Synthesis and characterization of novel liquid crystalline photoactive polymers with pendant chalcone moiety

Article abstract of DOI:10.1080/15421406.2011.599218

The side-chain liquid crystalline polymers containing terminally substituted biphenyl cinnamoyl esters were synthesized and characterized The structures of the synthesized photosensitive liquid crystalline polymers have been characterized by spectral tech

Full text of DOI:10.1080/15421406.2011.599218

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Synthesis and Characterization of Novel
Liquid Crystalline Photoactive Polymers
with Pendant Chalcone Moiety
Sivakumar Jeyasheela a & Kathavarayan Subramanian a
a Department of Chemistry, Anna University, Chennai, India
Published online: 27 Dec 2011.
To cite this article: Sivakumar Jeyasheela & Kathavarayan Subramanian (2012): Synthesis and
Characterization of Novel Liquid Crystalline Photoactive Polymers with Pendant Chalcone Moiety,
Molecular Crystals and Liquid Crystals, 552:1, 53-70
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Mol. Cryst. Liq. Cryst., Vol. 552: pp. 53–70, 2012
Copyright © Anna University
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.599218
Synthesis and Characterization of Novel Liquid
Crystalline Photoactive Polymers with Pendant
Chalcone Moiety
SIVAKUMAR JEYASHEELA AND KATHAVARAYAN
SUBRAMANIAN∗
Department of Chemistry, Anna University, Chennai, India
The side-chain liquid crystalline polymers containing terminally substituted biphenyl
cinnamoyl esters were synthesized and characterized The structures of the synthesized
photosensitive liquid crystalline polymers have been characterized by spectral tech-
1
niques such as IR, H NMR and 13C NMR, and UV visible spectrometer. The rates
of photocrosslinking behavior and photoconversion of the polymers have been stud-
ied by UV visible spectroscopy. The UV study reveals that the polymer follows (2π +
2π) cycloaddition reaction during their photocrosslinking. Polarizing optical micro-
scopic and differential scanning calorimetry (DSC) studies confirm the formation of
thermotropic mesophase upon heating. The above polymers exhibit nematic mesophase.
The thermogravimetric analysis (TGA) and DSC studies prove that the nature of the ter-
minal substituent has a significant effect on mesophase temperature as well as thermal
stability of these liquid crystalline photoactive polymers.
Keywords NMR; photocrosslinking; thermal stability; UV irradiation
Introduction
In recent years, photocrosslinkable polymers have attracted considerable attention for the
application in surface coatings, printing inks, printing plates, and photoresists due to their
faster curing and higher thermal stability [1,2]. Anisotropic photocrosslinking reaction of
a photosensitive moiety has long been known and has found its potential applications in
lithography and in advanced electro-optic application [3–5]. The combination of unique op-
tical properties of liquid crystals (LCs) with photosensitivity provides a great possibility for
the creation of a lathe variety of photochemical switches, which can be used in optics and op-
toelectronics [6–8]. The polymers with pendant photofunctional groups, such as cinnamoyl
esters of poly(vinyl alcohol) [9], poly(2-hydroxyethyl methacrylate) [10,11], poly(2-vinyl-
4-methoxycinnamate) [12], poly(2-vinyloxyethylcinnamate) [13], poly(vinyloxycarbonyl
chalcone) [14], and many other groups [15–19], have been prepared and tested for their
photosensitivity. The photochemistry involved in a number of photoresists and their tech-
nological applications have been reviewed [20–22]. Polymers containing α,β-unsaturated
carbonyl groups such as cinnamoyl [23,24], benzylidene [25], and so on, undergo pho-
todimerization (2π + 2π) upon irradiation with UV light. LCs occupy an important place
∗Address correspondence to Kathavarayan Subramanian, Department of Chemistry, Anna Uni-
versity, Chennai 6000025, Tamil Nadu, India. E-mail: kathsubramanian@yahoo.com
53

