Synthesis and characterization of electrically conducting copolymer of aniline and o-bromoaniline using methane sulfonic acid as dopant

Polyaniline (PAN), poly(o-bromoaniline) (POBA), and poly(aniline-co-o-bromoaniline) (PABA) were synthesized by oxidative coupling. These polymers are protonated by 10-20% methane sulfonic acid (MSA) and 1M HCl. The new polymer bases have greater solubility than that of PAN in common polar organic solvents; PAN-MSA was observed to be the most thermally stable of these polymers. POBA is associated with residual quinoid diimine units as illustrated in the IR and UV-vis spectra, after reduction with hydrazine dihydrochloride. Both the doping agents cause a downward shift of the quinoid absorption in the IR spectra. MSA- and HCl-doped PAN and PABA poly-mers exhibit a coil-like conformation in DMSO, whereas only MSA-doped PAN and PABA show an "expanded coil-like" conformation in m-cresol with a "free carrier tail" above 800 nm in their electronic spectra. XPS spectra indicated the presence of covalent bromine in the POBA and PABA polymers. Bromine retention was greater in the homopolymer as evidenced by the IR studies after aging at 350 C. Compared to HCI, MSA is found to be a more effective dopant, enhancing the conductivity of the copolymers by 10(2)-10(3) times in magnitude. (C) 2002 Wiley Periodicals, Inc.