Synthesis and phase structures of mesogen-jacketed liquid crystalline polyelectrolytes and their ionic complexes

Article abstract of DOI:10.1021/ma2001004

Two mesogen-jacketed liquid crystalline polyelectrolytes, poly{sodium 2,5-bis[(4-sulfophenyl)aminocarbonyl]-styrene} and poly{sodium 2.5-bis[(4-sulfophenyl)oxycarbonyl]-styrene} with rigid cores containing different linkages at the center and sulfonate gr

Full text of DOI:10.1021/ma2001004

ARTICLE
pubs.acs.org/Macromolecules
Synthesis and Phase Structures of Mesogen-Jacketed Liquid
Crystalline Polyelectrolytes and Their Ionic Complexes
†
,‡
‡
†
†
†
,†
Yan-Hua Cheng, Wen-Ping Chen, Cui Zheng, Wei Qu, Hongliang Wu, Zhihao Shen,*
†
,†
,‡
†
Dehai Liang, Xing-He Fan,* Mei-Fang Zhu,* and Qi-Feng Zhou
†
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education,
College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
‡
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University, Shanghai 201620, China
S Supporting Information
b
ABSTRACT: Two mesogen-jacketed liquid crystalline poly-
electrolytes, poly{sodium 2,5-bis[(4-sulfophenyl)aminocarbonyl]-
styrene} and poly{sodium 2.5-bis[(4-sulfophenyl)oxycarbonyl]-
styrene}, with rigid cores containing different linkages at the
center and sulfonate groups on the two ends in the side chains
were designed and successfully synthesized via conventional
radical polymerization. X-ray scattering experiments revealed
that the two polymers exhibited smectic A phases in bulk.
Comb-shaped nonstoichiometric polymerꢀsurfactant com-
plexes were obtained by mixing the anionic sulfonated polyelectrolytes and cationic lipids of different lengths and shapes. The
formation of ordered structures of the complexes depended on the length and shape of the lipids. Lamellar phases were observed
when the two polyelectrolytes complexed with cetyltrimethylammonium bromide and fan-shaped 3,4,5-tris(dodecyloxy)-
benzenamine. Owing to the stronger bond strength of electrostatic interactions, the types of mesophases of the complexes based
on the two polyelectrolytes with different linkages in the rigid cores were the same.
’
INTRODUCTION
“jacketing” effect. They can be easily synthesized by radical
polymerizations, and their physical characteristics can be tuned
In an attempt to mimic biological systems, construction of self-
2
0
by controlling the chemical structures of the side chains.
Smectic phases have also been reported in MJLCPs when the
assembled complex functional systems with ordered structures is
preferentially performed following the rules of supramolecular
chemistry based on secondary interactions, such as ionic inter-
2
1
length (or the rigidity) of the mesogen is increased, or when
22
1,2
semifluorinated tails are used,2 or when hydrogen bonding is
actions and hydrogen bonding rather than covalent bonding.
3
introduced into the mesogens. To better elucidate the mechan-
Compared with hydrogen bonding, ionic interactions have
3
stronger bond strength. Because of the facile synthesis and
ism of self-organizing behavior of biopolyelectrolytes, it is mean-
ingful to design and study LC properties of a special type of
polyelectrolyes based on the MJLCP model.
broad applications of ionic complexes, various polyelectrolyte
architectures, such as linear, hyperbranched, and dendronized,
have been used as polybases. When they complex with oppositely
charged surfactants, the resulting complexes have been shown to
In this work, we report for the first time the design and
synthesis of a new series of sulfonated mesogen-jacketed liquid
crystalline polyelectrolytes (MJLCPEs), in which the attached
mesogens had a rigid core containing amide or ester linkages,
with sulfonated groups appended on the two ends of the core.
The self-assembly and LC structures of the MJLCPEs in bulk
were investigated using various techniques. Furthermore, ionic
moieties were introduced into the side chains of the MJLCPEs by
forming complexes between the anionic MJLCPEs and cationic
surfactants. The effects of MJLCPE structure, alkyl tail length,
and surfactant shape on liquid crystalline structures of the
complexes were investigated.
