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Lyotropic Phases Formed by УMolecular BottlebrushesФ.

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COMMUNICATIONS
Lyotropic Phases Formed by
“Molecular Bottlebrushes”**
Matthias Wintermantel, Karl Fischer, Markus Gerle,
Roland Ries, Manfred Schmidt,* Kanji Kajiwara,
Hiroshi U r a k a w a , and Isao W d t a o k a
The polymerization of macromonomers (that is, end-functionalized oligomers. Scheme 1 ) has been a matter of extensive
research in order to prepare well-defined comblike polymers.[’]
XLi+
r
4 $&o
---t
/
n-1
u
d
0
i
Scheme 1. Reaction scheme for the preparation of the macromonomers.
However, the homopolymerization of macromonomers did not
yield degrees of polymerization significantly exceeding the
length of a macromonomer itself, unless copolymerized with
conventional small monomers. A major breakthrough was
achieved by Tsukahara et al., who in a radical mechanism homopolymerized anionically prepared oligostyrenes with molar
masses between lo3 and lo4 gmol-’ that were end-functionalized with methacryloyl groups and obtained degrees of polymerization (weight average) P, of up to 1000.[21Recent structure
characterization of such long-chain polymacromonomers revealed that the main chain exhibits an almost rodlike conformation as measured by the Kuhn statistical segment length of
I , > 1000
Apparently. the extended structure of the polymethacrylate (PMA) main chain is caused by the strong overcrowding of the oligostyrene side chains, which are only separated by a contour distance 1 = 2.5 8, at the polymer backbone.
Also, because of the length of the side chains, the diameter or
cross-section of this curved cylindrical macromolecule or “bottlebrush” is quite large ((1% 70- 150 8, for a side chain of molar
mass M , = 3950 gmol- dependent on whether hydrodynamic
data or X-ray investigations of the cross-sectional radius of
gyration were used for the determination of diameter).I3] Still,
the aspect ratio L,/d ( L , is the weight-averaged contour length,
L, = P,+./,
and d the diameter of the chain) is of the order of
’,
10-50 for most of the samples, and accordingly, such polymers
should form liquid-crystalline phases.
Here we report on X-ray scattering measurements of the polymacromonomers in toluene performed at the synchroton source
in Tsukuba, Japan. which indeed show the formation of lyotropic phases, probably nematic, in semi-concentrated solution. The
investigated polymacromonomer sample had a molar mass of
M , = (2.2.10’) gmol-’ corresponding to a contour length
L, = 1400 8,. The polydispersity index determined by gel permeation chromatography (GPC) was M,/M, z 1.5, and the
Kuhn statistical segment
length (as measure of chain
stiffness) I, = 1250
Figure 1 shows the X-ray
scattering intensity I(q) as a
function of the scattering
$ p o -/u n+
where
vector 3.I/ is[qthe
= (4n/I.sin(H/2).
wavelength in
the medium and ’6 the scattering angle) for polyinacromonomer concentrations 0.2 2 c 2 30% (w/w).
In
the dilute regime
c < 0.5 YO the form factor
P(4) of a single chain is measured: the intensity is seen to
decrease monotonically with
increasing 4. However, the q
regime investigated here reflects the scattering pattern
of the chain cross-section.
With increasing concentrations a shoulder develops into a clearly resolved scattering peak.
Particularly at the highest measured concentration of 31.5 %,
the width of the scattering peak narrows drastically. The scattering peaks observed at higher concentrations cannot be explained by single-particle scattering but rather reflect the interparticle structure factor S(4) originating from the intermolecular order of the molecules.
On application of Bragg’s relation, a mean distance dB between the scattering planes (100) of hexagonal order is obtained
from the scattering peak at q,,, [Eq. (a)]. The mean par-ticle
distance d2 is then derived from Equation(b). In order to
d,
= 2Wqmax
(a)
2d,il/l
(b)
=
520
i
440
200
-
120 -
[*I
[**I
Prof. Dr. M. Schmidt. Dr. M. Wintermantel, Dr. K. Fischer. M . Gerle.
Dr. R. Ries
Makromolekulare Chemie 11 der Universitit
D-95440 Bayreuth (Germany)
Telefax: Int. code + (921)55-3393
Prof. Dr. K . Kajiwara, Dr. H. Urakawa. Dr. I. Wataoka
Kyoto Institute of Technology
Kyoto 606 (Jnpan)
Financial support by the Deutsche Forschungspeinciiischafiand by the Fonds
der Chomiachen lndustrie is gratefully acknowledged ( M . W. and M. S.).
40 000
002
004
006
q [A-’1
008
-
010
Fig. 1 , X-ray scattering intensity I ( 4 ) in arbitrary units as a function of the scattering vector 4 for different polymacromonomer concentrations in wt Yo: o 0.306%.
n 0.3’93%. 0 0.481 %, n 0.964%. * 4.93%. m 8.0%. A 10.7%. o 12.3%. + 19.8%.
x 31.5%.
