THERMAL DEGRADATION OF POLY(ARYLENE SULFIDE SULFONE)/N- METHYLPYRROLIDONE CRYSTAL SOLVATE *

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1 Chinese Journal of Polymer Science Vol. 8, No. 1, (010), Chinese Journal of Polymer Science Chinese Chemical Society Institute of Chemistry, CAS Springer-Verlag 010 THMAL DGADATION OF POLY(AYLN SULFID SULFON)/N- MTHYLPYOLIDON CYSTAL SOLVAT * Xiao-jun Wang a, c, Mei-lin Zhang b, Jing Liu b, Gang Zhang b a, b, c** and Jie Yang a Institute of Materials Science & Technology, Sichuan University, Chengdu , China b College of Chemistry, Sichuan University, Chengdu , China c College of Polymer Science & ngineering, Sichuan University; State Key Laboratory of Polymer Materials ngineering, Sichuan University, Chengdu , China Abstract The thermal degradation of poly(arylene sulfide sulfone)/n-methylpyrrolidone (PASS/NMP) crystal solvate was studied by thermogravimetric analysis (TGA) and was compared with pure PASS in order to determine the way in which the formation of the crystal solvate affected the thermal properties of the polymer. The activation energy of the solid state process was determined using Kissinger s method, which does not require knowledge of the reaction mechanism (M), to be kj/mol which was lower than that for pure PASS ( = 14 kj/mol). The study of master curves together with interpretation of integral methods, allows confirmation that the thermal degradation mechanism for PASS in the crystal solvate system is a decelerated n type, which is a solid-state process based on a phase boundary controlled reaction, in the conversion range considered. Whereas, the pure PASS follows a decelerated D n thermodegradation mechanism in the same conversion range. Keywords: Poly(arylene sulfide sulfone); Crystal solvate; Thermal degradation; Thermogravimetric analysis (TGA). INTODUCTION Poly(arylene sulfide sulfone) (PASS) belongs to a new generation of heat-resistant engineering thermoplastics of the polyarylene sulfide (PAS) type and has already been used as a structural polymer. PASS can co-crystallize with N-methylpyrrolidone (NMP) and form crystal solvate [1, ]. Although some early literatures [3 6] contained a few reports on the formation of polymer crystal solvates, properties of this kind of crystal solvates have seldom been reported. Because of the potential importance of thermal properties of these structural polymers, we have investigated the thermal degradation and kinetic parameters of PASS/NMP crystal solvate in this work. Attention has also been directed to the comparison of thermal degradation of PASS as a homopolymer and in crystal solvates to determine how the formation of crystal solvate may affect the thermal property of PASS. There are many methods of kinetic analysis, but each of them is based on the hypothesis that, from a simple thermogravimetric trace, meaningful values can be obtained for parameters such as activation energy, preexponential factor and reaction order. A number of widely used methods will be discussed in the next sections. DIFFNTIAL MTHOD Kinetic information can be extracted from dynamic experiments by means of various methods [7, 8].The activation energy can be determined by Kissinger s method [9], which does not need a precise knowledge of the reaction * This work was financially supported by the 863 program of China (No. 007AA 03Z561). ** Corresponding author: Jie Yang ( 杨杰 ), -mail: ppsf@scu.edu.cn eceived November 17, 008; evised January 5, 009; Accepted February, 009 doi: /s x

