SYNTHESIS AND CHARACTERIZATION OF NEW PROCESSIBLE CONDUCTING COPOLYMERS DERIVED FROM THIOPHENES

Various poly(3-decylthiophene-co-3,3'-dibutoxy-2 and 2'-bithiophene-co -3,3'-dibutoxy-2,2'-bithiophene)s have been chemically prepared using iron trichloride as oxidizing agent in chloroform. These copolymers sh ould combine the excellent electrical properties of alkoxy-substituted polythiophenes with the good processibility of alkyl-substituted poly thiophenes. All copolymers of the first series have shown a good solub ility in chloroform but reduced electrical conductivities (10(-3)-10(- 1) S/cm) when compared to the homolymers (5-140 S/cm). This behavior h as been explained by an inhomogeneous distribution of the four differe nt electroactive moieties (triads) found in these copolymers and, cons equently, to a localization of the charge carriers created upon oxidat ion. In contrast, 2'-bithiophene-co-3,3'-dibutoxy-2,2'-bithiophene)s h ave exhibited both excellent processibility and electrical properties. Electrical conductivities up to 30 S/cm have been observed in some of these copolymers. At room temperature, alkoxy-rich polythiophenes sho wed also a good stability in the conducting state which can be partly related to their low oxidation potential. However, probably due to the rmally induced steric interactions between the side chains and the cou nterions, an exothermic dedoping reation takes place at higher tempera tures (> 100 degrees C). On the basis of these results, it is proposed that alkoxy-substituted polythiophenes bearing ionic moieties should lead to processible and thermally stable conducting materials.