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Determination of OH-number and functionality of polybutadiene-ol by FTIR and NMR spectroscopy
Polymer Testing 22 (2003) 165–168 www.elsevier.com/locate/polytest
Chemical Analysis
Determination of OH-number and functionality of polybutadiene-ol by FTIR and NMR spectroscopy G. Mir Mohammad Sadeghi ∗, J. Morshedian, M. Barikani Iran Polymer Institute, P.O. Box: 14965/115, Tehran, Iran Received 13 March 2002; accepted 9 May 2002
Abstract In this work, location and number of OH functional groups in polybutadiene-ol, a pre-polymer used for producing special purpose polyurethanes and unsaturated polyesters, was determined by a combination of two analytical methods: FTIR and H-NMR spectroscopy. Hydroxyl concentration or OH equivalent weight of the pre-polymer was measured through a comparison between the IR absorption band of THF-associated hydroxyl groups around 3450 cm⫺1 with the calibration curve, which was obtained using OH/THF-associated absorption plotted against concentration of various primary alcohols. The 500 MHz H-NMR spectrum of butadiene-ol was then obtained to determine molecular weight and concentration of hydroxyl groups. 2002 Elsevier Science Ltd. All rights reserved. Keywords: Polybutadiene-ol; Functionality; OH-number; IR absorption; H-NMR
1. Introduction Butadiene polyol is a pre-polymer with an average molecular weight of 1200–5000 g/mol, which is primarily used as a polymer additive and also in production of foams, special purpose polyurethane elastomers (high abrasion resistance, high hydrolytic stability, and high low-temperature flexibility), as well as unsaturated polyesters. Its molecular chains contain sufficient double bonds for further crosslinking reactions [1–3]. The type and properties of the final products, in the form of elastomeric and thermosetting networks, strongly depend on microstructure, functionality, and molecular weight of the initial polyol used. The chemical structure of polybutadiene consists of three major conformations: cis, trans, and 1,2-vinyl (isotactic, and syndiotactic). Therefore, OH groups may exist in different locations throughout the molecular chains in polybutadiene-ol.
∗ Corresponding author. Tel.: +98-21-6026317; fax: +9821-6026500. E-mail address: [email protected] (G.M.M. Sadeghi).
Different methods are available for measuring the concentration of OH groups: chemical analysis, IR, and NMR spectroscopy. In the FTIR analysis method, concentration of hydroxyl groups is determined by analyzing the appropriate absorption band in the 3450 cm⫺1 region, the intensity of which is not significantly affected by the change in temperature or molecular size in low concentrations [4]. In the NMR analysis method, the molecular weight of polyol is obtained through analyzing the backbone methylene protons and their peak areas in the NMR curve.
2. Experimental 2.1. Materials The following materials were prepared and used in the experiments: 1. Butadiene polyol (synthesized and provided locally; the preparation procedure is reported elsewhere);
0142-9418/03/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 4 1 8 ( 0 2 ) 0 0 0 6 5 - X
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2. THF solvent (Merck); 3. 2-ethyl 1-butanol (Merck); 4. 1-octanol (Merck). 2.2. Equipment The equipment listed below was used in this work: 1. Bruker 500 H-NMR spectrometer with TMS as internal reference and examined at 100 °C. 2. Bruker IFS-48 FTIR spectrometer based on 10 scans per second. 2.3. Procedure THF was refluxed for a few hours in the presence of sodium, until a dark blue color appeared. In this respect, THF and solutions were dry and oxygen-free. Alcohols were dried over 0.4 nm molecular sieves. Solutions of 30–200 meq./l of 1-octanol and 2-ethyl 1-butanol were prepared in distilled THF. A solution of polyol in THF was also prepared (5 g/100 cm3). To analyze the polyol by the NMR instrument, it was dissolved in 1,2-dichlorobenzene (5 g/100 cm3). Solutions of alcohols in THF were prepared using various concentrations. The calibration curve was obtained by plotting OH/THF-associated absorption versus concentration of various primary alcohols. The molecular weight of polyol, determined through NMR measurements divided by OH equivalent weight, obtained by means of FTIR, gives functionality. 3. Results and discussion Figs. 1 and 2 show FTIR spectra of 1-octanol and 2ethyl 1-butanol solutions in THF, with various concen-
Fig. 1. FTIR spectra of 1-octanol solutions with various concentrations (113, 58, 31, 16.5 mequiv./l) increasing with height.
