Synthesis and characterization of malonic acid-doped
polyaniline
M. KARAKISËLA, M. SACËAK
*
, E. ERDEM
à
, U. AKBULUT
§
Department of Chemistry, Faculty of Sciences, Ankara University 06100 Tandog
Ï
an, Ankara, Turkey
Received 9 February 1996; revised 21 May 1996
The conductive form of polyaniline was synthesized by the anodic and chemical oxidation of aniline
in malonic acid medium. The conductivity of polyaniline doped with malonic acid changed from
1.62 ´ 10
A6
to 2.5 ´ 10
A5
Scm
A1
depending on the way it was synthesized. The polymer growth rate
was observed to be very slow in malonic acid compared with H
2
SO
4
. Thermogravimetric data
revealed that the maximum thermal reaction rate of PANI doped with malonic acid was at 200 ëC
and 520 ëC compared with 290 ëC and 530 ëC of the polymer doped with H
2
SO
4
.
1. Introduction
There have been numerous studies on the synthesis,
characterization and use of conductive polymers such
as polypyrrole, poly(N-vinylcarbazole) and poly-
thiophene [1±4]. Polyaniline (PANI) has received
much attention due to its environmental stability,
ease of synthesis and cheapness.
PANI can be synthesized both chemically using
suitable oxidants such as FeCl
3
[5] and (NH
4
)
2
S
2
O
8
[6] in solutions containing mineral or organic acids,
and electrochemically, in which it is directly oxidized
on a suitable electrode [7±9]. In both methods PANI
is converted into a highly conducting metallic state
with no gap in the electronic band structure.
Some properties of conducting PANI are closely
related to the type of anion doped into it. For in-
stance, the solubility of PANI, which is an important
criterion for the processability and characterization,
can be improved by doping it with big anions such as
camphor sulphonic acid [10] and 5-sulphosalicylic
acid [11]. It was reported that the dopant anions
which improve PANIs solubility generally contain
carboxyl groups [12].
The use of polymer electrolyte dopants also pro-
motes the solubility. PANI doped with poly (styrene
sulphonic acid) was observed to dissolve in water [13]
as well as in some organic solvents [14]. It was re-
ported that the ®lm growth rate increased and the
surface morphology of the PANI ®lm showed a
dramatic change by the addition of polymer electro-
lytes [7]. In a dierent study, it was shown that PANI
obtained in poly(styrene sulphonic acid) media had a
globular morphology while the polymer obtained in
poly(vinyl sulphonic acid) had a ®brous network
structure [15].
The conductivity of PANI synthesized electro-
chemically was dependent on the redox state of the
polymer, the solution pH, water content and, to a
lesser extent, the type of dopant anion [16]. The type
of dopant anion also aects the stability of the con-
ductivity in PANI at dierent atmospheres and at
temperatures [17]. Changing the nature of the anion
also has a signi®cant in¯uence on the kinetics and
conversion in the electrochemical polymerization of
aniline [18].
The synthesis and characterization of PANI doped
with dierent anions is critical, since many properties
of the ®nal polymer are in¯uenced by the nature of
the dopant anion. There is no literature data related
to malonic acid being used as dopant for PANI. In
the present work, the chemical and electrochemical
synthesis and characterization of malonic acid-doped
PANI were studied.
2. Experimental details
2.1. Materials
Aniline(BDH) was doubly distilled under vacuum.
Other chemicals such as malonic acid, H
2
SO
4
, and
dimethylsulfoxide (DMSO) were used as received
from Merck.
2.2. Procedures
The chemical polymerization was carried out by rig-
orous stirring of the 4
M
aqueous malonic acid solu-
tion containing 0.4
M
double distilled aniline and
adding FeCl
3
dropwise. The polymerization tem-
perature was 0 ëC. Following stirring for 2 h the
mixture was kept at 0 ëC for 24 h and the dark green
product was ®ltered, washed with water then with
*
To whom correspondence should be addressed
à
Present address: Department of Chemistry, Faculty of Education, Hacettepe University, 06532 Beytepe, Ankara, Turkey
§
Present address: Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
JOURNAL OF APPLIED ELECTROCHEMISTRY 27 (1997) 309±316
0021-891X
Ó
1997 Chapman & Hall
309