- Email: [email protected]
Synthesis and curing of a novel amino-containing phthalonitrile derivative
Chinese Chemical Letters 18 (2007) 523–526 www.elsevier.com/locate/cclet
Synthesis and curing of a novel amino-containing phthalonitrile derivative Ke Zeng, Ke Zhou, Wen Rui Tang, Yan Tang, Hong Fei Zhou, Tao Liu, Yi Peng Wang, Hai Bing Zhou, Gang Yang * State Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China Received 14 December 2006
Abstract A novel phthalonitrile derivative containing an amino group, 3,5-bis(3,4-dicyanophenoxy)aniline (CPA), was synthesized via a nucleophilic displacement of 4-nitrophthalonitrile and 5-aminoresorcinol hydrochloride. The structure of CPA was confirmed by Fourier transform infrared spectra (FT-IR) and nuclear magnetic resonance (1H NMR). Thermal analysis performed on CPA revealed that the novel phthalonitrile derivative showed a self-promotion curing behavior and the resulting polymer exhibited outstanding heat-resistance. # 2007 Gang Yang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Phthalonitrile derivative; Amino group; Self-promotion curing behavior
Phthalonitrile polymers are an important class of high performance polymers, which are easily processable, and display good mechanical properties, outstanding thermal and thermal-oxidative stability. Phthalonitrile polymers were firstly reported by Keller and Price [1] for aerospace, marine, and electronic packaging applications. By thermal treatment of phthalonitrile derivatives at elevated temperatures (generally high up to 350 8C) for an extended period of time, a curing reaction occurs between the nitrile groups and giving rise to a phthalonitrile polymer. The curing reaction was found to be readily promoted in the presence of a small amount of curing additives such as organic amines [1], strong organic acids [2], strong organic acids/amine salts [3], phenols [4], transition metals and their salts [5,6], and the temperatures of the curing reaction could be greatly lowered. 1,3-Bis(3-aminophenoxy)benzene (m-APB) as an aromatic diamine curing agent for phthalonitrile derivatives was focused on and investigated at the Naval Research Laboratory (NRL). To date, phthalonitrile polymers and phthalonitrile polymers-based composites have been successfully formulated with m-APB amine as the curing agent [7,8]. However, a slowdown of curing reaction was observed because of m-APB volatility. Two kinds of sulfone-containing diamines {bis[4-(3-amino phehnoxy)phenyl]sulfone and bis[4-(4-aminophehnoxy)phenyl]sulfone}, with relatively lower volatility at high temperatures due to their higher molecular weights, were chosen as the curing agent. As a result, the processability of phthalonitrilebased composites was clearly improved [9].
* Corresponding author. E-mail address: [email protected] (G. Yang). 1001-8417/$ – see front matter # 2007 Gang Yang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2007.03.035
524
K. Zeng et al. / Chinese Chemical Letters 18 (2007) 523–526
Scheme 1. Synthesis of CPA.
Until now, a variety of phthalonitrile derivatives have been reported [10] and confirmed to be able to thermally cure at high temperatures in the presence of the mentioned above additives. This current research focuses on development of a novel phthalonitrile derivative, 3,5-bis(3,4-dicyanophenoxy)aniline (CPA) Scheme 1, which has a relatively lower melting point and is relatively less volatile determined by thermogravimetric analysis (TGA) technology (TA Q500). The structure character of CPA is that nitrile groups and an amino group were successfully incorporated into one molecule. Interestingly, a self-promoted curing behavior between the nitrile groups was clearly observed by differential scanning calorimetry (DSC) technology (Netzsch 204) at high temperatures due to the presence of the amino group in one molecule of CPA. This offers a new preparing route to phthalonitrile-based polymers. 1. Experimental 4-Nitrophthalonitrile (compound 2), was purchased from Aldrich Chemical Co. and used as received. To a 100 mL, round-bottom flask were added 3.00 g (23.16 mmol) of 5-aminoresorcinol hydrochloride, 8.04 g (46.32 mmol) of 4-nitrophthalonitrile, 12.70 g (92.64 mmol) of pulverized anhydrous potassium carbonate, and 50 mL of N,N-dimethylformamide (DMF). The mixture was stirred at room temperature in nitrogen for 24 h, and the resulting mixture was poured into 500 mL of water. The precipitate was collected by filtration. After recrystallization from acetone/water (4:1 in volume) mixed solvent, CPA was obtained as yellow crystal (yield 81%), mp. 214 8C (DSC). 