Electrochemical synthesis and characterization of a copolymer made from the 2-biphenyl-3-octylthiophene monomer

An electrically conducting copolymer film synthesized by electrochemical polymerization from a comonomer molecule of 2-biphenyl-3-octylthiophene (BOT) was studied. A poly(2-biphenyl-3-octylthiophene) (PBOT) film adherent on a Pt working electrode was polymerized by potential cycling of 40 mM BOT in 0.1 M lithium hexafluoro arsenate (LiAsF6)-acetonitrile electrolyte solution. Many soluble intermediates were formed in the polymerization process. The effect of the concentration of the starting material, type of the electrolyte salt, the solvent and the scan rate used in polymerization and temperature was studied on the polymerization process of BOT. The formed PBOT film was characterized by cyclic voltammetry (CV), X-ray diffraction (XRD) analysis and electron ionization mass spectrometric (EIMS) analysis. The properties of the formed copolymer was compared with a copolymer synthesized using biphenyl and 3-octylthiophene as starting materials, poly(thienyl biphenyl) (PTB). The CV and EIMS measurements gave evidence of formation of a conductive material with a shorter effective conjugation length than in the PTB copolymer. XRD measurements showed that a semi-crystalline and rather amorphous structure was obtained in both electrochemically synthesized copolymers. But the structure of PBOT, however, was found to be according to the shape of the cyclic voltammogram and from EIMS and XRD data less cross-linked and more uniform than the structure of PTB.