COMMUNICATIONS
compare the present results with earlier investigations on the
tabacco mosaic virus (TMV)14] and on poly-;4enzylglutamate
(PBG),[51a reduced plot of &do ( d , is the mean distance between the particles and do their ”hard-core” diameter) versus the
volume fraction of solute is shown in Figure 2. Since a hard-core
10
9
8
7
single particles, that is, on the spatial distribution of the scattering centers within one macromolecule. Unfortunately, there is
no unique solution to this problem except to assume, a priori, a
certain density distribution of the molecules and calculate the
Fourier transform into q space.
For a preliminary treatment of more detailed data analysis we
assume Equation (d) to be approximately valid for our system.
Accordingly, the structure factor S(q) = I(y)/’P(q)is shown in
. reduce the noise
Figure 3 for the concentrations ~ 2 4 . 9 3 % To
ii
d2 ’do 3
2
1
10
x[Vo/.-%I
-
100
Fig. 2 . Iteduced interparticle distance dz:dovs. the volume fraction of polymer: x
T M V 141. + PBG [ 5 ] . , o polymacromonomer. The mean distance d2 IS derived
from I ( q ) ( x . + . o) or from S(q) ( 0 ) as explained in the text.
””
0.00
0.03
0.06
9
diameter for the polymacromonomer is impossible to define
(because of the radially decaying segment density), a value of do
of 67 A is assumed in order to obtain an approximate superposition with the other curves. This value of do compares well with
the cross-sectional radius of gyration
= 36.4 8, as determined by X-ray scattering (dg,c= 72.8 8,131).
For comparison,
the hypothetical “hard-core” diameter of a molecule with the
bulk density p =1.05 gcm-3 of polystyrene would amount to
d, = 57
and the hydrodynamically effective cross-section as
determined by diffusion measurements to d,, = 150 A. The solid
line shows the expected scaling relation for the packing of parallel cylinders [Eq. (c)].
A,
The observed agreement of the relative spacing as a function
of the volume fraction for the polymacromonomer (PBG and
TMV) is expected, because the aspect ratio L/d of all three
systems is of the order of 15. Surprisingly, the data evaluation
as described above does not give any evidence for the occurrence
of a biphasic (isotropic/anisotropic) regime, which is theoretically predicted by OnsagerE6Iand Flory[’I at volume fractions
between 10-20%. because in the biphasic region the mean distance is expected to be independent of the concentration of
polymers.
Although the influence of the decaying single-particle form
Factor P(q) might seriously influence the position of the maximum intensity, particularly at the lower q values, this has been
ignored in the presentation of the data so far. For spherically
symmetric particles, the total intensity I ( q ) is expressed by the
product of the particle scattering factor and the structure factor
[Eq. (d)]. Equation (d) breaks down for anisotropic particles,
because the structure Factor S(q) becomes a function of P(q) as
now the interparticle interference depends on the shape of the
0.09
WI
0 12
-
0.15
0 18
Fig. 3. The static structure factor S(q) in arbitrary units as a function of the scattering vector q for different polymacromonomer concentrations i n wt%: A 4.93%. o
KO%,
10.7%. 12.3%. 19.8%. o 31.5%. For the highest concentration even
higher order peaks are observed with a relative spacing of d, :dl:d, = 1: v 3 :2. which
supports the hexagonal packing.
in the data the single-particle form Factor P(q)was evaluated
from the average intensities of the concentrations c = 0.306%.
0.393%, and 0.481 %. For c < 12.3% the maximum of the observed broad structure peaks remains approximately constant
and increases in intensity with increasing concentration. This is
exactly the result expected from the biphasic regime where the
volume fraction of the anisotropic phase increases with increasing concentration but the interparticle distance within the ordered phase remains constant. From the position of the maximum, a mean distance of d2 =I56 A is calculated from
Equations (a) and (b), which is interpreted as the mean distance
of the cylinders in the ordered part of the biphasic region, that
is, between the A and B points. The solution becomes fully
anisotropic at concentrations above 12.8 YO(B point) as now the
interparticle separation starts to decrease with increasing concentration as expected ( d 2 z c - ” ’ , solid line in Fig. 2).
The formation of lyotropic liquid crystals by polymacromonomers is also detected by polarized light microscopy
on thin films that were prepared by slow evaporation of
the solvent. The resulting pictures shown in Figure 4 (bottom)
were developed by exposing the film for 10 min. This documentation of the small optical anisotropy of the particles is explained by an expanded, but still random conformation of
the polystyrene side chains, which hardly contribute to the birefringence. Upon heating (see thermal history. Fig. 4 top), the
birefringence of the film disappears at 140 ”C. which lies significantly above the glass transition temperature of Tgz 100 “C and
does not reappear on slow cooling (which may be due to kinetic
effects).
