Synthesis and Liquid Crystal Properties of Supramolecular Side-Chain Liquid-Crystalline Polymers Containing Poly(acrylic acid) Intermolecular Hydrogen Bonds

Article abstract of DOI:10.1080/15421406.2014.889531

Novel supramolecular side-chain liquid-crystalline polymers were prepared from poly(acrylic acid) (PAA) and pyridyl Schiff base derivatives through intermolecular hydrogen-bonding interaction between PAA and nitrogen of pyridyl Schiff base derivatives. PAA used as H-bond donor. Pyridyl Schiff base derivatives used as H-bond acceptors. The existence of H-bonding was confirmed by FT-IR spectroscopy. Polymer complexes exhibited stable thermotropic mesophase. Differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction measurements were used to investigate LC behavior. The complexes exhibited smectic C phase broken-fan shaped texture. On increasing spacer length of substituent, the clearing temperature range of the mesophase increased.

Full text of DOI:10.1080/15421406.2014.889531

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Synthesis and Liquid Crystal Properties
of Supramolecular Side-Chain Liquid-
Crystalline Polymers Containing
Poly(acrylic acid) Intermolecular
Hydrogen Bonds
P. Kandasamya, R. Keerthigaa, S. Vijayalakshmia & T. Kaliyappana
a Department of Chemistry, Pondicherry Engineering College,
Puducherry, India
Published online: 15 Jan 2015.
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To cite this article: P. Kandasamy, R. Keerthiga, S. Vijayalakshmi & T. Kaliyappan (2015) Synthesis
and Liquid Crystal Properties of Supramolecular Side-Chain Liquid-Crystalline Polymers Containing
Poly(acrylic acid) Intermolecular Hydrogen Bonds, Molecular Crystals and Liquid Crystals, 606:1, 1-11,
DOI: 10.1080/15421406.2014.889531
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Mol. Cryst. Liq. Cryst., Vol. 606: pp. 1–11, 2015
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2014.889531
Synthesis and Liquid Crystal Properties
of Supramolecular Side-Chain Liquid-Crystalline
Polymers Containing Poly(acrylic acid)
Intermolecular Hydrogen Bonds
P. KANDASAMY, R. KEERTHIGA, S. VIJAYALAKSHMI,
AND T. KALIYAPPAN∗
Department of Chemistry, Pondicherry Engineering College, Puducherry, India
Novel supramolecular side-chain liquid-crystalline polymers were prepared from
poly(acrylic acid) (PAA) and pyridyl Schiff base derivatives through intermolecular
hydrogen-bonding interaction between PAA and nitrogen of pyridyl Schiff base deriva-
tives. PAA used as H-bond donor. Pyridyl Schiff base derivatives used as H-bond
acceptors. The existence of H-bonding was confirmed by FT-IR spectroscopy. Polymer
complexes exhibited stable thermotropic mesophase. Differential scanning calorime-
try, polarized optical microscopy, and X-ray diffraction measurements were used to
investigate LC behavior. The complexes exhibited smectic C phase broken-fan shaped
texture. On increasing spacer length of substituent, the clearing temperature range of
the mesophase increased.
Keywords Liquid crystal; mesogen; self-assembly; smectic; thermal properties
1. Introduction
Side-chain liquid-crystalline polymers (SCLCPs) bearing noncovalent interaction has been
found to be interesting topics in material science and optical technologies, due to their spe-
cial application in electro-optical display, information storage, optical processing, and
so on [1–7]. The use of specific intermolecular interactions plays major roles in the
supramolecular assembly of liquid crystals. In nature, functional biomolecules, such as
nucleic acids, sugar, and protein have hydrogen donor and acceptor moieties, which serve
for self-assembly and molecular recognition. The use of self-assembly through specific
interactions, such as hydrogen bonding, ionic-dipolar and charge transfer interactions has
been recognized as a new strategy for constructing SCLCPs [8,9].
For synthetic liquid crystals, the hydrogen bonding interaction is one of the most
prominent and widely used as noncovalent interaction in the design and construction of
supramolecular functional materials. A great variety of hydrogen bonds have been used to
build the supramolecular mesogenic structures. The hydrogen bonding interaction should
∗Address correspondence to T. Kaliyappan, Department of Chemistry, Pondicherry Engineering
College, Puducherry 605014, India. E-mail: tkaliyappan2001@pec.edu
Color versions of one or more of the figures in the article can be found online at
www.tandfonline.com/gmcl.
1