2,4ꢀ8
form microphase-separated morphologies,
the surface, optoelectronic, and mechanical properties.
which influence
9
ꢀ11
Rigid-rod polyelectrolytes are rich in living organisms. They
have great abilities to form specific well-ordered structures by
spontaneous self-assembly and play an important role in the
12ꢀ14
normal function of lives.
In order to study the mechanisms
and properties of these biopolyelectrolytes in living organisms,
recent efforts have been focused on the synthesis of rigid-rod
liquid crystalline (LC) polyelectrolytes and the investigation of
15ꢀ19
their properties in solutions and in bulk.
In our previous
study, we have systematically investigated a special type of side-
chain LC polymers, mesogen-jacketed liquid crystalline poly-
mers (MJLCPs), which have a short spacer or a single bond
between the attached side-on side chains and the polymer
backbone. MJLCPs behave like a rigid rod because of the
Received: January 15, 2011
Revised:
April 15, 2011
Published: April 28, 2011
r 2011 American Chemical Society
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|Macromolecules 2011, 44, 3973–3980

Macromolecules
ARTICLE
Scheme 1. Synthetic Routes of Monomers and Polyelectrolytes
’
EXPERIMENTAL SECTION
Two-dimensional (2D) wide-angle X-ray diffraction (WAXD) ex-
periments were performed on a Bruker D8Discover diffractometer with
GADDS as a 2D detector. The 2D diffraction patterns were recorded in a
transmission mode at ambient temperature. The background scattering
was recorded and subtracted from the sample patterns.
Materials. The compound vinylterephthalic acid was synthesized
using the method reported previously. 4,4 -Azobis(4-cyanovaleric acid)
2
4
0
0
(V-501, Aldrich) was used as received. N,N -Dimethylformamide
2
(DMF, Beijing Chemical Co., A.R.) was distilled over CaH prior to
All time-resolved FTIR spectra were collected on a Nicolet 8700
ꢀ
1
use. Acetone was refluxed over potassium permanganate and distilled
out, followed by drying with anhydrous calcium sulfate powder and
distilling out before use. All other reagents and solvents were used as
received from commercial sources.
Measurements. H NMR spectra were obtained using a Bruker
ARX400 MHz with tetramethylsilane (TMS) as the internal standard at
FTIR spectrometer with a resolution of 4 cm , 32 scans coadded for
each spectrum, and the samples were mixed with KBr and then pressed
into thin transparent disks.
Synthesis of Sulfonated Monomers. The synthesis of the
monomers, sodium 2,5-bis[(4-sulfophenyl)aminocarbonyl]styrene (SPAS)
and sodium 2,5-bis[(4-sulfophenyl)oxycarbonyl]styrene (SPCS), fol-
1
2
5
ambient temperature in dimethyl-d
6
sulfoxide and methanol-d
4
. Mass
lowed the method described in the literature. The synthetic routes of
SPAS and SPCS are shown in Scheme 1. The experimental details of the
monomer synthesis and characterization are described below using
SPAS as an example.
spectra were recorded on a Bruker Apex IV FTMS spectrometer.
Polarized light microscopy (PLM) was used to observe the LC
textures of the samples on a Leitz Laborlux 12 microscope. The images
were captured using an insight digital camera. The film was prepared by
solution-casting from water. The specimens were slightly sheared from
concentrated solutions to increase the LC domain size.
