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Studies of dielectric relaxation and a.c. conductivity in cellulose acetate hydrogen phthalate–poly(methyl methacrylate) blends
Materials Science and Engineering A281 (2000) 213 – 220 www.elsevier.com/locate/msea
Studies of dielectric relaxation and a.c. conductivity in cellulose acetate hydrogen phthalate–poly(methyl methacrylate) blends Vijayalakshmi Rao *, P.V. Ashokan, M.H. Shridhar Department of Materials Science, Mangalore Uni6ersity, Mangalagangotri, Karnataka, D.K. 574199, India Received 6 August 1999; received in revised form 18 October 1999
Abstract Dielectric constant, dielectric loss and a.c. conductivity of polyblends of cellulose acetate hydrogen phthalate(CAP) and poly(methyl methacrylate) (PMMA) of different compositions have been measured in the temperature range 300 – 430 K and in the frequency range 50–100 kHz. Variations in dielectric constant with temperature of the blends exhibit unique behavior, different from the component polymers. In the blends, the dielectric loss as a function of temperature displays a single peak corresponding to the glass transition temperature (Tg), in the region between the Tg values of the pure polymers. The Tg values observed agree well with those values obtained from DSC. Dielectric studies show that CAP forms miscible blends with PMMA. AC conductivity values are calculated from dielectric data and the conduction mechanism is discussed. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Miscible blends; Dielectric relaxation; AC conductivity
1. Introduction Dielectric measurements such as dielectric constant and dielectric loss reveal significant information about the chemical and physical state of polymers. These properties are drastically affected by the presence of another polymer or a dopant in the polymer [1–5]. The study of dielectric relaxation provides valuable information about the intermolecular interaction and hence miscibility. Paul and Newman [6] and Olabisi et al. [7] have reviewed methods of determination of polymer– polymer miscibility in blends. The methods include Tg determination (by DSC, dielectric relaxation, mechanical relaxation, dilatometry), optical clarity, IR spectroscopy, SEM, ultrasonic and viscometry. However dielectric relaxation studies in polymer blends are found to be very limited. Hence in this paper we report the dielectric relaxation studies of a new blend system of cellulose acetate hydrogen phthalate (CAP) and poly(-
* Corresponding author. E-mail address: [email protected] (V. Rao)
methyl methacrylate) (PMMA) and make an attempt to understand the interaction involved in blending PMMA with a proton donor polymer CAP. CAP and PMMA have been selected for the present study because of their pharmaceutical applications [8,9]. PMMA is a proton acceptor polymer and it forms miscible blends with hydroxyl-containing polymers such as poly(vinyl phenol), poly (hydroxy ethyl methacrylate), poly(vinyl alcohol) etc. [10–12]. The specific interaction is hydrogen bonding. Studies on the miscibility of this blend system using DSC, ultrasonic and viscometric methods have been reported in our earlier publication [13].
2. Experimental Polymers used in the study, CAP and PMMA were obtained from commercial sources. The structure of CAP and PMMA are given in Fig. 1. The composition and molecular weight of the CAP and PMMA are as follows. For CAP, phthalate content is 30–40%, acetyl content 19–24%, hydroxyl content 36–51% and viscosity average molecular weight is Mv= 70 000. For
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Fig. 1. Structure of PMMA and CAP.
Fig. 2. (a – e) Variation of dielectric constant with temperature at different frequencies for PMMA, CM-3, CM-5, CM-7 and CAP. (f) Variation of dielectric constant with temperature for different blend compositions at 100 Hz.
V. Rao et al. / Materials Science and Engineering A281 (2000) 213–220
215
Fig. 2. (Continued)
Fig. 3. Variation of dielectric constant with frequency at different temperatures of CM-5 blend.
