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Synthesis and properties of phenolphthalein-based polyarylene ether nitrile copolymers
Materials Letters 60 (2006) 137 – 141 www.elsevier.com/locate/matlet
Synthesis and properties of phenolphthalein-based polyarylene ether nitrile copolymers Cao Li a,b,*, Yi Gu a, Xiaobo Liu b a
College of polymer engineering and science, State key laboratory of polymeric materials engineering, Sichuan University, Chengdu 610065, China b Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China Received 11 March 2005; accepted 3 August 2005 Available online 6 September 2005
Abstract Phenolphthalein-modified polyarylene ether nitrile copolymers were synthesized by nucleophilic substitution reaction of 2,6difluorobenzonitrile (DFBN) with varying molar ratios of phenolphthalein (PP) and hydroquinone (HQ). The copolymers were chemically and physically characterized to have good thermal and mechanical properties. PP content of the copolymers has influence on glass transition temperature (Tg) as well as decomposition temperature (Tid). Coats – Redfern method was applied to study the thermal decomposition kinetics of the copolymers to predict the lifespan under thermal aging process of the copolymers, the results show that the lifespan increases with increasing PP content. D 2005 Elsevier B.V. All rights reserved. Keywords: Polyarylene ether nitrile; Copolymer; Synthesis; Thermal decomposition; Kinetics study
1. Introduction In recent decades, polyarylene ether nitrile (PEN) as special engineering plastics has gained wide applications for its excellent properties in aerospace, electric and automotive industry. Various bisphenol have been studied for synthesis of PEN via nucleophilic aromatic substitution polymerization, these PEN materials exhibit excellent thermal stabilities over a wide-range of temperature [1– 6]. The cyano group at main chain serves as a potential site for crosslinking reaction and can make polymer transform from thermoplastic to thermosetting [7– 10]. Matsuo et al [3] systematically studied the synthesis of 2,6-dihalo benzonitrile with different kinds of bisphenol including the phenolphthalein and found that mechanical properties of phenolphthalein based PEN were better than that of the corresponding ketone or sulfone containing polymers. However the above-mentioned PEN are all * Corresponding author. Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China. Tel./fax: +86 28 8540 0377. E-mail address: [email protected] (C. Li). 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.08.004
homopolymers, and insolubility has limited their applications in many areas. Many attempts have been made to improve the solubility of the PEN by copolymerization or incorporation of pendant group [4,5,11,12]. Mechanical properties such as elongation is low for phenolphthalein based PEN homopolymer have limited its applications [3,6]. There are also relatively few studies on thermal decomposition kinetics of thermoplastic PEN, but these polymers often encounter elevated temperature during applications. In this paper, we synthesized the copolymers of phenolphthalein and hydroquinone with various ratios and studied their thermal and mechanical properties. We also used Coats – Redfern method to study the thermal decomposition kinetics of PEN copolymers and predicted their lifespan under the thermal aging process.
2. Experimental 2.1. Materials 2,6-difluorobenzonitrile, hydroquinone and phenolphthalein were available commercially and purified by
138
C. Li et al. / Materials Letters 60 (2006) 137 – 141
HO
C
OH
m
O
CN
+(m+n) F
K2CO3
F + n HO OH
C
NMP
O CN
O
C
O
O O
O C
m
n
O Scheme 1. Polymerization of PEN(PP/HQ).
sublimation or recrystallization before use. Anhydrous K2CO3 was dried under vacuum at 100 -C before use. N-methyl pyrrolidone (NMP) was distilled under reduced pressure over calcium hydride and stored over 4A molecular sieves. 2.2. Polymer synthesis The synthesis of the PEN have been described in other reports [6], and the structure of the polymer synthesized is shown in Scheme 1.
eter. Tensile strength and elongation at break of the films were measured on LG500 mechanical testing instrument, and gained as average value for every five samples. Glass transition temperature of the films was measured on PERKIN-ELMER 7 DSC, at a heating rate of 10 -C min 1. TG/DTG analysis of the copolymers was carried out under N2 atmosphere at a heating rate of 10 -C min 1 using PERKIN-ELMER 7 series analyzer system combination with PE3700 data processing station.
