Synthesis and characterization of composites based on polyaniline and styrene-divinylbenzene copolymer using benzoyl peroxide as oxidant agent

Article abstract of DOI:10.1016/j.reactfunctpolym.2013.06.008

This work presents a method to prepare composites based on polyaniline (Pani) and styrene-divinylbenzene copolymers (SD) by in situ polymerization of aniline using benzoyl peroxide as oxidant agent. The composites were obtained from copolymers with two degrees of porosities which have higher and lower surface areas. Emeraldine Pani was prepared using hydrochloric acid as dopant. One cycle or four cycles of aniline polymerization were performed. The copolymers and their respective composites characterizations were performed by infrared spectroscopy, thermogravimetric analysis, physical nitrogen adsorption-desorption measurements, morphology analysis, elemental analysis and determination of Br?nsted acid sites. The Pani was distributed overall porous SD copolymer producing composites with high surface area. Then, they were evaluated as catalysts for esterification reaction of a fat acid. It was found that that composites prepared with four cycles of in situ polymerization presented best catalytic activity than one cycle composites.

Full text of DOI:10.1016/j.reactfunctpolym.2013.06.008

Reactive & Functional Polymers 73 (2013) 1255–1261
Contents lists available at SciVerse ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Synthesis and characterization of composites based on polyaniline
and styrene–divinylbenzene copolymer using benzoyl peroxide
as oxidant agent
⇑
B.H.F. Moura, R.H.B. Assis, P.I.B.M. Franco, N.R. Antoniosi Filho, D. Rabelo
Instituto de Química, Universidade Federal de Goiás, P.O. Box 131, 74001-970 Goiânia-GO, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
This work presents a method to prepare composites based on polyaniline (Pani) and styrene–divinylben-
zene copolymers (SD) by in situ polymerization of aniline using benzoyl peroxide as oxidant agent. The
composites were obtained from copolymers with two degrees of porosities which have higher and lower
surface areas. Emeraldine Pani was prepared using hydrochloric acid as dopant. One cycle or four cycles
of aniline polymerization were performed. The copolymers and their respective composites characteriza-
tions were performed by infrared spectroscopy, thermogravimetric analysis, physical nitrogen adsorp-
tion–desorption measurements, morphology analysis, elemental analysis and determination of
Brönsted acid sites. The Pani was distributed overall porous SD copolymer producing composites with
high surface area. Then, they were evaluated as catalysts for esterification reaction of a fat acid. It was
found that that composites prepared with four cycles of in situ polymerization presented best catalytic
activity than one cycle composites.
Received 7 February 2013
Received in revised form 30 May 2013
Accepted 21 June 2013
Available online 28 June 2013
Keywords:
Polyaniline
Styrene-divinylbenzene copolymer
Porosity
Composites
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
One of the biggest problems concerning electrical conducting
materials as Pani has been the difficulty associated with the pro-
Electrically conducting polymers are a class of organic com-
pounds that combine the chemical and mechanics characteristics
of polymers with the electronic properties of metals and semicon-
ductors [1]. Polyaniline (Pani) is a electrically conducting polymer
that have attracted great interest because of its possibilities of
applications in many areas, such as electrostatic discharge materi-
als, gas sensor (NH3 and volatile organic compounds), acid–base
indicator, ion-exchange material, energy storage devices and solar
cell [2–7]. The easy synthesis from an inexpensive monomer, good
conductivity and remarkable environmental stability are some
reasons why Pani has been one of the most studied conductor poly-
mers [8,9].
