentene was much more abundant than 3-ethylidene-1-cyclopentene. Propylene is a common pyrolysis product formed from both ethylene and propylene sequences, and is the most abundant pyrolysis product. In order to investigate the influence of the pyrolysis temperature on the formation of ENB-derived pyrolysis products in detail, variations of the relative abundance ratios of benzene, toluene and 4-ethylidene-1-cyclopentene (reference: propylene) were plotted as a function of the pyrolysis temperature in Figs. 6–8, respectively. The peak intensity ratios of benzene/
Fig. 3. Mass spectrum of the peak 10 in Fig. 2.
Fig. 5. Mass spectrum of the peak 18 in Fig. 2.
Scheme 2. Mechanism for formation of benzene from 5-ethylidene-2-norbornene unit of EPDM by pyrolysis.
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Scheme 3. Mechanism for formation of toluene from 5-ethylidene-2-norbornene unit of EPDM by pyrolysis.
Fig. 7. Variations of the peak intensity ratios of toluene/propylene with the pyrolysis temperature. Squares, circles, up-triangles, and down-triangles indicate the peak intensity ratios of EPDM with the ENB contents of 0, 2.3, 5.7, and 8.9 wt%, respectively.
propylene and toluene/propylene increased as the ENB content increased and as the pyrolysis temperature increased. The benzene/propylene ratios were larger than those of toluene/propylene. EPM (without ENB) also generated benzene and toluene by pyrolysis. The benzene/ propylene and toluene/propylene ratios notably increased
at temperatures higher than 800 C. This indicates that the formation of both benzene and toluene needs high energy. The peak intensity ratios of 4-ethylidene-1-cyclopentene/ propylene increased as the ENB content increased, but decreased as the pyrolysis temperature increased. EPM did not generate 4-ethylidene-1-cyclopentene by pyrolysis. The decreasing 4-ethylidene-1-cyclopentene/propylene ratio with the pyrolysis temperature indicates that the formation of 4-ethylidene-1-cyclopentene does not need high energy. According to the formation mechanisms of toluene and 4-ethylidene-1-cyclopentene in Schemes 3 and 4, toluene and 4-ethylidene-1-cyclopentene can be formed through the same intermediate of biradical species. Thus, this can lead to the conclusion that the rearrangement to form a 6-membered ring from a 5-membered one is not a thermodynamically favorable process compared to the retaining 5-membered ring.
Fig. 6. Variations of the peak intensity ratios of benzene/propylene with the pyrolysis temperature. Squares, circles, up-triangles, and down-triangles indicate the peak intensity ratios of EPDM with the ENB contents of 0, 2.3, 5.7, and 8.9 wt%, respectively.
Fig. 8. Variations of the peak intensity ratios of 4-ethylidene-1-cyclopentene/propylene with the pyrolysis temperature. Squares, circles, uptriangles, and down-triangles indicate the peak intensity ratios of EPDM with the ENB contents of 0, 2.3, 5.7, and 8.9 wt%, respectively.
Scheme 4. Mechanism for formation of 4-ethylidene-1-cyclopentene (and 3-ethylidene-1-cyclopentene) from 5-ethylidene-2-norbornene unit of EPDM by pyrolysis.
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Fig. 9. Variations of the differences in benzene/propylene peak ratios between EPDM and EPM with the ENB content. Squares, circles, and triangles indicate the difference at 800, 850, and 900 C respectively.
In order to suggest an analytical method to determine the ENB content of EPDM, the differences in the ENB-derived pyrolysis products/propylene peak ratios between EPDM and EPM were plotted as a function of the ENB content in Figs. 9–11 for the benzene/propylene, toluene/propylene, and 4-ethylidene-1-cyclopentene/propylene ratios, respectively. The differences in peak intensity ratios increased as the ENB content increased and the variations showed good linear relationships. For the benzene/propylene ratios, the curve fitting equations at 800, 850, and 900 C were nearly the same: y ¼ 3.10 102x 5.0 103 (r ¼ 0.998) at 800 C, y ¼ 3.05 102x 8.9 103 (r ¼ 0.997) at 850 C, and y ¼ 3.30 102x þ 3.2 103 (r ¼ 0.997) at 900 C. Since the curve fitting equations show good linear relationships and differences in the curve fitting equations according to the pyrolysis temperatures are very small, ENB content of an unknown EPDM sample can be determined using the curve fitting equations. The average curve fitting equation at 800– 900 C was y ¼ 3.15 102x 3.6 103.For the toluene/ propylene ratios, the curve fitting equations at 800, 850, and 900 C were also nearly the same: y ¼ 1.62 102x þ 1.3 103 (r ¼ 0.998) at 800 C, y ¼ 1.56 102x þ 2.5 103 (r ¼ 0.997)
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Fig. 11. Variations of the differences in 4-ethylidene-1-cyclopentene/ propylene peak ratios between EPDM and EPM with the ENB content. Squares, circles, and triangles indicate the difference at 800, 850, and 900 C respectively.
