Synthesis, characterization, and properties of thermotropic novel liquid crystal photosensitive polymers containing mesogen and photocrosslinkable group

Article abstract of DOI:10.1080/15421406.2012.657135

A series of side chain liquid crystalline photosensitive polymers containing methyl methacrylate followed by the spacer and chalcone moiety were synthesized and characterized. Monomers, namely 4-[4{biphenyl oxy carbonyl phenyl oxy carbonyl} phenyl carbonyl ethylene phenyl] oxy butyl methacrylate (BOCPOCPCEPOBMA) and 4-[4{1-methoxy phenyl oxy carbonyl phenyl oxy carbonyl} phenyl carbonyl ethylene phenyl] oxy octyl methacrylate (MPOCPOCPCEPOOMA) was synthesized and subsequently polymerized using benzoyl peroxide as an initiator. The chemical structures and purity were characterized by FT-IR, ¹H- NMR, and ¹³C-NMR analyses. The photocrosslinking studies of the polymers were investigated by UV spectroscopy. The rate of crosslinking increased with increase in the length of the methylene chain. The results of differential scanning calorimeter (DSC) analysis confirmed the formation of mesophase in the polymers. Hot stage optical polarized microscopy (HOPM) showed presence of nematic phase for poly (BOCPOCPCEPOBMA) and poly (MPOCPOCPCEPOOMA). Taylor and Francis Group, LLC.

Full text of DOI:10.1080/15421406.2012.657135

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Synthesis, Characterization, and
Properties of Thermotropic Novel
Liquid Crystal Photosensitive
Polymers Containing Mesogen and
Photocrosslinkable Group
Sivakumar Jeyasheela a & Kathavarayan Subramanian a
a Department of Chemistry, Anna University, Chennai, India
Version of record first published: 30 Jul 2012
To cite this article: Sivakumar Jeyasheela & Kathavarayan Subramanian (2012): Synthesis,
Characterization, and Properties of Thermotropic Novel Liquid Crystal Photosensitive Polymers
Containing Mesogen and Photocrosslinkable Group, Molecular Crystals and Liquid Crystals, 562:1,
10-27
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Mol. Cryst. Liq. Cryst., Vol. 562: pp. 10–27, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.657135
Synthesis, Characterization, and Properties
of Thermotropic Novel Liquid Crystal
Photosensitive Polymers Containing Mesogen
and Photocrosslinkable Group
SIVAKUMAR JEYASHEELA AND KATHAVARAYAN
SUBRAMANIAN∗
Department of Chemistry, Anna University, Chennai, India
A series of side chain liquid crystalline photosensitive polymers containing methyl
methacrylate followed by the spacer and chalcone moiety were synthesized and char-
acterized. Monomers, namely 4-[4{biphenyl oxy carbonyl phenyl oxy carbonyl} phenyl
carbonyl ethylene phenyl] oxy butyl methacrylate (BOCPOCPCEPOBMA) and 4-[4{1-
methoxy phenyl oxy carbonyl phenyl oxy carbonyl} phenyl carbonyl ethylene phenyl]
oxy octyl methacrylate (MPOCPOCPCEPOOMA) was synthesized and subsequently
polymerized using benzoyl peroxide as an initiator. The chemical structures and purity
were characterized by FT-IR, 1H- NMR, and 13C-NMR analyses. The photocrosslinking
studies of the polymers were investigated by UV spectroscopy. The rate of crosslinking
increased with increase in the length of the methylene chain. The results of differen-
tial scanning calorimeter (DSC) analysis confirmed the formation of mesophase in the
polymers. Hot stage optical polarized microscopy (HOPM) showed presence of nematic
phase for poly (BOCPOCPCEPOBMA) and poly (MPOCPOCPCEPOOMA).
Keywords Nematic phase; side chain liquid crystalline polymer; thermal properties
Introduction
Liquid crystalline polymers [1,2] have been actively studied recently because of their tech-
nological potential and specific challenges [3–5]. Liquid crystalline polymers are regarded
as materials with promising optical and electro optical properties for potential application
in optical switching and image storage [6]. They are also used to transducer and amplify
bimolecular events into optical outputs that are visible to the naked eye [7–9]. Polymers
having a photo functional group that can be crosslinked by irradiation with ultraviolet
(UV) light or electron beam have attracted much interest in microlithography [10], photo
curable coatings [11], energy exchange materials [12], etc. The combination of unique
optical properties of liquid crystals with photosensitivity provides a great possibility for
the creation of a large variety of photochemical switches that can be used in optics and
opto electronics [13–15]. A flexible photocrosslinkable main chain liquid crystalline poly-
mer consists of mesogenic units separated by flexible alkyl spacers [16 and 17]. The
∗Address correspondence to Kathavarayan Subramanian, Department of Chemistry, Anna Uni-
versity, Chennai 600025, India. Tel.: +914422358660. E-mail: kathsubramanian@yahoo.com
10

