In-plane modulated smectic ? vs smectic 'A' lamellar structures in poly(ethyl or propyl ether imine) dendrimers

Article abstract of DOI:10.1016/j.polymer.2016.01.043

A pair of first and second generation poly(alkyl ether imine) dendrimers is prepared, having covalently attached cholesteryl moieties at their peripheries. The pairs in each generation differ in the alkyl-linker which constitute the dendritic core moieties, even when the number of cholesteryl moieties remains uniform in each pair. The dendrimer pairs are two first and second generation poly(ethyl ether imine) and poly(propyl ether imine) dendrimers, modified with 4 and 8 cholesteryl esters at the peripheries in each pair, respectively. The dendrimer pairs exhibit differing thermotropic mesophase properties. Microscopic, thermal and X-ray diffraction studies reveal a lamellar mesophase for the first generation ethyl-, first and second generation propyl-linker dendrimers. Whereas, the second generation ethyl-linker dendrimer exhibits a layered structure with a superimposed in-plane modulation, the length of which corresponds to a rectangular column width. The role of the dendrimer core moieties with differing linkers in modifying the mesophase properties is studied.

Full text of DOI:10.1016/j.polymer.2016.01.043

Polymer 86 (2016) 98e104
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
~
In-plane modulated smectic A vs smectic ‘A’ lamellar structures in
poly(ethyl or propyl ether imine) dendrimers
,
, *
Prabhat Kumar a, D.S. Shankar Rao b, S. Krishna Prasad b **, N. Jayaraman a
a Indian Institute of Science, Bangalore, 560 012, India
b Centre for Nano and Soft Matter Sciences, Jalahalli, Bangalore, 560 013, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A pair of first and second generation poly(alkyl ether imine) dendrimers is prepared, having covalently
attached cholesteryl moieties at their peripheries. The pairs in each generation differ in the alkyl-linker
which constitute the dendritic core moieties, even when the number of cholesteryl moieties remains
uniform in each pair. The dendrimer pairs are two first and second generation poly(ethyl ether imine)
and poly(propyl ether imine) dendrimers, modified with 4 and 8 cholesteryl esters at the peripheries in
each pair, respectively. The dendrimer pairs exhibit differing thermotropic mesophase properties.
Microscopic, thermal and X-ray diffraction studies reveal a lamellar mesophase for the first generation
ethyl-, first and second generation propyl-linker dendrimers. Whereas, the second generation ethyl-
linker dendrimer exhibits a layered structure with a superimposed in-plane modulation, the length of
which corresponds to a rectangular column width. The role of the dendrimer core moieties with differing
linkers in modifying the mesophase properties is studied.
Received 29 October 2015
Received in revised form
11 January 2016
Accepted 19 January 2016
Available online 21 January 2016
Keywords:
Dendrimers
Liquid crystals
Mesophase
Powder X-ray diffraction
Smectic phases
© 2016 Elsevier Ltd. All rights reserved.
1. Introduction
third generation poly(amido amine) dendrimer, functionalized
with varying proportions of two types of promesogenic moieties,
Introduction of dendritic structural principles to liquid crystals
has emerged as a prominent direction of studies in liquid crystals
[1e3]. Commercial availability, as well as, synthetic feasibility [4e7]
contributed to the growth of the field of dendritic liquid crystals
(DLCs). Functionalization of the peripheries of several generations
of dendrimers with chosen monomeric mesogens and studies of
their mesophase properties led to immense developments in DLCs.
Different types of mesophase structures form when the peripheries
are installed with several mesogenic moieties. A layered structure is
observed commonly in DLCs of lower generation dendrimers,
having an open, annular shape. Whereas higher generation den-
drimers encounter steric congestion at the peripheries and, as a
result, a change of the mesophase structures is observed. Changes
in the mesophase structures by varying the peripheral moieties
across different dendrimer generations, i.e. from lower generations
to higher generations, are known commonly [8e13]. In a study,
transitions between lamellar and columnar mesophases within a
were demonstrated by Serrano and co-workers [14]. By systematic
variation in the proportion of the promesogenic moieties, smectic C
to smectic A, or rectangular columnar to smectic A, or rectangular
columnar to hexagonal columnar mesophase transitions occurring
upon increasing the temperature were observed. The mesomorphic
properties were dependent on the mesogenic peripheral moieties
of DLCs, independent of the central dendritic core portion [15].
Linear dendritic block copolymers constituted with a linear poly(-
ethylene glycol) block and dendritic poly(amido amine) segment
functionalized with an azobenzene moiety were demonstrated to
show rich mesophase changes with different generations of the
dendritic poly(amido amine) segment [16]. Development of DLCs
within one particular generation which contains identical number
peripheral mesogenic moieties, yet differs only in the linkers that
constitute the dendritic core moiety alone has so-far eluded the
attention. A systematic variation of the linker length constituting
the dendrimer structure would provide a clue as to how the den-
drimer core moiety affects the mesophase structures. As an effort in
this direction, we undertook studies on the poly(alkyl ether imine)
dendrimer pairs functionalized with cholesteryl moieties as the
mesogen-inducing moieties. The dendrimer pairs were constituted
with either ethyl or n-propyl linkers as the linker of the dendrimer
* Corresponding author.
