- Email: [email protected]
Synthesis and dielectric properties of polyarylene ether nitriles with high thermal stability and high mechanical strength
Materials Letters 65 (2011) 2758–2761
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Synthesis and dielectric properties of polyarylene ether nitriles with high thermal stability and high mechanical strength Hailong Tang, Jian Yang, Jiachun Zhong, Rui Zhao, Xiaobo Liu ⁎ Research Branch of Advanced Functional Materials, Institute of Microelectronic and Solid State Electronic, University of Electronic Science and Technology of China, Chengdu 610054, PR China
a r t i c l e
i n f o
Article history: Received 20 April 2011 Accepted 2 June 2011 Available online 12 June 2011 Keywords: Polyarylene ether nitriles Polymers Electrical properties Thermal properties Mechanical properties
a b s t r a c t A series of polyarylene ether nitriles were synthesized by the nucleophilic aromatic substitution polymerization of 2, 6-dichlorobenzonitrile with various bisphenol monomers. Owing to the different structural units, the derived copolymers showed different glass transition temperatures in the range of 166–260 °C. Moreover, they all showed good film-forming properties and high mechanical strength ranging from 75 MPa to 117 MPa, and also exhibited high thermal stability with the 5% weight loss temperatures ranging from 373 °C to 498 °C. Furthermore, both the dielectric constant and dielectric loss were found to be relatively stable with respect to temperature before the turning point temperature, which is very near to the glass transition temperature. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
In recent decades, poly(aryl ether)s, such as poly(aryl ether sulfone)s, poly(aryl ether ketone)s, poly(phenylene oxide) and poly (phenylene sulfide), have been attracting consideration attention as engineering plastics. They have also been developed as matrixes in advanced composites for applications in the aerospace industry [1]. Among these, polyether ether ketone [2,3] (PEEK, ICI, Wilmington, Del) and polyarylene ether nitrile [4,5] (PEN, Idemitsu) have been identified as excellent matrix resins for their outstanding mechanical properties, high thermal stability, good chemical inertia and excellent radiation resistance [6]. In addition, the pendant nitrile groups on aromatic rings in PEN appear to promote adhesion of the polymer to many substrates, possibly through polar interaction with other functional groups [7,8], and it also serves as a potential site for polymer cross-linking [9,10]. At present, there is little literature about performance comparison of different structure polyarylene ether nitriles, especially on the dielectric properties, and the relationship between their structures and properties have not been reported. In this paper, we present the synthesis and characterization of a series of polyarylene ether nitrile copolymers, and their chemical structures, thermal stability, mechanical and dielectric properties were also studied.
Polyarylene ether nitrile copolymers were synthesized by the nucleophilic aromatic substitution polymerization of 2, 6-dichlorobenzonitrile (DCBN) with various bisphenol monomers using anhydrous K2CO3 as catalyst in NMP medium (Fig. 1), as per the procedure described earlier [11]. In order to get a series of PEN copolymers with different structures and properties, we used different phenolic compounds as monomers, such as hydroquinone (HQ), resorcinol (RS), bisphenol A (BPA), phenolphthalein (PP) and phenolphthalin (PPL). The reaction mixture was poured into ethanol to precipitate the copolymer, and then the precipitate was acidified by dilute hydrochloric acid after crushing. Finally, the collected copolymer was washed three times with boiling water, and dried in a vacuum oven at 130 °C for 12 h. The PEN films were prepared by casting the PEN/NMP solutions with the concentration of 10% on a clean glass plate, and then dried in an oven at 80 °C, 100 °C, 120 °C, 160 °C, and 200 °C (1 h each) to remove the solvent completely. The as-prepared films are yellow and transparent, with the thickness of 50–70 μm. Fourier transform infrared (FTIR) spectra were recorded on a Shimadzu 8000S spectrophotometer. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed on TA Instruments DSC-Q100 and TGA-Q50 modules respectively, at a heating rate of 10 °C/min under flowing nitrogen. Mechanical properties were measured using a SANS CMT6104 series desktop electromechanical universal testing machine and are reported as average values for five samples. Dielectric properties were monitored according to the ASTM D150 on a HP4284A precision LCR meter.