at 850 C, and y ¼ 1.79 102x þ 5.4 103 (r ¼ 0.990) at 900 C. Since the curve fitting equations show good linear relationships and differences in the curve fitting equations according to the pyrolysis temperatures are very small, ENB content of an unknown EPDM sample can also be determined using these curve fitting equations. The average curve fitting equation at 800–900 C was y ¼ 1.66 102x þ 3.1 103. For the 4-ethylidene-1-cyclopentene/propylene ratios, the curve fitting equations at different pyrolysis temperatures were not similar. The values of the slope and intercept decreased as the pyrolysis temperature increased. The curve fitting equations at 800, 850, and 900 C were y ¼ 1.97 102x þ 2.6 103 (r ¼ 0.997), y ¼ 9.53 103x þ 1.6 103 (r ¼ 0.999), and y ¼ 8.58 103x 1.53 103 (r ¼ 0.997), respectively. The decreasing trends of the curve fitting equations with the pyrolysis temperature may be due to the decreasing 4ethylidene-1-cyclopentene/propylene ratios. When determining ENB content of an unknown EPDM sample using the 4-ethylidene-1-cyclopentene/propylene ratios, the pyrolysis temperature should be considered. 4. Conclusions
Fig. 10. Variations of the differences in toluene/propylene peak ratios between EPDM and EPM with the ENB content. Squares, circles, and triangles indicate the difference at 800, 850, and 900 C respectively.
Benzene, toluene, 4-ethylidene-1-cyclopentene, and 3ethylidene-1-cyclopentene were principal pyrolysis products formed from the ENB unit of EPDM. Benzene and toluene were also generated from EPM (without ENB), but 4-ethylidene-1-cyclopentene and 3-ethylidene-1-cyclopentene were not generated from EPM. 4-Ethylidene-1cyclopentene was much more abundant than 3-ethylidene1-cyclopentene. Relative abundances of benzene, toluene, and 4-ethylidene-1-cyclopentene increased as the ENB content increased. The relative abundances of benzene and toluene increased as the pyrolysis temperature increased, whereas that of 4-ethylidene-1-cyclopentene decreased. The differences in the ENB-derived pyrolysis products/ propylene peak ratios (benzene/propylene, toluene/ propylene, and 4-ethylidene-1-cyclopentene/propylene
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ratios) between EPDM and EPM linearly increased as the ENB content increased. Therefore, using the good linear relationships of variations of the ENB-derived pyrolysis product ratio differences, ENB content of an unknown EPDM sample can be determined. Acknowledgements This research was supported by a grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea.
