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SYNOPSISConducting composites consisting of polybithiophene and based on porous crosslinked polystyrene as host polymer have been synthetized in the vicinity and above the percolation threshold by oxidative polymerization with FeC13. Electrical conductivity and thermoelectric power measurements for different degrees of doping have been carried out in the temperature range 80-300 K. The electrical conductivity variations are weakly thermally activated while the thermoelectric power has metallic magnitude with positive sign and increases with temperature. Conduction mechanisms are interpreted on the basis of an hopping model involving bipolaronic clusters. 0 1996 John Wiley & Sons, Inc. I NTRO DUCT1 0 N Among the electrically conducting polyheterocycles, polythiophene (PTh) exhibits several interesting properties, among which are ease of preparation procedure and relative conducting stability to atmospheric exposure.'r2 PTh has been prepared by both electrochemical polymerization3 and chemical polymerizati~n,~.~ but the highly conducting PTh's have been obtained by the first synthesis method with conductivities in the range 10-100 S cm-l. In order to improve these mechanic features such as processability and atmospheric stability, a number of methods6 have been suggested by combining strong insulating materials with conducting polyheterocycles.In this article we discuss about the electrical properties of conducting polybithiophene-polystyrene (PBTh-PSt) composites chemically prepared. The effect of the FeCl,/bithiophene molar ratio ( y ) on the conductivity of the composites (a) is shown in Figure 1. The conductivity variations reveal the formation of an electrical network of polythiophene inside the composite and exhibit features characteristic of percolation systems. Below the percolation threshold which is found a t about y = 0.3, the low conductivities must be attributed to the low connectivities among the deposited polythiophene domains. A t high molar ratios of the oxidant concentration to monomer concentration, the formation of an electrical network of P T h inside the composite explain the high conductivity values. EXPERIMENTAL RESULTS A N D DISCUSSION 213

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An investigation of the structure, stability, and charge distributions of conducting polybithiophene-polystyrene composite chemically synthetized using X-ray photoelectron spectroscopy (XPS) and electron microprobe analysis is described. XPS results confirm the reduction of the oxidant (Fe 3/ is reduced to Fe 2/ and Cu 2/ to Cu / ) during the bithiophene polymerization and indicate that the positive charges of doped polybithiophene are preferentially localized on the carbon atoms. Measurements versus ambient atmosphere exposure support a decreasing of the atomic ratio Cl/Fe or Cl/Cu and an increasing of the atomic ratio O/C, which could be responsible for the observed electrical conductivity instability.