1H NMR (CDCl3, d ppm): 7.74–7.82 (q, 2H, 3J = 8.58, Ar–H); 7.34–7.36 (q, 2H, 4J = 4.02, Ar–H); 7.29–7.33 (m, 2H, Ar–H); 6.26 (d, 2H, 4J = 2.07, Ar–H); 6.12–6.13 (t, 1H, 4J = 2.07, Ar–H); 4.09–4.13 (t, 2H, 1JNH = 7.14, NH2). FT-IR (KBr, cm 1): 3472, 3377 (–NH2); 3079 (aromatic C C–H); 2233 (CBBN); 1473-1628 (C C); 1283 (C– O); 1248 (C–N); 1169 (C–O). 2. Results and discussion 5-Aminoresorcinol hydrochloride (compound 1), was synthesized according to the published literature [11]. Using the nucleophilic displacement reaction between compounds 1 and 2, CPA was synthesized in a high yield in the presence of weak base (potassium carbonate). Dipolar aprotic solvent, e.g. dimehtylsulfoxide (DMSO) or DMF was used as reaction medium, due to their good solubility for compound 1 and product CPA. This reaction could be improved at higher reaction temperatures, however, some side reactions such as the oxidation of amino groups were also enhanced at higher temperatures. So the reaction was carried out at room temperature (RT). The reaction progress was followed by thin-layer chromatography (TLC). The structure of target product CPA was characterized by Fourier transform infrared spectra (FT-IR) and nuclear magnetic resonance (1H NMR) spectra (Bruker Advance 300 spectrometer). FT-IR spectrum (Fig. 1) of CPA shows the characteristic absorption bands of primary amine (NH2) at 3472 cm 1 and 3377 cm 1. The absorption band at 2233 cm 1 is typically for cyano (CN) stretching vibration. 1H NMR spectrum was measured to further confirm the structure of CPA, as shown in Fig. 2. The peak at d 4.10 ppm is corresponding to primary amine (NH2) protons, and other peaks at d 6.12–7.82 ppm are assigned to aromatic protons. In order to investigate the thermal behavior of the novel amino-containing phthalonitrile derivative CPA, DSC and TGA studies were performed on the CPA at the heating rate of 10 8C/min in nitrogen atmosphere. The DSC (Fig. 3) first scan for phthalonitrile derivative CPA exhibited the melting endotherm peak around 214 8C. Interestingly, an obvious exothermic peak after the melting transition of the CPA was observed between 257 8C and 274 8C, where no obvious weight loss was found on the TGA plot and the resulting product after thermal treatment by DSC at high temperatures was almostly insoluble in concentrated sulfuric acid at room temperature. These results indicated that a
K. Zeng et al. / Chinese Chemical Letters 18 (2007) 523–526
525
Fig. 1. FT-IR of phthalonitrile derivative CPA.
Fig. 2. 1H NMR of phthalonitrile derivative CPA.
highly cross-linked network was achieved by the reaction among amino groups and phthalonitrile units [12]. Therefore, a self-promoted curing behavior was realized for amino-containing phthalonitrile derivative CPA, indicating that the CPA can be thermally polymerized to a network polymer at high temperatures without addition of any other curing additives. The phthalonitrile derivative CPA shows a char yield of 70.6% at 800 8C in nitrogen atmosphere determined by TGA analysis (Fig. 4), which shows that the resulting phthalonitrile polymer exhibits outstanding heat-resistance. As a result, a new preparing route to the phthalonitrile polymers has been successfully achieved by thermal treatment of amino-containing phthalonitrile derivative CPA at high temperatures. The further detailed researches on CPA will be reported in the near future.
Fig. 3. DSC curve for CPA at the heating rate of 10 8C/min in N2.
526
K. Zeng et al. / Chinese Chemical Letters 18 (2007) 523–526
Fig. 4. TGA curve for CPA at the heating rate of 10 8C/min in N2.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
T.M. Keller, T.K. Price, J. Macromol. Sci. Chem. 18 (1982) 931. T.M. Keller, Polym. Prep. 33 (1992) 422. P.J. Burchill, J. Polym. Sci., Part A: Polym. Chem. 32 (1994) 1. T.M. Keller, J.R. Griffith, ACS. Org. Coat. Plast. Chem. Prep. 43 (1980) 804. D. Woehrle, B. Schulte, Makromol. Chem. 189 (1988) 1167. D. Woehrle, B. Schulte, Makromol. Chem. 190 (1989) 1573. S.B. Sastri, J.P. Armistead, T.M. Keller, Polym. Compos. 17 (1996) 816. S.B. Sastri, J.P. Armistead, T.M. Keller, Polym. Compos. 18 (1997) 48. S.B. Sastri, T.M. Keller, J. Polym. Sci., Part A: Polym. Chem. 36 (1998) 1885. S.B. Sastri, T.M. Keller, J. Polym. Sci., Part A: Polym. Chem. 37 (1999) 2105. M.A. Thorn, G.H. Denny, R.D. Babson, J. Org. Chem. 40 (1975) 1556. D.D. Dominguez, T.M. Keller, Polymer 46 (2005) 4614.