54
S. Jeyasheela and K. Subramanian
C
O
C
HO
CH
OH
C
O
+
H
3
O
HCI
20OC 25OC
NaOH
EtOH
C
O
HO
C
CH = CH
OH
O
Scheme 1.
in modern optical technology; π-conjugated polymers are promising candidates for thin-
film transistors, light-emitting diodes, and organic lasers [26–28]. High photosensitivity,
thermal stability, and good solubility are the required properties for a photocrosslinkable
polymer. In the present investigation, we report the novel synthesis of side-chain liquid
crystalline polymers with photoresponsive group containing methylene spacer and acetyl
phenyl group and methyl phenyl group in the polymeric chain.
Experiment
Material
4-phenyl phenols, 6-bromobutanol, and 8-bromohexanol (Aldrich) were used as re-
ceived. 4-formyl benzoic acids, 4-hydroxyacetophenone, and 4-methoxy phenol were
purchased from Spectrochem chemicals. Triethylamine, N,Nꢀ-dicyclohexyl carbodiimide,
and 4-dimethylamino pyridine were purchased from Lancaster. Dichloromethane, ethanol,
methanol, tetrahydrofuran (THF), and ethyl methyl ketone (EMK; SRL) were purified by
the usual procedure and dried before use. Anhydrous potassium carbonate (Merk) and ben-
zoyl peroxide (BPO) were freshly recrystallized from a chloroform/methanol (1:1) mixture.
All other chemicals and solvent were analytical grade samples used as received.
Synthesis of Precursors
Synthesis of 4-Carboxy Styryl 4ꢀ-Hydroxy Phenyl Ketone (CSHPK). Synthesis of 4-carboxy
styryl -4-hydroxy phenyl ketone (CSHPK) was carried out following the reported procedure
(Scheme 1) [29]. 4-hydroxyacetophenone (0.05 mol, 6.8 g) was dissolved in ethanol (80
ml) in a 500 ml round bottom flask. 4-formyl benzoic acid (0.05 mol, 7.5 g) was dissolved
in ethanol (80 ml) and was added dropwise to the flask and while stirring, NaOH (7%)
solution was simultaneously added into the reaction mixture. The stirring was continued for
48 hr and then the reaction mixture was poured into ice-cold 1:1 HCl for neutralization to
get yellow-colored solid, which is then filtered and washed with distilled water. The crude
product thus obtained was recrystallized from methanol to get a pure compound CSHPK.
The structure of CSHPK was confirmed by IR, 1H NMR, and 13C NMR spectra, which is
in good agreement with the assigned structure.

Synthesis and Characterization of Novel Liquid Crystalline Photoactive Polymers 55
C
O
HO
CH = CH
C
O
OH
KI / K2CO3
DMF
Br - (CH2)6 - OH
C
HO
CH = CH
C
O - (CH2)6 -OH
O
O
CH3
CH3
C
THF / TEA
CH2
C
C
CH2
O
C
O
CI
CH = CH
O - (CH2)6 - 0
C
OH
C
O
O
CH3
DCC, DMAP
DCM
OH
CH2
C
C
O
O - (CH2)6 - 0
C
O
CH = CH
- O
C
O
EMK
70 C
BPO
°
CH3
C
CH2
C
O
O - (CH2)6 - 0
C
O
CH = CH
- O
C
O
Scheme 2. Synthesis of polymer BOCCPOHMA (polymer 1a).

56
S. Jeyasheela and K. Subramanian
Scheme 3. Polymer MPOCCPOOMA (polymer 1b).
CH3
C
CH2
0
C
(CH2)6
0
CH = CH
O
C
O
C
O
O
UV Irradiation
O
C
O
CH
CH
CH
CH
C
O
C
P
O
O
+
O
P
C
O
O
O
O
C
O
C
CH
P
CH
CH
O
O
P
O
C
C
CH
O
O
O
CH3
CH2
C
C
P
O
0
(CH2)6
0
O
Scheme 4. Photocrosslinking studies on polymer BOCCPOHMA.

Synthesis and Characterization of Novel Liquid Crystalline Photoactive Polymers 57
Scheme 5. Photocrosslinking of polymer MPOCCPOOMA.
IR (KBr, cm−1): 3510 (phenolic-OH), 1600 (ethylene CH = CH ), 1750 (ester
>C O), 1500 (aromatic ring breathing). 1H NMR (CDCl3, δ in ppm): 7.32 (m, 5H, aromatic
pendant phenyl), 8.22 (s, aromatic carbon, OCO attached), 6.3 (d, 2H, CH CH ).
13C NMR (CDCl3, δ in ppm): 160–180 (carbonyl), 120–140 (aromatic carbon), 60–10
(aliphatic carbon).
Synthesis of 4-Carboxy Styryl (m-Hydroxy Alkyloxy) Phenyl Ketone (m = 6, 8). Synthesis
of 4-carboxy styryl (m- hydroxy alkyloxy) phenyl ketone (m = 6, 8) was carried out
as reported previously (Schemes 2 and 3) [30]. A typical procedure for the synthesis of
4-carboxy styryl (6-hydroxy hexyloxy) phenyl ketone (CSHHPOK) is as follows. The
pendant chalcone CSHPK (0.01149 mol, 3 g) was dissolved in dry dimethylformamide