4. Results and discussion
2.3. Preparation of polymer films Dissolved the polymer in DMF again to get a solution with 10% polymer content and filtered then. After vigorous stirring, the solution was cast onto a clean glass plate to obtain the film. The film then was heated at elevated temperature to 160 -C to remove the solvent completely. The films with a thickness of 20– 30 um were obtained.
3. Characterization
Polyarylene ether nitriles copolymers were synthesized by nucleophilic substitution reaction of 2,6-difluorobenzonitrile with phenolphthalein and hydroquinone. Molar ratio, yields and inherent viscosity values of the reactions are shown in Table 1. 4.1. Solubility All samples are insoluble in common organic solvents at room temperature, But three samples can dissolve in NMP solvent on heating. Sample 2 and 3 can be dissolved in DMF on heating while sample 1 cannot. It reveal that introduction of HQ improve the solubility of PEN.
Inherent viscosities of the samples were determined at 20 -C for 0.5% polymer solution in DMF using Ubbelhode viscometer. The FT-IR spectra of the films were recorded using Nicolet 20 SXB-IR spectrophotom-
Table 1 Conditions for the synthesis of PEN(PP/HQ) Sample
Molar ratio (PP : HQ)
Inherent viscosity (g/dL)
Dehydration time (h)
Polycondensation time (h)
Yield ratio (%)
1 2 3
70 : 30 50 : 50 30 : 70
0.87 0.76 1.12
2.5 2.5 2.5
4 4 4
98.3 98.8 99.0
Fig. 1. FT-IR of PEN(PP/HQ) polymer.
C. Li et al. / Materials Letters 60 (2006) 137 – 141
100
1 2 3
Tg (-C) 220 212 199
Tid (-C) 465 434 455
Tid5% (-C) 470 464 477
Tid30% (-C) 593 588 580
Tensile strength (MPa)
Elongation at break (%)
96 107 90
7 13 11
1 3
80
2
Weight
Table 2 Thermal and mechanical property of PEN(PP/HQ) Sample
139
60 40 20 0
4.2. FT-IR characterization
0
The structure of the copolymers was characterized with a FT-IR spectroscopy as shown in Fig. 1. From top to bottom the five samples have a structure of PP: HQ = 100 : 0, 70 : 30, 50 : 50, 30 : 70 and 0 : 100, respectively. For copolymer, the characteristic stretching vibration absorption of – OH of PP and HQ at 3290 and 3260 cm 1 as well as C-F of DFBN at 790 cm 1 disappeared. The absorption at 2231 cm 1 is characteristic symmetrical stretching of CN group. The absorption at 1247 cm 1 and 1287 cm 1 are assigned to – C – O – C – of PP, and absorption at 1190 cm 1 are the characteristic peak of – C – O – C – of HQ, both of them are ortho to CN, respectively. All these information confirmed that PP, DFBN and HQ have reacted as showed in Scheme 1. 4.3. Mechanical measurement and analysis The mechanical measurement such as tensile strength and elongation at break are listed in Table 2. The values of elongation
25
480
560
640
Temperature(°C) Fig. 3. TGA curves of PEN(PP/HQ) copolymers.
at break decrease with the increasing content of PP, which may be attributed to the rigidity brought about by the PP component. The mechanical measurements of the samples also show that tensile strength of PEN (PP/HQ) is higher than that of PEN (RE/HQ) copolymer [6]. Fig. 2 displays the fracture surface morphology of the films using SEM. It can be found that morphology of the three films differ from each other so obviously. The sample 1 and 3 is rough and anisotropic, which means the transfer of tensile stress has no orientation. For PP: HQ = 50 : 50 copolymer as shown in Fig. 2(2), the fracture surface morphology demonstrates a orientation characteristic and is in accordance with the results that sample 2 has the largest tensile strength.
Fig. 2. SEM of fracture surface morphology of the PEN(PP/HQ) copolymer films.
140
C. Li et al. / Materials Letters 60 (2006) 137 – 141
-1.4
Table 3 Results of E and A for thermal decomposition kinetics of the copolymers
lg[-ln(1-c)]
-1.05
-0.7
-0.35
0 1.05
1.15
1.25
1.35
1.45
1/T(103/K) Fig. 4. Plots of 1 / T versus log[ln(1 c)], the linear relationship between 1 / T and log[ln(1 c)] means that assumption that reaction order is 1 is correct (0: sample 1; n: sample 2; r: sample 3).
