Amphotropic LC polymers and their multilayer buildup

Article abstract of DOI:10.1021/ma051131t

Cationic and anionic LC ionomers, which possess both thermotropic and lyotropic phases, are suitable materials to fabricate multilayers with an internal structure. The LC ionomers were synthesized using a reactive precursor polymer and used for the multil

Full text of DOI:10.1021/ma051131t

9124
Macromolecules 2005, 38, 9124-9134
Amphotropic LC Polymers and Their Multilayer Buildup
Kyungsun Choi,† Ralf Mruk,† Alain Moussa,‡ Alain M. Jonas,‡ and Rudolf Zentel*,†
Institute of Organic Chemistry, University of Mainz, Duesbergweg 10-14, D-55099 Mainz, Germany,
and Unite´ de physique et de chimie des hauts polyme`res, Universite´ catholique de Louvain,
Place Croix du Sud, 1, B-1348 Louvain-la-Neuve, Belgium
Received June 1, 2005; Revised Manuscript Received August 26, 2005
ABSTRACT: Cationic and anionic LC ionomers, which possess both thermotropic and lyotropic phases,
are suitable materials to fabricate multilayers with an internal structure. The LC ionomers were
synthesized using a reactive precursor polymer and used for the multilayer buildup by solution-dipping
and spin-coating methods based on the electrostatic attraction between polycations and polyanions.
Multilayers prepared by the spin-coating method were thicker and showed a smoother surface than the
ones prepared by the solution-dipping method. The multilayers prepared by the solution-dipping method
showed, on the other hand, a better internal order with respect to layering and orientation of the mesogens,
as a result of the liquid crystalline phase. The LC ionomers and multilayers thereof were fully characterized
by NMR, UV, IR, DSC (differential scanning calorimetry), XRR (X-ray reflectometry), SPR (surface
plasmon resonance), AFM (atomic force microscopy), and polarizing microscopy analyses.
Introduction
to correlate molecular and processing parameters with
the final film structure.12-15
The layer-by-layer (LBL) fabrication of molecularly
organized film has received tremendous attention in
recent years1,2,11 as a simple, effective, and versatile
method to prepare uniform and ultrathin structures.
Since composition, thickness, and orientation of each
layer can be effectively manipulated using this tech-
nique, it provides a route for the formation of various
structures layered at the molecular level.3-7 These
manipulations at the molecular level offer many poten-
tial advantages in device applications such as active
components in nonlinear optical devices (NLO),4,8 em-
ploying materials with selective chemical responses for
sensor applications,7 stable charge-separated assemblies
for photovoltaics,9 and organic light-emitting diodes
(OLED’s).10 Since the first report of Decher and co-
workers in the early 1990s,11 there have been numerous
reports on the LBL deposition technique based on the
electrostatic attraction between polycations and poly-
anions. Many types of charged molecules and nanoob-
jects seem are suitable for deposition by the LBL
method, but the use of polyelectrolytes rather than low
molecular weight polyelectrolytes is advantageous mainly
because good adhesion of a layer to the underlying
substrate or film requires a certain number of ionic
bonds. So far, mostly commercially available polyelec-
trolytes have been studied, and only in rare cases were
functional polyelectrolytes prepared for this purpose.17,18
Concerning the multilayer buildup by the LBL tech-
nique, there is a general interest in obtaining multi-
layers with an internal structure.19 However, multilay-
ers prepared by LBL usually present a low degree of
internal organization, and this may be a limitation of
the technique. Well-organized multilayers would be
advantageous for the applications mentioned, especially
for those requiring a vectorial transfer of energy,
electrons, or matter or when a precise placement of
active functional groups in confined layers is desired.
Usually, multilayer films prepared by the LBL method
show a strong interpenetration between the oppositely
charged polymer layers. Because of this interpenetra-
tion, these multilayer films do not contain defined
internal sublayers, and no Bragg peaks are observed
by grazing angle specular scattering measurements (X-
ray reflectometry, XRR, or neutron reflectometry,
NR).19,20 Several attempts have been presented to use
multilayers containing rigid ionic blocks for reduction
of interpenetration in order to observe Bragg peaks.
However, very particular conditions seem to be neces-
sary, but still the appearance of Bragg peaks is
exceptional.19-23
To get multilayer films with well-defined internal
structure, we have studied multilayers of ionic liquid-
crystalline (LC) polyelectrolytes by LBL.24,25,36 However,
even in the case when both anionic and cationic LC
ionomers showed a smectic phasesas neat materials
in their bulk state, no Bragg peaks could be detected
for the multilayers prepared by the LBL technique.36
This might be explained by the fact that thermotropic
liquid crystals show only liquid-crystalline properties
in bulk and not in solution. Accordingly, LC ionomers
do not show any liquid-crystalline properties during the
adsorption from solution. After ion pairing, the forma-
tion of the liquid-crystalline order is not possible because
of the low mobility inside the polyelectrolyte complex.
As a consequence, it seems desirable to investigate novel
LC polyelectrolytes, which preorganize in solution
through a lyotropic LC phase (high mobility) prior to
drying a thermotropic LC phase (bulk state); thereby,
The electrostatic attraction between the oppositely
charged polyelectrolytes and especially the entropy gain
of the low molar mass counterions are generally thought
to drive the depositions. The amount and conformation
of adsorbed chains depend on dramatically processing
parameters, particularly ionic strength and pH of the
deposition solution, as well as the charge densities of
both polyelectrolytes. A number of articles have explored
the electrostatic parameter in order to delineate condi-
tions of polyelectrolyte multilayer film formation and
† University of Mainz.
‡ Universite´ catholique de Louvain.
* Corresponding author. E-mail: zentel@uni-mainz.de.
10.1021/ma051131t CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/01/2005

Macromolecules, Vol. 38, No. 22, 2005
Amphotropic LC Polymers 9125
Scheme 1. Synthesis of the Mesogen-Containing
Primary Amine
The synthesis of the polymers started with the po-
lymerization of N-acryloyloxysuccinimide.28-30 To de-
termine the molecular weight, the reactive ester poly-
mer was reacted with an excess of N-methylhexylamine.