** Corresponding author.
E-mail addresses: skpras@gmail.com (S. Krishna Prasad), jayaraman@orgchem.
iisc.ernet.in (N. Jayaraman).
http://dx.doi.org/10.1016/j.polymer.2016.01.043
0032-3861/© 2016 Elsevier Ltd. All rights reserved.

P. Kumar et al. / Polymer 86 (2016) 98e104
99
core structures. These two generations of dendrimer pairs were
covalently modified with uniform number of cholesteryl moieties.
We premised that size of the dendrimer core would differ consid-
erably in such pairs. Thus, a denser periphery of the dendrimers
might be achieved through shortening of the linker at the dentritic
core. In the present study, a change from n-propyl linker to an
ethyl-linker was identified, in order to study the effect of dendritic
core size on mesophase properties. This report describes the
observation of a change in the mesophase structure when the size
of the dendritic core is modified through linkers that constitute the
dendrimer, without changing the number of covalently coupled
mesogenic moieties at their peripheries.
Further, elemental composition analysis confirmed the structural
homogeneities of the dendritic mesogens.
Studies of the mesophase characteristics of the first and second
generation dendrimer pairs were conducted using polarizing op-
tical microscopy (POM), differential scanning calorimetry (DSC)
and powder X-ray diffraction (XRD) analyses. The POM analysis
showed that all four compounds were enantiotropic mesogens,
having either a focal-conic or fan-like textures (Fig. 2).
The isotropization temperatures were 141 and 212 ꢁC for G1Et4
and G2Et8, respectively. Whereas in the case of G1Pr4 and G2Pr8,
the isotropization temperatures were considerably lower, at 100
and 128 ꢁC, respectively. Thus, only a change of ethyl linker to n-
propyl linker at the dendritic core moiety, without altering the
number of cholesteryl units at the peripheries of each generation,
reduced the isotropization temperature by >80 ꢁC. Upon cooling
from isotropic melt, G1Et4 converted to a fan shaped texture with
homeotropic region, indicative of a lamellar arrangement. G2Et8
showed a birefringent texture upon cooling from isotropic melt,
and the texture persisted till room temperature. G1Pr4 showed a
fan shaped texture, in addition to homeotropically oriented region,
upon cooling the isotropic melt. Further growth of the texture was
not observed even after annealing for a long period. Whereas, a fan
shaped texture with feather like appearance developed in the case
of G2Pr8 on slow cooling. The textures observed by POM were
essentially the same in the second and subsequent heating-cooling
cycles. A complete extinction of the textures was observed when
using substrate coated with cetyltrimethylammonium bromide,
which indicated that a non-tilted type mesophase structure. G2Et8
was also observed to be much less viscous than G1Et4, G1Pr4 and
G2Pr8 to a mechanical shearing at lower temperatures.
2. Results and discussion
The first and second generation dendrimer pairs with ethyl and
n-propyl spacers, functionalized with 4 and 8 cholesteryl moieties,
are shown in Fig. 1. Covalent modification of the peripheries of
hydroxyl group terminated dendrimers [17] was conducted using
cholesterylhemisuccinoyl chloride (CSCl) [18], in the presence of
Et3N, so as to form ester linkage connecting the mesogen-inducing
moieties with the dendrimer scaffold (Scheme 1). The reactions
were facile and products were obtained in good yields. The con-
stitutions and structural homogeneities of the DLCs were ascer-
tained by physical methods and elemental composition analysis.
Vibrational peak at 1704 cmꢀ1, corresponding to eCO2H function-
ality of the starting material disappeared and appearance of peaks
at ~1730 cmꢀ1, corresponding to the ester functionalities of the
product appeared in the IR spectra. A downfield shift of eCH2OH
protons of the un-functionalized dendrimers from 3.6 ppm to
4.1 ppm in cholesteryl-functionalized dendrimers occurred in the
1H NMR spectra. Similar changes in the chemical shifts were
observed in 13C NMR spectra, resonances at 171.4 and ~172.3 ppm
corresponded to carbonyl-moiety of the ester functionalized den-
drimer, which in the case of CSCl was observed at 177.6 ppm.
The DSC scans showed clearing transition temperatures in
agreement with that observed through POM analysis. A crystal-to-
glass transition appeared near room temperature in the second
heating-cooling cycles onwards (Fig. 3).
For G1Et4, the glass transition and clearing temperatures were
Fig. 1. Molecular structures of cholesterol functionalized pairs of PETIM dendrimers.

100
P. Kumar et al. / Polymer 86 (2016) 98e104
Scheme 1. Synthesis of the first and second generation dendritic liquid crystal pairs.