⁎ Corresponding author. Tel./fax: + 86 28 83207326. E-mail address: [email protected] (X. Liu). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.06.007
H. Tang et al. / Materials Letters 65 (2011) 2758–2761
2759
Fig. 1. The synthetic route of PEN copolymers and the structures of bisphenol monomers.
3. Results and discussion 3.1. FTIR characterization The FTIR spectra of PEN copolymers are shown in Fig. 2. As can be seen, two sharp and strong absorption bands at 1500 and 1460 cm −1 were clearly observed, which are attributed to skeleton vibration of benzene rings. Another two weak bands at 1600 and 1580 cm −1 also
belong to benzene rings absorption features. Besides, a characteristic ether band at 1243 cm −1 was obtained [12]. These results indicate the formation of aryl ether (Ar–O–Ar). The absorption band at 2231 cm −1 is assigned to the symmetrical stretching vibration of nitrile groups [13]. They are all the characteristic absorption of polyarylene ether nitriles and appeared in all PEN copolymers. The characteristic absorption band of PEN(BPA) to distinguish from other PEN copolymers was observed at 2969 cm −1 (Fig. 2b), which corresponds to the stretching vibration of C–H of methyl groups. As shown in Fig. 2c and e, a same characteristic absorption band for PEN(PP/HQ) and PEN (PP) was observed at 1770 cm −1, which corresponds to the stretching vibration of C_O of phenolphthalein lactone rings [11]. However, it is important to note that the intensity of absorption band at 1770 cm −1 in Fig. 2c is weaker than that in Fig. 2e. These results are consistent with the structures of PEN(PP/HQ) and PEN(PP). Furthermore, the characteristic absorption band of PEN(PPL) to distinguish from other PENs was observed at 1712 cm −1 (Fig. 2d), which is attributed to carboxyl groups on the phenolphthalin units. 3.2. Thermal and mechanical properties
Fig. 2. FTIR spectra of PEN copolymers: (a) PEN(HQ/RS), (b) PEN(BPA), (c) PEN(PP/HQ), (d) PEN(PPL), and (e) PEN(PP).
Thermally induced phase transition behavior of the PEN copolymers was investigated with DSC over two heating cycles under a nitrogen atmosphere, and the glass transition temperatures (Tg) of them are summarized in Table 1. As we can see, the Tg of the copolymers gradually became higher from PEN(HQ/RS) to PEN(PP). This is attributed to the different structural units, which determine the rigidity and flexibility of molecular chains. Through a comparison with PEN(BPA), PEN(PP/HQ) and PEN(PP), it was found that the PP units show a stronger rigidity than BPA and HQ units, which is
2760
H. Tang et al. / Materials Letters 65 (2011) 2758–2761
Table 1 The mechanical properties and thermal stability of PEN copolymers. Copolymer
PEN(HQ/RS) PEN(BPA) PEN(PP/HQ) PEN(PPL) PEN(PP)
Thermal stability
Mechanical properties
Tg (°C)
T5% (°C)
Tensile strength (MPa)
Breaking elongation (%)
166 178 228 237 260
498 490 450 373 455
107.3 ± 2.3 98.5 ± 1.5 117.4 ± 2.0 75.1 ± 2.5 100.2 ± 3.4
5.5 6.2 6.6 3.5 5.5
attributed to phenolphthalein lactone rings. Moreover, the Tg of PEN (PPL) (237 °C) is obviously lower than that of PEN(PP) (260 °C). This is mainly due to the internal rotation of benzoyloxy hanging on the tertiary carbons of PPL units, which suggests that the PPL units derived from the reduction of PP units show a certain flexibility, compared with rigid PP units. In addition, the flexible side groups such as carboxyl groups will also lead to the decrease in Tg. Furthermore, the thermal stability of the PEN copolymers is evaluated by the 5% weight loss temperatures (T5%). As shown in Table 1, all the copolymers are stable up to 450 °C (T5% = 450 to 498 °C), with the exception of PEN(PPL) (T5% = 373 °C). This is mainly because a large number of flexible carboxyl side groups exist in PEN(PPL). The mechanical properties such as tensile strength and breaking elongation of the PEN copolymers are listed in Table 1. As we can see, except for PEN(PPL), all the copolymers show excellent mechanical properties, with tensile strengths exceeding 95 MPa and breaking elongations over 5.5%. For PEN(PPL), although its tensile strength (75 MPa) and breaking elongation (3.5%) are lower than those of other PEN copolymers, it can also meet ordinary application requirements. All in all, the PEN copolymers possess a high thermal stability as well as a high mechanical strength, which will have a good prospect of extension and application.