[6]
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References [11] [1] H. Yu, G. Xu, X. Shen, X. Yan, C. Hu, Y. Wang, Corrosion resistance and infrared emissivity properties of EPDM (EPDM-g-MAH) film on low infrared emissivity PU/Cu coating, Electrochim. Acta 55 (2010) 1843. [2] S.-S. Choi, H.-S. Chung, Y.-T. Joo, K.-M. Yang, S.-H. Lee, Appearance contamination of EPDM article from water solution, Elast. Comps 45 (2010) 100. [3] K.H. Seo, K.-S. Cho, I.-S. Yun, W.-H. Choi, B.-K. Hur, D.-G. Kang, The study of characteristics on EPDM, NBR, FKM, VMQ, and FVMQ for sealing applications to lithium ion battery, Elast. Comps 45 (2010) 212. [4] J. Su, S. Chen, J. Zhang, Z. Xu, Comparison of cure, mechanical, electric properties of EPDM filled with Sm2O3 treated by different coupling agents, Polym. Test. 28 (2009) 235. [5] S. Mitra, M. Jørgensen, W.B. Pedersen, K. Almdal, D. Banerjee, Structural determination of ethylene-propylene-diene rubber
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(EPDM) containing high degree of controlled long-chain branching, J. Appl. Polym. Sci. 113 (2009) 2962. Q. Zhao, X. Li, J. Gao, Aging behavior and mechanism of ethylene– propylene- diene monomer (EPDM) rubber in fluorescent UV/ condensation weathering environment, Polym. Deg. Stab 94 (2009) 339. Q. Zhao, X. Li, J. Gao, Z. Jia, Evaluation of ethylene–propylene–diene monomer (EPDM) aging in UV/condensation environment by principal component analysis (PCA), Mater. Lett. 63 (2009) 1647. B.K. Hwang, K.H. Hong, H.Y. Park, I.R. Jeon, K.H. Seo, Thermal and mechanical properties of EPDM and CR compounds with various fillers and its contents for V-rib belt, Elast. Compos 44 (2009) 299. T. Lee, C. Yoon, D.-S. Bang, D.-Y. Ahn, H. Kye, K.-C. Shin, A study on the manufacturing and mechanical properties of the PA66/EPDM/PP composites for enhanced low temperature fracture resistances, Elast. Compos 44 (2009) 164. J.S. Kim, J.H. Lee, W.S. Jung, J.W. Bae, H.C. Park, D.P. Kang, Effects of reinforcing fillers on far-infrared vulcanization characteristics of EPDM, Elast. Compos 44 (2009) 47. F. Barroso-Bujans, R. Verdejo, A. Lozano, J.L.G. Fierro, M.A. LopezManchado, Sulfonation of vulcanized ethylene–propylene–diene terpolymer membranes, Acta Mater. 56 (2008) 4780. L. Michajlov, H.-J. Cantow, P. Zugenmaier, Investigation of the sequence length distribution in ethylene-propylene copolymers by pyrolysis and reaction gas chromatography, Polymer 12 (1971) 70. S. Tsuge, Y. Sugimura, T. Nagaya, Structural characterization of polyolifins by pyrolysis-hydrogenation glass capillary gas chromatography, J. Anal. Appl. Pyrolysis 1 (1980) 221. T. Yamada, T. Okumoto, H. Ohtani, S. Tsuge, Structural characterization of ethylene-propylene-diene rubbers by high-resolution pyrolysis gas chromatography, Rubber Chem. Technol. 63 (1990) 191. T. Okumoto, T. Yamada, S. Tsuge, H. Ohtani, Structural characterization by pyrolysis gas chromatography of ethylene-propylenediene rubbers cured with sulfur/thiazole accelerator, Kobunshi Ronbunshu 54 (1997) 108.
Contents lists available at ScienceDirect
Polymer Testing journal homepage: www.elsevier.com/locate/polytest
Analysis Method
Analysis of 5-ethylidene-2-norbornene in ethylene-propylene-diene terpolymer using pyrolysis-GC/MS Sung-Seen Choi*, Yun-Ki Kim Department of Chemistry, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 February 2011 Accepted 10 April 2011
Ethylene-propylene-diene terpolymer (EPDM) having 5-ethylidene-2-norbornene (ENB) as a diene unit was pyrolyzed and the pyrolysis products were analyzed using gas chromatography/mass spectrometry (GC/MS) to develop a method for identification and quantitation of ENB. Pyrolysis products formed from ENB units were determined by comparing pyrolysis products of EPDMs with different ENB contents. Principal pyrolysis products generated from ENB units were benzene, toluene and 4-ethylidene-1-cyclopentene. Relative peak intensities of benzene and toluene increased as the pyrolysis temperature increased, whereas that of 4-ethylidene-1-cyclopentene decreased. The differences in peak intensity ratios of the ENB-derived pyrolysis products/propylene between EPDM and EPM (ENB content ¼ 0 wt%) linearly increased as the ENB content of EPDM increased. ENB content in EPDM can be determined using the linear relationship between the difference in the peak intensity ratios and the ENB content. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: EPDM ENB Pyrolysis Benzene Toluene 4-Ethylidene-1-cyclopentene
1. Introduction Ethylene-propylene-diene terpolymer (EPDM) consisting of ethylene, propylene and unsaturated diene is one of the popular synthetic rubbers. In general, 5-ethylidene-2norbornene (ENB), dicyclopentadiene (DCPD) and 1,4hexadiene (HD) are used as the diene, with ENB being the most frequently used. Scheme 1 shows the chemical structure of EPDM having ENB as the diene. Since EPDM has saturated a carbon–carbon backbone, it possesses excellent resistance to oxygen, ozone, heat and UV light, whereas the non-polar structure endows EPDM with excellent electrical resistivity and resistance to polar solvents. Hence, it has broad application in the electrical insulation, building, construction and automotive sectors. Due to its importance, a significant number of studies concerning EPDM in various fields have been performed [1–11].