2 86 X.J. Wang et al. mechanism, using the following equation: β A n 1 ln = ln + ln[ n( 1 α max ) ] (1) Tmax Tmax where β is the heating rate, T max is the temperature corresponding to the inflection point of the thermal degradation curves at the maximum reaction rate, A is the pre-exponential factor, α max is the maximum conversion, and n is the reaction order. The activation energy can be calculated from the slope of the plot of ln(β/ T )versus 1000/T max. INTGAL MTHODS The integral methods discussed in this paper are the Flynn-Wall-Ozawa and Coats-edfern methods. Flynn-Wall-Ozawa Method A lg β = lg[ ] () g( α) T max where β, A, and T have the known meanings [10, 11]. The activation energy for different conversion values can be calculated from a lnβ versus 1000/T plot. Coats-edfern Method g( α) A ln = ln T β T (3) The different degradation processes g(α) are listed in Table 1. The activation energy can be determined from the plot of ln(g(α)/t ) versus 1000/T [1]. Table 1. Algebraic expressions for the most frequently used mechanisms of degradation processes [15] Symbol f (α) g (α) Degradation processes Sigmoidal curves A (1 α)[ ln(1 α)] 1/ 1/ Nucleation and growth (Avrami q. 1) A 3 3(1 α)[ ln(1 α)] /3 1/3 Nucleation and growth (Avrami q. ) A 4 4(1 α)[ ln(1 α)] 3/4 [ ln(1 α)] 1/4 Nucleation and growth (Avrami q. 3) Deceleration curves 1 1 α Phase boundary controlled reaction (contracting linear) (1 α) 1/ [1 (1 α) 1/ ] Phase boundary controlled reaction (contracting area) 3 3(1 α) /3 [1 (1 α) 1/3 ] Phase boundary controlled reaction (contracting volume) D 1 1/(α) α One-dimensional diffusion D 1/ln(1 α) (1 α)ln(1 α) + α Two-dimensional diffusion D 3 3(1 α) /3 /[1 (1 α) 1/3 ] [1 (1 α) 1/3 ] Three-dimensional diffusion (Jander equation) D 4 3/[(1 α) 1/3 1] (1 /3α) (1 α) /3 Three-dimensional diffusion (Ginstling-Brounshtein equation) F 1 1 α ln(1 α) andom nucleation with one nucleus on the individual F (1 α) 1/(1 α) particle andom nucleation with two nuclei on the individual particle F 3 1/(1 α) 3 1/(1 α) andom nucleation with two nuclei on the individual particle Criado Method for Determination of eaction Mechanism Criado method [13] defines a function dα ( ) z ( α ) = dt π ( x) T (4) β

3 Thermal Degradation of Poly(arylene sulfide sulfone)/n-methylpyrrolidone Crystal Solvate 87 where x = /T; and π(x) is an approximation of the temperature integral which cannot be expressed in a simple analytical form. In this study we used the fourth rational expression of Senum and Young [14], which gives errors lower than 10% 5% for x = 0. A combination of qs. (1) and (4) gives: z ( α ) = f ( α ) g( α ) (5) This last equation was used to obtain the master curves as a function of the reaction degree corresponding to the different models listed in Table 1. Plotting the z(α) function calculated using experimental data and q. (4), and comparing with the master curves leads to easy and precise determination of the mechanism of a solid state process. XPIMNTAL POCDU Materials PASS was prepared by polycondensation of 4,4 -dichlorodipheneyl sulfone with sodium sulfide in a polar organic solvent at atmospheric pressure according to a polymerization process described elsewhere [8]. The product was extracted repeatedly with boiling water and acetone. Sample Preparation PASS/NMP crystal solvate was reprecipitated from 18 wt% PASS-NMP solution and dried at room temperature in vacuum for 30 h. Analysis Techniques Thermalgravimetric analysis was performed using an XSTA6000 thermal analysis equipment. The system was operated in the dynamic mode in the temperature range C, at different heating rates: 5, 10, 0 and 40 K/min. All experiments were carried out under a nitrogen atmosphere. SULTS AND DISCUSSION Thermal degradation curves obtained at different heating rates: 5, 10, 0, 40 K/min are shown in Fig. 1. These TG curves correspond to a double-stage decomposition reaction distinguished by the two significant and distinct mass changes over the temperature range of C for all four heating rates investigated. The NMP content in samples is about 5 wt%. Up to 300 C, the first stage of weight loss approximately corresponds to elimination of the bound NMP in the crystal solvate system, and the second one should represent the degradation process of PASS. Based on the purpose of this report, the following analysis is mainly focused on the second part, the degradation process of PASS. The initial, final and maximum rate decomposition temperatures (T i, T f and T max ) of PASS and residual mass after initial and complete degradation at 300 C and 700 C (W 300 and W 700 ) can be determined from these curves and are shown in Table. Compared with our previously report of the decomposition temperatures of pure PASS (shown in Table 3) [8], the decomposition temperature of PASS in the crystal solvate is decreased by different levels. This suggests a variation of thermaldegradation activation energy and kinetic mechanism of the resin. Table. The degradation temperatures of PASS in the crystal solvate system and residual masses at different heating rates in nitrogen Heating rate (K/min) T i ( C) T max ( C) T f ( C) W 300 (wt%) W 700 (wt%)

