Synthesis, characterization, conductivity and antimicrobial study of a novel thermally stable polyphenol containing azomethine group

Article abstract of DOI:10.1016/j.molstruc.2016.06.028

Poly(4-[[(4-methylphenyl)methylene]amino]phenol) (P(4-MMAP)), which is a Schiff base polymer, was synthesized by an oxidative polycondensation reaction of 4-[[(4-methylphenyl)methylene]amino]phenol (4-MMAP) with the oxidants NaOCl, H₂O₂ and O₂ in an aqueous alkaline medium. The polymerizations were carried out at various temperatures and times, and the highest polymer yield could be obtained when using 37% with NaOCl oxidant. The structures of the monomer and polymer were characterized by UV-Vis, FTIR ¹H NMR and X-ray diffraction techniques. The thermal behaviors of the monomer and polymer were identified by the TG and DTG techniques. The thermal degradation of the polymer which was observed thermally stable up to 1000 °C, was also supported by the Thermo-IR spectra recorded in the temperature range of 25-800 °C. The number average molecular weight (M_n), weight average molecular weight (M_w) and polydispersity index (PDI) of the polymer were found to be 16682, 57796 g/mol and 3.4, respectively. The highest electrical conductivity value of P(4-MMAP) doped with iodine vapor at different temperatures and times was measured to be 7.8 × 10^-5 Scm^-1 after doping for 48 h at 60 °C. The antibacterial and antifungal activities of 4-MMAP and P(4-MMAP) were also assayed against the bacteria Sarcina lutea, Enterobacter aerogenes, Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, Bacillus subtilis and the fungi Candida albicans, Saccharomyces cerevisiae, respectively.

Full text of DOI:10.1016/j.molstruc.2016.06.028

Journal of Molecular Structure 1123 (2016) 153e161
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Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis, characterization, conductivity and antimicrobial study of a
novel thermally stable polyphenol containing azomethine group
a
b
c
b, *
€
Nuray Yılmaz Baran , Meral Karakıs¸ la , Hacı Okkes¸ Demir , Mehmet Saçak
a Aksaray University, Faculty of Science and Arts, Department of Chemistry, Aksaray, 68100, Turkey
b Ankara University, Faculty of Science, Department of Chemistry, Ankara, 06100, Turkey
c
_
Kahramanmaras¸ Sütçü Imam University, Faculty of Science and Arts, Department of Chemistry, Kahramanmaras¸, 46100, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Poly(4-[[(4-methylphenyl)methylene]amino]phenol) (P(4-MMAP)), which is a Schiff base polymer, was
synthesized by an oxidative polycondensation reaction of 4-[[(4-methylphenyl)methylene]amino]phenol
(4-MMAP) with the oxidants NaOCl, H2O2 and O2 in an aqueous alkaline medium. The polymerizations
were carried out at various temperatures and times, and the highest polymer yield could be obtained
when using 37% with NaOCl oxidant. The structures of the monomer and polymer were characterized by
UVeVis, FTIR 1H NMR and X-ray diffraction techniques. The thermal behaviors of the monomer and
polymer were identified by the TG and DTG techniques. The thermal degradation of the polymer which
was observed thermally stable up to 1000 ꢀC, was also supported by the Thermo-IR spectra recorded in
the temperature range of 25e800 ꢀC. The number average molecular weight (Mn), weight average mo-
lecular weight (Mw) and polydispersity index (PDI) of the polymer were found to be 16682, 57796 g/mol
and 3.4, respectively. The highest electrical conductivity value of P(4-MMAP) doped with iodine vapor at
different temperatures and times was measured to be 7.8 ꢁ 10ꢂ5 Scmꢂ1 after doping for 48 h at 60 ꢀC.
The antibacterial and antifungal activities of 4-MMAP and P(4-MMAP) were also assayed against the
bacteria Sarcina lutea, Enterobacter aerogenes, Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae,
Bacillus subtilis and the fungi Candida albicans, Saccharomyces cerevisiae, respectively.
