Fibers of Conducting Polymers: High Electrical Conductivity Combined with Attractive Mechanical Properties
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FIBERS OF CONDUCTING POLYMERS: HIGH ELECTRICAL CONDUCTIVITY COMBINED WITH ATTRACTIVE MECHANICAL PROPERTIES ALEJANDRO. ANDREATTA*, S. TOKITO**, P. SMITH-** and A.J. HEEGER*,**** Institute for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106 Materials Department **Permanent address: Department of Materials Science and Technology, Kyushu University, Kasuga-shi, Fukuoka 816, JAPAN, :**Chemical and Nuclear Engineering Department ***Physics Department ABSTRACT We present a summary of our recent results on the electrical and mechanical properties of fibers made from poly(2,5-dimethoxy-p-phenylene vinylene), PDMPV and poly(2,5-thienylene vinylene), PTV, using the precursor polymer methodology, and from polyaniline, PANI, using the method of processing as polyblends with poly-(p-phenylene terephthalamide), PPTA, from sulfuric acid. The solubility of both PANI and PPTA in H2 SO 4 presents a unique opportunity for co-dissolving and blending PANI and PPTA to exploit the excellent mechanical properties of PPTA and the electrical conductivity of PANI; we summarize the electrical and mechanical properties of such composite fibers. For PDMPV and PTV fibers, we find a strong correlation between the conductivity and the tensile strength (and/or modulus), and we show from basic theoretical concepts that this relationship is an intrinsic feature of conducting polymers. I. INTRODUCTION In conjugated polymers, the ic-bonding leads to ic-electron delocalization along the polymer chains and to the possibility of relatively high charge carrier mobility, gL,which is extended into three dimensional transport by the interchain electron transfer interactions.1 The high density of redox sites within the Xelectron system (essentially one per monomer) offers the additional advantage of a relatively high density, n, of carriers (charge e) through doping. Thus, high electrical conductivity, a=nejt, is possible. As a result of the same intrachain itbonding and relatively strong interchain electron transfer interactions, the mechanical properties (Young's modulus and tensile strength) of conjugated polymers are potentially superior to those of saturated polymers, such as polyolefins. Moreover, because of these two features, it may be possible to achieve exceptional mechanical properties with aligned conjugated polymers at lower chain lengths than required for their saturated counterparts. 2 Thus, conjugated polymers are of special interest because of the potential of a unique 3 combination of electrical and mechanical properties. Since the electrical and mechanical properties are currently limited by defects and structural disorder, improvement in material quality that will enable the exploration of intrinsic properties has become an important goal of conducting polymer research. 3 It has been long recognized, however, that conjugated polymers tend to be insoluble and infusible. Thus, the question to be answered is whether or not processing methods can be developed that will lead to chain Mat. Res. Soc. Symp. Proc. Vol.
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