Sample
E (kJ/mol)
A (min 1)
1 2 3
185.5 159.4 110.3
5.42 109 5.16 109 2.65 106
the copolymers qualitatively. But in some applications polymer will encounter elevated temperature at every step such as manufacturing, processing for a long period, so a detailed analysis on the thermal decomposition would be valuable. For this purpose, the thermal decomposition kinetics of the phenolphthalein based PEN copolymers was investigated with the aid of the TG/DTG analysis for the first time and their lifespan under thermal aging process are also estimated.
4.4. Thermal properties
5.1. The calculation of E and A Glass transition temperature of the copolymers were calculated from the curves of DSC, and listed in Table 2. It can be seen that Tg increase with the increasing PP content in the copolymers, and the Tg of PEN(PP/HQ) copolymers is higher than that of PEN(RE/HQ) [9]. Fig. 3 shows the TGA profile of the three copolymers, the initial decomposition temperature (Tid) of three copolymers is higher than 430 -C. The thermal properties of three samples are listed in the Table 2. The Tid of PP homopolymer is higher than 500 -C, the introduction of HQ decreases Tid of the copolymers, but with the HQ content increase, the Tid of the copolymer increase again, which could be attributed to the decrease of distance between CN group on the main chain.
dc ¼ kf ðcÞ dt
ð1Þ
where k is rate constant given by the Eq. (2) k ¼ AeE=RT
ð2Þ
where A is frequency factor, R is the gas constant and E is activation energy of the reaction f ð cÞ ¼ ð 1 cÞ n
ð3Þ
where c is the fraction decomposed at time t and n is the order of reaction, for a linear heating reaction, b is the heating rate given by Eq. (4)
5. Thermal decomposition kinetics study As a kind of thermal stable engineering plastics, polyarylene ether nitriles could be used under high temperature for a long period without sacrificing its excellent mechanical and electric properties. The data such as Tid, the maximum thermal decomposition temperature (Tdmax) can only describe the thermal stability of
b¼
dT dt
ð4Þ
Combining Eqs. (1) –(4) and rearranging to get Eq. (5) dc A ¼ eE=RT ð1 cÞn dT b
ð5Þ
Firstly assume that n = 1, then Eq. (5) can be changed as
1.2
dc ¼ AeE=RT dt 1c
1
∆ lg(dc/dT)
The order of thermal decomposition reactions is determined by Coats –Redfern method [13].
0.8
ð6Þ
Integrating Eq. (6) to get:
0.6
log½ lnð1 cÞ ¼ E=RT loge þ logAt
0.4 0.2 0 -2
-4
-6
-8
-10
-12
-14
∆ (1/T)(10-5/K) Fig. 5. Plots of D(1 / T) versus Dlog(dc / dT),from the slope of the line to get the values of E (0: sample 1; n: sample 2; r: sample 3).
ð7Þ
Plot log[ ln(1 c)] against the T1 , TGA data are connected to be a line, as shown in Fig. 4, which means the assumption is correct and the type of thermal decomposition have no relation to the heating rate and to be the first order reaction.n = 1, Eq. (5) should be as: dc A ¼ eE=RT ð1 cÞ dT b
ð8Þ
C. Li et al. / Materials Letters 60 (2006) 137 – 141 Table 4 Results of constant a and b for the lifespan prediction of copolymers Sample
a
b 3
9.69 10 8.325 103 5.76 103
1 2 3
11.02 11.00 7.71
From Eq. (8) to get: E 1 dc D ¼ Dlog 2:3R T dt
6. Conclusions
5.2. The lifespan predication of thermal aging process for PEN (PP/HQ) Dakin et al. [14] considered that thermal aging reaction is chemical reaction in nature, and should also follow the rules of chemical reaction kinetics, so Eq. (10) is brought to describe it. 1 þb T
ð10Þ
Where s is the lifespan of PEN(PP/HQ) when the temperature is T, both a and b are constant da=dt ¼ AeE=RT a Where a is the fraction of residue Z Z a n ¼ 1; da=a ¼ AeE=RT 1
s
dt
0
logs ¼ E=2:303RT þ log½ð lnaÞ=A
ð11Þ
Compare Eq. (10) with Eq. (11) to get: a ¼ E=2:303R;
be calculated. For example, the highest service temperature of the three samples with a 95% residue for a 10-years service period are calculated to be 273, 196 and 126 -C, respectively. It can be seen from the results that the highest service temperature as well as lifespan of the copolymers also increase with the increasing PP content.
