Hydrogen-bond induced side-chain liquid crystalline polymers based on nicotinic acid derivatives

Article abstract of DOI:10.1016/j.reactfunctpolym.2009.12.002

Supramolecular side-chain liquid crystalline poly(acrylate)s have been prepared by self-assembly of H-bond donor and acceptor complexes through intermolecular complementary hydrogen bond formation. Poly[4-(m-acryloyloxyalkyloxy)benzoic acid]s [m = 6 (P1) and 8 (P2)] were employed as polymer components. Liquid crystalline nicotinic acid derivatives (C1, C2, C3, and C4) were used as complementary H-bond donor/acceptor counterparts. The liquid crystalline properties of the nicotinic acid derivatives, the polymers and their complexes were investigated by DSC and POM. Methylene spacers present at the terminal position of the nicotinic acid derivatives played a key role in mesophase arrangements. The columnar phase exhibited by the nicotinic acid derivatives completely disappeared in the H-bonded complexes to afford a nematic phase, thereby substantiating the complex formation.

Full text of DOI:10.1016/j.reactfunctpolym.2009.12.002

Reactive & Functional Polymers 70 (2010) 217–222
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Hydrogen-bond induced side-chain liquid crystalline polymers based
on nicotinic acid derivatives
*
C. Saravanan, V. Ambili, P. Kannan
Department of Chemistry, Anna University, Chennai 600 025, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Supramolecular side-chain liquid crystalline poly(acrylate)s have been prepared by self-assembly of H-
bond donor and acceptor complexes through intermolecular complementary hydrogen bond formation.
Poly[4-(m-acryloyloxyalkyloxy)benzoic acid]s [m = 6 (P1) and 8 (P2)] were employed as polymer compo-
nents. Liquid crystalline nicotinic acid derivatives (C1, C2, C3, and C4) were used as complementary H-
bond donor/acceptor counterparts. The liquid crystalline properties of the nicotinic acid derivatives,
the polymers and their complexes were investigated by DSC and POM. Methylene spacers present at
the terminal position of the nicotinic acid derivatives played a key role in mesophase arrangements.
The columnar phase exhibited by the nicotinic acid derivatives completely disappeared in the H-bonded
complexes to afford a nematic phase, thereby substantiating the complex formation.
Received 9 September 2009
Received in revised form 3 December 2009
Accepted 3 December 2009
Available online 13 December 2009
Keywords:
Liquid crystalline compounds
H-bonded complexes
Nicotinic acid derivatives
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
lix[4]arene was reacted with 6-hydroxynicotinic acid using
carbonyldiimidazole as a coupling reagent to give a dipyridone ca-
Molecules capable of forming self-assembled and self-organized
structures have attracted an increasing amount of attention in
materials chemistry [1]. Biomolecules are prime examples of
hydrogen-bonded molecules [2]. A wide variety of self-organized
molecular systems such as liquid crystals can be used to produce
artificial biological systems and numerous other functional materi-
als for different purposes [3]. The H-bonded self-assembly ap-
proach has significantly enriched the variety of liquid crystals
(LCs) in supramolecular chemistry and has provided many types
of liquid crystalline phases with either calamitic or columnar
arrangements [4–7]. The design of highly organized soft matter
arises from strong cohesive forces like hydrogen bonding between
identical or complementary molecules [8,9]. The mesophase mor-
phology is largely determined by the mean lateral area of compet-
ing molecular blocks. Linear mesogens mostly display nematic or
smectic mesophases [10,11]. Kihara et al. reported supramolecular
liquid-crystalline networks prepared by the self-assembly of mul-
tifunctional H-bond donor and acceptor molecules through the for-
mation of intermolecular H-bonds [12]. So far, not only rodlike and
disk-like LCs, but also polymeric LCs with side-chain, main chain,
network and guest–host structures have been prepared by molec-
ular self-assembly through intra or intermolecular H-bond forma-
tion between H-donors and H-acceptors [13–15]. Otterholm and
Walba have synthesized a variety of LCs and ferroelectric LCs bear-
ing core groups derived from nicotinic acids [15]. 1,3-Diaminoca-
lix[4]arene receptor. Due to the self-complementarity of the recep-
tor, oligomerization has been observed in CDCl3 by vapor pressure
osmometry and light scattering experiments [17]. Addition of imi-
dazolidone (a cyclic urea) disrupts oligomer due to the formation
of a 1:1 H-bonded complex as shown in Fig. 1 [17,18]. Along sim-
ilar lines, the present work deals with the synthesis and character-
ization of novel H-bonded liquid crystalline compounds derived
from the complementary H-bond donor and acceptor functions of
nicotinic acid derivatives containing two different spacer lengths
at the terminal position with the goal of analyzing the liquid crys-
talline properties of H-bonded polymer complexes.
