Comparative study of chemically synthesized and plasma polymerized pyrrole and thiophene thin films

Pyrrole and thiophene polymers prepared via chemical means or plasma polymerization at different radio frequency (RF) power input on different substrates were compared using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy and UV-visible absorption spectroscopy. These polymers were deposited as thin films on either low-density polyethylene (LDPE) or LDPE surface graft copolymerized with acrylic acid (AAc). The results indicate that the structures of plasma polymerized pyrrole and thiophene are rather different from those of polymers synthesized by conventional chemical methods, due to a higher degree of crosslinking and branching reactions in plasma polymerization. A higher and more stable conductivity can be obtained with chemically synthesized polypyrrole and polythiophene, but the thin films generated from the plasma polymerization process are much smoother and more uniform. The lack of stability in the plasma polymerized samples' conductivity may be due to the unstable nature of the charge transfer complex with the dopant (iodine) resulting in a greater ease of diffusion of the iodine from the film. Under the conditions tested, the thickness of plasma polymerized pyrrole and thiophene thin layers increases almost linearly with the RF power. The modification of the LDPE substrates using AAc-graft copolymerization can enhance the growth and adhesion of the thin film and its conductivity. (C) 2003 Elsevier B.V. All rights reserved.