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Ind. Eng. Chem. hod. Res. Dev. lQ82, 21, 23-28
technology could be selected for commercialization by private industry. Acknowledgment The work reported herein was a part of a large five-year research program sponsored by the US. State Department (USAID). Besides the authors, important team members whose major contributions should be recognized include Mr. George L. Ball, I11 (Monsanto), Mr. Dennis W. Werkmeister (Monsanto), Professor J. P. R. Falconer (Washington University), and Professor B. S. Bryant (University of Washington). The authors thank Mr. D. Robert Askins and Mrs. Jeanne Drake (both of the University of Dayton) for their help in preparation of this paper. Literature Cited
Conclusions 1. In the total program, we have developed several processes and binder resins that utilize the renewable agricultural residue bagasse as the major component in a low-cost composite material that can be used for roofing and other structural and decorative applications (Ball et al., 1978; Usmani et al., 1980). 2. Of the fillers and resin binder systems investigated, the two described in this paper (bagasse-phenolic, oriented bagasse-phenolic) have the moat overall merit, lowest cost, best tailorability, and utility for widest variety of applications. 3. Sawdust can also be used as an alternate filler, but has more processing difficulties and resulting higher cost. 4. A wide range of composite materials for many different applications can be manufactured using the two processes reported. Potential products include corrugated and shingle roofing, panels for interior and sidewall construction, decorative laminates, counter tops, furniture, insulation, and phenolic molding powder. 5. The technology is applicable in all countries where sugar cane is grown in quantity, including the United States. It is especially applicable in tropical developing countries where scarce foreign exchange is required to import the alternate roofing CGI. Other developing country benefits include local industry development, increased employment, etc. 6. In view of the overall cost effectiveness and merit of the composite materials developed, the research should certainly be continued to further optimize the compositions and processes and economics to the point where the
Bail, G. L., 111; Saber, I.0.;Werkmeister, D. W.; Cass, R. A.; Usmani, A. M.; Bryant, 8. S.; Falconer, J. P. R. “Development of Low-Cost Roofing from Indlgenow, Materials in Developing Nations”; Final report, Contract AID/CM-ta-G73-12, Feb 20, 1978. Bryant, 0. S. Approprtete fechndogy 1978, 4 , 28. (kidstein, I. S. science 1975, 169, 847. Ladkch, M. R.; Fllcklnger, M. C.; Tsao, (3. T. Energy 1979, 4 , 263. Lethrop, E. C.; Aronovsky, S. I. Tappi 1964, 37(23), 24A. Usmanl, A. M.; Ball, 0. L., 111; Saber, I . 0.; Werkmelster, D. W.; Bryant, B. S. J . Ekstomers &st. 1980, 12, 18. Usmani, A. M.; Saber, I.0. Repr. Am. Chem. SOC.Dlv. Org. Coat. Plast. Chem. I W I , 45, 459 (1981).
Received for review June 4 , 1981 Accepted September 28, 1981 Presented at the 181st National Meeting of the American Chemical Society, Atlanta, Ga., Mar 29-Apr 3, 1981, in the Division of Cellulose, Paper, and Textiles.
REVIEW SECTION Conducting Polymers. A Short Revlew Kenneth J. Wynne’ Chemlsby Program, Office of Naval Research, Arllngton, Virgln& 22217
0. Bryan Street IBM Research Lalwratoty, San Jose, Callforn& 95193
computation, guidance, and robotic systems as well as in other high technology systems such as in the area of solar energy collection and storage. This article describes an entirely new class of electrically active materials, conducting polymers, and explores the preparation, properties, and potential applications for these interesting new materials. Present electronic devices and electrically active materials are composed of a variety of metals, semimetals, ceramics, and other inorganic substances. These materials serve as electrodes, electrical conductors, and semiconductors and as transducers of electromagnetic or acoustic radiation. Systems in which these materials are found include computers, communications equipment, batteries,
This article describes an entirely new class of electrically active materials, conducting polymers, and explores the preparation, properties, and potential applications for these Interesting new materials. The principal focus Is on conducting polymers obtained by chemical or electrochemical modlflcatlon of Insulating polymers such Polyaoetylene, polypyrrde, polyphenand polyphenylene sulfide. The intrinslcally conducting poly(su1fur nitride) is also Included. Applications, problems, and future a p ~ i t l e for s the uwizatlon of conducting polymeric materlais are outlined.