2. Experimental
2.1. Materials
6-Hydroxynicotinic acid, 4-hydroxybenzoate, acrylic acid, a, -
a0
azobisisobutyronitrile (AIBN), 4-(dimethylamino)pyridine (DMAP)
and N,N0-dicyclohexylcarbodiimide (DCC) (Merck, Germany) were
used as received. Methanol, ethanol, THF, diethyl ether, chloroform,
triethylamine, dimethylformamide (DMF) (SRL, India) and other
solvents were purified by standard procedures [19]. Silica gel
(100–200 mesh) (SRL, India) was dried in a hot air oven at 100 °C
for 2 h and cooled before use. 10-Bromo-1-decanol (1) [20], 4-(6-
hydroxyhexyloxy)benzoic acid (2), 4-(8-hydroxyoctyloxy)benzoic
acid (3), 4-(6-acryloyloxyhexyloxy)benzoic acid (M1), 4-(8-acryl-
oyloxyoctyloxy)benzoic acid (M2), poly[4-(6-acryloyloxyhexyl-
oxy)benzoic acid] (P1) and poly[4-(6-acryloyloxy)hexyloxy
* Corresponding author. Tel.: +91 2220 3155; fax: +91 2220 0660.
E-mail address: pakannan@annauniv.edu (P. Kannan).
1381-5148/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2009.12.002

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C. Saravanan et al. / Reactive & Functional Polymers 70 (2010) 217–222
148.4, 115.1, 114.7 (aromatic), 67.7 (AOACH2), 30.8, 28.3, 28.2,
25.0, 21.6, 13.0 (aliphatic carbon).
2.3. 5-(40-Hexyloxyphenyloxy)carbonyl-2-pyridone (C1)
A solution of 6-hydroxynicotinic acid (1.3 mmol, 181 mg) and
4-hexyloxyphenol (1.3 mmol, 0.250 mg) in dichloromethane was
added to DMAP a nitrogen atmosphere. After cooling the mixture
in an ice-water bath, DCC was added, and the mixture was stirred
overnight at room temperature. The salt that formed was filtered
off, and the solvent was evaporated. The crude product thus ob-
tained was washed with diethyl ether to remove unreacted DCC
and 4-hexyloxyphenol. It was then dissolved in THF to remove 6-
hydroxynicotinic acid as solid particles that deposited on the bot-
tom of the flask. The solid particles were filtered off and washed
exhaustively with THF. The THF was removed under vacuum to
give a white solid that was further purified by column chromatog-
raphy (yield 54%). Compounds C2, C3 and C4 were also prepared
using similar procedures.
Fig. 1. Schematic denaturation of oligomerization of calix[4]arenes by its ability to
form 1:1 H-bonded complex with pyridone.
C1: IR (KBr disc) (cmꢀ1): 3324 (ANH), 1733 (ester carbonyl),
1170 (ArAOACH2), 2934 and 2850 (ACH2A). 1H NMR (CDCl3) d
(ppm): 8.20 (s, 1H, Ar), 7.02 (d, 1H, Ar), 6.92 (d, 1H, Ar), 6.52 (d,
1H, Ar), 6.43 (d, 1H, Ar), 3.94 (t, 2H, ArAOACH2A), 0.88–1.89 (m,
benzoic acid] (P2) [21,22] were prepared based on the reported
procedures.
11H, ACH2A(CH2)3ACH3). 13C NMR (CDCl3)
d (ppm): 166.6
(AC@O), 156.2, 143.7, 157.2, 154.6, 141.9, 140.1, 136.4, 122.8 (aro-
matic), 68.4 (ArAOACH2A), 32.8, 32.2, 31.8, 30.8, 29.5, 29.2, 26.1,
25.9, 24.9, 22.6, 15.2, 14.6 (aliphatic). C18H21NO4; calculated: C,
68.48; H, 6.78; N, 4.41; O, 20.32. Found: C, 67.74; H, 6.74; N,
4.13; O, 19.99.
