Poly(azomethine-epoxy-ether) containing phenyl and etoxy moieties: synthesis, characterization and fluorescence property

Article abstract of DOI:10.1007/s11696-018-0525-4

The design and synthesis of poly(azomethine-epoxy-ether) (PAZ-EP) containing epoxide moiety was described. The purpose of the research was the improvement of poly(azomethine-ether) containing epoxide by introduction of Schiff base moiety. PAZ-EP was synthesized using epichlorohydrin (EP). The structure of the Schiff base (SB) and PAZ-EP were verified by FT-IR, ¹H-NMR, ¹³C-NMR and UV–Vis spectroscopic analyses. Further characterization was employed using photophysical, electrochemical and fluorescence (PL) measurements. Application of TGA and differential scanning calorimetry analyses revealed thermal stability and thus propose a thermal processibility, which makes them potential materials for many contemporary practices. The number of average molecular weight of polymer with a polydispersity index of 1.14 was found to be 6750?Da using a gel permeation chromatography instrument. The highest occupied–lowest unoccupied energy levels and electrochemical (Eg′) band gap values of PAZ-EP were determined by cyclic voltammetry (CV) measurement. Scanning electron microscopy (SEM) images were illustrated at different magnifications to study the morphologic property of PAZ-EP.

Full text of DOI:10.1007/s11696-018-0525-4

Chemical Papers
https://doi.org/10.1007/s11696-018-0525-4
ORIGINAL PAPER
Poly(azomethine‑epoxy‑ether) containing phenyl and etoxy moieties:
synthesis, characterization and fuorescence property
Feyza Kolcu1,2 · İsmet Kaya1
Received: 20 February 2018 / Accepted: 30 May 2018
© Institute of Chemistry, Slovak Academy of Sciences 2018
Abstract
The design and synthesis of poly(azomethine-epoxy-ether) (PAZ-EP) containing epoxide moiety was described. The purpose
of the research was the improvement of poly(azomethine-ether) containing epoxide by introduction of Schif base moiety.
PAZ-EP was synthesized using epichlorohydrin (EP). The structure of the Schif base (SB) and PAZ-EP were verifed by
FT-IR, 1H-NMR, 13C-NMR and UV–Vis spectroscopic analyses. Further characterization was employed using photophysi-
cal, electrochemical and fuorescence (PL) measurements. Application of TGA and diferential scanning calorimetry analyses
revealed thermal stability and thus propose a thermal processibility, which makes them potential materials for many con-
temporary practices. The number of average molecular weight of polymer with a polydispersity index of 1.14 was found to
be 6750 Da using a gel permeation chromatography instrument. The highest occupied–lowest unoccupied energy levels and
ꢀ
electrochemical (E ) band gap values of PAZ-EP were determined by cyclic voltammetry (CV) measurement. Scanning
g
electron microscopy (SEM) images were illustrated at diferent magnifcations to study the morphologic property of
PAZ-EP.
Keywords Poly(azomethine-ether) · Epichlorohydrin · SEM · Photoluminescence
Introduction
and photonics wherefore their good mechanical properties,
thermal stability and molecular-doping-controlled features
(Iwan and Sek 2008; Sek et al. 2008; Barik and Skene 2011;
Bourgeaux and Skene 2007; Niu et al. 2011; Park et al. 2010;
Işık et al. 2012; Ma et al. 2015; Koole et al. 2016, Marin
et al. 2017; Yeh et al. 2016).
Poly(azomethine) (PAM) containing imine group (C=N) in
the backbone are a potential category of polymers owing
to their high mechanical strength, thermal stability, metal-
chelating ability, liquid crystalline potential and semicon-
ducting electrical properties under doping (Kobzar et al.
2016; Pron and Rannou 2002; Grigoras and Catanescu 2004;
Iwan and Sek 2008; Kumar et al. 2009; Hussein et al. 2012;
Zhang et al. 2014; Ravikumar et al. 2014). PAMs are cru-
cial conjugated polymers attracting the researchers’ interest
for their applications in optoelectronics, electronics, sensors
The synthesis of poly(azomethine)s (PAM)s is achieved
under the traditional path using a polycondensation of
diamine and dialdehyde (Iwan and Sek 2008; Saegusa et al.
1994; Gutch et al. 2001; Grimm et al. 2002; Choi et al. 2004;
Fukukawa et al. 2004; Krebs and Jørgensen 2004; Ishii et al.
2010; Cerrada et al. 1996). The macromolecular chains of
PAMs with high molecular weight precipitated from the
solution have slight solubility in common organic solvents,
which is considered as a major drawback in their practi-
cal applications (Grigoras and Catanescu 2004; Iwan and
Sek 2008; Hussein et al. 2012; Stefanache et al. 2014). Due
to the aforementioned problem, poly(azomethine-ether)s,
poly(azomethine-urethane)s and poly(azomethine-ester)s
included in PAMs have been lately synthesized using sev-
eral techniques (Dutta et al. 2003; Shukla et al. 2003). The
participation of aliphatic units and fexible ether linkages
along the polymer chain provides fractional mobility to the
* Feyza Kolcu
feyzakolcu@comu.edu.tr
* İsmet Kaya
kayaismet@hotmail.com
1
Department of Chemistry, Polymer Synthesis and Analysis
Laboratory, Çanakkale Onsekiz Mart University,
17020 Çanakkale, Turkey
2
Department of Chemistry and Chemical Processing
Technologies, Lapseki Vocational School, Çanakkale
Onsekiz Mart University, Çanakkale, Turkey
Vol.:(0123456789)
1 3

