Hydrophobically modified water-soluble polymers and polyelectrolytes as micellar promotors in the Rh(I) catalyzed hydrogenation of an amino acid precursor in water

Article abstract of DOI:10.1039/b202992h

Hydrophobically modified water-soluble polymers (HMWSP's) and hydrophobically modified polyelectrolytes (HMPE's, "polysoaps") of various compositions and different molecular weights have been prepared and used in the micellar promoted enantioselective hydrogenation of methyl (Z)-α-acetamidocinnamate with a chiral Rh(I) catalyst in aqueous medium. The efficiency of the micellar polymers in the catalytic reaction is greatly determined by their solubility (dispersibility) behavior and solubilization capacity for catalyst and substrate. The latters depends on the compactness of the polyamphiphiles as revealed by transmission electron microscopy (TEM) and light microscopy images. The highest catalytic performance was obtained with polymer-surfactant complexes prepared by micellar copolymerization with neutral or anionic tensides, regardless of the electrical charge of the hydrophobically modified polymer. In most cases a synergism between rate and enantioselectivity has been observed.

Full text of DOI:10.1039/b202992h

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Hydrophobically modified water-soluble polymers and polyelectrolytes
as micellar promotors in the Rh(I) catalyzed hydrogenation of an
amino acid precursor in water
a
Hans Fuhrmann, Ingrid Grassert, Gerd Holzh u¨ ter, Cordula Gr u¨ ttner and G u¨ nther Oehme*
a
b
c
a
a
Institut f u¨ r Organische Katalyseforschung an der Universit a¨ t Rostock e.V., Buchbinderstr.
5
Fax: +49 381 466 9324
Fachbereich Physik der Universit a¨ t Rostock, Universit a¨ tsplatz 3, D-18051, Rostock, Germany
micromod GmbH, Friedrich-Barnewitz-Str. 4, D-18119, Rostock, Germany
-6, D-18055, Rostock, Germany. E-mail: guenther.oehme@ifok.uni-rostock.de;
b
c
Received (in Montpellier, France) 25th March 2002, Accepted 16th July 2002
First published as an Advance Article on the web 26th September 2002
Hydrophobically modified water-soluble polymers (HMWSP’s) and hydrophobically modified polyelectrolytes
(
HMPE’s,‘‘polysoaps’’) of various compositions and different molecular weights have been prepared and
used in the micellar promoted enantioselective hydrogenation of methyl (Z)-a-acetamidocinnamate with a
chiral Rh(I) catalyst in aqueous medium. The efficiency of the micellar polymers in the catalytic reaction is
greatly determined by their solubility (dispersibility) behavior and solubilization capacity for catalyst and
substrate. The latters depends on the compactness of the polyamphiphiles as revealed by transmission electron
microscopy (TEM) and light microscopy images. The highest catalytic performance was obtained with
polymer-surfactant complexes prepared by micellar copolymerization with neutral or anionic tensides,
regardless of the electrical charge of the hydrophobically modified polymer. In most cases a synergism between
rate and enantioselectivity has been observed.
The advantage of water as a solvent in organic reactions con-
sists not only in that it is the cheapest, most environmentally
friendly and ubiquitous solvent, but also that it is the base of
all chemical and physical processes in living organisms. There-
fore, water has been chosen as a solvent even where the react-
ing components are scarcely water-soluble. In such cases the
reactivity can be dramatically enhanced when amphiphiles
are present, which above a certain concentration (critical
micelle concentration, CMC) may self-assemble into aggre-
gates (micelles, vesicles) that are capable of solubilizing the
reactants. The enhancement of reaction rates within micelles
spectra (Bruker ARX-400), FTIR spectroscopy (Nicolet
magna 550) and elemental analysis (Leco C, H, N, S automatic
analyzer).
The separation and purification of the polymers was done by
gel filtration on Sephadex G25 and dialysis (3 500 NMWL tub-
ing from Spectra/Por). The molecular weights (MW’s) were
measured by membrane osmometry (Knauer No. A 0330 with
digital display, regenerated cellulose membrane 1 000 NMWL
and cellulose acetate membrane 5 000 NMWL).