Received 23 February 2016
Received in revised form
7 June 2016
Accepted 7 June 2016
Available online 10 June 2016
Keywords:
Doping
Oxidative polycondensation
Polyazomethines
Schiff base polymers
Thermal analysis
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
been reported on the synthesis of this class of polymers using these
oxidants up to the present by Kaya and co-workers [15e18].
Schiff base polymers are one class of conjugated polymers,
which are also called as poly(azomethines). They have drawn the
attention of researchers in recent years due to their some proper-
ties such as, optoelectronic [1e3], semiconductive [4,5], and
photovoltaic [6,7], antimicrobial activities [8] and high thermal
stability [8,9].
Schiff base polymers have been synthesized using electro-
chemical [10] and chemical [11,12] methods. Oxidative poly-
condensation reactions carried out using NaOCl, H2O2 and O2
oxidants are one of the most widely used method for the chemical
polymerization. The advantages of this approach are the cheapness
of the oxidants, high solubility of the synthesized polymer, mild
reaction conditions and occurrence of environmentally friendly
byproducts, such as NaCl and H2O [13,14]. A number of studies have
It has been reported that Schiff base polymers can be synthe-
sized by oxidative polycondensation with good thermal stability
and conductivity that could be increased with doping up to a
certain level [13,18]. The conductivities of undoped Schiff base
polymers are generally about 10ꢂ10e10ꢂ15 Scmꢂ1 [19,20]. However,
the conductivities of these polymers could be increased by doping
with various dopants. It was reported that iodine was the most
suitable dopant for Schiff base polymers [21]. Moreover, this easy
process also improved the thermal and optical properties of the
polymer [22]. Therefore, researchers have widely investigated the
application of iodine-doped Schiff base polymers for lithium bat-
teries [23]. Kaya et al. reported that the conductivity of the Schiff
base polymer, poly(4-{[(4-hydroxyphenyl)imino]methyl}benzene-
1,2,3-triol) [PHPIMB], increased from 10ꢂ10 Scmꢂ1 to 10ꢂ8 Scmꢂ1
after doping with iodine vapor for 48 h at 25 ꢀC and that the
polymer showed thermal stability to 1000 ꢀC without remaining
any carbon residue [15]. In another study, it was reported that the
conductivities of poly(2-(4-bromobenzylideneamino)phenol) and
* Corresponding author. Tel.: þ90 3122126720x1289; fax: þ90 312 2232395.
E-mail address: sacak@science.ankara.edu.tr (M. Saçak).
http://dx.doi.org/10.1016/j.molstruc.2016.06.028
0022-2860/© 2016 Elsevier B.V. All rights reserved.

154
N. Yılmaz Baran et al. / Journal of Molecular Structure 1123 (2016) 153e161
poly(2-(4-bromobenzylideneamino)-5-methylphenol]) increased
from 11.33 ꢁ 10ꢂ10 and 6.40 ꢁ 10ꢂ10 Scmꢂ1 to 25.10 ꢁ 10ꢂ10 and
219 ꢁ 10ꢂ10 Scmꢂ1, respectively, after doping with iodine for 48 h at
25 ꢀC and concluded that the products were thermally resistant
because carbon residues of the polymers were 23.63% and 28.21%,
respectively at 1000 ꢀC [16]. In the present study, it was determined
that the conductivity of P(4-MMAP) increased from 5 ꢁ 10ꢂ11
Scmꢂ1 to 7.30 ꢁ 10ꢂ6 and 7.75 ꢁ 10ꢂ5 Scmꢂ1 after doping for 48 h at
20 ꢀC and 60 ꢀC, respectively, and it was thermally resistant to
1200 ꢀC (30% carbon residue at 1000 ꢀC).
