B. Rasch et W. Vielstich, POLYTHIOPHENES VIA THIOPHENE, BITHIOPHENE AND TERTHIOPHENE IN PROPYLENE CARBONATE - AN ELECTROCHEMICAL AND IN-SITU FTIR STUDY, Journal of electroanalytical chemistry [1992], 370(1-2), 1994, pp. 109-117
Polythiophene films obtained by the galvanostatic polymerization of th
iophene (Th), bithiophene (BTh) and terthiophene (TTh) in 0.5 M LiClO4
+ propylene carbonate have been investigated by cyclic voltammetry an
d in-situ Fourier transform IR (FTIR) spectroscopy. The polymerization
potential in the propylene carbonate electrolyte decreases in the ord
er Th > BTh > TTh. Both the charge capacity and the doping level of th
e resulting polymers increase in the order polythiophene (PTh) < polyb
ithiophene (PBTh) much less than polyterthiophene (PTTh). For PTTh, a
doping level of 37% is obtained during cycle 10 and 31% during cycle 1
000. In-situ FTIR spectra of the neutral PBTh and PTTh films show a si
ngle band at 3063 cm-1 (corresponding to aromatic beta-(C-H)-groups) w
hich suggests a regular alpha,alpha'-linking of the monomeric units. F
or thin PTh films the intensity of this band is very weak, indicating
a disordered cross-linked polymer structure. During the electrochemica
l oxidation of the three polythiophenes investigated from 3.3 V up to
4.4 V vs. Li/Li+ the intensity of the electronic absorption band (abov
e 2000 cm-1) increases with increasing potential, but it strongly decr
eases at potentials above about 4.4 V, indicating a strong irreversibl
e oxidation of the polymer films. Furthermore, strong CO2 evolution is
observed at potentials above 4.2 V.