Studies on the Polymers Having a High Dielectric Constant. VIII. T Blend Polymer Systems Consisting of a Monomeric-TCNQ Salt and Insulating Polymers

Polymer Journal, Vol. 10, No.2, pp 231-234 (1978)

SHORT COMMUNICATION

Studies on the Polymers Having a High Dielectric Constant. VIII. t Blend Polymer Systems Consisting of a Monomeric-TCNQ Salt and Insulating Polymers

Shinobu lKENo,* Masaaki YoKOYAMA, and Hiroshi MIKAWA

Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565, Japan.

(Received August 29, 1977)

KEY WORDS Dielectric Constant I Dielectric Loss I Blend Polymer I TCNQ Salt I Insulating Polymer I Conductivity I Heterogeneous Dielectrics I

Polymeric materials having a high dielectric cyanoquinodimethane) complex salt in nonconduct• constant and low dielectric loss are highly desired ing polymers such as polystyrene and polysulfone. for the purpose of making film type capacitors The preparation of these blend polymers will be small. Attempts made so far to meet this need described later. The electrical properties of the have been mostly based on the orientation polari• blend polymers are summarized in Table I and zation of the side groups with large dipole mo• Figures 1 and 2. Table I shows specific resistivities ments, as is exemplified by such polymers as at room temperature. As shown in the table, cyanoethylated cellulose1 and poly(vinylidene fluo• the blend polymers containing more than 10 wt% ride).2 The dielectric constant of 10-15 was the of the complex salt have a somewhat lower re• maximum in these polymers. sistivity and are considered no longer suitable as In order to attain a higher c"' we have been dielectric material. Figure 1 shows the frequency investigating a new approach3 based on a polari• dependence of sr and tan o at room temperature zation process other than the orientation polari• for the blend polymers of the polystyrene matrix. zation, i.e., interfacial polarization. An electrical• As shown in the figure, the value of sr in the low ly conductive component is microscopically dis• frequency region ( < 1 kHz) is high (cr > 30) and persed in an insulating polymer component, and increases with greater concentration of the complex the interfacial polarization induced by the migra• salt. However, cr decreases in a high frequency tion of electronic carriers in the dispersed conduc• region, and tan omaximum appears at 10-40kHz. tive phases is expected to be effective in these sys• In contrast to the blend polymers with the complex tems. We wish to report in this paper that we salt, the value of sr of the blend polymer with a were able to succeed in preparing a polymer blend simple salt (D in Figure 1) is very low and nearly system having relatively high c"' 100, in commer• equal to the value of just the polystyrene. In cial frequency region with a relatively low tan o Figure 2, sr and tan o values for the blend polymers value, being about 3 %, by dispersing a highly of the polysulfone matrix are plotted against conductive n-butylquinolinium-TCNQ (tetra- frequency. The dielectric behavior of these blend polymers is similar to the case of the polystyrene matrix, i.e., cr in low frequency region below 110Hz 1 The preceding paper VII, S. Ikeno, M. Yokoyama is high and increases with the complex salt concen• and H. Mikawa, Kobunshi Ronbunshu, 35, 137 (1978). tt * On leave of absence from Research Division, Ma• tration up to 10 wt %. However, sr decreases when tsushita Electric Works Co. Ltd., Kadoma, Osaka 571, the content of the complex salt becomes 20 wt %. Japan. Tano maximum also appears at 2-5kHz for the

231 S. !KENO, M. YOKOYAMA, and H. MIKAWA

Table I. Specific resistivities p of blend polymers at room temperature, and the shape factor n and specific resistivities P2 of the conductive phase in the blend polymers calculated by Sillars theory