ð9Þ
dc ) against D( T1 ),the results were connected to be Plot Dlog( dT lines in Fig. 5, the values of E can be calculated from the slope of lines and then the values of A can be calculated from Eq. (7) subsequently, the results are listed in Table 3.
logs ¼ a
141
b ¼ log½ð lnaÞ=A
If a = 95%, according to the values of E and A listed in Table 3 to get the values of a and b of the three samples, respectively, in Table 4. From Eq. (10) and the data listed in Table 4, the lifespan of thermal aging under N2 atmosphere with a final residue of 95% at given temperature can be estimated, and the highest service temperature within a fixed lifespan can also
The PEN(PP/HQ) copolymers exhibit a excellent thermal and mechanical properties, the introduction of PP enhance the Tg of the copolymers, but the Tid of the copolymers do not have obvious relationship with the PP content. Through the lifespan prediction it was found that the lifespan increase with the increasing PP content under the thermal aging process, which is accordance with the observations got in Tg characterizations.
Acknowledgements The research was financially supported by National Natural Science Foundation (NO.59783003) and the key project of Jiangsu province of China (BE2003074).
References [1] D.K. Mohanty, J.L. Hedrick, K. Gobetz, B.C. Johnson, I. Yilgor, E. Yilgor, R. Yang, J.E. McGrath, Polymer Preprints 23 (1982) 284. [2] D.K. Mohanty, A.M. Walstrom, T.C. Ward, J.E. McGrath, Polymer Preprints 24 (1983) 147. [3] S. Matsuo, T. Murakami, R.J. Takasawa, Polym. Sci., Polym. Chem. 31 (1993) 3439. [4] A. Saxena, R. Sadhana, V.L. Rao, M. Kanakavel, K.N. Ninan, Polym. Bull. 50 (2003) 219. [5] A. Saxena, V.L. Rao, K.N. Ninan, Eur. Polym. J. 39 (2003) 57. [6] J.H. Zhang, X.B. Liu, Chinese Journal of Synthetic Chemistry 7 (1999) 42. [7] J. Verbort, C.S. Marvel, J. Polym. Sci., Polym. Chem. 11 (1973) 2793. [8] K.V. Sivaramakrishnan, C.S. Marvel, J. Polym. Sci., Polym. Chem. 12 (1974) 651. [9] T.M. Keller, J. Polym. Sci., Polym. Chem. 26 (1988) 3199. [10] T.M. Keller, Polymer 34 (1993) 952. [11] A.R. Hill, Y. Meng, A.S. Hay, I.A. Abuyousef, J. Polym. Sci., Polym. Chem. 38 (2000) 1318. [12] A. Saxena, V.L. Rao, P.V. Prabbakaran, Eur. Polym. J. 39 (2003) 401. [13] A.W. Coats, J.R. Redfern, Nature 68 (1964) 291. [14] T.W. Dakin, IEEE Trans. 62 (1946) 113.