Thermotropic Novel LC Photosensitive Polymers
11
polymer backbones of side chain liquid crystalline polymers are primarily polyacrylates,
polymethacrylate, however, because of polyacrylates and poly methacyrlates backbones
their polymer show higher glass transition temperature and higher viscosity. In order to
get a higher mobility of the liquid crystalline phase at moderate temperature to display
mesomorphic properties at room temperature and the flexible spacer are chosen and used
[18]. Thermotropic liquid crystalline polymers have unique combined properties of both
liquid crystal and conventional thermoplastics as shown by their anisotropic mechanical
properties, excellent thermal stability, and chemical resistance. The novel thermotropic
liquid crystalline photoactive polymer may contain stiff mesogenic units containing three
aromatic ring connected by suitable ester linkage [19]. Crosslinking is another effective
approach for enhancing the glass transition and it is frequently assumed to high thermal
stability of polymer system [20–22]. Since methylene spacers bonded to polymers were re-
ported to contribute to liquid crystalline properties and feasibility of crosslinking chalcone
moiety. We planned to synthesis the polymers possessing methylene spacer and chalcone
moiety within built liquid crystals and photo resist characteristics. In this paper, we report
the synthesis and characterization of polymers possessing both liquid crystalline and pho-
tosensitive properties by incorporating methylene spacers and pendant chalcone moiety of
variable chain lengths. Their structures were confirmed by FT-IR, 1H NMR, and 13C NMR
techniques. The differential scanning calorimeter (DSC) analysis was used to verify the
existence of liquid crystalline phase and to confirm the nature of the phase observed by the
hot stage optical polarized microscopy (HOPM). Because of their methylene spacers, they
showed excellent liquid crystalline property and with the pendant chalcone moiety they
exhibit excellent photosensitivity.
HO
C
O
C
O
CH3
H
C
O
OH
+
NaOH
EtOH
HCI
20 - 25OC
HO
C
O
C
O
CH
CH
OH
Scheme 1. Synthesis of chalcone.
Experimental
Materials and Methods
4-carboxy acetophenone, 4-hydroxy benzaldehyde, 4-hydroxy benzoic acid, 4-phenyl
phenol, 4-methoxy phenol, 4-bromobutanol, 8-bromooctanol, triethylamine, and N,Nꢀ-
dicylohexyl carbodimide (DCC) were purchased from a cross chemical Co. from Lancaster
chemical Co. All organic solvents were purchased from Sigma-Aldrich Co. LLC (St. Louis,
MO). Solvents, like dichloromethane, ethanol methanol, tetrahydrofuran (THF), and ethyl

12
S. Jeyasheela and K. Subramanian
HO
C
O
C
O
CH
CH
OH
KI / K2CO3
DMF
(CH2)4
Br
OH
HO
C
O
C
OH
CH
CH
(CH2)4
O
O
CH3
C
CH2
CH3
C
THF / TEA
C
O
CH2
CI
C
O
O
(CH2)4
O
OH
CH
CH
C
C
O
O
CH3
O
OH
C
O
DCC,DMAP
DCM
CH2
C
C
O
O
(CH2)4
O
CH
C
CH
C
O
O
C
O
O
O
EMK
BPO
70OC
CH3
C
CH2
n
C
O
O
(CH2)4
O
CH
CH
C
O
C
C
O
O
O
O
Scheme 2. Synthesis of poly 4-[4{1-biphenyl oxy carbonyl}-phenyl oxy carbonyl phenyl carbonyl
ethylene phenyl] oxy butyl methacrylate (BOCPOCPCEPOBMA).