PMMA, viscosity average molecular weight is Mv= 101 000. Thin films of 5 mm thickness of CAP, PMMA and their blends of compositions CAP/PMMA, 70/30 (CM7), 50/50 (CM-5), 30/70 (CM-3) were grown by an isothermal immersion technique, using dimethyl formamide (DMF) as solvent [14]. The bottom Al electrode is vacuum coated on one side of a clean glass slide and then dipped vertically in 4% polymer/blend
solution for 15 min at constant temperature (30°C). The slide is taken out and kept horizontally for drying in a vacuum drier at 40°C. The thickness of the films is determined by the mechanical stylus method. The top electrode of aluminum was vacuum deposited on the dried polymer film to form a sandwich configuration Al–polymer–Al. The dielectric properties (capacitance and tan d) of the blends and individual polymers were measured as a function of temperature using Gen. Rad.
216
V. Rao et al. / Materials Science and Engineering A281 (2000) 213–220
1689 Precision RLC Digibridge in the frequency range of 50 Hz–100 kHz. The sample temperature was monitored with a Cu– constantan thermocouple in the range of 300–450 K using a digital multimeter. Sample films were annealed before actual measurements, in order to remove solvent and obtain constant loss peak temperatures.
3. Results and discussion Dielectric constant and tan d of CAP, PMMA and CAP-PMMA blend films as a function of field frequency and temperature and a.c. conductivity values are given in Figs. 2–6.
Fig. 4. (a – e) Tan d as a function of temperature at different frequencies for pure PMMA, CM-3, CM-5, CM-7 and CAP. (f) Tan d as a function of temperature for different blend compositions at a frequency of 50 Hz.
V. Rao et al. / Materials Science and Engineering A281 (2000) 213–220
217
Fig. 4. (Continued)
3.1. Variation of dielectric constant with temperature and frequency
to orient themselves in the direction of the applied field [17].
In the frequency range between 50 and 100 kHz, for pure PMMA, the dielectric constant decreases with increasing temperature up to Tg and thereafter increases with temperature. For blends with 70 and 50% PMMA, the dielectric constant increases throughout with temperature. Similar behavior has been observed for compatible blends of PVDF and PMMA (with 60% PVDF) [15]. In a blend of 30% PMMA and pure CAP, the dielectric constant first increases up to Tg and then decreases with further increase in temperature (Fig. 2a–e). The variation of dielectric constant with temperature is different for polar and nonpolar polymers. Dielectric constant is independent of temperature for nonpolar polymers whereas for strong polar polymers dielectric constant increases with temperature. The dielectric constant increase with temperature is due to an increase of total polarization arising from dipoles and trapped charge carriers. However since the specific volume of the polymer is temperature-dependent, i.e. it increases with temperature, dielectric constant decreases with temperature in the case of weakly polar polymers [16]. Fig. 2a clearly shows the weak polar nature of PMMA. As CAP content is increased, the polar nature of the blend increases and the dielectric constant increases (Fig. 2f). The dielectric constant decreases with increasing frequency in the case of PMMA, CAP and all blends. A typical plot is shown in Fig. 3. This may be due to the tendency of induced dipoles in the polymer
3.2. Variation of tan d with temperature and frequency Fig. 4a–e shows the variations of tan d with temperature for field frequencies between 50 Hz and 100 kHz for the blends and components. A loss peak is observed at the Tg of blend. The peak shifts to the high temperature side with an increase in frequency. The study of miscibility in blends by dielectric relaxation involves the assessment of one or more loss peaks and the accurate location of these temperature maxima. In a binary blend, there is either one or multiple loss peaks. Occurrence of a single loss peak corresponds to miscibility of the blend. From Fig. 4f, it is seen that a single loss peak is observed corresponding to Tg for all the compositions studied and the temperature of the loss peak shifts regularly between the two composition extremes corresponding to PMMA and CAP. The Tg values obtained from the loss peak agree well with the Tg values observed in DSC measurements [13]. At very low frequency, i.e. at 50 Hz, a b-relaxation peak is also observed for pure CAP and for blends with higher content of CAP, i.e. at 52°C, but not for blends with lower content of CAP and pure PMMA. The b-relaxation may be due to the orientation of the polar OH group in CAP. In blends with a low percentage of CAP, this peak disappears because all free OH groups may be involved in hydrogen bonding with the CO groups of PMMA. From the structure of CAP and PMMA, it is clear that the blends with a higher percentage of CAP,
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even though OH groups are involved in hydrogen bond formation, may have free OH groups and this contributes to the b-relaxation peak in blends with higher content of CAP and in pure CAP. Variation of tan d with field frequency at fixed temperature is shown in Fig. 5a – e. Tan d exhibits a relax-
ation peak around 10 kHz at temperatures corresponding to the Tg of the blends. The peak frequency is found to shift to higher frequency with an increase in temperature. Activation energies of relaxation are calculated based on the following equation [15]
Fig. 5. (a – e) Variation of tan d as a function of log f at different temperatures for PMMA, CM-3, CM-5, CM-7 and CAP.