Fig. 2. POM textures of dendritic LCs: (from left to right) G1Et4 at 130 ꢁC; G2Et8 at 148 ꢁC; G1Pr4 at 85 ꢁC; and G2Pr8 at 105 ꢁC.
Fig. 3. DSC thermograms of dendritic liquid crystals in the second heating-cooling cycle (scan rate 10 ꢁC minꢀ1).
20 and 141 ꢁC, and 16 and 139 ꢁC, in heating and cooling cycles,
respectively. For G2Et8, the crystal to glass transition was 18 ꢁC, but
the clearing temperature enhanced to 212 ꢁC in the heating cycle.
The cooling cycle did not exhibit isotropic to mesophase transition
in DSC, although the transition was observed in POM study. Similar
glass transition and clearing temperatures were observed with
G1Pr4, although at much lower temperatures of 19 and 100 ꢁC,
respectively. In the case of G2Pr8, both the glass transition and
clearing temperatures increased to 24 and 128 ꢁC, respectively. The
molar enthalpy changes were between 1.1 and 1.2 kJ molꢀ1 per
mesogenic unit (Table 1).
Among the four derivatives studied herein, DSC scan of G2Et8
showed an additional weak transition at 99 and 114 ꢁC, in the
heating-cooling cycles, respectively. POM studies did not reveal any
textural differences at these temperatures. We infer that this
transition is due to smectic glass to
a smectic mesophase.
Remaining three derivatives did not show such an additional
transition. It is also seen that the transition temperatures associated
with the crystal to glass transition is quite similar in the heating-
cooling cycles, a feature not commonly observed. We do not have
an understanding of this behavior at present.
The mesophase structures were analyzed by variable tempera-
ture X-ray diffraction technique [19]. The diffraction patterns of
G1Et4, G1Pr4 and G2Pr8 dendritic LCs, recorded within the meso-
morphic range, consisted of sharp peaks in the low-angle region
and a broad, diffuse maximum in the wide-angle region (Figs. 4 and
5). Such reflections are characteristic of a lamellar arrangement of
molecules in the mesophase. The ratios of reciprocal of the spacings
of low angle reflections were integral numbers, as a further
confirmation of the lamellar nature, the spacings of different re-
flections are summarized in Table 2. From the dimensions of the
molecule, we assign the mesophase to be the smectic A phase.
The XRD pattern of G2Et8 differed significantly in comparison to
Table 1
Phase transitions observed in the second heating-cooling scan of DSC analysis.a
DLC
M. Wt. (kDa)
Transition temperature (ꢁC) H (kJ molꢀ1
D )
G1Et4
G2Et8
2.11
4.56
Cr 20 SmA 141 (8.0) I 139 (8.4) SmA 16 Cr
Cr 18 Smg 99 (5.1) SmAc 212 (1.36) I
b
~
I 208d SmA 114 (5.1) Smg 5.3 Cr
~
G1Pr4
G2Pr8
2.24
4.81
g 19 SmA 100 (5.0) I 100 (5.4) SmA 18 g
g 24 SmA 128 (7.7) I 121 (8.5) SmA 12 g
a
DSC scans heating-cooling rate ¼ 10 ꢁC/min.
Smg ¼ smectic glass.
b
c
~
SmA ¼ modulated smectic A.
d
Observed in POM.

P. Kumar et al. / Polymer 86 (2016) 98e104
101
Fig. 4. X-ray diffraction profiles: (a) small angle XRD of G1Et4 at 140 ꢁC; (b) G2Et8 at 60 ꢁC. The insets show the data in the wide angle region; while the data in (a) were fit to a
single Lorentzian, a sum of two Lorentzians (solid red line) was used for the data in (b). The latter consisted of two diffuse reflections (green lines), and two sharp peaks. (For
interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. X-ray diffraction profiles: (a) small angle XRD of G1Pr4, at 90 ꢁC; (b) G2Pr8, at 100 ꢁC. Insets show data in the wide angle region fit to a sum of two Lorentzians (blue line), the
individual contributions being shown as black and green lines. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this
article.)
Table 3
Table 2
Observed and calculated diffraction spacings describing a rectangular lattice, cor-
responding Miller indices, and the lattice parameters at different temperatures for
G2Et8.
X-ray diffraction spacings corresponding to the fundamental (d100), and harmonics
(dn00, n ¼ 2, 3) of the layer periodicity. Dw1 and Dw2 correspond to the separation
between the cholesterol and linker entities within the layer of DLCs.
