Synthesis, characterizations, and liquid crystalline property of photoresponsive poly (2-[4-methoxy benzoyl styryloyloxy] ethyl methacrylate)

Article abstract of DOI:10.1080/15421406.2011.611734

A novel liquid crystalline mesophase as well as photoreactive property of photo-cross-linkable liquid crystalline polymer has been studied in detail. The crosslinkable liquid crystalline polymer was synthesized by newer route and its structure has been characterized by ¹H and ¹³C-Nuclear Magnetic Resonance, Fourier Transformation Infrared, and ultraviolet spectral studies. The photocrosslinking property was studied by using both ultraviolet and fluorescence spectral techniques. The thermogravimetric analysis was used to determine the thermal stability of the polymer. Molecular weight of the polymer was determined using gel permeation chromatography technique. The grainy texture mesophase of the polymer was identified by Differential Scanning Calorimeter thermogram and also from the hot stage optical polarization microphotograph images, and all the results obtained were discussed. The morphology of the polymer network was observed using scanning electron microscopy before and after photocrosslinking process.

Full text of DOI:10.1080/15421406.2011.611734

This article was downloaded by: [Universitat Politècnica de València]
On: 15 October 2014, At: 03:11
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Molecular Crystals and Liquid Crystals
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gmcl20
Synthesis, Characterizations, and Liquid
Crystalline Property of Photoresponsive
Poly (2-[4-Methoxy Benzoyl Styryloyloxy]
Ethyl Methacrylate)
a
a
G. Kumar & K. Subramanian
a
Department of Chemistry , Anna University , Chennai , India
Published online: 27 Dec 2011.
To cite this article: G. Kumar & K. Subramanian (2012) Synthesis, Characterizations, and Liquid
Crystalline Property of Photoresponsive Poly (2-[4-Methoxy Benzoyl Styryloyloxy] Ethyl Methacrylate),
Molecular Crystals and Liquid Crystals, 552:1, 158-173, DOI: 10.1080/15421406.2011.611734
To link to this article: http://dx.doi.org/10.1080/15421406.2011.611734
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“
Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Mol. Cryst. Liq. Cryst., Vol. 552: pp. 158–173, 2012
Copyright © Anna University
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.611734
Synthesis, Characterizations, and Liquid Crystalline
Property of Photoresponsive Poly (2-[4-Methoxy
Benzoyl Styryloyloxy] Ethyl Methacrylate)
∗
G. KUMAR AND K. SUBRAMANIAN
Department of Chemistry, Anna University, Chennai, India
A novel liquid crystalline mesophase as well as photoreactive property of photo-cross-
linkable liquid crystalline polymer has been studied in detail. The crosslinkable liquid
crystalline polymer was synthesized by newer route and its structure has been charac-
1
13
terized by H and C-Nuclear Magnetic Resonance, Fourier Transformation Infrared,
and ultraviolet spectral studies. The photocrosslinking property was studied by using
both ultraviolet and fluorescence spectral techniques. The thermogravimetric analysis
was used to determine the thermal stability of the polymer. Molecular weight of the
polymer was determined using gel permeation chromatography technique. The grainy
texture mesophase of the polymer was identified by Differential Scanning Calorimeter
thermogram and also from the hot stage optical polarization microphotograph images,
and all the results obtained were discussed. The morphology of the polymer network
was observed using scanning electron microscopy before and after photocrosslinking
process.
Keywords Differential scanning calorimetry (DSC); hot stage optical polarized mi-
croscopy (HOPM); irradiation effects; liquid crystals; thermal properties
1. Introduction
A side chain liquid crystalline polymer (SC-LCP) comprises a polymer backbone, a meso-
genic unit, and a flexible spacer in which the mesogenic unit and the polymer backbone
are bridged together. Based on mesogen attached to the polymer backbones, SC-LCPs can
be categorized into either “side-end-fixed” or “side-on-fixed” type [1,2]. Liquid crystalline
polymers have generated considerable interest in recent years and the photo-cross-linkable
LCPs have driven special attention if they contain both mesogen and photoactive groups
in their structure [3–7]. Mesogens incorporate liquid crystalline (LC) properties to the
polymer and photoreactive group facilitates cross-linking of the chain under the influence
of UV light radiation. These types of polymers were useful in fabricating anisotropic net-
works and thin films, information storage devices [8], non-linear optical (NLO) devices
[9,10] aligned membrane for permeation of gases and drugs, etc. [11]. The liquid crys-
talline property of polymers depends on the nature of the polymer backbone, type of the
mesogen, the flexible spacer and its length, and nature of the terminal groups [12–16].
Among many promising photo-cross-linkable groups, the chalcone group has been well
∗
Address correspondence to K. Subramanian, Department of Chemistry, Anna University,
yC ah he on on . ac io- m6 00 025, India. Tel: 044-22358660; Fax: +91-44-22200660. E-mail: kathsubramanian@
158