Thermotropic Novel LC Photosensitive Polymers
13
CH3
C
CH2
n
C
O
O
O
(CH2)8
C
O
CH
CH
O
C
O
C
O
O
CH
O
3
Scheme 3. Poly 4-[4{1-methoxy phenyl oxy carbonyl}-phenyl oxy carbonyl phenyl carbonyl ethy-
lene phenyl] oxy octyl methacrylate (MPOCPOCPCEPOOMA).
methyl ketone (EMK), were purified by the usual procedure [23]. Methacryloyl chloride
was synthesized according to the method of stempel et al. [24]. Anhydrous sodium sulphate
was used to dry all organic extracts. Benzoyl peroxide (BPO) was freshly recrystallized
from 1:1 methanol and chloroform.
Synthesis of Precursors
Synthesis of 4-hydroxy styryl-4ꢀ carboxy phenyl ketone (HSCPK). The chalcone was syn-
thesized according to the literature procedure [25]. 4-Carboxy acetophenone (0.07 mol)
was dissolved in ethanol (80 ml) in a 500 ml round bottomed flask and kept under stirring.
4-Hydroxyl benzaldehyde (0.07 mol) dissolved in ethanol (80 ml) was slowly adder to it
and the temperature was brought down to 5◦C. To the mixture NaOH (5%) solution in
ethanol was added dropwise and the stirring continued for 48 hr. The reaction mixture was
then poured to ice cold water and then neutralized with 3 ml HCl. The precipitated product
was filtered, washed with distilled water, and dried in vacuum (m.p. 105◦C 108◦C). The
crude product was recrystallized with methanol (Scheme 1). The structure of the compound
4-Hydroxy styryl-4ꢀ carboxy phenyl ketone was confirmed by IR, 1H-NMR, and 13C-NMR
spectra.
IR (KBr cm−1): 3500 (Phenolic-OH), 1610(ethylene CH CH ), 1710 (ester >c o),
1550 (aromatic ring breathing).
1H-NMR (CDCl3. δ in ppm): 7.3 (m, 4H, aromatic ring bonded to OH), 8.05 (s, 4H
aromatic ring bonded to COOH), 6.01 (m 2H; CH CH ), 10.8 ppm (S, COOH).
13C- NMR (CDCl3), δ in ppm) 170 ( COOH), 125–140 (aromatic rings), 115
( CH CH ).
Synthesis of 4-carboxy (m-hydroxy alkoxy styryl) phenyl ketone (m = 4 and 8). 4-Carboxy
(4-hydroxy butyl oxy styryl) phenyl ketone was synthesized by following Williamson aryl
ether synthesis method in these precursors was synthesized [26]. The typical procedure
of synthesis was follows: A solution of potassium carbonate (0.09 mol) and 4-hydroxy
styryl 4-carboxy phenyl ketone (0.42 mol) in ethanol (80 ml) were taken in a round
bottomed flask and refluxed. 4-Bromobutanol (0.06 ml) and a pinch of KI were added to