Pani can be obtained through electrochemical and chemical oxi-
dation synthesis. Currently, chemical oxidation has the advantage
to result better yields being preferred for larger scale processes
[10,11]. Furthermore, the chemical oxidation route allows modifi-
cations of Pani chain structure [12]. Many oxidizing agents can be
used to produce polyaniline by the chemical oxidation route, for
example, potassium iodate [13,14], ferric chloride [15], hydrogen
peroxide [16], potassium dichromate [17], and the most commonly
used ammonium persulfate [18–23].
cessing, especially for that synthesized by chemical oxidation of
the monomers [24]. The oxidative polymerization of aniline or pyr-
rol in the presence of supports is one way to produce conducting
polymeric materials with definite shape. Composites materials of
conducting polymers and conventional polymers have been pre-
pared in order to produce membranes and Pani coated latex. Tan
et al. prepared composites of Pani and a sulfonated styrene–divi-
nylbenze (SD) copolymer membrane through oxidative polymeri-
zation of aniline with different oxidants [25]. They concluded
that the Pani layer was found solely at the surface, within, or both
at the surface and within the membrane by the control of aniline
polymerization conditions. The polymerization of Pani in the pres-
ence of polystyrene (PS) latex can be carried out to produce nearly
monodispersed Pani-PS composites with core–shell morphology,
where the conducting polymer forms the shell [26]. Wang and Jing
synthesized Pani by chemical oxidative polymerization of aniline
with ammonium persulfate in the presence of sulfonated cross-
linked polystyrene particles in neutral water obtaining a core–shell
morphology. Since they used a low DVB:styrene molar ratio (1:15)
and no diluents to form pores the structure of the copolymer
should be gel type, i.e., nonporous [27]. Although the polystyrene
chains were sulfonated, the aniline polymerized preferentially on
the particle surface forming a continuous shell. More recently, Ince
et al. produced composites of Pani and SD copolymer also with a
⇑
Corresponding author. Tel.: +55 (62) 3521 1097; fax: +55 (62) 3521 1167.
E-mail address: denilson@quimica.ufg.br (D. Rabelo).
1381-5148/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.reactfunctpolym.2013.06.008

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B.H.F. Moura et al. / Reactive & Functional Polymers 73 (2013) 1255–1261
core–shell structure but with very rough surface. They grafted
polystyrene on the SD copolymer particles via surface initiated
atom transfer radical polymerization. Then the polystyrene chain
brushes on the particle surface were sulfonated and neutralized
with aniline which was polymerized with potassium persulfate
as oxidant [28]. For the core–shell morphology presented by some
Pani composites with gel type SD copolymers is expected specific
surface areas relatively low. For the composites of Pani over parti-
cles containing grafted polystyrene chains was suggested an in-
crease of specific surface area due the very rough surface of the
particles, although the authors did not presented no surface area
measurement.
applying it to the esterification of ricinoleic acid obtaining ester
yields about 95%.
The aim of this work was to produce SD copolymer/Pani com-
posites with high porosity and surface area with Pani dispersed
overall support surface. The in situ polymerization was carried
out with one and four cycles to vary the amounts of Pani in the
supports. The composites were evaluated as acid catalyst in the
esterification of stearic acid with methanol.
2. Experimental
2.1. Materials
Yagudaeva et al. prepared Pani coatings of a sulfonated SD
copolymer (Dowex-gel type) and composite materials based on sil-
ica gel surface modified by a sulfonated SD copolymer [29]. Aniline
was polymerized with ammonium persulfate as oxidant forming a
thin polymeric coating on the macroporous support surface based
on silica gel and sulfonated SD copolymer. It is expected these
macroporous Pani composites present higher specific surface area
than Pani/Gel type SD copolymer composites. The morphology of
the macroporous Pani composites and the original support were
characterized by mercury porosimetry but no SEM image was
showed.
1,4-Dioxane UV/HPLC grade stabilized with 1.5 mg/L of 2,6-di-
tert-butyl-4-methyl-phenol, toluene 99.5%, heptane 98%, acetone
99.5%, methyl alcohol 99.8%, ethanol 99.5%, hydroxyethylcellulose,
gelatin powder, benzoyl peroxide 65% (BP), Aniline PA, sodium
chloride 99%, sodium dodecyl sulfate 99%, sodium hydroxide 97%,
phenolphthalein 1% solution, stearic acid 95%, sulphuric acid 95–
98%, nitric acid 65%, hydrochloric acid 37% were used as received.