Dynamic light scattering (DLS) and static light scattering (SLS) were
conducted on a commercialized spectrometer from Brookhaven Instru-
ments Corp. in a scattering angular range of 20°ꢀ120° at 25 °C. A solid-
state laser polarized at the vertical direction (CNI Changchun GXC-III,
Synthesis of Sodium 2,5-Bis[(4-Sulfophenyl)aminocar-
bonyl]styrene (SPAS). Vinylterephthalic acid (2.4 g, 12.5 mmol),
20 mL oxalyl chloride, and a few drops of DMF were dissolved in
dichloromethane (30 mL) in a 50 mL round-bottom flask. The mixture
was stirred for 5 h. After evaporation of the solvent under reduced
pressure, the residue was dissolved in anhydrous acetone. The resultant
light yellow solution of vinylterephthal chloride was slowly dropped into
an intensely stirred mixture of 25 mL of saturated brine aqueous solution
and sodium 4-aminobenzenesulfonate (4.88 g, 25 mmol) in an ice/water
5
32 nm, 100 mW) operating at 532 nm was used as the light source.
Viscosities of PSPAS and PSPCS were measured in water solutions at
0 °C with an Ubbelohde capillary viscometer.
3
3
bath and stirred for 15 min. Then saturated NaHCO (30 mL) was
added to the residue, and the reaction mixture was further stirred for
20 min. After SPAS was separated out, it was washed with DMF and
Small-angle X-ray scattering (SAXS) experiments were performed
using a SAXSess instrument (Anton Paar) equipped with a Kratky block-
collimation system. The X-ray was generated using a Philips PW3080
sealed-tube X-ray generator with the Cu target. The wavelength was
recrystallized from methanol/H O (5/1, v/v) to give the product as a
2
1
pale yellow solid. H NMR (400 MHz, DMSO-d
6
, δ, ppm): 5.46 (d, 1H, =
), 6.96ꢀ7.03 (q, 1H, ꢀCH=), 7.58ꢀ7.80
(m, 9H, ArꢀH), 7.99 (d, 1H, ArꢀH), 8.34 (s, 1H, ArꢀH), 10.54
0.1542 nm. A highly sensitive SAXS imaging plate which was 264.5 mm
2 2
CH ), 6.05 (d, 1H, =CH
away from the sample was used to collect the signal in vacuum. Samples
were placed in between aluminum foils which were folded and sand-
wiched in a steel sample holder. Scattering data were acquired for a 30
min exposure. The background scattering from aluminum foils was
acquired and then subtracted from the sample profiles.
1
3
(s, 1H, ꢀNHꢀ), 10.62 (s, 1H, ꢀNHꢀ). C NMR (100 MHz, DMSO-
d
6
, δ, ppm): 117.73, 118.73, 119.53, 124.59, 126.05, 126.14, 126.93, 127.69,
133.25, 134.93, 135.84, 138.63, 139.06, 143.70, 164.69, 166.83. Anal.
Calcd for C H N Na O S (%): C 48.35, H 2.95, N 5.13. Found (%):
2
2
16
2
2 8 2
3
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Scheme 2. Preparation of the MJLCPEꢀSurfactant Complexes
þ
C 48.15, H 3.17, N 5.06. HRMS (ESI) m/z Calcd, [M þ H] , 547.0216.
stirring. For the complexation with Ar-3C12, the cationic dendritic
ammonium amphiphile was dissolved in THF (pH = 2ꢀ3 adjusted with
HCl, with a concentration of 10 mg/mL). All complexation experiments
were carried out at a stoichiometric ratio of the negative sulfonate and
the positive ammonium groups. Taking PSPAS as an example, the
polymer was dissolved in water (1 mg/mL) at 60 °C and stirred for 5 h,
and the solution was then added into the surfactant solution under an
intense stirring. The surfactant solution immediately became turbid,
indicating the formation of complexes. In order to remove the un-
bound polyelectrolytes and surfactants in PSPAS-C12 and PSPAS-Ar-
3C12, the raw products were redissolved in ethanol and THF and
reprecipitated in a large excess of water and water/THF (2/1, v/v)
sequentially. Finally, pure complexes were obtained after two dissolu-
tionꢀprecipitation cycles. However, PSPAS-C16 was directly used for
the characterization without further purification due to its poor solubility
in organic solvents. The procedures for preparing PSPCS-C12, PSPCS-
C16, and PSPCS-Ar-3C12 were similar to those for preparing PSPAS
complexes. All complexes obtained were dried at 35 °C for 72 h before
characterization.