14
S. Jeyasheela and K. Subramanian
this reaction mixture. The reaction was continued for 48 hr, cooled and neutralized with
10% hydrochloric acid. The resultant precipitate was filtered and the residue was washed
with distilled water and recrystallized with methanol (m.p. 85◦C 90◦C). 4-Carboxy (8-
hydroxy octyl oxy styryl) phenyl ketone was synthesized by adopting the same procedure.
The structure 4-carboxy (4-hydroxy butyl oxy styryl) phenyl ketone was confirmed by the
spectroscopy techniques IR, 1H- NMR, and 13C-NMR.
IR (cm−1): 3490 (methylene chain OH), 3000 (acid OH), 1240(ether–o–), 1600
( CH CH ), 1710 (acid carbonyl group).
1H-NMR (δ ppm): 3.5 (s 1H,-OH), 3.4(t, 2H-CH2-OH), 3.6 (t, 2H, ph-o-CH2-), 1.5
(m, 4H, -CH2-CH2-), 5.8 (m, 2H, CH CH ), 7.5 (dd, aromatic ring)
13C-NMR (δ ppm): 169 ( COOH), 140–150 (Aromatic protons), 110 (olefinic pro-
tons), 10–60 (Aliphatic protons).
Synthesis of 4-carboxy phenyl carbonyl ethylene phenyl oxy m-alkyl meth acrylate. A
typical procedure for the synthesis of 4-carboxy phenyl carbonyl ethylene phenyl oxy -4-
butyl meth acrylate was as follows. 4-Carboxy (4-hydroxy butyl oxy styryl) phenyl ketone
(0.04 mol) in THF (50 ml) was taken in a 250 ml round bottomed flask. Triethylamine (0.03)
was added slowly to it. The reaction mixture was cooled at 5◦C. Methacryloyl chloride
(0.04 mol) was added dropwise and allowed to stirred for 5 hr. The precipitate triethylamine
hydrochloride was filtered and the filtrate was evaporated at 40◦C under reduced pressure.
The residue was washed with petroleum ether to remove unreacted methacryloyl chloride
and recrystallized using methanol (m.p. 90◦C–95◦C). 4-Carboxy phenyl carbonyl ethylene
phenyl oxy -8-octyl meth acrylate was synthesized by similar procedure. The structure of
4-carboxy phenyl carbonyl ethylene phenyl oxy -4-butyl meth acrylate was confirmed by
the IR, 1H-NMR, and 13C-NMR spectra.
IR (cm−1): 3010 (acid OH), 2852 (aliphatic CH2), 1705 (carbonyl group), 1625
( CH CH ), 1230 (ester–o–ph),
1H-NMR (δ ppm): 1.5 (s, 3H, C CH3 ), 3.01 (t, 2H, CH2 O methacroyl), 5.5
(s, 2H ( C CH2), 3.6 (t, 2H, ph—o CH2 ), 1.6 (m, 4H, CH2 CH2), 6.5 (dd, 2H,
CH CH ) 9.5 (s, 1H COOH).
13C-NMR (δ ppm): 172 ( COOH), 120–140 (aromatic protons), 115 ( CH CH ),
60–20 (aliphatic protons).
Synthesis of 4-[4{biphenyl oxy carbonyl phenyl oxy carbonyl}phenyl carbonyl ethylene
phenyl] oxy butyl methacrylate (BOCPOCPCEPOBMA) (Monomer). A mixture of 4-
carboxy phenyl carbonyl ethylene phenyl oxy -4-butyl methacrylate (0.005 mol), 4-biphenyl
oxy carbonyl phenol (0.005 mol). DMAP (0.0005 mol) and DCC (0.005 mol) in 100 ml
of dry methylene chloride were stirred at room temperature over night. The precipitated
form of urea was removed by filtration and the filtrate was washed with 5% acetic acid and
the saturated sodium chloride solution. The organic layer was then dried over anhydrous
sodium sulphate and vacuum distilled. The liquid was purified by column chromatography
techniques. Another monomer 4-[4{1-methoxy phenyl oxy carbonyl phenyl oxy carbonyl}
phenyl carbonyl ethylene phenyl] oxy octyl methacrylate (MPOCPOCPCEPOOMA) also
synthesized by adopting similar procedure.
IR (cm−1):1268 (ether–o–ph), 1610 ( CH CH group), 2840 (methylene spacer),
1715 (ester carbonyl), 1540 ( C CH2 group) and 830 (aromatic bend).
1H-NMR (δ ppm): 1.5 (δ, 3H, CH C (CH3)), 3.01(t, 2H, CH2–o–methacryloyl),
5.2 (s, 2H, ( C CH2), 3.5(t, 2H, Ph o CH2 ), 1.6 (m, 4H, CH2 CH2 ), 6.5 (dd,
2H, cinnomoyl Ph), 7.5 (m, 9 biphenyl ring)