T/ꢁC
60
dobs/nm
dcal/nm
hka
Lattice parameter/nm
DLC
T/ꢁC
d100/nm
d200/nm
d
300/nm
Dw1/nm
Dw2/nm
4.63
7.06
2.75
2.32
0.54
0.53
0.50
0.45
4.24
7.36
2.79
0.67
0.58
0.54
0.51
5.17
7.40
0.57
4.63
7.06
2.81
2.31
10
01
12
20
Diffuse
85
87
Diffuse
10
01
12
63
Diffuse
76
77
10
01
Diffuse
cr ¼ 4.63
ar ¼ 7.06
G1Pr4
23
50
60
80
90
5.05
4.99
4.99
4.93
4.88
4.93
4.92
4.83
4.65
2.52
2.49
2.49
2.46
2.44
2.47
2.47
2.43
2.33
1.68
1.66
1.66
0.54
0.55
0.55
0.55
0.55
0.55
0.56
0.45
0.46
0.46
0.45
0.45
0.44
0.45
0.54
0.50
G2Pr8
G1Et4
24
100
130
140
150 ꢁC
4.24
7.36
2.78
0.68
cr ¼ 4.24
ar ¼ 7.36
0.56
0.45
other DLCs. At 180 ꢁC, the small angle region showed only two
intense peaks. Upon lowering the temperature, more reflections
were seen in the small angle region (Table 3). It is emphasized that
at any temperature, the ratio of the spacings of first two reflections
is not an integral number, thus ruling out a simple layered phase for
G2Et8 (Fig. 4b). In fact, the reflections can be indexed unambigu-
ously to arise from a 2-D rectangular lattice. Rectangular lattice is
identified in many instances previously. Following are the exam-
ples: (i) Ostrowski and co-workers observed a Colr phase for a fifth
generation carbosilane dendrimer functionalized fully with alky-
loxyazo derivative [20] or butoxyphenylbenzoate derivative at its
periphery [21]; (ii) Serrano co-workers showed a Colr phase to (a) a
fourth generation amine-terminated cationic poly(amido amine)
when complexed with anionic polyalkanoic acid [22] and (b) a third
generation poly(amido amine) dendrimer functionalized with
0.54
0.53
5.17
7.40
180 ꢁC
cr ¼ 5.17
ar ¼ 7.40
a
2-digit Miller indices are given, the third index is zero for all the reflections.
varying numbers of two types of mesogens at the periphery [14].
The possible molecular packing supporting the features
observed for G2Et8 was analyzed further. We begin by noting that
one of the lattice dimensions compares with the layer thickness of
remaining three compounds studied here. Thus we infer that the
mesophase exhibited by G2Et8 is a layered phase, but with an in-
plane modulation. A smectic phase with an in-plane modulation

102
P. Kumar et al. / Polymer 86 (2016) 98e104
has been observed in rod-like molecules, with a strong terminal
lamellar arrangement. G2Et8 presents an interesting situation,
wherein it exhibits a modulated smectic phase than a simple
smectic phase as with remaining three derivatives (Fig. 6b). De-
rivative G2Pr8 presented with identical number of cholesteryl
moieties at the peripheries as that of G2Et8 still retains a simple
smectic A phase. Dendritic liquid crystals are known to show a
rectangular columnar phase. For example, carbosilane dendrimers
across the generations, i.e. lower to higher generations, function-
alized with mesogenic azobenzene moieties at their peripheries
were demonstrated to exhibit a lamellar phase for the generations
one to four, possessing 4 to 64 peripheral moieties, whereas fifth
generation dendrimer, possessing 128 azobenzene moieties
showed a rectangular columnar phase [20]. This change in the
mesophase arrangement is accounted for by the dense packing of
peripheral mesogen moieties at generation 5. Rectangular
columnar arrangement was also demonstrated for higher genera-
tion dendrimers, where anionic long alkyl chain moieties complex
with cationic fourth poly(amido amine) dendrimer [22]. In both
these instances the rectangular columnar phase was observed only
for the higher generations. The present study is aimed to study the
role of dendrimer core structures installed with either ethyl or n-
propyl moieties that connect the branch points of the dendrimer
structures, without changing the generation number and thus
without changing the number of mesogen inducing moieties at the
peripheries of such pairs of dendrimers. Volume fractions of den-
dritic core vs the peripheral moieties are lesser for the ethyl
spacered G1Et4 and G2Et8, with identical number of cholesteryl
moieties when compared with those of the n-propyl series. The
calculated molecular length of G2Et8 is ~5.7 nm, when compared to
G2Pr8 of ~6.2 nm, both having identical number of cholesteryl
moieties at the periphery. This reduced molecular length might
lead to the formation of an in-plane modulated lamellar structure
of G2Et8 (Fig. 6b). It thus emerges that the control of the dendritic
core alone to varying volume fractions and accessible regions to the
peripheral moieties appears to provide a significant contribution to
the molecular arrangement in the mesophase structures. For
similar reasons, PAMAM dendritic mesogens showed a lamellar
arrangement even for a higher generation dendrimer presented
with 128 peripheral mesogenic units. In contrast, PPI dendritic
mesogen, having shorter linker lengths between the branch points,
showed a columnar arrangement in the mesophase, when the pe-
riphery contains 64 mesogenic units [27]. Such changes in the
mesophase structures are known so far only in the case of DLCs
across different dendrimer generations, i.e. lower to higher gener-
ations. Taking an alternate approach to identify the role of dendritic
cores alone, the present study illustrates changes in mesophase
structures when the dendritic core moiety size is modified through
structural changes within the same generation, containing identical
number of cholesteryl moieties at the peripheries.