Liquid Crystalline Property of Photo-Cross-Linkable Poly (MBSOEMA)
159
recognized and can be incorporated in photo-cross-linkable side chain polymers. The effect
of photocrosslinked chalcone moiety on the stability of photochromism was investigated
intensively [17–19]. A chemically different approach to convert a soluble material into an
insoluble material can be achieved by using photocrosslinking reaction. This technique has
been well established in the coatings industry and in photoresist technology. The resulting
crosslinked polymer layers are insoluble and not meltable [20]. The polymers that carry
dual properties of both liquid crystalline and photocrosslinking seem to be indispensable
material in NLO applications [21].
The present paper reports a hitherto unreported newer route of Photoresponsive LCP
containing chalcone moiety, which is responsible for photocrosslinking without photosen-
sitizer in the presence of UV irradiation.
2. Experimental
2.1. Materials
4-Formyl benzoic acid (FBA), methoxy acetophenone, and benzoylperoxide (BPO) were
obtained from Sisco Research Laboratories (SRL) and 2-hydroxy ethyl methacrylate
HEMA) was obtained from Fluka (Switzerland) and used without further purification. For
(
making thin layer chromatography (TLC), silica gel-coated aluminum sheet from Merck
was used.
2.2. Instruments
The Furier Transformation Infrared (FTIR) spectrum of polymer was recorded on Perkin
Elmer FT-IR Spectrometer RXI. The specimen was prepared in the pellet form using KBr.
1
H-Nuclear Magnetic Resonance (NMR) spectroscopic measurement was recorded with
Bruker MSC 300 spectrometer. Thermal stability of polymer was investigated by ther-
mogravimetric analysis using NETZSCH STA 409 C/CD. The number average molecular
weight (Mn) and weight average molecular weight (Mw) of the polymer were determined
by PL-GPC 650. Glass transition temperature of polymer was measured from differential
scanning calorimeter (DSC) NETZSCH DSC 204. The photocrosslinking studies have been
done by Perkin Elmer Lambda 35 UV-visible spectrometer. The fluorescence spectrum of
the polymer has been recorded in FluroMax 2.0. The texture of the prepared sample was
studied by Euromax polarizing microscope equipped with a Linken HFS91 heating stage.
The sample was prepared by a small quantity of the material being melted between two
thin glass cover slips to get uniform film and anisotropic behavior observed by heating and
cooling with Kodak film.
2.3. Synthesis
2.3.1. 4-methoxy phenyl-4-carboxylic styryl ketone (MPCSK). Methoxy acetophenone 6 g
(0.04 mol) and 4-formyl benzoic acid 6 g (0.04 mol) were dissolved in 50 mL of ethanol. A
solution of NaOH was prepared by adding 1.6 g of NaOH in 20 mL of distilled water. The
NaOH solution was added drop wise to the above mixture with constant stirring at room
◦
temperature (27 C) and stirred over night. The reaction mixture was poured into ice water
and neutralized with 2 M HCl to form precipitate, which was then filtered and washed with
distilled water several times. The crude product was recrystallized from ethanol to obtain
◦
yellow crystalline product (1) and it was dried under vacuum at 50 C (yield: 70%–75%). The
structure of MPCSK was identified by elemental analysis, IR, and proton NMR techniques.