Thermotropic Novel LC Photosensitive Polymers
15
13C-NMR (δ ppm): 175 ( C O.O), 120–140 (Aromatic carbons), 110 (olefinic car-
bon), 60–10 (aromatic carbons).
Polymerization of 4-[4{biphenyl oxy carbonyl phenyl oxy carbonyl} phenyl carbonyl ethy-
lene phenyl] oxy butyl methacrylate (BOCPOCPCEPOBMA). The polymers were syn-
thesized according to the literature procedure [25]. The polymer was synthesized by free
radical polymerization of 4-[4{biphenyl oxy carbonyl phenyl oxy carbonyl} phenyl car-
bonyl ethylene phenyl] oxy butyl methacrylate (0.01 mol) dissolved in dry oxygen free THF
(30 ml) using BPO (1 wt%). At 70◦C the reaction was carried out for 24 hr. The mixture
was cooled and treated with excess methanol to precipitate the polymer, the polymer was
purified by repeated reprecipitation from chloroform using methanol and dried in vacuum
at 50◦C .The another polymer also synthesized by the same route (Schemes 2, 3).
Measurements
The FT-IR spectra were recorded on a Hitachi 270–50 spectrophotometer using KBr. 1H-
NMR was run on a Bruker 270 MHz spectroscopic measurement was recorded with Bruker
MSC 300 spectrometer. The molecular weights (Mw and Mn) were determined in the Water
501 gel permeation chromatograph, THF was used as an eluent and poly styrene standards
were employed for calibration. Thermal stability of polymers was investigated by TGA on a
NETZSCH STA 409 C/CD. Glass transition temperatures of polymer were measured from
differential scanning calorimeter (DSC) NETZSCH.DSC.204. UV-visible spectra were
recorded on a Hitachi UV-2000 spectrophotometer. The textures of the polymer samples
were studied on a Euromax polarizing microscope equipped with a Linken HFS91 heating
stage. The samples were prepared by melting the sample between two thin glass cover slips
to get uniform film and anisotropic behavior observed by heating and cooling with Kodak
film.
Results and Discussion
FT-IR Spectra of Polymer
The FT-IR Spectra of the poly (BOCPOCPCEPOBMA) is shown in Fig. 1(a). The aromatic
and CH and olefinic vibrations occurred close to 3010 cm−1. The CH2– stretching vibra-
tion observed at 2927 cm−1 and 2849 cm−1. The C O vibration of the ester occurred at
1718 cm−1. The C C and aromatic ring vibration yielded their peaks at 1606 cm−1. The
peak at 1464 cm−1 was due to CH2 bending and aromatic ring skeletal vibration. The CH2
bending vibration also gives a shoulder close to 1375 cm−1. The COO vibration gave peak at
1287 cm−1, 1272 cm−1 and 1255 cm−1. The phenoxide C O vibration occurred at
1120 cm−1 and 1064 cm−1. The group of peaks occurring below 1000 cm−1 was due
to aromatic ring CH bending modes.
The olefinic CH stretching vibration occurs at 3036 cm−1. The corresponding C C
stretching vibration occurs at 1600 cm−1. The C O stretching occurs at 1734 cm−1. The
aromatic ring a vibration occurs at 641 cm−1 and 1438 cm−1. The CH2 bending modes occurs
at 1311 cm−1. The ester COO vibration gives a peak at 1291 cm−1. The C O vibrations
gives group of peaks at 1167 cm−1, 1088 cm−1, and 1015 cm−1. The peaks at 949 cm−1 and
1311 cm−1 illustrates trans position which occurs for the C C bond substituents. Hence,
the IR spectra establish the structure of the poly (MPOCPOCPCEPOOMA) is shown in
Fig. 1(b).

16
S. Jeyasheela and K. Subramanian
Figure 1. (a) FT-IR spectra of poly (BOCPOCPCEPOBMA). (b) FT-IR spectra of poly
(MPOCPOCPCEPOOMA).

Thermotropic Novel LC Photosensitive Polymers
17
1
1
Figure 2. (a) H -NMR spectra of poly (BOCPOCPCEPOBMA). (b) H -NMR spectra of poly
(MPOCPOCPCEPOOMA).
1H-NMR Spectra of Polymer
1
The H-NMR spectrum of poly (BOCPOCPCEPOBMA) is shown in Fig. 2(a). The poly
(BOCPOCPCEPOBMA) shows multiplet resonance signals at 6.05–7.99 ppm correspond-
ing to the aromatic protons. The resonance signals of the olefinic protons of the pendant
chalcone moiety were observed as doublets at 5.7 ppm and 5.9 ppm. The backbone methy-
lene ( CH2) protons signals appeared at 1.7 ppm. The broad resonance signals at 2.1 ppm
were due to the α-CH3 protons. The resonance signals are at 3.3 ppm and 3.6 ppm were
due to methoxy protons.
The 1H-NMR spectrum of poly (MPOCPOCPCEPOOMA) is shown in Fig. 2(b). The
olefinic protons produce their signals between 5.8 ppm and 6.1 ppm. All the aromatic ring
protons show their peaks between 6.5 ppm and 8 ppm. The alkyl CH3 and CH2 protons
give peaks at about 2 ppm and 1.8 ppm. The CH2
O
and CH3
O
protons produce

18
S. Jeyasheela and K. Subramanian
Figure 3. C13NMR spectrum of poly (BOCPOCPCEPOBMA) and poly (MPOCPOCPEPOOMA).
1
their peaks between 3.5 ppm and 4 ppm. Thus, H-NMR spectrum carries signals due to
different types of protons of poly (MPOCPOCPCEPOOMA) .
13C NMR Spectra of Polymer
The proton decoupled 13C-NMR spectrum of poly (BOCPOCPCEPOBMA) and poly
(MPOCPOCPCEPOOMA) is shown in Fig. 3. 13C-NMR chemical shift assignments were
made from the off resonance decoupled spectra of the polymers. The keto-carbonyl carbon
resonances were observed at 189 ppm and 190 ppm. The ester carbonyl carbon gave their
characteristic signals are at 180 ppm and 178 ppm. The signals at 110 ppm are due to