Introduction It is evident that electronic devicea and electrically active materials play a vital role in advanced communications, 01~8-43211a211221-0023~01.2510
0
1982 American Chemical Society
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 1, 1982
creasing insight into the complex mechanism of the conductivity in these novel systems. This progress has been achieved despite the difficulties of characterizationof these systems whose insolubility and lack of crystallinity frequently combine to frustrate the normal characterization techniques used in polymer chemistry.
l
o=F;
a = 8.58 O=C;
A
1
o=H
Figure 1. The planar zig-zag conformation of PVF, in the crystalline, highly active fl phase (form I).
and acoustic arrays. Depending on the application, the utility of available electrically active materials may be limited by factors such as weight, mechanical fragility, fabrication problems, corrosion, scarcity, and high cost. For many applications, if electrical functionality were possible, the physical and chemical properties of polymers such as high strength-to-weight ratios, toughness, low cost, molecular tailoring of desired properties, and ease of processing into films, filaments, and complex shapes would make polymeric materials extremely attractive for applications. However, polymeric materials are traditionally known only for their application in electrically passive situations, such as insulators, dielectrics, and resists. Nonetheless, research in the last decade has brought to light a new class of polymeric materials known as electroactive polymers. This exciting area of research encompasses piezoelectric (pyroelectric)polymers, i.e., polymeric transducers which convert an acoustic (thermal) input into an electrical output, and conducting polymers, i.e., polymers which display metallic, semiconductor, or ionic conductivity. The piezoelectric polymer field largely revolves about poly(viny1idene fluoride) (PVF,, Figure 1)and related copolymers (I,2), although there are indications that additional polymer classes may be made active. Because of their low density, excellent physical properties, environmental stability, and high piezoelectric activity, PVF2-basedmaterials are of interest for a broad range of sensor and speaker materials. While this article focusses on conducting polymers, it should be pointed out immediately that this effort is far from comprehensive in scope. First, we exclude from consideration polymeric materials which display ionic conductivity, such as polymer/salt electrolytes which have been studied by Schriver (3) and by Armand (4). Secondly, the research discussed below concerns polymers which, by virtue of their chemical structure, have a backbone which permits electronic conductivity. Thus "conducting polymers" such as those derived from the addition of metals or graphite particles to organic polymers are excluded from consideration. The current resurgence of interest in the field of conducting polymers has its origins in Little's theoretical work on room-temperature superconductors (5). Despite the absence of the hoped-for progress in this spectacular direction, the field has maintained its impetus encouraged by systematic advances resulting from the strongly interactive efforts of chemists and physicists. These advances can be measured not only by the rapidly increasing number of widely different polymeric systems which can now be made to exhibit conductivity but also by the in-
Classification of Conducting Polymers Intrinsically Conducting Polymers. Polymers generally exhibit covalent bonding involving closed valence shells. This leads to their characteristic electrically insulating behavior. The discovery, in 1973, by Walatka et al. (6) that polymeric (SN), crystals were metallic provided the first example of an intrinsically metallic polymer. Despite extensive efforts to produce analogues, (SN), still remains the only example of a polymer with the open-shell electronic structure necessary for metallic conductivity (7). Thus (SN), is presently the only member of this class of intrinsically conducting polymers. Conducting Polymers Obtained by Electronic Modification of Insulating Polymers. The open-shell electronic configuration which is a prerequisite for conductivity can be achieved by oxidation or reduction of insulating polymers which contain an extended ?r-bonded system. Oxidation leads to the partial emptying of previously filled bands, while reduction leads to partial filling of previously empty bands giving rise to p- and n-type conductivity, respectively (8). Most attempts to modify a-bonded systems in this way have not yet been successful, perhaps because such modification of the u system is energetically less favorable and more disruptive to the stability of the polymer. One exception t~ this rule may