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Fig. 6. (a) Variation of a.c. conductivity with temperature at different frequencies for CM-5 blend. (b) Variation of a.c. conductivity as a function of frequency f at 300 K for CM-5 blend.
Table 1 Tg, activation energy and n-values of CAP–PMMA blends Blend composition CAP/PMMA
0/100 30/70 50/50 70/30 100/0
(PMMA) (CM-3) (CM-5) (CM-7) (CAP)
Tg values (°C)
Activation energies (eV)
DSC
Dielectric relaxation
Dielectric relaxation
a.c. conductivity
92 110 119 128 142
89 108 117 127 140
0.0592 0.0633 0.0676 0.0736 0.082
0.0677 0.0738 0.088 0.0923 0.0799
n-values
0.83 0.98 0.95 0.917 0.85
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fm = foe( − E/kBT)
(1)
where fm is the frequency at relaxation peak, fo is a constant, E is the activation energy, kB the Boltzmann’s constant and T the absolute temperature. The logarithm of frequency corresponding to tan d maximum is plotted against 1/T (Fig. 5a – e) and the activation energy is calculated from the slope. The activation energies of blends and individual polymers are given in Table 1. Activation energy linearly varies with increase in content of CAP. As temperature is increased, the b-relaxation shifts to higher frequency with activation energies ranging between 0.06 and 0.08 eV. This low activation energy indicates an electronic hopping conduction mechanism [18].
3.3. AC conducti6ity as a function of temperature and frequency AC conductivity (sa.c.) values are calculated from dielectric measurements using the following expression [16] sa.c. =fo% tan d/1.8 ×1010
(2)
The a.c. conductivity of amorphous substances is governed by sa.c.af n
(3)
The exponent n decreases with increasing temperature and is within the limits 0.5Bn B1. In the present study, sa.c. varies as a function of n which lies between 0.8 and 0.98 for all blends in the frequency range 100 Hz to 50 kHz. This characterizes electronic conduction via a hopping process [18]. A very weak temperature dependence is observed for PMMA, CAP and their blends (a typical plot is shown in Fig. 6a). The increase in a.c. conductivity with frequency and a weak temperature dependence indicate that charge carriers are transported by hopping through defect sites along the chains [19]. A representative plot of log sa.c. versus frequency, log f (at 300 K and for CAP/PMMA blend composition 50/50) is given in Fig. 6b. A similar observation is reported for PVDF – PMMA blends [20].
.