3.3. Dielectric properties The dielectric properties of PEN copolymers were measured as a function of both frequency and temperature. As shown in Fig. 3a, the dielectric constant of all the PEN copolymers show a weak frequency dependence, and the dielectric constant has a slight decrease with increasing frequency over the range of 100 Hz to 1 MHz. However, the frequency dependence of dielectric loss does not show this trend. The dielectric loss of the copolymers except for PEN(BPA) decreased at first and then increased in the measured frequency from 100 Hz to 1 MHz. Furthermore, Fig. 3a also shows the relative value of their dielectric constants at the same frequency (from high to low): PEN (PPL) N PEN(PP/HQ) N PEN(HQ/RS) N PEN(PP) N PEN(BPA). The relationship between their structures and dielectric properties can be explained by the same theory in the literature [14,15]. Due to the presence of the strongly polar carboxyl groups, PEN(PPL) has the highest dielectric constant (5.13 at 100 Hz) than other PEN polymers. Moreover, from the comparison of their chemical structures, the polarizability of PP units is higher than that of RS units. However, the presence of phenolphthalein lactone rings in PP units induces the increase in free volume, which results in a decrease in the number of polarizable groups per unit volume [14]. Due to the comprehensive effects of these two factors, the dielectric constant of PEN(HQ/RS) is slightly lower than that of PEN(PP/HQ), and higher than that of PEN (PP) (Fig. 3a). Furthermore, because of the completely symmetrical structure of BPA units, as well as the presence of the non-polar methyl groups, PEN(BPA) has the lowest dielectric constant (3.77 at 100 Hz) than other PEN polymers. Fig. 3c and d describe the temperature dependence of the dielectric constant and dielectric loss at 1 kHz, respectively. The dielectric properties were found to be relatively stable with respect to temperature before a turning point temperature. Both the dielectric constant and dielectric loss displayed an abrupt increase at temperatures exceeding the turning point temperature. It is important to
Fig. 3. Frequency dependence of (a) dielectric constant and (b) dielectric loss of the PEN copolymers at 20 °C. Temperature dependence of (c) dielectric constant and (d) dielectric loss of the PEN copolymers at 1 kHz.
H. Tang et al. / Materials Letters 65 (2011) 2758–2761
note that these turning point temperatures are very near to glass transition temperatures of the copolymers, suggesting that the amorphous domains of the copolymers play a dominant role in determining the dielectric properties at temperatures above Tg [16]. These results can be explained by the theory of molecular motions. When the temperature is below Tg, there are mainly local motions of side groups on macromolecular chains, which are relatively weak. With the increase of temperatures to and higher than the Tg, the sidegroups motions grow in intensity. Meanwhile, the segment motions of macromolecular chains begin to occur [17,18]. 4. Conclusion In summary, a series of polyarylene ether nitrile copolymers were synthesized by the nucleophilic aromatic substitution polymerization of 2, 6-dichlorobenzonitrile with various bisphenol monomers. The PEN copolymers exhibited excellent mechanical properties and high thermal stability. Moreover, the dielectric properties of the PEN copolymers were characterized as a function of both frequency and temperature. It was found that the PEN copolymers showed a weak frequency dependence, and the dielectric constant had a slight decrease with increasing frequency. Furthermore, their dielectric properties were found to be relatively stable with respect to temperature before the turning point temperature (very near to the Tg). These performances will make the copolymers attractive for applications in dielectric energy storage at high temperatures.