Found, 547.0208.
Synthesis of Sodium 2,5-Bis[(4-Sulfophenyl)oxycarbonyl]-
styrene (SPCS). SPCS was similarly prepared as mentioned for
1
SPAS. H NMR (400 MHz, DMSO-d
6
, δ, ppm): 5.54 (d, 1H, =
CH ), 5.95 (d, 1H, =CH ), 7.29 (d, 4H, ArꢀH), 7.39ꢀ7.46 (q, 1H,
2
2
ꢀ
CH=), 7.73 (d, 4H, ArꢀH), 8.19ꢀ8.26 (m, 2H, ArꢀH), 8.39 (s, 1H,
13
ArꢀH). C NMR (100 MHz, DMSO-d
6
, δ, ppm): 119.11, 121.19,
27.01, 128.06, 128.85, 131.15, 132.03, 132.60, 133.95, 139.14, 146.24,
46.29, 150.28, 150.42, 163.79, 164.68. Anal. Calcd for C H Na -
1
1
2
2
14
2
O
10
S
2
(%): C 48.18, H 2.57. Found (%): C 48.01, H 2.77. HRMS (ESI)
þ
m/z Calcd, [M þ Na] , 570.9716. Found, 570.9704.
Polymerization of MJLCPEs. As shown in Scheme 1, the
MJLCPE polymers were obtained by conventional radical polymeriza-
tion in solution. A typical polymerization procedure was carried out as
the following using PSPAS as an example. SPAS (0.5 g, 0.46 mmol), 100
μL of DMF solution of 0.02 M V-501, and 9.5 mL of DMF/water (2/1,
v/v) were transferred into a polymerization tube. After three free-
zeꢀpumpꢀthaw cycles, the tube was sealed off under vacuum. Polym-
erization was carried out at 60 °C for 24 h. The tube was then opened,
and the reaction mixture was diluted with 10 mL of water. The resultant
polymer was precipitated and washed with a mixed solvent methanol/
water (5/1, v/v). To completely eliminate the unreacted monomer, the
precipitate was redissolved in water and then reprecipitated in metha-
nol/water (5/1, v/v) for three times. The absence of the monomer in the
product was confirmed by thin-layer chromatography. Finally, the
polymer PSPAS was dried in vacuum at 60 °C for 72 h. The polymer-
ization method for PSPCS was similar to that for PSPAS, except that the
polymerization solvent for PSPCS was pure water.
’
RESULTS AND DISCUSSION
Synthesis and Characterization of Monomers and
MJLCPEs. The monomers were synthesized according to
Scheme 1. The structures of the monomers were confirmed by
1
13
conventional analyses, including H NMR, C NMR, elemental
analysis, and mass spectrometry. The two monomers were easily
polymerized via the conventional radical polymerization method
in aqueous solutions. For SPAS, the viscosity increased signifi-
cantly and formed a gel during polymerization when polymerized
in pure water, which could be attributed to the hydrogen bonding
Preparation of MJLCPEꢀSurfactant Complexes. Cetyltri-
methylammonium bromide (C16), dodecyltrimethylammonium bro-
mide (C12), and fan-shaped 3,4,5-tris(dodecyloxy)benzenamine (Ar-3C12)
were selected to form ionic supramolecular complexes with PSPAS and
PSPCS, as illustrated in Scheme 2, following the method described in the
between water and PSPAS. Hence, DMF/H O was used in order
2
to decrease the viscosity of the system. The resultant polymers
PSPAS and PSPCS were water-soluble because of their ionic
nature.