2
P. Kandasamy et al.
Figure 1. IR spectra of polymer and its complex: (a) pyridyl H-acceptor (N1); (b) polymer PAA; and
(c) polymer complex PAA-N1.
be dynamic to enhance the thermotropic liquid-crystalline state [10,11]. Moreover, these
liquid-crystalline networks consisting of multifunctional hydrogen bonding components,
show reversible mesomorphic-isotropic phase transitions as a results of the thermal for-
mation and breaking (ON/OFF switching) of the hydrogen bonds [12–16]. Such reversible
cross-linking materials can be used to prepare dynamic materials [17–21]. Kato and Frechet
first exploited two different and independent components to generate liquid crystals through
intermolecular hydrogen bonding interaction, and this concept inturn resulted in numerous
finding of such supramolecular liquid crystals [22]. Cui et al. reported the new series of azo
pyridine supramolecular SCLCPs by H-bonding interaction. In addition the photoinduced
birefringence of complexes also investigated by the complexation of various carboxylic acid
derivatives [23]. Malik et al. reported the traditional important non-covalently bound liquid-
crystalline polymers using a flexible carbon atom spacer and rigid aromatic core compounds
[24]. Han et al. reported a supramolecular host-guest polymers for successfully used to pre-
pare new variation of liquid-crystalline materials by poly(4-vinylpyridine) and hydroxyl
cyanobiphenyl derivatives [25]. However, these reported side-chain supramolecular liquid
crystals always consist of two complementary bifunctional monomers, a proton donor and
a proton acceptor, which hold together through the intermolecular hydrogen bonds. To the
best of our knowledge, limited studies are reported on side-chain liquid crystals generated
by poly(acrylic acid) (PAA) and Schiff base derivatives through intermolecular hydrogen
bonding interaction.
The aim of present study is to attach pyridyl Schiff base mesogenic derivatives to a PAA
backbone through H-bonding interaction. Fig. 1 shows the structures used to construct new
SCLCPs throughself-assemblyinvolvingintermolecular hydrogenbondinginteraction. The
SCLCP complexes were characterized by using differential scanning calorimetry (DSC),
polarizing optical microscopy (POM), and X-ray diffraction (XRD) analysis to determine
the liquid-crystalline and thermal properties of the supramolecular complexes on dependent
on the substituted spacer length.