58
S. Jeyasheela and K. Subramanian
(DMF; 20 ml). Anhydrous potassium carbonate (K2CO3; 0.0111 mol, 2.76 g) and a pinch
of KI were added to it. The reaction mixture was continuously heated to 90◦C with constant
stirring. 6-bromo-1-butanol (0.011 mol, 1.66 g) was added dropwise to the reaction mixture
and stirred for 48 hr. Then, the reaction mixture was cooled to room temperature and poured
into ice-cold dilute HCl. The precipitated product was filtered, washed, and dried in vacuum
(yield 85%, mp 78◦C–80◦C). Synthesis of 4-carboxy styryl (8-hydroxy octyloxy) phenyl
ketone (CSHOOPK) was carried out by adopting the similar procedure (yield 77%, mp
70◦C–75◦C). The structure of the compound CSHHPOK was identified by the spectroscopic
techniques (IR, 1H NMR, and 13C NMR).
IR (KBr, cm−1): 1265 (C O stretch), 1640 (olefinic CH CH ), 1640 (C C
stretching), 1540 (aromatic, C C), 2230 (aliphatic CH2), 1743 (ester C O), 1255
1
(Ar O CH2). H NMR (CDCl3, δ in ppm): 9.00 (O H), 7.23 (m, 5H, aromatic pen-
dant phenyl), 8.15 (s, aromatic carbon, OCO attached), 6.5 (d, 2H, CH CH ), 7.5
(m, biphenyl oxy group). 13C NMR (CDCl3, δ in ppm): 169–175 (carbonyl), 120–140
(aromatic carbon), 60–10 (aliphatic carbon).
Synthesis of 4[4-Carbonyl Styryl Carbonyl-4-Phenyl Oxy-6-Hexylene] Methacrylate
(CSCPOHMA). The compound CSHHPOK (0.008 mol, 2.5 g) was dissolved in THF (50
ml), triethylamine (0.008 mol, 2 ml) was added to the reaction mixture, and then the reaction
mixture was cooled to 0◦C–5◦C. Chlorocarbonyl phenyl methacrylate (0.008 mol, 1.8 g)
was added to the reaction mixture and continuously stirred for 5 hr. The precipitated triethy-
lamine hydrochloride was filtered and the filtrate was evaporated under reduced pressure by
keeping the bath temperature below 40◦C. The residue obtained was treated with petroleum
ether to remove unreacted chloro carbonyl phenyl methacrylate. The precipitate thus ob-
tained was recrystallized using methanol (yield 71%, mp 90◦C–93◦C). Another compound
4[4-carbonyl styryl carbonyl-4-phenyloxy-8-octylene] methacrylate (CSCPOOMA) was
synthesized by adopting the same procedure (yield 77%, mp 70◦C–75◦C). The structure of
the compound CSCPOHMA was identified by the IR, NMR, and 13C NMR spectra.
IR (KBr, cm−1): 1748 (C OO), 3024 ( CH3), 2915 (methylene chain), 1693 ( C O),
1655 ( C CH2), 1611 ( C C CH3). NMR (CDCl3, δ in ppm): 7.59 (d, 1, Ar, aromatic
pendant phenyl), 8.15 (s, aromatic carbon, OCO attached), 6.5 (d, 2H, CH CH ).
13C NMR (CDCl3, δ in ppm): 170 (carbonyl), 120–140 (aromatic carbon), 60 (aliphatic
carbon), 68 (O CH2).
Synthesis of Monomers
Synthesis of 4[4{1-Biphenyl Oxy Carbonyl} Cinnamoyl Phenyl Oxy Hexyl] Methacrylate
(BOCCPOHMA) (M1). The compound CSCPOHMA (0.004 mol, 2 g), 4-phenyl phenol
(0.004 mol, 0.6 g), N,Nꢀ-dimethylaminopyridine (DMAP) (0.004 mol, 0.488 g), and N,Nꢀ-
dicyclohexylcarbodiimide (DCC; 0.004 mol, 0.82 g) were suspended into 100 ml of dry
methylene chloride and stirred at room temperature overnight. The precipitated urea was
removed by filtration and the solution was washed with 5% acetic acid followed by saturated
brine solution. Organic layer was dried over anhydrous sodium sulfate and removed under
vacuum distillation. The residue thus obtained was purified by column chromatography
using 10% methanol in chloroform as an eluent (yield 85%, mp 75◦C–80◦C). Another
monomer 4-{4-(1-methoxy phenyl oxy carbonyl) cinnamoyl phenyl oxy octyl} methacry-
late. (MPOCCPOOMA) (M2) was synthesized by following the similar procedure (yield
77%, mp 70◦C–75◦C). The structure of the compound was identified by the spectroscopic
techniques (IR, 1H NMR, and 13C NMR).