160
G. Kumar and K. Subramanian
4
000
3500
3000
2500
2000
1500
1000
500
−
1
Wave number (cm )
Figure 1. FT-IR spectrum of 4-methoxy phenyl-4carboxylic styryl ketone (MPCSK).
Elemental Analysis Calculated for C17H14O4: C, 72.33%; H, 4.99%. Found: C, 72.21%;
−1
H, 4.94%; IR (KBr, cm ) (Fig. 1): 1511, 1535 (aromatic ring); 1605 and 1678 (olefinic
CH CH ); 3437 (OH stretching of COOH); 1678 (>C O); 2837 (C H out of plane
1
bending): H-NMR (CDCl3, TMS) (Fig. 2): 10.1 (acidic OH); 6.8–8.2 (8H, aromatic);
5.8 and 6.1 (2H, CH CH ); 4.5(3H, OCH3).
Figure 2. NMR-spectrum of 4-methoxy phenyl-4carboxylic styryl ketone (MPCSK).

Liquid Crystalline Property of Photo-Cross-Linkable Poly (MBSOEMA)
161
2.3.4. 2-[4-methoxy benzoyl styryloyloxy] ethyl methacrylate (MBSOEMA). In 250-mL
two-neck flask, predetermined volume of triethyl amine and 2-hydroxy ethyl methacrylate
◦
◦
were dissolved in tetrahydrofuran (THF) and was allowed to cool between −5 C and 0 C.
The chlorination of MPCSK was carried out as described by Kadokawa et al. [22] to
get the intermediate acid chloride compound 2. After chlorination of MPCSK, benzene
◦
was removed by distillation at 100 C. The intermediate acid chloride compound 2 was
dissolved in THF, then added dropwise for 30 min to the mixture of triethyl amine and
◦
◦
2
-hydroxy ethyl methacrylate maintained between −5 C and 0 C with constant stirring.
The above reaction mixture was allowed to stir for overnight and quaternary ammonium
salt was filtered. THF was removed by rotary evaporation; the crude monomer was purified
by column chromatography using 96:4 percentage ratio of hexane and ethylacetate mixture.
The product obtained was dark brown solid of 2-[4-methoxy benzoyl styryloyloxy] ethyl
methacrylate (MBSOEMA) 3 (yield: 49%–50%). The structure of monomer MBSOEMA
was confirmed by elemental analysis, IR, and proton NMR techniques.
Elemental Analysis Calculated for C23H22O6: C, 70.03%; H, 5.62%. Found: C, 69.98%;
−1
H, 5. IR (KBr, cm ) 1690, 1640 (>C O); 1600 (olefinic, CH CH); 1745 (ester, >C O);
2
8
5
960, 2850 (aliphatic, C H); 1381, 1450 ( CH3 bending); 1285, 1165 (C O stretching);
07, 804, 700 (C H, out of plane bending); H-NMR (CDCl3, TMS): 8–6.8 (8H, aromatic);
.5, 6.2 (2H, CH CH ); 1.5 (2H, methylenic proton) 1.3 (3H, CH3).
1
2.4. Polymerization
2.4.1. Poly (2-[4-methoxy benzoyl styryloyloxy] ethyl methacrylate). The predetermined
quantities of MBSOEMA 3, the initiator (5 wt% of monomer), and the solvent THF were
placed in a polymerization tube and the mixture was flushed with a slow stream of nitrogen
◦
for 15 min. Then the tube was closed and placed in an oil bath at 70 C for 48 h, subsequently,
the contents were added to excess methanol to precipitate the polymer. The crude polymer
was purified by redissolving in chloroform and reprecipitated by methanol, filtered, washed
◦
with methanol, and dried under vacuum at 50 C (yield: 55%–60%).
2.4.2. Photoreactive Measurements. The photoreactivity of the prepared polymer was
studied by dissolving the sample in chloroform and irradiated with UV light at 254 nm
using photoreactor kept at a distance of 10 cm from the light source for different time
intervals. After each irradiation period, the UV spectra were recorded using Perkin Elmer
Scanning spectrometer. The rate of disappearance of double bond in photosensitive group
was calculated by the following expression:
Rate of conversion(%) = (A0 − AT /A0 − A∞) × 100,
where A0, AT, and A∞ are absorption intensities due to the >C C< group after the
irradiation time t = 0, t = T, and t = ∞ (maximum irradiation time), respectively.
2.4.3. Liquid Crystalline Characterization of Monomeric and Polymeric Liquid Crystals.
The liquid crystalline property of both monomer 2-[4-methoxy benzoyl styryloyloxy] ethyl
methacrylate and poly (2-[4-methoxy benzoyl styryloyloxy] ethyl methacrylate) (polymer
4) were characterized by DSC NETZSCH DSC 204 and polarizing microscope equipped
with Linken HFS91 heating stage. The DSC thermogram shows mesomorphic transitions
of monomer and polymer. It was inferred from the DSC thermogram that two endother-
mic transitions were observed on heating the sample that revealed the transition at lower