exist. Poly(diorganosilanes)which contain a backbone comprised entirely of silicon atoms, (R2S&,, have recently been reported to become conducting (0.5 ohm-' cm-') upon treatment with AsFS(9). The mechanism of conductivity may involve removal of an electron from the Si-Si abonded system. In general, there are two approaches which have been successfully used for electronic modification of polymers-direct chemical oxidation or reduction and electrochemical oxidation and reduction. Chemical Oxidation or Reduction. The first intrinsically insulating polymer converted to metallic conductivity by chemical oxidation or reduction was polyacetylene, (CHI,, Figure 2b. An extensive list of the oxidizing and reducing agents effective in modifying the conductivity of (CH), has been compiled by MacDiarmid et al. (IO, 11). Although a wide variety of common oxidizing agents have been shown to be effective, the only reducing agents are the alkali m e a . The charge transfer which takes place during a typical oxidation and reduction process for (CH), is shown in eq 1 and 2, respectively.
(cH), + 3 / 9 1 ,
-
-
(CH),Y+(IJ~
(1)
(CH), + yNao (CH),Y-(Na+)y (2) It is evident from these equations that the conducting derivatives of (CH),consist of polyolefinic ions, chargeneutralized by counterions formed from the oxidizing and reducing agents (12). In polyacetylene these counterions have been shown to intercalate between the planes of polyolefinic ion chains (12,13). Although polyacetylene was the first and in many respects remains the most attractive member of this class of polymers, the class has now been extended to include many quite different polymers, which will be discussed in some detail below. In some instances it is possible to react the monomer with oxidizing agents and simultaneously carry out polymerization and oxidation in a single step. For example,
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 1, 1982
'02
H
H BFh
H
t
25
- 1
[I~vrl,BF,l
H
il)
Figure 2. Conducting polymers: (a) poly(sulfur nitride); (b) polyacetylene, (c) poly(l,6-heptadiyne); (d) polypyrrole; (e) polythiophene; (f) poly@-phenylene); (g) poly@-phenylenesulfide); (h) poly@-phenylene vinylene); (i) structure of electrochemically produced poly(pyrro1e tetrafluoroborate).
solid S4N4reacts with Br2vapor to give brominated (SN), (14,15),terphenyl reacts with AsF, gas to give oxidized polyphenylene (16), and solid acetylene reacts with AsF, to give conducting polyacetylenes (I7). Electrochemical Oxidation or Reduction. Polyacetylene can also be oxidized or reduced electrochemically (18, 19). In this case the counterion comes from the electrolyte solution and the use of sometimes undesirable oxidizing or reducing chemicals can be avoided. Just as is the case for chemical modification, electrochemical polymerization and oxidation can be made to proceed simultaneously. This technique has been used to prepare stable, somewhat flexible films of polypyrrole by simultaneous electrochemical polymerization and oxidation of pyrrole (20, 21). Survey of Conducting Polymers Figure 2 shows the structural formulas of many of the conducting polymer systems currently known. The conductivities of selected doped compositions derived from these polymers and (SN),are shown in Figure 3. The discovery that (SN),has metallic conductivity and becomes superconducting below 0.3 K led chemists to try various synthetic routes to analogous compounds (7). Unfortunately, these efforts have not yet been rewarded with success; as we have already mentioned, (SN),remains the only intrinsically metallic synthetic polymer. As can be seen from Figure 3, the room temperature conductivity of (SN),along the chain direction is 1000 ohm-' cm-', approximately three orders of magnitude less than that of copper. Reaction with halogens, particularly bromine, caused the conductivity to increase by an order of magnitude to lo4 ohm-' cm-' (22,23)without destroying the superconductivity (24,25). (CH),Derivatives. Oxidized polyacetylenes can be prepared with conductivities as high as lo3 ohm-' cm-l. With polyacetylene the conductivity is a function of the degree of oxidation and can span the range lo+' to lo3 ohm-' cm-', which includes the semiconducting and metallic regimes (IO). Initially it was hoped that substitution of the hydrogens of polyacetylene with various functional groups would allow organic chemists to tailor an extensive family of conducting polymers whose properties could be systematically varied. Some derivatives of (CH), have been prepared by replacing the hydrogens by methyl (26) or
T ('K)
Figure 3. Room temperature conductivity for various conducting polymers, classical metals, and AsF, intercalated graphite, and conductivity vs. temperature curves for (top to bottom) brominated (SN),,(SN),,AsF6-dopedpoly@-phenylene), and poly(pyrro1e tetrafluoroborate).