Thermotropic Novel LC Photosensitive Polymers
19
Table 1. TGA and molecular weight data of poly (BOCPOCPCEPOBMA) and poly
(MPOCPOCPCEPOOMA)
Temperature (◦C)
at weight loss (%)
Polymers
Mn × 104 PDI IDT
20
40
60
80
Poly (BOCPOCPCEPOBMA)
Poly (MPOCPOCPCEPOOMA)
2.69
2.44
1.75 200 280 320 370 393
1.54 190 285 300 355 375
IDT – Initial decomposition temperature (◦C).
PDI – Poly dispersity index.
Mn and Mw – Number and weight average molecular weight of polymer.
>CH CH< (olefinic) carbon connected to the benzene ring. The aromatic carbon gave
signals at 120–140 ppm and the aliphatic carbon gave signals at 18 ppm, 21 ppm, 29 ppm,
35 ppm, 18 ppm, 43 ppm, and 46 ppm. The signal observed at 40–50 ppm is assignable to
the backbone carbon ( C ) of the polymer unit.
Molecular Weight
The values of number average molecular weight (Mn), weight average molecular weight
(Mn) and polydispersity index (PDI) of polymers were determined by gel permeation
chromatography and the data are represented in Table 1. The PDI of polymers are close
to the theoretical values of PDI for polymers produced via radical recombination and
disproportionation [27 and 28].
Mw × 10−4 = 4.72; Mn × 10−4 = 2.69,
Mw × 10−4 = 3.78; Mn × 10−4 = 2.44,
Mw/Mn = 1.75
Mw/Mn = 1.54
Figure 4. DSC trace of poly (BOCPOCPCEPOBMA) and poly (MPOCPOCPCEPOOMA).

20
S. Jeyasheela and K. Subramanian
Table 2. DSC and HOPM data of poly (BOCPOCPCEPOBMA) and poly
(MPOCPOCPCEPOOMA)
DSC
HOPM
Polymers
Tm ◦C
Ti
δT
Tg
Mesophase
Poly (BOCPOCPCEPOBMA)
Poly (MPOCPOCPCEPOOMA)
169
145
210
190
41
45
87
75
Nematic
Nematic
Tm – Crystal–liquid melting temperature.
Ti – Mesophase-isotropic phase transition temperature.
Tg – Glass transition temperature.
Hence, the PDI value of termination by disproportionation was more than that for dimeri-
sation.
Thermal Studies
DSC Analysis
DSC analysis investigates the mesogenic transition of the polymers. The DSC thermo-
gram of the polymers was measured at a heating rate of 10◦C min−1 and representative
thermogram of polymers has been shown in Fig. 4. The phase transition temperature of
the polymers was summarized in Table 1. The DSC thermograms show three endothermic
Figure 5. TGA thermogram of the poly (BOCPOCPCEPOBMA) and poly (MPOCPOCPCE-
POOMA).

Thermotropic Novel LC Photosensitive Polymers
21
Figure 6. (a) Change in UV spectral characteristics, during the photolysis of the polymer poly
(BOCPOCPCEPOBMA). (b) Change in UV spectral characteristics, during the photolysis of the
polymer poly (MPOCPOCPCEPOOMA).
peaks which reveals that the mesogenic transition values decreases with increase in methy-
lene group. The synthesized polymers show higher mesogenic transition temperature due to
the effect of substituent of biphenyl ring on the thermal properties of the polymer. The poly
(BOCPOCPCEPOBMA) exhibits higher glass transition temperature due to the presence
of shorter methylene chain and rigidity of the biphenyl ring. The poly (MPOCPOCPCE-
POOMA) shows lower glass transition temperature due to the presence of longer methylene
chain of the polymer backbone.