4. Conclusions 1. Trends in dielectric constant as a function of temperature and frequency reveal that dielectric properties are drastically affected by blending a strongly polar polymer with a weakly polar polymer. 2. The dielectric loss exhibits a single relaxation peak, corresponding to Tg, for blends and the temperature of loss peak shifts between the two composition extremes corresponding to PMMA and CAP, showing that PMMA forms a miscible blend with CAP. 3. From the relaxation behavior, the activation energy for relaxation is found to lie between 0.06 and 0.08 eV indicating an electronic hopping conduction mechanism. 4. The nearly linear dependence of a.c. conductivity with frequency accounts for the electronic conduction via a hopping process. References [1] H. Saito, B. Stuhn, Polymer (UK) 3 (35) (1994) 475. [2] C. Ramu, Y.R.V. Naidu, A.K. Sharma, Ferroelectrics 159 (1994) 275. [3] M.M. Mosad, J. Mater. Sci. Lett. 9 (1990) 32. [4] R. Turch, Phys. Stat. Solids (a) k121 (1990) 119. [5] Y. Tsujitha, et al., J. Macromol. Sci. Phys. B 23 (3) (1984) 311. [6] D.R. Paul, S. Newman (Eds.), Polymer – Polymer Miscibility in Polymer Blends, vol. II, Academic Press, New York, 1978. [7] O. Olabisi, L.M. Robsen, M.T. Shaw, Polymer – Polymer Miscibility, Academic Press, New York, 1979. [8] P. Gutler, R. Gurny, Drug Dev. Ind. Pharm. 1 (1995) 21. [9] H.A. Weber, A.P. Molenaar, U.S. Pat. (3)557,280, Jan. 19, 1971. [10] J.F. Parana, L.C. Dikinson, J.C.W. Chien, R.S. Porter, Macromolecules 22 (1989) 1078. [11] V.N. Kleznew, O.L. Melinkova, V.D. Kilkova, Eur. Polym. J. 14 (1978) 455. [12] Y.P. Singh, R.P. Singh, Eur. Polym. J. 19 (1983) 535. [13] V. Rao, P.V. Ashokan, M.H. Shridhar, Polymer 40 (1999) 7167. [14] A.C. Rastogi, K.L. Chopra, Thin Solid Films 26 (1973) 201. [15] G.K. Narula, P.K.C. Pillai, J. Mater. Sci. Lett. 8 (1989) 608. [16] B. Tareev, Physics of Dielectric Materials, MIR, Moscow, 1979. [17] F.M. Reicha, et al., J. Phys. D Appl. Phys. 24 (1991) 369. [18] A. Kuezkowski, R. Zielinski, J. Phys. D Appl. Phys. 15 (1982) 1765. [19] A.K. Jonscher, Thin Solid Films 1 (1967) 213. [20] G.K. Narula, P.K.C. Pillai, J. Mater. Sci. Mater. Electron. 2 (1991) 209.
Studies of dielectric relaxation and a.c. conductivity in cellulose acetate hydrogen phthalate–poly(methyl methacrylate) blends Vijayalakshmi Rao *, P.V. Ashokan, M.H. Shridhar Department of Materials Science, Mangalore Uni6ersity, Mangalagangotri, Karnataka, D.K. 574199, India Received 6 August 1999; received in revised form 18 October 1999
Abstract Dielectric constant, dielectric loss and a.c. conductivity of polyblends of cellulose acetate hydrogen phthalate(CAP) and poly(methyl methacrylate) (PMMA) of different compositions have been measured in the temperature range 300 – 430 K and in the frequency range 50–100 kHz. Variations in dielectric constant with temperature of the blends exhibit unique behavior, different from the component polymers. In the blends, the dielectric loss as a function of temperature displays a single peak corresponding to the glass transition temperature (Tg), in the region between the Tg values of the pure polymers. The Tg values observed agree well with those values obtained from DSC. Dielectric studies show that CAP forms miscible blends with PMMA. AC conductivity values are calculated from dielectric data and the conduction mechanism is discussed. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Miscible blends; Dielectric relaxation; AC conductivity
1. Introduction Dielectric measurements such as dielectric constant and dielectric loss reveal significant information about the chemical and physical state of polymers. These properties are drastically affected by the presence of another polymer or a dopant in the polymer [1–5]. The study of dielectric relaxation provides valuable information about the intermolecular interaction and hence miscibility. Paul and Newman [6] and Olabisi et al. [7] have reviewed methods of determination of polymer– polymer miscibility in blends. The methods include Tg determination (by DSC, dielectric relaxation, mechanical relaxation, dilatometry), optical clarity, IR spectroscopy, SEM, ultrasonic and viscometry. However dielectric relaxation studies in polymer blends are found to be very limited. Hence in this paper we report the dielectric relaxation studies of a new blend system of cellulose acetate hydrogen phthalate (CAP) and poly(-
* Corresponding author. E-mail address: [email protected] (V. Rao)
methyl methacrylate) (PMMA) and make an attempt to understand the interaction involved in blending PMMA with a proton donor polymer CAP. CAP and PMMA have been selected for the present study because of their pharmaceutical applications [8,9]. PMMA is a proton acceptor polymer and it forms miscible blends with hydroxyl-containing polymers such as poly(vinyl phenol), poly (hydroxy ethyl methacrylate), poly(vinyl alcohol) etc. [10–12]. The specific interaction is hydrogen bonding. Studies on the miscibility of this blend system using DSC, ultrasonic and viscometric methods have been reported in our earlier publication [13].