The resulting polymer was analyzed by GPC with THF
as eluent; a Mn of 28 000 g/mol and a Mw of 49 000 g/mol
were found.37
For the synthesis of the LC polymers (Scheme 2), the
reactive ester polymer was reacted, at first, with the
primary amine 4 (slight excess for homopolymer P1 and
varying amounts for the LC ionomers P2 and P3). The
completeness of the reaction was checked by thin-layer
chromatography. For the synthesis of the LC ionomers
P2 and P3, afterward, an excess of 4-aminobutyric acid
methyl ester hydrochloride or 4-amino-1-triethylphos-
phoniumbutane dihydrochloride was added, respec-
tively. The resulting nonionic polymer was precipitated
and dried. Finally, the anionic ionomer P2 was created
by hydrolysis of the ester group (Scheme 2 and Experi-
mental Section), and in the case of the cationic side
chains of the polymer, P3 was already ionic. The
incorporation of biphenyl-containing side chains in
polymer P2 was confirmed by UV/vis spectroscopy
measurements. 50% of the polymer side chains contain
biphenyl mesogens, corresponding to the amount of the
biphenyl-containing primary amine used for the polymer
analogous reaction.
Liquid Crystalline Behavior. The LC phases of
P1-P3 were characterized by polarizing microscopy,
differential scanning calorimetry (DSC), and X-ray
reflectivity measurements. The polymer melts and
especially the ones from the LC ionomers P2 showed a
rather high viscosity, which might be explained by the
fact that H-bonding of amide groups reduces mobility.
For P2 and P3 in addition the formation of ion pairs
has to be considered (see ref 36 for similar observations),
which are especially strong for the carboxylate groups.
Nevertheless, LC phases with smectic textures (ba-
tonetts)41 were observed for all polymers by polarizing
microscopy after prolonged annealing (see Figure 1a).
For P1 the clearing temperature was 163 °C. In the
series of the cationic LC ionomers (P3a,b), the decreas-
ing temperature decreased with increasing amount of
the bulky triethylphosphonium groups (see ref 36 for
similar behavior). A different effect was observed for P2.
The clearing point was higher than 200 °C and occurred
at decomposition. This happens presumably because of
a strong tendency of the small carboxylate groups to
demix from the hydrophobic mesogens (see X-ray mea-
surements and Figure 2). As a result, this segregation
stabilizes the smectic phase. The phase transition
temperatures are included in the reaction scheme 2.
LBL multilayers with internal order may be achieved.
After the removal of the solvent, these lyotropic phases
change into thermotropic phases, which can stabilize
the internal structure within the dried multilayer film.
In this paper, we describe the synthesis of such new
LC ionomers, possessing an amphotropic character.37
The polymers show both thermotropic phases in bulk
and lyotropic phases in concentrated solution. They can
be used for the multilayer buildup by LBL (solution-
dipping) and self-assembly spin-coating (spin-coating)
method.27 X-ray reflectivity measurements indicate
internal layering in multilayer films, and angular
dependent UV/vis measurements present a preferred
orientation of the mesogens perpendicular to the sur-
face.
Results and Discussion
Synthesis of the Amphotrophic Polymers. The
chemical structures and reaction schemes of the LC
polymers and ionomers prepared in this study are
shown in Schemes 1 and 2. The new LC ionomers P2
and P3 were synthesized by a reaction of a biphenyl-
functionalized amine and ionic amines with a reactive
precursor polymer (Scheme 2). The side groups (ionic
groups and mesogens) are attached to the main chain
by amide bonds which are stable against hydrolysis. The
mesogens consist of a long alkyl chain to increase the
amphiphilicity of the structure. Branched alkyl chains
are used to prevent side-chain crystallization. A larger
variety of polymers, which are synthesized under the
variation of concentration of mesogens and ionic groups,
were briefly described elsewhere.26 Here we selected
homopolymer P1, the anionic LC ionomer P2, and the
cationic LC ionomers P3a,b. First, the mesogen-
containing primary amine 4 had to be synthesized, as
shown in Scheme 1. Phthalimide potassium, which was
transformed into the corresponding N-(6-bromohexyl)-
phthalimide 1. The phenol 2 was obtained by reaction
of 4,4′-dihydroxybiphenyl and racemic p-toluenesulfonic
acid-2-octyl ester. Compounds 1 and 2 were afterward
reacted to obtain the phthalimide protected primary
amine 3. In the final step, the protection group was then
cleaved by treatment with hydrazine hydrate in ethanol,
yielding 60% of 4.
X-ray reflectivity measurements showed a smectic
layer spacing of 48.5 Å for P1 and of 72 Å for the LC
ionomer P2 in bulk state. Based on the molecular model
presented in Figure 2a, these spacings correspond to an
interdigitated smectic structure for the homopolymer P1
(smectic layer thickness is about 1.6 times the length
of the mesogen, which is 30 Å) and a bilayer structure
for the LC ionomer P2 (distance from end of mesogen
to the ionic group is ∼39 Å).42,43 The difference between
the “ideal” bilayer length of 78 Å and the experimentally
determined length of 72 Å can be explained due to
partial coiling, some tilting of the mesogens, and/or a
partial interdigitation of the ends of the alkyl chains.
The bilayer structure is a result of the segregation
between the hydrophilic ionic groups and the hydro-

9126 Choi et al.
Macromolecules, Vol. 38, No. 22, 2005
Figure 1. Polarizing microscopy image of (a) a thermotropic phase of P1 (163 °C) and (b) a lyotropic phase of P3b (50 °C) with
ethylene glycol.
Scheme 2. Structures of Mesogen-Containing Polymers (s: Smectic Phase; i: Isotropic Phase)
phobic mesogens. It is the precondition for the formation
of a lyotropic phase in polar solvents. P2 and P3b do
not dissolve in water; only slight swelling can be
observed, while preserving their liquid crystalline phase.
To prove their potential to form lyotropic phases in polar
solvents, ethylene glycol was used as polar solvent.
Contact preparations in ethylene glycol show clearly the
formation of lyotropic phases at high concentrations of
P2 and P3b (see Figure 1b). The observation of lyotropic
phases has also been made for a large variety of other
LC ionomers of similar structure.26,37 As a result, P2
and P3b are amphotropic polymers, which form both
thermotropic smectic phases in the bulk and lyotropic
phases in polar solvents, such as ethylene glycol.
Multilayer Buildup. After analysis of the phase
behaviors of the LC ionomers P2 and P3b, the multi-
layer buildup with oppositely charged polyelectrolytes
was successfully examined using the method introduced
by Decher.11 For P2, a comparison between the LBL
solution-dipping method and the subsequent spin-coat-
ing method31-34 was done. For both processes, P2 and
P3b were dissolved in THF with the addition of some
ethylene glycol or water (5:1 ratio), and in this solvent
mixture, no lyotropic phases are formed. During the
drying procedure, THF evaporates first, increasing the
concentration of ethylene glycol or water to a range,
where lyotropic phases can be expected. Before alter-
nately depositing polymer P2 (anionic LC ionomer) and
poly(choline methacrylate) (PCM) or poly(2-acryloy-
lamino-2-methylpropyl sulfonate sodium salt) (PAMPS)
and P3b (cationic LC ionomer) onto the substrate, poly-
(ethylenimine) (PEI) and PAMPS were predeposited two
times as basis layers.