162
G. Kumar and K. Subramanian
◦
◦
temperature due to melting temperature (Tm) at 75 C and higher temperature at 174 C for
grainy mesophase to isotropic transition (Ti). The ethyl methacrylate present on the ter-
minal position of the monomer plays an important role in transition temperature. Polymer
◦
◦
4
showed melting temperature (Tm) at 80 C and isotropic transition (Ti) at 208 C. The
Tm and Ti values of polymer were higher than the monomer. HOPM photographs of both
◦
monomer and polymer are shown in Figs. 12(a–d). The monomer shows Tm at 73 C (Fig.
◦
1
2(a)) and isotropic (Ti) from grainy mesophase occurs at 171 C (Fig. 12(b)), whereas
polymer showed Tm at 84 C and isotropic from grainy-like mesophase was observed at
◦
◦
2
10 C.
3. Results and Discussion
3.1. Synthesis
The photoresponsive liquid monomer and polymer were prepared by attaching ethylene
spacer with photo-cross-linkable chalcone moiety as outlined in Schemes 1 and 2. The
mesogenic and photoreactive chalcone moiety 1 was prepared by reacting 4-formyl benzoic
acid with methoxy acetophenone in ethanol in the presence of NaOH as base. The ethylene
spacer group was attached with chalcone moiety 1 by reacting 2-hydroxy ethyl methacrylate
◦
◦
(
3
HEMA) in THF in the presence of triethyl amine from −5 C to 0 C to obtain monomer
. The photoresponsive LCP 4 was synthesized by a mixture of predetermined amount
of monomer with BPO (5% mol ratio of monomer) in THF at 70 C. The polymerization
◦
o
O
NaOH
CHO
+
H
3
C
C
O
O
CH
3
CH
CH
c
HOOC
OCH3
HO
Ethanol
1
SOCl2
Benzene
CH
o
c
CH
Cl
C
O
OCH3
2
THF/Et N HEMA
3
CH3
O
C
CH
2
C
O
CH2
CH2
O
C
CH O
3
C
CH
CH
O
O
3
Scheme 1. Synthesis of monomer MBSOEMA.

Liquid Crystalline Property of Photo-Cross-Linkable Poly (MBSOEMA)
163
CH3
O
C
CH
2
C
C
O
CH2 CH2
O
CH O
C
O
CH
CH
3
O
O
C
O
C
CH
2
O
CH2 CH2
O
C
CH O
C
O
CH
CH
3
n
CH3
4
Scheme 2. Polymerization of MBSOEMA.
was carried out for 48 h. The above contents were poured into methanol and filtered. The
1
13
structure of LCP was confirmed by FT-IR, H-NMR, and C-NMR spectroscopy. The
weight and number average weight of polymer were determined by the gel permeation
chromatography (GPC) technique.
3.2. Solubility Studies
The solubility of the prepared polymer was tested in various solvents. It was soluble in polar
aprotic solvents such as dimethyl formamide, dimethyl sulphoxide, N-methylpyrrolidiene,
dioxane, THF, and chlorinated solvents such as chloroform, dichloromethane, and
chlorobenzene. It was insoluble in methanol, ethanol, 2-propanol, and hydrocarbons such
as toluene, benzene, and n-hexane.
3.3. FT-IR Spectrum of Polymer
−
1
Figure 3 shows the FT-IR spectrum of polymer 4. The absorption bands at 2930 cm
−1
and 1422 cm are due to CH2 CH2 group. The aromatic >C C< stretching was
−1
−1
observed at 1510 cm . The olefinic double bond shows characteristic bands at 1605 cm .
−1
The methoxy group shows absorption stretching at 2930 cm . The C H out of plane
bending of aromatic nuclei occurred at 776 cm and 834 cm . The C O stretching of
ester was observed between 1200 cm and 1077 cm . The carbonyl stretching occurred
−1
−1
−1
−1
−
1
at 1689 cm .
1
3
.4. H-NMR Spectra of Polymer
1
The H-NMR spectrum of polymer 4 is shown in Fig. 4. The polymer shows signals between
6.8 ppm and 8.2 ppm due to aromatic protons. The assignable ethylenic proton of chalcone
unit of polymer was obtained at 5.8 ppm and 6.2 ppm as doublet. Signal appeared at