2. Experimental Polymers used in the study, CAP and PMMA were obtained from commercial sources. The structure of CAP and PMMA are given in Fig. 1. The composition and molecular weight of the CAP and PMMA are as follows. For CAP, phthalate content is 30–40%, acetyl content 19–24%, hydroxyl content 36–51% and viscosity average molecular weight is Mv= 70 000. For
0921-5093/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 9 9 ) 0 0 7 2 3 - 6
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Fig. 1. Structure of PMMA and CAP.
Fig. 2. (a – e) Variation of dielectric constant with temperature at different frequencies for PMMA, CM-3, CM-5, CM-7 and CAP. (f) Variation of dielectric constant with temperature for different blend compositions at 100 Hz.
V. Rao et al. / Materials Science and Engineering A281 (2000) 213–220
215
Fig. 2. (Continued)
Fig. 3. Variation of dielectric constant with frequency at different temperatures of CM-5 blend.
PMMA, viscosity average molecular weight is Mv= 101 000. Thin films of 5 mm thickness of CAP, PMMA and their blends of compositions CAP/PMMA, 70/30 (CM7), 50/50 (CM-5), 30/70 (CM-3) were grown by an isothermal immersion technique, using dimethyl formamide (DMF) as solvent [14]. The bottom Al electrode is vacuum coated on one side of a clean glass slide and then dipped vertically in 4% polymer/blend
solution for 15 min at constant temperature (30°C). The slide is taken out and kept horizontally for drying in a vacuum drier at 40°C. The thickness of the films is determined by the mechanical stylus method. The top electrode of aluminum was vacuum deposited on the dried polymer film to form a sandwich configuration Al–polymer–Al. The dielectric properties (capacitance and tan d) of the blends and individual polymers were measured as a function of temperature using Gen. Rad.
216
V. Rao et al. / Materials Science and Engineering A281 (2000) 213–220
1689 Precision RLC Digibridge in the frequency range of 50 Hz–100 kHz. The sample temperature was monitored with a Cu– constantan thermocouple in the range of 300–450 K using a digital multimeter. Sample films were annealed before actual measurements, in order to remove solvent and obtain constant loss peak temperatures.
3. Results and discussion Dielectric constant and tan d of CAP, PMMA and CAP-PMMA blend films as a function of field frequency and temperature and a.c. conductivity values are given in Figs. 2–6.
Fig. 4. (a – e) Tan d as a function of temperature at different frequencies for pure PMMA, CM-3, CM-5, CM-7 and CAP. (f) Tan d as a function of temperature for different blend compositions at a frequency of 50 Hz.
V. Rao et al. / Materials Science and Engineering A281 (2000) 213–220
217
Fig. 4. (Continued)
3.1. Variation of dielectric constant with temperature and frequency
to orient themselves in the direction of the applied field [17].