Styrene and divinylbenzene were purified washing with NaOH
solution followed by reduced pressure distillation.
The composites of Pani and SD copolymers described before
were produced with the sulfonated copolymer in general with a
gel-type porosity. In this paper we used macroporous SD copoly-
mers with different surface areas and no previous chemical modi-
fication to produce composites with Pani. SD copolymers have
been widely used to prepared ion exchange resins. They were cho-
sen because the surface area, porosity and particle size can be
easily controlled to produce different polymeric supports [30,31].
The effects of porogenic agent or diluent type, dilution degree
and divinylbenzene (DVB) content on the porosity and swelling
properties of SD copolymer are well known [30–32]. The use of dil-
uents which solvate the copolymer chains produce small pores and
higher surface areas than nonsolvating diluents. The SD copolymer
prepared with solvating diluents swell more in good solvents than
that prepared with nonsolvating ones. Generally, a large amount of
DVB also leads to increasing in the specific surface area. For the SD
copolymers prepared with nonsolvating diluents the increasing in
DVB content has little effect on swelling of the entangled chains
[32]. In this work we prepared two macroporous SD copolymers
with different DVB contents in order to produce SD copolymers/
Pani composites with high and low specific surface areas. We used
high proportions of nonsoltanting diluents to produced structures
with similar swelling properties.
In a previous work, the in situ polymerization of aniline in a
macroporous SD copolymer with ammonium persulfate as oxi-
dizing agent and HCl as dopant did not produce a homogeneous
distribution inside the support [18]. The high hydrophobicity of
the copolymer and the beginning of polymerization as soon as
the oxidant was added favored the Pani formation on the sup-
port external surface. In order to overcome this difficulty, we
chose an alternative Pani synthetic route using benzoyl peroxide
as oxidizing agent. Benzoyl peroxide (BP) has been described as
an oxidizing agent for Pani synthesis, presenting advantages as
good stability in the synthesis conditions, the reaction can be
carry out at room temperature and BP can be easily solubilized
in organic solvents [33–37].
2.2. Synthesis
2.2.1. Synthesis of styrene–divinylbenzene (SD) copolymers
Copolymers synthesis was carried out through aqueous suspen-
sion polymerization in
a 1 L three-neck round-bottom flask,
equipped with a mechanic stirrer, reflux condenser and a ther-
mometer. The aqueous phase (AP) was composed by hydroxyethyl-
cellulose at 0.26% (w/v), sodium chloride at 0.59% (w/v) and gelatin
at 0.12% (w/v). The organic phase (OP) was prepared dissolving 1%
of initiator BP in a mixture containing styrene and divinylbenzene
monomers at room temperature. Heptane and toluene were used
as porogenic agents with a volume ratio of 85/15 and 150% dilution
degree in relation to monomers volume. Two kinds of copolymers
were produced and denominated SD29 and SD84 for which nomi-
nal molar percentages of DVB were 29% and 84%, respectively. The
real percentages of DVB were approximately 16% and 46%, since
technical grade DVB used had concentration of 55%. The proportion
between AP and OP was maintained 4/1 (v/v). The organic phase
was added to aqueous phase leaving the system under stirring
about 15 min before initial heating. The temperature was kept at
70 °C with stirring at 250 rpm for 24 h. Finally, the copolymer
beads were filtrated and washed with water and then with ethanol
at 50 °C about 1 h several times until the filtrated to be miscible
with water. The copolymers were dried at 70 °C for 24 h. The
copolymer beads were sieved and the particles in the range of
400–600 lm were used to prepare the composites.