2.2. 4-Hexyloxyphenol (4)
Compound 4 was prepared by using a modification of the liter-
ature procedure [23]. To a solution of hydroquinone (0.18 mol,
20 g) and bromohexane (0.09 mol, 7.01 mL) in ethanol (65 mL)
was added a solution of KOH (0.36 mol, 20 g) in ethanol (60 mL)
at room temperature. The reaction mixture was slowly heated to
80 °C and then refluxed for 24 h, cooled and extracted with ethyl
acetate. The solvent was evaporated, and the residue was purified
by column chromatography (silica gel, ethyl acetate/hexane) to
give a colorless solid (yield 52%). The compounds 5, 6 and 7 were
also prepared using similar procedures.
C2: IR (KBr disc) (cmꢀ1): 3324 (ANH), 1733 (ester carbonyl),
1172 (ArAOACH2), 2935 and 2851 (ACH2A). 1H NMR (CDCl3) d
(ppm): 8.21 (s, 1H, Ar), 7.02 (d, 1H, Ar), 6.92 (d, 1H, Ar), 6.50 (d,
1H, Ar), 6.45 (d, 1H, Ar), 3.94 (t, 2H, ArAOACH2A), 0.82–1.91 (m,
15H, ACH2A(CH2)6ACH3). 13C NMR (CDCl3)
d (ppm): 166.8
(AC@O), 156.2, 143.7, 157.8, 154.2, 141.9, 140.1, 136.5, 122.8 (aro-
matic), 68.4 (ArAOACH2A), 33.4, 32.9, 31.4, 31.1, 29.5, 28.9, 26.7,
26.3, 24.9, 22.6, 18.4, 61.8, 15.2, 13.2 (aliphatic). C20H25NO4; calcu-
lated: C, 69.98; H, 7.31; N, 4.12; O, 18.68. Found: C, 69.46; H, 6.96;
N, 4.01; O, 18.12.
IR (KBr disc) (cmꢀ1): 3312 (AOH), 2954 and 2834 (ACH2A),
1246 (aryl–alkyl ether linkage). 1H NMR (CDCl3) d (ppm): 6.76 (d,
4H, Ar), 5.51 (s, 1H, ArAOH), 3.88 (t, 2H, ArAOACH2A), 0.86–1.78
(m, 11H, ACH2A(CH2)3ACH3). 13C NMR (CDCl3) d (ppm): 152.3,
C3: IR (KBr disc) (cmꢀ1): 3325 (ANH), 1731 (ester carbonyl),
1170 (ArAOACH2), 2928 and 2846 (ACH2A). 1H NMR (CDCl3) d
Scheme 1. Synthesis of C1, C2, C3, C4, monomers and polymers.

C. Saravanan et al. / Reactive & Functional Polymers 70 (2010) 217–222
219
Table 1
Thermal property of polymers and nicotinic acid derivatives.
Polymer/compounds
Tg (°C)
DSC (°C)
POM (°C)
PDI
Mesophase
Mn
Tm
Ti
D
T
Tm
Ti
DT
P1
P2
C1
C2
C3
C4
–
–
–
–
–
–
142
131
99
101
105
104
184
216
138
141
146
149
42
85
39
40
41
45
139
130
97
103
106
105
186
219
139
143
147
150
47
89
42
40
41
45
24,300
28,600
–
–
–
–
1.03
1.14
–
–
–
Nematic, smectic A
Nematic, smectic A
Smectic A
Columnar
Columnar
–
Columnar
(ppm): 8.23 (s, 1H, Ar), 7.03 (d, 1H, Ar), 6.92 (d, 1H, Ar), 6.52 (d, 1H,
Ar), 6.43 (d, 1H, Ar), 3.94 (t, 2H, ArAOACH2A), 0.71–1.96 (m, 19H,
ACH2A(CH2)8ACH3). 13C NMR (CDCl3) d (ppm): 166.6 (AC@O),
156.3, 143.5, 157.2, 154.6, 142.2, 140.1, 136.4, 122.7 (aromatic),
68.4 (ArAOACH2A), 34.6, 33.2, 32.4, 31.7, 30.9, 29.6, 28.6, 27.2,
26.7, 25.3, 24.6, 22.9, 22.1, 19.5, 16.2, 15.4, 14.1 (aliphatic).