Synthesis and Characterization of Novel Liquid Crystalline Photoactive Polymers 59
The structure of the monomer M1 was identified by the spectral techniques.
IR (KBr, cm−1): 1748 (C OO), 3024 ( CH3), 2915 (methylene chain), 1693 ( C O),
1655 ( C CH2), 1611 ( C C CH3). NMR (CDCl3, δ in ppm): 7.59 (d, 1, Ar, aromatic
pendant phenyl), 8.15 (s, aromatic carbon, OCO attached), 6.5 (d, 2H, CH CH ).
13C NMR (CDCl3, δ in ppm): 170 (carbonyl), 120–140 (aromatic carbon), 60 (aliphatic
carbon), 68 (O CH2).
The structure of the monomer M2 was identified by the spectral techniques.
IR (KBr, cm−1): 1718 (C OO), 3014 ( CH3), 2905 (methylene chain), 1653 ( C O),
1645 ( C CH2), 1611 ( C C CH3). NMR (CDCl3, δ in ppm): 7.6 (s, 1H, Ar CH C),
7.59 (d, 1, Ar, aromatic pendant phenyl), 8.15 (s, aromatic carbon, OCO attached), 6.5
(d, 2H, CH CH ), 7.5 (m, biphenyloxy group). 13C NMR (CDCl3, δ in ppm): 170
(carbonyl), 120–140 (aromatic carbon), 60 (aliphatic carbon), 68 (O CH2).
Polymerization
Both polymers were prepared by the free radical solution polymerization method at 70◦C
using BPO as initiator. They were polymerized as 1 M solution in dry THF using benzoyl
peroxide as initiator at 70◦C. Appropriate quantities of monomer, the initiator (0.5 wt%),
and solvent were taken in a polymerization tube and the mixture was purged with dry
nitrogen gas for 10 min. Then the tube was closed and kept in the thermostat at 70◦C for
24 hr. After that the contents were cooled and poured into excess methanol to precipitate
the polymers. The above polymers were purified by reprecipitation by methanol, filtered,
washed, and dried under vacuum at 50◦C (yield 60%).
Measurements
The FT-IR spectra of polymers were recorded on a Perkin Elmer FT-IR spectrometer
RXI. The specimen was prepared using KBr pellets. 1H NMR spectroscopic measurement
was recorded using a Bruker MSC 300 spectrometer. Thermal stability of polymers was
investigated by thermogravimetric analysis (TGA) using NETZSCH STA 409 C/CD. The
number average and weight average molecular weight of the polymers were determined
by PL-GPC 650. Glass transition temperatures of polymer were measured by differential
scanning calorimeter (DSC) NETZSCH.DSC.204. The photolysis studies were carried
out by using a Perkin Elmer Lambda 35 UV visible spectrometer. The four fluorescence
spectra of the polymers were recorded in FluroMax 2.0. The textures of the prepared
polymer sample were studied by a Euromax polarizing microscope equipped with a Linken
HFS91 heating stage. The samples were prepared by a small quantity of the material being
melted between two thin glass coverslips to get a uniform film and anisotropic behavior
observed by heating and cooling with Kodak film.
Result and Discussion
Synthesis
The polymers 1a and 1b were prepared by free radical polymerization method at 70◦C
using BPO as initiator. Table 1 shows the molecular weight data of poly (BOCCPOHMA)
and poly (MPOCCPOOMA).