2761
References [1] Li C, Liu X. Mater Lett 2007;61:2239–42. [2] Searle OB, Pfeiffer RH. Polym Eng Sci 1985;25:474–6. [3] Rao VL, Sabeena PU, Saxena A, Gopalakrishnan C, Krishnan K, Ravindran PV, et al. Eur Polym J 2004;40:2645–51. [4] Matsuo S, Murakami T, Takasawa R. J Polym Sci Pol Chem 1993;31:3439–46. [5] Saxena A, Sadhana R, Rao VL, Kanakavel M, Ninan KN. Polym Bull 2003;50:219–26. [6] Liu X, Long S, Luo D, Chen W, Cao G. Mater Lett 2008;62:19–22. [7] Verbort J, Marvel CS. J Polym Sci: Polym Chem Ed 1973;11:2793–811. [8] Sivaramakrishnan KV, Marvel CS. J Polym Sci: Polym Chem Ed 1974;12:651–8. [9] Keller TM. J Polym Sci: Polym Chem Ed 1988;26:3199–212. [10] Keller TM. Polymer 1993;34:952–5. [11] Tang H, Yang J, Zhong J, Zhao R, Liu X. Mater Lett 2011;65:1703–6. [12] Saxena A, Rao VL, Ninan KN. Eur Polym J 2003;39:57–61. [13] Li C, Gu Y, Liu X. Mater Lett 2006;60:137–41. [14] Maier G. Prog Polym Sci 2001;26:3–65. [15] Maex K, Baklanov MR, Shamiryan D, Iacopi F, Brongersma SH, Yanovitskaya ZS. J Appl Phys 2003;93:8793–841. [16] Pan J, Li K, Li J, Hsu T, Wang Q. Appl Phys Lett 2009;95:022902. [17] Tang H, Ma Z, Zhong J, Yang J, Zhao R, Liu X. Colloid Surf A 2011, doi:10.1016/j.colsurfa. 2011.04.007. [18] Hancock BC, Shamblin SL, Zografi G. Pharm Res 1995;12:799–806.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Synthesis and dielectric properties of polyarylene ether nitriles with high thermal stability and high mechanical strength Hailong Tang, Jian Yang, Jiachun Zhong, Rui Zhao, Xiaobo Liu ⁎ Research Branch of Advanced Functional Materials, Institute of Microelectronic and Solid State Electronic, University of Electronic Science and Technology of China, Chengdu 610054, PR China
a r t i c l e
i n f o
Article history: Received 20 April 2011 Accepted 2 June 2011 Available online 12 June 2011 Keywords: Polyarylene ether nitriles Polymers Electrical properties Thermal properties Mechanical properties
a b s t r a c t A series of polyarylene ether nitriles were synthesized by the nucleophilic aromatic substitution polymerization of 2, 6-dichlorobenzonitrile with various bisphenol monomers. Owing to the different structural units, the derived copolymers showed different glass transition temperatures in the range of 166–260 °C. Moreover, they all showed good film-forming properties and high mechanical strength ranging from 75 MPa to 117 MPa, and also exhibited high thermal stability with the 5% weight loss temperatures ranging from 373 °C to 498 °C. Furthermore, both the dielectric constant and dielectric loss were found to be relatively stable with respect to temperature before the turning point temperature, which is very near to the glass transition temperature. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
In recent decades, poly(aryl ether)s, such as poly(aryl ether sulfone)s, poly(aryl ether ketone)s, poly(phenylene oxide) and poly (phenylene sulfide), have been attracting consideration attention as engineering plastics. They have also been developed as matrixes in advanced composites for applications in the aerospace industry [1]. Among these, polyether ether ketone [2,3] (PEEK, ICI, Wilmington, Del) and polyarylene ether nitrile [4,5] (PEN, Idemitsu) have been identified as excellent matrix resins for their outstanding mechanical properties, high thermal stability, good chemical inertia and excellent radiation resistance [6]. In addition, the pendant nitrile groups on aromatic rings in PEN appear to promote adhesion of the polymer to many substrates, possibly through polar interaction with other functional groups [7,8], and it also serves as a potential site for polymer cross-linking [9,10]. At present, there is little literature about performance comparison of different structure polyarylene ether nitriles, especially on the dielectric properties, and the relationship between their structures and properties have not been reported. In this paper, we present the synthesis and characterization of a series of polyarylene ether nitrile copolymers, and their chemical structures, thermal stability, mechanical and dielectric properties were also studied.