* Corresponding author. Tel.: þ82 2 3408 3815. E-mail address: [email protected] (S.-S. Choi). 0142-9418/$ – see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2011.04.005
ENB content in EPDM determines the grade of EPDM and cure characteristics of EPDM compounds. Pyrolysisgas chromatography (pyrolysis-GC) has been applied to characterize EPMs and EPDMs [12–15]. Yamada and coworkers [14,15] reported benzene, toluene, C7H8 species (5-ethylidene-1,3-cyclopentadiene) and C7H10 species (4-ethylidene-1-cyclopentene and 3-ethylidene-1-cyclopentene) as pyrolysis products formed from ENB. They estimated their structures by comparing the retention data with the boiling points empirically expected from their structures. In the present work, pyrolysis products formed from ENB units were determined by comparing pyrolysis products of EPDMs with different ENB contents, and the chemical structures of pyrolysis products formed from ENB were identified by interpreting their mass spectra. Formation mechanisms of ENB-derived pyrolysis products are proposed. Variations of the pyrolysis products with pyrolysis temperature were also examined, and a method to determine the ENB content of EPDM is suggested via analysis of the experimental results.
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Scheme 1. General chemical structure of EPDM having ENB as a diene.
2. Experimental Four EPDMs with different ENB contents of 0, 2.3, 5.7, and 8.9 wt%, identified as KEP-070P, KEP-435, KEP-210, and KEP-2490, respectively, were obtained from Kumho Polychem Co. (Korea). Pyrolysis–GC/MS was carried out using a pyroprobe 2000 system with a CDS 1500 interface (Chemical Data System, Oxford, USA) coupled to an Agilent 6890 gas chromatograph equipped with a 5973 mass spectrometer from Agilent Technology Inc. (USA). The sample (about 0.2 mg) was preheated at 250 C for 15 s and pyrolyzed at 700–940 C for 5 s under helium (He) atmosphere. A HP-PLOT/Q capillary column (0.32 mm 15 m, 20 mm film thickness) from Agilent Technology Inc. (USA) was used. The temperatures of the interface and injector were 250 C. The GC oven temperature program was as follows: 100 C (held for 2 min) to 130 C (held for 5 min) at 1 C/min and raised again to 220 C (held for 5 min) at 5 C/ min. The interface temperature of GC to MS was 250 C, electron ionization (70 eV) was used to ionize the pyrolysis products, and the MS source temperature was 230 C. Each experiment was performed at least three times. 3. Results and discussion Fig. 1 shows the pyrolysis-GC/MS TIC chromatograms of EPDMs with different ENB contents, and the major pyrolysis products are listed in Table 1. In order to determine the unique pyrolysis products formed from ENB, the pyrolysisGC/MS TIC chromatograms were compared. Peak intensities of some pyrolysis products increased as the ENB content in EPDM increased, as shown in Fig. 1. Peaks at 36.35, 48.94, 50.20, and 51.10 min notably increased with increases in the ENB content. Therefore, it can be concluded that those pyrolysis products were generated from ENB. The pyrolysis products at 36.35, 48.94, 50.20, and 51.10 min were identified by interpreting their mass spectra as shown in Fig. 3–5, and they were assigned to benzene, toluene, 4ethylidene-1-cyclopentene and 3-ethylidene-1-cyclopentene, respectively. Benzene can be formed from ENB by C–C bond cleavage between the ENB unit and the other unit (ethylene or propylene unit) and following rearrangement, as shown in Scheme 2. However, benzene was detected in EPM (ENB content 0 wt%) in a trace amount, as shown in Fig. 2(a). Toluene can be also formed from the ENB by C–C bond cleavage of the 6-membered ring of the ENB unit to generate biradical intermediate and the following rearrangement, as
Fig. 1. Pyrolysis-GC/MS TIC chromatograms of EPDMs with ENB contents of 0 (a), 2.3 (b), 5.7 (c), and 8.9 wt% (d) at 700 C.
shown in Scheme 3. However, toluene was detected in EPM in trace amount, as shown in Fig. 2(a). 4-Ethylidene-1cyclopentene and 3-ethylidene-1-cyclopentene can also be formed from the ENB by C–C bond cleavage of the 6membered ring of the ENB unit to generate biradical intermediate and the following rearrangement, as shown in Scheme 4. 4-Ethylidene-1-cyclopentene and 3-ethylidene1-cyclopentene were not observed in the pyrolysis-GC/MS TIC chromatogram of EPM, as shown in Fig. 2(a). 4-
Table 1 Major pyrolysis products. Peak No.