Chemical Papers
polymers and consequently, intensifes their solubility (Gul
et al. 2014; Marin et al. 2006). The incorporation of the
fexible aliphatic segments into poly(azomethine) chains
is indeed a method to induce the occurrence of the liquid
crystalline properties (Grigoras and Catanescu 2004; Hus-
sein et al. 2012; Abid and Al-barody 2014). The azomethine
linkage can be easily obtained in mild reaction conditions
(Nitschke et al. 2017; Kaya et al. 2018).
were provided by Merck Chemical Company (Germany),
and used with no further purifcation.
Synthesis of dialdehyde (DA)
The synthetic procedure for dialdehyde monomer, (DA)
was presented according to the literature (Kaya and Culhao-
glu 2009) in Scheme 1. 4-Hydroxybenzaldehyde, 0.740 g,
0.006 mol) in 30 mL of DMF was placed into 250 mL three-
necked fask provided with a condenser and magnetic stir-
rer, and containing anhydrous sodium carbonate (0.795 g,
0.0075 mol). p-Xylene dibromide (0.792 g, 0.003 mol) dis-
solved in 30 mL of DMF was added into the reaction mixture
under argon atmosphere. The mixture was maintained for 4 h
at 150 °C. As soon as it cooled, the product was transferred
into 200 mL of cold water. After completing the washing
process of the precipitated dialdehyde with 200 mL of water,
it was fltered to separate mineral salts. The product of DA
was recrystallized from methanol and dried in a vacuum
oven for a day at 50 °C.
Epoxy resins are reactive intermediates used to produce a
versatile class of thermosetting polymers. They are charac-
terized by the presence of a three-member cyclic ether group
commonly referred to as an epoxy group, or oxirane. The
largest single use of epoxy resins is in the protective coatings
market where high corrosion resistance and adhesion to sub-
strates are important. Epoxies gain wide acceptance in pro-
tective coatings and in electrical and structural applications
because of their exceptional combination of properties such
as toughness, adhesion, chemical and thermal resistance,
and good electrical properties (Adams and Gannon 1986).
From application point of view, the aim of this study
was to design a poly(azomethine) by a chemical structure
modifcation (introduction of solubility epoxy group as a
side chain) and to see the impacts on the optical, thermal,
morphological and fuorescence properties. The synthesis
of poly(azomethine-epoxy-ether) (PAZ-EP) was divided
into three steps: (1) synthesis of dialdehyde, (2) synthe-
sis of Schiff base containing diol, and (3) synthesis of
For DA Yield 45%; melting point: 166–167 °C; Elemental
analyses results: Calc. (Found): C, 76.28 (76.20); H, 5.23
(5.19). 1H NMR (DMSO-d6, δH ppm): 9.88 (s, 2H, –CHO),
7.87–7.49 (m, 12H, aromatic hydrogens), 5.18 ppm (s,
4H, aliphatic hydrogens); 13C NMR (DMSO-d6, δ ppm):
190.69 (aldehyde –CHO), 163.47–115.29 (aromatic –CH),
70.70 ppm (aliphatic –CH).
1
poly(azomethine-ether) (PAZ-EP). FT-IR, H NMR and
13C NMR analyses were performed for the structural char-
acterization of the products obtained in each step. Thermal
stability and the transition temperatures were analyzed using
thermogravimetric techniques (TG) and diferential scan-
ning calorimetry (DSC), respectively. Optical, photolumi-
nescence (PL) and electrochemical properties were investi-
gated using UV–Vis, fuorescence spectroscopy and cyclic
voltammetry (CV), respectively.
Synthesis of Schif base
To synthesize Schif base (SB), a mixture of DGA (0.314 g,
0.003 mol) and DA (0.519 g, 0.0015 mol) dissolved in
25 mL DMF were placed in a 250 mL three-necked round
bottom-fask provided with a refux condenser and a collec-
tor tube. Reaction mixture was refuxed for 6 h at 105 °C
under argon atmosphere. As soon as it cooled to room
temperature, the Schif base was precipitated, fltered of,
washed by methanol (3× 50 mL) and dried at 50 °C for a
day in a vacuum oven. The synthesis of Schif base was pre-
sented in Scheme 1. The yield was found to be 70%.
Experimental
Materials
Elemental analyses results: Calc. (Found): C, 69.23
(69.05); H, 6.92 (6.85); N, 5.39 (5.32).
4-({4-[(4-Formylphenoxy)methyl]benzyl}oxy)benzalde-
hyde, abbreviated as (DA) was synthesized based on the
previously reported procedure (Kaya and Culhaoglu 2009).
4-Hydroxybenzaldehyde (4-HB), 4-aminophenol (4-AP),
p-xylene dibromide (XB), diglycolamine agent (DGA,
98%) and epichlorohydrin (EP, 99%) purchased from
Sigma-Aldrich Chemical Company (Germany) were used as
received. Methanol, ethanol, chloroform, N,N-dimethylfor-
mamide (DMF), tetrahydrofuran (THF), dimethyl sulfoxide
(DMSO), toluene, acetonitrile, and all other solvents used
For SB FT-IR (cm−1): 3334 υ(–OH), 2922 υ(C–H, aro-
matic), 2840 υ(C–H, aliphatic), 1678 υ(C=O, impurity),
1642 υ(C=N), 1598, 1505 υ(C=C phenyl), 1350 υ(C–N),
1244 υ(C–O, phenyl). 1H NMR (DMSO-d6): δH ppm, 8.23
(s, 2H, –CH=N–), 7.75 (d, J=98 Hz, 4H, He), 7.46 (s, 4H,
Hh), 7.12 (d, J = 78 Hz, 4H, Hf), 5.17 (t, J = 24 Hz, 4H,
Hd), 4.57 (s, 4H, Hg), 3.64 (s, 2H, –OH), 3.46 (t, J=24 Hz,
4H, Hc), 3.42 (t, J=15 Hz, 4H, Hb), 3.36 (t, J=15 Hz, 4H,
Ha). 13C NMR (DMSO-d6): δ ppm, 163.64 (C8), 161.63
(C4), 136.91 (C2), 132.23 (C7), 129.90 (C6), 128.37 (C1),
1 3