~
~
dipole moment, and referred to as smecticA (SmA) [23]. The in-
plane modulated layer phase is also seen in bent-core molecules
and labeled as B1 [24]. The molecular arrangement in such a phase
mimics the structure of a rectangular columnar phase, wherein the
wavelength of modulation represents the width of a column. The
second lattice dimension, ar ~7 nm, obtained from the indexing
scheme, in fact, corresponds to the wavelength of the modulation,
whereas the dimension cr is due to the layer spacing. Variable
temperature XRD further shows that variation in the cr values are
more significant than the ar values, suggesting that the temperature
coefficient of expansion affects cr dimension more than the ar
dimension. Furthermore, lower temperature plots show funda-
mental [10] and the higher order [20] peaks, reflecting a layered
phase. A value of ar ~7 nm obtained suggests that there are about 3
molecules (12 cholesteryl moieties) per column width. Considering
the shape of the molecules as depicted in Fig. 1, a second possibility
for the molecular packing other than a lamellar arrangement in
G2Et8 was also considered. Among the compounds investigated,
the shape of G2Et8 might resemble to that of a disc. Thus the phase
observed may be considered to arise from a stacking of the discs
into a columnar arrangement, which, in turn, form the rectangular
lattice. However, we rule of this possibility for reasons that (i) one
of the lattice parameters ([10]) in G2Et8 closely matches with the
lattice parameter [100] in compounds G1Et4, G1Pr4 and G2Pr8, that
possess SmA phase; (ii) calculated molecular length between two
farthest atoms within a molecule of G2Et8 in the fully extended
conformation is ~5.7 nm, whereas the observed molecular length
(cr) is 4.6 nm (at 60 ꢁC). This shortening of molecular length do not
change the periodicity of modulation, which corresponds to the
second lattice parameter (ar) greatly, and (iii) the fundamental peak
for G2Et8 is seen with next higher order peak at lower temperature,
presence of such a higher order peak corresponds to the smectic
layering of this derivative. For all the compounds studied herein,
the wide angle region presents a diffraction profile that can be
resolved into two diffuse reflections with spacings 0.55 and
0.45 nm. The latter is a typical value for the liquid-like ordering of
the alkylene region, and is common feature of lamellar liquid
crystalline structures. The lower angle peak, with a spacing of
0.55 nm, must be arising due to the packing of the bulky cholesterol
units. Such a differential packing of the subunits is quite rare in
smectic phases, but has been reported in systems comprising
fluorocarbon/hydrocarbon terminal chains [25]. A few cases of
cholesterol/hydrocarbon units giving rise to such twin-diffuse peak
profile are also known [13c,26]. The lamellar arrangement of G1Et4,
G1Pr4 and G2Pr8 suggests that these molecules prefer open annular
or prolate structures, in which the peripheral cholesteryl moieties
reside above and below the dendritic core (Fig. 6a). Calculated
molecular lengths between two farthest atoms of G1Et4, G1Pr4 and
G2Pr8 in the fully extended conformation, as determined by energy
minimization protocol, are ~5.4, 5.6 and 6.2 nm, respectively, and
the observed layer thickness are 4.7, 5.0 and 4.9 nm, respectively.
The shortening of layer spacing relates to either compaction of the
molecules or alternatively an intercalation. Importance of the
lamellar structure in these dendritic liquid crystal pairs differing
only in the ethyl vs n-propyl spacer constituting dendrimer core
structure is that the peripheral cholesteryl moieties do not
encounter a steric hindrance and accessible regions around the
cholesteryl moieties are larger. The volume fractions of dendritic
core vs the peripheral moieties is ~5e9% larger with n-propyl spacer
derivatives, in comparison to ethyl spacer derivatives, by which the
accessible region for individual peripheral cholesteryl moiety is
larger for G1Pr4 and G2Pr8 derivatives. This increased accessible
region, in turn, facilitates peripheral moieties independent of each
other within the molecule, causing them to adopt a preferred
3. Conclusions
In conclusion, two dendrimer generation pairs, each with an
ethyl or n-propyl linker constituting the four dendrimer structures,
were prepared in order to assess the effect of the linkers that
connect the branch points of the dendrimer structures on the
ensuing mesogenic properties. Whereas a smectic A phase was
observed for the first and second generation n-propyl spacered
dendrimers and the first generation ethyl spacered dendrimer, the
second generation ethyl-spacered dendrimer preferred an in-plane
modulated smectic
A phase. The latter possesses a two-
dimensional lattice, in which the lattice dimension corresponding
to the wavelength of modulation defines the width of a rectangular
column. The presence of an in-plane modulated smectic A phase in
this derivative was inferred by XRD analysis, in comparison to that

P. Kumar et al. / Polymer 86 (2016) 98e104
103
~
Fig. 6. Molecular packing diagrams of (a) SmA and (b) in-plane modulated SmA lamellar structures.
of the remaining derivatives studied herein.
in CH2Cl2 (50 mL). The solution was stirred at room temperature for
15 h. Progress of the reaction was monitored by TLC. After
completion of the reaction, solvent was removed in vacuo and the
resultant residue was dissolved in chloroform (50 mL). The organic
layer was subsequently washed with aq. HCl (1 N) (2 ꢂ 50 mL),
saturated NaHCO3 (2 ꢂ 50 mL), brine solution (50 mL) and dried
over anhydrous Na2SO4, followed by solvent evaporation in vacuo.