Size and size distribution of amphiphilic assemblies were
determined by photon correlation spectroscopy (Zetasizer
3 000, Malvern Instrument, analysis model: multimodal) and
transmission electron microscopy (Zeiss EM 912 Omega,
120 kV). The micrographs were obtained after shock-frozen
lamellas of the aqueous solution of the amphiphiles (0.1–
0.2 wt %) had been carefully evaporated from a carbon-coated
copper grid (200 mesh) under high vacuum at room tempera-
ture. Specimens were examined in a low-dose imaging mode
to minimize electron beam radiation damage. Images were
recorded at appropriate objective lens underfocus conditions
to enhance phase contrast. High-resolution light microscopy
was performed by differential interference contrast microscopy
(AVEC-DIC) with a Nicon Diaphot 300 instrument and a
Hamamatsu C 2 400-07 Newvicon Kamera.
1
is designated as micellar catalysis. Several attempts have been
made to use polymerized micelles and micellar polymers as
2
–4
microreactors for catalytic reactions.
An important argu-
ment to chose polymer micelles for the encapsulation of the
catalyst in place of micelles from monomer amphiphiles was
the intention to use them in the future in a membrane reactor
with the purpose to separate the micellar entrapped catalyst
from the reaction medium. The aim of this work was to use
hydrophobically modified water-soluble polymers (HMWSP’s)
and polymer-surfactant complexes (PSC’s) as carriers for a
chiral Rh(I) catalyst and see whether there is any relation
between the chemical nature and structure of the polyamphi-
philes and the catalytic activity and stereoselectivity exampli-
fied in the asymmetric hydrogenation of a prochiral amino
acid precursor in water.
The enantiomeric excess of the hydrogenation product
methyl N-acetylphenylalaninate was determined by GLC on a
HP chromatograph 5880A fitted with a 10 m capillary column
coated with XE-60–1-N-tert-butylvalinamide (FID, split 1 : 60,
ꢀ
1
50 C).
All chemicals were used as purchased from Aldrich or
Experimental
Fluka. Solvents were purified and dried following standard
procedures. The hydrogenation educt methyl (Z)-a-acetamido-
General
5
cinnamate and the hydrogenation precatalyst [Rh(cod) ]BF
were prepared by known methods.
6
Synthesis and turnover control were performed by recording
1 13
of H NMR (400.13 MHz) and C NMR (100.63 MHz)
2
4
DOI: 10.1039/b202992h
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of both the solvent and excess amine the residue was dissolved
in warm acetone from which 1 precipitated on cooling. 1 was
recrystallized from acetone. Elemental analysis of 1: calcd for
C
C 56.71, H 9.70, N 3.39, S 7.38%.
19
H38NO
4
SNa: C 57.14, H 9.52, N 3.51, S 8.02%. Found:
1a was obtained after polymerization of 1 in water under the
ꢀ
following conditions: UV light 185 nm, 60 C, 6 h, 2 mol %
K
2
S
2
O
8
/Na
2
S
2
O
5
(Scheme 2). The copolymerization with
ꢀ
acrylamide (20 mol %) at 60 C, 4 h, 254 nm UV, 1 mol %
a,a-diethoxyacetophenone (DEAP)/triethylamine as initiator
gave 1b. The copolymerization of 1 in a micellar medium of
sodium dodecylsulfate (SDS) under the aforementioned con-
ditions but with 70 mol % acrylamide resulted in a polymer-
surfactant complex 1d with a content of 8 mol % SDS.
Scheme 1
The copolymerization of dimethylacrylamide with 2 mol %
of sodium methacryloyloxyundecyltrimethylammonium sul-
fate 2, the synthesis of which was described in ref. 4d, afforded
Water was purified and deionized by a TAK-LAB system.
The measured conductivity value was as low as 0.056 mS cm
ꢁ
1
.
ꢀ
2b. Polymerization conditions were 254 nm UV, 30 C, 4 h,
0
2 mol % 4,4 -azobis(4-cyanovaleric acid) (ACVS) as initiator
(Scheme 3).
Polymerization and copolymerization of amphiphiles
3
was obtained by copolymerization of N-vinyl-2-pyrroli-
The photoinitiated free-radical polymerization of the mono-
mers and comonomers in water was carried out in a quartz
reactor mostly in the presence of 1–2 mol % of a radical initia-
tor. For details see ref. 4d. The concentration of the monomers
was 3–5 wt %. In all cases the polymerization experiments were
conducted to completion as was judged by the disappearance
done with sodium N-dodecylmaleamate (prepared by reaction
of maleic anhydride with dodecylamine in dioxane following
neutralization with NaOH in a 1 : 1 molar ratio). Polymeriza-
tion conditions were 254 nm UV, 60 C, 6 h, 2 mol % azoiso-
butyronitrile (AIBN) (Scheme 4).