60
S. Jeyasheela and K. Subramanian
Table 1. TGA and molecular weight data of polymers BOCCPOHMA and
MPOCCPOOMA
Temperature (◦C) at weight loss (%)
Polymers
Mn
PDI
IDT
10
30
50
60
70
BOCCPOHMA
MPOCCPOOMA
3.92
3.61
1.78
1.76
150
140
190
78
248
225
255
240
270
260
280
276
Note: IDT, initial decomposition temperature (◦C); PDI, polydispersity index; Mn and Mw are
−
the number and average molecular weight of polymer.
Characterization of Polymers
IR Spectroscopy of Polymers. IR Spectra of Polymer 1a. The olefinic CH stretching vibra-
tion occurs at 3067 cm−1. The corresponding C C stretching vibration occurs at 1627 cm−1
.
The CH2 symmetric and asymmetric stretching vibrations are at 850 and 2920 cm−1 respec-
tively. The C O stretching occurs at 1727 cm−1. The aromatic ring breathing vibrations
occur at 603, 1514, and 1449 cm−1. The CH2 bending modes are at 1361 and 1449 cm−1
.
The ester COO vibration gives a broad band at 1274 cm−1. The C O vibrations give
a group of peaks at 1112, 1068, and 1024 cm−1 and the para-substituted aromatic ring
gives its CH bending vibration at 840 cm−1. The free phenyl in biphenyl shows its CH
bending vibrations at 713 and 769 cm−1. Hence, the IR spectra establish the structure of
the polymer as shown in Fig. 1. The phenolic C O vibration also occurs close to it. The
Figure 1. FT-IR spectrum of polymer BOCCPOHMA.

Synthesis and Characterization of Novel Liquid Crystalline Photoactive Polymers 61
Figure 2. FT-IR spectrum of polymer MPOCCPOOMA.
peaks at 962 and 1310 cm−1 illustrate trans position, which occurs for the C C bond
substituents.
IR Spectra of Polymer 1b. The olefinic CH stretching vibration produces its peak at
3056 cm−1. The corresponding C C stretching vibration occurs at 1627 cm−1. The CH2
symmetric and asymmetric stretching vibrations occur at 2851 and 2932 cm−1 respectively.
The C O stretching occurs at 1718 cm−1. The aromatic ring breathing vibrations occur at
1602 and 1450 cm−1. The CH2 bending modes are observed at 1450 and 1383 cm−1. The
ester COO vibration gives a broad band at 1262 cm−1. The C O vibrations give a group
of peaks at 1160, 1070, and 1025 cm−1 and the para-substituted aromatic ring gives its
CH bending vibration at 891 cm−1. Hence, the IR spectrum establishes the structure of the
polymer as shown in Fig. 2. The peak at 1261 cm−1 is also common to Ar O stretching
vibration.
1
1H NMR Spectra of Polymers. H NMR Spectra of Polymer 1a. The 1H NMR spectrum of
poly (BOCCPOHMA) is shown in Fig. 3. The aromatic protons give a group of multiplets
between 7.75 ppm and 6.95 ppm. The olefinic protons of the pendant chalcone moiety give
their characteristic signal at 6.4 ppm. The backbone methylene ( CH2) groups show their
peak at 2.3 ppm. The resonance signals at 3.4 ppm is due to alkoxy methylene protons and
the peak at 1.7 ppm is due to the methyl protons.
1H NMR Spectra of Polymer 1b. The 1H NMR spectrum of polymer MPOCCPOOMA
is shown in Fig. 4. The aromatic protons show multiplets between 6.5 ppm and 7.9 ppm.
The signal due to olefinic protons of the pendant chalcone moiety is located at 6.1 ppm.