164
G. Kumar and K. Subramanian
4000
3500
3000
2500
2000
1500
1000
500
−1
Wavenumber (cm )
Figure 3. FT-IR spectrum of poly (MBSOEMA).
.5 ppm due to methylenic protons. Signals at 3.8 ppm and 4.2 ppm were due protons in
3
the CH2 CH2 group and terminal methoxy group. Signals at 1.03 ppm and 2.1 ppm
were due to methyl and methylenic protons of polymeric backbone.
3
.5. 13C-NMR Spectra of Polymer
The proton-decoupled 13C-NMR spectrum of poly (MBSOEMA) is shown in Fig. 5. The
ketone carbonyl carbon resonance is observed at 189.5 ppm due to the presence of extended
conjugations. The signals at 176.2 ppm are due to ester carbonyl carbon. The resonance of
Figure 4. 1H-NMR of poly (MBSOEMA).

Liquid Crystalline Property of Photo-Cross-Linkable Poly (MBSOEMA)
165
Figure 5. 13C-NMR spectrum of poly (MBSOEMA).
aromatic carbons shows signals at 122, 160.5, and 118 ppm. The olefinic carbon signal was
observed at 143.5 ppm. The backbone methylene and methyne carbon show signals at 52.5
and 45 ppm, respectively. The methoxy carbon resonates at 58.7 ppm. The α-methyl carbon
appears at 18.9 ppm. The ethyl carbons in the polymeric unit show resonating signals at
50.5 ppm.
3.6. Thermal Study of the Polymer
Thermogravimetric analysis (TGA) of the polymer was carried out under nitrogen atmo-
◦
◦
sphere in the temperature range of 20 C–600 C in order to investigate the thermal stability
of the polymer. The TGA of the polymer is shown in Fig. 6. The homopolymer undergoes
◦
◦
single stage thermal decomposition between 225 C and 475 C with the weight loss of
9
◦
0%. The initial decomposition temperature (IDT) of polymer starts at 225 C. Due to the
presence of ethylene spacer in the polymer backbone and pendant unit of chalcone showed
◦
◦
weight loss of 50% and 75% at 390 C and 437 C, respectively. The thermal decomposition
was almost completed at 450 C.
◦
3.7. Molecular Weight
The number and weight average molecular weight of polymer 4 were determined by
PL-GPC 650. The (Mn) and (Mw) values were 89,300 and 135,700 g/mole, respectively.
The molar mass distribution of polymer given by polydispersity index (PDI) value was
1.52. The theoretical values of PDI for polymer produced by radical combination and

166
G. Kumar and K. Subramanian
disproportionate were 1.5 and 2.0, respectively. The PDI value of photo-cross-linkable
liquid crystalline polymer (PCLCP) was found to be 1.51 from the values of Mn and Mw,
which suggests the strong tendency of chain termination by radical combination rather than
disproportionation.
3.8. Photocrosslinking Properties
The photocrosslinking studies were carried out to study the changes occurred in the polymer
during UV irradiation, which indicates photoresist nature of the polymer. The polymer
solution was prepared in the concentration range of 10–20 mg/L using chloroform. It was
irradiated with UV light of 254 nm and the photocrosslinking ability of the polymer was
followed by the rate of disappearance of the C C bond of photosensitive group in the UV
spectrum. The photocrosslinking behavior of polymer 4 is shown in Scheme 3. The change
in the absorption peak of polymer 4 is illustrated in Fig. 7. It is seen that the polymer
O
C
O
C
O
CH2 CH
2
O
C
CH
2
CH O
C
O
CH
CH
3
n
CH
3
CH3
C
+
O
OCH
3
O
C
CH
CH
C
CH
2
O
C
O
CH2
CH2
n
O
UV IRRADIATION
3
H CO
R
C
O
O
C
R
O CH
3
PHOTO DIMERIZATION
O
C
O
C
R :
O
CH2 CH
2
O
C
CH
2
n
CH
3
Scheme 3. Photocrosslinking of poly (MBSOEMA).