In the present study, it was aimed at preparing a Schiff base
polymer which had good solubility, thermal resistivity and semi-
conductivity. For this purpose, P(4-MMAP) with an active hydroxyl
group was synthesized by the oxidative polycondensation of 4-
MMAP using NaOCl, H2O2 and O2 mild oxidants in an aqueous
alkaline medium. The structures of 4-MMAP and P(4-MMAP) were
then characterized by various techniques. Finally, the antimicrobial
and thermal degradation properties of the polymer were compared
to the monomer and electrical conductivity of P(4-MMAP) was
measured depending on the doping temperature and time.
recrystallized from methanol for purifying, it was dried in a vacuum
desiccator and 88% yield was obtained with melting point of 135 ꢀC.
2.2.2. Synthesis of P(4-MMAP)
P(4-MMAP) was synthesized by oxidative polycondensation of
4-MMAP in an aqueous alkaline medium using NaOCl (15%), H2O2
(30%) and O2 (flow rate: 0.56 Lhꢂ1) oxidants (Scheme 1). 4-MMAP
(1 mmol) was dissolved in an aqueous KOH solution (10%,
1 mmol) in a 50 mL flask with three necks. The reaction was carried
out under a nitrogen atmosphere. After reaching the reaction
temperature,1 mmol NaOCl (15%) or H2O2 (30%) was added drop by
drop into the monomer solution. The color of the solution imme-
diately turned from yellow to brown with the addition of the
oxidant. When O2 was used, it passed through the reaction solution
during the polymerization. After the reaction was completed, the
polymer was precipitated by neutralizing the reaction medium
with the addition of solution of HCl into the mixture that had been
cooled to room temperature. After the precipitated polymer was
filtered and washed with hot water (3 ꢁ 25 mL) and methanol to
remove the mineral salts and unreacted monomer, respectively. It
was dried at 60 ꢀC in a vacuum oven.
2. Experimental
The polymer yield was determined using Eq. (1):
wp
wm
2.1. Materials
Polymer Yieldð%Þ ¼
ꢁ 100
(1)
4-aminophenol, p-tolualdehyde, KOH, hydrochloric acid (HCl,
37%), methanol, ethanol, ethyl acetate, acetone, n-heptane, 1,4-
dioxane, N-methylpyrrolidone, tetrahydrofuran (THF), dime-
thylformamide (DMF), dimethyl sulfoxide (DMSO), iodine, sodium
hypochlorite (NaOCl) (15% aqueous solution) and H2O2 were used
as supplied by Merck Chem. Co. (Germany). Sarcina lutea (ATCC
9341NA), Enterobacter aerogenes (ATCC 13048), Escherichia coli
(ATCC 39628), Enterococcus feacalis (ATCC 29212), Klebsiella pneu-
monia, Bacillus subtilis (ATCC 6633) bacteria, and Saccharomyces
cerevisiae, Candida albicans yeasts obtained from Biology Depart-
ment of University of Celal Bayar and Medical Faculty-Microbiology
Where wp and wm correspond to the polymer and initial monomer
mass, respectively.
2.3. Characterization
The UVeVis spectra measurements of 4-MMAP and P(4-MMAP)
were carry out with Shimadzu UV-1700 PharmaSpec UVeVisible
Spectrophotometer by dissolving them in DMSO. The FTIR spectra
of the samples were taken using Perkin Elmer FTIR Spectrometer.
The 1H NMR spectra were recorded using Bruker Avance 500 MHz
NMR in solutions of DMSO. The X-ray diffraction (XRD) patterns
were performed using Rigaku D max 2000 Diffractometer with
_
laboratory of University of Kahramanmaras¸ Sütçü Imam were used
to investigate the antimicrobial activities of the monomer and
polymer.
monochromic CuK
a radiation (1.5405 Å) operated at 40 kV, 30 mA
and 2
q
with a scan angle from 5ꢀ to 60ꢀ.