ꢀ
The copolymerization of acryloyloxyethyltrimethylammo-
ꢀ
1
of the H NMR signals of the vinylic (6.3–5.5 ppm) protons.
nium methyl sulfate (Aldrich) with 2 mol % 2 at 60 C, 4 h,
UV 254 nm, yielded a copolymer with amphiphilic properties
The polymerization conditions were chosen according to the
reactivity of the components to be polymerized and are indi-
cated in the next paragraph. To remove initiator residues
and low molecular side products the polymerization products
were dialyzed against water (72 h). In case of micellar polymer-
ization in the presence of tensides the dialysis was continued
until no tenside could be detected in the filtrate. Samples of
the isolated or re-dispersed polymerized amphiphiles were
taken for elemental analysis, molecular mass determination,
structural characterization (particle size analysis, high-resolu-
tion light microscopy, TEM) and catalysis.
(
4a, Scheme 5). The same reaction in the presence of SDS at
a concentration of about 7 times the CMC resulted in the poly-
mer-surfactant complex 4b containing after dialysis 6 mol %
SDS as checked by sulfur analysis.
The copolymerization of acrylic acid (Fluka) with 1 mol %
dodecylacrylate (Fluka) and the neutral amphiphile poly(ox-
4c
yethylene)23dodecylether methacrylate (5 mol %) resulted in
5a (Scheme 6). The micellar copolymerization of acrylic acid
with 1 mol % dodecylacrylate in an aqueous solution of SDS
afforded 5b. Polymerization conditions were 254 nm UV,
ꢀ
4
0 C, 4 h, 1 mol % DEAP/Et
3
N. The copolymer solutions
Syntheses
of 5a and 5b were neutralized with NaOH. After dialysis 5b
contained 3 mol % SDS.
Sodium diallyldodecylmethylammonium sulfate 1 (Scheme 1)
was prepared by reaction of the dodecyl monoester of sulfuric
The polymer-surfactant complex 6 was prepared by mixing
the quaternized and sulfated poly(ethylenimine), the synthesis
of which was described in ref. 4d, with an exess of the sur-
factant Tween 20. The aqueous solution was stirred for 3 h.
Thereafter the mixture was dialyzed until no surfactant could
be detected in the filtrate. The amount of the entrapped sur-
factant was ꢃ6 mol % (from elemental analysis) (Scheme 7).
acid [from 1-dodecanol and SO
3
ꢂ(CH
3 3
) N in DMF] and diallyl-
amine (1 : 1 in the presence of N,N-dicyclohexylmethylamine
as the binding agent for the released sulfuric acid). In a further
step the quaternization of the tertiary amine was effected by an
excess of (CH
from the reaction mixture with hot ethanol. After evaporation
3
)
2
SO
4
in dilute NaOH (pH ꢃ9). 1 was extracted
Scheme 2
1
676
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Scheme 3
argon was replaced by hydrogen at ambient pressure and the
reaction was started and followed volumetrically.
The time necessary to consume half of the theoretical
amount of hydrogen (t1/2) was taken as a measure of the activ-
ity. After finishing the experiment the mixture was extracted
with 5 mL chloroform. The enantiomeric exess of the product
was determined by GLC on a chiral column as mentioned
above.
Results and discussion
In contrast to polymerized nonionic amphiphiles showing a
high efficacy in the asymmetric hydrogenation of methyl
(
Z)-a-acetamidocinnamate with the [Rh(bppm)(cod)]BF cata-
4
4c
Scheme 4
lyst, ionic polyamphiphiles proved to be less efficient in many
cases because of their poor water solubility and unfavorable
4
d
solubilization properties. Therefore, to improve both proper-
ties, the polymerizable ionic amphiphiles were copolymerized
with water-soluble monomers remaining dispersable also in
the polymeric state. In general, most water-dispersable asso-
ciating polymers are copolymers of a water-soluble monomer
and a very hydrophobic comonomer at low mole fraction
(usually between 0.1–2 mol %). In aqueous solution the hydro-
phobic moieties self-assemble intra- or intermolecularly. Inter-
molecular associations give rise to three-dimensional networks.