Chemical Papers
Scheme 1 Possible mechanism for the synthesis of dialdehyde (DA), Schif base (SB) and poly(azomethine-epoxy-ether) (PAZ-EP)
115.71 (C5), 72.65 (C10), 70.70 (C3), 69.81 (C11), 69.51
(C9), 60.66 (C12).
Elemental analyses results: Calc. (Found): C, 68.75
(68.25); H, 6.94 (6.50); N, 4.86 (4.35).
For PAZ-EP FT-IR (cm−1): 3334 υ(OH), 2944 υ(C–H,
aromatic), 2876 υ(C–H, aliphatic), 1648 υ(C=N), 1601,
1510 υ(C=C phenyl), 1360 υ(C–N), 1241 υ(C–O, phenyl).
1H NMR (DMSO-d6): δH ppm, 8.25 (s, –CH=N), 7.85 (d,
J=12 Hz, He), 7.47 (s, Hh), 7.17 (d, J =12 Hz, Hf), 5.21
(t, J=6 Hz, Hd), 5.12 (s, Hg), 4.74 (d, J=54 Hz, Hk), 4.44
(d, J = 36 Hz, Hm), 3.89 (t, J = 6.0 Hz, Hl), 3.77 (s, 2H,
–OH), 3.61(t, J = 6 Hz, Hc), 3.32 (t, J = 12 Hz, Ha), 3.42
(t, J = 12 Hz, Hb). 13C NMR (DMSO-d6): δ ppm, 163.64
(C8), 162.90 (C4), 136.62 (C2), 132.24 (C7), 130.22 (C6),
128.42 (C1), 115.73 (C5), 78.78 (C18), 78.62 (C15), 72.91
(C10), 71.69(C3), 70.92 (C11), 70.30 (C9), 69.80 (C12),
63.46 (C14, C17), 63.06 (C16), 62.70 (C13).
Synthesis of poly(azomethine‑epoxy‑ether)
(PAZ‑EP)
The synthesis of PAZ-EP is outlined in Scheme 1 and the
synthetic procedure of a diferent type of PAZ-EP was given
in a previous study (Kaya et al. 2011). The epoxidation of the
synthesized Schif base was carried out by refuxing SB and
EP in 1:2 mol ratio placed in a three-necked round-bottom
fask equipped with a condenser, thermometer and dropping
funnel. The reaction mixture was maintained at 40 °C under
nitrogen atmosphere for 1 h followed by raising the reaction
temperature up to 90 °C. A concentrated solution of 50%
NaOH (2 mL) transferred to a dropping funnel was added
to the reaction mixture in 2 h by stirring. The solid product
obtained from a rotary evaporator was dissolved in THF. The
salt was removed by fltering the solution. The excess EP and
THF were separated by distillation under reduced pressure.
The yield of PAZ-EP was found to be 79%. The synthesis of
Schif base is outlined in Scheme 1.
Characterization
To carry out the solubility test in various solvents at room
temperature, 1 mg of sample and 1 mL of solvent were used.
Fourier transform infrared (FT-IR) spectrometry (Perkin
Elmer FT-IR with ATR sampling accessory between wave
numbers of 650 and 4000 cm−1, USA) was employed to
1 3

Chemical Papers
identify the functional groups on the polymer. All samples
electrochemical HOMO and LUMO energy levels and band
ꢀ
1
were dissolved in dimethyl sulfoxide-d6 to obtain H and
gaps (Eg) were estimated from the oxidation and reduction
13C-NMR spectra using Agilent Premium compact FT-
NMR series performing at the range of 600 and 150 MHz,
respectively. As an internal standard, tetramethylsilane was
used in NMR measurements. Elemental analyses of the com-
pounds were carried out by a CHNS (Costech ECS 4010)
analyzer. Gel permeation chromatography–light scattering
(GPC–LS) instrument of Malvern Viscotek GPC Dual 270
max (UK) was employed to perform for the measurements of
the polydispersity index (PDI), the number-average molec-
ular weight (Mn), the average molecular weight (Mw), the
viscosity average molecular weight (Mv) and the Z-average
molecular weight (Mz) with a light-scattering detector (LS)
of a medium 8.00 mm×300 mm Dual column and a refrac-
tive index detector (RID). DMF at a fow rate of 1 mL min−1
was used as eluent including 40 mM LiBr. GPC analysis
was carried out at a column temperature of 55 °C. The cali-
bration of the instrument was completed using a mixture
of polystyrene standards (Polymer Laboratories; the peak
molecular weights, Mp, between 162 and 60,000).
values (Cervini et al. 1997).
PAZ-EP was sprayed on an aluminum surface using a
custom-built electro spinning setup, which consisted of
a 2.5 mL syringe containing the polymer solution. The
polymer solution was driven out of the syringe using an
NE-300 single syringe pump (Pump Systems Inc., USA).
A metal 25-gauge syringe needle (Cole Palmer Ltd., UK)
was attached to the syringe. The needle tip and collect-
ing plate were connected to a high voltage–power supply
(model 73030P, Genvolt Ltd., UK). The applied voltage was
set at 7 kV and fow rate of 1 mL h−1 was used. Distance
between the needle tip and collecting plate was maintained
at 12.5 cm.
Particle morphology was investigated using JEOL JSM
7100F feld emission scanning electron microscopy (FE-
SEM). Sputter coating process was used to create a thin
gold/palladium flm onto the polymer samples.
Ultraviolet–visible (UV–Vis) spectra were recorded to
investigate the optical properties of the synthesized com-
pounds in DMSO using Analytikjena Specord 210 Plus
(United Kingdom) at room temperature. To obtain photolu-
minescence properties of the sample in DMSO, a Shimadzu
RF-5301PC spectrofuorophotometer (Japan) was employed.
Slit width in PL measurements was specifed as 5 nm.
Thermogravimetric and differential thermal analyses
(TG-DTG-DTA) using Perkin Elmer Pyris Sapphire (USA)
were implemented to determine the mass change regarding
thermal degradation for the polymer under nitrogen fow of
200 mL min−1 from ambient temperature up to 1000 °C at a
heating rate of 10 °C min−1. Diferential scanning calorim-
etry (DSC, Perkin Elmer Sapphire) was used to determine
the glass transition temperature (Tg) of the synthesized com-
pounds between 25 and 420 °C under nitrogen atmosphere
on the frst heating run of 10 °C min−1.
Results and discussion
Synthesis and characterization of SB and PAZ‑EP
The synthesized Schif base was in the form of yellow pow-
der, whereas the polymerization of Schif base resulted
in highly viscous yellow colored PAZ-EP, as shown in
Scheme 1. SB was soluble in aprotic polar solvents, DMSO
and DMF in spite of partial solubility in polar solvents, such
as ethanol. SB was insoluble in THF and acetonitrile. Epoxi-
dation yielded an imine polymer PAZ-EP that was soluble
in DMF, DMSO and ethanol, but insoluble in THF. Both
SB and PAZ-EP were insoluble in methanol. In solvent with
the reduced polarity, such as dichloromethane, hexane and
heptane, SB and its imine polymer became insoluble.
The proposed mechanism for the syntheses of SB and
PAZ-EP are given in Scheme 1. In NaOH solution, the
sodium salt attacks the ethylene oxide, resulting in the ring
opening reaction of epoxide. A water molecule comes along
and the negative oxygen swipes a proton from it. This way,
an –OH group appears and NaOH is regenerated. Oxirane
rings are always present as terminal groups.
To investigate electrochemical properties, cyclic voltam-
metry (CV) assessments were performed using a CHI 660C
Electrochemical Analyzer (Texas, USA) at a potential scan
rate of 25 mV s−1 in a dry box flled with argon atmosphere
at room temperature. Silver wire, glassy carbon electrode
(GCE; d=0.3 cm in diameter) and platinum wire were used
as a reference electrode, as a working electrode and as a
counter electrode, respectively. The calibration of electro-
chemical potential of Ag was regulated with respect to the
ferrocene/ferrocenium (Fc/Fc+) couple. The half-wave
potentials (E1/2) of (Fc/Fc+) in 0.1 M tetrabutylammonium
hexafuorophosphate (TBAPF6)/acetonitrile solution are
0.39 and 0.38 V vs. Ag wire and supporting calomel elec-
trolyte, respectively. The voltammetric measurements were
carried out in DMSO/acetonitrile mixture. The
FT-IR spectra of the synthesized Schiff base and its
imine polymer (PAZ-EP) are illustrated in Fig. 1. It is seen
that the characteristic stretching vibrations of imine bond
(C=N) were observed at 1642 and 1648 cm−1 for SB and
PAZ-EP, respectively, proving the creation of azomethine
linkage. The vibration at 1678 cm−1 of SB was attributed
to C=O stretching frequency of DA as impurity which was
removed by washing Schif base by methanol. The peak at
3364 cm−1 was assigned to the O–H stretching mode of
1 3