Liquid Crystalline Property of Photo-Cross-Linkable Poly (MBSOEMA)
167
Figure 6. TGA analysis of poly (MBSOEMA) (Color figure available online).
containing chalcone moiety directly attached shows maximum absorption at 318 nm. The
rapid photcrosslinking may be due to resonance effect produced by electron releasing
methoxy group present in the pendant chalcone unit of polymer 4. The photocrosslinking
∗
ability of polymer 4 was accelerated faster than π-π transition of pendant methoxy styryl
Figure 7. UV-Irradiation of poly (MBSOEMA) at various time intervals in chloroform solution.

168
G. Kumar and K. Subramanian
120
100
8
0
0
0
0
6
4
2
0
0
20
40
60
80
100
120
140
160
180
200
Irradiation time (S)
Figure 8. The disappearance rate of olefin double bond in the pendant chalcone unit with irradiation
time.
group, which is evident from the appearance of isobestic point at 290 nm. The absorption
intensity decreased rapidly with increasing irradiation time and band disappeared almost
completely within 3 min of irradiation. The decrease in the UV absorption intensity is due
to the crosslinking of polymer through 2π + 2π cyclodimerization of CH CH group
of methoxy styryl group and leads to the formation of cyclobutane ring [23–25]. The photo-
cross-linkable liquid crystalline homo polymer is insoluble in polar aprotic and chlorinated
solvents, in which it was soluble before irradiation. The rate of disappearance of olefinic
double bond in the pendant chalcone unit with irradiation time is shown in Fig. 8. Thus, the
poly (MBSOEMA) with pendant chalcone moiety has a higher rate of photocrosslinking,
even in the absence of sensitizers, leading to insolubility of the polymer. It is expected that
this type of polymer might be useful as a negative photoresist for various applications.
3.9. Fluorescence Spectral Study
The photoresponsive nature of polymer 4 evidenced by fluorescence spectra is shown in
Fig. 9. The fluorescence study of polymer was carried out by irradiation of the polymer
in chloroform solution at 254 nm. The polymer was excited at a wavelength of 300 nm.
Polymer 4 shows emission between 320 nm and 570 nm. It was observed from Fig. 9
that the fluorescence intensity showed drastic decrease after 10 s of irradiation and the
decrease was continuous. This is because the electron releasing OCH3 group (donor)
facilitates faster photocrosslinking and destroy the π−electron conjugation due to 2π
+
2π cycloaddition reaction. The decrease in intensity continues until the formation of
cyclobutane ring [26]. The fluorescence study reveals the indispensable use of polymer 4
in photoresist applications.

Liquid Crystalline Property of Photo-Cross-Linkable Poly (MBSOEMA)
169
Figure 9. Fluorescence spectra of the poly (MBSOEMA).
Figure 10. (a) SEM image of virgin polymer sample; (b) SEM image of photocrosslinked polymer.

170
G. Kumar and K. Subramanian
Figure 11. DSC thermogram of monomer and polymer.
3.10. Scanning Electron Microscopy (SEM)
The SEM technique can give high resolution images, which enables the visualization of
morphological information without losing any accuracy during analysis. The synthesized
photo-cross-linkable LCP poly (MBSOEMA) was irradiated with UV light of 254 nm for
30 min. The SEM analysis was carried out for both virgin polymer and photocrosslinked
polymer samples. Figures 10(a) and (b) show morphology of virgin and photocrosslinked
polymer samples, respectively. As observed from the SEM images in Figs. 10(a) and (b), the
photocrosslinked polymer sample confirms loosely held dispsersion of polymeric materials,
while virgin polymer exhibits compact stringent dispersion of polymeric surface.
3.11. Liquid Crystalline Properties
The development of photosensitive media based on liquid crystalline compounds for data
recording, optical storage, and reproduction is one of the most rapidly developing areas in
the physical chemistry of low molecular mass and polymer liquid crystals [27]. The rigidity
of the mesogenic core, the flexible spacer length, and terminal units highly influence
the molting temperature, mesophase temperature, and even molecular arrangement. The
polymer shown in Scheme 2 is rod-like molecules and contain highly polar hindered
Table 1. Thermal and liquid crystalline properties of monomer and polymer
◦
◦
DSC ( C)
HOPM ( C)
◦
Sample
Mesophase
Tg ( C)
Tm
Ti
ꢀT
Tm
Ti
ꢀT
Monomer
Polymer
Grainy
Grainy
50
53
75
80
174
208
99
122
73
84
171
210
98
126

