Synthesis and characterization of new processible conducting copolymers derived from thiophenes

Various poly(3-decylthiophene-co-3,3'-dibutoxy-2 and poly(4,4'-didecyl-2,2'-bithiophene-co-3,3'-dibutoxy-2,2'-bithiophene)s have been chemically prepared using iron trichloride as oxidizing agent in chloroform. These copolymers should combine the excellent electrical properties of alkoxy-substituted polythiophenes with the good processibility of alkyl-substituted polythiophenes. All copolymers of the first series have shown a good solubility in chloroform but reduced electrical conductivities (10(-3)-10(-1) S/cm) when compared to the homolymers (5-140 S/cm). This behavior has been explained by an inhomogeneous distribution of the four different electroactive moieties (triads) found in these copolymers and, consequently, to a localization of the charge carriers created upon oxidation. In contrast, poly(4,4'-didecyl-2,2'-bithiophene-co-3,3'-dibutoxy-2,2'-bithiophene)s have 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 showed also a good stability in the conducting state which can be partly related to their low oxidation potential. However, probably due to thermally induced steric interactions between the side chains and the counterions, an exothermic dedoping reation takes place at higher temperatures (> 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.