The values of ηsp/c (viscosity/concentration) of PSPAS
(1 mg/mL) and PSPCS (1 mg/mL) in aqueous solutions were
6.4 and 9.2 dL/g, respectively. The weight-average molecular
8
literature. The Ar-3C12 molecule was synthesized according to the
26
reported method. For the complexation with C12 and C16, the
concentrations of surfactants in water were lower than the critical
micelle concentration. In order to improve the dispersion of the
surfactants in water, the solutions were heated at 60 °C for 5 h under
3
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Figure 2. SAXS profiles of PSPAS and PSPCS bulk samples at ambient
temperature, with intensity in log scale.
ꢀ1
higher-order diffraction peak at q = 5.96 nm for PSPAS. The
2
ratio of the scattering vectors of the two peaks q :q was
1
2
approximately 1:2, indicating a smectic structure with a periodi-
city of 2.04 nm (d100 = 2π/q ) for PSPAS. PSPCS had the similar
1
ꢀ1
structure with the first peak appearing at a q value of 2.88 nm
,
revealing the periodicity of 2.18 nm. These two layer spacing
values were close to the calculated lengths of the monomers
(
1.82 nm, without considering the size of the sodium ion), which
Figure 1. Polarized light micrographs of PSPAS (a) and PSPCS (b) in
the solid state.
indicated that the side chains were perpendicular or almost
perpendicular to the main chain, as in our previous packing
models of smectic phases formed by MJLCPs.
20
6
weight (M ) of PSPAS was about 1.1 ꢁ 10 g/mol, and the
To identify the smectic structures of the two polymers, 2D
WAXD experiments were carried out. Taking PSPAS as an
example, the sample was put on the sample stage, and the
point-focused X-ray beam was aligned normal to the film
(Figure 3a). Figure 3b shows the pattern of PSPAS. Low-angle
diffraction arcs appeared on the equator, and second-order
diffractions also appeared on the equator. The scattering vector
ratio of the two diffractions was 1:2, which was consistent with
the SAXS result shown in Figure 2, as expected. In the high-angle
region, the scattering halo was more or less concentrated on the
meridian. The pattern in Figure 3b proved that the smectic phase
w
polydispersity index (PDI) was 2.64, as determined by laser light
scattering (LLS) at 25 °C in water with the addition of KCl to
screen out the electrostatic interactions. The value of the
absolute M of PSPAS determined by LLS demonstrated good
w
polymerizability of the monomer SPAS. However, LLS could not
be used to characterize PSPCS which had the ester linkage due to
aggregation of PSPCS in the KCl solution. We speculated that
the difference in the applicability of LLS in characterizing PSPAS
and PSPCS was caused by the difference in the linkage in the side
chains. The amide linkage was more hydrophilic than the ester
one, and therefore, PSPAS was more soluble in aqueous solution.
Structures of MJLCPEs in Bulk. PLM, SAXS, and 2D WAXD
results allowed a detailed analysis of the structures of the
MJLCPEs. In the PSPAS and PSPCS solutions, no birefringence
was observed by PLM. During the evaporation of water, gelation
occurred. Birefringence was observed when a shear stress was
applied to the gel-like samples by sliding the cover glass plates.
The textures of the PSPAS and PSPCS in the solid state at
ambient temperature shown in Figure 1 indicated the formation
of ordered structures in PSPAS and PSPCS films.
of PSPAS was smectic A (S ). Similar patterns were obtained
from PSPCS samples, suggesting that PSPCS also formed an S
phase (Figure 3c).
A
A
On the basis of SAXS and 2D WAXD results, we proposed the
packing model sketched in Figure 4. Because of the strong
segregation between the end groups and the rigid cores and
the repulsion between the ionic end groups, the smectic phases
were formed for the two MJLCPEs. The polymers took a more
sheetlike conformation to pack into the smectic structures.
Comparison with poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]-
styrene} (PMPCS), which is different from PSPCS only in end
groups but exhibits columnar phases, indicated that the ionic
interactions in PSPCS played an important role in generating the
S phase, confirming again that strong side-chain interactions in
A
MJLCPs favored smectic phases.