Fig. 2. FTIR spectra of 2-ethyl 1-butanol solutions with various concentrations increasing with height.
trations ranging from 30 to 200 meq./l, respectively. The level of OH interactions was low enough for OH groups to be completely associated with THF molecules. Fig. 3 illustrates the calibration curve, which indicates absorption at 3450 cm⫺1 plotted against concentration of primary alcohols. Fig. 4 shows the FTIR spectrum for polyol solution in THF (5 g/100 cm3). A comparison between Fig. 4 and the calibration curve leads to a hydroxyl value of 0.78 meq./g, polyol OH equivalent weight of 1280 g, and OH-number of 43.7. It is noteworthy to mention that using the FTIR method, the equivalent weight of polyol is determined by a comparison between absorption band of THF-associated hydroxyl groups for the polyol sample and the calibration curve. The terminal alcohol groups are mostly primary [5]. Therefore, the calibration curve in our study was based on a primary alcohol such as 1-octanol, or 2ethyl 1-butanol and other alcohols likewise. Fig. 5 gives an illustration of the H-NMR spectrum
Fig. 3. IR calibration curve.
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Fig. 6. 500 MHz H-NMR spectrum of polyol in 1,2-dichlorobenzene at 100 °C in 3.4–4.2 ppm region. Fig. 4.
FTIR spectrum of polyol solution (5 g/100 cm).
In Scheme 1, the first resonance peak (3.4 ppm) corresponds to a primary alcohol (–CH2OH) adjacent to a saturated carbon (c), while 3.9 and 4 ppm bands are assigned to primary alcohols adjacent to olefins (a, b). Moreover, simultaneous existence of 4.3 and 5.9 ppm NMR peaks indicates the presence of OH groups attached to the backbone of the chains in addition to the observed terminal ones. This can explain, and is in agreement with, the rather high value of functionality arrived at.
4. Conclusion
Fig. 5. 500 MHz H-NMR spectrum of polyol in 1,2-dichlorobenzene at 100 °C.
for polyol. The resonance groupings centered at 1.4, 2, 4, 5.4, and 5.6 ppm represent 1,2-methylene, 1,4-methylene, hydroxyl, 1,2-terminal, 1,4-olefinic, and non-terminal vinyl protons, respectively [6]. Fig. 6 shows a surface integral of 4 ppm, which is related to hydroxyl groups. The ratio of the sum of other protons to hydroxylic ones gives the degree of polymerization, which was found to be 85. As a result, number average molecular weight and functionality of polyol are calculated to be 4630 g/mol and 3.6, respectively.
With respect to the drawbacks in using common chemical methods in this work, it was learnt that functionality and OH number could be measured faster and more thoroughly through the use of FTIR and NMR analysis techniques. Furthermore, it is only by use of this method that it is possible to determine the percentage of OH groups relevant to 1,2-vinyl conformation, and other two cis and trans conformations. This knowledge is of utmost importance in determination of the properties and behavior of polyol in the polyurethane network.
Acknowledgements We wish to thank Mrs. Asgari and Mr. Bijanzadeh for their efforts in preparing FTIR and NMR Spectrums.
Scheme 1.
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References [1] R.T. Humpidge, D. Mattews, S.H. Morrel, J.R. Pyne, Processing and properties of liquid rubbers, Rubber Chemistry and Technology 46, (1973) 148–197. [2] Cenes, et al., Use of polydiene diols in thermoplastic polyurethanes, 1999 US patent 5925724. [3] Polybutadiene-ol Resins in Urethane Elastomers, Sartomer Company sales brochure, 1988. [4] C.S. Youn Kim, A.L. Dodge, S. Lau, A. Kawasaki,
Detrmination of hydrhxyl concentration in pre-polymers from the infrared absoaption bands of THF-associated hydrhxyl groups, Anal. Chem. 54 (1982) 232–238. [5] K.C. Ramey, M.W. Hayes, A.G. Altenav, W.A. Hines, E. T. Samulski, Macromolecules (1973) 6(5) 795 [6] 300 MHz proton NMR of polybutadiene, J. Polym. Sci. Polymer Edition 11 (1973) 449–452.