Macromolecules, Vol. 38, No. 22, 2005
Amphotropic LC Polymers 9127
Figure 2. (a) Molecular model structure with distance of P2 by using Chem 3D Ultra 7.0. (b) X-ray scattering diagram of P1
(homopolymer) and P2 (anionic LC ionomer) in bulk state (using Ni-filtered Cu KR radiation, λ ) 1.54 Å). (c) Schematic
representation of the smectic bulk structure of P1 and (d) P2. (e) Interdigitated layer structure present in the multilayer.
Figure 3. Multilayer buildup from LC ionomer P2. (a) UV/vis spectra measured during the multilayer buildup of P2 and PCM
by solution-dipping. (b) Growth of the solution-dipping films at 267 nm. (c) Comparison of the growth of the multilayer films
assembled by solution-dipping (b) and spin-coating (2).
For a comparative study, multilayers were assembled
using solution-dipping as well as spin-coating methods
applying the same conditions. The preparation of mul-
tilayer assemblies based on the solution-dipping method
was achieved by dipping the substrate alternately for
10 min in cationic aqueous solution of PCM and then
in anionic polymer P2 solution and rinsing three times
with plenty of Milli-Q water fir 1 min between these
two steps. A similar procedure was adopted when
assembling the multilayers by the spin-coating method.
The polymer solution and the aqueous solution of PCM
were poured onto a substrate, and then the substrate
was spun at a speed of 4000 rpm for 15 s.
Figure 3a showed the multilayer buildup from LC
ionommer P2 investigated by UV/vis; the increase of the
maximum of the π-π* absorbance of the biphenyl
mesogen at 267 nm as a function of the number of
bilayers for both the solution-dipping and spin-coating
multilayers, respectively. According to Figure 3b, the
deposition process was linear, indicating that the amount
of material deposited per bilayer is completely reproduc-
ible from layer to layer. Similar behavior of the multi-

9128 Choi et al.
Macromolecules, Vol. 38, No. 22, 2005
Figure 4. Tapping mode AFM images of 12 double layers of P2 and PCM multilayer films prepared by (a) the solution-dipping
method and (b) the spin-coating method.
layer buildup using the spin-coating method was inves-
tigated as well. Thus, with both methods, it is possible
to prepare multilayers, which grow constantly in thick-
ness according to the number of bilayers. Figure 3c
showed the difference in UV/vis absorbance of multi-
layer films with alternating P2 and PCM layers pre-
pared by solution-dipping and spin-coating methods. It
is obvious that the absorbance of the spin-coated films
was about 20 times as high as those prepared by
solution-dipping. This happens despite the fact that the
spin-coated film was adsorbed onto only one side of a
quartz substrate, while the film prepared by the solu-
tion-dipping method was adsorbed onto both sides of a
quartz substrate. This was in agreement with literature
data.27,31-33 With regard to the formation of an internal
order, both types of films could be different: This
significant difference of the absorption between the
multilayers from the solution-dipping and the spin-
coating method was caused by the different adsorption
mechanisms. During the solution-dipping process, LC
ionomer chains diffused toward the substrate, and then
the adsorbed chains rearranged themselves on the
surface. After evaporation of the THF, during the drying
process, the concentration of polymers in the water
phase increased, whereby the formation of a lyotropic
phase was expected. This drying process was quite slow,
and it can provide enough time to rearranged adsorbed
LC ionomers and to oriented mesogens during the
drying process. Subsequently, solution-dipping samples
had preferably structured order due to the oriented
mesogens, and it would be perpendicular to the surface.
On the other hand, the spin-coating method results
in thicker films. In the spin-coating process, the adsorp-
tion and rearrangement of adsorbed chains on the
surface and the elimination of weakly bound LC-
ionomer chains from the substrate are almost simulta-
neously achieved at a high spinning speed for a short
time. A very fast elimination of the solvent yields thick
layers. Quick solidification and polyelectrolyte formation
compete with the ordering process. With regard to the
formation of an internal order in the multilayer system,
the film of the spin-coating method may possess less
well-ordered internal structures than that of the solu-
tion-dipping method.
force microscopy (AFM, roughness, topology), X-ray
reflectometry (XRR, internal order), and angular de-
pendent UV/vis measurements to monitor the order
within the multilayers. AFM images can give informa-
tion about the surface coverage and roughness of the
assembled multilayers. These AFM images were taken
in air at room temperature in the tapping mode on
multilayer samples prepared by solution-dipping and
spin-coating on quartz (12 double layers each). The
results are displayed in Figure 4.
A clear difference can be seen between the solution-
dipped (Figure 4a) and the spin-coated sample (Figure
4b). The solution-dipped sample showed relatively large
flat plateaus, separated by sharp steps, whereas the
spin-coated sample showed a smoother variation of the
height and a finer structure. As a result, the surface
roughness (standard deviation from average) of a solu-
tion-dipped film is about 5.9 Å and that of a spin-coated
film only 3.7 Å. This demonstrates that the shear forces
during the spinning process enhance the planarization
of the multilayer film. On the other hand, the solution-
dipped sample resembles the thin films of smectic liquid
crystals,38-40 which display also large plateaus sepa-
rated by sharp layer steps.
To determine the thickness of the multilayer films,
surface plasmon resonance (SPR) measurements were
performed at various stages during the solution adsorp-
tion process (solution-dipping).35 For the much thicker
samples obtained by spin-coating method a proper
evaluation was not possible. Examples of SPR curves
are depicted in Figure 5. Measurements were performed
after adsorption of each bilayer from THF/water mixture
onto a thin gold film, which was brought into optical
contact with a prism afterward. Then the reflectivity of
the sample is monitored as a function of incident angle
Θ (see Figure 5).
The shift in the SPR angle (minimum of curve)
observed during the formation of the multilayer (P2 and
PCM) can be used to determine the film thickness, if
the refractive index of the film is known. As a starting
point, we assumed the refractive index of LC-ionomer
P2 to be 1.5, as generally used.35 A value of about 6 Å
was found for the initially adsorbed anionic layer of
3-mercaptopropionic acid used to functionalize the metal
gold layer. The resulting evaluation (Figure 5b) showed
a linear thickness increase with a thickness per bilayer
(cationic layer (PCM) and anionic ionomer layer (P2))
To investigate the difference between both types of
multilayers in more detail, they were characterized by
surface plasmon resonance (SPR, thickness), atomic

Macromolecules, Vol. 38, No. 22, 2005
Amphotropic LC Polymers 9129
Figure 5. (a) Angular dependent SPR curves after different deposition cycles of the LC polymer P2 and PCM by the solution-
dipping method. (b) The film thickness according to the number of bilayers.