2.2. Method
TG and DTG measurements were recorded with EXSTAR S11
7300 model thermal analyzer under nitrogen atmosphere with a
heating rate of 10 ꢀC/min. For the determination of Mn, Mw and PDI
values of the synthesized polymer, Shimadzu Prominence Gel
Permeation Chromatography equipped with a preparative Nucle-
ogel GPC 103-5 VA300/7.7 column was used (eluent: dime-
2.2.1. Synthesis of 4-MMAP
As can be seen from Scheme 1, 4-MMAP Schiff base was syn-
thesized with the mechanism of a general condensation reaction
[24]. Solution of p-tolualdehyde (10 mmol) in 5 mL of methanol was
added drop by drop into the solution of 4-aminophenol (10 mmol)
prepared in 15 mL of methanol. The reaction was performed at
60 ꢀC with continuous stirring. A yellow product formed approxi-
mately 6 h later in the solution, and it was separated by filtering
and washed with cold methanol. After the monomer was
thylformamide, flow rate: 0.5 mL minꢂ1
polystyrene standards).
, calibrated with
To measure the surface resistivity of P(4-MMAP), pellet samples
with 2 mm thick and diameter of 1.3 cm were prepared under a
hydraulic pressure of 1.7 ton/cm2. The measurements of the surface
Scheme 1. Synthesis of 4-MMAP and P(4-MMAP).

N. Yılmaz Baran et al. / Journal of Molecular Structure 1123 (2016) 153e161
155
resistivity were performed by two probe method using either
ideal oxidant.
Thurlby 1503 or Keithley 6517A digital multimeter, depending on
the surface resistivity of the samples.
3.1.2. Polymerization temperature and time
To monitor the effect of the polymerization temperature and
time on the yield of P(4-MMAP) the polymerizations were per-
formed at 70, 80 and 90 ꢀC for different periods, and the poly-
merization conditions that gave the highest yield were determined
(Fig. 1). As can be seen from the figure, the yield increased with an
increase in the polymerization time at 70 ꢀC. At the temperatures of
80 and 90 ꢀC, for the polymerizations went on for further 2 h, it was
observed that the yields did not increase. This shows that the ef-
fects of polymerization temperature and time on the yield are in
agreement with data reported in the literature [20].
2.4. Antimicrobial test
The antimicrobial activities of the monomer and polymer were
monitored using Mueller-Hinton agar and Sabouraud dextrose agar
with the agar-well diffusion method [25] against the bacteria Sar-
cina lutea (ATCC 9341NA), Enterobacter aerogenes (ATCC 13048),
Escherichia coli (ATCC 39628), Enterococcus feacalis (ATCC 29212),
Klebsiella pneumonia and Bacillus subtilis (ATCC 6633) as well as the
yeasts Saccharomyces cerevisiae and Candida albicans. Culture sus-
pensions were prepared from standardized inoculums of the bac-
3.2. Solubility behavior
teria and yeasts containing 108 cfu mLꢂ1 and 106 cfu mLꢂ1
,
respectively [26]. After inoculation, the suspensions were gently
shaken and then poured into sterile petri dishes. Solutions of 4-
MMAP and P(4-MMAP) in DMSO with different concentrations
The solubility behavior of 4-MMAP and P(4-MMAP) were
studied qualitatively by dissolving 1 mg samples in 1 mL of solvent
at 25 ꢀC, and the observations are given in Table 2. The monomer
dissolved exactly in all the solvents tested except heptane. While
the polymer was soluble in N-methylpyrrolidone (NMP), dime-
thylformamide (DMF), dimethylsulphoxide (DMSO) and ethyl-
acetate; it was insoluble in ethanol, heptane, and tetrahydrofuran
(THF). In addition, it was observed that the polymer was poorly
soluble in methanol, acetone and 1,4-dioxane. In addition to the
solubility of the synthesized polymer in common organic solvents,
the dissolution of the polymer in mild solvents such as ethylacetate,
derivative of ester, also plays a facilitator role in the processability
of the polymer.
(100 and 200
mg/100
mL) were loaded into wells 6 mm in diameter.
Nystatin (100U) and Chloramphenicol (30
mg) were used as the
standards and DMSO was used as the solvent control. The plates
were incubated at 36 ꢀC for bacteria and at 30 ꢀC for yeasts for 24 h.