Chemical Analysis
Determination of OH-number and functionality of polybutadiene-ol by FTIR and NMR spectroscopy G. Mir Mohammad Sadeghi ∗, J. Morshedian, M. Barikani Iran Polymer Institute, P.O. Box: 14965/115, Tehran, Iran Received 13 March 2002; accepted 9 May 2002
Abstract In this work, location and number of OH functional groups in polybutadiene-ol, a pre-polymer used for producing special purpose polyurethanes and unsaturated polyesters, was determined by a combination of two analytical methods: FTIR and H-NMR spectroscopy. Hydroxyl concentration or OH equivalent weight of the pre-polymer was measured through a comparison between the IR absorption band of THF-associated hydroxyl groups around 3450 cm⫺1 with the calibration curve, which was obtained using OH/THF-associated absorption plotted against concentration of various primary alcohols. The 500 MHz H-NMR spectrum of butadiene-ol was then obtained to determine molecular weight and concentration of hydroxyl groups. 2002 Elsevier Science Ltd. All rights reserved. Keywords: Polybutadiene-ol; Functionality; OH-number; IR absorption; H-NMR
1. Introduction Butadiene polyol is a pre-polymer with an average molecular weight of 1200–5000 g/mol, which is primarily used as a polymer additive and also in production of foams, special purpose polyurethane elastomers (high abrasion resistance, high hydrolytic stability, and high low-temperature flexibility), as well as unsaturated polyesters. Its molecular chains contain sufficient double bonds for further crosslinking reactions [1–3]. The type and properties of the final products, in the form of elastomeric and thermosetting networks, strongly depend on microstructure, functionality, and molecular weight of the initial polyol used. The chemical structure of polybutadiene consists of three major conformations: cis, trans, and 1,2-vinyl (isotactic, and syndiotactic). Therefore, OH groups may exist in different locations throughout the molecular chains in polybutadiene-ol.
∗ Corresponding author. Tel.: +98-21-6026317; fax: +9821-6026500. E-mail address: [email protected] (G.M.M. Sadeghi).
Different methods are available for measuring the concentration of OH groups: chemical analysis, IR, and NMR spectroscopy. In the FTIR analysis method, concentration of hydroxyl groups is determined by analyzing the appropriate absorption band in the 3450 cm⫺1 region, the intensity of which is not significantly affected by the change in temperature or molecular size in low concentrations [4]. In the NMR analysis method, the molecular weight of polyol is obtained through analyzing the backbone methylene protons and their peak areas in the NMR curve.
2. Experimental 2.1. Materials The following materials were prepared and used in the experiments: 1. Butadiene polyol (synthesized and provided locally; the preparation procedure is reported elsewhere);
0142-9418/03/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 4 1 8 ( 0 2 ) 0 0 0 6 5 - X
166
G.M.M. Sadeghi et al. / Polymer Testing 22 (2003) 165–168
2. THF solvent (Merck); 3. 2-ethyl 1-butanol (Merck); 4. 1-octanol (Merck). 2.2. Equipment The equipment listed below was used in this work: 1. Bruker 500 H-NMR spectrometer with TMS as internal reference and examined at 100 °C. 2. Bruker IFS-48 FTIR spectrometer based on 10 scans per second. 2.3. Procedure THF was refluxed for a few hours in the presence of sodium, until a dark blue color appeared. In this respect, THF and solutions were dry and oxygen-free. Alcohols were dried over 0.4 nm molecular sieves. Solutions of 30–200 meq./l of 1-octanol and 2-ethyl 1-butanol were prepared in distilled THF. A solution of polyol in THF was also prepared (5 g/100 cm3). To analyze the polyol by the NMR instrument, it was dissolved in 1,2-dichlorobenzene (5 g/100 cm3). Solutions of alcohols in THF were prepared using various concentrations. The calibration curve was obtained by plotting OH/THF-associated absorption versus concentration of various primary alcohols. The molecular weight of polyol, determined through NMR measurements divided by OH equivalent weight, obtained by means of FTIR, gives functionality. 3. Results and discussion Figs. 1 and 2 show FTIR spectra of 1-octanol and 2ethyl 1-butanol solutions in THF, with various concen-
Fig. 1. FTIR spectra of 1-octanol solutions with various concentrations (113, 58, 31, 16.5 mequiv./l) increasing with height.