Figure 6. (a) X-ray reflectivity of different multilayer films: (a-1) basis double layer prepared with PEI and PAMPS; (a-2) 16
bilayers sample with P2/PCM prepared by the solution-dipping method; (a-3) annealed solution-dipping sample for 12 h at 150
°C; (a-4) 16 bilayers sample with P2/PCM prepared by the spin-coating method. kz0 is the vertical component of the incident
photons in a vacuum. (b) Patterson function of samples shown in (a). In (a) and (b), the curves are shifted vertically for clarity.
about 40 Å. This value per double layer is rather high
compared to “usual” polyelectrolytes, but still it is in
the range of values found for other LC ionomers.24,25,36
This is a consequence of the low charge density of the
rather hydrophobic LC ionomers.
polyanion, and a smectic structure is the assumption
of the adsorption of fully interdigitated monolayers of
P2 (see Figure 2e). That is to assume a structure in the
multilayer, which is different from the double layers
stable in the melt. Such fully interdigitated monolayers
result if mesogens are originating from different poly-
mer chains interdigitate, as found for homopolymer P1.
The mesogens may pack well in such an arrangement,
but the distance between the ionic groups must be
increased compared to the situation in bulk (Figure 2).
This might be possible in the lyotropic phase due to the
presence of solvent.
To determine of the order within the multilayer
assembly, X-ray reflectivity measurements were made.
For these measurements, samples were made differently
that they consisted of 16 bilayers, and they were
assembled on a polished silicon wafer. The results
obtained from solution-dipped and spin-coated samples
are displayed in Figure 6.
The question to be answered is: Is there an influence
of the liquid-crystalline phase on the adsorption process?
SPR measurement gives only an averaged thickness of
the adsorbed film. Following the arguments of the
introduction (difficulty of complete reorganization of
polyelectrolyte multilayer assembly; preorganization in
lyotropic phase), there should be a relation between the
smectic structure and the thickness of the adsorbed
layer. On the basis of the X-ray results of P2 and the
molecular model (see Figure 2), a thickness of about 80
Å would have been expected per adsorbed double layer
of LC ionomer and polycation (an anionic smectic double
layer of P2 and some thickness for the cationic PCM
layer). However, the thickness of the double layer
adsorbed from solution is only half as thick (40 Å, SPR).
Concerning the alternating deposition sequence in mul-
tilayer buildup between P2 and PCM, the P2 layer must
expose negative charges to both sides as presented in
Figure 2e. A possibility to combine a thickness of 40 Å
per double layer, fabricated between polycation and
The evaluation of the X-ray reflectivity measurements
shows for all samples a weak Bragg peak at a kz0 value
of about 0.17 Å-1, suggesting an internal ordering. We
assume that this is the second order of a Bragg peak
located at about kz0 ) 0.085 Å-1 and buried below
Kiessig fringes. This would correspond to a layering of

9130 Choi et al.
Macromolecules, Vol. 38, No. 22, 2005
Figure 7. (a) Geometry scheme for the angular dependent UV/vis measurement with unpolarized light, i.e., light polarized
within the paper plane and perpendicular. Note that the absorption of light polarized perpendicular to the paper plane should
not vary while changing the angle Θ. (b) Results of angular dependent UV/vis measurement of 12 bilayers consisting of P2 and
PCM prepared by the solution-dipping method and (c) by the spin-coating method. For comparison of the both spectra the absorption
perpendicular to the substrate A was subtracted. 2: primary data; b: after thickness correction by factor d.
about 37 Å, in agreement with the values of the
increment determined by SPR measurements. To check
this hypothesis, we have computed the Patterson func-
tions from the X-ray reflectograms, as described previ-
ously.19 The Patterson function P(z) is proportional to
the probability of finding in the film two interfaces
spaced apart by a distance z. For all P2-based samples,
a strong peak develops at 36 Å in the Patterson
functions, indicating the existence of a periodic fluctua-
tion in the film. Indications for correlation between
second neighbors can also be seen in these functions.
This inner periodic fluctuation is found independent of
the preparation of the sample. It is, however, better
developed for the sample obtained by solution-dipping,
and it decreases during annealing. Nevertheless, these
experiments clearly demonstrate that layering exist in
all P2-based films, albeit of limited spatial extent. Next,
only samples obtained by solution-dipping show Kiessig
fringes. These fringes transform in the Patterson func-
tion into a final peak whose position directly determines
the film thickness. This shows that the films from the
solution-dipping method are flat and smooth. However,
the thickness of the films prepared by the solution-
dipping method is much lower than expected, indicating
incomplete growth on the silicon wafer. Interestingly,
the film contracts upon annealing; its thickness de-
creasing from 109 to about 77 Å, testifying for substan-
tial rearrangements occurring upon annealing. By
contrast, the film prepared by spin-coating does not
present Kiessig fringes or a strong final peak in the
Patterson function. Since the outer surface of this film
was shown to be very flat by AFM, the absence of
Kiessig fringes most probably results from a very large
film thickness, which prevents to get fringes due to the
finite resolution of the X-ray reflectometer.
As a smectic layering exists, the mesogenic groups
should be oriented perpendicular to the surface. UV/
vis dichroism offers a possibility to determine the order
parameter of the mesogens by angular dependent UV/
vis measurements, using unpolarized light. These were
done with the multilayer samples obtained by solution-
dipping and spin-coating methods. The results are
displayed in Figure 7. In addition, it must be noted that
the measurements were repeated with same samples
after 6 months. The samples were stored at room
temperature without special precaution, and we can
conclude that the samples do not change. This proves
that a stable orientation in multilayer is achieved.
First, the measurements had to be corrected for the
absorbance by a correction factor d (see Experimental
Section). The corrected values showed a strong increase
of the absorption on increasing the angle, too. As the
biphenyl chromophores absorb light polarized along
their long axis, this proved that the biphenyl units were
oriented preferably perpendicular to the surface.
As the measurements were carried out with unpolar-
ized light (Figure 7a), 50% of the light is always
polarized perpendicular to the long axis of the biphenyl
chromophores independent of the angle. The absorption
of the other 50% of the light (polarized within the paper
plane of Figure 7a) should follow eq 1. With this
equation the angular dependence of both types of

Macromolecules, Vol. 38, No. 22, 2005
Amphotropic LC Polymers 9131
samples can be fitted for angles from -50° to +50°.