phenyl groups (27,B). However, their conductivity cannot be raised to very high levels either by oxidizing or reducing agents. This failure emphasizes the importance of solidstate effects in determining the electronic properties. Karasz and co-workers have shown that copolymer films of acetylene and methylacetylene can be chemically oxidized with AsF, to give conductivities as high as 50 ohm-' cm-l (26). An interesting derivative of polyacetylene has been prepared by Gibson et al. by polymerization of 1,6heptadiyne (29). The proposed structure of these films is shown in Figure 3c. Oxidation of these films leads to material with a conductivity of about lo-' ohm-' cm-'. MacDiarmid et al. have reacted polyacetylene films with bromine to replace some of the hydrogen by bromine (30). As with (CH),, subsequent oxidation of these brominated films with AsF5or I2 leads to material with a conductivity of 10 ohm-' cm-'. Phenylene Polymers. The first demonstration that high conductivity could be achieved by oxidation or reduction of nonpolyolefinic material involved poly@phenylene) (PPP), Figure 2f. Using AsF5,Ivory et al. (31) were able to oxidize PPP increasing ita conductivity from ohm-' cm-' to 500 ohm-' cm-'. By using the alkali metals as reducing agents, n-type PPP has also been prepared. As in the case of polyacetylene derivatives, the actual conductivity of the final polymer is dependent on the degree of oxidation or reduction and both semiconducting and metallic samples can be obtained. Oligomers of poly@-phenylene),for example biphenyl, terphenyl, and tetraphenyl, react with AsF, in a simultaneous oxidative polymerization leading to conducting polypbenylene (16). Single crystal plates of terphenyl can be reacted with h F 5 to give a polymer exhibiting strong optical and electrical anisotropy. This type of ordering has not been possible to achieve using PPP itself (16). Obviously, if polyacetylene and poly@-phenylene) can each be doped to high levels of conductivity, the copolymer consisting of alternating phenylene and double bond units might have interesting properties. Wnek et al. (32)have examined the properties of oligomers (chains of 7-9 mo-
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 1, 1982
Figure 4. Schematic structure of a bridged-stacked metal phthalocyanine. Known M-X groupings include Si-0, Ge-0, Sn-O, AI-F, Ga-F, and Cr-F.
presence of an (M-X), repeat unit which “skewers” the disk-like phthalocyanine (Pc) rings. A variety of oxidants have been used to prepare conducting to 1 ohm-’ cm-’) oxo-bridged silicon, germanium, and tin phthalocyanines (45). The conductivity decreases with increasing size of the metalloid in this series, because of increasing ring-ring separation. This and other evidence point to a conduction band resulting from a-orbital overlap of the Pc rings, rather than conduction along the M-X backbone (45). Polymers with fluorine-bridged structures (PcAlF, PcGaF, PcCrF) have also been prepared and partially oxidized with iodine to give conducting compositions (0.1-5 ohm-’ cm-’) (46-48). Interest in these PcMF-based materials stems from their high thermal stability, processability (they can be sublimed to form films), and potential optoelectronic properties. Compared to the classical metals, present conducting polymers have relatively low conductivities which are at least two orders of magnitude less than copper. However, in the case of the AsF5 graphite system the conductivity can approach that of copper. This suggests that higher conducting polymers may yet become available.