4 88 X.J. Wang et al. Fig. 1 xperimental TG curves of PASS-NMP crystal solvate at different heating rates in nitrogen Table 3. The degradation temperatures of pure PASS at different heating rates in nitrogen [8] Heating rate (K/min) T i ( C) T max ( C) T f ( C) Kissinger s method was first employed to analyze the TG data of PASS/NMP crystal solvate, because it was independent of any thermal degradation mechanism and was used most widely. Using q. (1) and the experimental data recorded in the Fig. 1, the activation energy of the decomposition of PASS was calculated from a straight line fit of a plot of ln(β/ T max ) versus 1000/T max (Fig. ). The value obtained from Fig. for the activation energy was kj/mol. Fig. Kissinger method applied to experimental data at different heating rates Flynn-Wall-Ozawa method is also independent of the degradation mechanism. q. () was also used and the activation energy determined from a linear fitting of lnβ versus 1000/T at different conversions. According to the fact that the Dyle approximation was used in q. (), only conversion values in the range of 5% 0% can be considered for discussion in the method. In this work, the conversion values 5%, 8%, 11%, 14%, 17% and 0% were used for calculation. The results of the Flynn-Wall-Ozawa analysis are given in Fig. 3, which shows that the best fitting straight lines are nearly parallel, indicating a constant activation energy in the range of conversions analyzed and confirming the validity of the approach used. Activation energies corresponding to the different conversions are shown in Table 4. According to these values a mean value of 173. kj/mol was obtained. From Table 4, it can be also found that the activation energy corresponding to an 11% conversion is

5 Thermal Degradation of Poly(arylene sulfide sulfone)/n-methylpyrrolidone Crystal Solvate 89 close to the value calculated by using Kissinger method. This result suggests that the values of the activation energies of PASS in the crystal solvate obtained from these two methods are reasonable. Fig. 3 Plots of lgβ against 1000/T of PASS at various conversion values in the range 5% 0% Table 4. Activation energies obtained using the Flynn-Wall-Ozawa method α (%) a According to our previously report, the activation energies of PASS in the homopolymer was determined to be 14 kj/mol [8]. This indicates that the change of aggregation structure has significant effect on the activation energies of PASS. And this effect should be attributed to an alternation of the solid state thermodegradation mechanism of PASS. Compare to other methods, the above used two methods present the advantage that they do not require previous knowledge of the reaction mechanism for determining the activation energy. According to some literatures, the obtained activation energies can be used to check the thermodegradation mechanism models of the polymer. To investigate the solid-state processes for the second thermal degradation of PASS/NMP crystal solvate, Coats-edfern method was chosen as it involved the mechanisms of solid-state processes. Using q. (3), proposed by Coats and edfern, the activation energy for every g(α) function listed in Table 1 can be obtained at constant heating rates from fitting of ln(g(α)/t ) versus 1000/T plots. This method used the same conversion values as those previous methods. Table 5 shows activation energies and correlations for conversion at constant heating rate values 5, 10, 0 and 40 K/min. Analysis of these data shows that the activation energies which are in best agreement with those obtained by using Kissinger s method correspond to an n type mechanism. For comparison, we have chosen Kissinger s method because it is independent of a particular kinetics mechanism. Moreover, from these tables it can be conclude that the optimum heating rate value is 0 K/min, at which the activation energy corresponding to a mechanism 1 is kj/mol, very close to kj/mol obtained from Kissinger s method. These facts strongly suggest that the solid state thermodegradation mechanism followed by our PASS crystal solvate system is a deceleration ( n ) type.