Retention time (min)
Product
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
2.04 2.19 6.17 15.78 16.69 17.48 19.73 33.50 34.96 36.35 37.50 45.80 46.40 47.32 47.80 48.47 48.94 50.20 51.10
Propylene Propane Butane Pentenes 2-methyl-1,3-butadiene Pentane 1,4-pentadiene 2-methyl-1-pentene 1-hexene Benzene Hexane 3-methyl-1-hexene 4-methyl-1-hexene 2-methyl-1-hexene 1-heptene Heptane Toluene 4-ethylidene-1-cyclopentene 3-ethylidene-1-cyclopentene
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Fig. 4. Mass spectrum of the peak 17 in Fig. 2.
Fig. 2. Expanded pyrolysis-GC/MS TIC chromatograms of EPDMs with ENB contents of 0 (a), 2.3 (b), 5.7 (c), and 8.9 wt% (d) at 700 C.
Ethylidene-1-cyclopentene was much more abundant than 3-ethylidene-1-cyclopentene. Propylene is a common pyrolysis product formed from both ethylene and propylene sequences, and is the most abundant pyrolysis product. In order to investigate the influence of the pyrolysis temperature on the formation of ENB-derived pyrolysis products in detail, variations of the relative abundance ratios of benzene, toluene and 4-ethylidene-1-cyclopentene (reference: propylene) were plotted as a function of the pyrolysis temperature in Figs. 6–8, respectively. The peak intensity ratios of benzene/
Fig. 3. Mass spectrum of the peak 10 in Fig. 2.
Fig. 5. Mass spectrum of the peak 18 in Fig. 2.
Scheme 2. Mechanism for formation of benzene from 5-ethylidene-2-norbornene unit of EPDM by pyrolysis.
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Scheme 3. Mechanism for formation of toluene from 5-ethylidene-2-norbornene unit of EPDM by pyrolysis.
Fig. 7. Variations of the peak intensity ratios of toluene/propylene with the pyrolysis temperature. Squares, circles, up-triangles, and down-triangles indicate the peak intensity ratios of EPDM with the ENB contents of 0, 2.3, 5.7, and 8.9 wt%, respectively.
propylene and toluene/propylene increased as the ENB content increased and as the pyrolysis temperature increased. The benzene/propylene ratios were larger than those of toluene/propylene. EPM (without ENB) also generated benzene and toluene by pyrolysis. The benzene/ propylene and toluene/propylene ratios notably increased
at temperatures higher than 800 C. This indicates that the formation of both benzene and toluene needs high energy. The peak intensity ratios of 4-ethylidene-1-cyclopentene/ propylene increased as the ENB content increased, but decreased as the pyrolysis temperature increased. EPM did not generate 4-ethylidene-1-cyclopentene by pyrolysis. The decreasing 4-ethylidene-1-cyclopentene/propylene ratio with the pyrolysis temperature indicates that the formation of 4-ethylidene-1-cyclopentene does not need high energy. According to the formation mechanisms of toluene and 4-ethylidene-1-cyclopentene in Schemes 3 and 4, toluene and 4-ethylidene-1-cyclopentene can be formed through the same intermediate of biradical species. Thus, this can lead to the conclusion that the rearrangement to form a 6-membered ring from a 5-membered one is not a thermodynamically favorable process compared to the retaining 5-membered ring.
Fig. 6. Variations of the peak intensity ratios of benzene/propylene with the pyrolysis temperature. Squares, circles, up-triangles, and down-triangles indicate the peak intensity ratios of EPDM with the ENB contents of 0, 2.3, 5.7, and 8.9 wt%, respectively.
Fig. 8. Variations of the peak intensity ratios of 4-ethylidene-1-cyclopentene/propylene with the pyrolysis temperature. Squares, circles, uptriangles, and down-triangles indicate the peak intensity ratios of EPDM with the ENB contents of 0, 2.3, 5.7, and 8.9 wt%, respectively.
Scheme 4. Mechanism for formation of 4-ethylidene-1-cyclopentene (and 3-ethylidene-1-cyclopentene) from 5-ethylidene-2-norbornene unit of EPDM by pyrolysis.
