Oxireductases in the Enzymatic Synthesis of Water-Soluble Conducting Polymers - Enzymatic Polymerisation - page 11

Fig. 7 Atomic force
microscopy pictures obtained
from a PEDOT/PSSNa film
(6 ) synthesized at an

EDOT to PSSNa ratio of 1:1.
(Reprinted with permission
from Rumbau et al. [ 43 ].
c

μ × 6 μ

2007, American Chemical
Society)

reaction mixture. The terthiophene monomer, having a slightly lower oxidation po-
tential ( 1.02 V), acts as a redox mediator, and the polymerization of EDOT is

performed in the presence of PSSNa (upper scheme, Scheme 5 ) . This polymer-
ization was observed not to proceed without the addition of terthiophene. When
the polymerization of EDOT was performed under the same conditions without
terthiophene, only low molecular weight oligomeric products were obtained [ 45 ] .
In this work, as the concentration of terthiophene used was 100 times lower than
that of EDOT monomer, the amount of oligomeric species formed by the oxida-
tion of terthiophene was expected to be significantly low (1%). The oxidation of
the EDOT monomer is the most difficult step in the polymerization process and the
introduction of small amounts of terthiophene facilitated the process, as already es-
tablished in earlier works on the enhancement of the electrochemical polymerization
rate of thiophene by addition of terthiophene and/or bithiophene [ 46 ] . The authors
extended the mechanism proposed by these earlier works to the polymerization of
EDOT (lower scheme, Scheme 5 ) , proposing that the terthiophene is incorporated
along with the PEDOT in the final polymer.
The effect of concentration of the redox mediator on the formation of PE-
DOT/PSSNa was studied by these researchers by varying the concentration of
terthiophene (0.025-1%) in a series of reactions. At least 0.5% (by weight of
monomer concentration) of the terthiophene was observed to be required to initiate
the polymerization of EDOT using SBP (Fig. 8 ) . PEDOT/PSSNa was not formed
when the concentration of terthiophene was 0.025%. The polymerization was also
performed at various pH conditions, and the concentration of the final polymer was
monitored spectroscopically, as shown in Fig. 8 b . It could also be observed that the

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