Polyarylene ether nitrile copolymers were synthesized by the nucleophilic aromatic substitution polymerization of 2, 6-dichlorobenzonitrile (DCBN) with various bisphenol monomers using anhydrous K2CO3 as catalyst in NMP medium (Fig. 1), as per the procedure described earlier [11]. In order to get a series of PEN copolymers with different structures and properties, we used different phenolic compounds as monomers, such as hydroquinone (HQ), resorcinol (RS), bisphenol A (BPA), phenolphthalein (PP) and phenolphthalin (PPL). The reaction mixture was poured into ethanol to precipitate the copolymer, and then the precipitate was acidified by dilute hydrochloric acid after crushing. Finally, the collected copolymer was washed three times with boiling water, and dried in a vacuum oven at 130 °C for 12 h. The PEN films were prepared by casting the PEN/NMP solutions with the concentration of 10% on a clean glass plate, and then dried in an oven at 80 °C, 100 °C, 120 °C, 160 °C, and 200 °C (1 h each) to remove the solvent completely. The as-prepared films are yellow and transparent, with the thickness of 50–70 μm. Fourier transform infrared (FTIR) spectra were recorded on a Shimadzu 8000S spectrophotometer. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed on TA Instruments DSC-Q100 and TGA-Q50 modules respectively, at a heating rate of 10 °C/min under flowing nitrogen. Mechanical properties were measured using a SANS CMT6104 series desktop electromechanical universal testing machine and are reported as average values for five samples. Dielectric properties were monitored according to the ASTM D150 on a HP4284A precision LCR meter.
⁎ Corresponding author. Tel./fax: + 86 28 83207326. E-mail address: [email protected] (X. Liu). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.06.007
H. Tang et al. / Materials Letters 65 (2011) 2758–2761
2759
Fig. 1. The synthetic route of PEN copolymers and the structures of bisphenol monomers.
3. Results and discussion 3.1. FTIR characterization The FTIR spectra of PEN copolymers are shown in Fig. 2. As can be seen, two sharp and strong absorption bands at 1500 and 1460 cm −1 were clearly observed, which are attributed to skeleton vibration of benzene rings. Another two weak bands at 1600 and 1580 cm −1 also
belong to benzene rings absorption features. Besides, a characteristic ether band at 1243 cm −1 was obtained [12]. These results indicate the formation of aryl ether (Ar–O–Ar). The absorption band at 2231 cm −1 is assigned to the symmetrical stretching vibration of nitrile groups [13]. They are all the characteristic absorption of polyarylene ether nitriles and appeared in all PEN copolymers. The characteristic absorption band of PEN(BPA) to distinguish from other PEN copolymers was observed at 2969 cm −1 (Fig. 2b), which corresponds to the stretching vibration of C–H of methyl groups. As shown in Fig. 2c and e, a same characteristic absorption band for PEN(PP/HQ) and PEN (PP) was observed at 1770 cm −1, which corresponds to the stretching vibration of C_O of phenolphthalein lactone rings [11]. However, it is important to note that the intensity of absorption band at 1770 cm −1 in Fig. 2c is weaker than that in Fig. 2e. These results are consistent with the structures of PEN(PP/HQ) and PEN(PP). Furthermore, the characteristic absorption band of PEN(PPL) to distinguish from other PENs was observed at 1712 cm −1 (Fig. 2d), which is attributed to carboxyl groups on the phenolphthalin units. 3.2. Thermal and mechanical properties
Fig. 2. FTIR spectra of PEN copolymers: (a) PEN(HQ/RS), (b) PEN(BPA), (c) PEN(PP/HQ), (d) PEN(PPL), and (e) PEN(PP).