We have reported on a new concept for preparing stiff polymers that form liquid crystals and consist of “commodity”
monomers such as styrene and methacrylate. This concept
is simply based on the overcrowding of bulky side chains
COMMUNICATIONS
Enhancement of Catalytic Activity for
Hydroformylation of Methyl Acrylate
by Using Biphasic and
“Supported Aqueous Phase” Systems**
D
1
‘C
ii
‘B
G e o r g e s F r e m y , Eric Monflier, Jean-Franqois
Carpentier, Yves Castanet, and Andre M o r t r e u x *
I
401
20
Among the numerous hydroformylation reactions, those of
a,p-unsaturated esters are of particular interest. In this area,
much attention has been focused on the hvdroformvlation of
acrylate esters to give 2-formylpropanoate esters, since the latter
are used extensively for the synthesis of pharmaceuticals[’] and
may also be considered a potential source of the extremely important methacrylate esters (Scheme 1 ) .[21 Generally, rhodiumbased homogeneous catalytic systems show good catalytic activities as well as high iso/n regioselectivities for acrylate esters, and
I
I
I
i
--A
I
0
50
150
100
t[min]
-
250
200
.
Monomers
”
/
Minor
Pharmaceuticals
Scheme 1
Fig. 4. Top. Thermal history of the anisotropic polymacromonomer film Bottom
Polarization microscopy pictures at temperatures A - D as depicted above.
which forces the otherwise flexible main chain into a stretched
conformation with significantly reduced degrees of freedom
RecelLed: February 17, 1995 [Z77241E]
German version: Angew. Clriw 1995, 107, 160661608
Keywords: liquid crystals
X-ray scattering
*
polymacromonomers
*
polymers
*
[I] P. Chaumont, J Herz, P Rempp, Eur.. P o l w i . J 1979. 15, 459: Y. Yamashita. J
Appl. Pulym. Sci. Appl. Polym. Sunp. 1981, 36, 193; P. Rempp, E. Franta, P.
Masson, P. Lutr, Prog. Colloid Polrm. Sci. 1986, 72. 312.
1990,23.
[2] Y. Tsukahara, K. Tsutsumi. S. Yamashita. S. Shirnada. Mrf~romo/f~cu/i,.\
5201: Y. Tsukahara. K. Mikano. A. Segawa. Y. Yamashita. ihid. 1989,ZZ. 1546:
Y. Tsukahara. K. Tsutsumi. Y Ukamoto. Macromol. CIwm. Rupid. Comrnun.
1992, 13, 409.
[3] M. Wintermantel. M. Schmidt, Y. Tsukahara, K . Kajiwara. S. Kohjiya, Mircromol. Rupid Conumin. 1994, 15. 279; M. Wintermantel. Dissertation. Universitit
Bayreuth, 1994: M. Wintermantel, M. Gerle. K . Fischer. M . Schmidt. I. Wataoka. H. Urakawd, K. Kajiwara. Y. Tsukahara. S Kohjiya. Mocromol~wdrs.submitted.
[4] J D. Bernal, I. Fankuchen. J G m . Pliysioi 1941. 25, 111.
[5] C. Robinson, E~frnizf~ibon
1961. 13, 219
[6] L. Onsager. Ann. N . Y. Acail Sci 1949. 51. 627.
(71 P. J Flory. Proc. R. Soc. London Sw. A 1956. 234. 73.
1474
i‘ VCH V~~lajisjii~.srlIsi~hoff
m h H . 0-69451 Wwdrrim, 1YY5
many examples have been reported.[31However, due to the high
cost of rhodium, alternative ways for recovering the catalyst
have been developed for many hydroformylation reactions, for
example through the use of b i p h a s i ~ [and
~ ] “supported aqueous
phase” (SAP)[’] systems using water-soluble phosphanes. Despite their advantages, these catalytic systems almost always
suffer from poor activities; put simply, they are always far slower than analogous reactions in the homogeneous phase. However, very recently, an acceleration effect on the rhodium-based
biphasic hydroformylation of 1-octene using trisulfonated
triphenylphosphane (TPPTS) in the presence of triphenylphosphane (TPP) was reported.16] Under these biphasic conditions,
turnover frequencies (TOFs) were almost comparable to those
obtained with homogeneous
In this paper, we describe biphasic and heterogeneous catalytic systems for the hydroformylation of methyl acrylate which have much higher activities than the homogeneous variant.
[*I Prof. Dr. A. Mortreux. Dipl.-Chem. G. Fremy. Dr. JLF. Carpentier.
Prof. Dr. Y Castanet
Lahoratoire de Catalyse Heterogkne e t Homogene
Unibersite des Sciences et Technologies de Lille, BP 108
F-59652 Villeneuve d‘Ascq Cedex (FI-ance)
Telehx: Int. code + 20436588
Dr. E. Monnier
Universite d’Artois, Facuke des Sciences Jean Perrin. Lens (France)
[**I This work was supported by ELF-AT0 Co.
0570-0833.95..13/3-1474
B 10.00+ .25:0
Angew Chem. I n f . Ed. Engl. 1995, 34, No. 1 3 : / 4
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