Characterization on Ionic Complexes. Electrostatic com-
plexation of rigid polyelectrolytes and flexible surfactants offers a
facile way to tune the physical properties of polymers. The first
indication of the complex formation was the change in solubility
of the complexes comparing with solubilities of the polyelectrolytes
SAXS experiments were carried out to determine their struc-
tures. About 10 mg of the MJLCPE was dissolved in water and
cast onto a glass substrate, and then water was allowed to
evaporate at ambient temperature. The samples were directly
used for SAXS experiments without any further treatment.
Figure 2 shows the SAXS profiles of PSPAS and PSPCS. The
introduction of the sodium sulfonate group induced the strong
segregation between the hydrophobic rigid cores and the hydro-
philic end groups, which was reflected in the SAXS patterns with
27
ꢀ
1
a first-order sharp peak centered at q = 3.08 nm along with a
1
3
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Figure 3. Schematic of the geometry in 2D WAXD experiments with the X-ray incident beam normal to the film (a) and 2D WAXD patterns of PSPAS
b) and PSPCS (c). Note that the equator and meridian directions are arbitrary.
(
A
Figure 4. Schematic representation of the S phases of PSPAS and
PSPCS polymers with sulfonate end groups.
and surfactants. For PSPAS-C12 and PSPCS-C12, the MJLCPEs
and the surfactant C12 were all water-soluble, while the PSPAS-C12
and PSPCS-C12 precipitates survived several washing steps in water
to remove unbound surfactant and polymers, indicating that the
resultant precipitates could be the corresponding complexes instead
1
Figure 5. H NMR spectra of C12 and PSPAS-C12. The asterisk
indicates the signal of CH OH.
3
1
of polymer/surfactant blends. H NMR results also provided the
When PSPAS complexed with C12, the doublet vibration at
ꢀ
1
evidence of electrostatic complexation between PSPAS and C12.
∼1200 (1189 and 1216 cm ) appeared. The splitting of the
1
Figure 5 shows the H NMR spectra of the C12 surfactant and the
asymmetric stretching vibration was related to the different
þ
ꢀ1
complex PSPAS-C12 in methanol-d . The resonance peak at 3.14
electrostatic interaction strengths of the ionic pairs with N ꢀ-
4
þ 31
ppm in the spectrum of C12 and that at 2.93 ppm in the spectrum of
(CH ) and Na . The vibration band at around 1473 cm ,
3 3
32
PSPAS-C12 corresponded to the methyl protons of the ꢀN(CH )
which could be assigned to the CH scissoring mode for C12,
2
3
3
28
group. The upfield chemical shift for PSPAS-C12, owing to the
fact that the sulfonate group shielded the protons of the methyl
groups attaching to the quaternary ammonium following the
complex formation, indicated the electrostatic interactions between
was present in the spectrum of PSPAS-C12 complex but absent
in that of PSPAS. These results could prove the complexation
between the sulfonate groups of PSPAS and the ammonium
groups of C12. The similar phenomenon was also observed in
spectra of PSPAS-C16 and PSPAS-Ar-3C12. Compared with
C12, there was a benzene ring in Ar-3C12, which was demon-
strated by the increased area of the CdC stretching vibration of
benzene ring centered around 1595 cm in the spectrum of
PSPAS-Ar-3C12 (Figure 6b) in comparison with that of PSPAS-
C12. The spectrum of PSPAS-Ar-3C12 showed a larger splitting
of the asymmetric stretching vibration compared with that of
PSPAS-C12, indicating stronger electrostatic interactions in ionic
29
the anionic polyelectrolyte and the cationic surfactant. Compared
with C12, the spectrum of the complex PSPAS-C12 showed an
increase in widths of the resonance peaks, implying reduced mobility
of the surfactant in the complex due to the attachment of C12 to
ꢀ
1
29
PSPAS.