Such systems are used as thickeners because of their high visc-
osity. A special case of associating polymers are the hydropho-
bically modified polyelectrolytes (HMPE’s, ‘‘polysoaps’’)
whose aqueous solutions have a rather low viscosity reflecting
their compact conformation, which arises because the hydro-
phobic groups of the polyelectrolyte associate and form hydro-
phobic microdomains. This is obviously the case when the
amphiphilic diallylammonium salt 1 is homopolymerized,
giving a scarcely water-dispersable polymer which shows no
catalytic effect (Table 1, 1a). The free-radical-initiated poly-
Asymmetric hydrogenation
The hydrogenation was performed by an isobaric method at
ꢀ
2
5 C under air-free conditions in a thermostatted apparatus
4d
(
Scheme 8). [Rh(cod)
the chiral, nonracemic ligand (2S,4S)-N-tert-butoxycarbonyl-
-diphenylphosphino-2-diphenylphosphinomethylpyrrolidine
BPPM) together with 0.1–0.2 mmol of the polymer amphi-
2 4
]BF (0.01 mmol) and 0.01 mmol of
4
(
phile and 1 mmol of methyl (Z)-a-acetamidocinnamate were
stirred in 15 mL water under argon. Thus, the molar ratio cat-
alyst : amphiphile : substrate was 1 : 20 : 100. The amount of
polymerized amphiphile was related to the molar percentage of
amphiphile within the polymer. In the case of the polymer-
surfactant complexes (micellar polymerization) the percentage
of the entrapped tenside was estimated by comparison of the
elemental analysis data of the amphiphilic polymers generated
in the absence or presence of the tenside. Also, in these cases
the polymerization was conducted quantitatively and the sam-
ples had been dialyzed as mentioned above. The time of stir-
ring (equilibration time) of the dissolved polyamphiphile
with the catalyst and the substrate varied between 1 h and
7
merization, being a cyclopolymerization, generates a rather
hydrophobic main chain, which does not allow for sufficient
water solubility. Therefore, the copolymerization with the
2
0 h, depending on the bulkiness of the polyamphiphile. The
Scheme 5
New J. Chem., 2002, 26, 1675–1681
1677

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Scheme 6
water-soluble acrylamide was envisaged to obtain a water-
soluble HMPE. The copolymer is presumed to be random.
concentration was too low as to assure a continuous micellar
phase during the polymerization. This is why the external sur-
factant SDS was used in excess. The role of the surfactant is
two-fold: it ensures the solubilization of the hydrophobic/
amphiphilic monomer in the aqueous medium and induces
the formation of hydrophobic sequences whose length depends
on the micellar concentration. In a micellar polymerization
process one cannot a priori exclude compositional heterogene-
ity of full conversion samples because a greater incorporation
of the hydrophobe at the beginning of the copolymerization
3
e
However, it may be possible that a blocky microstructure is
formed due to the formation of micelles by the polymerizable
surfactant 1, providing a high concentration of the reactive
8
allyl groups in the micelles. Real block copolymers containing
uncharged hydrophilic and cationic polysoap blocks were pre-
pared for the first time by use of poly(ethylene oxide) based
macroinitiators. Contrary to what we expected, the catalytic
9
effect of the amphiphilic copolymer 1b was only moderate
(
1
0
Table 1, 1b). Increasing the amount of acrylamide in the copo-
may occur. In general, micellar polymerization should favor
although Hill et al.
1
1–13
14
lymer from 20 to 70 mol % (Table 1, 1b and 1c) led to a con-
siderable increase of the hydrogenation rate, but practically
did not affect the enantioselectivity. Obviously, the change of
the hydrophilic/hydrophobic balance has improved the solubi-
lity behavior while leaving the stereoselectivity unchanged. But
it was substantially increased when the copolymerization was
run in micellar medium (Table 1, 1d). This points to a favor-
able influence of the anionic surfactant SDS, which was
embedded within the polyamphiphile at a level of 8 mol %.
Micellar polymerization is characterized by a large excess of
the surfactant in the polymerization solution. Surfactant/
hydrophobe ratios of 20–100 are not uncommon in order
to solubilize the hydrophobic monomer in the aqueous
phase. Although we used an amphiphile as comonomer, its
a blocky structure of the copolymers,
demonstrated that the microstructure of hydrophobically asso-
ciating polyacrylamides—random or blocky—is determined by
the hydrophobe/micelle ratio. Unfortunately, a detailed analy-
sis of the microstructure of our amphiphilic copolymers by
NMR spectroscopy (determination of block sequences and
block lengths) gave no reliable results on account of low
signals resolution.