22
S. Jeyasheela and K. Subramanian
Thermogravimetric Analysis
The thermal stability of the polymer was studied by thermogravimetric analysis in nitrogen
atmosphere. Temperatures corresponding weight loss between 10% and 80% were given
in Table 2. The representative thermograms are shown in Fig. 5. The poly (BOCPOCP-
CEPOBMA) was showing good thermal stability up to 190◦C due to the presence of
rigid biphenyl ring, increase in the aromaticity and shorter methylene chain. The poly
(MPOCPOCPCEPOOMA) shows lower thermal stability due to the presence of longer
methylene chain of the polymer backbone.
Photochemical Properties
The photocrosslinking reactions of the synthesized liquid crystalline photosensitive poly-
mers were studied in polymer solutions. The polymers showed the absorbance band at 230
due to the π–π∗ transition of the exocyclic double bond, during this absorption intensity
was decreased. The change in UV spectral pattern during the photolysis of polymer at var-
ious intervals of time is shown in Fig. 6(a) and 6(b). The corresponding photo-crosslinking
rate on irradiation time of the polymer is shown in Fig. 7. The photocrosslinking of the
polymer chain, which involves the 2π + 2π cycloaddition leading to the formation of the
cyclobutane ring [29 and 30]. The UV spectrum of the polymer solution was recorded
at a definite intervals and the rate of disappearance of >C C< of the pendant α,β-
unsaturated ketone unit of the polymer was followed by measuring the UV absorption
intensity of the solution (Schemas 4 and 5) after each exposure interval using the following
Figure 7. Dependence of the photocrosslinking rate on irradiation time of the polymer poly
(BOCPOCPCEPOBMA) and poly (MPOCPOCPCEPOOMA).

Thermotropic Novel LC Photosensitive Polymers
23
CH3
C
CH2
n
C
O
O
CH
C
O
(CH2)4
O
CH
O
C
O
C
O
O
UV irradiation
O
C
O
O
C
P
O
O
C
O
CH3
C
C
P
O
CH2
O
P
n
O
C
O
O
C
O
O
(CH2)4
O
O
C
C
+
O
O
O
O
O
C
P
O
C
O
C
O
P
O
C
O
O
C
O
O
Scheme 4. Photocrosslinking reaction (2π + 2π cycloaddition) of poly (BOCPOCPCEPOBMA).
expression:
Rate of conversion (%) = (A0 − AT )/(A0 − Aα) × 100
Where A0, AT, and Aα are absorption intensities due to the C C group after the irradiation
times t = 0, t = T, and t = α (maximum irradiation time), respectively.

24
S. Jeyasheela and K. Subramanian
CH3
C
CH2
C
O
O
CH
CH
C
O
(CH2)8
O
O
C
O
C
O
O
CH
O
3
UV irradiation
O
C
CH
O
3
O
O
O
P
O
C
C
O
CH3
C
C
CH3
P
CH2
O
O
O
P
O
C
O
O
C
O
O
O
(CH2)8
O
C
C
+
O
O
O
O
O
C
CH
O
3
P
O
C
O
C
O
P
O
C
O
O
C
O
O
CH
O
3
Scheme 5. Photocrosslinking reaction (2π + 2π cycloaddition) of poly (MPOCPOCPCEPOOMA).

Thermotropic Novel LC Photosensitive Polymers
Polarized Optical Microscopy Analysis
25
The DSC trace of the polymer shows three endothermic peaks, corresponding to glass
transition temperature, melting (Tm) and isotropic (Ti) transition temperature. Generally,
the melting transition temperature decreases with increase in aliphatic spacers as expected.
The polymers exhibited liquid crystalline nature with nematic textures on heating. The
polymer was heated to 191◦C which exhibits Nematic texture as shown in Figs. 8(a) and
(b). On the cooling of the polymer from isotropic melt (Ti), the reproducibility of the phase
was satisfactory. The rigidity of the mesogenic core with the flexible spacer length and
Figure 8. (a) HOPM photograph of poly (BOCPOCPCEPOBMA). (b) HOPM photograph of poly
(MPOCPOCPCEPOOMA).