The crude product was purified by column chromatography (SiO2,
20% EtOAc-hexane) to afford CS [29], as a white amorphous powder.
3.1. Experimental section
3.1.1. Materials
Chemicals were purchased from commercial sources and were
used without further purification. Solvents were dried and distilled
using literature procedures. Triethylamine (TEA) was stored over
KOH. Analytical TLC was performed on commercial plates, coated
with silica gel 60 F254 (0.25 mm) and aluminum oxide 60 F254
(0.25 mm) and detection using iodine as a staining agent. Com-
pounds were purified by column chromatography using neutral
Al2O3 (230e400 mesh). FT-IR spectra were recorded on a Per-
kineElmer spectrophotometer, as neat samples. 1H and 13C NMR
spectral analyses were performed on a Bruker-ARX400 NMR in-
strument, operating at 400 MHz for proton and 100 MHz for 13C
nuclei. Chemical shifts are reported with respect to tetramethylsi-
lane for 1H NMR and the central line of CDCl3 (77.0 ppm) for 13C
NMR spectra. Elemental analysis was performed on an automated
Carlo-Erba C, H, and N analyzer. High resolution mass spectra were
conducted on a Micromass Q-TOF instrument, operating with
electrospray ionization (ESI) technique.
Yield ¼ 5.98 g (95%); Rf 0.5 (1:9 MeOH/CHCl3); mp: 178.85 ꢁC from
20
DSC trace, second cycle; [
n
a
]
¼ ꢀ36.02 (c 1.00, CHCl3); FT-IR (Neat):
D
2930, 1704, 1434, 1314, 1178, 998 cmꢀ1
;
1H NMR (400 MHz,
CDCl3):
d
0.5e2.1 (m, 41H, cholesterol), 2.35 (d, J ¼ 7.0 Hz, 2H, CH2),
2.60 (t, J ¼ 6.0 Hz, 2H, CH2), 2.65 (t, J ¼ 6.0 Hz, 2H, CH2), 4.50 (m, 1H,
OCH), 5.37 (m, 1H, CH); 13C NMR (100 MHz, CDCl3):
d
177.6, 171.6,
139.5, 122.7, 74.2, 56.7, 56.1, 50.0, 42.2, 39.7, 39.5, 37.9, 36.9, 36.5,
36.2, 35.8, 31.9, 31.9, 29.2, 28.21, 28.0, 27.7, 24.2, 23.8, 22.8, 22.5,
21.0, 19.3, 18.7, 11.8; HRMS: m/z C31H50O4Na calcd. 509.3607, found
509.3608.
3.1.4. G1Pr4
Oxalyl chloride (92 mL, 1.08 mmol) was added to a solution of CS
(0.44 g, 0.90 mmol) in CH2Cl2 (10 mL), stirred for 10 min at 0 ꢁC and
then for 2 h at room temperature and solvents were removed in
vacuo to afford cholesteryl hemisuccinate acid chloride. A solution
of the acid chloride in CHCl3 (10 mL) was added to a solution of first
generation hydroxypropyl group terminated PETIM dendrimer
(0.06 g, 0.15 mmol), Et3N (0.17 mL, 1.2 mmol) and DMAP (cat.) in
CH2Cl2 (15 mL). The reaction mixture stirred at room temperature
for ~8 h, diluted with CHCl3 (20 mL), washed with water
(2 ꢂ 25 mL), organic portion dried (Na2SO4), filtered, filtrate
concentrated in vacuo and dried to afford a crude product. The
crude product was triturated with n-hexane (25 mL), centrifuged,
filtrate collected, evaporated in vacuo and the procedure was
3.1.2. Instrumentation
The mesophase was characterized on untreated glass plate using
a polarizing optical microscope fitted with a hot stage. The transi-
tion temperatures and enthalpies were determined by DSC with
nitrogen purging at a heating-cooling rate of 10 ꢁC minꢀ1 for three
cycles. From the second cycle, the maxima of the peaks were taken
as transition temperatures and the mid-point of the heat capacity
change were taken as glass transition temperature. X-ray diffrac-
tion measurements were carried out using an image plate and a
solid-state detector. Cu K
a
(l
¼ 0.15418 nm) radiation from a source
(GeniX3D, Xenocs) operating at 50 kV and 0.6 mA in conjunction
with a multilayer mirror was used in the image plate detector to
illuminate the sample contained in a glass capillary tube (Capillary
Tube 20 Supplies Ltd.). The temperature of the sample was varied
using a Mettler hot stage/programmer (FP82HT/FP90) [28].