Thermally induced phase transition behavior of the PEN copolymers was investigated with DSC over two heating cycles under a nitrogen atmosphere, and the glass transition temperatures (Tg) of them are summarized in Table 1. As we can see, the Tg of the copolymers gradually became higher from PEN(HQ/RS) to PEN(PP). This is attributed to the different structural units, which determine the rigidity and flexibility of molecular chains. Through a comparison with PEN(BPA), PEN(PP/HQ) and PEN(PP), it was found that the PP units show a stronger rigidity than BPA and HQ units, which is
2760
H. Tang et al. / Materials Letters 65 (2011) 2758–2761
Table 1 The mechanical properties and thermal stability of PEN copolymers. Copolymer
PEN(HQ/RS) PEN(BPA) PEN(PP/HQ) PEN(PPL) PEN(PP)
Thermal stability
Mechanical properties
Tg (°C)
T5% (°C)
Tensile strength (MPa)
Breaking elongation (%)
166 178 228 237 260
498 490 450 373 455
107.3 ± 2.3 98.5 ± 1.5 117.4 ± 2.0 75.1 ± 2.5 100.2 ± 3.4
5.5 6.2 6.6 3.5 5.5
attributed to phenolphthalein lactone rings. Moreover, the Tg of PEN (PPL) (237 °C) is obviously lower than that of PEN(PP) (260 °C). This is mainly due to the internal rotation of benzoyloxy hanging on the tertiary carbons of PPL units, which suggests that the PPL units derived from the reduction of PP units show a certain flexibility, compared with rigid PP units. In addition, the flexible side groups such as carboxyl groups will also lead to the decrease in Tg. Furthermore, the thermal stability of the PEN copolymers is evaluated by the 5% weight loss temperatures (T5%). As shown in Table 1, all the copolymers are stable up to 450 °C (T5% = 450 to 498 °C), with the exception of PEN(PPL) (T5% = 373 °C). This is mainly because a large number of flexible carboxyl side groups exist in PEN(PPL). The mechanical properties such as tensile strength and breaking elongation of the PEN copolymers are listed in Table 1. As we can see, except for PEN(PPL), all the copolymers show excellent mechanical properties, with tensile strengths exceeding 95 MPa and breaking elongations over 5.5%. For PEN(PPL), although its tensile strength (75 MPa) and breaking elongation (3.5%) are lower than those of other PEN copolymers, it can also meet ordinary application requirements. All in all, the PEN copolymers possess a high thermal stability as well as a high mechanical strength, which will have a good prospect of extension and application.
3.3. Dielectric properties The dielectric properties of PEN copolymers were measured as a function of both frequency and temperature. As shown in Fig. 3a, the dielectric constant of all the PEN copolymers show a weak frequency dependence, and the dielectric constant has a slight decrease with increasing frequency over the range of 100 Hz to 1 MHz. However, the frequency dependence of dielectric loss does not show this trend. The dielectric loss of the copolymers except for PEN(BPA) decreased at first and then increased in the measured frequency from 100 Hz to 1 MHz. Furthermore, Fig. 3a also shows the relative value of their dielectric constants at the same frequency (from high to low): PEN (PPL) N PEN(PP/HQ) N PEN(HQ/RS) N PEN(PP) N PEN(BPA). The relationship between their structures and dielectric properties can be explained by the same theory in the literature [14,15]. Due to the presence of the strongly polar carboxyl groups, PEN(PPL) has the highest dielectric constant (5.13 at 100 Hz) than other PEN polymers. Moreover, from the comparison of their chemical structures, the polarizability of PP units is higher than that of RS units. However, the presence of phenolphthalein lactone rings in PP units induces the increase in free volume, which results in a decrease in the number of polarizable groups per unit volume [14]. Due to the comprehensive effects of these two factors, the dielectric constant of PEN(HQ/RS) is slightly lower than that of PEN(PP/HQ), and higher than that of PEN (PP) (Fig. 3a). Furthermore, because of the completely symmetrical structure of BPA units, as well as the presence of the non-polar methyl groups, PEN(BPA) has the lowest dielectric constant (3.77 at 100 Hz) than other PEN polymers. Fig. 3c and d describe the temperature dependence of the dielectric constant and dielectric loss at 1 kHz, respectively. The dielectric properties were found to be relatively stable with respect to temperature before a turning point temperature. Both the dielectric constant and dielectric loss displayed an abrupt increase at temperatures exceeding the turning point temperature. It is important to
Fig. 3. Frequency dependence of (a) dielectric constant and (b) dielectric loss of the PEN copolymers at 20 °C. Temperature dependence of (c) dielectric constant and (d) dielectric loss of the PEN copolymers at 1 kHz.