Supramolecular SCLCPs Containing PAA Intermolecular H-Bonds
2. Experimental Section
2.1 Materials
3
Tetrahydrofuran (THF) was distilled under normal pressure from sodium benzophenone
ketyl under nitrogen immediately prior to use. Dichloromethane (DCM) was distilled
in normal pressure over calcium hydride under nitrogen before use. Triethylaminne was
distilled and dried over potassium hydroxide. N,N’-dicyclohexylcarbodiimide (DCC), 4-
dimethylaminopryidine (DMAP), isonicotinic acid, 4-formylphenol, 4-methoxyaniline, 4-
butoxyaniline, acrylic acid, and potassium carbonate were purchased from Aldrich and
used as received. Other solvents were used as purified according to the standard procedure.
PAA was prepared by reported literature (number average molecular weight (Mn) = 44391,
weight average molecular weight (Mw) = 58263, polydispersity index (PDI) = 1.31, degree
of polymer (DP) = 616, [η] = 0.21 in DMF at 30◦C) [26].
2.2 Preparation of 4-formylphenylisonicotinate
To a mixture of isonicotinic acid (10 g, 0.08 mol), 4-formylphenol (9.7 g, 0.08 mol), DCC
(17.8 g, 0.085 mol), and DMAP (5% w/w) were dissolved in DCM (200 mL), and the
resulting mixture was stirred for 12 hr at room temperature under nitrogen atmosphere.
Precipitated byproduct urea was filtered from the reaction mixture and the filtrate was
concentrated by vacuum distillation. The crude product was recrystallized from n-hexane
to get a pure white solid product. Yield 86%, 1H-NMR (400 MHz, CDCl3) δ (ppm): 9.91
(s, 1H, –CHO), 8.89–8.88 (m, 2H, Ar–H), 7.96–7.92 (m, 4H, Ar–H), 7.33 (d, J = 8.4 Hz,
2H, Ar–H). 13C-NMR (400 MHz, CDCl3) δ (ppm): 165.6 (–C O), 157.2, 149.3, 144.7,
137.8, 123.6, 122.6, 114.7 (aromatic), and 55.8 (–OCH3).
2.3 Preparation of 4-((4ꢀ-methoxyphenylimino)methyl)phenylisonicotinate (N1)
To a mixture of 4-formylphenylisonicotinate (0.07 mol) and 4-methoxy aniline (0.07 mol),
were dissolved in absolute ethanol, refluxed at 75◦C for 2 hr and the resulting solution
was poured to crushed ice to precipitate the product. The precipitated crude product was
purified by recrystallization from ethanol to get a pure pale greenish yellow solid. Yield
91%, 1H- NMR (400 MHz, CDCl3) δ (ppm): 8.87–8.86 (m, 2H, Ar–H), 8.48 (s, 1H, CH N),
8.01–7.96 (m, 4H, Ar–H), 7.33 (d, J = 8.4 Hz, 2H, Ar–H), 7.24 (d, J = 8.8 Hz, 2H, Ar–H),
6.93 (d, J = 8.8 Hz, 2H, Ar–H), 3.82 (s, 3H, –OCH3). 13C-NMR (400 MHz, CDCl3) δ
(ppm): 163.6 (–C O), 158.6 (–CH N), 156.8, 152.5, 150.9, 144.7, 136.7, 134.8, 129.9,
123.3, 122.3, 121.9, 114.5 (aromatic), and 55.6 (–OCH3). EA: Calcd for C20H16N2O3: C,
72.28, H, 4.51, N, 8.43. Found: C, 72.42, H, 4.85, N, 8.42.
2.4 Preparation of 4-((4ꢀ-butoxyphenylimino)methyl)phenylisonicotinate (N2)
4-Hydroxyacetanilide reacts with 1-bromobutane and hydrochloric acid to get 4-
1
butoxyaniline. The desired Schiff base was prepared as for N1. Yield 92%, H-NMR
(400 MHz, CDCl3) δ (ppm): 8.66–8.85 (m, 2H, Ar–H), 8.48 (s, 1H, CH N), 8.03–7.96
(m, 4H, Ar–H), 7.32 (d, J = 8.4 Hz, 2H, Ar–H), 7.24 (d, J = 8.8 Hz, 2H, Ar–H), 6.93
(d, J = 8.8 Hz, 2H, Ar–H), 4.02 (t, 2H, –OCH2–), 1.75 (m, 2H, –OCH2CH2–), 1.48
(m, 2H, –OCH2CH2CH2–), 1.01 (m, 3H, –OCH2CH2CH2CH3). 13C-NMR (400 MHz,
CDCl3) δ (ppm): 164.3 (–C O), 158.4 (–CH N), 156.2, 153.2, 150.8, 144.9, 135.6,

4
P. Kandasamy et al.
134.8, 130.6, 123.7, 122.9, 121.8, 114.2 (aromatic), 65.4 (–OCH2–), 32.1 (–OCH2CH2–),
20.6 (–OCH2CH2–CH2–), and 14.5 (–OCH2CH2CH2CH3). EA: Calcd for C23H22N2O3:
C, 73.79, H, 5.88, N, 7.48. Found: C, 7384, H, 5.86, N, 7.52.
2.5 Preparation of Hydrogen-Bonded Complexes
All the hydrogen-bonded side-chain polymer complexes in the present study were pre-
pared by slow evaporation method. The polymer complexes were constructed by mixing
appropriate molar ratio of H-donor polymer and pyridyl H-acceptor in the solutions of
chloroform/THF (1:1 vol), which were self-assembled into supramolecules by evaporating
solvents slowly. Polymeric binary complexes were prepared by mixing equimolar amounts
of the PAA H-donor and two different pyridyl H-acceptor Schiff base (N1 and N2) molecules
followed by slow evaporation method.
2.6 Measurements
Infrared spectra were recorded on a Shimadzu FT-IR 8300/8700 spectrometer in the fre-
quency range 4000–400 cm−1. The measurements were made using transparent KBr pellets,
containing fine powder sample at room temperature. 1H-NMR and 13C-NMR spectra were
measured using Joel EX-400 FT-NMR spectrometer in CDCl3 with TMS as an internal stan-
dard. Gel permeation chromatography analysis were conducted on a LC-20AD/RID-10A
instrument, using polystyrene as standard and THF as eluent. The intrinsic viscosity of the
polymer was measured on DMF solution with an Ubbelohde viscometer at 30◦C. Transition
temperature and phase transition enthalpies were determined by DSC using Perkin-Elmer
DSC7 calorimeter at a heating rate of 5◦C per minute under nitrogen atmosphere. The
liquid-crystalline texture was obtained by using Euromex polarizing microscope equipped
with Linkem HFS91 heating stage and TP93 temperature programmer. Samples were made
by placing between two thin glass cover slips with a heating-cooling rate of 5◦C/min. The-
mogravimetric analysis was carried on SDT Q600 V20.5 Build 15 Universal V4.5 A TA
Instruments at heating rate of 5◦C/min in nitrogen. X-ray powder diffraction data for pow-
der samples were collected on an 800 W Philips (PANANALYTICAL, Netherland) powder
diffractometer using an etched glass plate sample holder by rotating anode diffractometer
using Cu-Kα irradiation. Samples placed on a mettle FP 52 hot stage.
3. Results and Discussion
The PAA and pyridyl Schiff base derivatives were used as hydrogen bonding
donor and acceptor. The structure of the SCLCP complexes formed by intermolec-
ular hydrogen bonding between PAA and pyridyl Schiff base derivatives is de-
picted in Scheme 1. The structure of pyridyl Schiff base derivatives, such as 4-((4ꢀ-
methoxyphenylimino)methyl)phenylisonicotinate (N1) and 4-((4ꢀ-butoxy- phenylim-
1
ino)methyl)phenylisonicotinate (N2) were investigated by H-NMR and 13C-NMR mea-
surements. NMR patterns of 4-((4ꢀ-methoxyphenylimino)methyl)phenylisonicotinate (N1)
as show the resonance peaks in the chemical shift range of 8.7–6.93 ppm attributed to
the signal of aromatic proton. Meanwhile, the resonance signal of imine proton observed
at 8.48 ppm (see Supporting Information). The carbonyl peak of ester group observed at
163.6 ppm, C N signal of imine carbon at 158.6 ppm and the signal of aromatic carbon
observed in the range of 156.8–114.2 ppm.