Sample Insulating Complex salt• p,RT, ne ajbd P2, Qcm fm, Hz• Erof polymer content (wt %) Qcmb I Polystyrene 2.5 1011 431 38 6.4 X 104 2.5 X 104 32 II Polystyrene 5.0 JOll 531 43 8.1 X J04 1.6 X J04 73 III Polystyrene 10.0 JOB 808 55 3.9 X 104 2.2 X 104 214 IV Polysulfone 5.0 JQ13 368 35 7.8 X 105 2.0 X 103 62 v Polysulfone 10.0 JOB 823 55 1.6 X J05 4.5xl03 260 VI Polysulfone 20.0 JOB ------·--- • n-Butylquinolinium-TCNQ complex salt. Multiplication of this content (wt%) by a factor of 0.69 gives the TCNQ content (wt %) of the blend polymer. Specific resistivities of the simple and complex salts at room temperature are 6.0 x JOB and 8.8 x J03 Qcm, respectively, from compressed powder measurements. b Resistivities are dependent to some extent on applied voltage. Values are given to illustrate the order of resistivity. e Shape factor of the conductive phase calculated by eq 3. d Ratio of major and minor axes of ellipsoid of rotation. • Determined by the data of frequency dependence of tan o as plotted in Figures 1 and 2. r Low frequency relative dielectric constant of blend polymers.

1k 3k IOk lOOk Frequency (Hz)

Figure 2. Plots of er and tan ii vs. frequency for blend 30 110 lk 3k JOk JM polymers of polysulfone matrix at room temperature: Frequency (Hz) (6), sample IV; (0), sample V; (D), sample VI.

Figure 1. Plots of dielectric constant, er and tan ii vs. frequency for blend polymers of the polystyrene matrix blend polymers of the polysulfone matrix and the at room temperature: (ct), sample I; (6), sample II; relaxation frequencies fm at which tanil maximum (0), sample III; (D), blend polymer with simple salt appears are lower by about one order of magni• (6.7 wt%), TCNQ content is nearly equal to that of tude than that of the blend polymers of the poly• sample II. styrene matrix. According to the theorl of heterogeneous di• electrics in which conducting particles (2), having

232 Polymer J., Vol. 10, No. 2, 1978 Studies on the Polymers Having a High Dielectric Constant. VIII. rotation ellipsoid shapes, are dispersed in an than that in the polystyrene matrix. This (1) is insulating matrix (1), the relaxation time 1: and conceivable, since the complex salt tends to be the relaxation strength k are expressed by separated in needle like crystals from the solution. It is probable that the crystal structure of the pure 7:= _1_ (n-1)eoerl +eoer2 (1) complex salt might be destroyed or deformed in 2rrfm a2 the polymer matrix. This deformation of crystal structure leads to a lowering of the conductivity of the conductive phase in the polymer matrix. The reason for this may be attributed to (2). where eo is the permittivity of free space (eo= Owing to the nonpolar nature of polystyrene, the 12 8.855 X 10- F/m), a is the conductivity, erl and er2 complex salt is expected to have a poorer com• are relative dielectric constants of insulating matrix patibility with polystyrene than with polysulfone and conducting particles, ero and eroo are the low and thus, the crystalline structure of the complex and high frequency relative dielectric constants of salt is destroyed or deformed less in the poly• heterogeneous dielectrics, q is the volume fraction styrene matrix than in the polysulfone matrix. of conducting particles, and n is the shape factor This may be explained by (3). For further dis• of conducting particles, and is calculated by cussion, the information on the microscopic struc• ture of blend polymers is necessary. 3 Nevertheless, if we could find the blend polymer n= ( ) in which the complex salt is able to keep its where a and b are major and minor axes of ellip• inherent high conductivity even in polymer matrix, soids of ratation. Owing to low conductivities of we should be able to expect a material having high the insulating matrix, a1 is omitted in eq 1 and 2. er and low tan a up to high frequency region. The As the blend polymers may be considered as blending of various kinds of highly conducting heterogeneous dielectrics in which conductive TCNQ salts with different kinds of insulating phases, consisting of the complex salt, are micro• polymers should be investigated. scopically dispersed in the insulating polymer Experimental details are as follows :-n-Butyl• matrix, the dielectric behavior observed in blend quinolinium-TCNQ (simple salt) was prepared by polymers can be analyzed by this theory. The reacting the corresponding iodide and LiTCNQ, parameter values for calculation have been chosen using the method in the literature. 5 Complex as the following: er1 and eroo are 2.6 and 4.0 in the salt was prepared by reacting an equimolar amount case of polystyrene matrix, and 3.1 and 5.0 in of simple salt and neutral TCNQ molecule. The the case of polysulfone matrix, and er2 is 10. decomposition temperatures of the simple and The results are tabulated in Table I along with complex salts were 154°C and 203°C, respectively. the values of other parameters used for calculation. Identification of both salts was carried out by For the calculation of n in eq 2, the volume fraction elemental analyses, infrared and visible spectra, of the conductive phase is assumed to be equal to and were consistent with the expected structures. the weight fraction. All of the values chosen for Reagent grade polystyrene was purified by pre• calculation are considered reasonable. Change in cipitation. Polysulfone (Union Carbide Corp. parameter values within a conceivable range, and P-1700) was used as received. Blend polymer the assumption regarding the fraction of the con• films were prepared by mixing a weighed amount ductive phase do not alter the calculated result so of complex salt and insulating polymers in purified much. DMF (dimethyl formamide), and casting the clear As clearly shown in the table, (1) the shape of solution onto a glass plate and evaporating the the conductive phase is slender and becomes more solvent under vacuum. As the solvent evaporates, so with an increase in the fraction of conductive the transparent greenish solution becomes dark and component; (2) the specific resistivity of the con• opaque. Crystals separated macroscopically could ductive phase is higher than that of the pure com• not be seen on the film. In order to eliminate plex salt; (3) the specific resistivity of the conduc• the remaining solvent thoroughly, films were dried tive phase in polysulfone matrix seems to be higher further for 30 hr at 95°C in 10-2 torr. The thick-