From the fit, A| (parallel absorbance) and A (perpen-
dicular absorbance) were obtained (see Experimental
Part). Using these results, it was possible to estimate
the nematic order parameter S (quality of the orienta-
tion of the long axis of the biphenyl chromophores
perpendicular to the surface) using eq 2.44 As a result,
an order as high as S ) 0.25 was obtained for the
sample prepared by solution-dipping, and a value of only
S ) 0.07 was obtained for the sample obtained by spin-
coating. In LC phases, typical order parameters between
0.3 and 0.6 are found for nematic phases and 0.6 and
0.8 for smectic phases.43,44 Consequently, the value
observed for the solution-dipped sample is very close to
the value of monodomain liquid crystalline phases, and
the value for the spin-coated sample corresponds only
to “some” preferred orientation.
structure present in the multilayers? And how is their
long-term stability?
At first, a direct comparison of the LC behavior of
multilayers and the bulk or lyotropic phase of the LC
ionomer is impossible because of the different composi-
tion. The LC ionomer contains low molar mass coun-
terions in both bulk and lyotropic phase; on the other
hand, the multilayer contains polymeric counterions
(the polycation). Thus, from a thermodynamic point of
view the phase behavior should be different, and the
LC phases of the multilayer have to be compared to that
of a one to one mixture of LC ionomer and the polyelec-
trolyte. Now, the one-to-one composition from polycation
and polyanionspresent in the multilayersscorresponds
to a polyelectrolyte complex, in which the viscosity is
extremely high and the equilibrium is hardly reached.
If e.g. LC ionomer and poly(choline methacrylate) (PCM,
polycation) solutions are mixed, an unmeltable poly-
electrolyte complex is formed immediately. So there is
no equilibrium reference state for a bulk phase of the
mixture, to which the multilayers can be compared. In
addition, no equilibrium state is reached for the mul-
tilayer, too. On the contrary, the structure present
during adsorption and drying (lyotropic phase, transi-
tion to thermotropic bulk phase) is frozen-in. This
structure is, however, long-term stable. This can be
shown e.g. by a repetition of the angular dependent UV
measurements done with samples stored at room tem-
perature for 6 months, which reproduced the old pa-
rameters.
A(Θ) ) A sin2 Θ + A cos2 Θ
(1)
(2)
x
|
A| - A
S )
A| + 2A
Conclusions
In this work, new amphotropic LC ionomers, which
possess smectic thermotropic phases in bulk and lyo-
tropic phases in solution, were synthesized. These LC
ionomers could successfully be used for the multilayer
buildup by solution-dipping and spin-coating methods.
Although both methods showed quite linear and repro-
ducible multilayer buildup performances by UV/vis
measurements, the AFM, SPR, and XRR measurements
indicated differences between multilayer samples pre-
pared by both methods. The differences between the
solution-dipped and spin-coated samples can be ratio-
nalized by the different mechanisms.
During the solution-dipping process, the charged LC
ionomers diffused toward the substrate, and then ad-
sorbed chains rearranged themselves as thin films. The
amount of adsorption is controlled by charge compensa-
tion, and the whole deposition process (including final
drying) is quite slow. It gives enough time to orient
mesogens in the lyotropic phases. After removal of the
solvents, the lyotropic phases (in concentrated solution)
change into thermotropic phases (in bulk), resulting in
a stabilized internal structure. The orientation of the
mesogens is well improved due to the liquid crystallin-
ity. However, the amount of the adsorbed LC ionomers
willsin most casessnot be the exact amount needed to
form the smectic layers; thus layer steps arise. As a
result of a lyotropic phase, which is different from the
thermotropic bulk phase (monolayers vs double layers),
the films rearranged during annealing, decreasing the
order and flatness of the films.
Consequently, we obtained multilayers with synthe-
sized amphotropic LC ionomers, which are suitable
materials to fabricate internal ordered multilayers. The
multilayers deposited by the solution-dipping method
show the order parameter closed to that of real liquid-
crystalline monodomins, and based on that parameter,
the mesogens of the LC ionomers are oriented perpen-
dicular to the substrate.
Experimental Section
LC Polyelectrolytes. N-(6-Bromohexyl)phthalimide (1). A
solution of 1,6-dibromohexane (44.8 g, 0.183 mol) in 300 mL
of acetone was heated to reflux. Potassium phthalimide (17 g,
0.092 mol) was added in four portions over a period of 4 h.
The resulting mixture was kept under reflux for an additional
24 h. After cooling to room temperature, the mixture was
filtered and the solvent was evaporated. The crude product
was purified by column chromatography (eluent petrol ether/
ethyl acetate 8:1), yielding 19.7 g (0.063 mol, 69%) of colorless
powder (melting point: 60 °C).
1H NMR (CDCl3/200 MHz): δ ) 7.77 (m, 2H, arom H), 7.70
(m, 2H, arom H), 3.66 (t, 2H, N-CH2), 3.37 (t, 2H, Br-CH2),
1.2-1.9 (m, 8H, aliphatic H).
(()-4-Toluenesulfonic Acid 2-Octyl Ester. A solution of 90.6
mL (74.2 g/0.57 mol) of (()-2-octanol in 300 mL of pyridine
was cooled to 0 °C. Within 30 min, 104.9 g (0.55 mol) of
p-toluenesulfonyl chloride was added. After that, the mixture
was stirred for 20 h at room temperature. The reaction mixture
was then poured on a mixture of 400 mL of concentrated
hydrochloric acid and 600 mL of ice water. The resulting
mixture was extracted three times with 300 mL of diethyl
ether. The unified organic phases were dried over magnesium
sulfate and filtered. After that, the solvent was evaporated in
a vacuum. The reaction yielded 122.4 g of colorless oil that
still contained ∼10 wt % of unreacted (()-2-octanol (equals
110.2 g/0.387 mol (()-4-toluenesulfonic acid 2-octyl ester,
yield: 70%). The product was reacted without further purifica-
tion.
On the other hands, the spin-coating method gave
much thicker films due to the fast elimination of the
solvent and the high spinning process. In addition, spin-
coated films possessed less internal order. The drying
process happens very quickly, and it provides not
enough time for the formation of the LC phase. Thus,
the surface of the film was smoother because it does not
fabricate the smectic layer. At the same time, the LC
order, with respect to both layering and parallel orien-
tation of the mesogens, was poorer compared to the
solution-dipped sample.