Synthesis and curing of a novel amino-containing phthalonitrile derivative Ke Zeng, Ke Zhou, Wen Rui Tang, Yan Tang, Hong Fei Zhou, Tao Liu, Yi Peng Wang, Hai Bing Zhou, Gang Yang * State Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China Received 14 December 2006
Abstract A novel phthalonitrile derivative containing an amino group, 3,5-bis(3,4-dicyanophenoxy)aniline (CPA), was synthesized via a nucleophilic displacement of 4-nitrophthalonitrile and 5-aminoresorcinol hydrochloride. The structure of CPA was confirmed by Fourier transform infrared spectra (FT-IR) and nuclear magnetic resonance (1H NMR). Thermal analysis performed on CPA revealed that the novel phthalonitrile derivative showed a self-promotion curing behavior and the resulting polymer exhibited outstanding heat-resistance. # 2007 Gang Yang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Phthalonitrile derivative; Amino group; Self-promotion curing behavior
Phthalonitrile polymers are an important class of high performance polymers, which are easily processable, and display good mechanical properties, outstanding thermal and thermal-oxidative stability. Phthalonitrile polymers were firstly reported by Keller and Price [1] for aerospace, marine, and electronic packaging applications. By thermal treatment of phthalonitrile derivatives at elevated temperatures (generally high up to 350 8C) for an extended period of time, a curing reaction occurs between the nitrile groups and giving rise to a phthalonitrile polymer. The curing reaction was found to be readily promoted in the presence of a small amount of curing additives such as organic amines [1], strong organic acids [2], strong organic acids/amine salts [3], phenols [4], transition metals and their salts [5,6], and the temperatures of the curing reaction could be greatly lowered. 1,3-Bis(3-aminophenoxy)benzene (m-APB) as an aromatic diamine curing agent for phthalonitrile derivatives was focused on and investigated at the Naval Research Laboratory (NRL). To date, phthalonitrile polymers and phthalonitrile polymers-based composites have been successfully formulated with m-APB amine as the curing agent [7,8]. However, a slowdown of curing reaction was observed because of m-APB volatility. Two kinds of sulfone-containing diamines {bis[4-(3-amino phehnoxy)phenyl]sulfone and bis[4-(4-aminophehnoxy)phenyl]sulfone}, with relatively lower volatility at high temperatures due to their higher molecular weights, were chosen as the curing agent. As a result, the processability of phthalonitrilebased composites was clearly improved [9].
* Corresponding author. E-mail address: [email protected] (G. Yang). 1001-8417/$ – see front matter # 2007 Gang Yang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2007.03.035
524
K. Zeng et al. / Chinese Chemical Letters 18 (2007) 523–526
Scheme 1. Synthesis of CPA.
Until now, a variety of phthalonitrile derivatives have been reported [10] and confirmed to be able to thermally cure at high temperatures in the presence of the mentioned above additives. This current research focuses on development of a novel phthalonitrile derivative, 3,5-bis(3,4-dicyanophenoxy)aniline (CPA) Scheme 1, which has a relatively lower melting point and is relatively less volatile determined by thermogravimetric analysis (TGA) technology (TA Q500). The structure character of CPA is that nitrile groups and an amino group were successfully incorporated into one molecule. Interestingly, a self-promoted curing behavior between the nitrile groups was clearly observed by differential scanning calorimetry (DSC) technology (Netzsch 204) at high temperatures due to the presence of the amino group in one molecule of CPA. This offers a new preparing route to phthalonitrile-based polymers. 1. Experimental 4-Nitrophthalonitrile (compound 2), was purchased from Aldrich Chemical Co. and used as received. To a 100 mL, round-bottom flask were added 3.00 g (23.16 mmol) of 5-aminoresorcinol hydrochloride, 8.04 g (46.32 mmol) of 4-nitrophthalonitrile, 12.70 g (92.64 mmol) of pulverized anhydrous potassium carbonate, and 50 mL of N,N-dimethylformamide (DMF). The mixture was stirred at room temperature in nitrogen for 24 h, and the resulting mixture was poured into 500 mL of water. The precipitate was collected by filtration. After recrystallization from acetone/water (4:1 in volume) mixed solvent, CPA was obtained as yellow crystal (yield 81%), mp. 214 8C (DSC). 