At the end of the incubation, the evaluation was performed by
measuring the diameters of the inhibition zones.
3. Results and discussion
3.1. Effect of synthesis conditions on polymerization of 4-MMAP
3.1.1. Oxidant type
3.3. UVevis spectra
The changes in the yield, conductivity, molecular weights (Mw,
Mn) and PDI values of P(4-MMAP) obtained by an oxidative poly-
condensation reaction of 4-MMAP using various oxidants such as
NaOCl, H2O2 and O2 are given Table 1. In the experiments carried
out to detect the effects of the oxidant types, oxidant were used
oxidants at concentrations of [NaOCl]0 ¼ [H2O2]0 ¼ 0.1 mol Lꢂ1 or
O2 at a flow rate of 0.56 L hꢂ1. After the conductivity values for all
the polymer samples synthesized with each oxidants and doped
with I2 for 24 h at 20 ꢀC were obtained, they were compared to the
other oxidant types and it was observed that, while the conduc-
tivities of products after doping increase about 109 fold, the changes
were all related to the initial conductivity values. As seen from
Table 1, the conductivity values of P(4-MMAP) were in the
descending order of NaOCl>H2O2> O2. The highest yield was also
obtained as 36.4% with the NaOCl oxidant. In addition, the polymer
synthesized with the NaOCl oxidant had the highest molecular
weight values (Mw: 57796, Mn: 16682 g/mol and PDI: 3.4). Ac-
cording to the evaluations of the molecular weight, yield and
conductivity values of P(4-MBAP), it can be concluded that NaOCl
was found to be the most suitable oxidant. Therefore, the following
experiments were performed with this oxidant. According to the
evaluations of the molecular weight, yield and conductivity values
of P(4-MMAP), it can be concluded that NaOCl was found to be the
The UVeVis spectra of 4-MMAP and P(4-MMAP) taken in DMSO
in the wavelength range of 260e700 nm (Supplementary data).
Two bands at the wavelengths of 278 and 348 nm as well as 293
and 409 nm can be observed in the UVeVis spectra of 4-MMAP and
P(4-MMAP), respectively. The bands observed at 278 and 293 nm in
the spectra of the monomer and polymer, respectively, can be
attributed to the
other peaks at 348 and 409 nm are due to the
p
e
p* transitions of benzene (eC]C-) while the
pep
* transitions of
the eCH]Ne functional group [8,20]. It was observed that the
bands in the P(4-MMAP) spectrum were broadened and the band of
the eCH]Ne functional group shifted when compared to the 4-
MMAP spectrum. Moreover, while the spectrum of 4-MMAP
Table 1
Effect of oxidants types on yield (%), Mw, Mn, PDI and conductivity of P(4-MMAP).
Oxidant
Yield (%)
Mw
Mn
PDI
Conductivity (Scmꢂ1
)
Initial
Doped
NaOCl
H2O2
O2
36.4
14.2
23.4
57796
9305
9184
16682
6633
8800
3.4
1.4
1.04
5 ꢁ 10ꢂ11
7.3 ꢁ 10ꢂ6
1.9 ꢁ 10ꢂ6
3.7 ꢁ 10ꢂ7
2.2 ꢁ 10ꢂ15
6.2 ꢁ 10ꢂ15
([4-MMAP]0 ¼ [KOH]0 ¼ [NaOCl]0 ¼ [ H2O2]0 ¼ 0.1 mol Le and flow rate of
Fig. 1. The change on yield of P(4-MMAP) (%) with the polymerization temperature
and time ([4-MMAP]0 ¼ [KOH]0 ¼ [NaOCl]0 ¼ 0.1 mol Lꢂ).
O2 ¼ 0.56 L he, doping time: 24 h).

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N. Yılmaz Baran et al. / Journal of Molecular Structure 1123 (2016) 153e161
Table 2
The results of solubility test of 4-MMAP and P(4-MMAP) in various solvents.