Fig. 2. FTIR spectra of 2-ethyl 1-butanol solutions with various concentrations increasing with height.
trations ranging from 30 to 200 meq./l, respectively. The level of OH interactions was low enough for OH groups to be completely associated with THF molecules. Fig. 3 illustrates the calibration curve, which indicates absorption at 3450 cm⫺1 plotted against concentration of primary alcohols. Fig. 4 shows the FTIR spectrum for polyol solution in THF (5 g/100 cm3). A comparison between Fig. 4 and the calibration curve leads to a hydroxyl value of 0.78 meq./g, polyol OH equivalent weight of 1280 g, and OH-number of 43.7. It is noteworthy to mention that using the FTIR method, the equivalent weight of polyol is determined by a comparison between absorption band of THF-associated hydroxyl groups for the polyol sample and the calibration curve. The terminal alcohol groups are mostly primary [5]. Therefore, the calibration curve in our study was based on a primary alcohol such as 1-octanol, or 2ethyl 1-butanol and other alcohols likewise. Fig. 5 gives an illustration of the H-NMR spectrum
Fig. 3. IR calibration curve.
G.M.M. Sadeghi et al. / Polymer Testing 22 (2003) 165–168
167
Fig. 6. 500 MHz H-NMR spectrum of polyol in 1,2-dichlorobenzene at 100 °C in 3.4–4.2 ppm region. Fig. 4.
FTIR spectrum of polyol solution (5 g/100 cm).
In Scheme 1, the first resonance peak (3.4 ppm) corresponds to a primary alcohol (–CH2OH) adjacent to a saturated carbon (c), while 3.9 and 4 ppm bands are assigned to primary alcohols adjacent to olefins (a, b). Moreover, simultaneous existence of 4.3 and 5.9 ppm NMR peaks indicates the presence of OH groups attached to the backbone of the chains in addition to the observed terminal ones. This can explain, and is in agreement with, the rather high value of functionality arrived at.
4. Conclusion
Fig. 5. 500 MHz H-NMR spectrum of polyol in 1,2-dichlorobenzene at 100 °C.
for polyol. The resonance groupings centered at 1.4, 2, 4, 5.4, and 5.6 ppm represent 1,2-methylene, 1,4-methylene, hydroxyl, 1,2-terminal, 1,4-olefinic, and non-terminal vinyl protons, respectively [6]. Fig. 6 shows a surface integral of 4 ppm, which is related to hydroxyl groups. The ratio of the sum of other protons to hydroxylic ones gives the degree of polymerization, which was found to be 85. As a result, number average molecular weight and functionality of polyol are calculated to be 4630 g/mol and 3.6, respectively.
With respect to the drawbacks in using common chemical methods in this work, it was learnt that functionality and OH number could be measured faster and more thoroughly through the use of FTIR and NMR analysis techniques. Furthermore, it is only by use of this method that it is possible to determine the percentage of OH groups relevant to 1,2-vinyl conformation, and other two cis and trans conformations. This knowledge is of utmost importance in determination of the properties and behavior of polyol in the polyurethane network.
Acknowledgements We wish to thank Mrs. Asgari and Mr. Bijanzadeh for their efforts in preparing FTIR and NMR Spectrums.
Scheme 1.
168
G.M.M. Sadeghi et al. / Polymer Testing 22 (2003) 165–168
References [1] R.T. Humpidge, D. Mattews, S.H. Morrel, J.R. Pyne, Processing and properties of liquid rubbers, Rubber Chemistry and Technology 46, (1973) 148–197. [2] Cenes, et al., Use of polydiene diols in thermoplastic polyurethanes, 1999 US patent 5925724. [3] Polybutadiene-ol Resins in Urethane Elastomers, Sartomer Company sales brochure, 1988. [4] C.S. Youn Kim, A.L. Dodge, S. Lau, A. Kawasaki,
Detrmination of hydrhxyl concentration in pre-polymers from the infrared absoaption bands of THF-associated hydrhxyl groups, Anal. Chem. 54 (1982) 232–238. [5] K.C. Ramey, M.W. Hayes, A.G. Altenav, W.A. Hines, E. T. Samulski, Macromolecules (1973) 6(5) 795 [6] 300 MHz proton NMR of polybutadiene, J. Polym. Sci. Polymer Edition 11 (1973) 449–452.