FTIR experiments were carried out to further prove the
complex formation in bulk. The surfactants, the MJLCPEs, and
their supramolecular complexes were characterized individually
by FTIR. As an example, the spectra of C12, PSPAS, and PSPAS-
ꢀ
þ
ꢀ
3
þ
pairs of SO /N ꢀH compared with those in SO /N ꢀ-
3
3
33
C12 are shown in Figure 6a. The asymmetric and symmetric
(CH ) . When the polyelectrolyte was changed to PSPCS, as
3 3
ꢀ
stretching vibration bands of the characteristic SO group in
demonstrated by FTIR spectra, the similar behavior was found
for PSPCS-C12, PSPCS-C16, and PSPCS-Ar-3C12.
3
ꢀ
1
30,31
PSPAS were found at about 1190 and 1039 cm , respectively.
3
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ꢀ1
Figure 6. Infrared spectra in the 600ꢀ2000 cm region: C12 surfac-
tant, PSPAS polymer, and PSPAS-C12 complex (a); Ar-3C12 surfactant,
PSPAS polymer, and PSPAS-Ar-3C12 complex (b).
Figure 7. SAXS profiles of PSPAS (a) and PSPCS (b) polymers
complexed with C12, C16, and Ar-3C12 surfactants at ambient tem-
perature, with intensities in log scale.
Table 1. Elemental Analysis and SAXS Results of the
MJLCPE Complexes
the complete protonation. However, the composition of each
complex was in the region of 40ꢀ50%, which made it easier to
characterize the complexes at the similar level of neutralization
degree (x).
neutralization
layer
c
degree x (mol %
spacing
SAXS experiments were used to identify the types of liquid
crystalline phases of these complexes. Parts a and b in Figure 7
show two sets of SAXS profiles of PSPAS and PSPCS complexed
with C12, C16, and Ar-3C12 surfactants at ambient temperature,
respectively. In order to clearly show multiple reflections, the
intensities were plotted in log scale. Taking the complexes of
PSPAS as an example, in the case of PSPAS-C12, only a single
broad peak was present in Figure 7a, indicating that the system
was poorly ordered, although it showed birefringence under
PLM. The d-spacing of the broad peak corresponding to the
average chain-to-chain distance was 3.47 nm, which was much
larger than the chain-to-chain distance of 2.04 nm for PSPAS
discussed above, indicating that the surfactant indeed acted as a
relatively long spacer between PSPAS backbones in the complex.
However, judging from the lack of higher-order peaks in the
SAXS profile, the flexible content in the C12 surfactant was not
enough to stabilize an ordered packing of the complex. The phenom-
enon was similar to the case of the polymers formed from a
dendronized polymer (PG1) and the C8 surfactant, where the
a
b
c
sample
(wt %)
surfactant)
d (nm)
mesophase
PSPAS-C12
PSPAS-Ar-3C12
PSPAS-C16
PSPCS-C12
PSPCS-Ar-
61.0
66.8
62.2
58.9
67.3
52.3
48.5
47.6
36.5
53.9
d
4.79
4.33
lamellar
lamellar
d
4.79
4.19
lamellar
3C12
PSPCS-C16
60.7
38.2
lamellar
a
c
b
Obtained from elemental analysis. Calculated from C content.
Values of d100 from SAXS profiles. Birefringent under PLM.
d
In order to calculate the composition of the complexes,
elemental analysis was carried out. The composition was de-
duced from the C content in the complex. The results are
summarized in Table 1. It could be found that substoichiometric
complexes were obtained, although the experiments were carried
out at a stoichiometric ratio of the anionic sulfonate and the
cationic ammonium groups. Because of the poor solubility of the
resultant complexes, they would precipitate out even when a
fraction of the surfactants was bound onto the polymers. It was
a challenge to find a good solvent which could dissolve the
surfactants, polymers, and complexes at the same time. On the
other hand, due to the steric hindrance and the high density of
the ionic groups in the polyelectrolytes, it was difficult to reach
7,8
amorphous state was also observed because of the short alkyl chains.