Liquid Crystalline Property of Photo-Cross-Linkable Poly (MBSOEMA)
171
◦
Figure 12. (a) Monomer shows liquid crystal phase from unidentified phase at 73 C; (b) monomer
◦
shows isotropic transition from grainy-like mesophase at 171 C; (c) poly (MBSOEMA) shows liquid
◦
◦
crystal phase from unidentified phase at 80 C; (d) poly (MBSOEMA) at 208 C shows isotropic
transition from mesophase.

172
G. Kumar and K. Subramanian
pendant group revealed to have high interaction leading to the formation of liquid crystalline
phases [28]. In LCPs, the polymer having rigid mesogen and shorter spacer should show
higher transition temperature [29,30]; the presented novel LCP may show higher transition
temperature due to the above-mentioned reason. The phase transition temperature and
mesophase of this polymer were studied by the DSC thermogram and HOPM images.
Generally, in the DSC thermogram, at the highest transition temperature there will be an
endotherm corresponding to the transition from the LC phase to the isotropic phase. The
transition in some cases from crystal to LC was marked by more than one endotherm. When
such multiple curves were observed, the one having the highest temperature was attributed
to the crystal to mesophase transition. The liquid crystalline properties of monomer and
polymer were characterized by using DSC and HOPM studies. The DSC thermogram of
monomer and polymer (Fig. 11) indicates that two endothermic transitions occurred on
heating the monomer and polymer samples. The monomer sample showed lower transition
◦
◦
at 75 C (Tm) whereas polymer sample showed at 80 C due to unidentified crystal to
◦
◦
crystalline transformation. The higher endothermic transitions occurred at 174 C and 208 C
for monomer and polymer, respectively. These higher endothermic transitions are due to
transformation of grainy-like mesophase to isotropic transition. The thermal and liquid
crystalline properties of monomer and polymer are shown in Table 1. The above recorded
thermogram of monomer and polymer samples were compared with HOPM photographs
◦
shown in Figs. 12(a), (b), (c), and (d). The lower transition (Tm) that occurred at 73 C is
shown in Fig. 12(a); it represents transition from the unidentified phase to the crystalline
◦
phase. Figure 12(b) shows grainy-like mesophase to isotropic at 171 C. In polymer 4, it
◦
shows crystalline phase at 84 C (Tm) and grainy-like mesophase to isotropic transition at
10 C that are shown in Figs. 12(c) and (d). Both DSC and HOPM photographs showed
◦
2
negligible variations in their liquid crystalline properties.
4. Conclusions
The photo-cross-linkable LCP poly (MBSOEMA) was synthesized by free radical poly-
merization in THF using BPO as initiator. The synthesized polymer has been characterized
1
13
by FT-IR, H-NMR, and C-NMR spectroscopy studies. The TGA analysis clearly indi-
cates that the polymer shows good thermal and thermo-oxidative stability. The PDI value
obtained from GPC indicates that the polymerization process was terminated by free radical
recombination. The photocrosslinking study of the polymer was carried out at predeter-
mined time interval by UV irradiation at 254 nm. From the UV study, the photoconversion
of the polymer increases with increasing length of pendant chalcone unit in the polymer
chain. The liquid crystalline property of the polymer was identified from the DSC thermo-
gram as well as from HOPM studies. The UV studies reveal that the polymer may found
application as a photoresist material. Since this polymer exhibits dual property of both
liquid crystalline and photocrosslinking ability, it could be exploited in NLO applications
[31].
Acknowledgments
The authors are thankful to Professor (Dr.) S. Ganesan, Director of Students Affair, Anna
University, Chennai, India, for providing fluorescence and UV spectrophotometer facility
to carry out this research.