1H NMR (CDCl3, 200 MHz): δ ) 7.73 (d, 2H, arom H, meta
to CH3), 7.27 (d, 2H, arom H, ortho to CH3), 4.53 (m, 1H,
The questions remaining are: What is the relation
between the bulk phase of the LC ionomers and the

9132 Choi et al.
Macromolecules, Vol. 38, No. 22, 2005
RCH2-OR), 2.39 (s, 3H, Ar-CH ), 1.0-1.7 (m, 13H, aliphatic
H + remaining reactant), 0.80 (t, 3H, R-CH3 + remaining
reactant).
amine in 10 mL of DMF was added. The reacting mixture was
stirred for 24 h at room temperature under a nitrogen
atmosphere; afterward, the mixture was concentrated in a
vacuum to 5 mL. The polymer was precipitated by pouring
the solution into 100 mL of methanol. After centrifugation,
the solvent was decanted, and the product was washed several
times with methanol and dried. The reaction yielded 340 mg
of a pale yellow solid.
(()-4′-(1-Methylheptyloxy)biphenyl-4-ol (2). A solution of 16.9
g (0.3 mol) of potassium hydroxide and 57.6 g (0.3 mol) of 4,4′-
dihydroxybiphenyl in 750 mL of methanol was heated to reflux
under a nitrogen atmosphere. After that, a solution of 95.6 g
(0.3 mol) of (()-4-toluenesulfonic acid-2-octyl ester prepared
according to ref 37 in 160 mL of methanol was added in small
portions during 8 h. The reaction mixture was then refluxed
for another 40 h, and the solvent was removed in a vacuum.
The residue was stirred for 1 h with 2 N hydrochloric acid,
filtered, and washed twice with water and once with a small
amount of ethanol. The crude product was purified by column
chromatography (petrol ether/ethyl acetate 8:1). The reaction
yielded 25.3 g (0.084 mol, 28%) of colorless solid (mp: 76 °C).
1H NMR (CDCl3, 200 MHz): δ ) 7.41 (m, 4H, arom H, meta
to O), 6.88 (m, 4H, arom H, ortho to O), 4.36 (m, 1H, RCH2O-
R), 3.32 (bs, 1 H, OH), 1.1-1.8 (m, 13H, aliphatic H), 0.87 (t,
3H, CH3).
1H NMR (CDCl3, 200 MHz): δ ) 7.45 (4H, arom H, meta to
O), 6.92 (4H, ortho to O), 4.27 (1H, O-CH), 3.99 (2H, NH-
R-CH2), 3.25 (2H, NH-CH2), 1.31-1.24 (12H, aliphatic H +
main chain), 0.86 (3H, O-R-CH3).
LC Ionomers P2. A sample of 501 mg (2.96 mmol repeating
units) of poly(N-acryloyloxysuccinimide) was dissolved in 40
mL of DMF and heated to 50 °C. Subsequently, a solution of
587 mg (1.48 mmol repeating units) of primary amine in 10
mL of DMF was added for P2. The reacting mixture was
stirred for 5 h at RT under a nitrogen atmosphere. It was
checked by thin-layer chromatography that no free amine was
left after this time. For P2, a solution of 454 mg (2.96 mmol)
of the 4-aminobutyric acid methyl ester hydrochloride in 10
mL of DMF was then supplemented, and then 4 mL of
triethylamine was added. The mixture was stirred for a further
24 h at 50 °C. Afterward, the mixture was concentrated in a
vacuum to 10 mL. The polymer was precipitated by pouring
the solution into 100 mL of methanol. After centrifugation,
the solvent was decanted, and the product was washed several
times with methanol and dried. The reaction yielded P2 as
bright-yellow solids.
13C NMR (CDCl3, 50.3 MHz): δ ) 157.4 (1C, arom C, ipso
to -OR), 154.6 (1C, arom C, ipso to OH), 133.8 and 133.2 (2C,
arom C, para to O), 127.9 and 127.7 (4C, arom C, meta to O),
116.2 and 115.6 (4C, arom C, ortho to O), 68.5 (1C, RCH2O),
36.5, 31.8, 29.3, 25.6, 22.6, 19.8, 14.1 (7C, aliphatic C).
(()-N-{6-[4′-(1-Methylheptyloxy)biphenyl-4-yloxy]hexyl}-
phthalimide (3). A mixture of N-(6-bromohexyl)phthalimide
(14.05 g, 45 mmol), (()-4′-(1-methylheptyloxy)biphenyl-4-ol
(13.57 g, 45 mmol), potassium hydroxide (2.7 g, 48 mmol), and
a catalytic amount of KI in 100 mL of methanol was heated to
reflux for 4 days under a nitrogen atmosphere. After cooling
to 4 °C, a white solid precipitated which was isolated and
washed with a small amount of cool methanol. The product
yielded 10.3 g (19.5 mmol, 43%) of a white solid (mp: 64 °C).
1H NMR (DMSO-d6/200 MHz): δ ) 7.83 (m, 4H, arom H of
phthalimide), 7.46 (d, 4H, arom H, meta to O of biphenyl), 6.91
(d, 4H, arom H, ortho to O), 4.41 (m, 1H, O-CH), 3.92 (t, 2H,
O-CH2), 3.56 (t, 2H, N-CH2), 1.1-1.8 (m, 21H, H-6-H-9,
H-19, R-CH2), 0.81 (t, 3H, R-CH3).
1H NMR (CDCl3, 200 MHz): δ ) 7.41 (4H, arom H, meta to
O), 6.87 (4H, ortho to O), 4.31 (1H, O-CH), 3.89 (2H, O-CH2),
3.61 (3H, COOCH3), 3.21 (4H, NH-CH2), 2.31 (2H, CH2-CH2-
COOCH3), 1.71-1.23 (15H, aliphatic H + main chain), 0.86
(3H, O-R-CH3).
IR (ATR): 2927, 2853 (C-H aliphatic), 1737 (COO-CH3),
1644 (CO- NHR), 1497, 1238, 1173, 1035, 822 cm-1
.
Cleavage of the Ester Bond To Obtain LC Ionomer P2. A
solution of 200 mg of the precursor of P2 in 15 mL of DMF
was heated to 40 °C under a nitrogen atmosphere. After that
a solution of 1.1 g of potassium hydroxide in 5.5 mL of water
was added to the reaction mixture with a syringe. The mixture
was stirred for 5 h at 40 °C. As a white product had formed,
the solvent was evaporated, and the residue was washed three
times with 100 mL of water. The mixture was then centrifuged,
and the solvent was decanted. The crude product was added
to the solution of K2CO3 (pH ) 9) and then again centrifuged,
and the solvent was decanted. After drying, 229 mg (9.6 mmol
repeating units, 72%) of a pink solid was obtained.