nomer units) of poly@-phenylene vinylene) (PPV, Figure 2h). Pressed pellets of PPV show a conductivity ohm-’ cm-’ at ambient temperature. Exposure to AsF5 gives conductivities as high as 3 ohm-’ cm-’. Perhaps the most interesting of the polyphenylene derivatives investigated to date are the sulfur-linked phenylene polymer chains (Figure 2g) (33-35). Treatment of films of poly@-phenylene sulfide) (PPS)with AsF, leads to conductivities of 1-10 ohm-’ cm-’. The conductivity of AsF5-treated PPS is somewhat surprising in view of the grossly nonplanar structure of the undoped polymer. Heterocyclic Aromatic Polymers. An extensive literature exists on powders of conducting aniline blacks (36) and pyrrole blacks (37) produced by chemical oxidation of aniline and pyrrole. Dall’Olio (38)prepared high-conductivity (10 ohm-’ cm-’) films of pyrrole polymer by stoichiometric electrochemical polymerization of pyrrole. Recent improvements on Dall’Olio’s technique have given more flexible fibs with conductivities of 1-100 0hm-l cm-’ (20, 21). These pyrrole polymers are very difficult to characterize, but the pyrrole polymerization is believed to involve oxidative coupling predominantly at the a position to generate the structure shown in Figure 2d. Simultaneously however, the polymer is oxidized electrochemically, charge neutrality being maintained by ions derived from the electrolyte (Figure 2i). N-Substituted pyrrole polymers have also been prepared electrochemically, but their conductivities were found to be much lower ( ohm-’ cm-’) (39). Copolymers can also be synthesized and they show intermediate conductivities (40). Polythiophene (Figure 2e) has been synthesized both chemically (38)and electrochemically (42). As in the case of polypyrrole, the electrochemically generated polymer is simultaneously oxidized. The chemically prepared polymer was subjected to subsequent oxidation by iodine. In neither case were high conductivities obtained, however. Typical values are in the range to ohm-’ cm-’. Conductivitiesas high-as 70 ohm-’ cm-’ have been reported for halogen-doped polymers derived from polyacrylonitrile (43). Bridged-Stacked Phthalocyanines. A number of bridged-stacked phthalocyanines have been prepared and have been oxidized with a variety of reagents to the metallic regime (44).A general structure for this class of materials is shown in Figure 4. The polymeric nature of the bridged-stacked phthalocyanines arises from the
Applications of Conducting Polymers As indicated in the previous section, polymers can be made to exhibit semiconducting, metallic, or even superconducting properties not traditionally associated with these materials. This has encouraged the belief that conducting polymers may eventually challenge the more classical materials in certain areas. It has been suggested that conducting polymers might compete with metals forming lightweight wiring. Of the presently known systems, only AsF5-graphite appears to have sufficiently high conductivity (49,50). Barrier height measurements of (SN), films and various semiconductor substrates have shown that (SN), has a higher work function than elemental metals (51). Cohen and Harris (52)have taken advantage of this fact to enhance the open circuit voltage of GaAs solar cells. Polyacetylene has also been shown to form Schottky barriers (53,551 and heterojunctions (55). Tskukamoto et al. (56)have fabricated Schottky barrier type solar cells using HC1 doped (CH), as the semiconductive element. The energy efficiency is about 0.2%. Grant (57)has evaluated the metal-insulator field effects in polyacetylene. Pristine (CH), has been used as the photoelectrode in a photochemical photovoltaic cell (58). In addition to their use in the role of classical semiconductors and metals, which may challenge established materials in established technologies, conducting polymers offer additional technological opportunities which take advantage of their unique properties. The electroactive properties of polypyrroles and (CH), have been explored, and it has been shown that these materials can be repeatedly electrically switched between the metallic and the insulating states-a change which can be followed optically as well as electrically (43). The large surface area of polyacetylene (60m2g-l) (10)and the fact that the fibrils can be covered with finely divided silver metal (59) suggest possible catalytic applications. It is also possible that replacing carbon-loaded “conducting” polymers with intrinsically conducting polymers would lead to superior performance, avoiding problems with high-frequencycutoff and high-field breakdown associated with the carbon particles. The metallic properties of conducting polymers permit them to be utilized as electrode materials. Nowak et al. (60) have shown that (SN), has good electrode characteristics, and Diaz et al. (43)have shown that polypyrrole
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 1, 1982
L I
(I) (II)
k
L
i METAL
YLI+YLI++ ye-
ICH):Y+y(CPO,)-
+ye--(CHI:+
NET DISCHARGE REACTION (CH):Y+xy (C!O,)+xyLi-(CH),
y (C10,)-
.*a
Figure 6.
