Processible and environmentally stable conducting polymers

Highly conducting polythiophene is rendered environmentally stable and solution processible in both its neutral and conductive forms in common organic solvents by appropriate alkyl substitution on the thiophene rings. Solubility increases with increasing chain length of the substituent in the order n-butyl > ethyl ≫ methyl. Neither the size of the substituent, nor the nature of the dopant has much influence on the conductivity of the doped complexes - typical conductivities are 1-5 ohm^-1 cm^-1. Copolymers of thiophenes containing different alkyl substituents were also prepared and were found to exhibit properties similar to the homopolymers. Dialkyl substitution on the thiophene rings gives polymers with less extended conjugation and lower conductivities on doping. © 1986.