C22H29NO4; calculated: C, 71.08; H, 7.83; N, 3.82; O, 17.27. Found:
C, 69.76; H, 7.81; N, 3.59; O, 17.01.
polydispersity (Mw=Mn) of polymers were obtained on a PL-GPC
model 210 chromatograph calibrated with polystyrene standard
using DMF as eluent at 25 °C. DSC measurements were performed
at a heating rate of 10 °C/min up to 400 °C; samples were taken in
an aluminum pan with a pierced lid in a dry nitrogen atmosphere
with an empty atmosphere pan as reference. The textures of the
polymers, the nicotinic acid derivatives and their H-bonded com-
plexes were observed using a Euromex polarizing microscope
equipped with a Linkem HFS91 heating stage and a TP-93 temper-
ature programmer with a scanning rate of 5 °C/min.
C4: IR (KBr disc) (cmꢀ1): 3324 (ANH), 1732 (ester carbonyl),
1171 (ArAOACH2), 2939 and 2858 (ACH2A). 1H NMR (CDCl3) d
(ppm): 8.20 (s, 1H, Ar), 7.02 (d, 1H, Ar), 6.93 (d, 1H, Ar), 6.52 (d,
1H, Ar), 6.434 (d, 1H, Ar), 3.95 (t, 2H, ArAOACH2A), 0.69–2.01
(m, 23H, ACH2A(CH2)10ACH3). 13C NMR (CDCl3) d (ppm): 166.5
(AC@O), 156.2, 143.8, 157.2, 154.6, 141.9, 140.1, 136.6, 123.1 (aro-
matic), 68.5 (ArAOACH2A), 36.4, 35.8, 35.2, 34.6, 33.1, 32.9, 32.3,
31.8, 31.5, 30.6, 29.8, 29.2, 27.5, 26.5, 25.3, 24.9, 23.7, 22.8, 19.6,
17.5, 15.8, 14.9 (aliphatic). C24H33NO4; calculated: C, 72.14; H,
8.29; N, 3.55; O, 16.06. Found: C, 72.28; H, 8.12; N, 3.66; O, 15.84.
3. Results and discussion
3.1. Synthesis
H-bonded liquid crystalline compounds C1–C4 were obtained
as colorless solids by O-alkylation of hydroquinone under William-
son aryl ether synthesis conditions and then reacted with 6-
hydroxynicotinic acid using DCC (Scheme 1). The chemical struc-
tures of all the compounds and polymers were characterized by
FT-IR, 1H and 13C NMR spectral techniques. Fig. S1, Supplementary
materials shows the 1H NMR spectrum of C3 in a chloroform solu-
tion with the resonance signals of all the protons assigned using
letters of the alphabet. It indicates that all the protons in the
molecular structure agreed well with the corresponding signals
in the spectrum. P1 and P2 were prepared from their monomers
by the free radical addition polymerization technique in THF solu-
tion at 60 °C using AIBN as initiator. The number-average molecu-
lar weight and polydispersity index (PDI) were obtained from GPC
data (Table 1), and they revealed that the polymers possess moder-
ate molecular masses.
2.4. Preparation of H-bonded complexes
H-bonded complexes were prepared by the evaporation tech-
nique. A THF solution containing stoichiometric amounts of the
carboxylic acid-containing polymer and the nicotinic acid deriva-
tive were evaporated slowly at room temperature. The resulting
solid was dried under vacuum for 24 h.
2.5. Measurements
Infrared spectra were obtained on a Bruker IFS 66 V Fourier
transform spectrometer using KBr pellets. High-resolution 1H and
13C NMR spectra were recorded on a Bruker 400 MHz spectrometer
in CDCl3 with TMS as an internal standard. Weight-average molec-
ular weight (Mw), number-average molecular weight (Mn), and
Scheme 2. Comparative mesogenic cores of nicotinic acid derivatives for the
thermotropic liquid crystals.
Fig. 2. DSC thermograms of C1, C2, C3 and C4.