Ethanol
Methanol
Acetone
Dioxane
DMF
DMSO
NMP
Ethyl acetate
Heptane
THF
4-MMAP
P-4-MMAP
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
e
e
e
(þ): soluble, ( ): partially soluble, (ꢂ): insoluble.
ended at 420 nm, the spectrum of P(4-MMAP) was extended up to
700 nm. This case can be explained by the extension of the
conjugation in the polymeric structure [8,20], which is evidence
that polymer structure is formed.
3.5. 1H NMR spectra
The 1H NMR spectra of 4-MMAP and P(4-MMAP) recorded in
DMSO-d6 are given in Fig. 3. In the 1H NMR spectrum of 4-MMAP,
while the protons belonging to the characteristic eOH and eCH]
Ne functional groups are observed at
d
¼ 9.52 (s, 1H) ppm and
d
¼ 8.54 (s, 1H) ppm, respectively, the peak of the protons from the
eCH3 group is at
d
¼ 2.33 (s, 3H) ppm. These peaks are at
¼ 2.51 (s, 3H) ppm in the spectrum of P(4-MMAP),
respectively. The other peaks that verify the aromatic structure of
4-MMAP and P(4-MMAP) were detected in the spectra at
¼ 7.78
(d, 2H, Ar-Ha), 7.27 (d, 2H, Ar-Hb), 7.18 (d, 2H, Ar-Hc) and 6.82 (d, 1H,
Ar-Hd) ppm as well as
¼ 7.17 (d, 1H, Ar-Ha), 7.08 (d, 1H, Ar-Hb) and
d
¼ 9.90,
9.12 (s, 1H) and
d
3.4. FTIR spectra
d
Fig. 2 shows the FTIR spectra of 4-MMAP and P(4-MMAP). The
peaks observed at 3150 and 3272 cmꢂ1 are due to the phenolic eOH
groups of 4-MMAP and P(4-MMAP), respectively. While the sharp
peak observed at 1621 cmꢂ1 in the spectrum of the monomer be-
longs to the characteristic eCH]Ne vibration, and the same peak
is seen as a shoulder at 1624 cmꢂ1 in the spectrum of the polymer
[8,14,20]. The presence of the characteristic eCH]Ne peak of the
Schiff base in the FTIR spectrum of P(4-MMAP) indicates that the
azomethine groups are preserved in the polymeric structure [20].
Additionally, the bands observed at 1586, 1568, 1512, 1506 and
1445 cmꢂ1 correspond to eC]Ce vibrations in the spectrum of the
monomer [20]. These peaks are seen at 1542, 1509 and 1448 cmꢂ1
in the spectrum of the polymer [20]. While the peaks recorded at
1377 and 1365 cmꢂ1 originate from the aliphatic CeH bending vi-
brations, and the peaks at 1280 and 1217 cmꢂ1 are due to eCeOe
stretching vibrations in the spectra of 4-MMAP and P(4-MMAP),
respectively [20]. Moreover, (I) the shift of the peaks in the polymer
spectrum, (II) the decrease in the number of the peaks and (III) the
broadening of the peaks in the spectrum of the polymer compared
to that of the monomer can all be ascribed to the polymer structure
[20,27].
d
6.84 (s, 2H, Ar-Hd) ppm, respectively [20]. The observed broadening
of the peaks belonging to the aromatic region in the spectrum of
the polymer indicates the polyconjugated structure [20]. Addi-
tionally, (I) the absence of the doublet peaks originating from the Hc
protons belonging to the monomer in the polymer spectrum and
(II) the observation of the doublet Hd protons of the monomer as
singlet in the spectrum of the polymer indicate that the polymer-
ization proceeds from the ortho positions according to the OH
groups due to the CeC bonds formed during polymerization [20,17].