In Fig. 1 are shown TEM micrographs from a 0.1 wt % aqu-
eous solution of the polymer-surfactant complex 1d in the
absence (a) and presence (b) of the solubilized catalytic system.
Within a gel-like polymeric network consisting of cross-linked
Table 1 Hydrogenation of methyl (Z)-a-acetamidocinnamate in
water with the catalytic system [Rh(bppm)(cod)]BF
polymeric amphiphiles. Molar ratio catalyst : amphiphil : substrate ¼
: 20 : 100
4
in the presence of
1
Molecular
weight/
Halftime of Excess of the
Equilibration hydrogenation R enantiomer
ꢁ1
Polyamphiphile g mol
time/h
(t1/2)/min
(eeR) (%)
Without
a
–
399
1
1
90
11
78
88
–
1
1
1
1
1
2
2
2
3
3
4
4
4
5
5
6
6
6
a
b
c
5 300
16 900
21 000
12 900
395
20
20
20
1
–
51
82
83
92
80
83
86
89
88
80
91
91
83
91
94
93
92
Scheme 7
19
7
d
b
1
480
720
7
b
a
b
2 200
20
2
58 000
45 000
45 000
6 300
1
110
117
114
187
176
128
16
20
20
2
a
b
b
a
b
8 100
8 100
20
2
86 400
71 500
12 700
12 700
12 700
1
1
6
10
c
1
d
1
13
a
ꢁ1
The monomer amphiphile, concentration 45 mmol L (correspond-
b
ing to two times the CMC). The data from ref. 4d are shown for
c
d
comparison. Molar ratio amphiphile : catalyst ¼ 10 : 1. Molar
ratio amphiphile : catalyst ¼ 5 : 1.
Scheme 8
1
678
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Fig. 2 Light microscope images of a 2 wt % aqueous solution of the
PSC 1d: (a) at the glass–solution interface before solubilization of the
catalytic system, (b) in solution after solubilization of the catalytic sys-
tem.
Fig. 1 TEM micrographs from a 0.1 wt % aqueous solution of the
PSC 1d after sublimation of the vitrified ice (a) before and (b) after
solubilization of the catalytic system.
polymer strands individual spherical micelles are seen to be
embedded into the polymer structure. There is a significant dif-
ference in size between micellar assemblies before and after
solubilization of the catalytic system. The solubilization entails
an enlargement of the aggregates up to a diameter of 300 nm
and leads partially to the formation of micellar clusters, which
is not seen without solubilization. In the latter case only
spheres with a diameter < 100 nm could be detected within
the polymeric network. The polymer network that is seen in
the TEM micrographs was not visible in the light microscope.
The solution was optically void even at a 20-fold higher con-
centration (corresponding to the conditions of the catalytic
reaction), although the detection limit of the used high-resolu-
tion light microscope was as low as 50 nm. This discrepancy
can be explained by the fact that the contrast of the strings
of the water-swollen hydrogel is too low to be perceptible. This
is different for the TEM images of the 0.1 wt % solutions where
after sublimation of the vitrified ice from the specimens in the
high vacuum a xerogel remains, which is decorated with spher-
oidal micelles. This recalls the well-known ‘‘beads-on-a-string
structure’’ or the ‘‘necklace’’ model for hydrophobically mod-
and 800 nm are seen in the light microscope [Fig. 2(b)]. The
increase of particle size upon solubilization, which has also
been manifested by TEM [Fig. 1(b)] was confirmed by photon
correlation spectroscopy. Fig. 3 shows the particle size distri-
bution of PSC 1d before (a) and after (b) solubilization has
occurred. In the latter case the shift of the average particle size
is remarkable.
A good example for rate enhancement of the hydrogenation
reaction by copolymerization of the amphiphile 2 with
dimethylacrylamide is the HMWSP 2b (Table 1). Due to the
lack of hydrogen atoms in the amide group, polydimethylacryl-
amide cannot form inter- or intrachain hydrogen bonds and
therefore it does not exhibit the time and stability drawbacks
1
7
encountered with polyacrylamide.
While the monomer
amphiphile as well as the homopolymer need very long reac-
tion times for complete turnover, the copolymer works faster
by two orders of magnitude. HMWSP 3, a copolymer of
sodium dodecylmaleamate with N-vinyl-2-pyrrolidone, showed
an enhanced enantioselectivity but a rather low rate. As may
be seen from Table 1, a prolonged equilibration time does
not necessarily raise the activity. The same was observed
for HMPE 4b: an extension of the equilibration time from
2 h to 20 h did not alter considerably the catalytic result.