13C NMR (DMSO-d6, 50.3 MHz): δ ) 167.9 (2C, carbonyl),
157.6 + 156.8 (2C, arom C, ipso to O), 134.3 (2C, arom C of
phthalimide), 132.1 +132.0 (2C, arom C, para to O), 131.5 (2C,
arom C of phthalimide), 127.1 + 127.0 (4C, arom C, meta to
O), 122.9 (2C, arom C of phthalimide), 115.8 + 114.7 (2C, arom
C, ortho to O), 72.9 (1C, O-CH), 67.3 (1C, O-CH2), 37.3 (1C,
N-CH2), 35.8 (1C, O-CH-CH2), 31.2 + 28.6 + 28.4 + 27.7 +
25.9 + 25.1 + 24.8 + 21.9 (8C, aliphatic C), 19.5 (1C, OCH-
CH3), 13.8 (1C, R-CH3).
(()-6-[4′-(1-Methylheptyloxy)biphenyl-4-yloxy]hexylamine (4).
Hydrazine hydrate (1.03 g, 20.6 mmol) was added to a solution
of (()-N-{6-[4′-(1-methylheptyloxy)biphenyl-4-yloxy]hexyl}-
phthalimide (10.2 g, 19.2 mmol) in 100 mL of ethanol. The
mixture was kept under reflux for 16 h. After addition of 10
mL of concentrated HCl, the resulting solution was kept under
reflux for 1 h. After cooling to 4 °C a white solid precipitated
which was isolated. The solid was stirred for 30 min in 1 M
aqueous NaOH. After filtration, the crude product was heated
with 200 mL of CHCl3 and 5 g of Na2SO4 under reflux for 2 h.
Filtration after cooling and evaporation of the organic solvent,
the reaction yielded 4.53 g (11.3 mmol, 60%) of a white product.
1H NMR (CDCl3/200 MHz): δ ) 7.43 (m, 4H, arom H, meta
to O), 6.91 (m, 4H, arom H, ortho to O), 4.35 (m, 1H, O-CH),
3.96 (t, 2H, O-CH2), 2.71 (t, 2H, NH2-CH2), 1.2-2.2 (m + bs,
23H, aliphatic H, NH2), 0.87 (t, 3H, R-CH3).
IR (ATR): 2928, 2856 (C-H aliphatic), 1642 (CO- NHR),
1564, 1497, 1397, 1239, 821 cm-1
.
P3 LC Ionomer. For the synthesis of P3a with 20% of ionic
amines or P3b with 50% of ionic amines, 251.9 mg (1.487 mmol
repeating units) of poly(N-acryloyloxysuccinimide) was dis-
solved in 15 mL of DMF and heated to 50 °C. Subsequently, a
solution of 473.6 mg (1.191 mmol repeating units) of primary
amine for P3a or 295.6 mg (0.744 mmol repeating units) of
primary amine for P3b in 10 mL of DMF was added. The
mixture was stirred for 5 h at 70 °C and then cooled to 50 °C.
After that, a solution of 239 mg (0.912 mmol) of 4-aminobu-
tyltriethylphosphonium chloride hydrochloride in 10 mL of
methanol and 4 mL of triethylamine for P3a or 194 mg (0.744
mmol) of 4-aminobutyltriethylphosphonium chloride hydro-
chloride in 8 mL of methanol and 4 mL of triethylamine for
P3b was added. The mixture was stirred for another 24 h at
50 °C. Afterward, the mixture was concentrated in a vacuum
to 10 mL. The polymer was precipitated by pouring the
solution into 100 mL of diethyl ether. After centrifugation, the
solvent was decanted, and the product was washed several
times with diethyl ether and dried. The reaction yielded P3a
or P3b.
Poly(N-acryloyloxysuccinimide) was prepared as described
in ref 37.
1H NMR (DMSO-d6, 200 MHz): δ ) 3.11 (1H, CH, main
chain), 2.80 (4H, CH2, side groups), 2.08 (2H, CH2, main chain).
13C NMR (DMSO-d6, 50.3 MHz): δ ) 169.8 (2C, RC(O)N),
162.3 (1C, RC(O)O), 35.7 (1C, CH, main chain), 30.7 (1C, CH2,
main chain), 25.4 (2C, CH2, side chain).
Polyelectrolytes. Branched poly(ethylenimine) (PEI) was
purchased from Aldrich and used without further purification.
The synthesis of poly(2-acryloylamino-2-methylpropyl sul-
fonate sodium salt) (PAMPS) and poly(choline methacrylate)
(PCM) were already described elsewhere.36
LC Homopolymer P1. A sample of 255 mg (1.51 mmol
repeating units) of poly(N-acryloyloxysuccinimide) was dis-
solved in 40 mL of DMF and heated to 50 °C. Subsequently, a
solution of 720 mg (1.81 mmol repeating units) of primary

Macromolecules, Vol. 38, No. 22, 2005
Amphotropic LC Polymers 9133
Substrates for the Multilayer Buildup. The formation
of multilayers was performed on a quartz glass or a silicon
wafer used as substrates. Cleaning of these substrates was
achieved using a classical procedure.10 The substrates were
immersed for 20 min in a 1:1 mixture of concentrated H2SO4
and a 30% H2O2 (“piranha solution”; caution: piranha reacts
violently with organic compounds and should not be stored in
closed containers) and then extensively rinsed with ultrapure
water (obtained by deionization and purification using the
Milli-Q system from Millipore) at three times. And then the
substrates were treated with a 1:1:5 mixture of 25% aqueous
NH3, 30% H2O2, and H2O at 80 °C to functionalize and
thoroughly rinsed with ultrapure Milli-Q water. After further
washing, the substrates were used for multilayer adsorption.
Multilayer buildup. In the beginning, two double layers
of poly(ethylene imine) (PEI) (from a solution of 2.5 mg/mL
PEI in 1 N hydrochloric acid) and poly(2-acryloylamino-2-
methylpropyl sulfonate sodium salt) (PAMPS) (from a solution
of 3.5 mg/mL PAMPS in water) were adsorbed on the sub-
strates as basis layers. At each time, the substrates were
dipped into the solution for 20 min, and then the substrates
were rinsed three times with plenty of Milli-Q water (each time
for 1 min) between these two steps, as already described in
the literature.1 The initially deposited double basis layers are
sufficient to start the multilayer deposition process; the surface
coverage and charge density appear to be more uniform after
a number of bilayers of highly charged polyelectrolytes have
been deposited, thereby eliminating any effects that the
substrate itself may have on the adsorption process.1 After
fabrication of these basis layers, substrates were sequentially
dipped in a cationic poly(choline methacrylate) (PCM) solution
for 10 min (from a solution of 2.5 mg/mL PCM in water) rinsed
three times by immersion in ultrapure water (1 min). And then
dipped for 10 min in a polyanion solution and three times
rinsing steps were performed. This deposition procedure was
then cycled to obtain multilayers. The multilayers were dried
under nitrogen gas purging at the end of their fabrication.