Schematic illustration
of a
+ xyLi+ (CPOi)
(CH),-lithium
battery.
tetrafluoroborate forms a stable nonporous electrode. Noufi et al. (61) have used polypyrrole as a passivating layer to prevent dissolution of n-GaAs photoanodes in a photochemical solar cell. Polypyrrole films also produce a dramatic improvement in the stability of n-type silicon against photooxidation in aqueous electrolyte; high photocurrents (6 mA/cm2) are still observed after 5 days (62). The polymer film is easy to apply and exhibits excellent adhesion (62, 63). Conducting polymeric materials derived from (CH), have been shown to function as electrode materials which show promise for use in lightweight high-energy density rechargeable storage batteries (64). The (CH),/lithium cell shown in Figure 5 displays an initial open circuit voltage of 3.7 V and a short circuit current of 25 mA for 0.5 cm2 (2 mg) polymer. Another arrangement employs only (CH), electrodes, wherein (CH+*), and (CH-b)xare formed upon charging. During discharge electrons flow from the anode, (CH-”), to the cathode, (CH+*),. A polymer electrode cell utilizing a LiC104 electrolyte has been reported to give an open circuit voltage of 3.7 V with a current in excess of 0.1 A/cm2 of (CH), film (4mg) (65). These results are important in demonstrating an unprecedented utilization of a conducting polymer. Furthermore, a projection of the above data suggests that a (CH), polymer electrode battery would have about three times the energy density of a conventional lead acid battery.
Problems and Future Opportunities in Conducting Polymers Exciting as the above outlined prospects may be, it is important to recognize the problems that must be solved before conducting polymers can find widespread technological application. From the discussion of the magnitude of the conductivities of presently known conducting polymers (except perhaps AsF5-treated graphite), it is obvious that they will not displace copper or the classical metals. In most applications, if they are to become practical materials rather than laboratory curiosities, their usefulness will most probably be found in a rather unique blend of their electronic, mechanical, and processing characteristics. Indeed, conducting polymers are probably best considered not as competitors for the classical metals or semiconductors, but as materials providing new opportunities due to the incorporation into conducting materials of such attractive polymer properties as melt and solution processibilities, low density, and plasticity or elasticity. Ideally, these polymers would also satisfy a variety of increasingly important ecological considerations such as low toxicity and non-energy-intensive synthesis and processing. Preparation from nonpolluting aqueous media would, of course,
27
be desirable. Advantage could also conceivably follow from the relatively high thermal conductivities and high optical absorption coefficients of these metallic polymers. Though some of these properties, such as low density and high optical absorption coefficient, characterize all of the existing conducting polymers, some of the other desirable properties described here are not typical of either (SN), or the chemically (as opposed to electrochemically) modified systems. In particular, neither (SN), nor the chemically modified conducting polymers are stable in air (particularly the alkali metal reduced n-type polymers) nor are they thermally stable much above room temperature. However, it is possible to stabilize (CH), to