Polymer J., Vol. 10, No. 2, 1978 233. S. IKENO, M. YoKOYAMA, and H. MIKAWA

ness of the films was 100-200 ,urn. Gold was 2. S. Osaki, S. Uemura, and Y. Ishida, ibid., Polym. evaporated onto the films to form a three terminal Phys. Ed., 9, 585 (1971). electrode. Measurements of the electrical pro• 3. S. Ikeno, K. Matsumoto, M. Yokoyama, and perties were carried out under a vacuum of 10-2 H. Mikawa, Kobunshi Ronbunshu, 35, 61 (1978). 4. R. W. Sillars, J.I.E.E., 80, 378 (1937). torr, using a three terminal guarded electrode cell6, 5. L. R. Melby, R. J. Harder, W. R. Hertler, W. in a manner similar to that described previously. 7 Mahler, R. E. Benson, and W. E. Mochel, J. Am. Acknowledgement. The authors should like to Chern. Soc., 84, 3374 (1962). express their gratitude to Dr. S. Uemura of Osaka 6. S. Uemura, J. Polym. Sci., Polym. Phys. Ed., 12, 1177 (1974). university for his instruction on the three terminal 7. S. lkeno, K. Matsumoto, M. Yokoyama, and H. electrode cell. One of our members (S.I.) expresses Mikawa, Polym. J., 9, 261 (1977). his appreciation to the Managing Director of the tt The previous papers concerning the polymers Matsushita Electric Works Ltd., K. Kobayashi and having high dielectric constant; I. S. Ikeno, H. the Manager of Chemical Products Section, T. Mikawa, (late) K. Uno, andY. Iwakura, Kobunshi Murakami, for providing him the opportunity of Ronbunshu, 34, 225 (1977). II, ref No. 7, III, working at Osaka University. S. Ikeno, M. Yokoyama and H. Mikawa, Polym. J., 10, No.2, 123 (1978). IV, S. Ikeno, M. Yoko• yama and H. Mikawa, Rep. Prog. Polym. Phys. REFERENCES Jpn., 20, 381 (1977). V, ref No. 3. VI, S. I keno, M. Yokoyama, and H. Mikawa, Kobunshi Ronbun• 1. C. W. Lewis and D. H. Hogle, J. Polym. Sci., 21, shu, 35, No. 3, 199 (1978). 411 (1956).

234 Polymer J., Vol. 10, No. 2, 1978