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C. Saravanan et al. / Reactive & Functional Polymers 70 (2010) 217–222
Fig. 3. (a) Dimer formation of C1. (b) POM image of smectic-A phase of C1 at 132 °C.
3.2. Mesophase characterization of polymers (P1 and P2)
the nicotinic acid was O-alkylated with various chiral spacer units,
as shown in Scheme 2. Both compounds I and II exhibited a nema-
tic phase in the range of 25–76 °C. The AC@O and NAH linkages of
nicotinic acid have the potential to show two H-bonded self-
assembly patterns, as shown in Fig. 1. In this study, the H-bonded
self-assembly pattern of nicotinic acid a derivative was employed
for the development of novel complementary H-bonded thermo-
tropic LCs. The most common rigid cores in supramolecular LCs
are linear structures with para-substituted aromatic rings H-
bonded to pyridyl and carboxylic acid moieties. Nevertheless, some
supramolecular LCs with nonlinear structures has been reported to
display interesting mesomorphic properties [24,25]. Herein, the
Han et al. [6] have synthesized hydrogen bonded side-chain li-
quid crystalline polymers in which a pyridine ring in the backbone
acts as a donor unit, and a hydroxyl at the terminal position acts as
an acceptor unit. Based on these polymeric systems, we synthe-
sized two polymers containing hexamethylene (P1) and octameth-
ylene (P2) spacers in their side-chains that end with 4-oxybenzoic
acid. These two polymers display liquid crystalline phases due to
the formation of complementary donor/acceptor H-bonded com-
plexes (Fig. S2, Supplementary materials). The phase transition
temperatures and liquid crystalline phases of the polymers were
examined by DSC and POM, respectively. DSC thermograms for
P1 and P2 at a scanning rate of 5 °C/min during the second heating
cycles are shown in Fig. S3 (Supplementary materials). Both poly-
mers exhibited two endothermic transitions attributable to liquid
crystalline characteristics [13c]. The endothermic transition at
the lower temperature corresponds to melting (Tm), while the tran-
sition at the higher temperature corresponds to the isotropic (Ti)
transition. The thermal properties of the polymers are presented
in Table 1. On cooling from an isotropic melt, P1 shows nematic
and smectic-A phases at 171 and 149 °C, which are characterized
by the observation of marble and fan-like textures on the POM,
respectively. Similarly, P2 exhibited nematic and smectic phases
in the range of 142–184 °C. It also displays nematic and smectic
mesophases while cooling from an isotropic melt at 187 and
142 °C, respectively. The representative POM images of P1 are
shown in Fig. S4 (Supplementary materials).
3.3. Mesophase characterization of nicotinic acid derivatives (C1, C2,
C3 and C4)
Derivatives of nicotinic acid are employed as a mesogenic core
for the construction of ferroelectric LCs in energy-efficient, volt-
age-controlled light valves such as watch and calculator display
applications [16]. In the present study, the OH group present in
Fig. 4. Formation of disc like structures of C2, C3 and C4.

C. Saravanan et al. / Reactive & Functional Polymers 70 (2010) 217–222
221
Fig. 6. Formation of various hydrogen bonded complexes.
Table 2
DSC and POM data of polyacrylates and nicotinic acid derivatives.
Complex
DSC (°C)
POM (°C)
Mesophase
Tg
Tm
Ti
D
T
Tm
Ti
DT
6CI
67
59
56
51
58
54
50
51
112
121
113
119
106
112
132
146
184
214
215
231
213
234
254
274
72
93
113
123
112
119
104
111
129
147
183
213
217
231
212
237
253
272
70
90
Nematic
Nematic
Nematic
Nematic
Nematic
Nematic
Nematic
Nematic
6CII
6CIII
6CIV
8CI
8CII
8CIII
8CIV
102
112
107
122
122
128
105
112
108
126
124
125
3.4. Mesophase characterization complexes (6CI–6CIV and 8CI–8CIV)
One-to-one complexes of acid-functionalized polyacrylates and
nicotinic acid derivatives were prepared by direct mixing in THF
and subsequent evaporation at room temperature (Fig. 6). DSC
thermograms of complexes 6CI–6CIV and 8CI–8CIV are shown in
Figs. S5 and S6 (Supplementary materials), respectively. On heat-
ing, all the complexes exhibited glass transition temperatures in
the range of 65–70 °C, followed by melting and isotropic transi-
tions. The phase transition temperatures of 6CI–6CIV and 8CI–
8CIV are shown in Table 2. Significant effects attributable to hydro-
gen bonding are observed on the thermal properties of the com-
plexes. All the complexes from 6CI–6CIV to 8CI–8CIV behave as
undivided polymeric materials and demonstrated sharp phase
transitions and homogeneous mesophases. On cooling from isotro-
pic melts, polymers and nicotinic acid derivatives displayed nema-
tic, smectic and columnar mesophases. By contrast, on cooling
from isotropic melts, 6CI–6CIV and 8CI–8CIV delivered merely
nematic phases. Representative POM images of 6CII and 8CIV are
shown in Fig. 7.