The results with HMPE 4 suggest that the catalytic activity
is mainly determined by the secondary structure of the poly-
amphiphile.
1
5,16
ified polymer-surfactant complexes.
However, light micro-
scopy revealed composed structures at the polar glass–solution
interface [Fig. 2(a)]. Possibly, these are floccules formed in a
coagulation/precipitation process. At the moment when the
reaction components (catalyst and substrate) were solubilized
within the polyamphiphiles, the solution became milky.
Mainly agglomerated particles of a diameter between 500
In contrast to the gel-like structure of the PSC 1d, the
TEM images of the salt-like PSC 4b show an ordered and
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Fig. 4 TEM micrographs from a 0.1 wt % aqueous solution of the
PSC 4b after sublimation of the vitrified ice: (a) ordered tubular struc-
tures and (b) pseudo-crystalline aggregates are seen.
structures could not be formed without charges in the polymer
network. Neutral polyacrylamide gel does not show any
ordered structure. Comparing the enantioselectivities of 4a
and 4b it seems reasonable to assume that they are influenced
by the charge of the micelles: micelles from neutral or anionic
amphiphiles afford higher enantioselectivities of the positively
charged chiral Rh(I) phosphine complex than cationic
micelles do.
Fig. 3 Particle size distribution in a 2 wt % aqueous solution of the
PSC 1d measured by photon correlation spectroscopy: (a) before and
21
(b) after solubilization of the catalytic system.
rather compact structure (Fig. 4). It is fair to assume that
equilibration time and halftime of hydrogenation are increased
because transport processes are retarded. The binding of the
anionic SDS with the positively charged polyelectrolyte 4a is
a highly cooperative process where hydrophobic interactions
between adjacently bond surfactant molecules stabilize the
complex aggregate. When a large amount of surfactant is
The PSC’s 5b and 6 show a similar catalytic behavior as the
PSC 1c, although they have another charge combination. In
the PSC 5b the HMPE 5a and the surfactant SDS are both
negatively charged: the quantity of SDS that is left after dialy-
sis within the polymer network depends on the chemical nature
1
8
23
included, the polyelectrolyte gel collapses. In an aqueous dis-
persion the charged surfactant chains associate inside the poly-
electrolyte gel network even when the external solution
and the number of hydrophobic sites or microdomains. It
has been shown for like-charged complexes
2
4,25
that a strong
hydrophobic interaction may overcome the electrostatic repul-
sion. Additionally, the observed favorable results (Table 1, 5b)
might be traced to a facilitated diffusion due to an extended
hydrogel structure of the PSC. It is known that PSC chains
can form a cross-linked network upon UV-initiated polymeri-
1
9
concentration is significantly lower than the CMC. The com-
plex of the polyelectrolyte gel and the oppositely charged sur-
factant can form three-dimensional supramolecular structures
in aqueous solutions due to a combination of hydrophobic and
2
0
26
electrostatic interactions. Moreover, the interaction of the
polyelectrolyte gel with SDS can induce a sharp conforma-
zation.
A similar structure may be considered in the case of the
highly branched amphiphilic polyethylene imine 6 complexed
with the neutral surfactant Tween 20. Here the best catalytic
result in our study was obtained (Table 1, 6). Obviously, the
solubilization capacity of this PSC is high enough as to reduce
the molar ratio amphiphile : catalyst from 20 : 1 to 5 : 1 (Table
2
1
tional transition, giving rise to sharp diffraction peaks. The
latter indicates that the structure in the gel must be in a highly
ordered state, in agreement with the results of Okuzaki and
2
2
Osada, who have reported a polycrystalline structure formed
in a cationic surfactant-anionic polymer network complex. The
degree of supramolecular order in the PSC increases with
increasing amount of SDS. There is no doubt, crystalline
c
d
1, 6 and 6 ) without changing substantially the hydrogenation
activity and stereoselectivity.
1
680
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catalytic reactions. Exemplified by the asymmetric hydrogena-
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that the catalytic performance is greatly determined by the
microstructure of the polyamphiphile. Visualization of the
associates by TEM and light microscopy supported the view
that a loose gel structure with embedded micelles is most favor-
able for the solubilization of catalyst and substrate. The com-
pactness of oppositely charged polymer-surfactant complexes
proved to be a hindrance for the micellar catalysis. As will
be shown in a further report, polymer-surfactant complexes
are suitable as recyclable micellar catalysts.
3
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