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Fig. 9. Variations of the differences in benzene/propylene peak ratios between EPDM and EPM with the ENB content. Squares, circles, and triangles indicate the difference at 800, 850, and 900 C respectively.
In order to suggest an analytical method to determine the ENB content of EPDM, the differences in the ENB-derived pyrolysis products/propylene peak ratios between EPDM and EPM were plotted as a function of the ENB content in Figs. 9–11 for the benzene/propylene, toluene/propylene, and 4-ethylidene-1-cyclopentene/propylene ratios, respectively. The differences in peak intensity ratios increased as the ENB content increased and the variations showed good linear relationships. For the benzene/propylene ratios, the curve fitting equations at 800, 850, and 900 C were nearly the same: y ¼ 3.10 102x 5.0 103 (r ¼ 0.998) at 800 C, y ¼ 3.05 102x 8.9 103 (r ¼ 0.997) at 850 C, and y ¼ 3.30 102x þ 3.2 103 (r ¼ 0.997) at 900 C. Since the curve fitting equations show good linear relationships and differences in the curve fitting equations according to the pyrolysis temperatures are very small, ENB content of an unknown EPDM sample can be determined using the curve fitting equations. The average curve fitting equation at 800– 900 C was y ¼ 3.15 102x 3.6 103.For the toluene/ propylene ratios, the curve fitting equations at 800, 850, and 900 C were also nearly the same: y ¼ 1.62 102x þ 1.3 103 (r ¼ 0.998) at 800 C, y ¼ 1.56 102x þ 2.5 103 (r ¼ 0.997)
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Fig. 11. Variations of the differences in 4-ethylidene-1-cyclopentene/ propylene peak ratios between EPDM and EPM with the ENB content. Squares, circles, and triangles indicate the difference at 800, 850, and 900 C respectively.
at 850 C, and y ¼ 1.79 102x þ 5.4 103 (r ¼ 0.990) at 900 C. Since the curve fitting equations show good linear relationships and differences in the curve fitting equations according to the pyrolysis temperatures are very small, ENB content of an unknown EPDM sample can also be determined using these curve fitting equations. The average curve fitting equation at 800–900 C was y ¼ 1.66 102x þ 3.1 103. For the 4-ethylidene-1-cyclopentene/propylene ratios, the curve fitting equations at different pyrolysis temperatures were not similar. The values of the slope and intercept decreased as the pyrolysis temperature increased. The curve fitting equations at 800, 850, and 900 C were y ¼ 1.97 102x þ 2.6 103 (r ¼ 0.997), y ¼ 9.53 103x þ 1.6 103 (r ¼ 0.999), and y ¼ 8.58 103x 1.53 103 (r ¼ 0.997), respectively. The decreasing trends of the curve fitting equations with the pyrolysis temperature may be due to the decreasing 4ethylidene-1-cyclopentene/propylene ratios. When determining ENB content of an unknown EPDM sample using the 4-ethylidene-1-cyclopentene/propylene ratios, the pyrolysis temperature should be considered. 4. Conclusions
Fig. 10. Variations of the differences in toluene/propylene peak ratios between EPDM and EPM with the ENB content. Squares, circles, and triangles indicate the difference at 800, 850, and 900 C respectively.
Benzene, toluene, 4-ethylidene-1-cyclopentene, and 3ethylidene-1-cyclopentene were principal pyrolysis products formed from the ENB unit of EPDM. Benzene and toluene were also generated from EPM (without ENB), but 4-ethylidene-1-cyclopentene and 3-ethylidene-1-cyclopentene were not generated from EPM. 4-Ethylidene-1cyclopentene was much more abundant than 3-ethylidene1-cyclopentene. Relative abundances of benzene, toluene, and 4-ethylidene-1-cyclopentene increased as the ENB content increased. The relative abundances of benzene and toluene increased as the pyrolysis temperature increased, whereas that of 4-ethylidene-1-cyclopentene decreased. The differences in the ENB-derived pyrolysis products/ propylene peak ratios (benzene/propylene, toluene/ propylene, and 4-ethylidene-1-cyclopentene/propylene
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ratios) between EPDM and EPM linearly increased as the ENB content increased. Therefore, using the good linear relationships of variations of the ENB-derived pyrolysis product ratio differences, ENB content of an unknown EPDM sample can be determined. Acknowledgements This research was supported by a grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea.
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