6 90 X.J. Wang et al. Table 5. Activation energies obtained using the Coats-edfern method for several solid state processes at different heating rates 5 K/min 10 K/min 0 K/min 40 K/min Mechamism a a a a A A A D D D D F F F In order to confirm this deceleration thermodegradation mechanism, that is, a phase boundary controlled reaction (contracting linear) solid state process, we have used the method proposed by Criado et al [13]. This method uses reference theoretical curves called master plots, which are compared to experimental data. Accordingly, the experimental results are obtained from q. (4) at a heating rate of 0 K/min, which is considered the optimum through studies based on integral methods. Because we used the Doyle approximation, only conversion values in the range of 5% 0% are considered for discussion. Master curves and experimental data are shown in Fig. 4. As can be seen in Fig. 4, in this range of conversion experimental results show better agreement with the z( 1 ) master curve, which corresponds to a deceleration 1 mechanism. Fig. 4 Master curves z(α) experimental data calculated by q. (4) From the foregoing analysis, it is obtained that PASS in its NMP crystal solvate yields a deceleration 1 thermodegradation mechanism. However, as a homogenous polymer, pure PASS shows a D n thermodegradation mechanism [8]. The probable reason for this kinetic mechanism variation may be related to the presence of microdosage NMP remaining in PASS matrix. The exact cause remains unknown and is worthy of further study. CONCLUSIONS The activation energy and thermodegradation mechanism of PASS in its NMP crystal solvate were obtained and confirmed by means of different kinetic methods. The activation energy ( = kj/mol) obtained is lower than that for pure PASS ( = 14 kj/mol). The study of master curves together with interpretation of integral methods, allows confirmation that the thermal degradation mechanism for PASS in the crystal solvate system is

7 Thermal Degradation of Poly(arylene sulfide sulfone)/n-methylpyrrolidone Crystal Solvate 91 a decelerated n type, which is a solid-state process based on a phase boundary controlled reaction, in the conversion range considered. Whereas, the pure PASS follows a decelerated D n thermodegradation mechanism in the same conversion range. FNCS 1 Gladkova,.A., Nedel'kin, V.I., Ovsyannikova, S.I., Andrianova, O.B., Genin, Ya V., Komarova, L.I., Pavlova, S.A., Dubrovina, L.V. and Sergeev, V.A., Vysokomolekularnye Soedineniya. Seriya A, 199, 34(1): 80 Liu, Y., Bhatnagar, A., Ji, Q., iffle, J.S., McGrath, J.., Geibel, J.F. and Kashiwagi, T., Polymer, 000, 41(13): Iovleva, M.M. and Papkov, S.P., Vysokomol Soyed, 198, A4(): 33 4 Turska,. and Janeczek, H., Polymer, 1978, 19(1): 81 5 Izumi, Y., Takezawa, H., Kikuta, N., Uemura, S. and Tsutsumi, A., Macromolecules, 1998, 31(): Cohen, Y. and Adams, W.W., Polymer, 1996, 37(13): Nunez, L., Fraga, F., Nunez, M.. and Villanueva, M., Polymer, 000, 41: Wang, H.D., Yang, J., Long, S.., Wang, X.J., Yang, Z. and Li, G.X., Polym. Degrad. Stab., 004, 83(): 9 9 Kissinger, H.., Anal. Chem., 1957, 9: Flynn, J.H. and Wall, L.A., J. Polym. Sci. Part B: Polym. Lett., 1966, 4(3): Ozawa, T., Bull. Chem. Soc. Jpn., 1965, 38(11): Coats, A.W. and edfern, J.P., Nature, 1964, 01(4914): Criado, J., Málek, J. and Ortega, A., Thermochim. Acta, 1989, 147(1-): Senum, G.I. and Yang,.T., J. Therm. Anal., 1977, 11(13): Vyazovkin, S., Int. ev. Phys. Chem., 000, 19(1): 45