62
S. Jeyasheela and K. Subramanian
Figure 3. 1H NMR spectrum of polymer BOCCPOHMA.
The signal due to the backbone methylene oxy ( OCH2) groups is observed at 3.5 ppm.
The methoxy protons show their signal at 3.1 ppm. The methyl proton signal occurs at
1.2 ppm.
13C NMR Spectra of Polymers. 13C NMR Spectra of Polymers 1a and 1b. The proton
decoupled 13C NMR spectrum of polymers 1a and 1b is presented in Fig. 5. 13C NMR
chemical shift assignment was made from the off-resonance decoupled spectra of the
polymer. The resonance signals appear at 179 and 177 ppm, which correspond to ester
carbonyl carbon. The ketone carbon signal is observed at 192 and 191 ppm. The signals
at 105 ppm are due to >CH CH< (olefinic) carbon connected to the benzene ring. The
aromatic carbon gives signals at 120–140 ppm and the aliphatic carbon gives signals at 14,
15, 16, 18, 23, and 25 ppm. The signal observed at 40–50 ppm is assignable to the backbone
carbon ( C ) of the polymer BOCCPOHMA and MPOCCPOOMA units.
Molecular Weight. The number and weight average molecular weight of polymers
BOCCPOHMA and MPOCCPOOMA were determined by gel permeation chromatogra-
phy presented in Table 1. The polydispersity indexes of polymers BOCCPOHMA and
MPOCCPOOMA are 1.78 and 1.76, respectively; the theoretical values of Mw/Mn for poly-
mers produced via radical combination and disproportionation are 1.5 and 2.0, respectively
[31,32]. The weight (Mw) and number average molecular weight (Mn) and the polydis-
persity index of polymers BOCCPOHMA and MPOCCPOOMA determined by the gel

Synthesis and Characterization of Novel Liquid Crystalline Photoactive Polymers 63
Figure 4. 1H NMR spectrum of polymer MPOCCPOOMA.
permeation chromatography are as follows.
Mw × 10−4 = 3.92; Mn × 10−4 = 2.20; Mw/Mn = 1.78,
Mw × 10−4 = 3.61; Mn × 10−4 = 2.05; Mw/Mn = 1.76.
Usually the polydisperstiy index Mw/Mn of poly(meth)acrylates prepared by free rad-
ical polymerization of the monomer depends, among other factors, on the chain termina-
tion mechanism. The polydispersity index value of polymers BOCCPOHMA and MPOC-
CPOOMA suggests that the tendency for chain termination by disproportionation is more
than that for dimerisation.
Thermal Studies. DSC Analysis of Polymers. DSC analysis investigated the mesogenic
transition of the polymers 1a and 1b. The DSC thermograms of the polymers were measured
at a heating rate of 10 c/min and representative thermograms of polymers are shown in
Figs. 6 and 7. The phase transition temperatures of all the polymers are summarized in
Table 2. The two DSC thermograms show two endothermic peaks, which reveals that the
mesogenic transition values decrease with an increase in methylene group. The polymer
1a shows higher mesogenic transition temperature as compared with polymer 1b, which is
due to the effect of substituent of benzene ring on the thermal properties of the polymer.
TGA of Polymers. The TGA traces of the polymers are shown in Figs. 8 and 9 and
the data are given in Table 1. The thermal stability of all polymers was investigated at
various temperatures and the weight loss (%) was observed. TGA revealed that poly-
mer 1a was stable up to 210◦C–270◦C and was found to be more stable than that of

64
S. Jeyasheela and K. Subramanian
Table 2. DSC data of polymers BOCCPOHMA and MPOCCPOOMA
DSC
Polymers
Tm (◦C)
Ti
ꢀT
Tg
BOCCPOHMA
MPOCCPOOMA
110
98
138
36
28
38
78
65
Figure 5. 13C NMR spectrum of polymers BOCCPOHMA and MPOCCPOOMA.

Synthesis and Characterization of Novel Liquid Crystalline Photoactive Polymers 65
Figure 6. DSC trace of polymer BOCCPOHMA.
Figure 7. DSC trace of polymer MPOCCPOOMA.
Figure 8. TGA thermogram of polymer BOCCPOHMA.