1H NMR (CDCl3, d ppm): 7.74–7.82 (q, 2H, 3J = 8.58, Ar–H); 7.34–7.36 (q, 2H, 4J = 4.02, Ar–H); 7.29–7.33 (m, 2H, Ar–H); 6.26 (d, 2H, 4J = 2.07, Ar–H); 6.12–6.13 (t, 1H, 4J = 2.07, Ar–H); 4.09–4.13 (t, 2H, 1JNH = 7.14, NH2). FT-IR (KBr, cm 1): 3472, 3377 (–NH2); 3079 (aromatic C C–H); 2233 (CBBN); 1473-1628 (C C); 1283 (C– O); 1248 (C–N); 1169 (C–O). 2. Results and discussion 5-Aminoresorcinol hydrochloride (compound 1), was synthesized according to the published literature [11]. Using the nucleophilic displacement reaction between compounds 1 and 2, CPA was synthesized in a high yield in the presence of weak base (potassium carbonate). Dipolar aprotic solvent, e.g. dimehtylsulfoxide (DMSO) or DMF was used as reaction medium, due to their good solubility for compound 1 and product CPA. This reaction could be improved at higher reaction temperatures, however, some side reactions such as the oxidation of amino groups were also enhanced at higher temperatures. So the reaction was carried out at room temperature (RT). The reaction progress was followed by thin-layer chromatography (TLC). The structure of target product CPA was characterized by Fourier transform infrared spectra (FT-IR) and nuclear magnetic resonance (1H NMR) spectra (Bruker Advance 300 spectrometer). FT-IR spectrum (Fig. 1) of CPA shows the characteristic absorption bands of primary amine (NH2) at 3472 cm 1 and 3377 cm 1. The absorption band at 2233 cm 1 is typically for cyano (CN) stretching vibration. 1H NMR spectrum was measured to further confirm the structure of CPA, as shown in Fig. 2. The peak at d 4.10 ppm is corresponding to primary amine (NH2) protons, and other peaks at d 6.12–7.82 ppm are assigned to aromatic protons. In order to investigate the thermal behavior of the novel amino-containing phthalonitrile derivative CPA, DSC and TGA studies were performed on the CPA at the heating rate of 10 8C/min in nitrogen atmosphere. The DSC (Fig. 3) first scan for phthalonitrile derivative CPA exhibited the melting endotherm peak around 214 8C. Interestingly, an obvious exothermic peak after the melting transition of the CPA was observed between 257 8C and 274 8C, where no obvious weight loss was found on the TGA plot and the resulting product after thermal treatment by DSC at high temperatures was almostly insoluble in concentrated sulfuric acid at room temperature. These results indicated that a
K. Zeng et al. / Chinese Chemical Letters 18 (2007) 523–526
525
Fig. 1. FT-IR of phthalonitrile derivative CPA.
Fig. 2. 1H NMR of phthalonitrile derivative CPA.
highly cross-linked network was achieved by the reaction among amino groups and phthalonitrile units [12]. Therefore, a self-promoted curing behavior was realized for amino-containing phthalonitrile derivative CPA, indicating that the CPA can be thermally polymerized to a network polymer at high temperatures without addition of any other curing additives. The phthalonitrile derivative CPA shows a char yield of 70.6% at 800 8C in nitrogen atmosphere determined by TGA analysis (Fig. 4), which shows that the resulting phthalonitrile polymer exhibits outstanding heat-resistance. As a result, a new preparing route to the phthalonitrile polymers has been successfully achieved by thermal treatment of amino-containing phthalonitrile derivative CPA at high temperatures. The further detailed researches on CPA will be reported in the near future.
Fig. 3. DSC curve for CPA at the heating rate of 10 8C/min in N2.
526
K. Zeng et al. / Chinese Chemical Letters 18 (2007) 523–526
Fig. 4. TGA curve for CPA at the heating rate of 10 8C/min in N2.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
T.M. Keller, T.K. Price, J. Macromol. Sci. Chem. 18 (1982) 931. T.M. Keller, Polym. Prep. 33 (1992) 422. P.J. Burchill, J. Polym. Sci., Part A: Polym. Chem. 32 (1994) 1. T.M. Keller, J.R. Griffith, ACS. Org. Coat. Plast. Chem. Prep. 43 (1980) 804. D. Woehrle, B. Schulte, Makromol. Chem. 189 (1988) 1167. D. Woehrle, B. Schulte, Makromol. Chem. 190 (1989) 1573. S.B. Sastri, J.P. Armistead, T.M. Keller, Polym. Compos. 17 (1996) 816. S.B. Sastri, J.P. Armistead, T.M. Keller, Polym. Compos. 18 (1997) 48. S.B. Sastri, T.M. Keller, J. Polym. Sci., Part A: Polym. Chem. 36 (1998) 1885. S.B. Sastri, T.M. Keller, J. Polym. Sci., Part A: Polym. Chem. 37 (1999) 2105. M.A. Thorn, G.H. Denny, R.D. Babson, J. Org. Chem. 40 (1975) 1556. D.D. Dominguez, T.M. Keller, Polymer 46 (2005) 4614.