repeated 4 times. Solvents were then evaporated in vacuo and dried
20
to afford G1Pr4, as a gum. Yield ¼ 0.32 g (95%); [
1.00, CHCl3); FT-IR (Neat):
1H NMR (400 MHz, CDCl3):
CH2eCH2eCH2), 2.30 (d, J ¼ 7.2 Hz, 8H, CH2), 2.45 (m, 12H, NeCH2),
2.59 (m, 16H, OCeCH2eCH2eCO), 3.32 (t, 5.8 Hz, 4H,
a
]
¼ ꢀ34.66 (c
D
n
2947, 1732, 1467, 1376, 1166, 760 cm-1;
0.5e2.1 (band, 176H, cholesterol,
d
3.1.3. Synthesis of cholesteryl hemisuccinate (CS)
DMAP (1.58 g, 12.9 mmol) and succinic anhydride (1.29 g,
12.9 mmol) were added to a solution of cholesterol (5 g, 12.9 mmol)
J
¼
OeCH2eCH2), 4.09 (t, J ¼ 5.8 Hz, 8H, COOeCH2), 4.58 (br, 4H, OCH),
5.28 (br, 4H, ¼CH); 13C NMR (100 MHz, CDCl3):
d 172.3, 171.6, 139.5,

104
P. Kumar et al. / Polymer 86 (2016) 98e104
122.6, 74.2, 68.9, 63.0, 56.7, 56.1, 50.5, 50.2, 50.0, 42.2, 39.6, 39.4,
38.0, 36.9, 36.5, 36.1, 35.7, 31.7, 31.4, 29.4, 29.0, 28.1, 27.7, 27.2, 26.2,
24.2, 23.8, 22.8, 22.5, 21.0, 19.3, 18.7, 11.8; MALDI-TOF mass: m/z
calcd for C142H232O17N2: 2239.364; found: 2239.554; elemental
analysis calcd. for C142H232O17N2: C 76.16, H 10.44, N 1.25; found: C
76.21, H 10.13, N 1.22.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.polymer.2016.01.043.
References
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Oxalyl chloride (58
mL, 0.68 mmol), a solution of cholesteryl
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(15 mL) and the reaction was proceeded further as given in the
20
general method. Yield ¼ 205 mg (90%); [
CHCl3); FT-IR (Neat):
NMR (400 MHz, CDCl3):
a]
¼ ꢀ24.5 (c 1.00,
D
n
2948, 1731, 1469, 1375, 1168, 762 cmꢀ1
;
1H
d
0.5e2.1 (band, 348H; cholesterol,
ꢀ
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CH2eCH2eCH2), 2.30 (d, J ¼ 7.2 Hz, 16H, CH2), 2.45 (m, 36H,
NeCH2), 2.59 (m, 32H, OCeCH2eCH2eCO), 3.38 (t, J ¼ 5.8 Hz, 20H,
OeCH2eCH2), 4.10 (t, J ¼ 5.8 Hz, 32H, COOeCH2), 4.61 (br, 8H, OCH),
Soft Matter 10 (2014) 281;
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V.P. Shibaev, Liq. Cryst. 33 (2006) 1497;
5.35 (br, 8H, ¼CH); 13C NMR (100 MHz, CDCl3):
d 172.3, 171.6, 139.6,
122.7, 74.2, 69.3, 68.9, 63.0, 56.7, 56.1, 50.5, 50.3, 40.0, 42.3, 39.7,
39.5, 38.0, 36.9, 36.6, 36.2, 35.8, 31.9, 31.4, 29.4, 29.1, 28.2, 28.0, 27.8,
24.3, 23.8, 22.8, 22.5, 21.0, 19.3, 18.7, 11.8; elemental analysis calcd.
for C302H500O37N6: C 75.45, H 10.48, N 1.75; found: C 75.42, H 10.58,
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(c) I. Bury, B. Heinrich, C. Bourgogne, G.H. Mehl, D. Guillon, B. Donnio, New J.
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3.1.6. G1Et4
This derivative was obtained by following the procedure for the
preparation of G1Pr4, using hydroxyethyl group terminated first
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generation PETIM dendrimer (0.045 g, 0.16 mmol). Yield ¼ 0.32 g
20
(92%); [
a
]
¼ ꢀ32.3 (c 1.00, CHCl3); FT-IR (Neat):