FT-IR spectra have been obtained for 6CII to compare the effects
of hydrogen bonding. FT-IR spectra of C2, P2 and 6CII are shown in
Fig. 8. The stretching vibrations of the carbonyl group of the car-
boxylic acid in P2 appeared at 1684 cmꢀ1 and were attributed to
the formation of a dimer [26]. Nicotinic acid derivative C2 exhib-
ited a characteristic band at 1733 cmꢀ1 that was assigned to the
stretching vibrations of the carbonyl group adjacent to the ANH
group in nicotinic acid. Incorporation of CII into the P2 polymer
matrix leads to a decrease and shift of the band to 1723 cmꢀ1, indi-
cating complementary hydrogen bond formation between the car-
Fig. 5. POM images of columnar phase of C2, C3 and C4 at 132, 134 and 139 °C,
respectively.
spacer-dependent H-bond-induced mesophase formation of nico-
tinic acid derivatives was studied. The formation of a mesophase
through hydrogen bonding depends on the spacer lengths at the
terminal position of nicotinic derivatives. DSC thermograms of var-
ious spacer-substituted nicotinic acid derivatives (C1, C2, C3 and
C4) are depicted in Fig. 2. Owing to the liquid crystalline nature
of the compounds, each thermogram has two endothermic transi-
tions. The phase transition temperatures and types of mesophases
are given in Table 1. The thermotropic LC properties of the nicotinic
acid derivatives were induced by complementary hydrogen bond-
ing between two core units. It is interesting to note that the phase
behaviors of C1–C4 are greatly dependent on spacer lengths. Upon
cooling from an isotropic melt, compound C1 shows focal conic fan
texture at 132 °C, a characteristic of a smectic-A phase. This sug-
gests that formation of a dimer-like structure is responsible for this
smectic-like arrangement (Fig. 3). Upon cooling from the isotropic
liquid, the compounds C2, C3 and C4 display columnar mesophases
at 132, 134 and 139 °C, respectively, due to the formation of disk-
like structure (Fig. 4). POM images of C2, C3, and C4 are shown in
Fig. 5. Clearly, the spacer lengths present at the terminal position
play a key role in the mesophase formation.

222
C. Saravanan et al. / Reactive & Functional Polymers 70 (2010) 217–222
4. Conclusion
Supramolecular side-chain liquid-crystalline poly(acrylate)s
have been prepared by self-assembly of H-bond donor and accep-
tor complexes through intermolecular complementary hydrogen
bond formation. The polymers P1 and P2 were employed as side-
chain components in the hydrogen bonding system. On cooling
from isotropic melts, both the polymers show the nematic and
smectic A phases due to the formation of complementary hydrogen
bonds. The liquid crystalline nicotinic acid derivatives (C1, C2, C3,
and C4) were used as another complementary H-bond donor/
acceptor counterpart. The spacer unit present at the terminal posi-
tion of all the derivatives played a major role in the formation of
liquid crystalline phases. Methylene spacers present at the termi-
nal position of the nicotinic acid derivatives also played a major
role in mesophase arrangements of all the complexes. Smectic-A
and columnar phases that appeared for the nicotinic acid deriva-
tives completely disappeared in the H-bonded complexes to afford
nematic phases, thereby substantiating the formation of the
complexes.
Acknowledgement
The author C.S. gratefully acknowledges the Council of Scientific
and Industrial Research (CSIR), New Delhi, India, for the award of
Senior Research Fellowship.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.reactfunctpolym.2009.12.002.
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