2.2.2. Synthesis of SD copolymer/Pani composites
SD copolymer/Pani composites prepared using SD29 and SD84
with one reaction cycle were called SD29/Pani-Cl and SD84/Pani-
Cl, respectively. In a 100 mL Erlenmeyer, 4 g of each resin were
put in contact with 40 mL of ethanol/aniline solution with a vol-
ume ratio of 80/20. Each system was mechanically stirred in a sha-
ker for 3 h in order the copolymer become swollen by aniline. In
another 100 mL Erlenmeyer, a reactive solution were prepared
mixing 2.3 ꢀ 10ꢁ3 mol of benzoyl peroxide (BP) in 20 mL of diox-
ane, 1.4 ꢀ 10ꢁ3 mol of sodium lauryl sulfate in 6 mL of water and
0.06 mol of hydrochloric acid. The swollen copolymer in the first
Erlenmeyer was filtrated and added to the reactive solution. The
aniline polymerization was carried out under mechanical stirring
in a thermo regulated bath at 25 °C for 24 h. After, the composites
were vacuum filtrated and washed with methanol and ketone until
Pani has been described as a promising polymer to be used as
catalyst in the esterification reaction of carboxyl acids and transe-
sterification of triglycerides. Palaniappan et al. [36] has presented
good results for direct esterification of lauric, caproic, stearic and
cinnamic acids obtaining above 90% yield of product conversion
under 70 °C, 24 h and 20 wt% of polyaniline as catalyst. Zieba
et al. [38] has synthesized polyaniline over carbon support and

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1257
the filtered solution became colorless. The composites were dried
3. Results and discussion
at 70 °C for 24 h. All procedure was repeat 4 times to prepare the
four cycle composites which were called SD29/Pani-Cl* and
SD84/Pani-Cl*.
The suspension polymerization process produced Sty-DVB
copolymers (SD) in the form of opaque and white beads with char-
acteristics of macroporous resins. The polianiline/SD composites
presented green color characteristic of Pani emeraldine salt form,
which became darker with the increase of the polymerization cycle
number. Beads of the different composites were cut off with a
blade and showed a homogeneous distribution of Pani inside the
particles. The following sections describe the characterization re-
sults of the SD copolymers (SD29, SD84), the composites prepared
with one polymerization cycle (SD29/Pani-Cl, SD84/Pani-Cl) and
the composites prepared with four polymerization cycle (SD29/
Pani-Cl*, SD84/Pani-Cl*).
2.3. Physico-chemical characterization
2.3.1. Fourier transform infrared spectroscopy
Fourier-transform infrared spectra were recorded using a Perkin
Elmer Spectrum ASCII 1.60 in the range of 4000–400 cmꢁ1 for SD29
and SD84 copolymers and the synthesized composites. Samples
were prepared as KBr tablets.
2.3.2. Thermogravimetric analysis
Thermogravimetric curves of all samples were recorded on a
DTG 60 Shimadzu thermogravimetric analyzer from 25 to 800 °C
3.1. Infrared spectroscopy
at
a
heating rate of 10 °C minꢁ1 under air atmosphere at
50 mL minꢁ1 flux.
Fig. 1 shows the FTIR spectra for copolymers and composites. It
can be note that the spectra profiles of one cycle composites are
very similar to copolymers spectra profiles, probably due to its
lower Pani content indicated by lighter green color. The four cycle
composites spectra were also similar but they show more clearly
some characteristics bands of Pani. A spectrum of emeraldine salt
Pani was included in order to facilitate the identification of Pani
bands in the composites.
2.3.3. Nitrogen adsorption measurements
The specific surface area and pore size distribution measure-
ments were performed using a Micrometrics ASAP 2010 nitrogen
sorption porosimeter. Analysis was via nitrogen sorption carried
out at 77 K. Specific surface area was determined by BET method
and the pore size distribution by the BJH method based on nitrogen
desorption isotherm.
The Pani characteristic bands are observed at: 1589 cmꢁ1 and
1491 cmꢁ1, attributed to the stretching of the quinone (Q) and ben-
zenic (B) rings, respectively; 1310 cmꢁ1, attributed to the symmet-
rical stretching of CN groups of secondary aromatic amines;
1248 cmꢁ1, attributed to the symmetric stretching of the bipolar
2.3.4. Morphology analysis
Morphology of SD copolymers and synthesized composites
were examined by scanning electron microscopy (SEM) using a
JSM-6610 instrument. Samples were coated in gold prior to SEM
imaging.