Chemical Papers
Fig. 1 FT-IR spectra of SB and
PAZ-EP
SB. The stretching frequency for O–H bond was seen as a
broader peak around 3300 cm−1 in the spectrum of PAZ-
EP due to the ring opening reaction of epoxide, as seen in
Scheme 1. The absorption peaks at 2912 and 2944 cm−1
were attributable to the stretching modes of aromatic C–H
bonds present in SB and PAZ-EP, respectively. The ali-
phatic C–H stretching modes were prominently observed
at 2864–2840 cm−1 for SB, shifted to 2944–2876 cm−1 for
PAZ-EP. In FT-IR spectra SB and PAZ-EP, the frequencies
at 1244 and 1241 cm−1 were due to C–O–C vibrations.
1
To identify the structures, H NMR spectra of SB and
PAZ-EP are presented in Figs. 2 and 3, respectively. The res-
onance signals attributed to two imine (–CH=N–) and two
primary –OH protons were observed at 8.23 and 3.64 ppm,
respectively, as seen in Fig. 2. The signal ratio of 14 protons
in the range of 3.64–3.36 ppm, regarding to Ha, Hb, Hc and
–OH, to –CH=N– protons was found to be 14/2. Addition-
ally, the signal ratio of –CH=N– to –OH was found to be
2/2, proving the formation of Schif base. After epoxidation,
1H NMR spectrum of PAZ-EP elucidated that –CH=N– pro-
tons shifted downfeld and were seen at 8.25 ppm (Fig. 3).
The aromatic proton signals of He, Hf and Hh were observed
in the range of 7.75, 7.12 and 7.46 ppm and 7.85, 7.17 and
7.47 ppm for SB and PAZ-EP, respectively. The multiplet
peaks ranging from 3.61 to 3.28 ppm were interpreted as
owing to the presence of aliphatic C–H protons of Ha, Hb
and Hc in Fig. 3. The signal ratio of –CH=N– protons to
–OH proton was found to be 2/1, indicating that two azome-
thine protons were present together with one –OH group
in the unit structure of PAZ-EP. New peaks correspond-
ing to a linkage of epichlorohydrin to SB appeared in the
region of 4.74–3.89 ppm related to Hk, Hl and Hm protons
of epichlorohydrin.
Fig. 2 1H NMR spectrum of SB
at 163.64 ppm in PAZ-EP. The only diference of PAZ-
EP in carbon signals from SB was due to the presence of
ethylene oxide and oxirane rings, as seen in Fig. 5. The
carbon signals attributed to the ring opening reaction of
epoxide were observed at 78.62, 63.46 and 62.70 ppm for
C15, C14 and C13, respectively. These results adequately
indicated the establishment of a linkage between SB and
EP. Three more carbon signals appeared at 78.78, 63.46
Evidently, the existence of carbon signal for azomethine
at 163.64 ppm in Fig. 4 could be ascribed to the formation
of Schif base. The same carbon signal was also observed
1 3