In the frequency range between 50 and 100 kHz, for pure PMMA, the dielectric constant decreases with increasing temperature up to Tg and thereafter increases with temperature. For blends with 70 and 50% PMMA, the dielectric constant increases throughout with temperature. Similar behavior has been observed for compatible blends of PVDF and PMMA (with 60% PVDF) [15]. In a blend of 30% PMMA and pure CAP, the dielectric constant first increases up to Tg and then decreases with further increase in temperature (Fig. 2a–e). The variation of dielectric constant with temperature is different for polar and nonpolar polymers. Dielectric constant is independent of temperature for nonpolar polymers whereas for strong polar polymers dielectric constant increases with temperature. The dielectric constant increase with temperature is due to an increase of total polarization arising from dipoles and trapped charge carriers. However since the specific volume of the polymer is temperature-dependent, i.e. it increases with temperature, dielectric constant decreases with temperature in the case of weakly polar polymers [16]. Fig. 2a clearly shows the weak polar nature of PMMA. As CAP content is increased, the polar nature of the blend increases and the dielectric constant increases (Fig. 2f). The dielectric constant decreases with increasing frequency in the case of PMMA, CAP and all blends. A typical plot is shown in Fig. 3. This may be due to the tendency of induced dipoles in the polymer
3.2. Variation of tan d with temperature and frequency Fig. 4a–e shows the variations of tan d with temperature for field frequencies between 50 Hz and 100 kHz for the blends and components. A loss peak is observed at the Tg of blend. The peak shifts to the high temperature side with an increase in frequency. The study of miscibility in blends by dielectric relaxation involves the assessment of one or more loss peaks and the accurate location of these temperature maxima. In a binary blend, there is either one or multiple loss peaks. Occurrence of a single loss peak corresponds to miscibility of the blend. From Fig. 4f, it is seen that a single loss peak is observed corresponding to Tg for all the compositions studied and the temperature of the loss peak shifts regularly between the two composition extremes corresponding to PMMA and CAP. The Tg values obtained from the loss peak agree well with the Tg values observed in DSC measurements [13]. At very low frequency, i.e. at 50 Hz, a b-relaxation peak is also observed for pure CAP and for blends with higher content of CAP, i.e. at 52°C, but not for blends with lower content of CAP and pure PMMA. The b-relaxation may be due to the orientation of the polar OH group in CAP. In blends with a low percentage of CAP, this peak disappears because all free OH groups may be involved in hydrogen bonding with the CO groups of PMMA. From the structure of CAP and PMMA, it is clear that the blends with a higher percentage of CAP,
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V. Rao et al. / Materials Science and Engineering A281 (2000) 213–220
even though OH groups are involved in hydrogen bond formation, may have free OH groups and this contributes to the b-relaxation peak in blends with higher content of CAP and in pure CAP. Variation of tan d with field frequency at fixed temperature is shown in Fig. 5a – e. Tan d exhibits a relax-
ation peak around 10 kHz at temperatures corresponding to the Tg of the blends. The peak frequency is found to shift to higher frequency with an increase in temperature. Activation energies of relaxation are calculated based on the following equation [15]
Fig. 5. (a – e) Variation of tan d as a function of log f at different temperatures for PMMA, CM-3, CM-5, CM-7 and CAP.
V. Rao et al. / Materials Science and Engineering A281 (2000) 213–220
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Fig. 6. (a) Variation of a.c. conductivity with temperature at different frequencies for CM-5 blend. (b) Variation of a.c. conductivity as a function of frequency f at 300 K for CM-5 blend.
Table 1 Tg, activation energy and n-values of CAP–PMMA blends Blend composition CAP/PMMA
0/100 30/70 50/50 70/30 100/0
(PMMA) (CM-3) (CM-5) (CM-7) (CAP)
Tg values (°C)
Activation energies (eV)
DSC
Dielectric relaxation
Dielectric relaxation
a.c. conductivity
92 110 119 128 142
89 108 117 127 140
0.0592 0.0633 0.0676 0.0736 0.082
0.0677 0.0738 0.088 0.0923 0.0799
n-values
0.83 0.98 0.95 0.917 0.85
220
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fm = foe( − E/kBT)
(1)
where fm is the frequency at relaxation peak, fo is a constant, E is the activation energy, kB the Boltzmann’s constant and T the absolute temperature. The logarithm of frequency corresponding to tan d maximum is plotted against 1/T (Fig. 5a – e) and the activation energy is calculated from the slope. The activation energies of blends and individual polymers are given in Table 1. Activation energy linearly varies with increase in content of CAP. As temperature is increased, the b-relaxation shifts to higher frequency with activation energies ranging between 0.06 and 0.08 eV. This low activation energy indicates an electronic hopping conduction mechanism [18].