2.3.5. Elemental analysis
CHNS elemental analysis was performed using a Thermo Scien-
tific Flash 2000 Organic Elementar Analyzer. Nitrogen content indi-
cates the polyaniline amount adhered on resin surface. Eq. (1) was
used to estimate the amount of polyaniline in the composites from
the nitrogen percent weight:
%Pani-Cl ¼ ½nN=4ꢂ ꢃ ½MRU þ þ2MHCl
ꢂ
ð1Þ
where %Pani-Cl = percent weight of emeraldine polyaniline; nN = -
nitrogen mol number in 100 g of composite (% mN/14); MRU = molar
mass of repetitive unit of emeraldine polyaniline; MHCl = molar
mass of HCl. The molar mass of HCl was multiplied by two because
it was considered that the two imine groups are preferentially pro-
tonated [39].
2.3.6. Acid capacity
The total amount of Brönsted acid sites was determined by
acid–base titration. The composites were put in contact with
50 mL of NaOH (0.01 mol Lꢁ1) during 24 h at room temperature.
Then, the composites were filtered and the liquid was subse-
quently titrated with hydrochloric acid solution (0.005 mol Lꢁ1).
2.3.7. Catalytic tests
Esterification was performed using commercial stearic acid
(0.01 mol), with methanol (0.3 mol). This reaction was carried
out in a 100 mL round-bottom flask coupled with a reflux con-
denser, on an oil bath magnetically stirred heated to 70 °C for
8 h. All synthesized composites were used as catalyst at 15%
weight related to carboxylic acid mass. At the end of each reaction
the product was recovered and analyzed by GC/MS Agilent 7890
GC equipment using a HP-5 column.
Fig. 1. Infrared spectra of copolymers and composites: (a) Pani-Cl; (b) SD29; (c)
SD84; (d) SD84/Pani-Cl*; (e) SD29/Pani-Cl*; (f) SD84/Pani-Cl and (g) SD29/Pani-Cl.

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CNÅ+ group of benzenic species; 1159 cmꢁ1 attributed to the CH
group, which is an electronic or vibrational band due to nitrogen
linked to the quinone group [40].
Table 1
Degradation onset temperature of SD copolymers and their composites.
Sample
Degradation onset temperature (°C)
SD29
238
300
314
268
285
303
3.2. Thermogravimetric analysis
SD29-Pani-Cl
SD29-Pani-Cl*
SD84
TGA experiments were performed to evaluate the thermal sta-
bility of the produced composites at air atmosphere. Fig. 2 shows
the copolymers and composites thermal degradation curves. It
can be seen that the thermal degradation of composites occurred
at higher temperatures than the corresponding Sty-DVB copoly-
mer, specially, for the four cycle composites (SD29/Pani-Cl*,
SD84/Pani-Cl*). Further, we observed that until the point where
decomposition begins the composites kept their structural integ-
rity, after that the mass losses occurred more suddenly than for
the corresponding copolymers.
SD84-Pani-Cl
SD84-Pani-Cl*
did not presented a core–shell morphology. Then, the increasing of
the onset temperature can be explained by the protection induced
by Pani covering all surface of the macroporous SD copolymers.
3.3. Nitrogen adsorption measurements
Table 1 presents degradation onset temperature for copolymers
and composites determined by DTG curves (not showed). The Pani
composites presented higher onset temperatures than the original
SD copolymers. Kim et al. attributed higher onset temperature for
Pani than for polystyrene chains [41]. Davodi et al. also found an
increase of onset temperature of polystyrene particles covered by
thin Pani layers [42]. The composites beads cut off showed green
color characteristic of emeraldine Pani inside the particles, i.e., they
Fig. 3 shows that even after incorporation of polyaniline over
copolymer surface only small changes in their morphological char-
acteristics were observed. The total volume adsorbed by compos-
ites and copolymers are very close. Copolymers and composites
have the same kind of isotherm (type IV), typical for meso or mac-
roporous absorbents. This kind of isotherm is a function of pore
size effect upon adsorption phenomena. According to IUPAC,
Fig. 2. Thermal degradation of (a) SD29 and (b) SD84 copolymers and their
composites.