Chemical Papers
solutions. The optical absorption spectra of SB and PAZ-
EP are shown in Fig. 6a. Taking into account the structure
of the chromophoric units, such as multiple bonds (–C=C–,
–CH=N–) and lone pairs of electrons (N, O), generating
a delocalization along the polymer backbone, peak wave-
lengths tend to be shifted toward the long wavelength region
as the conjugated system gets larger. The peaks of π→π*
electronic transition for the aromatic ring and azomethine
(–CH=N–) group in SB and PAZ-EP were observed in the
range of 270–290 nm and 273–314 nm; 290–331 nm and
314–348 nm, respectively. The characteristic absorption of
n →ꢀ* transitions for azomethine (–CH=N) group of the
synthesized SB and PAZ-EP were observed in the range of
332–355 nm and 348–366 nm, respectively. In comparison
to the starting material (SB), it was possible to verify that
the maximum peak at 330 nm for PAZ-EP was red-shifted
with a broadened absorption.
Fig. 3 1H NMR spectrum of PAZ-EP
The optical band gap values (Eg) were calculated using
the formula of Eg=1242/λonset (Colladet et al. 2004) where
λonset, the starting wavelength for the electronic transition
(the onset wavelength) can be identifed by intersection of
two tangents on the absorption edges. Table 1 elucidated that
the synthesized PAZ-EP had lower optical band gap than
that of its Schif base. Eg values calculated for the longer
wavelength absorption maximum and absorption edge were
found to be 3.77 and 3.38 eV for SB and PAZ-EP, respec-
tively, which were close to the band gap values of organic
semiconductors (Liu et al. 2009).
Figure 6b displayed the diference in visible color of PAZ-
EP under room light and UV light. The pale yellow color of
PAZ-EP turned into blue under UV-lamp. The reduction in
the band gap after epoxidation resulted in easier electronic
transition and made PAZ-EP more electro-conductive.
The photoluminescence spectrum of PAZ-EP in DMF solu-
tion is depicted in Fig. 7. The maxima of the photolumines-
cence emission peaks were located in the range of 439–456 nm
with an emission of blue light and 538–556 nm with an emis-
sion of green light as a result of the excitation of PAZ-EP
by UV and visible light, respectively. The emission intensity
changes when the excitation wavelength changes. As depicted
in Fig. 7a, when excited at 370 nm of UV light and 460 nm of
blue light, PAZ-EP emitted blue and green fuorescence light at
455 and 553 nm with photoluminescence emission intensities
of 400 and 221 a.u., respectively. This emission behavior has
been reported in the literature for several polymeric systems.
The origin of this phenomenon is considered to originate from
the broad chain dispersity of the polymeric system studied (Qu
and Shi 2004; Vaganova et al. 2000). In this study, the conju-
gated polymer was considered as bi-chromophoric system and
each unit consisting of diferent conjugation behaved as a dif-
ferent chromophore group. As a result, the light was absorbed
by a multitude of chromophores. In other words, the longer
conjugated chains emitted the light with longer wavelength
Fig. 4 13C NMR spectrum of SB
and 63.06 ppm for C18, C17 and C16, respectively, attrib-
uted to the ethylene oxide present as terminal groups.
GPC chromatogram indicated that Mn, Mw, Mv and Mz of
PAZ-EP were calculated as 5900, 6750, 6800 and 5000 Da,
respectively, with a mono modal particle size distribution.
PAZ-EP had a polydispersity index (PDI) value of 1.14. The
number for the constitutional units in PAZ-EP was found to
be 10 and 12 with respect to the number-average molecular
weight and the average molecular weight, respectively.
Photophysical and electrochemical properties
To have an insight into the electronic structure, photo-
physical properties of SB and PAZ-EP were analyzed using
UV–Vis and photoluminescence spectroscopy in DMF
1 3

Chemical Papers
Fig. 5 13C NMR spectrum of
PAZ-EP
the applied excitation wavelength (Qu and Shi 2004). Since
DA and SB did not show any fuorescence property, imine
bonds and epoxy connections along the polymer chain of PAZ-
EP could be considered as bi-chromophoric units which emit-
ted blue and green lights, respectively. PAZ-EP emitted blue
and green colors when excited at 370 and 460 nm with their
quantum yields of 2.4 and 1.1%, respectively.
Figure 7b shows the time-dependent (0–600 s) fuorescence
measurements depending on excitation of 370 and 460 nm
light. No obvious fuorescence changes were observed within
600 s under the same conditions, demonstrating that PAZ-EP
was stable with respect to 370 and 460 nm of exciting light.
It is noteworthy that the bicolor property made PAZ-EP be
efective for the production of light emitting diodes.
Cyclic voltammograms (CVs) of SB and PAZ-EP in ace-
tonitrile/DMSO mixture as the supporting electrolyte at room
temperature under argon atmosphere were investigated to iden-
tify the highest occupied (EHOMO)–the lowest unoccupied
ꢀ
(ELUMO) energy levels and electrochemical band gaps (Eg)
using the oxidation (Eox) and reduction (Ered) peak potentials
Fig. 6 a Absorption spectra of Schif base (SB) and its polymer
(PAZ-EP) in DMF, b the colors of PAZ-EP under sunlight and UV
light
depended on the following equations (Liu et al. 2001):
(
)
EHOMO = − 4.39 + Eox
,
(1)
(2)
(
)
ELUMO = − 4.39 + Ered
,
(470 nm), whereas the shorter conjugated chains emitted the
light with shorter wavelength (360 nm), and thus the diferent
fuorescence emission colors could be achieved by changing
Eg� = ELUMO − EHOMO
.
(3)
Table 1 Electronic and optical
structure parameters of SB and
PAZ-EP
Eox (eV)
Ered (eV)
HOMO (eV)
LUMO (eV)
λonset (nm)
Eꢀ (eV)
Eg (eV)
g
SB
PAZ-EP
1.512
1.491
−1.244
−1.195
−5.90
−5.88
−3.15
−3.19
329
368
2.76
2.69
3.77
3.38
HOMO highest occupied molecular orbital, LUMO lowest unoccupied molecular orbital, λonset absorbance
wavelength, Egꢀ electrochemical band gap, Eg optical band gap
1 3

Chemical Papers
Fig. 7 a Photographs and the
corresponding maximum emis-
sion spectra of PAZ-EP solution
in DMF. Slit width: 5 nm and
conc.: 10 mg L−1 in all meas-
urements. Photographs were
recorded in PL analysis cell.
b Time-course fuorescence
responses of PAZ-EP
An irreversible peak at both oxidation and reduction areas
was observed for both SB and PAZ-EP. The reduction peak
potentials of –HC=N– via protonation of imine nitrogen
were observed in the range of − 1.19 and −1.24 V for SB
and PAZ-EP. The peaks around 1.49 and 1.51 V were for the
TG-DTG analyses clarifed that thermal degradation of
DA, SB and PAZ-EP took place in two stages as seen in
Fig. 8. As indicated in Table 2, although (DA) and Schif
base had high thermal stability, the imine polymer (PAZ-
EP) showed low thermal resistance, because Ton of DA
and SB were obtained to be 301 and 281 °C, respectively,
whereas PAZ-EP had 127 °C for initial degradation tem-
perature. The temperatures corresponding to 20% of weight
loss (T20) were calculated as 321, 316 and 151 °C, and the
temperatures corresponding to 50% of weight loss (T50)
were fgured out as 355, 522 and 244 °C for DA, SB and
PAZ-EP, respectively. SB decomposed in two steps starting
from the temperature of 213–389 °C with 29.6% of weight
loss then, 30% of weight loss was observed until 1000 °C.
However, PAZ-EP degraded 40% of its initial weight in the
temperature range of 39–216 °C. The second degradation
in the range of 216–362 °C and the third degradation in the
range of 366–1000 °C were analyzed with 36 and 12% of
weight loss, respectively, until the end of the thermal study.
The maximum rate of weight loss (Tmax) values obtained
from the derivative thermogravimetry (DTG) curves were
found to be 342 °C; 303 and 438 °C; 159, 245 and 442 °C,
oxidation of hydroxyl groups (Bilici et al. 2010). According
ꢀ
to Table 1, the values of (Eg) and (Eg) values were found to
be coherent.
Thermal properties
The thermal degradation (TGA-DTG) curves from ambi-
ent temperature to 1000 °C under nitrogen atmosphere are
shown in Fig. 8. The values of the initial degradation temper-
ature for Ton and the residual weight percent at 1000 °C (char
%) are tabulated in Table 2. Based on Fig. 8 and Table 2, Ton
and char % of PAZ-EP were lower than those of SB. This
result indicated that PAZ-EP thermally decomposed more
easily compared to SB since PAZ-EP owned easily cleavable
ether linkages.
1 3