H. Tang et al. / Materials Letters 65 (2011) 2758–2761
note that these turning point temperatures are very near to glass transition temperatures of the copolymers, suggesting that the amorphous domains of the copolymers play a dominant role in determining the dielectric properties at temperatures above Tg [16]. These results can be explained by the theory of molecular motions. When the temperature is below Tg, there are mainly local motions of side groups on macromolecular chains, which are relatively weak. With the increase of temperatures to and higher than the Tg, the sidegroups motions grow in intensity. Meanwhile, the segment motions of macromolecular chains begin to occur [17,18]. 4. Conclusion In summary, a series of polyarylene ether nitrile copolymers were synthesized by the nucleophilic aromatic substitution polymerization of 2, 6-dichlorobenzonitrile with various bisphenol monomers. The PEN copolymers exhibited excellent mechanical properties and high thermal stability. Moreover, the dielectric properties of the PEN copolymers were characterized as a function of both frequency and temperature. It was found that the PEN copolymers showed a weak frequency dependence, and the dielectric constant had a slight decrease with increasing frequency. Furthermore, their dielectric properties were found to be relatively stable with respect to temperature before the turning point temperature (very near to the Tg). These performances will make the copolymers attractive for applications in dielectric energy storage at high temperatures.
2761
References [1] Li C, Liu X. Mater Lett 2007;61:2239–42. [2] Searle OB, Pfeiffer RH. Polym Eng Sci 1985;25:474–6. [3] Rao VL, Sabeena PU, Saxena A, Gopalakrishnan C, Krishnan K, Ravindran PV, et al. Eur Polym J 2004;40:2645–51. [4] Matsuo S, Murakami T, Takasawa R. J Polym Sci Pol Chem 1993;31:3439–46. [5] Saxena A, Sadhana R, Rao VL, Kanakavel M, Ninan KN. Polym Bull 2003;50:219–26. [6] Liu X, Long S, Luo D, Chen W, Cao G. Mater Lett 2008;62:19–22. [7] Verbort J, Marvel CS. J Polym Sci: Polym Chem Ed 1973;11:2793–811. [8] Sivaramakrishnan KV, Marvel CS. J Polym Sci: Polym Chem Ed 1974;12:651–8. [9] Keller TM. J Polym Sci: Polym Chem Ed 1988;26:3199–212. [10] Keller TM. Polymer 1993;34:952–5. [11] Tang H, Yang J, Zhong J, Zhao R, Liu X. Mater Lett 2011;65:1703–6. [12] Saxena A, Rao VL, Ninan KN. Eur Polym J 2003;39:57–61. [13] Li C, Gu Y, Liu X. Mater Lett 2006;60:137–41. [14] Maier G. Prog Polym Sci 2001;26:3–65. [15] Maex K, Baklanov MR, Shamiryan D, Iacopi F, Brongersma SH, Yanovitskaya ZS. J Appl Phys 2003;93:8793–841. [16] Pan J, Li K, Li J, Hsu T, Wang Q. Appl Phys Lett 2009;95:022902. [17] Tang H, Ma Z, Zhong J, Yang J, Zhao R, Liu X. Colloid Surf A 2011, doi:10.1016/j.colsurfa. 2011.04.007. [18] Hancock BC, Shamblin SL, Zografi G. Pharm Res 1995;12:799–806.