Synthesis and properties of phenolphthalein-based polyarylene ether nitrile copolymers Cao Li a,b,*, Yi Gu a, Xiaobo Liu b a
College of polymer engineering and science, State key laboratory of polymeric materials engineering, Sichuan University, Chengdu 610065, China b Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China Received 11 March 2005; accepted 3 August 2005 Available online 6 September 2005
Abstract Phenolphthalein-modified polyarylene ether nitrile copolymers were synthesized by nucleophilic substitution reaction of 2,6difluorobenzonitrile (DFBN) with varying molar ratios of phenolphthalein (PP) and hydroquinone (HQ). The copolymers were chemically and physically characterized to have good thermal and mechanical properties. PP content of the copolymers has influence on glass transition temperature (Tg) as well as decomposition temperature (Tid). Coats – Redfern method was applied to study the thermal decomposition kinetics of the copolymers to predict the lifespan under thermal aging process of the copolymers, the results show that the lifespan increases with increasing PP content. D 2005 Elsevier B.V. All rights reserved. Keywords: Polyarylene ether nitrile; Copolymer; Synthesis; Thermal decomposition; Kinetics study
1. Introduction In recent decades, polyarylene ether nitrile (PEN) as special engineering plastics has gained wide applications for its excellent properties in aerospace, electric and automotive industry. Various bisphenol have been studied for synthesis of PEN via nucleophilic aromatic substitution polymerization, these PEN materials exhibit excellent thermal stabilities over a wide-range of temperature [1– 6]. The cyano group at main chain serves as a potential site for crosslinking reaction and can make polymer transform from thermoplastic to thermosetting [7– 10]. Matsuo et al [3] systematically studied the synthesis of 2,6-dihalo benzonitrile with different kinds of bisphenol including the phenolphthalein and found that mechanical properties of phenolphthalein based PEN were better than that of the corresponding ketone or sulfone containing polymers. However the above-mentioned PEN are all * Corresponding author. Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China. Tel./fax: +86 28 8540 0377. E-mail address: [email protected] (C. Li). 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.08.004
homopolymers, and insolubility has limited their applications in many areas. Many attempts have been made to improve the solubility of the PEN by copolymerization or incorporation of pendant group [4,5,11,12]. Mechanical properties such as elongation is low for phenolphthalein based PEN homopolymer have limited its applications [3,6]. There are also relatively few studies on thermal decomposition kinetics of thermoplastic PEN, but these polymers often encounter elevated temperature during applications. In this paper, we synthesized the copolymers of phenolphthalein and hydroquinone with various ratios and studied their thermal and mechanical properties. We also used Coats – Redfern method to study the thermal decomposition kinetics of PEN copolymers and predicted their lifespan under the thermal aging process.
2. Experimental 2.1. Materials 2,6-difluorobenzonitrile, hydroquinone and phenolphthalein were available commercially and purified by
138
C. Li et al. / Materials Letters 60 (2006) 137 – 141
HO
C
OH
m
O
CN
+(m+n) F
K2CO3
F + n HO OH
C
NMP
O CN
O
C
O
O O
O C
m
n
O Scheme 1. Polymerization of PEN(PP/HQ).
sublimation or recrystallization before use. Anhydrous K2CO3 was dried under vacuum at 100 -C before use. N-methyl pyrrolidone (NMP) was distilled under reduced pressure over calcium hydride and stored over 4A molecular sieves. 2.2. Polymer synthesis The synthesis of the PEN have been described in other reports [6], and the structure of the polymer synthesized is shown in Scheme 1.
eter. Tensile strength and elongation at break of the films were measured on LG500 mechanical testing instrument, and gained as average value for every five samples. Glass transition temperature of the films was measured on PERKIN-ELMER 7 DSC, at a heating rate of 10 -C min 1. TG/DTG analysis of the copolymers was carried out under N2 atmosphere at a heating rate of 10 -C min 1 using PERKIN-ELMER 7 series analyzer system combination with PE3700 data processing station.
4. Results and discussion
2.3. Preparation of polymer films Dissolved the polymer in DMF again to get a solution with 10% polymer content and filtered then. After vigorous stirring, the solution was cast onto a clean glass plate to obtain the film. The film then was heated at elevated temperature to 160 -C to remove the solvent completely. The films with a thickness of 20– 30 um were obtained.
3. Characterization
Polyarylene ether nitriles copolymers were synthesized by nucleophilic substitution reaction of 2,6-difluorobenzonitrile with phenolphthalein and hydroquinone. Molar ratio, yields and inherent viscosity values of the reactions are shown in Table 1. 4.1. Solubility All samples are insoluble in common organic solvents at room temperature, But three samples can dissolve in NMP solvent on heating. Sample 2 and 3 can be dissolved in DMF on heating while sample 1 cannot. It reveal that introduction of HQ improve the solubility of PEN.
Inherent viscosities of the samples were determined at 20 -C for 0.5% polymer solution in DMF using Ubbelhode viscometer. The FT-IR spectra of the films were recorded using Nicolet 20 SXB-IR spectrophotom-
Table 1 Conditions for the synthesis of PEN(PP/HQ) Sample
Molar ratio (PP : HQ)
Inherent viscosity (g/dL)
Dehydration time (h)
Polycondensation time (h)
Yield ratio (%)
1 2 3
70 : 30 50 : 50 30 : 70
0.87 0.76 1.12
2.5 2.5 2.5
4 4 4
98.3 98.8 99.0
Fig. 1. FT-IR of PEN(PP/HQ) polymer.
