Formation of Adducts of Poly(thienylene)s with Electron Acceptors and Electric Conductivities of the Adducts

Affinities of poly(thienylene) type polymers toward electron acceptors (iodine and SO3) and electric conductivities of the polymer–electron acceptor adducts have been investigated. π-Conjugated poly(2,5-thienylene) has a high affinity toward iodine to absorb 60 wt% of iodine per the polymer. Poly(3-methyl-2,5-thienylene) has a higher affinity toward iodine and absorbs 136 wt% of iodine per the polymer. In the case of copolymer composed of 2,5- and 2,4-thienylene units the affinity against iodine increases with increase in the proportion of the 2,5-thienylene unit in the copolymer. The poly(2,5-thienylene)–iodine and poly(3-methyl-2,5-thienylene)–iodine adducts show electric conductivities of 5×10−2 S cm−1 and 4×10−1 S cm−1, respectively, at room temperature. The activation energies of the electric conduction are 10 kJ/mol and 7.6 kJ/mol for the poly(2,5-thienylene)–iodine adduct (wt% of iodine=60) and poly(3-methyl-2,5-thienylene)–iodine adduct (wt% of iodine=136), respectively. The electric conductivity of the copolymer–iodine adduct sharply decreases on introduction of the 2,4-thienylene unit into the copolymer. The electric conductivity of the iodine adduct of the copolymer containing only 6% of 2,4-thienylene unit drops to ca. 1/100 of that of the iodine adduct of pure poly(2,5-thienylene). The activation energy of the electric conduction of the polymer-iodine adducts decreases with increase in the content of the 2,5-thienylene unit as well as with the increase in the amount of iodine absorbed. Every poly(thienylene) type polymer has a high affinity toward SO3, a stronger electron acceptor than iodine, to absorb about 70 wt% of SO3 per the polymer. The SO3–polymer adducts have electric conductivities of ca. 10−4 S cm−1.