Possible resonance structures forming during the polymerization of
the Schiff base polymers, which are derivatives of polyphenol have
been reported in the literature [14,17]. In accordance with these
reports, it was determined that the Schiff base monomer can have
three different possible resonance structures for the polymeriza-
tion in an aqueous alkaline medium by the oxidative poly-
condensation method (Scheme 2(a)). The 1H NMR data of P(4-
MMAP) showed the polymerization proceeds from II and III reso-
nance structure given Scheme 2(a) [14,17]. Dimers which form with
the combining of the resonances undergo enolization [14,17]. In this
way, the suggested polymerization mechanism of P(4-MMAP),
which consists of a recombination of dimers, trimers, etc. is intro-
duced in Scheme 2(b).
3.6. XRD patterns
The XRD patterns of 4-MMAP and P(4-MMAP), which were
recorded in the region 2
q
¼ 5ꢂ60ꢀ to investigate the crystalline
structure differences of the monomer and polymer, are displayed in
Fig. 4. There are various sharp diffraction peaks in the monomer
diffractogram, which indicate a high degree of crystalline structure
in the Schiff base. However, only two sharp diffraction peaks can be
observed at about 2
q
¼ 28ꢀ and 40ꢀ in the polymer diffractogram
and the peaks indicate that the polymer has semicrystalline
structure [28]. It was reported in the literature that the presence of
eCH]Ne polar group and C]C bonds in the aromatic ring of
structure leads to some crystallinity [29]. Moreover, the broadening
of the polymer diffractogram according to that of the monomer
point out that the polymer has also amorphous nature in addition
to semicrystalline behavior [29].
Fig. 2. FTIR spectra of 4-MMAP and P(4-MMAP).

N. Yılmaz Baran et al. / Journal of Molecular Structure 1123 (2016) 153e161
157
Fig. 3. 1H NMR spectra of 4-MMAP and P(4-MMAP).
3.7. Thermal analysis and thermal degradation process of P(4-
MMAP)
were observed at 285 ꢀC, 404 ꢀC and 547 ꢀC for each degradation
step, respectively. It was determined that 77.9% of the monomer
degraded between 180 and 650 ꢀC, with 22.1% left as a carbon
residue.
It was observed from the TG-DTG curves of P(4-MMAP) that the
weight losses occurred in three steps within the temperature range
of 30e1000 ꢀC. In the first step with a minimum of DTG at 190 ꢀC,
7.9% (theoretically calculated: 7.9%) weight loss was observed in the
temperature range of 30e200 ꢀC, which indicates the removal of
crystallization water [30,31]. In addition, in the thermo-IR spectra
of P(4-MMAP), there was a decrease in the intensity of the eOH
peak around 3200 cmꢂ1 with the increase in the temperature in the
The TG and DTG curves belong to 4-MMAP and P(4-MMAP) are
shown in Fig. 5. Additionally, to support the thermal analysis
measurements of the polymer, the thermo-IR spectra recorded in
the temperature range of 25e800 ꢀC (Supplementary data). 8. It
was determined from the TG curve of 4-MMAP that the degradation
occurred in three steps (Fig. 5). In the first step (180e350 ꢀC) 58.4%,
in the second step (350e470 ꢀC) 11.9% and in the third step
(470e650 ꢀC) 7.6% weight losses were determined. The maximum
degradation temperatures (Tmax) obtained from the DTG curves

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N. Yılmaz Baran et al. / Journal of Molecular Structure 1123 (2016) 153e161
Scheme 2. (a) Possible resonance structures for the polymerization of 4-MMAP, (b) the polymerization mechanism of P(4-MMAP).
range of 30e200 ꢀC, which was further evidence for the water loss.
In the second step, 52% (theoretically calculated: 51.5%) weight loss
was recorded in the temperature range of 200e767 ꢀC in the TG
curve of P(4-MMAP), which shows the degradation of the eN]
CHeAreCH3 group. The peak with a maximum at 410 ꢀC in the DTG
curve corresponds to this degradation step. It was determined from
the thermo-IR spectra that the absence of the eCH]Ne functional
group around 1600e1610 cmꢂ1 at 500 ꢀC and higher temperatures,
indicated that the degradation of this functional group was
completed at 500 ꢀC. Moreover, in the range of 200e600 ꢀC, with
the increase in the temperature, the decrease observed in the
number and intensities of the eC]Ce (1500 cmꢂ1) stretching and

N. Yılmaz Baran et al. / Journal of Molecular Structure 1123 (2016) 153e161
159
Fig. 4. XRD patterns of 4-MMAP and P(4-MMAP).