Chemical Papers
Table 2 Thermal degradation values of the synthesized compounds
DA
SB
PAZ-EP
Ton
301
281
127
Tmax
342
321
355
22
162/358
–/–
303, 438
316
522
38
109/359
–/–
158, 245, 442
151
244.8
9.2
140/–
20% weight loss
50% weight loss
char % at 1000 °C
DTA (endo/exo)
DSC [Tg (°C)/ΔCp (J g−1)]
113/1.208
Ton the onset temperature, Tmax maximum weight loss temperature, Tg
glass transition temperature, ΔCp change of specifc heat during glass
transition
observed on DTA curve at the same temperature as an
endothermic peak. Subsequently, the temperature at 359 °C
corresponded to the degradation of imine bond seen as an
exothermic peak on DTA curve.
In addition, the residual weight percent (char %) of DA,
SB and PAZ-EP at 1000 °C were obtained as 22, 38 and
9.2%, respectively. In accordance with foregoing thermal
analyses, it can be said that the synthesized imine polymer is
not thermally stable with respect to its corresponding Schif
base.
Morphological properties
The morphology of PAZ-EP has been conducted by scan-
ning electron microscopy (SEM). The preparation of PAZ-
EP samples was performed using electro spinning system
and vacuum spin coater, respectively. DMF was used to dis-
solve PAZ-EP with a solution concentration of 25 wt% in
electro spinning. SEM views at diferent amplifcations are
shown in Figs. 9 and 10.
Then, SEM views of PAZ-EP demonstrated that parti-
cles were intertwined along the chain, as seen in Fig. 9. The
cohesion property between the particles ofered a stack of
cottons, yielding a viscous yellow color form. The other pro-
cess was to prepare a sample of PAZ-EP covered over a thin
glass using a vacuum spin coater and let to dry in a vacuum
oven at 50 °C for 2 days. Figure 10 denoted that the smooth
surface of PAZ-EP with randomly aligned fat particles was
morphologically diferent from the particles in Fig. 9. This
diference is attributable to the processing variations in pre-
paring the polymer samples for SEM analysis.
Fig. 8 TG/DTG profles for (DA), (SB) and (PAZ-EP) at 10 °C heat-
ing rate in nitrogen atmosphere
indicating that the thermal degradation took place in one
step, two steps and three steps for DA, SB and PAZ-EP,
respectively. The weight loss curve of PAZ-EP with a Tmax
value of 259 °C corresponded to ether linkage, and with
a Tmax value of 442 °C, confrming that –N=CH– group
was breaking at this step (Saegusa et al. 1990; Grigoras and
Antonoaia 2005).
Conclusion
The glass transition temperature (Tg) of PAZ-EP was
studied by (DSC) and was found to be 113 °C. The melting
point observed in DSC curve of SB at 109 °C was clearly
In a summary, PAZ-EP with epichlorohydrin was synthe-
sized using Schif base prepared by combining dialdehyde
and diglycolamine agent. Methods of synthesis and detailed
1 3

Chemical Papers
Fig. 9 SEM views of electro spinning results for PAZ-EP
Fig. 10 SEM views of PAZ-EP prepared as a thin flm
characterization of Schif base and poly(azomethine-epoxy-
ether) were presented. With a combined implementation of
spectroscopic and electrochemical methods, the molecular
structural details of poly(azomethine) containing ether link-
ages were studied in detail. The polymerization of azome-
thine-based compound (Schif base) improved the thermal,
photophysical and morphological properties. The incorpo-
ration of ether linkages and epoxy groups into the polymer
backbone increased the solubility. Although the thermal sta-
bility of the polymer decreased, the optical and the electro-
chemical band gap values decreased via binding epoxies into
the polymer chain. Based on the optical band gap value as in
the case of semiconductors, PAZ-EP could be used in LED
application (Kolcu and Kaya 2016). Fluorescent spectral
studies indicated that PAZ-EP was a comprising model for
a blue-light emitter. Depending on these attractive features,
the synthesized PAZ-EP would improve photophysical prop-
erties with a lower band gap value than that of monomer.
SEM views of electro spinning and spin-coating methods
allowed obtaining diferent morphological properties. Thin
flm obtained by spin coating method showed fat surfaces
with epoxy side chains appeared to be smoother compared to
the view obtained by electro spinning method. Film depos-
ited by electro spinning method resulted in formation of
granules intertwined with other granular particles. Increased
solubility may also open the door to the processing potential
of these materials for applications in polymer composites,
protective coatings and for tuning the physical, thermal, and
electrochemical properties of PAZ-EP. Curing process of
PAZ-EP is under progress to enlighten its impacts on the
thermal, optical and fuorescence properties of the polymer.
Acknowledgements The authors thank Çanakkale Onsekiz Mart Uni-
versity scientifc research project commission for support with the
Project number (Project no.: FBA-2017-1135).
References
Abid KK, Al-barody SM (2014) Synthesis, characterization and liquid
crystalline behaviour of some lanthanides complexes containing
two azobenzene Schif base. Liq Cryst 41:1303–1314. https://doi.
org/10.1080/02678292.2014.919670
1 3