26
S. Jeyasheela and K. Subramanian
terminal units highly influence the melting temperature, mesophase temperature, and even
molecular arrangement.
Conclusions
The novel liquid crystalline photoactive was synthesized by free radical polymerization
method. The polymers were synthesized and characterized by spectroscopically. The spec-
tral data supported the structural assignment of the polymers. Glass transition temperatures
were determined by DSC analysis. The synthesized polymers have higher thermal stability
due to the presence of increase in the aromaticity of the polymer backbone. The polymers
showed photocrosslinking behavior via. 2π + 2π cycloaddition under UV irradiation. The
poly (MPOCPOCPCEPOOMA) containing the longer methylene chain unit showed faster
photolysis than that of lower methylene chain of the poly (BOCPOCPCEPOBMA). The
HOPM analysis showed that the synthesized polymers were exhibited LC properties with
nematic texture.
References
[1] Weiss, R. A., & Ober, C. K. (1990). Liquid Crystalline Polymers, America Chemical Society:
Washington, DC.
[2] Papadimitrakopoulos, F., Hus, S. L., & Macknight, W. (1992). J. Macro Mol., 25, 4671.
[3] Isayev, A. L., & kyu, T. (1996). Liquid-Crystalline Polymer System, American Chemical Society:
Washington, DC.
[4] Narasimhaswamy, T., Lee, D. K., Yamamoto, K., Somanathan, N., & Ramamurthy, A. (2005).
Am. Chem. Soc., 127(69), 58.
[5] Gao, X., Liu, R., & Zhang, J. (2008). Ind. Eng. Chem. Res., 47, 2590.
[6] Finkelmann, H., Keichle, U., & Reharge, G. (1983). Mol. Cryst. Liq. Cryst., 94, 3453.
[7] Brake, J. M., Daschner, M. K., Luk, Y. Y., & Abbott, N. L. (2003). Science, 302, 2094.
[8] Jang, C. H., Tingey, M. L., Korpi, N. L., Wiepz, G. J., Schiller, J. H., Bertics, P. J., & Abbott,
N. L. (2005). J. Am. Chem. Soc., 127, 8912.
[9] Jang, C. H., Cheng, L. L., Olsen, C. W., & Abbott, N. L. (2006). Nano Lett., 6, 1053.
[10] Ito, H., Wilson, C.G., & Davidson, T. (1984). (Ed.), Polymers in Electronics, ACS Symposium
Series 242, American Chemical Society: Washington, DC.
[11] Reiser, A. (1989). Photoreactive Polymers—The Science and Technology of Resists, Wiley: New
York.
[12] Tazuke, S. (1982). Developments in Polymer Photochemistry, Vol. 3, Applied Science Publish-
ers: London.
[13] Sekkat, Y., & Knoll, W. (2002). Photoreactive Organic Thin Flims, Academic Press: New York.
[14] Shibaev, V. P., Bobrovesky, A., & Boiko, N. I. (2003). Progr. Polym. Sci., 28, 729.
[15] Simoni, F., & Lucchelti, L. (2007). Photo refractive effects in liquid crystals. In Photorefractive
materials and their applications. Springer: Berlin, pp. 571–606.
[16] Strumpe, J., Muller, L., Kreysig, D., Hauck, G., Koswig, H. D., & Ruhmann, R. (1991).
Macromol. Chem. Rapid Commun., 12, 81.
[17] Kumaresan, S., & Kannan, P. (2003). J. Polym. Sci., Part A Polym. Chem., 41, 3188.
[18] She-Jian, H., Liu, C., Zhang, X., & Baomeng, Q. (2009). E Poly. Journals, 45, 3392–3301.
[19] Massoumeh, B., & Reza, Z. (2008). Reactive Functional Polymer, 68, 613.
[20] Taguchi, Y., Uyama, H., & Kubayashi, S. (1997). J. Polym Sci. Part A Polym. Chem., 35(2), 271.
[21] Lin, S. C., & Pearce, E. M. (1994). High Performance Thermosets: Chemistry, Properties,
Application, Carl Hanser Verlag: Munich, Vienna, and New York.
[22] Gandhara, S., & Kishore, K. (1993). Macromolecules, 26, 2995.
[23] Perrin D. D., & Armarigo W. L. F. (1998). Purification of Laboratory Chemicals, 3rd edition,
New York: Programme press.

Thermotropic Novel LC Photosensitive Polymers
27
[24] Stampel, G. M., Cross, R. P., & Maliella, R. P. (1950). J. Am. Chem. Soc., 72, 2899.
[25] Subramanian, K., Rami Reddy, A. V., & Krishnasamy, V. (1991). Macromol. Chem. Rapid
Commun., 12, 211.
[26] Sakthivel, P., & Kannan, P. (2004). J. Polym Sci. Part A Polym Chem., 42, 5215.
[27] Teramachi, S., Hasegava, A., Akatsuka, M., Yamashita, A., & Takemoto, N. (1978). Macro-
molecules, 11, 1206.
[28] Melville, H. W., Noble, B., & Watson, W. F. (1949). J. Polym. Sci., 4, 629.
[29] Tibor, T. N., Bela, T., Tibor, T., & Ferenc, T. (1980). Polym. Bull, 12, 1703.
[30] Rehab, A. (1998). Eur. Polym. J., 34, 1845.