Identical procedure was adopted when the multilayers
assembled by the spin-coating method. In this case, however,
the polymer/solvent solution and aqueous solution of PCM
were poured onto a substrate, and then the substrate was spun
at a speed of 4000 rpm for 15 s. Subsequently, plenty of Milli-Q
water was put on the substrate, and then the substrate was
spun again at the same conditions. Before alternately deposit-
ing polymer P2 and PCM onto the prepared substrate by the
spin-coating method, PEI and PAMPS were also predeposited
two times as basis layers alternately in cationic aqueous
solution of PEI and then in anionic aqueous PAMPS like the
solution-dipping method at same condition. The washing steps
were repeated three times. At the end of every adsorption cycle,
the multilayers were dried under nitrogen gas purging, and
UV/vis spectra were measured.
phases) for bulk state were carried out on a Siemens D-500
diffractometer using Cu KR radiation (λ ) 1.54 Å) and a single-
crystal graphite monochromator. Additionally, X-ray reflec-
tivity measurements for multilayers were done with the setup
described in ref 19.
Samples were imaged at room temperature with a com-
mercial AFM (Nanoscope IIIa, Digital Instruments, Santa
Barbara, CA) employing TappingMode using rectangular
silicon cantilevers (Nanosensors, 125 µm long, 30 µm wide, 4
µm thick) with an integrated tip, a nominal spring constant
of 42 N m-1, and a resonance frequency of 330 kHz. To control
and enhance the range of the attractive interaction regime,
the instrument was equipped with a special active feedback
circuit, called Q-control (Nanoanalytics, Germany). The quality
factor Q of this oscillating system is increased up to 1 order of
magnitude. As a consequence, the sensitivity and lateral
resolution are enhanced, allowing us to prevent the onset of
intermittent repulsive contact and thereby to operate the AFM
constantly in the attractive interaction regime.
SPR measurements were performed in the Kretschmann
configuration against ethanol. Optical coupling was achieved
with a LASFN 9 prism, n ) 1.85 at λ ) 632.8 nm and index
matching fluid n ) 1.70 between prism and the BK270 glass
sildes. The plasmon was excited with P-polarized radiation
using a He/Ne laser (632.6 nm, 5 mW). For SPR, glass slides
(3.5 cm × 2.5 cm) were used, and glass slides were cleaned
with aqueous NH3/H2O2/H2O (1:1:5) for 10 min at 80 °C,
washed with water and 2-propanol, and dried in a stream of
nitrogen. These glass slides were coated with gold using a
Balzer BAE 250 vacuum coating unit under pressure of less
than 5 × 10-6 hPa, typically depositing 50 nm of gold after
first depositing 2 nm of Cr. The slides were exposed to
3-mercaptopropionic acid solution (1 mmol) for 12 h and then
deprotonated by using 1 mmol of aqueous NaOH solution.
UV/vis measurements were performed on a Shimadzu UV-
2102 PC spectrometer. Angular dependent UV/vis spectra were
also examined by using the same spectrometer. A custom-built
sample holder equipped with a rotation stage to which the
quartz substrates were affixed was placed in the middle of the
light path. Rotation of the sample holder resulted in illumina-
tion of the same area of the sample both in the parallel (0°,
shear direction parallel to the electric field vector of the
incident radiation) and perpendicular (90°, shear direction
perpendicular to the electric field vector of the incident
radiation) configurations. We performed the angular depen-
dence of both types of samples for angles from -70° to +70°.
The spectra were plotted as the absorbance at a given angle
of the incident light beam; however, there is a tendency for
the absorbance to increase with increase in the angle used.
Above all, increasing absorption which is related to the
increasing optical thickness has to be corrected by a correction
factor d.
1
Instruments. H and 13C NMR spectra were mostly mea-
sured on a Bruker 200 MHz FT spectrometer. In some cases
spectra were also measured on a Bruker 400 MHz FT
spectrometer. The spectra were analyzed with the software
Win-NMR 6.1. Infrared spectra were measured on a Bruker
Vector 22 FT-IR spectrometer with a Harrick ATR unit. The
analysis of the spectra was performed with the software OPUS
3.1. The phase transitions temperatures of the polymers were
investigated by differential scanning calorimetry (DSC) per-
formed with a Perkin-Elmer DSC 7 at a scan rate of 10 °C
min-1. To determine the molecular weight of the polymers, gel
permeation chromatography (GPC) was performed on a Jasco
instrument and THF was used as mobile phase. The separa-
tion was done on a MZ-Gel SD plus precolumn (8 mm × 50
mm) and three MZ-Gel SD plus main columns (8 mm × 50
mm) produced by Mainz Analysentechnik. For each measure-
ment 100 µL solution of the polymer in THF (2 mg/mL) was
injected. The detection was performed with Jasco refractive
index and UV detectors and a Viscotek light scattering
detector. Polarizing microscopy investigations were performed
with a Zeiss Jenapol SL 100 microscope. The samples were
analyzed in a Linkam THMS 600 hot stage and tempered with
a Linkam TMS 93-control module. X-ray measurements (LC
1
d )
sin θ
1.65
cos arcsin
(
(
))
where θ is the angle and d is the correction factor.
To correct for the light polarized perpendicular to the plane
defined in Figure 7a (paper plane), 50% of the absorption at
0° was subtracted. This corresponds to 0.350 05 for the spin-
coated sample and to 0.013 75 for the solution-dipped sample
(two times this value plus the corrected absorption resulted
in Figure 7b,c representing therefore the real measured
absorption). The angular dependent absorption minus the 50%
absorption at 0° was fitted with formula 1 from -50° to +50°.
This yielded an A of 0.011 44 and A| of 0.028 28 for the
solution-dipped sample and A of 0.3484 and A| of 0.4253 for
the spin-coated sample. These values were used for the
estimate of the order parameter.
Acknowledgment. The authors gratefully thank
Hosub Kim for the help given to the SPR measurements.

9134 Choi et al.
Macromolecules, Vol. 38, No. 22, 2005
(21) Kotov, N. A.; Haraszti, T.; Turi, L.; Zavala, G.; Geer, R. E.;
De´ka´ny, I.; Fendler, J. H. J. Am. Chem. Soc. 1997, 119, 6821.
(22) Kim, H. N.; Keller, S. W.; Mallouk, T. E.; Schmitt, J.; Decher,
G. Chem. Mater. 1997, 9, 1414.
Part of the work has been supported by the DFG (Ze
230/9-2).
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