Supramolecular SCLCPs Containing PAA Intermolecular H-Bonds
5
Scheme 1. Synthesis of hydrogen bonded polymer liquid crystal complexes.
3.1 IR Characterization
The existence and stability of H-bonds in polymer complexes were characterized by FT-IR
spectra, and the IR spectra of hydrogen donor polymer PAA and pyridyl hydrogen acceptor
N1 were compared with that of polymer complex PAA-N1 to examine the existence of
hydrogen bonds as shown in Fig. 1. In contrast to the O−H stretching band of pure PAA at
2648 cm−1, the weaker O−H stretching band observed at 2516 cm−1 in the complex PAA-
N1. This shifting indicates the presence of hydrogen bonding between the pyridyl group of N
and acidic group of H. On the other hand, a C O stretching vibration appeared at 1748 cm−1
in complex PAA-N1, which showed that the carbonyl group is in a less associated state than
in pure PAA with weaker C O stretching vibration appeared at 1682 cm−1 [27,28]. The
results suggested that H-bonds of polymer complex PAA–N1 are formed between polymer
PAA and H-acceptor N1. In addition, the other polymer complexes were also confirmed
to exhibit of H-bonded frameworks as polymer complex PAA-N1, so the supramolecular
structures were established in all the polymer complexes.
3.2 Formation of Liquid Crystal
In order to understand the influence of the mesomorphic behavior of side-chain polymer
complexes were investigated by POM, DSC, and XRD measurements. The phase behavior

6
P. Kandasamy et al.
Table 1. Thermal transition parameters of H-bonded side-chain LC polymeric complexes
H-bonded complex phase transition ◦C (corresponding enthalpy change, J/g)
Heating
PAA–N1 (7.46)
PAA–N2 (6.97)
PAA–(N1–N2) (12.7)
G 53.4
G 59.6
G 63.8
SmC
SmC
SmC
178.4
181.2
192
I
I
I
G = Glassy; SmC = smectic C; I = isotropic state.
temperature and associated enthalpy change (ꢀH) of polymeric complexes are listed in
Table 1. These complexes exhibited stable mesomorphic behavior. Fig. 2 shows the DSC
curves of PAA-N1 and PAA-N2 homo polymeric and PAA(N1/N2) copolymeric complexes.
In PAA-N1 complex shows two endothermic peaks at 53.3 and 178.4◦C. The first transition
peak corresponds to glass transition (Tg) and the second peak corresponds to transition from
liquid-crystalline phase to isotropic transition (Ti). The DSC curves for a PAA-N2 complex
also shows melting peak at 59.6◦C, which was 6◦C higher than for PAA-N1 complex and a
second endothermic peak appeared at 181.8◦C, correspond to the liquid-crystalline phase
to isotropic phase transition (Ti). Comparing the phase transition temperatures of PAA-N1
complex, slight increase of isotropization temperature was observed for PAA-N2 complex.
The existence of the mesophase was further tested explicitly using POM (shown in
Fig. 3). Observations show that the polymeric complexes form liquid-crystalline properties
in the temperature range between the glass transition temperature (Tg) and the isotropization
temperature (Ti). In order to obtain a clear characteristic optical texture for phase identifica-
tion, the complex was cooled slowly from its isotropization temperature at 2◦C/min prior to
Figure 2. DSC thermograms of hydrogen bonded liquid-crystalline polymers: (a) homopolymeric
complex of PAA-N1; (b) homopolymeric complex of PAA-N2; and (c) copolymeric complex of PAA
and the 1:1 mixture of N1 and N2.