Fig. 3. Adsorption Isotherms for (a) SD copolymers and (b) their composites.

B.H.F. Moura et al. / Reactive & Functional Polymers 73 (2013) 1255–1261
1259
Table 2
hysteresis of all samples in Fig. 3 fit H1 of adsorbent with cylindri-
Textural proprieties of SD copolymers and their composites.
cal pores [43]. It was observed for SD84 and their composites, as
expected, higher adsorbed volumes in comparison to SD29 and
their composites. The high cross-linking degree in SD84 promotes
a stronger phase separation during the copolymer synthesis [30–
32].
According to IUPAC, micropores do not exceed 2 nm of
diameter, mesopores occurs between a range of 2–50 nm and mac-
ropores are larger than 50 nm. Fig. 4 shows that pore size distribu-
tion was also very similar for copolymers and composites, where
most pores are in the range of 10–60 nm. So both copolymers
and their composites presented meso and macropores. We can also
observe that the composites from SD84 had a considerable amount
of pores between 3 and 10 nm which contribute to its higher ad-
sorbed volume and surface area in comparison to composites from
SD29.
Table 2 shows the specific surface areas, total pore volumes and
average pore diameters of SD copolymers and their composites
with Pani. The surface areas of the Pani composites varied between
77 and 412 m2 gꢁ1 indicating good characteristics for use as cata-
lysts. Both composites prepared with one cycle of aniline polymer-
ization presented an increasing of their specific surface areas and
pore volumes in relation to the starting copolymers. This probably
happened due the copolymer be in a swollen state during aniline
Sample
SBET (m2 gꢁ1
)
VP (cm3 gꢁ1
)
Dm (nm)
SD29
85
106
77
341
412
354
0.40
0.54
0.35
0.71
0.83
0.67
20
22
22
11
12
11
SD29/Pani-Cl
SD29/Pani-Cl*
SD84
SD84/Pani-Cl
SD84/Pani-Cl*
SBET (m2 gꢁ1): specific surface area; VP (cm3 gꢁ1): total pore volume; Dm (nm):
average pore diameter.
polymerization. So the porosity increased even with the filling of
pores by the Pani and after drying process. For composites synthe-
sized with one cycle, the considerable increase in specific surface
area suggests the formation of a thin layer of Pani overall SD
copolymer surface. Yagudaeva et al. observed a small reduction
on porosity of macroporous support based on silica gel and sulfo-
nated SD copolymer after aniline polymerization [29]. The struc-
ture of silica gel is rigid so its pores cannot expand as the pores
of SD copolymers solvated by aniline.
For composites synthesized with four cycles of polymerization,
it was observed that the specific surface area remains almost the
same when compared to the starting copolymer, while the pore
volumes had a small reduction. We believe that the larger amount
of polyaniline filling the pores counterbalanced the swelling effect
so that the starting copolymer characteristics were lightly changed.
The average pore diameter of SD84 copolymer and their compos-
ites were smaller than of SD29 copolymer and their composites.
The average pore diameters practically did not change between
the SD copolymers and their respective composites.
3.4. Morphology analysis
Fig. 5 shows micrographs of external surface and inner of
copolymers and their composites obtained by SEM. The SD29
copolymer presented a rough external surface (Fig. 5a) and an in-
ner surface formed by microspheres agglomerates separated by
meso and macropores (Fig. 5b). This morphology is characteristic
of macroporous styrene–divinilbenzene copolymers [44]. Fig. 5c
shows only the external surface of SD29/Pani-Cl, while Fig. 5d
shows both internal and external portions of SD29/Pani-Cl* com-
posite. It can be noticed that both composites are very similar to
SD29 copolymer concerning external and inner portions.