C. Li et al. / Materials Letters 60 (2006) 137 – 141
100
1 2 3
Tg (-C) 220 212 199
Tid (-C) 465 434 455
Tid5% (-C) 470 464 477
Tid30% (-C) 593 588 580
Tensile strength (MPa)
Elongation at break (%)
96 107 90
7 13 11
1 3
80
2
Weight
Table 2 Thermal and mechanical property of PEN(PP/HQ) Sample
139
60 40 20 0
4.2. FT-IR characterization
0
The structure of the copolymers was characterized with a FT-IR spectroscopy as shown in Fig. 1. From top to bottom the five samples have a structure of PP: HQ = 100 : 0, 70 : 30, 50 : 50, 30 : 70 and 0 : 100, respectively. For copolymer, the characteristic stretching vibration absorption of – OH of PP and HQ at 3290 and 3260 cm 1 as well as C-F of DFBN at 790 cm 1 disappeared. The absorption at 2231 cm 1 is characteristic symmetrical stretching of CN group. The absorption at 1247 cm 1 and 1287 cm 1 are assigned to – C – O – C – of PP, and absorption at 1190 cm 1 are the characteristic peak of – C – O – C – of HQ, both of them are ortho to CN, respectively. All these information confirmed that PP, DFBN and HQ have reacted as showed in Scheme 1. 4.3. Mechanical measurement and analysis The mechanical measurement such as tensile strength and elongation at break are listed in Table 2. The values of elongation
25
480
560
640
Temperature(°C) Fig. 3. TGA curves of PEN(PP/HQ) copolymers.
at break decrease with the increasing content of PP, which may be attributed to the rigidity brought about by the PP component. The mechanical measurements of the samples also show that tensile strength of PEN (PP/HQ) is higher than that of PEN (RE/HQ) copolymer [6]. Fig. 2 displays the fracture surface morphology of the films using SEM. It can be found that morphology of the three films differ from each other so obviously. The sample 1 and 3 is rough and anisotropic, which means the transfer of tensile stress has no orientation. For PP: HQ = 50 : 50 copolymer as shown in Fig. 2(2), the fracture surface morphology demonstrates a orientation characteristic and is in accordance with the results that sample 2 has the largest tensile strength.
Fig. 2. SEM of fracture surface morphology of the PEN(PP/HQ) copolymer films.
140
C. Li et al. / Materials Letters 60 (2006) 137 – 141
-1.4
Table 3 Results of E and A for thermal decomposition kinetics of the copolymers
lg[-ln(1-c)]
-1.05
-0.7
-0.35
0 1.05
1.15
1.25
1.35
1.45
1/T(103/K) Fig. 4. Plots of 1 / T versus log[ln(1 c)], the linear relationship between 1 / T and log[ln(1 c)] means that assumption that reaction order is 1 is correct (0: sample 1; n: sample 2; r: sample 3).
Sample
E (kJ/mol)
A (min 1)
1 2 3
185.5 159.4 110.3
5.42 109 5.16 109 2.65 106
the copolymers qualitatively. But in some applications polymer will encounter elevated temperature at every step such as manufacturing, processing for a long period, so a detailed analysis on the thermal decomposition would be valuable. For this purpose, the thermal decomposition kinetics of the phenolphthalein based PEN copolymers was investigated with the aid of the TG/DTG analysis for the first time and their lifespan under thermal aging process are also estimated.
4.4. Thermal properties
5.1. The calculation of E and A Glass transition temperature of the copolymers were calculated from the curves of DSC, and listed in Table 2. It can be seen that Tg increase with the increasing PP content in the copolymers, and the Tg of PEN(PP/HQ) copolymers is higher than that of PEN(RE/HQ) [9]. Fig. 3 shows the TGA profile of the three copolymers, the initial decomposition temperature (Tid) of three copolymers is higher than 430 -C. The thermal properties of three samples are listed in the Table 2. The Tid of PP homopolymer is higher than 500 -C, the introduction of HQ decreases Tid of the copolymers, but with the HQ content increase, the Tid of the copolymer increase again, which could be attributed to the decrease of distance between CN group on the main chain.