Supramolecular SCLCPs Containing PAA Intermolecular H-Bonds
7
Figure 3. POM textures at the cooling process: (a) smectic C, broken fan shaped texture of PAA-N1;
(b) smectic C, broken-fan shaped texture of PAA-N2; and (c) smectic C, broken-fan shaped texture
of copolymeric complex of 1:1 mixture of N1and N2.
observation of LC phase. The intermolecular H-bonded PAA-N1 complex formed smectic C
phase broken fan shaped texture at 170◦C on cooling from the isotropic phase and PAA-N2
complex also formed smectic C phase broken fan shaped texture at 179◦C, which is higher
temperature than PAA-N1 complex. The interaction between the noncovalently assembled
mesogenic units was apparently strong to drive the microphase separation needed for a
smectic phase. From DSC and POM studies, both polymeric complexes exhibited smectic
phase during cooling from isotropic melt.
The temperature dependent XRD patterns obtained from powder sample of PAA-
N1 and PAA-N2 complexes for each phase obtained on heating at 120◦C are presented
Figure 4. Powder X-ray diffraction of hydrogen bonded polymer: (a) PAA-N1 complex at 175◦C
and (b) PAA-N2 complex at 185◦C.

8
P. Kandasamy et al.
Table 2. Thermal stability of polymer and its H-bonded LC complexes
Sample
T5% (◦C)
Tmax(◦C)
T95%(◦C)
PAA
PAA-N1
PAA-N2
185.5
278.1
305.0
205.0
302.3
316.5
280.4
348.5
408.2
T5% = 5% weight loss; Tmax = maximum weight loss; T95% = 95% weight loss.
in Fig. 4. A reflection peak at lower angles (associated with the smectic layer) is ob-
served for PAA-N1 and PAA-N2 complexes. In PAA-N1 complex show sharp reflection at
2θ = 5.5◦ corresponding d-spacing value of 16.1 Å in small angle region. The intensity
curve of PAA-N2 complex at 120◦C also disclose very similar pattern (d-spacing 23.8 Å),
indicating the presence of ordered smectic layer arrangements. These results indicate that
the overlapping of the H-bonded mesogenic cores in the smectic layer for the complexes and
inhibition of the molecular orientation fluctuations and an increase in the order of molecular
arrangement.
3.3 Thermal Properties
The obtained powder complexes were subjected to thermal analysis to determine their
stability behavior by thermogravimetic analysis under nitrogen atmosphere at a heating
rate of 5◦C/min. TGA curves showed (Fig. 5) that both the complexes are thermally more
stable than the polymer. As shown in Table 2, the 5% weight loss temperature (denoted
as T5%) of polymer and its complexes observed in the range of 185–305◦C, due to the
breakage of carbon atom of alkyl chain of polymer and its complexes. However, complexes
exhibit a much higher temperature than polymer, which means that the thermal stability of
complexes has been improved greatly due to the presence of H-bond and more cross-linking
ability than polymer. This result also showed that the thermal stability increase slightly with
increasing of their substituted spacer length.
Figure 5. TGA thermograms: (a) PAA; (b) PAA-N1; and (c) PAA-N2.