Fig. 5e and f shows the inner of SD84 copolymer and SD84/Pani-
Cl composite, respectively. It is clear the similarity between their
internal morphology formed by microspheres agglomerates. It is
important to remember that the four cycles composites presented
a dark green color of emeraldine Pani inside the beads cut off. SEM
results and the nitrogen adsorption measurements allow us to con-
clude that the composites were formed by polyaniline deposits
overall copolymer surface copying its morphological structure.
This distribution of Pani on the porous matrix is an interesting fea-
ture of these composites, since they have potentially the chemical
properties of Pani with the copolymer textural properties.
3.5. Elemental analysis, acid capacity and catalytic tests
Table 3 presents the Pani content, acid capacity (A.C.) and the
ester yield for the reaction of stearic acid with methanol. Esterifi-
cation reaction was carried out using the produced composites as
catalysts under the same conditions: 70 °C, 8 h, 15 wt% related to
carboxylic acid mass. It can be observed that the four cycles com-
posites presented, as expected, higher amounts of Pani and higher
acid capacity than one cycle composites. The esterification using
Fig. 4. Pore size distribution for (a) SD copolymers and (b) their composites.

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B.H.F. Moura et al. / Reactive & Functional Polymers 73 (2013) 1255–1261
Fig. 5. Microscopy of (a) surface of SD 29 copolymer, (b) inner of SD29 copolymer, (c) surface of SD29/Pani-Cl, (d) surface and partial inner of SD29/Pani-Cl*, (e) inner of SD84
copolymer and (f) inner of SD84/Pani-Cl.
Table 3
1 g of carboxylic acid, 4 mL of methanol and 200 mg of Pani at
70 °C for 24 h. For stearic acid esterification the yield was 99%. In
Pani percentage, acid capacity and ester yield of SD copolymer/Pani composites.
Sample
% Pani-Cl
A.C. (H+ mmol gꢁ1
)
Yield (%)
this paper we used a proportion of 4.3 mL of methanol and
150 mg of catalyst for 1 g stearic acid obtaining ester yield of
96% in only 8 h at the same temperature. Considering that Pani
content in the four cycle composites was approximately 9%, the
amount Pani used as catalyst was 13.5 mg. The high efficiency of
the Pani in the composites compared to unsupported Pani can be
attributed to their higher surface areas and the Pani distribution
overall SD copolymer porous structures. Another advantage of
the composites in relation to unsupported Pani is the particle size
in the range of 400–600 lm so that the firsts are easily separated of
esterification product by simple filtration. The particle size of
unsupported Pani prepared with benzoyl peroxide in our labora-
tory was between 0.2 and 30 lm what require filtration with
SD29/Pani-Cl
SD29/Pani-Cl*
SD84/Pani-Cl
SD84/Pani-Cl*
1.4
9.0
2.6
7.9
0.22
0.63
0.25
0.44
47
96
29
95
the one cycle composites as catalyst showed low yields due the
low Pani content. The ester yield increased significantly with the
improvement of Pani content and acid capacity of four cycles com-
posites. Although SD84/Pani-Cl* composite had smaller acid capac-
ity than SD29/Pani-Cl* the ester yield was very close. This can be
explained by the high surface area of the SD84/Pani-Cl* composite
and the homogeneous distribution of Pani overall porous structure
indicated by SEM analysis and nitrogen adsorption measurements.
Ram and Palaniappan prepared unsupported Pani using benzoyl
peroxide as oxidant and H2SO4 as dopant [45]. They used the syn-
thesized Pani salt as catalyst for the esterification of different car-
boxylic acids with methanol. The particle size of the Pani salt was
membranes or centrifugation to separate from esterification
products.
4. Conclusion
found to be in the range of 0.3–300
lm and the specific surface
The present work has demonstrated that SD copolymers/Pani
composites can be prepared using benzoyl peroxide as oxidant.
area was 42 m2 gꢁ1. Most of the reactions were carried out with

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1261
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