dc ¼ kf ðcÞ dt
ð1Þ
where k is rate constant given by the Eq. (2) k ¼ AeE=RT
ð2Þ
where A is frequency factor, R is the gas constant and E is activation energy of the reaction f ð cÞ ¼ ð 1 cÞ n
ð3Þ
where c is the fraction decomposed at time t and n is the order of reaction, for a linear heating reaction, b is the heating rate given by Eq. (4)
5. Thermal decomposition kinetics study As a kind of thermal stable engineering plastics, polyarylene ether nitriles could be used under high temperature for a long period without sacrificing its excellent mechanical and electric properties. The data such as Tid, the maximum thermal decomposition temperature (Tdmax) can only describe the thermal stability of
b¼
dT dt
ð4Þ
Combining Eqs. (1) –(4) and rearranging to get Eq. (5) dc A ¼ eE=RT ð1 cÞn dT b
ð5Þ
Firstly assume that n = 1, then Eq. (5) can be changed as
1.2
dc ¼ AeE=RT dt 1c
1
∆ lg(dc/dT)
The order of thermal decomposition reactions is determined by Coats –Redfern method [13].
0.8
ð6Þ
Integrating Eq. (6) to get:
0.6
log½ lnð1 cÞ ¼ E=RT loge þ logAt
0.4 0.2 0 -2
-4
-6
-8
-10
-12
-14
∆ (1/T)(10-5/K) Fig. 5. Plots of D(1 / T) versus Dlog(dc / dT),from the slope of the line to get the values of E (0: sample 1; n: sample 2; r: sample 3).
ð7Þ
Plot log[ ln(1 c)] against the T1 , TGA data are connected to be a line, as shown in Fig. 4, which means the assumption is correct and the type of thermal decomposition have no relation to the heating rate and to be the first order reaction.n = 1, Eq. (5) should be as: dc A ¼ eE=RT ð1 cÞ dT b
ð8Þ
C. Li et al. / Materials Letters 60 (2006) 137 – 141 Table 4 Results of constant a and b for the lifespan prediction of copolymers Sample
a
b 3
9.69 10 8.325 103 5.76 103
1 2 3
11.02 11.00 7.71
From Eq. (8) to get: E 1 dc D ¼ Dlog 2:3R T dt
6. Conclusions
5.2. The lifespan predication of thermal aging process for PEN (PP/HQ) Dakin et al. [14] considered that thermal aging reaction is chemical reaction in nature, and should also follow the rules of chemical reaction kinetics, so Eq. (10) is brought to describe it. 1 þb T
ð10Þ
Where s is the lifespan of PEN(PP/HQ) when the temperature is T, both a and b are constant da=dt ¼ AeE=RT a Where a is the fraction of residue Z Z a n ¼ 1; da=a ¼ AeE=RT 1
s
dt
0
logs ¼ E=2:303RT þ log½ð lnaÞ=A
ð11Þ
Compare Eq. (10) with Eq. (11) to get: a ¼ E=2:303R;
be calculated. For example, the highest service temperature of the three samples with a 95% residue for a 10-years service period are calculated to be 273, 196 and 126 -C, respectively. It can be seen from the results that the highest service temperature as well as lifespan of the copolymers also increase with the increasing PP content.
ð9Þ
dc ) against D( T1 ),the results were connected to be Plot Dlog( dT lines in Fig. 5, the values of E can be calculated from the slope of lines and then the values of A can be calculated from Eq. (7) subsequently, the results are listed in Table 3.
logs ¼ a
141
b ¼ log½ð lnaÞ=A
If a = 95%, according to the values of E and A listed in Table 3 to get the values of a and b of the three samples, respectively, in Table 4. From Eq. (10) and the data listed in Table 4, the lifespan of thermal aging under N2 atmosphere with a final residue of 95% at given temperature can be estimated, and the highest service temperature within a fixed lifespan can also
The PEN(PP/HQ) copolymers exhibit a excellent thermal and mechanical properties, the introduction of PP enhance the Tg of the copolymers, but the Tid of the copolymers do not have obvious relationship with the PP content. Through the lifespan prediction it was found that the lifespan increase with the increasing PP content under the thermal aging process, which is accordance with the observations got in Tg characterizations.
Acknowledgements The research was financially supported by National Natural Science Foundation (NO.59783003) and the key project of Jiangsu province of China (BE2003074).
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