Liquid Crystalline Property of Photo-Cross-Linkable Poly (MBSOEMA)
References
173
[
[
[
1] Percec, V., Pugh, C., & McArdle, C. B. (1989). In: Side Chain Liquid Crystal Polymers, 1st ed.,
Chapman and Hall: New York.
2] Magagnini, P. L., Marchetti, A., Matera, F., Pizzirani, G., & Turchi, G. (1974). Eur Polym. J.,
10, 585.
3] Creed, D., Griffin, A. C., Gross, J. R. D., Hoyle, C. E., & Venkataram, K. (1988). Mol. Cryst.
Liq. Cryst., 57, 155.
[
[
[
4] Ikeda, T., Itakura, H., Lee, C., Winnik, F. M., & Tazuke, S. (1988). Macromolecules, 21, 3537.
5] Keller, P. (1990). Chem. Mater., 2, 3–4.
6] Whitecombe, M. J., Gilbert, A., Hiraj, A., & Mitchell, G. R. (1991). J. Polym. Sci. Polym. Chem.,
29, 251–259.
[7] Whitecombe, M. J., Gilbert, A., & Mitchell, G. R. (1993). Br. Polym. J., 34, 1347.
[8] Legge, C. H., Whitcombe, M. J., Gilbert, A., & Mitchell, G. R. (1991). J. Mater. Chem., 1, 303.
[9] Mohlmann, G. R., Van der Vorst, C. P. J. M., & McArdle, C. B. (1989). Side Chain Liquid
Crystal Polymers, 1st ed., Chapman and Hall: New York.
[10] Marturunkakul, S., Chen, I. J., Li, L., Jeng, R. J., Kumar, J., & Tripathy, S. K. (1993). Chem.
Mater., 5, 592.
[11] Loth, H., & Euschem, A. (1988). Makromol. Chem. Rapid Commun., 9, 35.
[12] Hsu, C. S., & Percec, V. (1989). J. Polym. Sci. Polym. Chem. Ed., 27, 453.
[13] Hsu, C. S., Lin, J. H., Chou, L. R., & Hsiue, G. H. (1992). Macromolecules, 2, 7126.
[14] Le Barney, P., Dubois, J. C., Friedrich, C., & Noel, C. (1986). Polym. Bull. (Berlin), 15, 341.
[15] Hsiech, C. J., Wu, S. H., Hsiue, G. H., & Hsu, C. S. (1994). J. Polym. Sci. Polym. Chem., 32,
1077.
[
[
[
[
[
[
[
[
[
16] Wu, Y. H., Lu, Y. H., & Hsu, C. S. (1995). J. Macromol. Sci. Pure Appl. Chem. A, 32, 1471.
17] Choi, D. H., & Cha, Y. K. (2002). Bull. Korean Chem. Soc., 23, 4.
18] Choi, D. H., Oh, S. J., Cha, H. B., & Lee, J. Y. (2001). Eur. Polym. J., 37, 1951.
19] Kim, J. H., Ban, S. Y., Kaihua, S., & Choi, D. H. (2003). Dyes Pigm., 58, 105.
20] Pappas, S. P. (1984). UV Curing Science and Technology, Marketing Corp: Norwalk, CT.
21] Gangadhra, & Kaushal, K. (1995). Macromolecules, 28, 4.
22] Kadokawa, J., Suzuki, T., Iwasaki, Y., & Tagaya, H. (2003). Eur. Polym. J., 39, 985–989.
23] Madeswari, D., Subramanian, K., & Rami Reddy, A. V. (1996). Eur. Polym. J., 32, 417.
24] Rami Reddy, A. V., Subramanian, K., Krishnasamy, V., & Ravichandran, J. (1996). Eur. Polym.
J., 32, 919.
[25] Rami Reddy, A. V., Subramanian, K., & Seshasainath, A. V. (1998). J. Appl. Polym. Sci., 70,
2111.
[
[
[
[
[
[
26] Bobrovsky, A., & Shibaev, V. (2006). Polymer, 47, 4310.
27] Po-Chih Y., Ming-Zu W., & Jui-Hsiang, L. (2008). Polymer, 49, 2851.
28] Gangadhra, & Kaushal, K. (1995). Polymer, 36, 1903.
29] Cheng, S. Z. D. (1988). Macromolecules, 21, 2475.
30] Stephen, Z. D., Cheng, J. J., Janimak, A. Z., & Zhenglong Z. (1989). Macromolecules, 22, 4240.
31] Gangadhra, & Kaushal K. (1995). Macromolecules, 28, 4.