Fig. 5. TG ( ) and DTG ( ) curves of 4-MMAP and P(4-MMAP).
aliphatic eCeH bending vibrations (1370 cmꢂ1) support the results
obtained from the thermal analysis curves. In the third degradation
step of P(4-MMAP), the 18.6% weight loss can be attributed to the
degradation of the phenol group in the temperature range
767e1000 ꢀC. This was also proven by the preservation of the peaks
belonging to eOH, CeO vibrations and aromatic eC]Ce stretching
around 800 ꢀC.
activated behavior’, in the literature [33]. It can be explained by the
increase in the charge transfer efficiency between the polymer
chains and the mobility of I3 dopant anions with temperature
[16,33].
3.9. Antimicrobial properties
3.8. Doping with iodine
Schiff base monomers and polymers containing active hydroxyl
groups are known to inhibit enzyme production [34]. The inacti-
vating process takes place by inhibiting free OH groups which is
necessary to show the activity of the enzyme due to having both N
and O donor structures [34]. For this reason, the usability of 4-
MMAP and P(4-MMAP) as antimicrobial agents was investigated.
The bactericide and fungicide activities of them were tested against
six bacteria and two yeasts using the conventional well diffusion
method [25]. S. lutea, E. aerogenes, E. coli, E. faecalis, K. pneumonia
and B. subtilis as well as C. albicans and S. cerevisiae were selected as
the bacteria and yeasts, respectively and the test results are pre-
sented in Table 3. As can be seen from the table, 4-MMAP showed
strong antibacterial activity against all the tested bacteria, apart
from E. coli. Whereas, P(4-MMAP) was active against the following
bacteria: S. lutea, K. pneumoniae and B. subtilis. Additionally, it was
detected that 4-MMAP demonstrated antifungal activity against
S. cerevisia, while P(4-MMAP) did not show any activity against the
It has been reported in the literature that the doping process of
the Schiff base polymers occurs with the coordination of the highly
electronegative N atoms of the polymers with iodine molecules
[21,32].
The conductivity values calculated using resistivity values
measured of the P(4-MMAP) before and after doping with iodine
vapor for up to 48 h were monitored for the temperatures of 20, 40
and 60 ꢀC (Fig. 6). While the initial conductivity of the polymer was
5 ꢁ 10ꢂ11 Scmꢂ1, the conductivity values were measured to be
7.30 ꢁ 10ꢂ6, 15.5 ꢁ 10ꢂ6 and 7.8 ꢁ 10ꢂ5 Scmꢂ1 after doping for
48 h at 20, 40 and 60 ꢀC, respectively. It can be seen from figure that
the conductivity of the P(4-MMAP) increased remarkably with the
increase in doping time at each temperature, but then stabilized.
The increase in the conductivity with temperature is typical for
conductive polymers, and this situation is defined as ‘thermally

160
N. Yılmaz Baran et al. / Journal of Molecular Structure 1123 (2016) 153e161
semiconductive material. According to the antimicrobial test re-
sults, P(4-MMAP) also has potential to be used as an antibacterial
agent.
Acknowledgments
We would like to thank to Dr. Ashabil AYGAN (Kahramanmaras¸
_
Sütçü Imam University, Faculty of Science and Arts, Department of
Biology, Kahramanmaras¸ , Turkey) for his help on antimicrobial
tests. In addition to, we are grateful to the Ankara University
Research Funds for the financial support of this work (Project No.
13B4240008).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.molstruc.2016.06.028.
Fig. 6. The change in conductivity of P(4-MMAP) as function of temperature and time
during doping with iodine.
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