66
S. Jeyasheela and K. Subramanian
Figure 9. TGA thermogram of polymer MPOCCPOOMA.
polymer 1b. Thermal stability of the polymer usually decreases with an increase in methy-
lene spacer in pendant chains. The polymer MPOCCPOOMA is less stable than the polymer
BOCCPOHMA. Thermal stability of the polymer BOCCPOHMA was higher than that of
polymer MPOCCPOOMA, which is due to the increased aromaticity of the polymer back-
bone. The thermal stability of the polymer MPOCCPOOMA decreases with an increase in
the methylene spacer.>
Photocrosslinking Behavior Studies. The polymers containing the mesogenic chalcone
pendant unit undergo photo crosslinking by UV irradiation and the structural changes
were monitored by UV spectroscopy. The photosensitivity of polymers BOCCPOHMA
and MPOCCPOOMA was measured by irradiation with a high-pressure mercury lamp
(schemes 4 and 5) [29]. The pendant chalcone moiety (>C C<) of the polymers shows
a UV absorption band at 290 and 320 nm due to the π−π∗transition. The irradiation of
polymer solutions, poly (BOCCPOHMA) and poly (MPOCCPOOMA) chloroform, was
carried out using a light of 290 and 320 nm at room temperature and the results are illustrated
in Figs 10 and 11. In poly (BOCCPOHMA) the absorption bond around 290nm corresponds
to π−π∗ transition of the olefinic double bond of the mesogenic unit in the polymer back
bone. During irradiation with UV light a decrease in intensity of the absorption was absorbed
due to formation of cyclo butane ring through 2π + 2π cyclo addition of carbon-carbon
double of bond chalcone unit. The plots of conversion versus irradiation time of the poly
(BOCCPOHMA) and poly (MPOCCPOOMA) are shown in Figs. 12 and 13.
Polarized Optical Microscopy Analysis. The DSC trace of the polymers shows two
endothermic peaks, corresponding to the melting (Tm) and isotropic (Ti) transition temper-
atures. Generally, the melting transition temperature decreases with an increase in aliphatic
spacers as expected. The two polymers exhibited liquid crystalline nature with nematic
textures on heating. The polymer BOCCPOHMA was heated to 135◦C to exhibit a nematic
texture as shown in Fig. 14. The optical texture is always stable throughout the whole

Synthesis and Characterization of Novel Liquid Crystalline Photoactive Polymers 67
Figure 10. Change in UV spectral characteristics, during the photolysis of polymer BOCCPOHMA.
Figure 11. Change in UV spectral characteristics, during the photolysis of polymer MPOC-
CPOOMA.
Figure 12. Dependence of the photocrosslinking rate on irradiation time of polymer BOCCPOHMA.

68
S. Jeyasheela and K. Subramanian
Figure 13. Dependence of the photocrosslinking rate on irradiation time of polymer MPOC-
CPOOMA.
mesogenic range. On cooling the polymer from isotropic melt (Ti), the reproducibility of
the phase was satisfactory. The polymer MPOCCPOOMA was heated to 130◦C to exhibit
a grainy texture as shown in Fig. 15. The rigidity of the mesogenic core with the flexible
spacer length and terminal units highly influences the melting temperature, mesophase tem-
perature, and even molecular arrangement. Highly polar, hindered pendant groups revealed
to have high interaction leading to the formation of liquid crystalline phase.
Figure 14. HOPM photograph of polymer BOCCPOHMA.

Synthesis and Characterization of Novel Liquid Crystalline Photoactive Polymers 69
Figure 15. HOPM photograph of polymer MPOCCPOOMA.
Conclusions
The polymers BOCCPOHMA and MPOCCPOOMA were synthesized by free radical poly-
merization in solution using benzoyl peroxide as initiator. The synthesized polymers were
characterized by the IR, 1H NMR, 13C NMR spectral techniques. The photocrosslinkable
liquid crystalline polymers containing cinnamoyl moiety with various terminally substituted
phenyl groups in the side chains, which act as mesogen, were synthesized and characterized
spectroscopically. The intrinsic viscosity of the polymer data reveals that these polymers
have reasonable molecular weight. Thermal stability of the polymer 1a was higher than the
polymer 1b due to the increased aromaticity of the polymer backbone in the former. The
thermal stability decreases with an increase in the methylene spacer. The Tm and Ti of the
polymers decrease with an increase in even number of methylene spacer. The HOPM (Hot
stage polarized microscopy) study indicates that the two prepared polymers exhibit LC
properties with nematic texture. The photocrosslinking properties of two polymers were
examined by UV spectroscopy, and the photocrosslinking polymers proceed through (2π +
2π) cycloaddition reaction of the olefinic group present in the mesogen of the polymer. The
two polymers showed photocrosslinking behavior under UV radiation and the photolysis
reaction completed within 5–7 min. The photolysis studies of various methylene-spacer-
containing polymers reveal that the rate of photocrosslinking depends on the length of
methylene chain and it follows via octamethylene > hexamethylene. Finally, it may be
concluded that these polymers can be suitably exploited for developing photoresists, print-
ing plate integrated circuit technology, photofabrication, surface coating, energy exchange
materials, etc.
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