Chemical Papers
Işık D, Santato C, Satyananda B, Skene WG (2012) Charge-carrier
transport in thin flms of π-conjugated thiopheno-azomethines.
Org Electron 13:3022–3031. https://doi.org/10.1016/j.orgel
.2012.08.018
Adams MC, Gannon JA (1986) Epoxy resins. In: Mark HF (ed) Ency-
clopedia of polymer science and engineering, 2nd edn. Wiley,
New York, pp 322–382
Barik S, Skene WG (2011) A fuorescent all-fuorene polyazome-
thine-towards soluble conjugated polymers exhibiting high fuo-
rescence and electrochromic properties. Polym Chem 2:1091–
1097. https://doi.org/10.1039/c0py00394h
Iwan A, Sek D (2008) Processible polyazomethines and polyketanils:
from aerospace to light-emitting diodes and other advanced appli-
cations. Prog Polym Sci 33:289–345. https://doi.org/10.1016/j.
progpolymsci.2007.09.005
Bilici A, Kaya I, Yildirim M, Dogan F (2010) Enzymatic polym-
erization of hydroxy-functionalized carbazole monomer. J
Mol Catal B Enzym 64:89–95. https://doi.org/10.1016/j.molca
tb.2010.02.007
Kaya I, Culhaoglu S (2009) Syntheses, structures and properties of
novel oligo(azomethine ether)s containing or not chlorine atoms in
the main chain. Polimery 54:266–274 (WOS: 000264697600005)
Kaya I, Doğan F, Gül M (2011) A new Schif base epoxy oligomer
resin: synthesis, characterization, and thermal decomposi-
tion kinetics. J Appl Polym Sci 121:3211–3222. https://doi.
org/10.1002/app.33843
Bourgeaux M, Skene WG (2007) A highly conjugated p- and n-type
polythiophenoazomethine: synthesis, spectroscopic, and electro-
chemical investigation. Macromolecules 40:1792–1795. https://
doi.org/10.1021/ma070292p
Kaya İ, Ayten B, Şenol D (2018) Syntheses of poly(phenoxy-imine)s
anchored with carboxyl group: characterization and photovoltaic
studies. Opt Mater 78:421–431. https://doi.org/10.1016/j.optma
t.2018.02.057
Cerrada P, Oriol L, Pinol M, Serrano JL (1996) Alternative
synthetic strategies for Schiff base derived liquid crys-
tal polymers: a comparative study. J Polym Sci Part A
Polym Chem 34:2603–2611. https://doi.org/10.1002/
(sici)1099-0518(19960930)34:13<2603::aid-pola6>3.0.CO;2-S
Cervini R, Li XC, Spencer GWC, Holmes AB, Moratti SC, Friend RH
(1997) Electrochemical and optical studies of PPV derivatives and
poly(aromatic oxadiazoles). Synth Met 84:359–360
Kobzar YL, Tkachenko IM, Bliznyuk VN, Shekera OV, Turiv TM,
Soroka PV, Nazarenko VG, Shevchenko VV (2016) Synthe-
sis and characterization of fuorinated poly(azomethine ether)
s from new core-fuorinated azomethine-containing monomers.
Des Monomers Polym 19:1–11. https://doi.org/10.1080/15685
551.2015.1092007
Choi EJ, Ahn JC, Chien LC, Lee CK, Zin WC, Kim DC, Shin ST
(2004) Main chain polymers containing banana-shaped meso-
gens: synthesis and mesomorphic properties. Macromolecules
37:71–78. https://doi.org/10.1021/ma0348122
Kolcu F, Kaya I (2016) Synthesis and characterization of novel conju-
gated polyphenols of terephthaldehyde derived from symmetri-
cal bis-azomethine groups in the polymer backbone via oxidative
polycondensation. J Macromol Sci A 53:438–451. https://doi.
org/10.1080/10601325.2016.1176445
Colladet K, Nicolas M, Goris L, Lutsen L, Vanderzande D (2004) Low-
band gap polymers for photovoltaic applications. Thin Solid Films
451:7–11. https://doi.org/10.1016/j.tsf.2003.10.085
Koole M, Frisenda R, Petrus ML, Perrin ML, van der Zant HSJ, Ding-
emans TJ (2016) Charge transport through conjugated azome-
thine-based single molecules for optoelectronic applications. Org
Electron 34:38–41. https://doi.org/10.1016/j.orgel.2016.03.043
Krebs FC, Jørgensen M (2004) The efect of fuorination in semicon-
ducting polymers of the polyphenyleneimine type. Synth Met
142:181–185. https://doi.org/10.1016/j.synthmet.2003.08.015
Kumar S, Dhar DN, Saxena P (2009) Applications of metal complexes
of Schif bases—a review. J Sci Ind Res 68:181–187 (WOS:
000264035600001)
Dutta PK, Jain P, Sen P, Trivedi R, Sen PK, Dutta J (2003) Synthesis
and characterization of a novel polyazomethine ether for NLO
application. Eur Polym J 39:1007–1011. https://doi.org/10.1016/
S0014-3057(02)00328-2
Fukukawa K, Shibasaki Y, Ueda M (2004) Photosensitive
poly(benzoxazole) via poly(o-hydroxy azomethine) II. Environ-
mentally benign process in ethyl lactate. Polym J 36:489–494.
https://doi.org/10.1295/polymj.36.489
Grigoras M, Antonoaia NC (2005) Synthesis and characterization of
some carbazole-based imine polymers. Eur Polym J 41:1079–
1089. https://doi.org/10.1016/j.eurpolymj.2004.11.019
Grigoras M, Catanescu CO (2004) Imine oligomers and polymers.
J Macromol Sci Part C Polym Rev 44:131–173. https://doi.
org/10.1081/mc-120034152
Liu W, Lee SH, Yang SZ, Bian SP, Li L, Samuelson LA, Kumar J,
Tripathy SK (2001) Biologically derived photoactive macromo-
lecular azodyes. J Macromol Sci Pure Appl Chem 38:1355–1370.
https://doi.org/10.1081/ma-100108390
Liu P, Wu YL, Pan HL, Li YN, Gardner S, Ong BS, Zhu SP (2009)
Novel high-performance liquid-crystalline organic semiconduc-
tors for thin-flm transistors. Chem Mater 21:2727–2732. https://
doi.org/10.1021/cm900265q
Grimm B, Krüger RP, Schrader S, Prescher D (2002) Molecular struc-
ture investigations on fuorine containing polyazomethines by
means of the MALDI-TOF-MS technique. J Fluor Chem 113:85–
91. https://doi.org/10.1016/s0022-1139(01)00498-5
Ma BB, Zhang H, Wang Y, Peng W, Wang MK, Shen Y (2015) Visual-
ized acid–base discoloration and optoelectronic investigations of
azines and azomethines having double 4-[N,N-di(4-methoxyphe-
nyl)amino]phenyl terminals. J Mater Chem C 3:7748–7755. https
://doi.org/10.1039/c5tc00909j
Gul A, Akhter Z, Siddiq M, Qureshi R, Bhatti AS (2014) Synthesis
and physicochemical characterization of poly(azomethine)esters
containing aliphatic/aromatic moieties: electrical studies comple-
mented by DFT calculation. J Appl Polym Sci 13:40698–40706.
https://doi.org/10.1002/app.40698
Marin L, Cozan V, Bruma M, Grigoras VC (2006) Synthesis and
thermal behaviour of new poly(azomethine-ether). Eur Polym J
42:1173–1182. https://doi.org/10.1016/j.eurpolymj.2005.11.010
Marin L, Bejan A, Ailincai D, Belei D (2017) Poly(azomethine-phe-
nothiazine)s with efcient emission in solid state. Eur Polymer
J 95:127–137. https://doi.org/10.1016/j.eurpolymj.2017.08.006
Nitschke P, Jarząbek B, Wanic A, Domański M, Hajduk B, Janeczek H,
Kaczmarczyk B, Musioł M, Kawalec M (2017) Efect of chemical
structure and deposition method on optical properties of polya-
zomethines with alkyloxy side groups. Synth Met 232:171–180.
https://doi.org/10.1016/j.synthmet.2017.08.011
Gutch PK, Banerjee S, Gupta DC, Jaiswal DK (2001) Poly-Schif
bases. V. Synthesis and characterization of novel soluble fuo-
rine-containing polyether azomethines. J Polym Sci Part A Polym
Chem 39:383–388. https://doi.org/10.1002/1099-0518(20010201)
Hussein MA, Abdel-Rahman MA, Asiri AM, Alamry KA, Aly KI
(2012) Review on: liquid crystalline polyazomethines polymers.
Basics, syntheses and characterization. Des Monomers Polym
15:431–463. https://doi.org/10.1080/1385772x.2012.688325
Ishii J, Tanaka Y, Hasegawa M (2010) Film properties of polyazome-
thines (2). Poly(imide-azomethine)s derived from ester-con-
taining dialdehydes, tetracarboxylic dianhydrides, and a fuori-
nated diamine. High Perform Polym 22:145–148. https://doi.
org/10.1177/0954008309349459
Niu HJ, Kang HQ, Cai JW, Wang C, Bai HD, Wang W (2011)
Novel soluble polyazomethines with pendant carbazole and
1 3