3.3. AC conducti6ity as a function of temperature and frequency AC conductivity (sa.c.) values are calculated from dielectric measurements using the following expression [16] sa.c. =fo% tan d/1.8 ×1010
(2)
The a.c. conductivity of amorphous substances is governed by sa.c.af n
(3)
The exponent n decreases with increasing temperature and is within the limits 0.5Bn B1. In the present study, sa.c. varies as a function of n which lies between 0.8 and 0.98 for all blends in the frequency range 100 Hz to 50 kHz. This characterizes electronic conduction via a hopping process [18]. A very weak temperature dependence is observed for PMMA, CAP and their blends (a typical plot is shown in Fig. 6a). The increase in a.c. conductivity with frequency and a weak temperature dependence indicate that charge carriers are transported by hopping through defect sites along the chains [19]. A representative plot of log sa.c. versus frequency, log f (at 300 K and for CAP/PMMA blend composition 50/50) is given in Fig. 6b. A similar observation is reported for PVDF – PMMA blends [20].
.
4. Conclusions 1. Trends in dielectric constant as a function of temperature and frequency reveal that dielectric properties are drastically affected by blending a strongly polar polymer with a weakly polar polymer. 2. The dielectric loss exhibits a single relaxation peak, corresponding to Tg, for blends and the temperature of loss peak shifts between the two composition extremes corresponding to PMMA and CAP, showing that PMMA forms a miscible blend with CAP. 3. From the relaxation behavior, the activation energy for relaxation is found to lie between 0.06 and 0.08 eV indicating an electronic hopping conduction mechanism. 4. The nearly linear dependence of a.c. conductivity with frequency accounts for the electronic conduction via a hopping process. References [1] H. Saito, B. Stuhn, Polymer (UK) 3 (35) (1994) 475. [2] C. Ramu, Y.R.V. Naidu, A.K. Sharma, Ferroelectrics 159 (1994) 275. [3] M.M. Mosad, J. Mater. Sci. Lett. 9 (1990) 32. [4] R. Turch, Phys. Stat. Solids (a) k121 (1990) 119. [5] Y. Tsujitha, et al., J. Macromol. Sci. Phys. B 23 (3) (1984) 311. [6] D.R. Paul, S. Newman (Eds.), Polymer – Polymer Miscibility in Polymer Blends, vol. II, Academic Press, New York, 1978. [7] O. Olabisi, L.M. Robsen, M.T. Shaw, Polymer – Polymer Miscibility, Academic Press, New York, 1979. [8] P. Gutler, R. Gurny, Drug Dev. Ind. Pharm. 1 (1995) 21. [9] H.A. Weber, A.P. Molenaar, U.S. Pat. (3)557,280, Jan. 19, 1971. [10] J.F. Parana, L.C. Dikinson, J.C.W. Chien, R.S. Porter, Macromolecules 22 (1989) 1078. [11] V.N. Kleznew, O.L. Melinkova, V.D. Kilkova, Eur. Polym. J. 14 (1978) 455. [12] Y.P. Singh, R.P. Singh, Eur. Polym. J. 19 (1983) 535. [13] V. Rao, P.V. Ashokan, M.H. Shridhar, Polymer 40 (1999) 7167. [14] A.C. Rastogi, K.L. Chopra, Thin Solid Films 26 (1973) 201. [15] G.K. Narula, P.K.C. Pillai, J. Mater. Sci. Lett. 8 (1989) 608. [16] B. Tareev, Physics of Dielectric Materials, MIR, Moscow, 1979. [17] F.M. Reicha, et al., J. Phys. D Appl. Phys. 24 (1991) 369. [18] A. Kuezkowski, R. Zielinski, J. Phys. D Appl. Phys. 15 (1982) 1765. [19] A.K. Jonscher, Thin Solid Films 1 (1967) 213. [20] G.K. Narula, P.K.C. Pillai, J. Mater. Sci. Mater. Electron. 2 (1991) 209.