Supramolecular SCLCPs Containing PAA Intermolecular H-Bonds
9
Table 3. Smectic-isotropic change of PAA-N1 complexes of different
molar ratio
Mole fraction of N1/mol%
ꢀH/(kJ mol−1
)
0
0.95
2.65
3.84
3.98
4.25
4.68
20
40
60
80
100
3.4 Effect of Complex Composition
Figure 6 shows the DSC curves for the first heating scans of PAA-N1 complexes with
different composition. The corresponding transition temperature and enthalpy changes are
listed in Table 3. The complexes appear miscible over the entire composition range when
viewed under a microscope. As can be seen in Fig. 6, when the molar ratio of N1 to the acidic
group of the PAA in the complex increased from 0.4 to 1.0 and the Tg – TI temperature
range also changed. Therefore, the thermal stability of the mesogenic phase increased with
increasing N1 content in the complexes. The formation of these supramolecular SCLCP
ascended from the assembly of low molar mass compounds with the polymer backbone
through hydrogen-bond interactions between the acidic group of the PAA and the nitrogen
group of N1. The connection of the mesogenic unit to the polymer backbone increased the
softness of the polymer backbone, which in turn hindered the movement of the mesogenic
units and thus facilitated the ordered packing of the mesogenic units along a specific
direction. When higher the molar ratio of N1, forms more hydrogen-bonding mesogenic
units there were in the complex and the higher the isotropization temperature was observed.
The decrease in stiffness of the polymer backbone was shown by a change of Tg from 103◦C.
This indicated that the physico-chemical nature of the main chain affected the mesogenic
behavior. As a result, the formation of SCLCP at molar ratio of 0.4 levels indicated that
Figure 6. DSC curves of PAA-N1 complexes of different molar ratio, first heating scan: (a) 1:1, (b)
1:0.8, (c) 1:0.6, (d) 1:0.4, and (e) 1:0.2.

10
P. Kandasamy et al.
hydrogen-bonded PAA-N1 complex was sufficient for the formation of a LC phase. When
the molar ratio of N1 to the polymer chain was above 1.0 molar ratio, there were insufficient
acidic groups to ensure a 1:1 interaction. Some of the N1 could not be connected to the
main chain through hydrogen-bonding, although the excess N1 could be incorporated into
a liquid crystal and disrupted the ordering of the LC phase and also phase separation
was not observed optically for all complexes. A similar result was observed for PAA-N2
complex.
3.5 Formation of Supramolecular Copolymeric Complexes
The advantages of hydrogen-bonded liquid-crystalline polymers are the ease with which
various copolymers can be prepared. Copolymers of any desired composition can be pre-
pared by self-assembly of H-donor polymer and mixture of two different H-bond acceptors
can control the mesomorphic properties of a copolymers. This is in contrast to conventional
method in which separate monomers must be prepared.
Figure 3c shows an polarized optical micrograph of supramolecular copolymeric com-
plex PAA-(N1/N2) derived from PAA and a mixture of N1 and N2, in which the complexes
were formed using 1:1 molar ratio of hydrogen bond donor and acceptor groups. Figure 2c
shows the phase transition diagram of liquid-crystalline copolymeric PAA-(N1/N2) com-
plexes. Higher Tg and Ti values are observed for the copolymeric complexes than for the
corresponding homopolymeric complexes due to the additional electron donor-acceptor
interaction between polymeric side-chain and mesogens [25]. Furthermore, the enthalpy
changes of isotropization are also significant positive deviation than those homopolymeric
systems. POM studies showed that the copolymeric complexes formed a smectic C phase
broken-fan shaped texture at 189◦C.
4. Conclusions
The supramolecular SCLCP complexes were prepared by polymer (PAA) and pyridyl Schiff
base derivatives (N1 and N2) through intermolecular hydrogen bonding interaction. The
appropriate molar ratios of proton donor polymer and pyridyl Schiff base proton acceptor
derivatives were complexed. This co-operation of noncovalent hydrogen bonding interac-
tion resulted in the formation of liquid-crystalline polymer. The effect of substituted spacer
length on liquid-crystalline properties was discussed. The supramolecular copolymeric
complexes containing a 1:1 molar ratio of hydrogen bond donor polymer and a mixture
of hydrogen bond acceptors were also discussed. The electron donor-acceptor interaction
of copolymeric system enhanced the thermal stability of the liquid-crystalline phase. The
phase behavior of complexes were investigated by DSC, POM, and XRD measurements and
the results proved the presence of smectic C phase broken-fan shaped textures. This study
showed that the adjusting the combination of molar ratio of different pyridyl Schiff base
derivatives in copolymeric complexes could be controlled the formation of liquid-crystalline
phase.
Funding
The authors acknowledge the financial support from Council of Scientific and Industrial
Research (CSIR F. No. 01(2310)/09/EMR II), New Delhi, India.

Supramolecular SCLCPs Containing PAA Intermolecular H-Bonds
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