16
W.-L. Lim et al. / Polymer 71 (2015) 15e22
harmonic generation materials in non-linear optics materials [21],
as photorefractive polymers [22], holographic recording materials
and fluorescent probes for sensing of metal ions, biological mac-
romolecules and microenvironment in micelles [21,23]. Besides,
they can be used in manufacturing of industrial products such as
integrated circuits, compact discs, cathode ray tubes and printed
circuit boards [24].
absorption spectra were recorded on Shimadzu UV-2600 UVeVis
spectrophotometer while fluorescence measurements were per-
formed using an LS-55 fluorescence spectrophotometer (Perkin
Elmer) equipped with a plotter unit and a quartz cell (1 cm ꢂ 1 cm).
The samples were prepared by dissolving the polymer in chloro-
form. Photocrosslinking studies were carried out using 6 W high-
pressure Hg lamp (Vilber Lourmat, 365 nm) by placing the poly-
mer solution in chloroform at a distance of 10 cm from the light
source for different time intervals before recording the spectra with
UVeVis spectrophotometer. The morphological studies of the vir-
gin and the photocrosslinked polymers were carried out using
Scanning Electron Microscope (SEM) with the model of Leo Supra
50vp. The transmission electron microscopy images (TEM) were
recorded on Philips CM12 by placing a drop of sample solution
(0.05 mL) onto a copper EM grid. The solubility of the polymers was
examined using 0.2e0.3 mg of sample in 5 mL of different solvents
at room temperature.
To the best of our knowledge, incorporating chalcone, a photo-
sensitive group into poly(azomethine)esters is relatively an unex-
plored area. Hereby, chalcone is introduced into the side chain or
branches of the polymer due to poor solubility resulting from the
rigid-rod nature of chalcone in the polymers backbone [18]. Chal-
cone give rise to the additional features of photocrosslinkable
ability of the polymers, as it affords high sensitivity to UV radiation
besides providing the photoluminescence properties [6,15e17].
This work dealt with the synthesis and characterization of new
class of soluble photosensitive poly(azomethine)esters, bearing
various substituents on the chalcone-based side chain with even
methylene spacers on the main chains. The synthesis approach of
these polymers mainly focused on the various substituents on the
side chain and the spacer length in the backbones which can be
easily varied, thereby allowing the possibility to study their influ-
ence on the thermal, photocrosslinking and photoluminescence
properties of the polymers. The structures of the synthesized
polymers were elucidated using various spectroscopic techniques.
2.3. Synthesis of monomers and polymers
The synthesis steps of all the monomers and polymers were
described in Scheme 1. The percentage yields, elemental data and
spectral data of the monomers and polymers were illustrated in the
Supplementary Material.
3. Results and discussion
2
. Experimental
3.1. Characterizations of PSBH (6e12), PSBL (6e12) and PSBO
2.1. Materials
(6e12)
1
Benzaldehyde, 4-chlorobenzaldehyde, 4-methoxybenzaldeh
The structures of the polymers were elucidated via FTIR, H NMR
and 1 C NMR spectroscopic techniques. The present of strong band
3
yde, 4-hydroxyacetophenone, 5-hydroxyisophthalic acid, 4-hydro
xybenzaldehyde, 1,4-dibromobutane, 1,6-diaminohexane, 1,8-
diaminooctane, 1,10-diaminodecane and 1,12-diaminododecane
were purchased from TCI Chemicals. Potassium hydroxide and
potassium carbonate were obtained from Q-Rec Chemicals and
solvents (ethanol, acetone, benzene, thionyl chloride and chloro-
form) were purchased from Merck Chemicals. All the chemicals
were used as received without further purification.
ꢀ1
at around 1739 cm after the polymerization depicted the func-
tional group of C]O ester, which confirmed the success of poly-
merization [25,26] to form PSBO8 as illustrated in Fig. 1a. The other
two homologous series were found to have similar observations.
The H NMR spectrum of PSBO8 (Fig. 2.) showed the occurrence of
signal broadening, and the complexity of the signals further sub-
stantiated that polymerization was successfully carried out [27].
1
13
The proton decoupled C NMR spectrum of PSBO8 (Fig. 3.)
exhibited the expected peaks for each of the carbon atoms of the
polymer in which the chemical shift of C]O ester appeared at
163.90 ppm and the chemical shift of C]O ketone was assigned at
188.76 ppm [24].
The molecular weights of the resulting polymers were deter-
mined via gel permeation chromatography (GPC). The number
average and weight average molecular weights of the PSBO were
found to be in the range of 2051e4196 and 3502 to 5946, respec-
tively with the polydispersity indexes of 1.42e1.84. PSBL were
found to have number average and weight average molecular
weights in the range 2136e4236 and 3388 to 5425, respectively
with the polydispersity indexes of 1.28e1.70. PSBH have number
average and weight average molecular weights in the range of
2997e5217 and 4061 to 6994, respectively with the polydispersity
indexes around 1.34 to 1.43.
All of the synthesized polymers were found to be insoluble in
alcoholic solvents and some non polar solvents like benzene, n-
hexane and toluene but they were soluble in various organic sol-
vents like chloroform, tetrahydrofuran, dimethylformamide,
dimethylsulfoxide and dichloromethane. The polymers were solu-
ble in most of the organic solvents may be due to the induction of
the flexibility via the spacer chain in the polymer backbone in
addition to the inclusion of bent shaped dicarboxylic acid mono-
mers which then make them more processable and feasible for
various potential applications.
2
.2. Physical measurements
The IR spectra of the monomers and polymers were recorded
using Perkin Elmer 2000-FTIR spectrophotometer in the frequency
ꢀ
1
range of 4000e400 cm
with sample prepared in KBr discs.
Brucker Avance 500 MHz ultrashield spectrometer equipped with
1
13
ultrashield magnets was used to record the H NMR and C NMR
spectra of the synthesized monomers and polymers. Deuterated
3 6
chloroform (CDCl ) and dimethysulphoxide (DMSO-d ) were used
as the NMR solvents and TMS as internal standard. Thin layer
chromatography (TLC) was performed with TLC sheets coated with
silica and spots were visualized under UV light to monitor the
progress of the reaction. Perkin Elmer 2400 LS Series CHNS/O
analyzer was used to carry out the elemental analysis. Thermal
behaviour of the polymers were evaluated via thermogravimetric
analyses (TGA) which were performed with Mettler 851e TGA un-
ꢁ
der nitrogen atmosphere with the heating rate of 10 C/min. Dif-
ferential scanning calorimetry (DSC) analyses of the polymers were
carried out using with Perkin Elmer Pyris 1 Differential Scanning
ꢁ
Calorimeter with the heating and cooling rates of 10 C/min. The
average molecular weights of the polymers were determined by
using Waters Gel Permeation Chromatography (GPC) equipped
with a Waters 1515 Isocratic HPLC Pump and Waters 2414 refractive
index (RI) detector. Polystyrene standards (Polymer Laboratories)
were used for calibration and THF was used as the eluent. UV
Lim, Wan-Leng