atmospheric oxidation; this has been accomplished by in one case through a proprietary coating process (66). The majority of dopants used to impart conductivity to the polymers (e.g., AsF5, 12,Br2,etc.) are highly toxic. In addition, the chemical doping process universally appears to degrade the mechanical properties of these polymers, making them brittle where previously they were flexible. In contrast to the chemically oxidized system, electrochemically oxidized polypyrrole-BF4, after initial air oxidation, is stable in air for several weeks and shows appreciable thermal stability, though its flexibility is not yet ideal. Some of the copolymer films of acetylene and methylacetylene reported by Karasz and co-workers have exhibited elastic properties when wet with solvent (26). When dry these films are relatively brittle but on wetting again with solvent they can be readily stretched and reatin their elongation if dried under tension. Obviously there will be certain applications such as batteries in which the conducting polymer system can be maintained in a restricted atmosphere and considerations of air stability and flexibility are perhaps not as crucial. For widespread applications, however, if full advantage is to be taken of these materials a significant amount of polymer chemistry and engineering will be necessary to stabilize them and improve their polymeric properties in the metallic and semiconducting state. The increasingly wide variety and complexity of polymers which can be made to show high conductivity bode well for the ability of scientists to incorporate these desirable properties into such materials. Literature Cited Broadhurst, M. 0.; Davis, 0.T. “Toplcs in Applled Physics, Electrets”; Sessler, G. M., Ed.; Springer-Verlag: Berlin, 1980; Voi. 33, pp 285-3 19. Bloomfield, P. E.; Ferren, R. A.; Radlce, P. F.; Stefanou, H.; Sprout, 0. S. NevalRes. Rev. 1978, 31, 1. Dupon, R.; Whitmore, D. H.; Schrhrer, D. F. J . Hectrochem. Soc. 1981, 128, 715. Armand, M.; Chabagno, J. M.; Duclot, M. J. Abstract 8.5. Extended Abstracts, Second International Conference on SolM Electrolytes, St. Andrews, Scotland, Sept 20-22, 1978. Little, W. A. Phys. Rev. A 1984, 134, 1418. Walatka, V. V.; Labes, M. M.; Perlstein, J. H. Phys. Rev. Left. 1973, 31, 1139. Street, G. B.; Greene, R. L. IBM J . Res. Dev. 1977, 99, 21. Street. G. B.; Clarke, T. C. A&. Chem. Ser. 1980. No. 186, 177. West, R.; David, L. D.; Djurovich, P. I.; Stearley, K. L.; Srinlvasan, K. S. V.; Yu, H. J . Am. Chem. SOC.1981, 103, 7352. Heeger, A. J. Synth. Met. 1980, 1 , 101. MacDiarmld, A. 0.; Chiang, C. K.; Heeger, A. J.; MacDlarmM, A. G. Ber. Bunsenges. Phys. Chem. 1979, 83, 407. Street, G. B.; Clarke, T. C. IBM J . Res. Dev. 1981, 2 5 , 51. Hsu, S. L.; Slgnorelli, A. J.; Pez, 0. P.; Baughman. R. H. J . Chem. Phys. 1978, 69. 108. Street, G. B.; Blngham, R. L.; Crowley, J. I.; Kuyper, J. J . Chem. Soc., Chem. Commun. 1977, 464. Akhtar, M.; Chlang, C. K.; Heeger, A. J.; Mllllken. J.; MacDiarmM, A. G. Inorg. Chem. 1978. 17, 1539. Shacklette, L. W.; Eckhardt, H.; Chance, R. R.; Miller, G. G.; Ivory, D. M.; Baughman, R. H. J . Chem. Phys. 1980, 73, 4098. Soga. K.; Kobayashi. Y.; Ikeda, S.; Kawakari, S. J . Chem. SOC., Chem. Commun. 1980, 931. Nigrey, P. J.; MacDLarmld. A. G.; Heeger, A. J. J . Chem. SOC.,Ghem. Commun. 1979, 594. Dlaz, A. F.; Clarke, T. J . Electroenal. Chem. 1980, 1 1 1 , 115.
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all,
Received for reuiew September 14, 1981 Accepted November 20, 1981