By using the C16 surfactant with a longer alkyl tail, the
microphase separation between the polar polybases and the
nonpolar alkyl chains resulted in the formation of ordered
structures, which could be attributed to the increased volume
fraction of the flexible component. This was reflected in the
SAXS profile of PSPAS-C16 in Figure 7a, with three diffraction
3
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Macromolecules
ARTICLE
’
CONCLUSIONS
In summary, we synthesized a new series of water-soluble
MJLCPEs containing the amide or ester linkage in the side chains
via conventional radical polymerization. Both polymers formed
smectic A phases in bulk after the evaporation of water from the
cast solutions. The liquid crystalline behavior of the nonstoichio-
metric complexes between the polyelectrolytes and surfactants
depended on the length and shape of the surfactants. Our results
indicated that the LC structures of the complexes were not
affected by the different linkages in the side chains of the two
polyelectrolytes because the electrostatic interactions played a
dominant role in determining the structures. The complexes
were amorphous when the MJLCPEs were complexed with C12
because the alkyl tails were too short to induce the formation of
ordered LC structures. However, by increasing the length of the
alkyl tails as in C16 or by changing the shape of surfactant as
in the fan-shaped amphiphilic molecule with three C12 tails
(
Ar-3C12), lamellar phases were observed for the complexes. In
addition, we have demonstrated that MJLCPEꢀsurfactant com-
plexes could be easily synthesized through electrostatic interac-
tions, which provided a green and simple method to construct
new functional MJLCPs.
Figure 8. Schematic representation of lamellar phases of PSPAS-Ar-
3C12 (PSPCS-Ar-3C12) and PSPAS-C16 (PSPCS-C16) complexes,
formed by the addition of surfactants to MJLCPEs.
’
ASSOCIATED CONTENT
peaks having a scattering vector ratio of 1:2:4, which was typical
of a lamellar phase with a larger d-spacing of 4.33 nm.
When a fan-shaped amphiphile Ar-3C12 with a polar head at
the tip of the fan and three C12 nonpolar tails was used, two
diffraction peaks could be observed in the SAXS profile of the
complex in Figure 7a, with a scattering vector ratio of 1:2,
indicating a lamellar phase having a larger d-spacing of
S
Supporting Information. Details about the laser light
b
scattering experiments on PSPAS and the results. This material is
available free of charge via the Internet at http://pubs.acs.org.
’
AUTHOR INFORMATION
4
.79 nm. The lack of even higher-order diffractions indicated
Corresponding Author
*E-mail: fanxh@pku.edu.cn (X.-H.F.); zshen@pku.edu.cn
(Z.S.); zhumf@dhu.edu.cn (M.-F.Z.).
the poorer ordering of PSPAS-Ar-3C12 compared with that of
the PSPAS-C16 complex. On the one hand, the increase in the
volume fraction of the alkyl tails had a pronounced consequence
on the microphase separation. On the other hand, the length of
the rigid side chains was increased by the introduction of the
’ ACKNOWLEDGMENT
2
0
benzene ring in Ar-3C12. From our previous study, smectic
phases could be induced by extending the length of the meso-
genic side chain. Consequently, the lamellar phase was obtained
for PSPAS-Ar-3C12. However, the fan shape of the Ar-3C12
surfactant might have caused some difficulty in packing of the
complex, leading to a poorer ordering of PSPAS-Ar-3C12.
The similar behavior was also observed for the PSPCS-C12,
PSPCS-C16, and PSPCS-Ar-3C12 complexes, which was de-
monstrated in Figure 7b. The layer spacing values of the
complexes are listed in Table 1. Furthermore, there was no
distinct difference in the type of mesophases between the
complexes formed by PSPAS and PSPCS. Because electrostatic
interactions had much larger bond strength than hydrogen
Financial support from the National Natural Science Founda-
tion of China (Grants 50925312, 50973016, 20974002, and
2
0990232) and the Programme of Introducing Talents of Dis-
cipline to University (No. 111-2-04) is gratefully acknowledged.
’
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