n
2928, 1733,
0.67e2.0
D
(b) L.-.L. Lai, S.-J. Hsu, H.-C. Hsu, S.-W. Wang, K.-L. Cheng, C.-J. Chen, T.-
H. Wang, H.-F. Hsu, Chem. Eur. J. 18 (2012) 6542.
1466, 1377, 1165, 736 cmꢀ1;1H NMR (400 MHz, CDCl3):
d
ꢀ
(band, 164H, cholesterol), 2.31 (d, J ¼ 7.2 Hz, 8H, CH2), 2.60 (m, 16H,
OCeCH2eCH2eCO), 2.76 (m, 8H, NeCH2), 2.83 (m, 4H, NeCH2), 3.47
(t, J ¼ 5.8 Hz, 4H, OeCH2eCH2), 4.15 (t, J ¼ 5.8 Hz, 8H, COOeCH2),
4.60 (br, 4H, OCH), 5.36 (br, 4H, ¼CH); 13C NMR (100 MHz, CDCl3):
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ꢀ
ꢀ
ꢀ
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(2002) 6466;
d
172.3, 171.6, 139.6, 122.7, 74.3, 68.9, 63.0, 56.7, 56.2, 49.9, 50.2,
(b) D. Tsiourvas, T. Felekis, Z. Sideratou, C.M. Paleos, Liq. Cryst. 31 (2004) 739;
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1705.
50.0, 42.3, 39.7, 39.5, 38.0, 36.9, 36.6, 36.2, 35.8, 31.9, 31.8, 29.4, 29.1,
28.2, 27.7, 27.2, 26.2, 24.3, 23.9, 22.8, 22.5, 21.0, 19.3, 18.7, 11.8;
elemental analysis calcd. for C136H220N2O17: C, 75.79; H, 10.29; N,
1.30; found: C, 75.62; H, 10.18; N, 1.35.
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[16] Z. Shi, D. Chen, H. Lu, B. Wu, J. Ma, R. Cheng, J. Fang, X. Chen, Soft Matter 8
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Int. J. Pharm. 397 (2010) 147.
3.1.7. G2Et8
This derivative was obtained by following the procedure for the
preparation of G1Pr4, using hydroxyethyl group terminated first
generation PETIM dendrimer (0.060 g, 0.075 mmol), Et3N
(0.125 mL, 0.90 mmol) and DMAP (cat.) in CHCl3 (15 mL) and the
[19] M.V. Kumar, S.K. Prasad, D.S.S. Rao, P.K. Mukherjee, Langmuir 30 (2013) 4465.
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E.A. Rebrov, A.M. Muzafarov, Polym. Sci. Ser. A 49 (2007) 412.
reaction was proceeded further as given in the general method.
20
Yield ¼ 0.30 g (88%); [
a
]
¼ ꢀ27.8 (c 1.00, CHCl3); FT-IR (Neat):
n
D
2928, 1733, 1465, 1378, 1165, 737 cmꢀ1;1H NMR (400 MHz, CDCl3):
ꢀ
[22] S. Hernandez-Ainsa, J. Barbera, M. Marcos, J.L. Serrano, Soft Matter 7 (2011)
d
0.66e2.1 (band, 312H; cholesterol), 2.30e2.32 (d, J ¼ 7.2 Hz, 16H,
2560.
CH2), 2.55 (m, 36H, NeCH2), 2.66 (m, 32H, OCeCH2eCH2eCO), 3.68
(t, J ¼ 5.8 Hz, 20H, OeCH2eCH2), 4.10 (t, J ¼ 5.8 Hz, 32H, COOeCH2),
4.62 (br, 8H, OCH), 5.36 (br, 8H, ¼CH); 13C NMR (100 MHz, CDCl3):
[23] F. Hardouin, A.M. Levelut, M.F. Achard, G. Sigaud, J. Chim. Phys. 30 (1983) 53.
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ꢁ
d
171.6,139.4,122.6, 74.3, 69.3, 68.9, 63.0, 56.5, 55.9, 49.8, 42.2, 39.6,
(c) M. Sepelj, A. Lesac, U. Baumeister, S. Diele, H.C. Nguyen, D.W. Bruce,
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39.4, 37.8, 36.8, 36.4, 36.0, 35.6, 31.8, 31.7, 29.6, 29.3, 27.8, 27.5, 24.1,
23.7, 22.7, 22.4, 20.9, 19.2, 18.6, 11.7; elemental analysis calcd. for
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(1996) 603;
C
284H464N6O37: C 74.89, H 10.27, N 1.85; found: C 74.57, H 10.10, N
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(2014) 2538;
1.70.
(c) L.M. Wilson, A.C. Griffin, Macromolecules 27 (1994) 4611.
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Acknowledgments
ꢀ
[27] R. Martin-Rapún, M. Marcos, A. Omenat, J. Barbera, P. Ramero, J.L. Serrano,
J. Am. Chem. Soc. 127 (2005) 7397.
We thank Department of Science and Technology, New Delhi, for
a financial support. Council of Scientific and Industrial Research,
New Delhi, is acknowledged for a research fellowship to PK.
[28] M.V. Kumar, S.K. Prasad, D.S.S. Rao, P.K. Mukherjee, Langmuir 30 (2013) 4465.
[29] Z.Y. He, X. Zheng, X.H. Wu, X.R. Song, G. He, W.F. Wu, S. Yu, S.J. Mao, Y.Q. Wei,
Int. J. Pharm. 397 (2010) 147.