Chemical Papers
triphenylamine derivatives: preparation, characterization, and
optical, electrochemical and electrochromic properties. Polym
Chem 2:2804–2817. https://doi.org/10.1039/c1py00237f
Park Y, Lee JH, Jung DH, Liu SH, Lin YH, Chen LY, Wud CC, Park
J (2010) An aromatic imine group enhances the EL efciency
and carrier transport properties of highly efcient blue emitter for
OLEDs. J Mater Chem 20:5930–5936. https://doi.org/10.1039/
c0jm00581a
isopropylidene group-containing aromatic diamines and phthala-
dehydes. Macromol Chem Phys 195:1877–1889. https://doi.
org/10.1002/macp.1994.021950535
Sek D, Iwan A, Jarzabek B, Kaczmarczyk B, Kasperczyk J, Mazurak
Z, Domanski M, Karon M, Lapkowski M (2008) Hole transport
triphenylamine–azomethine conjugated system: synthesis and
optical, photoluminescence, and electrochemical properties. Mac-
romolecules 41:6653–6663. https://doi.org/10.1021/ma702637k
Shukla U, Rao KV, Rakshit AK (2003) Thermotropic liquid-crys-
talline polymers: synthesis, characterization, and properties of
poly(azomethine esters). J Appl Polym Sci 88:153–160. https://
doi.org/10.1002/app.11618
Pron A, Rannou P (2002) Processible conjugated polymers: from
organic semiconductors to organic metals and superconduc-
tors. Prog Polym Sci 27:135–190. https://doi.org/10.1016/s0079
-6700(01)00043-0
Qu L, Shi G (2004) Crystalline oligopyrene nanowires with multi-
colored emission. Chem Commun 24:2800–2801. https://doi.
org/10.1039/b412638f
Stefanache A, Balan M, Harabagiu V, Aubert PH, Guegan P, Farcas A
(2014) Electro-optical properties of aromatic oligoazomethine/
permethylated alpha-cyclodextrin main-chain polyrotaxanes.
Chem Phys Lett 599:104–109. https://doi.org/10.1016/j.cplet
t.2014.03.027
Ravikumar L, Kalaivani S, VidhyadeviT Murugasen A, Kirupha SD,
Sivanesan S (2014) Synthesis, characterization and metal ion
adsorption studies on novel aromatic poly(azomethine amide)s
containing thiourea groups. Open J Polym Chem 4:1–11. https://
doi.org/10.4236/ojpchem.2014.41001
Vaganova E, Rozenberg M, Yitzchaik S (2000) Multicolor emission in
poly(4-vinyl-pyridine). Gel Chem Mater 12:261–263. https://doi.
org/10.1021/cm990480x
Saegusa Y, Sekiba K, Nakamura S (1990) Synthesis and characteri-
zation of novel 1,3,4-oxadiazole-containing or 1,3,4-thiadiazole-
containing wholly conjugated polyazomethines. J Polym Sci
Part A Polym Chem 28:3647–3659. https://doi.org/10.1002/
pola.1990.080281311
Yeh LC, Huang TC, Lai FY, Lai HG, Lo AY, Hsu SC, Yang TI, Yeh JM
(2016) Synthesis of electroactive polyazomethine and its appli-
cation in electrochromic property and electrochemical sensor.
Surf Coat Technol 303:154–161. https://doi.org/10.1016/j.surfc
oat.2016.03.094
Saegusa Y, Kuriki M, Nakamura S (1994) Preparation and charac-
terization of fuorine-containing aromatic condensation poly-
mers, 4.Preparation and characterization of fuorine-containing
aromatic polyazomethines and copolyazomethines from per-
fuoroisopropylidene group-containing aromatic diamines and/or
Zhang WB, Wang C, Liu G, Wang J, Chen Y, Li RW (2014) Structural
efect on the resistive switching behavior of triphenylamine-based
poly(azomethine)s. Chem Commun 50:11496–11499. https://doi.
org/10.1039/c4cc05233a
1 3